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Sample records for time-varying plasma currents

  1. An integrative time-varying frequency detection and channel sounding method for dynamic plasma sheath

    Science.gov (United States)

    Shi, Lei; Yao, Bo; Zhao, Lei; Liu, Xiaotong; Yang, Min; Liu, Yanming

    2018-01-01

    The plasma sheath-surrounded hypersonic vehicle is a dynamic and time-varying medium and it is almost impossible to calculate time-varying physical parameters directly. The in-fight detection of the time-varying degree is important to understand the dynamic nature of the physical parameters and their effect on re-entry communication. In this paper, a constant envelope zero autocorrelation (CAZAC) sequence based on time-varying frequency detection and channel sounding method is proposed to detect the plasma sheath electronic density time-varying property and wireless channel characteristic. The proposed method utilizes the CAZAC sequence, which has excellent autocorrelation and spread gain characteristics, to realize dynamic time-varying detection/channel sounding under low signal-to-noise ratio in the plasma sheath environment. Theoretical simulation under a typical time-varying radio channel shows that the proposed method is capable of detecting time-variation frequency up to 200 kHz and can trace the channel amplitude and phase in the time domain well under -10 dB. Experimental results conducted in the RF modulation discharge plasma device verified the time variation detection ability in practical dynamic plasma sheath. Meanwhile, nonlinear phenomenon of dynamic plasma sheath on communication signal is observed thorough channel sounding result.

  2. Research on the FDTD method of scattering effects of obliquely incident electromagnetic waves in time-varying plasma sheath on collision and plasma frequencies

    Science.gov (United States)

    Chen, Wei; Guo, Li-xin; Li, Jiang-ting

    2017-04-01

    This study analyzes the scattering characteristics of obliquely incident electromagnetic (EM) waves in a time-varying plasma sheath. The finite-difference time-domain algorithm is applied. According to the empirical formula of the collision frequency in a plasma sheath, the plasma frequency, temperature, and pressure are assumed to vary with time in the form of exponential rise. Some scattering problems of EM waves are discussed by calculating the radar cross section (RCS) of the time-varying plasma. The laws of the RCS varying with time are summarized at the L and S wave bands.

  3. Current relaxation time scales in toroidal plasmas

    International Nuclear Information System (INIS)

    Mikkelsen, D.R.

    1987-02-01

    An approximate normal mode analysis of plasma current diffusion in tokamaks is presented. The work is based on numerical solutions of the current diffusion equation in cylindrical geometry. Eigenvalues and eigenfunctions are shown for a broad range of plasma conductivity profile shapes. Three classes of solutions are considered which correspond to three types of tokamak operation. Convenient approximations to the three lowest eigenvalues in each class are presented and simple formulae for the current relaxation time scales are given

  4. Current control for magnetized plasma in direct-current plasma-immersion ion implantation

    International Nuclear Information System (INIS)

    Tang Deli; Chu, Paul K.

    2003-01-01

    A method to control the ion current in direct-current plasma-immersion ion implantation (PIII) is reported for low-pressure magnetized inductively coupled plasma. The ion current can be conveniently adjusted by applying bias voltage to the conducting grid that separates plasma formation and implantation (ion acceleration) zones without the need to alter the rf input power, gas flux, or other operating conditions. The ion current that diminishes with an increase in grid bias in magnetized plasmas can be varied from 48 to 1 mA by increasing the grid voltage from 0 to 70 V at -50 kV sample bias and 0.5 mTorr hydrogen pressure. High implantation voltage and monoenergetic immersion implantation can now be achieved by controlling the ion current without varying the macroscopic plasma parameters. The experimental results and interpretation of the effects are presented in this letter. This technique is very attractive for PIII of planar samples that require on-the-fly adjustment of the implantation current at high implantation voltage but low substrate temperature. In some applications such as hydrogen PIII-ion cut, it may obviate the need for complicated sample cooling devices that must work at high voltage

  5. Energy confinement in JT-60 lower hybrid current driven plasmas

    International Nuclear Information System (INIS)

    Ushigusa, K.; Imai, T.; Naito, O.; Ikeda, Y.; Tsuji, S.; Uehara, K.

    1990-01-01

    The energy confinement in high power lower hybrid current driven (LHCD) plasmas has been studied in the JT-60 tokamak. At a plasma current of 1 MA, the diamagnetically estimated energy confinement time in LHCD plasmas has almost the same value as the confinement time in ohmically heated plasmas at n-bar e ∼ 1.0x10 19 m -3 . The confinement time of high power LHCD plasmas (P LH E varies as to P LH α n e β I p 0 with α + β ∼ -0.3. (author). Letter-to-the-editor. 12 refs, 5 figs

  6. FDTD analysis of reflection of electromagnetic wave from a conductive plane covered with inhomogeneous time-varying plasma

    International Nuclear Information System (INIS)

    Liu Shaobin; Mo Jinjun; Yuan Naichang

    2003-01-01

    A finite-difference time-domain (FDTD) algorithm is applied to study the electro-magnetic reflection of conduction plane covered with inhomogeneous time-varying plasma, homogeneous plasma and inhomogeneous plasma. The collisions frequency of plasma is a function of electron density and plasma temperature. The number density profile follows a parabolic function. A discussion on the effect of various plasma parameters on the reflection coefficient is presented. Under the one-dimensional case, transient electromagnetic propagation through various plasmas has been obtained, and the reflection coefficients of EM wave through various plasma are calculated under different conditions. The results illustrate that a plasma cloaking system can successfully absorb the incident EM wave

  7. Propagation of a laser beam in a time-varying waveguide. [plasma heating for controlled fusion

    Science.gov (United States)

    Chapman, J. M.; Kevorkian, J.

    1978-01-01

    The propagation of an axisymmetric laser beam in a plasma column having a radially parabolic electron density distribution is reported. For the case of an axially uniform waveguide it is found that the basic characteristics of alternating focusing and defocusing beams are maintained. However, the intensity distribution is changed at the foci and outer-beam regions. The features of paraxial beam propagation are discussed with reference to axially varying waveguides. Laser plasma coupling is considered noting the case where laser heating produces a density distribution radially parabolic near the axis and the energy absorbed over the focal length of the plasma is small. It is found that: (1) beam-propagation stability is governed by the relative magnitude of the density fluctuations existing in the axial variation of the waveguides due to laser heating, and (2) for beam propagation in a time-varying waveguide, the global instability of the propagation is a function of the initial fluctuation growth rate as compared to the initial time rate of change in the radial curvature of the waveguide.

  8. Real-time control of current and pressure profiles in tokamak plasmas

    International Nuclear Information System (INIS)

    Laborde, L.

    2005-12-01

    Recent progress in the field of 'advanced tokamak scenarios' prefigure the operation regime of a future thermonuclear fusion power plant. Compared to the reference regime, these scenarios offer a longer plasma confinement time thanks to increased magnetohydrodynamic stability and to a better particle and energy confinement through a reduction of plasma turbulence. This should give access to comparable fusion performances at reduced plasma current and could lead to a steady state fusion reactor since the plasma current could be entirely generated non-inductively. Access to this kind of regime is provided by the existence of an internal transport barrier, linked to the current profile evolution in the plasma, which leads to steep temperature and pressure profiles. The comparison between heat transport simulations and experiments allowed the nature of the barriers to be better understood as a region of strongly reduced turbulence. Thus, the control of this barrier in a stationary manner would be a remarkable progress, in particular in view of the experimental reactor ITER. The Tore Supra and JET tokamaks, based in France and in the United Kingdom, constitute ideal instruments for such experiments: the first one allows stationary plasmas to be maintained during several minutes whereas the second one provides unique fusion performances. In Tore Supra, real-time control experiments have been accomplished where the current profile width and the pressure profile gradient were controlled in a stationary manner using heating and current drive systems as actuators. In the JET tokamak, the determination of an empirical static model of the plasma allowed the current and pressure profiles to be simultaneously controlled and so an internal transport barrier to be sustained. Finally, the identification of a dynamic model of the plasma led to the definition of a new controller capable, in principle, of a more efficient control. (author)

  9. Time development of electric fields and currents in space plasmas

    Directory of Open Access Journals (Sweden)

    A. T. Y. Lui

    2006-05-01

    Full Text Available Two different approaches, referred to as Bu and Ej, can be used to examine the time development of electric fields and currents in space plasmas based on the fundamental laws of physics. From the Bu approach, the required equation involves the generalized Ohm's law with some simplifying assumptions. From the Ej approach, the required equation can be derived from the equation of particle motion, coupled self-consistently with Maxwell's equation, and the definition of electric current density. Recently, some strong statements against the Ej approach have been made. In this paper, we evaluate these statements by discussing (1 some limitations of the Bu approach in solving the time development of electric fields and currents, (2 the procedure in calculating self-consistently the time development of the electric current in space plasmas without taking the curl of the magnetic field in some cases, and (3 the dependency of the time development of magnetic field on electric current. It is concluded that the Ej approach can be useful to understand some magnetospheric problems. In particular, statements about the change of electric current are valid theoretical explanations of change in magnetic field during substorms.

  10. Theory of current-drive in plasmas

    International Nuclear Information System (INIS)

    Fisch, N.J.

    1986-12-01

    The continuous operation of a tokamak fusion reactor requires, among other things, a means of providing continuous toroidal current. Such operation is preferred to the conventional pulsed operation, where the plasma current is induced by a time-varying magnetic field. A variety of methods has been proposed to provide continuous current, including methods which utilize particle beams or radio frequency waves in any of several frequency regimes. Currents as large as half a mega-amp have now been produced in the laboratory by such means, and experimentation in these techniques has now involved major tokamak facilities worldwide

  11. Velocity distribution of electrons in time-varying low-temperature plasmas: progress in theoretical procedures over the past 70 years

    Science.gov (United States)

    Makabe, Toshiaki

    2018-03-01

    A time-varying low-temperature plasma sustained by electrical powers with various kinds of fRequencies has played a key role in the historical development of new technologies, such as gas lasers, ozonizers, micro display panels, dry processing of materials, medical care, and so on, since World War II. Electrons in a time-modulated low-temperature plasma have a proper velocity spectrum, i.e. velocity distribution dependent on the microscopic quantum characteristics of the feed gas molecule and on the external field strength and the frequency. In order to solve and evaluate the time-varying velocity distribution, we have mostly two types of theoretical methods based on the classical and linear Boltzmann equations, namely, the expansion method using the orthogonal function and the procedure of non-expansional temporal evolution. Both methods have been developed discontinuously and progressively in synchronization with those technological developments. In this review, we will explore the historical development of the theoretical procedure to evaluate the electron velocity distribution in a time-varying low-temperature plasma over the past 70 years.

  12. Temperature of thermal plasma jets: A time resolved approach

    Energy Technology Data Exchange (ETDEWEB)

    Sahasrabudhe, S N; Joshi, N K; Barve, D N; Ghorui, S; Tiwari, N; Das, A K, E-mail: sns@barc.gov.i [Laser and Plasma Technology Division, Bhabha Atomic Research Centre, Mumbai - 400 094 (India)

    2010-02-01

    Boltzmann Plot method is routinely used for temperature measurement of thermal plasma jets emanating from plasma torches. Here, it is implicitly assumed that the plasma jet is 'steady' in time. However, most of the experimenters do not take into account the variations due to ripple in the high current DC power supplies used to run plasma torches. If a 3-phase transductor type of power supply is used, then the ripple frequency is 150 Hz and if 3- phase SCR based power supply is used, then the ripple frequency is 300 Hz. The electrical power fed to plasma torch varies at ripple frequency. In time scale, it is about 3.3 to 6.7 ms for one cycle of ripple and it is much larger than the arc root movement times which are within 0.2 ms. Fast photography of plasma jets shows that the luminosity of plasma jet also varies exactly like the ripple in the power supply voltage and thus with the power. Intensity of line radiations varies nonlinearly with the instantaneous power fed to the torch and the simple time average of line intensities taken for calculation of temperature is not appropriate. In this paper, these variations and their effect on temperature determination are discussed and a method to get appropriate data is suggested. With a small adaptation discussed here, this method can be used to get temperature profile of plasma jet within a short time.

  13. Current status of DIII-D real-time digital plasma control

    International Nuclear Information System (INIS)

    Penaflor, B.G.; Piglowski, D.A.; Ferron, J.R.; Walker, M.L.

    1999-06-01

    This paper describes the current status of real-time digital plasma control for the DIII-D tokamak. The digital plasma control system (PCS) has been in place at DIII-D since the early 1990s and continues to expand and improve in its capabilities to monitor and control plasma parameters for DIII-D fusion science experiments. The PCs monitors over 200 tokamak parameters from the DIII-D experiment using a real-time data acquisition system that acquires a new set of samples once every 60 micros. This information is then used in a number of feedback control algorithms to compute and control a variety of parameters including those affecting plasma shape and position. A number of system related improvements has improved the usability and flexibility of the DIII-D PCS. These include more graphical user interfaces to assist in entering and viewing the large and ever growing number of parameters controlled by the PCS, increased interaction and accessibility from other DIII-D applications, and upgrades to the computer hardware and vended software. Future plans for the system include possible upgrades of the real-time computers, further links to other DIII-D diagnostic measurements such as real-time Thomson scattering analysis, and joint collaborations with other tokamak experiments including the NSTX at Princeton

  14. Time evolution of the bootstrap current profile in LHD plasmas

    International Nuclear Information System (INIS)

    Nakamura, Yuji; Kawaoto, K.; Watanabe, K.Y.

    2008-10-01

    The direction of the bootstrap current is inverted in the outward shifted plasmas of the Large Helical Device (LHD). In order to verify the reliability of the theoretical models of the bootstrap current in helical plasmas, the rotational transform profiles are observed by the Motional Stark Effect measurement in the bootstrap current carrying plasmas of the LHD, and they are compared with the numerical simulations of the toroidal current profile including the bootstrap current. Since the toroidal current profile is not in the steady state in these plasmas, taking care of the inversely induced component of the toroidal current and finite duration of the resistive diffusion of the toroidal current are important in the numerical simulations. Reasonable agreement can be obtained between the rotational transform profiles measured in the experiments and those calculated in the numerical simulations. (author)

  15. Estimation of post disruption plasma temperature for fast current quench Aditya plasma shots

    International Nuclear Information System (INIS)

    Purohit, S.; Chowdhuri, M.B.; Joisa, Y.S.; Raval, J.V.; Ghosh, J.; Jha, R.

    2013-01-01

    Characteristics of tokamak current quenches are an important issue for the determination of electromagnetic forces that act on the in-vessel components and vacuum vessel during major disruptions. It is observed that thermal quench is followed by a sharp current decay. Fast current quench disruptive plasma shots were investigated for ADITYA tokamak. The current decay time was determined for the selected shots, which were in the range of 0.8 msec to 2.5 msec. This current decay information was then applied to L/R model, frequently employed for the estimation of the current decay time in tokamak plasmas, considering plasma inductance and plasma resistivity. This methodology was adopted for the estimation of the post disruption plasma temperature using the experimentally observed current decay time for the fast current quench disruptive ADITYA plasma shots. The study reveals that for the identified shots there is a constant increase in the current decay time with the post disruption plasma temperature. The investigations also explore the behavior post disruption plasma temperature and the current decay time as a function of the edge safety factor, Q. Post disruption plasma temperature and the current decay time exhibits a decrease with the increase in the value Q. (author)

  16. Time varying voltage combustion control and diagnostics sensor

    Science.gov (United States)

    Chorpening, Benjamin T [Morgantown, WV; Thornton, Jimmy D [Morgantown, WV; Huckaby, E David [Morgantown, WV; Fincham, William [Fairmont, WV

    2011-04-19

    A time-varying voltage is applied to an electrode, or a pair of electrodes, of a sensor installed in a fuel nozzle disposed adjacent the combustion zone of a continuous combustion system, such as of the gas turbine engine type. The time-varying voltage induces a time-varying current in the flame which is measured and used to determine flame capacitance using AC electrical circuit analysis. Flame capacitance is used to accurately determine the position of the flame from the sensor and the fuel/air ratio. The fuel and/or air flow rate (s) is/are then adjusted to provide reduced flame instability problems such as flashback, combustion dynamics and lean blowout, as well as reduced emissions. The time-varying voltage may be an alternating voltage and the time-varying current may be an alternating current.

  17. Effect of time-varying flow-shear on the nonlinear stability of the boundary of magnetized toroidal plasmas

    Directory of Open Access Journals (Sweden)

    Youngmin Oh

    2018-02-01

    Full Text Available We propose a phenomenological yet general model in a form of extended complex Ginzburg-Landau equation to understand edge-localized modes (ELMs, a class of quasi-periodic fluid instabilities in the boundary of toroidal magnetized high-temperature plasmas. The model reproduces key dynamical features of the ELMs (except the final explosive relaxation stage observed in the high-confinement state plasmas on the Korea Superconducting Tokamak Advanced Research: quasi-steady states characterized by field-aligned filamentary eigenmodes, transitions between different quasi-steady eigenmodes, and rapid transition to non-modal filamentary structure prior to the relaxation. It is found that the inclusion of time-varying perpendicular sheared flow is crucial for reproducing all of the observed dynamical features.

  18. Impact of the storm-time plasma sheet ion composition on the ring current energy density

    Science.gov (United States)

    Mouikis, C.; Kistler, L. M.; Petrinec, S. M.; Fuselier, S. A.; Cohen, I.

    2017-12-01

    The adiabatic inward transport of the night-side near-earth ( 6 Re) hot plasma sheet is the dominant contributor to the ring current pressure during storm times. During storm times, the plasma sheet composition in the 6 - 12 Re tail region changes due to O+ entry from the lobes (from the cusp) and the direct feeding from the night side auroral region. In addition, at substorm onset the plasma sheet O+ ions can be preferentially accelerated. We use MMS and observations during two magnetic storms, 5/8/2016 and 7/16/2017, to monitor the composition changes and energization in the 6 - 12 Re plasma sheet region. For both storms the MMS apogee was in the tail. In addition, we use subsequent Van Allen Probe observations (with apogee in the dawn and dusk respectively) to test if the 6-12 Re plasma sheet, observed by MMS, is a sufficient source of the O+ in the ring current. For this we will compare the phase space density (PSD) of the plasma sheet source population and the PSD of the inner magnetosphere at constant magnetic moment values as used in Kistler et al., [2016].

  19. Diagnostics for real-time plasma control in PBX-M

    Science.gov (United States)

    Kaita, R.; Batha, S.; Bell, R. E.; Bernabei, S.; Hatcher, R.; Kozub, T.; Kugel, H.; Levinton, F.; Okabayashi, M.; Sesnic, S.; von Goeler, S.; Zolfaghari, A.; PBX-M Group

    1995-01-01

    An important issue for future tokamaks is real-time plasma control for the avoidance of magnetohydrodynamic instabilities and other applications that require detailed plasma profile and fluctuation data. Although measurements from diagnostics providing this information require significantly more processing than magnetic flux data, recent advancements could make them practical for adjusting operational settings for plasma heating and current drive systems as well as field coil currents. On the Princeton Beta Experiment-Modification (PBX-M), the lower hybrid current drive phasing can be varied during a plasma shot using digitally programmable ferrite phase shifters, and neural beam functions can be fully computer controlled. PBX-M diagnostics that may be used for control purposes include motional Stark-effect polarimetry for magnetic field pitch angle profiles, soft x-ray arrays for plasma position control and the separation of βp from li, hard x-ray detectors for energetic electron distributions, a multichannel electron cyclotron emission radiometer for ballooning mode identification, and passive plate eddy current monitors for kink stabilization. We will describe the present status of these systems on PBX-M, and discuss their suitability for feedback applications.

  20. Diagnostics for real-time plasma control in PBX-M

    International Nuclear Information System (INIS)

    Kaita, R.; Batha, S.; Bell, R.E.; Bernabei, S.; Hatcher, R.; Kozub, T.; Kugel, H.; Levinton, F.; Okabayashi, M.; Sesnic, S.; Goeler, S. von; Zolfaghari, A.

    1995-01-01

    An important issue for future tokamaks is real-time plasma control for the avoidance of magnetohydrodynamic instabilities and other applications that require detailed plasma profile and fluctuation data. Although measurements from diagnostics providing this information require significantly more processing than magnetic flux data, recent advancements could make them practical for adjusting operational settings for plasma heating and current drive systems as well as field coil currents. On the Princeton Beta Experiment-Modification (PBX-M), the lower hybrid current drive phasing can be varied during a plasma shot using digitally programmable ferrite phase shifters, and neural beam functions can be fully computer controlled. PBX-M diagnostics that may be used for control purposes include motional Stark-effect polarimetry for magnetic field pitch angle profiles, soft x-ray arrays for plasma position control and the separation of β p from l i , hard x-ray detectors for energetic electron distributions, a multichannel electron cyclotron emission radiometer for ballooning mode identification, and passive plate eddy current monitors for kink stabilization. We will describe the present status of these systems on PBX-M, and discuss their suitability for feedback applications

  1. Time-dependent analysis of the resistivity of post-disruption tokamak plasmas

    International Nuclear Information System (INIS)

    Bakhtiari, M.; Whyte, D. G.

    2006-01-01

    The effect of neutrals on plasma resistivity due to electron-neutral collisions is studied with respect to its effect on tokamak disruptions. The resistivity of the tokamak plasma after the thermal quench is critical in determining the current quench rate, the plasma temperature, and runaway electron generation in tokamaks through the electric field, all features which are important for mitigating the damaging effect of disruptions. It is shown that the plasma resistivity during tokamak disruptions is a time-dependent parameter which may vary with disruption time scales due to the increasing fraction of neutrals. However the effect of neutrals on resistivity is found to be small for the expected neutral fraction, mostly due to power balance considerations between radiation and Ohmic heating in the plasma

  2. Current ramp-up experiments in full current drive plasmas in TRIAM-1M

    International Nuclear Information System (INIS)

    Hanada, K.; Nakamura, K.; Hasegawa, M.; Itoh, S.; Zushi, H.; Sakamoto, M.; Jotaki, E.; Iyomasa, A.; Kawasaki, S.; Nakashima, H.; Yoshida, N.; Tokunaga, K.; Fujiwara, T.; Kulkarni, S.V.; Mitarai, O.

    2004-01-01

    Four types of plasma current ramp-up experiments in full non-inductively lower hybrid current driven (LHCD) plasmas were executed in TRIAM-1M: (1) current start-up by a combination of electron cyclotron resonance heating (ECRH) and LHCD, (2) tail heating by additional LHCD, (3) bulk heating by ECRH and (4) spontaneous ramp-up by a transition to enhanced current drive (ECD) mode. The time evolutions of plasma current during four types of ramp-up phase were adjusted by a simple model with two different time constants, which are a time defined by the total current diffusion time and a time constant for improving the current drive efficiency. In the case of (1) and (4), the latter time constant is significant during the current ramp-up phase. The improvement in the current drive efficiency in the ECD mode is likely to be caused by the increase in the effective refractive index along the magnetic field of the lower hybrid wave. (author)

  3. Tokamak plasma current disruption infrared control system

    International Nuclear Information System (INIS)

    Kugel, H.W.; Ulrickson, M.

    1987-01-01

    This patent describes a device for magnetically confining a plasma driven by a plasma current and contained within a toroidal vacuum chamber, the device having an inner toroidal limiter on an inside wall of the vacuum chamber and an arrangement for the rapid prediction and control in real time of a major plasma disruption. The arrangement is described which includes: scanning means sensitive to infrared radiation emanating from within the vacuum chamber, the infrared radiation indicating the temperature along a vertical profile of the inner toroidal limiter. The scanning means is arranged to observe the infrared radiation and to produce in response thereto an electrical scanning output signal representative of a time scan of temperature along the vertical profile; detection means for analyzing the scanning output signal to detect a first peaked temperature excursion occurring along the profile of the inner toroidal limiter, and to produce a detection output signal in repsonse thereto, the detection output signal indicating a real time prediction of a subsequent major plasma disruption; and plasma current reduction means for reducing the plasma current driving the plasma, in response to the detection output signal and in anticipation of a subsequent major plasma disruption

  4. Current ramp-up experiments in full current drive plasmas on TRIAM-1M

    International Nuclear Information System (INIS)

    Hanada, K.; Nakamura, K.; Hasegawa, M.

    2003-01-01

    Four types of plasma current ramp-up experiments were executed on TRIAM-1M in full lower hybrid current drive plasmas (LHCD: 8.2GHz, up to 0.4 MW, 8 x 2 grill antenna); 1) the current start up by the combination between electron cyclotron resonance heating (ECH: 170GHz, up to 0.2 MW, O-mode launching) and LHCD at the density of ∼2x10 19 m -3 at B t =6.7T, 2) the tail heating by the additional LHCD, 3) the bulk heating by ECH, 4) the spontaneous ramp up by the transition to enhanced current drive (ECD) mode. The time evolutions of plasma current during four types of ramp-up phase were investigated and an exponential type and a tangent-hyperbolic one were observed. The time evolutions of plasma current during the tail and the bulk heating show the exponential type except the tail heating with high n parallel and it has a tangent-hyperbolic one during the ECD mode and the current start-up. A simple model with two different time constants, which are a time defined by L/R, τ L/R , and a time caused by change of the effective refractive index along the magnetic field, τ, is proposed to explain two types of the time evolution of the plasma current. The estimated τ L/R is consistent with the calculated one from the plasma parameter. It is found that τ are less than τ L/R in the cases of the tail and the bulk heating, and comparable in the cases of the ECD mode, and more than τ L/R in the cases of the plasma start-up. This indicates that the value of the effective refractive index along the magnetic field, parallel >, develops during the ECD mode and the current start-up. The value of τ depends on the RF power. The estimated is close to the expected up-shifted n parallel due to the toroidal effect and the magnetic shear. (author)

  5. Adaptation of the MAST passive current simulation model for real-time plasma control

    International Nuclear Information System (INIS)

    McArdle, G.J.; Taylor, D.

    2008-01-01

    Successful equilibrium reconstruction on MAST depends on a reliable estimate of the passive current induced in the thick vacuum vessel (which also acts as the load assembly) and other toroidally continuous internal support structures. For the EFIT reconstruction code, a pre-processing program takes the measured plasma and PF coil current evolution and uses a sectional model of the passive structure to solve the ODEs for electromagnetic induction. The results are written to a file, which is treated by EFIT as a set of virtual measurements of the passive current in each section. However, when a real-time version of EFIT was recently installed in the MAST plasma control system, a similar function was required for real-time estimation of the instantaneous passive current. This required several adaptation steps for the induction model to reduce the computational overhead to the absolute minimum, whilst preserving accuracy of the result. These include: ·conversion of the ODE to use an auxiliary variable, avoiding the need to calculate the time derivative of current; ·minimise the order of the system via model reduction techniques with a state-space representation of the problem; ·transformation to eigenmode form, to diagonalise the main matrix for faster computation; ·discretisation of the ODE; ·hand-optimisation to use vector instruction extensions in the real-time processor; ·splitting the task into two parts: the time-critical feedback part, and the next cycle pre-calculation part. After these optimisations, the algorithm was successfully implemented at a cost of just 65 μs per 500 μs control cycle, with only 27 μs added to the control latency. The results show good agreement with the original off-line version. Some of these optimisations have also been used subsequently to improve the performance of the off-line version

  6. Scaling of energy confinement with minor radius, current and density in Doublet III Ohmically heated plasmas

    International Nuclear Information System (INIS)

    Ejima, S.; Petrie, T.W.; Riviere, A.C.

    1982-01-01

    The dependence of plasma energy confinement on minor radius, density and plasma current is described for Ohmically heated near-circular plasmas in Doublet III. A wide range of parameters is used for the study of scaling laws; the plasma minor radius defined by the flux surface in contact with limiter is varied by a factor of 2 (a = 44, 32, and 23 cm), the line average plasma density, nsub(e)-bar, is varied by a factor of 20 from 0.5 to 10 x 10 13 cm -3 (nsub(e)-bar R 0 /Bsub(T) = 0.3 to 6 x 10 14 cm -2 .kG -1 ) and the plasma current, I, is varied by a factor of 6 from 120 to 718 kA. The range of the limiter safety factor, qsub(L), is from 2 to 12. - For plasmas with a = 23 and 32 cm, the scaling law at low nsub(e)-bar for the gross electron energy confinement time can be written as (s, cm) tausub(Ee)sup(G) approx.= 3.6 x 10 -19 nsub(e)-bar a 2 qsub(c)sup(3/4), where qsub(c) = 2πa 2 Bsub(T)/μ 0 IR 0 . For the 44-cm plasmas, tausub(Ee)sup(G) is about 1.8 times less than predicted by this scaling, possibly owing to the change in limiter configuration and small plasma-wall separation and/or the aspect ratio change. At high nsub(e)-bar, tausub(Ee)sup(G) saturates and in many cases decreases with nsub(e)-bar but increases with I in a classical-like manner. The dependence of tausub(Ee)sup(G) on a is considerably weakened. The confinement behaviour can be explained by taking an ion thermal conductivity 2 to 7 times that given by Hinton-Hazeltine's neoclassical theory with a lumped-Zsub(eff) impurity model. Within this range the enhancement factor increases with a or a/R 0 . The electron thermal conductivity evaluated at half-temperature radius where most of the thermal insulation occurs sharply increases with average current density within that radius, but does not depend on a within the uncertainties of the measurements. (author)

  7. Experimental studies of coaxial plasma gun current

    International Nuclear Information System (INIS)

    Price, D.W.

    1988-01-01

    In this investigation of a coaxial plasma gun, plasma sheath currents and related behavior are examined. Plasma behavior in the gun affects gun characteristics. Plasma gun applications are determined by the plasma behavior. The AFWL PUFF capacitor bank (72 μF, 29 nH, 120 kV) drives the plasma gun using a deuterium fill gas. The gas breakdown site is isolated from the dielectric/vacuum interface in the AFWL system. Two gas values deliver gas in the system. The first delivers gas from the gun breech and the second optional valve delivers gas to the gun muzzle. Currents and voltages are measured by Rogowski coils, B probes and capacitive voltage probes. A O-D slug model is used to predict the current, inductance, gun voltage and plasma sheath velocity. The slug model assumes the sheath transits the gun with all mass in the sheath. In the snowplow mode, the plasma sheath is thin with a sharp current rise and drop. Our system operated in a transition mode between the snowplow and deflagration modes with early snowplow behavior and late deflagration behavior. Neutrons are produced in a plasma pinch at the gun muzzle, indicating snowplow behavior. The slug theory models overall gun behavior to experimental accuracy. Experimental results are compared to four theories for plasma sheath velocities: the Alfven collisionally limited model, the Rosenbluth model, the Fishbine saturated model and a single particle drift model. Experimental velocities vary from 10 5 to 10 6 m/s. Only the single particle drift and the slug model calculations are of the right magnitude (8 x 10 5 m/s). The Fishbine and the Rosenbluth models predict slower velocities (2 x 10 5 m/s). The Alfven model is not applicable to this system

  8. Asymmetric SOL Current in Vertically Displaced Plasma

    Science.gov (United States)

    Cabrera, J. D.; Navratil, G. A.; Hanson, J. M.

    2017-10-01

    Experiments at the DIII-D tokamak demonstrate a non-monotonic relationship between measured scrape-off layer (SOL) currents and vertical displacement event (VDE) rates with SOL currents becoming largely n=1 dominant as plasma is displaced by the plasma control system (PCS) at faster rates. The DIII-D PCS is used to displace the magnetic axis 10x slower than the intrinsic growth time of similar instabilities in lower single-null plasmas. Low order (n VDE instabilities observed when vertical control is disabled. Previous inquiry shows VDE asymmetry characterized by SOL current fraction and geometric parameters of tokamak plasmas. We note that, of plasmas displaced by the PCS, short displacement time scales near the limit of the PCS temporal control appear to result in larger n=1/n=2 asymmetries. Work supported under USDOE Cooperative Agreement DE-FC02-04ER54698 and DE-FG02-04ER54761.

  9. Relation between magnetic fields and electric currents in plasmas

    Directory of Open Access Journals (Sweden)

    V. M. Vasyliunas

    2005-10-01

    Full Text Available Maxwell's equations allow the magnetic field B to be calculated if the electric current density J is assumed to be completely known as a function of space and time. The charged particles that constitute the current, however, are subject to Newton's laws as well, and J can be changed by forces acting on charged particles. Particularly in plasmas, where the concentration of charged particles is high, the effect of the electromagnetic field calculated from a given J on J itself cannot be ignored. Whereas in ordinary laboratory physics one is accustomed to take J as primary and B as derived from J, it is often asserted that in plasmas B should be viewed as primary and J as derived from B simply as (c/4π∇×B. Here I investigate the relation between ∇×B and J in the same terms and by the same method as previously applied to the MHD relation between the electric field and the plasma bulk flow vmv2001: assume that one but not the other is present initially, and calculate what happens. The result is that, for configurations with spatial scales much larger than the electron inertial length λe, a given ∇×B produces the corresponding J, while a given J does not produce any ∇×B but disappears instead. The reason for this can be understood by noting that ∇×B≠4π/cJ implies a time-varying electric field (displacement current which acts to change both terms (in order to bring them toward equality; the changes in the two terms, however, proceed on different time scales, light travel time for B and electron plasma period for J, and clearly the term changing much more slowly is the one that survives. (By definition, the two time scales are equal at λe. On larger scales, the evolution of B (and hence also of ∇×B is governed by

  10. Characteristics of disruptive plasma current decay in the HT-2 tokamak

    International Nuclear Information System (INIS)

    Abe, Mitsushi; Takeuchi, Kazuhiro; Otsuka, Michio

    1993-01-01

    Motions of plasma current channel and time evolutions of eddy current distribution on the vacuum vessel during disruptive plasma current decay were studied experimentally in the Hitachi tokamak HT-2. The plasmas are vertically elongated and circularly shaped plasmas. A disruptive plasma current decay has three phases. During the first phase, a large displacement of the plasma position without plasma current decay is observed. Rapid plasma current decay is observed during the second phase and the decay rate is roughly constant with time. The eddy current distribution is like that due to the shell effect which creates a poloidal field to reduce the plasma displacement. During the third phase, the plasma current decays exponentially. The second phase is observed in slightly elongated and high plasma current (> 20 kA) circularly shaped plasmas. The plasma current decay rates in the second phase depend on the plasma cross sectional shape, but they do not in the third phase. The magnetic axis moves from the plasma area to the vacuum vessel wall between the second and third phases. (author)

  11. Device for plasma confinement and heating by high currents and nonclassical plasma transport properties

    Science.gov (United States)

    Coppi, B.; Montgomery, D.B.

    1973-12-11

    A toroidal plasma containment device having means for inducing high total plasma currents and current densities and at the same time emhanced plasma heating, strong magnetic confinement, high energy density containment, magnetic modulation, microwaveinduced heating, and diagnostic accessibility is described. (Official Gazette)

  12. Evolution of perturbation in charge-varying dusty plasmas

    International Nuclear Information System (INIS)

    Popel, S.I.; Golub, A.P.; Losseva, T.V.; Bingham, R.; Benkadda, S.

    2001-01-01

    The nonstationary problem of the evolution of perturbation and its transformation into nonlinear wave structure in dusty plasmas is considered. For this purpose two one-dimensional models based on a set of fluid equations, Poisson's equation, and a charging equation for dust are developed. The first (simplified) model corresponds to the case [Popel et al., Phys. Plasmas 3, 4313 (1996)] when exact steady-state shock wave solutions can exist. This simplified model includes variable-charged dust grains, Boltzmann electrons, and inertial ions. The second (ionization source) model takes into account the variation of the ion density and the ion momentum dissipation due to dust particle charging as well as the source of plasma particles due to ionization process. The computational method for solving the set of equations which describe the evolution in time of a nonlinear structure in a charge-varying dusty plasma is developed. The case of the evolution of an intensive initial nonmoving region with a constant enhanced ion density is investigated on the basis of these two models. The consideration within the ionization source model is performed for the data of the laboratory experiment [Luo et al., Phys. Plasmas 6, 3455 (1999)]. It is shown that the ionization source model allows one to obtain shock structures as a result of evolution of an initial perturbation and to explain the experimental value of the width of the shock wave front. Comparison of the numerical data obtained on the basis of the ionization source model and the simplified model shows that the main characteristic features of the shock structure are the same for both models. Nevertheless, the ionization source model is much more sensitive to the form of the initial perturbation than the simplified model. The solution of the problem of the evolution of perturbation and its transformation into shock wave in charge-varying dusty plasmas opens up possibilities for description of the real phenomena like supernova

  13. Plasma-current structures of plasma focus during the current disruption

    International Nuclear Information System (INIS)

    Krokhin, O.N.; Kalachev, N.V.; Malafeev, Yu.S.; Nikulin, V.Ya; Polukhin, S.N.; Tsybenko, S.P.

    2000-01-01

    The results are presented of an investigation of the plasma structures arising during the current disruption in the Dense Plasma Focus (DPF). The study was performed using the laser-shadow and interferometry methods together with measurements of current and X-ray radiation. An analysis of the experimental results shows that for the construction of a multi mega-amperes current disruption device, the Filippov type of DPF (in comparison with the Mather type) is to be preferred since the processes occurring in the X-ray regime are much faster than in the pinch regime, and this type of plasma focus is geometrically more suitable for the assembly of such a current disrupter.This disrupter is now under construction, based on the 'Tulip' DPF installation

  14. Plasma current sustained by fusion charged particles in a field reversed configuration

    International Nuclear Information System (INIS)

    Berk, H.L.; Momota, H.; Tajima, T.

    1987-04-01

    The distribution of energetic charged particles generated by thermonuclear fusion reactions in a field reversed configuration (FRC) are studied analytically and numerically. A fraction of the charged fusion products escapes directly while the others are trapped to form a directed particle flow parallel to the plasma current. It is shown that the resultant current density produced by these fusion charged particles can be comparable to background plasma current density that produces the original field reversed configuration in a D- 3 He reactor. Self-consistent equilibria arising from the currents of the background plasma and proton fusion products are constructed where the Larmor radius of the fusion product is of arbitrary size. Reactor relevant parameters are examined, such as how the fusion reactivity rate varies as a result of supporting the pressure associated with the fusion products. We also model the synchrotron emission from various pressure profiles and quantitatively show how synchrotron losses vary with different pressure profiles in an FRC configuration

  15. Plasma acceleration in a wave with varying frequency

    International Nuclear Information System (INIS)

    Petrzilka, V.A.

    1978-01-01

    The averaged velocity of a test particle and the averaged velocity of a plasma in an electromagnetic wave packet with varying frequency (e.g., a radiation pulse from pulsar) is derived. The total momentum left by the wave packet in regions of plasma inhomogeneity is found. In case the plasma concentration is changing due to ionization the plasma may be accelerated parallelly or antiparallelly to the direction of the wave packet propagation which is relevant for a laser induced breakdown in gas. (author)

  16. Effect of current profile evolution on plasma-limiter interaction and the energy confinement time

    International Nuclear Information System (INIS)

    Hawryluk, R.J.; Bol, K.; Bretz, N.

    1979-04-01

    Experiments conducted on the PLT tokamak have shown that both plasma-limiter interaction and the gross energy confinement time are functions of the gas influx during the discharge. By suitably controlling the gas influx, it is possible to contract the current channel, decrease impurity radiation from the core of the discharge, and increase the gross energy confinement time, whether the aperture limiters were of tungsten, stainless steel or carbon

  17. Current distribution measurements inside an electromagnetic plasma gun operated in a gas-puff mode.

    Science.gov (United States)

    Poehlmann, Flavio R; Cappelli, Mark A; Rieker, Gregory B

    2010-12-01

    Measurements are presented of the time-dependent current distribution inside a coaxial electromagnetic plasma gun. The measurements are carried out using an array of six axially distributed dual-Rogowski coils in a balanced circuit configuration. The radial current distributions indicate that operation in the gas-puff mode, i.e., the mode in which the electrode voltage is applied before injection of the gas, results in a stationary ionization front consistent with the presence of a plasma deflagration. The effects of varying the bank capacitance, transmission line inductance, and applied electrode voltage were studied over the range from 14 to 112 μF, 50 to 200 nH, and 1 to 3 kV, respectively.

  18. Time resolved plasma characterization in a long conduction time planar plasma opening switch

    International Nuclear Information System (INIS)

    Adler, L.K.; Greenly, J.B.; Qi, N.; Hammer, D.A.

    1989-01-01

    The authors discuss additional experiments in which the plasma dynamics and properties will be monitored in detail before and during opening. Space and time resolved density, temperature and motion information about the plasma and neutrals is given by emission spectroscopy and streak photography and correlated to the current and voltage traces. Specifically, we will look for the effects of neutrals evolving off of surfaces, stagnation of the switch plasma, and rvec J x rvec B motion of the plasma downstream of the switch. Diagnostics include current and voltage monitors, a multi-aperture biased Faraday cup, emission spectroscopy and streak photography. Pairs of B dot loops are positioned in the stripline just upstream and downstream of the POS. Also, two single B loops were placed further downstream to look for bulk plasma motion. An inductive monitor gives the voltage at the upstream side of the POS and the Faraday cup monitors the gun plasma consistency from shot to shot

  19. The dispersion relation of charge and current compensated relativistic electron beam-plasma system

    International Nuclear Information System (INIS)

    Vrba, P.; Schroetter, J.; Jarosova, P.; Koerbel, S.

    1978-01-01

    The unstable regions of relativistic electron beam-plasma system were determined by analysing the general dispersion relation numerically. The external parameters were varied to ensure more effective instability excitations. The full charge- and current compensation presumptions lead to the new synchronism predictions. The slow space charge wave and slow cyclotron wave of the return current are synchronous with the plasma ion wave. (author)

  20. Plasma equilibrium control during slow plasma current quench with avoidance of plasma-wall interaction in JT-60U

    Science.gov (United States)

    Yoshino, R.; Nakamura, Y.; Neyatani, Y.

    1997-08-01

    In JT-60U a vertical displacement event (VDE) is observed during slow plasma current quench (Ip quench) for a vertically elongated divertor plasma with a single null. The VDE is generated by an error in the feedback control of the vertical position of the plasma current centre (ZJ). It has been perfectly avoided by improving the accuracy of the ZJ measurement in real time. Furthermore, plasma-wall interaction has been avoided successfully during slow Ip quench owing to the good performance of the plasma equilibrium control system

  1. RF current drive and plasma fluctuations

    International Nuclear Information System (INIS)

    Peysson, Yves; Decker, Joan; Morini, L; Coda, S

    2011-01-01

    The role played by electron density fluctuations near the plasma edge on rf current drive in tokamaks is assessed quantitatively. For this purpose, a general framework for incorporating density fluctuations in existing modelling tools has been developed. It is valid when rf power absorption takes place far from the fluctuating region of the plasma. The ray-tracing formalism is modified in order to take into account time-dependent perturbations of the density, while the Fokker–Planck solver remains unchanged. The evolution of the electron distribution function in time and space under the competing effects of collisions and quasilinear diffusion by rf waves is determined consistently with the time scale of fluctuations described as a statistical process. Using the ray-tracing code C3PO and the 3D linearized relativistic bounce-averaged Fokker–Planck solver LUKE, the effect of electron density fluctuations on the current driven by the lower hybrid (LH) and the electron cyclotron (EC) waves is estimated quantitatively. A thin fluctuating layer characterized by electron drift wave turbulence at the plasma edge is considered. The effect of fluctuations on the LH wave propagation is equivalent to a random scattering process with a broadening of the poloidal mode spectrum proportional to the level of the perturbation. However, in the multipass regime, the LH current density profile remains sensitive to the ray chaotic behaviour, which is not averaged by fluctuations. The effect of large amplitude fluctuations on the EC driven current is found to be similar to an anomalous radial transport of the fast electrons. The resulting lower current drive efficiency and broader current profile are in better agreement with experimental observations. Finally, applied to the ITER ELMy H-mode regime, the model predicts a significant broadening of the EC driven current density profile with the fluctuation level, which can make the stabilization of neoclassical tearing mode potentially

  2. Electrodynamic forces and plasma conductivity inside the current sheet

    International Nuclear Information System (INIS)

    Bogdanov, S.Yu.; Frank, A.G.; Markov, V.S.

    1985-01-01

    The process of accumulation and explosive release of magnetic energy was studied in a current sheet of plasma of a high-current linear discharge. The distribution of current density and of electrodynamic forces were measured and the time evolution of these quantities was determined. The evolution of the plasma conductivity was also obtained. The measured and calculated electrodynamic forces may explain the plasma acceleration up to the velocities about 3x10 4 m/s only near the sheet edges. (D.Gy.)

  3. Transient, Small-Scale Field-Aligned Currents in the Plasma Sheet Boundary Layer During Storm Time Substorms

    Science.gov (United States)

    Nakamura, R.; Sergeev, V. A.; Baumjohann, W.; Plaschke, F.; Magnes, W.; Fischer, D.; Varsani, A.; Schmid, D.; Nakamura, T. K. M.; Russell, C. T.; hide

    2016-01-01

    We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small-scale field-aligned currents were found embedded in fluctuating PSBL flux tubes near the Separatrix region. We resolve, for the first time, short-lived earthward (downward) intense field-aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward earth ward during outward plasma sheet expansion. They coincide with upward field-aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high-energy ion beam-produced disturbances. The observations highlight coupling of multiscale processes in PSBL as a consequence of magnetotail reconnection.

  4. Electric fields in plasmas under pulsed currents

    International Nuclear Information System (INIS)

    Tsigutkin, K.; Doron, R.; Stambulchik, E.; Bernshtam, V.; Maron, Y.; Fruchtman, A.; Commisso, R. J.

    2007-01-01

    Electric fields in a plasma that conducts a high-current pulse are measured as a function of time and space. The experiment is performed using a coaxial configuration, in which a current rising to 160 kA in 100 ns is conducted through a plasma that prefills the region between two coaxial electrodes. The electric field is determined using laser spectroscopy and line-shape analysis. Plasma doping allows for three-dimensional spatially resolved measurements. The measured peak magnitude and propagation velocity of the electric field is found to match those of the Hall electric field, inferred from the magnetic-field front propagation measured previously

  5. Plasma dynamics in current sheets

    International Nuclear Information System (INIS)

    Bogdanov, S.Yu.; Drejden, G.V.; Kirij, N.P.; AN SSSR, Leningrad

    1992-01-01

    Plasma dynamics in successive stages of current sheet evolution is investigated on the base of analysis of time-spatial variations of electron density and electrodynamic force fields. Current sheet formation is realized in a two-dimensional magnetic field with zero line under the action of relatively small initial disturbances (linear regimes). It is established that in the limits of the formed sheet is concentrated dense (N e ∼= 10 16 cm -3 ) (T i ≥ 100 eV, bar-Z i ≥ 2) hot pressure of which is balanced by the magnetic action of electrodynamic forces is carried out both plasma compression in the sheet limits and the acceleration along the sheet surface from a middle to narrow side edges

  6. Measurement of toroidal plasma current in RF heated helical plasmas

    International Nuclear Information System (INIS)

    Besshou, Sakae

    1993-01-01

    This report describes the measurement of toroidal plasma current by a semiflexible Rogowski coil in a helical vacuum chamber. A Rogowski coil measures the toroidal plasma current with a resolution of 0.1 kA, frequency range of up to 1 kHz and sensitivity of 6.5 x 10 -9 V · s/A. We measured the spontaneous toroidal plasma current (from -1.2 to +1.2 kA) under electron cyclotron resonance heating at 0.94 T toroidal field in the Heliotron-E device. We found that the measured direction of toroidal plasma current changes its sign as in the predicted behavior of a neoclassical diffusion-driven bootstrap current, depending on the horizontal position of the plasma column. We explain the observed plasma currents in terms of the compound phenomenon of an ohmic current and a neoclassical diffusion-driven current. The magnitude of the neoclassical current component is smaller than the value predicted by a collisionless neoclassical theory. (author)

  7. Theoretical relation between halo current-plasma energy displacement/deformation in EAST

    Science.gov (United States)

    Khan, Shahab Ud-Din; Khan, Salah Ud-Din; Song, Yuntao; Dalong, Chen

    2018-04-01

    In this paper, theoretical model for calculating halo current has been developed. This work attained novelty as no theoretical calculations for halo current has been reported so far. This is the first time to use theoretical approach. The research started by calculating points for plasma energy in terms of poloidal and toroidal magnetic field orientations. While calculating these points, it was extended to calculate halo current and to developed theoretical model. Two cases were considered for analyzing the plasma energy when flows down/upward to the diverter. Poloidal as well as toroidal movement of plasma energy was investigated and mathematical formulations were designed as well. Two conducting points with respect to (R, Z) were calculated for halo current calculations and derivations. However, at first, halo current was established on the outer plate in clockwise direction. The maximum generation of halo current was estimated to be about 0.4 times of the plasma current. A Matlab program has been developed to calculate halo current and plasma energy calculation points. The main objective of the research was to establish theoretical relation with experimental results so as to precautionary evaluate the plasma behavior in any Tokamak.

  8. Plasma and current structures in dynamical pinches

    International Nuclear Information System (INIS)

    Butov, I.Ya.; Matveev, Yu.V.

    1981-01-01

    Dynamics of plasma layers and current structure in aZ-pinch device has been experimentally investigated. It is found that shaping of a main current envelope is ended with its explosion-like expansion, the pinch decaying after compression to separated current filaments. It is also shown that filling of a region outside the pinch with plasma and currents alternating in directions occurs owing to interaction of current loops (inductions) formed in a magnetic piston during its compression with reflected shock wave. Current circulating in the loops sometimes exceeds 1.5-2 times the current of discharge circuit. The phenomena noted appear during development of superheat instability and can be realized, for example, in theta-pinches, plasma focuses, tokamaks. The experiments were carried out at the Dynamic Zeta-pinch device at an energy reserse of up to 15 kJ (V 0 =24 kV) in a capacitor bank. Half-period of the discharge current is 9 μs; Isub(max)=3.5x10sup(5) A. Back current guide surrounding a china chamber of 28 cm diameter and 50 cm length is made in the form of a hollow cylinder. Initial chamber vacuum is 10 -6 torr [ru

  9. Time-Domain Modeling of RF Antennas and Plasma-Surface Interactions

    Directory of Open Access Journals (Sweden)

    Jenkins Thomas G.

    2017-01-01

    Full Text Available Recent advances in finite-difference time-domain (FDTD modeling techniques allow plasma-surface interactions such as sheath formation and sputtering to be modeled concurrently with the physics of antenna near- and far-field behavior and ICRF power flow. Although typical sheath length scales (micrometers are much smaller than the wavelengths of fast (tens of cm and slow (millimeter waves excited by the antenna, sheath behavior near plasma-facing antenna components can be represented by a sub-grid kinetic sheath boundary condition, from which RF-rectified sheath potential variation over the surface is computed as a function of current flow and local plasma parameters near the wall. These local time-varying sheath potentials can then be used, in tandem with particle-in-cell (PIC models of the edge plasma, to study sputtering effects. Particle strike energies at the wall can be computed more accurately, consistent with their passage through the known potential of the sheath, such that correspondingly increased accuracy of sputtering yields and heat/particle fluxes to antenna surfaces is obtained. The new simulation capabilities enable time-domain modeling of plasma-surface interactions and ICRF physics in realistic experimental configurations at unprecedented spatial resolution. We will present results/animations from high-performance (10k-100k core FDTD/PIC simulations of Alcator C-Mod antenna operation.

  10. Density measurements of microsecond-conduction-time POS plasmas

    International Nuclear Information System (INIS)

    Hinshelwood, D.; Goodrich, P.J.; Weber, B.V.; Commisso, R.J.; Grossmann, J.M.; Kellogg, J.C.

    1993-01-01

    Measurements of the electron density in a coaxial microsecond conduction time plasma opening switch during switch operation are described. Current conduction is observed to cause a radial redistribution of the switch plasma. A local reduction in axial line density of more than an order of magnitude occurs by the time opening begins. This reduction, and the scaling of conduction current with plasma density, indicate that current conduction in this experiment is limited by hydrodynamic effects. It is hypothesized that the density reduction allows the switch to open by an erosion mechanism. Initial numerical modeling efforts have reproduced the principal observed results. A model that predicts accurately the conduction current is presented

  11. Energy confinement of tokamak plasma with consideration of bootstrap current effect

    International Nuclear Information System (INIS)

    Yuan Ying; Gao Qingdi

    1992-01-01

    Based on the η i -mode induced anomalous transport model of Lee et al., the energy confinement of tokamak plasmas with auxiliary heating is investigated with consideration of bootstrap current effect. The results indicate that energy confinement time increases with plasma current and tokamak major radius, and decreases with heating power, toroidal field and minor radius. This is in reasonable agreement with the Kaye-Goldston empirical scaling law. Bootstrap current always leads to an improvement of energy confinement and the contraction of inversion radius. When γ, the ratio between bootstrap current and total plasma current, is small, the part of energy confinement time contributed from bootstrap current will be about γ/2

  12. Time-varying BRDFs.

    Science.gov (United States)

    Sun, Bo; Sunkavalli, Kalyan; Ramamoorthi, Ravi; Belhumeur, Peter N; Nayar, Shree K

    2007-01-01

    The properties of virtually all real-world materials change with time, causing their bidirectional reflectance distribution functions (BRDFs) to be time varying. However, none of the existing BRDF models and databases take time variation into consideration; they represent the appearance of a material at a single time instance. In this paper, we address the acquisition, analysis, modeling, and rendering of a wide range of time-varying BRDFs (TVBRDFs). We have developed an acquisition system that is capable of sampling a material's BRDF at multiple time instances, with each time sample acquired within 36 sec. We have used this acquisition system to measure the BRDFs of a wide range of time-varying phenomena, which include the drying of various types of paints (watercolor, spray, and oil), the drying of wet rough surfaces (cement, plaster, and fabrics), the accumulation of dusts (household and joint compound) on surfaces, and the melting of materials (chocolate). Analytic BRDF functions are fit to these measurements and the model parameters' variations with time are analyzed. Each category exhibits interesting and sometimes nonintuitive parameter trends. These parameter trends are then used to develop analytic TVBRDF models. The analytic TVBRDF models enable us to apply effects such as paint drying and dust accumulation to arbitrary surfaces and novel materials.

  13. Determination of plasma spot current and arc discharge plasma current on the system of plasma cathode electron sources using Rogowski coil technique

    International Nuclear Information System (INIS)

    Wirjoadi; Bambang Siswanto; Lely Susita RM; Agus Purwadi; Sudjatmoko

    2015-01-01

    It has been done the function test experiments of ignitor electrode system and the plasma generator electrode system to determine the current spot plasma and arc discharge plasma current with Rogowski coil technique. Ignitor electrode system that gets power supply from IDPS system can generate the plasma spot current of 11.68 ampere to the pulse width of about 33 μs, this value is greater than the design probably because of electronic components used in the IDPS system was not as planned. For the plasma generator electrode system that gets power from ADPS system capable of producing an arc discharge plasma current around 103.15 amperes with a pulse width of about 96 μs, and this value as planned. Based on the value of the arc discharge plasma current can be determined plasma electron density, which is about 10.12 10"1"9 electrons/m"3, and with this electron density value, an ignitor electrode system and a plasma generator system is quite good if used as a plasma cathode electron source system. (author)

  14. Alternative model of space-charge-limited thermionic current flow through a plasma

    Science.gov (United States)

    Campanell, M. D.

    2018-04-01

    It is widely assumed that thermionic current flow through a plasma is limited by a "space-charge-limited" (SCL) cathode sheath that consumes the hot cathode's negative bias and accelerates upstream ions into the cathode. Here, we formulate a fundamentally different current-limited mode. In the "inverse" mode, the potentials of both electrodes are above the plasma potential, so that the plasma ions are confined. The bias is consumed by the anode sheath. There is no potential gradient in the neutral plasma region from resistivity or presheath. The inverse cathode sheath pulls some thermoelectrons back to the cathode, thereby limiting the circuit current. Thermoelectrons entering the zero-field plasma region that undergo collisions may also be sent back to the cathode, further attenuating the circuit current. In planar geometry, the plasma density is shown to vary linearly across the electrode gap. A continuum kinetic planar plasma diode simulation model is set up to compare the properties of current modes with classical, conventional SCL, and inverse cathode sheaths. SCL modes can exist only if charge-exchange collisions are turned off in the potential well of the virtual cathode to prevent ion trapping. With the collisions, the current-limited equilibrium must be inverse. Inverse operating modes should therefore be present or possible in many plasma devices that rely on hot cathodes. Evidence from past experiments is discussed. The inverse mode may offer opportunities to minimize sputtering and power consumption that were not previously explored due to the common assumption of SCL sheaths.

  15. Propagation of a laser beam in a time-varying waveguide

    International Nuclear Information System (INIS)

    Chapman, J.M.; Kevorkian, J.

    1978-01-01

    The propagation of an axisymmetric laser beam in a plasma column having a radially parabolic electron density distribution is examined. First, an extended paraxial procedure is developed for the case of an axially uniform waveguide. It is shown that the essential feature of an alternate focusing and defocusing beam is retained, but that the intensity distribution is cumulatively modified at the foci and at the outer portions of the beam as compared to that of the paraxial case. Second, some general features of paraxial beam propagation are examined for the case of axially varying waveguides. Finally, laser plasma coupling is examined for the case when laser heating generates a density distribution that is radially parabolic near the axis and when the energy absorbed over a focal length of a plasma lens is small. It is shown that stable or unstable beam propagation depends upon the relative magnitude of the density fluctuations which exist in the axial variation of the waveguides as a result of laser heating. When the fluctuations are small, the propagation is stable, and a simple algebraic expression is obtained which relates the beam diameter to the axially slow averaged variation in the waveguide. When the fluctuations are large, the propagation stability can be determined only by consistently combining plasma dynamics and beam propagation to interrelate the axial variation of the beam to that of the waveguide. In this case of beam propagation in a time-varying waveguide, it is shown that the global stability of the propagation depends upon the initial fluctuation growth rate compared to the initial time rate of change in the radial curvature of the waveguide

  16. Separation of Evans and Hiro currents in VDE of tokamak plasma

    Science.gov (United States)

    Galkin, Sergei A.; Svidzinski, V. A.; Zakharov, L. E.

    2014-10-01

    Progress on the Disruption Simulation Code (DSC-3D) development and benchmarking will be presented. The DSC-3D is one-fluid nonlinear time-dependent MHD code, which utilizes fully 3D toroidal geometry for the first wall, pure vacuum and plasma itself, with adaptation to the moving plasma boundary and accurate resolution of the plasma surface current. Suppression of fast magnetosonic scale by the plasma inertia neglecting will be demonstrated. Due to code adaptive nature, self-consistent plasma surface current modeling during non-linear dynamics of the Vertical Displacement Event (VDE) is accurately provided. Separation of the plasma surface current on Evans and Hiro currents during simulation of fully developed VDE, then the plasma touches in-vessel tiles, will be discussed. Work is supported by the US DOE SBIR Grant # DE-SC0004487.

  17. Plasma currents and anisotropy in the tail-dipole transition region

    Science.gov (United States)

    Artemyev, A.; Zhang, X. J.; Angelopoulos, V.; Runov, A.

    2017-12-01

    Using conjugated THEMIS and Van Allen Probes observations in the nightside magnetosphere, we examine statistically plasma and magnetic field characteristics at multiple locations simultaneously across the 3-10 RE region (i.e., across the tail-dipole transition region, whose location depends on tail flux loading and the strength of global convection). We find that the spatial distributions of ion and electron anisotropies vary significantly but systematically with radial distance and geomagnetic activity. For low Kp (4), the anisotropy profiles for ions and electrons reverse: ions are isotropic closer to the Earth and field-aligned in the tail, whereas electrons are transversely anisotropic closer to Earth but isotropic in the tail. Using the measured plasma anisotropy radial profiles we estimate the currents from curvature drifts and compare them with diamagnetic currents. We also discuss the implications of the observed plasma anisotropies for the presence and spatial distribution of field-aligned electric fields.

  18. Real-time control of Tokamak plasmas: from control of physics to physics-based control

    International Nuclear Information System (INIS)

    Felici, F. A. A.

    2011-11-01

    Stable, high-performance operation of a tokamak requires several plasma control problems to be handled simultaneously. Moreover, the complex physics which governs the tokamak plasma evolution must be studied and understood to make correct choices in controller design. In this thesis, the two subjects have been merged, using control solutions as experimental tool for physics studies, and using physics knowledge for developing new advanced control solutions. The TCV tokamak at CRPP-EPFL is ideally placed to explore issues at the interface between plasma physics and plasma control, by combining a digital realtime control system with a flexible and powerful set of actuators, in particular the electron cyclotron heating and current drive system (ECRH/ECCD). This experimental platform has been used to develop and test new control strategies for three plasma physics instabilities: sawtooth, edge localized mode (ELM) and neoclassical tearing mode (NTM). The period of the sawtooth crash, a periodic MHD instability in the core of a tokamak plasma, can be varied by localized deposition of ECRH/ECCD near the q = 1 surface (q: safety factor). A sawtooth pacing controller was developed which is able to control the time of appearance of the next sawtooth crash. Each individual sawtooth period can be controlled in real-time. A similar scheme is applied to H-mode plasmas with type-I ELMs, where it is shown that pacing regularizes the ELM period. The regular, reproducible and therefore predictable sawtooth crashes have been used to study the relationship between sawteeth and NTMs. Postcrash MHD activity can provide the ‘seed’ island for an NTM, which then grows under its neoclassical bootstrap drive. The seeding of 3/2 NTMs by long sawtooth crashes can be avoided by preemptive, crash-synchronized EC power injection pulses at the q = 3/2 rational surface location. NTM stabilization experiments in which the ECRH deposition location is moved in real-time with steerable mirrors have

  19. Comparing Sources of Storm-Time Ring Current O+

    Science.gov (United States)

    Kistler, L. M.

    2015-12-01

    The first observations of the storm-time ring current composition using AMPTE/CCE data showed that the O+ contribution to the ring current increases significantly during storms. The ring current is predominantly formed from inward transport of the near-earth plasma sheet. Thus the increase of O+ in the ring current implies that the ionospheric contribution to the plasma sheet has increased. The ionospheric plasma that reaches the plasma sheet can come from both the cusp and the nightside aurora. The cusp outflow moves through the lobe and enters the plasma sheet through reconnection at the near-earth neutral line. The nightside auroral outflow has direct access to nightside plasma sheet. Using data from Cluster and the Van Allen Probes spacecraft, we compare the development of storms in cases where there is a clear input of nightside auroral outflow, and in cases where there is a significant cusp input. We find that the cusp input, which enters the tail at ~15-20 Re becomes isotropized when it crosses the neutral sheet, and becomes part of the hot (>1 keV) plasma sheet population as it convects inward. The auroral outflow, which enters the plasma sheet closer to the earth, where the radius of curvature of the field line is larger, does not isotropize or become significantly energized, but remains a predominantly field aligned low energy population in the inner magnetosphere. It is the hot plasma sheet population that gets accelerated to high enough energies in the inner magnetosphere to contribute strongly to the ring current pressure. Thus it appears that O+ that enters the plasma sheet further down the tail has a greater impact on the storm-time ring current than ions that enter closer to the earth.

  20. High current plasma electron emitter

    International Nuclear Information System (INIS)

    Fiksel, G.; Almagri, A.F.; Craig, D.

    1995-07-01

    A high current plasma electron emitter based on a miniature plasma source has been developed. The emitting plasma is created by a pulsed high current gas discharge. The electron emission current is 1 kA at 300 V at the pulse duration of 10 ms. The prototype injector described in this paper will be used for a 20 kA electrostatic current injection experiment in the Madison Symmetric Torus (MST) reversed-field pinch. The source will be replicated in order to attain this total current requirement. The source has a simple design and has proven very reliable in operation. A high emission current, small size (3.7 cm in diameter), and low impurity generation make the source suitable for a variety of fusion and technological applications

  1. Plasma position from ring current measurements in Extrap T1

    International Nuclear Information System (INIS)

    Brunsell, P.; Jin Li.

    1989-11-01

    The inductive coupling between the plasma and the four octupole field coils in the Extrap T1 device is utilized as a means of estimating the plasma position. The current in each octupole ring as well as the plasma current is measured by a Rogowski coil and the ring - plasma mutual inductance is then computed assuming axisymmetric plasma displacements. The obtained position is in agreement with internal magnetic probe measurements. The time - evolution of the plasma position for different external vertical and toroidal field strengths is studied. For the present discharge parameter a vertical field of about .008 T is found to give an almost radially stationary plasma. The results are compared with a simple equilibrium model

  2. Simulation of vibration-induced effect on plasma current measurement using a fiber optic current sensor.

    Science.gov (United States)

    Descamps, Frédéric; Aerssens, Matthieu; Gusarov, Andrei; Mégret, Patrice; Massaut, Vincent; Wuilpart, Marc

    2014-06-16

    An accurate measurement of the plasma current is of paramount importance for controlling the plasma magnetic equilibrium in tokamaks. Fiber optic current sensor (FOCS) technology is expected to be implemented to perform this task in ITER. However, during ITER operation, the vessel and the sensing fiber will be subject to vibrations and thus to time-dependent parasitic birefringence, which may significantly compromise the FOCS performance. In this paper we investigate the effects of vibrations on the plasma current measurement accuracy under ITER-relevant conditions. The simulation results show that in the case of a FOCS reflection scheme including a spun fiber and a Faraday mirror, the error induced by the vibrations is acceptable regarding the ITER current diagnostics requirements.

  3. Current-driven turbulence in plasmas

    International Nuclear Information System (INIS)

    Kluiver, H. de.

    1977-10-01

    Research on plasma heating in linear and toroidal systems using current-driven turbulence is reviewed. The motivation for this research is presented. Relations between parameters describing the turbulent plasma state and macroscopic observables are given. Several linear and toroidal devices used in current-driven turbulence studies are described, followed by a discussion of special diagnostic methods used. Experimental results on the measurement of electron and ion heating, anomalous plasma conductivity and associated turbulent fluctuation spectra are reviewed. Theories on current-driven turbulence are discussed and compared with experiments. It is demonstrated from the experimental results that current-driven turbulence occurs not only for extreme values of the electric field but also for an experimentally much more accessible and wide range of parameters. This forms a basis for a discussion on possible future applications in fusion-oriented plasma research

  4. Visualization of particle trajectories in time-varying electromagnetic fields by CAVE-type virtual reality system

    International Nuclear Information System (INIS)

    Ohno, Nobuaki; Ohtani, Hiroaki; Horiuchi, Ritoku; Matsuoka, Daisuke

    2012-01-01

    The particle kinetic effects play an important role in breaking the frozen-in condition and exciting collisionless magnetic reconnection in high temperature plasmas. Because this effect is originating from a complex thermal motion near reconnection point, it is very important to examine particle trajectories using scientific visualization technique, especially in the presence of plasma instability. We developed interactive visualization environment for the particle trajectories in time-varying electromagnetic fields in the CAVE-type virtual reality system based on VFIVE, which is interactive visualization software for the CAVE system. From the analysis of ion trajectories using the particle simulation data, it was found that time-varying electromagnetic fields around the reconnection region accelerate ions toward the downstream region. (author)

  5. Plasma density evolution in plasma opening switch obtained by a time-resolved sensitive He-Ne interferometer

    Science.gov (United States)

    Chen, Lin; Ren, Jing; Guo, Fan; Zhou, LiangJi; Li, Ye; He, An; Jiang, Wei

    2014-03-01

    To understand the formation process of vacuum gap in coaxial microsecond conduction time plasma opening switch (POS), we have made measurements of the line-integrated plasma density during switch operation using a time-resolved sensitive He-Ne interferometer. The conduction current and conduction time in experiments are about 120 kA and 1 μs, respectively. As a result, more than 85% of conduction current has been transferred to an inductive load with rise time of 130 ns. The radial dependence of the density is measured by changing the radial location of the line-of-sight for shots with the same nominal POS parameters. During the conduction phase, the line-integrated plasma density in POS increases at all radial locations over the gun-only case by further ionization of material injected from the guns. The current conduction is observed to cause a radial redistribution of the switch plasma. A vacuum gap forms rapidly in the plasma at 5.5 mm from the center conductor, which is consistent with the location where magnetic pressure is the largest, allowing current to be transferred from the POS to the load.

  6. Rotating field current drive in spherical plasmas

    International Nuclear Information System (INIS)

    Brotherton-Ratcliffe, D.; Storer, R.G.

    1988-01-01

    The technique of driving a steady Hall current in plasmas using a rotating magnetic field is studied both numerically and analytically in the approximation of negligible ion flow. A spherical plasma bounded by an insulating wall and immersed in a uniform magnetic field which has both a rotating component (for current drive) and a constant ''vertical'' component (for MHD equilibrium) is considered. The problem is formulated in terms of an expansion of field quantities in vector spherical harmonics. The numerical code SPHERE solves the resulting pseudo-harmonic equations by a multiple shooting technique. The results presented, in addition to being relevant to non-inductive current drive generally, have a direct relevance to the rotamak experiments. For the case of no applied vertical field the steady state toroidal current driven by the rotating field per unit volume of plasma is several times less than in the long cylinder limit for a plasma of the same density, resistivity and radius. The application of a vertical field, which for certain parameter regimes gives rise to a compact torus configuration, improves the current drive dramatically and in many cases gives ''better'' current drive than the long cylinder limit. This result is also predicted by a second order perturbation analysis of the pseudo-harmonic equations. A steady state toroidal field is observed which appears consistent with experimental observations in rotamaks regarding magnitude and spatial dependence. This is an advance over previous analytical theory which predicted an oppositely directed toroidal field of undefined magnitude. (author)

  7. Suppression of vertical instability in elongated current-carrying plasmas by applying stellarator rotational transform

    International Nuclear Information System (INIS)

    ArchMiller, M. C.; Cianciosa, M. R.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Knowlton, S. F.; Ma, X.; Maurer, D. A.; Pandya, M. D.; Traverso, P.

    2014-01-01

    The passive stability of vertically elongated current-carrying toroidal plasmas has been investigated in the Compact Toroidal Hybrid, a stellarator/tokamak hybrid device. In this experiment, the fractional transform f, defined as the ratio of the imposed external rotational transform from stellarator coils to the total rotational transform, was varied from 0.04 to 0.50, and the elongation κ was varied from 1.4 to 2.2. Plasmas that were vertically unstable were evidenced by motion of the plasma in the vertical direction. Vertical drifts are measured with a set of poloidal field pickup coils. A three chord horizontally viewing interferometer and a soft X-ray diode array confirmed the drifts. Plasmas with low fractional transform and high elongation are the most susceptible to vertical instability, consistent with analytic predictions that the vertical mode in elongated plasmas can be stabilized by the poloidal field of a relatively weak stellarator equilibrium

  8. Numerical simulation of the plasma current quench following a disruptive energy loss

    International Nuclear Information System (INIS)

    Strickler, D.J.; Peng, Y.K.M.; Holmes, J.A.; Miller, J.B.; Rothe, K.E.

    1983-11-01

    The plasma electromagnetic interaction with poloidal field coils and nearby passive conductor loops during the current quench following a disruptive loss of plasma energy is simulated. By solving a differential/algebraic system consisting of a set of circuit equations (including the plasma circuit) coupled to a plasma energy balance equation and an equilibrium condition, the electromagnetic consequences of an abrupt thermal quench are observed. Limiters on the small and large major radium sides of the plasma are assumed to define the plasma cross section. The presence of good conductors near the plasma and a small initial distance (i.e., 5 to 10% of the plasma minor radius) between the plasma edge and an inboard limiter are shown to lead to long current decay times. For a plasma with an initial major radius R/sub o/ = 4.3 m, aspect ratio A = 3.6, and current I/sub P/ = 4.0 MA, introducing nearby passive conductors lengthens the current decay from milliseconds to hundreds of milliseconds

  9. Characteristic time for halo current growth and rotation

    Energy Technology Data Exchange (ETDEWEB)

    Boozer, Allen H., E-mail: ahb17@columbia.edu [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)

    2015-10-15

    A halo current flows for part of its path through the plasma edge and for part through the chamber walls and during tokamak disruptions can be as large as tenths of the plasma current. The primary interest in halo currents is the large force that they can exert on machine components particularly if the toriodal rotation of the halo current resonates with a natural oscillation frequency of the tokamak device. Halo currents arise when required to slow down the growth of a kink that is too unstable to be stabilized by the chamber walls. The width of the current channel in the halo plasma is comparable to the amplitude of the kink, and the halo current grows linearly, not exponentially, in time. The current density in the halo is comparable to that of the main plasma body. The rocket force due to plasma flowing out of the halo and recombining on the chamber walls can cause the non-axisymmetric magnetic structure produced by the kink to rotate toroidally at a speed comparable to the halo speed of sound. Gerhardt's observations of the halo current in NSTX shot 141 687 [Nucl. Fusion 53, 023005 (2013)] illustrate many features of the theory of halo currents and are discussed as a summary of the theory.

  10. Time-Varying Periodicity in Intraday Volatility

    DEFF Research Database (Denmark)

    Andersen, Torben Gustav; Thyrsgaard, Martin; Todorov, Viktor

    We develop a nonparametric test for deciding whether return volatility exhibits time-varying intraday periodicity using a long time-series of high-frequency data. Our null hypothesis, commonly adopted in work on volatility modeling, is that volatility follows a stationary process combined...... with a constant time-of-day periodic component. We first construct time-of-day volatility estimates and studentize the high-frequency returns with these periodic components. If the intraday volatility periodicity is invariant over time, then the distribution of the studentized returns should be identical across...... with estimating volatility moments through their sample counterparts. Critical values are computed via easy-to-implement simulation. In an empirical application to S&P 500 index returns, we find strong evidence for variation in the intraday volatility pattern driven in part by the current level of volatility...

  11. Current filaments in turbulent magnetized plasmas

    DEFF Research Database (Denmark)

    Martines, E.; Vianello, N.; Sundkvist, D.

    2009-01-01

    gradient region of a fusion plasma confined in reversed field pinch configuration and in a density gradient region in the Earth magnetosphere are measured and compared, showing that in both environments they can be attributed to drift-Alfvén vortices. Current structures associated with reconnection events......Direct measurements of current density perturbations associated with non-linear phenomena in magnetized plasmas can be carried out using in situ magnetic measurements. In this paper we report such measurements for three different kinds of phenomena. Current density fluctuations in the edge density...... measured in a reversed field pinch plasma and in the magnetosheath are detected and compared. Evidence of current filaments occurring during ELMs in an H-mode tokamak plasma is displayed....

  12. On the estimation of the current density in space plasmas: Multi- versus single-point techniques

    Science.gov (United States)

    Perri, Silvia; Valentini, Francesco; Sorriso-Valvo, Luca; Reda, Antonio; Malara, Francesco

    2017-06-01

    Thanks to multi-spacecraft mission, it has recently been possible to directly estimate the current density in space plasmas, by using magnetic field time series from four satellites flying in a quasi perfect tetrahedron configuration. The technique developed, commonly called ;curlometer; permits a good estimation of the current density when the magnetic field time series vary linearly in space. This approximation is generally valid for small spacecraft separation. The recent space missions Cluster and Magnetospheric Multiscale (MMS) have provided high resolution measurements with inter-spacecraft separation up to 100 km and 10 km, respectively. The former scale corresponds to the proton gyroradius/ion skin depth in ;typical; solar wind conditions, while the latter to sub-proton scale. However, some works have highlighted an underestimation of the current density via the curlometer technique with respect to the current computed directly from the velocity distribution functions, measured at sub-proton scales resolution with MMS. In this paper we explore the limit of the curlometer technique studying synthetic data sets associated to a cluster of four artificial satellites allowed to fly in a static turbulent field, spanning a wide range of relative separation. This study tries to address the relative importance of measuring plasma moments at very high resolution from a single spacecraft with respect to the multi-spacecraft missions in the current density evaluation.

  13. Eddy currents in a nonperiodic vacuum vessel induced by axisymmetric plasma motion

    International Nuclear Information System (INIS)

    DeLucia, J.

    1985-12-01

    A method is described for calculating the two-dimensional trajectory of a vertically or horizontally unstable axisymmetric tokamak plasma in the presence of a resistive vacuum vessel. The vessel is not assumed to have toroidal symmetry. The plasma is represented by a current-filament loop that is free to move vertically and to change its major radius. Its position is evolved in time self-consistently with the vacuum vessel eddy currents. The plasma current, internal inductance, and poloidal beta can be specified functions of time so that eddy currents resulting from a disruption can be modeled. The vacuum vessel is represented by a set of current-filaments whose positions and orientations are chosen to model the dominant eddy current paths. Although the specific application is to TFTR, the present model is of general applicability. 7 refs., 4 figs., 2 tabs

  14. Characterization of plasma current quench during disruptions at HL-2A

    Science.gov (United States)

    Zhu, Jinxia; Zhang, Yipo; Dong, Yunbo; HL-2A Team

    2017-05-01

    The most essential assumptions of physics for the evaluation of electromagnetic forces on the plasma-facing components due to a disruption-induced eddy current are characteristics of plasma current quenches including the current quench rate or its waveforms. The characteristics of plasma current quenches at HL-2A have been analyzed during spontaneous disruptions. Both linear decay and exponential decay are found in the disruptions with the fastest current quenches. However, there are two stages of current quench in the slow current quench case. The first stage with an exponential decay and the second stage followed by a rapid linear decay. The faster current quench rate corresponds to the faster movement of plasma displacement. The parameter regimes on the current quench time and the current quench rates have been obtained from disruption statistics at HL-2A. There exists no remarkable difference for distributions obtained between the limiter and the divertor configuration. This data from HL-2A provides basic data of the derivation of design criteria for a large-sized machine during the current decay phase of the disruptions.

  15. Controlling the emission current from a plasma cathode

    International Nuclear Information System (INIS)

    Bagaev, S.P.; Gushenets, V.I.; Schanin, P.M.

    1993-01-01

    The processes determining the time and amplitude characteristics of the grid-controlled electron emission from the plasma of an arc discharge have been analyzed. It has been shown that by applying to the grid confining the plasma emission boundary of a modulated voltage it is possible to form current pulse of up to 1 kA with nanosecond risetimes and falltimes and a pulse repetitive rate of 100 kHz

  16. Observation of instability-induced current redistribution in a spherical-torus plasma.

    Science.gov (United States)

    Menard, J E; Bell, R E; Gates, D A; Kaye, S M; LeBlanc, B P; Levinton, F M; Medley, S S; Sabbagh, S A; Stutman, D; Tritz, K; Yuh, H

    2006-09-01

    A motional Stark effect diagnostic has been utilized to reconstruct the parallel current density profile in a spherical-torus plasma for the first time. The measured current profile compares favorably with neoclassical theory when no large-scale magnetohydrodynamic instabilities are present in the plasma. However, a current profile anomaly is observed during saturated interchange-type instability activity. This apparent anomaly can be explained by redistribution of neutral beam injection current drive and represents the first observation of interchange-type instabilities causing such redistribution. The associated current profile modifications contribute to sustaining the central safety factor above unity for over five resistive diffusion times, and similar processes may contribute to improved operational scenarios proposed for ITER.

  17. Holographic cinematography of time-varying reflecting and time-varying phase objects using a Nd:YAG laser

    Science.gov (United States)

    Decker, A. J.

    1982-01-01

    The use of a Nd:YAG laser to record holographic motion pictures of time-varying reflecting objects and time-varying phase objects is discussed. Sample frames from both types of holographic motion pictures are presented. The holographic system discussed is intended for three-dimensional flow visualization of the time-varying flows that occur in jet-engine components.

  18. Profile formation and sustainment of autonomous tokamak plasma with current hole configuration

    International Nuclear Information System (INIS)

    Hayashi, N.; Takizuka, T.; Ozeki, T.

    2005-01-01

    We have investigated the profile formation and sustainment of tokamak plasmas with the current hole (CH) configuration by using 1.5D time-dependent transport simulations. A model of the current limit inside the CH on the basis of the Axisymmetric Tri-Magnetic-Islands equilibrium is introduced into the transport simulation. We found that a transport model with the sharp reduction of anomalous transport in the reversed-shear (RS) region can reproduce the time evolution of profiles observed in JT-60U experiments. The transport becomes neoclassical-level in the RS region, which results in the formation of profiles with internal transport barrier (ITB) and CH. The CH plasma has an autonomous property because of the strong interaction between a pressure profile and a current profile through the large bootstrap current fraction. The ITB width determined by the neoclassical-level transport agrees well with that measured in JT-60U. The energy confinement inside the ITB agrees with the scaling based on the JT-60U data. The scaling means the autonomous limitation of energy confinement in the CH plasma. The plasma with the large CH is sustained with the full current drive by the bootstrap current. The plasma with the small CH and the small bootstrap current fraction shrinks due to the penetration of inductive current. This shrink is prevented and the CH size can be controlled by the appropriate external current drive (CD). The CH plasma is found to respond autonomically to the external CD. (author)

  19. On the relationship between auroral absorption, electrojet currents and plasma convection

    Directory of Open Access Journals (Sweden)

    A. C. Kellerman

    2009-02-01

    Full Text Available In this study, the relationship between auroral absorption, electrojet currents, and ionospheric plasma convection velocity is investigated using a series of new methods where temporal correlations are calculated and analysed for different events and MLT sectors. We employ cosmic noise absorption (CNA observations obtained by the Imaging Riometer for Ionospheric Studies (IRIS system in Kilpisjärvi, Finland, plasma convection measurements by the European Incoherent Scatter (EISCAT radar, and estimates of the electrojet currents derived from the Tromsø magnetometer data. The IRIS absorption and EISCAT plasma convection measurements are used as a proxy for the particle precipitation component of the Hall conductance and ionospheric electric field, respectively. It is shown that the electrojet currents are affected by both enhanced conductance and electric field but with the relative importance of these two factors varying with magnetic local time (MLT. The correlation between the current and electric field (absorption is the highest at 12:00–15:00 MLT (00:00–03:00 MLT. It is demonstrated that the electric-field-dominant region is asymmetric with respect to magnetic-noon-midnight meridian extending from 09:00 to 21:00 MLT. This may be related to the recently reported absence of mirror-symmetry between the effects of positive and negative IMF By on the high-latitude plasma convection pattern. The conductivity-dominant region is somewhat wider than previously thought extending from 21:00 to 09:00 MLT with correlation slowly declining from midnight towards the morning, which is interpreted as being in part due to high-energy electron clouds gradually depleting and drifting from midnight towards the morning sector. The conductivity-dominant region is further investigated using the extensive IRIS riometer and Tromsø magnetometer datasets with results showing a distinct seasonal dependence. The region of high current

  20. Improved plasma confinement by modulated toroidal current on HT-7 superconducting tokamak

    International Nuclear Information System (INIS)

    Mao Jianshan; Zhao Junyu; Shen Biao; Luo Jiarong

    2004-01-01

    The improved confinement phase was observed during modulating toroidal current on the Hefei superconducting Tokamak-7 (HT-7). This improved plasma confinement phase is characterized by suppressing magnetohydrodynamic (MHD) instabilities effectively, thus increased the central line averaged electron density and the central electron temperature about 33%, out-put steeper density profiles, and reduced hydrogen radiation from the edge as well. The global energy confinement time was increased by 27%-45%; The impurity radiation was reduced by modulation of plasma toroidal current; particle confinement time was increased about two times; a stronger radial negative electric field formed inside the limiter. The radial electric field during modulating current was calculated and disscused. (authors)

  1. Real-time control for long ohmic alternate current discharges

    International Nuclear Information System (INIS)

    Carvalho, Ivo S.; Duarte, Paulo; Fernandes, Horácio; Valcárcel, Daniel F.; Carvalho, Pedro J.; Silva, Carlos; Duarte, André S.; Neto, André; Sousa, Jorge; Batista, António J.N.; Hekkert, Tiago; Carvalho, Bernardo B.; Gomes, Rui B.

    2014-01-01

    Highlights: • 40 Alternate plasma current (AC) semi-cycles without loss of ionization, more than 1 s of operation. • AC discharges automatic control: feedback loops, time-windows control strategy, goal oriented time-windows and exception handling. • Energy deposition and Carbon radiation evolution during the AC discharges. - Abstract: The ISTTOK tokamak has a long tradition on alternate plasma current (AC) discharges, but the old control system was limiting and lacked full system integration. In order to improve the AC discharges performance the ISTTOK fast control system was updated. This control system developed on site based on the Advanced Telecommunications Computing Architecture (ATCA) standard now integrates the information gathered by all the tokamak real-time diagnostics to produce an accurate observation of the plasma parameters. The real-time actuators were also integrated, allowing a Multiple Input Multiple Output (MIMO) control environment with several synchronization strategies available. The control system software was developed in C++ on top of a Linux system with the Multi-threaded Application Real-Time executor (MARTe) Framework to synchronize the real-time code execution under a 100μs control cycle. In addition, to simplify the discharge programming, a visual Human–Machine Interface (HMI) was also developed using the BaseLib2 libraries included in the MARTe Framework. This paper presents the ISTTOK control system and the optimizations that extended the AC current discharges duration to more than 1 s, corresponding to 40 semi-cycles without apparent degradation of the plasma parameters. This upgrade allows ISTTOK to be used as a low-cost material testing facility with long time exposures to nuclear fusion relevant plasmas, comparable (in duration) with medium size tokamaks

  2. Real-time control for long ohmic alternate current discharges

    Energy Technology Data Exchange (ETDEWEB)

    Carvalho, Ivo S., E-mail: ivoc@ipfn.ist.utl.pt; Duarte, Paulo; Fernandes, Horácio; Valcárcel, Daniel F.; Carvalho, Pedro J.; Silva, Carlos; Duarte, André S.; Neto, André; Sousa, Jorge; Batista, António J.N.; Hekkert, Tiago; Carvalho, Bernardo B.; Gomes, Rui B.

    2014-05-15

    Highlights: • 40 Alternate plasma current (AC) semi-cycles without loss of ionization, more than 1 s of operation. • AC discharges automatic control: feedback loops, time-windows control strategy, goal oriented time-windows and exception handling. • Energy deposition and Carbon radiation evolution during the AC discharges. - Abstract: The ISTTOK tokamak has a long tradition on alternate plasma current (AC) discharges, but the old control system was limiting and lacked full system integration. In order to improve the AC discharges performance the ISTTOK fast control system was updated. This control system developed on site based on the Advanced Telecommunications Computing Architecture (ATCA) standard now integrates the information gathered by all the tokamak real-time diagnostics to produce an accurate observation of the plasma parameters. The real-time actuators were also integrated, allowing a Multiple Input Multiple Output (MIMO) control environment with several synchronization strategies available. The control system software was developed in C++ on top of a Linux system with the Multi-threaded Application Real-Time executor (MARTe) Framework to synchronize the real-time code execution under a 100μs control cycle. In addition, to simplify the discharge programming, a visual Human–Machine Interface (HMI) was also developed using the BaseLib2 libraries included in the MARTe Framework. This paper presents the ISTTOK control system and the optimizations that extended the AC current discharges duration to more than 1 s, corresponding to 40 semi-cycles without apparent degradation of the plasma parameters. This upgrade allows ISTTOK to be used as a low-cost material testing facility with long time exposures to nuclear fusion relevant plasmas, comparable (in duration) with medium size tokamaks.

  3. The Tethered Balloon Current Generator - A space shuttle-tethered subsatellite for plasma studies and power generation

    Science.gov (United States)

    Williamson, P. R.; Banks, P. M.

    1976-01-01

    The objectives of the Tethered Balloon Current Generator experiment are to: (1) generate relatively large regions of thermalized, field-aligned currents, (2) produce controlled-amplitude Alfven waves, (3) study current-driven electrostatic plasma instabilities, and (4) generate substantial amounts of power or propulsion through the MHD interaction. A large balloon (a diameter of about 30 m) will be deployed with a conducting surface above the space shuttle at a distance of about 10 km. For a generally eastward directed orbit at an altitude near 400 km, the balloon, connected to the shuttle by a conducting wire, will be positive with respect to the shuttle, enabling it to collect electrons. At the same time, the shuttle will collect positive ions and, upon command, emit an electron beam to vary current flow in the system.

  4. Electron heat transport in current carrying and currentless thermonuclear plasmas. Tokamaks and stellarators compared

    International Nuclear Information System (INIS)

    Peters, M.

    1996-01-01

    In the first experiment the plasma current in the RTP tokamak is varied. Here the underlying idea was to check whether at a low plasma current, transport in the tokamak resembles transport in stellarators more than at higher currents. Secondly, experiments have been done to study the relation of the diffusivity χ to the temperature and its gradient in both W7-AS and RTP. In this case the underlying idea was to find the explanation for the phenomenon observed in both tokamaks and stellarators that the quality of the confinement degrades when more heating is applied. A possible explanation is that the diffusivity increases with the temperature or its gradient. Whereas in standard tokamak and stellarator experiments the temperature and its gradient are strongly correlated, a special capability of the plasma heating system of W7-AS and RTP can force them to decouple. (orig.)

  5. Electron heat transport in current carrying and currentless thermonuclear plasmas. Tokamaks and stellarators compared

    Energy Technology Data Exchange (ETDEWEB)

    Peters, M

    1996-01-16

    In the first experiment the plasma current in the RTP tokamak is varied. Here the underlying idea was to check whether at a low plasma current, transport in the tokamak resembles transport in stellarators more than at higher currents. Secondly, experiments have been done to study the relation of the diffusivity {chi} to the temperature and its gradient in both W7-AS and RTP. In this case the underlying idea was to find the explanation for the phenomenon observed in both tokamaks and stellarators that the quality of the confinement degrades when more heating is applied. A possible explanation is that the diffusivity increases with the temperature or its gradient. Whereas in standard tokamak and stellarator experiments the temperature and its gradient are strongly correlated, a special capability of the plasma heating system of W7-AS and RTP can force them to decouple. (orig.).

  6. Plasma rotation under a driven radial current in a tokamak

    International Nuclear Information System (INIS)

    Chang, C.S.

    1999-01-01

    The neoclassical behaviour of plasma rotation under a driven radial electrical current is studied in a tokamak geometry. An ambipolar radial electric field develops instantly in such a way that the driven current is balanced by a return current j p in the plasma. The j p x B torque pushes the plasma into a new rotation state both toroidally and poloidally. An anomalous toroidal viscosity is needed to avoid an extreme toroidal rotation speed. It is shown that the poloidal rotation relaxes to a new equilibrium speed, which is in general smaller than the E x B poloidal speed, and that the timescale for the relaxation of poloidal rotation is the same as that of toroidal rotation generation, which is usually much longer than the ion-ion collision time. (author)

  7. Behavior of Triple Langmuir Probes in Non-Equilibrium Plasmas

    Science.gov (United States)

    Polzin, Kurt A.; Ratcliffe, Alicia C.

    2018-01-01

    The triple Langmuir probe is an electrostatic probe in which three probe tips collect current when inserted into a plasma. The triple probe differs from a simple single Langmuir probe in the nature of the voltage applied to the probe tips. In the single probe, a swept voltage is applied to the probe tip to acquire a waveform showing the collected current as a function of applied voltage (I-V curve). In a triple probe three probe tips are electrically coupled to each other with constant voltages applied between each of the tips. The voltages are selected such that they would represent three points on the single Langmuir probe I-V curve. Elimination of the voltage sweep makes it possible to measure time-varying plasma properties in transient plasmas. Under the assumption of a Maxwellian plasma, one can determine the time-varying plasma temperature T(sub e)(t) and number density n(sub e)(t) from the applied voltage levels and the time-histories of the collected currents. In the present paper we examine the theory of triple probe operation, specifically focusing on the assumption of a Maxwellian plasma. Triple probe measurements have been widely employed for a number of pulsed and timevarying plasmas, including pulsed plasma thrusters (PPTs), dense plasma focus devices, plasma flows, and fusion experiments. While the equilibrium assumption may be justified for some applications, it is unlikely that it is fully justifiable for all pulsed and time-varying plasmas or for all times during the pulse of a plasma device. To examine a simple non-equilibrium plasma case, we return to basic governing equations of probe current collection and compute the current to the probes for a distribution function consisting of two Maxwellian distributions with different temperatures (the two-temperature Maxwellian). A variation of this method is also employed, where one of the Maxwellians is offset from zero (in velocity space) to add a suprathermal beam of electrons to the tail of the

  8. Scattering of a TEM wave from a time varying surface

    Science.gov (United States)

    Elcrat, Alan R.; Harder, T. Mark; Stonebraker, John T.

    1990-03-01

    A solution is given for reflection of a plane wave with TEM polarization from a planar surface with time varying properties. These properties are given in terms of the currents on the surface. The solution is obtained by numerically solving a system of differential-delay equations in the time domain.

  9. Observation of minor collapse of current-carrying plasma in LHD

    International Nuclear Information System (INIS)

    Narushima, Yoshiro; Sakakibara, Satoru; Watanabe, Kiyomasa

    2006-01-01

    A minor collapse observed in current-carrying plasma has been investigated in Large Helical Device (LHD). The magnetic configuration with high central rotational transform has ι/2π=1 surface at the core region and is relatively unstable for the m/n=1/1 mode (here, m and n are the poloidal and toroidal mode number, respectively). When the beam-driven current exceeds a certain value, the m/n=1/1 mode grows with a growth time of ∼30 ms and causes a sudden drop of the plasma stored energy and the electron temperature, and it also limits the plasma current itself. A local flattening in an electron temperature profile appears just after the minor collapse. The mode does not rotate and stays at the same spatial location. The possibility of pressure- and current-driven magneto-hydro dynamics (MHD) instabilities is discussed. (author)

  10. Dissipative dust-acoustic shock waves in a varying charge electronegative magnetized dusty plasma with trapped electrons

    Energy Technology Data Exchange (ETDEWEB)

    Bacha, Mustapha [Faculty of Physics, Theoretical Physics Laboratory, Plasma Physics Group, University of Bab-Ezzouar, USTHB, B.P. 32, El Alia, Algiers 16111 (Algeria); Tribeche, Mouloud, E-mail: mouloudtribeche@yahoo.fr, E-mail: mtribeche@usthb.dz [Faculty of Physics, Theoretical Physics Laboratory, Plasma Physics Group, University of Bab-Ezzouar, USTHB, B.P. 32, El Alia, Algiers 16111 (Algeria); Algerian Academy of Sciences and Technologies, Algiers (Algeria)

    2016-08-15

    The combined effects of an oblique magnetic field and electron trapping on dissipative dust-acoustic waves are examined in varying charge electronegative dusty plasmas with application to the Halley Comet plasma (∼10{sup 4} km from the nucleus). A weakly nonlinear analysis is carried out to derive a modified Korteweg-de Vries-Burger-like equation. Making use of the equilibrium current balance equation, the physically admissible values of the electron trapping parameter are first constrained. We then show that the Burger dissipative term is solely due to the dust charge variation process. It is found that an increase of the magnetic field obliqueness or a decrease of its magnitude renders the shock structure more dispersive.

  11. Dynamics of low density coronal plasma in low current x-pinches

    International Nuclear Information System (INIS)

    Haas, D; Bott, S C; Vikhrev, V; Eshaq, Y; Ueda, U; Zhang, T; Baranova, E; Krasheninnikov, S I; Beg, F N

    2007-01-01

    Experiments were performed on an x-pinch using a pulsed power current generator capable of producing an 80 kA current with a rise time of 50 ns. Molybdenum wires with and without gold coating were employed to study the effect of high z coating on the low-density ( 18 cm -3 ) coronal plasma dynamics. A comparison of images from XUV frames and optical probing shows that the low density coronal plasma from the wires initially converges at the mid-plane immediately above and below the cross-point. A central jet is formed which moves with a velocity of 6 x 10 4 ms -1 towards both electrodes forming a z-pinch column before the current maximum. A marked change in the low density coronal plasma dynamics was observed when molybdenum wires coated with ∼ 0.09 μm of gold were used. The processes forming the jet structure were delayed relative to bare Mo x-pinches, and the time-resolved x-ray emission also showed differences. An m = 0 instability was observed in the coronal plasma along the x-pinch legs, which were consistent with x-ray PIN diode signals in which x-ray pulses were observed before x-ray spot formation. These early time x-ray pulses were not observed with pure molybdenum x-pinches. These observations indicate that a thin layer of gold coating significantly changes the coronal plasma behaviour. Two dimensional MHD simulations were performed and qualitatively agree with experimental observations of low density coronal plasma

  12. Magnetoacoustic waves in current-carrying plasmas

    International Nuclear Information System (INIS)

    Brennan, M.H.

    1980-04-01

    The results of theoretical and experimental investigations of the characteristics of magnetoacoustic waves in non-uniform, current-carrying plasmas are reviewed. Dissipative MHD and collisionless theories are considered. Also discussed is the use of magnetoacoustic waves in plasma diagnostics and plasma heating

  13. Optimizing platelet-rich plasma gel formation by varying time and gravitational forces during centrifugation.

    Science.gov (United States)

    Jo, Chris H; Roh, Young Hak; Kim, Ji Eun; Shin, Sue; Yoon, Kang Sup

    2013-10-01

    Despite the increasing clinical use of topical platelet-rich plasma (PRP) to enhance tissue healing and regeneration, there is no properly standardized method of autologous PRP gel preparation. This study examined the effect of the centrifugation time and gravitational force (g) on the platelet recovery ratio of PRP and determined the most effective centrifugation conditions for preparing PRP. Two-step centrifugations for preparing PRP were used in 39 subjects who had consented prior to the study's start. The separating centrifugation (Step 1, used to separate whole blood into its two main components: red blood cells and plasma) was tested from 500g to 1900g at 200g increments for 5 minutes (min), and from 100g to 1300g at 200g increments for 10 minutes. After separating centrifugation, upper plasma layer was transferred to another plain tube for the condensation centrifugation and remaining lower cell layer was discarded. The condensation centrifugation (Step 2, used to condense the platelets in the separated plasma) was tested at 1000g for 15 min, 1500g for 15 min, 2000g for 5 min and 3000g for 5 min, additionally at 1000g for 10 min and 1500g for 10 min. Platelet gelation was induced by adding 10% calcium gluconate to final PRP with volume ratio of 1:10. The optimal separating centrifugation conditions were followed by 900g for 5 minutes and the condensation conditions were followed by 1500g for 15 minutes, of which recovery ratios were 92.0 ± 3.1% and 84.3 ± 10.0%, respectively.

  14. KINETIC-J: A computational kernel for solving the linearized Vlasov equation applied to calculations of the kinetic, configuration space plasma current for time harmonic wave electric fields

    Science.gov (United States)

    Green, David L.; Berry, Lee A.; Simpson, Adam B.; Younkin, Timothy R.

    2018-04-01

    We present the KINETIC-J code, a computational kernel for evaluating the linearized Vlasov equation with application to calculating the kinetic plasma response (current) to an applied time harmonic wave electric field. This code addresses the need for a configuration space evaluation of the plasma current to enable kinetic full-wave solvers for waves in hot plasmas to move beyond the limitations of the traditional Fourier spectral methods. We benchmark the kernel via comparison with the standard k →-space forms of the hot plasma conductivity tensor.

  15. Spatial and Time Dynamics of Non-Linear Vortices in Plasma Lens for High-Current Ion Beam Focusing

    Science.gov (United States)

    Goncharov, Alexei A.; Maslov, Vasyl I.; Onishchenko, Ivan N.; Tretyakov, Vitalij N.

    2002-11-01

    It is known from numerical simulation (see, for example, [1]) and from experiments (see, for example, [2]), that an electron density bunches as discrete vortices are long - living structures in vacuum. However, in laboratory experiments [2] it has been shown that the vortices are changed faster, when they are submersed in electrons, distributed around them. The charged plasma lens intended for a focussing of high-current ion beams, has the same crossed configuration of a radial electrical and longitudinal magnetic field [3], as only electron plasma. In this lens the vortical turbulence is excited [3]. The vortex - bunch and vortex - hole are rotated in the inverse directions in system of their rest. The instability development in initially homogeneous plasma causes that the vortices are excited by pairs. Namely, if the vortex - bunch of electrons is generated, near the vortex - hole of electrons is also generated. It is shown, that in nonuniform plasma the vortices behave is various in time. Namely, the vortex - bunch goes to area of larger electron density, and the vortex - hole goes to area of smaller electron density. The speed of the vortex - hole is less than speed of the vortex - bunch. It is shown, that the electron vortices, generated in the plasma lens, can result in to formation of spiral distribution of electron density. The physical mechanism of coalescence of electron vortices - bunches is proposed. 1.Driscoll C.F. et al. Plasma Phys. Contr. Fus. Res. 3 (1989) 507. 2.Kiwamoto Y. et al. Non-neutral plasma physics. Princeton. 1999. P. 99-105. 3.Goncharov A. et al. Plasma Phys. Rep. 20 (1994) 499.

  16. Fast wave current drive in H mode plasmas on the DIII-D tokamak

    International Nuclear Information System (INIS)

    Petty, C.C.; Grassie, J.S. de; Baity, F.W.

    1999-01-01

    Current driven by fast Alfven waves is measured in H mode and VH mode plasmas on the DIII-D tokamak for the first time. Analysis of the poloidal flux evolution shows that the fast wave current drive profile is centrally peaked but sometimes broader than theoretically expected. Although the measured current drive efficiency is in agreement with theory for plasmas with infrequent ELMs, the current drive efficiency is an order of magnitude too low for plasmas with rapid ELMs. Power modulation experiments show that the reduction in current drive with increasing ELM frequency is due to a reduction in the fraction of centrally absorbed fast wave power. The absorption and current drive are weakest when the electron density outside the plasma separatrix is raised above the fast wave cut-off density by the ELMs, possibly allowing an edge loss mechanism to dissipate the fast wave power since the cut-off density is a barrier for fast waves leaving the plasma. (author)

  17. Zhang neural network for online solution of time-varying convex quadratic program subject to time-varying linear-equality constraints

    International Nuclear Information System (INIS)

    Zhang Yunong; Li Zhan

    2009-01-01

    In this Letter, by following Zhang et al.'s method, a recurrent neural network (termed as Zhang neural network, ZNN) is developed and analyzed for solving online the time-varying convex quadratic-programming problem subject to time-varying linear-equality constraints. Different from conventional gradient-based neural networks (GNN), such a ZNN model makes full use of the time-derivative information of time-varying coefficient. The resultant ZNN model is theoretically proved to have global exponential convergence to the time-varying theoretical optimal solution of the investigated time-varying convex quadratic program. Computer-simulation results further substantiate the effectiveness, efficiency and novelty of such ZNN model and method.

  18. High-Current Plasma Electron Sources

    International Nuclear Information System (INIS)

    Gushenets, J.Z.; Krokhmal, V.A.; Krasik, Ya. E.; Felsteiner, J.; Gushenets, V.

    2002-01-01

    In this report we present the design, electrical schemes and preliminary results of a test of 4 different electron plasma cathodes operating under Kg h-voltage pulses in a vacuum diode. The first plasma cathode consists of 6 azimuthally symmetrically distributed arc guns and a hollow anode having an output window covered by a metal grid. Plasma formation is initiated by a surface discharge over a ceramic washer placed between a W-made cathode and an intermediate electrode. Further plasma expansion leads to a redistribution of the discharge between the W-cathode and the hollow anode. An accelerating pulse applied between the output anode grid and the collector extracts electrons from this plasma. The operation of another plasma cathode design is based on Penning discharge for preliminary plasma formation. The main glow discharge occurs between an intermediate electrode of the Penning gun and the hollow anode. To keep the background pressure in the accelerating gap at P S 2.5x10 4 Torr either differential pumping or a pulsed gas puff valve were used. The operation of the latter electron plasma source is based on a hollow cathode discharge. To achieve a sharp pressure gradient between the cathode cavity and the accelerating gap a pulsed gas puff valve was used. A specially designed ferroelectric plasma cathode initiated plasma formation inside the hollow cathode. This type of the hollow cathode discharge ignition allowed to achieve a discharge current of 1.2 kA at a background pressure of 2x10 4 Torr. All these cathodes were developed and initially tested inside a planar diode with a background pressure S 2x10 4 Torr under the same conditions: accelerating voltage 180 - 300 kV, pulse duration 200 - 400 ns, electron beam current - 1 - 1.5 kA, and cross-sectional area of the extracted electron beam 113 cm 2

  19. Current control necessary for toroidal plasma equilibrium

    International Nuclear Information System (INIS)

    Nagao, S.

    1987-01-01

    It is shown that a significant amount of dipole current is necessary for the plasma equilibrium of toroidal configurations in general. Through the vector product with the poloidal field, this dipole current force has to balance with the hoop force of plasma pressure itself of the annular shape. The measurement of such a current of dipole type may be interesting for the confirmation of the plasma equilibrium in the toroidal system. Moreover it is certained that there is a new mode of a tokamak operation with such a dipole current component and with smaller vertical field than that based on the classical tokamak theory. (author) [pt

  20. Time-varying Crash Risk

    DEFF Research Database (Denmark)

    Christoffersen, Peter; Feunoua, Bruno; Jeon, Yoontae

    We estimate a continuous-time model with stochastic volatility and dynamic crash probability for the S&P 500 index and find that market illiquidity dominates other factors in explaining the stock market crash risk. While the crash probability is time-varying, its dynamic depends only weakly on re...

  1. A New Time-varying Concept of Risk in a Changing Climate

    Science.gov (United States)

    Sarhadi, Ali; Ausín, María Concepción; Wiper, Michael P.

    2016-10-01

    In a changing climate arising from anthropogenic global warming, the nature of extreme climatic events is changing over time. Existing analytical stationary-based risk methods, however, assume multi-dimensional extreme climate phenomena will not significantly vary over time. To strengthen the reliability of infrastructure designs and the management of water systems in the changing environment, multidimensional stationary risk studies should be replaced with a new adaptive perspective. The results of a comparison indicate that current multi-dimensional stationary risk frameworks are no longer applicable to projecting the changing behaviour of multi-dimensional extreme climate processes. Using static stationary-based multivariate risk methods may lead to undesirable consequences in designing water system infrastructures. The static stationary concept should be replaced with a flexible multi-dimensional time-varying risk framework. The present study introduces a new multi-dimensional time-varying risk concept to be incorporated in updating infrastructure design strategies under changing environments arising from human-induced climate change. The proposed generalized time-varying risk concept can be applied for all stochastic multi-dimensional systems that are under the influence of changing environments.

  2. A New Time-varying Concept of Risk in a Changing Climate.

    Science.gov (United States)

    Sarhadi, Ali; Ausín, María Concepción; Wiper, Michael P

    2016-10-20

    In a changing climate arising from anthropogenic global warming, the nature of extreme climatic events is changing over time. Existing analytical stationary-based risk methods, however, assume multi-dimensional extreme climate phenomena will not significantly vary over time. To strengthen the reliability of infrastructure designs and the management of water systems in the changing environment, multidimensional stationary risk studies should be replaced with a new adaptive perspective. The results of a comparison indicate that current multi-dimensional stationary risk frameworks are no longer applicable to projecting the changing behaviour of multi-dimensional extreme climate processes. Using static stationary-based multivariate risk methods may lead to undesirable consequences in designing water system infrastructures. The static stationary concept should be replaced with a flexible multi-dimensional time-varying risk framework. The present study introduces a new multi-dimensional time-varying risk concept to be incorporated in updating infrastructure design strategies under changing environments arising from human-induced climate change. The proposed generalized time-varying risk concept can be applied for all stochastic multi-dimensional systems that are under the influence of changing environments.

  3. Experimental study of current loss and plasma formation in the Z machine post-hole convolute

    Directory of Open Access Journals (Sweden)

    M. R. Gomez

    2017-01-01

    Full Text Available The Z pulsed-power generator at Sandia National Laboratories drives high energy density physics experiments with load currents of up to 26 MA. Z utilizes a double post-hole convolute to combine the current from four parallel magnetically insulated transmission lines into a single transmission line just upstream of the load. Current loss is observed in most experiments and is traditionally attributed to inefficient convolute performance. The apparent loss current varies substantially for z-pinch loads with different inductance histories; however, a similar convolute impedance history is observed for all load types. This paper details direct spectroscopic measurements of plasma density, temperature, and apparent and actual plasma closure velocities within the convolute. Spectral measurements indicate a correlation between impedance collapse and plasma formation in the convolute. Absorption features in the spectra show the convolute plasma consists primarily of hydrogen, which likely forms from desorbed electrode contaminant species such as H_{2}O, H_{2}, and hydrocarbons. Plasma densities increase from 1×10^{16}  cm^{−3} (level of detectability just before peak current to over 1×10^{17}  cm^{−3} at stagnation (tens of ns later. The density seems to be highest near the cathode surface, with an apparent cathode to anode plasma velocity in the range of 35–50  cm/μs. Similar plasma conditions and convolute impedance histories are observed in experiments with high and low losses, suggesting that losses are driven largely by load dynamics, which determine the voltage on the convolute.

  4. Plasma flow discharge researches at the PIRIT-2000 facility

    International Nuclear Information System (INIS)

    Popkov, N.F.; Ryaslov, E.A.; Kargin, V.I.; Pikar', A.S.; Vorontsov, V.I.; Kotel'nikov, D.V.; Melkozerov, A.V.

    1996-01-01

    Investigation of a plasma flow switch at the PIRIT-2000 fast operating capacitor bank is reported. The maximum current of the plasma flow discharge (PFD) reaches 5 MA, the current rise time being as low as 100 ns. The magnetic field strength of the plasma flow switch (0.15 T) is about 15 times higher than that of the plasma erosion switch used earlier. Both magnetic probe and optical methods were used in the experiments. From the magnetic probes data the propagating velocity of a current carrying shell (205 cm/s) has been derived, while the optical method is used for determining the velocity of a glowing plasma layer. At varying the operation delay in the range 2-10 s the PFD load current rise time increases up to 150-200 ns, the prepulse increment reaching its maximum at the delays higher than 6 s. (J.U.). 5 figs., 5 refs

  5. Plasma flow discharge researches at the PIRIT-2000 facility

    Energy Technology Data Exchange (ETDEWEB)

    Popkov, N F; Ryaslov, E A; Kargin, V I; Pikar` , A S; Vorontsov, V I; Kotel` nikov, D V; Melkozerov, A V [All-Russian Scientific Research Inst. of Experimental Physics, Sarov (Russian Federation)

    1997-12-31

    Investigation of a plasma flow switch at the PIRIT-2000 fast operating capacitor bank is reported. The maximum current of the plasma flow discharge (PFD) reaches 5 MA, the current rise time being as low as 100 ns. The magnetic field strength of the plasma flow switch (0.15 T) is about 15 times higher than that of the plasma erosion switch used earlier. Both magnetic probe and optical methods were used in the experiments. From the magnetic probes data the propagating velocity of a current carrying shell (205 cm/s) has been derived, while the optical method is used for determining the velocity of a glowing plasma layer. At varying the operation delay in the range 2-10 s the PFD load current rise time increases up to 150-200 ns, the prepulse increment reaching its maximum at the delays higher than 6 s. (J.U.). 5 figs., 5 refs.

  6. Compression enhancement by current stepping in a multicascade liner gas-puff Z-pinch plasma

    Energy Technology Data Exchange (ETDEWEB)

    Khattak, N A D [Department of Physics, Gomal Unversity, D I Khan (Pakistan); Ahmad, Zahoor; Murtaza, G [National Tokamak Fusion Program, PAEC, Islamabad (Pakistan); Zakaullah, M [Department of Physics, Quaid-i-Azam University, Islamabad 45320 (Pakistan)], E-mail: ktk_nad@yahoo.com

    2008-04-15

    Plasma dynamics of a liner consisting of two or three annular cascade gas-puffs with entrained axial magnetic field is studied using the modified snow-plow model. The current stepping technique (Les 1984 J. Phys. D: Appl. Phys. 17 733) is employed to enhance compression of the imploding plasma. A small-diameter low-voltage-driven system of imploding plasma is considered in order to work out the possibility of the highest gain, in terms of plasma parameters and radiation yield with a relatively simple and compact system. Our numerical results demonstrate that current stepping enhances the plasma compression, yielding high values of the plasma parameters and compressed magnetic field B{sub z} (in magnitudes), if the switching time for the additional current is properly synchronized.

  7. Compression enhancement by current stepping in a multicascade liner gas-puff Z-pinch plasma

    International Nuclear Information System (INIS)

    Khattak, N A D; Ahmad, Zahoor; Murtaza, G; Zakaullah, M

    2008-01-01

    Plasma dynamics of a liner consisting of two or three annular cascade gas-puffs with entrained axial magnetic field is studied using the modified snow-plow model. The current stepping technique (Les 1984 J. Phys. D: Appl. Phys. 17 733) is employed to enhance compression of the imploding plasma. A small-diameter low-voltage-driven system of imploding plasma is considered in order to work out the possibility of the highest gain, in terms of plasma parameters and radiation yield with a relatively simple and compact system. Our numerical results demonstrate that current stepping enhances the plasma compression, yielding high values of the plasma parameters and compressed magnetic field B z (in magnitudes), if the switching time for the additional current is properly synchronized

  8. Determination of the plasma position for its real-time control in the COMPASS tokamak

    International Nuclear Information System (INIS)

    Janky, F.; Havlicek, J.; Valcarcel, D.; Hron, M.; Horacek, J.; Kudlacek, O.; Panek, R.; Carvalho, B.B.

    2011-01-01

    An efficient horizontal and vertical stabilization of the plasma column position are essential for a reliable tokamak operation. Plasma position is generally determined by plasma current, plasma pressure and external vertical and horizontal magnetic fields. Such fields are generated by poloidal field coils and proper algorithm for the current control have to by applied, namely, in case of fast feedback loops. This paper presents a real-time plasma position reconstruction algorithms developed for the COMPASS tokamak. Further, its implementation in the MARTe (Multithreaded Application Real-Time executor) is described and the first results from test of the algorithm for real-time control of horizontal plasma positions are presented.

  9. Determination of the plasma position for its real-time control in the COMPASS tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Janky, F., E-mail: jankyf@ipp.cas.cz [Institute of Plasma Physics, AS CR, v.v.i., Association EURATOM/IPP.CR, Za Slovankou 3, 182 00 Prague (Czech Republic); Charles University in Prague, Faculty of Mathematics and Physics, V Holesovickach 2, CZ-18000 Prague (Czech Republic); Havlicek, J. [Institute of Plasma Physics, AS CR, v.v.i., Association EURATOM/IPP.CR, Za Slovankou 3, 182 00 Prague (Czech Republic); Charles University in Prague, Faculty of Mathematics and Physics, V Holesovickach 2, CZ-18000 Prague (Czech Republic); Valcarcel, D. [Associacao EURATOM/IST, Instituto de Plasmas e Fusao Nuclear - Laboratorio Associado, Instituto Superior Tecnico, P1049-001 Lisboa (Portugal); Hron, M.; Horacek, J. [Institute of Plasma Physics, AS CR, v.v.i., Association EURATOM/IPP.CR, Za Slovankou 3, 182 00 Prague (Czech Republic); Kudlacek, O. [Czech Technical University, Faculty of Nuclear Sciences and Physical Engineering, Technicka 2, 166 27 Prague (Czech Republic); Panek, R. [Institute of Plasma Physics, AS CR, v.v.i., Association EURATOM/IPP.CR, Za Slovankou 3, 182 00 Prague (Czech Republic); Carvalho, B.B. [Associacao EURATOM/IST, Instituto de Plasmas e Fusao Nuclear - Laboratorio Associado, Instituto Superior Tecnico, P1049-001 Lisboa (Portugal)

    2011-10-15

    An efficient horizontal and vertical stabilization of the plasma column position are essential for a reliable tokamak operation. Plasma position is generally determined by plasma current, plasma pressure and external vertical and horizontal magnetic fields. Such fields are generated by poloidal field coils and proper algorithm for the current control have to by applied, namely, in case of fast feedback loops. This paper presents a real-time plasma position reconstruction algorithms developed for the COMPASS tokamak. Further, its implementation in the MARTe (Multithreaded Application Real-Time executor) is described and the first results from test of the algorithm for real-time control of horizontal plasma positions are presented.

  10. Heating of plasmas in tokamaks by current-driven turbulence

    International Nuclear Information System (INIS)

    Kluiver, H. de.

    1985-10-01

    Investigations of current-driven turbulence have shown the potential to heat plasmas to elevated temperatures in relatively small cross-section devices. The fundamental processes are rather well understood theoretically. Even as it is shown to be possible to relax the technical requirements on the necessary electric field and the pulse length to acceptable values, the effect of energy generation near the plasma edge, the energy transport, the impurity influx and the variation of the current profile are still unknown for present-day large-radius tokamaks. Heating of plasmas by quasi-stationary weakly turbulent states caused by moderate increases of the resistivity due to higher loop voltages could be envisaged. Power supplies able to furnish power levels 5-10 times higher than the usual values could be used for a demonstration of those regimes. At several institutes and university laboratories the study of turbulent heating in larger tokamaks and stellarators is pursued

  11. The role of surface currents in plasma confinement

    International Nuclear Information System (INIS)

    Webster, Anthony J.

    2011-01-01

    During plasma instabilities, ''surface currents'' can flow at the interface between the plasma and the surrounding vacuum, and in most cases, they are a harmless symptom of the instability that is causing them. Large instabilities can lead to ''disruptions,'' an abrupt termination of the plasma with the potential to damage the machine in which it is contained. For disruptions, the correct calculation of surface currents is thought to be essential for modelling disruptions properly. Recently, however, there has been debate and disagreement about the correct way to calculate surface currents. The purpose of this paper is to clarify as simply as possible the role of surface currents for plasma confinement and to show that a commonly used representation for surface currents σ-vector with σ-vector=∇I and n-vector, I a scalar function, and n-vector the unit normal to the plasma surface, is only appropriate for the calculation of surface currents that are in magnetohydrodynamic equilibrium. Fortunately, this is the situation thought to be of most relevance for disruption calculations.

  12. Dynamic voltage-current characteristics for a water jet plasma arc

    International Nuclear Information System (INIS)

    Yang Jiaxiang; Lan Sheng; Xu Zuoming

    2008-01-01

    A virtual instrument technology is used to measure arc current, arc voltage, dynamic V-I characteristics, and nonlinear conductance for a cone-shaped water jet plasma arc under ac voltage. Experimental results show that ac arc discharge mainly happens in water vapor evaporated from water when heated. However, due to water's cooling effect and its conductance, arc conductance, reignition voltage, extinguish voltage, and current zero time are very different from those for ac arc discharge in gas work fluid. These can be valuable to further studies on mechanism and characteristics of plasma ac discharge in water, and even in gas work fluid

  13. TFTR plasma feedback systems

    International Nuclear Information System (INIS)

    Efthimion, P.; Hawryluk, R.J.; Hojsak, W.; Marsala, R.J.; Mueller, D.; Rauch, W.; Tait, G.D.; Taylor, G.; Thompson, M.

    1985-01-01

    The Tokamak Fusion Test Reactor employs feedback control systems for four plasma parameters, i.e. for plasma current, for plasma major radius, for plasma vertical position, and for plasma density. The plasma current is controlled by adjusting the rate of change of current in the Ohmic Heating (OH) coil system. Plasma current is continuously sensed by a Rogowski coil and its associated electronics; the error between it and a preprogrammed reference plasma current history is operated upon by a ''proportional-plusintegral-plus-derivative'' (PID) control algorithm and combined with various feedforward terms, to generate compensating commands to the phase-controlled thyristor rectifiers which drive current through the OH coils. The plasma position is controlled by adjusting the currents in Equilibrium Field and Horizontal Field coil systems, which respectively determine the vertical and radial external magnetic fields producing J X B forces on the plasma current. The plasma major radius position and vertical position, sensed by ''B /sub theta/ '' and ''B /sub rho/ '' magnetic flux pickup coils with their associated electronics, are controlled toward preprogrammed reference histories by allowing PID and feedforward control algorithms to generate commands to the EF and HF coil power supplies. Plasma density is controlled by adjusting the amount of gas injected into the vacuum vessel. Time-varying gains are used to combine lineaveraged plasma density measurements from a microwave interferometer plasma diagnostic system with vacuum vessel pressure measurements from ion gauges, with various other measurements, and with preprogrammed reference histories, to determine commands to piezoelectric gas injection valves

  14. Measurement of plasma current in Tokamaks using an optical fibre reflectometry technique

    Directory of Open Access Journals (Sweden)

    Wuilpart Marc

    2018-01-01

    Full Text Available An optical time-domain reflectometer sensitive to the polarization of light is proposed for the measurement of plasma current in the Tore Supra fusion reactor. The measurement principle relies on the Faraday effect i.e. on the generation of a circular birefringence along an optical fiber subject to an axial magnetic field. The circular birefringence induces a polarization rotation that can be mapped along the fiber thanks to an opticaltime domain reflectometer followed by an linear polarizer. A proper fitting of the measurement trace then allows determining the applied plasma current. The sensor has been experimentally validated on the Tore Supra tokamak fusion reactor for a plasma current range going from 0.6 to 1.5 MA. A maximum error of 13.50% has been observed for the lowest current.

  15. The formation of metallic plasmas in transient capillary discharges at high current

    International Nuclear Information System (INIS)

    Wyndham, E S; Favre, M; Aliaga-Rossel, R

    2006-01-01

    We report observations of the formation of a metallic plasma in a high aspect ratio z-pinch confined within a ceramic capillary. A series of experiments on different capillary geometries was undertaken in which titanium metal rings were used to promote the formation of a titanium plasma through preferential ablation. In an initial vacuum a titanium seed plasma is formed in the hollow cathode (HC) volume by a low energy laser spark. This pre-ionizing plasma is assisted in its expansion into the z-pinch volume by the electron beams generated by a pre-ionizing discharge in the capillary, due to the HC effect. Further intense e-beam activity occurs on applying the main driver current to the capillary electrodes before the discharge impedance abruptly drops to give rise to an ensuing high current z-pinch. A segmented titanium ring structure within the capillary promotes metal ablation. The discharges are performed in tubes of 60 to 110 mm length and 3 and 5 mm effective internal diameter. The main discharge current is provided from a small pulsed power switched coaxial line, at up to 150 kA. The generator may be configured to deliver two different rates of current rise and this is found to have a significant effect on the plasma dynamics. The plasma properties are obtained from observations of the axial x-ray emission. The diagnostics used are filtered Si diodes, filtered time-resolved multi-pinhole camera images and the time resolved soft x-ray spectrum from 3 to 20 nm. While a single species metal plasma is not obtained, a very significant proportion of Ti is achieved in the higher rate of current rise configuration. The fraction of Ti diminishes for the longest length discharges and for the larger diameter tube diameter, as does the observed z-pinch uniformity. There is a weak dependance of the electron temperature with tube geometry, but the plasma density falls substantially in the longer discharges. This coincides with diminished effectiveness of the transient HC

  16. Current drive by asymmetrical heating in a toroidal plasma

    International Nuclear Information System (INIS)

    Gahl, J.M.

    1986-01-01

    This report describes the first experimental observation of current generation by asymmetrical heating of ions. A unidirectional fast Alfven wave launched by a slow-wave antenna inside the Texas Tech Tokamak, asymmetrically heated the ions. Measurements of the asymmetry of the toroidal plasma current with probes at the top and bottom of the toroidal plasma column confirmed the current generation indirectly. Current generation, obtained in a one-species, hydrogen plasma, is a phenomenon which had not been predicted previously. Calculations of the dispersion relation for the fast Alfven wave near the fundamental cyclotron resonance in a one-species, hydrogen plasma, using warm plasma theory, support the experimental results

  17. Off-axis current drive and real-time control of current profile in JT-60U

    International Nuclear Information System (INIS)

    Suzuki, T.; Ide, S.; Oikawa, T.; Fujita, T.; Ishikawa, M.; Seki, M.; Matsunaga, G.; Hatae, T.; Naito, O.; Hamamatsu, K.; Sueoka, M.; Hosoyama, H.; Nakazato, M.

    2008-01-01

    Aiming at optimization of current profile in high-β plasmas for higher confinement and stability, a real-time control system of the minimum of the safety factor (q min ) using the off-axis current drive has been developed. The off-axis current drive can raise the safety factor in the centre and help to avoid instability that limits the performance of the plasma. The system controls the injection power of lower-hybrid waves, and hence its off-axis driven current in order to control q min . The real-time control of q min is demonstrated in a high-β plasma, where q min follows the temporally changing reference q min,ref from 1.3 to 1.7. Applying the control to another high-β discharge (β N = 1.7, β p = 1.5) with m/n = 2/1 neo-classical tearing mode (NTM), q min was raised above 2 and the NTM was suppressed. The stored energy increased by 16% with the NTM suppressed, since the resonant rational surface was eliminated. For the future use for current profile control, current density profile for off-axis neutral beam current drive (NBCD) is for the first time measured, using the motional Stark effect diagnostic. Spatially localized NBCD profile was clearly observed at the normalized minor radius ρ of about 0.6-0.8. The location was also confirmed by multi-chordal neutron emission profile measurement. The total amount of the measured beam driven current was consistent with the theoretical calculation using the ACCOME code. The CD location in the calculation was inward shifted than the measurement

  18. Time-Varying Networks of Inter-Ictal Discharging Reveal Epileptogenic Zone.

    Science.gov (United States)

    Zhang, Luyan; Liang, Yi; Li, Fali; Sun, Hongbin; Peng, Wenjing; Du, Peishan; Si, Yajing; Song, Limeng; Yu, Liang; Xu, Peng

    2017-01-01

    The neuronal synchronous discharging may cause an epileptic seizure. Currently, most of the studies conducted to investigate the mechanism of epilepsy are based on EEGs or functional magnetic resonance imaging (fMRI) recorded during the ictal discharging or the resting-state, and few studies have probed into the dynamic patterns during the inter-ictal discharging that are much easier to record in clinical applications. Here, we propose a time-varying network analysis based on adaptive directed transfer function to uncover the dynamic brain network patterns during the inter-ictal discharging. In addition, an algorithm based on the time-varying outflow of information derived from the network analysis is developed to detect the epileptogenic zone. The analysis performed revealed the time-varying network patterns during different stages of inter-ictal discharging; the epileptogenic zone was activated prior to the discharge onset then worked as the source to propagate the activity to other brain regions. Consistence between the epileptogenic zones detected by our proposed approach and the actual epileptogenic zones proved that time-varying network analysis could not only reveal the underlying neural mechanism of epilepsy, but also function as a useful tool in detecting the epileptogenic zone based on the EEGs in the inter-ictal discharging.

  19. Time resolved EUV spectra from Zpinching capillary discharge plasma

    Science.gov (United States)

    Jancarek, Alexandr; Nevrkla, Michal; Nawaz, Fahad

    2015-09-01

    We developed symmetrically charged driver to obtain high voltage, high current Z-pinching capillary discharge. Plasma is created by up to 70 kA, 29 ns risetime current pulse passing through a 5 mm inner diameter, 224 mm long capillary filled with gas to initial pressure in the range of 1 kPa. Due to the low inductance design of the driver, the pinch is observable directly from the measured current curve. Time-integrated and time-resolved spectra of discharge plasma radiation are recorded together with the capillary current and analyzed. The most encouraging spectra were captured in the wavelength range 8.3 ÷ 14 nm. This spectral region contains nitrogen Balmer series lines including potentially lasing NVII 2 - 3 transition. Spectral lines are identified in the NIST database using the FLY kinetic code. The line of 13.38 nm wavelength, transition NVII 2 - 3, was observed in gated, and also in time-integrated spectra for currents >60 kA. This work has been supported by the Ministry of Education, Youth and Sports of the Czech Republic grants LG13029.

  20. Characterization of the plasma current quench during disruptions in the National Spherical Torus Experiment

    International Nuclear Information System (INIS)

    Gerhardt, S.P.; Menard, J.E.

    2008-01-01

    A detailed analysis of the plasma current quench in the National Spherical Torus Experiment (M.Ono, et al Nuclear Fusion 40, 557 (2000)) is presented. The fastest current quenches are fit better by a linear waveform than an exponential one. Area-normalized current quench times down to .4 msec/m2 have been observed, compared to the minimum of 1.7 msec/m2 recommendation based on conventional aspect ratio tokamaks; as noted in previous ITPA studies, the difference can be explained by the reduced self-inductance at low aspect ratio and high-elongation. The maximum instantaneous dIp/dt is often many times larger than the mean quench rate, and the plasma current before the disruption is often substantially less than the flat-top value. The poloidal field time-derivative during the disruption, which is directly responsible for driving eddy currents, has been recorded at various locations around the vessel. The Ip quench rate, plasma motion, and magnetic geometry all play important roles in determining the rate of poloidal field change

  1. Electron cyclotron heating for current profile control of non-circular plasmas

    International Nuclear Information System (INIS)

    Chan, V.S.; Davidson, R.; Guest, G.; Hacker, M.; Miller, L.

    1981-01-01

    Electron Cyclotron Heating (ECH) offers a promising approach to modifying the radial profiles of electron temperature and plasma current in tokamaks to increase the ideal MHD beta limits and permit experimental access to particular noncircular cross-section tokamaks that cannot be achieved with the peaked current profiles characteristic of ohmically heated tokamaks. We use a one-and-one-half-dimensional, time-dependent transport model that incorporates a self-consistent model of electron cyclotron power absorption to study the temporal evolution of electron temperature and plasma current profiles and the resulting noncircular equilibria. Startup scenarios for high-beta dees and doublets are investigated with this transport modeling

  2. Current scaling of plasma focus devices

    International Nuclear Information System (INIS)

    Schiuma, C.; Herold, H.; Kaeppeler, H.J.; Shakhatre, M.; Auluck, S.K.H.

    1990-03-01

    In continuation of the work by G. Decker et al. on current and neutron yield scaling of plasma focus devices an analytical solution for the circuit equation (with resistance R = 0) in the compression phase was derived. Together with the solution for the rundown phase from G. Decker et al, which was extended for finite resistance (R ≠ 0), there follows an analytical scaling theory for maximum and pinch currents. At the same time there exists the possibility to discuss the influence of finite resistance on current variation and scaling parameters. The model solutions were checked out by numerical integrations of the current equation. While at the beginning of the rundown phase the ohmic resistance cannot be neglected (the magnitude R/L plays an important role), its influence at the end of the rundown phase and in the compression phase is negligible. The theoretically determined values are compared with the results of numerous probe measurements. (orig.)

  3. Simulations of plasma heating caused by the coalescence of multiple current loops in a proton-boron fusion plasma

    International Nuclear Information System (INIS)

    Haruki, T.; Yousefi, H. R.; Sakai, J.-I.

    2010-01-01

    Two dimensional particle-in-cell simulations of a dense plasma focus were performed to investigate a plasma heating process caused by the coalescence of multiple current loops in a proton-boron-electron plasma. Recently, it was reported that the electric field produced during the coalescence of two current loops in a proton-boron-electron plasma heats up all plasma species; proton-boron nuclear fusion may therefore be achievable using a dense plasma focus device. Based on this work, the coalescence process for four and eight current loops was investigated. It was found that the return current plays an important role in both the current pinch and the plasma heating. The coalescence of four current loops led to the breakup of the return current from the pinched plasma, resulting in plasma heating. For the coalescence of eight current loops, the plasma was confined by the pinch but the plasma heating was smaller than the two and four loop cases. Therefore the heating associated with current loop coalescence depends on the number of initial current loops. These results are useful for understanding the coalescence of multiple current loops in a proton-boron-electron plasma.

  4. Plasma response to sustainment with imposed-dynamo current drive in HIT-SI and HIT-SI3

    Science.gov (United States)

    Hossack, A. C.; Jarboe, T. R.; Chandra, R. N.; Morgan, K. D.; Sutherland, D. A.; Penna, J. M.; Everson, C. J.; Nelson, B. A.

    2017-07-01

    The helicity injected torus—steady inductive (HIT-SI) program studies efficient, steady-state current drive for magnetic confinement plasmas using a novel experimental method. Stable, high-beta spheromaks have been sustained using steady, inductive current drive. Externally induced loop voltage and magnetic flux are oscillated together so that helicity and power injection are always positive, sustaining the edge plasma current indefinitely. Imposed-dynamo current drive (IDCD) theory further shows that the entire plasma current is sustained. The method is ideal for low aspect ratio, toroidal geometries with closed flux surfaces. Experimental studies of spheromak plasmas sustained with IDCD have shown stable magnetic profiles with evidence of pressure confinement. New measurements show coherent motion of a stable spheromak in response to the imposed perturbations. On the original device two helicity injectors were mounted on either side of the spheromak and the injected mode spectrum was predominantly n  =  1. Coherent, rigid motion indicates that the spheromak is stable and a lack of plasma-generated n  =  1 energy indicates that the maximum q is maintained below 1 during sustainment. Results from the HIT-SI3 device are also presented. Three inductive helicity injectors are mounted on one side of the spheromak flux conserver. Varying the relative injector phasing changes the injected mode spectrum which includes n  =  2, 3, and higher modes.

  5. Effects of varying doses of β-nerve growth factor on the timing of ovulation, plasma progesterone concentration and corpus luteum size in female alpacas (Vicugna pacos).

    Science.gov (United States)

    Stuart, C C; Vaughan, J L; Kershaw-Young, C M; Wilkinson, J; Bathgate, R; de Graaf, S P

    2015-11-01

    Ovulation in camelids is induced by the seminal plasma protein ovulation-inducing factor (OIF), recently identified as β-nerve growth factor (β-NGF). The present study measured the total protein concentration in alpaca seminal plasma using a bicinchoninic acid (BCA) protein quantification assay and found it to be 22.2±2.0mgmL(-1). To measure the effects of varying doses of β-NGF on the incidence and timing of ovulation, corpus luteum (CL) size and plasma progesterone concentration, 24 female alpacas were synchronised and treated with either: (1) 1mL 0.9% saline (n=5); (2) 4µg buserelin (n=5); (3) 1mg β-NGF protein (n=5); (4) 0.1mg β-NGF (n=5); or (5) 0.01mg β-NGF (n=4). Females were examined by transrectal ultrasonography at 1-2-h intervals between 20 and 45h after treatment or until ovulation occurred, as well as on Day 8 to observe the size of the CL, at which time blood was collected to measure plasma progesterone concentrations. Ovulation was detected in 0/5, 5/5, 5/5, 3/5 and 0/4 female alpacas treated with saline, buserelin, 1, 0.1 and 0.01mg β-NGF, respectively. Mean ovulation interval (P=0.76), CL diameter (P=0.96) and plasma progesterone concentration (P=0.96) did not differ between treatments. Mean ovulation interval overall was 26.2±1.0h. In conclusion, buserelin and 1mg β-NGF are equally effective at inducing ovulation in female alpacas, but at doses ≤0.1mg, β-NGF is not a reliable method for the induction of ovulation.

  6. Plasma current profile during current reversal in a tokamak

    International Nuclear Information System (INIS)

    Huang Jianguo; Yang Xuanzong; Zheng Shaobai; Feng Chunhua; Zhang Houxian; Wang Long

    1999-01-01

    Alternating current operation with one full cycle and a current level of 2.5 kA have been achieved in the CT-6B tokamak. The poloidal magnetic field in the plasma is measured with two internal magnetic probes in repeated discharges. The current distribution is reconstructed with an inversion algorithm. The inverse current first appears on the weak field side. The existence of magnetic surfaces and rotational transform provide particle confinement in the current reversal phase

  7. Relativistic current sheets in electron-positron plasmas

    International Nuclear Information System (INIS)

    Zenitani, S.

    2008-01-01

    The current sheet structure with magnetic field reversal is one of the fundamental structure in space and astrophysical plasmas. It draws recent attention in high-energy astrophysical settings, where relativistic electron-positron plasmas are considered. In this talk we will review the recent progress of the physical processes in the relativistic current sheet. The kinetic stability of a single current sheet, the nonlinear behavior of these instabilities, and recent challenges on the multi current sheet systems are introduced. We will also introduce some problems of magnetic reconnection in these relativistic environments. (author)

  8. Langmuir probe characteristic in a current - carrying magnetized plasma

    International Nuclear Information System (INIS)

    Stanojevic, M.; Cercek, M.; Gyergyek, T.

    1995-01-01

    Experimental investigation of the Langmuir probe characteristic is a magnetized plasma with an electron current along the magnetic field direction shows that the standard procedure for determination of the electron temperature and plasma density, which is applicable in a current - free magnetized plasma, gives erroneous results for these plasma parameters. However, more precise values of the plasma parameters can be calculated from the ion saturation currents and electron temperatures obtained with that procedure for two opposite orientations of the one - sided planar probe collecting surface with respect to the direction of the electron drift. With the existing theoretical models only the order of magnitude of the electron drift velocity can be accurately determined from the measured electron saturation currents for the two probe orientations. (author)

  9. Characterization of plasma current quench at JET

    International Nuclear Information System (INIS)

    Riccardo, V; Barabaschi, P; Sugihara, M

    2005-01-01

    Eddy currents generated during the fastest disruption current decays represent the most severe design condition for medium and small size in-vessel components of most tokamaks. Best-fit linear and instantaneous plasma current quench rates have been extracted for a set of recent JET disruptions. Contrary to expectations, the current quench rate spectrum of high and low thermal energy disruptions is not substantially different. For most of the disruptions with the highest instantaneous current quench rate an exponential fit of the early phase of the current decay provides a more accurate estimate of the maximum current decay velocity. However, this fit is only suitable to model the fastest events, for which the current quench is dominated by radiation losses rather than the plasma motion

  10. Burn stability of tokamak fusion plasmas with synergetic current drive

    International Nuclear Information System (INIS)

    Anderson, D.; Lisak, M.; Kolesnichenko, Ya.

    1991-01-01

    The stability of thermonuclear burn in Tokamak-reactors with non-inductive current generated with the simultaneous application of various methods is investigated. Particular emphasis is given to the ITER synergetic current drive scenario involving LH waves, neoclassical effects and NB injection. For ITER-like confinement laws, it is shown that this scenario may be unstable on the plasma skin time scale. Figs

  11. Axisymmetric MHD simulation of ITB crash and following disruption dynamics of Tokamak plasmas with high bootstrap current

    International Nuclear Information System (INIS)

    Takei, Nahoko; Tsutsui, Hiroaki; Tsuji-Iio, Shunji; Shimada, Ryuichi; Nakamura, Yukiharu; Kawano, Yasunori; Ozeki, Takahisa; Tobita, Kenji; Sugihara, Masayoshi

    2004-01-01

    Axisymmetric MHD simulation using the Tokamak Simulation Code demonstrated detailed disruption dynamics triggered by a crash of internal transport barrier in high bootstrap current, high β, reversed shear plasmas. Self-consistent time-evolutions of ohmic current bootstrap current and induced loop voltage profiles inside the disrupting plasma were shown from a view point of disruption characterization and mitigation. In contrast with positive shear plasmas, a particular feature of high bootstrap current reversed shear plasma disruption was computed to be a significant change of plasma current profile, which is normally caused due to resistive diffusion of the electric field induced by the crash of internal transport barrier in a region wider than the internal transport barrier. Discussion based on the simulation results was made on the fastest record of the plasma current quench observed in JT-60U reversed shear plasma disruptions. (author)

  12. Direct currents produced by hf heating of plasma

    International Nuclear Information System (INIS)

    Klima, R.

    1974-01-01

    In addition to the well-known diffusion currents, toroidal direct currents arise in h.f. heated plasmas as a result of a momentum transfer from the h.f. field to plasma particles. The estimates of steady-state conditions are given for these currents. Particularly, the possibility of stationary operation of a Tokamak device is analyzed. (author)

  13. Development of a visible framing camera diagnostic for the study of current initiation in z-pinch plasmas

    International Nuclear Information System (INIS)

    Muron, D.J.; Hurst, M.J.; Derzon, M.S.

    1996-01-01

    The authors assembled and tested a visible framing camera system to take 5 ns FWHM images of the early time emission from a z-pinch plasma. This diagnostic was used in conjunction with a visible streak camera allowing early time emissions measurements to diagnose current initiation. Individual frames from gated image intensifiers were proximity coupled to charge injection device (CID) cameras and read out at video rate and 8-bit resolution. A mirror was used to view the pinch from a 90-degree angle. The authors observed the destruction of the mirror surface, due to the high surface heating, and the subsequent reduction in signal reflected from the mirror. Images were obtained that showed early time ejecta and a nonuniform emission from the target. This initial test of the equipment highlighted problems with this measurement. They observed non-uniformities in early time emission. This is believed to be due to either spatially varying current density or heating of the foam. Images were obtained that showed early time ejecta from the target. The results and suggestions for improvement are discussed in the text

  14. Design of 2D time-varying vector fields.

    Science.gov (United States)

    Chen, Guoning; Kwatra, Vivek; Wei, Li-Yi; Hansen, Charles D; Zhang, Eugene

    2012-10-01

    Design of time-varying vector fields, i.e., vector fields that can change over time, has a wide variety of important applications in computer graphics. Existing vector field design techniques do not address time-varying vector fields. In this paper, we present a framework for the design of time-varying vector fields, both for planar domains as well as manifold surfaces. Our system supports the creation and modification of various time-varying vector fields with desired spatial and temporal characteristics through several design metaphors, including streamlines, pathlines, singularity paths, and bifurcations. These design metaphors are integrated into an element-based design to generate the time-varying vector fields via a sequence of basis field summations or spatial constrained optimizations at the sampled times. The key-frame design and field deformation are also introduced to support other user design scenarios. Accordingly, a spatial-temporal constrained optimization and the time-varying transformation are employed to generate the desired fields for these two design scenarios, respectively. We apply the time-varying vector fields generated using our design system to a number of important computer graphics applications that require controllable dynamic effects, such as evolving surface appearance, dynamic scene design, steerable crowd movement, and painterly animation. Many of these are difficult or impossible to achieve via prior simulation-based methods. In these applications, the time-varying vector fields have been applied as either orientation fields or advection fields to control the instantaneous appearance or evolving trajectories of the dynamic effects.

  15. Anomalous plasma heating induced by modulation of the current-density profile

    International Nuclear Information System (INIS)

    Lopes Cardozo, N.J.

    1985-05-01

    The usual plasma heating in a tokamak needs additional heating to reach ignition temperature (approx. 10 8 K). The method used in the TORTUR III experiment is to induce anomalous plasma resistivity by applying a short (10 microseconds) high-voltage pulse. A sharp rise of the plasma temperature is found almost simultaneously, but this effect, though considerable, is too short-lived to be of interest for a thermonuclear chain reaction. A second pulse gives a second rise of temperature, but this time a slow one, extending over several milliseconds. The mechanism of this delayed heating and the reservoir within the plasma supplying the energy are subjects of investigation in the TORTUR III experiments. Some conclusions concerning the plasma heating mechanism are presented. The conclusion is reached that the application of the high-voltage pulse results in a modulation of the current-density profile: the (normally already peaked) profile sharpens, the current concentrates in the centre of the plasma column. This is a non-equilibrium situation. It relaxes to the noraml current distribution within approximately 2 milliseconds. As long as this relaxation process is not finished, the dissipation is on an enhanced level and anomalous plasma heating is observed. Many plasma parameters are surveyed and evaluated: temperature (both of the ions and the electrons), density, emission spectrum (from microwaves to hard X-rays) and the fluctuation spectrum. Main subject of this report is the measurement and interpretation of the X-rays of the emission spectrum. Experimental results are presented and discussed

  16. Design of 2D Time-Varying Vector Fields

    KAUST Repository

    Chen, Guoning

    2012-10-01

    Design of time-varying vector fields, i.e., vector fields that can change over time, has a wide variety of important applications in computer graphics. Existing vector field design techniques do not address time-varying vector fields. In this paper, we present a framework for the design of time-varying vector fields, both for planar domains as well as manifold surfaces. Our system supports the creation and modification of various time-varying vector fields with desired spatial and temporal characteristics through several design metaphors, including streamlines, pathlines, singularity paths, and bifurcations. These design metaphors are integrated into an element-based design to generate the time-varying vector fields via a sequence of basis field summations or spatial constrained optimizations at the sampled times. The key-frame design and field deformation are also introduced to support other user design scenarios. Accordingly, a spatial-temporal constrained optimization and the time-varying transformation are employed to generate the desired fields for these two design scenarios, respectively. We apply the time-varying vector fields generated using our design system to a number of important computer graphics applications that require controllable dynamic effects, such as evolving surface appearance, dynamic scene design, steerable crowd movement, and painterly animation. Many of these are difficult or impossible to achieve via prior simulation-based methods. In these applications, the time-varying vector fields have been applied as either orientation fields or advection fields to control the instantaneous appearance or evolving trajectories of the dynamic effects. © 1995-2012 IEEE.

  17. Design of 2D Time-Varying Vector Fields

    KAUST Repository

    Chen, Guoning; Kwatra, Vivek; Wei, Li-Yi; Hansen, Charles D.; Zhang, Eugene

    2012-01-01

    Design of time-varying vector fields, i.e., vector fields that can change over time, has a wide variety of important applications in computer graphics. Existing vector field design techniques do not address time-varying vector fields. In this paper, we present a framework for the design of time-varying vector fields, both for planar domains as well as manifold surfaces. Our system supports the creation and modification of various time-varying vector fields with desired spatial and temporal characteristics through several design metaphors, including streamlines, pathlines, singularity paths, and bifurcations. These design metaphors are integrated into an element-based design to generate the time-varying vector fields via a sequence of basis field summations or spatial constrained optimizations at the sampled times. The key-frame design and field deformation are also introduced to support other user design scenarios. Accordingly, a spatial-temporal constrained optimization and the time-varying transformation are employed to generate the desired fields for these two design scenarios, respectively. We apply the time-varying vector fields generated using our design system to a number of important computer graphics applications that require controllable dynamic effects, such as evolving surface appearance, dynamic scene design, steerable crowd movement, and painterly animation. Many of these are difficult or impossible to achieve via prior simulation-based methods. In these applications, the time-varying vector fields have been applied as either orientation fields or advection fields to control the instantaneous appearance or evolving trajectories of the dynamic effects. © 1995-2012 IEEE.

  18. Plasma auxiliary heating and current drive

    International Nuclear Information System (INIS)

    1999-01-01

    Heating and current drive systems must fulfil several roles in ITER operating scenarios: heating through the H-mode transition and to ignition; plasma burn control; current drive and current profile control in steady state scenarios; and control of MHD instabilities. They must also perform ancillary functions, such as assisting plasma start-up and wall conditioning. It is recognized that no one system can satisfy all of these requirements with the degree of flexibility that ITER will require. Four heating and current drive systems are therefore under consideration for ITER: electron cyclotron waves at a principal frequency of 170 GHz; fast waves operating in the range 40-70 MHz (ion cyclotron waves); lower hybrid waves at 5 GHz; and neutral beam injection using negative ion beam technology for operation at 1 MeV energy. It is likely that several of these systems will be employed in parallel. The systems have been chosen on the basis of the maturity of physics understanding and operating experience in current experiments and on the feasibility of applying the relevant technology to ITER. Here, the fundamental physics describing the interaction of these heating systems with the plasma is reviewed, the relevant experimental results in the exploitation of the heating and current drive capabilities of each system are discussed, key aspects of their application to ITER are outlined, and the major technological developments required in each area are summarized. (author)

  19. Stability of plasma cylinder with current in a helical plasma flow

    Science.gov (United States)

    Leonovich, Anatoly S.; Kozlov, Daniil A.; Zong, Qiugang

    2018-04-01

    Stability of a plasma cylinder with a current wrapped by a helical plasma flow is studied. Unstable surface modes of magnetohydrodynamic (MHD) oscillations develop at the boundary of the cylinder enwrapped by the plasma flow. Unstable eigenmodes can also develop for which the plasma cylinder is a waveguide. The growth rate of the surface modes is much higher than that for the eigenmodes. It is shown that the asymmetric MHD modes in the plasma cylinder are stable if the velocity of the plasma flow is below a certain threshold. Such a plasma flow velocity threshold is absent for the symmetric modes. They are unstable in any arbitrarily slow plasma flows. For all surface modes there is an upper threshold for the flow velocity above which they are stable. The helicity index of the flow around the plasma cylinder significantly affects both the Mach number dependence of the surface wave growth rate and the velocity threshold values. The higher the index, the lower the upper threshold of the velocity jump above which the surface waves become stable. Calculations have been carried out for the growth rates of unstable oscillations in an equilibrium plasma cylinder with current serving as a model of the low-latitude boundary layer (LLBL) of the Earth's magnetic tail. A tangential discontinuity model is used to simulate the geomagnetic tail boundary. It is shown that the magnetopause in the geotail LLBL is unstable to a surface wave (having the highest growth rate) in low- and medium-speed solar wind flows, but becomes stable to this wave in high-speed flows. However, it can remain weakly unstable to the radiative modes of MHD oscillations.

  20. Global Stability of Polytopic Linear Time-Varying Dynamic Systems under Time-Varying Point Delays and Impulsive Controls

    Directory of Open Access Journals (Sweden)

    M. de la Sen

    2010-01-01

    Full Text Available This paper investigates the stability properties of a class of dynamic linear systems possessing several linear time-invariant parameterizations (or configurations which conform a linear time-varying polytopic dynamic system with a finite number of time-varying time-differentiable point delays. The parameterizations may be timevarying and with bounded discontinuities and they can be subject to mixed regular plus impulsive controls within a sequence of time instants of zero measure. The polytopic parameterization for the dynamics associated with each delay is specific, so that (q+1 polytopic parameterizations are considered for a system with q delays being also subject to delay-free dynamics. The considered general dynamic system includes, as particular cases, a wide class of switched linear systems whose individual parameterizations are timeinvariant which are governed by a switching rule. However, the dynamic system under consideration is viewed as much more general since it is time-varying with timevarying delays and the bounded discontinuous changes of active parameterizations are generated by impulsive controls in the dynamics and, at the same time, there is not a prescribed set of candidate potential parameterizations.

  1. Magnetohydrodynamically stable plasma with supercritical current density at the axis

    Energy Technology Data Exchange (ETDEWEB)

    Burdakov, A. V. [Budker Institute of Nuclear Physics, 11 Lavrentjev Avenue, 630090 Novosibirsk (Russian Federation); Novosibirsk State Technical University, 20 Karl Marks Avenue, 630092 Novosibirsk (Russian Federation); Postupaev, V. V., E-mail: V.V.Postupaev@inp.nsk.su; Sudnikov, A. V. [Budker Institute of Nuclear Physics, 11 Lavrentjev Avenue, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, 2 Pirogova st., 630090 Novosibirsk (Russian Federation)

    2014-05-15

    In this work, an analysis of magnetic perturbations in the GOL-3 experiment is given. In GOL-3, plasma is collectively heated in a multiple-mirror trap by a high-power electron beam. During the beam injection, the beam-plasma interaction maintains a high-level microturbulence. This provides an unusual radial profile of the net current (that consists of the beam current, current of the preliminary discharge, and the return current). The plasma core carries supercritical current density with the safety factor well below unity, but as a whole, the plasma is stable with q(a) ≈ 4. The net plasma current is counter-directed to the beam current; helicities of the magnetic field in the core and at the edge are of different signs. This forms a system with a strong magnetic shear that stabilizes the plasma core in good confinement regimes. We have found that the most pronounced magnetic perturbation is the well-known n = 1, m = 1 mode for both stable and disruptive regimes.

  2. Slow convection of a magnetized plasma and the earth plasma sheet

    International Nuclear Information System (INIS)

    Hruska, A.

    1980-01-01

    Stationary convection of an isotropic, infinitely conducting plasma in a magnetic field with non-trivial geometry is discussed under the assumption that the inertial term in the equation of motion may be ignored. The energy gained or lost by a volume element of plasma per unit time does not vary along the field-lines. Simple relations between the components of the current density, depending on the field-line geometry, exist. Similar relations hold for the components of the plasma velocity. The theoretical analysis is applied to the geomagnetically-quiet plasma sheet and a qualitative physical picture of the sheet is suggested. The observed structure of the sheet is compatible with Axford-Hines type of convection perhaps combined with a low-speed flow from a distant neutral point. The magnetic-field-aligned currents are driven by the deformations of the closed field-lines which are enforced by the solar wind. (orig.)

  3. Experimental breakdown of selected anodized aluminum samples in dilute plasmas

    Science.gov (United States)

    Grier, Norman T.; Domitz, Stanley

    1992-01-01

    Anodized aluminum samples representative of Space Station Freedom structural material were tested for electrical breakdown under space plasma conditions. In space, this potential arises across the insulating anodized coating when the spacecraft structure is driven to a negative bias relative to the external plasma potential due to plasma-surface interaction phenomena. For anodized materials used in the tests, it was found that breakdown voltage varied from 100 to 2000 volts depending on the sample. The current in the arcs depended on the sample, the capacitor, and the voltage. The level of the arc currents varied from 60 to 1000 amperes. The plasma number density varied from 3 x 10 exp 6 to 10 exp 3 ions per cc. The time between arcs increased as the number density was lowered. Corona testing of anodized samples revealed that samples with higher corona inception voltage had higher arcing inception voltages. From this it is concluded that corona testing may provide a method of screening the samples.

  4. The Role of Ionospheric O+ in Forming the Storm-time Ring Current

    Science.gov (United States)

    Kistler, L. M.; Mouikis, C.; Menz, A.; Bingham, S.

    2017-12-01

    During storm times, the particle pressure that creates the storm-time ring current in the inner magnetosphere can be dominated by O+. This is surprising, as the immediate source for the ring current is the nightside plasma sheet, and O+ is usually not the dominant species in the plasma sheet. In this talk we examine the many factors that lead to this result. The O+ outflow is enhanced during geomagnetically active times. The transport paths of O+ and H+ are different, such that the O+ that reaches the near-earth plasma sheet is more energetic than H+. The source spectrum in the near-earth plasma sheet can be harder for O+ than for H+, perhaps due to substorm injections, so that the more energetic plasma has a higher O+/H+ ratio. And finally the plasma sheet O+ can be more abundant towards the beginning of the storm, when the convection is largest, so the enhanced O+ is brought the deepest into the inner magnetosphere. We will discuss the interrelationships between these different effects as well as the ways in which O+ itself may influence the system.

  5. Real time control of plasmas and ECRH systems on TCV

    International Nuclear Information System (INIS)

    Paley, J.I.; Berrino, J.; Coda, S.; Duval, B.P.; Felici, F.; Goodman, T.P.; Martin, Y.; Moret, J.M.; Piras, F.; Cruz, N.; Rodriques, A.P.; Santos, B.; Varandas, C.A.F.

    2009-01-01

    Developments in the real time control hardware on Tokamak a Configuration Variable (TCV) coupled with the flexibility of plasma shaping and electron cyclotron (EC) heating and current drive actuators are opening many opportunities to perform real time experiments and develop algorithms and methods for fusion applications. The ability to control magnetohydrodynamic instabilities is particularly important for achieving high performance fusion plasmas and EC is envisaged as a key actuator in maintaining high performance. We have successfully demonstrated control of the sawtooth instability using the EC launcher injection angle to modify the current profile around the q =1 surface. This paper presents an overview of recent real time control experiments on TCV, developments in the hardware and algorithms together with plans for the future.

  6. A real-time current driving control system for the TJ-II coils

    International Nuclear Information System (INIS)

    Pena, Angel de la; Pacios, Luis; Carrasco, Ricardo; Lapayese, Fernando

    2009-01-01

    Since the start of plasma operation in the TJ-II stellarator, the required values of DC currents that are fed to its different coil sets have been controlled to high precision along the complete discharge flat-top. As a result each current configuration produced a highly stable magnetic-field configuration. Recently, the configurational flexibility of the TJ-II has been broadened by the commissioning of a new mode of operation that allows magnetic configurations to be varied dynamically during the discharge flat-top. In order to achieve this, new hardware and software features have been added to the TJ-II Control System. These new features may also provide new strategies for feedback control in accordance with parameters measured in one or more diagnostics. In this new set-up, coil current profiles are generated and controlled to millisecond timescales by a system based on VMEbus and OS9 real-time operating system. A new communication middleware architecture called XML-based Messages Distribution Service (X-MDS) has been designed to exchange XML-based data with calling clients. Furthermore, with this software, a fully functional Java application for supervision and for current profiles settings has been developed. This paper provides a detailed description of the complete TJ-II real-time current-profile control system and results obtained during its operation.

  7. A real-time current driving control system for the TJ-II coils

    Energy Technology Data Exchange (ETDEWEB)

    Pena, Angel de la [Association EURATOM - CIEMAT, Avda. Complutense 22, 28040 Madrid (Spain)], E-mail: a.delapena@ciemat.es; Pacios, Luis; Carrasco, Ricardo; Lapayese, Fernando [Association EURATOM - CIEMAT, Avda. Complutense 22, 28040 Madrid (Spain)

    2009-06-15

    Since the start of plasma operation in the TJ-II stellarator, the required values of DC currents that are fed to its different coil sets have been controlled to high precision along the complete discharge flat-top. As a result each current configuration produced a highly stable magnetic-field configuration. Recently, the configurational flexibility of the TJ-II has been broadened by the commissioning of a new mode of operation that allows magnetic configurations to be varied dynamically during the discharge flat-top. In order to achieve this, new hardware and software features have been added to the TJ-II Control System. These new features may also provide new strategies for feedback control in accordance with parameters measured in one or more diagnostics. In this new set-up, coil current profiles are generated and controlled to millisecond timescales by a system based on VMEbus and OS9 real-time operating system. A new communication middleware architecture called XML-based Messages Distribution Service (X-MDS) has been designed to exchange XML-based data with calling clients. Furthermore, with this software, a fully functional Java application for supervision and for current profiles settings has been developed. This paper provides a detailed description of the complete TJ-II real-time current-profile control system and results obtained during its operation.

  8. Current distribution in a plasma erosion opening switch

    International Nuclear Information System (INIS)

    Weber, B.V.; Commisso, R.J.; Meger, R.A.; Neri, J.M.; Oliphant, W.F.; Ottinger, P.F.

    1984-01-01

    The current distribution in a plasma erosion opening switch is determined from magnetic field probe data. During the closed state of the switch the current channel broadens rapidly. The width of the current channel is consistent with a bipolar current density limit imposed by the ion flux to the cathode. The effective resistivity of the current channel is anomalously large. Current is diverted to the load when a gap opens near the cathode side of the switch. The observed gap opening can be explained by erosion of the plasma. Magnetic pressure is insufficient to open the gap

  9. Current distribution in a plasma erosion opening switch

    International Nuclear Information System (INIS)

    Weber, B.V.; Commisso, R.J.; Meger, R.A.; Neri, J.M.; Oliphant, W.F.; Ottinger, P.F.

    1985-01-01

    The current distribution in a plasma erosion opening switch is determined from magnetic field probe data. During the closed state of the switch the current channel broadens rapidly. The width of the current channel is consistent with a bipolar current density limit imposed by the ion flux to the cathode. The effective resistivity of the current channel is anomalously large. Current is diverted to the load when a gap opens near the cathode side of the switch. The observed gap opening can be explained by erosion of the plasma. Magnetic pressure is insufficient to open the gap

  10. Time variations of hf induced plasma waves

    International Nuclear Information System (INIS)

    Showen, R.L.

    1976-01-01

    Intense plasma waves are generated by an HF pump wave in an ionospheric heating experiment at the Arecibo Observatory. These plasma waves can be observed as enhancements to the ion and plasma lines of the incoherent backscatter echo. The enhancements can be three or four orders of magnitude more intense than the unenhanced lines, and tend to fluctuate wildly. Both the purely growing and the decay mode parametric instabilities are present. When the pump wave is turned on abruptly the enhancements develop in time in a repeatable manner. A rather remarkable feature on time scales of seconds is an overshoot in instability power. These overshoots occur frequently but not universally and last for 1 to 6 seconds. They can have a magnitude from ten to hundreds of times the average instability level. Field aligned irregularities may be the cause of the overshoots. The overshoots appear definitely related to an unusually rapid rise in measured electron temperature that cannot be understood in terms of ohmic energy deposition. On time scales of milliseconds there is a ''mini-overshoot'' before the growth of the instability to a large value. The spectral details also change in a striking manner. The instabilities can first be detected 2 to 4 msec after the pump wave turn-on. The decay mode is present as well as a broad featureless ''noise bump'', which partially sharpens into a line as time progresses. These changes of the spectra in time seem to run counter to the currently accepted theories of plasma wave saturation

  11. A time-dependent anisotropic plasma chemistry model of the Io plasma torus

    Science.gov (United States)

    Arridge, C. S.

    2016-12-01

    The physics of the Io plasma torus is typically modelled using one box neutral-plasma chemistry models, often referred to as neutral cloud theory models (e.g., Barbosa 1994; Delamere and Bagenal 2003). These models incorporate electron impact and photoionisation, charge exchange, molecular dissociation/recombination reactions, atomic radiatiative losses and Coulomb collisional heating. Isotropic Maxwellian distributions are usually assumed in the implementation of these models. Observationally a population of suprathermal electrons has been identified in the plasma torus and theoretically they have been shown to be important in reproducing the observed ionisation balance in the torus (e.g., Barbosa 1994). In this paper we describe an anisotropic plasma chemistry model for the Io torus that is inspired by ion cyclotron wave observations (Huddleston et al. 1994; Leisner et al. 2011), ion anisotropies due to pick up (Wilson et al. 2008), and theoretical ideas on the maintenance of the suprathermal electron population (Barbosa 1994). We present both steady state calculations and also time varying solutions (e.g., Delamere et al. 2004) where increases in the neutral source rate in the torus generates perturbations in ion anisotropies that subsequently decay over a timescale much longer than the duration of the initial perturbation. We also present a method for incorporating uncertainties in reaction rates into the model.

  12. Using advanced oxidation treatment for biofilm inactivation by varying water vapor content in air plasma

    Science.gov (United States)

    Ryota, Suganuma; Koichi, Yasuoka

    2015-09-01

    Biofilms are caused by environmental degradation in food factories and medical facilities. The inactivation of biofilms involves making them react with chemicals including chlorine, hydrogen peroxide, and ozone, although inactivation using chemicals has a potential problem because of the hazardous properties of the residual substance and hydrogen peroxide, which have slow reaction velocity. We successfully performed an advanced oxidation process (AOP) using air plasma. Hydrogen peroxide and ozone, which were used for the formation of OH radicals in our experiment, were generated by varying the amount of water vapor supplied to the plasma. By varying the content of the water included in the air, the main product was changed from air plasma. When we increased the water content in the air, hydrogen peroxide was produced, while ozone peroxide was produced when we decreased the water content in the air. By varying the amount of water vapor, we realized a 99.9% reduction in the amount of bacteria in the biofilm when we discharged humidified air only. This work was supported by JSPS KAKENHI Grant Number 25630104.

  13. Observation of bulk-ion heating in a tokamak plasma by application of positive and negative current pulses in TRIAM-1

    Energy Technology Data Exchange (ETDEWEB)

    Toi, K; Hiraki, N; Nakamura, K; Mitarai, O; Kawai, Y; Itoh, S [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics

    1980-09-01

    A positive of negative current pulse induced by a pulsed toroidal electric field much higher than the Dreicer field increases the bulk-ion temperature of the plasma centre two to three times, without macroscopic plasma destruction. The decay time of the raised ion temperature agrees well with the prediction from neoclassical transport theory. The magnitude of the positive current pulse is limited by violent current disruption, and that of the negative current by a lack of MHD equilibrium which is due to a marked reduction of the total plasma current. The relevant current-driven instabilities in the turbulent heating of a tokamak plasma, skin heating and inward transfer of the energy deposition in the skin layer are briefly discussed.

  14. Scale size and life time of energy conversion regions observed by Cluster in the plasma sheet

    Directory of Open Access Journals (Sweden)

    M. Hamrin

    2009-11-01

    Full Text Available In this article, and in a companion paper by Hamrin et al. (2009 [Occurrence and location of concentrated load and generator regions observed by Cluster in the plasma sheet], we investigate localized energy conversion regions (ECRs in Earth's plasma sheet. From more than 80 Cluster plasma sheet crossings (660 h data at the altitude of about 15–20 RE in the summer and fall of 2001, we have identified 116 Concentrated Load Regions (CLRs and 35 Concentrated Generator Regions (CGRs. By examining variations in the power density, E·J, where E is the electric field and J is the current density obtained by Cluster, we have estimated typical values of the scale size and life time of the CLRs and the CGRs. We find that a majority of the observed ECRs are rather stationary in space, but varying in time. Assuming that the ECRs are cylindrically shaped and equal in size, we conclude that the typical scale size of the ECRs is 2 RE≲ΔSECR≲5 RE. The ECRs hence occupy a significant portion of the mid altitude plasma sheet. Moreover, the CLRs appear to be somewhat larger than the CGRs. The life time of the ECRs are of the order of 1–10 min, consistent with the large scale magnetotail MHD simulations of Birn and Hesse (2005. The life time of the CGRs is somewhat shorter than for the CLRs. On time scales of 1–10 min, we believe that ECRs rise and vanish in significant regions of the plasma sheet, possibly oscillating between load and generator character. It is probable that at least some of the observed ECRs oscillate energy back and forth in the plasma sheet instead of channeling it to the ionosphere.

  15. Plasma diffusion due to magnetic field fluctuations

    International Nuclear Information System (INIS)

    Okuda, H.; Lee, W.W.; Lin, A.T.

    1979-01-01

    Plasma diffusion due to magnetic field fluctuations has been studied in two dimensions for a plasma near thermal equilibrium and when the fluctuations are suprathermal. It is found that near thermal equilibrium electron diffusion varies as B -2 when the collisionless skin depth is greater than the thermal electron gyroradius and is generally smaller than the diffusion due to collisions or electrostatic fluctuations for a low-β plasma. When the suprathermal magnetic fluctuation exists because of macroscopic plasma currents, electron diffusion is enhanced due to the coalescence of current filaments and magnetic islands. Magnetic field energy is found to condense to the longest wavelength available in the system and stays there longer than the electron diffusion time scale

  16. Plasma current startup by lower hybrid waves in the JIPP T-IIU tokamak

    International Nuclear Information System (INIS)

    Toi, K.; Ohkubo, K.; Kawahata, K.

    1987-04-01

    This paper describes the characteristic behaviours of lower hybrid current startup in JIPP T-IIU. The current startup is carried out by injection of 800 MHz lower hybrid waves into cold and low density plasmas (Te = 10 - 20 eV, n-bar e = 1 - 2 x 10 12 cm -3 ) produced by electron cyclotron resonance or lower hybrid waves only. The plasma current rises up with a characteristic rise time τ r (> approx 30 - 50 ms) and approaches a quasi-steady state value I pm (= 5 - 20 kA), when LHW power of 10 - 50 kW is injected into a torus, controlling the vertical field. The rise time is inversely proportional to the bulk electron density n-bar e , and is comparable to the collision time of current-carrying high energy electrons with bulk plasmas. On the other hand, the current drive efficiency in the quasi-steady state is almost independent of n-bar e , i.e., I pm /P LH = 0.4 - 0.7 A/W for n-bar e = 0.8 - 4 x 10 12 cm -3 . The conversion efficiency of rf energy injected into the torus is typically 5 % during current rise phase, and 10 % at the most efficient case. The effects of the initial injection of ECH power and the observed parametric instabilities on the current startup are investigated from a viewpoint of seed current generation. During rapid current rise when appreciably negative loop voltage is observed the bulk electrons are heated up to 150 eV. Various heating mechanisms responsible for the bulk electron heating are discussed. (author)

  17. Hot spots and dark current in advanced plasma wakefield accelerators

    Directory of Open Access Journals (Sweden)

    G. G. Manahan

    2016-01-01

    Full Text Available Dark current can spoil witness bunch beam quality and acceleration efficiency in particle beam-driven plasma wakefield accelerators. In advanced schemes, hot spots generated by the drive beam or the wakefield can release electrons from higher ionization threshold levels in the plasma media. These electrons may be trapped inside the plasma wake and will then accumulate dark current, which is generally detrimental for a clear and unspoiled plasma acceleration process. Strategies for generating clean and robust, dark current free plasma wake cavities are devised and analyzed, and crucial aspects for experimental realization of such optimized scenarios are discussed.

  18. The evolution of the plasma current during tokamak disruptions

    International Nuclear Information System (INIS)

    Helander, P.; Andersson, F.; Anderson, D.; Lisak, M.; Eriksson, L.G.

    2004-01-01

    In a tokamak disruption, the ohmic plasma current is partly replaced by a current carried by runaway electrons. This process is analysed by combining the equations for runaway electron generation with Maxwell's equations for the evolution of the electric field. This allows a quantitative understanding to be gained of runaway production in present experiments, and extrapolation to be made to ITER. The runaway current typically becomes more peaked on the magnetic axis than the pre-disruption current. In fact, the central current density can rise although the total current falls, which may have implications for post-disruption plasma stability. Furthermore, it is found that the runaway current easily spreads radially in a filament way due to the high sensitivity of the runaway generation efficiency to plasma parameters. (authors)

  19. Effects of drive current rise-time and initial load density distribution on Z-pinch characteristics

    Institute of Scientific and Technical Information of China (English)

    Duan Yao-Yong; Guo Yong-Hui; Wang Wen-Sheng; Qiu Ai-Ci

    2005-01-01

    A two-dimensional, three-temperature radiation magneto-hydrodynamics model is applied to the investigation of evolutional trends in x-ray radiation power, energy, peak plasma temperature and density as functions of drive current rise-time and initial load density distribution by using the typical experimental parameters of tungsten wire-array Z-pinch on the Qiangguang-Ⅰ generator. The numerical results show that as the drive current rise-time is shortened, x-ray radiation peak power, energy, peak plasma density and peak ion temperature increase approximately linearly, but among them the x-ray radiation peak power increases more quickly. As the initial plasma density distribution in the radial direction becomes gradually flattened, the peak radiation power and the peak ion-temperature almost exponentially increase, while the radiation energy and the peak plasma density change only a little. The main effect of shortening drive current rise-time is to enhance compression of plasma, and the effect of flattening initial load density distribution in the radial direction is to raise the plasma temperature. Both of the approaches elevate the x-ray peak radiation power.

  20. Real-time control of the current density and pressure profiles in Jet

    International Nuclear Information System (INIS)

    Mazon, D.; Moreau, D.; Litaudon, X.; Joffrin, E.; Laborde, L.; Zabeo, L.; Crisanti, F.; Riva, M.; Felton, R.; Murari, A.; Tala, T.

    2003-01-01

    In order to ultimately control internal transport barriers during advanced operation scenarios, new algorithms using a truncated singular value decomposition of a linearized model operator have been implemented in the JET real-time controller, with the potentiality of retaining the distributed nature of plasma parameter profiles. First experiments using the simplest, lumped-parameter, version of this technique have been dedicated to the feedback control of the current density profile in a negative shear plasma using three heating and current drive actuators, namely neutral beam injection (NBI), ion cyclotron resonant frequency heating (ICRH) and lower hybrid current drive (LHCD). Successful control of the safety factor profile has been achieved on the time scale of the current redistribution time, first during an extended preheat phase with only LHCD as actuator and, then, in quasi steady-state conditions during the main heating phase of a discharge, using the three heating and current drive actuators

  1. Plasma bullet current measurements in a free-stream helium capillary jet

    Science.gov (United States)

    Oh, Jun-Seok; Walsh, James L.; Bradley, James W.

    2012-06-01

    A commercial current monitor has been used to measure the current associated with plasma bullets created in both the positive and negative half cycles of the sinusoidal driving voltage sustaining a plasma jet. The maximum values of the positive bullet current are typically ˜750 µA and persist for 10 µs, while the peaks in the negative current of several hundred μA are broad, persisting for about 40 µs. From the time delay of the current peaks with increasing distance from the jet nozzle, an average bullet propagation speed has been measured; the positive and negative bullets travel at 17.5 km s-1 and 3.9 km s-1 respectively. The net space charge associated with the bullet(s) has also been calculated; the positive and negative bullets contain a similar net charge of the order of 10-9 C measured at all monitor positions, with estimated charged particle densities nb of ˜1010-1011 cm-3 in the bullet.

  2. Trapping and dark current in plasma-based accelerators

    International Nuclear Information System (INIS)

    Schroder, C.B.; Esarey, E.; Shadwick, B.A.; Leemans, W.P.

    2004-01-01

    The trapping of thermal electrons in a nonlinear plasma wave of arbitrary phase velocity is investigated. The threshold plasma wave amplitude for trapping plasma electrons is calculated, thereby determining the fraction trapped and the expected dark current in a plasma-based accelerator. It is shown that the presence of a laser field (e.g., trapping in the self-modulated regime of the laser wakefield accelerator) increases the trapping threshold. Implications for experimental and numerical laser-plasma studies are discussed

  3. Timed arrays wideband and time varying antenna arrays

    CERN Document Server

    Haupt, Randy L

    2015-01-01

    Introduces timed arrays and design approaches to meet the new high performance standards The author concentrates on any aspect of an antenna array that must be viewed from a time perspective. The first chapters briefly introduce antenna arrays and explain the difference between phased and timed arrays. Since timed arrays are designed for realistic time-varying signals and scenarios, the book also reviews wideband signals, baseband and passband RF signals, polarization and signal bandwidth. Other topics covered include time domain, mutual coupling, wideband elements, and dispersion. The auth

  4. Real time control of plasmas and ECRH systems on TCV

    NARCIS (Netherlands)

    Paley, J.I.; Berrino, J.; Coda, S.; Cruz, N.; Duval, B.P.; Felici, F.; Goodman, T.P.; Martin, Y.; Moret, J.-M.; Piras, F.; Rodriques, A.P.; Santos, B.; Varandas, C.A.F.

    2009-01-01

    Developments in the real time control hardware on Tokamak Configuration Variable (TCV) coupled with the flexibility of plasma shaping and electron cyclotron (EC) heating and current drive actuators are opening many opportunities to perform real time experiments and develop algorithms and methods for

  5. Current density distribution during disruptions and sawteeth in a simple model of plasma current in a tokamak

    International Nuclear Information System (INIS)

    Stefanovskii, A. M.

    2011-01-01

    The processes that are likely to accompany discharge disruptions and sawteeth in a tokamak are considered in a simple plasma current model. The redistribution of the current density in plasma is supposed to be primarily governed by the onset of the MHD-instability-driven turbulent plasma mixing in a finite region of the current column. For different disruption conditions, the variation in the total plasma current (the appearance of a characteristic spike) is also calculated. It is found that the numerical shape and amplitude of the total current spikes during disruptions approximately coincide with those measured in some tokamak experiments. Under the assumptions adopted in the model, the physical mechanism for the formation of the spikes is determined. The mechanism is attributed to the diffusion of the negative current density at the column edge into the zero-conductivity region. The numerical current density distributions in the plasma during the sawteeth differ from the literature data.

  6. Analysis of plasma equilibrium based on orbit-driven current density profile in steady-state plasma on QUEST

    Energy Technology Data Exchange (ETDEWEB)

    Nakamura, K., E-mail: nakamura@triam.kyushu-u.ac.jp [RIAM, Kyushu University, Kasuga 816-8580 (Japan); Alam, M.M. [IGSES, Kyushu University, Kasuga 816-8580 (Japan); Jiang, Y.Z. [Tsinghua University, Beijing 100084 (China); Mitarai, O. [Tokai University, Kumamoto 862-8652 (Japan); Kurihara, K.; Kawamata, Y.; Sueoka, M.; Takechi, M. [Japan Atomic Energy Agency, Naka 311-0193 (Japan); Hasegawa, M.; Tokunaga, K.; Araki, K.; Zushi, H.; Hanada, K.; Fujisawa, A.; Idei, H.; Nagashima, Y.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Nagata, T. [RIAM, Kyushu University, Kasuga 816-8580 (Japan); and others

    2016-11-01

    Highlights: • High energy particle guiding center orbit is calculated as a contour plot of conserved variable. • Current density profile is analyzed based on the orbit-driven current. • Plasma equilibrium is reconstructed by considering the hollow current profile. - Abstract: In the present RF-driven (ECCD) steady-state plasma on QUEST (B{sub t} = 0.25 T, R = 0.68 m, a = 0.40 m), plasma current seems to flow in the open magnetic surface outside of the closed magnetic surface in the low-field region according to plasma current fitting (PCF) method. We consider that the current in the open magnetic surface is due to orbit-driven current by high-energy particles in RF-driven plasma. So based on the analysis of current density profile based on the orbit-driven current, plasma equilibrium is to be calculated. We calculated high energy particles guiding center orbits as a contour plot of conserved variable in Hamiltonian formulation and considered particles initial position with different levels of energy and pitch angles that satisfy resonance condition. Then the profile of orbit-driven current is estimated by multiplying the particle density on the resonance surface and the velocity on the orbits. This analysis shows negative current near the magnetic axis and hollow current profile is expected even if pressure driven current is considered. Considering the hollow current profile shifted toward the low-field region, the equilibrium is fitted by J-EFIT coded by MATLAB.

  7. Preliminary experiment of non-induced plasma current startup on SUNIST spherical tokamak

    International Nuclear Information System (INIS)

    He Yexi; Zhang Liang; Xie Lifeng; Tang Yi; Yang Xuanzong; Fu Hongjun

    2005-01-01

    Non-inductive plasma current startup is an important motivation on the SUNIST spherical tokamak. In this experiment, a 100 kW, 2.45 GHz magnetron microwave system has been applied to the plasma current startup. Besides the toroidal field, a vertical field was applied to generate a preliminary toroidal plasma current without action of the central solenoid. As the evidence of the plasma current startup by the vertical field drift effect, the direction of the plasma current is changed with the changing direction of the vertical field during ECR startup discharge. We have also observed the plasma current maximum by scanning the vertical field in both directions. Additionally, we have used electrode discharge to assist the ECR current startup. (author)

  8. Electron current extraction from a permanent magnet waveguide plasma cathode

    Energy Technology Data Exchange (ETDEWEB)

    Weatherford, B. R.; Foster, J. E. [University of Michigan, Ann Arbor, Michigan 48109 (United States); Kamhawi, H. [NASA Glenn Research Center, Cleveland, Ohio 44135 (United States)

    2011-09-15

    An electron cyclotron resonance plasma produced in a cylindrical waveguide with external permanent magnets was investigated as a possible plasma cathode electron source. The configuration is desirable in that it eliminates the need for a physical antenna inserted into the plasma, the erosion of which limits operating lifetime. Plasma bulk density was found to be overdense in the source. Extraction currents over 4 A were achieved with the device. Measurements of extracted electron currents were similar to calculated currents, which were estimated using Langmuir probe measurements at the plasma cathode orifice and along the length of the external plume. The influence of facility effects and trace ionization in the anode-cathode gap are also discussed.

  9. Current distribution measurements inside an electromagnetic plasma gun operated in a gas-puff mode

    OpenAIRE

    Poehlmann, Flavio R.; Cappelli, Mark A.; Rieker, Gregory B.

    2010-01-01

    Measurements are presented of the time-dependent current distribution inside a coaxial electromagnetic plasma gun. The measurements are carried out using an array of six axially distributed dual-Rogowski coils in a balanced circuit configuration. The radial current distributions indicate that operation in the gas-puff mode, i.e., the mode in which the electrode voltage is applied before injection of the gas, results in a stationary ionization front consistent with the presence of a plasma def...

  10. Electric currents in cosmic plasmas

    International Nuclear Information System (INIS)

    Alfven, H.

    1977-05-01

    Since the beginning of the century physics has been dualistic in the sense that some phenomena are described by a field concept, others by a particle concept. This dualism is essential also in the physics of cosmical plasmas: some phenomena should be described by a magnetic field formalism, others by an electric current formalism. During the first period of evolution of cosmic plasma physics the magnetic field aspect has dominated, and a fairly exhaustive description has been given of those phenomena--like the propagation of waves--which can be described in this way. We have now entered a second period which is dominated by a systematic exploration of the particle (or current) aspect. A survey is given of a number of phenomena which can be understood only from the particle aspect. These include the formation of electric double layers, the origin of explosive events like magnetic substorms and solar flares, and further, the transfer of energy from one region to another. A useful method of exploring many of these phenomena is to draw the electric circuit in which the current flows and study its properties. A number of simple circuits are analyzed in this way. (author)

  11. Estimating time-varying RSA to examine psychophysiological linkage of marital dyads.

    Science.gov (United States)

    Gates, Kathleen M; Gatzke-Kopp, Lisa M; Sandsten, Maria; Blandon, Alysia Y

    2015-08-01

    One of the primary tenets of polyvagal theory dictates that parasympathetic influence on heart rate, often estimated by respiratory sinus arrhythmia (RSA), shifts rapidly in response to changing environmental demands. The current standard analytic approach of aggregating RSA estimates across time to arrive at one value fails to capture this dynamic property within individuals. By utilizing recent methodological developments that enable precise RSA estimates at smaller time intervals, we demonstrate the utility of computing time-varying RSA for assessing psychophysiological linkage (or synchrony) in husband-wife dyads using time-locked data collected in a naturalistic setting. © 2015 Society for Psychophysiological Research.

  12. Avoidance of VDEs during plasma current quench in JT-60U

    International Nuclear Information System (INIS)

    Yoshino, R.; Nakamura, Y.; Neyatani, Y.

    1996-01-01

    Vertical displacement events (VDEs) during plasma current quench (I p quench) are one of the serious problems encountered in designing tokamak fusion reactors, owing to the generation of enormously high electromagnetic forces on the vacuum vessel and in-vessel components, but they have been passively and actively avoided in JT-60U. In JT-60U 'slow I p quench' is ended with very fast plasma current termination (final I p termination), and the halo current is frequently measured at this final I p termination. VDEs make the final I p termination severe by increasing the halo current and the electromagnetic force. A strong dependence of VDE growth rate on the initial vertical position of the plasma current centre (Z J ) has been clarified experimentally, and a neutral point of Z J for VDE has been found at ∼ 15 cm above the midplane of the vacuum vessel. According to these measurements, VDE has been avoided by the selection of Z J at the start of I p quench (passive control) and by the control of Z J during I p quench (active control) eventually obtained owing to the small deviation of Z J in real time calculations from its actual value. Furthermore, passive avoidance of VDEs by the injection of a neon ice pellet has been demonstrated. (author). 29 refs, 14 figs

  13. Lower hybrid current drive at ITER-relevant high plasma densities

    International Nuclear Information System (INIS)

    Cesario, R.; Amicucci, L.; Cardinali, A.; Castaldo, C.; Marinucci, M.; Panaccione, L.; Pericoli-Ridolfini, V.; Tuccillo, A. A.; Tudisco, O.; Calabro, G.

    2009-01-01

    Recent experiments indicated that a further non-inductive current, besides bootstrap, should be necessary for developing advanced scenario for ITER. The lower hybrid current drive (LHCD) should provide such tool, but its effectiveness was still not proved in operations with ITER-relevant density of the plasma column periphery. Progress of the LH deposition modelling is presented, performed considering the wave physics of the edge, and different ITER-relevant edge parameters. Operations with relatively high edge electron temperatures are expected to reduce the LH || spectral broadening and, consequently, enabling the LH power to propagate also in high density plasmas ( || is the wavenumber component aligned to the confinement magnetic field). New results of FTU experiments are presented, performed by following the aforementioned modeling: they indicate that, for the first time, the LHCD conditions are established by operating at ITER-relevant high edge densities.

  14. Pair plasma relaxation time scales.

    Science.gov (United States)

    Aksenov, A G; Ruffini, R; Vereshchagin, G V

    2010-04-01

    By numerically solving the relativistic Boltzmann equations, we compute the time scale for relaxation to thermal equilibrium for an optically thick electron-positron plasma with baryon loading. We focus on the time scales of electromagnetic interactions. The collisional integrals are obtained directly from the corresponding QED matrix elements. Thermalization time scales are computed for a wide range of values of both the total-energy density (over 10 orders of magnitude) and of the baryonic loading parameter (over 6 orders of magnitude). This also allows us to study such interesting limiting cases as the almost purely electron-positron plasma or electron-proton plasma as well as intermediate cases. These results appear to be important both for laboratory experiments aimed at generating optically thick pair plasmas as well as for astrophysical models in which electron-positron pair plasmas play a relevant role.

  15. Current status and prospect of plasma control system for steady-state operation on QUEST

    International Nuclear Information System (INIS)

    Hasegawa, Makoto; Nakamura, Kazuo; Zushi, Hideki; Hanada, Kazuaki; Fujisawa, Akihide; Tokunaga, Kazutoshi; Idei, Hiroshi; Nagashima, Yoshihiko; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki

    2016-01-01

    Highlights: • Overall configuration of plasma control system on QUEST are presented. • Multi core system and reflective memories are used for the real-time control. • Hall sensors are used for the identification of plasma current and its position. • Repetitive gas fueling with the feed-back control of Hα signal is implemented. - Abstract: The plasma control system (PCS) of QUEST is developed according to the progress of QUEST project. Since one of the critical goals of the project is to achieve the steady-state operation with high temperature vacuum vessel wall, the PCS is also required to have the capability to control the plasma for a long period. For the increase of the loads to processing power of the PCS, the PCS is decentralized with the use of reflective memories (RFMs). The PCS controls the plasma edge position with the real-time identification of plasma current and its position. This identification is done with not only flux loops but also hall sensors. The gas fueling method by piezo valve with monitoring the Hα signal filtered by a digital low-pass filter are proposed and suitable for the steady-state operation on QUEST. The present status and prospect of the PCS are presented with recent topics.

  16. Current status and prospect of plasma control system for steady-state operation on QUEST

    Energy Technology Data Exchange (ETDEWEB)

    Hasegawa, Makoto, E-mail: hasegawa@triam.kyushu-u.ac.jp; Nakamura, Kazuo; Zushi, Hideki; Hanada, Kazuaki; Fujisawa, Akihide; Tokunaga, Kazutoshi; Idei, Hiroshi; Nagashima, Yoshihiko; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki

    2016-11-15

    Highlights: • Overall configuration of plasma control system on QUEST are presented. • Multi core system and reflective memories are used for the real-time control. • Hall sensors are used for the identification of plasma current and its position. • Repetitive gas fueling with the feed-back control of Hα signal is implemented. - Abstract: The plasma control system (PCS) of QUEST is developed according to the progress of QUEST project. Since one of the critical goals of the project is to achieve the steady-state operation with high temperature vacuum vessel wall, the PCS is also required to have the capability to control the plasma for a long period. For the increase of the loads to processing power of the PCS, the PCS is decentralized with the use of reflective memories (RFMs). The PCS controls the plasma edge position with the real-time identification of plasma current and its position. This identification is done with not only flux loops but also hall sensors. The gas fueling method by piezo valve with monitoring the Hα signal filtered by a digital low-pass filter are proposed and suitable for the steady-state operation on QUEST. The present status and prospect of the PCS are presented with recent topics.

  17. Energization of the Ring Current through Convection of Substorm Enhancements of the Plasma Sheet Source.

    Science.gov (United States)

    Menz, A.; Kistler, L. M.; Mouikis, C.; Spence, H. E.; Henderson, M. G.; Matsui, H.

    2017-12-01

    It has been shown that electric field strength and night-side plasma sheet density are the two best predictors of the adiabatic energy gain of the ring current during geomagnetic storms (Liemohn and Khazanov, 2005). While H+ dominates the ring current during quiet times, O+ can contribute substantially during geomagnetic storms. Substorm activity provides a mechanism to enhance the energy density of O+ in the plasma sheet during geomagnetic storms, which is then convected adiabatically into the inner-magnetosphere. Using the Van Allen Probes data in the the plasma sheet source region (defined as L>5.5 during storms) and the inner magnetosphere, along with LANL-GEO data to identify substorm injection times, we show that adiabatic convection of O+ enhancements in the source region can explain the observed enhancements in the inner magnetosphere. We use the UNH-IMEF electric field model to calculate drift times from the source region to the inner magnetosphere to test whether enhancements in the inner-magnetosphere can be explained by dipolarization driven enhancements in the plasma sheet source hours before.

  18. Mediation analysis with time varying exposures and mediators.

    Science.gov (United States)

    VanderWeele, Tyler J; Tchetgen Tchetgen, Eric J

    2017-06-01

    In this paper we consider causal mediation analysis when exposures and mediators vary over time. We give non-parametric identification results, discuss parametric implementation, and also provide a weighting approach to direct and indirect effects based on combining the results of two marginal structural models. We also discuss how our results give rise to a causal interpretation of the effect estimates produced from longitudinal structural equation models. When there are time-varying confounders affected by prior exposure and mediator, natural direct and indirect effects are not identified. However, we define a randomized interventional analogue of natural direct and indirect effects that are identified in this setting. The formula that identifies these effects we refer to as the "mediational g-formula." When there is no mediation, the mediational g-formula reduces to Robins' regular g-formula for longitudinal data. When there are no time-varying confounders affected by prior exposure and mediator values, then the mediational g-formula reduces to a longitudinal version of Pearl's mediation formula. However, the mediational g-formula itself can accommodate both mediation and time-varying confounders and constitutes a general approach to mediation analysis with time-varying exposures and mediators.

  19. Surface modification of polyacrylonitrile co-polymer membranes using pulsed direct current nitrogen plasma

    Energy Technology Data Exchange (ETDEWEB)

    Pal, Dipankar; Neogi, Sudarsan; De, Sirshendu, E-mail: sde@che.iitkgp.ernet.in

    2015-12-31

    Low temperature plasma treatment using pulsed direct current discharge of nitrogen gas was employed to enhance hydrophilicity of the polyacrylonitrile co-polymer membranes. The membranes were characterized in terms of morphology, structure, hydrophilicity, and membrane performance. Properties and functional groups on the surface of polyacrylonitrile co-polymer membranes were investigated by contact angle, scanning electron microscopy, Fourier transform infrared and X-ray photoelectron spectroscopy. Effects of plasma conditions, namely, pulsed voltage, duty cycle and treatment time on increase in membrane hydrophilicity were studied. Permeability of treated membrane was increased by 47% and it was retained up to 70 days. Surface etching due to plasma treatment was confirmed by weight loss of the treated membranes. Due to surface etching, average pore size increased and rejection of 200 kDa polyethylene glycol decreased to about 70% for the treated membrane. Oxygen and nitrogen functional groups were responsible for surface hydrophilicity. - Highlights: • Surface modification of polyacrylonitrile co-polymer membranes by pulsed direct current nitrogen plasma • Hydrophilic functional groups incorporated on the membrane surface • Significant enhancement of the permeability and wettability of the membranes • Water contact angle increased with storage time and finally stabilized.

  20. Surface modification of polyacrylonitrile co-polymer membranes using pulsed direct current nitrogen plasma

    International Nuclear Information System (INIS)

    Pal, Dipankar; Neogi, Sudarsan; De, Sirshendu

    2015-01-01

    Low temperature plasma treatment using pulsed direct current discharge of nitrogen gas was employed to enhance hydrophilicity of the polyacrylonitrile co-polymer membranes. The membranes were characterized in terms of morphology, structure, hydrophilicity, and membrane performance. Properties and functional groups on the surface of polyacrylonitrile co-polymer membranes were investigated by contact angle, scanning electron microscopy, Fourier transform infrared and X-ray photoelectron spectroscopy. Effects of plasma conditions, namely, pulsed voltage, duty cycle and treatment time on increase in membrane hydrophilicity were studied. Permeability of treated membrane was increased by 47% and it was retained up to 70 days. Surface etching due to plasma treatment was confirmed by weight loss of the treated membranes. Due to surface etching, average pore size increased and rejection of 200 kDa polyethylene glycol decreased to about 70% for the treated membrane. Oxygen and nitrogen functional groups were responsible for surface hydrophilicity. - Highlights: • Surface modification of polyacrylonitrile co-polymer membranes by pulsed direct current nitrogen plasma • Hydrophilic functional groups incorporated on the membrane surface • Significant enhancement of the permeability and wettability of the membranes • Water contact angle increased with storage time and finally stabilized.

  1. Extreme degree of ionization in homogenous micro-capillary plasma columns heated by ultrafast current pulses.

    Science.gov (United States)

    Avaria, G; Grisham, M; Li, J; Tomasel, F G; Shlyaptsev, V N; Busquet, M; Woolston, M; Rocca, J J

    2015-03-06

    Homogeneous plasma columns with ionization levels typical of megaampere discharges are created by rapidly heating gas-filled 520-μm-diameter channels with nanosecond rise time current pulses of 40 kA. Current densities of up to 0.3  GA cm^{-2} greatly increase Joule heating with respect to conventional capillary discharge Z pinches, reaching unprecedented degrees of ionization for a high-Z plasma column heated by a current pulse of remarkably low amplitude. Dense xenon plasmas are ionized to Xe^{28+}, while xenon impurities in hydrogen discharges reach Xe^{30+}. The unique characteristics of these hot, ∼300:1 length-to-diameter aspect ratio plasmas allow the observation of unexpected spectroscopic phenomena. Axial spectra show the unusual dominance of the intercombination line over the resonance line of He-like Al by nearly an order of magnitude, caused by differences in opacities in the axial and radial directions. These plasma columns could enable the development of sub-10-nm x-ray lasers.

  2. Plasma bullet current measurements in a free-stream helium capillary jet

    International Nuclear Information System (INIS)

    Oh, Jun-Seok; Walsh, James L; Bradley, James W

    2012-01-01

    A commercial current monitor has been used to measure the current associated with plasma bullets created in both the positive and negative half cycles of the sinusoidal driving voltage sustaining a plasma jet. The maximum values of the positive bullet current are typically ∼750 µA and persist for 10 µs, while the peaks in the negative current of several hundred μA are broad, persisting for about 40 µs. From the time delay of the current peaks with increasing distance from the jet nozzle, an average bullet propagation speed has been measured; the positive and negative bullets travel at 17.5 km s −1 and 3.9 km s −1 respectively. The net space charge associated with the bullet(s) has also been calculated; the positive and negative bullets contain a similar net charge of the order of 10 −9 C measured at all monitor positions, with estimated charged particle densities n b of ∼10 10 –10 11 cm −3 in the bullet. (special)

  3. On the evaluation of currents in a tokamak plasma during combined Ohmic and RF current drive

    International Nuclear Information System (INIS)

    Eckhartt, D.

    1986-09-01

    By taking into account the rf-generated enhancement of the plasma electric conductivity (as formulated by Fisch in the limit of weak dc electric fields) a relation is derived between the ratio of rf to Ohmically driven currents and other plasma parameters to be measured before and after the rf onset under the condition of constant net plasma current. (author)

  4. The low-current low-temperature plasma generators

    International Nuclear Information System (INIS)

    Dautov, G.Yu.

    2000-01-01

    In this article, the results of low-current gas-discharge plasma generator investigations carried out by a group of scientists from the Kazan' Aviation Institute are presented. When considered necessary, the results are compared with the data obtained by other authors. The basic configurations and theoretical calculation peculiarities of plasma generators are described. The electrical, thermal and energy characteristics of discharges in gas flows, as well as summarised empirical formulae and experimental data necessary for calculations and design of plasma devices are presented. (author)

  5. Ponderomotive force of a uniform electromagnetic wave in a time varying dielectric medium

    International Nuclear Information System (INIS)

    Mori, W.B.; Katsouleas, T.

    1992-01-01

    A ponderomotive force associated with a uniform electromagnetic wave propagating in a medium with time varying dielectric properties [e.g., ε=ε(x-v 0 t)] is identified. In particular, when a laser ionizes a gas through which it propagates, a force is exerted on the medium at the ionization front that is proportional to (∇ε)E 2 rather than the usual (ε-1)∇E 2 . This force excites a wake in the plasma medium behind the ionization front. The ponderomotive force and wake amplitude are derived and tested with 1D particle-in-cell simulations

  6. Plasma conditions for non-Maxwellian electron distributions in high current discharges and laser-produced plasmas

    International Nuclear Information System (INIS)

    Whitney, K.G.; Pulsifer, P.E.

    1993-01-01

    Results from the standard quasilinear theory of ion-acoustic and Langmuir plasma microturbulence are incorporated into the kinetic theory of the electron distribution function. The theory is then applied to high current discharges and laser-produced plasmas, where either the current flow or the nonlinear laser-light absorption acts, respectively, as the energy source for the microturbulence. More specifically, the theory is applied to a selenium plasma, whose charge state is determined under conditions of collisional-radiative equilibrium, and plasma conditions are found under which microturbulence strongly influences the electron kinetics. In selenium, we show that this influence extends over a wide range of plasma conditions. For ion-acoustic turbulence, a criterion is derived, analogous to one previously obtained for laser heated plasmas, that predicts when Ohmic heating dominates over electron-electron collisions. This dominance leads to the generation of electron distributions with reduced high-energy tails relative to a Maxwellian distribution of the same temperature. Ion-acoustic turbulence lowers the current requirements needed to generate these distributions. When the laser heating criterion is rederived with ion-acoustic turbulence included in the theory, a similar reduction in the laser intensity needed to produce non-Maxwellian distributions is found. Thus we show that ion-acoustic turbulence uniformly (i.e., by the same numerical factor) reduces the electrical and heat conductivities, as well as the current (squared) and laser intensity levels needed to drive the plasma into non-Maxwellian states

  7. Dust-acoustic shock waves in a charge varying electronegative magnetized dusty plasma with nonthermal ions: Application to Halley Comet plasma

    Energy Technology Data Exchange (ETDEWEB)

    Tribeche, Mouloud; Bacha, Mustapha [Plasma Physics Group (PPG), Theoretical Physics Laboratory (TPL), Faculty of Physics, University of Bab-Ezzouar, USTHB, B. P. 32, El Alia, Algiers 16111 (Algeria)

    2013-10-15

    Weak dust-acoustic waves (DAWs) are addressed in a nonthermal charge varying electronegative magnetized dusty plasmas with application to the Halley Comet. A weakly nonlinear analysis is carried out to derive a Korteweg-de Vries-Burger equation. The positive ion nonthermality, the obliqueness, and magnitude of the magnetic field are found to modify the dispersive and dissipative properties of the DA shock structure. Our results may aid to explain and interpret the nonlinear oscillations that may occur in the Halley Comet Plasma.

  8. Preliminary scaling laws for plasma current, ion kinetic temperature, and plasma number density in the NASA Lewis bumpy torus plasma

    Science.gov (United States)

    Roth, J. R.

    1976-01-01

    Parametric variation of independent variables which may affect the characteristics of bumpy torus plasma have identified those which have a significant effect on the plasma current, ion kinetic temperature, and plasma number density, and those which do not. Empirical power law correlations of the plasma current, and the ion kinetic temperature and number density were obtained as functions of potential applied to the midplane electrode rings, the background neutral gas pressure, and the magnetic field strength. Additional parameters studied included the type of gas, the polarity of the midplane electrode rings, the mode of plasma operation, and the method of measuring the plasma number density. No significant departures from the scaling laws appear to occur at the highest ion kinetic temperatures or number densities obtained to date.

  9. Calculation of voltages and currents induced in the vacuum vessel of ASDEX by plasma disruptions

    International Nuclear Information System (INIS)

    Preis, H.

    1978-01-01

    An approximation method is used to analyze the electromagnetic diffusion process induced in the walls of the ASDEX vacuum vessel by plasma disruptions. For this purpose the rotational-symmetric vessel is regarded as N = 82 circular conductors connected in parallel and inductively coupled with one another and with the plasma. The transient currents and voltages occurring in this circuit are calculated with computer programs. From the calculated currents it is possible to determine the time behavior of the distributions of the current density and magnetic force density in the vessel walls. (orig.) [de

  10. Current drive for rotamak plasmas

    Indian Academy of Sciences (India)

    Abstract. Experiments which have been undertaken over a number of years have shown that a rotating magnetic field can drive a significant non-linear Hall current in a plasma. Successful experiments of this concept have been made with a device called rotamak. In its original configuration this device was a field reversed ...

  11. Scale size and life time of energy conversion regions observed by Cluster in the plasma sheet

    Directory of Open Access Journals (Sweden)

    M. Hamrin

    2009-11-01

    Full Text Available In this article, and in a companion paper by Hamrin et al. (2009 [Occurrence and location of concentrated load and generator regions observed by Cluster in the plasma sheet], we investigate localized energy conversion regions (ECRs in Earth's plasma sheet. From more than 80 Cluster plasma sheet crossings (660 h data at the altitude of about 15–20 RE in the summer and fall of 2001, we have identified 116 Concentrated Load Regions (CLRs and 35 Concentrated Generator Regions (CGRs. By examining variations in the power density, E·J, where E is the electric field and J is the current density obtained by Cluster, we have estimated typical values of the scale size and life time of the CLRs and the CGRs. We find that a majority of the observed ECRs are rather stationary in space, but varying in time. Assuming that the ECRs are cylindrically shaped and equal in size, we conclude that the typical scale size of the ECRs is 2 RE≲ΔSECR≲5 RE. The ECRs hence occupy a significant portion of the mid altitude plasma sheet. Moreover, the CLRs appear to be somewhat larger than the CGRs. The life time of the ECRs are of the order of 1–10 min, consistent with the large scale magnetotail MHD simulations of Birn and Hesse (2005. The life time of the CGRs is somewhat shorter than for the CLRs. On time scales of 1–10 min, we believe that ECRs rise and vanish in significant regions of the plasma sheet, possibly oscillating between load and generator character. It is probable that at least some of the observed ECRs oscillate energy back and forth in the plasma sheet instead of channeling it to the ionosphere.

  12. Control of tokamak plasma current and equilibrium with hybrid poloidal field coils

    International Nuclear Information System (INIS)

    Shimada, Ryuichi

    1982-01-01

    A control method with hybrid poloidal field system is considered, which comprehensively implements the control of plasma equilibrium and plasma current, those have been treated independently in Tokamak divices. Tokamak equilibrium requires the condition that the magnetic flux function value on plasma surface must be constant. From this, the current to be supplied to each coil is determined. Therefore, each coil current is the resultant of the component related to plasma current excitation and the component required for holding equilibrium. Here, it is intended to show a method by which the current to be supplied to each coil can easily be calculated by the introduction of hybrid control matrix. The text first considers the equilibrium of axi-symmetrical plasma and the equilibrium magnetic field outside plasma, next describes the determination of current using the above hybrid control matrix, and indicates an example of controlling Tokamak plasma current and equilibrium by the hybrid poloidal field coils. It also shows that the excitation of plasma current and the maintenance of plasma equilibrium can basically be available with a single power supply by the appropriate selection of the number of turns of each coil. These considerations determine the basic system configuration as well as decrease the installed capacity of power source for the poloidal field of a Tokamak fusion reactor. Finally, the actual configuration of the power source for hybrid poloidal field coils is shown for the above system. (Wakatsuki, Y.)

  13. Time-varying properties of renal autoregulatory mechanisms

    DEFF Research Database (Denmark)

    Zou, Rui; Cupples, Will A; Yip, K P

    2002-01-01

    In order to assess the possible time-varying properties of renal autoregulation, time-frequency and time-scaling methods were applied to renal blood flow under broad-band forced arterial blood pressure fluctuations and single-nephron renal blood flow with spontaneous oscillations obtained from...... normotensive (Sprague-Dawley, Wistar, and Long-Evans) rats, and spontaneously hypertensive rats. Time-frequency analyses of normotensive and hypertensive blood flow data obtained from either the whole kidney or the single-nephron show that indeed both the myogenic and tubuloglomerular feedback (TGF) mechanisms...... have time-varying characteristics. Furthermore, we utilized the Renyi entropy to measure the complexity of blood-flow dynamics in the time-frequency plane in an effort to discern differences between normotensive and hypertensive recordings. We found a clear difference in Renyi entropy between...

  14. Time-varying value of electric energy efficiency

    Energy Technology Data Exchange (ETDEWEB)

    Mims, Natalie A.; Eckman, Tom; Goldman, Charles

    2017-06-30

    Electric energy efficiency resources save energy and may reduce peak demand. Historically, quantification of energy efficiency benefits has largely focused on the economic value of energy savings during the first year and lifetime of the installed measures. Due in part to the lack of publicly available research on end-use load shapes (i.e., the hourly or seasonal timing of electricity savings) and energy savings shapes, consideration of the impact of energy efficiency on peak demand reduction (i.e., capacity savings) has been more limited. End-use load research and the hourly valuation of efficiency savings are used for a variety of electricity planning functions, including load forecasting, demand-side management and evaluation, capacity and demand response planning, long-term resource planning, renewable energy integration, assessing potential grid modernization investments, establishing rates and pricing, and customer service. This study reviews existing literature on the time-varying value of energy efficiency savings, provides examples in four geographically diverse locations of how consideration of the time-varying value of efficiency savings impacts the calculation of power system benefits, and identifies future research needs to enhance the consideration of the time-varying value of energy efficiency in cost-effectiveness screening analysis. Findings from this study include: -The time-varying value of individual energy efficiency measures varies across the locations studied because of the physical and operational characteristics of the individual utility system (e.g., summer or winter peaking, load factor, reserve margin) as well as the time periods during which savings from measures occur. -Across the four locations studied, some of the largest capacity benefits from energy efficiency are derived from the deferral of transmission and distribution system infrastructure upgrades. However, the deferred cost of such upgrades also exhibited the greatest range

  15. Real-Time Clinical Decision Support Decreases Inappropriate Plasma Transfusion.

    Science.gov (United States)

    Shah, Neil; Baker, Steven A; Spain, David; Shieh, Lisa; Shepard, John; Hadhazy, Eric; Maggio, Paul; Goodnough, Lawrence T

    2017-08-01

    To curtail inappropriate plasma transfusions, we instituted clinical decision support as an alert upon order entry if the patient's recent international normalized ratio (INR) was 1.7 or less. The alert was suppressed for massive transfusion and within operative or apheresis settings. The plasma order was automatically removed upon alert acceptance while clinical exception reasons allowed for continued transfusion. Alert impact was studied comparing a 7-month control period with a 4-month intervention period. Monthly plasma utilization decreased 17.4%, from a mean ± SD of 3.40 ± 0.48 to 2.82 ± 0.6 plasma units per hundred patient days (95% confidence interval [CI] of difference, -0.1 to 1.3). Plasma transfused below an INR of 1.7 or less decreased from 47.6% to 41.6% (P = .0002; odds ratio, 0.78; 95% CI, 0.69-0.89). The alert recommendation was accepted 33% of the time while clinical exceptions were chosen in the remaining cases (active bleeding, 31%; other clinical indication, 33%; and apheresis, 2%). Alert acceptance rate varied significantly among different provider specialties. Clinical decision support can help curtail inappropriate plasma use but needs to be part of a comprehensive strategy including audit and feedback for comprehensive, long-term changes. © American Society for Clinical Pathology, 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com

  16. An advanced plasma control system for Tore Supra

    International Nuclear Information System (INIS)

    Wijnands, T.; Martin, G.

    1996-01-01

    First results on plasma control with the new plasma control system of Tore Supra are presented. The system has been especially designed for long pulse operation: plasmas are controlled on reference signals, which can be varied in real time by using diagnostic measurements. On line determination of the global plasma equilibrium has enabled new operation scenarios in which both the power from the poloidal field generators and the total Lower Hybrid (LH) power are used to control the plasma. Experiments with feedback control of the safety factor on the plasma boundary, control of the LH driven current, control of the flux on the plasma boundary and control of the internal inductance are discussed. (author)

  17. An advanced plasma control system for Tore Supra

    Energy Technology Data Exchange (ETDEWEB)

    Wijnands, T.; Martin, G.

    1996-01-01

    First results on plasma control with the new plasma control system of Tore Supra are presented. The system has been especially designed for long pulse operation: plasmas are controlled on reference signals, which can be varied in real time by using diagnostic measurements. On line determination of the global plasma equilibrium has enabled new operation scenarios in which both the power from the poloidal field generators and the total Lower Hybrid (LH) power are used to control the plasma. Experiments with feedback control of the safety factor on the plasma boundary, control of the LH driven current, control of the flux on the plasma boundary and control of the internal inductance are discussed. (author). 12 refs.

  18. Modeling and application of plasma charge current in deep penetration laser welding

    International Nuclear Information System (INIS)

    Zhang, Xudong; Chen, Wuzhu; Jiang, Ping; Guo, Jing; Tian, Zhiling

    2003-01-01

    Plasma charge current distribution during deep penetration CO 2 laser welding was analyzed theoretically and experimentally. The laser-induced plasma above the workpiece surface expands up to the nozzle, driven by the particle concentration gradient, forming an electric potential between the workpiece and the nozzle due to the large difference between the diffusion velocities of the ions and the electrons. The plasma-induced current obtained by electrically connecting the nozzle and the workpiece can be increased by adding a negative external voltage. For a fixed set of welding conditions, the plasma charge current increases with the external voltage to a saturation value. The plasma charge current decreases as the nozzle-to-workpiece distance increases. Therefore, closed-loop control of the nozzle-to-workpiece distance for laser welding can be based on the linear relationship between the plasma charge current and the distance. In addition, the amount of plasma above the keyhole can be reduced by a transverse magnetic field, which reduces the attenuation of the incident laser power by the plasma so as to increase the laser welding thermal efficiency

  19. Flexible Demand Management under Time-Varying Prices

    Science.gov (United States)

    Liang, Yong

    In this dissertation, the problem of flexible demand management under time-varying prices is studied. This generic problem has many applications, which usually have multiple periods in which decisions on satisfying demand need to be made, and prices in these periods are time-varying. Examples of such applications include multi-period procurement problem, operating room scheduling, and user-end demand scheduling in the Smart Grid, where the last application is used as the main motivating story throughout the dissertation. The current grid is experiencing an upgrade with lots of new designs. What is of particular interest is the idea of passing time-varying prices that reflect electricity market conditions to end users as incentives for load shifting. One key component, consequently, is the demand management system at the user-end. The objective of the system is to find the optimal trade-off between cost saving and discomfort increment resulted from load shifting. In this dissertation, we approach this problem from the following aspects: (1) construct a generic model, solve for Pareto optimal solutions, and analyze the robust solution that optimizes the worst-case payoffs, (2) extend to a distribution-free model for multiple types of demand (appliances), for which an approximate dynamic programming (ADP) approach is developed, and (3) design other efficient algorithms for practical purposes of the flexible demand management system. We first construct a novel multi-objective flexible demand management model, in which there are a finite number of periods with time-varying prices, and demand arrives in each period. In each period, the decision maker chooses to either satisfy or defer outstanding demand to minimize costs and discomfort over a certain number of periods. We consider both the deterministic model, models with stochastic demand or prices, and when only partial information about the stochastic demand or prices is known. We first analyze the stochastic

  20. A high-current pulsed cathodic vacuum arc plasma source

    International Nuclear Information System (INIS)

    Oates, T.W.H.; Pigott, J.; Mckenzie, D.R.; Bilek, M.M.M.

    2003-01-01

    Cathodic vacuum arcs (CVAs) are well established as a method for producing metal plasmas for thin film deposition and as a source of metal ions. Fundamental differences exist between direct current (dc) and pulsed CVAs. We present here results of our investigations into the design and construction of a high-current center-triggered pulsed CVA. Power supply design based on electrolytic capacitors is discussed and optimized based on obtaining the most effective utilization of the cathode material. Anode configuration is also discussed with respect to the optimization of the electron collection capability. Type I and II cathode spots are observed and discussed with respect to cathode surface contamination. An unfiltered deposition rate of 1.7 nm per pulse, at a distance of 100 mm from the source, has been demonstrated. Instantaneous plasma densities in excess of 1x10 19 m -3 are observed after magnetic filtering. Time averaged densities an order of magnitude greater than common dc arc densities have been demonstrated, limited by pulse repetition rate and filter efficiency

  1. Current sheath curvature correlation with the neon soft x-ray emission from plasma focus device

    International Nuclear Information System (INIS)

    Zhang, T; Lin, X; Chandra, K A; Tan, T L; Springham, S V; Patran, A; Lee, P; Lee, S; Rawat, R S

    2005-01-01

    The insulator sleeve length is one of the major parameters that can severely affect the neon soft x-ray yield from a plasma focus. The effect of the insulation sleeve length on various characteristic timings of plasma focus discharges and hence the soft x-ray emission characteristics has been investigated using a resistive divider. The pinhole images and laser shadowgraphy are used to explain the observed variation in the average soft x-ray yield (measured using a diode x-ray spectrometer) with variation of the insulator sleeve length. We have found that for a neon filled plasma focus device the change in insulator sleeve length changes the current sheath curvature angle and thus the length of the focused plasma column. The optimized current sheath curvature angle is found to be between 39 0 and 41 0 , at the specific axial position of 6.2-9.3 cm from the cathode support plate, for our 3.3 kJ plasma focus device. A strong dependence of the neon soft x-ray yield on the current sheath curvature angle has thus been reported

  2. Estimates on the mean current in a sphere of plasma

    International Nuclear Information System (INIS)

    Nunez, Manuel

    2003-01-01

    Several turbulent dynamo models predict the concentration of the magnetic field in chaotic plasmas in sheets with the field vector pointing alternatively in opposite directions, which should produce strong current sheets. It is proved that if the plasma is contained in a rigid sphere with perfectly conducting boundary the geometry of these sheets must be balanced so that the mean current remains essentially bounded by the Coulomb gauged mean vector potential of the field. This magnitude remains regular even for the sharp field variations expected in a chaotic flow. For resistive plasmas the same arguments imply that the contribution to the total current of the regions near the boundary compensates the current of the central part of the sphere

  3. RF generator interlock by plasma grid bias current - An alternate to Hα interlock

    Science.gov (United States)

    Bandyopadhyay, M.; Gahlaut, A.; Yadav, R. K.; Pandya, K.; Tyagi, H.; Vupugalla, M.; Bhuyan, M.; Bhagora, J.; Chakraborty, A.

    2017-08-01

    ROBIN is inductively coupled plasma (ICP) based negative hydrogen ion source, operated with a 100kW, 1MHz Tetrode based RF generator (RFG). Inductive plasma ignition by the RFG in ROBIN is associated with electron seeding by a hot filament and a gas puff. RFG is triggered by the control system to deliver power just at the peak pressure of the gas puff. Once plasma is ignited due to proper impedance matching, a bright light, dominated by Hα (˜656nm wavelength) radiation is available inside RF driver which is used as a feedback signal to the RFG to continue its operation. If impedance matching is not correct, plasma is not produced due to lack of power coupling and bright light is not available. During such condition, reflected RF power may damage the RFG. Therefore, to protect the RFG, it needs to be switched off automatically within 200ms by the control system in such cases. This plasma light based RFG interlock is adopted from BATMAN ion source. However, in case of vacuum immersed RF ion source in reactor grade NBI system, such plasma light based interlock may not be feasible due to lack of adequate optical fiber interfaces. In reactor grade NBI system, neutron and gamma radiations have impact on materials which may lead to frequent maintenance and machine down time. The present demonstration of RFG interlock by Bias Current (BC) in ROBIN testbed gives an alternate option in this regard. In ROBIN, a bias plate (BP) is placed in the plasma chamber near the plasma grid (PG). BP is electrically connected to the plasma chamber wall of the ion source and PG is isolated from the wall. A high current ˜85 A direct current (DC) power supply of voltage in the range of 0 - 33V is connected between the PG and the BP in such a way that PG can be biased positively with respect to the BP or plasma chamber. This arrangement is actually made to absorb electrons and correspondingly reduce co-extracted electron current during beam extraction. However, in case of normal plasma

  4. Pemodelan Markov Switching Dengan Time-varying Transition Probability

    OpenAIRE

    Savitri, Anggita Puri; Warsito, Budi; Rahmawati, Rita

    2016-01-01

    Exchange rate or currency is an economic variable which reflects country's state of economy. It fluctuates over time because of its ability to switch the condition or regime caused by economic and political factors. The changes in the exchange rate are depreciation and appreciation. Therefore, it could be modeled using Markov Switching with Time-Varying Transition Probability which observe the conditional changes and use information variable. From this model, time-varying transition probabili...

  5. Comparison of bootstrap current and plasma conductivity models applied in a self-consistent equilibrium calculation for Tokamak plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Andrade, Maria Celia Ramos; Ludwig, Gerson Otto [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil). Lab. Associado de Plasma]. E-mail: mcr@plasma.inpe.br

    2004-07-01

    Different bootstrap current formulations are implemented in a self-consistent equilibrium calculation obtained from a direct variational technique in fixed boundary tokamak plasmas. The total plasma current profile is supposed to have contributions of the diamagnetic, Pfirsch-Schlueter, and the neoclassical Ohmic and bootstrap currents. The Ohmic component is calculated in terms of the neoclassical conductivity, compared here among different expressions, and the loop voltage determined consistently in order to give the prescribed value of the total plasma current. A comparison among several bootstrap current models for different viscosity coefficient calculations and distinct forms for the Coulomb collision operator is performed for a variety of plasma parameters of the small aspect ratio tokamak ETE (Experimento Tokamak Esferico) at the Associated Plasma Laboratory of INPE, in Brazil. We have performed this comparison for the ETE tokamak so that the differences among all the models reported here, mainly regarding plasma collisionality, can be better illustrated. The dependence of the bootstrap current ratio upon some plasma parameters in the frame of the self-consistent calculation is also analysed. We emphasize in this paper what we call the Hirshman-Sigmar/Shaing model, valid for all collisionality regimes and aspect ratios, and a fitted formulation proposed by Sauter, which has the same range of validity but is faster to compute than the previous one. The advantages or possible limitations of all these different formulations for the bootstrap current estimate are analysed throughout this work. (author)

  6. Plasma current sustainment after iron core saturation in the STOR-M tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Mitarai, O., E-mail: omitarai@ktmail.tokai-u.jp [Kumamoto Liberal Arts Education Center, Tokai University, 9-1-1 Toroku, Higashi-ku, Kumamoto 862-8652 (Japan); Ding, Y.; Hubeny, M.; Lu, Y.; Onchi, T.; McColl, D.; Xiao, C.; Hirose, A. [Plasma Physics Laboratory, University of Saskatchewan, 116 Science Place, Saskatoon, SK S7N 5E2 (Canada)

    2014-10-15

    Highlights: • Plasma current can be started up by small iron core without central solenoid. • Iron core removes central solenoid. • Plasma current can be maintained after iron core saturation. • Hysteresis curve shows the partial core saturation. • Image field from iron core is estimated during discharge. • Spherical tokamak reactor without CS is proposed using the small iron core. - Abstract: We propose to use of a small iron core transformer to start up the plasma current in a spherical tokamak (ST) reactor without central solenoid (CS). Taking advantage of the high aspect ratio of the STOR-M iron core tokamak, we have demonstrated that the plasma current up to 10–15 kA can be started up using the outer Ohmic heating (OH) coils without CS, and that the plasma current can be maintained further by increasing the outer OH coil current during iron core saturation phase. When the magnetizing current reaches 1.2 kA and the iron core becomes saturated, the third capacitor bank connected to the outer OH coils is discharged to maintain the plasma current. The plasma current is slightly increased and maintained for additional 5 ms as expected from numerical calculations. Core saturation has been clearly observed on the hysteresis curve. This is the first experimental demonstration of the feasibility of slow transition from the iron core to air core transformer phase without CS. The results implies that a plasma current can be initiated by a small iron core and could be ramped up by additional heating and vertical field after iron core saturation in future STs without CS.

  7. Development of net-current free heliotron plasmas in the Large Helical Device

    International Nuclear Information System (INIS)

    Komori, A.; Yamada, H.; Kaneko, O.; Kawahata, K.; Mutoh, T.; Ohyabu, N.; Imagawa, S.; Ida, K.; Nagayama, Y.; Shimozuma, T.; Watanabe, K.Y.; Mito, T.; Kobayashi, M.; Nagaoka, K.; Sakamoto, R.; Ohdachi, S.; Sakakibara, S.; Ashikawa, N.; Igami, H.; Kasahara, H.; Kubo, S.; Kumazawa, R.; Nishiura, M.; Masuzaki, S.; Tanaka, K.; Toi, K.; Yoshinuma, M.; Narushima, Y.; Tamura, N.; Saito, K.; Seki, T.; Sudo, S.; Tanaka, H.; Tokuzawa, T.; Yanagi, N.; Yokoyama, M.; Yoshimura, Y.; Akiyama, T.; Chikaraishi, H.; Emoto, M.; Funaba, H.; Goncharov, P.; Goto, M.; Ichiguchi, K.; Ido, T.; Ikeda, K.; Yoshida, N.; Inagaki, S.; Idei, H.; Feng, Y.; Weller, A.; Fukuda, T.; Mitarai, O.; Murakami, S.; Nakamura, Y.; Hino, T.; Ohno, N.; Okamura, T.; Iio, S.; Chowdhuri, M.; Ezumi, N.; Garcia, L.; Ichimura, M.; Irie, M.; Isayama, Akihiko; Iwamae, Atsushi; Takenaga, Hidenobu; Urano, Hajime

    2008-10-01

    Remarkable progress in the physical parameters of net-current free plasmas has been made in the Large Helical Device (LHD) since the last Fusion Energy Conference in Chengdu, 2006 (O. Motojima et al., Nucl. Fusion 47 (2007) S668). The beta value reached 5 % and a high beta state beyond 4.5% from the diamagnetic measurement has been maintained for longer than 100 times the energy confinement time. The density and temperature regimes also have been extended. The central density has exceeded 1.0x10 21 m -3 due to the formation of an Internal Diffusion Barrier (IDB). The ion temperature has reached 6.8 keV at the density of 2x10 19 m -3 , which is associated with the suppression of ion heat conduction loss. Although these parameters have been obtained in separated discharges, each fusion-reactor relevant parameter has elucidated the potential of net-current free heliotron plasmas. Diversified studies in recent LHD experiments are reviewed in this paper. (author)

  8. Glow-to-arc transition events in H2-Ar direct current pulsed plasma: Automated measurement of current and voltage

    International Nuclear Information System (INIS)

    Mendes, Luciano A.; Rodrigues, Jhonatam C.; Mafra, Marcio

    2012-01-01

    The glow-to-arc transition phenomena (arcing) observed in plasma reactors used in materials processing was studied through the arcs characteristic current and voltage waveforms. In order to capture these arcs signals, a LABVIEW based automated instrumentation system (ARCVIEW) was developed, including the integration of an oscilloscope equipped with proper current and voltage probes. The system also allows capturing the process parameters at the arc occurrence moments, which were used to map the arcs events conditions. Experiments in H 2 -Ar DC pulsed plasma returned signals data from 215 arcs events, which were analyzed through software routines. According to the results, an anti-arcing system should react in the time order of few microseconds to prevent most of the damage caused by the undesired arcing phenomena.

  9. Experimental Study of Current Discharge Behavior and Hard X-ray Anisotropy by APF Plasma Focus Device

    Science.gov (United States)

    Habibi, M.; Amrollahi, R.; Attaran, M.

    2009-03-01

    Amirkabir (APF) is a new Mather-type plasma focus device (16 kV, 36 μf, and 115 nH). In this work we present some experimental results as variation of discharge current signal respect to applied voltage at the optimum pressure, focusing time of plasma versus gas pressure, and variations of current discharge with different insulator sleeve dimensions. As we prospected optimum pressure tending to increase as we tried to higher voltage levels. The time taken by the current sheath to lift-off the insulator surface and therefore quality of pinched plasma depends on the length of the insulator sleeve. The results show that the insulator diameter can influence on pinch quality. Behavior of hard X-ray (HXR) signals with the pressure and also anisotropy of HXR investigated by the use of two scintillation detectors. The distribution of HXR intensity shows a large anisotropy with a maximum intensity between 22.5° and 45° and also between -22.5° and -67.5°.

  10. Maximum time-dependent space-charge limited diode currents

    Energy Technology Data Exchange (ETDEWEB)

    Griswold, M. E. [Tri Alpha Energy, Inc., Rancho Santa Margarita, California 92688 (United States); Fisch, N. J. [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)

    2016-01-15

    Recent papers claim that a one dimensional (1D) diode with a time-varying voltage drop can transmit current densities that exceed the Child-Langmuir (CL) limit on average, apparently contradicting a previous conjecture that there is a hard limit on the average current density across any 1D diode, as t → ∞, that is equal to the CL limit. However, these claims rest on a different definition of the CL limit, namely, a comparison between the time-averaged diode current and the adiabatic average of the expression for the stationary CL limit. If the current were considered as a function of the maximum applied voltage, rather than the average applied voltage, then the original conjecture would not have been refuted.

  11. Experimental evidence for amplitude death induced by a time-varying interaction

    Energy Technology Data Exchange (ETDEWEB)

    Suresh, K. [Centre for Nonlinear Dynamics, School of Physics, Bharathidasan University, Tiruchirappalli 620024, Tamil Nadu (India); Shrimali, M.D. [Department of Physics, Central University of Rajasthan, NH-8, Bandar Sindri, Ajmer 305 801 (India); Prasad, Awadhesh [Department of Physics and Astrophysics, University of Delhi, Delhi 110 007 (India); Thamilmaran, K., E-mail: maran.cnld@gmail.com [Centre for Nonlinear Dynamics, School of Physics, Bharathidasan University, Tiruchirappalli 620024, Tamil Nadu (India)

    2014-08-01

    In this paper, we study the time-varying interaction in coupled oscillatory systems. For this purpose, we have designed a novel time-varying resistive network using an analog switch and inverter circuits. We have applied this time-varying resistive network to mutually coupled identical Chua's oscillators. When the resistances are varied in time, we find that amplitude death arises in coupled identical oscillators. This has been observed numerically as well as verified through hardware experiments. - Highlights: • We have implemented the time-varying interaction in coupled oscillatory systems. • We have designed a novel time-varying resistive network using an analog switch and inverter circuits. • When the resistances are varied in time, we find that amplitude death arises in coupled identical oscillators.

  12. The plasmasheet H+ and O+ contribution on the storm time ring current

    Science.gov (United States)

    Mouikis, C.; Bingham, S.; Kistler, L. M.; Spence, H. E.; Gkioulidou, M.; Claudepierre, S. G.; Farrugia, C. J.

    2015-12-01

    The source population of the storm time ring current is the night side plasma sheet. We use Van Allen Probes and Cluster observations to determine the contribution of the convecting plasma sheet H+ and O+ particles in the storm time development of the ring current. Using the Volland-Stern model with a dipole magnetic field together with the identification of the observed energy cutoffs in the particle spectra, we specify the pressure contributed by H+ and O+ populations that are on open drift paths vs. the pressure contributed by the trapped populations, for different local times. We find that during the storm main phase most of the ring current pressure in the pre-midnight inner magnetosphere is contributed by particles on open drift paths that cause the development of a strong partial ring current that causes most of the main phase Dst drop. These particles can reach as deep as L~2 and their pressure compares to the local magnetic field pressure as deep as L~3. During the recovery phase, if these particles are not lost at the magnetopause, will become trapped and will contribute to the symmetric ring current.

  13. Microsecond plasma opening switch experiments on GIT-4

    Energy Technology Data Exchange (ETDEWEB)

    Bystritskij, V M; Lisitsyn, I V; Sinebryukhov, A A; Sinebryukhov, V A [Russian Academy of Sciences, Tomsk (Russian Federation). Inst. of Electrophysics; Kim, A A; Kokshenev, V A; Koval` chuk, B M [Russian Academy of Sciences, Tomsk (Russian Federation). High Current Electronics Inst.

    1997-12-31

    The plasma opening switch (POS) operation at the current level up to 2 MA was studied at the terawatt power GIT-4 generator. The experiments are described in which the electrode diameter and the strength of the applied magnetic field were varied, and different plasma sources were used. It is shown that the high voltage / low impedance switch operation can be achieved if the linear current density at the POS cathode does not exceed 20 kA/cm. This value limits the maximum cathode diameter of the magnetically insulated transmission line. The anode diameter is limited by the requirement of no gap closure with a dense electrode plasma. The application of external magnetic field decreases the plasma density necessary for achieving a long POS conduction time operation regime. (J.U.). 1 tab., 4 refs.

  14. Microsecond plasma opening switch experiments on GIT-4

    International Nuclear Information System (INIS)

    Bystritskij, V.M.; Lisitsyn, I.V.; Sinebryukhov, A.A.; Sinebryukhov, V.A.; Kim, A.A.; Kokshenev, V.A.; Koval'chuk, B.M.

    1996-01-01

    The plasma opening switch (POS) operation at the current level up to 2 MA was studied at the terawatt power GIT-4 generator. The experiments are described in which the electrode diameter and the strength of the applied magnetic field were varied, and different plasma sources were used. It is shown that the high voltage / low impedance switch operation can be achieved if the linear current density at the POS cathode does not exceed 20 kA/cm. This value limits the maximum cathode diameter of the magnetically insulated transmission line. The anode diameter is limited by the requirement of no gap closure with a dense electrode plasma. The application of external magnetic field decreases the plasma density necessary for achieving a long POS conduction time operation regime. (J.U.). 1 tab., 4 refs

  15. Local inertial oscillations in the surface ocean generated by time-varying winds

    Science.gov (United States)

    Chen, Shengli; Polton, Jeff A.; Hu, Jianyu; Xing, Jiuxing

    2015-12-01

    A new relationship is presented to give a review study on the evolution of inertial oscillations in the surface ocean locally generated by time-varying wind stress. The inertial oscillation is expressed as the superposition of a previous oscillation and a newly generated oscillation, which depends upon the time-varying wind stress. This relationship is employed to investigate some idealized wind change events. For a wind series varying temporally with different rates, the induced inertial oscillation is dominated by the wind with the greatest variation. The resonant wind, which rotates anti-cyclonically at the local inertial frequency with time, produces maximal amplitude of inertial oscillations, which grows monotonically. For the wind rotating at non-inertial frequencies, the responses vary periodically, with wind injecting inertial energy when it is in phase with the currents, but removing inertial energy when it is out of phase. The wind rotating anti-cyclonically with time is much more favorable to generate inertial oscillations than the cyclonic rotating wind. The wind with a frequency closer to the inertial frequency generates stronger inertial oscillations. For a diurnal wind, the induced inertial oscillation is dependent on latitude and is most significant at 30 °. This relationship is also applied to examine idealized moving cyclones. The inertial oscillation is much stronger on the right-hand side of the cyclone path than on the left-hand side (in the northern hemisphere). This is due to the wind being anti-cyclonic with time on the right-hand side, but cyclonic on the other side. The inertial oscillation varies with the cyclone translation speed. The optimal translation speed generating the greatest inertial oscillations is 2 m/s at the latitude of 10 ° and gradually increases to 6 m/s at the latitude of 30 °.

  16. Analysis of time-varying psoriasis lesion image patterns

    DEFF Research Database (Denmark)

    Maletti, Gabriela Mariel; Ersbøll, Bjarne Kjær; Nielsen, Allan Aasbjerg

    2004-01-01

    The multivariate alteration detection transform is applied to pairs of within and between time varying registered psoriasis image patterns. Color band contribution to the variates explaining maximal change is analyzed.......The multivariate alteration detection transform is applied to pairs of within and between time varying registered psoriasis image patterns. Color band contribution to the variates explaining maximal change is analyzed....

  17. Impurities, temperature, and density in a miniature electrostatic plasma and current source

    International Nuclear Information System (INIS)

    Den Hartog, D.J.; Craig, D.J.; Fiksel, G.; Sarff, J.S.

    1996-10-01

    We have spectroscopically investigated the Sterling Scientific miniature electrostatic plasma source-a plasma gun. This gun is a clean source of high density (10 19 - 10 20 m -3 ), low temperature (5 - 15 eV) plasma. A key result of our investigation is that molybdenum from the gun electrodes is largely trapped in the internal gun discharge; only a small amount escapes in the plasma flowing out of the gun. In addition, the gun plasma parameters actually improve (even lower impurity contamination and higher ion temperature) when up to 1 kA of electron current is extracted from the gun via the application of an external bias. This improvement occurs because the internal gun anode no longer acts as the current return for the internal gun discharge. The gun plasma is a virtual plasma electrode capable of sourcing an electron emission current density of 1 kA/cm 2 . The high emission current, small size (3 - 4 cm diameter), and low impurity generation make this gun attractive for a variety of fusion and plasma technology applications

  18. Critical condition for current-driven instability excited in turbulent heating of TRIAM-1 tokamak plasma

    Energy Technology Data Exchange (ETDEWEB)

    Nakamura, Y; Watanabe, T; Nagao, A; Nakamura, K; Kikuchi, M; Aoki, T; Hiraki, N; Itoh, S [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics; Mitarai, O

    1982-02-01

    Critical condition for current-driven instability excited in turbulently heated TRIAM-1 tokamak plasma is investigated experimentally. Resistive hump in loop voltage, plasma density fluctuation and rapid increase of electron temperature in a skin layer are simultaneously observed at the time when the electron drift velocity amounts to the critical drift velocity for low-frequency ion acoustic instability.

  19. Numerical simulation on current spike behaviour of JT-60U disruptive plasmas

    International Nuclear Information System (INIS)

    Takei, N; Nakamura, Y; Tsutsui, H; Yoshino, R; Kawano, Y; Ozeki, T; Tobita, K; Tsuji-Iio, S; Shimada, R; Jardin, S C

    2004-01-01

    Characteristics and underlying mechanisms for plasma current spikes, which have been frequently observed during the thermal quench of JT-60U disruptions, were investigated through tokamak simulation code simulations including the passive shell effects of the vacuum vessel. Positive shear and reversed shear (PS and RS) plasmas were shown to have various current spike features in the experiments, e.g. an impulsive increase in the plasma current (positive spike) in the majority of thermal quenches, and a sudden decrease (negative spike), that has been excluded from past consideration, as an exception. It was first clarified that the shell effects, which become significant especially at a strong pressure drop due to the thermal quench of high β p plasmas, play an important role in the current spike in accordance with the initial relation of the radial location between the plasma equilibria and the vacuum vessel. As a consequence, a negative current spike may appear at thermal quench when the plasma is positioned further out from the geometric centre of the vacuum vessel. It was also pointed out that a further lowering in the internal inductance, in contradiction to previous interpretation in the past, is a plausible candidate for the mechanism for positive current spikes observed even in RS plasmas. The new interpretation enables us to reason out the whole character of current spikes of JT-60U disruptions

  20. Finite-time stability of neutral-type neural networks with random time-varying delays

    Science.gov (United States)

    Ali, M. Syed; Saravanan, S.; Zhu, Quanxin

    2017-11-01

    This paper is devoted to the finite-time stability analysis of neutral-type neural networks with random time-varying delays. The randomly time-varying delays are characterised by Bernoulli stochastic variable. This result can be extended to analysis and design for neutral-type neural networks with random time-varying delays. On the basis of this paper, we constructed suitable Lyapunov-Krasovskii functional together and established a set of sufficient linear matrix inequalities approach to guarantee the finite-time stability of the system concerned. By employing the Jensen's inequality, free-weighting matrix method and Wirtinger's double integral inequality, the proposed conditions are derived and two numerical examples are addressed for the effectiveness of the developed techniques.

  1. Identification of time-varying structural dynamic systems - An artificial intelligence approach

    Science.gov (United States)

    Glass, B. J.; Hanagud, S.

    1992-01-01

    An application of the artificial intelligence-derived methodologies of heuristic search and object-oriented programming to the problem of identifying the form of the model and the associated parameters of a time-varying structural dynamic system is presented in this paper. Possible model variations due to changes in boundary conditions or configurations of a structure are organized into a taxonomy of models, and a variant of best-first search is used to identify the model whose simulated response best matches that of the current physical structure. Simulated model responses are verified experimentally. An output-error approach is used in a discontinuous model space, and an equation-error approach is used in the parameter space. The advantages of the AI methods used, compared with conventional programming techniques for implementing knowledge structuring and inheritance, are discussed. Convergence conditions and example problems have been discussed. In the example problem, both the time-varying model and its new parameters have been identified when changes occur.

  2. Study of plasma equilibrium during the AC current reversal phase in STOR-M

    International Nuclear Information System (INIS)

    Xiao, C.

    2002-01-01

    Alternating current (AC) tokamak operation and equilibrium studies have been performed on the STOR-M tokamak. The recent experiments have achieved consistent smooth current reversal through the implementation of a hybrid digital-analog position controller and by careful density control. In order to study the plasma equilibrium during the current reversal phase with negligible rotational transform, a segmented limiter with four isolated conducting plates has been installed. The plates can be connected outside the vacuum vessel, which allows measurements of currents flowing between limiter plates. When the current reversal is smooth with zero dwell time, the hydrogen line emission level and electron density remain finite, indicating a finite particle confinement. The current from the top to the bottom limiter plate is also finite and its direction is consistent with that of the grad-B drift. The observation suggests that the limiter and other conducting structures surrounding the plasmas plays the role, during the current reversal phase of AC tokamak operation, to short out the charge separation arising from the grad-B drift and to maintain a finite particle confinement. (author)

  3. 3D eddy-current distribution in a tokamak first wall during a plasma disruption using 'TRIFOU'

    International Nuclear Information System (INIS)

    Chaussecourte, P.; Bossavit, A.; Verite, J.C.; Crutzen, Y.R.

    1989-01-01

    In fusion reactor studies there is a lack of knowledge concerning the electromagnetic-type of phenomena generated by a plasma disruption event (rapid quenching of the plasma current). The induced eddy current distribution in space and time in the passive conducting structural components surrounding the plasma ring needs to be accurately investigated. TRIFOU is a full 3D eddy-current computer program based on a mixed FEM and BIEM technique, using the magnetic field, h, as a state variable, It has already been used in various areas of interest including static or rotating machines, non-destructive testing, induction heating, and research devices such as tokamaks. It can take into account various geometries and a wide range of physical situations (time dependency, physical properties, etc.). The present application is related to the eddy-current situation arising from a strong electromagnetic transient generated in the NET (Next European Torus) first wall segment. With respect to previous numerical simulations, the general 3D approach for the current density shows different eddy current circulations in the front/side shells and in the stiff back plate. The results obtained by TRIFOU are illustrated by means of advanced computer graphic displays and an animation movie. (orig.)

  4. Hall Current Plasma Source Having a Center-Mounted or a Surface-Mounted Cathode

    Science.gov (United States)

    Martinez, Rafael A. (Inventor); Williams, John D. (Inventor); Moritz, Jr., Joel A. (Inventor); Farnell, Casey C. (Inventor)

    2018-01-01

    A miniature Hall current plasma source apparatus having magnetic shielding of the walls from ionized plasma, an integrated discharge channel and gas distributor, an instant-start hollow cathode mounted to the plasma source, and an externally mounted keeper, is described. The apparatus offers advantages over other Hall current plasma sources having similar power levels, including: lower mass, longer lifetime, lower part count including fewer power supplies, and the ability to be continuously adjustable to lower average power levels using pulsed operation and adjustment of the pulse duty cycle. The Hall current plasma source can provide propulsion for small spacecraft that either do not have sufficient power to accommodate a propulsion system or do not have available volume to incorporate the larger propulsion systems currently available. The present low-power Hall current plasma source can be used to provide energetic ions to assist the deposition of thin films in plasma processing applications.

  5. Entropy Rate of Time-Varying Wireless Networks

    DEFF Research Database (Denmark)

    Cika, Arta; Badiu, Mihai Alin; Coon, Justin P.

    2018-01-01

    In this paper, we present a detailed framework to analyze the evolution of the random topology of a time-varying wireless network via the information theoretic notion of entropy rate. We consider a propagation channel varying over time with random node positions in a closed space and Rayleigh...... fading affecting the connections between nodes. The existence of an edge between two nodes at given locations is modeled by a Markov chain, enabling memory effects in network dynamics. We then derive a lower and an upper bound on the entropy rate of the spatiotemporal network. The entropy rate measures...

  6. The dynamic current-voltage characteristic as a powerful tool to analyze fast phenomena in plasma

    International Nuclear Information System (INIS)

    Ivan, L. M.; Mihai-Plugaru, M.; Amarandei, G.; Aflori, M.; Dimitriu, D. G.

    2006-01-01

    The static current-voltage characteristic of an electrode immersed in plasma is obtained by slowly increasing and subsequently decreasing the potential on the electrode with respect to the plasma potential or the ground. This characteristic can give us important information about the phenomena that take place in front of the electrode. Current jumps can be evidenced which were often associated with an hysteresis effect, regions with S-type or N-type negative differential resistance, etc. The method is always used when we investigate the appearance of complex space charge configurations (CSCC) in front of an electrode immersed in plasma. However, to investigate the dynamics of such structures or other fast phenomena (like instabilities) which take place in plasma devices with frequencies of tenth, hundred kHz or more, complex investigation techniques must be used. One of the most efficient methods to investigate fast phenomena in plasma devices is the dynamic current-voltage characteristic. This is obtained by recording the time series of the current collected by the electrode when the voltage applied on it is very fast modified (most likely increased) by using a signal generator. In this way, very fast oscillations of the current can be recorded and new phenomena can be evidenced. We used this technique to study the phenomena which take place at the onset of electrostatic instabilities in Q-machine plasma, namely the potential relaxation instability (PRI) and the electrostatic ion-cyclotron instability (EICI). The obtained experimental results prove that the negative differential resistance region in the static current-voltage characteristic is the result of a nonlinear dynamics of a CSCC in form of a double layer (DL) which takes place just before the onset of the instabilities. In the case of the PRI we emphasized current jumps related with the DL appearance, which are not present in the static current-voltage characteristic at high plasma density. (authors)

  7. Time resolved two- and three-dimensional plasma diagnostics

    International Nuclear Information System (INIS)

    1991-03-01

    This collection of papers on diagnostics in fusion plasmas contains work on the data analysis of inverse problems and on the experimental arrangements presently used to obtain spatially and temporally resolved plasma radial profiles, including electron and ion temperature, plasma density and plasma current profiles. Refs, figs and tabs

  8. Simulation of current generation in a 3-D plasma model

    International Nuclear Information System (INIS)

    Tsung, F.S.; Dawson, J.M.

    1996-01-01

    Two wires carrying current in the same direction will attract each other, and two wires carrying current in the opposite direction will repel each other. Now, consider a test charge in a plasma. If the test charge carries current parallel to the plasma, then it will be pulled toward the plasma core, and if the test charge carries current anti-parallel to the plasma, then it will be pushed to the edge. The electromagnetic coupling between the plasma and a test charge (i.e., the A parallel circ v parallel term in the test charge's Hamiltonian) breaks the symmetry in the parallel direction, and gives rise to a diffusion coefficient which is dependent on the particle's parallel velocity. This is the basis for the open-quotes preferential lossclose quotes mechanism described in the work by Nunan et al. In our previous 2+1/2 D work, in both cylindrical and toroidal geometries, showed that if the plasma column is centrally fueled, then an initial current increases steadily. The results in straight, cylindrical plasmas showed that self generated parallel current arises without trapped particle or neoclassical diffusion, as assumed by the bootstrap theory. It suggests that the fundamental mechanism seems to be the conservation of particles canonical momenta in the direction of the ignorable coordinate. We have extended the simulation to 3D to verify the model put forth. A scalable 3D EM-PIC code, with a localized field-solver, has been implemented to run on a large class of parallel computers. On the 512-node SP2 at Cornell Theory Center, we have benchmarked the 2+1/2 D calculations using 32 grids in the previously ignored direction, and a 100-fold increase in the number of particles. Our preliminary results show good agreements between the 2+1/2 D and the 3D calculations. We will present our 3D results at the meeting

  9. Advanced real-time control systems for magnetically confined fusion plasmas

    International Nuclear Information System (INIS)

    Goncalves, B.; Sousa, J.; Fernandes, H.; Rodrigues, A.P.; Carvalho, B.B.; Neto, A.; Varandas, C.A.F.

    2008-01-01

    Real-time control of magnetically confined plasmas is a critical issue for the safety, operation and high performance scientific exploitation of the experimental devices on regimes beyond the current operation frontiers. The number of parameters and the data volumes used for the plasma properties identification scale normally not only with the machine size but also with the technology improvements, leading to a great complexity of the plant system. A strong computational power and fast communication infrastructure are needed to handle in real-time this information, allowing just-in-time decisions to achieve the fusion critical plasma conditions. These advanced control systems require a tiered infrastructure including the hardware layer, the signal-processing middleware, real-time timing and data transport, the real-time operating system tools and drivers, the framework for code development, simulation, deployment and experiment parameterization and the human real-time plasma condition monitoring and management. This approach is being implemented at CFN by offering a vertical solution for the forthcoming challenges, including ITER, the first experimental fusion reactor. A given set of tools and systems are described on this paper, namely: (i) an ATCA based hardware multiple-input-multiple-output (MIMO) platform, PCI and PCIe acquisition and control modules; (ii) FPGA and DSP parallelized signal processing algorithms; (iii) a signal data and event distribution system over a 2.5/10Gb optical network with sub-microsecond latencies; (iv) RTAI and Linux drivers; and (v) the FireSignal, FusionTalk, SDAS FireCalc application tools. (author)

  10. Inferring time-varying network topologies from gene expression data.

    Science.gov (United States)

    Rao, Arvind; Hero, Alfred O; States, David J; Engel, James Douglas

    2007-01-01

    Most current methods for gene regulatory network identification lead to the inference of steady-state networks, that is, networks prevalent over all times, a hypothesis which has been challenged. There has been a need to infer and represent networks in a dynamic, that is, time-varying fashion, in order to account for different cellular states affecting the interactions amongst genes. In this work, we present an approach, regime-SSM, to understand gene regulatory networks within such a dynamic setting. The approach uses a clustering method based on these underlying dynamics, followed by system identification using a state-space model for each learnt cluster--to infer a network adjacency matrix. We finally indicate our results on the mouse embryonic kidney dataset as well as the T-cell activation-based expression dataset and demonstrate conformity with reported experimental evidence.

  11. Time-Varying Value of Energy Efficiency in Michigan

    Energy Technology Data Exchange (ETDEWEB)

    Mims, Natalie; Eckman, Tom; Schwartz, Lisa C.

    2018-04-02

    Quantifying the time-varying value of energy efficiency is necessary to properly account for all of its benefits and costs and to identify and implement efficiency resources that contribute to a low-cost, reliable electric system. Historically, most quantification of the benefits of efficiency has focused largely on the economic value of annual energy reduction. Due to the lack of statistically representative metered end-use load shape data in Michigan (i.e., the hourly or seasonal timing of electricity savings), the ability to confidently characterize the time-varying value of energy efficiency savings in the state, especially for weather-sensitive measures such as central air conditioning, is limited. Still, electric utilities in Michigan can take advantage of opportunities to incorporate the time-varying value of efficiency into their planning. For example, end-use load research and hourly valuation of efficiency savings can be used for a variety of electricity planning functions, including load forecasting, demand-side management and evaluation, capacity planning, long-term resource planning, renewable energy integration, assessing potential grid modernization investments, establishing rates and pricing, and customer service (KEMA 2012). In addition, accurately calculating the time-varying value of efficiency may help energy efficiency program administrators prioritize existing offerings, set incentive or rebate levels that reflect the full value of efficiency, and design new programs.

  12. Numerical experimentation on focusing time and neutron yield in GN1 plasma focus machine

    International Nuclear Information System (INIS)

    Singh, Arwinder; Lee, Sing; Saw, S.H.

    2014-01-01

    In this paper, we have shown how we have fitted Lee's six phase model code to analyze the current waveform of the GN1 plasma focus machine working in deuterium gas. The Lee's 6-phase model codes was later configured to work between 0.5 to 6 Torr and the results of both focusing time and neutron yield was then compared with the published experimental results. The final results indicate that Lee's code, gives realistic plasma dynamics and focus properties together with a realistic neutron yield for GN1 plasma focus, without the need of any adjustable parameters, needing only to fit the computed current trace to a measured current trace. (author)

  13. Multivariate time-varying volatility modeling using probabilistic fuzzy systems

    NARCIS (Netherlands)

    Basturk, N.; Almeida, R.J.; Golan, R.; Kaymak, U.

    2016-01-01

    Methods to accurately analyze financial risk have drawn considerable attention in financial institutions. One difficulty in financial risk analysis is the fact that banks and other financial institutions invest in several assets which show time-varying volatilities and hence time-varying financial

  14. Outlook for the use of microsecond plasma opening switches to generate high-power nanosecond current pulses

    International Nuclear Information System (INIS)

    Dolgachev, G.I.; Maslennikov, D.D.; Ushakov, A.G.

    2006-01-01

    Paper deals with a phenomenon of current breaking in a conducting plasma volume of plasma opening switchers with a nanosecond time of energy initiation and their application in high-power generators. One determined the conditions to ensure megavolt voltages under the erosion mode making use of external applied magnetic field to ensure magnetic insulation of gap of plasma opening switchers. One studied the peculiar features of application of plasma opening switchers under 5-6 MV voltages to ensure X-ray and gamma-radiation pulses [ru

  15. Long memory of financial time series and hidden Markov models with time-varying parameters

    DEFF Research Database (Denmark)

    Nystrup, Peter; Madsen, Henrik; Lindström, Erik

    Hidden Markov models are often used to capture stylized facts of daily returns and to infer the hidden state of financial markets. Previous studies have found that the estimated models change over time, but the implications of the time-varying behavior for the ability to reproduce the stylized...... facts have not been thoroughly examined. This paper presents an adaptive estimation approach that allows for the parameters of the estimated models to be time-varying. It is shown that a two-state Gaussian hidden Markov model with time-varying parameters is able to reproduce the long memory of squared...... daily returns that was previously believed to be the most difficult fact to reproduce with a hidden Markov model. Capturing the time-varying behavior of the parameters also leads to improved one-step predictions....

  16. Plasma confinement in a magnetic field of the internal ring current

    International Nuclear Information System (INIS)

    Shafranov, Vitaly; Popovich, Paul; Samitov, Marat

    2000-01-01

    Plasma confinement in compact region surrounding an internal ring current is considered. As the limiting case of large aspect ratio system the cylindrical plasma is considered initially. Analysis of the cylindrical tubular plasma equilibrium and stability against the most dangerous flute (m=0) and kink (m=1) modes revealed the possibility of the MHD stable plasma confined by magnetic field of the internal rod current, with rather peaked plasma pressure and maximal local beta β(γ)=0.4. In case of the toroidal internal ring system an additional external magnetic field creates the boundary separatrix witch limits the plasma volume. The dependence of the plasma pressure profiles, marginally stable with respect to the flute modes, from the shape of the external plasma boundary (separatrix) in such kind closed toroidal systems is investigated. The internal ring system with circular poloidal magnetic mirror, where the ring supports could be placed, is proposed. (author)

  17. Resistive Instabilities in Hall Current Plasma Discharge

    International Nuclear Information System (INIS)

    Litvak, Andrei A.; Fisch, Nathaniel J.

    2000-01-01

    Plasma perturbations in the acceleration channel of a Hall thruster are found to be unstable in the presence of collisions. Both electrostatic lower-hybrid waves and electromagnetic Alfven waves transverse to the applied electric and magnetic field are found to be unstable due to collisions in the E X B electron flow. These results are obtained assuming a two-fluid hydrodynamic model in slab geometry. The characteristic frequencies of these modes are consistent with experimental observations in Hall current plasma thrusters

  18. Electron current generated in a toroidal plasma on injection of high-energy neutrals

    International Nuclear Information System (INIS)

    Kolesnichenko, Ya.I.; Reznik, S.N.

    1981-01-01

    Problem of generation of electron current in toroidal plasma with a high-energy ion beam produced during neutral injection has been considered. The analysis was performed on the assumption that plasma is in the regime of rare collisions (banana regime) and ion beam velocity is considerably lower than thermal velocity of plasma ions. Formulae establishing the relation between beam current and electron current have been derived. It follows from them that toroidal affect considerably plasma current generated with the beam and under certain conditions result in changing this current direction in an area remoted from magne-- tic axis [ru

  19. The analysis of Alfven wave current drive and plasma heating in TCABR tokamak

    International Nuclear Information System (INIS)

    Ruchko, L.F.; Lerche, E.A.; Galvao, R.M.O.; Elfimov, A.G.; Nascimento, I.C.; Sa, W.P. de; Sanada, E.; Elizondo, J.I.; Ferreira, A.A.; Saettone, E.A.; Severo, J.H.F.; Bellintani, V.; Usuriaga, O.N.

    2002-01-01

    The results of experiments on Alfven wave current drive and plasma heating in the TCABR tokamak are analyzed with the help of a numerical code for simulation of the diffusion of the toroidal electric field. It permits to find radial distributions of plasma current density and conductivity, which match the experimentally measured total plasma current and loop voltage changes, and thus to study the performance of the RF system during Alfven wave plasma heating and current drive experiments. Regimes with efficient RF power input in TCABR have been analyzed and revealed the possibility of noninductive current generation with magnitudes up to ∼8 kA. The increase of plasma energy content due to RF power input is consistent with the diamagnetic measurements. (author)

  20. The Current-Driven, Ion-Acoustic Instability in a Collisionless Plasma

    DEFF Research Database (Denmark)

    Michelsen, Poul; Pécseli, Hans; Juul Rasmussen, Jens

    1979-01-01

    The current-driven, ion-acoustic instability was investigated by means of an experiment performed in a collisionless plasma produced in a single-ended Q-machine. Reflections at the ends of the plasma column gave rise to a standing wave. Parameters of the instability were investigated, and it was ......, and it was demonstrated that the fluctuations in the plasma column behave as a classical Van der Pol oscillator. Accurate measurements of the growth rate of the instability can be performed by making explicit use of the particular properties of such a system.......The current-driven, ion-acoustic instability was investigated by means of an experiment performed in a collisionless plasma produced in a single-ended Q-machine. Reflections at the ends of the plasma column gave rise to a standing wave. Parameters of the instability were investigated...

  1. Observation of the bootstrap current reduction at magnetic island in a neoclassical tearing mode plasma

    International Nuclear Information System (INIS)

    Oikawa, T.; Suzuki, T.; Isayama, A.; Hayashi, N.; Fujita, T.; Naito, O.; Tuda, T.; Kurita, G.

    2005-01-01

    Evolution of the current density profile associated with magnetic island formation in a neoclassical tearing mode plasma is measured for the first time in JT-60U by using a motional Stark effect diagnostic. As the island grows, the current density profile turns flat at the radial region of the island and a hollow structure appears at the rational surface. As the island shrinks the deformed region becomes narrower and finally diminishes after the disappearance of the island. In a quiescent plasma without magnetohydrodynamic instabilities, on the other hand, no deformation is observed. The observed deformation in the current density profile associated with the tearing mode is reproduced in a time dependent transport simulation assuming the reduction of the bootstrap current in the radial region of the island. Comparison of the measurement with a calculated steady-state solution also shows that the reduction and recovery of the bootstrap current at the island explains the temporal behaviours of the current density and safety factor profiles. From the experimental observation and simulations, we reach the conclusion that the bootstrap current decreases within the island O-point

  2. Time and space-correlated plasma potential measurements in the near field of a coaxial Hall plasma discharge

    International Nuclear Information System (INIS)

    Smith, A. W.; Cappelli, M. A.

    2009-01-01

    Space- and time-correlated measurements of floating and plasma potential are made in the near field, external flow cathode region of a coaxial Hall plasma discharge using an emissive probe synchronized to quasicoherent fluctuations in discharge current. The luminous axial feature frequently observed in the near field of operating plasma accelerators is found to be concomitant with a spike in the plasma potential (and electron temperature). The structure of the plasma potential allows for multiple avenues for back-streaming ions to accelerate toward the discharge front pole and may pull some classes of ions toward the central axis. The fluctuations in plasma properties exhibit a complex structure at frequencies on the order of the so-called 'breathing mode' ionization instability often seen in these types of discharges. Most notably, the plasma potential appears to fluctuate in a helical fashion, resembling tilted drift waves rotating about the central axis. A simple analysis of these waves draws attention to the possible role that they may play in driving anomalous cross-field electron transport in the near field region.

  3. Current-driven plasmonic boom instability in three-dimensional gated periodic ballistic nanostructures

    Science.gov (United States)

    Aizin, G. R.; Mikalopas, J.; Shur, M.

    2016-05-01

    An alternative approach of using a distributed transmission line analogy for solving transport equations for ballistic nanostructures is applied for solving the three-dimensional problem of electron transport in gated ballistic nanostructures with periodically changing width. The structures with varying width allow for modulation of the electron drift velocity while keeping the plasma velocity constant. We predict that in such structures biased by a constant current, a periodic modulation of the electron drift velocity due to the varying width results in the instability of the plasma waves if the electron drift velocity to plasma wave velocity ratio changes from below to above unity. The physics of such instability is similar to that of the sonic boom, but, in the periodically modulated structures, this analog of the sonic boom is repeated many times leading to a larger increment of the instability. The constant plasma velocity in the sections of different width leads to resonant excitation of the unstable plasma modes with varying bias current. This effect (that we refer to as the superplasmonic boom condition) results in a strong enhancement of the instability. The predicted instability involves the oscillating dipole charge carried by the plasma waves. The plasmons can be efficiently coupled to the terahertz electromagnetic radiation due to the periodic geometry of the gated structure. Our estimates show that the analyzed instability should enable powerful tunable terahertz electronic sources.

  4. Effect of resistivity profile on current decay time of initial phase of current quench in neon-gas-puff inducing disruptions of JT-60U

    Energy Technology Data Exchange (ETDEWEB)

    Kawakami, S.; Ohno, N. [Graduate School of Engineering, Nagoya University, Nagoya 464-8603 (Japan); Shibata, Y.; Isayama, A.; Kawano, Y. [Japan Atomic Energy Agency, Naka 311-0193 (Japan); Watanabe, K. Y. [Graduate School of Engineering, Nagoya University, Nagoya 464-8603 (Japan); National Institute for Fusion Science, Toki 509-5292 (Japan); Takizuka, T. [Graduate School of Engineering, Osaka University, Suita 565-0871 (Japan); Okamoto, M. [Ishikawa National College of Technology, Ishikawa 929-0392 (Japan)

    2013-11-15

    According to an early work [Y. Shibata et al., Nucl. Fusion 50, 025015 (2010)] on the behavior of the plasma current decay in the JT-60U disruptive discharges caused by the radiative collapse with a massive neon-gas-puff, the increase of the internal inductance mainly determined the current decay time of plasma current during the initial phase of current quench. To investigate what determines the increase of the internal inductance, we focus attention on the relationship between the electron temperature (or the resistivity) profile and the time evolution of the current density profile and carry out numerical calculations. As a result, we find the reason of the increase of the internal inductance: The current density profile at the start of the current quench is broader than an expected current density profile in the steady state, which is determined by the temperature (or resistivity) profile. The current density profile evolves into peaked one and the internal inductance is increasing.

  5. Quasi-steady state, low current behaviour of a magnetized coaxial plasma source

    International Nuclear Information System (INIS)

    Gray, Travis K; Mayo, Robert M; Bourham, Mohamed A

    2005-01-01

    The Coaxial Plasma Source-1 facility (Mayo R M et al 1995 Plasma Sources Sci. Technol. 4 47) was modified from a short pulse, high current (SPHC) pulse forming network (PFN) with very low inductance (∼200 nH) to a large inductance ladder circuit. This modification allows for a longer, flat top gun current pulse that eliminates the under-damped, sinusoidal behaviour of the gun current with consequent interruptions in plasma parameters. The new PFN was designed to produce a current waveform for a much longer period (∼1 ms). As a consequence of increasing the pulse length, the magnitude of the gun current was reduced as no additional energy storage was added to the PFN. The characterization of the electrical and plasma behaviour of the experiment operated with the long pulse, low current (LPLC) PFN is presented. The gun currents produced by the LPLC PFN are approximately one-fifth in magnitude of the gun currents produced by the SPHC PFN. Axial plasma parameters were measured near the muzzle of the plasma source, and electron densities were found to range from 1 x 10 19 m -3 to 7 x 10 19 m -3 depending upon the axial location. These values are approximately 1-2 orders of magnitude less than the electron densities produced by the SPHC PFN at the same locations. Electron temperatures range from 30 to 60 eV at these locations and are very similar to those produced by the SPHC PFN. A resistive MHD model was applied as an order estimate of the plasma resistivity and demonstrates reasonable agreement with measured values of the magnetized coaxial gun resistance

  6. Quasi-steady state, low current behaviour of a magnetized coaxial plasma source

    Energy Technology Data Exchange (ETDEWEB)

    Gray, Travis K; Mayo, Robert M; Bourham, Mohamed A [Department of Nuclear Engineering, North Carolina State University, Raleigh, NC 27695-7909 (United States)

    2005-11-15

    The Coaxial Plasma Source-1 facility (Mayo R M et al 1995 Plasma Sources Sci. Technol. 4 47) was modified from a short pulse, high current (SPHC) pulse forming network (PFN) with very low inductance ({approx}200 nH) to a large inductance ladder circuit. This modification allows for a longer, flat top gun current pulse that eliminates the under-damped, sinusoidal behaviour of the gun current with consequent interruptions in plasma parameters. The new PFN was designed to produce a current waveform for a much longer period ({approx}1 ms). As a consequence of increasing the pulse length, the magnitude of the gun current was reduced as no additional energy storage was added to the PFN. The characterization of the electrical and plasma behaviour of the experiment operated with the long pulse, low current (LPLC) PFN is presented. The gun currents produced by the LPLC PFN are approximately one-fifth in magnitude of the gun currents produced by the SPHC PFN. Axial plasma parameters were measured near the muzzle of the plasma source, and electron densities were found to range from 1 x 10{sup 19} m{sup -3} to 7 x 10{sup 19} m{sup -3} depending upon the axial location. These values are approximately 1-2 orders of magnitude less than the electron densities produced by the SPHC PFN at the same locations. Electron temperatures range from 30 to 60 eV at these locations and are very similar to those produced by the SPHC PFN. A resistive MHD model was applied as an order estimate of the plasma resistivity and demonstrates reasonable agreement with measured values of the magnetized coaxial gun resistance.

  7. Overcoming Spurious Regression Using time-Varying Fourier ...

    African Journals Online (AJOL)

    Non-stationary time series data have been traditionally analyzed in the frequency domain by assuming constant amplitudes regardless of the timelag. A new approach called time-varying amplitude method (TVAM) is presented here. Oscillations are analyzed for changes in the magnitude of Fourier Coefficients which are ...

  8. Vesicle biomechanics in a time-varying magnetic field.

    Science.gov (United States)

    Ye, Hui; Curcuru, Austen

    2015-01-01

    Cells exhibit distortion when exposed to a strong electric field, suggesting that the field imposes control over cellular biomechanics. Closed pure lipid bilayer membranes (vesicles) have been widely used for the experimental and theoretical studies of cellular biomechanics under this electrodeformation. An alternative method used to generate an electric field is by electromagnetic induction with a time-varying magnetic field. References reporting the magnetic control of cellular mechanics have recently emerged. However, theoretical analysis of the cellular mechanics under a time-varying magnetic field is inadequate. We developed an analytical theory to investigate the biomechanics of a modeled vesicle under a time-varying magnetic field. Following previous publications and to simplify the calculation, this model treated the inner and suspending media as lossy dielectrics, the membrane thickness set at zero, and the electric resistance of the membrane assumed to be negligible. This work provided the first analytical solutions for the surface charges, electric field, radial pressure, overall translational forces, and rotational torques introduced on a vesicle by the time-varying magnetic field. Frequency responses of these measures were analyzed, particularly the frequency used clinically by transcranial magnetic stimulation (TMS). The induced surface charges interacted with the electric field to produce a biomechanical impact upon the vesicle. The distribution of the induced surface charges depended on the orientation of the coil and field frequency. The densities of these charges were trivial at low frequency ranges, but significant at high frequency ranges. The direction of the radial force on the vesicle was dependent on the conductivity ratio between the vesicle and the medium. At relatively low frequencies (biomechanics under a time-varying magnetic field. Biological effects of clinical TMS are not likely to occur via alteration of the biomechanics of brain

  9. Atomic emission and atomic fluorescence spectroscopy in the direct current plasma

    International Nuclear Information System (INIS)

    Hendrick, M.S.

    1985-01-01

    The Direct Current Plasma (DCP) was investigated as a source for Atomic Emission (AE) and Atomic Fluorescence Spectrometry (AFS). The DCP was optimized for AE analyses using simplex optimization and Box-Behnken partial factorial experimental design, varying argon flows, and plasma position. Results were compared with a univariate search carried out in the region of the simplex optimum. Canonical analysis demonstrated that no true optimum exists for sensitivity, precision, or drift. A stationary ridge, where combinations of conditions gave comparable instrumental responses, was found. The DCP as an excitation source for AFS in a flame was used for diagnostic studies of the DCP. Moving the aerosol introduction tube behind the DCP with respect to the flame improved the characteristics of the DCP as a narrow line source, although self-absorption was observed at high concentrations of metal salt solutions in the DCP. Detection limits for Cd, Co, Cr, Cu, Fe, Mg, Mn, Zn, and Ni were in the low ng/mL region. Theoretical expressions for scatter correction with a two-line technique were derived, although no correction was necessary to achieve accurate results for standard reference materials

  10. Application-oriented research on plasma channeling of a large pulsed current

    International Nuclear Information System (INIS)

    Liu Jingye

    2000-01-01

    Utilizing the avalanche effect of plasma produced by the collision of energetic primary electrons with hydrogen molecules in a plasma, channeling of a large pulsed current is achieved, with the plasma acting as the carrier

  11. A uniform laminar air plasma plume with large volume excited by an alternating current voltage

    Science.gov (United States)

    Li, Xuechen; Bao, Wenting; Chu, Jingdi; Zhang, Panpan; Jia, Pengying

    2015-12-01

    Using a plasma jet composed of two needle electrodes, a laminar plasma plume with large volume is generated in air through an alternating current voltage excitation. Based on high-speed photography, a train of filaments is observed to propagate periodically away from their birth place along the gas flow. The laminar plume is in fact a temporal superposition of the arched filament train. The filament consists of a negative glow near the real time cathode, a positive column near the real time anode, and a Faraday dark space between them. It has been found that the propagation velocity of the filament increases with increasing the gas flow rate. Furthermore, the filament lifetime tends to follow a normal distribution (Gaussian distribution). The most probable lifetime decreases with increasing the gas flow rate or decreasing the averaged peak voltage. Results also indicate that the real time peak current decreases and the real time peak voltage increases with the propagation of the filament along the gas flow. The voltage-current curve indicates that, in every discharge cycle, the filament evolves from a Townsend discharge to a glow one and then the discharge quenches. Characteristic regions including a negative glow, a Faraday dark space, and a positive column can be discerned from the discharge filament. Furthermore, the plasma parameters such as the electron density, the vibrational temperature and the gas temperature are investigated based on the optical spectrum emitted from the laminar plume.

  12. A simple analytical model for dynamics of time-varying target leverage ratios

    Science.gov (United States)

    Lo, C. F.; Hui, C. H.

    2012-03-01

    In this paper we have formulated a simple theoretical model for the dynamics of the time-varying target leverage ratio of a firm under some assumptions based upon empirical observations. In our theoretical model the time evolution of the target leverage ratio of a firm can be derived self-consistently from a set of coupled Ito's stochastic differential equations governing the leverage ratios of an ensemble of firms by the nonlinear Fokker-Planck equation approach. The theoretically derived time paths of the target leverage ratio bear great resemblance to those used in the time-dependent stationary-leverage (TDSL) model [Hui et al., Int. Rev. Financ. Analy. 15, 220 (2006)]. Thus, our simple model is able to provide a theoretical foundation for the selected time paths of the target leverage ratio in the TDSL model. We also examine how the pace of the adjustment of a firm's target ratio, the volatility of the leverage ratio and the current leverage ratio affect the dynamics of the time-varying target leverage ratio. Hence, with the proposed dynamics of the time-dependent target leverage ratio, the TDSL model can be readily applied to generate the default probabilities of individual firms and to assess the default risk of the firms.

  13. Experiments on microsecond conduction time plasma opening switch mechanisms

    International Nuclear Information System (INIS)

    Rix, W.; Coleman, M.; Miller, A.R.; Parks, D.; Robertson, K.; Thompson, J.; Waisman, E.; Wilson, A.

    1993-01-01

    The authors describe a series of experiments carried out on ACE 2 and ACE 4 to elucidate the mechanisms controlling the conduction and opening phases on plasma opening switches in a radial geometry with conduction times on the order of a microsecond. The results indicate both conduction and opening physics are similar to that observed on lower current systems in a coaxial geometry

  14. Dynamics of the plasma current sheath in plasma focus discharges in different gases

    Energy Technology Data Exchange (ETDEWEB)

    Vinogradov, V. P.; Krauz, V. I., E-mail: krauz-vi@nrcki.ru [National Research Center Kurchatov Institute (Russian Federation); Mokeev, A. N. [Project Center ITER (Russian Federation); Myalton, V. V.; Kharrasov, A. M. [National Research Center Kurchatov Institute (Russian Federation)

    2016-12-15

    The shape of the plasma current sheath (PCS) in the final stage of its radial compression, the dynamics of pinching, and the subsequent pinch decay in plasma focus (PF) discharges in different gases are studied using an improved multichannel system of electron-optical plasma photography and a newly elaborated synchronization system. The PCS structure in discharges in heavy gases (Ne, Ar) is found to differ significantly from that in discharges in hydrogen and deuterium. The influence of a heavy gas (Xe) additive to hydrogen and deuterium on the structure and compression dynamics of the PCS is investigated.

  15. Nonextensive dust acoustic waves in a charge varying dusty plasma

    Science.gov (United States)

    Bacha, Mustapha; Tribeche, Mouloud

    2012-01-01

    Our recent analysis on nonlinear nonextensive dust-acoustic waves (DA) [Amour and Tribeche in Phys. Plasmas 17:063702, 2010] is extended to include self-consistent nonadiabatic grain charge fluctuation. The appropriate nonextensive electron charging current is rederived based on the orbit-limited motion theory. Our results reveal that the amplitude, strength and nature of the nonlinear DA waves (solitons and shocks) are extremely sensitive to the degree of ion nonextensivity. Stronger is the electron correlation, more important is the charge variation induced nonlinear wave damping. The anomalous dissipation effects may prevail over that dispersion as the electrons evolve far away from their Maxwellian equilibrium. Our investigation may be of wide relevance to astronomers and space scientists working on interstellar dusty plasmas where nonthermal distributions are turning out to be a very common and characteristic feature.

  16. Effect of cathode and anode plasma motion on current characteristics of pinch diode

    International Nuclear Information System (INIS)

    Yang Hailiang; Qiu Aici; Sun Jianfeng; Li Jingya; He Xiaoping; Tang Junping; Li Hongyu; Wang Haiyang; Huang Jianjun; Ren Shuqing; Yang Li; Zou Lili

    2005-01-01

    The preliminary research results for the effect of cathode and anode plasma motion on current characteristics of the pinch ion diode on FLASH II accelerator are reported. The structure and principle of pinch reflex ion beam diode are introduced. The time dependent evolution of electron and ion flow in large aspect-ratio relativistic diodes is studied by analytic models. The equation of Child-langmuir, weak focused-flow, strong focused-flow and parapotential flow are corrected to reduce the diode A-C gap caused by the motion of cathode and anode plasma. The diode current and ion current are calculated with these corrected equations, and the results are consistent with the experimental data. The methods of increasing ion current and efficiency are also presented. The high power ion beam peak current about 160 kA with a peak energy about 500 keV was produced using water-dielectric transmission-line generators with super-pinch reflex ion diodes on FLASH II accelerator at Northwest Institute of Nuclear Technology (NINT). (authors)

  17. Relaxation time of acoustically disturbed plasma

    International Nuclear Information System (INIS)

    Mkrtchyan, K.S.; Abrahamyan, A.S.

    2005-01-01

    The conservation time of an acoustic structure in plasma after relieving of external acoustic influence is investigated. Dependences of the conservation time on discharge parameters are presented. It is asserted that the plasma becomes an anisotropic uniaxial medium with an acoustic superlattice under the acoustic influence

  18. Modelling Time-Varying Volatility in Financial Returns

    DEFF Research Database (Denmark)

    Amado, Cristina; Laakkonen, Helinä

    2014-01-01

    The “unusually uncertain” phase in the global financial markets has inspired many researchers to study the effects of ambiguity (or “Knightian uncertainty”) on the decisions made by investors and their implications for the capital markets. We contribute to this literature by using a modified...... version of the time-varying GARCH model of Amado and Teräsvirta (2013) to analyze whether the increasing uncertainty has caused excess volatility in the US and European government bond markets. In our model, volatility is multiplicatively decomposed into two time-varying conditional components: the first...... being captured by a stable GARCH(1,1) process and the second driven by the level of uncertainty in the financial market....

  19. Ion production and bipolar fluxes in a high-current plasma-filled diode

    International Nuclear Information System (INIS)

    Ivanenkov, G.V.

    1982-01-01

    The model and the evolution of behaviour of binary layers (BL) in expanding plasma of high current plasma-filled diode are described. The model estimates ion current and the laws of plasma expansion at the stage of BL intensive growth. The density range (10 12 -10 15 cm -3 ) is determined in which diode impedance growth takes place in connection with BL appearance. The density of ion current at the outlet of diode is 10 A/cm 2

  20. Identification of time-varying nonlinear systems using differential evolution algorithm

    DEFF Research Database (Denmark)

    Perisic, Nevena; Green, Peter L; Worden, Keith

    2013-01-01

    (DE) algorithm for the identification of time-varying systems. DE is an evolutionary optimisation method developed to perform direct search in a continuous space without requiring any derivative estimation. DE is modified so that the objective function changes with time to account for the continuing......, thus identification of time-varying systems with nonlinearities can be a very challenging task. In order to avoid conventional least squares and gradient identification methods which require uni-modal and double differentiable objective functions, this work proposes a modified differential evolution...... inclusion of new data within an error metric. This paper presents results of identification of a time-varying SDOF system with Coulomb friction using simulated noise-free and noisy data for the case of time-varying friction coefficient, stiffness and damping. The obtained results are promising and the focus...

  1. Time resolved measurements of plasma potential across an anode double layer

    International Nuclear Information System (INIS)

    Pohoata, V.; Popa, Gh.; Schrittwieser, R.; Ionita, Codrina

    2002-01-01

    Experimental results are presented on self-sustained oscillations produced by the dynamics of an anode double layer or fireball in a DP-machine. By additional ionisation processes the fireball is formed in front of an additional small plane anode inserted in the diffusive plasma. An annular (ring) electrode surrounds the anode. The thickness of the ion sheath in front of this ring affects the anode current by controlling its effective diameter during the fireball oscillations. The ring potential controls first the oscillation frequency of the anode current, but also other characteristics of the instability. The ring potential was chosen as a pulsed one so that only single anode double layer instability can be excited. The ring signal was used for triggering the data acquisition system. The spatial distribution of the plasma potential in front of the anode is presented as a time resolved measurement one. A negative drop potential was found that controls the charge flux particle across the double layer. Also the plasma density inside the fireball relaxes during the disrupting time controlled by ambipolar diffusion and also by the negative potential drop. (authors)

  2. Real-Time Software for the Compass Tokamak Plasma Control

    Energy Technology Data Exchange (ETDEWEB)

    Valcarcel, D.F.; Duarte, A.S.; Neto, A.; Carvalho, I.S.; Carvalho, B.B.; Fernandes, H.; Sousa, J. [Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, Lisboa (Portugal); Sartori, F. [Euratom-UKAEA, Culham Science Centre, Abingdon, OX14 3DB Oxon (United Kingdom); Janky, F.; Cahyna, P.; Hron, M.; Panek, R. [Institute of Plasma Physics AS CR, v.v.i., Association EURATOM / IPP.CR, Prague (Costa Rica)

    2009-07-01

    This poster presents the flexible and high-performance real time system that guarantees the desired time cycles for plasma control on the COMPASS tokamak: 500 {mu}s for toroidal field, current, equilibrium and shaping; 50 {mu}s for fast control of the equilibrium and vertical instability. This system was developed on top of a high-performance processor and a software framework (MARTe) tailored for real-time. The preliminary measurements indicate that the time constraints will be met on the final solution. The system allows the making of modifications in the future to improve software components. (A.C.)

  3. Plasma erosion opening switch in the double-pulse operation mode of a high-current electron accelerator

    International Nuclear Information System (INIS)

    Isakov, I.F.; Lopatin, V.S.; Remnev, G.E.

    1987-01-01

    This paper reports the results of investigations of the operation of a fast current opening switch, with a 10/sup 13/-10/sup 16/ plasma density produced either by dielectric surface flashover or by explosive emission of graphite. A series of two pulses was applied to two diodes in parallel. The first pulse produced plasma in the first diode which closed that diode gap by the arrival time of the second pulse. The first, shorted, diode then acted as an erosion switch for the second pulse. A factor of 2.5-3 power multiplication was obtained under optimum conditions. The opening-switch resistance during the magnetic insulation phase, neglecting the electron losses between the switch and the generating diode, exceeded 100 Ω. The duration of the rapid opening phase was less than 5 ns under optimum conditions. This method of plasma production does not require external plasma sources, and permits a wide variation of plasma density, which in turn allows high inductor currents and stored energies

  4. Direct current plasma jet at atmospheric pressure operating in nitrogen and air

    Science.gov (United States)

    Deng, X. L.; Nikiforov, A. Yu.; Vanraes, P.; Leys, Ch.

    2013-01-01

    An atmospheric pressure direct current (DC) plasma jet is investigated in N2 and dry air in terms of plasma properties and generation of active species in the active zone and the afterglow. The influence of working gases and the discharge current on plasma parameters and afterglow properties are studied. The electrical diagnostics show that discharge can be sustained in two different operating modes, depending on the current range: a self-pulsing regime at low current and a glow regime at high current. The gas temperature and the N2 vibrational temperature in the active zone of the jet and in the afterglow are determined by means of emission spectroscopy, based on fitting spectra of N2 second positive system (C3Π-B3Π) and the Boltzmann plot method, respectively. The spectra and temperature differences between the N2 and the air plasma jet are presented and analyzed. Space-resolved ozone and nitric oxide density measurements are carried out in the afterglow of the jet. The density of ozone, which is formed in the afterglow of nitrogen plasma jet, is quantitatively detected by an ozone monitor. The density of nitric oxide, which is generated only in the air plasma jet, is determined by means of mass-spectroscopy techniques.

  5. Dynamics of a plasma shell with a carrying out current

    International Nuclear Information System (INIS)

    Komel'kov, V.S.; Kuznetsov, A.P.; Perebejnos, V.V.; Pleshanov, A.S.; Solomonov, M.T.

    1982-01-01

    Experimental data on hydrogen plasma acceleration in continuous medium after plasma escape out from the coaxial plasma accelerator with discharge current approximately 1 MA and initial gas pressure approximately 10 4 Pa are obtained. Modified method of particle calculation in cells qualitatively satisfactorily describes the experiment and indicate a number of quantitative regularities of the process. The investigation made it possible to obtain qualitative characteristics on hydrogen plasma flow and displayed a number of quantitative regularities. Calculation results show the real possibility to obtain high-temperature dense plasma in continuous medium beyond the accelerator boundary

  6. Experiment and simulation on one-dimensional plasma photonic crystals

    International Nuclear Information System (INIS)

    Zhang, Lin; Ouyang, Ji-Ting

    2014-01-01

    The transmission characteristics of microwaves passing through one-dimensional plasma photonic crystals (PPCs) have been investigated by experiment and simulation. The PPCs were formed by a series of discharge tubes filled with argon at 5 Torr that the plasma density in tubes can be varied by adjusting the discharge current. The transmittance of X-band microwaves through the crystal structure was measured under different discharge currents and geometrical parameters. The finite-different time-domain method was employed to analyze the detailed properties of the microwaves propagation. The results show that there exist bandgaps when the plasma is turned on. The properties of bandgaps depend on the plasma density and the geometrical parameters of the PPCs structure. The PPCs can perform as dynamical band-stop filter to control the transmission of microwaves within a wide frequency range

  7. Lyapunov-based distributed control of the safety-factor profile in a tokamak plasma

    International Nuclear Information System (INIS)

    Bribiesca Argomedo, Federico; Witrant, Emmanuel; Prieur, Christophe; Brémond, Sylvain; Nouailletas, Rémy; Artaud, Jean-François

    2013-01-01

    A real-time model-based controller is developed for the tracking of the distributed safety-factor profile in a tokamak plasma. Using relevant physical models and simplifying assumptions, theoretical stability and robustness guarantees were obtained using a Lyapunov function. This approach considers the couplings between the poloidal flux diffusion equation, the time-varying temperature profiles and an independent total plasma current control. The actuator chosen for the safety-factor profile tracking is the lower hybrid current drive, although the results presented can be easily extended to any non-inductive current source. The performance and robustness of the proposed control law is evaluated with a physics-oriented simulation code on Tore Supra experimental test cases. (paper)

  8. Eddy current analysis in fusion devices

    International Nuclear Information System (INIS)

    Turner, L.R.

    1988-06-01

    In magnetic fusion devices, particularly tokamaks and reversed field pinch (RFP) experiments, time-varying magnetic fields are in intimate contact with electrically conducting components of the device. Induced currents, fields, forces, and torques result. This note reviews the analysis of eddy current effects in the following systems: Interaction of a tokamak plasma with the eddy currents in the first wall, blanket, and shield (FWBS) systems; Eddy currents in a complex but two-dimensional vacuum vessel, as in TFTR, JET, and JT-60; Eddy currents in the FWBS system of a tokamak reactor, such as NET, FER, or ITER; and Eddy currents in a RFP shell. The cited studies are chosen to be illustrative, rather than exhaustive. 42 refs

  9. Filamentary structures in dense plasma focus: Current filaments or vortex filaments?

    Energy Technology Data Exchange (ETDEWEB)

    Soto, Leopoldo, E-mail: lsoto@cchen.cl; Pavez, Cristian; Moreno, José [Comisión Chilena de Energía Nuclear, CCHEN, Casilla 188-D, Santiago (Chile); Center for Research and Applications in Plasma Physics and Pulsed Power, P4, Departamento de Ciencias Físicas, Facultad de Ciencias Exactas, Universidad Andrés Bello, República 220, Santiago (Chile); Castillo, Fermin [Universidad Nacional Autónoma de México, Cuernavaca, México (Mexico); Veloso, Felipe [Instituto de Física, Pontificia Universidad Católica de Chile, 7820436 Santiago (Chile); Auluck, S. K. H. [Bhabha Atomic Research Center, Mumbai 400 085 (India)

    2014-07-15

    Recent observations of an azimuthally distributed array of sub-millimeter size sources of fusion protons and correlation between extreme ultraviolet (XUV) images of filaments with neutron yield in PF-1000 plasma focus have re-kindled interest in their significance. These filaments have been described variously in literature as current filaments and vortex filaments, with very little experimental evidence in support of either nomenclature. This paper provides, for the first time, experimental observations of filaments on a table-top plasma focus device using three techniques: framing photography of visible self-luminosity from the plasma, schlieren photography, and interferometry. Quantitative evaluation of density profile of filaments from interferometry reveals that their radius closely agrees with the collision-less ion skin depth. This is a signature of relaxed state of a Hall fluid, which has significant mass flow with equipartition between kinetic and magnetic energy, supporting the “vortex filament” description. This interpretation is consistent with empirical evidence of an efficient energy concentration mechanism inferred from nuclear reaction yields.

  10. Time-varying linear control for tiltrotor aircraft

    Directory of Open Access Journals (Sweden)

    Jing ZHANG

    2018-04-01

    Full Text Available Tiltrotor aircraft have three flight modes: helicopter mode, airplane mode, and transition mode. A tiltrotor has characteristics of highly nonlinear, time-varying flight dynamics and inertial/control couplings in its transition mode. It can transit from the helicopter mode to the airplane mode by tilting its nacelles, and an effective controller is crucial to accomplish tilting transition missions. Longitudinal dynamic characteristics of the tiltrotor are described by a nonlinear Lagrange-form model, which takes into account inertial/control couplings and aerodynamic interferences. Reference commands for airspeed velocity and attitude in the transition mode are calculated dynamically by visiting a command library which is founded in advance by analyzing the flight envelope of the tiltrotor. A Time-Varying Linear (TVL model is obtained using a Taylor-expansion based online linearization technique from the nonlinear model. Subsequently, based on an optimal control concept, an online optimization based control method with input constraints considered is proposed. To validate the proposed control method, three typical tilting transition missions are simulated using the nonlinear model of XV-15 tiltrotor aircraft. Simulation results show that the controller can be used to control the tiltrotor throughout its operating envelop which includes a transition flight, and can also deal with vertical gust disturbances. Keywords: Constrained optimal control, Inertia/control couplings, Tiltrotor aircraft, Time-varying control, Transition mode

  11. Efficient ion heating of tokamak plasma by application of positive and negative current pulse in TRIAM-1

    International Nuclear Information System (INIS)

    Toi, Kazuo; Hiraki, Naoji; Nakamura, Kazuo; Mitarai, Osamu; Kawai, Yoshinobu

    1980-01-01

    The efficient heating of bulk ions of tokamak plasma is observed by application of the pulsed toroidal electric field much higher than the Dreicer field with the positive and negative polarities for the ohmic heating field. No deleterious effect on the confinement properties of tokamak plasma appears by the heating. The decay time of ion temperature raised by the heating pulse agrees well with the prediction by the neoclassical transport theory. The magnitude of the current induced by the pulsed electric field with the positive polarity is limited by the violent current disruption. In the case of the negative polarity, this is limited by lack of the MHD equilibrium due to vanishing the total plasma current. The ratio of drift velocity to electron thermal one / attains around 0.5, which suggests that the efficient ion heating may be due to the current-driven turbulence. (author)

  12. Efficient ion heating of tokamak plasma by application of positive and negative current pulse in TRIAM-1

    Energy Technology Data Exchange (ETDEWEB)

    Toi, K; Hiraki, N; Nakamura, K; Mitarai, O; Kawai, Y [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics

    1980-02-01

    The efficient heating of bulk ions of tokamak plasma is observed by application of the pulsed toroidal electric field much higher than the Dreicer field with the positive and negative polarities for the ohmic heating field. No deleterious effect on the confinement properties of tokamak plasma appears by the heating. The decay time of ion temperature raised by the heating pulse agrees well with the prediction by the neoclassical transport theory. The magnitude of the current induced by the pulsed electric field with the positive polarity is limited by the violent current disruption. In the case of the negative polarity, this is limited by lack of the MHD equilibrium due to vanishing the total plasma current. The ratio of drift velocity to electron thermal one / attains around 0.5, which suggests that the efficient ion heating may be due to the current-driven turbulence.

  13. Fluctuating interaction network and time-varying stability of a natural fish community

    Science.gov (United States)

    Ushio, Masayuki; Hsieh, Chih-Hao; Masuda, Reiji; Deyle, Ethan R.; Ye, Hao; Chang, Chun-Wei; Sugihara, George; Kondoh, Michio

    2018-02-01

    Ecological theory suggests that large-scale patterns such as community stability can be influenced by changes in interspecific interactions that arise from the behavioural and/or physiological responses of individual species varying over time. Although this theory has experimental support, evidence from natural ecosystems is lacking owing to the challenges of tracking rapid changes in interspecific interactions (known to occur on timescales much shorter than a generation time) and then identifying the effect of such changes on large-scale community dynamics. Here, using tools for analysing nonlinear time series and a 12-year-long dataset of fortnightly collected observations on a natural marine fish community in Maizuru Bay, Japan, we show that short-term changes in interaction networks influence overall community dynamics. Among the 15 dominant species, we identify 14 interspecific interactions to construct a dynamic interaction network. We show that the strengths, and even types, of interactions change with time; we also develop a time-varying stability measure based on local Lyapunov stability for attractor dynamics in non-equilibrium nonlinear systems. We use this dynamic stability measure to examine the link between the time-varying interaction network and community stability. We find seasonal patterns in dynamic stability for this fish community that broadly support expectations of current ecological theory. Specifically, the dominance of weak interactions and higher species diversity during summer months are associated with higher dynamic stability and smaller population fluctuations. We suggest that interspecific interactions, community network structure and community stability are dynamic properties, and that linking fluctuating interaction networks to community-level dynamic properties is key to understanding the maintenance of ecological communities in nature.

  14. Identification of Time-Varying Pilot Control Behavior in Multi-Axis Control Tasks

    Science.gov (United States)

    Zaal, Peter M. T.; Sweet, Barbara T.

    2012-01-01

    Recent developments in fly-by-wire control architectures for rotorcraft have introduced new interest in the identification of time-varying pilot control behavior in multi-axis control tasks. In this paper a maximum likelihood estimation method is used to estimate the parameters of a pilot model with time-dependent sigmoid functions to characterize time-varying human control behavior. An experiment was performed by 9 general aviation pilots who had to perform a simultaneous roll and pitch control task with time-varying aircraft dynamics. In 8 different conditions, the axis containing the time-varying dynamics and the growth factor of the dynamics were varied, allowing for an analysis of the performance of the estimation method when estimating time-dependent parameter functions. In addition, a detailed analysis of pilots adaptation to the time-varying aircraft dynamics in both the roll and pitch axes could be performed. Pilot control behavior in both axes was significantly affected by the time-varying aircraft dynamics in roll and pitch, and by the growth factor. The main effect was found in the axis that contained the time-varying dynamics. However, pilot control behavior also changed over time in the axis not containing the time-varying aircraft dynamics. This indicates that some cross coupling exists in the perception and control processes between the roll and pitch axes.

  15. Scaling properties in time-varying networks with memory

    Science.gov (United States)

    Kim, Hyewon; Ha, Meesoon; Jeong, Hawoong

    2015-12-01

    The formation of network structure is mainly influenced by an individual node's activity and its memory, where activity can usually be interpreted as the individual inherent property and memory can be represented by the interaction strength between nodes. In our study, we define the activity through the appearance pattern in the time-aggregated network representation, and quantify the memory through the contact pattern of empirical temporal networks. To address the role of activity and memory in epidemics on time-varying networks, we propose temporal-pattern coarsening of activity-driven growing networks with memory. In particular, we focus on the relation between time-scale coarsening and spreading dynamics in the context of dynamic scaling and finite-size scaling. Finally, we discuss the universality issue of spreading dynamics on time-varying networks for various memory-causality tests.

  16. Plasma Heating and Current Drive by Neutral Beam and Alpha Particles

    Energy Technology Data Exchange (ETDEWEB)

    Kikuchi, M; Okumura, Y [Fusion Research and Development Directorate, Japan Atomic Energy Agency (Japan)

    2012-09-15

    The purpose of plasma heating is to raise the plasma temperature enough to produce a deuterium and tritium reaction (D + T {yields} {sup 4}He + n). The required plasma temperature T is in the range of 10-30 keV. Since the high temperature plasma is confined by a strong magnetic field, injection of energetic ions from outside to heat the plasma is difficult due to the Lorenz force. The most efficient way to heat the plasma by energetic particles is to inject high energy 'neutrals' which get ionized in the plasma. Neutral beam injection (NBI) with a beam energy much above the average kinetic energy of the plasma electrons or ions is used (beam energy typically {approx}40 keV - 1 MeV). This heating scheme is similar to warming up cold water by pouring in hot water. There are two types of neutral beam, called P-NBI and N-NBI (P- and N- means 'positive' and 'negative', respectively). P-NBI uses the acceleration of positively charged ions and their neutralization, while N-NBI uses the acceleration of negative ions (electrons attached to neutral atoms) and their neutralization. Details are given in NBI technology Section. The first demonstration of plasma heating by P-NBI was made in ORMAK and ATC in 1974, while that by N-NBI was made in JT-60U for the first time in 1996. ITER has also adopted the N-NBI system as the heating and current drive system with a beam energy of 1 MeV. Figure A typical bird's eye view of a tokamak with N-NBI and N-NBI (JT-60U) is shown. (author)

  17. High Current, High Density Arc Plasma as a New Source for WiPAL

    Science.gov (United States)

    Waleffe, Roger; Endrizzi, Doug; Myers, Rachel; Wallace, John; Clark, Mike; Forest, Cary; WiPAL Team

    2016-10-01

    The Wisconsin Plasma Astrophysics Lab (WiPAL) has installed a new array of nineteen plasma sources (plasma guns) on its 3 m diameter, spherical vacuum vessel. Each gun is a cylindrical, molybdenum, washer-stabilized, arc plasma source. During discharge, the guns are maintained at 1.2 kA across 100 V for 10 ms by the gun power supply establishing a high density plasma. Each plasma source is fired independently allowing for adjustable plasma parameters, with densities varying between 1018 -1019 m-3 and electron temperatures of 5-15 eV. Measurements were characterized using a 16 tip Langmuir probe. The plasma source will be used as a background plasma for the magnetized coaxial plasma gun (MCPG), the Terrestrial Reconnection Experiment (TREX), and as the plasma source for a magnetic mirror experiment. Temperature, density, and confinement results will be presented. This work is supported by the DoE and the NSF.

  18. X-ray measurements during plasma current start-up experiments using the lower hybrid wave on the TST-2 spherical tokamak

    International Nuclear Information System (INIS)

    Wakatsuki, Takuma; Ejiri, Akira; Kakuda, Hidetoshi

    2012-01-01

    Non-inductive plasma current start-up experiments using RF power in the lower hybrid frequency range is being conducted on the TST-2 spherical tokamak. Plasma currents of up to 15 kA have been achieved. The effect of direct current drive can be seen by comparing the cases with co-drive and counter-drive. X-rays in various energy ranges were measured to investigate the interaction between the wave and the electrons. Soft X-ray (SX) measurements revealed that the perpendicular SX emission increased significantly as the plasma current increased, and that the tangential SX emission in the direction of RF drive was enhanced more strongly in the co-drive case compared to the counter-drive case. These observations imply that the fast electrons accelerated by the lower hybrid wave contribute to the plasma current. However, RF amplitude modulation experiments showed that the confinement time of these fast electrons are very short (less than 0.05 ms), much shorter than the collisional slowing down time. Hard X-ray spectral measurements showed that the radiation temperature of fast electrons in the co-direction for current drive was higher than that in the counter-direction. These observations are consistent with the existence of RF-driven fast electrons. (author)

  19. Simulative research on the expansion of cathode plasma in high-current electron beam diode

    International Nuclear Information System (INIS)

    Xu Qifu; Liu Lie

    2012-01-01

    The expansion of cathode plasma has long been recognized as a limiting factor in the impedance lifetime of high-current electron beam diode. Realistic modeling of such plasma is of great necessity in order to discuss the dynamics of cathode plasma. Using the method of particle-in-cell, the expansion of cathode plasma is simulated in this paper by a scaled-down diode model. It is found that the formation of cathode plasma increases the current density in the diode. This consequently leads to the decrease of the potential at plasma front. Once the current density has been increased to a certain value, the potential at plasma front would then be equal to or lower than the plasma potential. Then the ions would move towards the anode, and the expansion of cathode plasma is thereby formed. Different factors affecting the plasma expansion velocity are discussed in this paper. It is shown that the decrease of proton genatation rate has the benefit of reducing the plasma expansion velocity.

  20. Testing for time-varying loadings in dynamic factor models

    DEFF Research Database (Denmark)

    Mikkelsen, Jakob Guldbæk

    Abstract: In this paper we develop a test for time-varying factor loadings in factor models. The test is simple to compute and is constructed from estimated factors and residuals using the principal components estimator. The hypothesis is tested by regressing the squared residuals on the squared...... there is evidence of time-varying loadings on the risk factors underlying portfolio returns for around 80% of the portfolios....

  1. Current sustaining by RF travelling field in a collisional toroidal plasma

    International Nuclear Information System (INIS)

    Fukuda, Masaji; Matsuura, Kiyokata

    1978-01-01

    The relation between the current generated by RF travelling field and the absorbed power is studied in a collisional toroidal plasma, parameters being phase velocity and filling gap pressure or electron collision frequency. It is observed at a low magnetic field that the current is proportional to the plasma conductivity and an effective electromotive force, which is a new concept introduced on the basis of fluid model; the electromotive force is proportional to the absorbed RF power and inversely proportional to the plasma density and the phase velocity of the travelling field. (author)

  2. Current sustaining by RF travelling field in a collisional toroidal plasma

    International Nuclear Information System (INIS)

    Fukuda, Masaji; Matsuura, Kiyokata.

    1977-06-01

    The relation between the current generation by RF travelling field and the accompanied power absorption is studied in a collisional toroidal plasma, parameters being phase velocity and filling gas pressure or electron collision frequency. It is observed at a low magnetic field that the current is proportional to the plasma conductivity and an effective electromotive force, which is a new concept introduced on the basis of fluid model; the electromotive force is proportional to the absorbed RF power and inversely proportional to the plasma density and the phase velocity of the travelling field. (auth.)

  3. Control of ordered mesoporous titanium dioxide nanostructures formed using plasma enhanced glancing angle deposition

    Energy Technology Data Exchange (ETDEWEB)

    Gibson, Des [Institute of Thin Films, Sensors & Imaging, Scottish Universities Physics Alliance, University of West of Scotland, Paisley, PA1 2BE (United Kingdom); Child, David, E-mail: david.child@uws.ac.uk [Institute of Thin Films, Sensors & Imaging, Scottish Universities Physics Alliance, University of West of Scotland, Paisley, PA1 2BE (United Kingdom); Song, Shigeng; Zhao, Chao [Institute of Thin Films, Sensors & Imaging, Scottish Universities Physics Alliance, University of West of Scotland, Paisley, PA1 2BE (United Kingdom); Alajiani, Yahya [Institute of Thin Films, Sensors & Imaging, Scottish Universities Physics Alliance, University of West of Scotland, Paisley, PA1 2BE (United Kingdom); Department of Physics, Faculty of Science, Jazan University, Jazan (Saudi Arabia); Waddell, Ewan [Thin Film Solutions Ltd, West of Scotland Science Park, Glasgow, G20 0TH (United Kingdom)

    2015-10-01

    Three dimensional nanostructures of mesoporous (pore diameter between 2-50 nm) nanocrystalline titania (TiO{sub 2}) were produced using glancing angle deposition combined with plasma ion assisted deposition, providing plasma enhanced glancing angle deposition eliminating the need for post-annealing to achieve film crystallinity. Electron beam evaporation was chosen to deposit nanostructures at various azimuthal angles, achieving designed variation in three dimensional nanostructure. A thermionic broad beam hollow cathode plasma source was used to enhance electron beam deposition, with ability to vary in real time ion fluxes and energies providing a means to modify and control TiO{sub 2} nanostructure real time with controlled density and porosity along and lateral to film growth direction. Plasma ion assisted deposition was carried out at room temperature using a hollow cathode plasma source, ensuring low heat loading to the substrate during deposition. Plasma enhanced glancing angle TiO{sub 2} structures were deposited onto borosilicate microscope slides and used to characterise the effects of glancing angle and plasma ion energy distribution function on the optical and nanostructural properties. Variation in TiO{sub 2} refractive index from 1.40 to 2.45 (@ 550 nm) using PEGLAD is demonstrated. Results and analysis of the influence of plasma enhanced glancing angle deposition on evaporant path and resultant glancing angle deviation from standard GLAD are described. Control of mesoporous morphology is described, providing a means of optimising light trapping features and film porosity, relevant to applications such as fabrication of dye sensitised solar cells. - Highlights: • Plasma assistance during glancing angle deposition enables control of morphology. • Ion energy variation during glancing angle deposition varies columnar angle • Column thickness of glancing angle deposition dependant on ion current density • Ion current density variation during

  4. Real time equilibrium reconstruction for tokamak discharge control

    International Nuclear Information System (INIS)

    Ferron, J.R.; Walker, M.L.; Lao, L.L.; St John, H.E.; Humphreys, D.A.; Leuer, J.A.

    1998-01-01

    A practical method for performing a tokamak equilibrium reconstruction in real time for arbitrary time varying discharge shapes and current profiles is described. An approximate solution to the Grad-Shafranov equilibrium relation is found which best fits the diagnostic measurements. Thus, a solution for the spatial distribution of poloidal flux and toroidal current density is available in real time that is consistent with plasma force balance, allowing accurate evaluation of parameters such as discharge shape and safety factor profile. The equilibrium solutions are produced at a rate sufficient for discharge control. This equilibrium reconstruction algorithm has been implemented on the digital plasma control system for the DIII-D tokamak. The first application of real time equilibrium reconstruction to discharge shape control is described. (author)

  5. Control-focused, nonlinear and time-varying modelling of dielectric elastomer actuators with frequency response analysis

    International Nuclear Information System (INIS)

    Jacobs, William R; Dodd, Tony J; Anderson, Sean R; Wilson, Emma D; Porrill, John; Assaf, Tareq; Rossiter, Jonathan

    2015-01-01

    Current models of dielectric elastomer actuators (DEAs) are mostly constrained to first principal descriptions that are not well suited to the application of control design due to their computational complexity. In this work we describe an integrated framework for the identification of control focused, data driven and time-varying DEA models that allow advanced analysis of nonlinear system dynamics in the frequency-domain. Experimentally generated input–output data (voltage-displacement) was used to identify control-focused, nonlinear and time-varying dynamic models of a set of film-type DEAs. The model description used was the nonlinear autoregressive with exogenous input structure. Frequency response analysis of the DEA dynamics was performed using generalized frequency response functions, providing insight and a comparison into the time-varying dynamics across a set of DEA actuators. The results demonstrated that models identified within the presented framework provide a compact and accurate description of the system dynamics. The frequency response analysis revealed variation in the time-varying dynamic behaviour of DEAs fabricated to the same specifications. These results suggest that the modelling and analysis framework presented here is a potentially useful tool for future work in guiding DEA actuator design and fabrication for application domains such as soft robotics. (paper)

  6. Finite-Time Stability of Large-Scale Systems with Interval Time-Varying Delay in Interconnection

    Directory of Open Access Journals (Sweden)

    T. La-inchua

    2017-01-01

    Full Text Available We investigate finite-time stability of a class of nonlinear large-scale systems with interval time-varying delays in interconnection. Time-delay functions are continuous but not necessarily differentiable. Based on Lyapunov stability theory and new integral bounding technique, finite-time stability of large-scale systems with interval time-varying delays in interconnection is derived. The finite-time stability criteria are delays-dependent and are given in terms of linear matrix inequalities which can be solved by various available algorithms. Numerical examples are given to illustrate effectiveness of the proposed method.

  7. Surface currents on the plasma-vacuum interface in MHD equilibria

    Science.gov (United States)

    Hanson, James

    2017-10-01

    The VMEC non-axisymmetric MHD equilibrium code can compute free-boundary equilibria. Since VMEC assumes that magnetic fields within the plasma form closed and nested flux surfaces, the plasma-vacuum interface is a flux surface, and the total magnetic field there has no normal component. VMEC imposes this condition of zero normal field using the potential formulation of Merkel, and solves a Neumann problem for the magnetic potential in the exterior region. This boundary condition necessarily admits the possibility of a surface current on the interface. While this surface current may be small in MHD equilibrium, it is readily computed in terms of the magnetic potentials in both the interior and exterior regions, evaluated on the surface. If only the external magnetic potential is known (as in VMEC), then the surface current can be computed from the discontinuity of the tangential field across the interface. Examples of the surface current for VMEC equilibria will be shown for a zero-pressure stellarator equilibrium. Field-line following of the vacuum magnetic field shows magnetic islands within the plasma region.

  8. Research of transportation efficiency of low-energy high- current electron beam in plasma channel in external magnetic field

    International Nuclear Information System (INIS)

    Vagin, E S; Grigoriev, V P

    2015-01-01

    Effective high current (5-20 kA) and low energy (tens of keV) electrons beam transportation is possible only with almost complete charging neutralization. It is also necessary to use quite high current neutralization for elimination beam self-pinching effect. The research is based on the self-consistent mathematical model that takes into account beam and plasma particles dynamic, current and charge neutralization of electron beam and examines the transportation of electron beam into a chamber with low-pressure plasma in magnetic field. A numerical study was conducted using particle in cell (PIC) method. The study was performed with various system parameters: rise time and magnitude of the beam current, gas pressure and plasma density and geometry of the system. Regularities of local virtual cathode field generated by the beam in the plasma channel, as well as ranges of parameters that let transportation beam with minimal losses, depending on the external magnetic field were determined through a series of numerical studies. In addition, the assessment of the impact of the plasma ion mobility during the transition period and during steady beam was performed. (paper)

  9. RF generated currents in a magnetized plasma using a slow wave structure

    International Nuclear Information System (INIS)

    Poole, B.R.; Cheo, B.R.; Kuo, S.P.; Tang, M.G.

    1983-01-01

    The generation of a dc current in a plasma by using RF waves is of importance for the operation of steadystate toroidal devices. An experimental investigation in the use of unidirectional, low frequency RF waves to drive currents has been made. Instead of using a natural plasma wave a slow wave guiding structure is used along the entire length of the plasma. When the RF wave is injected an increase in ionization and T/sub e/, and hence the background current is observed. However, the change depends on wave direction: The +k/sub z/ excitation yields a much larger electron current compared with the -k/sub z/ excitation indicating a net wave driven current. The measured modification in electron density and T/sub e/ is independent of wave direction. The current with a standing wave excitation generally falls at the average of the travelling wave (+ or - k/sub z/) driven currents. The net wave driven current is proportional to the feed power at approx. = 10 mA/kW. No saturation of the current is observed with feed powers up to 1 kW. Since the exciting structure is only 1 wavelength long, its k/sub z/ spectrum is relatively broad and hence no sharp resonances are observed as various plasma parameters and B/sub O/ are changed. There is no measurable difference between the power absorbed by the load resistors and the input power to the slow wave structure. Thus the current is driven by the wave field exclamation E exclamation 2 rather than the power absorbed in the plasma. The theoretical background and the physical mechanism is presented

  10. Study on possibility of plasma current profile determination using an analytical model of tokamak equilibrium

    International Nuclear Information System (INIS)

    Moriyama, Shin-ichi; Hiraki, Naoji

    1996-01-01

    The possibility of determining the current profile of tokamak plasma from the external magnetic measurements alone is investigated using an analytical model of tokamak equilibrium. The model, which is based on an approximate solution of the Grad-Shafranov equation, can set a plasma current profile expressed with four free parameters of the total plasma current, the poloidal beta, the plasma internal inductance and the axial safety factor. The analysis done with this model indicates that, for a D-shaped plasma, the boundary poloidal magnetic field prescribing the external magnetic field distribution is dependent on the axial safety factor in spite of keeping the boundary safety factor and the plasma internal inductance constant. This suggests that the plasma current profile is reversely determined from the external magnetic analysis. The possibility and the limitation of current profile determination are discussed through this analytical result. (author)

  11. Modeling information diffusion in time-varying community networks

    Science.gov (United States)

    Cui, Xuelian; Zhao, Narisa

    2017-12-01

    Social networks are rarely static, and they typically have time-varying network topologies. A great number of studies have modeled temporal networks and explored social contagion processes within these models; however, few of these studies have considered community structure variations. In this paper, we present a study of how the time-varying property of a modular structure influences the information dissemination. First, we propose a continuous-time Markov model of information diffusion where two parameters, mobility rate and community attractiveness, are introduced to address the time-varying nature of the community structure. The basic reproduction number is derived, and the accuracy of this model is evaluated by comparing the simulation and theoretical results. Furthermore, numerical results illustrate that generally both the mobility rate and community attractiveness significantly promote the information diffusion process, especially in the initial outbreak stage. Moreover, the strength of this promotion effect is much stronger when the modularity is higher. Counterintuitively, it is found that when all communities have the same attractiveness, social mobility no longer accelerates the diffusion process. In addition, we show that the local spreading in the advantage group has been greatly enhanced due to the agglomeration effect caused by the social mobility and community attractiveness difference, which thus increases the global spreading.

  12. Do Time-Varying Covariances, Volatility Comovement and Spillover Matter?

    OpenAIRE

    Lakshmi Balasubramanyan

    2005-01-01

    Financial markets and their respective assets are so intertwined; analyzing any single market in isolation ignores important information. We investigate whether time varying volatility comovement and spillover impact the true variance-covariance matrix under a time-varying correlation set up. Statistically significant volatility spillover and comovement between US, UK and Japan is found. To demonstrate the importance of modelling volatility comovement and spillover, we look at a simple portfo...

  13. Beat-wave excitation and current driven in tokamak plasma. Vol. 2

    Energy Technology Data Exchange (ETDEWEB)

    Mohamed, B F [Plasma physics Department, Nuclear Research Center, Atomic Energy Authority, Cairo (Egypt)

    1996-03-01

    Wave heating current drive in tokamaks is a growing subject in the plasma physics literature. For current drive in tokamaks by electromagnetic waves, different methods have been proposed recently. One of the promising schemes for current drive remains the beat wave scheme. This technique employs two CO- or counterpropagating monochromatic laser beams (or microwaves) whose frequency difference matches the plasma frequency, while the wave number difference (or sum, in the case of counterpropagating) determine the wave number of the resulting plasma beat wave. In this work, the basic analysis of a beat wave current drive scheme in which collinear waves are used is discussed. by assuming a Gaussian profile for the amplitude of these pump waves, the amplitudes of the longitudinal and radial fields of the beat wave due to the nonlinear wave interactions have been calculated. Besides, the transfer of momentum flux that accompanies the transfer of wave action in beat-wave scattering will be used to drive the toroidal radial currents in tokamaks. self-generated magnetic fields due to those currents were also calculated. 1 fig.

  14. Newtonian cosmology with a time-varying constant of gravitation

    International Nuclear Information System (INIS)

    McVittie, G.C.

    1978-01-01

    Newtonian cosmology is based on the Eulerian equations of fluid mechanics combined with Poisson's equation modified by the introduction of a time-varying G. Spherically symmetric model universes are worked out with instantaneously uniform densities. They are indeterminate unless instantaneous uniformity of the pressure is imposed. When G varies as an inverse power of the time, the models can in some cases be shown to depend on the solution of a second-order differential equation which also occurs in the Friedmann models of general relativity. In Section 3, a method for 'passing through' a singularity of this equation is proposed which entails making four arbitrary mathematical assumptions. When G varies as (time) -1 , models with initially cycloidal motion are possible, each cycle becoming longer as time progresses. Finally, gravitation becomes so weak that the model expands to infinity. Kinetic and potential energies for the whole model are derived from the basic equations; their sum is not constant. (author)

  15. Mapping return currents in laser-generated Z-pinch plasmas using proton deflectometry

    International Nuclear Information System (INIS)

    Manuel, M. J.-E.; Sinenian, N.; Seguin, F. H.; Li, C. K.; Frenje, J. A.; Rinderknecht, H. G.; Casey, D. T.; Zylstra, A. B.; Petrasso, R. D.; Beg, F. N.

    2012-01-01

    Dynamic return currents and electromagnetic field structure in laser-generated Z-pinch plasmas have been measured using proton deflectometry. Experiments were modeled to accurately interpret deflections observed in proton radiographs. Current flow is shown to begin on axis and migrate outwards with the expanding coronal plasma. Magnetic field strengths of ∼1 T are generated by currents that increase from ∼2 kA to ∼7 kA over the course of the laser pulse. Proton deflectometry has been demonstrated to be a practical alternative to other magnetic field diagnostics for these types of plasmas.

  16. A Time-Varied Probabilistic ON/OFF Switching Algorithm for Cellular Networks

    KAUST Repository

    Rached, Nadhir B.; Ghazzai, Hakim; Kadri, Abdullah; Alouini, Mohamed-Slim

    2018-01-01

    In this letter, we develop a time-varied probabilistic on/off switching planning method for cellular networks to reduce their energy consumption. It consists in a risk-aware optimization approach that takes into consideration the randomness of the user profile associated with each base station (BS). The proposed approach jointly determines (i) the instants of time at which the current active BS configuration must be updated due to an increase or decrease of the network traffic load, and (ii) the set of minimum BSs to be activated to serve the networks’ subscribers. Probabilistic metrics modeling the traffic profile variation are developed to trigger this dynamic on/off switching operation. Selected simulation results are then performed to validate the proposed algorithm for different system parameters.

  17. A Time-Varied Probabilistic ON/OFF Switching Algorithm for Cellular Networks

    KAUST Repository

    Rached, Nadhir B.

    2018-01-11

    In this letter, we develop a time-varied probabilistic on/off switching planning method for cellular networks to reduce their energy consumption. It consists in a risk-aware optimization approach that takes into consideration the randomness of the user profile associated with each base station (BS). The proposed approach jointly determines (i) the instants of time at which the current active BS configuration must be updated due to an increase or decrease of the network traffic load, and (ii) the set of minimum BSs to be activated to serve the networks’ subscribers. Probabilistic metrics modeling the traffic profile variation are developed to trigger this dynamic on/off switching operation. Selected simulation results are then performed to validate the proposed algorithm for different system parameters.

  18. Cosmic plasma

    Energy Technology Data Exchange (ETDEWEB)

    Alfven, H [California Univ., San Diego, La Jolla (USA)

    1981-01-01

    The properties of space plasmas are analyzed, based on laboratory results and data obtained by in situ measurements in the magnetosphere (including the heliosphere). Attention is given to the question of how much knowledge can be gained by a systematic comparison of different regions of plasma, and plasmas are considered with linear dimensions varying from laboratory size up to the Hubble distance. The traditional magnetic field description of plasmas is supplemented by an electric current description and it is demonstrated that many problems are easier to understand with a dualistic approach. Using the general plasma properties obtained, the origin and evolution of the solar system is summarized and the evolution and present structure of the universe (cosmology) is discussed.

  19. Long-Time Plasma Membrane Imaging Based on a Two-Step Synergistic Cell Surface Modification Strategy.

    Science.gov (United States)

    Jia, Hao-Ran; Wang, Hong-Yin; Yu, Zhi-Wu; Chen, Zhan; Wu, Fu-Gen

    2016-03-16

    Long-time stable plasma membrane imaging is difficult due to the fast cellular internalization of fluorescent dyes and the quick detachment of the dyes from the membrane. In this study, we developed a two-step synergistic cell surface modification and labeling strategy to realize long-time plasma membrane imaging. Initially, a multisite plasma membrane anchoring reagent, glycol chitosan-10% PEG2000 cholesterol-10% biotin (abbreviated as "GC-Chol-Biotin"), was incubated with cells to modify the plasma membranes with biotin groups with the assistance of the membrane anchoring ability of cholesterol moieties. Fluorescein isothiocyanate (FITC)-conjugated avidin was then introduced to achieve the fluorescence-labeled plasma membranes based on the supramolecular recognition between biotin and avidin. This strategy achieved stable plasma membrane imaging for up to 8 h without substantial internalization of the dyes, and avoided the quick fluorescence loss caused by the detachment of dyes from plasma membranes. We have also demonstrated that the imaging performance of our staining strategy far surpassed that of current commercial plasma membrane imaging reagents such as DiD and CellMask. Furthermore, the photodynamic damage of plasma membranes caused by a photosensitizer, Chlorin e6 (Ce6), was tracked in real time for 5 h during continuous laser irradiation. Plasma membrane behaviors including cell shrinkage, membrane blebbing, and plasma membrane vesiculation could be dynamically recorded. Therefore, the imaging strategy developed in this work may provide a novel platform to investigate plasma membrane behaviors over a relatively long time period.

  20. Modeling of Electricity Demand for Azerbaijan: Time-Varying Coefficient Cointegration Approach

    Directory of Open Access Journals (Sweden)

    Jeyhun I. Mikayilov

    2017-11-01

    Full Text Available Recent literature has shown that electricity demand elasticities may not be constant over time and this has investigated using time-varying estimation methods. As accurate modeling of electricity demand is very important in Azerbaijan, which is a transitional country facing significant change in its economic outlook, we analyze whether the response of electricity demand to income and price is varying over time in this economy. We employed the Time-Varying Coefficient cointegration approach, a cutting-edge time-varying estimation method. We find evidence that income elasticity demonstrates sizeable variation for the period of investigation ranging from 0.48% to 0.56%. The study has some useful policy implications related to the income and price aspects of the electricity consumption in Azerbaijan.

  1. Design and experiment of high-current low-pressure plasma-cathode e-gun

    International Nuclear Information System (INIS)

    Xie Wenkai; Li Xiaoyun; Wang Bin; Meng Lin; Yan Yang; Gao Xinyan

    2006-01-01

    The preliminary design of a new high-power low pressure plasma-cathode e-gun is presented. Based on the hollow cathode effect and low-pressure glow discharge empirical formulas, the hollow cathode, the accelerating gap, and the working gas pressure region are given. The general experimental device of the low-pressure plasma cathode electron-gun generating high current density e-beam source is shown. Experiments has been done in continuous filled-in gases and gases-puff condition, and the discharging current of 150-200 A, the width of 60 μs and the collector current of 30-80 A, the width of 60 μs are obtained. The results show that the new plasma cathode e-gun can take the place of material cathode e-gun, especially in plasma filled microwave tubes. (authors)

  2. Real time control of the sawtooth period using EC launchers

    International Nuclear Information System (INIS)

    Paley, J I; Felici, F; Coda, S; Goodman, T P; Piras, F

    2009-01-01

    Tokamak plasmas operating at high performance are limited by several MHD instabilities. The sawtooth instability limits the core plasma pressure and can drive the neoclassical tearing mode unstable, but also prevents accumulation of impurities in the core. Electron cyclotron heating and current drive systems can be used to modify the local current profile and therefore tailor the sawtooth period. This paper reports on demonstrations of continuous real time feedback control of the sawtooth period by varying the EC injection angle.

  3. Towards the conceptual design of the ITER real-time plasma control system

    International Nuclear Information System (INIS)

    Winter, A.; Makijarvi, P.; Simrock, S.; Snipes, J.A.; Wallander, A.; Zabeo, L.

    2014-01-01

    Highlights: • We describe the main control areas and interfaces for the ITER real-time plasma control system and the current state of their design. • An overview is given for the implementation strategy for the plasma control system as part of the ITER control, data access and communication system. • Current efforts on the creation of simulation and development tools are presented. - Abstract: ITER will be the world's largest magnetic confinement tokamak fusion device and is currently under construction in southern France. The ITER Plasma Control System (PCS) is a fundamental component of the ITER Control, Data Access and Communication system (CODAC). It will control the evolution of all plasma parameters that are necessary to operate ITER throughout all phases of the discharge. The design and implementation of the PCS poses a number of unique challenges. The timescales of phenomena to be controlled spans three orders of magnitude, ranging from a few milliseconds to seconds. Novel control schemes, which have not been implemented at present-day machines need to be developed, and control schemes that are only done as demonstration experiments today will have to become routine. In addition, advances in computing technology and available physics models make the implementation of real-time or faster-than-real-time predictive calculations to forecast and subsequently to avoid disruptions or undesired plasma regimes feasible. This requires the PCS design to be adaptable in real-time to the results of these forecasting algorithms. A further novel feature is a sophisticated event handling system, which provides a means to deal with plasma related events (such as MHD instabilities or L-H transitions) or component failure. Finally, the schedule for design and implementation poses another challenge. The beginning of ITER operation will be in late 2020, but the conceptual design activity of the PCS has already commenced as required by the on-going development of

  4. Surface currents associated with external kink modes in tokamak plasmas during a major disruption

    Science.gov (United States)

    Ng, C. S.; Bhattacharjee, A.

    2017-10-01

    The surface current on the plasma-vacuum interface during a disruption event involving kink instability can play an important role in driving current into the vacuum vessel. However, there have been disagreements over the nature or even the sign of the surface current in recent theoretical calculations based on idealized step-function background plasma profiles. We revisit such calculations by replacing step-function profiles with more realistic profiles characterized by a strong but finite gradient along the radial direction. It is shown that the resulting surface current is no longer a delta-function current density, but a finite and smooth current density profile with an internal structure, concentrated within the region with a strong plasma pressure gradient. Moreover, this current density profile has peaks of both signs, unlike the delta-function case with a sign opposite to, or the same as the plasma current. We show analytically and numerically that such current density can be separated into two parts, with one of them, called the convective current density, describing the transport of the background plasma density by the displacement, and the other part that remains, called the residual current density. It is argued that consideration of both types of current density is important and can resolve past controversies.

  5. Electron-Beam Produced Air Plasma: Optical Measurement of Beam Current

    Science.gov (United States)

    Vidmar, Robert; Stalder, Kenneth; Seeley, Megan

    2006-10-01

    Experiments to quantify the electron beam current and distribution of beam current in air plasma are discussed. The air plasma is produced by a 100-keV 10-mA electron beam source that traverses a transmission window into a chamber with air as a target gas. Air pressure is between 1 mTorr and 760 Torr. Strong optical emissions due to electron impact ionization are observed for the N2 2^nd positive line at 337.1 nm and the N2^+ 1^st negative line at 391.4 nm. Calibration of optical emissions using signals from the isolated transmission window and a Faraday plate are discussed. The calibrated optical system is then used to quantify the electron distribution in the air plasma.

  6. Investigation of the helicon discharge plasma parameters in a hybrid RF plasma system

    International Nuclear Information System (INIS)

    Aleksandrov, A. F.; Petrov, A. K.; Vavilin, K. V.; Kralkina, E. A.; Neklyudova, P. A.; Nikonov, A. M.; Pavlov, V. B.; Ayrapetov, A. A.; Odinokov, V. V.; Sologub, V. A.; Pavlov, G. Ya.

    2016-01-01

    Results of an experimental study of the helicon discharge plasma parameters in a prototype of a hybrid RF plasma system equipped with a solenoidal antenna are described. It is shown that an increase in the external magnetic field leads to the formation of a plasma column and a shift of the maximum ion current along the discharge axis toward the bottom flange of the system. The shape of the plasma column can be controlled via varying the configuration of the magnetic field.

  7. Investigation of the helicon discharge plasma parameters in a hybrid RF plasma system

    Energy Technology Data Exchange (ETDEWEB)

    Aleksandrov, A. F.; Petrov, A. K., E-mail: alpetrov57@gmail.com; Vavilin, K. V.; Kralkina, E. A.; Neklyudova, P. A.; Nikonov, A. M.; Pavlov, V. B. [Moscow State University, Faculty of Physics (Russian Federation); Ayrapetov, A. A.; Odinokov, V. V.; Sologub, V. A.; Pavlov, G. Ya. [Research Institute of Precision Engineering (Russian Federation)

    2016-03-15

    Results of an experimental study of the helicon discharge plasma parameters in a prototype of a hybrid RF plasma system equipped with a solenoidal antenna are described. It is shown that an increase in the external magnetic field leads to the formation of a plasma column and a shift of the maximum ion current along the discharge axis toward the bottom flange of the system. The shape of the plasma column can be controlled via varying the configuration of the magnetic field.

  8. Time-varying correlation and common structures in volatility

    NARCIS (Netherlands)

    Liu, Yang

    2016-01-01

    This thesis studies time series properties of the covariance structure of multivariate asset returns. First, the time-varying feature of correlation is investigated at the intraday level with a new correlation model incorporating the intraday correlation dynamics. Second, the thesis develops a

  9. Lower hybrid wave current ramp-up and plasma equilibrium

    International Nuclear Information System (INIS)

    Gong Xueyu

    1996-01-01

    Questions on lower hybrid driven current and plasma equilibrium are studied. With the induced electric field taken into account, a system of self-consistent equations is obtained. This theory has been applied to some moments of the current ramp-up phase for the Tokamak Engineering Test Breeder (TETB) to study the lower hybrid current drive and MHD equilibrium. So, better electron current and safety factor profiles are obtained

  10. National Spherical Torus Experiment Real Time Plasma Control Data Acquisition Hardware

    International Nuclear Information System (INIS)

    R.J. Marsala; J. Schneider

    2002-01-01

    The National Spherical Torus Experiment (NSTX) is currently providing researchers data on low aspect-ratio toroidal plasmas. NSTX's Plasma Control System adjusts the firing angles of thyristor rectifier power supplies, in real time, to control plasma position, shape and density. A Data Acquisition system comprised of off-the-shelf and custom hardware provides the magnetic diagnostics data required in calculating firing angles. This VERSAmodule Eurocard (VME) bus-based system utilizes Front Panel Data Port (FPDP) for high-speed data transfer. Data coming from physically different locations is referenced to several different ground potentials necessitating the need for a custom FPDP multiplexer. This paper discusses the data acquisition system configuration, the in-house designed 4-to-1 FPDP Input Multiplexing Module (FIMM), and future expansion plans

  11. The role of current sheet formation in driven plasmoid reconnection in laser-produced plasma bubbles

    Science.gov (United States)

    Lezhnin, Kirill; Fox, William; Bhattacharjee, Amitava

    2017-10-01

    We conduct a multiparametric study of driven magnetic reconnection relevant to recent experiments on colliding magnetized laser produced plasmas using the PIC code PSC. Varying the background plasma density, plasma resistivity, and plasma bubble geometry, the results demonstrate a variety of reconnection behavior and show the coupling between magnetic reconnection and global fluid evolution of the system. We consider both collision of two radially expanding bubbles where reconnection is driven through an X-point, and collision of two parallel fields where reconnection must be initiated by the tearing instability. Under various conditions, we observe transitions between fast, collisionless reconnection to a Sweet-Parker-like slow reconnection to complete stalling of the reconnection. By varying plasma resistivity, we observe the transition between fast and slow reconnection at Lundquist number S 103 . The transition from plasmoid reconnection to a single X-point reconnection also happens around S 103 . We find that the criterion δ /di < 1 is necessary for fast reconnection onset. Finally, at sufficiently high background density, magnetic reconnection can be suppressed, leading to bouncing motion of the magnetized plasma bubbles.

  12. Time-frequency analysis of non-stationary fusion plasma signals using an improved Hilbert-Huang transform

    International Nuclear Information System (INIS)

    Liu, Yangqing; Tan, Yi; Xie, Huiqiao; Wang, Wenhao; Gao, Zhe

    2014-01-01

    An improved Hilbert-Huang transform method is developed to the time-frequency analysis of non-stationary signals in tokamak plasmas. Maximal overlap discrete wavelet packet transform rather than wavelet packet transform is proposed as a preprocessor to decompose a signal into various narrow-band components. Then, a correlation coefficient based selection method is utilized to eliminate the irrelevant intrinsic mode functions obtained from empirical mode decomposition of those narrow-band components. Subsequently, a time varying vector autoregressive moving average model instead of Hilbert spectral analysis is performed to compute the Hilbert spectrum, i.e., a three-dimensional time-frequency distribution of the signal. The feasibility and effectiveness of the improved Hilbert-Huang transform method is demonstrated by analyzing a non-stationary simulated signal and actual experimental signals in fusion plasmas

  13. Generation of longitudinal current by a transverse electromagnetic field in classical and quantum plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Latyshev, A. V., E-mail: avlatyshev@mail.ru; Yushkanov, A. A. [Moscow State Regional University (Russian Federation)

    2015-09-15

    A distribution function for collisionless plasma is derived from the Vlasov kinetic equation in the quadratic approximation with respect to the electromagnetic field. Formulas for calculation of the electric current at an arbitrary temperature (arbitrary degree of degeneration of the electron gas) are deduced. The case of small wavenumbers is considered. It is shown that nonlinearity leads to the generation of an electric current directed along the wave vector. This longitudinal current is orthogonal to the classical transverse current, well known in the linear theory. A distribution function for collisionless quantum plasma is derived from the kinetic equation with the Wigner integral in the quadratic approximation with respect to the vector potential. Formulas for calculation of the electric current at an arbitrary temperature are deduced. The case of small wavenumbers is considered. It is shown that, at small values of the wavenumber, the value of the longitudinal current for quantum plasma coincides with that for classical plasma. The dimensionless currents in quantum and classical plasmas are compared graphically.

  14. Neoclassical Physics for Current Drive in Tokamak Plasmas

    International Nuclear Information System (INIS)

    Duthoit, F.X.

    2012-03-01

    The Lie transform formalism is applied to charged particle dynamics in tokamak magnetic topologies, in order to build a Fokker-Planck type operator for Coulomb collisions usable for current drive. This approach makes it possible to reduce the problem to three dimensions (two in velocity space, one in real space) while keeping the wealth of phase-space cross-term coupling effects resulting from conservation of the toroidal canonical momentum (axisymmetry). This kinetic approach makes it possible to describe physical phenomena related to the presence of strong pressure gradients in plasmas of an unspecified form, like the bootstrap current which role will be paramount for the future ITER machine. The choice of coordinates and the method used are particularly adapted to the numerical resolution of the drift kinetic equation making it possible to calculate the particle distributions, which may present a strong variation with respect to the Maxwellian under the effect of an electric field (static or produced by a radio-frequency wave). This work, mainly dedicated to plasma physics of tokamaks, was extended to those of space plasmas with a magnetic dipole configuration. (author)

  15. Reusable Launch Vehicle Attitude Control Using a Time-Varying Sliding Mode Control Technique

    Science.gov (United States)

    Shtessel, Yuri B.; Zhu, J. Jim; Daniels, Dan; Jackson, Scott (Technical Monitor)

    2002-01-01

    In this paper we present a time-varying sliding mode control (TVSMC) technique for reusable launch vehicle (RLV) attitude control in ascent and entry flight phases. In ascent flight the guidance commands Euler roll, pitch and yaw angles, and in entry flight it commands the aerodynamic angles of bank, attack and sideslip. The controller employs a body rate inner loop and the attitude outer loop, which are separated in time-scale by the singular perturbation principle. The novelty of the TVSMC is that both the sliding surface and the boundary layer dynamics can be varied in real time using the PD-eigenvalue assignment technique. This salient feature is used to cope with control command saturation and integrator windup in the presence of severe disturbance or control effector failure, which enhances the robustness and fault tolerance of the controller. The TV-SMC ascent and descent designs are currently being tested with high fidelity, 6-DOF dispersion simulations. The test results will be presented in the final version of this paper.

  16. Discrete-Time LPV Current Control of an Induction Motor

    DEFF Research Database (Denmark)

    Bendtsen, Jan Dimon; Trangbæk, Klaus

    2001-01-01

    In this paper we apply a new method for gain-scheduled output feedback control of nonlinear systems to current control of an induction motor. The method relies on recently developed controller synthesis results for linear parameter-varying (LPV) systems, where the controller synthesis is formulated...... without further complications. The synthesis method is applied to the model, yielding an LPV discrete-time controller. Finally, the efficiency of the control scheme is validated via simulations as well as experimentally on the actual induction motor, both in open-loop current control and when an outer...... speed control loop is closed around the current loop...

  17. Discrete-Time LPV Current Control of an Induction Motor

    DEFF Research Database (Denmark)

    Bendtsen, Jan Dimon; Trangbæk, Klaus

    2003-01-01

    In this paper we apply a new method for gain-scheduled output feedback control of nonlinear systems to current control of an induction motor. The method relies on recently developed controller synthesis results for linear parameter-varying (LPV) systems, where the controller synthesis is formulated...... further complications. The synthesis method is applied to the model, yielding an LPV discrete-time controller. Finally, the efficiency of the control scheme is validated via simulations as well as on the actual induction motor, both in open-loop current control and when an outer speed control loop...... is closed around the current loop....

  18. Thermal energy and bootstrap current in fusion reactor plasmas

    International Nuclear Information System (INIS)

    Becker, G.

    1993-01-01

    For DT fusion reactors with prescribed alpha particle heating power P α , plasma volume V and burn temperature i > ∼ 10 keV specific relations for the thermal energy content, bootstrap current, central plasma pressure and other quantities are derived. It is shown that imposing P α and V makes these relations independent of the magnitudes of the density and temperature, i.e. they only depend on P α , V and shape factors or profile parameters. For model density and temperature profiles analytic expressions for these shape factors and for the factor C bs in the bootstrap current formula I bs ∼ C bs (a/R) 1/2 β p I p are given. In the design of next-step devices and fusion reactors, the fusion power is a fixed quantity. Prescription of the alpha particle heating power and plasma volume results in specific relations which can be helpful for interpreting computer simulations and for the design of fusion reactors. (author) 5 refs

  19. Studies of the disruption prevention by ECRH at plasma current rise stage in limiter discharges

    International Nuclear Information System (INIS)

    Alikaev, V.V.; Borshegovskij, A.A.; Chistyakov, V.V.

    1999-01-01

    Studies of disruption prevention by means of ECRH in T-10 at the plasma current rise phase in limiter discharges with circular plasma cross-section were performed. Reliable disruption prevention by ECRH at HF power (P HF ) min level equal to 20% of ohmic heating power P OH was demonstrated. m/n=2/1 mode MHD-activity developed before disruption (with characteristic time ∼120 ms) can be considered as disruption precursor and can be used in a feedback system. (author)

  20. Simultaneous real-time control of the current and pressure profiles in JET: experiments and modelling

    Energy Technology Data Exchange (ETDEWEB)

    Mazon, D.; Laborde, L.; Litaudon, X.; Moreau, D.; Zabeo, L.; Joffrin, E. [Association Euratom-CEA Cadarache (DSM/DRFC), 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee; Murari, A. [Consorzio RFX Association Euratom-ENEA, Padova (Italy); Ariola, M.; Albanese, R.; Tommasi, G. de; Pironti, A. [Association Euratom-ENEA, CREATE, Napoly (Italy); Moreau, D. [EFDA-JET CSU, Culham Science Centre, Abingdon, OX (United Kingdom); Tala, T. [Euratom-Tekes Association, VTT Processes (Finland); Crisanti, F.; Pericoli-Ridolfini, V.; Tuccillo, A. [Association Euratom-ENEA, C.R. Frascati (Italy); Baar, M. de; Vries, P. de [Euratom-FOM Association, TEC Cluster, Nieuwegein (Netherlands); De la Luna, E. [Euratom-Ciemat Association (Spain); Felton, R.; Corrigan, G. [Euratom-UKAEA Association, Culham Science Centre, Abingdon (United Kingdom)

    2004-07-01

    Real-time control of the plasma profiles (current density, pressure and flow) is one of the major issues for sustaining internal transport barriers (ITB) in a high performance plasma, with a large bootstrap current fraction. We have recently investigated the experimental and numerical aspects of the simultaneous control of the current and pressure profiles in JET ITB discharges. The current density and the electron temperature were successfully controlled via the safety factor profile (or via its inverse the tau-profile) and the {rho}{sup *}{sub Te} profile respectively. The results of these new studies are presented. With only a limited number of actuators, the technique aims at minimizing an integral square error signal which combines the 2 profiles, rather than attempting to control plasma parameters at some given radii with great precision. The resulting fuzziness of the control scheme allows the plasma to relax towards a physically accessible non-linear state which may not be accurately known in advance, but is close enough to the requested one to provide the required plasma performance. Closed loop experiments have allow to reach different target q and {rho}{sup *}{sub Te} profiles, and to some degree, to displace the region of maximum electron temperature gradient. The control has also shown some robustness in front of rapid transients.

  1. Turbulent current heating of dense plasma

    International Nuclear Information System (INIS)

    Suprunenko, V.A.; Sukhomlin, E.A.; Volkov, E.D.; Perepelkij, N.F.

    1976-01-01

    Based upon experimental results an attempt is made for systematizing and analysing conditions of experiments in anomalous resistance and turbulent heating of a plasma. The extensive program of such investigations aims at a direct practical study on quasistationary heating and plasma containment in magnetic traps. It has been shown that in real conditions turbulent heating turns out to be a far more complicated phenomenon than that described within the framework of theories developed so far. It has been established that the phenomenon alters in the transition through the critical values of electric and magnetic fields. This makes it possible to separate four characteristic experimental regimes. For all the regimes the stabilization of the electron current drift rate is typical. On the basis of the experimental results obtained an explanation is given of the sporadic character of the ultrathermal radiation in a quasistationary discharge

  2. Introduction to wave heating and current drive in magnetized plasmas

    International Nuclear Information System (INIS)

    Pinsker, R. I.

    2001-01-01

    The development of high-power wave heating and current drive in magnetized plasmas in the last 40 years is a major ongoing success story in plasma science. A hallmark of this area of research has been the detailed quantitative comparison of theory and experiment; the good agreement consistently found is indicative of the robustness and the predictive power of the underlying theory. This tutorial paper is a brief overview of the fundamental concepts and applications of this branch of plasma science. Most of the high-power applications have been in three frequency regimes: the ion cyclotron range of frequencies (ICRF), the lower hybrid range of frequencies (LHRF), and the electron cyclotron range of frequencies (ECRF). The basic physics of wave propagation and damping in these regimes is briefly discussed. Some of the coupling structures (antennas) used to excite the waves at the plasma boundary are described, and the high-power systems used to generate the wave energy are touched on. Representative examples of the remarkably wide range of applications of high-power wave heating and current drive in high-temperature fusion plasmas will be discussed

  3. Current sheets with inhomogeneous plasma temperature: Effects of polarization electric field and 2D solutions

    International Nuclear Information System (INIS)

    Catapano, F.; Zimbardo, G.; Artemyev, A. V.; Vasko, I. Y.

    2015-01-01

    We develop current sheet models which allow to regulate the level of plasma temperature and density inhomogeneities across the sheet. These models generalize the classical Harris model via including two current-carrying plasma populations with different temperature and the background plasma not contributing to the current density. The parameters of these plasma populations allow regulating contributions of plasma density and temperature to the pressure balance. A brief comparison with spacecraft observations demonstrates the model applicability for describing the Earth magnetotail current sheet. We also develop a two dimensional (2D) generalization of the proposed model. The interesting effect found for 2D models is the nonmonotonous profile (along the current sheet) of the magnetic field component perpendicular to the current sheet. Possible applications of the model are discussed

  4. Current sheets with inhomogeneous plasma temperature: Effects of polarization electric field and 2D solutions

    Energy Technology Data Exchange (ETDEWEB)

    Catapano, F., E-mail: menacata3@gmail.com; Zimbardo, G. [Dipartimento di Fisica, Università della Calabria, Rende, Cosenza (Italy); Artemyev, A. V., E-mail: ante0226@gmail.com; Vasko, I. Y. [Space Research Institute, RAS, Moscow (Russian Federation)

    2015-09-15

    We develop current sheet models which allow to regulate the level of plasma temperature and density inhomogeneities across the sheet. These models generalize the classical Harris model via including two current-carrying plasma populations with different temperature and the background plasma not contributing to the current density. The parameters of these plasma populations allow regulating contributions of plasma density and temperature to the pressure balance. A brief comparison with spacecraft observations demonstrates the model applicability for describing the Earth magnetotail current sheet. We also develop a two dimensional (2D) generalization of the proposed model. The interesting effect found for 2D models is the nonmonotonous profile (along the current sheet) of the magnetic field component perpendicular to the current sheet. Possible applications of the model are discussed.

  5. Observation of Self-Generated Flows in Tokamak Plasmas with Lower-Hybrid-Driven Current

    International Nuclear Information System (INIS)

    Ince-Cushman, A.; Rice, J. E.; Reinke, M.; Greenwald, M.; Wallace, G.; Parker, R.; Fiore, C.; Hughes, J. W.; Bonoli, P.; Shiraiwa, S.; Hubbard, A.; Wolfe, S.; Hutchinson, I. H.; Marmar, E.; Bitter, M.; Wilson, J.; Hill, K.

    2009-01-01

    In Alcator C-Mod discharges lower hybrid waves have been shown to induce a countercurrent change in toroidal rotation of up to 60 km/s in the central region of the plasma (r/a∼<0.4). This modification of the toroidal rotation profile develops on a time scale comparable to the current redistribution time (∼100 ms) but longer than the energy and momentum confinement times (∼20 ms). A comparison of the co- and countercurrent injected waves indicates that current drive (as opposed to heating) is responsible for the rotation profile modifications. Furthermore, the changes in central rotation velocity induced by lower hybrid current drive (LHCD) are well correlated with changes in normalized internal inductance. The application of LHCD has been shown to generate sheared rotation profiles and a negative increment in the radial electric field profile consistent with a fast electron pinch

  6. Coupling between eddy current and deflection in cantilevered beams in magnetic fields

    International Nuclear Information System (INIS)

    Hua, T.Q.

    1986-01-01

    Experiments were performed to investigate the coupling between eddy currents and deflection in cantilevered beams in longitudinal and transverse magnetic fields. This coupling effect reduces the current, deflection, and material stress to levels far less severe than would be predicted if coupling is disregarded. The experiments were conducted using the FELIX (Fusion ELectromagnetic Induction experiment) facility at the Argonne National Laboratory. The beams, which provide a simple model for the limiter blades in a tokamak fusion reactor, are subjected to crossed time-varying and constant magnetic fields. The time-varying field simulates the decaying field during a plasma disruption and the constant field models the toroidal field. Several test pieces are employed to allow variations in thicknesses and mechanical and electrical properties. Various magnetic field levels and decay time constants of time-varying are used to study the extent of the coupling from weak to strong coupling. The ratios of constant field to time-varying field are kept in the range from 10:1 to 20:1 as would be appropriate to tokamak limiters. Major parameters measured as functions of time are beam deflection, measured with an electro-optical device; total circulating current, measured with a Rogowski coil; strain recorded by strain gauges; and magnetic fields measured with Hall probes

  7. Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse

    Energy Technology Data Exchange (ETDEWEB)

    Grishkov, V. E.; Uryupin, S. A., E-mail: uryupin@sci.lebedev.ru [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

    2017-03-15

    Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse is analyzed within the kinetic approach. It is shown that the most efficient source of plasma waves is the nonlinear current arising due to the gradient of the energy density of the high-frequency field. Generation of plasma waves by the drag current is usually less efficient but not negligibly small at relatively high frequencies of electron–ion collisions. The influence of electron collisions on the excitation of plasma waves by pulses of different duration is described quantitatively.

  8. Computer simulation of a plasma focus device driven by a magnetic pulser

    Energy Technology Data Exchange (ETDEWEB)

    Georgescu, N; Zoita, V [Inst. of Physics and Technology of Radiation Devices, Bucharest (Romania); Larour, J [Ecole Polytechnique, Palaiseau (France). Lab. de Physique des Milieux Ionises

    1997-12-31

    A plasma focus device, driven by a magnetic pulse compression circuit, is simulated by using a PSPICE proffam. The elaborated program is much simpler than the other existing ones, which analyse the circuit by directly solving a system of integral-differential equations. The pre-pulse voltage and the high-voltage rise-times are obtained for a set of values of the bypass impedance (R or L). The optimum bypass impedance turns out to be an inductance. During the discharge period, the plasma load is considered as an LR impedance, each component being time dependent. A method is presented for giving us the possibility to introduce the time varying impedances in a PSPICE program. Finally, a set of simulation results (plasma current and voltage, plasma magnetic energy, plasma sheath mechanical energy, pinch voltage) is shown. The results are in good agreement with the classical experimental data. (author). 2 figs., 4 refs.

  9. Linear waves in a resistive plasma with Hall current

    International Nuclear Information System (INIS)

    Almaguer, J.A.

    1992-01-01

    Dispersion relations for the case of a magnetized plasma are determined taking into account the Hall current and a constant resistivity, η, in Ohm's law. It is found that the Hall effect is relevant only for parallel (to the equilibrium magnetic field) wave numbers in the case of uniform plasmas, giving place to a dispersive behavior. In particular, the cases of η→0 and small (nonzero) resistivity are discussed

  10. Role of plasma equilibrium current in Alfven wave antenna optimization

    International Nuclear Information System (INIS)

    Puri, S.

    1986-12-01

    The modifications in the antenna loading produced by the plasma equilibrium current, the Faraday shield, and the finite electron temperature for coupling to the Alfven waves are studied using a self-consistent, three-dimensional, fully analytic periodic-loop-antenna model. The only significant changes are found to occur due to the plasma current and consist of an improved coupling (by a factor of ∝ 2.5) at low toroidal numbers (n ∝ 1-3). Despite this gain, however, the coupling to low n continues to be poor with R=0.03 Ω and Q=180 for n=2. Optimum coupling with R=0.71 Ω and Q=16.8 occurs for n=8 as was also the case in the absence of the plasma current. For the large n values, mode splitting due to the removal of the poloidal degeneracy combined with the finite electron temperatures effects lead to significant broadening of the energy absorption profile. Direct antenna coupling to the surface shear wave is small and no special provision, such as Faraday shielding, may be needed for preventing surface losses. The introduction of the Faraday screen, in fact, increases the coupling to the surface shear wave, possibly by acting as an impedance matching transformer between the antenna and the plasma. The finite electron temperature causes the predictable increase in the absorption width without influencing the antenna coupling. Thus the recommendations for antenna design for optimum coupling to the Alfven wave remain unaffected by the inclusion of the plasma current. Efficient coupling with capabilities for dynamic impedance tracking through purely electronic means may be obtained using a dense-cluster-array antenna with a toroidal configuration of n ∝ 8. (orig.)

  11. Mendelian randomization analysis of a time-varying exposure for binary disease outcomes using functional data analysis methods.

    Science.gov (United States)

    Cao, Ying; Rajan, Suja S; Wei, Peng

    2016-12-01

    A Mendelian randomization (MR) analysis is performed to analyze the causal effect of an exposure variable on a disease outcome in observational studies, by using genetic variants that affect the disease outcome only through the exposure variable. This method has recently gained popularity among epidemiologists given the success of genetic association studies. Many exposure variables of interest in epidemiological studies are time varying, for example, body mass index (BMI). Although longitudinal data have been collected in many cohort studies, current MR studies only use one measurement of a time-varying exposure variable, which cannot adequately capture the long-term time-varying information. We propose using the functional principal component analysis method to recover the underlying individual trajectory of the time-varying exposure from the sparsely and irregularly observed longitudinal data, and then conduct MR analysis using the recovered curves. We further propose two MR analysis methods. The first assumes a cumulative effect of the time-varying exposure variable on the disease risk, while the second assumes a time-varying genetic effect and employs functional regression models. We focus on statistical testing for a causal effect. Our simulation studies mimicking the real data show that the proposed functional data analysis based methods incorporating longitudinal data have substantial power gains compared to standard MR analysis using only one measurement. We used the Framingham Heart Study data to demonstrate the promising performance of the new methods as well as inconsistent results produced by the standard MR analysis that relies on a single measurement of the exposure at some arbitrary time point. © 2016 WILEY PERIODICALS, INC.

  12. Investigation on broadband propagation characteristic of terahertz electromagnetic wave in anisotropic magnetized plasma in frequency and time domain

    Energy Technology Data Exchange (ETDEWEB)

    Tian, Yuan; Han, Yiping, E-mail: yphan@xidian.edu.cn [School of Physics and Optoelectronic Engineering, Xidian University, Xi' an 710071 (China); Ai, Xia [National Key Laboratory of Science and Technology on Test physics and Numerical Mathematical, Beijing 100076 (China); Liu, Xiuxiang [Science and Technology on Space Physics Laboratory, Beijing 100076 (China)

    2014-12-15

    In this paper, we investigate the propagation of terahertz (THz) electromagnetic wave in an anisotropic magnetized plasma by JE convolution-finite difference time domain method. The anisotropic characteristic of the plasma, which leads to right-hand circularly polarized (RCP) and right-hand circularly polarized (LCP) waves, has been taken into account. The interaction between electromagnetic waves and magnetized plasma is illustrated by reflection and transmission coefficients for both RCP and LCP THz waves. The effects of both the magnetized plasma thickness and the external magnetized field are analyzed and numerical results demonstrate that the two factors could influence the THz wave greatly. It is worthy to note that besides the reflection and transmission coefficients in the frequency domain, the waveform of the electric field in the time domain varying with thicknesses and external magnetic fields for different polarized direction has been studied.

  13. Visualizing time-varying harmonics using filter banks

    NARCIS (Netherlands)

    Duque, C.A.; Da Silveira, P.M.; Ribeiro, P.F.

    2011-01-01

    Although it is well known that Fourier analysis is in reality only accurately applicable to steady state waveforms, it is a widely used tool to study and monitor time-varying signals, such as are commonplace in electrical power systems. The disadvantages of Fourier analysis, such as frequency

  14. Plasma-induced evolution behavior of space-charge-limited current for multiple-needle cathodes

    International Nuclear Information System (INIS)

    Li Limin; Liu Lie; Zhang Jun; Wen Jianchun; Liu Yonggui; Wan Hong

    2009-01-01

    Properties of the plasma and beam flow produced by tufted carbon fiber cathodes in a diode powered by a ∼500 kV, ∼400 ns pulse are investigated. Under electric fields of 230-260 kV cm -1 , the electron current density was in the range 210-280 A cm -2 , and particularly at the diode gap of 20 mm, a maximum beam power density of about 120 MW cm -2 was obtained. It was found that space-charge-limited current exhibited an evolution behavior as the accelerating pulse proceeded. There exists a direct relation between the movement of plasma within the diode and the evolution of space-charge-limited current. Initially in the accelerating pulse, the application of strong electric fields caused the emission sites to explode, forming cathode flares or plasma spots, and in this stage the space-charge-limited current was approximately described by a multiple-needle cathode model. As the pulse proceeded, these plasma spots merged and expanded towards the anode, thus increasing the emission area and shortening the diode gap, and the corresponding space-charge-limited current followed a planar cathode model. Finally, the space-charge-limited current is developed from a unipolar flow into a bipolar flow as a result of the appearance of anode plasma. In spite of the nonuniform distribution of cathode plasma, the cross-sectional uniformity of the extracted electron beam is satisfactory. The plasma expansion within the diode is found to be a major factor in the diode perveance growth and instability. These results show that these types of cathodes can offer promising applications for high-power microwave tubes.

  15. Oscillation of the current sheet velocity in plasma focus discharges

    International Nuclear Information System (INIS)

    Melzacki, K.; Nardi, V.

    1994-01-01

    The oscillation of the propagation speed of the plasma focus current sheet has been recorded with schlieren photography. The sheet stuttering in the propagation during the implosion phase has a frequency of about 60 MHz. The effect could be recorded due to application of long exposure time (60 ns) technique. It is not detectable in the subnanosecond pictures. The pictures are taken in black schlieren. The probing range of the electron density gradient, with integration along the path of the 1 J, Q-switched ruby laser beam, has been selected by the size of the stop and aperture within 3 x 10 18 cm -3 and 3 x 10 20 cm -3 . Raising the sensitivity threshold to 2 x 10 19 cm -3 (refraction angle of 4 mrad) has helped to clear the pictures by limiting their image to high gradients of density only. With this technique (and other diagnostic methods) the dynamics of 6 kJ, 16 kV plasma focus discharges in deuterium at 5 torr, with a 10% decrease of the magnetic insulation at the breech has been investigated. The average implosion velocity of the current sheath obtained with this effect, 5 x 10 6 cm/s, is consistent with those measured by the smear effect, and the electric probe. The electron density gradient has been determined at several instants; at the pinch time it is (3 ± 1.5) x 10 20 cm -4 . The data are discussed on the basis of several pictures

  16. Stabilization of the Wave Equation with Boundary Time-Varying Delay

    Directory of Open Access Journals (Sweden)

    Hao Li

    2014-01-01

    Full Text Available We study the stabilization of the wave equation with variable coefficients in a bounded domain and a time-varying delay term in the time-varying, weakly nonlinear boundary feedbacks. By the Riemannian geometry methods and a suitable assumption of nonlinearity, we obtain the uniform decay of the energy of the closed loop system.

  17. On resonance phenomena in a stellarator with longitudinal current in a plasma

    International Nuclear Information System (INIS)

    Aleksin, V.F.; Pyatov, V.N.; Sebko, V.P.; Tyupa, V.I.

    1976-01-01

    A magnetic configuration structure of a stellarator with a current plasma has been considered in the presence of small disturbances. Structures of magnetic fields of a real stellarator configuration with a longitudinal current in a plasma have been obtained by means of averaged coordinates with the subsequent transition to real coordinates. The development of a socket structure and destruction of an integral configuration with an increase of the disturbance amplitude are demonstrated, its range of variation is within the limits of 0.1+-0.01%. Deformations of sockets in different cross sections of the magnetic system along the toroidal axis have been investigated. The results of calculations agree with experimental data obtained at stellarators with a current plasma

  18. Online Estimation of Time-Varying Volatility Using a Continuous-Discrete LMS Algorithm

    Directory of Open Access Journals (Sweden)

    Jacques Oksman

    2008-09-01

    Full Text Available The following paper addresses a problem of inference in financial engineering, namely, online time-varying volatility estimation. The proposed method is based on an adaptive predictor for the stock price, built from an implicit integration formula. An estimate for the current volatility value which minimizes the mean square prediction error is calculated recursively using an LMS algorithm. The method is then validated on several synthetic examples as well as on real data. Throughout the illustration, the proposed method is compared with both UKF and offline volatility estimation.

  19. Investigating Time-Varying Drivers of Grid Project Emissions Impacts

    Energy Technology Data Exchange (ETDEWEB)

    Barrett, Emily L.; Thayer, Brandon L.; Pal, Seemita; Studarus, Karen E.

    2017-11-15

    The emissions consequences of smart grid technologies depend heavily on their context and vary not only by geographical location, but by time of year. The same technology operated to meet the same objective may increase the emissions associated with energy generation for part of the year and decrease emissions during other times. The Grid Project Impact Quantification (GridPIQ) tool provides the ability to estimate these seasonal variations and garner insight into the time-varying drivers of grid project emissions impacts. This work leverages GridPIQ to examine the emissions implications across years and seasons of adding energy storage technology to reduce daily peak demand in California and New York.

  20. Schlieren Cinematography of Current Driven Plasma Jet Dynamics

    Science.gov (United States)

    Loebner, Keith; Underwood, Thomas; Cappelli, Mark

    2016-10-01

    Schlieren cinematography of a pulsed plasma deflagration jet is presented and analyzed. An ultra-high frame rate CMOS camera coupled to a Z-type laser Schlieren apparatus is used to obtain flow-field refractometry data for the continuous flow Z-pinch formed within the plasma deflagration jet. The 10 MHz frame rate for 256 consecutive frames provides high temporal resolution, enabling turbulent fluctuations and plasma instabilities to be visualized over the course of a single pulse (20 μs). The Schlieren signal is radiometrically calibrated to obtain a two dimensional mapping of the refraction angle of the axisymmetric pinch plasma, and this mapping is then Abel inverted to derive the plasma density distribution as a function radius, axial coordinate, and time. Analyses of previously unknown discharge characteristics and comparisons with prior work are discussed.

  1. Influence of an External DC Electric Current on Plasma Cleaning Rate: an Application on the Enlarged Plasma-Surface Theory

    International Nuclear Information System (INIS)

    Xaplanteris, Constantine L.; Filippaki, Eleni D.

    2013-01-01

    During the last decades many researchers have been occupied with other plasma applications apart from the big challenge which the thermonuclear fusion poses. Many experiments have been carried out on the plasma behavior in contact with a solid surface; when the surface material consists of chemical compounds (e.g. oxides of metals), then the plasma chemistry takes place. The present paper contains the final experimental and theoretical work of Plasma Laboratory at “Demokritos , which consists of an elaboration of plasma sheath parameters adapted to experimental conditions, a suitable choice of plasma gases (either H 2 or N 2 ), and an electric potential current enforcement on objects. Additionally, a brief theory is given to explain the results, with a short reference to both boundary phenomena in thermonuclear reactors and low pressure plasma of glow discharges, so as to reveal the similarities and differences of these two cases. An extensive examination of the treated objects by X-ray diffraction method (XRD) gives results in agreement with the theoretical predictions. Using this improvement on plasma restoration system, (a combination of electric current on metallic object into suitable plasma), it is shown that better results can be achieved on the cleaning and conservation of archaeological objects. (plasma technology)

  2. A Control Method of Current Type Matrix Converter for Plasma Control Coil Power Supply

    International Nuclear Information System (INIS)

    Shimada, K.; Matsukawa, M.; Kurihara, K.; Jun-ichi Itoh

    2006-01-01

    In exploration to a tokamak fusion reactor, the control of plasma instabilities of high β plasma such as neoclassical tearing mode (NTM), resistive wall mode (RWM) etc., is the key issue for steady-state sustainment. One of the proposed methods to avoid suppressing RWM is that AC current having a phase to work for reduction the RWM growth is generated in a coil (sector coil) equipped spirally on the plasma vacuum vessel. To stabilize RWM, precise and fast real-time feedback control of magnetic field with proper amplitude and frequency is necessary. This implies that an appropriate power supply dedicated for such an application is expected to be developed. A matrix converter as one of power supply candidates for this purpose could provide a solution The matrix converter, categorized in an AC/AC direct converter composed of nine bi-directional current switches, has a great feature that a large energy storage element is unnecessary in comparison with a standard existing AC/AC indirect converter, which is composed of an AC/DC converter and a DC/AC inverter. It is also advantageous in cost and size of its applications. Fortunately, a voltage type matrix converter has come to be available at the market recently, while a current type matrix converter, which is advantageous for fast control of the large-inductance coil current, has been unavailable. On the background above mentioned, we proposed a new current type matrix converter and its control method applicable to a power supply with fast response for suppressing plasma instabilities. Since this converter is required with high accuracy control, the gate control method is adopted to three-phase switching method using middle phase to reduce voltage and current waveforms distortion. The control system is composed of VME-bus board with DSP (Digital Signal Processor) and FPGA (Field Programmable Gate Array) for high speed calculation and control. This paper describes the control method of a current type matrix converter

  3. Control of the tokamak safety factor profile with time-varying constraints using MPC

    International Nuclear Information System (INIS)

    Maljaars, E.; Felici, F.; De Baar, M.R.; Geelen, P.J.M.; Steinbuch, M.; Van Dongen, J.; Hogeweij, G.M.D.

    2015-01-01

    A controller is designed for the tokamak safety factor profile that takes real-time-varying operational and physics limits into account. This so-called model predictive controller (MPC) employs a prediction model in order to compute optimal control inputs that satisfy the given limits. The use of linearized models around a reference trajectory results in a quadratic programming problem that can easily be solved online. The performance of the controller is analysed in a set of ITER L-mode scenarios simulated with the non-linear plasma transport code RAPTOR. It is shown that the controller can reduce the tracking error due to an overestimation or underestimation of the modelled transport, while making a trade-off between residual error and amount of controller action. It is also shown that the controller can account for a sudden decrease in the available actuator power, while providing warnings ahead of time about expected violations of operational and physics limits. This controller can be extended and implemented in existing tokamaks in the near future. (paper)

  4. Exploration of one-dimensional plasma current density profile for K-DEMO steady-state operation

    Energy Technology Data Exchange (ETDEWEB)

    Kang, J.S. [Seoul National University, Seoul 151-742 (Korea, Republic of); Jung, L. [National Fusion Research Institute, Daejeon (Korea, Republic of); Byun, C.-S.; Na, D.H.; Na, Y.-S. [Seoul National University, Seoul 151-742 (Korea, Republic of); Hwang, Y.S., E-mail: yhwang@snu.ac.kr [Seoul National University, Seoul 151-742 (Korea, Republic of)

    2016-11-01

    Highlights: • One-dimensional current density and its optimization for the K-DEMO are explored. • Plasma current density profile is calculated with an integrated simulation code. • The impact of self and external heating profiles is considered self-consistently. • Current density is identified as a reference profile by minimizing heating power. - Abstract: Concept study for Korean demonstration fusion reactor (K-DEMO) is in progress, and basic design parameters are proposed by targeting high magnetic field operation with ITER-sized machine. High magnetic field operation is a favorable approach to enlarge relative plasma performance without increasing normalized beta or plasma current. Exploration of one-dimensional current density profile and its optimization process for the K-DEMO steady-state operation are reported in this paper. Numerical analysis is conducted with an integrated plasma simulation code package incorporating a transport code with equilibrium and current drive modules. Operation regimes are addressed with zero-dimensional system analysis. One-dimensional plasma current density profile is calculated based on equilibrium, bootstrap current analysis, and thermal transport analysis. The impact of self and external heating profiles on those parameters is considered self-consistently, where thermal power balance and 100% non-inductive current drive are the main constraints during the whole exploration procedure. Current and pressure profiles are identified as a reference steady-state profile by minimizing the external heating power with desired fusion power.

  5. Negative edge plasma currents in the SINP tokamak

    Indian Academy of Sciences (India)

    RAE is the maximum runaway energy emitted during a burst period of tdur. HXR. There being no plasma control feedback system in the SINP tokamak, the dynamics of the plasma equilibrium is time-dependent and the column shift is now made by the discharge dynamics itself. We measured DRAE for the two discharges ...

  6. The effect of plasma minor-radius expansion in the current build-up phase of a large tokamak

    International Nuclear Information System (INIS)

    Kobayashi, Tomofumi; Tazima, Teruhiko; Tani, Keiji; Tamura, Sanae

    1977-03-01

    A plasma simulation code has been developed to study the plasma current build-up process in JT-60. Plasma simulation is made with a model which represents well overall plasma behavior of the present-day tokamaks. The external electric circuit is taken into consideration in simulation calculation. An emphasis is placed on the simulation of minor-radius expansion of the plasma and behavior of neutral particles in the plasma during current build-up. A calculation with typical parameters of JT-60 shows a week skin distribution in the current density and the electron temperature, if the minor radius of the plasma expands with build-up of the plasma current. (auth.)

  7. Lower hybrid current drive in tokamak plasmas

    International Nuclear Information System (INIS)

    Ushigusa, Kenkichi

    1999-03-01

    Past ten years progress on Lower Hybrid Current Drive (LHCD) experiments have demonstrated the largest non-inductive current (3.6 MA, JT-60U), the longest current sustainment (2 hours, TRIAM-1M), non-inductive current drive at the highest density (n-bar e - 10 20 m -3 , ALCATOR-C) and the highest current drive efficiency (η CD = 3.5x10 19 m -2 A/W, JT-60). These results indicate that LHCD is one of the most promising methods to drive non-inductive current in the present tokamak plasmas. This paper presents recent experimental results on LHCD experiments. Basic theories of LH waves, the wave propagation and the current drive are briefly summarized. The main part of this paper describes several important results and their physical pictures on recent LHCD experiments; 1) the experimental set-up, 2) the current drive efficiency, 3) the control of current profile and MHD activities, 4) the global energy confinement, 5) the global power flow, 6) fast electron behavior, 7) interaction between LH waves and thermal/fast ions, 8) combination with other CD method. (author)

  8. Nonlinear recurrent neural networks for finite-time solution of general time-varying linear matrix equations.

    Science.gov (United States)

    Xiao, Lin; Liao, Bolin; Li, Shuai; Chen, Ke

    2018-02-01

    In order to solve general time-varying linear matrix equations (LMEs) more efficiently, this paper proposes two nonlinear recurrent neural networks based on two nonlinear activation functions. According to Lyapunov theory, such two nonlinear recurrent neural networks are proved to be convergent within finite-time. Besides, by solving differential equation, the upper bounds of the finite convergence time are determined analytically. Compared with existing recurrent neural networks, the proposed two nonlinear recurrent neural networks have a better convergence property (i.e., the upper bound is lower), and thus the accurate solutions of general time-varying LMEs can be obtained with less time. At last, various different situations have been considered by setting different coefficient matrices of general time-varying LMEs and a great variety of computer simulations (including the application to robot manipulators) have been conducted to validate the better finite-time convergence of the proposed two nonlinear recurrent neural networks. Copyright © 2017 Elsevier Ltd. All rights reserved.

  9. Electromagnetic particle in cell modeling of the plasma focus: Current sheath formation and lift off

    International Nuclear Information System (INIS)

    Seng, Y. S.; Lee, P.; Rawat, R. S.

    2014-01-01

    The shaping and formation of the current sheath takes place in the breakdown phase of a plasma focus device and critically controls the device performance. Electrostatic particle in cell codes, with magnetic effects ignored, have been used to model the breakdown phase. This Letter reports the successful development and implementation of an electromagnetic particle in cell (EMPIC) code, including magnetic effects self-consistently, to simulate the breakdown phase; from the ionization, localization and gliding discharge along the insulator to the time instant of current sheath lift off. The magnetic field was found to be appreciable from the time the current sheath came into contact with the anode with increased local current, initiating the voltage breakdown of the device as a result

  10. Long Memory of Financial Time Series and Hidden Markov Models with Time-Varying Parameters

    DEFF Research Database (Denmark)

    Nystrup, Peter; Madsen, Henrik; Lindström, Erik

    2016-01-01

    Hidden Markov models are often used to model daily returns and to infer the hidden state of financial markets. Previous studies have found that the estimated models change over time, but the implications of the time-varying behavior have not been thoroughly examined. This paper presents an adaptive...... to reproduce with a hidden Markov model. Capturing the time-varying behavior of the parameters also leads to improved one-step density forecasts. Finally, it is shown that the forecasting performance of the estimated models can be further improved using local smoothing to forecast the parameter variations....

  11. Continuous time modelling with individually varying time intervals for oscillating and non-oscillating processes.

    Science.gov (United States)

    Voelkle, Manuel C; Oud, Johan H L

    2013-02-01

    When designing longitudinal studies, researchers often aim at equal intervals. In practice, however, this goal is hardly ever met, with different time intervals between assessment waves and different time intervals between individuals being more the rule than the exception. One of the reasons for the introduction of continuous time models by means of structural equation modelling has been to deal with irregularly spaced assessment waves (e.g., Oud & Delsing, 2010). In the present paper we extend the approach to individually varying time intervals for oscillating and non-oscillating processes. In addition, we show not only that equal intervals are unnecessary but also that it can be advantageous to use unequal sampling intervals, in particular when the sampling rate is low. Two examples are provided to support our arguments. In the first example we compare a continuous time model of a bivariate coupled process with varying time intervals to a standard discrete time model to illustrate the importance of accounting for the exact time intervals. In the second example the effect of different sampling intervals on estimating a damped linear oscillator is investigated by means of a Monte Carlo simulation. We conclude that it is important to account for individually varying time intervals, and encourage researchers to conceive of longitudinal studies with different time intervals within and between individuals as an opportunity rather than a problem. © 2012 The British Psychological Society.

  12. Performance Improvement of Real-Time System for Plasma Control in RFX-mod

    International Nuclear Information System (INIS)

    Luchetta, A.; Manduchi, G.; Soppelsa, A.; Taliercio, C.

    2006-01-01

    The real-time system for plasma control has been used routinely in RFX-mod since commissioning (mid 2005). It is based on a modular hardware/software infrastructure, currently including 7 VME stations, capable of fulfilling the tight system requirements in terms of input/output channels (> 700 / > 250), real-time data flow (> 2 Mbyte/s), computation capability (> 1 GFLOP/s per station), and real-time constraints (application cycle times rd EPS Conf. on Plasma Physics, Rome Italy, June 19 - 23 2006]. The high flexibility of the system has stimulated the development of a large number of control schemes with progressively increasing requests in terms of computation complexity and real-time data flow, demanding, at the same time, strict control on cycle times and system latency. Even though careful optimisation of algorithm implementation and real-time data transmission have been performed, allowing to keep pace, so far, with the increased control requirements, future developments require to evolve the current technology, retaining the basic architecture and concepts. Two system enhancements are envisaged in the near future. The 500 MHz PowerPC-based Single Board Computer currently in use will be substituted with the 1 GHz version, whereas the real-time communication system will increase in bandwidth from 100 Mbit/s to 1 Gbit/s. These improvements will surely enhance the overall system performance, even if it is not possible to quantify a priori the exact performance boost, since other components may limit the performance in the new configuration. The paper reports in detail on the analysis of the bottlenecks of the current architecture. Based on measurements carried out in laboratory, it presents the results achieved with the proposed enhancements in terms of real-time data throughput, cycle times and latency. The paper analyses in detail the effects of the increased computing power on the components of the control system and of the improved bandwidth in real-time

  13. Lyapunov Functions to Caputo Fractional Neural Networks with Time-Varying Delays

    Directory of Open Access Journals (Sweden)

    Ravi Agarwal

    2018-05-01

    Full Text Available One of the main properties of solutions of nonlinear Caputo fractional neural networks is stability and often the direct Lyapunov method is used to study stability properties (usually these Lyapunov functions do not depend on the time variable. In connection with the Lyapunov fractional method we present a brief overview of the most popular fractional order derivatives of Lyapunov functions among Caputo fractional delay differential equations. These derivatives are applied to various types of neural networks with variable coefficients and time-varying delays. We show that quadratic Lyapunov functions and their Caputo fractional derivatives are not applicable in some cases when one studies stability properties. Some sufficient conditions for stability of equilibrium of nonlinear Caputo fractional neural networks with time dependent transmission delays, time varying self-regulating parameters of all units and time varying functions of the connection between two neurons in the network are obtained. The cases of time varying Lipschitz coefficients as well as nonLipschitz activation functions are studied. We illustrate our theory on particular nonlinear Caputo fractional neural networks.

  14. The necessity for a time local dimension in systems with time-varying attractors

    DEFF Research Database (Denmark)

    Særmark, Knud H; Ashkenazy, Y; Levitan, J

    1997-01-01

    We show that a simple non-linear system for ordinary differential equations may possess a time-varying attractor dimension. This indicates that it is infeasible to characterize EEG and MEG time series with a single time global dimension. We suggest another measure for the description of non...

  15. On transport and the bootstrap current in toroidal plasmas

    International Nuclear Information System (INIS)

    Connor, J.W.; Taylor, J.B.

    1987-01-01

    The recently reported observation of the bootstrap current in a tokamak plasma highlights the problem of reconciling this neoclassical effect with the anomalous (i.e., non-neoclassical) electron thermal transport. This Comment reviews the bootstrap current and considers the implications of a self-consistent modification of neoclassical theory based on an enhanced electron-electron interaction. (author)

  16. External kink mode stability of tokamaks with finite edge current density in plasma outside separatrix

    International Nuclear Information System (INIS)

    Degtyarev, L.; Martynov, A.; Medvedev, S.; Troyon, F.; Villard, L.

    1996-01-01

    Large pressure gradients and current density at the plasma edge and accompanying edge-localized MHD instabilities are typical for H-mode discharges. Low-n external kink modes are a possible cause of the instabilities. The paper mostly deals with external kink modes driven by a finite current density at the plasma boundary (so called peeling modes). It was shown earlier that for a single axis plasma embedded into vacuum the peeling modes are stabilized when separatrix is approaching the plasma boundary. For doublet configurations a finite current density at the internal separatrix does not necessarily lead to external kink instability when the current density vanishes at the boundary. However, a finite current density at the plasma boundary outside the separatrix can drive outer peeling modes. The stability properties and structure of these modes depend on the plasma equilibrium outside the separatrix. The influence of plasma shear and pressure gradient at the boundary on the stability of the outer peeling modes in doublets is studied. The stability of kink modes in divertor configurations with plasma outside the separatrix is very sensitive to the boundary conditions set at open field lines. The choice of the boundary conditions and kink mode stability calculations for the divertor configurations are discussed. (author) 4 figs., 5 refs

  17. Theory of free-electron-laser heating and current drive in magnetized plasmas

    International Nuclear Information System (INIS)

    Cohen, B.I.; Cohen, R.H.; Nevins, W.M.; Rognlien, T.D.

    1991-01-01

    The introduction of a powerful new microwave source, the free-electron laser, provides new opportunities for novel heating and current-drive schemes to be used in toroidal fusion devices. This high-power, pulsed source has a number of technical advantages for these applications, and its use is predicted to lead to improved current-drive efficiencies and opacities in reactor-grade fusion plasmas in specific cases. The Microwave Tokamak Experiment at the Lawrence Livermore National Laboratory will provide a test for some of these new heating and current-drive schemes. Although the motivation for much of this research has derived from the application of a free-electron laser to the heating of a tokamak plasma at a frequency near the electron cyclotron frequency, the underlying physics, i.e., the highly nonlinear interaction of an intense, pulsed, coherent electromagnetic wave with an electron in a magnetized plasma including relativistic effects, is of general interest. Other relevant applications include ionospheric modification by radio-frequency waves, high-energy electron accelerators, and the propagation of intense, pulsed electromagnetic waves in space and astrophysical plasmas. This review reports recent theoretical progress in the analysis and computer simulation of the absorption and current drive produced by intense pulses, and of the possible complications that may arise, e.g., parametric instabilities, nonlinear self-focusing, trapped-particle sideband instability, and instabilities of the heated plasma

  18. Generation of Low-Energy High-Current Electron Beams in Plasma-Anode Electron Guns

    Science.gov (United States)

    Ozur, G. E.; Proskurovsky, D. I.

    2018-01-01

    This paper is a review of studies on the generation of low-energy high-current electron beams in electron guns with a plasma anode and an explosive-emission cathode. The problems related to the initiation of explosive electron emission under plasma and the formation and transport of high-current electron beams in plasma-filled systems are discussed consecutively. Considerable attention is given to the nonstationary effects that occur in the space charge layers of plasma. Emphasis is also placed on the problem of providing a uniform energy density distribution over the beam cross section, which is of critical importance in using electron beams of this type for surface treatment of materials. Examples of facilities based on low-energy high-current electron beam sources are presented and their applications in materials science and practice are discussed.

  19. Stability of a plasma filament with a skinned current

    International Nuclear Information System (INIS)

    Blekher, P.M.

    1984-01-01

    An effective sufficient condition of existence of ideal helical plasma filament instability in a strong longitUdinal magnetic field for skinned current profiles is deduced in the paper. The results of numerical calculations of current skinned profiles of instability diagrams are presented and these results are compared with the obtained sufficient condition. An analytical solution for one model current profile skinning and this solution also is compared with the sufficient condition of instability

  20. Anomalous cross-field current and fluctuating equilibrium of magnetized plasmas

    DEFF Research Database (Denmark)

    Rypdal, K.; Garcia, O.E.; Paulsen, J.V.

    1997-01-01

    It is shown by simple physical arguments and fluid simulations that electrostatic flute-mode fluctuations can sustain a substantial cross-field current in addition to mass and energy transport. The simulations show that this current determines essential features of the fluctuating plasma...

  1. Current and Perspective Applications of Dense Plasma Focus Devices

    Science.gov (United States)

    Gribkov, V. A.

    2008-04-01

    Dense Plasma Focus (DPF) devices' applications, which are intended to support the main-stream large-scale nuclear fusion programs (NFP) from one side (both in fundamental problems of Dense Magnetized Plasma physics and in its engineering issues) as well as elaborated for an immediate use in a number of fields from the other one, are described. In the first direction such problems as self-generated magnetic fields, implosion stability of plasma shells having a high aspect ratio, etc. are important for the Inertial Confinement Fusion (ICF) programs (e.g. as NIF), whereas different problems of current disruption phenomenon, plasma turbulence, mechanisms of generation of fast particles and neutrons in magnetized plasmas are of great interest for the large devices of the Magnetic Plasma Confinement—MPC (e.g. as ITER). In a sphere of the engineering problems of NFP it is shown that in particular the radiation material sciences have DPF as a very efficient tool for radiation tests of prospect materials and for improvement of their characteristics. In the field of broad-band current applications some results obtained in the fields of radiation material sciences, radiobiology, nuclear medicine, express Neutron Activation Analysis (including a single-shot interrogation of hidden illegal objects), dynamic non-destructive quality control, X-Ray microlithography and micromachining, and micro-radiography are presented. As the examples of the potential future applications it is proposed to use DPF as a powerful high-flux neutron source to generate very powerful pulses of neutrons in the nanosecond (ns) range of its duration for innovative experiments in nuclear physics, for the goals of radiation treatment of malignant tumors, for neutron tests of materials of the first wall, blankets and NFP device's constructions (with fluences up to 1 dpa per a year term), and ns pulses of fast electrons, neutrons and hard X-Rays for brachytherapy.

  2. Current and Perspective Applications of Dense Plasma Focus Devices

    International Nuclear Information System (INIS)

    Gribkov, V. A.

    2008-01-01

    Dense Plasma Focus (DPF) devices' applications, which are intended to support the main-stream large-scale nuclear fusion programs (NFP) from one side (both in fundamental problems of Dense Magnetized Plasma physics and in its engineering issues) as well as elaborated for an immediate use in a number of fields from the other one, are described. In the first direction such problems as self-generated magnetic fields, implosion stability of plasma shells having a high aspect ratio, etc. are important for the Inertial Confinement Fusion (ICF) programs (e.g. as NIF), whereas different problems of current disruption phenomenon, plasma turbulence, mechanisms of generation of fast particles and neutrons in magnetized plasmas are of great interest for the large devices of the Magnetic Plasma Confinement--MPC (e.g. as ITER). In a sphere of the engineering problems of NFP it is shown that in particular the radiation material sciences have DPF as a very efficient tool for radiation tests of prospect materials and for improvement of their characteristics. In the field of broad-band current applications some results obtained in the fields of radiation material sciences, radiobiology, nuclear medicine, express Neutron Activation Analysis (including a single-shot interrogation of hidden illegal objects), dynamic non-destructive quality control, X-Ray microlithography and micromachining, and micro-radiography are presented. As the examples of the potential future applications it is proposed to use DPF as a powerful high-flux neutron source to generate very powerful pulses of neutrons in the nanosecond (ns) range of its duration for innovative experiments in nuclear physics, for the goals of radiation treatment of malignant tumors, for neutron tests of materials of the first wall, blankets and NFP device's constructions (with fluences up to 1 dpa per a year term), and ns pulses of fast electrons, neutrons and hard X-Rays for brachytherapy

  3. Calculation of DC Arc Plasma Torch Voltage- Current Characteristics Based on Steebeck Model

    International Nuclear Information System (INIS)

    Gnedenko, V.G.; Ivanov, A.A.; Pereslavtsev, A.V.; Tresviatsky, S.S.

    2006-01-01

    The work is devoted to the problem of the determination of plasma torches parameters and power sources parameters (working voltage and current of plasma torch) at the predesigning stage. The sequence of calculation of voltage-current characteristics of DC arc plasma torch is proposed. It is shown that the simple Steenbeck model of arc discharge in cylindrical channel makes it possible to carry out this calculation. The results of the calculation are confirmed by the experiments

  4. Chaotic behavior of current-carrying plasmas in external periodic oscillations

    Energy Technology Data Exchange (ETDEWEB)

    Ohno, Noriyasu; Tanaka, Masayoshi; Komori, Akio; Kawai, Yoshinobu

    1989-01-01

    A set of cascading bifurcations and a chaotic state in the presence of an external periodic oscillation are experimentally investigated in a current-carrying plasma. The measured bifurcation sequence leading to chaos, which is controlled by changing plasma densities and the frequencies of external oscillations, is in qualitative agreement with a theory which describes anharmonic systems in periodic fields. (author).

  5. Simulation of lower hybrid current drive in enhanced reversed shear plasmas in the tokamak fusion test reactor using the lower hybrid simulation code

    International Nuclear Information System (INIS)

    Kaita, R.; Bernabei, S.; Budny, R.

    1996-01-01

    The Enhanced Reversed Shear (ERS) mode has already shown great potential for improving the performance of the Tokamak Fusion Test Reactor (TFTR) and other devices. Sustaining the ERS, however, remains an outstanding problem. Lower hybrid (LH) current drive is a possible method for modifying the current profile and controlling its time evolution. To predict its effectiveness in TFTR, the Lower Hybrid Simulation Code (LSC) model is used in the TRANSP code and the Tokamak Simulation Code (TSC). Among the results from the simulations are the following. (1) Single-pass absorption is expected in TFTR ERS plasmas. The simulations show that the LH current follows isotherms of the electron temperature. The ability to control the location of the minimum in the q profile (q min ) has been demonstrated by varying the phase velocity of the launched LH waves and observing the change in the damping location. (2) LH current drive can been used to sustain the q min location. The tendency of qmin to drift inward, as the inductive current diffuses during the formation phase of the reversed shear discharge, is prevented by the LH current driven at a fixed radial location. If this results in an expanded plasma volume with improved confinement as high power neutral beam injection is applied, the high bootstrap currents induced during this phase can then maintain the larger qmin radius. (3) There should be no LH wave damping on energetic beam particles. The values of perpendicular index of refraction in the calculations never exceed about 20, while ions at TFR injection energies are resonant with waves having values closer to 100. Other issues being addressed in the study include the LH current drive efficiency in the presence of high bootstrap currents, and the effect of fast electron diffusion on LH current localization

  6. Start-up of plasma current by electron Bernstein wave

    International Nuclear Information System (INIS)

    Maekawa, Takashi; Tanaka, Hitoshi; Uehide, Masaki

    2009-01-01

    Electron cyclotron current drive by electron Bernstein (EB) waves for the start-up and ramp-up of toroidal plasma current with no central solenoid in tokamaks is discussed. It is shown that high N// EB waves have ability to ramp-up the current against the counter voltage from self-induction, where N// is the parallel refractive index to the magnetic field, and they are especially suitable for initial current start-up phase where the bulk electron temperature is low enough to ensure high N// EB waves. (author)

  7. Flexible time-varying filter banks

    Science.gov (United States)

    Tuncer, Temel E.; Nguyen, Truong Q.

    1993-09-01

    Linear phase maximally flat FIR Butterworth filter approximations are discussed and a new filter design method is introduced. This variable cutoff filter design method uses the cosine modulated versions of a prototype filter. The design procedure is simple and different variants of this procedure can be used to obtain close to optimum linear phase filters. Using this method, flexible time-varying filter banks with good reconstruction error are introduced. These types of oversampled filter banks have small magnitude error which can be easily controlled by the appropriate choice of modulation frequency. This error can be further decreased by magnitude equalization without increasing the computational complexity considerably. Two dimensional design examples are also given.

  8. Discrete-Time LPV Current Control of an Induction Motor

    DEFF Research Database (Denmark)

    Bendtsen, Jan Dimon; Trangbæk, Klaus

    2003-01-01

    In this paper we apply a new method for gain-scheduled output feedback control of nonlinear systems to current control of an induction motor. The method relies on recently developed controller synthesis results for linear parameter-varying (LPV) systems, where the controller synthesis is formulated...... as a set of linear matrix inequalities with full-block multipliers. A standard nonlinear model of the motor is constructed and written on LPV form. We then show that, although originally developed in continuous time, the controller synthesis results can be applied to a discrete-time model as well without...... further complications. The synthesis method is applied to the model, yielding an LPV discrete-time controller. Finally, the efficiency of the control scheme is validated via simulations as well as on the actual induction motor, both in open-loop current control and when an outer speed control loop...

  9. External kinks in plasmas with helical boundary deformation and net toroidal current

    Energy Technology Data Exchange (ETDEWEB)

    Ardelea, A. [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP)

    1997-11-01

    The investigation of the global ideal magnetohydrodynamic (MHD) stability of plasmas with helical boundary shape and nonvanishing toroidal plasma current constitutes the principal aim of this work. Global external modes with small values of m,n (typically n = 1,2,3 and m = n+1) are studied, where m and n are the poloidal and toroidal mode numbers, respectively. The first and main part of the work concentrates on fixed boundary equilibria generated by systematically varying parameters such as the type and the magnitude of the boundary deformation, the number of equilibrium field periods N{sub per}, the aspect ratio, the toroidal current density profile, {beta} and the pressure profile. Due to the periodicity of the equilibrium, couplings between Fourier perturbation components with different toroidal mode numbers n occur and lead to the apparition of families of modes. The study of a particular (m,n) mode has to take into account all (m{sub l}, n{sub l}) perturbation components with n{sub 1} belonging to the same family as n. The stability analysis is carried out in the parameter region where the inverse rotational transform (the safety factor in the traditional tokamak notation) q{<=}2.0 and {beta}{<=}2%. A particular property of the configurations investigated is that equilibrium Fourier components (m{sub e}, N{sub per}n{sub e}) which are involved in the couplings between the (m,n) mode studied and the (m{sub k},n{sub k}) perturbation components with m{sub k}>n{sub k}>n that exhibit resonances in the q>1 region are very small. As a consequence, the contributions of the (m,n)x(m{sub k},n{sub k}) couplings to the potential energy are very weak. It is shown that a helical boundary deformation can stabilize the n=1,2,3 external modes; if {delta} is a measure of the plasma boundary deformation, then windows of stability [{delta}{sub min}, {delta}{sub max}] may exist for a large variety of equilibrium parameters. (author) figs., tabs., 44 refs.

  10. ICRF Mode Conversion Current Drive for Plasma Stability Control in Tokamaks

    International Nuclear Information System (INIS)

    Grekov, D.; Kock, R.; Lyssoivan, A.; Noterdaeme, J. M.; Ongena, J.

    2007-01-01

    There is a substantial incentive for the International Thermonuclear Experimental Reactor (ITER) to operate at the highest attainable beta (plasma pressure normalized to magnetic pressure), a point emphasized by requirements of attractive economics in a reactor. Recent experiments aiming at stationary high beta discharges in tokamak plasmas have shown that maximum achievable beta value is often limited by the onset of instabilities at rational magnetic surfaces (neoclassical tearing modes). So, methods of effective control of these instabilities have to be developed. One possible way for neoclassical tearing modes control is an external current drive in the island to locally replace the missing bootstrap current and thus to suppress the instability. Also, a significant control of the sawtooth behaviour was demonstrated when the magnetic shear was modified by driven current at the magnetic surface where safety factor equals to 1. In the ion cyclotron range of frequencies (ICRF), the mode conversion regime can be used to drive the local external current near the position of the fast-to-slow wave conversion layer, thus providing an efficient means of plasma stability control. The slow wave energy is effectively absorbed in the vicinity of mode conversion layer by electrons with such parallel to confining magnetic field velocities that the Landau resonance condition is satisfied. For parameters of present day tokamaks and for ITER parameters the slow wave phase velocity is rather low, so the large ratio of momentum to energy content would yield high current drive efficiency. In order to achieve noticeable current drive effect, it is necessary to create asymmetry in the ICRF power absorption between top and bottom parts of the plasma minor cross-section. Such asymmetric electron heating may be realized using: - shifted from the torus midplane ICRF antenna in TEXTOR tokamak; - plasma displacement in vertical direction that is feasible in ASDEX-Upgrade; - the

  11. Tail anisotropy instability during plasma current rise by lower-hybrid waves in a tokamak

    International Nuclear Information System (INIS)

    Yamagiwa, Mitsuru.

    1986-01-01

    Tail anisotropy instability during lower-hybrid current rise is investigated. Tail formation by lower-hybrid waves is studied by using a Fokker-Planck equation combined with the return field and the rf associated terms. Quasi-linear relaxation of the electron tail distribution under the influence of the plasma waves excited due to the instability is examined. It is found that the instability condition is related to the strength of the parallel diffusion by lower-hybrid waves and the ratio of the electron cyclotron frequency to the electron plasma frequency. The time scale between the instability spikes and the suppression of the instability by electron cyclotron heating are also discussed. (author)

  12. Fivefold confinement time increase in the Madison Symmetric Torus using inductive poloidal current drive

    International Nuclear Information System (INIS)

    Stoneking, M.R.; Lanier, N.E.; Prager, S.C.; Sarff, J.S.; Sinitsyn, D.

    1997-01-01

    Current profile control is employed in the Madison Symmetric Torus [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] reversed field pinch to reduce the magnetic fluctuations responsible for anomalous transport. An inductive poloidal electric-field pulse is applied in the sense to flatten the parallel current profile, reducing the dynamo fluctuation amplitude required to sustain the equilibrium. This technique demonstrates a substantial reduction in fluctuation amplitude (as much as 50%), and improvement in energy confinement (from 1 to 5 ms); a record low fluctuation (0.8%) and record high temperature (615 eV) for this device were observed simultaneously during current drive experiments. Plasma beta increases by 50% and the Ohmic input power is three times lower. Particle confinement improves and plasma impurity contamination is reduced. The results of the transient current drive experiments provide motivation for continuing development of steady-state current profile control strategies for the reversed field pinch. copyright 1997 American Institute of Physics

  13. Lower hybrid current drive in tokamak plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Ushigusa, Kenkichi [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment

    1999-03-01

    Past ten years progress on Lower Hybrid Current Drive (LHCD) experiments have demonstrated the largest non-inductive current (3.6 MA, JT-60U), the longest current sustainment (2 hours, TRIAM-1M), non-inductive current drive at the highest density (n-bar{sub e} - 10{sup 20}m{sup -3}, ALCATOR-C) and the highest current drive efficiency ({eta}{sub CD} = 3.5x10{sup 19} m{sup -2}A/W, JT-60). These results indicate that LHCD is one of the most promising methods to drive non-inductive current in the present tokamak plasmas. This paper presents recent experimental results on LHCD experiments. Basic theories of LH waves, the wave propagation and the current drive are briefly summarized. The main part of this paper describes several important results and their physical pictures on recent LHCD experiments; 1) the experimental set-up, 2) the current drive efficiency, 3) the control of current profile and MHD activities, 4) the global energy confinement, 5) the global power flow, 6) fast electron behavior, 7) interaction between LH waves and thermal/fast ions, 8) combination with other CD method. (author)

  14. Development of real-time plasma analysis and control algorithms for the TCV tokamak using SIMULINK

    International Nuclear Information System (INIS)

    Felici, F.; Le, H.B.; Paley, J.I.; Duval, B.P.; Coda, S.; Moret, J.-M.; Bortolon, A.; Federspiel, L.; Goodman, T.P.; Hommen, G.; Karpushov, A.; Piras, F.; Pitzschke, A.; Romero, J.; Sevillano, G.; Sauter, O.; Vijvers, W.

    2014-01-01

    Highlights: • A new digital control system for the TCV tokamak has been commissioned. • The system is entirely programmable by SIMULINK, allowing rapid algorithm development. • Different control system nodes can run different algorithms at varying sampling times. • The previous control system functions have been emulated and improved. • New capabilities include MHD control, profile control, equilibrium reconstruction. - Abstract: One of the key features of the new digital plasma control system installed on the TCV tokamak is the possibility to rapidly design, test and deploy real-time algorithms. With this flexibility the new control system has been used for a large number of new experiments which exploit TCV's powerful actuators consisting of 16 individually controllable poloidal field coils and 7 real-time steerable electron cyclotron (EC) launchers. The system has been used for various applications, ranging from event-based real-time MHD control to real-time current diffusion simulations. These advances have propelled real-time control to one of the cornerstones of the TCV experimental program. Use of the SIMULINK graphical programming language to directly program the control system has greatly facilitated algorithm development and allowed a multitude of different algorithms to be deployed in a short time. This paper will give an overview of the developed algorithms and their application in physics experiments

  15. Frequency variations of gravity waves interacting with a time-varying tide

    Energy Technology Data Exchange (ETDEWEB)

    Huang, C.M.; Zhang, S.D.; Yi, F.; Huang, K.M.; Gan, Q.; Gong, Y. [Wuhan Univ., Hubei (China). School of Electronic Information; Ministry of Education, Wuhan, Hubei (China). Key Lab. of Geospace Environment and Geodesy; State Observatory for Atmospheric Remote Sensing, Wuhan, Hubei (China); Zhang, Y.H. [Nanjing Univ. of Information Science and Technology (China). College of Hydrometeorolgy

    2013-11-01

    Using a nonlinear, 2-D time-dependent numerical model, we simulate the propagation of gravity waves (GWs) in a time-varying tide. Our simulations show that when aGW packet propagates in a time-varying tidal-wind environment, not only its intrinsic frequency but also its ground-based frequency would change significantly. The tidal horizontal-wind acceleration dominates the GW frequency variation. Positive (negative) accelerations induce frequency increases (decreases) with time. More interestingly, tidal-wind acceleration near the critical layers always causes the GW frequency to increase, which may partially explain the observations that high-frequency GW components are more dominant in the middle and upper atmosphere than in the lower atmosphere. The combination of the increased ground-based frequency of propagating GWs in a time-varying tidal-wind field and the transient nature of the critical layer induced by a time-varying tidal zonal wind creates favorable conditions for GWs to penetrate their originally expected critical layers. Consequently, GWs have an impact on the background atmosphere at much higher altitudes than expected, which indicates that the dynamical effects of tidal-GW interactions are more complicated than usually taken into account by GW parameterizations in global models.

  16. Expansion of a multicomponent current-carrying plasma jet into vacuum

    International Nuclear Information System (INIS)

    Krasov, V. I.; Paperny, V. L.

    2017-01-01

    An expression for the ion−ion coupling in a multicomponent plasma jet is derived for an arbitrary ratio between the thermal and relative velocities of the components. The obtained expression is used to solve the problem on the expansion of a current-carrying plasma microjet emitted from the cathode surface into vacuum. Two types of plasmas with two ion components are analyzed: (i) plasma in which the ion components of equal masses are in the charge states Z 1 = +1 and Z 2 = +2 and (ii) plasma with ions in equal charge states but with the mass ratio m 1 /m 2 = 2. It is shown that, for such plasmas, the difference between the velocities of the plasma components remains substantial (about 10% of the average jet velocity in case (i) and 15% in case (ii)) at distances of several centimeters from the emission center, where it can be measured experimentally, provided that its initial value at the emitting cathode surface exceeds a certain threshold. This effect is investigated as a function of the mass ratio and charge states of the ion components.

  17. Nonlinear localized dust acoustic waves in a charge varying dusty plasma with nonthermal ions

    International Nuclear Information System (INIS)

    Tribeche, Mouloud; Amour, Rabia

    2007-01-01

    A numerical investigation is presented to show the existence, formation, and possible realization of large-amplitude dust acoustic (DA) solitary waves in a charge varying dusty plasma with nonthermal ions. These nonlinear localized structures are self-consistent solutions of the collisionless Vlasov equation with a population of fast particles. The spatial patterns of the variable charge DA solitary wave are significantly modified by the nonthermal effects. The results complement and provide new insights into previously published results on this problem

  18. Current Density and Plasma Displacement Near Perturbed Rational Surface

    International Nuclear Information System (INIS)

    Boozer, A.H.; Pomphrey, N.

    2010-01-01

    The current density in the vicinity of a rational surface of a force-free magnetic field subjected to an ideal perturbation is shown to be the sum of both a smooth and a delta-function distribution, which give comparable currents. The maximum perturbation to the smooth current density is comparable to a typical equilibrium current density and the width of the layer in which the current flows is shown to be proportional to the perturbation amplitude. In the standard linearized theory, the plasma displacement has an unphysical jump across the rational surface, but the full theory gives a continuous displacement.

  19. Effect of laser induced plasma ignition timing and location on Diesel spray combustion

    International Nuclear Information System (INIS)

    Pastor, José V.; García-Oliver, José M.; García, Antonio; Pinotti, Mattia

    2017-01-01

    Highlights: • Laser plasma ignition is applied to a direct injection Diesel spray, compared with auto-ignition. • Critical local fuel/air ratio for LIP provoked ignition is obtained. • The LIP system is able to stabilize Diesel combustion compared to auto-ignition cases. • Varying LIP position along spray axis directly affects Ignition-delay. • Premixed combustion is reduced both by varying position and delay of the LIP ignition system. - Abstract: An experimental study about the influence of the local conditions at the ignition location on combustion development of a direct injection spray is carried out in an optical engine. A laser induced plasma ignition system has been used to force the spray ignition, allowing comparison of combustion’s evolution and stability with the case of conventional autoignition on the Diesel fuel in terms of ignition delay, rate of heat release, spray penetration and soot location evolution. The local equivalence ratio variation along the spray axis during the injection process was determined with a 1D spray model, previously calibrated and validated. Upper equivalence ratios limits for the ignition event of a direct injected Diesel spray, both in terms of ignition success possibilities and stability of the phenomena, could been determined thanks to application of the laser plasma ignition system. In all laser plasma induced ignition cases, heat release was found to be higher than for the autoignition reference cases, and it was found to be linked to a decrease of ignition delay, with the premixed peak in the rate of heat release curve progressively disappearing as the ignition delay time gets shorter. Ignition delay has been analyzed as a function of the laser position, too. It was found that ignition delay increases for plasma positions closer to the nozzle, indicating that the amount of energy introduced by the laser induced plasma is not the only parameter affecting combustion initiation, but local equivalence ratio

  20. Modeling polar cap F-region patches using time varying convection

    International Nuclear Information System (INIS)

    Sojka, J.J.; Bowline, M.D.; Schunk, R.W.; Decker, D.T.; Valladares, C.E.; Sheehan, R.; Anderson, D.N.; Heelis, R.A.

    1993-01-01

    Here the authors present the results of computerized simulations of the polar cap regions which were able to model the formation of polar cap patches. They used the Utah State University Time-Dependent Ionospheric Model (TDIM) and the Phillips Laboratory (PL) F-region models in this work. By allowing a time varying magnetospheric electric field in the models, they were able to generate the patches. This time varying field generates a convection in the ionosphere. This convection is similar to convective changes observed in the ionosphere at times of southward pointing interplanetary magnetic field, due to changes in the B y component of the IMF

  1. Computing Conditional VaR using Time-varying CopulasComputing Conditional VaR using Time-varying Copulas

    Directory of Open Access Journals (Sweden)

    Beatriz Vaz de Melo Mendes

    2005-12-01

    Full Text Available It is now widespread the use of Value-at-Risk (VaR as a canonical measure at risk. Most accurate VaR measures make use of some volatility model such as GARCH-type models. However, the pattern of volatility dynamic of a portfolio follows from the (univariate behavior of the risk assets, as well as from the type and strength of the associations among them. Moreover, the dependence structure among the components may change conditionally t past observations. Some papers have attempted to model this characteristic by assuming a multivariate GARCH model, or by considering the conditional correlation coefficient, or by incorporating some possibility for switches in regimes. In this paper we address this problem using time-varying copulas. Our modeling strategy allows for the margins to follow some FIGARCH type model while the copula dependence structure changes over time.

  2. The effect of plasma parameter on the bootstrap current of fast ions in neutral beam injection

    International Nuclear Information System (INIS)

    Huang Qianhong; Gong Xueyu; Cao Jinjia; Yang Lei

    2014-01-01

    The effect of plasma parameters on the distribution of net current density of fast ions produced by neutral beam injection is investigated in a large-aspect-ratio Tokamak with circular cross-section under specific parameters. Numerical results show that the value of net current density increases with the temperature of plasma increasing and decreases with the density of plasma increasing. The value of net current density is weakly affected by the effective charge number, but the peak of net current density moves towards edge plasma with effective charge number increasing. (authors)

  3. Linear MHD stability analysis of post-disruption plasmas in ITER

    Energy Technology Data Exchange (ETDEWEB)

    Aleynikova, K., E-mail: ksenia.aleynikova@gmail.com [EURATOM Association, Max-Planck-Institut für Plasmaphysik (Germany); Huijsmans, G. T. A. [ITER Organization (France); Aleynikov, P. [EURATOM Association, Max-Planck-Institut für Plasmaphysik (Germany)

    2016-05-15

    Most of the plasma current can be replaced by a runaway electron (RE) current during plasma disruptions in ITER. In this case the post-disruption plasma current profile is likely to be more peaked than the pre-disruption profile. The MHD activity of such plasma will affect the runaway electron generation and confinement and the dynamics of the plasma position evolution (Vertical Displacement Event), limiting the timeframe for runaway electrons and disruption mitigation. In the present paper, we evaluate the influence of the possible RE seed current parameters on the onset of the MHD instabilities. By varying the RE seed current profile, we search for subsequent plasma evolutions with the highest and the lowest MHD activity. This information can be applied to a development of desirable ITER disruption scenario.

  4. Preliminary investigation on the use of low current pulsed power Z-pinch plasma devices for the study of early stage plasma instabilities

    Science.gov (United States)

    Kaselouris, E.; Dimitriou, V.; Fitilis, I.; Skoulakis, A.; Koundourakis, G.; Clark, E. L.; Chatzakis, J.; Bakarezos, Μ; Nikolos, I. K.; Papadogiannis, N. A.; Tatarakis, M.

    2018-01-01

    This article addresses key features for the implementation of low current pulsed power plasma devices for the study of matter dynamics from the solid to the plasma phase. The renewed interest in such low current plasma devices lies in the need to investigate methods for the mitigation of prompt seeding mechanisms for the generation of plasma instabilities. The low current when driven into thick wires (skin effect mode) allows for the simultaneous existence of all phases of matter from solid to plasma. Such studies are important for the concept of inertial confinement fusion where the mitigation of the instability seeding mechanisms arising from the very early moments within the target’s heating is of crucial importance. Similarly, in the magnetized liner inertial fusion concept it is an open question as to how much surface non-uniformity correlates with the magneto-Rayleigh-Taylor instability, which develops during the implosion. This study presents experimental and simulation results, which demonstrate that the use of low current pulsed power devices in conjunction with appropriate diagnostics can be important for studying seeding mechanisms for the imminent generation of plasma instabilities in future research.

  5. H-mode access during plasma current ramp-up in TCV

    International Nuclear Information System (INIS)

    Martin, Y.; Behn, R.; Furno, I.; Labit, B.; Reimerdes, H.

    2014-01-01

    A recent TCV experiment has investigated the dependence of the L–H transition threshold power on the plasma current ramp-rate and the X-point height above the divertor target, which both have previously been seen to affect the transition behaviour. Systematic scans in ohmically heated plasmas do not show any dependence on the plasma current ramp-up rate. In contrast, the threshold power is found to increase by a factor of two while the X-point is moved from about 10 cm up to 35 cm above the vessel floor. However, further increase, up to 60 cm, does not lead to any further increase of the required power. The Fundamenski et al model is tested against the measurements. Estimates of the Wagner number (Wa) at L–H transitions are generally close to unity, in accordance with the model. In contrast, estimates of Wa before the L–H transition, i.e. in L-mode, do not show the expected evolution towards unity. (paper)

  6. Integrated modeling of plasma ramp-up in DIII-D ITER-like and high bootstrap current scenario discharges

    Science.gov (United States)

    Wu, M. Q.; Pan, C. K.; Chan, V. S.; Li, G. Q.; Garofalo, A. M.; Jian, X.; Liu, L.; Ren, Q. L.; Chen, J. L.; Gao, X.; Gong, X. Z.; Ding, S. Y.; Qian, J. P.; Cfetr Physics Team

    2018-04-01

    Time-dependent integrated modeling of DIII-D ITER-like and high bootstrap current plasma ramp-up discharges has been performed with the equilibrium code EFIT, and the transport codes TGYRO and ONETWO. Electron and ion temperature profiles are simulated by TGYRO with the TGLF (SAT0 or VX model) turbulent and NEO neoclassical transport models. The VX model is a new empirical extension of the TGLF turbulent model [Jian et al., Nucl. Fusion 58, 016011 (2018)], which captures the physics of multi-scale interaction between low-k and high-k turbulence from nonlinear gyro-kinetic simulation. This model is demonstrated to accurately model low Ip discharges from the EAST tokamak. Time evolution of the plasma current density profile is simulated by ONETWO with the experimental current ramp-up rate. The general trend of the predicted evolution of the current density profile is consistent with that obtained from the equilibrium reconstruction with Motional Stark effect constraints. The predicted evolution of βN , li , and βP also agrees well with the experiments. For the ITER-like cases, the predicted electron and ion temperature profiles using TGLF_Sat0 agree closely with the experimental measured profiles, and are demonstrably better than other proposed transport models. For the high bootstrap current case, the predicted electron and ion temperature profiles perform better in the VX model. It is found that the SAT0 model works well at high IP (>0.76 MA) while the VX model covers a wider range of plasma current ( IP > 0.6 MA). The results reported in this paper suggest that the developed integrated modeling could be a candidate for ITER and CFETR ramp-up engineering design modeling.

  7. Alternating current electrical properties of Argon plasma treated jute

    Directory of Open Access Journals (Sweden)

    Md. Masroor Anwer

    2012-09-01

    Full Text Available Low temperature plasma (LTP treatment, a kind of environment friendly surface modification technique, was applied to biodegradable and environment friendly jute fibre with the use of nonpolymerizing gas, namely argon, at various discharge power levels and exposure times with a definite flow rate. Scanning electron microscopy (SEM microphotographs reveal that the roughness of the fibre surfaces increases with the increase of discharge power and exposure time. This is caused due to the bombardment of high energetic ions on the fibre surface and the fibres become sputtered. The capacitance and the electrical conductance of raw and LTP treated jute fibre were measured as a function of frequency at room temperature. The dielectric constant, conductivity, dielectric loss-tangent and the surface morphology of raw and LTP treated jute as a function of frequency were studied at room temperature. It was observed that for all the samples the dielectric constant almost constant at lower frequencies and then decreases gradually in the high frequency region. In addition, dielectric constant increases with the increase of plasma treatment time as well as discharge power. It is also observed for all the samples that the conductivity increases as the frequency increases with a lower slope in the low frequency region and with a higher slope in the higher frequency region. In addition, the conductivity decreases with the increase of plasma exposure time as well as discharge power. The conductivity increases with frequency due to the hopping mechanism of electrons. The dependence of the dielectric loss-tangent with frequency at different treatment times and discharge powers for all the jute samples show small relaxation peaks in the very low frequency region. The dielectric loss-tangent decreases with the increase of both plasma treatment time and discharge power. In addition, the relaxation peaks are shifted to the higher frequency region as the plasma treatment

  8. Noncircular plasma shape analysis in long-pulse current drive experiment in TRIAM-1M

    International Nuclear Information System (INIS)

    Minooka, Mayumi; Kawasaki, Shoji; Jotaki, Eriko; Moriyama, Shin-ichi; Nagao, Akihiro; Nakamura, Kazuo; Hiraki, Naoji; Nakamura, Yukio; Itoh, Satoshi

    1991-01-01

    Plasma cross section was noncircularized and the plasma shape was analyzed in order to study the characteristics of the plasma in long-pulse current drive experiments in high-field superconducting tokamak TRIAM-1M. Filament approximation method was adopted, since on-line processing by data processing computer is possible. The experiments of the noncircularization were carried out during 30-to 60-sec discharges. As a result, it became clear that D-shape plasma of elongation ratio 1.4 was maintained stably. By the analysis the internal inductance and poloidal beta were assessed, and so informations about the plasma current profile and internal pressure were obtained. (author)

  9. Transverse current at the periphery of the start plasma of the AMBAL-M open device

    International Nuclear Information System (INIS)

    Taskaev, S.Yu.

    1999-01-01

    Essential longitudinal electron current was experimentally detected earlier in a start plasma of AMBAL-M open trap and system. This paper studies the current at a plasma periphery and the process resulting in occurrence of transverse current, and determines the value of a transverse current in a transporting range. This study enables to determine that filling of a trap with a thin circular flow and formation of nonequilibrium distribution of a radial electrical field in a plasma by potentials of an electrode front gun are the indium peculiarities of the experiment ensuring essential transverse current [ru

  10. Modeling the Plasma Flow in the Inner Heliosheath with a Spatially Varying Compression Ratio

    Energy Technology Data Exchange (ETDEWEB)

    Nicolaou, G. [Swedish Institute of Space Physics, Kiruna (Sweden); Livadiotis, G. [Southwest Research Institute, San Antonio, Texas (United States)

    2017-03-20

    We examine a semi-analytical non-magnetic model of the termination shock location previously developed by Exarhos and Moussas. In their study, the plasma flow beyond the shock is considered incompressible and irrotational, thus the flow potential is analytically derived from the Laplace equation. Here we examine the characteristics of the downstream flow in the heliosheath in order to resolve several inconsistencies existing in the Exarhos and Moussas model. In particular, the model is modified in order to be consistent with the Rankine–Hugoniot jump conditions and the geometry of the termination shock. It is shown that a shock compression ratio varying along the latitude can lead to physically correct results. We describe the new model and present several simplified examples for a nearly spherical, strong termination shock. Under those simplifications, the upstream plasma is nearly adiabatic for large (∼100 AU) heliosheath thickness.

  11. Characteristics of cold atmospheric plasma source based on low-current pulsed discharge with coaxial electrodes

    Science.gov (United States)

    Bureyev, O. A.; Surkov, Yu S.; Spirina, A. V.

    2017-05-01

    This work investigates the characteristics of the gas discharge system used to create an atmospheric pressure plasma flow. The plasma jet design with a cylindrical graphite cathode and an anode rod located on the axis of the system allows to realize regularly reproducible spark breakdowns mode with a frequency ∼ 5 kHz and a duration ∼ 40 μs. The device generates a cold atmospheric plasma flame with 1 cm in diameter in the flow of various plasma forming gases including nitrogen and air at about 100 mA average discharge current. In the described construction the cathode spots of individual spark channels randomly move along the inner surface of the graphite electrode creating the secondary plasma stream time-average distributed throughout the whole exit aperture area after the decay of numerous filamentary discharge channels. The results of the spectral diagnostics of plasma in the discharge gap and in the stream coming out of the source are presented. Despite the low temperature of atoms and molecules in plasma stream the cathode spots operation with temperature of ∼ 4000 °C at a graphite electrode inside a discharge system enables to saturate the plasma by CN-radicals and atomic carbon in the case of using nitrogen as the working gas.

  12. Experimental observation of current generation by asymmetrical heating of ions in a tokamak plasma

    International Nuclear Information System (INIS)

    Gahl, J.; Ishihara, O.; Wong, K.L.; Kristiansen, M.; Hagler, M.

    1986-01-01

    The first experimental observation of current generation by asymmetrical heating of ions is reported. Ions were asymmetrically heated by a unidirectional fast Alfven wave launched by a slow wave antenna inside a tokamak. Current generation was detected by measuring the asymmetry of the toroidal plasma current with probes at the top and bottom of the toroidal plasma column

  13. Effects of varying levels of n-6:n-3 fatty acid ratio on plasma fatty acid ...

    African Journals Online (AJOL)

    This study investigated the effects of varying dietary levels of n-6:n-3 fatty acid ratio on plasma fatty acid composition and prostanoid synthesis in pregnant rats. Four groups consisting of seven rats per group of non pregnant rats were fed diets with either a very low n-6:n-3 ratio of 50% soybean oil (SBO): 50% cod liver oil ...

  14. Electromagnetic radiation in a time-varying background medium

    NARCIS (Netherlands)

    Budko, N.V.

    2009-01-01

    Analytical solutions are presented for the electromagnetic radiation by an arbitrary pulsed source into a homogeneous time-varying background medium. In the constant-impedance case an explicit radiation formula is obtained for the synchronous permittivity and permeability described by any positive

  15. Experimental observations of the tearing of an electron current sheet

    International Nuclear Information System (INIS)

    Gekelman, W.; Pfister, H.

    1988-01-01

    A neutral magnetic sheet, in which the current is carried mainly by the electrons, is set up in a laboratory plasma. By forcing the current through a thin slot, the ratio of the length to height t of the sheet may be varied; the current is observed to tear when tapprox. >30. The structure of the magnetic islands and their associated currents is fully three dimensional, although a linear two-dimensional theory gives a very good estimate of the tearing mode growth time. Tearing is accompanied by the generation of significant Hall currents, and magnetic disturbances are observed to propagate at the whistler wave speed

  16. Cross effects on electron-cyclotron and lower-hybrid current drive in tokamak plasmas

    International Nuclear Information System (INIS)

    Fidone, I.; Giruzzi, G.; Krivenski, V.; Mazzucato, E.; Ziebell, L.F.

    1986-11-01

    Electron cyclotron resonance current drive in a tokamak plasma in the presence of a lower hybrid tail is investigated using a 2D Fokker-Planck code. For an extraordinary mode at oblique propagation and down-shifted frequency it is shown that the efficiency of electron cyclotron current drive becomes, i) substantially greater than the corresponding efficiency of a Maxwellian plasma at the same bulk temperature, ii) equal or greater than that of the lower hybrid waves, iii) comparable with the efficiency of a Maxwellian plasma at much higher temperature. This enhancement results from a beneficial cross-effect of the two waves on the formation of the current carrying electron tail. (5 fig; 17 refs)

  17. Housing Cycles in Switzerland - A Time-Varying Approach

    OpenAIRE

    Drechsel, Dirk

    2015-01-01

    In light of the strong increase of house prices in Switzerland, we analyze the effects of mortgage rate shocks, changes in the interplay between housing demand and supply and GDP growth on house prices for the time period 1981- 2014. We employ Bayesian time-varying coefficients vector autoregressions to allow different monetary and immigration regimes over time. A number of structural changes, such as regulatory changes in the aftermath of the 1990s real estate crisis, the introduction of fre...

  18. A current profile model for magnetic analysis of the start-up phase of toroidal plasmas driven by electron cyclotron heating and current drive

    International Nuclear Information System (INIS)

    Yoshinaga, T.; Uchida, M.; Tanaka, H.; Maekawa, T.

    2007-01-01

    An estimation model of plasma current density distribution for the start-up phase of toroidal plasmas generated by electron cyclotron heating (ECH) in the low aspect ratio torus experiment device is presented. The model assumes a power law parabolic current profile having seven fitting parameters. Its position, extent and broadness (or steepness) are fitted by adjusting these parameters to the observed magnetic flux signals. The adequacy of the model has been examined and confirmed by comparisons of the reconstructed current profiles and the resultant poloidal flux surfaces with the plasma images at visible light range at various stages of start-up discharges, including both the initial open field phase, the subsequent closed field phase, the current decay phase after ECH is turned off and also by a current-profile limiting experiment. This method may be useful for the study of non-inductive start-up experiments by ECH, where there is no appropriate MHD constraint on the current distribution as that in the full tokamak discharge plasmas

  19. Alleviating Border Effects in Wavelet Transforms for Nonlinear Time-varying Signal Analysis

    Directory of Open Access Journals (Sweden)

    SU, H.

    2011-08-01

    Full Text Available Border effects are very common in many finite signals analysis and processing approaches using convolution operation. Alleviating the border effects that can occur in the processing of finite-length signals using wavelet transform is considered in this paper. Traditional methods for alleviating the border effects are suitable to compression or coding applications. We propose an algorithm based on Fourier series which is proved to be appropriate to the application of time-frequency analysis of nonlinear signals. Fourier series extension method preserves the time-varying characteristics of the signals. A modified signal duration expression for measuring the extent of border effects region is presented. The proposed algorithm is confirmed to be efficient to alleviate the border effects in comparison to the current methods through the numerical examples.

  20. Nonlinear time-series analysis of current signal in cathodic contact glow discharge electrolysis

    International Nuclear Information System (INIS)

    Allagui, Anis; Abdelkareem, Mohammad Ali; Rojas, Andrea Espinel; Bonny, Talal; Elwakil, Ahmed S.

    2016-01-01

    In the standard two-electrode configuration employed in electrolytic process, when the control dc voltage is brought to a critical value, the system undergoes a transition from conventional electrolysis to contact glow discharge electrolysis (CGDE), which has also been referred to as liquid-submerged micro-plasma, glow discharge plasma electrolysis, electrode effect, electrolytic plasma, etc. The light-emitting process is associated with the development of an irregular and erratic current time-series which has been arbitrarily labelled as “random,” and thus dissuaded further research in this direction. Here, we examine the current time-series signals measured in cathodic CGDE configuration in a concentrated KOH solution at different dc bias voltages greater than the critical voltage. We show that the signals are, in fact, not random according to the NIST SP. 800-22 test suite definition. We also demonstrate that post-processing low-pass filtered sequences requires less time than the native as-measured sequences, suggesting a superposition of low frequency chaotic fluctuations and high frequency behaviors (which may be produced by more than one possible source of entropy). Using an array of nonlinear time-series analyses for dynamical systems, i.e., the computation of largest Lyapunov exponents and correlation dimensions, and re-construction of phase portraits, we found that low-pass filtered datasets undergo a transition from quasi-periodic to chaotic to quasi-hyper-chaotic behavior, and back again to chaos when the voltage controlling-parameter is increased. The high frequency part of the signals is discussed in terms of highly nonlinear turbulent motion developed around the working electrode.

  1. Optimization and control of the plasma shape and current profile in noncircular cross-section tokamaks

    International Nuclear Information System (INIS)

    Moore, R.W.; Bernard, L.C.; Chan, V.S.; Davidson, R.H.; Dobrott, D.R.; Helton, F.J.; Miller, R.L.; Pfeiffer, W.; Waltz, R.E.; Wang, T.S.

    1980-06-01

    High-β equilibria which are stable to all ideal MHD modes are found by optimizing the plasma shape and current profile for doublets, up-down asymmetric dees, and symmetric dees. The ideal MHD stability of these equilibria for low toroidal mode number n is analyzed with a global MHD stability code, GATO. The stability to high-n modes is analyzed with a localized ballooning code, BLOON. The attainment of high β is facilitated by an automated optimization search on shape and current parameters. The equilibria are calculated with a free-boundary equilibrium code using coils appropriate for the Doublet III experimental device. The optimal equilibria are characterized by broad current profiles with values of β/sub poloidal/ approx. =1. Experimental realization of the shapes and current profiles giving the highest β limits is explored with a 1 1/2-D transport code, which simulates the time evolution of the 2-D MHD equilibrium while calculating consistent current profiles from a 1-D transport model. Transport simulations indicate that nearly optimal shapes may be obtained provided that the currents in the field-shaping coils are appropriately programmed and the plasma current profile is sufficiently broad. Obtaining broad current profiles is possible by current ramping, neutral beam heating, and electron cyclotron heating. With combinations of these techniques it is possible to approach the optimum β predicted by the MHD theory

  2. To the mechanism of modulated REB current increase during its propagation through plasma

    International Nuclear Information System (INIS)

    Kiselev, V.A.; Linnik, A.F.; Maslov, V.I.; Uskov, V.V.

    2002-01-01

    The mechanism of full current increase is investigated in this paper. This current arises at transporting of the short relativistic electron bunches in the plasma,formed by them at gas of large pressure. This phenomenon is determined by the electric field, arising at motion of the relativistic electron bunches, having an angular divergence, in the plasma

  3. The Storm Time Evolution of the Ionospheric Disturbance Plasma Drifts

    Science.gov (United States)

    Zhang, Ruilong; Liu, Libo; Le, Huijun; Chen, Yiding; Kuai, Jiawei

    2017-11-01

    In this paper, we use the C/NOFS and ROCSAT-1 satellites observations to analyze the storm time evolution of the disturbance plasma drifts in a 24 h local time scale during three magnetic storms driven by long-lasting southward IMF Bz. The disturbance plasma drifts during the three storms present some common features in the periods dominated by the disturbance dynamo. The newly formed disturbance plasma drifts are upward and westward at night, and downward and eastward during daytime. Further, the disturbance plasma drifts are gradually evolved to present significant local time shifts. The westward disturbance plasma drifts gradually migrate from nightside to dayside. Meanwhile, the dayside downward disturbance plasma drifts become enhanced and shift to later local time. The local time shifts in disturbance plasma drifts are suggested to be mainly attributed to the evolution of the disturbance winds. The strong disturbance winds arisen around midnight can constantly corotate to later local time. At dayside the westward and equatorward disturbance winds can drive the F region dynamo to produce the poleward and westward polarization electric fields (or the westward and downward disturbance drifts). The present results indicate that the disturbance winds corotated to later local time can affect the local time features of the disturbance dynamo electric field.

  4. Time varying, multivariate volume data reduction

    Energy Technology Data Exchange (ETDEWEB)

    Ahrens, James P [Los Alamos National Laboratory; Fout, Nathaniel [UC DAVIS; Ma, Kwan - Liu [UC DAVIS

    2010-01-01

    Large-scale supercomputing is revolutionizing the way science is conducted. A growing challenge, however, is understanding the massive quantities of data produced by large-scale simulations. The data, typically time-varying, multivariate, and volumetric, can occupy from hundreds of gigabytes to several terabytes of storage space. Transferring and processing volume data of such sizes is prohibitively expensive and resource intensive. Although it may not be possible to entirely alleviate these problems, data compression should be considered as part of a viable solution, especially when the primary means of data analysis is volume rendering. In this paper we present our study of multivariate compression, which exploits correlations among related variables, for volume rendering. Two configurations for multidimensional compression based on vector quantization are examined. We emphasize quality reconstruction and interactive rendering, which leads us to a solution using graphics hardware to perform on-the-fly decompression during rendering. In this paper we present a solution which addresses the need for data reduction in large supercomputing environments where data resulting from simulations occupies tremendous amounts of storage. Our solution employs a lossy encoding scheme to acrueve data reduction with several options in terms of rate-distortion behavior. We focus on encoding of multiple variables together, with optional compression in space and time. The compressed volumes can be rendered directly with commodity graphics cards at interactive frame rates and rendering quality similar to that of static volume renderers. Compression results using a multivariate time-varying data set indicate that encoding multiple variables results in acceptable performance in the case of spatial and temporal encoding as compared to independent compression of variables. The relative performance of spatial vs. temporal compression is data dependent, although temporal compression has the

  5. Real time determination and control of the plasma localisation and internal inductance in Tore Supra

    Energy Technology Data Exchange (ETDEWEB)

    Saint-Laurent, F. E-mail: stlauren@drfc.cad.cea.fr; Martin, G

    2001-10-01

    The study of long-duration high-power discharges need an efficient real time control of the plasma parameters, especially the plasma position when RF heating systems are used. On Tore Supra, recent improvements have been carried out (i) for the poloidal interpolation and the radial extrapolation of the magnetic measurements, (ii) for a better feedback matrix converting the radial errors of the plasma position to voltage values for the poloidal generators, and (iii) for a very fast solution to find the plasma parameters from the knowledge of its surface. The plasma edge localisation is now controlled with a precision better than 1 cm and controlled within a few millimetres uncertainty for several tenths of seconds. Moreover, for advanced tokamak scenarios, a precise real time determination of safety factor, poloidal beta, internal inductance, Shafranov shift as well as the online computation of the electron density and current density profiles are now available on Tore Supra. These quantities compare well with results from batch calculations using an equilibrium code. To fulfil the new requirements of plasma control for the CIEL project, a local control of the plasma edge position and curvature is planned for the near future.

  6. A Tentative Application Of Morphological Filters To Time-Varying Images

    Science.gov (United States)

    Billard, D.; Poquillon, B.

    1989-03-01

    In this paper, morphological filters, which are commonly used to process either 2D or multidimensional static images, are generalized to the analysis of time-varying image sequence. The introduction of the time dimension induces then interesting prop-erties when designing such spatio-temporal morphological filters. In particular, the specification of spatio-temporal structuring ele-ments (equivalent to time-varying spatial structuring elements) can be adjusted according to the temporal variations of the image sequences to be processed : this allows to derive specific morphological transforms to perform noise filtering or moving objects discrimination on dynamic images viewed by a non-stationary sensor. First, a brief introduction to the basic principles underlying morphological filters will be given. Then, a straightforward gener-alization of these principles to time-varying images will be pro-posed. This will lead us to define spatio-temporal opening and closing and to introduce some of their possible applications to process dynamic images. At last, preliminary results obtained us-ing a natural forward looking infrared (FUR) image sequence are presented.

  7. Characteristics of an elongated plasma column produced by magnetically coupled hollow cathode plasma source

    Science.gov (United States)

    Bhuva, M. P.; Karkari, S. K.; Kumar, Sunil

    2018-03-01

    An elongated plasma column in the presence of an axial magnetic field has been formed using a cylindrical hollow cathode (HC) and a constricted anode (CA). The plasma characteristics of the central line have been found to vary with the magnetic field strength and the axial distance from the source. It is believed that the primary electrons constituting the discharge current are steered by the axial magnetic field to undertake ionizing collisions along the plasma column. The current carrying electrons from the HC reach the anode by cross-field diffusion towards the central line. The above observation has been substantiated using a phenomenological model which links the observed characteristics of the source with the plasma column. The experimental results are found to be in qualitative agreement with the model.

  8. Physics-electrical hybrid model for real time impedance matching and remote plasma characterization in RF plasma sources.

    Science.gov (United States)

    Sudhir, Dass; Bandyopadhyay, M; Chakraborty, A

    2016-02-01

    Plasma characterization and impedance matching are an integral part of any radio frequency (RF) based plasma source. In long pulse operation, particularly in high power operation where plasma load may vary due to different reasons (e.g. pressure and power), online tuning of impedance matching circuit and remote plasma density estimation are very useful. In some cases, due to remote interfaces, radio activation and, due to maintenance issues, power probes are not allowed to be incorporated in the ion source design for plasma characterization. Therefore, for characterization and impedance matching, more remote schemes are envisaged. Two such schemes by the same authors are suggested in these regards, which are based on air core transformer model of inductive coupled plasma (ICP) [M. Bandyopadhyay et al., Nucl. Fusion 55, 033017 (2015); D. Sudhir et al., Rev. Sci. Instrum. 85, 013510 (2014)]. However, the influence of the RF field interaction with the plasma to determine its impedance, a physics code HELIC [D. Arnush, Phys. Plasmas 7, 3042 (2000)] is coupled with the transformer model. This model can be useful for both types of RF sources, i.e., ICP and helicon sources.

  9. HARDENING OF CRANE RAILS BY PLASMA DISCRETE-TIME SURFACE TREATMENT

    Directory of Open Access Journals (Sweden)

    S. S. Samotugin

    2017-01-01

    Full Text Available Crane wheels and rails are subjected to intensive wear in the process of operation. Therefore, improvement of these components’ performance can be considered a task of high importance. A promising direction in this regard is surface treatment by highly concentrated energy flows such as laser beams or plasma jets. This thesis suggests that the use of gradient plasma surface treatment can improve the performance of crane rails. A research was conducted, according to which hardened zones were deposited on crane rails under different treatment modes. Microhardness was measured both at the surface and in depth using custom-made microsections. The article includes the results of study of plasma surface hardening effects on wear resistance of crane rails. Change of plasma surface treatment parameters (current, plasma torch movement speed, argon gas flow rate allows for desired steel hardness and structure, while the choice of optimal location for hardened zones makes it possible to significantly improve wear resistance and crack resistance. As a result of plasma surface hardening, the fine-grained martensite structure is obtained with mainly lamellar morphology and higher hardness rate compared toinduction hardening or overlaying. Wear test of carbon steels revealed that plasma surfacing reduces abrasive wear rate compared to the irinitial state by 2 to 3 times. Enough sharp boundary between hardened and non-hardened portions has a positive effect on the performance of parts under dynamic loads, contributing to the inhibition of cracks during the transition from solid to a soft metal. For carbon and low alloy rail steels, the properties achieved by plasma surface hardening can effectively replace induction hardening or overlaying.The mode range for plasma surface treatment that allow sobtaining a surface layer with certain operating properties has been determined.

  10. Projected space-time and varying speed of light

    International Nuclear Information System (INIS)

    Iovane, G.; Bellucci, S.; Benedetto, E.

    2008-01-01

    In this paper starting from El Naschie's Cantorian space-time and our model of projected Universe, we consider its properties in connection with varying speed of light. A possible way-out of the related problem is provided by the Fantappie group approach

  11. Algebraic motion of vertically displacing plasmas

    Science.gov (United States)

    Pfefferlé, D.; Bhattacharjee, A.

    2018-02-01

    The vertical motion of a tokamak plasma is analytically modelled during its non-linear phase by a free-moving current-carrying rod inductively coupled to a set of fixed conducting wires or a cylindrical conducting shell. The solutions capture the leading term in a Taylor expansion of the Green's function for the interaction between the plasma column and the surrounding vacuum vessel. The plasma shape and profiles are assumed not to vary during the vertical drifting phase such that the plasma column behaves as a rigid body. In the limit of perfectly conducting structures, the plasma is prevented to come in contact with the wall due to steep effective potential barriers created by the induced Eddy currents. Resistivity in the wall allows the equilibrium point to drift towards the vessel on the slow timescale of flux penetration. The initial exponential motion of the plasma, understood as a resistive vertical instability, is succeeded by a non-linear "sinking" behaviour shown to be algebraic and decelerating. The acceleration of the plasma column often observed in experiments is thus concluded to originate from an early sharing of toroidal current between the core, the halo plasma, and the wall or from the thermal quench dynamics precipitating loss of plasma current.

  12. Design and implementation of multi-signal and time-varying neural reconstructions.

    Science.gov (United States)

    Nanda, Sumit; Chen, Hanbo; Das, Ravi; Bhattacharjee, Shatabdi; Cuntz, Hermann; Torben-Nielsen, Benjamin; Peng, Hanchuan; Cox, Daniel N; De Schutter, Erik; Ascoli, Giorgio A

    2018-01-23

    Several efficient procedures exist to digitally trace neuronal structure from light microscopy, and mature community resources have emerged to store, share, and analyze these datasets. In contrast, the quantification of intracellular distributions and morphological dynamics is not yet standardized. Current widespread descriptions of neuron morphology are static and inadequate for subcellular characterizations. We introduce a new file format to represent multichannel information as well as an open-source Vaa3D plugin to acquire this type of data. Next we define a novel data structure to capture morphological dynamics, and demonstrate its application to different time-lapse experiments. Importantly, we designed both innovations as judicious extensions of the classic SWC format, thus ensuring full back-compatibility with popular visualization and modeling tools. We then deploy the combined multichannel/time-varying reconstruction system on developing neurons in live Drosophila larvae by digitally tracing fluorescently labeled cytoskeletal components along with overall dendritic morphology as they changed over time. This same design is also suitable for quantifying dendritic calcium dynamics and tracking arbor-wide movement of any subcellular substrate of interest.

  13. An Explicit MOT-TD-VIE Solver for Time Varying Media

    KAUST Repository

    Sayed, Sadeed Bin; Ulku, Huseyin Arda; Bagci, Hakan

    2016-01-01

    An explicit marching on-in-time (MOT) scheme for solving the time domain electric field integral equation enforced on volumes with time varying dielectric permittivity is proposed. Unknowns of the integral equation and the constitutive relation, i

  14. Epidemic spreading in time-varying community networks.

    Science.gov (United States)

    Ren, Guangming; Wang, Xingyuan

    2014-06-01

    The spreading processes of many infectious diseases have comparable time scale as the network evolution. Here, we present a simple networks model with time-varying community structure, and investigate susceptible-infected-susceptible epidemic spreading processes in this model. By both theoretic analysis and numerical simulations, we show that the efficiency of epidemic spreading in this model depends intensively on the mobility rate q of the individuals among communities. We also find that there exists a mobility rate threshold qc. The epidemic will survive when q > qc and die when q epidemic spreading in complex networks with community structure.

  15. Time-varying Concurrent Risk of Extreme Droughts and Heatwaves in California

    Science.gov (United States)

    Sarhadi, A.; Diffenbaugh, N. S.; Ausin, M. C.

    2016-12-01

    Anthropogenic global warming has changed the nature and the risk of extreme climate phenomena such as droughts and heatwaves. The concurrent of these nature-changing climatic extremes may result in intensifying undesirable consequences in terms of human health and destructive effects in water resources. The present study assesses the risk of concurrent extreme droughts and heatwaves under dynamic nonstationary conditions arising from climate change in California. For doing so, a generalized fully Bayesian time-varying multivariate risk framework is proposed evolving through time under dynamic human-induced environment. In this methodology, an extreme, Bayesian, dynamic copula (Gumbel) is developed to model the time-varying dependence structure between the two different climate extremes. The time-varying extreme marginals are previously modeled using a Generalized Extreme Value (GEV) distribution. Bayesian Markov Chain Monte Carlo (MCMC) inference is integrated to estimate parameters of the nonstationary marginals and copula using a Gibbs sampling method. Modelled marginals and copula are then used to develop a fully Bayesian, time-varying joint return period concept for the estimation of concurrent risk. Here we argue that climate change has increased the chance of concurrent droughts and heatwaves over decades in California. It is also demonstrated that a time-varying multivariate perspective should be incorporated to assess realistic concurrent risk of the extremes for water resources planning and management in a changing climate in this area. The proposed generalized methodology can be applied for other stochastic nature-changing compound climate extremes that are under the influence of climate change.

  16. On the HL-1M tokamak plasma confinement time

    International Nuclear Information System (INIS)

    Qin Yunwen

    2001-01-01

    Emphasizing that the tokamak plasma confinement time is the plasma particle or thermal energy loss characteristic time, the relevant physical concept and HL-1M tokamak experimental data analyses are reviewed

  17. Expansion of a multicomponent current-carrying plasma jet into vacuum

    Energy Technology Data Exchange (ETDEWEB)

    Krasov, V. I.; Paperny, V. L., E-mail: paperny@math.isu.runnet.ru [Irkutsk State University (Russian Federation)

    2017-03-15

    An expression for the ion−ion coupling in a multicomponent plasma jet is derived for an arbitrary ratio between the thermal and relative velocities of the components. The obtained expression is used to solve the problem on the expansion of a current-carrying plasma microjet emitted from the cathode surface into vacuum. Two types of plasmas with two ion components are analyzed: (i) plasma in which the ion components of equal masses are in the charge states Z{sub 1}= +1 and Z{sub 2}= +2 and (ii) plasma with ions in equal charge states but with the mass ratio m{sub 1}/m{sub 2} = 2. It is shown that, for such plasmas, the difference between the velocities of the plasma components remains substantial (about 10% of the average jet velocity in case (i) and 15% in case (ii)) at distances of several centimeters from the emission center, where it can be measured experimentally, provided that its initial value at the emitting cathode surface exceeds a certain threshold. This effect is investigated as a function of the mass ratio and charge states of the ion components.

  18. On Current Drive and Wave Induced Bootstrap Current in Toroidal Plasmas

    International Nuclear Information System (INIS)

    Hellsten, T.; Johnson, T.

    2008-01-01

    A comprehensive treatment of wave-particle interactions in toroidal plasmas including collisional relaxation, applicable to heating or anomalous wave induced transport, has been obtained by using Monte Carlo operators satisfying quasi-neutrality. This approach enables a self-consistent treatment of wave-particle interactions applicable to the banana regime in the neoclassical theory. It allows an extension into a regime with large temperature and density gradients, losses and transport of particles by wave-particle interactions making the method applicable to transport barriers. It is found that at large gradients the relationship between radial electric field, parallel velocity, temperature and density gradient in the neoclassical theory is modified such that coefficient in front of the logarithmic ion temperature gradient, which in the standard neoclassical theory is small and counteracts the electric field caused by the density gradient, now changes sign and contributes to the built up of the radial electric field. The possibility to drive current by absorbing the waves on trapped particles has been studied and how the wave-particle interactions affect the bootstrap current. Two new current drive mechanisms are studied: current drive by wave induced bootstrap current and selective detrapping into passing orbits by directed waves.

  19. Characterisation Of The Beam Plasma In High Current, Low Energy Ion Beams For Implanters

    International Nuclear Information System (INIS)

    Fiala, J.; Armour, D. G.; Berg, J. A. van der; Holmes, A. J. T.; Goldberg, R. D.; Collart, E. H. J.

    2006-01-01

    The effective transport of high current, positive ion beams at low energies in ion implanters requires the a high level of space charge compensation. The self-induced or forced introduction of electrons is known to result in the creation of a so-called beam plasma through which the beam propagates. Despite the ability of beams at energies above about 3-5 keV to create their own neutralising plasmas and the development of highly effective, plasma based neutralising systems for low energy beams, very little is known about the nature of beam plasmas and how their characteristics and capabilities depend on beam current, beam energy and beamline pressure. These issues have been addressed in a detailed scanning Langmuir probe study of the plasmas created in beams passing through the post-analysis section of a commercial, high current ion implanter. Combined with Faraday cup measurements of the rate of loss of beam current in the same region due to charge exchange and scattering collisions, the probe data have provided a valuable insight into the nature of the slow ion and electron production and loss processes. Two distinct electron energy distribution functions are observed with electron temperatures ≥ 25 V and around 1 eV. The fast electrons observed must be produced in their energetic state. By studying the properties of the beam plasma as a function of the beam and beamline parameters, information on the ways in which the plasma and the beam interact to reduce beam blow-up and retain a stable plasma has been obtained

  20. Electricity Futures Prices : Time Varying Sensitivity to Fundamentals

    NARCIS (Netherlands)

    S-E. Fleten (Stein-Erik); R. Huisman (Ronald); M. Kilic (Mehtap); H.P.G. Pennings (Enrico); S. Westgaard (Sjur)

    2014-01-01

    textabstractThis paper provides insight in the time-varying relation between electricity futures prices and fundamentals in the form of prices of contracts for fossil fuels. As supply curves are not constant and different producers have different marginal costs of production, we argue that the

  1. Emissions from heavy current carrying high density plasma and their diagnostics

    International Nuclear Information System (INIS)

    Hirano, Katsumi

    1987-06-01

    Workshop on ''Emissions from heavy current carrying high density plasma and diagnostics'' was held at Institute of Plasma Physics, Nagoya University on 3. and 4. December 1986 under a collaborating research Program. The workshop was attended by 43 researchers from 19 labolatories. A total of 22 papers were submitted and are presented in these proceedings. The largest group of papers was that on soft X-ray emission. It seems this topic is a foremost interest for groups which engaged in research of the Z pinch and the plasma focus. A variety of problems in pinched dense plasmas, namely spectroscopy, diagnostics, pinch dynamics, and related engineering aspects were also discussed. (author)

  2. Discrete-Time Sliding-Mode Control of Uncertain Systems with Time-Varying Delays via Descriptor Approach

    Directory of Open Access Journals (Sweden)

    Maode Yan

    2008-01-01

    Full Text Available This paper considers the problem of robust discrete-time sliding-mode control (DT-SMC design for a class of uncertain linear systems with time-varying delays. By applying a descriptor model transformation and Moon's inequality for bounding cross terms, a delay-dependent sufficient condition for the existence of stable sliding surface is given in terms of linear matrix inequalities (LMIs. Based on this existence condition, the synthesized sliding mode controller can guarantee the sliding-mode reaching condition of the specified discrete-time sliding surface for all admissible uncertainties and time-varying delays. An illustrative example verifies the effectiveness of the proposed method.

  3. Current-drive and plasma formation experiments on the Versator-II tokamak using lower-hybrid and electron-cyclotron waves

    International Nuclear Information System (INIS)

    Colborn, J.A.

    1992-01-01

    During lower-hybrid current-driven (LHCD) tokamak discharges with thermal electron temperature T e ∼ 150 eV, a two-parallel-temperature tail is observed in the electron distribution function. The cold tail extends to parallel energy E parallel ∼ 4.5 keV with temperature T cold tail ∼ 1.5 keV, and the hot tail extends to E parallel > 150 keV with T hot tail > 40 keV. Fokker-Planck computer simulations suggest the cold tail is created by low power, high-N parallel sidelobes in the lower-hybrid antenna spectrum, and that these sidelobes bridge the spectral gap, enabling current drive on small tokamaks such as Versator. During plasma-formation experiments using 28 GHz electroncyclotron (EC) waves, the plasma is born near the EC layer, then moves toward the upper-hybrid (UH) layer within 100-200μs. Wave power is detected in the plasma with frequency f = 300 MHz. Measured turbulent plasma fluctuations are correlated with decay-wave amplitude. Electron-cyclotron current-drive (ECCD) is observed with loop voltage V loop ≤ 0 and fully sustained plasma current I p approx-lt 15 kA at densities up to [n e ] = 2 x 10 12 cm -3 . The efficiency falls rapidly to zero as the density is raised, suggesting the ECCD depends on low collisonality. The EC waves enhance magnetic turbulence in the frequency range 50 kHz approx-lt f approx-lt 400 kHz by up to an order of magnitude. The time-of-arrival of the turbulence to probes at the plasma boundary is longer when the EC layer is farther from the probes

  4. Current limitation and formation of plasma double layers in a non-uniform magnetic field

    International Nuclear Information System (INIS)

    Plamondon, R.; Teichmann, J.; Torven, S.

    1986-07-01

    Formation of strong double layers has been observed experimentally in a magnetised plasma column maintained by a plasma source. The magnetic field is approximately axially homogenous except in a region at the anode where the electric current flows into a magnetic mirror. The double layer has a stationary position only in the region of non-uniform magnetic field or at the aperture separating the source and the plasma column. It is characterized by a negative differential resistance in the current-voltage characteristic of the device. The parameter space,where the double layer exists, has been studied as well as the corresponding potential profiles and fluctuation spectra. The electric current and the axial electric field are oppositely directed between the plasma source and a potential minimum which is formed in the region of inhomogeneous magnetic field. Electron reflection by the resulting potential barrier is found to be an important current limitation mechanism. (authors)

  5. Influence of the laser parameters on the space and time characteristics of an aluminum laser-induced plasma

    International Nuclear Information System (INIS)

    Barthelemy, O.; Margot, J.; Chaker, M.; Sabsabi, M.; Vidal, F.; Johnston, T.W.; Laville, S.; Le Drogoff, B.

    2005-01-01

    In this work, an aluminum laser plasma produced in ambient air at atmospheric pressure by laser pulses at a fluence of 10 J/cm 2 is characterized by time- and space-resolved measurements of electron density and temperature. Varying the laser pulse duration from 6 ns to 80 fs and the laser wavelength from ultraviolet to infrared only slightly influences the plasma properties. The temperature exhibits a slight decrease both at the plasma edge and close to the target surface. The electron density is found to be spatially homogeneous in the ablation plume during the first microsecond. Finally, the plasma expansion is in good agreement with the Sedov's model during the first 500 ns and it becomes subsonic, with respect to the velocity of sound in air, typically 1 μs after the plasma creation. The physical interpretation of the experimental results is also discussed to the light of a one-dimensional fluid model which provides a good qualitative agreement with measurements

  6. Electronegative Plasma Equilibria with Spatially-Varying Ionization

    Science.gov (United States)

    Lieberman, M. A.; Kawamura, E.; Lichtenberg, A. J.

    2012-10-01

    Electronegative inductive discharges in higher pressure ranges typically exhibit localized ionization near the coil structure, with decay of the ionization into the central discharge. We use a two-dimensional fluid code [1] with chlorine feedstock to determine the spatial profiles of the plasma parameters in a cylindrical transformer-coupled plasma device excited by a planar coil. To compare with one-dimensional (1D) analytic modeling, the results are area-averaged. The ionization is found to decay roughly exponentially along the axial direction, allowing the ansatz of an exponentially decaying ionization to be used in a 1D computational model. The model captures the main features of the axial variations of the area-averaged fluid simulation, indicating that the main diffusion mechanisms act along the axial direction. A simple analytic global discharge model is developed, accounting for the asymmetric density and ionization profiles. The global model gives the scalings with power and pressure of volume-averaged densities, electron temperature, and ionization decay rate, also in reasonable agreement with the scalings obtained by averaging the simulation results. [4pt] [1] E. Kawamura, D.B. Graves, and M.A. Lieberman, Plasma Sources Sci. Technol. 20, 035009 (2012)

  7. Non-inductive plasma initiation and plasma current ramp-up on the TST-2 spherical tokamak

    International Nuclear Information System (INIS)

    Takase, Y.; Ejiri, A.; Oosako, T.; Shinya, T.; Ambo, T.; Furui, H.; Kato, K.; Nakanishi, A.; Sakamoto, T.; Kakuda, H.; Wakatsuki, T.; Hashimoto, T.; Hiratsuka, J.; Kasahara, H.; Kumazawa, R.; Mutoh, T.; Saito, K.; Seki, T.; Moeller, C.P.; Nagashima, Y.

    2013-01-01

    Plasma current (I p ) start-up in a spherical tokamak (ST) by waves in the lower-hybrid (LH) frequency range was investigated on TST-2. A low current (∼1 kA) ST configuration can be formed by waves over a broad frequency range (21 MHz–8.2 GHz in TST-2), but further I p ramp-up (to ∼10 kA) is most efficient with waves in the LH frequency range. I p ramp-up to 15 kA was achieved with 60 kW of net RF power P RF in the fast wave (FW) polarization at 200 MHz excited by the inductively coupled combline antenna. X-ray measurements showed that the photon flux and temperature are higher in the direction opposite to I p , consistent with acceleration of electrons by a uni-directional RF wave. There is evidence that the LH wave is excited nonlinearly by the FW, based on the frequency spectra measured by magnetic probes. Similar efficiencies of I p ramp-up were obtained with the inductive combline antenna and the dielectric-loaded waveguide array (‘grill’) antenna, and tendencies for the current drive efficiency to increase with plasma current and toroidal field were observed. During operation of the grill antenna, wavevector components were measured by an array of magnetic probes. Results were qualitatively consistent with expectations based on dispersion relations for the FW and the LH wave. A capacitively coupled combline antenna has been developed to improve coupling to the plasma and the wavenumber spectrum of the excited LH wave, and will be tested in 2013. (paper)

  8. Effects of electrode polarization and particle deposition profile on TJ-I plasma confinement

    International Nuclear Information System (INIS)

    Zurro, B.; Tabares, F.; Pardo, C.; Tafalla, D.; Cal, E. de la; Garcia-Castaner, B.; Pedrosa, M.A.; Sanchez, J.; Rodriguez-Yunta, A.

    1991-01-01

    The role of self-created radial electric field on particle confinement in TJ-I plasmas was addressed using plasma rotation data in conjunction with particle confinement times measured by laser ablation. In this paper following the pioneer work of Taylor, we have started to study the influence of a polarized electrode inserted into the plasma on particle confinement and plasma rotation in this ohmically heated tokamak. To have a supportive frame of reference, the confinement time of background particles and their transport into plasma without electrode, has been studied by measuring with space-time resolution the H α emission on varying plasma conditions. These experiments have been carried out in ohmically heated discharges of the TJ-I tokamak (R 0 =30 cm, a=10 cm) which was operated with plasma currents between 20 and 45 kA and a toroidal field ranging from 0.8 to 1.5 T. In this paper, firstly the experimental plasma and specific diagnostics are described, secondly, the parametric dependence of the particle confinement time and radial transport of background plasma is presented and finally, the influence of polarizing an inserted electrode on a particular discharge is given and discussed in the context of other polarization experiments. (author) 7 refs., 4 figs

  9. Time and space resolved observation of hot spots in a plasma focus

    International Nuclear Information System (INIS)

    Choi, P.; Aliaga, R.; Herold, H.

    1990-01-01

    The authors report some recent results on the time and space evolution of hot spots on the DPF-78 plasma focus at the University of Stuttgart. The experiments were carried out in mixtures of deuterium and krypton at a bank voltage of 60 kV and a stored energy of 28 kJ. A modification of the ADRRM streak technique carried out in the soft x-ray region allowed us to directly examine some characteristics of the hot spots. Simultaneous measurements were carried out on the hard x-ray radiation (80 keV), the spatially resolved optical emissions, the neutron yield rate with TOF information and the plasma and bank currents

  10. Synchronization of uncertain time-varying network based on sliding mode control technique

    Science.gov (United States)

    Lü, Ling; Li, Chengren; Bai, Suyuan; Li, Gang; Rong, Tingting; Gao, Yan; Yan, Zhe

    2017-09-01

    We research synchronization of uncertain time-varying network based on sliding mode control technique. The sliding mode control technique is first modified so that it can be applied to network synchronization. Further, by choosing the appropriate sliding surface, the identification law of uncertain parameter, the adaptive law of the time-varying coupling matrix element and the control input of network are designed, it is sure that the uncertain time-varying network can synchronize effectively the synchronization target. At last, we perform some numerical simulations to demonstrate the effectiveness of the proposed results.

  11. Plasma boundary shape control and real-time equilibrium reconstruction on NSTX-U

    Science.gov (United States)

    Boyer, M. D.; Battaglia, D. J.; Mueller, D.; Eidietis, N.; Erickson, K.; Ferron, J.; Gates, D. A.; Gerhardt, S.; Johnson, R.; Kolemen, E.; Menard, J.; Myers, C. E.; Sabbagh, S. A.; Scotti, F.; Vail, P.

    2018-03-01

    The upgrade to the National Spherical Torus eXperiment (NSTX-U) included two main improvements: a larger center-stack, enabling higher toroidal field and longer pulse duration, and the addition of three new tangentially aimed neutral beam sources, which increase available heating and current drive, and allow for flexibility in shaping power, torque, current, and particle deposition profiles. To best use these new capabilities and meet the high-performance operational goals of NSTX-U, major upgrades to the NSTX-U control system (NCS) hardware and software have been made. Several control algorithms, including those used for real-time equilibrium reconstruction and shape control, have been upgraded to improve and extend plasma control capabilities. As part of the commissioning phase of first plasma operations, the shape control system was tuned to control the boundary in both inner-wall limited and diverted discharges. It has been used to accurately track the requested evolution of the boundary (including the size of the inner gap between the plasma and central solenoid, which is a challenge for the ST configuration), X-point locations, and strike point locations, enabling repeatable discharge evolutions for scenario development and diagnostic commissioning.

  12. Excitation of surface waves and electrostatic fields by a RF (radiofrequency systems) wave in a plasma sheath with current

    International Nuclear Information System (INIS)

    Gutierrez Tapia, C.

    1990-01-01

    It is shown in a one-dimensional model that when a current in a plasma sheath is present, the excitation of surface waves and electrostatic fields by a RF wave is possible in the sheath. This phenomena depends strongly on the joint action of Miller's and driven forces. It is also shown that the action of these forces are carried out at different characteristic times when the wave front travels through the plasma sheath. The influence of the current, in the steady limit, is taken into account by a small functional variation of the density perturbations and generated electrostatic field. (Author)

  13. Late-time particle emission from laser-produced graphite plasma

    Energy Technology Data Exchange (ETDEWEB)

    Harilal, S. S.; Hassanein, A.; Polek, M. [School of Nuclear Engineering, Center for Materials Under Extreme Environment, Purdue University, West Lafayette, Indiana 47907 (United States)

    2011-09-01

    We report a late-time ''fireworks-like'' particle emission from laser-produced graphite plasma during its evolution. Plasmas were produced using graphite targets excited with 1064 nm Nd: yttrium aluminum garnet (YAG) laser in vacuum. The time evolution of graphite plasma was investigated using fast gated imaging and visible emission spectroscopy. The emission dynamics of plasma is rapidly changing with time and the delayed firework-like emission from the graphite target followed a black-body curve. Our studies indicated that such firework-like emission is strongly depended on target material properties and explained due to material spallation caused by overheating the trapped gases through thermal diffusion along the layer structures of graphite.

  14. Late-time particle emission from laser-produced graphite plasma

    International Nuclear Information System (INIS)

    Harilal, S. S.; Hassanein, A.; Polek, M.

    2011-01-01

    We report a late-time ''fireworks-like'' particle emission from laser-produced graphite plasma during its evolution. Plasmas were produced using graphite targets excited with 1064 nm Nd: yttrium aluminum garnet (YAG) laser in vacuum. The time evolution of graphite plasma was investigated using fast gated imaging and visible emission spectroscopy. The emission dynamics of plasma is rapidly changing with time and the delayed firework-like emission from the graphite target followed a black-body curve. Our studies indicated that such firework-like emission is strongly depended on target material properties and explained due to material spallation caused by overheating the trapped gases through thermal diffusion along the layer structures of graphite.

  15. Conceptual Modeling of Time-Varying Information

    DEFF Research Database (Denmark)

    Gregersen, Heidi; Jensen, Christian S.

    2004-01-01

    A wide range of database applications manage information that varies over time. Many of the underlying database schemas of these were designed using the Entity-Relationship (ER) model. In the research community as well as in industry, it is common knowledge that the temporal aspects of the mini......-world are important, but difficult to capture using the ER model. Several enhancements to the ER model have been proposed in an attempt to support the modeling of temporal aspects of information. Common to the existing temporally extended ER models, few or no specific requirements to the models were given...

  16. A time-varying magnetic flux concentrator

    International Nuclear Information System (INIS)

    Kibret, B; Premaratne, M; Lewis, P M; Thomson, R; Fitzgerald, P B

    2016-01-01

    It is known that diverse technological applications require the use of focused magnetic fields. This has driven the quest for controlling the magnetic field. Recently, the principles in transformation optics and metamaterials have allowed the realization of practical static magnetic flux concentrators. Extending such progress, here, we propose a time-varying magnetic flux concentrator cylindrical shell that uses electric conductors and ferromagnetic materials to guide magnetic flux to its center. Its performance is discussed based on finite-element simulation results. Our proposed design has potential applications in magnetic sensors, medical devices, wireless power transfer, and near-field wireless communications. (paper)

  17. Study on the Variation of Groundwater Level under Time-varying Recharge

    Science.gov (United States)

    Wu, Ming-Chang; Hsieh, Ping-Cheng

    2017-04-01

    The slopes of the suburbs come to important areas by focusing on the work of soil and water conservation in recent years. The water table inside the aquifer is affected by rainfall, geology and topography, which will result in the change of groundwater discharge and water level. Currently, the way to obtain water table information is to set up the observation wells; however, owing to that the cost of equipment and the wells excavated is too expensive, we develop a mathematical model instead, which might help us to simulate the groundwater level variation. In this study, we will discuss the groundwater level change in a sloping unconfined aquifer with impermeable bottom under time-varying rainfall events. Referring to Child (1971), we employ the Boussinesq equation as the governing equation, and apply the General Integral Transforms Method (GITM) to analyzing the groundwater level after linearizing the Boussinesq equation. After comparing the solution with Verhoest & Troch (2000) and Bansal & Das (2010), we get satisfactory results. To sum up, we have presented an alternative approach to solve the linearized Boussinesq equation for the response of groundwater level in a sloping unconfined aquifer. The present analytical results combine the effect of bottom slope and the time-varying recharge pattern on the water table fluctuations. Owing to the limitation and difficulty of measuring the groundwater level directly, we develop such a mathematical model that we can predict or simulate the variation of groundwater level affected by any rainfall events in advance.

  18. Grid system design on the plasma cathode electron source

    International Nuclear Information System (INIS)

    Agus Purwadi

    2014-01-01

    It has been designed the grid system on the Plasma Cathode Electron Source (PCES). Grid system with the electron emission hole of (15 x 60) cm 2 , the single aperture grid size of (0,5 x O,5) mm 2 and the grid wire diameter of 0,25 mm, will be used on the plasma generator chamber. If the sum of grid holes known and the value of electron emission current through every the grid hole known too then the total value of electron emission Current which emits from the plasma generator chamber can be determined It has been calculated the value of electron emission current I e as function of the grid radius r e =(0.28, 0.40, 0.49, 0.56, 0.63, 0.69) mm on the electron temperature of T e = 5 eV for varying of the value plasma electron densities n e = (10 15 , 10 16 , 10 17 , 10 18 ) m -3 . Also for the value of electron emission current fe as function of the grid radius r e = (0.28, 0.40, 0.49. 0.56, 0.63,0.69) mm on the electron density n e = 10 17 m -3 for varying of the value of plasma electron temperatures T e = (1, 2, 3, 4, 5) eV. electron emission current will be increase by increasing grid radius, electron temperature as well as plasma electron density. (author)

  19. Algebraic motion of vertically displacing plasmas

    Science.gov (United States)

    Bhattacharjee, Amitava; Pfefferle, David; Hirvijoki, Eero

    2017-10-01

    The vertical displacement of tokamak plasmas is modelled during the non-linear phase by a free-moving current-carrying rod coupled to a set of fixed conducting wires and a cylindrical conducting shell. The models capture the leading term in a Taylor expansion of the Green's function for the interaction between the plasma column and the vacuum vessel. The plasma is assumed not to vary during the VDE such that it behaves as a rigid body. In the limit of perfectly conducting structures, the plasma is prevented from coming in contact with the wall due to steep effective potential barriers by the eddy currents, and will hence oscillate at Alfvénic frequencies about a given force-free position. In addition to damping oscillations, resistivity allows for the column to drift towards the vessel on slow flux penetration timescales. The initial exponential motion of the plasma, i.e. the resistive vertical instability, is succeeded by a non-linear sinking behaviour, that is shown analytically to be algebraic and decelerative. The acceleration of the plasma column often observed in experiments is thus conjectured to originate from an early sharing of toroidal current between the core, the halo plasma and the wall or from the thermal quench dynamics precipitating loss of plasma current

  20. Plasma density control in real-time on the COMPASS tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Janky, F., E-mail: filip.janky.work@gmail.com [Institute of Plasma Physics AS CR, v.v.i., Association EURATOM/IPP.CR, Za Slovankou 3, 182 00 Praha 8 (Czech Republic); Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University in Prague, V Holešovičkách 2, 180 00 Praha 8 (Czech Republic); Hron, M. [Institute of Plasma Physics AS CR, v.v.i., Association EURATOM/IPP.CR, Za Slovankou 3, 182 00 Praha 8 (Czech Republic); Havlicek, J. [Institute of Plasma Physics AS CR, v.v.i., Association EURATOM/IPP.CR, Za Slovankou 3, 182 00 Praha 8 (Czech Republic); Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University in Prague, V Holešovičkách 2, 180 00 Praha 8 (Czech Republic); Varavin, M.; Zacek, F.; Seidl, J.; Panek, R. [Institute of Plasma Physics AS CR, v.v.i., Association EURATOM/IPP.CR, Za Slovankou 3, 182 00 Praha 8 (Czech Republic)

    2015-10-15

    Highlights: • We fitted length of the chord of the interferometry crossing plasma in the different plasma scenarios. • We add correction to the actual length of the chord of the interferometry according to plasma shape and position in real-time code. • We used this correction to control plasma density in real-time. - Abstract: The electron density on COMPASS is measured using 2 mm microwave interferometer. Interferometer signal is used as an input for the feedback control loop, running under the MARTe real-time framework. Two different threads are used to calculate (fast 50 μs thread) and to control (slow 500 μs thread) the electron density. The interferometer measures a line averaged density along a measurement chord. This paper describes an approach to control the line-averaged electron density in a real-time loop, using a correction to the real plasma shape, the plasma position, and non-linear effects of the electron density measurement at high densities. Newly developed real-time electron density control give COMPASS the chance to control the electron density more accurately which is essential for parametric scans for diagnosticians, for physics experiments and also for achieving plasma scenarios with H-mode.

  1. Duality of the magnetic flux tube and electric current descriptions magnetospheric plasma and energy flow

    International Nuclear Information System (INIS)

    Atkinson, G.

    1981-01-01

    The duality between electric current and magnetic flux tubes is outlined for the magnetosphere. Magnetic flux tubes are regarded as fluid elements subjected to various stresses. Current closure then becomes the dual of stress balance, and Poynting vector energy flow a dual of J x E dissipation. The stresses acting on a flux tube are magnetic stresses, which correspond to currents at a distance, and plasma stresses, which correspond to local currents. The duality between current and stress is traced for ionospheric ion drag forces, solar wind stresses at the magnetopause, inertial effects, and the effects of energetic plasma on flux tubes. The stress balance and dual current systems are outlined for idealized magnetospheres of increasing complexity. For a simple magnetosphere with no convective flow, the balance stresses are solar wind pressure and neutral sheet plasma pressure. The corresponding current systems are the Chapman-Ferraro magnetopause currents and the magetotail current system. The introduction of convective flow introduces further stresses: ionospheric ion drag. Alfven layer shielding, and an imbalance in day-night magnetic stresses due to transport of flux tubes to the nightside by the solar wind. These stresses balance, and hence the corresponding additional currents (the ionospheric Pedersen current and the electrojets, the partial ring current, and two other current systems from the magnetopause and tail) must form a closed current system and do so by the region I and II field-aligned currents of Iijima and Potemra. The energy flow in the above models is described in terms of both Poynting vectors and the above current systems. Temporal variations examined are (1) an increase in dayside merging and/or nightside reconnection, (2) an increase in the energy density of plasma in the plasma sheet, (3) an increase in ionospheric conductivity, and (4) an increase in solar wind pressure

  2. Electron dynamics in solid state via time varying wavevectors

    Science.gov (United States)

    Khaneja, Navin

    2018-06-01

    In this paper, we study electron wavepacket dynamics in electric and magnetic fields. We rigorously derive the semiclassical equations of electron dynamics in electric and magnetic fields. We do it both for free electron and electron in a periodic potential. We do this by introducing time varying wavevectors k(t). In the presence of magnetic field, our wavepacket reproduces the classical cyclotron orbits once the origin of the Schröedinger equation is correctly chosen to be center of cyclotron orbit. In the presence of both electric and magnetic fields, our equations for wavepacket dynamics differ from classical Lorentz force equations. We show that in a periodic potential, on application of electric field, the electron wave function adiabatically follows the wavefunction of a time varying Bloch wavevector k(t), with its energies suitably shifted with time. We derive the effective mass equation and discuss conduction in conductors and insulators.

  3. Time varying determinants of bond flows to emerging markets

    Directory of Open Access Journals (Sweden)

    Yasemin Erduman

    2016-06-01

    Full Text Available This paper investigates the time varying nature of the determinants of bond flows with a focus on the global financial crisis period. We estimate a time varying regression model using Bayesian estimation methods, where the posterior distribution is approximated by Gibbs sampling algorithm. Our findings suggest that the interest rate differential is the most significant pull factor of portfolio bond flows, along with the inflation rate, while the growth rate does not play a significant role. Among the push factors, global liquidity is the most important driver of bond flows. It matters the most, when unconventional monetary easing policies were first announced; and its importance as a determinant of portfolio bond flows decreases over time, starting with the Eurozone crisis, and diminishes with the tapering talk. Global risk appetite and the risk perception towards the emerging countries also have relatively small and stable significant effects on bond flows.

  4. Non-linear Simulations of MHD Instabilities in Tokamaks Including Eddy Current Effects and Perspectives for the Extension to Halo Currents

    International Nuclear Information System (INIS)

    Hoelzl, M; Merkel, P; Lackner, K; Strumberger, E; Huijsmans, G T A; Aleynikova, K; Liu, F; Atanasiu, C; Nardon, E; Fil, A; McAdams, R; Chapman, I

    2014-01-01

    The dynamics of large scale plasma instabilities can be strongly influenced by the mutual interaction with currents flowing in conducting vessel structures. Especially eddy currents caused by time-varying magnetic perturbations and halo currents flowing directly from the plasma into the walls are important. The relevance of a resistive wall model is directly evident for Resistive Wall Modes (RWMs) or Vertical Displacement Events (VDEs). However, also the linear and non-linear properties of most other large-scale instabilities may be influenced significantly by the interaction with currents in conducting structures near the plasma. The understanding of halo currents arising during disruptions and VDEs, which are a serious concern for ITER as they may lead to strong asymmetric forces on vessel structures, could also benefit strongly from these non-linear modeling capabilities. Modeling the plasma dynamics and its interaction with wall currents requires solving the magneto-hydrodynamic (MHD) equations in realistic toroidal X-point geometry consistently coupled with a model for the vacuum region and the resistive conducting structures. With this in mind, the non-linear finite element MHD code JOREK [1, 2] has been coupled [3] with the resistive wall code STARWALL [4], which allows us to include the effects of eddy currents in 3D conducting structures in non-linear MHD simulations. This article summarizes the capabilities of the coupled JOREK-STARWALL system and presents benchmark results as well as first applications to non-linear simulations of RWMs, VDEs, disruptions triggered by massive gas injection, and Quiescent H-Mode. As an outlook, the perspectives for extending the model to halo currents are described

  5. METHOD FOR EXCHANGING ENERGY WITH A PLASMA BY MAGNETIC PUMPING

    Science.gov (United States)

    Hall, L.S.

    1963-12-31

    A method of heating a plasma confined by a static magnetic field is presented. A time-varying magnetic field having a rise time to a predetermined value substantially less than its fall time is applied to a portion of the plasma. Because of the much shorter rise time, the plasma is reversibly heated. This cycle is repeated until the desired plasma temperature is reached. (AEC)

  6. Global stabilization of linear continuous time-varying systems with bounded controls

    International Nuclear Information System (INIS)

    Phat, V.N.

    2004-08-01

    This paper deals with the problem of global stabilization of a class of linear continuous time-varying systems with bounded controls. Based on the controllability of the nominal system, a sufficient condition for the global stabilizability is proposed without solving any Riccati differential equation. Moreover, we give sufficient conditions for the robust stabilizability of perturbation/uncertain linear time-varying systems with bounded controls. (author)

  7. Stationary, high bootstrap fraction plasmas in DIII-D without inductive current control

    International Nuclear Information System (INIS)

    Politzer, P.A.; Hyatt, A.W.; Luce, T.C.; Prater, R.; Turnbull, A.D.; Ferron, J.R.; Greenfield, C.M.; La Haye, R.J.; Petty, C.C.; Perkins, F.W.; Brennan, D.P.; Lazarus, E.A.; Jayakumar, J.; Wade, M.R.

    2005-01-01

    We have initiated an experimental program to address some of the questions associated with operation of a tokamak with high bootstrap current fraction under high performance conditions, without assistance from a transformer. In these discharges stationary (or slowly improving) conditions are maintained for > 3.7 s at β N ∼ β p ≤ 3.3. The achievable current and pressure are limited by a relaxation oscillation, involving growth and collapse of an ITB at ρ ≥ 0.6. The pressure gradually increases and the current profile broadens throughout the discharge. Eventually the plasma reaches a more stable, high confinement (H89P ∼ 3) state. Characteristically these plasmas have 65%-85% bootstrap current, 15%-30% NBCD, and 0%-10% ECCD. (author)

  8. Bootstrap current control studies in the Wendelstein 7-X stellarator using the free-plasma-boundary version of the SIESTA MHD equilibrium code

    Science.gov (United States)

    Peraza-Rodriguez, H.; Reynolds-Barredo, J. M.; Sanchez, R.; Tribaldos, V.; Geiger, J.

    2018-02-01

    The recently developed free-plasma-boundary version of the SIESTA MHD equilibrium code (Hirshman et al 2011 Phys. Plasmas 18 062504; Peraza-Rodriguez et al 2017 Phys. Plasmas 24 082516) is used for the first time to study scenarios with considerable bootstrap currents for the Wendelstein 7-X (W7-X) stellarator. Bootstrap currents in the range of tens of kAs can lead to the formation of unwanted magnetic island chains or stochastic regions within the plasma and alter the boundary rotational transform due to the small shear in W7-X. The latter issue is of relevance since the island divertor operation of W7-X relies on a proper positioning of magnetic island chains at the plasma edge to control the particle and energy exhaust towards the divertor plates. Two scenarios are examined with the new free-plasma-boundary capabilities of SIESTA: a freely evolving bootstrap current one that illustrates the difficulties arising from the dislocation of the boundary islands, and a second one in which off-axis electron cyclotron current drive (ECCD) is applied to compensate the effects of the bootstrap current and keep the island divertor configuration intact. SIESTA finds that off-axis ECCD is indeed able to keep the location and phase of the edge magnetic island chain unchanged, but it may also lead to an undesired stochastization of parts of the confined plasma if the EC deposition radial profile becomes too narrow.

  9. Volumetric plasma source development and characterization

    International Nuclear Information System (INIS)

    Crain, Marlon D.; Maron, Yitzhak; Oliver, Bryan Velten; Starbird, Robert L.; Johnston, Mark D.; Hahn, Kelly Denise; Mehlhorn, Thomas Alan; Droemer, Darryl W.

    2008-01-01

    The development of plasma sources with densities and temperatures in the 10 15 -10 17 cm -3 and 1-10eV ranges which are slowly varying over several hundreds of nanoseconds within several cubic centimeter volumes is of interest for applications such as intense electron beam focusing as part of the x-ray radiography program. In particular, theoretical work (1,2) suggests that replacing neutral gas in electron beam focusing cells with highly conductive, pre-ionized plasma increases the time-averaged e-beam intensity on target, resulting in brighter x-ray sources. This LDRD project was an attempt to generate such a plasma source from fine metal wires. A high voltage (20-60kV), high current (12-45kA) capacitive discharge was sent through a 100 (micro)m diameter aluminum wire forming a plasma. The plasma's expansion was measured in time and space using spectroscopic techniques. Lineshapes and intensities from various plasma species were used to determine electron and ion densities and temperatures. Electron densities from the mid-10 15 to mid-10 16 cm -3 were generated with corresponding electron temperatures of between 1 and 10eV. These parameters were measured at distances of up to 1.85 cm from the wire surface at times in excess of 1 (micro)s from the initial wire breakdown event. In addition, a hydrocarbon plasma from surface contaminants on the wire was also measured. Control of these contaminants by judicious choice of wire material, size, and/or surface coating allows for the ability to generate plasmas with similar density and temperature to those given above, but with lower atomic masses

  10. The use of internal transport barriers in tokamak plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Challis, C D [Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon, OX14 3DB (United Kingdom)

    2004-12-01

    Internal transport barriers (ITBs) can provide high tokamak confinement at modest plasma current. This is desirable for operation with most of the current driven non-inductively by the bootstrap mechanism, as currently envisaged for steady-state power plants. Maintaining such plasmas in steady conditions with high plasma purity is challenging, however, due to MHD instabilities and impurity transport effects. Significant progress has been made in the control of ITB plasmas: the pressure profile has been varied using the barrier location; q-profile modification has been achieved with non-inductive current drive, and means have been found to affect density peaking and impurity accumulation. All these features are, to some extent, interdependent and must be integrated self-consistently to demonstrate a sound basis for extrapolation to future devices.

  11. The effects of varying plasma parameters on silicon thin film growth by ECR plasma CVD

    International Nuclear Information System (INIS)

    Summers, S.; Reehal, H.S.; Shirkoohi, G.H.

    2001-01-01

    The technique of electron cyclotron resonance (ECR) plasma enhanced chemical vapour deposition (PECVD) is increasingly being used in electronic and photonic device applications. ECR offers a number of advantages including improved control of the deposition process, less damage to the growing film and the possibility of high deposition rates. ECR occurs in a plasma under appropriate magnetic and electric field conditions. In most cases, as in our system, this is achieved with a combination of 2.45 GHz microwave radiation and a 0.0875 T magnetic field, due to the use of standardized microwave supplies. We have studied the effects on silicon film growth of changing the magnetic field configuration to produce one or more planes of ECR within the system, and of changing the positions of the plane(s) relative to the deposition substrate. The films were grown in silane-hydrogen discharges. The magnetic field in our system was provided by two electromagnets. It was measured experimentally for a number of operating current values and then a detailed profile achieved by modelling using a proprietary software package. A process condition discharge under identical magnetic field configurations to growth was analysed by the use of a Langmuir probe and the results correlated with film properties determined by Raman spectroscopy and Dektak profilometry. (author)

  12. Finite-Time Reentry Attitude Control Using Time-Varying Sliding Mode and Disturbance Observer

    Directory of Open Access Journals (Sweden)

    Xuzhong Wu

    2015-01-01

    Full Text Available This paper presents the finite-time attitude control problem for reentry vehicle with redundant actuators in consideration of planet uncertainties and external disturbances. Firstly, feedback linearization technique is used to cancel the nonlinearities of equations of motion to construct a basic mode for attitude controller. Secondly, two kinds of time-varying sliding mode control methods with disturbance observer are integrated with the basic mode in order to enhance the control performance and system robustness. One method is designed based on boundary layer technique and the other is a novel second-order sliding model control method. The finite-time stability analyses of both resultant closed-loop systems are carried out. Furthermore, after attitude controller produces the torque commands, an optimization control allocation approach is introduced to allocate them into aerodynamic surface deflections and on-off reaction control system thrusts. Finally, the numerical simulation results demonstrate that both of the time-varying sliding mode control methods are robust to uncertainties and disturbances without chattering phenomenon. Moreover, the proposed second-order sliding mode control method possesses better control accuracy.

  13. Fokker-Planck modeling of current penetration during electron cyclotron current drive

    International Nuclear Information System (INIS)

    Merkulov, A.; Westerhof, E.; Schueller, F. C.

    2007-01-01

    The current penetration during electron cyclotron current drive (ECCD) on the resistive time scale is studied with a Fokker-Planck simulation, which includes a model for the magnetic diffusion that determines the parallel electric field evolution. The existence of the synergy between the inductive electric field and EC driven current complicates the process of the current penetration and invalidates the standard method of calculation in which Ohm's law is simply approximated by j-j cd =σE. Here it is proposed to obtain at every time step a self-consistent approximation to the plasma resistivity from the Fokker-Planck code, which is then used in a concurrent calculation of the magnetic diffusion equation in order to obtain the inductive electric field at the next time step. A series of Fokker-Planck calculations including a self-consistent evolution of the inductive electric field has been performed. Both the ECCD power and the electron density have been varied, thus varying the well known nonlinearity parameter for ECCD P rf [MW/m -3 ]/n e 2 [10 19 m -3 ] [R. W. Harvey et al., Phys. Rev. Lett 62, 426 (1989)]. This parameter turns out also to be a good predictor of the synergetic effects. The results are then compared with the standard method of calculations of the current penetration using a transport code. At low values of the Harvey parameter, the standard method is in quantitative agreement with Fokker-Planck calculations. However, at high values of the Harvey parameter, synergy between ECCD and E parallel is found. In the case of cocurrent drive, this synergy leads to the generation of large amounts of nonthermal electrons and a concomitant increase of the electrical conductivity and current penetration time. In the case of countercurrent drive, the ECCD efficiency is suppressed by the synergy with E parallel while only a small amount of nonthermal electrons is produced

  14. Axisymmetrical particle-in-cell/Monte Carlo simulation of narrow gap planar magnetron plasmas. I. Direct current-driven discharge

    International Nuclear Information System (INIS)

    Kondo, Shuji; Nanbu, Kenichi

    2001-01-01

    An axisymmetrical particle-in-cell/Monte Carlo simulation is performed for modeling direct current-driven planar magnetron discharge. The axisymmetrical structure of plasma parameters such as plasma density, electric field, and electron and ion energy is examined in detail. The effects of applied voltage and magnetic field strength on the discharge are also clarified. The model apparatus has a narrow target-anode gap of 20 mm to make the computational time manageable. This resulted in the current densities which are very low compared to actual experimental results for a wider target-anode gap. The current-voltage characteristics show a negative slope in contrast with many experimental results. However, this is understandable from Gu and Lieberman's similarity equation. The negative slope appears to be due to the narrow gap

  15. Finite-time and fixed-time synchronization analysis of inertial memristive neural networks with time-varying delays.

    Science.gov (United States)

    Wei, Ruoyu; Cao, Jinde; Alsaedi, Ahmed

    2018-02-01

    This paper investigates the finite-time synchronization and fixed-time synchronization problems of inertial memristive neural networks with time-varying delays. By utilizing the Filippov discontinuous theory and Lyapunov stability theory, several sufficient conditions are derived to ensure finite-time synchronization of inertial memristive neural networks. Then, for the purpose of making the setting time independent of initial condition, we consider the fixed-time synchronization. A novel criterion guaranteeing the fixed-time synchronization of inertial memristive neural networks is derived. Finally, three examples are provided to demonstrate the effectiveness of our main results.

  16. Temperature profiles of time dependent tokamak plasmas from the parallel Ohm's law

    International Nuclear Information System (INIS)

    Micozzi, P.; Roccella, M.

    1993-01-01

    Profile consistency based on the parallel component of Ohm's law has been used to obtain electron temperature profiles. A resistive neoclassical term and a term that accounts for the bootstrap current contributions have been considered in Ohm's law. A numerical code has been developed to find solutions according to the MHD equilibrium equations. For stationary plasmas, the temperature profiles, obtained by a procedure in which a pseudo-parabolic shape of (J φ /R) is assumed and the peak temperature known from experiments is used, are close to the experimental data for several very different machines (JET, TFTR, ASDEX, ALCATOR-C and FT). The main feature of the model is its capability to provide an easy parametrization of Ohm's law also in non-stationary cases, without going through the complication of a detailed solution of the magnetic field diffusion equation. A rule for estimating a maximum value of the current diffusion time inside the plasma volume in such situations is given. This rule accounts for both the temperature profiles and the stabilization times in some non-stationary pulses observed in JET. (author). 28 refs, 12 figs

  17. MHD dynamo action in space plasmas

    International Nuclear Information System (INIS)

    Faelthammar, C.G.

    1984-05-01

    Electric currents are now recognized to play a major role in the physical process of the Earths magnetosphere as well as in distant astrophysical plasmas. In driving these currents MHD dynamos as well as generators of a thermoelectric nature are important. The primary source of power for the Earths magnetospheric process is the solar wind, which supplies a voltage of the order of 200 kV across the magnetosphere. The direction of the large-scale solar wind electric field varies of many different time scales. The power input to the magnetosphere is closely correlated with the direction of the large-scale solar wind electric field in such a fashion as to mimick the response of a half-wave rectifier with a down-to-dusk conduction direction. Behind this apparently simple response there are complex plasma physical processes that are still very incompletely understood. They are intimately related to auroras, magnetic storms, radiation belts and changes in magnetospheric plasma populations. Similar dynamo actions should occur at other planets having magnetospheres. Recent observations seem to indicate that part of the power input to the Earths magnetosphere comes through MHD dynamo action of a forced plasma flow inside the flanks of the magnetopause and may play a role in other parts of the magnetosphere, too. An example of a cosmical MHD connected to a solid load is the corotating plasma of Jupiters inner magnetosphere, sweeping past the plants inner satelites. In particular the electric currents thereby driven to and from the satellite Io have attracted considerable interest.(author)

  18. Real-time evaluation of electron and current density profile parameters on TEXTOR

    International Nuclear Information System (INIS)

    Bruessau, W.D.; Soltwisch, H.

    1985-08-01

    The shapes of electron and current density profiles are monitored in real-time mode in order to get rapid qualitative information on the development of a TEXTOR tokamak plasma. The profiles are described by form parameters which relate to the signals of a 9-channel FIR-polari/interferometer in simple mathematical formulae. These profile parameters are obtained by real-time conversion of measured quantities for display on a storage oscilloscope or on a chart recorder. The application of the parameters is demonstrated in some examples. (orig.)

  19. Effect of solenoidal magnetic field on drifting laser plasma

    Science.gov (United States)

    Takahashi, Kazumasa; Okamura, Masahiro; Sekine, Megumi; Cushing, Eric; Jandovitz, Peter

    2013-04-01

    An ion source for accelerators requires to provide a stable waveform with a certain pulse length appropriate to the application. The pulse length of laser ion source is easy to control because it is expected to be proportional to plasma drifting distance. However, current density decay is proportional to the cube of the drifting distance, so large current loss will occur under unconfined drift. We investigated the stability and current decay of a Nd:YAG laser generated copper plasma confined by a solenoidal field using a Faraday cup to measure the current waveform. It was found that the plasma was unstable at certain magnetic field strengths, so a baffle was introduced to limit the plasma diameter at injection and improve the stability. Magnetic field, solenoid length, and plasma diameter were varied in order to find the conditions that minimize current decay and maximize stability.

  20. Effect of solenoidal magnetic field on drifting laser plasma

    International Nuclear Information System (INIS)

    Takahashi, Kazumasa; Sekine, Megumi; Okamura, Masahiro; Cushing, Eric; Jandovitz, Peter

    2013-01-01

    An ion source for accelerators requires to provide a stable waveform with a certain pulse length appropriate to the application. The pulse length of laser ion source is easy to control because it is expected to be proportional to plasma drifting distance. However, current density decay is proportional to the cube of the drifting distance, so large current loss will occur under unconfined drift. We investigated the stability and current decay of a Nd:YAG laser generated copper plasma confined by a solenoidal field using a Faraday cup to measure the current waveform. It was found that the plasma was unstable at certain magnetic field strengths, so a baffle was introduced to limit the plasma diameter at injection and improve the stability. Magnetic field, solenoid length, and plasma diameter were varied in order to find the conditions that minimize current decay and maximize stability.

  1. Effect of solenoidal magnetic field on drifting laser plasma

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Kazumasa; Sekine, Megumi [Tokyo Institute of Technology, Yokohama 226-8502 (Japan); Okamura, Masahiro [Brookhaven National Laboratory, Upton, NY 11973 (United States) and RIKEN, Wako-shi, Saitama 351-0198 (United States); Cushing, Eric [Pennsylvania State University, University Park, PA 16802 (United States); Jandovitz, Peter [Cornell University, Ithaca, NY 14853 (United States)

    2013-04-19

    An ion source for accelerators requires to provide a stable waveform with a certain pulse length appropriate to the application. The pulse length of laser ion source is easy to control because it is expected to be proportional to plasma drifting distance. However, current density decay is proportional to the cube of the drifting distance, so large current loss will occur under unconfined drift. We investigated the stability and current decay of a Nd:YAG laser generated copper plasma confined by a solenoidal field using a Faraday cup to measure the current waveform. It was found that the plasma was unstable at certain magnetic field strengths, so a baffle was introduced to limit the plasma diameter at injection and improve the stability. Magnetic field, solenoid length, and plasma diameter were varied in order to find the conditions that minimize current decay and maximize stability.

  2. Time-Resolved Emission Spectroscopic Study of Laser-Induced Steel Plasmas

    International Nuclear Information System (INIS)

    Shah, M. L.; Pulhani, A. K.; Suri, B. M.; Gupta, G. P.

    2013-01-01

    Laser-induced steel plasma is generated by focusing a Q-switched Nd:YAG visible laser (532 nm wavelength) with an irradiance of ∼ 1 × 10 9 W/cm 2 on a steel sample in air at atmospheric pressure. An Echelle spectrograph coupled with a gateable intensified charge-coupled detector is used to record the plasma emissions. Using time-resolved spectroscopic measurements of the plasma emissions, the temperature and electron number density of the steel plasma are determined for many times of the detector delay. The validity of the assumption by the spectroscopic methods that the laser-induced plasma (LIP) is optically thin and is also in local thermodynamic equilibrium (LTE) has been evaluated for many delay times. From the temporal evolution of the intensity ratio of two Fe I lines and matching it with its theoretical value, the delay times where the plasma is optically thin and is also in LTE are found to be 800 ns, 900 ns and 1000 ns.

  3. Space-time-dependent development of the plasma in a pulsed hollow-cathode discharge

    International Nuclear Information System (INIS)

    Schaefer, G.; Wages, M.

    1988-01-01

    This paper presents streak camera investigations on the space-time-dependent development of pulsed hollow-cathode discharges (HCD's) starting from low-current preionization discharges. The discharges started closer to the end of the cathode, then moved further into the cathode, and then spread over a longer range along the axis of the cathode. The depth range of the intense pulsed hollow-cathode plasma was found to be two to eight times the cathode diameter

  4. Radiofrequency Waves, Heating and Current Drive in Magnetically Confined Plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Porkolab, M; Bonoli, P T; Temkin, R J [Plasma Science and Fusion Center, MIT, Cambridge, MA (United States); Pinsker, R I; Prater, R [General Atomics, San Diego, California (United States); Wilson, J R [Princeton Plasma Physics Laboratory, Princeton, NJ (United States)

    2012-09-15

    The need for supplementary heating of magnetically confined plasmas to fusion relevant temperatures ({approx}20 keV) has been recognized from the beginning of modern fusion plasma research. Although in tokamaks the plasmas are formed initially by ohmic heating (P{Omega}{approx}{eta}{sub R}j, where j is the current density and {eta}{sub R} is the resistivity) its effectiveness deteriorates with increasing temperature since the resistivity decreases as T{sub e}{sup -3/2}, and losses due to bremsstrahlung radiation increase as Z{sub eff}{sup 3} T{sub e}{sup 1/2} (where Z{sub eff} is the effective ion charge), and the plasma current cannot be raised to arbitrarily large values because of MHD stability limits. In addition, energy losses due to thermal conduction P{sub loss} are typically anomalously large compared to neoclassical predictions and the dependence on temperature is not well understood. Thus, the simplest form of steady state power balance indicates that losses due to radiation and heat conduction must be balanced by auxiliary heating of some form, P{sub aux}, which may simply be stated as P{sub {Omega}} + P{sub {alpha}} - P{sub loss} P{sub aux} where P{sub {alpha}} is the power input provided by alpha particles, which does not become significant until the temperature exceeds some tens of keV, depending on confinement and density. (author)

  5. Necking down of sausages in current-carrying plasma pinches

    International Nuclear Information System (INIS)

    Trubnikov, B.A.; Zhdanov, S.K.

    1986-01-01

    The evolution of long-wave perturbations is shown to be equivalent, for various unstable media, to the dynamics of a gas with a negative adiabatic index γ. This evolution is described (for various values at N) by the quasi-Chaplygin system of equations Several examples of such media are considered, including a ''Chaplygin gas'' (N = 3), drops on a ceiling or ''solitons which have broken'' (N = 0), necks in a current-carrying plasma pinch with a skin effect, for both incompressible and compressible models (N = 2), and the breakup of liquid jets into drops (N = 3/2). A principle for selecting evolutionary solutions corresponding to the absence of perturbations in the limit t → -∞ is formulated. In the cases N = 0 and N = 2, a hodograph transformation reduces system (1) to a magnetostatic equation (ΔA)/sub phi/ = -(4π/c)j/sub phi/ and all the instability modes are equivalent to multipoles of circular currents which are localized on a circle. Exact solutions are given for periodic and isolated (localized) perturbations. The breakup of a medium into distinct blobs, in particular, the rupture of necks in a current-carrying plasma pinch, is demonstrated

  6. Assessment of plasma impedance probe for measuring electron density and collision frequency in a plasma with spatial and temporal gradients

    International Nuclear Information System (INIS)

    Hopkins, Mark A.; King, Lyon B.

    2014-01-01

    Numerical simulations and experimental measurements were combined to determine the ability of a plasma impedance probe (PIP) to measure plasma density and electron collision frequency in a plasma containing spatial gradients as well as time-varying oscillations in the plasma density. A PIP is sensitive to collision frequency through the width of the parallel resonance in the Re[Z]-vs.-frequency characteristic, while also being sensitive to electron density through the zero-crossing of the Im[Z]-vs.-frequency characteristic at parallel resonance. Simulations of the probe characteristic in a linear plasma gradient indicated that the broadening of Re[Z] due to the spatial gradient obscured the broadening due to electron collision frequency, preventing a quantitative measurement of the absolute collision frequency for gradients considered in this study. Simulation results also showed that the PIP is sensitive to relative changes in electron collision frequency in a spatial density gradient, but a second broadening effect due to time-varying oscillations made collision frequency measurements impossible. The time-varying oscillations had the effect of causing multiple zero-crossings in Im[Z] at parallel resonance. Results of experiments and simulations indicated that the lowest-frequency zero-crossing represented the lowest plasma density in the oscillations and the highest-frequency zero-crossing represented the highest plasma density in the oscillations, thus the PIP probe was found to be an effective tool to measure both the average plasma density as well as the maximum and minimum densities due to temporal oscillations

  7. Vector-field statistics for the analysis of time varying clinical gait data.

    Science.gov (United States)

    Donnelly, C J; Alexander, C; Pataky, T C; Stannage, K; Reid, S; Robinson, M A

    2017-01-01

    In clinical settings, the time varying analysis of gait data relies heavily on the experience of the individual(s) assessing these biological signals. Though three dimensional kinematics are recognised as time varying waveforms (1D), exploratory statistical analysis of these data are commonly carried out with multiple discrete or 0D dependent variables. In the absence of an a priori 0D hypothesis, clinicians are at risk of making type I and II errors in their analyis of time varying gait signatures in the event statistics are used in concert with prefered subjective clinical assesment methods. The aim of this communication was to determine if vector field waveform statistics were capable of providing quantitative corroboration to practically significant differences in time varying gait signatures as determined by two clinically trained gait experts. The case study was a left hemiplegic Cerebral Palsy (GMFCS I) gait patient following a botulinum toxin (BoNT-A) injection to their left gastrocnemius muscle. When comparing subjective clinical gait assessments between two testers, they were in agreement with each other for 61% of the joint degrees of freedom and phases of motion analysed. For tester 1 and tester 2, they were in agreement with the vector-field analysis for 78% and 53% of the kinematic variables analysed. When the subjective analyses of tester 1 and tester 2 were pooled together and then compared to the vector-field analysis, they were in agreement for 83% of the time varying kinematic variables analysed. These outcomes demonstrate that in principle, vector-field statistics corroborates with what a team of clinical gait experts would classify as practically meaningful pre- versus post time varying kinematic differences. The potential for vector-field statistics to be used as a useful clinical tool for the objective analysis of time varying clinical gait data is established. Future research is recommended to assess the usefulness of vector-field analyses

  8. Time-varying economic dominance in financial markets: A bistable dynamics approach

    Science.gov (United States)

    He, Xue-Zhong; Li, Kai; Wang, Chuncheng

    2018-05-01

    By developing a continuous-time heterogeneous agent financial market model of multi-assets traded by fundamental and momentum investors, we provide a potential mechanism for generating time-varying dominance between fundamental and non-fundamental in financial markets. We show that investment constraints lead to the coexistence of a locally stable fundamental steady state and a locally stable limit cycle around the fundamental, characterized by a Bautin bifurcation. This provides a mechanism for market prices to switch stochastically between the two persistent but very different market states, leading to the coexistence and time-varying dominance of seemingly controversial efficient market and price momentum over different time periods. The model also generates other financial market stylized facts, such as spillover effects in both momentum and volatility, market booms, crashes, and correlation reduction due to cross-sectional momentum trading. Empirical evidence based on the U.S. market supports the main findings. The mechanism developed in this paper can be used to characterize time-varying economic dominance in economics and finance in general.

  9. Optimal critic learning for robot control in time-varying environments.

    Science.gov (United States)

    Wang, Chen; Li, Yanan; Ge, Shuzhi Sam; Lee, Tong Heng

    2015-10-01

    In this paper, optimal critic learning is developed for robot control in a time-varying environment. The unknown environment is described as a linear system with time-varying parameters, and impedance control is employed for the interaction control. Desired impedance parameters are obtained in the sense of an optimal realization of the composite of trajectory tracking and force regulation. Q -function-based critic learning is developed to determine the optimal impedance parameters without the knowledge of the system dynamics. The simulation results are presented and compared with existing methods, and the efficacy of the proposed method is verified.

  10. Discharge characteristics of He-Ne-Xe gas mixture with varying Xe contents and at varying sustain electrode gap lengths in the plasma display panel

    International Nuclear Information System (INIS)

    Kwon, Ohyung; Whang, Ki-Woong; Bae, Hyun Sook

    2009-01-01

    The discharge characteristics of He-Ne-Xe gas mixture in the plasma display panel were investigated using a two-dimensional numerical simulation to understand the effects of adding He and varying the Xe contents in the gas mixture, and also varying sustain electrode gap. With 5% Xe content and 60 μm sustain electrode gap, decreased ionization led to the improvement of the vacuum ultraviolet (vuv) efficacy at increasing He mixing ratios. However, at 20% Xe content and 60 μm sustain electrode gap, increased electron heating improved the vuv efficacy until the He mixing ratio reached 0.7, but the efficacy decreased beyond the ratio of 0.7 due to the increased ionization of Xe atoms. At 5% Xe content and 200 μm sustain electrode gap, the vuv efficacy increased as a result of increased electron heating at the gap space at increasing He mixing ratios.

  11. Application of Electron Bernstein Wave heating and current drive to high beta plasmas

    International Nuclear Information System (INIS)

    Efthimion, P.C.

    2002-01-01

    Electron Bernstein Waves (EBW) can potentially heat and drive current in high-beta plasmas. Electromagnetic waves can convert to EBW via two paths. O-mode heating, demonstrated on W-7AS, requires waves be launched within a narrow k-parallel range. Alternately, in high-beta plasmas, the X-mode cutoff and EBW conversion layers are millimeters apart, so the fast X-mode can tunnel to the EBW branch. We are studying the conversion of EBW to the X-mode by measuring the radiation temperature of the cyclotron emission and comparing it to the electron temperature. In addition, mode conversion has been studied with an approximate kinetic full-wave code. We have enhanced EBW mode conversion to ∼ 100% by encircling the antenna with a limiter that shortens the density scale length at the conversion layer in the scrape off of the CDX-U spherical torus (ST) plasma. Consequently, a limiter in front of a launch antenna achieves efficient X-mode coupling to EBW. Ray tracing and Fokker-Planck codes have been used to develop current drive scenarios in NSTX high-beta (∼ 40%) ST plasmas and a relativistic code will examine the potential synergy of EBW current drive with the bootstrap current. (author)

  12. Current delivery and radiation yield in plasma flow switch-driven implosions

    International Nuclear Information System (INIS)

    Baker, W.L.; Degnan, J.H.; Beason, J.D.

    1995-01-01

    Vacuum inductive-store, plasma flow switch-driven implosion experiments have been performed using the Shiva Star capacitor bank (1300 μf, 3 nH, 120 kV, 9.4 MJ). A coaxial plasma gun arrangement is employed to store magnetic energy in the vacuum volume upstream of a dynamic discharge during the 3- to 4-μs rise of current from the capacitor bank. Motion of the discharge off the end of the inner conductor of the gun releases this energy to implode a coaxial cylindrical foil. The implosion loads are 5-cm-radius, 2-cm-long, 200 to 400 μg/cm 2 cylinders of aluminum or aluminized Formvar. With 5 MJ stored initially in the capacitor bank, more than 9 MA are delivered to the implosion load with a rise time of nearly 200 ns. The subsequent implosion results in a radiation output of 0.95 MJ at a power exceeding 5 TW (assuming isotropic emission). Experimental results and related two-dimensional magnetohydrodynamic simulations are discussed. 10 refs., 12 figs

  13. Passive cyclotron current drive for fusion plasmas

    International Nuclear Information System (INIS)

    Kernbichler, W.

    1995-01-01

    The creation of toroidal current using cyclotron radiation in a passive way is, together with the well known bootstrap current, an interesting method for stationary current drive in high-temperature fusion reactors. Here, instead of externally applied RF-waves, fish-scale like structures at the first wall help to create enough asymmetry in the self generated cyclotron radiation intensity to drive a current within the plasma. The problem of computing passive cyclotron current drive consists of actually two linked problems, which are the computation of the electron equilibrium under the presence of self-generated radiation, and the computation of the photon equilibrium in a bounded system with a distorted electron distribution. This system of integro-differential equations cannot be solved directly in an efficient way. Therefore a linearization procedure was developed to decouple both sets of equations, finally linked through a generalized local current drive efficiency. The problem of the exact accounting for the wall profile effects was reduced to the solution of a Fredholm-type integral equation of the 2 nd -kind. Based on all this an extensive computer code was developed to compute the passively driven current as well as radiation losses, radiation transport and overall efficiencies. The results therefrom give an interesting and very detailed insight into the problems related to passive cyclotron current drive

  14. Influence of coil current modulation on polycrystalline diamond film deposition by irradiation of Ar/CH4/H2 inductively coupled thermal plasmas

    Science.gov (United States)

    Betsuin, Toshiki; Tanaka, Yasunori; Arai, T.; Uesugi, Y.; Ishijima, T.

    2018-03-01

    This paper describes the application of an Ar/CH4/H2 inductively coupled thermal plasma with and without coil current modulation to synthesise diamond films. Induction thermal plasma with coil current modulation is referred to as modulated induction thermal plasma (M-ITP), while that without modulation is referred to as non-modulated ITP (NM-ITP). First, spectroscopic observations of NM-ITP and M-ITP with different modulation waveforms were made to estimate the composition in flux from the thermal plasma by measuring the time evolution in the spectral intensity from the species. Secondly, we studied polycrystalline diamond film deposition tests on a Si substrate, and we studied monocrystalline diamond film growth tests using the irradiation of NM-ITP and M-ITP. From these tests, diamond nucleation effects by M-ITP were found. Finally, following the irradiation results, we attempted to use a time-series irradiation of M-ITP and NM-ITP for polycrystalline diamond film deposition on a Si substrate. The results indicated that numerous larger diamond particles were deposited with a high population density on the Si substrate by time-series irradiation.

  15. Epidemic spreading in time-varying community networks

    Energy Technology Data Exchange (ETDEWEB)

    Ren, Guangming, E-mail: wangxy@dlut.edu.cn, E-mail: ren-guang-ming@163.com [School of Electronic and Information, Guangdong Polytechnic Normal University, Guangzhou 510665 (China); Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116024 (China); Wang, Xingyuan, E-mail: wangxy@dlut.edu.cn, E-mail: ren-guang-ming@163.com [Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116024 (China)

    2014-06-15

    The spreading processes of many infectious diseases have comparable time scale as the network evolution. Here, we present a simple networks model with time-varying community structure, and investigate susceptible-infected-susceptible epidemic spreading processes in this model. By both theoretic analysis and numerical simulations, we show that the efficiency of epidemic spreading in this model depends intensively on the mobility rate q of the individuals among communities. We also find that there exists a mobility rate threshold q{sub c}. The epidemic will survive when q > q{sub c} and die when q < q{sub c}. These results can help understanding the impacts of human travel on the epidemic spreading in complex networks with community structure.

  16. Epidemic spreading in time-varying community networks

    International Nuclear Information System (INIS)

    Ren, Guangming; Wang, Xingyuan

    2014-01-01

    The spreading processes of many infectious diseases have comparable time scale as the network evolution. Here, we present a simple networks model with time-varying community structure, and investigate susceptible-infected-susceptible epidemic spreading processes in this model. By both theoretic analysis and numerical simulations, we show that the efficiency of epidemic spreading in this model depends intensively on the mobility rate q of the individuals among communities. We also find that there exists a mobility rate threshold q c . The epidemic will survive when q > q c and die when q  c . These results can help understanding the impacts of human travel on the epidemic spreading in complex networks with community structure

  17. Time-dependent plasma behavior triggered by a pulsed electron gun under conditions of beam-plasma-discharge

    International Nuclear Information System (INIS)

    Szuszczewicz, E.P.; Lin, C.S.

    1982-01-01

    This chapter reports on experiments whose purpose was to simulate spaceborne applications of energetic electron guns while exploring the ''in situ'' diagnostics of time-dependent beam-plasma behavior under pulsed electron gun conditions. Beam-plasma-discharge (BPD), the BPD afterglow that exists after gun-pulse termination, and the plasma decay process are considered. It is concluded that there is a rapid enhancement in plasma density as the gas turns on; that during the pulse-ON time a quasi-steady-state BPD can be maintained with characteristics identical with its dc counterpart; that in the period immediately following gun-pulse termination the plasma loss process is dominated by cross-field radial diffusion; and that the afterglow plasma is within + or -10% of being an isodensity contour

  18. Analysis of radiofrequency discharges in plasma

    Science.gov (United States)

    Kumar, D.; McGlynn, S.P.

    1992-08-04

    Separation of laser optogalvanic signals in plasma into two components: (1) an ionization rate change component, and (2) a photoacoustic mediated component. This separation of components may be performed even when the two components overlap in time, by measuring time-resolved laser optogalvanic signals in an rf discharge plasma as the rf frequency is varied near the electrical resonance peak of the plasma and associated driving/detecting circuits. A novel spectrometer may be constructed to make these measurements. Such a spectrometer would be useful in better understanding and controlling such processes as plasma etching and plasma deposition. 15 figs.

  19. The spherical segmented Langmuir probe in a flowing thermal plasma: numerical model of the current collection

    Directory of Open Access Journals (Sweden)

    E. Séran

    2005-07-01

    Full Text Available The segmented Langmuir probe (SLP has been recently proposed by one of the authors (Lebreton, 2002 as an instrument to derive the bulk velocity of terrestrial or planetary plasmas, in addition to the electron density and temperature that are routinely measured by Langmuir probes. It is part of the scientific payload on the DEMETER micro-satellite developed by CNES. The basic concept of this probe is to measure the current distribution over the surface using independent collectors under the form of small spherical caps and to use the angular anisotropy of these currents to obtain the plasma bulk velocity in the probe reference frame. In order to determine the SLP capabilities, we have developed a numerical PIC (Particles In Cell model which provides a tool to compute the distribution of the current collected by a spherical probe. Our model is based on the simultaneous determination of the charge densities in the probe sheath and on the probe surface, from which the potential distribution in the sheath region can be obtained. This method is well adapted to the SLP problem and has some advantages since it provides a natural control of the charge neutrality inside the simulation box, allows independent mesh sizes in the sheath and on the probe surface, and can be applied to complex surfaces. We present in this paper initial results obtained for plasma conditions corresponding to a Debye length equal to the probe radius. These plasma conditions are observed along the Demeter orbit. The model results are found to be in very good agreement with those published by Laframboise (1966 for a spherical probe in a thermal non-flowing plasma. This demonstrates the adequacy of the computation method and of the adjustable numerical parameters (size of the numerical box and mesh, time step, number of macro-particles, etc. for the considered plasma-probe configuration. We also present the results obtained in the case of plasma flowing with mesothermal conditions

  20. The spherical segmented Langmuir probe in a flowing thermal plasma: numerical model of the current collection

    Directory of Open Access Journals (Sweden)

    E. Séran

    2005-07-01

    Full Text Available The segmented Langmuir probe (SLP has been recently proposed by one of the authors (Lebreton, 2002 as an instrument to derive the bulk velocity of terrestrial or planetary plasmas, in addition to the electron density and temperature that are routinely measured by Langmuir probes. It is part of the scientific payload on the DEMETER micro-satellite developed by CNES. The basic concept of this probe is to measure the current distribution over the surface using independent collectors under the form of small spherical caps and to use the angular anisotropy of these currents to obtain the plasma bulk velocity in the probe reference frame. In order to determine the SLP capabilities, we have developed a numerical PIC (Particles In Cell model which provides a tool to compute the distribution of the current collected by a spherical probe. Our model is based on the simultaneous determination of the charge densities in the probe sheath and on the probe surface, from which the potential distribution in the sheath region can be obtained. This method is well adapted to the SLP problem and has some advantages since it provides a natural control of the charge neutrality inside the simulation box, allows independent mesh sizes in the sheath and on the probe surface, and can be applied to complex surfaces. We present in this paper initial results obtained for plasma conditions corresponding to a Debye length equal to the probe radius. These plasma conditions are observed along the Demeter orbit. The model results are found to be in very good agreement with those published by Laframboise (1966 for a spherical probe in a thermal non-flowing plasma. This demonstrates the adequacy of the computation method and of the adjustable numerical parameters (size of the numerical box and mesh, time step, number of macro-particles, etc. for the considered plasma-probe configuration. We also present the results obtained in the case of plasma flowing with mesothermal conditions

  1. Nonlinear Charge and Current Neutralization of an Ion Beam Pulse in a Pre-formed Plasma

    International Nuclear Information System (INIS)

    Kaganovich, Igor D.; Shvets, Gennady; Startsev, Edward; Davidson, Ronald C.

    2001-01-01

    The propagation of a high-current finite-length ion beam in a cold pre-formed plasma is investigated. The outcome of the calculation is the quantitative prediction of the degree of charge and current neutralization of the ion beam pulse by the background plasma. The electric magnetic fields generated by the ion beam are studied analytically for the nonlinear case where the plasma density is comparable in size with the beam density. Particle-in-cell simulations and fluid calculations of current and charge neutralization have been performed for parameters relevant to heavy ion fusion assuming long, dense beams with el >> V(subscript b)/omega(subscript b), where V(subscript b) is the beam velocity and omega subscript b is the electron plasma frequency evaluated with the ion beam density. An important conclusion is that for long, nonrelativistic ion beams, charge neutralization is, for all practical purposes, complete even for very tenuous background plasmas. As a result, the self-magnetic force dominates the electric force and the beam ions are always pinched during beam propagation in a background plasma

  2. Nonlinear Charge and Current Neutralization of an Ion Beam Pulse in a Pre-formed Plasma

    Energy Technology Data Exchange (ETDEWEB)

    Igor D. Kaganovich; Gennady Shvets; Edward Startsev; Ronald C. Davidson

    2001-01-30

    The propagation of a high-current finite-length ion beam in a cold pre-formed plasma is investigated. The outcome of the calculation is the quantitative prediction of the degree of charge and current neutralization of the ion beam pulse by the background plasma. The electric magnetic fields generated by the ion beam are studied analytically for the nonlinear case where the plasma density is comparable in size with the beam density. Particle-in-cell simulations and fluid calculations of current and charge neutralization have been performed for parameters relevant to heavy ion fusion assuming long, dense beams with el >> V(subscript b)/omega(subscript b), where V(subscript b) is the beam velocity and omega subscript b is the electron plasma frequency evaluated with the ion beam density. An important conclusion is that for long, nonrelativistic ion beams, charge neutralization is, for all practical purposes, complete even for very tenuous background plasmas. As a result, the self-magnetic force dominates the electric force and the beam ions are always pinched during beam propagation in a background plasma.

  3. Technique for fabrication of ultrathin foils in cylindrical geometry for liner-plasma implosion experiments with sub-megaampere currents

    Science.gov (United States)

    Yager-Elorriaga, D. A.; Steiner, A. M.; Patel, S. G.; Jordan, N. M.; Lau, Y. Y.; Gilgenbach, R. M.

    2015-11-01

    In this work, we describe a technique for fabricating ultrathin foils in cylindrical geometry for liner-plasma implosion experiments using sub-MA currents. Liners are formed by wrapping a 400 nm, rectangular strip of aluminum foil around a dumbbell-shaped support structure with a non-conducting center rod, so that the liner dimensions are 1 cm in height, 6.55 mm in diameter, and 400 nm in thickness. The liner-plasmas are imploded by discharging ˜600 kA with ˜200 ns rise time using a 1 MA linear transformer driver, and the resulting implosions are imaged four times per shot using laser-shadowgraphy at 532 nm. This technique enables the study of plasma implosion physics, including the magneto Rayleigh-Taylor, sausage, and kink instabilities on initially solid, imploding metallic liners with university-scale pulsed power machines.

  4. Time- and space-resolved light emission and spectroscopic research of the flashover plasma

    Energy Technology Data Exchange (ETDEWEB)

    Gleizer, J. Z.; Krasik, Ya. E. [Physics Department, Technion, Haifa 32000 (Israel); Leopold, J. [Department of Applied Physics, Rafael Laboratories, Box 2250, Haifa 31021 (Israel)

    2015-02-21

    The results of an experimental study of the evolution of surface flashover across the surface of an insulator in vacuum subject to a high-voltage pulse and the parameters of the flashover plasma are reported. For the system studied, flashover is always initiated at the cathode triple junctions. Using time-resolved framing photography of the plasma light emission the velocity of the light emission propagation along the surface of the insulator was found to be ∼2.5·10{sup 8} cm/s. Spectroscopic measurements show that the flashover is characterized by a plasma density of 2–4 × 10{sup 14} cm{sup −3} and neutral and electron temperatures of 2–4 eV and 1–3 eV, respectively, corresponding to a plasma conductivity of ∼0.2 Ω{sup −1} cm{sup −1} and a discharge current density of up to ∼10 kA/cm{sup 2}.

  5. Statistical survey of day-side magnetospheric current flow using Cluster observations: magnetopause

    Directory of Open Access Journals (Sweden)

    E. Liebert

    2017-05-01

    Full Text Available We present a statistical survey of current structures observed by the Cluster spacecraft at high-latitude day-side magnetopause encounters in the close vicinity of the polar cusps. Making use of the curlometer technique and the fluxgate magnetometer data, we calculate the 3-D current densities and investigate the magnetopause current direction, location, and magnitude during varying solar wind conditions. We find that the orientation of the day-side current structures is in accordance with existing magnetopause current models. Based on the ambient plasma properties, we distinguish five different transition regions at the magnetopause surface and observe distinctive current properties for each region. Additionally, we find that the location of currents varies with respect to the onset of the changes in the plasma environment during magnetopause crossings.

  6. Data acquisition and real-time signal processing of plasma diagnostics on ASDEX Upgrade using LabVIEW RT

    International Nuclear Information System (INIS)

    Giannone, L.; Cerna, M.; Cole, R.; Fitzek, M.; Kallenbach, A.; Lueddecke, K.; McCarthy, P.J.; Scarabosio, A.; Schneider, W.; Sips, A.C.C.; Treutterer, W.; Vrancic, A.; Wenzel, L.; Yi, H.; Behler, K.; Eich, T.; Eixenberger, H.; Fuchs, J.C.; Haas, G.; Lexa, G.

    2010-01-01

    The existing VxWorks real-time system for the position and shape control in ASDEX Upgrade has been extended to calculate magnetic flux surfaces in real-time using a multi-core PCI Express system running LabVIEW RT 8.6. real-time signal processing of bolometers and manometers is performed with the on-board FPGA to calculate the measured radiated power flux and particle flux respectively from the raw data. Radiation feedback experiments use halo current measurements from the outer divertor with real-time median filter pre-processing to remove the excursions produced by ELMs. Integration of these plasma diagnostics into the control system by the exchange of XML sheets for communicating the real-time variables to be produced and consumed is in operation. Reflective memory and UDP are employed by the LabVIEW RT plasma diagnostics to communicate with the control system and other plasma diagnostics in a multi-platform real-time network.

  7. Data acquisition and real-time signal processing of plasma diagnostics on ASDEX Upgrade using LabVIEW RT

    Energy Technology Data Exchange (ETDEWEB)

    Giannone, L., E-mail: Louis.Giannone@ipp.mpg.d [Max-Planck-Institut fuer Plasmaphysik, EURATOM-IPP Association, D-85748 Garching (Germany); Cerna, M. [National Instruments, Austin, TX 78759-3504 (United States); Cole, R.; Fitzek, M. [Unlimited Computer Systems GmbH, 82393 Iffeldorf (Germany); Kallenbach, A. [Max-Planck-Institut fuer Plasmaphysik, EURATOM-IPP Association, D-85748 Garching (Germany); Lueddecke, K. [Unlimited Computer Systems GmbH, 82393 Iffeldorf (Germany); McCarthy, P.J. [Department of Physics, University College Cork, Association EURATOM-DCU, Cork (Ireland); Scarabosio, A.; Schneider, W.; Sips, A.C.C.; Treutterer, W. [Max-Planck-Institut fuer Plasmaphysik, EURATOM-IPP Association, D-85748 Garching (Germany); Vrancic, A.; Wenzel, L.; Yi, H. [National Instruments, Austin, TX 78759-3504 (United States); Behler, K.; Eich, T.; Eixenberger, H.; Fuchs, J.C.; Haas, G.; Lexa, G. [Max-Planck-Institut fuer Plasmaphysik, EURATOM-IPP Association, D-85748 Garching (Germany)

    2010-07-15

    The existing VxWorks real-time system for the position and shape control in ASDEX Upgrade has been extended to calculate magnetic flux surfaces in real-time using a multi-core PCI Express system running LabVIEW RT 8.6. real-time signal processing of bolometers and manometers is performed with the on-board FPGA to calculate the measured radiated power flux and particle flux respectively from the raw data. Radiation feedback experiments use halo current measurements from the outer divertor with real-time median filter pre-processing to remove the excursions produced by ELMs. Integration of these plasma diagnostics into the control system by the exchange of XML sheets for communicating the real-time variables to be produced and consumed is in operation. Reflective memory and UDP are employed by the LabVIEW RT plasma diagnostics to communicate with the control system and other plasma diagnostics in a multi-platform real-time network.

  8. Flux surface shape and current profile optimization in tokamaks

    International Nuclear Information System (INIS)

    Dobrott, D.R.; Miller, R.L.

    1977-01-01

    Axisymmetric tokamak equilibria of noncircular cross section are analyzed numerically to study the effects of flux surface shape and current profile on ideal and resistive interchange stability. Various current profiles are examined for circles, ellipses, dees, and doublets. A numerical code separately analyzes stability in the neighborhood of the magnetic axis and in the remainder of the plasma using the criteria of Mercier and Glasser, Greene, and Johnson. Results are interpreted in terms of flux surface averaged quantities such as magnetic well, shear, and the spatial variation in the magnetic field energy density over the cross section. The maximum stable β is found to vary significantly with shape and current profile. For current profiles varying linearly with poloidal flux, the highest β's found were for doublets. Finally, an algorithm is presented which optimizes the current profile for circles and dees by making the plasma everywhere marginally stable

  9. Plasma current start-up experiments without the central solenoid in the TST-2 spherical tokamak

    International Nuclear Information System (INIS)

    Takase, Y.; Ejiri, A.; Shiraiwa, S.; Adachi, Y.; Ishii, N.; Kasahara, H.; Nuga, H.; Ono, Y.; Oosako, T.; Sasaki, M.; Shimada, Y.; Sumitomo, N.; Taguchi, I.; Tojo, H.; Tsujimura, J.; Ushigome, M.; Yamada, T.; Hanada, K.; Hasegawa, M.; Idei, H.; Nakamura, K.; Sakamoto, M.; Sasaki, K.; Sato, K.N.; Zushi, H.; Nishino, N.; Mitarai, O.

    2006-01-01

    Several techniques for initiating the plasma current without the use of the central solenoid are being developed in TST-2. While TST-2 was temporarily located at Kyushu University, two types of start-up scenarios were demonstrated. (1) A plasma current of 4 kA was generated and sustained for 0.28 s by either electron cyclotron wave or electron Bernstein wave, without induction. (2) A plasma current of 10 kA was obtained transiently by induction using only outboard poloidal field coils. In the second scenario, it is important to supply sufficient power for ionization (100 kW of EC power was sufficient in this case), since the vertical field during start-up is not adequate to maintain plasma equilibrium. In addition, electron heating experiments using the X-B mode conversion scenario were performed, and a heating efficiency of 60% was observed at a 100 kW RF power level. TST-2 is now located at the Kashiwa Campus of the University of Tokyo. Significant upgrades were made in both magnetic coil power supplies and RF systems, and plasma experiments have restarted. RF power of up to 400 kW is available in the high-harmonic fast wave frequency range around 20 MHz. Four 200 MHz transmitters are now being prepared for plasma current start-up experiments using RF power in the lower-hybrid frequency range. Preparations are in progress for a new plasma merging experiment (UTST) aimed at the formation and sustainment of ultra-high β ST plasmas

  10. The control of TCV plasmas

    International Nuclear Information System (INIS)

    Lister, J.B.; Hofmann, F.; Moret, J.M.

    1996-07-01

    The general control of tokamak plasmas has evolved considerably over the last few years with an increase in the plasma pulse length, an increase in the control of additional heating and fuelling and an increase in the degree to which the shape of the plasma can be varied. The TCV tokamak is specifically designed to explore the operational benefits of plasma shaping over a wide variety of plasma shapes. Consequently, considerable attention has been given to the control of the poloidal field coil currents which impose the desired shape. This paper deals with all aspects of the control of TCV plasmas, from the diagnostic measurements to the power supplies, via control algorithms and overall supervision. (author) 44 figs., tabs., 25 refs

  11. The control of TCV plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Lister, J B; Hofmann, F; Moret, J M [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP); and others

    1996-07-01

    The general control of tokamak plasmas has evolved considerably over the last few years with an increase in the plasma pulse length, an increase in the control of additional heating and fuelling and an increase in the degree to which the shape of the plasma can be varied. The TCV tokamak is specifically designed to explore the operational benefits of plasma shaping over a wide variety of plasma shapes. Consequently, considerable attention has been given to the control of the poloidal field coil currents which impose the desired shape. This paper deals with all aspects of the control of TCV plasmas, from the diagnostic measurements to the power supplies, via control algorithms and overall supervision. (author) 44 figs., tabs., 25 refs.

  12. Representations of currents and magnetic fields in anisotropic magnetohydrostatic plasma. 2. General theory and examples

    International Nuclear Information System (INIS)

    Heinemann, M.; Pontius, D.H. Jr.

    1991-01-01

    The authors develop a general treatment of field-aligned currents in quasi-static adiabatic plasma. The formalism is an extension of an earlier analysis (Heinemann, 1990) to include electric and gravitational fields. The assumption that the particle motions are adiabatic along the magnetic field leads to an expression for the total current density that is a generalization of expressions given by Grad (1964) and Vasyliunas (1970). The current density is a vector function of the gradients of the field line constants characterizing the plasma and the gradients of field line integrals of the partial derivations of the parallel pressure with respect to the constants. The use of the expression as the current source in Ampere's law leads to an equation governing the equilibrium of the system of plasma and magnetic field. Examples based on bi-Maxwellian distribution functions suggest that the effects of thermal anisotropy can be about as large as the currents due to isotropic plasma and that the effects of parallel electric field are of the same order of magnitude

  13. Two-stream Stability Properties of the Return-Current Layer for Intense Ion Beam Propagation Through Background Plasma

    International Nuclear Information System (INIS)

    Startsev, Edward A.; Davidson, Ronald C.; Dorf, Mikhail

    2009-01-01

    When an ion beam with sharp edge propagates through a background plasma, its current is neutralized by the plasma return current everywhere except at the beam edge over a characteristic transverse distance Δx perpendicular ∼ (delta) pe , where (delta) pe = c/ω pe is the collisionless skin depth, and ω pe is the electron plasma frequency. Because the background plasma electrons neutralizing the ion beam current inside the beam are streaming relative to the background plasma electrons outside the beam, the background plasma can support a two-stream surface-mode excitation. Such surface modes have been studied previously assuming complete charge and current neutralization, and have been shown to be strongly unstable. In this paper we study the detailed stability properties of this two-stream surface mode for an electron flow velocity profile self-consistently driven by the ion beam. In particular, it is shown that the self-magnetic field generated inside the unneutralized current layer, which has not been taken into account previously, completely eliminates the instability

  14. TIME-VARYING DYNAMICAL STAR FORMATION RATE

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Eve J.; Chang, Philip; Murray, Norman, E-mail: evelee@berkeley.edu [Canadian Institute for Theoretical Astrophysics, 60 St. George Street, University of Toronto, Toronto, ON M5S 3H8 (Canada)

    2015-02-10

    We present numerical evidence of dynamic star formation in which the accreted stellar mass grows superlinearly with time, roughly as t {sup 2}. We perform simulations of star formation in self-gravitating hydrodynamic and magnetohydrodynamic turbulence that is continuously driven. By turning the self-gravity of the gas in the simulations on or off, we demonstrate that self-gravity is the dominant physical effect setting the mass accretion rate at early times before feedback effects take over, contrary to theories of turbulence-regulated star formation. We find that gravitational collapse steepens the density profile around stars, generating the power-law tail on what is otherwise a lognormal density probability distribution function. Furthermore, we find turbulent velocity profiles to flatten inside collapsing regions, altering the size-line width relation. This local flattening reflects enhancements of turbulent velocity on small scales, as verified by changes to the velocity power spectra. Our results indicate that gas self-gravity dynamically alters both density and velocity structures in clouds, giving rise to a time-varying star formation rate. We find that a substantial fraction of the gas that forms stars arrives via low-density flows, as opposed to accreting through high-density filaments.

  15. Time-varying and time-invariant dimensions of depression in children and adolescents: Implications for cross-informant agreement.

    Science.gov (United States)

    Cole, David A; Martin, Joan M; Jacquez, Farrah M; Tram, Jane M; Zelkowitz, Rachel; Nick, Elizabeth A; Rights, Jason D

    2017-07-01

    The longitudinal structure of depression in children and adolescents was examined by applying a Trait-State-Occasion structural equation model to 4 waves of self, teacher, peer, and parent reports in 2 age groups (9 to 13 and 13 to 16 years old). Analyses revealed that the depression latent variable consisted of 2 longitudinal factors: a time-invariant dimension that was completely stable over time and a time-varying dimension that was not perfectly stable over time. Different sources of information were differentially sensitive to these 2 dimensions. Among adolescents, self- and parent reports better reflected the time-invariant aspects. For children and adolescents, peer and teacher reports better reflected the time-varying aspects. Relatively high cross-informant agreement emerged for the time-invariant dimension in both children and adolescents. Cross-informant agreement for the time-varying dimension was high for adolescents but very low for children. Implications emerge for theoretical models of depression and for its measurement, especially when attempting to predict changes in depression in the context of longitudinal studies. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

  16. Varying Radii of On-Axis Anode Hollows For kJ-Class Dense Plasma Focus

    Science.gov (United States)

    Shaw, Brian; Chapman, Steven; Falabella, Steven; Pankin, Alexei; Liu, Jason; Link, Anthony; Schmidt, Andréa

    2017-10-01

    A dense plasma focus (DPF) is a compact plasma gun that produces high energy ion beams, up to several MeV, through strong potential gradients. Motivated by particle-in-cell simulations, we have tried a series of hollow anodes on our kJ-class DPF. Each anode has varying hollow sizes, and has been studied to optimize ion beam production in Helium, reduce anode sputter, and increase neutron yields in deuterium. We diagnose the rate at which electrode material is ablated and deposited onto nearby surfaces. This is of interest in the case of solid targets, which perform poorly in the presence of sputter. We have found that the larger the hollow radius produces more energetic ion beams, higher neutron yield, and sputter less than a flat top anode. A complete comparison is presented. This work was prepared by LLNL under Contract DE-AC52-07NA27344 and supported by Office of Defense Nuclear Nonproliferation Research and Development within U.S. Department of Energy's National Nuclear Security Administration.

  17. Performance Testing of Suspension Plasma Sprayed Thermal Barrier Coatings Produced with Varied Suspension Parameters

    Directory of Open Access Journals (Sweden)

    Nicholas Curry

    2015-07-01

    Full Text Available Suspension plasma spraying has become an emerging technology for the production of thermal barrier coatings for the gas turbine industry. Presently, though commercial systems for coating production are available, coatings remain in the development stage. Suitable suspension parameters for coating production remain an outstanding question and the influence of suspension properties on the final coatings is not well known. For this study, a number of suspensions were produced with varied solid loadings, powder size distributions and solvents. Suspensions were sprayed onto superalloy substrates coated with high velocity air fuel (HVAF -sprayed bond coats. Plasma spray parameters were selected to generate columnar structures based on previous experiments and were maintained at constant to discover the influence of the suspension behavior on coating microstructures. Testing of the produced thermal barrier coating (TBC systems has included thermal cyclic fatigue testing and thermal conductivity analysis. Pore size distribution has been characterized by mercury infiltration porosimetry. Results show a strong influence of suspension viscosity and surface tension on the microstructure of the produced coatings.

  18. PCA-based detection of damage in time-varying systems

    Science.gov (United States)

    Bellino, A.; Fasana, A.; Garibaldi, L.; Marchesiello, S.

    2010-10-01

    When performing Structural Health Monitoring, it is well known that the natural frequencies do not depend only on the damage but also on environmental conditions, such as temperature and humidity. The Principal Component Analysis is used to take this problem into account, because it allows eliminating the effect of external factors. The purpose of the present work is to show that this technique can be successfully used not only for time-invariant systems, but also for time-varying ones. Referring to the latter, one of the most studied systems which shows these characteristics is the bridge with crossing loads, such as the case of the railway bridge studied in present paper; in this case, the mass and the velocity of the train can be considered as "environmental" factors.This paper, after a brief description of the PCA method and one example of its application on time-invariant systems, presents the great potentialities of the methodology when applied to time-varying systems. The results show that this method is able to better detect the presence of damage and also to properly distinguish among different levels of crack depths.

  19. Calculation of the electromagnetic forces on the ASDEX upgrade vacuum vessel on disruption of the plasma current

    International Nuclear Information System (INIS)

    Preis, H.

    1986-01-01

    This study investigates the magnetic field diffusion through the vacuum vessel of the ASDEX Upgrade tokamak that occurs on sudden disruption of the plasma current. Eddy currents are thereby produced in the vessel wall. Their time behaviour and distribution are determined. Furthermore, the vessel is permeated by various magnetic fields which, together with the eddy currents, exert magnetic forces in the vessel wall. These are also calculated. These numerical analyses are performed for two of the modes of operation envisaged for ASDEX Upgrade: the so-called limiter and single-null magnetic field configurations. (orig.)

  20. Real time plasma control experiments using the JET auxiliary plasma heating systems as the actuator

    International Nuclear Information System (INIS)

    Zornig, N.H.

    1999-01-01

    The role of the Real Time Power Control system (RTPC) in the Joint European Torus (JET) is described in depth. The modes of operation are discussed in detail and a number of successful experiments are described. These experiments prove that RTPC can be used for a wide range of experiments, including: (1) Feedback control of plasma parameters in real time using Ion Cyclotron Resonance Heating (ICRH) or Neutral Beam Heating (NBH) as the actuator in various JET operating regimes. It is demonstrated that in a multi-parameter space it is not sufficient to control one global plasma parameter in order to avoid performance limiting events. (2) Restricting neutron production and subsequent machine activation resulting from high performance pulses. (3) The simulation of α-particle heating effects in a DT-plasma in a D-only plasma. The heating properties of α-particles are simulated using ICRH-power, which is adjusted in real time. The simulation of α-particle heating in JET allows the effects of a change in isotopic mass to be separated from α-particle heating. However, the change in isotopic mass of the plasma ions appears to affect not only the global energy confinement time (τ E ) but also other parameters such as the electron temperature at the plasma edge. This also affects τ E , making it difficult to make a conclusive statement about any isotopic effect. (4) For future JET experiments a scheme has been designed which simulates the behaviour of a fusion reactor experimentally. The design parameters of the International Thermonuclear Experimental Reactor (ITER) are used. In the proposed scheme the most relevant dimensionless plasma parameters are similar in JET and ITER. It is also shown how the amount of heating may be simulated in real time by RTPC using the electron temperature and density as input parameters. The results of two demonstration experiments are presented. (author)