International Nuclear Information System (INIS)
Omura, Yoshiharu; Matsumoto, Hiroshi.
1989-01-01
Past theoretical and numerical studies of the nonlinear evolution of electromagnetic cyclotron waves are reviewed. Such waves are commonly observed in space plasmas such as Alfven waves in the solar wind or VLF whistler mode waves in the magnetosphere. The use of an electromagnetic full-particle code to study an electron cyclotron wave and of an electromagnetic hybrid code to study an ion cyclotron wave is demonstrated. Recent achievements in the simulations of nonlinear revolution of electromagnetic cyclotron waves are discussed. The inverse cascading processes of finite-amplitude whistler and Alfven waves is interpreted in terms of physical elementary processes. 65 refs
International Nuclear Information System (INIS)
Stix, H.
1981-01-01
The physics of Alfven-wave heating is particularly sensitive to the character of the linear mode conversion which occurs at the Alfven resonance layer. Parameter changes can profoundly affect both the location within the plasma and the mechanism for the power absorption. Under optimal conditions the heating power may be absorbed by electron Landau damping and by electron transit-time magnetic pumping in the plasma interior, or by the same processes acting near the resonance layer on the mode-converted kinetic Alfven wave. The method is outlined for computing the coefficients for reflection, transmission and absorption at the resonance layer and some representative results are offered
Alfven Waves in Gyrokinetic Plasmas
International Nuclear Information System (INIS)
Lee, W.W.; Qin, H.
2003-01-01
A brief comparison of the properties of Alfven waves that are based on the gyrokinetic description with those derived from the MHD equations is presented. The critical differences between these two approaches are the treatment of the ion polarization effects. As such, the compressional Alfven waves in a gyrokinetic plasma can be eliminated through frequency ordering, whereas geometric simplifications are needed to decouple the shear Alfven waves from the compressional Alfven waves within the context of MHD. Theoretical and numerical procedures of using gyrokinetic particle simulation for studying microturbulence and kinetic-MHD physics including finite Larmor radius effects are also presented
Nonlinear surface Alfven waves
International Nuclear Information System (INIS)
Cramer, N.F.
1991-01-01
The problem of nonlinear surface Alfven waves propagating on an interface between a plasma and a vacuum is discussed, with dispersion provided by the finite-frequency effect, i.e. the finite ratio of the frequency to the ion-cyclotron frequency. A set of simplified nonlinear wave equations is derived using the method of stretched co-ordinates, and another approach uses the generation of a second-harmonic wave and its interaction with the first harmonic to obtain a nonlinear dispersion relation. A nonlinear Schroedinger equation is then derived, and soliton solutions found that propagate as solitary pulses in directions close to parallel and antiparallel to the background magnetic field. (author)
Shear Alfven waves in tokamaks
International Nuclear Information System (INIS)
Kieras, C.E.
1982-12-01
Shear Alfven waves in an axisymmetric tokamak are examined within the framework of the linearized ideal MHD equations. Properties of the shear Alfven continuous spectrum are studied both analytically and numerically. Implications of these results in regards to low frequency rf heating of toroidally confined plasmas are discussed. The structure of the spatial singularities associated with these waves is determined. A reduced set of ideal MHD equations is derived to describe these waves in a very low beta plasma
Perturbation theory for Alfven wave
International Nuclear Information System (INIS)
Yoshida, Z.; Mahajan, S.M.
1995-01-01
The Alfven wave is the dominant low frequency transverse mode of a magnetized plasma. The Alfven wave propagation along the magnetic field, and displays a continuous spectrum even in a bounded plasma. This is essentially due to the degeneracy of the wave characteristics, i.e. the frequency (ω) is primarily determined by the wave number in the direction parallel to the ambient magnetic field (k parallel ) and is independent of the perpendicular wavenumbers. The characteristics, that are the direction along which the wave energy propagates, are identical to the ambient magnetic field lines. Therefore, the spectral structure of the Alfven wave has a close relationship with the geometric structure of the magnetic field lines. In an inhomogeneous plasma, the Alfven resonance constitutes a singularity for the defining wave equation; this results in a singular eigenfunction corresponding to the continuous spectrum. The aim of this review is to present an overview of the perturbation theory for the Alfven wave. Emphasis is placed on those perturbations of the continuous spectrum which lead to the creation of point spectra. Such qualitative changes in the spectrum are relevant to many plasma phenomena
Alfven wave heating and stability
International Nuclear Information System (INIS)
Villard, L.; Brunner, S.; Jaun, A.; Vaclavik, J.
1994-10-01
Alfven waves in fusion plasmas play an important role in a number of situations. First, in Alfven Wave Heating (AWH) schemes. Second, both theory and experiment have demonstrated the existence of Global Alfven Eigenmodes (GAEs). GAEs have been observed in different tokamaks (PRETEXT, TCA, TEXTOR, etc.) and, more recently, in a stellarator (Wendelstein 7-AS) where they were shown to become unstable under intense Neutral Beam injection. Third, the existence and possible destabilization by fast ions of Toroidicity induced Alfven Eigenmodes (TAEs) has been evidenced both theoretically and experimentally. This destabilization could hamper the operation of a magnetically confined fusion reactor by setting a limit on the number of fusion alpha particles in the plasma. It is therefore crucial to understand the mechanisms leading to the occurrence of the instability and also those that can stabilize the TAEs by increasing the strength of the damping. The aim is to be able to devise possible ways to avoid the instability of Alfven eigenmodes in a region of parameter space that is compatible with the functioning of a fusion reactor. A global perturbative approach is presented to tackle the problem of the linear stability of TAEs. Our model computes the overall wave particle power transfers to the different species and thus could also be applied to the study of alpha power extraction in the presence of Alfven waves. We indicate also how to go beyond the perturbative approach. (author) 15 figs., 38 refs
International Nuclear Information System (INIS)
Besson, G.; Borg, G.G.; Lister, J.B.; Marmillod, Ph.; Braun, F.; Murphy, A.B.; Noterdaeme, J.M.; Ryter, F.; Wesner, F.
1990-01-01
An experiment has been completed on ASDEX to study the response of the plasma to Alfven wave heating (AWH). Antenna excitation was provided by the old TCA rf generator with an output power capability of 500 kW. Two poloidal loop antennas were installed at the east and west ends of the tokamak allowing either N=1 or N=2 phasings. Since the largest antenna coupling to the Alfven resonance is provided by the m=1 surface wave, the antenna consisted only of a single element on the low field side, whereas in TCA the antennas are located on the top and the bottom of the torus. The antenna elements consisted of 2 parallel bars of inductance 730 nH and, as in TCA, were left unshielded. A typical antenna circulating current of 2 kA peak at 1.80 MHz was provided for the experiments. (author) 3 refs., 4 figs
Resonant Alfven waves on auroral field lines
International Nuclear Information System (INIS)
Chiu, Y.T.
1987-01-01
It is shown that resonant Alfven waves on dipole magnetic field geometry and plasma distributions suitable for auroral field lines can be conveniently treated in the theory of Mathieu functions. Resurgent interest in invoking large-scale Alfven waves to structure some elements of auroral electrodynamics calls for interpretation of measured perpendicular electric and magnetic disturbance fields in terms of Alfven waves. The ability to express the resonant eigenmodes in closed form in terms of Mathieu functions allows for convenient tests of the Alfven wave structuring hypothesis. Implications for current vector electric and magnetic disturbance measurements are discussed
SURFACE ALFVEN WAVES IN SOLAR FLUX TUBES
Energy Technology Data Exchange (ETDEWEB)
Goossens, M.; Andries, J.; Soler, R.; Van Doorsselaere, T. [Centre for Plasma Astrophysics, Department of Mathematics, Katholieke Universiteit Leuven, Celestijnenlaan 200B, 3001 Leuven (Belgium); Arregui, I.; Terradas, J., E-mail: marcel.goossens@wis.kuleuven.be [Solar Physics Group, Departament de Fisica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain)
2012-07-10
Magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. Alfven waves and magneto-sonic waves are particular classes of MHD waves. These wave modes are clearly different and have pure properties in uniform plasmas of infinite extent only. Due to plasma non-uniformity, MHD waves have mixed properties and cannot be classified as pure Alfven or magneto-sonic waves. However, vorticity is a quantity unequivocally related to Alfven waves as compression is for magneto-sonic waves. Here, we investigate MHD waves superimposed on a one-dimensional non-uniform straight cylinder with constant magnetic field. For a piecewise constant density profile, we find that the fundamental radial modes of the non-axisymmetric waves have the same properties as surface Alfven waves at a true discontinuity in density. Contrary to the classic Alfven waves in a uniform plasma of infinite extent, vorticity is zero everywhere except at the cylinder boundary. If the discontinuity in density is replaced with a continuous variation of density, vorticity is spread out over the whole interval with non-uniform density. The fundamental radial modes of the non-axisymmetric waves do not need compression to exist unlike the radial overtones. In thin magnetic cylinders, the fundamental radial modes of the non-axisymmetric waves with phase velocities between the internal and the external Alfven velocities can be considered as surface Alfven waves. On the contrary, the radial overtones can be related to fast-like magneto-sonic modes.
Computer simulation of driven Alfven waves
International Nuclear Information System (INIS)
Geary, J.L. Jr.
1986-01-01
The first particle simulation study of shear Alfven wave resonance heating is presented. Particle simulation codes self-consistently follow the time evolution of the individual and collective aspects of particle dynamics as well as wave dynamics in a fully nonlinear fashion. Alfven wave heating is a possible means of increasing the temperature of magnetized plasmas. A new particle simulation model was developed for this application that incorporates Darwin's formulation of the electromagnetic fields with a guiding center approximation for electron motion perpendicular to the ambient magnetic field. The implementation of this model and the examination of its theoretical and computational properties are presented. With this model, several cases of Alfven wave heating is examined in both uniform and nonuniform simulation systems in a two dimensional slab. For the inhomogeneous case studies, the kinetic Alfven wave develops in the vicinity of the shear Alfven resonance region
Discrete Alfven waves in the TORTUS tokamak
International Nuclear Information System (INIS)
Amagishi, Y.; Ballico, M.J.; Cross, R.C.; Donnely, I.J.
1989-01-01
Discrete Alfven Waves (DAWs) have been observed as antenna resistance peaks and as enhanced edge fields in the TORTUS tokamak during Alfven wave heating experiments. A kinetic theory code has been used to calculate the antenna loading and the structure of the DAW fields for a range of plasma current and density profiles. There is fair agreement between the measured and predicted amplitude of the DAW fields in the plasma edge when both are normalized to the same antenna power
Alfven wave. DOE Critical Review Series
International Nuclear Information System (INIS)
Hasegawa, A.; Uberoi, C.
1982-01-01
This monograph deals with the properties of Alfven waves and with their application to fusion. The book is divided into 7 chapters dealing with linear properties in homogeneous and inhomogeneous plasmas. Absorption is treated by means of kinetic theory. Instabilities and nonlinear processes are treated in Chapters 1 to 6, and the closing chapter is devoted to theory and experiments in plasma heating by Alfven waves
Nonlinear evolution of astrophysical Alfven waves
Spangler, S. R.
1984-01-01
Nonlinear Alfven waves were studied using the derivative nonlinear Schrodinger equation as a model. The evolution of initial conditions, such as envelope solitons, amplitude-modulated waves, and band-limited noise was investigated. The last two furnish models for naturally occurring Alfven waves in an astrophysical plasma. A collapse instability in which a wave packet becomes more intense and of smaller spatial extent was analyzed. It is argued that this instability leads to enhanced plasma heating. In studies in which the waves are amplified by an electron beam, the instability tends to modestly inhibit wave growth.
The influence of multiple ion species on Alfven wave dispersion and Alfven wave plasma heating
International Nuclear Information System (INIS)
Elfimov, A.G.; Tataronis, J.A.; Hershkowitz, N.
1994-01-01
In this paper, the effects of light impurities, such as deuterium, helium, or carbon, on Alfven wave dispersion characteristics are explored. It is shown that a small population of light impurities in a hydrogen plasma modify the dispersion of the global Alfven waves and the Alfven continuum in such a way that the wave frequency depends weakly on the toroidal wave number. It is also shown that the global Alfven wave enters into the Alfven continuum. Under these conditions, it is possible to heat plasma efficiently by employing an antenna with a broad toroidal wavelength spectrum. The relationship between impurity concentration and the efficiency of Alfven wave heating is explored. Under appropriate conditions, the results indicate that in the presence of impurities, Alfven waves can heat electrons predominantly in the central part of the plasma. This effect is explored via a series of numerical calculations of the heating specifically for the Phaedrus-T Alfven wave heating experiment [Phys. Fluids B 5, 2506 (1993)
Particle acceleration by Alfven wave turbulence in radio galaxies
International Nuclear Information System (INIS)
Eilek, J.A.
1986-01-01
Radio galaxies show evidence for acceleration of relativistic electrons locally within the diffuse radio luminous plasma. One likely candidate for the reacceleration mechanism is acceleration by magnetohydrodynamic turbulence which exists within the plasma. If Alfven waves are generated by a fluid turbulent cascade described by a power law energy-wavenumber spectrum, the particle spectrum in the presence of synchrotron losses will evolve towards an asymptotic power law which agrees with the particle spectra observed in these sources
Plasma heating by kinetic Alfven wave
International Nuclear Information System (INIS)
Assis, A.S. de.
1982-01-01
The heating of a nonuniform plasma (electron-ion) due to the resonant excitation of the shear Alfven wave in the low β regime is studied using initially the ideal MHD model and posteriorly using the kinetic model. The Vlasov equation for ions and the drift kinetic equation for electrons have been used. Through the ideal MHD model, it is concluded that the energy absorption is due to the continuous spectrum (phase mixing) which the shear Alfven wave has in a nonuniform plasma. An explicit expression for the energy absorption is derived. Through the kinetic model it is concluded that the energy absorption is due to a resonant mode convertion of the incident wave into the kinetic Alfven wave which propagates away from the resonant region. Its electron Landau damping has been observed. There has been a concordance with the MHD calculations. (Author) [pt
Nonlinear Evolution of Alfvenic Wave Packets
Buti, B.; Jayanti, V.; Vinas, A. F.; Ghosh, S.; Goldstein, M. L.; Roberts, D. A.; Lakhina, G. S.; Tsurutani, B. T.
1998-01-01
Alfven waves are a ubiquitous feature of the solar wind. One approach to studying the evolution of such waves has been to study exact solutions to approximate evolution equations. Here we compare soliton solutions of the Derivative Nonlinear Schrodinger evolution equation (DNLS) to solutions of the compressible MHD equations.
The phase mixing of shear Alfven waves
International Nuclear Information System (INIS)
Uberoi, C.
1993-04-01
The phase mixing of shear Alfven waves is discussed as a current sheets crossover phenomena by using the well-behaved time dependent solution of the Alfven wave equation. This method is a more direct approach than the initial value problem technique to find the collisionless damping time of the surface waves, which as it represents the coherency loss is argued to be the phase mixing time. The phase mixing time obtained by both the methods compares well. The direct method however, has an advantage that no particular profile for the magnetic field variation need to be chosen and secondly the phase mixing time and the time scale for which the resistivity effects become important can be expressed conveniently in terms of Alfven transit times before crossover. (author). 11 refs
Alfven wave absorption in dissipative plasma
International Nuclear Information System (INIS)
Gavrikov, M B; Taiurskii, A A
2017-01-01
We consider nonlinear absorption of Alfven waves due to dissipative effects in plasma and relaxation of temperatures of electrons and ions. This study is based on an exact solution of the equations of two-fluid electromagnetic hydrodynamics (EMHD) of plasma. It is shown that in order to study the decay of Alfven waves, it suffices to examine the behavior of their amplitudes whose evolution is described by a system of ordinary differential equations (ODEs) obtained in this paper. On finite time intervals, the system of equations on the amplitudes is studied numerically, while asymptotic integration (the Hartman-Grobman theorem) is used to examine its large-time behavior. (paper)
Alfven wave heating in a tokamak reactor
International Nuclear Information System (INIS)
Borg, G.G.; Appert, K.; Knight, A.J.; Lister, J.B.; Vaclavik, J.
1990-01-01
A number of features of Alfven wave heating make it potentially attractive for use in large tokamak reactors. Among them are the availability and relativity low cost of the power supplies, the potential ability to act selectively on the current profile, and the probable absence of operational limits in size, fields or density. The physics of Alfven wave heating in a large tokamak is assessed. Present theoretical understanding of mode coupling and antenna loading is extrapolated to a large machine. The problem of a recessed antenna is analysed. Calculations of loading and discussion of various heating scenarios for the particular case of NET are also presented. (author). 23 refs, 18 figs, 4 tabs
Alfven wave resonances and flow induced by nonlinear Alfven waves in a stratified atmosphere
International Nuclear Information System (INIS)
Stark, B. A.; Musielak, Z. E.; Suess, S. T.
1996-01-01
A nonlinear, time-dependent, ideal MHD code has been developed and used to compute the flow induced by nonlinear Alfven waves propagating in an isothermal, stratified, plane-parallel atmosphere. The code is based on characteristic equations solved in a Lagrangian frame. Results show that resonance behavior of Alfven waves exists in the presence of a continuous density gradient and that the waves with periods corresponding to resonant peaks exert considerably more force on the medium than off-resonance periods. If only off-peak periods are considered, the relationship between the wave period and induced longitudinal velocity shows that short period WKB waves push more on the background medium than longer period, non-WKB, waves. The results also show the development of the longitudinal waves induced by finite amplitude Alfven waves. Wave energy transferred to the longitudinal mode may provide a source of localized heating
Scale separation closure and Alfven wave turbulence
International Nuclear Information System (INIS)
Chen, C.Y.; Mahajan, S.M.
1985-04-01
Based on the concept of scale separation between coherent response function and incoherent source for renormalized turbulence theories, a closure scheme is proposed. A model problem dealing with shear-Alfven wave turbulence is numerically solved; the solution explicitly shows expected turbulence features such as frequency shift from linear modes, band-broadening, and a power law dependence for the turbulence spectrum
The spectrum of axisymmetric torsional Alfven waves
International Nuclear Information System (INIS)
Sy, W.N.
1977-03-01
The spectrum of axisymmetric torsional Alfven waves propagating in a cylindrical, non-uniform, resistive plasma waveguide has been analysed by a method of singular perturbations. A simple condition has been derived which predicts whether the spectrum is continuous or discrete under given physical conditions. Application of this result to resolve an apparent discrepancy in experimental observations is briefly discussed. (Author)
Experimental observation of Alfven wave cones
International Nuclear Information System (INIS)
Gekelman, W.; Leneman, D.; Maggs, J.; Vincena, S.
1994-01-01
The spatial evolution of the radial profile of the magnetic field of a shear Alfven wave launched by a disk exciter with radius on the order of the electron skin depth has been measured. The waves are launched using wire mesh disk exciters of 4 mm and 8 mm radius into a helium plasma of density about 1.0x10 12 cm -3 and magnetic field 1.1 kG. The electron skin depth δ=c/ω pe is about 5 mm. The current channel associated with the shear Alfven wave is observed to spread with distance away from the exciter. The spreading follows a cone-like pattern whose angle is given by tan θ=k A δ, where k A is the Alfven wave number. The dependence of the magnetic profiles on wave frequency and disk size are presented. The effects of dissipation by electron--neutral collisions and Landau damping are observed. The observations are in excellent agreement with theoretical predictions [Morales et al., Phys. Plasmas 1, 3765 (1994)
Alfven wave studies on a tokamak
International Nuclear Information System (INIS)
Kortbawi, D.
1987-10-01
The continuum modes of the shear Alfven resonance are studied on the Tokapole II device, a small tokamak operated in a four node poloidal divertor configuration. A variety of antenna designs and the efficiency with which they deliver energy to the resonant layer are discussed. The spatial structure of the driven waves is studied by means of magnetic probes inserted into the current channel. In an attempt to optimize the coupling of energy in to the resonant layer, the angle of antenna currents with respect to the equilibrium field, antenna size, and plasma-to-antenna distance are varied. The usefulness of Faraday shields, particle shields, and local limiters are investigated. Antennas should be well shielded, either a dense Faraday shield or particle shield being satisfactory. The antenna should be large and very near to the plasma. The wave magnetic fields measured show a spatial resonance, the position of which varies with the value of the equilibrium field and mass density. They are polarized perpendicular to the equilibrium field. A wave propagates radially in to the resonant surface where it is converted to the shear Alfven wave. The signal has a short risetime and does not propagate far toroidally. These points are all consistent with a strongly damped shear Alfven wave. Comparisons of this work to theoretical predictions and results from other tokamaks are made
Nonlinear coupled Alfven and gravitational waves
International Nuclear Information System (INIS)
Kaellberg, Andreas; Brodin, Gert; Bradley, Michael
2004-01-01
In this paper we consider nonlinear interaction between gravitational and electromagnetic waves in a strongly magnetized plasma. More specifically, we investigate the propagation of gravitational waves with the direction of propagation perpendicular to a background magnetic field and the coupling to compressional Alfven waves. The gravitational waves are considered in the high-frequency limit and the plasma is modeled by a multifluid description. We make a self-consistent, weakly nonlinear analysis of the Einstein-Maxwell system and derive a wave equation for the coupled gravitational and electromagnetic wave modes. A WKB-approximation is then applied and as a result we obtain the nonlinear Schroedinger equation for the slowly varying wave amplitudes. The analysis is extended to 3D wave pulses, and we discuss the applications to radiation generated from pulsar binary mergers. It turns out that the electromagnetic radiation from a binary merger should experience a focusing effect, that in principle could be detected
Guided propagation of Alfven waves in a toroidal plasma
International Nuclear Information System (INIS)
Borg, G.G.; Brennan, M.H.; Cross, R.C.; Giannone, L.; Donnelly, I.J.
1985-01-01
Experimental results are presented which show that the Alfven wave is strongly guided by magnetic fields. The experiment was conducted in a Tokamak plasma using a small dipole loop antenna to generate a localised Alfven ray. The ray was observed, with magnetic probes, to propagate as a localised disturbance along the curved lines of the steady magnetic field without significant refraction due to the effects of finite frequency, resistivity or magnetic field gradients. These results agree with theoretical predictions and demonstrate that a localised Alfven wave may be excited, and may propagate, independently of the fast wave, as expected. The implication of these results for the Alfven wave heating scheme is discussed. (author)
Guided propagation of Alfven waves in a toroidal plasma
Energy Technology Data Exchange (ETDEWEB)
Borg, G G; Brennan, M H; Cross, R C; Giannone, L.; Donnelly, I J
1985-10-01
Experimental results are presented which show that the Alfven wave is strongly guided by magnetic fields. The experiment was conducted in a Tokamak plasma using a small dipole loop antenna to generate a localised Alfven ray. The ray was observed, with magnetic probes, to propagate as a localised disturbance along the curved lines of the steady magnetic field without significant refraction due to the effects of finite frequency, resistivity or magnetic field gradients. These results agree with theoretical predictions and demonstrate that a localised Alfven wave may be excited, and may propagate, independently of the fast wave, as expected. The implication of these results for the Alfven wave heating scheme is discussed.
Nonlinear propagation of short wavelength drift-Alfven waves
DEFF Research Database (Denmark)
Shukla, P. K.; Pecseli, H. L.; Juul Rasmussen, Jens
1986-01-01
Making use of a kinetic ion and a hydrodynamic electron description together with the Maxwell equation, the authors derive a set of nonlinear equations which governs the dynamics of short wavelength ion drift-Alfven waves. It is shown that the nonlinear drift-Alfven waves can propagate as two-dim...
Alfven wave experiments on the TORTUS tokamak
International Nuclear Information System (INIS)
Ballico, M.J.; Bowden, M.; Brand, G.F.; Brennan, M.H.; Cross, R.C.; Fekete, P.; James, B.W.
1989-01-01
Results are presented on the first observations of the Discrete Alfven Wave (DAW) and the first measurements of laser scattering off the kinetic Alfven wave in the TORTUS tokamak. TORTUS is a relatively small device, with major radius R=0.44m, minor radius 0.1m and has previously been operated routinely with B Φ =0.7T, I p =20 kA and n e ∼ 1x10 19 m -3 . Under these conditions, and over a wide frequency range (1-14 MHz), there has been no evidence of the DAW modes observed on TCA. Recently, a minor upgrade of TORTUS has permitted routine operation at B Φ =1.0 T, I p =39 kA, q(a)∼5 and n e ∼1-4 x 10 19 m -3 . At the operating frequency, 3.2 MHz, chosen for this study, DAW modes are observed clearly at both low and high densities. The appearance of DAW modes appears to be due to a steeper current profile at the higher plasma currents now generated in TORTUS. The general behaviour of DAW modes is in fact quite sensitive to the density and current profiles, indicating that DAW modes should provide a useful current profile diagnostic. (author) 6 refs., 2 figs
Nonlinear propagation of Alfven waves in cometary plasmas
International Nuclear Information System (INIS)
Lakhina, G.S.; Shukla, P.K.
1987-07-01
Large amplitude Alfven waves propagating along the guide magnetic field in a three-component plasma are shown to be modulationally unstable due to their nonlinear interaction with nonresonant electrostatic density fluctuations. A new class of subsonic Alfven soliton solutions are found to exist in the three-component plasma. The Alfven solitons can be relevant in explaining the properties of hydromagnetic turbulence near the comets. (author). 15 refs
Ion Acceleration in Plasmas with Alfven Waves
International Nuclear Information System (INIS)
Kolesnychenko, O.Ya.; Lutsenko, V.V.; White, R.B.
2005-01-01
Effects of elliptically polarized Alfven waves on thermal ions are investigated. Both regular oscillations and stochastic motion of the particles are observed. It is found that during regular oscillations the energy of the thermal ions can reach magnitudes well exceeding the plasma temperature, the effect being largest in low-beta plasmas (beta is the ratio of the plasma pressure to the magnetic field pressure). Conditions of a low stochasticity threshold are obtained. It is shown that stochasticity can arise even for waves propagating along the magnetic field provided that the frequency spectrum is non-monochromatic. The analysis carried out is based on equations derived by using a Lagrangian formalism. A code solving these equations is developed. Steady-state perturbations and perturbations with the amplitude slowly varying in time are considered
Alfven wave coupling in large tokamaks
International Nuclear Information System (INIS)
Borg, G.G.; Knight, A.J.; Lister, J.B.; Appert, K.; Vaclavik, J.
1988-01-01
Supplementary plasma heating by Alfven waves (AWH) has been extensively studied both theoretically and experimentally for small, low temperature plasmas. However, only a few studies of AWH have been performed for fusion plasmas. In this paper the cylindrical kinetic code ISMENE is used to address problems af AWH in a large tokamak. The results of calculations are presented which show that the antenna loading scales with frequency and vessel dimensions according to ideal MHD theory. A sample scaling of the experimental antenna loading measured in TCA to the loading predicted for a fusion plasma is presented. We discuss whether this loading leads to a realistic antenna design. The choice of a suitable antenna configuration, mode number and operating frequency is presented for NET parameters with a typical operating scenario. (author) 6 figs., 8 refs
Effect of Dust Grains on Solitary Kinetic Alfven Wave
International Nuclear Information System (INIS)
Li Yangfang; Wu, D. J.; Morfill, G. E.
2008-01-01
Solitary kinetic Alfven wave has been studied in dusty plasmas. The effect of the dust charge-to-mass ratio is considered. We derive the Sagdeev potential for the soliton solutions based on the hydrodynamic equations. A singularity in the Sagdeev potential is found and this singularity results in a bell-shaped soliton. The soliton solutions comprise two branches. One branch is sub-Alfvenic and the soliton velocities are much smaller than the Alfven speed. The other branch is super-Alfvenic and the soliton velocities are very close to or greater than the Alfven speed. Both compressive and rarefactive solitons can exist in each branch. For the sub-Alfvenic branch, the rarefactive soliton is a bell shape curve which is much narrower than the compressive one. In the super-Alfvenic branch, however, the compressive soliton is bell-shaped and the rarefactive one is broadened. We also found that the super-Alfvenic solitons can develop to other structures. When the charge-to-mass ratio of the dust grains is sufficiently high, the width of the rarefactive soliton will increase extremely and an electron density depletion will be observed. When the velocity is much higher than the Alfven speed, the bell-shaped soliton will transit to a cusped structure.
Alfven wave propagation in a partially ionized plasma
International Nuclear Information System (INIS)
Watts, Christopher; Hanna, Jeremy
2004-01-01
Results from a laboratory study of the dispersion relation of Alfven waves propagating through a partially ionized plasma are presented. The plasma is generated using a helicon source, creating a high density, current-free discharge, where the source can be adjusted to one of several modes with varying neutral fraction. Depending on the neutral fraction, the measured dispersion curve of shear Alfven waves can change significantly. Measurement results are compared with theoretical predictions of the effect of neutral particles on Alfven wave propagation. In fitting the theory, the neutral fraction is independently estimated using two simple particle transport models, one collisionless, the other collisional. The two models predict comparable neutral fractions, and agree well with the neutral fraction required for the Alfven dispersion theory
Excitation and Propagation of Alfven Waves in a Helicon Discharge
International Nuclear Information System (INIS)
Grulke, Olaf; Klinger, Thomas; Franck, Christian M.
2003-01-01
An experimental study of shear Alfven waves in a linearly magnetized plasma is presented. Shear Alfven waves are electromagnetic waves propagating parallel to the background magnetic field without compression of the plasma at a frequency well below the ion cyclotron frequency and a wavelength inversely proportional to the square root of the plasma density. A basic condition on laboratory investigations is that the Alfven wavelength must be significantly smaller than the device dimension. This makes Alfven waves difficult to investigate in laboratory experiments and most studies are performed in space, where typical Alfven wavelengths of several kilometers are observed. The results of these studies are often ambiguous due to difficulties concerning the measurements of plasma parameters and the magnetic field geometry. The primary motivation for the present paper is the investigation of Alfven wave propagation in a well defined laboratory situation. The experiments are conducted in the linear VINETA device. The necessary operational regime is achieved by the large axial device length of 4.5m and the use of a helicon plasma source providing high density plasmas with ionization degrees of up to 100%. The Argon plasma is magnetized by a set of 36 magnetic field coils, which produce a maximum magnetic field of 0.1T on the device axis. With this configuration a plasma-β of ≥ 10-4 is achieved, which exceeds the electron to ion mass ration, and the ion cyclotron frequency is ≅ 250kHz. Langmuir probes provide detailed informations on the time-averaged plasma profiles. Magnetic field perturbations for the excitation of Alfven waves are generated by a current loop, which is introduced into the plasma. The surface normal of the current loop is directed perpendicular to the magnetic field. The waves's dispersion relation in dependence of plasma parameters is determined by spatially resolved B probe measurements
Numerical analysis of quasiperiodic perturbations for the Alfven wave
International Nuclear Information System (INIS)
Yamakoshi, Y.; Muto, K.; Yoshida, Z.
1994-01-01
The Alfven wave may have a localized eigenfunction when it propagates on a chaotic magnetic field. The Arnold-Beltrami-Childress (ABC) flow is a paradigm of chaotic stream lines and is a simple exact solution to the three-dimensional force-free plasma equilibrium equations. The three-dimensional structure of the magnetic field is represented by sinusoidal quasiperiodic modulation. The short wavelength Alfven wave equation for the ABC-flow magnetic field has a quasiperiodic potential term, which induces interference among ''Bragg-reflected'' waves with irregular phases. Then the eigenfunction decays at long distance and a point spectrum occurs. Two different types of short wavelength modes have numerically analyzed to demonstrate the existence of localized Alfven wave eigenmodes
Alfven wave experiments in the Phaedrus-T tokamak
International Nuclear Information System (INIS)
Majeski, R.; Probert, P.; Moroz, P.; Intrator, T.; Breun, R.; Brouchous, D.; Che, H.Y.; DeKock, J.R.; Diebold, D.; Doczy, M.; Fonck, R.; Hershkowitz, N.; Johnson, R.D.; Kishinevsky, M.; McKee, G.; Meyer, J.; Nonn, P.; Oliva, S.P.; Pew, J.; Sorensen, J.; Tanaka, T.; Vukovic, M.; Winz, G.
1993-01-01
Heating in the Alfven resonant regime has been demonstrated in the Phaedrus-T tokamak [Fusion Technol. 19, 1327 (1991)]. Electron heating during injection of radio-frequency (rf) power is indicated by a 30%--40% drop in loop voltage and modifications in sawtooth activity. Heating was observed at a frequency ω rf ∼0.7Ω i on axis, using a two-strap fast wave antenna operated at 7 and 9.2 MHz with 180 degree phasing (N parallel ∼100). Numerical modeling with the fast wave code FASTWA [Plasma Phys. Controlled Fusion 33, 417 (1991)] indicates that for Phaedrus-T parameters the kinetic Alfven wave is excited via mode conversion from a surface fast wave at the Alfven resonance and is subsequently damped on electrons
Stable Alfven wave dynamo action in the reversed field pinch
International Nuclear Information System (INIS)
Werley, K.A.
1984-01-01
Recent advances in linear resistive MHD stability analysis are used to calculate the quasi-linear dynamo mean electromotive force of Alfven waves. This emf is incorporated into a one-dimensional transport and mean-field evolution code. The changing equilibrium is then fed back to the stability code to complete a computational framework that self-consistently evaluates a dynamic plasma dynamo. Static quasi-linear Alfven wave calculations have shown that dynamo emfs on the order of eta vector J are possible. This suggested a possible explanation of RFP behavior and a new (externally driven) mechanism for extending operation and controlling field profiles (possibly reducing plasma transport). This thesis demonstrates that the dynamo emf can quickly induce plasma currents whose emf cancels the dynamo effect. This thesis also contains extensive studies of resistive Alfven wave properties. This includes behavior versus spectral location, magnetic Reynolds number and wave number
Ion temperature in plasmas with intrinsic Alfven waves
International Nuclear Information System (INIS)
Wu, C. S.; Yoon, P. H.; Wang, C. B.
2014-01-01
This Brief Communication clarifies the physics of non-resonant heating of protons by low-frequency Alfvenic turbulence. On the basis of general definition for wave energy density in plasmas, it is shown that the wave magnetic field energy is equivalent to the kinetic energy density of the ions, whose motion is induced by the wave magnetic field, thus providing a self-consistent description of the non-resonant heating by Alfvenic turbulence. Although the study is motivated by the research on the solar corona, the present discussion is only concerned with the plasma physics of the heating process
ALFVEN WAVES IN A PARTIALLY IONIZED TWO-FLUID PLASMA
Energy Technology Data Exchange (ETDEWEB)
Soler, R.; Ballester, J. L.; Terradas, J. [Departament de Fisica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Carbonell, M., E-mail: roberto.soler@uib.es, E-mail: joseluis.ballester@uib.es, E-mail: jaume.terradas@uib.es, E-mail: marc.carbonell@uib.es [Departament de Matematiques i Informatica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain)
2013-04-20
Alfven waves are a particular class of magnetohydrodynamic waves relevant in many astrophysical and laboratory plasmas. In partially ionized plasmas the dynamics of Alfven waves is affected by the interaction between ionized and neutral species. Here we study Alfven waves in a partially ionized plasma from the theoretical point of view using the two-fluid description. We consider that the plasma is composed of an ion-electron fluid and a neutral fluid, which interact by means of particle collisions. To keep our investigation as general as possible, we take the neutral-ion collision frequency and the ionization degree as free parameters. First, we perform a normal mode analysis. We find the modification due to neutral-ion collisions of the wave frequencies and study the temporal and spatial attenuation of the waves. In addition, we discuss the presence of cutoff values of the wavelength that constrain the existence of oscillatory standing waves in weakly ionized plasmas. Later, we go beyond the normal mode approach and solve the initial-value problem in order to study the time-dependent evolution of the wave perturbations in the two fluids. An application to Alfven waves in the low solar atmospheric plasma is performed and the implication of partial ionization for the energy flux is discussed.
Solitary Alfven wave envelopes and the modulational instability
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Kennel, C.F.
1987-06-01
The derivative nonlinear Schroedinger equation describes the modulational instability of circularly polarized dispersive Alfven wave envelopes. It also may be used to determine the properties of finite amplitude localized stationary wave envelopes. Such envelope solitons exist only in conditions of modulational stability. This leaves open the question of whether, and if so, how, the modulational instability produces envelope solitons. 12 refs
Reflection of Alfven waves at an open magnetopause
International Nuclear Information System (INIS)
Cao, F.; Kan, J.R.
1990-01-01
Reflection of an Alfven wave incident on an open magnetopause form the magnetospheric side is examined. An open magnetopause, whose structure is different from the standard rotational discontinuity, is assumed to be a parameterized discontinuity with a nonzero normal field component. When an Alfven wave is incident on the open magnetopause, reflected and transmitted waves are generated. The emanating waves can be analyzed using linearized MHD conservation relations across the magnetopause, together with Snell's law. Under the assumption that the magnetic fields on the two sides of the open magnetopause are coplanar with the normal direction of the magnetopause, the governing equations are solved numerically. The results show that the electric fields of emanating Alfven waves depend mainly on the number density and the magnetic field jumps across the magnetopause. Under conditions representing the open magnetopause, it turns out that the open magnetopause behaves like a near perfect reflector. The corresponding reflection coefficient for the wave electric field can be approximated by R E = E r /E i ∼ -1 as has been deduced by Kan and Sun (1985) based on physical arguments. In other words, the solar wind flow is more or less unchanged by the loading effect of the Alfven wave incident on the magnetopause from the magnetospheric side. Therefore, under the assumptions of the model, the open magnetopause can be viewed as a constant voltage source
On WKB expansions for Alfven waves in the solar wind
International Nuclear Information System (INIS)
Hollweg, J.V.
1990-01-01
The author reexamines the WKB expansion for toroidal Alfven waves in the solar wind, as described by equations (9) of Heinemann and Olbert (1980). His principal conclusions are as follows: (1) The WKB expansion used by Belcher (1971) and Hollweg (1973) is nonuniformly convergent. (2) Using the method of multiple scales (Nayfeh, 1981), he obtains an expansion which is uniform. (3) The uniform expansion takes into account the small modification to the Alfven wave phase speed due to spatial gradients of the background. (4) Both the uniform and nonuniform expansions reveal that each normal mode has both Elsaesser variables δz + ≠ 0 and δz - ≠ 0. Thus if δz - corresponds to the outgoing mode in a homogeneous background, an observation of δz + ≠ 0 does not necessarily imply the presence of the inward propagating mode, as is commonly assumed. (5) Even at the Alfven critical point (where V = υ A ) he finds that δz + ≠ 0. Thus incompressible MHD turbulence, which requires both δz + ≠ 0 and δz - ≠ 0, can proceed at the Alfven critical point (cf. Roberts, 1989). (6) With very few exceptions, the predictions of these calculations do not agree with recent observations (Marsch and Tu, 1990) of the power spectra of δz + and δz - in the solar wind. Thus the evolution of Alfven waves in the solar wind is governed by dynamics not included in the Heinemann and Olbert equations
Resonant Alfven wave instabilities driven by streaming fast particles
International Nuclear Information System (INIS)
Zachary, A.
1987-01-01
A plasma simulation code is used to study the resonant interactions between streaming ions and Alfven waves. The medium which supports the Alfven waves is treated as a single, one-dimensional, ideal MHD fluid, while the ions are treated as kinetic particles. The code is used to study three ion distributions: a cold beam; a monoenergetic shell; and a drifting distribution with a power-law dependence on momentum. These distributions represent: the field-aligned beams upstream of the earth's bow shock; the diffuse ions upstream of the bow shock; and the cosmic ray distribution function near a supernova remnant shock. 92 refs., 31 figs., 12 tabs
Comments on the Alfven wave spectrum as measured on the TCA tokamak
International Nuclear Information System (INIS)
Puri, S.
1986-06-01
The heating in the TCA tokamak is ascribed to a combination of compressional Alfven wave heating (CAW) and discrete Alfven wave (DAW) heating. In this communication we invoke an alternative plasma heating mechanism by the direct excitation of torsional Alfven waves (TAW) to account for the observed features of the TCA experiment. (orig./GG)
Neutrino induced vorticity, Alfven waves and the normal modes
Energy Technology Data Exchange (ETDEWEB)
Bhatt, Jitesh R. [Theory Division, Physical Research Laboratory, Ahmedabad (India); George, Manu [Theory Division, Physical Research Laboratory, Ahmedabad (India); Indian Institute of Technology, Department of Physics, Ahmedabad (India)
2017-08-15
We consider a plasma consisting of electrons and ions in the presence of a background neutrino gas and develop the magnetohydrodynamic equations for the system. We show that the electron neutrino interaction can induce vorticity in the plasma even in the absence of any electromagnetic perturbations if the background neutrino density is left-right asymmetric. This induced vorticity supports a new kind of Alfven wave whose velocity depends on both the external magnetic field and on the neutrino asymmetry. The normal mode analysis show that in the presence of neutrino background the Alfven waves can have different velocities. We also discuss our results in the context of dense astrophysical plasma such as magnetars and show that the difference in the Alfven velocities can be used to explain the observed pulsar kick. We discuss also the relativistic generalisation of the electron fluid in presence of an asymmetric neutrino background. (orig.)
Dissipation of Alfven waves in compressible inhomogeneous media
International Nuclear Information System (INIS)
Malara, F.; Primavera, L.; Veltri, P.
1997-01-01
In weakly dissipative media governed by the magnetohydrodynamics (MHD) equations, any efficient mechanism of energy dissipation requires the formation of small scales. Using numerical simulations, we study the properties of Alfven waves propagating in a compressible inhomogeneous medium, with an inhomogeneity transverse to the direction of wave propagation. Two dynamical effects, energy pinching and phase mixing, are responsible for the small-scales formation, similarly to the incompressible case. Moreover, compressive perturbations, slow waves and a static entropy wave are generated; the former are subject to steepening and form shock waves, which efficiently dissipate their energy, regardless of the Reynolds number. Rough estimates show that the dissipation times are consistent with those required to dissipate Alfven waves of photospheric origin inside the solar corona
Shear Alfven wave excitation by direct antenna coupling and fast wave resonant mode conversion
International Nuclear Information System (INIS)
Borg, G.G.
1994-01-01
Antenna coupling to the shear Alfven wave by both direct excitation and fast wave resonant mode conversion is modelled analytically for a plasma with a one dimensional linear density gradient. We demonstrate the existence of a shear Alfven mode excited directly by the antenna. For localised antennas, this mode propagates as a guided beam along the steady magnetic field lines intersecting the antenna. Shear Alfven wave excitation by resonant mode conversion of a fast wave near the Alfven resonance layer is also demonstrated and we prove that energy is conserved in this process. We compare the efficiency of these two mechanisms of shear Alfven wave excitation and present a simple analytical formula giving the ratio of the coupled powers. Finally, we discuss the interpretation of some experimental results. 45 refs., 7 figs
Direct excitation of resonant torsional Alfven waves by footpoint motions
Ruderman, M. S.; Berghmans, D.; Goossens, M.; Poedts, S.
1997-01-01
The present paper studies the heating of coronal loops by linear resonant Alfven waves that are excited by the motions of the photospheric footpoints of the magnetic field lines. The analysis is restricted to torsionally polarised footpoint motions in an axially symmetric system so that only
Current drive by Alfven waves in elongated cross section tokamak
International Nuclear Information System (INIS)
Tsypin, V.S.; Elfimov, A.G.; Nekrasov, F.M.; Azevedo, C.A.; Assis, A.S. de
1997-01-01
Full text. The problem of the noninductive current drive in cylindrical plasma model and in circular cross-section tokamaks had been already discussed intensively. At the beginning of the study of this problem it have been clear that there are significant difficulties in using of the current-drive in toroidal magnetic traps, especially in a tokamak reactor. Thus, in the case of the lower-hybrid current-drive the efficiency of this current-drive drops strongly as the plasma density increases. For the Alfven waves, there is an opinion that the efficiency of the current-drive drops as a result of waves absorption by the trapped particles 1,2. Okhawa proposed that the current in a magnetized plasma can be maintained also by means of forces, depending on the radiofrequency (rf) field amplitude gradients (the helicity injection). This idea was developed later, some new hopes appeared, connected with the possibility of the current-drive efficiency increasing. It was shown that for the cylindrical plasmas the local efficiency of Alfev wave current drive can be increased by one order of magnitude due to gradient forces, for the kinetic Alfven waves (KAW) and the global Alfven waves 9GAW) at some range of the phase velocity. For tokamaks, this additional nonresonant current drive does not depend on the trapped particle effects, which reduce strongly the Alfven current drive efficiency in tokamaks, as it is supposed. Now, the theory development of the Alfven wave (AW) current drive is very important in the cource of the future experiments on the TCA/BR tokamak (Brazil). In this paper, an attempt is made to clarify some general aspects of this problems for magnetic traps. For large aspects ratio tokamaks, with an elongated cross-section, some general formulas concerning the untrapped and trapped particles dynamics and their input to the Landau damping of the Alfven waves, are presented. They are supposed to be used for the further development of the Alfven current drive theory
Current drive by Alfven waves in elongated cross section tokamak
Energy Technology Data Exchange (ETDEWEB)
Tsypin, V.S.; Elfimov, A.G.; Nekrasov, F.M.; Azevedo, C.A. [Universidade Federal, Rio de Janeiro, RJ (Brazil). Inst. de Fisica; Assis, A.S. de [Universidade Federal Fluminense, Niteroi, RJ (Brazil). Inst. de Fisica
1997-12-31
Full text. The problem of the noninductive current drive in cylindrical plasma model and in circular cross-section tokamaks had been already discussed intensively. At the beginning of the study of this problem it have been clear that there are significant difficulties in using of the current-drive in toroidal magnetic traps, especially in a tokamak reactor. Thus, in the case of the lower-hybrid current-drive the efficiency of this current-drive drops strongly as the plasma density increases. For the Alfven waves, there is an opinion that the efficiency of the current-drive drops as a result of waves absorption by the trapped particles 1,2. Okhawa proposed that the current in a magnetized plasma can be maintained also by means of forces, depending on the radiofrequency (rf) field amplitude gradients (the helicity injection). This idea was developed later, some new hopes appeared, connected with the possibility of the current-drive efficiency increasing. It was shown that for the cylindrical plasmas the local efficiency of Alfev wave current drive can be increased by one order of magnitude due to gradient forces, for the kinetic Alfven waves (KAW) and the global Alfven waves (GAW) at some range of the phase velocity. For tokamaks, this additional nonresonant current drive does not depend on the trapped particle effects, which reduce strongly the Alfven current drive efficiency in tokamaks, as it is supposed. Now, the theory development of the Alfven wave (AW) current drive is very important in the cource of the future experiments on the TCA/BR tokamak (Brazil). In this paper, an attempt is made to clarify some general aspects of this problems for magnetic traps. For large aspects ratio tokamaks, with an elongated cross-section, some general formulas concerning the untrapped and trapped particles dynamics and their input to the Landau damping of the Alfven waves, are presented. They are supposed to be used for the further development of the Alfven current drive theory
Beta-Suppression of Alfven Cascade Modes in the National Spherical Torus Experiment
International Nuclear Information System (INIS)
Fredrickson, E.D.; N.A. Crocker; N.N. Gorelenkov; W.W. Heidbrink; S. Kubota; F.M. Levinton; H. Yuh; J.E. Menard; Bell, R.E.
2007-01-01
The coupling of Alfven Cascade (AC) modes or reversed-shear Alfven eigenmodes (rsAE) to Geodesic Acoustic Modes (GAM) implies that the range of the AC frequency sweep is reduced as the electron β is increased. This model provides an explanation for the otherwise surprising absence of AC modes in reverse shear NSTX plasmas, given the rich spectrum of beam-driven instabilities typically seen in NSTX. In experiments done at very low β to investigate this prediction, AC modes were seen, and as the β e was increased from shot to shot, the range of the AC frequency sweep was reduced, in agreement with this theoretical prediction.
The stationary Alfven wave in laboratory and space regimes
Finnegan, S. M.
In this thesis, a non-linear, collisional, two-fluid model of uniform plasma convection across field-aligned current (FAC) sheets, describing stationary Alfven (StA) waves is developed in support of laboratory experiments performed to test the hypothesis that a stationary inertial Alfven wave pattern forms within a channel of parallel electron current across which plasma is convected. In a previous work, Knudsen (D. J. Knudsen, J. Geophys. Res. 101, 10,761 (1996)) showed that, for cold, collisionless plasma, stationary inertial Alfven (StIA) waves can accelerate electrons parallel to a background magnetic field and cause large, time-independent plasma-density variations having spatial periodicity in the direction of the convective flow over a broad range of spatial scales and energies. Here, Knudsen's model has been generalized for warm, collisional, anisotropic plasma. The inclusion of parallel electron thermal pressure introduces dispersive effects which extend the model to the kinetic (beta > me/mi) regime. The effects of both ion-neutral and electron-ion collisional resistivity on StIA and stationary kinetic Alfven (StKA) wave solutions is studied. Conditions for both periodic and solitary wave solutions are identified. In the small amplitude limit, it is shown that the StA wave equation reduces to the differential equation describing the behavior of a forced harmonic oscillator. Analytical solutions are obtained for both a step and impulse, of finite width, forcing functions. Plasma rotation experiments in the West Virginia University Q-machine (WVUQ) demonstrate that an electron-emitting spiral electrode produces controllable, parabolic radial profile of floating potential, while the space potential showed no such structure. Laser-induced fluorescence measurements confirmed that the azimuthal ion drift velocity is inconsistent with a drift due to a gradient in the space potential. Experiments designed to produce StIA wave signatures were performed in the
Fu, X.; Li, H.; Guo, F.; Li, X.; Roytershteyn, V.
2017-12-01
The solar wind is a turbulent magnetized plasma extending from the upper atmosphere of the sun to the edge of the heliosphere. It carries charged particles and magnetic fields originated from the Sun, which have great impact on the geomagnetic environment and human activities in space. In such a magnetized plasma, Alfven waves play a crucial role in carrying energy from the surface of the Sun, injecting into the solar wind and establishing power-law spectra through turbulent energy cascades. On the other hand, in compressible plasmas large amplitude Alfven waves are subject to a parametric decay instability (PDI) which converts an Alfven wave to another counter-propagating Alfven wave and an ion acoustic wave (slow mode). The counter-propagating Alfven wave provides an important ingredient for turbulent cascade, and the slow-mode wave provides a channel for solar wind heating in a spatial scale much larger than ion kinetic scales. Growth and saturation of PDI in quiet plasma have been intensively studied using linear theory and nonlinear simulations in the past. Here using 3D hybrid simulations, we show that PDI is still effective in turbulent low-beta plasmas, generating slow modes and causing ion heating. Selected events in WIND data are analyzed to identify slow modes in the solar wind and the role of PDI, and compared with our simulation results. We also investigate the validity of linear Vlasov theory regarding PDI growth and slow mode damping in turbulent plasmas. Since PDI favors low plasma beta, we expect to see more evidence of PDI in the solar wind close to the Sun, especially from the upcoming NASA's Parker Solar Probe mission which will provide unprecedented wave and plasma data as close as 8.5 solar radii from the Sun.
Three-dimensional stability of solitary kinetic Alfven waves and ion-acoustic waves
International Nuclear Information System (INIS)
Ghosh, G.; Das, K.P.
1994-01-01
Starting from a set of equations that lead to a linear dispersion relation coupling kinetic Alfven waves and ion-acoustic waves, three-dimensional KdV equations are derived for these waves. These equations are then used to investigate the three-dimensional stability of solitary kinetic Alfven waves and ion-acoustic waves by the small-k perturbation expansion method of Rowlands and Infeld. For kinetic Alfven waves it is found that there is instability if the direction of the plane-wave perturbation lies inside a cone, and the growth rate of the instability attains a maximum when the direction of the perturbation lies in the plane containing the external magnetic field and the direction of propagation of the solitary wave. For ion-acoustic waves the growth rate of instability attains a maximum when the direction of the perturbation lies in a plane perpendicular to the direction of propagation of the solitary wave. (Author)
Instability of drift Alfven wave accompanying polar magnetic storm
International Nuclear Information System (INIS)
Higuchi, Yoshihiro
1974-01-01
As the micro plasma instability due to the plasma non-uniformity in magnetosphere, there is the instability of drift Alfven wave. With the data obtained with the network of multiple observation points for geomagnetism, attempt was made to prove the hypothesis that the instability of drift Alfven wave due to the electron temperature gradient at the inner boundary of plasma sheet may be one of the causes for the geomagnetic pulsation (Pi 1) accompanying polar magnetic storm. Up to date, final conclusion is yet impossible as to the problems in it due to the discussion based on the data from widely separated observation points. The installation of economically efficient multi-point observation network is necessary for the solution. (Mori, K.)
Global Hybrid Simulation of Alfvenic Waves Associated with Magnetotail Reconnection and Fast Flows
Cheng, L.; Lin, Y.; Wang, X.; Perez, J. D.
2017-12-01
Alfvenic fluctuations have been observed near the magnetotail plasma sheet boundary layer associated with fast flows. In this presentation, we use the Auburn 3-D Global Hybrid code (ANGIE3D) to investigate the generation and propagation of Alfvenic waves in the magnetotail. Shear Alfven waves and kinetic Alfven waves (KAWs) are found to be generated in magnetic reconnection in the plasma sheet as well as in the dipole-like field region of the magnetosphere, carrying Poynting flux along magnetic field lines toward the ionosphere, and the wave structure is strongly altered by the flow braking in the tail. The 3-D structure of the wave electromagnetic field and the associated parallel currents in reconnection and the dipole-like field region is presented. The Alfvenic waves exhibit a turbulence spectrum. The roles of these Alfvenic waves in ion heating is discussed.
Coronal heating by Alfven waves dissipation in compressible nonuniform media
International Nuclear Information System (INIS)
Malara, Francesco; Primavera, Leonardo; Veltri, Pierluigi
1996-01-01
The possibility to produce small scales and then to efficiently dissipate energy has been studied by Malara et al. [1992b] in the case of MHD disturbances propagating in an weakly dissipative incompressible and inhomogeneous medium, for a strictly 2D geometry. We extend this work to include both compressibility and the third component for vector quantities. Numerical simulations show that, when an Alfven wave propagates in a compressible nonuniform medium, the two dynamical effects responsible for the small scales formation in the incompressible case are still at work: energy pinching and phase-mixing. These effects give rise to the formation of compressible perturbations (fast and slow waves or a static entropy wave). Some of these compressive fluctuations are subject to the steepening of the wave front and become shock waves, which are extremely efficient in dissipating their energy, their dissipation being independent of the Reynolds number. Rough estimates of the typical times the various dynamical processes take to produce small scales show that these times are consistent with those required to dissipate inside the solar corona the energy of Alfven waves of photospheric origin
Alfven waves and associated energetic ions downstream from Uranus
International Nuclear Information System (INIS)
Zhang, Ming; Belcher, J.W.; Richardson, J.D.; Smith, C.W.
1991-01-01
The authors report the observation of low-frequency waves in the solar wind downstream from Uranus. These waves are observed by the Voyager spacecraft for more than 2 weeks after the encounter with Uranus and are present during this period whenever the interplanetary magnetic field is oriented such that the field lines intersect the Uranian bow shock. The magnetic field and velocity components transverse to the background field are strongly correlated, consistent with the interpretation that these waves are Alfvenic and/or fast-mode waves. The waves have a spacecraft frame frequency of about 10 -3 Hz, and when first observed near the bow shock have an amplitude comparable to the background field. As the spacecraft moves farther from Uranus, the amplitude decays. The waves appear to propagate along the magnetic field lines outward from Uranus and are right-hand polarized. Theory suggests that these waves are generated in the upstream region by a resonant instability with a proton beam streaming along the magnetic field lines. The solar wind subsequently carries these waves downstream to the spacecraft location. These waves are associated with the presence of energetic (> 28 keV) ions observed by the low-energy charged particle instrument. These ions appear two days after the start of the wave activity and occur thereafter whenever the Alfven waves occur, increasing in intensity away from Uranus. The ions are argued to originate in the Uranian magnetosphere, but pitch-angle scattering in the upstream region is required to bring them downstream to the spacecraft location
International Nuclear Information System (INIS)
Chandran, Benjamin D. G.; Hollweg, Joseph V.
2009-01-01
We study the propagation, reflection, and turbulent dissipation of Alfven waves in coronal holes and the solar wind. We start with the Heinemann-Olbert equations, which describe non-compressive magnetohydrodynamic fluctuations in an inhomogeneous medium with a background flow parallel to the background magnetic field. Following the approach of Dmitruk et al., we model the nonlinear terms in these equations using a simple phenomenology for the cascade and dissipation of wave energy and assume that there is much more energy in waves propagating away from the Sun than waves propagating toward the Sun. We then solve the equations analytically for waves with periods of hours and longer to obtain expressions for the wave amplitudes and turbulent heating rate as a function of heliocentric distance. We also develop a second approximate model that includes waves with periods of roughly one minute to one hour, which undergo less reflection than the longer-period waves, and compare our models to observations. Our models generalize the phenomenological model of Dmitruk et al. by accounting for the solar wind velocity, so that the turbulent heating rate can be evaluated from the coronal base out past the Alfven critical point-that is, throughout the region in which most of the heating and acceleration occurs. The simple analytical expressions that we obtain can be used to incorporate Alfven-wave reflection and turbulent heating into fluid models of the solar wind.
How to turn gravity waves into Alfven waves and other such tricks
International Nuclear Information System (INIS)
Newington, Marie E; Cally, Paul S
2011-01-01
Recent observations of travelling gravity waves at the base of the chromosphere suggest an interplay between gravity wave propagation and magnetic field. Our aims are: to explain the observation that gravity wave flux is suppressed in magnetic regions; to understand why we see travelling waves instead of standing waves; and to see if gravity waves can undergo mode conversion and couple to Alfven waves in regions where the plasma beta is of order unity. We model gravity waves in a VAL C atmosphere, subject to a uniform magnetic field of various orientations, considering both adiabatic and radiatively damped propagation. Results indicate that in the presence of a magnetic field, the gravity wave can propagate as a travelling wave, with the magnetic field orientation playing a crucial role in determining the wave character. For the majority of magnetic field orientations, the gravity wave is reflected at low heights as a slow magneto-acoustic wave, explaining the observation of reduced flux in magnetic regions. In a highly inclined magnetic field, the gravity wave undergoes mode conversion to either field guided acoustic waves or Alfven waves. The primary effect of incorporating radiative damping is a reduction in acoustic and magnetic fluxes measured at the top of the integration region. By demonstrating the mode conversion of gravity waves to Alfven waves, this work identifies a possible pathway for energy transport from the solar surface to the upper atmosphere.
Non-axial-symmetric Alfven waves in cylindrical, radial inhomogeneous plasmas
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Raeuchle, E.
1978-08-01
The propagation of nonaxialsymmetric Alfven waves is investigated theoretically. Eigenfunctions and dispersion relations are calculated numerically for radial inhomogeneous cylindrical plasmas. In the MHD treatment resistivity, neutral particle loading and ion cyclotron effects are included. The investigations are of importance for plasma heating by Alfven waves. (orig.) [de
Alfven-wave current drive and magnetic field stochasticity
International Nuclear Information System (INIS)
Litwin, C.; Hegna, C.C.
1993-01-01
Propagating Alfven waves can generate parallel current through an alpha effect. In resistive MHD however, the dynamo field is proportional to resistivity and as such cannot drive significant currents for realistic parameters. In the search for an enhancement of this effect the authors investigate the role of magnetic field stochasticity. They show that the presence of a stochastic magnetic field, either spontaneously generated by instabilities or induced externally, can enhance the alpha effect of the wave. This enhancement is caused by an increased wave dissipation due to both current diffusion and filamentation. For the range of parameters of current drive experiments at Phaedrus-T tokamak, a moderate field stochasticity leads to significant modifications in the loop voltage
Parametric instabilities of parallel propagating incoherent Alfven waves in a finite ion beta plasma
International Nuclear Information System (INIS)
Nariyuki, Y.; Hada, T.; Tsubouchi, K.
2007-01-01
Large amplitude, low-frequency Alfven waves constitute one of the most essential elements of magnetohydrodynamic (MHD) turbulence in the fast solar wind. Due to small collisionless dissipation rates, the waves can propagate long distances and efficiently convey such macroscopic quantities as momentum, energy, and helicity. Since loading of such quantities is completed when the waves damp away, it is important to examine how the waves can dissipate in the solar wind. Among various possible dissipation processes of the Alfven waves, parametric instabilities have been believed to be important. In this paper, we numerically discuss the parametric instabilities of coherent/incoherent Alfven waves in a finite ion beta plasma using a one-dimensional hybrid (superparticle ions plus an electron massless fluid) simulation, in order to explain local production of sunward propagating Alfven waves, as suggested by Helios/Ulysses observation results. Parameter studies clarify the dependence of parametric instabilities of coherent/incoherent Alfven waves on the ion and electron beta ratio. Parametric instabilities of coherent Alfven waves in a finite ion beta plasma are vastly different from those in the cold ions (i.e., MHD and/or Hall-MHD systems), even if the collisionless damping of the Alfven waves are neglected. Further, ''nonlinearly driven'' modulational instability is important for the dissipation of incoherent Alfven waves in a finite ion beta plasma regardless of their polarization, since the ion kinetic effects let both the right-hand and left-hand polarized waves become unstable to the modulational instability. The present results suggest that, although the antisunward propagating dispersive Alfven waves are efficiently dissipated through the parametric instabilities in a finite ion beta plasma, these instabilities hardly produce the sunward propagating waves
International Nuclear Information System (INIS)
Sharapov, S.E.; Mikhailovskii, A.B.; Huysmans, G.T.A.
2004-01-01
The effects of nonresonating hot ions on the spectrum of magnetohydrodynamic (MHD) waves and instabilities in tokamaks are studied in the limit when the width of the hot ion drift orbits is much larger than the radial scale length of the MHD perturbations. Due to the large magnetic drift velocities the hot ions cannot contribute to the MHD perturbations directly, but two main effects of the hot ions, the hot-ion density-dependent effect and the hot-ion pressure-dependent effect, influence the MHD perturbations indirectly. The physics of both effects is elucidated and it is shown that both these effects can be described in MHD approach. A new code, MISHKA-H (MISHKA including the hot-ion indirect effects), is developed as an extension of the ideal MHD code MISHKA-D [Huysmans et al., Phys. Plasmas 8, 4292 (2002)]. Analytical benchmarks for this code are given. Results of the MISHKA-H code on Alfven spectrum in a shear-reversed discharges with ion-cyclotron resonance frequency (ICRF) heating are presented. Modeling of Alfven cascades and their transition into toroidal Alfven eigenmodes in shear-reversed tokamak equilibrium is considered. The hot-ion effect on the unstable branch of the MHD spectrum is studied for the test case of an n=1 ideal MHD internal kink mode, which is relevant to short-period sawteeth in low-density plasmas observed in Joint European Torus (JET) [Rebut et al., Proceedings of the 10th International Conference, Plasma Physics and Controlled Nuclear Fusion, London (International Atomic Energy Agency, Vienna, 1985), Vol. I, p. 11] experiments with high-power ICRF heating
On field line resonances of hydromagnetic Alfven waves in dipole magnetic field
International Nuclear Information System (INIS)
Chen, Liu; Cowley, S.C.
1989-07-01
Using the dipole magnetic field model, we have developed the theory of field line resonances of hydromagnetic Alfven waves in general magnetic field geometries. In this model, the Alfven speed thus varies both perpendicular and parallel to the magnetic field. Specifically, it is found that field line resonances do persist in the dipole model. The corresponding singular solutions near the resonant field lines as well as the natural definition of standing shear Alfven eigenfunctions have also been systematically derived. 11 refs
Resistive effects on helicity-wave current drive generated by Alfven waves in tokamak plasmas
International Nuclear Information System (INIS)
Bruma, C.; Cuperman, S.; Komoshvili, K.
1997-01-01
This work is concerned with the investigation of non-ideal (resistive) MHD effects on the excitation of Alfven waves by externally launched fast-mode waves, in simulated tokamak plasmas; both continuum range, CR ({ω Alf (r)} min Alf (r)} max ) and discrete range, DR, where global Alfven eigenmodes, GAEs (ω Alf (r)} min ) exist, are considered. (Here, ω Alf (r) ≡ ω Alf [n(r), B 0 (r)] is an eigenfrequency of the shear Alfven wave). For this, a cylindrical current carrying plasma surrounded by a helical sheet-current antenna and situated inside a perfectly conducting shell is used. Toroidicity effects are simulated by adopting for the axial equilibrium magnetic field component a suitable radial profile; shear and finite relative poloidal magnetic field are properly accounted for. A dielectric tensor appropriate to the physical conditions considered in this paper is derived and presented. (author)
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.)
Wave-Particle Energy Exchange Directly Observed in a Kinetic Alfven-Branch Wave
Gershman, Daniel J.; F-Vinas, Adolfo; Dorelli, John C.; Boardsen, Scott A. (Inventor); Avanov, Levon A.; Bellan, Paul M.; Schwartz, Steven J.; Lavraud, Benoit; Coffey, Victoria N.; Chandler, Michael O.;
2017-01-01
Alfven waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. These waves are important not only in planetary magnetospheres, heliospheres, and astrophysical systems, but also in laboratory plasma experiments and fusion reactors. Through measurement of charged particles and electromagnetic fields with NASAs Magnetospheric Multiscale (MMS) mission, we utilize Earths magnetosphere as a plasma physics laboratory. Here we confirm the conservative energy exchange between the electromagnetic field fluctuations and the charged particles that comprise an undamped kinetic Alfven wave. Electrons confined between adjacent wave peaks may have contributed to saturation of damping effects via non-linear particle trapping. The investigation of these detailed wave dynamics has been unexplored territory in experimental plasma physics and is only recently enabled by high-resolution MMS observations.
Alfven wave heating studies in Tokapole II tokamak
International Nuclear Information System (INIS)
Kortbawi, D.; Witherspoon, F.D.; Zhu, S.Y.; Casavant, T.; Sprott, J.C.; Prager, S.C.
1984-01-01
In earlier experiments at low power on the Tokapole II tokamak using the internal divertor rings as a launching structure the authors have observed a resonance with properties consistent with those expected for a shear Alfven wave. With these encouraging results, a second phase of experiments has begun where, eventually, 4 discrete antennas, located ≅180 0 apart in both the toroidal and poloidal directions and phased to establish proper mode numbers are driven from a 1 MW source. A prototype antenna has been installed and tested. It is a 2 turn Faraday shielded loop extending 54 0 along a toroidal arc. This orientation was chosen for the antenna currents based on the earlier experiments and the simple MHD result that the component of the wage magnetic field perpendicular to the equilibrium field is most strongly divergent. To test this the antenna can be rotated +.45 0 . It can also be inserted radially up to 6 cm
The Ion Cyclotron, Lower Hybrid, and Alfven Wave Heating Methods
International Nuclear Information System (INIS)
Koch, R.
2004-01-01
This lecture covers the practical features and experimental results of the three heating methods. The emphasis is on ion cyclotron heating. First, we briefly come back to the main non-collisional heating mechanisms and to the particular features of the quasilinear coefficient in the ion cyclotron range of frequencies (ICRF). The specific case of the ion-ion hybrid resonance is treated, as well as the polarisation issue and minority heating scheme. The various ICRF scenarios are reviewed. The experimental applications of ion cyclotron resonance heating (ICRH) systems are outlined. Then, the lower hybrid and Alfven wave heating and current drive experimental results are covered more briefly. Where applicable, the prospects for ITER are commented
Similon, Philippe L.; Sudan, R. N.
1989-01-01
The importance of field line geometry for shear Alfven wave dissipation in coronal arches is demonstrated. An eikonal formulation makes it possible to account for the complicated magnetic geometry typical in coronal loops. An interpretation of Alfven wave resonance is given in terms of gradient steepening, and dissipation efficiencies are studied for two configurations: the well-known slab model with a straight magnetic field, and a new model with stochastic field lines. It is shown that a large fraction of the Alfven wave energy flux can be effectively dissipated in the corona.
Vlasov simulations of Kinetic Alfven Waves at proton kinetic scales
C.L. Vasconez; F. Valentini (Francesco); E. Camporeale (Enrico); P. Veltri
2014-01-01
htmlabstractKinetic Alfv ́en waves represent an important subject in space plasma physics, since they are thought to play a crucial role in the development of the turbulent energy cascade in the solar wind plasma at short wavelengths (of the order of the proton inertial length d p and beyond). A
Particle energization by inertial Alfven wave in auroral ionosphere
Kumar, S.
2017-12-01
The role of inertial Alfven wave in auroral acceleration region and in the inertial regime to energize the plasma particles is an interesting field and widely discussed observationally as well as theoretically in recent years. In this work, we present the density perturbations by inertial Alfvén wave (AW) in the auroral ionosphere. We obtain dynamical equations for inertial AW and fast mode of AW using two-fluid model and then solve them numerically in order to analyze the localized structures and cavity formation. The ponderomotive force due to the high frequency inertial AW changes the background density and is believed to be responsible for the wave localization or for the formation of density cavities in auroral ionosphere. These density cavities are believed to be the sites for particle energization. This perturbed density channel grow with time until the modulation instability acquires steady state. We find that the density cavities are accompanied by the high amplitude magnetic fields. The amplitude of the strongest density cavity is estimated as ˜ 0.26n0 (n0 is unperturbed plasma number density). The results presented here are found consistent with the observational studies using FAST spacecraft.
Nonlinear inertial Alfven waves in plasmas with sheared magnetic field and flow
International Nuclear Information System (INIS)
Chen Yinhua; Wang Ge; Tan Liwei
2004-01-01
Nonlinear equations describing inertial Alfven waves in plasmas with sheared magnetic field and flow are derived. For some specific parameters chosen, authors have found a new type of electromagnetic coherent structures in the tripolar vortex-like form
Effects of Wind Velocity Driven by Alfven Waves on the Line Profiles for 32 CYG
Directory of Open Access Journals (Sweden)
Kyung-Mee Kim
1996-06-01
Full Text Available We calculate the theoretical line profiles for 32 Cyg in order to investigate the influence of various velocity fields. Line profiles are calculated with wind accelerations driven by Alfven waves and described by velocity parameters. The results for Alfvenic wave model show weakened line profiles. For the orbital phases ¥÷=0.78 and ¥÷=0.06 the Alfvenic models show strong absorption part due to very low densities at the surface of the supergiant. Hence, we conclude the velocity gradient of the wind near the supergiant could influence on the theoretical line formation.
International Nuclear Information System (INIS)
Gao Zhe; He Yexi; Tan Yi
2009-01-01
Using electromagnetic waves to startup and sustain plasma current takes a important role in the research program of the SUNIST spherical tokamak. Electron cyclotron ware (ECW) current startup have been investigated and revealed two totally different regimes. In the regime of very low working pressure, a plasma current of about 2 kA is obtained with a steadily applied vertical field of 12 Gauss and 40 kW/2.45 GHz microwave injection. In addition, the physics of the transient process during ECW startup in the relatively high working pressure regime is analyzed. The hardware preparation for the experimental research of Alfven wave current drive is being performed. The Alfven wave antenna system consists of four models in toroidal direction and two antenna straps in poloidal direction for each module and the rf generator has been designed as a four-phase oscillator (4x100 kW, 0.5 - 1 Mhz).The impedance spectrum of the antenna system is roughly evaluated by 1-D cylindrical magneto-hydrodynamic calculation. To investigate the wave-plasma interaction in ECW startup and Alfven wave current drive, upgrade of the device, especially in equilibrium control and diagnostics, is ongoing. (author)
Conditions for sustainment of magnetohydrodynamic turbulence driven by Alfven waves
International Nuclear Information System (INIS)
Dmitruk, P.; Matthaeus, W.H.; Milano, L.J.; Oughton, S.
2001-01-01
In a number of space and astrophysical plasmas, turbulence is driven by the supply of wave energy. In the context of incompressible magnetohydrodynamics (MHD) there are basic physical reasons, associated with conservation of cross helicity, why this kind of driving may be ineffective in sustaining turbulence. Here an investigation is made into some basic requirements for sustaining steady turbulence and dissipation in the context of incompressible MHD in a weakly inhomogeneous open field line region, driven by the supply of unidirectionally propagating waves at a boundary. While such wave driving cannot alone sustain turbulence, the addition of reflection permits sustainment. Another sustainment issue is the action of the nonpropagating or quasi-two dimensional part of the spectrum; this is particularly important in setting up a steady cascade. Thus, details of the wave boundary conditions also affect the ease of sustaining a cascade. Supply of a broadband spectrum of waves can overcome the latter difficulty but not the former, that is, the need for reflections. Implications for coronal heating and other astrophysical applications, as well as simulations, are suggested
Alfven-wave particle interaction in finite-dimensional self-consistent field model
International Nuclear Information System (INIS)
Padhye, N.; Horton, W.
1998-01-01
A low-dimensional Hamiltonian model is derived for the acceleration of ions in finite amplitude Alfven waves in a finite pressure plasma sheet. The reduced low-dimensional wave-particle Hamiltonian is useful for describing the reaction of the accelerated ions on the wave amplitudes and phases through the self-consistent fields within the envelope approximation. As an example, the authors show for a single Alfven wave in the central plasma sheet of the Earth's geotail, modeled by the linear pinch geometry called the Harris sheet, the time variation of the wave amplitude during the acceleration of fast protons
Convective cell excitation by inertial Alfven waves in a low density plasma
International Nuclear Information System (INIS)
Pokhotelov, O.A.; Onishchenko, O.G.; Sagdeev, R.Z.; Srenflo, L.; Balikhin, M.A.
2005-01-01
The parametric interaction of inertial Alfven waves with large-scale convective cells in a low-density plasma is investigated. It is shown that, in plasmas where the Alfven velocity is comparable to or exceeds the speed of light, the parametric interaction is substantially suppressed. A compact expression for the optimal scale and instability growth rate of the fastest growing mode is obtained [ru
Resistive effects on helicity-wave current drive generated by Alfven waves in tokamak plasmas
Energy Technology Data Exchange (ETDEWEB)
Bruma, C.; Cuperman, S.; Komoshvili, K. [Tel Aviv Univ. (Israel). Faculty of Exact Sciences
1997-05-01
This work is concerned with the investigation of non-ideal (resistive) MHD effects on the excitation of Alfven waves by externally launched fast-mode waves, in simulated tokamak plasmas; both continuum range, CR ({l_brace}{omega}{sub Alf}(r){r_brace}{sub min} < {omega} < {l_brace}{omega}{sub Alf}(r){r_brace}{sub max}) and discrete range, DR, where global Alfven eigenmodes, GAEs ({omega} < {l_brace}{sub Alf}(r){r_brace}{sub min}) exist, are considered. (Here, {omega}{sub Alf}(r) {identical_to} {omega}{sub Alf}[n(r), B{sub 0}(r)] is an eigenfrequency of the shear Alfven wave). For this, a cylindrical current carrying plasma surrounded by a helical sheet-current antenna and situated inside a perfectly conducting shell is used. Toroidicity effects are simulated by adopting for the axial equilibrium magnetic field component a suitable radial profile; shear and finite relative poloidal magnetic field are properly accounted for. A dielectric tensor appropriate to the physical conditions considered in this paper is derived and presented. (author).
Basic principles approach for studying nonlinear Alfven wave-alpha particle dynamics
International Nuclear Information System (INIS)
Berk, H.L.; Breizman, B.N.; Pekker, M.
1994-01-01
An analytical model and a numerical procedure are presented which give a kinetic nonlinear description of the Alfven-wave instabilities driven by the source of energetic particles in a plasma. The steady-state and bursting nonlinear scenarios predicted by the analytical theory are verified in the test numerical simulation of the bump-on-tail instability. A mathematical similarity between the bump-on-tail problem for plasma waves and the Alfven wave problem gives a guideline for the interpretation of the bursts in the wave energy and fast particle losses observed in the tokamak experiments with neutral beam injection
Energy Technology Data Exchange (ETDEWEB)
Ruderman, M S
1988-08-01
Nonlinear Alfven surface wave propagation at a magnetic interface in a compressible fluid is considered. It is supposed that the magnetic field directions at both sides of the interface and the direction of wave propagation coincide. The equation governing time-evolution of nonlinear small-amplitude waves is derived by the method of multiscale expansions. This equation is similar to the equation for nonlinear Alfven surface waves in an incompressible fluid derived previously. The numerical solution of the equation shows that a sinusoidal disturbance overturns, i.e. infinite gradients arise.
Experiments and Observations on Intense Alfven Waves in the Laboratory and in Space
International Nuclear Information System (INIS)
Gekelman, W.; VanZeeland, M.; Vincena, S.; Pribyl, P.
2003-01-01
There are many situations, which occur in space (coronal mass ejections, supernovas), or are man-made (upper atmospheric detonations) in which a dense plasma expands into a background magnetized plasma that can support Alfven waves. The LArge Plasma Device (LAPD) is a machine, at UCLA, in which Alfven wave propagation in homogeneous and inhomogeneous plasmas has been studied. These will be briefly reviewed. A new class of experiments which involve the expansion of a dense (initially, δn/no>>1) laser-produced plasma into an ambient highly magnetized background plasma capable of supporting Alfven waves will be presented. Measurements are used to estimate the coupling efficiency of the laser energy and kinetic energy of the dense plasma into wave energy. The wave generation mechanism is due to field aligned return currents, coupled to the initial electron current, which replace fast electrons escaping the initial blast
Stable Alfven-wave dynamo action in the reversed-field pinch
International Nuclear Information System (INIS)
Werley, K.A.
1984-01-01
Previous theoretical work has suggested that Alfven waves may be related to the anomalous toroidal magnetic flux generation and extended (over classical expectations) discharge times observed in the reversed-field pinch. This thesis examines the dynamo action of stable Alfven waves as a means of generating toroidal flux. Recent advances in linear resistive MHD stability analysis are used to calculate the quasi-linear dynamo mean electromotive force of Alfven waves. This emf is incorporated into a one-dimensional transport and mean-field evolution code. The changing equilibrium is then fed back to the stability code to complete a computational framework that self-consistently evaluates a dynamic plasma dynamo. This technique is readily extendable to other plasmas in which dynamic stable model action is of interest. Such plasmas include Alfven wave current-drive and plasma heating for fusion devices, as well as astrophysical and geophysical dynamo systems. This study also contains extensive studies of resistive Alfven wave properties. This includes behavior versus spectral location, magnetic Reynolds number and wave number
TURBULENCE IN THE SUB-ALFVENIC SOLAR WIND DRIVEN BY REFLECTION OF LOW-FREQUENCY ALFVEN WAVES
International Nuclear Information System (INIS)
Verdini, A.; Velli, M.; Buchlin, E.
2009-01-01
We study the formation and evolution of a turbulent spectrum of Alfven waves driven by reflection off the solar wind density gradients, starting from the coronal base up to 17 solar radii, well beyond the Alfvenic critical point. The background solar wind is assigned and two-dimensional shell models are used to describe nonlinear interactions. We find that the turbulent spectra are influenced by the nature of the reflected waves. Close to the base, these give rise to a flatter and steeper spectrum for the outgoing and reflected waves, respectively. At higher heliocentric distance both spectra evolve toward an asymptotic Kolmogorov spectrum. The turbulent dissipation is found to account for at least half of the heating required to sustain the background imposed solar wind and its shape is found to be determined by the reflection-determined turbulent heating below 1.5 solar radii. Therefore, reflection and reflection-driven turbulence are shown to play a key role in the acceleration of the fast solar wind and origin of the turbulent spectrum found at 0.3 AU in the heliosphere.
Alfven wave. [Book on linear and nonlinear properties for fusion applications
Energy Technology Data Exchange (ETDEWEB)
Hasegawa, A.; Uberoi, C.
1978-11-01
Seven chapters are included. Chapters 1 and 2 introduce the Alfven wave and describe its linear properties in a homogeneous medium. Chapters 3 and 4 cover the effects of inhomogeneities on these linear properties. Particular emphasis is placed on the appearance of a continuum spectrum and the associated absorption of the Alfven wave which arise due to the inhomogeneity. The explanation of the physical origin of absorption is given using kinetic theory. Chapter 5 is devoted to the associated plasma instabilities. Nonlinear effects discussed in Chapter 6 include quasilinear diffusion, decay, a solitary wave, and a modulational instability. The principles of Alfven wave heating, a design example and present-day experimental results are described in Chapter 7.
A KINETIC ALFVEN WAVE AND THE PROTON DISTRIBUTION FUNCTION IN THE FAST SOLAR WIND
International Nuclear Information System (INIS)
Li Xing; Lu Quanming; Chen Yao; Li Bo; Xia Lidong
2010-01-01
Using one-dimensional test particle simulations, the effect of a kinetic Alfven wave on the velocity distribution function (VDF) of protons in the collisionless solar wind is investigated. We first use linear Vlasov theory to numerically obtain the property of a kinetic Alfven wave (the wave propagates in the direction almost perpendicular to the background magnetic field). We then numerically simulate how the wave will shape the proton VDF. It is found that Landau resonance may be able to generate two components in the initially Maxwellian proton VDF: a tenuous beam component along the direction of the background magnetic field and a core component. The streaming speed of the beam relative to the core proton component is about 1.2-1.3 Alfven speed.
Destabilization of hydromagnetic drift-Alfven waves in a finite pressure collisional plasma
International Nuclear Information System (INIS)
Tang, J.T.
1974-01-01
In a finite beta (β = 8πn 0 kT 0 /B 0 2 ) plasma, where the plasma pressure n 0 kT 0 is an appreciable fraction of the confining magnetic field energy-density B 0 2 /8π, density-gradient driven drift waves couple with Alfven waves when the phase velocities of the two waves become comparable. The resulting hydromagnetic drift-Alfven waves separate into two branches--a drift mode and an Alfven mode, with both modes exhibiting magnetic field and localized density fluctuations near the coupling point. The dispersion relation of the collisional drift-Alfven wave is derived by using a slab-geometry, two-fluid model which includes finite beta, electron-ion collisions, ion-ion collisions, finite ion larmar radius, temperature fluctuations, and an axial electron current. A hydromagnetic drift mode is found to be unstable in a moderately dense plasma. A localized ''Alfven'' mode is destabilized only with the passage of an axial current along the plasma column. In order to check the theoretical predictions an experiment is performed in a finite-beta plasma of density n 0 = 10 13 -10 15 cm -3 and temperature T/sub e/ approximately T/sub i/ = 1-7 eV. (U.S.)
International Nuclear Information System (INIS)
Akiyama, H.; Hayler, M.O.; Kristiansen, M.
1985-01-01
The dispersion relations for the compressional Alfven waves in a two-ion species plasma of deuterium and hydrogen are calculated for a configuration which includes a vacuum layer between the cylindrical plasma and the conducting wall. The presence of the vacuum layer strongly affects the propagation of the compressional Alfven wave, permitting some branches to propagate and penetrate the plasma column over most frequencies in the ion-cyclotron range. Basic Alfven-wave propagation and heating experiments in two-ion species consequently should be possible using tokamak and mirror devices with minor radii smaller than the Alfven wavelength
Kinetic Alfven waves and electron physics. II. Oblique slow shocks
International Nuclear Information System (INIS)
Yin, L.; Winske, D.; Daughton, W.
2007-01-01
One-dimensional (1D) particle-in-cell (PIC; kinetic ions and electrons) and hybrid (kinetic ions; adiabatic and massless fluid electrons) simulations of highly oblique slow shocks (θ Bn =84 deg. and β=0.1) [Yin et al., J. Geophys. Res., 110, A09217 (2005)] have shown that the dissipation from the ions is too weak to form a shock and that kinetic electron physics is required. The PIC simulations also showed that the downstream electron temperature becomes anisotropic (T e parallel )>T e perpendicular ), as observed in slow shocks in space. The electron anisotropy results, in part, from the electron acceleration/heating by parallel electric fields of obliquely propagating kinetic Alfven waves (KAWs) excited by ion-ion streaming, which cannot be modeled accurately in hybrid simulations. In the shock ramp, spiky structures occur in density and electron parallel temperature, where the ion parallel temperature decreases due to the reduction of the ion backstreaming speed. In this paper, KAW and electron physics in oblique slow shocks are further examined under lower electron beta conditions. It is found that as the electron beta is reduced, the resonant interaction between electrons and the wave parallel electric fields shifts to the tail of the electron velocity distribution, providing more efficient parallel heating. As a consequence, for β e =0.02, the electron physics is shown to influence the formation of a θ Bn =75 deg. shock. Electron effects are further enhanced at a more oblique shock angle (θ Bn =84 deg.) when both the growth rate and the range of unstable modes on the KAW branch increase. Small-scale electron and ion phase-space vortices in the shock ramp formed by electron-KAW interactions and the reduction of the ion backstreaming speed, respectively, are observed in the simulations and confirmed in homogeneous geometries in one and two spatial dimensions in the accompanying paper [Yin et al., Phys. Plasmas 14, 062104 (2007)]. Results from this study
Small amplitude Kinetic Alfven waves in a superthermal electron-positron-ion plasma
Adnan, Muhammad; Mahmood, Sahahzad; Qamar, Anisa; Tribeche, Mouloud
2016-11-01
We are investigating the propagating properties of coupled Kinetic Alfven-acoustic waves in a low beta plasma having superthermal electrons and positrons. Using the standard reductive perturbation method, a nonlinear Korteweg-de Vries (KdV) type equation is derived which describes the evolution of Kinetic Alfven waves. It is found that nonlinearity and Larmor radius effects can compromise and give rise to solitary structures. The parametric role of superthermality and positron content on the characteristics of solitary wave structures is also investigated. It is found that only sub-Alfvenic and compressive solitons are supported in the present model. The present study may find applications in a low β electron-positron-ion plasma having superthermal electrons and positrons.
Che, H.; Goldstein, M. L.; Vinas, A. F.
2014-01-01
The observed steep kinetic scale turbulence spectrum in the solar wind raises the question of how that turbulence originates. Observations of keV energetic electrons during solar quiet time suggest them as a possible source of free energy to drive kinetic turbulence. Using particle-in-cell simulations, we explore how the free energy released by an electron two-stream instability drives Weibel-like electromagnetic waves that excite wave-wave interactions. Consequently, both kinetic Alfvénic and whistler turbulence are excited that evolve through inverse and forward magnetic energy cascades.
Mechanisms for the Dissipation of Alfven Waves in Near-Earth Space Plasma
Singh, Nagendra; Khazanov, George; Krivorutsky, E. N.; Davis, John M. (Technical Monitor)
2002-01-01
Alfven waves are a major mechanism for the transport of electromagnetic energy from the distant part of the magnetosphere to the near-Earth space. This is especially true for the auroral and polar regions of the Earth. However, the mechanisms for their dissipation have remained illusive. One of the mechanisms is the formation of double layers when the current associated with Alfven waves in the inertial regime interact with density cavities, which either are generated nonlinearly by the waves themselves or are a part of the ambient plasma turbulence. Depending on the strength of the cavities, weak and strong double layers could form. Such double layers are transient; their lifetimes depend on that of the cavities. Thus they impulsively accelerate ions and electrons. Another mechanism is the resonant absorption of broadband Alfven- wave noise by the ions at the ion cyclotron frequencies. But this resonant absorption may not be possible for the very low frequency waves, and it may be more suited for electromagnetic ion cyclotron waves. A third mechanism is the excitation of secondary waves by the drifts of electrons and ions in the Alfven wave fields. It is found that under suitable conditions, the relative drifts between different ion species and/or between electrons and ions are large enough to drive lower hybrid waves, which could cause transverse accelerations of ions and parallel accelerations of electrons. This mechanism is being further studied by means of kinetic simulations using 2.5- and 3-D particle-in-cell codes. The ongoing modeling efforts on space weather require quantitative estimates of energy inputs of various kinds, including the electromagnetic energy. Our studies described here contribute to the methods of determining the estimates of the input from ubiquitous Alfven waves.
Energy Technology Data Exchange (ETDEWEB)
Fierros Palacios, Angel [Instituto de Investigaciones Electricas, Temixco, Morelos (Mexico)
2001-02-01
In this work the complete set of differential field equations which describes the dynamic state of a continuos conducting media which flow in presence of a perturbed magnetic field is obtained. Then, the thermic equation of state, the wave equation and the conservation law of energy for the Alfven MHD waves are obtained. [Spanish] Es este trabajo se obtiene el conjunto completo de ecuaciones diferenciales de campo que describen el estado dinamico de un medio continuo conductor que se mueve en presencia de un campo magnetico externo perturbado. Asi, se obtiene la ecuacion termica de estado, la ecuacion de onda y la ley de la conservacion de la energia para las ondas de Alfven de la MHD.
Kinetic Alfven Waves at the Magnetopause-Mode Conversion, Transport and Formation of LLBL; TOPICAL
International Nuclear Information System (INIS)
Jay R. Johnson; C.Z. Cheng
2002-01-01
At the magnetopause, large amplitude, low-frequency (ULF), transverse MHD waves are nearly always observed. These waves likely result from mode conversion of compressional MHD waves observed in the magnetosheath to kinetic Alfven waves at the magnetopause where there is a steep gradient in the Alfven velocity[Johnson and Cheng, Geophys. Res. Lett. 24 (1997) 1423]. The mode-conversion process can explain the following wave observations typically found during satellite crossings of the magnetopause: (1) a dramatic change in wave polarization from compressional in the magnetosheath to transverse at the magnetopause, (2) an amplification of wave amplitude at the magnetopause, (3) a change in Poynting flux from cross-field in the magnetosheath to field-aligned at the magnetopause, and (4) a steepening in the wave power spectrum at the magnetopause. We examine magnetic field data from a set of ISEE1, ISEE2, and WIND magnetopause crossings and compare with the predictions of theoretical wave solutions based on the kinetic-fluid model with particular attention to the role of magnetic field rotation across the magnetopause. The results of the study suggest a good qualitative agreement between the observations and the theory of mode conversion to kinetic Alfven waves. Because mode-converted kinetic Alfven waves readily decouple particles from the magnetic field lines, efficient quasilinear transport (D(approx) 109m2/s) can occur. Moreover, if the wave amplitude is sufficiently large (Bwave/B0 and gt; 0.2) stochastic particle transport also occurs. This wave-induced transport can lead to significant heating and particle entry into the low latitude boundary layer across closed field lines.At the magnetopause, large amplitude, low-frequency (ULF), transverse MHD waves are nearly always observed. These waves likely result from mode conversion of compressional MHD waves observed in the magnetosheath to kinetic Alfven waves at the magnetopause where there is a steep gradient in
Energetic particle destabilization of shear Alfven waves in stellarators and tokamaks
International Nuclear Information System (INIS)
Spong, D.A.; Carreras, B.A.; Hedrick, C.L.; Leboeuf, J.N.; Weller, A.
1994-01-01
An important issue for ignited devices is the resonant destabilization of shear Alfven waves by energetic populations. These instabilities have been observed in a variety of toroidal plasma experiments in recent years, including: beam-destabilized toroidal Alfven instabilities (TAE) in low magnetic field tokamaks, ICRF destabilized TAE's in higher field tokamaks, and global Alfven instabilities (GAE) in low shear stellarators. In addition, excitation and study of these modes is a significant goal of the TFIR-DT program and a component of the ITER physics tasks. The authors have developed a gyrofluid model which includes the wave-particle resonances necessary to excite such instabilities. The TAE linear mode structure is calculated nonperturbatively, including many of the relevant damping mechanisms, such as: continuum damping, non-ideal effects (ion FLR and electron collisionality), and ion/electron Landau damping. This model has been applied to both linear and nonlinear regimes for a range of experimental cases using measured profiles
Alfven waves in the auroral ionosphere: A numerical model compared with measurements
International Nuclear Information System (INIS)
Knudsen, D.J.; Kelley, M.C.; Vickrey, J.F.
1992-01-01
The authors solve a linear numerical model of Alfven waves reflecting from the high-latitude ionosphere, both to better understanding the role of the ionosphere in the magnetosphere/ionosphere coupling process and to compare model results with in situ measurements. They use the model to compute the frequency-dependent amplitude and phase relations between the meridional electric and the zonal magnetic fields due to Alfven waves. These relations are compared with measurements taken by an auroral sounding rocket flow in the morningside oval and by the HILAT satellite traversing the oval at local noon. The sounding rocket's trajectory was mostly parallel to the auroral oval, and is measured enhanced fluctuating field energy in regions of electron precipitation. The rocket-measured phase data are in excellent agreement with the Alfven wave model, and the relation between the modeled and the measured by HILAT are related by the height-integrated Pedersen conductivity Σ p , indicating that the measured field fluctuations were due mainly to structured field-aligned current systems. A reason for the relative lack of Alfven wave energy in the HILAT measurements could be the fact that the satellite traveled mostly perpendicular to the oval and therefore quickly traversed narrow regions of electron precipitation and associated wave activity
Influence of the Alfven wave spectrum on the scrape-off layer of the TCA tokamak
International Nuclear Information System (INIS)
Martin, Y.; Hollenstein, C.
1989-01-01
The study of the scrape-off layer (SOL) during Alfven wave heating may lead to a better understanding of the antenna-plasma interaction. The scrape-off layer of the TCA tokamak has been widely investigated by means of Langmuir probes. The aim of this work is to present measurements on the influence of the Alfven wave spectrum on the scrape-off layer. These experiments have shown that the plasma boundary layer is strongly affected by the wave field, in particular the ion saturation current and the floating potential. In TCA, as the spectrum evolves due to a density rise, the passage of the Alfven continua and their associated eigenmodes, the Discrete Alfven Wave (DAW) induces a strong depletion in the edge density of up to 70% during the continuum part and a density increase during the crossing of an eigenmode. The floating potential becomes negative during the continua and even more negative crossing the eigenmodes. In case of MHD mode activity, this behaviour changes for power exceeding 100 kW. The profiles of basic parameters are modified, depending on the wave spectrum. MHD mode activity which can occur during the RF (radio frequency) phase considerably alters the behaviour mentioned above. Finally, the modulation of the RF power allows us to characterize the coupling between RF power and typical edge parameters. (orig.)
International Nuclear Information System (INIS)
Tsurutani, B.T.; Gonzalez, W.D.
1987-01-01
It is shown that high intensity (AE > 1,000 nT), long duration (T > 2 d) continuous auroral activity (HILDCAA) events are caused by outward (from the sun) propagating interplanetary Alfven wave trains. The Alfven waves are often (but not always) detected several days after major interplanetary events, such as shocks and solar wind density enhancements. Presumably magnetic reconnection between the southward components of the Alfven wave magnetic fields and magnetospheric fields is the mechanism for transfer of solar wind energy to the magnetosphere. If the stringent requirements for HILDCAA events are relaxed, there are many more AE events of this type. A brief inspection indicates that these are also related to interplanetary Alfvenic fluctuations. We therefore suggest that most auroral activity may be caused by reconnection associated with Alfven waves in the interplanetary medium. (author)
Effects of dust on the propagation and dissipation of Alfven waves in interstellar clouds
International Nuclear Information System (INIS)
Pilipp, W.; Morfill, G.E.; Hartquist, T.W.; Havnes, O.; Maryland Univ., College Park; Nordlysobservatoriet, Tromso, Norway)
1987-01-01
The propagation of circularly polarized Alfven waves in dusty, weakly ionized media consisting of three gaseous fluids and of one size of grains that are either neutral or singly ionized is numerically investigated. For a molecular hydrogen number density of 10,000/cu cm, a magnetic field strength of 0.0001 G, and a temperature of 20 K, the waves are well coupled when the wavelengths exceed about 1 pc. The grains can reduce the minimum wavelength for coupled waves to about 0.1 pc and the dissipation rates of well-coupled small-amplitude waves by an order of magnitude. The speeds and dissipation rates of decoupled Alfven waves with frequencies well above 0.01/yr and wavelengths well below 0.01 pc are altered greatly over a wide range of frequencies by the presence of grains. In particular, right-handed circularly polarized waves are affected strongly by gyroresonance and cutoff effects. 18 references
Improved model of quasi-particle turbulence (with applications to Alfven and drift wave turbulence)
International Nuclear Information System (INIS)
Mendonca, J. T.; Hizanidis, K.
2011-01-01
We consider the classical problem of wave stability and dispersion in a turbulent plasma background. We adopt a kinetic description for the quasi-particle turbulence. We describe an improved theoretical approach, which goes beyond the geometric optics approximation and retains the recoil effects associated with the emission and absorption of low frequency waves by nearly resonant quasi-particles. We illustrate the present approach by considering two particular examples. One is the excitation of zonal flows by drift wave turbulence or driftons. The other is the coupling between ion acoustic waves and Alfven wave turbulence, eventually leading to saturation of Alfven wave growth. Both examples are relevant to anomalous transport in magnetic fusion devices. Connection with previous results is established. We show that these results are recovered in the geometric optics approximation.
Anomalous transport due to shear-Alfven waves
International Nuclear Information System (INIS)
Lee, W.W.; Chance, M.S.; Okuda, H.
1980-10-01
The behavior of shear-Alfven eigenmodes and the accompanied anomalous transport have been investigated. In the particle simulation, equilibrium thermal fluctuations associated with the eigenmodes have been observed to nullify the zeroth-order shear near the rational surface through the induced second-order eddy current, and, in turn, give rise to the formation of magnetic islands which cause rapid electron energy transport in the region. The theoretical verification of the observed behavior is discussed
Velocity shear generated Alfven waves in electron-positron plasmas
International Nuclear Information System (INIS)
Rogava, A.D.; Berezhiani, V.I.; Mahajan, S.M.
1996-01-01
Linear MHD modes in cold, nonrelativistic electron-positron plasma shear flow are considered. The general set of differential equations, describing the evolution of perturbations in the framework of the nonmodal approach is derived. It is found, that under certain circumstances, the compressional and shear Alfven perturbations may exhibit large transient growth fuelled by the mean kinetic energy of the shear flow. The velocity shear also induces mode coupling allowing the exchange of energy as well as the possibility of a strong mutual transformation of these modes into each other. The compressional Alfven mode may extract the energy of the mean flow and transfer it to the shear Alfven mode via this coupling. The relevance of these new physical effects to provide a better understanding of the laboratory e + e - plasma is emphasized. It is speculated that the shear-induced effects in the electron-positron plasmas could also help solve some astrophysical puzzles (e.g., the generation of pulsar radio emission). Since most astrophysical plasma are relativistic, it is shown that the major results of the study remain valid for weakly sheared relativistic plasmas. (author). 21 refs, 4 figs
Influence of the Alfven wave spectrum on the scrape-off layer of the TCA tokamak
International Nuclear Information System (INIS)
Martin, Y.; Hollenstein, Ch.
1988-01-01
The study of the Scrape-Off Layer (SOL) during Alfven wave heating may lead to a better understanding of the antenna-plasma interaction. The SOL of the TCA tokamak has been widely investigated by means of Langmuir probes. The aim of the present work is to present in detail the influence of the Alfven wave spectrum on the SOL. The experiments have shown that the plasma boundary layer is strongly affected by the RF, in particular the ion density, the electron temperature and the floating potential. In TCA, as the spectrum evolves due to a density rise, the passage of the Alfven continua and their associated eigenmodes (DAW) induces a strong depletion in the edge density of up to 70% during the continuum part and a density increase during the crossing of an eigenmode. The floating potential becomes negative during the continua and even more negative crossing the eigenmodes. This behaviour changes as a function of the power transmitted to the plasma through the antennae, especially we have found with MHD modes a change around 100 kW. The profiles of the basic parameters are modified, depending on the wave spectrum. MHD mode activity which can occur during the RF phase considerably alters the behaviour mentioned above. Finally, the modulation of the RF power allows us to characterize the difference in coupling, for the continua and the eigenmodes, between the Alfven wave field and the scrape-off layer. (author) 5 figs., 6 refs
Energy balance in the TCA tokamak plasma with Alfven wave heating
International Nuclear Information System (INIS)
Ding Ning; Qu Wenxiao; Huang Li; Long Yongxing; Qiu Xiaoming
1993-01-01
The energy balance in TCA tokamak plasma with Alfven wave heating is studied, in which the equivalent electron thermal conductivity is determined by using the profile consistency principle. The results are in good agreement with experiments. It is shown that this method is applicable to various devices and other heating methods
The calculation for energy balance of heating plasmas by Alfven waves
International Nuclear Information System (INIS)
Long Yongxing; Ding Ning; He Qibing; Qu Wenxiao; Huang Lin; Qiu Xiaoming
1992-10-01
A numerical method for computing the energy balance of heating tokamak plasmas by Alfven waves is introduced. The results are in agreement with experiments. This method is not only simpler and more distinct but also considerably saving time in computation. It also can be used in kinetic problems with other types of radio frequency (RF) heating
Differential equation for Alfven ion cyclotron waves in finite-length plasma
International Nuclear Information System (INIS)
Watson, D.C.; Fateman, R.J.; Baldwin, D.E.
1977-01-01
One finds the fourth-order differential equation describing an Alfven-ion-cyclotron wave propagating along a magnetic field of varying intensity. The equation is self-adjoint and possesses non-trivial turning points. The final form of the equation is checked using MACSYMA, a system for performing algebra on a computer
Stability of Global Alfven Waves (Tae, Eae) in Jet Tritium Discharges
Kerner, W.; Borba, D.; Huysmans, G. T. A.; Porcelli, F.; Poedts, S.; Goedbloed, J. P.; Betti, R.
1994-01-01
The interaction of alpha-particles in JET tritium discharges with global Alfven waves via inverse Landau damping is analysed. It is found that alpha-particle driven eigenmodes were stable in the PTE1 and should also be stable in a future 50:50 deuterium-tritium mix discharge aiming at Q(DT) = 1,
International Nuclear Information System (INIS)
Prokopov, P A; Zakharov, Yu P; Tishchenko, V N; Shaikhislamov, I F; Boyarintsev, E L; Melekhov, A V; Ponomarenko, A G; Posukh, V G; Terekhin, V A
2016-01-01
Generation of Alfven waves propagating along external magnetic field B 0 and Collisionless Shock Waves propagating across B 0 are studied in experiments with laser- produced plasma and magnetized background plasma. The collisionless interaction of interpenetrating plasma flows takes place through a so-called Magnetic Laminar Mechanism (MLM) or Larmor Coupling. At the edge of diamagnetic cavity LP-ions produce induction electric field E φ which accelerates BP-ions while LP-ions rotate in opposite direction. The ions movement generates sheared azimuthal magnetic field B φ which could launches torsional Alfven wave. In previous experiments at KI-1 large scale facility a generation of strong perturbations propagating across B 0 with magnetosonic speed has been studied at a moderate value of interaction parameter δ∼0.3. In the present work we report on experiments at conditions of 5∼R2 and large Alfven-Mach number M A ∼10 in which strong transverse perturbations traveling at a scale of ∼1 m in background plasma at a density of ∼3*10 13 cm -3 is observed. At the same conditions but smaller M A ∼ 2 a generation, the structure and dynamic of Alfven wave with wavelength ∼0.5 m propagating along fields B 0 ∼100÷500 G for a distance of ∼2.5 m is studied. (paper)
Interaction of the precessional wave with free-boundary Alfven surface waves in tandem mirrors
International Nuclear Information System (INIS)
Berk, H.L.; Kaiser, T.B.
1984-04-01
We consider a symmetric tandem mirror plugging a long central cell, with plugs stabilized by a hot component plasma. The system is taken to have a flat pressure profile with a steep edge gradient. We then consider the interaction of the precessional mode with Alfven waves generated in the central cell. This analysis is non-eikonal and is valid when mΔ/r < 1 (m is the azimuthal mode number. r the plasma radius and Δ the radial gradient scale length) for long-wavelength radial modes. We find that without FLR effects the precessional mode is always destabilized by the excitation of the Alfven waves for m greater than or equal to 2. For m=1, it is possible to achieve stabilization with conducting walls. A discussion is given of how FLR affects stabilization of the m greater than or equal to 2 long-wavelength modes and of finite-Larmor-radius stabilization of modes described in the eikonal approximation
Plasma mass density, species mix and fluctuation diagnostics using fast Alfven wave
Energy Technology Data Exchange (ETDEWEB)
Ikezi, H.; deGrassie, J.S.; Pinsker, R.I.; Snider, R.T.
1996-06-01
The authors propose to employ a fast Alfven wave interferometer and reflectometer as a tokamak diagnostic to measure the plasma mass density, D-T species mix profile, and density fluctuations. Utilize the property that the phase velocity of the fast wave propagating across the magnetic field is the Alfven speed with thermal correction, this fast wave interferometer on the DIII-D tokamak was successfully used to obtain the line integrated density. Since the position of the ion-ion hybrid cut-off in tokamaks is uniquely determined by the species mix ratio and the wave frequency, the reflectometer arrangement finds the species mix profile. The inversion method of reflectometry is discussed. The multiple chord interferometer also measures the mass density fluctuation profile.
Plasma mass density, species mix and fluctuation diagnostics using fast Alfven wave
International Nuclear Information System (INIS)
Ikezi, H.; deGrassie, J.S.; Pinsker, R.I.; Snider, R.T.
1996-06-01
The authors propose to employ a fast Alfven wave interferometer and reflectometer as a tokamak diagnostic to measure the plasma mass density, D-T species mix profile, and density fluctuations. Utilize the property that the phase velocity of the fast wave propagating across the magnetic field is the Alfven speed with thermal correction, this fast wave interferometer on the DIII-D tokamak was successfully used to obtain the line integrated density. Since the position of the ion-ion hybrid cut-off in tokamaks is uniquely determined by the species mix ratio and the wave frequency, the reflectometer arrangement finds the species mix profile. The inversion method of reflectometry is discussed. The multiple chord interferometer also measures the mass density fluctuation profile
MONTE CARLO SIMULATION MODEL OF ENERGETIC PROTON TRANSPORT THROUGH SELF-GENERATED ALFVEN WAVES
Energy Technology Data Exchange (ETDEWEB)
Afanasiev, A.; Vainio, R., E-mail: alexandr.afanasiev@helsinki.fi [Department of Physics, University of Helsinki (Finland)
2013-08-15
A new Monte Carlo simulation model for the transport of energetic protons through self-generated Alfven waves is presented. The key point of the model is that, unlike the previous ones, it employs the full form (i.e., includes the dependence on the pitch-angle cosine) of the resonance condition governing the scattering of particles off Alfven waves-the process that approximates the wave-particle interactions in the framework of quasilinear theory. This allows us to model the wave-particle interactions in weak turbulence more adequately, in particular, to implement anisotropic particle scattering instead of isotropic scattering, which the previous Monte Carlo models were based on. The developed model is applied to study the transport of flare-accelerated protons in an open magnetic flux tube. Simulation results for the transport of monoenergetic protons through the spectrum of Alfven waves reveal that the anisotropic scattering leads to spatially more distributed wave growth than isotropic scattering. This result can have important implications for diffusive shock acceleration, e.g., affect the scattering mean free path of the accelerated particles in and the size of the foreshock region.
Alfven Wave Reflection Model of Field-Aligned Currents at Mercury
Lyatsky, Wladislaw; Khazanov, George V.; Slavin, James
2010-01-01
An Alfven Wave Reflection (AWR) model is proposed that provides closure for strong field-aligned currents (FACs) driven by the magnetopause reconnection in the magnetospheres of planets having no significant ionospheric and surface electrical conductance. The model is based on properties of the Alfven waves, generated at high altitudes and reflected from the low-conductivity surface of the planet. When magnetospheric convection is very slow, the incident and reflected Alfven waves propagate along approximately the same path. In this case, the net field-aligned currents will be small. However, as the convection speed increases. the reflected wave is displaced relatively to the incident wave so that the incident and reflected waves no longer compensate each other. In this case, the net field-aligned current may be large despite the lack of significant ionospheric and surface conductivity. Our estimate shows that for typical solar wind conditions at Mercury, the magnitude of Region 1-type FACs in Mercury's magnetosphere may reach hundreds of kilo-Amperes. This AWR model of field-aligned currents may provide a solution to the long-standing problem of the closure of FACs in the Mercury's magnetosphere. c2009 Elsevier Inc. All rights reserved.
Modification and damping of Alfven waves in a magnetized dusty plasma
International Nuclear Information System (INIS)
Salimullah, M.; Dasgupta, B.; Watanabe, K.; Sato, T.
1994-10-01
The dispersion characteristics of the circularly polarized electromagnetic waves along a homogeneous magnetic field in a dusty plasma have been investigated theoretically. The Vlasov equation has been employed to find the response of the magnetized plasma particles where the dust grains form a static background of highly charged and massive centers having certain correlation. It is found that in addition to the usual Landau damping which is negligible in the low temperature approximation, a novel mechanism of damping of the Alfven waves due to the dust comes into play. The modification and damping of the Alfven waves depend on the dust perturbation parameters, unequal densities of plasma particles, the average correlation length of the dust grains, temperature of the plasma and the magnetic field. (author)
Alfven wave stability in D-III-D
International Nuclear Information System (INIS)
Campbell, R.B.; Samec, T.K.
1989-09-01
Within the framework of the global Alfven eigenmode theory in a cylindrical background plasma, I examine the excitation of global Alfven eigenmodes by intense neutral beam injection in the D III-D tokamak operating at General Atomics. I have considered two separate sets of experimental conditions, a ''low power'' set of cases using 10MW of hydrogen beams, and a ''high power'' shot of 20MW of deuterium beams. My results are particularly sensitive to the background density profile. For parabolic background density profiles, n 0 x (1 - (r/a) 2 ), I have determined that the plasma is stable to all toroidal and poloidal mode numbers for both high and low power cases. For density profiles which are of the form n 0 x (1 - (r/a) 2 ) 1/2 , for the same n 0 , my calculation indicates that the m = -1, l = 0 mode is unstable in each case. The high power case has a considerably higher growth rate at the baseline conditions, which motivated me to study this case more extensively. The results are also sensitive to the beam source radial scalelength, L s , and the electron temperature T e . By narrowing the source from the baseline 36 cm to 20 cm, the growth rate of the (0,-1) actually decreases, but the (0,-2) mode appears with a substantial growth rate. If the source could be made even narrower, L s ∼ 10 cm, the (1,-1) mode would appear, also with a large growth rate. 12 refs., 16 figs., 6 tabs
Nonlinear interaction of fast particles with Alfven waves in toroidal plasmas
International Nuclear Information System (INIS)
Candy, J.; Borba, D.; Huysmans, G.T.A.; Kerner, W.; Berk, H.L.
1996-01-01
A numerical algorithm to study the nonlinear, resonant interaction of fast particles with Alfven waves in tokamak geometry has been developed. The scope of the formalism is wide enough to describe the nonlinear evolution of fishbone modes, toroidicity-induced Alfven eigenmodes and ellipticity-induced Alfven eigenmodes, driven by both passing and trapped fast ions. When the instability is sufficiently weak, it is known that the wave-particle trapping nonlinearity will lead to mode saturation before wave-wave nonlinearities are appreciable. The spectrum of linear modes can thus be calculated using a magnetohydrodynamic normal-mode code, then nonlinearly evolved in time in an efficient way according to a two-time-scale Lagrangian dynamical wave model. The fast particle kinetic equation, including the effect of orbit nonlinearity arising from the mode perturbation, is simultaneously solved of the deviation, δf = f - f 0 , from an initial analytic distribution f 0 . High statistical resolution allows linear growth rates, frequency shifts, resonance broadening effects, and nonlinear saturation to be calculated quickly and precisely. The results have been applied to an ITER instability scenario. Results show that weakly-damped core-localized modes alone cause negligible alpha transport in ITER-like plasmas--even with growth rates one order of magnitude higher than expected values. However, the possibility of significant transport in reactor-type plasmas due to weakly unstable global modes remains an open question
Flow shear suppression of turbulence using externally driven ion Bernstein and Alfven waves
International Nuclear Information System (INIS)
Biglari, H.; Ono, M.
1992-01-01
The utilization of externally-launched radio-frequency waves as a means of active confinement control through the generation of sheared poloidal flows is explored. For low-frequency waves, kinetic Alfven waves are proposed, and are shown to drive sheared E x B flows as a result of the radial variation in the electromagnetic Reynolds stress. In the high frequency regime, ion Bernstein waves are considered, and shown to generate sheared poloidal rotation through the pondermotive force. In either case, it is shown that modest amounts of absorbed power (∼ few 100 kW) are required to suppress turbulence in a region of several cm radial width
International Nuclear Information System (INIS)
Sakai, J.I.; Haruki, T.; Kazimura, Y.
2000-01-01
It is shown by using a 2-D fully relativistic electromagnetic particle-in-cell (PIC) code that the tearing instability in a current sheet of pair plasmas is caused by Landau resonances of both electrons and positrons. Strong magnetic flux can be generated during coalescence of magnetic islands in the nonlinear phase of the tearing instability. The magnetic flux produced in an O-type magnetic island is caused from the counter-streaming instability found by Kazimura et al. (1998). It is also shown that charge separation with a quadrupole-like structure is generated from the localized strong magnetic flux. During the decay of the quadrupole-like charge structure as well as the magnetic flux, there appear wave emission with high-frequency electromagnetic waves and Alfven waves as well as Langmuir waves. We also show by using a 3-D PIC code that current filaments associated with the O-type magnetic islands become unstable against the kink instability during the coalescence of current filaments. (orig.)
Energy densities of Alfven waves between 0.7 and 1.6 AU. [in interplanetary medium
Belcher, J. W.; Burchsted, R.
1974-01-01
Plasma and field data from Mariner 4 and 5 between 0.7 and 1.6 AU are used to study the radial dependence of the levels of microscale fluctuation associated with interplanetary Alfven waves. The observed decrease of these levels with increasing distance from the sun is consistent with little or no local generation or damping of the ambient Alfven waves over this range of radial distance.
Kinetic Alfven wave in the presence of kappa distribution function in plasma sheet boundary layer
Energy Technology Data Exchange (ETDEWEB)
Shrivastava, G., E-mail: geetphy9@gmail.com; Ahirwar, G. [School of Studies in Physics, Vikram University, Ujjain India (India); Shrivastava, J., E-mail: jayashrivastava2007@gmail.com [Dronacharya Group of Institutions, Greater Noida-India (India)
2015-07-31
The particle aspect approach is adopted to investigate the trajectories of charged particles in the electromagnetic field of kinetic Alfven wave. Expressions are found for the dispersion relation, damping/growth rate and associated currents in the presence of kappa distribution function. Kinetic effect of electrons and ions are included to study kinetic Alfven wave because both are important in the transition region. It is found that the ratio β of electron thermal energy density to magnetic field energy density and the ratio of ion to electron thermal temperature (T{sub i}/T{sub e}), and kappa distribution function affect the dispersion relation, damping/growth rate and associated currents in both cases(warm and cold electron limit).The treatment of kinetic Alfven wave instability is based on assumption that the plasma consist of resonant and non resonant particles. The resonant particles participate in an energy exchange process, whereas the non resonant particles support the oscillatory motion of the wave.
Non-inductive current drive via helicity injection by Alfven waves in low aspects ratio Tokamak
International Nuclear Information System (INIS)
Cuperman, S.; Bruma, C.; Komoshvili, K.
1996-01-01
A theoretical investigation of radio frequency (RF) current drive via helicity injection in low aspect ratio tokamaks was carried out. A current-carrying cylindrical plasma surrounded by a helical sheet-current antenna and situated inside a perfectly conducting shell was considered. Toroidal features of low aspect ratio tokamaks were simulated by incorporation of the following effects: (i) arbitrarily small aspect ratio, R o /a ≡ 1/ε (ii) strongly sheared equilibrium magnetic field; and (iii) relatively large poloidal component of the equilibrium magnetic field. The study concentrates on the Alfven continuum, i.e. the case in which the wave frequency satisfies the condition {ω Alf (r)} min ≤ω≥{ω Alf (r)} max , where ω Alf (r)≡ω[n(r),B o (o)] is an eigenfrequency of the shear Alfven wave (SAW). Thus, using low-p, ideal magneto-hydrodynamics, the wave equation with correct boundary (matching) conditions was solved, the RF field components were found and subsequently, current drive , power deposition and efficiency were computed. The results of our investigation clearly demonstrate the possibility of generation of RF-driven currents via helicity injection by Alfven waves in low aspect ratio tokamaks, in the SAW mode. A special algorithm was developed which enables the selection of the antenna parameters providing optimal current drive efficiency. (authors)
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)
International Nuclear Information System (INIS)
Li, Wann-Quan; Ross, D.W.; Mahajan, Swadesh M.
1989-06-01
Kinetic effects of Alfven wave spatial resonances near the plasma edge are investigated numerically and analytically in a cylindrical tokamak model. In Part 1, cold plasma surface Alfven eigenmodes (SAE's) in a pure plasma are examined. Numerical calculations of antenna-driven waves exhibiting absorption resonances at certain discrete frequencies are first reviewed. From a simplified kinetic equation, an analytical dispersion relation is then obtained with the antenna current set equal to zero. The real and imaginary parts of its roots, which are the complex eigenfrequencies, agree with the central frequencies and widths, respectively, of the numerical antenna-driven resonances. These results serve as an introduction to the companion paper, in which it is shown that, in the presence of a minority species, certain SAE's, instead of heating the plasma exterior, can dissipate substantial energy in the two-ion hybrid layer near the plasma center. 11 refs., 8 figs., 1 tab
International Nuclear Information System (INIS)
Meyerhofer, D.D.; Perkins, F.W.
1984-04-01
The kinetic Alfven wave is studied in a cylindrical force-free plasma with self-consistent magnetic fields. This equilibrium represents a reversed field pinch or a spheromak. The stability of the wave is found to depend on the ratio of the electron drift velocity to the Alfven velocity. This ratio varies inversely with the square root of the plasma line density. The critical line density using the Spitzer-Harm electron distribution function is found for reversed field pinches with deuterium plasmas to be approximately 2 x 10 18 m -1 and is 5 x 10 17 m -1 in spheromaks with hydrogen plasmas. The critical line density is in reasonable agreement with experimental data for reversed field pinches
International Nuclear Information System (INIS)
Cuperman, S.; Bruma, C.; Komoshvili, K.
1999-01-01
Theoretical results on the wave-plasma interactions in simulated toroidal configurations are presented. The study covers the cases of large to low aspect ratio tokamaks, in the pre-heated stage. Fast waves emitted from an external antenna with different wave numbers and frequencies are considered. The non-inductive Alfven wave current drive is evaluated and discussed. (author)
International Nuclear Information System (INIS)
Cuperman, S.; Bruma, C.; Komoshvili, K.
2001-01-01
Theoretical results on the wave-plasma interactions in simulated toroidal configurations are presented. The study covers the cases of large to low aspect ratio tokamaks, in the pre-heated stage. Fast waves emitted from an external antenna with different wave numbers and frequencies are considered. The non-inductive Alfven wave current drive is evaluated and discussed. (author)
International Nuclear Information System (INIS)
Evans, T.E.
1984-09-01
The first direct observation of the internal structure of driven global Alfven eigenmodes in a tokamak plasma is presented. A carbon dioxide laser scattering/interferometer has been designed, built, and installed on the PRETEXT tokamak. By using this diagnostic system in the interferometer configuration, we have for the first time, thoroughly investigated the resonance conditions required for, and the spatial wave field structure of, driven plasma eigenmodes at frequencies below the ion cyclotron frequency in a confined, high temperature, tokamak plasma
Analysis and design of the Alfven wave antenna system for the SUNIST spherical tokamak
International Nuclear Information System (INIS)
Tan Yi; Gao Zhe; He Yexi
2009-01-01
Analysis and design of the Alfven wave antenna system for the SUNIST spherical tokamak are presented. Two candidate antenna concepts, folded and unfolded, are analyzed and compared with each other. In the frequency range of Alfven resonance the impedance spectrums of both two concept antennas for major modes are numerically calculated in a 1-D MHD framework. The folded concept is chosen for engineering design. The antenna system is designed to be simple and requires least modification to the vacuum vessel. The definition of the antenna shape is guided by the analyses with constraints of existing hardware layouts. Each antenna unit consists of two stainless steel straps with a thickness of 1 mm. A number of boron nitride tiles are assembled together as the side limiters for plasma shielding. Estimation shows that the structure is robust enough to withstand the electromagnetic force and the heat load for typical discharge duty cycles.
Oscillations in sunspot umbras due to trapped Alfven waves excited by overstability
International Nuclear Information System (INIS)
Uchida, Yutaka; Sakurai, Takashi.
1975-01-01
Oscillations observed in sunspot umbras are interpreted as a vertical motion in the atmosphere induced by a standing Alfven wave trapped in the region between the overstable layer under the photosphere and the chromosphere-corona transition layer. The Alfven wave motion is considered to be excited by the overstable convection occurring at the bottom of the abovementioned oscillating layer, and waves with special frequencies are selected as eigen-mode waves standing in the ''cavity,'' while other waves which are out of phase with themselves after reflections will disappear. It is shown by solving the eigen-value problem that the fundamental eigen frequency falls in a range around 0.04 rad s -1 (corresponding to 140-180 s) for the condition in the umbra of a typical spot, and also that the eigen frequencies do not depend greatly on the circumstantial physical or geometric parameters of the model atmosphere, such as the temperature in the layer, or the height of the transition layer, etc. The eigen frequencies, however, depend on the Alfven velocity at the base of the oscillating layer (or at the top of the overstable layer), but the latter quantity, which represents the stiffness of the magnetic tube of force against the overturning motion, takes roughly a common value for different sunspots according to SAVAGE's (1969) stability analysis of the umbral atmosphere against thermal convection, and thus gives a comparatively narrow range of resonant frequencies. In addition to the selection mechanism for oscillations of 140-180-s period, some other aspects of the oscillation, such as the relation to the running penumbral waves, are discussed. (auth.)
Matsumoto, Takuma; Shibata, Kazunari
We have performed MHD simulations of Alfven wave propagation along an open ux tube in the solar atmosphere. In our numerical model, Alfven waves are generated by the photospheric granular motion. As the wave generator, we used a derived temporal spectrum of the photo-spheric granular motion from G-band movies of Hinode/SOT. It is shown that the total energy ux at the corona becomes larger and the transition region height becomes higher in the case when we use the observed spectrum rather than white/pink noise spectrum as the wave gener-ator. This difference can be explained by the Alfven wave resonance between the photosphere and the transition region. After performing Fourier analysis on our numerical results, we have found that the region between the photosphere and the transition region becomes an Alfven wave resonant cavity. We have conrmed that there are at least three resonant frequencies, 1, 3 and 5 mHz, in our numerical model. Alfven wave resonance is one of the most effective mechanisms to explain the dynamics of the spicules and the sufficient energy ux to heat the corona.
Observation of fast-ion Doppler-shifted cyclotron resonance with shear Alfven waves
International Nuclear Information System (INIS)
Zhang Yang; Heidbrink, W. W.; Boehmer, H.; McWilliams, R.; Vincena, S.; Carter, T. A.; Gekelman, W.; Leneman, D.; Pribyl, P.
2008-01-01
The Doppler-shifted cyclotron resonance (ω-k z v z =Ω f ) between fast ions and shear Alfven waves is experimentally investigated (ω, wave frequency; k z , axial wavenumber; v z , fast-ion axial speed; Ω f , fast-ion cyclotron frequency). A test particle beam of fast ions is launched by a Li + source in the helium plasma of the LArge Plasma Device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)], with shear Alfven waves (SAW) (amplitude δ B/B up to 1%) launched by a loop antenna. A collimated fast-ion energy analyzer measures the nonclassical spreading of the beam, which is proportional to the resonance with the wave. A resonance spectrum is observed by launching SAWs at 0.3-0.8ω ci . Both the magnitude and frequency dependence of the beam-spreading are in agreement with the theoretical prediction using a Monte Carlo Lorentz code that launches fast ions with an initial spread in real/velocity space and random phases relative to the wave. Measured wave magnetic field data are used in the simulation.
Fast wave absorption at the Alfven resonance during ion cyclotron resonance heating
International Nuclear Information System (INIS)
Heikkinen, J.A.; Hellsten, T.; Alava, M.J.
1991-01-01
For ICRH scenarii where the majority cyclotron resonance intersects the plasma core, mode conversion of the fast magnetosonic wave to an Alfven wave takes place at the plasma boundary on the high field side. Simple analytical estimates of the converted power for this mode conversion process are derived and compared with numerical calculations including finite electron inertia and kinetic effects. The converted power is found to depend on the local value of the wave field as well as on plasma parameters at the Alfven wave resonance. The interference with the reflected wave will therefore modify the mode conversion. If the conversion layer is localized near the wall, the conversion will be strongly reduced. The conversion coefficient is found to be strongest for small density gradients and high density and it is sensitive to the value of the parallel wave number. Whether it increases or decreases with the latter depends on the ion composition. Analysis of this problem for ICRH in JET predicts that a large fraction of the power is mode converted at the plasma boundary for first harmonic heating of tritium in a deuterium-tritium plasma. (author). 13 refs, 10 figs, 1 tab
On the definition of the momentum of an Alfven wave packet
International Nuclear Information System (INIS)
Khudik, V.N.
1993-01-01
The different definitions of the momentum of a wave disturbance are considered, corresponding to the invariance of the Lagrangian with respect to different kinds of translation in magnetohydrodynamics. It is shown that the value of the momentum of an Alfven wave packet calculated using the definition accepted in the electrodynamics of continuous media is not the same as the total momentum of the particles in the medium and the electromagnetic field in the region within which the packet is localized. 5 refs., 2 figs
Finite Larmor radius effects on Alfven wave current drive in low-aspect ratio tokamaks
International Nuclear Information System (INIS)
Komoshvili, K.; Cuperman, S.; Bruma, C.
1998-01-01
Alfven wave current drive (AWCD) in low-aspect ratio (A≡R/a=1/ε > or approx. 1) tokamaks (LARTs) is studied numerically. For this, the full-wave equation (E parallel ≠0) with a Vlasov-based dielectric tensor is solved by relaxation techniques, subject to appropriate boundary conditions at the plasma centre and at the plasma-vacuum interface, as well as the concentric antenna current sheet and at the external metallic wall. A systematic investigation of the physical characteristics of the AWCD generated in LARTs when kinetic effects are considered is carried out and illustrative results are presented and discussed. (author)
Re-ionization of a partially ionized plasma by an Alfven wave of moderate amplitude
International Nuclear Information System (INIS)
Brennan, M.H.; Sawley, M.L.
1980-01-01
The use of forced magnetic-acoustic oscillations to investigate the effect of a torsional hydromagnetic (Alfven) wave pulse of moderate amplitude on the properties of a partially ionized afterglow helium plasma is reported. Observations of the magnetic flux associated with the oscillations, measured at a number of frequencies are used to determine radial density profiles and to provide estimates of plasma temperature. The torsional wave is shown to cause significant re-ionization of the plasma with no corresponding increase in the plasma temperature. The presence of a number of energetic particles is evidenced by the production of a significant number of doubly charged helium ions. (author)
ULF Waves in the Ionospheric Alfven Resonator: Modeling of MICA Observations
Streltsov, A. V.; Tulegenov, B.
2017-12-01
We present results from a numerical study of physical processes responsible for the generation of small-scale, intense electromagnetic structures in the ultra-low-frequency range frequently observed in the close vicinity of bright discrete auroral arcs. In particular, our research is focused on the role of the ionosphere in generating these structures. A significant body of observations demonstrate that small-scale electromagnetic waves with frequencies below 1 Hz are detected at high latitudes where the large-scale, downward magnetic field-aligned current (FAC) interact with the ionosphere. Some theoretical studies suggest that these waves can be generated by the ionospheric feedback instability (IFI) inside the ionospheric Alfven resonator (IAR). The IAR is the region in the low-altitude magnetosphere bounded by the strong gradient in the Alfven speed at high altitude and the conducting bottom of the ionosphere (ionospheric E-region) at low altitude. To study ULF waves in this region we use a numerical model developed from reduced two fluid MHD equations describing shear Alfven waves in the ionosphere and magnetosphere of the earth. The active ionospheric feedback on structure and amplitude of magnetic FACs that interact with the ionosphere is implemented through the ionospheric boundary conditions that link the parallel current density with the plasma density and the perpendicular electric field in the ionosphere. Our numerical results are compared with the in situ measurements performed by the Magnetosphere-Ionosphere Coupling in the Alfven Resonator (MICA) sounding rocket, launched on February 19, 2012 from Poker Flat Research Range in Alaska to measure fields and particles during a passage through a discreet auroral arc. Parameters of the simulations are chosen to match actual MICA parameters, allowing the comparison in the most precise and rigorous way. Waves generated in the numerical model have frequencies between 0.30 and 0.45 Hz, while MICA measured
Signatures of mode conversion and kinetic Alfven waves at the magnetopause
International Nuclear Information System (INIS)
Johnson, Jay R.; Cheng, C. Z.
2000-01-01
It has been suggested that resonant mode conversion of compressional MHD waves into kinetic Alfven waves at the magnetopause can explain the abrupt transition in wave polarization from compressional to transverse commonly observed during magnetopause crossings. The authors analyze magnetic field data for magnetopause crossings as a function of magnetic shear angle (defined as the angle between the magnetic fields in the magnetosheath and magnetosphere) and compare with the theory of resonant mode conversion. The data suggest that amplification in the transverse magnetic field component at the magnetopause is not significant up to a threshold magnetic shear angle. Above the threshold angle significant amplification results, but with weak dependence on magnetic shear angle. Waves with higher frequency are less amplified and have a higher threshold angle. These observations are qualitatively consistent with theoretical results obtained from the kinetic-fluid wave equations
The Parametric Instability of Alfven Waves: Effects of Temperature Anisotropy
Czech Academy of Sciences Publication Activity Database
Tenerani, A.; Velli, M.; Hellinger, Petr
2017-01-01
Roč. 851, č. 2 (2017), 99/1-99/9 ISSN 0004-637X R&D Projects: GA ČR GA15-10057S Institutional support: RVO:67985815 Keywords : instabilities * plasmas * waves Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 5.533, year: 2016
Non-inductive electric current generation with the Alfven waves
International Nuclear Information System (INIS)
Assis, A.S. de.
1988-01-01
Non-inductive current generation by means of radio frequency waves is studied using one-dimensional (1D) quasilinear equations. The main results obtained in this thesis are the general expressions for the current generated, for the efficiency of current generation and for the critical power - the lowest power required for current saturation. (M.W.O.) [pt
Effects of heavy ion temperature on low-frequency kinetic Alfven waves
International Nuclear Information System (INIS)
Yang, L.; Wu, D. J.
2011-01-01
Heavy ion-electron (or proton) temperature ratio varies in a wide range in the solar and space environment. In this paper, proton and heavy ion temperatures are included in a three-fluid plasma model. For the specified parameters, low-frequency (<< heavy ion gyrofrequency) kinetic Alfven waves (KAWs) with sub- and super-Alfvenic speeds are found to coexist in the same plasma environment. Our results show that the temperature ratio of heavy ions to electrons can considerably affect the dispersion, propagation, and electromagnetic polarizations of the KAWs. In particular, the temperature ratio can increase the ratio of parallel to perpendicular electric fields and the normalized electric to magnetic field ratio, the variations of which are greatly different in regions with a high heavy ion temperature and with a low one. The results may help to understand the physical mechanism of some energization processes of heavy ions in the solar and space plasma environment. Effects of the ratio of electron thermal to Alfven speeds and the heavy ion abundance on these parameters are also discussed.
Design of the RF system for Alfven wave heating and current drive in a TCA/BR tokamak
International Nuclear Information System (INIS)
Ruchko, L.; Andrade, M.L.; Ozono, E.; Galvao, R.M.O.; Degaspari, F.T.; Nascimento, I.C.
1995-01-01
The advanced RF system for Alfven wave plasma heating and current drive in TCA/BR tokamak is presented. The antenna system is capable of exciting the standing and travelling wave M = -1,N = 1,N =-4,-6 with single helicity and thus provides the possibility to improve Alfven wave plasma heating efficiency in TCA/BR tokamak and to increase input power level up to P ≅ 1 MW, without the uncontrolled density rise which was encountered in previous TCA (Switzerland) experiments. (author). 4 refs., 3 figs
Advanced antenna system for Alfven wave plasma heating and current drive in TCABR tokamak
International Nuclear Information System (INIS)
Ruchko, L.F.; Ozono, E.; Galvao, R.M.O.; Nascimento, I.C.; Degasperi, F.T.; Lerche, E.
1998-01-01
An advanced antenna system that has been developed for investigation of Alfven wave plasma heating and current drive in the TCABR tokamak is described. The main goal was the development of such a system that could insure the excitation of travelling single helicity modes with predefined wave mode numbers M and N. The system consists of four similar modules with poloidal windings. The required spatial spectrum is formed by proper phasing of the RF feeding currents. The impedance matching of the antenna with the four-phase oscillator is accomplished by resonant circuits which form one assembly unit with the RF feeders. The characteristics of the antenna system design with respect to the antenna-plasma coupling and plasma wave excitation, for different phasing of the feeding currents, are summarised. The antenna complex impedance Z=Z R +Z I is calculated taking into account both the plasma response to resonant excitation of fast Alfven waves and the nonresonant excitation of vacuum magnetic fields in conducting shell. The matching of the RF generator with the antenna system during plasma heating is simulated numerically, modelling the plasma response with mutually coupled effective inductances with corresponding active Z R and reactive Z I impedances. The results of the numerical simulation of the RF system performance, including both the RF magnetic field spectrum analysis and the modeling of the RF generator operation with plasma load, are presented. (orig.)
Papadopoulos, K.; Eliasson, B.; Shao, X.; Labenski, J.; Chang, C.
2011-12-01
A new concept of generating ionospheric currents in the ULF/ELF range with modulated HF heating using ground-based transmitters even in the absence of electrojet currents is presented. The new concept relies on using HF heating of the F-region to modulate the electron temperature and has been given the name Ionospheric Current Drive (ICD). In ICD, the pressure gradient associated with anomalous or collisional F-region electron heating drives a local diamagnetic current that acts as an antenna to inject mainly Magneto-Sonic (MS) waves in the ionospheric plasma. The electric field associated with the MS wave drives Hall currents when it reaches the E region of the ionosphere. The Hall currents act as a secondary antenna that inject waves in the Earth-Ionosphere Waveguide (EIW) below and shear Alfven waves or EMIC waves upwards towards the conjugate regions. The paper presents: (i) Theoretical results using a cold Hall MHD model to study ICD and the generation of ULF/ELF waves by the modulation of the electron pressure at the F2-region with an intense HF electromagnetic wave. The model solves equations governing the dynamics of the shear Alfven and magnetosonic modes, of the damped modes in the diffusive Pedersen layer, and of the weakly damped helicon wave mode in the Hall-dominated E-region. The model incorporates realistic profile of the ionospheric conductivities and magnetic field configuration. We use the model to simulate propagation and dynamics of the low-frequency waves and their injection into the magnetosphere from the HAARP and Arecibo ionospheric heaters. (ii) Proof of principle experiments using the HAARP ionospheric heater in conjunction with measurements by the DEMETER satellite This work is supported by ONR MURI grant and DARPA BRIOCHE Program
Alfven waves in dusty plasmas with plasma particles described by anisotropic kappa distributions
Energy Technology Data Exchange (ETDEWEB)
Galvao, R. A.; Ziebell, L. F. [Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP: 91501-970, Porto Alegre, Rio Grande do Sul (Brazil); Gaelzer, R. [Instituto de Fisica e Matematica, Universidade Federal de Pelotas, Caixa Postal 354-Campus UFPel, CEP: 96010-900 Pelotas, Rio Grande do Sul (Brazil); Juli, M. C. de [Centro de Radio-Astronomia e Astrofisica Mackenzie-CRAAM, Universidade Presbiteriana Mackenzie, Rua da Consolacao 896, CEP: 01302-907 Sao Paulo, Sao Paulo (Brazil)
2012-12-15
We utilize a kinetic description to study the dispersion relation of Alfven waves propagating parallelly to the ambient magnetic field in a dusty plasma, taking into account the fluctuation of the charge of the dust particles, which is due to inelastic collisions with electrons and ions. We consider a plasma in which the velocity distribution functions of the plasma particles are modelled as anisotropic kappa distributions, study the dispersion relation for several combinations of the parameters {kappa}{sub Parallel-To} and {kappa}{sub Up-Tack }, and emphasize the effect of the anisotropy of the distributions on the mode coupling which occurs in a dusty plasma, between waves in the branch of circularly polarized waves and waves in the whistler branch.
Magnetic fluctuations due to thermally excited Alfven waves
International Nuclear Information System (INIS)
Agim, Y.Z.; Prager, S.C.
1990-01-01
Magnetic fluctuations due to the thermally excited MHD waves are investigated using fluid and kinetic models to describe a stable, uniform, compressible plasma in the range above the drift wave frequency and below the ion cyclotron frequency. It is shown that the fluid model with resistivity yields spectral densities which are roughly Lorentzian, exhibit equipartition with no apparent cutoff in wavenumber space and a Bohm-type diffusion coefficient. Under certain conditions, the ensuing transport may be comparable to classical values. For a phenomenological cutoff imposed on the spectrum, the typical fluctuating-to-equilibrium magnetic field ratio is found to be of the order of 10 -10 . Physical mechanisms to obtain decay profiles of the spectra with increasing wavenumber due to dispersion and/or different forms of damping are investigated analytically in a cold fluid approximation and numerically, with a kinetic model. The mode dispersion due to the finite ion-gyrofrequency is identified as the leading effect determining the spectral profile shapes. It is found that the amplitude of fluctuations may be within a factor of the value suggested by the cold plasma model. The results from both models are presented and compared in low- and high-β regimes. 21 refs., 6 figs
Scrape-off measurements during Alfven wave heating in the TCA tokamak
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Hofmann, F.; Hollenstein, C.; Joye, B.; Lietti, A.; Lister, J.B.; Pochelon, A.; Gimzewski, J.K.; Veprek, S.
1984-01-01
Plasma parameters and impurity fluxes in the scrape-off layer of the TCA tokamak have been measured during Alfven wave heating. Langmuir probes are used to measure electron density, electron temperature and plasma potential. Collection probes, in conjunction with XPS surface analysis, are used to determine impurity fluxes and ion impact energies. During RF heating, the electron edge temperature rises, the plasma potential drops and impurity fluxes are enhanced. Probe erosion due to impurity sputtering is clearly observed. The measurements are correlated with other diagnostics on TCA. (orig.)
Alpha effect of Alfven waves and current drive in reversed field pinches
International Nuclear Information System (INIS)
Litwin, C.; Prager, S.C.
1997-10-01
Circularly polarized Alfven waves give rise to an α-dynamo effect that can be exploited to drive parallel current. In a open-quotes laminarclose quotes magnetic the effect is weak and does not give rise to significant currents for realistic parameters (e.g., in tokamaks). However, in reversed field pinches (RFPs) in which magnetic field in the plasma core is stochastic, a significant enhancement of the α-effect occurs. Estimates of this effect show that it may be a realistic method of current generation in the present-day RFP experiments and possibly also in future RFP-based fusion reactors
International Nuclear Information System (INIS)
Klimushkin, D.Yu.
1998-01-01
The effect of bounce-drift instability on the structure of small-scale azimuthal Alfven waves in the magnetosphere is studied with allowance for the curvature of the geomagnetic field lines. The pressure of the background plasma is assumed to be zero. As early as 1993, Leonovich and Mazur showed that Alfven waves with m>>1, being standing waves along magnetic field lines, propagate, at the same time, across the magnetic surfaces. As these waves propagate through the magnetosphere, they interact with a group of high-energy particles and, thereby, are amplified with a growth rate dependent on the radial coordinate, i.e., a coordinate perpendicular to the magnetic sheaths. Near the Alfven resonance surface, the growth rate approaches zero, and the waves are damped completely due to the energy dissipation in the ionosphere. As the growth rate increases, the maximum of the wave amplitude is displaced to the Alfven resonance region and the most amplified waves are those whose magnetic field vectors oscillate in the azimuthal direction. Among the waves excited in a plasma resonator that is formed near the plasmapause, the most amplified are those with radial polarization
Alfven wave excitation in a cavity with a transverse magnetic field
International Nuclear Information System (INIS)
Bures, M.
1982-12-01
A transversely magnetized cylindrical plasma model with an internal rod conductor is used to approximate the FIVA internal ring device of Spherator type with a purely poloidal magnetic field. It is shown that an excitation asymmetry along the plasma column, i.e. with a wave number k sub (z) does not equal 0, introduces a coupling between the magnetoacoustic and shear Alfven waves in the frequency range #betta#<<#betta# sub (ci). The introduction of an equilibrium mass motion along the plasma cylinder introduces a flow continuum. Simultaneously the Alfven resonance frequency becomes Doppler shifted. The experimental observations indicate that cavity modes do not build up in the FIVA device in the case of nonsymmetric excitation. If on the other hand the exciting structure becomes symmetric, i.e. with k sub (z) equals 0, the magnetoacoustic resonance become excited. The resulting Q values are rather low which indicates that the coupling to the shear wave through the Hall electric field cannot be neglected. (Author)
The Dynamics of Current Carriers In Standing Alfven Waves
Wright, A. N.; Allan, W.; Ruderman, M. S.; Elphic, R. C.
The acceleration of current carriers in an Alfvén wave current system is considered. The model incorporates a dipole magnetic field geometry, and we present an analyt- ical solution of the two-fluid equations by successive approximations. The leading solution corresponds to the familiar single-fluid toroidal oscillations. The next order describes the nonlinear dynamics of electrons responsible for carrying a few µAm-2 field aligned current into the ionosphere. The solution shows how most of the elec- tron acceleration in the magnetosphere occurs within 1 RE of the ionosphere, and that a parallel electric field of the order of 1 mVm-1 is reponsible for energising the electrons to 1 keV. The limitations of the electron fluid approximation are considered, and a qualitative solution including electron beams and a modified E is developed in accord with observations. We find that the electron acceleration can be nonlinear, (ve )ve > ve , as a result of our nonuniform equilibrium field geometry even when ve is less than the Alfvén speed. Our calculation also elucidates the processes through which E is generated and supported.
The Role of Kinetic Alfven Waves in Plasma Transport in an Ion-scale Flux Rope
Tang, B.; Li, W.; Wang, C.; Dai, L.
2017-12-01
Magnetic flux ropes, if generated by multiply X-line reconnections, would be born as a crater type one, meaning the plasma density within is relatively high. They will then evolve into typical flux ropes as plasma are transported away along the magnetic field lines [Zhang et al., 2010]. In this study, we report an ion-scale flux rope observed by MMS on November 28, 2016, which is accompanied by strong kinetic Alfven waves (KAW). The related wave parallel electric field can effectively accelerate electrons inside the flux rope by Landau resonance, resulting into a significant decrease of the electron at 90° pitch angle. The change of electron pitch angle distribution would cause the rapid plasma transport along the magnetic field lines, and help the flux rope evolve into a strong magnetic core in a short time. This wave-particle interaction would be a candidate mechanism to explain the rareness of crater flux ropes in reality.
International Nuclear Information System (INIS)
Tsiklauri, D.
2014-01-01
Previous studies (e.g., Malara et al., Astrophys. J. 533, 523 (2000)) considered small-amplitude Alfven wave (AW) packets in Arnold-Beltrami-Childress (ABC) magnetic field using WKB approximation. They draw a distinction between 2D AW dissipation via phase mixing and 3D AW dissipation via exponentially divergent magnetic field lines. In the former case, AW dissipation time scales as S 1∕3 and in the latter as log(S), where S is the Lundquist number. In this work, linearly polarised Alfven wave dynamics in ABC magnetic field via direct 3D magnetohydrodynamic (MHD) numerical simulation is studied for the first time. A Gaussian AW pulse with length-scale much shorter than ABC domain length and a harmonic AW with wavelength equal to ABC domain length are studied for four different resistivities. While it is found that AWs dissipate quickly in the ABC field, contrary to an expectation, it is found the AW perturbation energy increases in time. In the case of the harmonic AW, the perturbation energy growth is transient in time, attaining peaks in both velocity and magnetic perturbation energies within timescales much smaller than the resistive time. In the case of the Gaussian AW pulse, the velocity perturbation energy growth is still transient in time, attaining a peak within few resistive times, while magnetic perturbation energy continues to grow. It is also shown that the total magnetic energy decreases in time and this is governed by the resistive evolution of the background ABC magnetic field rather than AW damping. On contrary, when the background magnetic field is uniform, the total magnetic energy decrease is prescribed by AW damping, because there is no resistive evolution of the background. By considering runs with different amplitudes and by analysing the perturbation spectra, possible dynamo action by AW perturbation-induced peristaltic flow and inverse cascade of magnetic energy have been excluded. Therefore, the perturbation energy growth is attributed to
Energy Technology Data Exchange (ETDEWEB)
Tsiklauri, D. [School of Physics and Astronomy, Queen Mary University of London, London E1 4NS (United Kingdom)
2014-05-15
Previous studies (e.g., Malara et al., Astrophys. J. 533, 523 (2000)) considered small-amplitude Alfven wave (AW) packets in Arnold-Beltrami-Childress (ABC) magnetic field using WKB approximation. They draw a distinction between 2D AW dissipation via phase mixing and 3D AW dissipation via exponentially divergent magnetic field lines. In the former case, AW dissipation time scales as S{sup 1∕3} and in the latter as log(S), where S is the Lundquist number. In this work, linearly polarised Alfven wave dynamics in ABC magnetic field via direct 3D magnetohydrodynamic (MHD) numerical simulation is studied for the first time. A Gaussian AW pulse with length-scale much shorter than ABC domain length and a harmonic AW with wavelength equal to ABC domain length are studied for four different resistivities. While it is found that AWs dissipate quickly in the ABC field, contrary to an expectation, it is found the AW perturbation energy increases in time. In the case of the harmonic AW, the perturbation energy growth is transient in time, attaining peaks in both velocity and magnetic perturbation energies within timescales much smaller than the resistive time. In the case of the Gaussian AW pulse, the velocity perturbation energy growth is still transient in time, attaining a peak within few resistive times, while magnetic perturbation energy continues to grow. It is also shown that the total magnetic energy decreases in time and this is governed by the resistive evolution of the background ABC magnetic field rather than AW damping. On contrary, when the background magnetic field is uniform, the total magnetic energy decrease is prescribed by AW damping, because there is no resistive evolution of the background. By considering runs with different amplitudes and by analysing the perturbation spectra, possible dynamo action by AW perturbation-induced peristaltic flow and inverse cascade of magnetic energy have been excluded. Therefore, the perturbation energy growth is
Ion beam generation at the plasma sheet boundary layer by kinetic Alfven waves
International Nuclear Information System (INIS)
Moghaddam-Taaheri, E.; Goertz, C.K.; Smith, R.A.
1989-01-01
The kinetic Alfven wave, an Alfven wave with a perpendicular wavelength comparable to the ion gyroradius, can diffuse ions both in velocity and coordinate spaces with comparable transport rates. This may lead to the generation of ion beams in the plasma sheet boundary layer (PSBL). To investigate the ion beam generation process numerically, a two-dimensional quasi-linear code was constructed. Assuming that the plasma β (the ratio of plasma pressure to the magnetic pressure) varies from β = 1 to β << 1 across the magnetic field, the dynamics of the ion beam generation in the PSBL was studied. It was found that if your start with an ion distribution function which monotonically decreases with velocity along the magnetic field and a density gradient across the magnetic field, ions diffuse in velocity-coordinate space until nearly a plateau is established along the diffusion path. Depending on the topology of the magnetic field at the lobe side of the simulation system, i.e., open or closed field lines, the ion distribution function may or may not reach a steady state. If the field lines are open there, i.e., if the diffusion extends into the lobe, the double diffusion process may provide a mechanism for continuously transferring the ions from the central plasma sheet to the lobe. The authors comment on the effect of the particle loss on the establishment of the pressure balance in the plasma sheet
Unified theory of damping of linear surface Alfven waves in inhomogeneous incompressible plasmas
International Nuclear Information System (INIS)
Ruderman, M.S.; Goossens, M.
1996-01-01
The viscous damping of surface Alfven waves in a non-uniform plasma is studied in the context of linear and incompressible MHD. It is shown that damping due to resonant absorption and damping on a true discontinuity are two limiting cases of the continuous variation of the damping rate with respect to the dimensionless number Rg = Δλ 2 Re, where Δ is the relative variation of the local Alfven velocity, λ is the ratio of the thickness of the inhomogeneous layer to the wavelength, and Re is the viscous Reynolds number. The analysis is restricted to waves with wavelengths that are long in comparison with the extent of the non-uniform layer (λ '' >'' 1) values of Rg. For very small values of Rg, the damping rate agrees with that found for a true discontinuity, while for very large values of Rg, it agrees with the damping rate due to resonant absorption. The dispersion relation is subsequently studied numerically over a wide range of values of Rg, revealing a continuous but non-monotonic variation of the damping rate with respect to Rg. (Author)
International Nuclear Information System (INIS)
Eckhartt, D.
1989-01-01
Supra-thermal ions can contribute to the steady-state current in future large tokamak machines like NET or ITER. The fast-ion population is generated by collisional slowing-down of high-energy ions which were injected as neutral atoms in quasi-tangential direction and ionized by plasma interactions. Depending on the initial beam shape these fast ions can excite microinstabilities of the Alfven-wave type which are driven by the gradients in velocity-space. The ensuring plasma turbulence is expected to slow down the fast ions very quickly. This effect reduces the current drive efficiency which otherwise is comparable to that of other current drive schemes like lower hybrid waves where the toroidal current is carried by high-energy resonant electrons. (author) 3 refs., 1 fig
International Nuclear Information System (INIS)
Descamps, P.; Wassenhove, G. van; Koch, R.; Messiaen, A.M.; Vandenplas, P.E.; Lister, J.B.; Marmillod, P.
1990-01-01
The use of the discrete Alfven wave spectrum to determine the current density profile and the effective mass density of the plasma in the TEXTOR tokamak is studied; the measurement, the validity of which is discussed, confirms independently the central q(r=0)<1 already obtained by polarimetry. (orig.)
An experimental study of Alfven wave heating using electrostatically shielded antennas in TCA
International Nuclear Information System (INIS)
Borg, G.G.; Joye, B.
1990-01-01
Despite the wide acceptance of electrostatic screens in ICRH for the protection of the plasma from the near fields of rf antennas, it has always been considered that low voltages at low frequency have made such screens unnecessary in Alfven wave heating (AWH). Despite this, AWH performs rather poorly as a heating method; the results being confused by a density rise up to 300 % of the target density. It is known that the density increase arises neither from impurity injection nor from a change in recycling. In addition, an extensive range of phenomena have been observed in the plasma scrape-off layer (SOL). During AWH, the SOL density is observed to decrease, the SOL floating potential is perturbed in a way that reflects the Alfven wave spectrum, the antennas charge negatively and draw a large current from the plasma and harmonics have been observed on the edge wave fields. The cause and correlation of these effects with each other and their impression on the bulk plasma response was not known. Experimental results from the TORTUS tokamak have indicated that the density increase might be eliminated by electrostatic screens. In their case, two AWH experiments were performed. In the first, an unshielded OFHC copper loop antenna was excited at a given power and, in the second, the same antenna was excited at the same power after installation of an aluminium, TiN coated, slotted screen. The density increase in the first case was shown to be completely eliminated in the second, although spectroscopic measurements revealed a difference in the plasma O(II) and Cu(I) content for each case. (author) 2 refs., 3 figs
Possible evidence for the driving of the winds of hot stars by Alfven waves
International Nuclear Information System (INIS)
Underhill, A.B.
1983-01-01
Ultraviolet spectra of the supergiants α Cam (09.5 Ia), HD 105056 (ON9.7 Iae), and 15 Sgr (09.7 Lab) are compared, and it is shown that the terminal outflow velocity ν/sub infinity/, of HD 105056 is one-half that of the other two stars even though HD 105056 has the highest effective temperature of the three stars. This anomaly, together with the fact that the observed ν/sub infinity/ values for early-type stars scatter about an empirical correlation between ν/sub infinity/ and log T/sub eff/ by an amount which is larger than the amount which is larger than the amount expected according to the observational errors in determining ν/sub infinity/ and log T/sub eff/, leads to the conclusion that an agent in addition to radiation. Alfven waves, is driving the winds of early-type stars
Antenna analysis and boundary conditions for Alfven wave studies in tokamaks
International Nuclear Information System (INIS)
Ross, D.W.; Li Yanming; Mahajan, S.M.; Michie, R.B.
1986-01-01
Previous studies of Alfven wave heating which employed kinetic theory are extended in order to take into account antenna configurations, in cylindrical geometry, consisting of arbitrary shell currents and their associated radial feeders. For each Fourier component of the form exp [-i(lzeta-mtheta)], the shell current consists of a divergence-free part having the helicity of the mode (l, m), plus an orthogonal part requiring the feeders. It is shown, both analytically and by including the full current in the numerical code, that only the divergence-free part of the current contributes significantly to the plasma response and antenna loading. The important effect of the feeders is to cancel the contribution from the surface current perpendicular to the helicity. This explicitly verifies results reported previously. (author)
Antenna analysis and boundary conditions for Alfven wave studies in tokamaks
International Nuclear Information System (INIS)
Ross, D.W.; Li, Y.M.; Mahajan, S.M.; Michie, R.B.
1985-07-01
Previous studies of Alfven wave heating which employed kinetic theory are extended to take into account antenna configurations, in cylindrical geometry, consisting of arbitrary shell currents and their associated radial feeders. For each Fourier component of the form esp/-i(l zeta - m theta)/, the shell current consists of a divergence-free part having the helicity of the mode (l,m), plus an orthogonal part requiring the feeders. It is shown, both analtically and by including the full current in the numerical code, that only the divergence-free part of the current contributes significantly to the plasma response and antenna loading. The important effect of the feeders is to cancel the contribution from the surface current perpendicular to the helicity. This explicitly verifies results reported previously
Energy Technology Data Exchange (ETDEWEB)
Evans, R. M. [NASA Goddard Space Flight Center, Space Weather Lab, Greenbelt, MD 20771 (United States); Opher, M. [Astronomy Department, Boston University, 675 Commonwealth Avenue, Boston, MA 02215 (United States); Oran, R.; Van der Holst, B.; Sokolov, I. V.; Frazin, R.; Gombosi, T. I. [Center for Space Environment Modeling, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109 (United States); Vasquez, A., E-mail: Rebekah.e.frolov@nasa.gov [Instituto de Astronomia y Fisica del Espacio (CONICET-UBA) and FCEN (UBA), CC 67, Suc 28, Ciudad de Buenos Aires (Argentina)
2012-09-10
The heating and acceleration of the solar wind is an active area of research. Alfven waves, because of their ability to accelerate and heat the plasma, are a likely candidate in both processes. Many models have explored wave dissipation mechanisms which act either in closed or open magnetic field regions. In this work, we emphasize the boundary between these regions, drawing on observations which indicate unique heating is present there. We utilize a new solar corona component of the Space Weather Modeling Framework, in which Alfven wave energy transport is self-consistently coupled to the magnetohydrodynamic equations. In this solar wind model, the wave pressure gradient accelerates and wave dissipation heats the plasma. Kolmogorov-like wave dissipation as expressed by Hollweg along open magnetic field lines was presented in van der Holst et al. Here, we introduce an additional dissipation mechanism: surface Alfven wave (SAW) damping, which occurs in regions with transverse (with respect to the magnetic field) gradients in the local Alfven speed. For solar minimum conditions, we find that SAW dissipation is weak in the polar regions (where Hollweg dissipation is strong), and strong in subpolar latitudes and the boundaries of open and closed magnetic fields (where Hollweg dissipation is weak). We show that SAW damping reproduces regions of enhanced temperature at the boundaries of open and closed magnetic fields seen in tomographic reconstructions in the low corona. Also, we argue that Ulysses data in the heliosphere show enhanced temperatures at the boundaries of fast and slow solar wind, which is reproduced by SAW dissipation. Therefore, the model's temperature distribution shows best agreement with these observations when both dissipation mechanisms are considered. Lastly, we use observational constraints of shock formation in the low corona to assess the Alfven speed profile in the model. We find that, compared to a polytropic solar wind model, the wave
Theory of charged particle heating by low-frequency Alfven waves
International Nuclear Information System (INIS)
Guo Zehua; Crabtree, Chris; Chen, Liu
2008-01-01
The heating of charged particles by a linearly polarized and obliquely propagating shear Alfven wave (SAW) at frequencies a fraction of the charged particle cyclotron frequency is demonstrated both analytically and numerically. Applying Lie perturbation theory, with the wave amplitude as the perturbation parameter, the resonance conditions in the laboratory frame are systematically derived. At the lowest order, one recovers the well-known linear cyclotron resonance condition k parallel v parallel -ω-nΩ=0, where v parallel is the particle velocity parallel to the background magnetic field, k parallel is the parallel wave number, ω is the wave frequency, Ω is the gyrofrequency, and n is any integer. At higher orders, however, one discovers a novel nonlinear cyclotron resonance condition given by k parallel v parallel -ω-nΩ/2=0. Analytical predictions on the locations of fixed points, widths of resonances, and resonance overlapping criteria for global stochasticity are also found to agree with those given by computed Poincare surfaces of section
International Nuclear Information System (INIS)
Bhattacharyya, B.; Chakraborty, B.
1979-01-01
Nonlinear corrections of a left and a right circularly polarized electromagnetic wave of the same frequency, propagating in the direction of a static and uniform magnetic field in a cold and collisionally damped two-component plasma, have been evaluated. The nonlinearly correct dispersion relation, self-generating nonlinear precessional rotation of the polarization ellipse of the wave and the shift in a wave parameter depend on linear combinations of products of the amplitude components taken two at a time and hence on the energies of the waves. Both in the low frequency resonance (that is when the ion cyclotron frequency equals the wave frequency) and in the high frequency resonance (that is when the electron cyclotron frequency equals the wave frequency), the self-precessional rate and wavenumber shift are found to be large and so have the possibility of detection in laboratory experiments. Moreover, for the limit leading to Alfven waves, these nonlinear effects have been found to have some interesting and significant properties. (Auth.)
Drift-Alfven wave mediated particle transport in an elongated density depression
International Nuclear Information System (INIS)
Vincena, Stephen; Gekelman, Walter
2006-01-01
Cross-field particle transport due to drift-Alfven waves is measured in an elongated density depression within an otherwise uniform, magnetized helium plasma column. The depression is formed by drawing an electron current to a biased copper plate with cross-field dimensions of 28x0.24 ion sound-gyroradii ρ s =c s /ω ci . The process of density depletion and replenishment via particle flux repeats in a quasiperiodic fashion for the duration of the current collection. The mode structure of the wave density fluctuations in the plane perpendicular to the background magnetic field is revealed using a two-probe correlation technique. The particle flux as a function of frequency is measured using a linear array of Langmuir probes and the only significant transport occurs for waves with frequencies between 15%-25% of the ion cyclotron frequency (measured in the laboratory frame) and with perpendicular wavelengths k perpendicular ρ s ∼0.7. The frequency-integrated particle flux is in rough agreement with observed increases in density in the center of the depletion as a function of time. The experiments are carried out in the Large Plasma Device (LAPD) [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] at the Basic Plasma Science Facility located at the University of California, Los Angeles
Basic toroidal Effects on Alfven Wave Current in Small Aspect Ratio Tokamaks
International Nuclear Information System (INIS)
Burma, C.; Cuperman, S.; Komoshvili, K.
1998-01-01
The Alfven wave current drive (AWCD) in small aspect ratio Tokamaks is properly calculated, with consideration of the basic toroidicity effects present in (i) the dielectric tensor-operator (involving the strongly toroidal equilibrium profiles), (ii) the structure of the r.f. fields obtained as a solution of the wave equation (through Maxwell's equations' toroidal operators as well as the conversion rate and conversion layer location, depending also on the equilibrium profiles) and (iii) the formulation of the AWCD (which, besides its dependence on the r.f. fields - affected by toroidicity as mentioned at points (i) and (ii) - also requires the equilibrium-magnetic-surface averaging of non-resonant forces involved). Thus, we consider consistent equilibrium profiles with neo-classical conductivity corresponding to an ohmic START-like discharge; use a resistive (anisotropic) MHD dielectric tensor-operator Edith practically no limitations, adequate to describe the plasma response in the pre-heated stage ; solve numerically the 2(1/2)D full- wave equation by the aid of an advanced finite element code developed in; and evaluate the AWCD by the aid of the recently proposed, quite general formulation holding in the case of strongly toroidal fusion devices and including contributions due to helicity injection, momentum transfer and plasma Bow. A general discussion of the results obtained in this work is presented
Hybrid Model of Inhomogeneous Solar Wind Plasma Heating by Alfven Wave Spectrum: Parametric Studies
Ofman, L.
2010-01-01
Observations of the solar wind plasma at 0.3 AU and beyond show that a turbulent spectrum of magnetic fluctuations is present. Remote sensing observations of the corona indicate that heavy ions are hotter than protons and their temperature is anisotropic (T(sub perpindicular / T(sub parallel) >> 1). We study the heating and the acceleration of multi-ion plasma in the solar wind by a turbulent spectrum of Alfvenic fluctuations using a 2-D hybrid numerical model. In the hybrid model the protons and heavy ions are treated kinetically as particles, while the electrons are included as neutralizing background fluid. This is the first two-dimensional hybrid parametric study of the solar wind plasma that includes an input turbulent wave spectrum guided by observation with inhomogeneous background density. We also investigate the effects of He++ ion beams in the inhomogeneous background plasma density on the heating of the solar wind plasma. The 2-D hybrid model treats parallel and oblique waves, together with cross-field inhomogeneity, self-consistently. We investigate the parametric dependence of the perpendicular heating, and the temperature anisotropy in the H+-He++ solar wind plasma. It was found that the scaling of the magnetic fluctuations power spectrum steepens in the higher-density regions, and the heating is channeled to these regions from the surrounding lower-density plasma due to wave refraction. The model parameters are applicable to the expected solar wind conditions at about 10 solar radii.
Non-inductive current drive via helicity injection by Alfven waves in low-aspect-ratio tokamaks
Energy Technology Data Exchange (ETDEWEB)
Cuperman, S.; Bruma, C.; Komoshvili, K. [Tel Aviv Univ. (Israel). Sackler Faculty of Exact Sciences
1996-08-01
A theoretical investigation of radio-frequency (RF) current drive via helicity injection in low aspect ratio tokamaks is carried out. A current-carrying cylindrical plasma surrounded by a helical sheet-current antenna and situated inside a perfectly conducting shell is considered. Toroidal features of low-aspect-ratio tokamaks are simulated by incorporating the following effects: (i) arbitrarily small aspect ratio, R{sub O}/a ``identical to`` 1/{epsilon}; (ii) strongly sheared equilibrium magnetic field; and (iii) relatively large poloidal component of the equilibrium magnetic field. This study concentrates on the Alfven continuum, i.e. the case in which the wave frequency satisfies the condition {l_brace}{omega}{sub Alf}({tau}){r_brace}{sub min}{r_brace} {<=} {omega} {<=} {l_brace}{omega}{sub Alf}({tau}){r_brace}{sub max}, where {omega}{sub Alf}({tau}) ``identical to`` {omega}{sub Alf}[n({tau}), B{sub O}({tau})] is an eigenfrequency of the shear Alfven wave (SAW). Thus, using low-{beta} magnetohydrodynamics, the wave equation with correct boundary (matching) conditions is solved, the RF field components are found, and subsequently current drive, power deposition and efficiency are computed. The results of our investigation clearly demonstrate the possibility of generation of RF-driven currents via helicity injection by Alfven waves in low-aspect-ratio tokamaks, in the SAW mode. A special algorithm is developed that enables one to select the antenna parameters providing optimal current drive efficiency. (Author).
On the stochastic interaction of monochromatic Alfven waves with toroidally trapped particles
International Nuclear Information System (INIS)
Krlin, L.; Pavlo, P.; Tluchor, Z.; Gasek, Z.
1987-07-01
Monochromatic Alfven wave interaction with toroidaly trapped particles in the intrinsic stochasticity regime is discussed. Both the diffusion in velocities and in the radial position of bananas is studied. Using a suitable Hamiltonian formalism, the effect of wave parallel components E-tilde paral and B-tilde paral is investigated. The stochasticity threshold is estimated for plasma electrons and for thermonuclear alpha-particles (neglecting the effect of B-tilde paral ) by means of direct numerical integration of the corresponding canonical equations. Stochasticity causes transfer between trapped and untrapped regimes and the induced radial diffusion of bananas. The latter effect can considerably exceed neoclassical diffusion. The effect of B-tilde paral was only estimated analytically. It consisted in frequency modulation of the banana periodic motion coupled with a possible Mathieu instability. Nevertheless, for B-tilde paral corresponding to E-tilde paral , the effect seems to be weaker than the effect of E-tilde paral when the thermonuclear regime is considered. (author). 14 figs., 36 refs
International Nuclear Information System (INIS)
Bruma, C.; Cuperman, S.; Komoshvili, K.
1998-01-01
Several low aspect ratio (spherical) Tokamaks (ST's) are now in operation or under construction. These devices would permit cost-effective and attractive embodiment of future fusion reactors: they would provide high β, good confinement and steady state operation at modest field values. Now, a steady state reactor has to be sustained by non-inductively driven currents. Recently, the generation of non-inductive current drive by Alfven waves (AWCD) has been investigated theoretically within the framework of ideal (E p arallel=0) MHD and non-ideal, resistive (E p arallel≠0) MHD; however, in all these cases, the tokamak device consisted of a cylindrical plasma with simulated toroidal effects. Rather encouraging results have been obtained. In this work we further investigate AWCD in ST's as follows: (i) we use consistent equilibrium profiles with neoclassical conductivity corresponding to an ohmic START discharge; (ii) incorporate effects due to neoclassical conductivity in the elements of the resistive MHD dielectric tensor, in the solution of the full (E p arallel≠0) wave equation as well as in the calculation of AWCD; and (iii) carry out a systematic search for antenna parameters optimizing the AWCD. (author)
Energy Technology Data Exchange (ETDEWEB)
Bruma, C.; Cuperman, S.; Komoshvili, K. [School of Physics and Astronomy, Tel Aviv University, Tel Aviv (Israel)
1998-08-01
Several low aspect ratio (spherical) Tokamaks (ST's) are now in operation or under construction. These devices would permit cost-effective and attractive embodiment of future fusion reactors: they would provide high {beta}, good confinement and steady state operation at modest field values. Now, a steady state reactor has to be sustained by non-inductively driven currents. Recently, the generation of non-inductive current drive by Alfven waves (AWCD) has been investigated theoretically within the framework of ideal (E{sub p}arallel=0) MHD and non-ideal, resistive (E{sub p}arallel{ne}0) MHD; however, in all these cases, the tokamak device consisted of a cylindrical plasma with simulated toroidal effects. Rather encouraging results have been obtained. In this work we further investigate AWCD in ST's as follows: (i) we use consistent equilibrium profiles with neoclassical conductivity corresponding to an ohmic START discharge; (ii) incorporate effects due to neoclassical conductivity in the elements of the resistive MHD dielectric tensor, in the solution of the full (E{sub p}arallel{ne}0) wave equation as well as in the calculation of AWCD; and (iii) carry out a systematic search for antenna parameters optimizing the AWCD. (author)
International Nuclear Information System (INIS)
Meyerhofer, D.D.; Perkins, F.W.
1984-01-01
The kinetic Alfven wave is studied in a cylindrical force-free plasma with self-consistent magnetic fields. This equilibrium represents a reversed field pinch or a spheromak. The stability of the wave is found to depend on the ratio of the electron drift velocity to the Alfven velocity. This ratio varies inversely with the square root of the plasma line density. The critical line density using the Spitzer--Harm electron distribution function is found for reversed field pinches with deuterium plasmas to be approximately 2 x 10 18 and is 5 x 10 17 m -1 in spheromaks with hydrogen plasmas. The critical line density is in reasonable agreement with experimental data for reversed field pinches
International Nuclear Information System (INIS)
Lyu, L.H.; Kan, J.R.
1989-01-01
Nonlinear one-dimensional constant-profile hydromagnetic wave solutions are obtained in finite-temperature two-fluid collisionless plasmas under adiabatic equation of state. The nonlinear wave solutions can be classified according to the wavelength. The long-wavelength solutions are circularly polarized incompressible oblique Alfven wave trains with wavelength greater than hudreds of ion inertial length. The oblique wave train solutions can explain the high degree of alignment between the local average magnetic field and the wave normal direction observed in the solar wind. The short-wavelength solutions include rarefaction fast solitons, compression slow solitons, Alfven solitons and rotational discontinuities, with wavelength of several tens of ion inertial length, provided that the upstream flow speed is less than the fast-mode speed
Monte-Carlo Orbit/Full Wave Simulation of Fast Alfven Wave (FW) Damping on Resonant Ions in Tokamaks
International Nuclear Information System (INIS)
Choi, M.; Chan, V.S.; Pinsker, R.I.; Tang, V.; Bonoli, P.; Wright, J.
2005-01-01
To simulate the resonant interaction of fast Alfven wave (FW) heating and Coulomb collisions on energetic ions, including finite orbit effects, a Monte-Carlo code ORBIT-RF has been coupled with a 2D full wave code TORIC4. ORBIT-RF solves Hamiltonian guiding center drift equations to follow trajectories of test ions in 2D axisymmetric numerical magnetic equilibrium under Coulomb collisions and ion cyclotron radio frequency quasi-linear heating. Monte-Carlo operators for pitch-angle scattering and drag calculate the changes of test ions in velocity and pitch angle due to Coulomb collisions. A rf-induced random walk model describing fast ion stochastic interaction with FW reproduces quasi-linear diffusion in velocity space. FW fields and its wave numbers from TORIC are passed on to ORBIT-RF to calculate perpendicular rf kicks of resonant ions valid for arbitrary cyclotron harmonics. ORBIT-RF coupled with TORIC using a single dominant toroidal and poloidal wave number has demonstrated consistency of simulations with recent DIII-D FW experimental results for interaction between injected neutral-beam ions and FW, including measured neutron enhancement and enhanced high energy tail. Comparison with C-Mod fundamental heating discharges also yielded reasonable agreement
Energy cascading in the beat-wave accelerator
International Nuclear Information System (INIS)
McKinstrie, C.J.; Batha, S.H.
1987-01-01
A review is given of energy cascading in the beat-wave accelerator. The properties of the electromagnetic cascade and the corresponding plasma-wave evolution are well understood within the framework of an approximate analytic model. Based on this model, idealized laser-plasma coupling efficiencies of the order of 10% do not seem unreasonable. 28 refs
Rankin, R.; Sydorenko, D.
2015-12-01
Results from a 3D global numerical model of Alfven wave propagation in a warm multi-species plasma in Earth's magnetosphere are presented. The model uses spherical coordinates, accounts for a non-dipole magnetic field, vertical structure of the ionosphere, and an air gap below the ionosphere. A realistic density model is used. Below the exobase altitude (2000 km) the densities and the temperatures of electrons, ions, and neutrals are obtained from the IRI and MSIS models. Above the exobase, ballistic (originating from the ionosphere and returning to ionosphere) and trapped (bouncing between two reflection points above the ionosphere) electron populations are considered similar to [Pierrard and Stegen (2008), JGR, v.113, A10209]. Plasma parameters at the exobase provided by the IRI are the boundary conditions for the ballistic electrons while the [Carpenter and Anderson (1992), JGR, v.97, p.1097] model of equatorial electron density defines parameters of the trapped electron population. In the simulations that are presented, Alfven waves with frequencies from 1 Hz to 0.01 Hz and finite azimuthal wavenumbers are excited in the magnetosphere and compared with Van Allen Probes data and ground-based observations from the CARISMA array of ground magnetometers. When short perpendicular scale waves reflect form the ionosphere, compressional Alfven waves are observed to propagate across the geomagnetic field in the ionospheric waveguide [e.g., Lysak (1999), JGR, v.104, p.10017]. Signals produced by the waves on the ground are discussed. The wave model is also applied to interpret recent Van Allen Probes observations of kinetic scale ULF waves that are associated with radiation belt electron dynamics and energetic particle injections.
Influence of gyroradius and dissipation on the Alfven-wave continuum
International Nuclear Information System (INIS)
Connor, J.W.; Tang, W.M.; Taylor, J.B.
1982-01-01
It is well known that in ideal magnetohydrodynamics there is a continuous spectrum of real frequencies associated with a singularity of the shear Alfven waves on the surface k/sub parallel to/v/sub A/ = omega. It is also known that the introduction of first-order gyroradius effects eliminates the continuum. In the present work we examine the influence of the full gyroradius response and of dissipation on the continuum. In the absence of dissipation we first confirm that if only first-order gyroradius effects are incorporated, the continuum disappears. However, when the full gyroradius response is included, this discrete spectrum vanishes, and a new continuum (associated with singularities at k/sub parallel to/v/sub A/ = 0) appears. The introduction of collisional dissipation removes the original MHD continuum leaving discrete modes whose frequency tends to zero with the collision rate as ν/sup 1/3/. collisions also remove the new continuum of the full gyroradius model leaving discrete modes whose frequency tends to zero as (log ν) -1 . Collisionless Landau damping has a similar effect
The dominant mode of standing Alfven waves at the synchronous orbit
International Nuclear Information System (INIS)
Cummings, W.D.; Countee, C.; Lyons, D.; Wiley, W. III
1975-01-01
Low-frequency oscillations of the earth's magnetic field recorded by the University of California at Los Angeles magnetometer on board ATS 1 have been examined for the 6-month interval January-June 1968. Using evidence from Ogo 5 and ATS 5 as well as the data from ATS 1, we argue that the dominant mode at ATS 1 must be the fundamental rather than the second harmonic of a standing Alfven wave. We also conclude that these transverse oscillations are more accurately associated with magnetically disturbed days than with quiet days. Both of these results represent changes of tentative conclusions based on our initial analysis. From 14 instances when oscillations of distinctly different periods occurred during the same time interval at ATS 1 we also conclude that higher harmonics can exist. The period ratio in seven of the 14 cases corresponds to the simultaneous occurrence of the second harmonic with the fundamental, and four other cases could be identified as the simultaneous occurrence of the fourth harmonic with the fundamental
Tamrakar, Radha; Varma, P.; Tiwari, M. S.
2018-05-01
Kinetic Alfven wave (KAW) generation due to variation of loss-cone index J and density of multi-ions (H+, He+ and O+) in the plasma sheet boundary layer region (PSBL) is investigated. Kinetic approach is used to derive dispersion relation of wave using Vlasov equation. Variation of frequency with respect to wide range of k⊥ρi (where k⊥ is wave vector across the magnetic field, ρi is gyroradius of ions and i denotes H+, He+ and O+ ions) is analyzed. It is found that each ion gyroradius and number density shows different effect on wave generation with varying width of loss-cone. KAW is generated with multi-ions (H+, He+ and O+) over wide regime for J=1 and shows dissimilar effect for J=2. Frequency is reduced with increasing density of gyrating He+ and O+ ions. Wave frequency is obtained within the reported range which strongly supports generation of kinetic Alfven waves. A sudden drop of frequency is also observed for H+ and He+ ion which may be due to heavy penetration of these ions through the loss-cone. The parameters of PSBL region are used for numerical calculation. The application of these results are in understanding the effect of gyrating multi-ions in transfer of energy and Poynting flux losses from PSBL region towards ionosphere and also describing the generation of aurora.
International Nuclear Information System (INIS)
Sen, S.; Roy Chowdhury, A.
1989-06-01
The nonlinear Alfven waves are governed by the Vector Derivative nonlinear Schroedinger (VDNLS) equation, which for parallel or quasi parallel propagation reduces to the Derivative Nonlinear Schroedinger (DNLS) equation for the circularly polarized waves. We have formulated the Quantum Inverse problem for a new type of Nonlinear Schroedinger Equation which has many properties similar to the usual NLS problem but the structure of classical and quantum R matrix are distinctly different. The commutation rules of the scattering data are obtained and the Algebraic Bethe Ansatz is formulated to derive the eigenvalue equation for the energy of the excited states. 10 refs
Propagation of large amplitude Alfven waves in the solar wind current sheet
International Nuclear Information System (INIS)
Malara, Francesco; Primavera, Leonardo; Veltri, Pierluigi
1996-01-01
The time evolution of Alfvenic perturbations in the Solar Wind current sheet is studied by using numerical simulations of the compressible magnetohydrodynamic (MHD) equations. The simulations show that the interaction between the large amplitude Alfvenic pertubation and the solar wind current sheet decreases the correlation between velocity and magnetic field fluctuations and produces compressive fluctuations. The characteristics of these compressive fluctuations compare rather well with spatial observations. The behavior of the correlation between density and magnetic field intensity fluctuations and of the their spectra are well reproduced so that the physical mechanisms giving rise to these behaviors can be identified
Kinetic Alfven Waves and the Depletion of the Thermal Population in Extragalactic Jets
Jafelice, L. C.; Opher, R.
1990-11-01
evident that both problems are intimately related to one another. Jafe- lice and Opher (1987a)(Astrophys. Space Sci. 137, 303)showed that an abundant generation of kinetic Alfven waves (KAw) within EJ and ERS is expected. In the present work we study the chain of processes: a) KAW accelerate thermal electrons along the background magnetic field producing suprathermal runaway electrons; b) which generate Langmuir waves and c) which in turn further accelerate a fraction of the runaway electrons to moderately relativistic energies. We show that assuming that there is no other source of a thermal population but the original one, the above sequence of processes can account for the consumption of thermal electrons in a time scale the source lifetime. Key o : GALAXIES-JETS - HYDROMAGNETICS
Alfven frequency modes and global Alfven eigenmodes
International Nuclear Information System (INIS)
Villard, L.; Vaclavik, J.
1996-07-01
The spectrum of n=0 Alfven modes is calculated analytically and numerically in cylindrical and toroidal geometries. It includes Global Alfven Eigenmodes (GAE) and Surface Modes (SM) of the fast magnetoacoustic wave. These modes are not induced by toroidicity. The n=0 GAEs owe their existence to the shear. The frequency spacing between different radial and poloidal modes and the correlation of eigenfrequencies with changes in the edge density are examined and found in complete agreement with experimental observations of what has been named the 'Alfven Frequency Mode' (AFM) so far. Although the eigenfrequency is related to the edge density, the n=0 GAE (AFM) is not necessarily edge-localized. (author) figs., tabs., refs
Finite amplitude solitary Alfven waves in a low-β plasma
International Nuclear Information System (INIS)
Kalita, M.K.; Kalita, B.C.
1985-01-01
Different exact forms of Alfven solitons were found recently in low-beta plasmas by different assumptions. The present paper studies the case of parallel ion inertia and current density. Both super and sub-Alfvenian rarefactive solitons were found to exist depending on the angle of inclination of the propagation vector with the magnetic field. (D.Gy.)
Energy Technology Data Exchange (ETDEWEB)
Zhao, G. Q.; Chen, L.; Wu, D. J. [Purple Mountain Observatory, CAS, Nanjing 210008 (China); Yan, Y. H., E-mail: djwu@pmo.ac.cn [Key Laboratory of Solar Activity, National Astronomical Observatories, CAS, Beijing 100012 (China)
2013-06-10
Solar type I radio storms are long-lived radio emissions from the solar atmosphere. It is believed that these type I storms are produced by energetic electrons trapped within a closed magnetic structure and are characterized by a high ordinary (O) mode polarization. However, the microphysical nature of these emissions is still an open problem. Recently, Wu et al. found that Alfven waves (AWs) can significantly influence the basic physics of wave-particle interactions by modifying the resonant condition. Taking the effects of AWs into account, this work investigates electron cyclotron maser emission driven by power-law energetic electrons with a low-energy cutoff distribution, which are trapped in coronal loops by closed solar magnetic fields. The results show that the emission is dominated by the O mode. It is proposed that this O mode emission may possibly be responsible for solar type I radio storms.
Energy Technology Data Exchange (ETDEWEB)
Maneva, Y. G. [Department of Physics, Catholic University of America, Washington DC, 20064 (United States) and Heliophysics Science Devision, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Ofman, L. [Department of Physics, Catholic University of America, Washington, DC 20064 (United States) and Heliophysics Science Devision, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Vinas, A. F. [Heliophysics Science Devision, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
2013-06-13
In anticipation of results from inner heliospheric missions such as the Solar Orbiter and the Solar Probe we present the results from 1.5D hybrid simulations to study the role of magnetic fluctuations for the heating and differential acceleration of He{sup ++} ions in the solar wind. We consider the effects of nonlinear Alfven-cyclotron waves at different frequency regimes. Monochromatic nonlinear Alfven-alpha-cyclotron waves are known to preferentially heat and accelerate He{sup ++} ions in collisionless low beta plasma. In this study we demonstrate that these effects are preserved when higherfrequency monochromatic and broad-band spectra of Alfven-proton-cyclotron waves are considered. Comparison between several nonlinear monochromatic waves shows that the ion temperatures, anisotropies and relative drift are quantitatively affected by the shift in frequency. Including a broad-band wave-spectrum results in a significant reduction of both the parallel and the perpendicular temperature components for the He{sup ++} ions, whereas the proton heating is barely influenced, with the parallel proton temperature only slightly enhanced. The differential streaming is strongly affected by the available wave power in the resonant daughter ion-acoustic waves. Therefore for the same initial wave energy, the relative drift is significantly reduced in the case of initial wave-spectra in comparison to the simulations with monochromatic waves.
International Nuclear Information System (INIS)
Bandyopadhyay, Anup; Das, K.P.
2002-01-01
The evolution equations describing both kinetic Alfven wave and ion-acoustic wave in a nonthermal magnetized plasma with warm ions including weak nonlinearity and weak dispersion with the effect of Landau damping have been derived. These equations reduce to two coupled equations constituting the KdV-ZK (Korteweg-de Vries-Zakharov-Kuznetsov) equation for both kinetic Alfven wave and ion-acoustic wave, including an extra term accounting for the effect of Landau damping. When the coefficient of the nonlinear term of the evolution equation for ion-acoustic wave vanishes, the nonlinear behavior of ion-acoustic wave, including the effect of Landau damping, is described by two coupled equations constituting the modified KdV-ZK (MKdV-ZK) equation, including an extra term accounting for the effect of Landau damping. It is found that there is no effect of Landau damping on the solitary structures of the kinetic Alfven wave. Both the macroscopic evolution equations for the ion-acoustic wave admits solitary wave solutions, the former having a sech 2 profile and the latter having a sech profile. In either case, it is found that the amplitude of the ion-acoustic solitary wave decreases slowly with time
International Nuclear Information System (INIS)
Bruma, C; Cuperman, S; Komoshvili, K
2003-01-01
In an effort to optimize the internal transport barriers (ITBs) generated by externally launched mode-converted fast waves (FWs) in pre-heated spherical tokamaks (STs), we have carried out a systematic parametric investigation with respect to the rf waves and antenna characteristics; as a study case, a START-like device has been considered. Within the framework of a plasma model including both kinetic effects (collisionless Landau damping on passing electrons) and collisional damping on both trapped and passing electrons and ions, and starting with the solution of the full wave equation for a ST-plasma, we show that optimized ITBs, suitable for the stabilization of plasma turbulence (e.g. overpassing the maximum growth rate of the ITG-instability, γ ITG ) in STs can be generated by the aid of externally launched FW and mode-converted to kinetic Alfven waves. This result holds in spite of the limiting trapped-particles associated squeezing factor S present in the non-linear equation for E r (via the viscosity coefficient μ θi ∝|S| 3/2 , S = S(dE r /dr))
Energy Technology Data Exchange (ETDEWEB)
Bruma, C [School of Physics and Astronomy, Tel Aviv University, 69978 Tel Aviv (Israel); Cuperman, S [School of Physics and Astronomy, Tel Aviv University, 69978 Tel Aviv (Israel); Komoshvili, K [School of Physics and Astronomy, Tel Aviv University, 69978 Tel Aviv (Israel)
2003-04-01
In an effort to optimize the internal transport barriers (ITBs) generated by externally launched mode-converted fast waves (FWs) in pre-heated spherical tokamaks (STs), we have carried out a systematic parametric investigation with respect to the rf waves and antenna characteristics; as a study case, a START-like device has been considered. Within the framework of a plasma model including both kinetic effects (collisionless Landau damping on passing electrons) and collisional damping on both trapped and passing electrons and ions, and starting with the solution of the full wave equation for a ST-plasma, we show that optimized ITBs, suitable for the stabilization of plasma turbulence (e.g. overpassing the maximum growth rate of the ITG-instability, {gamma}{sub ITG}) in STs can be generated by the aid of externally launched FW and mode-converted to kinetic Alfven waves. This result holds in spite of the limiting trapped-particles associated squeezing factor S present in the non-linear equation for E{sub r} (via the viscosity coefficient {mu}{sub {theta}}{sub i}{proportional_to}|S|{sup 3/2}, S = S(dE{sub r}/dr))
International Nuclear Information System (INIS)
Knudsen, D.J.; Kelley, M.C.; Earle, G.D.; Vickrey, J.F.; Boehm, M.
1990-01-01
The authors present and analyze sounding rocket and HILAT satellite measurements of the low frequency ( 0 in the auroral oval. By examining the time-domain field data it is often difficult to distinguish temporal fluctuations from static structures which are Doppler shifted to a non-zero frequency in the spacecraft frame. However, they show that such a distinction can be made by constructing the impedance function Z(f). Using Z(f) they find agreement with the static field interpretation below about 0.1 Hz in the spacecraft frame, i.e. Z(f) = Σ p -1 where Σ p is the height-integrated Pedersen conductivity of the ionosphere. About 0.1 Hz the authors find Z(f) > Σ p -1 , which they argue to be due to the presence of Alfven waves incident from the magnetosphere and reflecting from the lower ionosphere, forming a standing wave pattern. These waves may represent an electromagnetic coupling mechanism between the auroral acceleration region and the ionosphere
International Nuclear Information System (INIS)
Malkov, M.A.; Kennel, C.F.; Wu, C.C.; Pellat, R.; Shapiro, V.D.
1991-01-01
The Cohen--Kulsrud--Burgers equation (CKB) is used to consider the nonlinear evolution of resistive, quasiparallel Alfven waves subject to a long-wavelength, plane-polarized, monochromatic instability. The instability saturates by nonlinear steepening, which proceeds until the periodic waveform develops an interior scale length comparable to the dissipation length; a fast or an intermediate shock then forms. The result is a periodic train of Alfven shocks of one or the other type. For propagation strictly parallel to the magnetic field, there will be two shocks per instability wavelength. Numerical integration of the time-dependent CKB equation shows that an initial, small-amplitude growing wave asymptotes to a stable, periodic stationary wave whose analytic solution specifies how the type of shock embedded in the shock train, and the amplitude and speed of the shock train, depend on the strength and phase of the instability. Waveforms observed upstream of the Earth's bowshock and cometary shocks resemble those calculated here
International Nuclear Information System (INIS)
Bruma, C.; Cuperman, S.
2003-01-01
We investigate quantitatively the possibility of turbulence suppression through the generation of transport barriers in pre-heated low aspect ratio tokamaks (LARTs) by the sheared electric fields generated by externally driven rf waves in the frequency range ω A ≅ ci (ω A and ω ci are, respectively, Alfven and ion cyclotron frequencies). To this aim the following sequential steps are followed: (1) Solutions of the resistive two-fluid model full wave equation for a realistic LART configuration (D-shape cross-section and aspect ratio, R/a ∼> 1; as well as suitably located low field side, LFS, antenna) upon using a quite general dielectric tensor operator; (2) Calculation of the ponderomotive forces and their magnetic surface averages; (3) Solution of a strongly non-linear differential equation for the quasi-stationary radial electric field, including the particle orbit squeezing effects, based on the results of steps (1) and (2); and (4) Calculation of the radial flow shear, S perpend ; for both banana and potato collisional regimes
Energy Technology Data Exchange (ETDEWEB)
Bruma, C.; Cuperman, S. [Tel Aviv Univ. (Israel). School of Physics and Astronomy; Komoshvili, K. [The College of Judea and Samaria, Ariel (Israel)
2003-05-01
We investigate quantitatively the possibility of turbulence suppression through the generation of transport barriers in pre-heated low aspect ratio tokamaks (LARTs) by the sheared electric fields generated by externally driven rf waves in the frequency range {omega}{sub A} {approx_equal} <{omega}{sub ci} ({omega}{sub A} and {omega}{sub ci} are, respectively, Alfven and ion cyclotron frequencies). To this aim the following sequential steps are followed: (1) Solutions of the resistive two-fluid model full wave equation for a realistic LART configuration (D-shape cross-section and aspect ratio, R/a {approx}> 1; as well as suitably located low field side, LFS, antenna) upon using a quite general dielectric tensor operator; (2) Calculation of the ponderomotive forces and their magnetic surface averages; (3) Solution of a strongly non-linear differential equation for the quasi-stationary radial electric field, including the particle orbit squeezing effects, based on the results of steps (1) and (2); and (4) Calculation of the radial flow shear, S{sub perpend}; for both banana and potato collisional regimes.
International Nuclear Information System (INIS)
Nalesso, G.F.; Jacobson, A.R.
1988-01-01
We study the interaction of a plasma cloud, jetting across the geomagnetic field with the surrounding ionosphere. The cloud is assumed of finite extension in the direction normal to both the direction of motion and the magnetic field, while the ionosphere is considered a collisional anisotropic magnetized plasma. It is shown that two main mechanisms contribute to the cloud's braking: momentum exchange with the ionosphere via Alfven waves and momentum dissipation due to resistive currents. Due to the finite size of the cloud a differential braking of the different transverse harmonics of the Alfven wave appears when the momentum exchange mechanism is dominant. The result is a sharpening of the cloud's velocity field. copyright American Geophysical Union 1988
Drift-Alfven waves induced optical emission fluctuations in Aditya tokamak
International Nuclear Information System (INIS)
Manchanda, R.; Ghosh, J.; Chattopadhyay, P. K.; Chowdhuri, M. B.; Banerjee, Santanu; Ramasubramanian, N.; Patel, Ketan M.; Kumar, Vinay; Vasu, P.; Tanna, R. L.; Paradkar, B.; Gupta, C. N.; Bhatt, S. B.; Raju, D.; Jha, R.; Atrey, P. K.; Joisa, S.; Rao, C. V. S.; Saxena, Y. C.
2010-01-01
In Aditya tokamak [S. B. Bhatt et al. Indian J. Pure Appl. Phys. 27, 710 (1989)], an increase in the H α and C 2+ intensity fluctuations from the edge region is observed with an increase in the magnetohydrodynamic (MHD) activity. Very small fluctuation amplitudes of H α and C 2+ intensity are observed in discharges where there is no MHD activity compared to the discharges with MHD activity. These fluctuations in the H α and C 2+ , measured by optical filter--photomultiplier tube combination--are modulated by Mirnov oscillations having a dominant peak with a common frequency ∼7-10 kHz. Further investigation reveals the presence of strong coherent fluctuations in density and floating potential at same frequency as well. These observations indicate the existence of a nonelectrostatic instability, which may be based on the coupled mode of the drift mode and the Alfven mode. The coherent density fluctuations give rise to the experimentally observed coherent H α and C 2+ intensity fluctuations.
Computing the damping and destabilization of global Alfven waves in tokamaks
International Nuclear Information System (INIS)
Kerner, W.; Keegan, B.; Goedbloed, J.P.; Huysmans, G.T.A.
1991-01-01
The role of ideal MHD in magnetic fusion is in the first place to discover magnetic geometries with favourable equilibrium and stability properties. Non-ideal effects cause slower and weaker instabilities leading to enhanced transport and often to violent disruptions. MHD spectroscopy, i.e. the identification of ideal and dissipative MHD modes for the purpose of diagnosing tokamaks and optimising their stability properties, requires a numerical tool which accurately calculates the dissipative MHD spectra for measured equilibria. The new spectral code CASTOR (Complex Alfven Spectrum for TORoidal Plasmas), together with the equilibrium solver HELENA, provides such a tool. In CASTOR, the fluid variables ρ, v, T, and b are discretized by means of a combination of cubic Hermite and quadratic finite elements for the radial direction and Fourier modes for the poloidal coordinate. The equilibrium in non-orthogonal flux coordinates ψ, θ, φ with straight field lines is computed using isoparametric bicubic Hermite elements, resulting in a very accurate representation of the metric elements. Finally, for analysis of JET discharges the equilibrium solver HELENA is interfaced with the equilibrium identification code IDENTC(D). (author) 5 refs., 5 figs
International Nuclear Information System (INIS)
Horton, W.; Correa, C.; Chagelishvili, G. D.; Avsarkisov, V. S.; Lominadze, J. G.; Perez, J. C.; Kim, J.-H.; Carter, T. A.
2009-01-01
According to recent experiments, magnetically confined fusion plasmas with ''drift wave-zonal flow turbulence'' (DW-ZF) give rise to broadband electromagnetic waves. Sharapov et al. [Europhysics Conference Abstracts, 35th EPS Conference on Plasma Physics, Hersonissos, 2008, edited by P. Lalousis and S. Moustaizis (European Physical Society, Switzerland, 2008), Vol. 32D, p. 4.071] reported an abrupt change in the magnetic turbulence during L-H transitions in Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)] plasmas. A broad spectrum of Alfvenic-like (electromagnetic) fluctuations appears from ExB flow driven turbulence in experiments on the large plasma device (LAPD) [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] facility at UCLA. Evidence of the existence of magnetic fluctuations in the shear flow region in the experiments is shown. We present one possible theoretical explanation of the generation of electromagnetic fluctuations in DW-ZF systems for an example of LAPD experiments. The method used is based on generalizing results on shear flow phenomena from the hydrodynamics community. In the 1990s, it was realized that fluctuation modes of spectrally stable nonuniform (sheared) flows are non-normal. That is, the linear operators of the flows modal analysis are non-normal and the corresponding eigenmodes are not orthogonal. The non-normality results in linear transient growth with bursts of the perturbations and the mode coupling, which causes the generation of electromagnetic waves from the drift wave-shear flow system. We consider shear flow that mimics tokamak zonal flow. We show that the transient growth substantially exceeds the growth of the classical dissipative trapped-particle instability of the system.
International Nuclear Information System (INIS)
Li Wannquan.
1989-01-01
In a circular cylindrical geometry, the author solves a fourth-order set of differential equations numerically for the perturbed fields E τ and E perpendicular . The model takes into account the equilibrium current, magnetic shear, finite ω/ω c1 effect, mode conversion effects like finite ion gyroradius and electron inertia, and various dissipative mechanisms such as electron Landau and collisional damping, and minority fundamental and majority second harmonic cyclotron absorption. To illustrate the results, the author plots the perturbed electric fields and the energy absorbed by each species. He first examines cold plasma surface Alfven eigenmodes analytically and numerically in a pure plasma. The motivation for this work is to investigate how to avoid the undesirable edge absorption and introduce the methods for the study of impurity effects. In the two-species plasmas, he considers three special examples: (1) minority oxygen in hydrogen in PRETEXT, (2) minority T or H in deuterium in TFTR. He adopts two models: (i) a radially varying minority charge, or (ii) a radially varying magnetic field to investigate the minority gyroresonance heating. The model (ii) is used to examine these three examples. But the model (i) is only applied to the first one. In model (i), it is found that surface modes can induce the eigenmodes and dissipate substantial energy near the hybrid layer in the interior. Some cases analytically manageable are given an interpretation of why there is large or small energy deposition in this layer. It is shown that this strongly depends on poloidal mode numbers, minority concentrations, and minority charge profiles
International Nuclear Information System (INIS)
Bruma, C.; Cuperman, S.; Komoshvili, K.
1996-01-01
Supplementary non-inductive current drive and heating are necessary to bring Tokamak plasmas into the ignition regime. The resonant excitation of shear Alfven waves (SAW) - in the continuum range (CR) or/and in the discrete global Alfven eigenmode spectrum (GAE's) - represents one potential, suitable method for this purpose. Within the framework of ideal MHD, the current drive (CD) via helicity injection in Tokamak plasmas has been considered by Cuperman et al (1996) and Komoshvili et al. (1996). This work is concerned with the investigation of the non-ideal resistive MHD effects on both the excitation of SAW's (CR's and GAE's) and the generation of non-inductive current drive via helicity injection in Tokamak plasmas. The research covers Tokamak aspect ratios ranging between large value cases (R/a = 10) and the very tight value case (R/ a = 1.2). (authors)
Scenarios for the nonlinear evolution of alpha particle induced Alfven wave instability
International Nuclear Information System (INIS)
Berk, H.L.; Breizman, B.N.; Ye, Huanchun.
1992-03-01
Various nonlinear scenarios are given for the evolution of energetic particles that are slowing down in a background plasma and simultaneously causing instability of the background plasma waves. If the background damping is sufficiently weak, a steady-state wave is established as described by Berk and Breizman. For larger background damping rate pulsations develop. Saturation occurs when the wave amplitude rises to where the wave trapping frequency equals the growth rate. The wave then damps due to the small background dissipation present and a relatively long quiet interval exists between bursts while the free energy of the distribution is refilled by classical transport. In this scenario the anomalous energy loss of energetic particles due to diffusion is small compared to the classical collisional energy exchange with the background plasma. However, if at the trapping frequency, the wave amplitude is large enough to cause orbit stochasticity, a phase space ''explosion'' occurs where the wave amplitudes rise to higher levels which leads to rapid loss of energetic particles
International Nuclear Information System (INIS)
Komoshvili, K.; Cuperman, S.; Bruma, C.
1996-01-01
The non-inductive current drive via helicity injection by Global Alfven eigenmode (GAE) waves is studied. For illustration, the first radial mode of the discrete resonant GAE spectrum is considered. The following aspects are given special attention: spectral analysis, radial dependence and efficiency - all these as functions of the characteristics of the waves launched by an external, concentric antenna (i.e, wave frequency and poloidal and toroidal wave numbers). The results reveal the following conclusions. Generation of GAE waves. In the range of poloidal wave numbers -3 0 for m = -l, -2, -3 and -20 10; I-BAR < 0 for m = +1, +2, +3 and n < 10. (iv) The efficiency of the current drive, η = absolute I-BAR/absolute P-BAR, increases in the cases m = -1, -2, -3 with absolute m and absolute 1/n. (v) Detailed information on the relative direction and radial (core) localization of the current drive is obtained. (authors)
Effects of minority ions on the propagation of the Fast Alfven wave
International Nuclear Information System (INIS)
Wong, K.L.; Kristiansen, M.; Hagler, M.
1985-01-01
Minority ions play an important role in ICRF wave heating and fast wave current drive. The former provides supplemental heating to the plasma ions, and the latter enables a Tokamak reactor to operate in steady state. The injection of minority ions greatly perturbs the propagation and absorption properties of the fast waves provided that the excitation frequency and confining magnetic field strength make the hybrid layers exist inside the plasma. A cold-plasma slab model with gradient confining magnetic field, parabolic plasma density, vacuum layer, launching antenna and conducting walls was used in studying wave propagation with and without minority ions. The wave propagation was studied individually for each discrete toroidal eigenmode (N=Rk/sub z/). There exists an asymmetric density cutoff region which is mainly due to the density variation in a single-ion plasma. The larger the torodial mode number, the larger the density cutoff region. Therefore, there exists a maximum mode number N/sub m/, which can be excited for each operating frequency. With injection of minority ions, the cutoff region for each mode number is almost unchanged. But, if one carefully chooses the excitation frequency; the hybrid layers can exist inside the plamsa for all or part of the allowed eigenmodes. Those eigenmodes with hybrid layers inside the plasma will undergo drastic change in the propagation and absorption of the waves
Alfven continuum with toroidicity
International Nuclear Information System (INIS)
Riyopoulos, S.; Mahajan, S.M.
1985-06-01
The symmetry property of the MHD wave propagation operator is utilized to express the toroidal eigenmodes as a superposition of the mutually orthogonal cylindrical modes. Because of the degeneracy among cylindrical modes with the same frequency but resonant surfaces of different helicity the toroidal perturbation produces a zeroth order mixing of the above modes. The toroidal eigenmodes of frequency ω 0 2 have multiple resonant surfaces, with each surface shifted relative to its cylindrical position and carrying a multispectral content. Thus a single helicity toroidal antenna of frequency ω 0 couples strongly to all different helicity resonant surfaces with matching local Alfven frequency. Zeroth order coupling between modes in the continuum and global Alfven modes also results from toroidicity and degeneracy. Our perturbation technique is the MHD counterpart of the quantum mechanical methods and is applicable through the entire range of the MHD spectrum
Theoretical Studies of Alfven Waves and Energetic Particle Physics in Fusion Plasmas
Energy Technology Data Exchange (ETDEWEB)
Chen, Liu [Univ. of California, Irvine, CA (United States)
2017-12-20
This report summarizes major theoretical findings in the linear as well as nonlinear physics of Alfvén waves and energetic particles in magnetically confined fusion plasmas. On the linear physics, a variational formulation, based on the separation of singular and regular spatial scales, for drift-Alfvén instabilities excited by energetic particles is established. This variational formulation is then applied to derive the general fishbone-like dispersion relations corresponding to the various Alfvén eigenmodes and energetic-particle modes. It is further employed to explore in depth the low-frequency Alfvén eigenmodes and demonstrate the non-perturbative nature of the energetic particles. On the nonlinear physics, new novel findings are obtained on both the nonlinear wave-wave interactions and nonlinear wave-energetic particle interactions. It is demonstrated that both the energetic particles and the fine radial mode structures could qualitatively affect the nonlinear evolution of Alfvén eigenmodes. Meanwhile, a theoretical approach based on the Dyson equation is developed to treat self-consistently the nonlinear interactions between Alfvén waves and energetic particles, and is then applied to explain simulation results of energetic-particle modes. Relevant list of journal publications on the above findings is also included.
High-efficiency toroidal current drive using low-phase-velocity kinetic Alfven waves
International Nuclear Information System (INIS)
Puri, S.
1991-09-01
A method for obtaining efficient current drive in Tokamaks using low-phase-velocity (v ρ = ω/K parallel ∝ 0.1v te ) kinetic Alfen wave is proposed. The wave momentum, imparted primarily to the trapped electrons by Landau damping, is stored as the canonical angular momentum via the Ware pinch. In steady state, collisions restore the pinched electrons to their original phase-space configuration, in the process releasing the stored canonical angular momentum to the background ions and electrons in proportion to the respective collision frequencies. Despite the loss of a part of the original impulse to the plasma ions, well over half the wave momentum is ultimately delivered to the bulk-plasma electrons, resulting in an efficient current drive. A normalized current-drive efficiency γ = R 0 20 > I/P ∝ 2 would be feasible using the subthermal kinetic-Alfen-wave current drive in a Tokamak of reactor parameters. Optimum antenna loading conditions are described. The problem of accessibility is discussed. In an elongated, high-β plasma with a density dependence n e ∝ (1-ρ 2 ) Χn , accessibility is restricted to ρ > or approx. 3/(4A Χn ), where A is the aspect ratio. For current drive at still lower values of ρ, operation in conjunction with fast-wave current drive is suggested. (orig.)
International Nuclear Information System (INIS)
Fu, G.
1988-01-01
The problem of access to the high-beta ballooning second-stability regime by means of auxiliary heating and the problem of the stability of global-shear Alfven waves in an ignited tokamak plasma are theoretically investigated. These two problems are related to the confinement of both the bulk plasma as well as the fusion-product alpha particles an dare fundamentally important to the operation of ignited tokamak plasma. First, a model that incorporates both transport and ballooning mode stability was developed in order to estimate the auxiliary heating power required for tokamak plasma to evolve in time self-consistently into a high-beta, globally self-stabilized equilibrium. The critical heating power needed for access to second stability is found to be proportional to the square root of the anomalous diffusivity induced by the ballooning instability. Next, the full effects of toroidicity are retained in a theoretical description of global-type-shear Alfven modes whose stability can be modified by the fusion-product alpha particles that will present in an ignited tokamak plasma. Toroidicity is found to induce mode coupling and to stabilize the so-called Global Alfven Eigenmodes (GAE)
Continuous wave room temperature external ring cavity quantum cascade laser
Energy Technology Data Exchange (ETDEWEB)
Revin, D. G., E-mail: d.revin@sheffield.ac.uk; Hemingway, M.; Vaitiekus, D.; Cockburn, J. W. [Physics and Astronomy Department, The University of Sheffield, S3 7RH Sheffield (United Kingdom); Hempler, N.; Maker, G. T.; Malcolm, G. P. A. [M Squared Lasers Ltd., G20 0SP Glasgow (United Kingdom)
2015-06-29
An external ring cavity quantum cascade laser operating at ∼5.2 μm wavelength in a continuous-wave regime at the temperature of 15 °C is demonstrated. Out-coupled continuous-wave optical powers of up to 23 mW are observed for light of one propagation direction with an estimated total intra-cavity optical power flux in excess of 340 mW. The uni-directional regime characterized by the intensity ratio of more than 60 for the light propagating in the opposite directions was achieved. A single emission peak wavelength tuning range of 90 cm{sup −1} is realized by the incorporation of a diffraction grating into the cavity.
Continuous wave room temperature external ring cavity quantum cascade laser
International Nuclear Information System (INIS)
Revin, D. G.; Hemingway, M.; Vaitiekus, D.; Cockburn, J. W.; Hempler, N.; Maker, G. T.; Malcolm, G. P. A.
2015-01-01
An external ring cavity quantum cascade laser operating at ∼5.2 μm wavelength in a continuous-wave regime at the temperature of 15 °C is demonstrated. Out-coupled continuous-wave optical powers of up to 23 mW are observed for light of one propagation direction with an estimated total intra-cavity optical power flux in excess of 340 mW. The uni-directional regime characterized by the intensity ratio of more than 60 for the light propagating in the opposite directions was achieved. A single emission peak wavelength tuning range of 90 cm −1 is realized by the incorporation of a diffraction grating into the cavity
Rosner, R.; An, C.-H.; Musielak, Z. E.; Moore, R. L.; Suess, S. T.
1991-01-01
A simple qualitative model for the origin of the coronal and mass-loss dividing lines separating late-type giants and supergiants with and without hot, X-ray-emitting corona, and with and without significant mass loss is discussed. The basic physical effects considered are the necessity of magnetic confinement for hot coronal material on the surface of such stars and the large reflection efficiency for Alfven waves in cool exponential atmospheres. The model assumes that the magnetic field geometry of these stars changes across the observed 'dividing lines' from being mostly closed on the high effective temperature side to being mostly open on the low effective temperature side.
Ultrafast Ultrasound Imaging With Cascaded Dual-Polarity Waves.
Zhang, Yang; Guo, Yuexin; Lee, Wei-Ning
2018-04-01
Ultrafast ultrasound imaging using plane or diverging waves, instead of focused beams, has advanced greatly the development of novel ultrasound imaging methods for evaluating tissue functions beyond anatomical information. However, the sonographic signal-to-noise ratio (SNR) of ultrafast imaging remains limited due to the lack of transmission focusing, and thus insufficient acoustic energy delivery. We hereby propose a new ultrafast ultrasound imaging methodology with cascaded dual-polarity waves (CDWs), which consists of a pulse train with positive and negative polarities. A new coding scheme and a corresponding linear decoding process were thereby designed to obtain the recovered signals with increased amplitude, thus increasing the SNR without sacrificing the frame rate. The newly designed CDW ultrafast ultrasound imaging technique achieved higher quality B-mode images than coherent plane-wave compounding (CPWC) and multiplane wave (MW) imaging in a calibration phantom, ex vivo pork belly, and in vivo human back muscle. CDW imaging shows a significant improvement in the SNR (10.71 dB versus CPWC and 7.62 dB versus MW), penetration depth (36.94% versus CPWC and 35.14% versus MW), and contrast ratio in deep regions (5.97 dB versus CPWC and 5.05 dB versus MW) without compromising other image quality metrics, such as spatial resolution and frame rate. The enhanced image qualities and ultrafast frame rates offered by CDW imaging beget great potential for various novel imaging applications.
Quantum steering in cascaded four-wave mixing processes.
Wang, Li; Lv, Shuchao; Jing, Jietai
2017-07-24
Quantum steering is used to describe the "spooky action-at-a-distance" nonlocality raised in the Einstein-Podolsky-Rosen (EPR) paradox, which is important for understanding entanglement distribution and constructing quantum networks. Here, in this paper, we study an experimentally feasible scheme for generating quantum steering based on cascaded four-wave-mixing (FWM) processes in hot rubidium (Rb) vapor. Quantum steering, including bipartite steering and genuine tripartite steering among the output light fields, is theoretically analyzed. We find the corresponding gain regions in which the bipartite and tripartite steering exist. The results of bipartite steering can be used to establish a hierarchical steering model in which one beam can steer the other two beams in the whole gain region; however, the other two beams cannot steer the first beam simultaneously. Moreover, the other two beams cannot steer with each other in the whole gain region. More importantly, we investigate the gain dependence of the existence of the genuine tripartite steering and we find that the genuine tripartite steering exists in most of the whole gain region in the ideal case. Also we discuss the effect of losses on the genuine tripartite steering. Our results pave the way to experimental demonstration of quantum steering in cascaded FWM process.
Energy Technology Data Exchange (ETDEWEB)
Komoshvili, K.; Cuperman, S.; Bruma, C. [Tel Aviv Univ. (Israel). Sackler Faculty of Exact Sciences
1997-04-01
A systematic study of non-inductive current drive via helicity injection by global Alfven eigenmode (GAE) waves is carried out. For illustration, the first radial mode of the discrete resonant GAE spectrum is considered. The following aspects are given special attention: spectral analysis, radial dependence and efficiency - all of these functions of the characteristics of the waves launched by an external, concentric antenna (i.e. wave frequency and poloidal and toroidal wavenumbers). The tokamak plasma is simulated by a current-carrying cylindrical plasma column surrounded by a helical sheet current and situated inside a perfectly conducting shell, with incorporation of equilibrium (simulated) toroidal field, magnetic shear and a relatively large poloidal magnetic field component. Within the framework of low-{beta} MHD model equations and for typical tokamak physical parameters, the following basic results are obtained: (1) in the range of poloidal wavenumbers -3{<=} m {<=} 3 and toroidal wavenumbers -20{<=} n {<=}20, resonant GAE peaks below the Alfven continuum are found; (2) the power absorption (P), current drive (I) and corresponding frequency of the GAE modes depend strongly on the sets of (m,n) values considered; (3) the `net` current drive is positive (i.e. flows in the direction of the equilibrium current j{sub 0z} for m = -1, -2, -3 and -20 {<=} n {<=} -1 as well as for m +1, +2, +3 and n > 10); (4) in the cases m = -1, -2, -3, the efficiency of current drive, I/P, increases with /m/ and I/n/; (5) the radial localization of the current drive in each of the cases considered is determined and tabulated. (Author).
International Nuclear Information System (INIS)
Komoshvili, K.; Cuperman, S.; Bruma, C.
1997-01-01
A systematic study of non-inductive current drive via helicity injection by global Alfven eigenmode (GAE) waves is carried out. For illustration, the first radial mode of the discrete resonant GAE spectrum is considered. The following aspects are given special attention: spectral analysis, radial dependence and efficiency - all of these functions of the characteristics of the waves launched by an external, concentric antenna (i.e. wave frequency and poloidal and toroidal wavenumbers). The tokamak plasma is simulated by a current-carrying cylindrical plasma column surrounded by a helical sheet current and situated inside a perfectly conducting shell, with incorporation of equilibrium (simulated) toroidal field, magnetic shear and a relatively large poloidal magnetic field component. Within the framework of low-β MHD model equations and for typical tokamak physical parameters, the following basic results are obtained: (1) in the range of poloidal wavenumbers -3≤ m ≤ 3 and toroidal wavenumbers -20≤ n ≤20, resonant GAE peaks below the Alfven continuum are found; (2) the power absorption (P), current drive (I) and corresponding frequency of the GAE modes depend strongly on the sets of (m,n) values considered; (3) the 'net' current drive is positive (i.e. flows in the direction of the equilibrium current j 0z for m = -1, -2, -3 and -20 ≤ n ≤ -1 as well as for m +1, +2, +3 and n > 10; (4) in the cases m = -1, -2, -3, the efficiency of current drive, I/P, increases with /m/ and I/n/; (5) the radial localization of the current drive in each of the cases considered is determined and tabulated. (Author)
Cho, Jungyeon
2011-05-13
Electron magnetohydrodynamics (EMHD) provides a fluidlike description of small-scale magnetized plasmas. An EMHD wave propagates along magnetic field lines. The direction of propagation can be either parallel or antiparallel to the magnetic field lines. We numerically study propagation of three-dimensional (3D) EMHD wave packets moving in one direction. We obtain two major results. (1) Unlike its magnetohydrodynamic (MHD) counterpart, an EMHD wave packet is dispersive. Because of this, EMHD wave packets traveling in one direction create opposite-traveling wave packets via self-interaction and cascade energy to smaller scales. (2) EMHD wave packets traveling in one direction clearly exhibit inverse energy cascade. We find that the latter is due to conservation of magnetic helicity. We compare inverse energy cascade in 3D EMHD turbulence and two-dimensional (2D) hydrodynamic turbulence.
International Nuclear Information System (INIS)
Cho, Jungyeon
2011-01-01
Electron magnetohydrodynamics (EMHD) provides a fluidlike description of small-scale magnetized plasmas. An EMHD wave propagates along magnetic field lines. The direction of propagation can be either parallel or antiparallel to the magnetic field lines. We numerically study propagation of three-dimensional (3D) EMHD wave packets moving in one direction. We obtain two major results. (1) Unlike its magnetohydrodynamic (MHD) counterpart, an EMHD wave packet is dispersive. Because of this, EMHD wave packets traveling in one direction create opposite-traveling wave packets via self-interaction and cascade energy to smaller scales. (2) EMHD wave packets traveling in one direction clearly exhibit inverse energy cascade. We find that the latter is due to conservation of magnetic helicity. We compare inverse energy cascade in 3D EMHD turbulence and two-dimensional (2D) hydrodynamic turbulence.
Francois, N; Xia, H; Punzmann, H; Shats, M
2013-05-10
We report the generation of large coherent vortices via inverse energy cascade in Faraday wave driven turbulence. The motion of floaters in the Faraday waves is three dimensional, but its horizontal velocity fluctuations show unexpected similarity with two-dimensional turbulence. The inverse cascade is detected by measuring frequency spectra of the Lagrangian velocity, and it is confirmed by computing the third moment of the horizontal velocity fluctuations. This is observed in deep water in a broad range of wavelengths and vertical accelerations. The results broaden the scope of recent findings on Faraday waves in thin layers [A. von Kameke et al., Phys. Rev. Lett. 107, 074502 (2011)].
Magnetosphere as an Alfven maser
International Nuclear Information System (INIS)
Trakhtengerts, V.Yu.
1979-01-01
The Earth magnetosphere is considered as an Alfven maser. The operation mechanism of such a maser is duscussed. The main fact of this mechanism is ''overpopulation'' of the Earth radiation belt with particles moving with cross velocities. The cross velocity particles excess results in the excitation of cyclotron instability in the radiation belt and in the self-arbitrary increase of Alfven waves. At late the theory of cyclotron instability of radiation belts has been universally developed. On the basis of ideas on magnetosphere maser on cyclotron resonance it was possible to explain many geophysical phenomena such as periodical spillings out of particles from the radiation belts, pulsing polar lights, oscillations of magnetic force tubes etc. It is proposed to carry out active cosmic experiments to understand deeper the processes occuring in radiation belts
The 17/5 spectrum of the Kelvin-wave cascade
Kozik, Evgeny; Svistunov, Boris
2010-01-01
Direct numeric simulation of the Biot-Savart equation readily resolves the 17/5 spectrum of the Kelvin-wave cascade from the 11/3 spectrum of the non-local (in the wavenumber space) cascade scenario by L'vov and Nazarenko. This result is a clear-cut visualisation of the unphysical nature of the 11/3 solution, which was established earlier on the grounds of symmetry.
The compressional Alfven instability in ECRH plasmas
International Nuclear Information System (INIS)
El Nadi, A.
1982-01-01
It is shown that the hot electron component present in an electron cyclotron resonance heated plasma can destabilize the compressional Alfven wave if β of the background plasma exceeds a certain limit. The relevance of the result to the Elmo Bumpy Torus experiment is discussed. (author)
International Nuclear Information System (INIS)
Sugaya, R.; Ue, A.; Maehara, T.; Sugawa, M.
1996-01-01
Acceleration and heating of a relativistic electron beam by cascading nonlinear Landau damping involving three or four intense electromagnetic waves in a plasma are studied theoretically based on kinetic wave equations and transport equations derived from relativistic Vlasov endash Maxwell equations. Three or four electromagnetic waves excite successively two or three nonresonant beat-wave-driven relativistic electron plasma waves with a phase velocity near the speed of light [v p =c(1-γ -2 p ) 1/2 , γ p =ω/ω pe ]. Three beat waves interact nonlinearly with the electron beam and accelerate it to a highly relativistic energy γ p m e c 2 more effectively than by the usual nonlinear Landau damping of two electromagnetic waves. It is proved that the electron beam can be accelerated to more highly relativistic energy in the plasma whose electron density decreases temporally with an appropriate rate because of the temporal increase of γ p . copyright 1996 American Institute of Physics
The structure of ideal MHD Alfven modes
International Nuclear Information System (INIS)
Turnbull, A.D.; Chu, M.S.; Lao, L.L.; Greene, J.M.; Strait, E.J.; Chance, M.S.
1991-01-01
Continuum Alfven modes have undergone a resurgence in interest with the recent realization that so-called Toroidicity-Induced Alfven Eigenmodes (TAE modes) can be destabilized either by energetic beam ions in a strongly heated plasma or by alpha particles in a burning plasma. The GATO Ideal MHD Stability code, which minimizes the potential energy according to a variational formulation, has now been modified to isolate and calculate stable continuum eigenmodes. The existence of the TAE mode and its associated gap has been verified, using this code, for a circular cross-section, finite aspect ratio equilibrium. Moreover, the eigenfrequencies and eigenmodes obtained from this variational calculation are found to be in extremely good quantitative agreement with those obtained from the non-variational NOVA code. A systematic survey of the stable continuum has further revealed a surprising diversity in the structure of the continuum Alfven modes; the logarithmic singularity can be so broad, in some cases, as to occupy the whole cross-section. This has important implications for heating experiments which aim to locally excite the plasma by rf waves in the Alfven frequency range. The structure of several representative examples is discussed. The Alfven continuum, in general, and the TAE mode and its associated gap, in particular, are also found to be strongly modified by cross-sectional shaping. The dependence of the spectrum on various shaping factors is explored
Alfven continuum and high-frequency eigenmodes in optimized stellarators
International Nuclear Information System (INIS)
Kolesnichenko, Ya.I.; Lutsenko, V.V.; Wobig, H.; Yakovenko, Yu.V.; Fesenyuk, O.P.
2001-01-01
An equation of shear Alfven eigenmodes (AE) in optimized stellarators of Wendelstein line (Helias configurations) is derived. The metric tensor coefficients, which are contained in this equation, are calculated analytically. Two numerical codes are developed: the first one, COBRA (COntinuum BRanches of Alfven waves), is intended for the investigation of the structure of Alfven continuum; the second, BOA (Branches Of Alfven modes), solves the eigenvalue problem. The family of possible gaps in Alfven continuum of a Helias configuration is obtained. It is predicted that there exist gaps which arise due to or are strongly affected by the variation of the shape of the plasma cross section along the large azimuth of the torus. In such gaps, discrete eigenmodes, namely, helicity-induced eigenmodes (HAE 21 ) and mirror-induced eigenmodes (MAE) are found. It is shown that plasma inhomogeneity may suppress the AEs with a wide region of localization
Energy Technology Data Exchange (ETDEWEB)
Bruma, C.; Cuperman, S.; Komoshvili, K. [Tel Aviv Univ., Ramat Aviv (Israel)
2005-08-01
As it is the case with tokamaks in general, and moreover, due to their specific geometry (limited space for inboard solenoid magnets), low aspect ratio (spherical) tokamaks (STs) require additional auxiliary non-ohmic current startup and maintenance, generation of internal transport barriers (associated with underlying sheared poloidal flows and quasi-stationary radial electric fields), plasma heating, etc. One of the options to generate these necessary effects in STs is by the aid of rf waves launched from a suitable external antenna; in this option the effects just mentioned are a consequence of ponderomotive forces resulting from the interaction of the rf waves with the plasma. Since experimental data on STs (viz., the START-device) reveal the presence of an anomalous plasma resistivity (about four times Spitzer's one), we carried out a systematic parametric investigation of the effects of an increased plasma resistivity on the magnitude and spatial localization of the resulting power deposition.
von Kameke, A; Huhn, F; Fernández-García, G; Muñuzuri, A P; Pérez-Muñuzuri, V
2011-08-12
We report the experimental observation of Richardson dispersion and a double cascade in a thin horizontal fluid flow induced by Faraday waves. The energy spectra and the mean spectral energy flux obtained from particle image velocimetry data suggest an inverse energy cascade with Kolmogorov type scaling E(k) ∝ k(γ), γ ≈ -5/3 and an E(k) ∝ k(γ), γ ≈ -3 enstrophy cascade. Particle transport is studied analyzing absolute and relative dispersion as well as the finite size Lyapunov exponent (FSLE) via the direct tracking of real particles and numerical advection of virtual particles. Richardson dispersion with ∝ t(3) is observed and is also reflected in the slopes of the FSLE (Λ ∝ ΔR(-2/3)) for virtual and real particles.
Energetic particle parallel diffusion in a cascading wave turbulence in the foreshock region
Directory of Open Access Journals (Sweden)
F. Otsuka
2007-09-01
Full Text Available We study parallel (field-aligned diffusion of energetic particles in the upstream of the bow shock with test particle simulations. We assume parallel shock geometry of the bow shock, and that MHD wave turbulence convected by the solar wind toward the shock is purely transverse in one-dimensional system with a constant background magnetic field. We use three turbulence models: a homogeneous turbulence, a regular cascade from a large scale to smaller scales, and an inverse cascade from a small scale to larger scales. For the homogeneous model the particle motions along the average field are Brownian motions due to random and isotropic scattering across 90 degree pitch angle. On the other hand, for the two cascade models particle motion is non-Brownian due to coherent and anisotropic pitch angle scattering for finite time scale. The mean free path λ_{||} calculated by the ensemble average of these particle motions exhibits dependence on the distance from the shock. It also depends on the parameters such as the thermal velocity of the particles, solar wind flow velocity, and a wave turbulence model. For the inverse cascade model, the dependence of λ_{||} at the shock on the thermal energy is consistent with the hybrid simulation done by Giacalone (2004, but the spatial dependence of λ_{||} is inconsistent with it.
Confrontation Doederlein/Alfven
International Nuclear Information System (INIS)
Anon.
1977-01-01
In a brief article it is reported that Hannes Alfven has accepted an invitation to take part in the Salzburg Conference. He will participate in the section on 'Nuclear Power and Public Opinion'. It is anticipated that Jan M. Doederlein will be one of Alfven's opponents. The article concludes by presenting a synopsis of the views of the World Council of Churches, which will also take part in the Salzburg Conference. It is the Council's opinion that there are no ethical or religious objections to the exploitation of nuclear power. (JIW)
Alfven instability and micromagnetic islands in a plasma with sheared magnetic fields
International Nuclear Information System (INIS)
Hsu, J.; Kaw, P.; Chen, L.
1977-07-01
The normal mode equation for coupled drift and Alfven waves in a finite-β nonuniform plasma with a sheared magnetic field is solved, in the slab geometry, to investigate the instability of slow Alfven waves. It is shown, that, besides having an appreciable growth rate, the instability also produces microscopic ''tearing'' of the rational surfaces which has important implications for anomalous transport
Vortex algebra by multiply cascaded four-wave mixing of femtosecond optical beams.
Hansinger, Peter; Maleshkov, Georgi; Garanovich, Ivan L; Skryabin, Dmitry V; Neshev, Dragomir N; Dreischuh, Alexander; Paulus, Gerhard G
2014-05-05
Experiments performed with different vortex pump beams show for the first time the algebra of the vortex topological charge cascade, that evolves in the process of nonlinear wave mixing of optical vortex beams in Kerr media due to competition of four-wave mixing with self-and cross-phase modulation. This leads to the coherent generation of complex singular beams within a spectral bandwidth larger than 200nm. Our experimental results are in good agreement with frequency-domain numerical calculations that describe the newly generated spectral satellites.
Alfvenic resonant cavities in the solar atmosphere
International Nuclear Information System (INIS)
Hollweg, J.V.
1984-01-01
We investigate the propagation of Alfven waves in a simple medium consisting of three uniform layers; each layer is characterized by a different value for the Alfven speed, νsub(A). We show how the central layer can act as a resonant cavity under quite general conditions. If the cavity is driven externally, by an incident wave in one of the outer layers, there result resonant transmission peaks, which allow large energy fluxes to enter the cavity from outside. The transmission peaks result from the destructive interference between a wave which leaks out of the cavity, and a directly reflected wave. We show that there are two types of resonances. The first type occurs when the cavity has the largest (or smallest) of the three Alfven speeds; this situation occurs on coronal loops. The second type occurs when the cavity Alfven speed is intermediate between the other two values of νsub(A); this situation may occur on solar spicules. Significant heating of the cavity can occur if the waves are damped. We show that if the energy lost to heat greatly exceeds the energy lost by leakage out of the cavity, then the cavity heating can be independent of the damping rate. This conclusion is shown to apply to coronal resonances and to the spicule resonances. This conclusion agrees with a point made by Ionson in connection with the coronal resonances. Except for a numerical factor of order unity, we recover Ionson's expression for the coronal heating rate. However, Ionson's qualities are much too large. For solar parameters, the maximum quality is of the order of 100, but the heating is independent of the damping rate only when dissipation reduces the quality to less than about 10. (WB)
Superradiant cascade emissions in an atomic ensemble via four-wave mixing
Energy Technology Data Exchange (ETDEWEB)
Jen, H.H., E-mail: sappyjen@gmail.com
2015-09-15
We investigate superradiant cascade emissions from an atomic ensemble driven by two-color classical fields. The correlated pair of photons (signal and idler) is generated by adiabatically driving the system with large-detuned light fields via four-wave mixing. The signal photon from the upper transition of the diamond-type atomic levels is followed by the idler one which can be superradiant due to light-induced dipole–dipole interactions. We then calculate the cooperative Lamb shift (CLS) of the idler photon, which is a cumulative effect of interaction energy. We study its dependence on a cylindrical geometry, a conventional setup in cold atom experiments, and estimate the maximum CLS which can be significant and observable. Manipulating the CLS of cascade emissions enables frequency qubits that provide alternative robust elements in quantum network. - Highlights: • Superradiance from a cascade atomic transition. • Correlated photon pair generation via four-wave mixing. • Dynamical light–matter couplings in a phased symmetrical state. • Cooperative Lamb shift in a cylindrical atomic ensemble.
Alfven eigenmodes in shear reversed plasmas
International Nuclear Information System (INIS)
Breizman, B.N.; Berk, H.L.; Pekker, M.S.; Sharapov, S.E.; Hawkes, N.C.; Borba, D.N.; Pinches, S.D.
2003-01-01
Experiments on JT-60U and JET have shown that plasma configurations with shear reversal are prone to the excitation of unusual Alfven Eigenmodes by energetic particles. These modes emerge outside the TAE frequency gap, where one might expect them to be strongly damped. The modes often appear in bunches and they exhibit a quasi-periodic pattern of predominantly upward frequency sweeping (Alfven Cascades) as the safety factor q changes in time. This work presents a theory that explains the key features of the observed unusual modes including their connection to TAE's as well as the modifications of TAE's themselves near the shear reversal point. The developed theory has been incorporated into a reduced numerical model and verified with full geometry codes. JET experimental data on Alfven spectroscopy have been simulated to infer the mode numbers and the evolution of q min in the discharge. This analysis confirms the values of q that characterize the internal transport barrier triggering in reversed shear plasmas. (author)
Qin, Zhongzhong; Cao, Leiming; Jing, Jietai
2015-05-01
Quantum correlations and entanglement shared among multiple modes are fundamental ingredients of most continuous-variable quantum technologies. Recently, a method used to generate multiple quantum correlated beams using cascaded four-wave mixing (FWM) processes was theoretically proposed and experimentally realized by our group [Z. Qin et al., Phys. Rev. Lett. 113, 023602 (2014)]. Our study of triple-beam quantum correlation paves the way to showing the tripartite entanglement in our system. Our system also promises to find applications in quantum information and precision measurement such as the controlled quantum communications, the generation of multiple quantum correlated images, and the realization of a multiport nonlinear interferometer. For its applications, the degree of quantum correlation is a crucial figure of merit. In this letter, we experimentally study how various parameters, such as the cell temperatures, one-photon, and two-photon detunings, influence the degree of quantum correlation between the triple beams generated from the cascaded two-FWM configuration.
Cascade mode locking: a possible route to chaos in the two-waves hamiltonian system
International Nuclear Information System (INIS)
Gell, Y.; Nakach, R.
1989-06-01
We present a numerical study of the two-waves Hamiltonian system which reveals the route to large scale stochasticity as a process based on the mode-locking phenomenon. The final chaos is reached after a cascade of lockings, appearing successively for different independent modes of oscillation in the system. Using a Fourier analysis, the different steps in this cascade process are detected by following the change in the frequency of the pronounced modes in the power spectrum; when changing the strength of the pertubation, one observes the locking of the relevant mode to a fixed frequency inherent to the system. It is shown that this mechanism allows for the generation of low frequency oscillations which, due to the nonlinear coupling existing in the system, combine with all the existing peaks into a raised spectrum consisting of broad diffuse patterns, which is the signature of chaotic motion
Interband cascade lasers with >40% continuous-wave wallplug efficiency at cryogenic temperatures
International Nuclear Information System (INIS)
Canedy, C. L.; Kim, C. S.; Merritt, C. D.; Bewley, W. W.; Vurgaftman, I.; Meyer, J. R.; Kim, M.
2015-01-01
Broad-area 10-stage interband cascade lasers (ICLs) emitting at λ = 3.0–3.2 μm are shown to maintain continuous-wave (cw) wallplug efficiencies exceeding 40% at temperatures up to 125 K, despite having a design optimized for operation at ambient and above. The cw threshold current density at 80 K is only 11 A/cm 2 for a 2 mm cavity with anti-reflection/high-reflection coatings on the two facets. The external differential quantum efficiency for a 1-mm-long cavity with the same coatings is 70% per stage at 80 K, and still above 65% at 150 K. The results demonstrate that at cryogenic temperatures, where free carrier absorption losses are minimized, ICLs can convert electrical to optical energy nearly as efficiently as the best specially designed intersubband-based quantum cascade lasers
Terahertz wave polarization beam splitter using a cascaded multimode interference structure.
Li, Jiu-sheng; Liu, Han; Zhang, Le
2014-08-01
A terahertz wave polarization beam splitter, based on two cascaded multimode interference structures with different widths, is designed and numerically demonstrated. The numerical calculation results show that the designed polarization beam splitter can split transverse-electric (TE) and transverse-magnetic (TM)-polarized terahertz waves into different propagation directions with high efficiency over a frequency range from 6.40 to 6.50 THz. This polarization beam splitter shows more than a 22.06 dB extinction ratio for TE-polarization and a 31.65 dB extinction ratio for TM-polarization. Using such a polarization beam splitter, the whole length of the polarization beam splitter is reduced to about 1/12 that of a conventional design. This enables the polarization beam splitter to be used in terahertz wave integrated circuit fields.
Alfven Eigenmode Control in DIII-D
Hu, W.; Olofsson, E.; Welander, A.; van Zeeland, M.; Collins, C.; Heidbrink, W.
2017-10-01
Alfven eigenmodes (AE) driven by fast ions from neutral beam and ion cyclotron heating are common in present day tokamak plasmas and are expected to be destabilized by alpha particles in future burning plasma experiments. Because these waves have been shown to cause loss and redistribution of fast ions which can impact plasma performance and potentially device integrity, developing control techniques for AEs is of paramount importance. In the DIII-D plasma control system, spectral analysis of real-time ECE data is used as a monitor of AE amplitude, frequency, and location. These values are then used for feedback control of the neutral beam power to control Alfven waves and reduce fast ion loss. This work describes tests of AE control experiments in the current ramp up phase, during which multiple Alfven eigenmodes are typically unstable and fast ion confinement is degraded significantly. Comparisons of neutron emission and confined fast ion profiles with and without active AE control will be made. Work supported by the U.S. Dept. of Energy under Award Number DE-FC02-04ER54698.
Interplanetary Alfvenic fluctuations: A stochastic model
International Nuclear Information System (INIS)
Barnes, A.
1981-01-01
The strong alignment of the average directions of minimum magnetic variance and mean magnetic field in interplanetary Alfvenic fluctuations is inconsistent with the usual wave-propagation models. We investigate the concept of minimum variance for nonplanar Alfvenic fluctuations in which the field direction varies stochastically. It is found that the tendency of the minimum variance and mean field directions to be aligned may be purely a consequence of the randomness of the field direction. In particular, a well-defined direction of minimum variance does not imply that the fluctuations are necessarily planar. The fluctuation power spectrum is a power law for frequencies much higher than the inverse of the correlation time. The probability distribution of directions a randomly fluctuating field of constant magnitude is calculated. A new approach for observational studies of interplanetary fluctuations is suggested
Excitation of short wavelength Alfven oscillations by high energy ions in tokamak
International Nuclear Information System (INIS)
Beasley, C.O. Jr.; Lominadze, J.G.; Mikhailovskii, A.B.
1975-08-01
The excitation of Alfven waves by fast untrapped ions in axisymmetric tokamaks is described by the dispersion relation epsilon 11 - c 2 k/sub parallel bars/ 2 /ω 2 = 0. Using this relation a new class of instability connected with the excitation of Alfven oscillations is described. (U.S.)
Continuous wave power scaling in high power broad area quantum cascade lasers
Suttinger, M.; Leshin, J.; Go, R.; Figueiredo, P.; Shu, H.; Lyakh, A.
2018-02-01
Experimental and model results for high power broad area quantum cascade lasers are presented. Continuous wave power scaling from 1.62 W to 2.34 W has been experimentally demonstrated for 3.15 mm-long, high reflection-coated 5.6 μm quantum cascade lasers with 15 stage active region for active region width increased from 10 μm to 20 μm. A semi-empirical model for broad area devices operating in continuous wave mode is presented. The model uses measured pulsed transparency current, injection efficiency, waveguide losses, and differential gain as input parameters. It also takes into account active region self-heating and sub-linearity of pulsed power vs current laser characteristic. The model predicts that an 11% improvement in maximum CW power and increased wall plug efficiency can be achieved from 3.15 mm x 25 μm devices with 21 stages of the same design but half doping in the active region. For a 16-stage design with a reduced stage thickness of 300Å, pulsed roll-over current density of 6 kA/cm2 , and InGaAs waveguide layers; optical power increase of 41% is projected. Finally, the model projects that power level can be increased to 4.5 W from 3.15 mm × 31 μm devices with the baseline configuration with T0 increased from 140 K for the present design to 250 K.
Frequency chirpings in Alfven continuum
Wang, Ge; Berk, Herb; Breizman, Boris; Zheng, Linjin
2017-10-01
We have used a self-consistent mapping technique to describe both the nonlinear wave-energetic particle resonant interaction and its spatial mode structure that depends upon the resonant energetic particle pressure. At the threshold for the onset of the energetic particle mode (EPM), strong chirping emerges in the lower continuum close to the TAE gap and then, driven by strong continuum damping, chirps rapidly to lower frequencies in the Alfven continuum. An adiabatic theory was developed that accurately replicated the results from the simulation where the nonlinearity was only due to the EPM resonant particles. The results show that the EPM-trapped particles have their action conserved during the time of rapid chirping. This adiabaticity enabled wave trapped particles to be confined within their separatrix, and produce even larger resonant structures, that can produce a large amplitude mode far from linearly predicted frequencies. In the present work we describe the effect of additional MHD nonlinearity to this calculation. We studied how the zonal flow component and its nonlinear feedback to the fundamental frequency and found that the MHD nonlinearity doesn't significantly alter the frequency chirping response that is predicted by the calculation that neglects the MHD nonlinearity.
Interplay of energetic ions and Alfven modes in helical plasmas
International Nuclear Information System (INIS)
Kolesnichenko, Ya.I.; Lutsenko, V.V.; Yakovenko, Yu.Y.; Yamazaki, K.; Nakajima, N.; Narushima, Y.; Toi, K.; Yamamoto, S.
2003-08-01
Alfven eigenmodes and their destabilization by energetic ions in stellarators, mainly, in the Large Helical Device (LHD) plasmas, are considered. A general expression for the instability growth rate is derived, which generalizes that obtained in Ref. [Ya.I. Kolesnichenko et al., Phys. Plasmas 9, 517 (2002)] by taking into account the finite magnitude of the perturbed longitudinal magnetic field. The structures of the Alfven continuum and Alfven eigenmodes, as well as the resonances of the wave-particle interaction, are studied. A numerical simulation of the destabilization of Alfven waves with low mode numbers during neutral-beam injection in a particular LHD shot is carried out. The obtained solutions represent even and odd core-localized Toroidicity-induced Alfven Eigenmodes, the calculated frequencies and the mode numbers being in agreement with experimental data. The growth rates of the instabilities are calculated. This work was done during the stay of Ya.I. Kolesnichenko in NIFS as a Guest Professor from January 26, 2003 to April 25, 2003. (author)
Global structures of Alfven-ballooning modes in magnetospheric plasmas
International Nuclear Information System (INIS)
Vetoulis, G.; Chen, Liu.
1994-03-01
The authors show that a steep plasma pressure gradient can lead to radially localized Alfven modes, which are damped through coupling to filed line resonances. These have been called drift Alfven balloning modes (DABM) and are the prime candidates to explain Pc4-Pc5 geomagnetic pulsations observed during storms. A strong dependence of the damping rate on the azimuthal wave number m is established, as well as on the equilibrium profile. A minimum azimuthal mode number can be found for the DABM to be radially trapped. The authors find that higher m DABMs are better localized, which is consistent with high-m observations
Nonlinear hybrid simulation of toroidicity-induced alfven eigenmode
International Nuclear Information System (INIS)
Fu, G.Y.; Park, W.
1994-11-01
Gyrokinetic/Magnetohydrodynamics hybrid simulations have been carried out using MH3D-K code to study the nonlinear saturation of the toroidicity-induced Alfven eigenmode driven by energetic particles in a tokamak plasma. It is shown that the wave particle trapping is the nonlinear saturation mechanism for the parameters considered. The corresponding density profile flattening of hot particles is observed. The saturation amplitude is proportional to the square of linear growth rate. In addition to TAE modes, a new n = 1, m = 0 global Alfven eigenmode is shown to be excited by the energetic particles
Directory of Open Access Journals (Sweden)
Tawfig Eltaif
2017-01-01
Full Text Available A cascaded intensity modulator (IM and phase modulator (PM are used to modulate a continuous-wave (CW laser and generate an optical frequency comb (OFC. Thus, the generated comb is utilized as an initial seed and combined with another CW-laser to generate four-wave mixing (FWM in photonic crystal fiber (PCF. Results show that an initial flat 30 GHz OFC of 29, 55 lines within power fluctuation of 0.8 dB and 2 dB, respectively, can be achieved by setting the ratio of the DC bias to amplitude of sinusoidal signal at 0.1 and setting the modulation indices of both IM and PM at 10. Moreover, the 1st order of FWM created through 14 m of PCF has over 68 and 94 lines with fluctuation of 0.8 dB and 2 dB, respectively. Hence, the generated wavelengths of 1st left and right order of FWM can be tuned in a range from ~1500 nm to ~1525 nm and ~1590 nm to ~1604 nm, respectively.
Grid Connection of Wave Power Farm Using an N-Level Cascaded H-Bridge Multilevel Inverter
Directory of Open Access Journals (Sweden)
Rickard Ekström
2013-01-01
Full Text Available An N-level cascaded H-bridge multilevel inverter is proposed for grid connection of large wave power farms. The point-absorber wave energy converters are individually rectified and used as isolated DC-sources. The variable power characteristics of the wave energy converters are discussed, and a method of mitigating this issue is demonstrated. The complete power control system is given in detail and has been experimentally verified for a single-phase setup of the 9-level inverter. Theoretical expressions of the power sharing between multilevel cells are derived and show good correspondence with the experimental results.
Fundamentals of Highly Non-Degenerate Cascaded Four-Wave Mixing
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Rosa Weigand
2015-09-01
Full Text Available By crossing two intense ultrashort laser pulses with different colors in a transparent medium, like a simple piece of glass, a fan of multicolored broadband light pulses can be simultaneously generated. These newly generated pulses are emitted in several well-defined directions and can cover a broad spectral range, from the infrared to the ultraviolet and beyond. This beautiful phenomenon, first observed and described 15 years ago, is due to highly-nondegenerate cascaded four-wave mixing (cascaded FWM, or CFWM. Here, we present a review of our work on the generation and measurement of multicolored light pulses based on third-order nonlinearities in transparent solids, from the discovery and first demonstration of highly-nondegenerate CFWM, to the coherent synthesis of single-cycle pulses by superposition of the multicolored light pulses produced by CFWM. We will also present the development and main results of a dedicated 2.5-D nonlinear propagation model, i.e., with propagation occurring along a two-dimensional plane while assuming cylindrically symmetric pump beam profiles, capable of adequately describing noncollinear FWM and CFWM processes. A new method for the generation of femtosecond pulses in the deep-ultraviolet (DUV based on FWM and CFWM will also be described. These experimental and theoretical results show that highly-nondegenerate third-order nonlinear optical processes are formally well understood and provide broader bandwidths than other nonlinear optical processes for the generation of ultrashort light pulses with wavelengths extending from the near-infrared to the deep-ultraviolet, which have many applications in science and technology.
Suttinger, Matthew; Go, Rowel; Figueiredo, Pedro; Todi, Ankesh; Shu, Hong; Leshin, Jason; Lyakh, Arkadiy
2018-01-01
Experimental and model results for 15-stage broad area quantum cascade lasers (QCLs) are presented. Continuous wave (CW) power scaling from 1.62 to 2.34 W has been experimentally demonstrated for 3.15-mm long, high reflection-coated QCLs for an active region width increased from 10 to 20 μm. A semiempirical model for broad area devices operating in CW mode is presented. The model uses measured pulsed transparency current, injection efficiency, waveguide losses, and differential gain as input parameters. It also takes into account active region self-heating and sublinearity of pulsed power versus current laser characteristic. The model predicts that an 11% improvement in maximum CW power and increased wall-plug efficiency can be achieved from 3.15 mm×25 μm devices with 21 stages of the same design, but half doping in the active region. For a 16-stage design with a reduced stage thickness of 300 Å, pulsed rollover current density of 6 kA/cm2, and InGaAs waveguide layers, an optical power increase of 41% is projected. Finally, the model projects that power level can be increased to ˜4.5 W from 3.15 mm×31 μm devices with the baseline configuration with T0 increased from 140 K for the present design to 250 K.
A weakened cascade model for turbulence in astrophysical plasmas
International Nuclear Information System (INIS)
Howes, G. G.; TenBarge, J. M.; Dorland, W.
2011-01-01
A refined cascade model for kinetic turbulence in weakly collisional astrophysical plasmas is presented that includes both the transition between weak and strong turbulence and the effect of nonlocal interactions on the nonlinear transfer of energy. The model describes the transition between weak and strong MHD turbulence and the complementary transition from strong kinetic Alfven wave (KAW) turbulence to weak dissipating KAW turbulence, a new regime of weak turbulence in which the effects of shearing by large scale motions and kinetic dissipation play an important role. The inclusion of the effect of nonlocal motions on the nonlinear energy cascade rate in the dissipation range, specifically the shearing by large-scale motions, is proposed to explain the nearly power-law energy spectra observed in the dissipation range of both kinetic numerical simulations and solar wind observations.
Effect of Alfvenic fluctuations on the solar wind
International Nuclear Information System (INIS)
Chien, T.H.
1974-01-01
The major source of microscale fluctuations in the interplanetary medium due to the outwardly propagating Alfven waves is considered. The effect of the Alfven waves on the supersonic expansion of the solar wind is studied under the assumption that the motion of the interplanetary medium can be resolved physically into a comparatively smooth and slowly varying mesoscale flow and field with very irregular disordered incompressible microscale Alfvenic fluctuations superposed on it. The important features of the solar wind such as heat conduction flux, spiral interplanetary magnetic field, and proton thermal anisotropy are included in the theory. For inviscid, steady state, spherically symmetrical model of the solar wind, the two-fluid formulation of the background mesoscale MHD equations is obtained. The results show that during the expansion process, fluctuation energy is converted into the kinetic energy of the solar wind. Due to the presence of the Alfvenic fluctuations, the velocity of the solar wind is about 5 percent higher than that without considering the fluctuations. (U.S.)
An Alfven eigenmode similarity experiment
International Nuclear Information System (INIS)
Heidbrink, W W; Fredrickson, E; Gorelenkov, N N; Hyatt, A W; Kramer, G; Luo, Y
2003-01-01
The major radius dependence of Alfven mode stability is studied by creating plasmas with similar minor radius, shape, magnetic field (0.5 T), density (n e ≅3x10 19 m -3 ), electron temperature (1.0 keV) and beam ion population (near-tangential 80 keV deuterium injection) on both NSTX and DIII-D. The major radius of NSTX is half the major radius of DIII-D. The super-Alfvenic beam ions that drive the modes have overlapping values of v f /v A in the two devices. Observed beam-driven instabilities include toroidicity-induced Alfven eigenmodes (TAE). The stability threshold for the TAE is similar in the two devices. As expected theoretically, the most unstable toroidal mode number n is larger in DIII-D
Energy Technology Data Exchange (ETDEWEB)
Schekochihin, A. A.; Cowley, S. C.; Dorland, W.; Hammett, G. W.; Howes, G. G.; Quataert, E.; Tatsuno, T.
2009-04-23
become the slow and entropy modes of the conventional MHD). In the "dissipation range" below ion gyroscale, there are again two cascades: the kinetic-Alfven-wave (KAW) cascade governed by two fluid-like Electron Reduced Magnetohydrodynamic (ERMHD) equations and a passive cascade of ion entropy fluctuations both in space and velocity. The latter cascade brings the energy of the inertial-range fluctuations that was Landau-damped at the ion gyroscale to collisional scales in the phase space and leads to ion heating. The KAWenergy is similarly damped at the electron gyroscale and converted into electron heat. Kolmogorov-style scaling relations are derived for all of these cascades. The relationship between the theoretical models proposed in this paper and astrophysical applications and observations is discussed in detail.
International Nuclear Information System (INIS)
Schekochihin, A.A.; Cowley, S.C.; Dorland, W.; Hammett, G.W.; Howes, G.G.; Quataert, E.; Tatsuno, T.
2009-01-01
become the slow and entropy modes of the conventional MHD). In the 'dissipation range' below ion gyroscale, there are again two cascades: the kinetic-Alfven-wave (KAW) cascade governed by two fluid-like Electron Reduced Magnetohydrodynamic (ERMHD) equations and a passive cascade of ion entropy fluctuations both in space and velocity. The latter cascade brings the energy of the inertial-range fluctuations that was Landau-damped at the ion gyroscale to collisional scales in the phase space and leads to ion heating. The KAWenergy is similarly damped at the electron gyroscale and converted into electron heat. Kolmogorov-style scaling relations are derived for all of these cascades. The relationship between the theoretical models proposed in this paper and astrophysical applications and observations is discussed in detail.
Parametric decay of lower hybrid wave into drift waves
International Nuclear Information System (INIS)
Sanuki, Heiji.
1976-12-01
A dispersion relation describing the parametric decay of a lower hybrid wave into an electrostatic drift wave and a drift Alfven wave is derived for an inhomogeneous magnetized plasma. Particularly the stimulated scattering of a drift Alfven wave in such a plasma was investigated in detail. The resonance backscattering instability is found to yield the minimum threshold. (auth.)
Nonlinear gyrokinetic equations for low-frequency electromagnetic waves in general plasma equilibria
International Nuclear Information System (INIS)
Frieman, E.A.; Chen, L.
1981-10-01
A nonlinear gyrokinetic formalism for low-frequency (less than the cyclotron frequency) microscopic electromagnetic perturbations in general magnetic field configurations is developed. The nonlinear equations thus derived are valid in the strong-turbulence regime and contain effects due to finite Larmor radius, plasma inhomogeneities, and magentic field geometries. The specific case of axisymmetric tokamaks is then considered, and a model nonlinear equation is derived for electrostatic drift waves. Also, applying the formalism to the shear Alfven wave heating sceme, it is found that nonlinear ion Landau damping of kinetic shear-Alfven waves is modified, both qualitatively and quantitatively, by the diamagnetic drift effects. In particular, wave energy is found to cascade in wavenumber instead of frequency
Alfven Eigenmodes in spherical tokamaks
International Nuclear Information System (INIS)
Gryaznevich, Mikhail P.; Sharapov, Sergei E.; Berk, Herbert L.; Pinches, Simon D.
2005-01-01
Electromagnetic instabilities are often excited by fast super-Alfvenic ions produced by neutral beam injection (NBI) in plasmas of the spherical tokamaks START and MAST (toroidal magnetic confinement devices in which the minor a and major R 0 radii of the torus are comparable, R 0 /a≅1.2/1.8). These instabilities are seen as discrete weakly-damped toroidal and elliptical Alfven Eigenmodes (TAEs and EAEs) with frequencies tracing in time the Alfven scaling with the equilibrium magnetic field and plasma density, or as energetic particle modes (EPMs) whose frequencies don't start from TAE-frequency and sweep down in time faster than the equilibrium parameters change. In some discharges the beam drives Aflvenic-type modes that start from the TAE frequency and sweep in both up- and down- directions. Such electromagnetic perturbations are interpreted as 'hole-clump' long-living nonlinear fluctuations of the fast ion distribution function predicted by Berk-Breizman-Petviashvili [Phys. Lett. A238 (1998) 408]. It is found on both START and MAST that the Alfven instabilities weaken in their mode amplitude and in the number of unstable modes as the pressure of the thermal plasma increases, in agreement with increased thermal ion Landau damping and the pressure effect on core-localised TAEs. (author)
Kinetic global analysis of Alfven eigenmodes in toroidal plasmas
International Nuclear Information System (INIS)
Fukuyama, A.
2002-01-01
Systematic study on low to medium n (toroidal mode number) Alfven eigenmodes (AE) in tokamaks and helical systems is presented. Linear stability of AE in the presence of energetic ions was studied using the kinetic full-wave code TASK/WM.We have reproduced the destabilizing effect of toroidal co-rotation on TAE for JT-60U parameters. We have found the existence of reversed-shear-induced Alfven eigenmode (RSAE) which localizes near the q minimum in a reversed magnetic shear configuration. Two kinds of mode structures are identified for energetic particle mode (EPM) below the TAE frequency gap. The coupling to lower-frequency modes such as drift waves and MHD modes as well as the effect of trapped particles are also taken into account. For a helical plasma, the existence of GAE in the central region and TAE in the off-axis region was confirmed. (author)
Attractors of magnetohydrodynamic flows in an Alfvenic state
Energy Technology Data Exchange (ETDEWEB)
Nunez, Manuel; Sanz, Javier [Departamento de Analisis Matematico, Universidad de Valladolid, Valladolid (Spain)
1999-08-13
We present a simplified form of the magnetohydrodynamic system which describes the evolution of a plasma where the small-scale velocity and magnetic field are aligned in the form of Alfven waves, such as happens in several turbulent situations. Bounds on the dimension of the global attractor are found, and are shown to be an improvement of the standard ones for the full magnetohydrodynamic equations. (author)
Yuan, Jinhui; Kang, Zhe; Li, Feng; Zhang, Xianting; Mei, Chao; Zhou, Guiyao; Sang, Xinzhu; Wu, Qiang; Yan, Binbin; Zhou, Xian; Zhong, Kangping; Wang, Kuiru; Yu, Chongxiu; Farrell, Gerald; Lu, Chao; Tam, Hwa Yaw; Wai, P K A
2017-09-15
In this Letter, we demonstrate experimentally for the first time, to the best of our knowledge, discrete ultraviolet (UV) wavelength generation by cascaded intermodal FWM when femtosecond pump pulses at 800 nm are launched into the deeply normal dispersion region of the fundamental guided mode of a multimode photonic crystal fiber (MPCF). For pump pulses at average input powers of P av =450, 550, and 650 mW, the first anti-Stokes waves are generated at the visible wavelength of 538.1 nm through intermodal phase matching between the fundamental and second-order guided mode of the MPCF. The first anti-Stokes waves generated then serve as the secondary pump for the next intermodal FWM process. The second anti-Stokes waves in the form of the third-order guided mode are generated at the UV wavelength of 375.8 nm. The maximum output power is above 10 mW for P av =650 mW. We also confirm that the influences of fiber bending and intermodal walk-offs on the cascaded intermodal FWM-based frequency conversion process are negligible.
Sydoryk, Ihor; Lim, Alan; Jäger, Wolfgang; Tulip, John; Parsons, Matthew T
2010-02-20
We demonstrate the application of a commercially available widely tunable continuous-wave external cavity quantum cascade laser as a spectroscopic source for the simultaneous detection of multiple gases. We measured broad absorption features of benzene and toluene between 1012 and 1063 cm(-1) (9.88 and 9.41 microm) at atmospheric pressure using an astigmatic Herriott multipass cell. Our results show experimental detection limits of 0.26 and 0.41 ppm for benzene and toluene, respectively, with a 100 m path length for these two gases.
Signal-Pressure Curves of Cascaded Four-Wave Mixing in Gas-Filled Capillary by fs Pulses
International Nuclear Information System (INIS)
Chen Baozhen; Huang Zuqia
2005-01-01
The theoretical framework for the cascaded four waves mixing (CFWM) in gas-filled capillary by fs pulses is constructed. Based on the theoretical framework, the signal-pressure curves (SPC) of the CFWM in gas-filled capillary by fs pulses are calculated. With a comparison between the theoretical and experimental SPC we have discussed the influence of the walk-off and phase modulation on the SPC. At the same time, we have discussed the possible origin of the first three peaks of the SPC.
Compact toroids with Alfvenic flows
International Nuclear Information System (INIS)
Wang Zhehui; Tang, X.Z.
2004-01-01
The Chandrasekhar equilibria form a class of stationary ideal magnetohydrodynamics equilibria stabilized by magnetic-field-aligned Alfvenic flows. Analytic solutions of the Chandrasekhar equilibria are explicitly constructed for both field-reversed configurations and spheromaks. Favorable confinement property of nested closed flux surfaces and the ideal magnetohydrodynamic stability of the compact toroids are of interest for both magnetic trapping of high energy electrons in astrophysics and confinement of high temperature plasmas in laboratory
Alfven Continuum and Alfven Eigenmodes in the National Compact Stellarator Experiment
International Nuclear Information System (INIS)
Fesenyuk, O.P.; Kolesnichenko, Ya.I.; Lutsenko, V.V.; White, R.B.; Yakovenko, Yu.V.
2004-01-01
The Alfven continuum (AC) in the National Compact Stellarator Experiment (NCSX) is investigated with the AC code COBRA. The resonant interaction of Alfven eigenmodes and the fast ions produced by neutral beam injection is analyzed. Alfven eigenmodes residing in one of the widest gaps of the NCSX AC, the ellipticity-induced gap, are studied with the code BOA-E
Room temperature continuous wave operation of quantum cascade laser at λ ~ 9.4 μm
Hou, Chuncai; Zhao, Yue; Zhang, Jinchuan; Zhai, Shenqiang; Zhuo, Ning; Liu, Junqi; Wang, Lijun; Liu, Shuman; Liu, Fengqi; Wang, Zhanguo
2018-03-01
Continuous wave (CW) operation of long wave infrared (LWIR) quantum cascade lasers (QCLs) is achieved up to a temperature of 303 K. For room temperature CW operation, the wafer with 35 stages was processed into buried heterostructure lasers. For a 2-mm-long and 10-μm-wide laser with high-reflectivity (HR) coating on the rear facet, CW output power of 45 mW at 283 K and 9 mW at 303 K is obtained. The lasing wavelength is around 9.4 μm locating in the LWIR spectrum range. Project supported by the National Key Research And Development Program (No. 2016YFB0402303), the National Natural Science Foundation of China (Nos. 61435014, 61627822, 61574136, 61774146, 61674144, 61404131), the Key Projects of Chinese Academy of Sciences (Nos. ZDRW-XH-2016-4, QYZDJ-SSW-JSC027), and the Beijing Natural Science Foundation (No. 4162060, 4172060).
Reconstruction of a Broadband Spectrum of Alfvenic Fluctuations
Vinas, Adolfo F.; Fuentes, Pablo S. M.; Araneda, Jaime A.; Maneva, Yana G.
2014-01-01
Alfvenic fluctuations in the solar wind exhibit a high degree of velocities and magnetic field correlations consistent with Alfven waves propagating away and toward the Sun. Two remarkable properties of these fluctuations are the tendencies to have either positive or negative magnetic helicity (-1 less than or equal to sigma(sub m) less than or equal to +1) associated with either left- or right- topological handedness of the fluctuations and to have a constant magnetic field magnitude. This paper provides, for the first time, a theoretical framework for reconstructing both the magnetic and velocity field fluctuations with a divergence-free magnetic field, with any specified power spectral index and normalized magnetic- and cross-helicity spectrum field fluctuations for any plasma species. The spectrum is constructed in the Fourier domain by imposing two conditions-a divergence-free magnetic field and the preservation of the sense of magnetic helicity in both spaces-as well as using Parseval's theorem for the conservation of energy between configuration and Fourier spaces. Applications to the one-dimensional spatial Alfvenic propagation are presented. The theoretical construction is in agreement with typical time series and power spectra properties observed in the solar wind. The theoretical ideas presented in this spectral reconstruction provide a foundation for more realistic simulations of plasma waves, solar wind turbulence, and the propagation of energetic particles in such fluctuating fields.
Experiments on shear Alfven resonance in a tokamak
International Nuclear Information System (INIS)
Prager, S.C.; Witherspoon, F.D.; Kieras, C.E.; Kortbawi, D.; Sprott, J.C.; Tataronis, J.A.
1983-02-01
Detailed observations have been made of the spatial structure of the wave magnetic field. Measurements of the resonance properties such as radial location, wave polarization, resonance width and risetime are all consistent with shear Alfven resonance theory, although several measurements require improvement in resolution. The resonance location agrees with prediction of a fully two-dimensional ideal MHD theory for the Tokapole II device. To complete the identification a frequency scan and careful comparison of the observed resonance with antenna loading will be undertaken
Yuan, Jinhui; Kang, Zhe; Li, Feng; Zhang, Xianting; Zhou, Guiyao; Sang, Xinzhu; Wu, Qiang; Yan, Binbin; Zhou, Xian; Wang, Liang; Zhong, Kangping; Wang, Kuiru; Yu, Chongxiu; Tam, Hwa Yaw; Wai, P K A
2016-06-01
Generation of spectrally-isolated wavelengths in the violet to blue region based on cascaded degenerate four-wave mixing (FWM) is experimentally demonstrated for the first time in a tailor-made photonic crystal fiber, which has two adjacent zero dispersion wavelengths (ZDWs) at 696 and 852 nm in the fundamental mode. The influences of the wavelength λp and the input average power Pav of the femtosecond pump pulses on the phase-matched frequency conversion process are studied. When femtosecond pump pulses at λp of 880, 870, and 860 nm and Pav of 500 mW are coupled into the normal dispersion region close to the second ZDW, the first anti-Stokes waves generated near the first ZDW act as a secondary pump for the next FWM process. The conversion efficiency ηas2 of the second anti-Stokes waves, which are generated at the violet to blue wavelengths of 430, 456, and 472 nm, are 4.8, 6.48, and 9.66%, for λp equalling 880, 870, and 860 nm, respectively.
Compressional Alfven Eigenmode Similarity Study
Heidbrink, W. W.; Fredrickson, E. D.; Gorelenkov, N. N.; Rhodes, T. L.
2004-11-01
NSTX and DIII-D are nearly ideal for Alfven eigenmode (AE) similarity experiments, having similar neutral beams, fast-ion to Alfven speed v_f/v_A, fast-ion pressure, and shape of the plasma, but with a factor of 2 difference in the major radius. Toroidicity-induced AE with ˜100 kHz frequencies were compared in an earlier study [1]; this paper focuses on higher frequency AE with f ˜ 1 MHz. Compressional AE (CAE) on NSTX have a polarization, dependence on the fast-ion distribution function, frequency scaling, and low-frequency limit that are qualitatively consistent with CAE theory [2]. Global AE (GAE) are also observed. On DIII-D, coherent modes in this frequency range are observed during low-field (0.6 T) similarity experiments. Experiments will compare the CAE stability limits on DIII-D with the NSTX stability limits, with the aim of determining if CAE will be excited by alphas in a reactor. Predicted differences in the frequency splitting Δ f between excited modes will also be used. \\vspace0.25em [1] W.W. Heidbrink, et al., Plasmas Phys. Control. Fusion 45, 983 (2003). [2] E.D. Fredrickson, et al., Princeton Plasma Physics Laboratory Report PPPL-3955 (2004).
Ulvila, Ville; Phillips, C R; Halonen, Lauri; Vainio, Markku
2013-11-01
We report optical frequency comb generation by a continuous-wave pumped optical parametric oscillator (OPO) without any active modulation. The OPO is configured as singly resonant with an additional nonlinear crystal (periodically poled MgO:LiNbO3) placed inside the OPO for phase mismatched second harmonic generation (SHG) of the resonating signal beam. The phase mismatched SHG causes cascading χ(2) nonlinearities, which can substantially increase the effective χ(3) nonlinearity in MgO:LiNbO3, leading to spectral broadening of the OPO signal beam via self-phase modulation. The OPO generates a stable 4 THz wide (-30 dB) frequency comb centered at 1.56 μm.
Sigler, Chris; Gibson, Ricky; Boyle, Colin; Kirch, Jeremy D.; Lindberg, Donald; Earles, Thomas; Botez, Dan; Mawst, Luke J.; Bedford, Robert
2018-01-01
The modal characteristics of nonresonant five-element phase-locked arrays of 4.7-μm emitting quantum cascade lasers (QCLs) have been studied using spectrally resolved near- and far-field measurements and correlated with results of device simulation. Devices are fabricated by a two-step metal-organic chemical vapor deposition process and operate predominantly in an in-phase array mode near threshold, although become multimode at higher drive levels. The wide spectral bandwidth of the QCL's core region is found to be a factor in promoting multispatial-mode operation at high drive levels above threshold. An optimized resonant-array design is identified to allow sole in-phase array-mode operation to high drive levels above threshold, and indicates that for phase-locked laser arrays full spatial coherence to high output powers does not require full temporal coherence.
Ion Heating by Fast Particle Induced Alfven Turbulence
International Nuclear Information System (INIS)
Gates, D.; Gorelenkov, N.; White, R.B.
2001-01-01
A novel mechanism that directly transfers energy from Super-Alfvenic energetic ions to thermal ions in high-beta plasmas is described. The mechanism involves the excitation of compressional Alfvin eigenmodes (CAEs) in the frequency range with omega less than or approximately equal to omega(subscript ci). The broadband turbulence resulting from the large number of excited modes causes stochastic diffusion in velocity space, which transfers wave energy to thermal ions. This effect may be important on the National Spherical Torus Experiment (NSTX), and may scale up to reactor scenarios. This has important implications for low aspect ratio reactor concepts, since it potentially allows for the modification of the ignition criterion
International Nuclear Information System (INIS)
Chambrier, A. de; Heym, A.; Hofmann, F.; Joye, B.; Keller, R.; Lietti, A.; Lister, J.B.; Pochelon, A.; Simm, W.
1983-01-01
The aim of the TCA project is to investigate the heating effects of resonant absorption of Alfven waves in a Tokamak plasma. In TCA, the ion temperature increases linearly with the heating. Depending on the conditions, the ion temperature rises from 150 eV to 225 eV. (Auth./G.T.H.)
DEFF Research Database (Denmark)
Paoloni, Claudio; Di Carlo, Aldo; Bouamrane, Fayçal
2013-01-01
The design and fabrication challenges in the first ever attempt to realize a 1-THz vacuum tube amplifier are described. Implementation of innovative solutions including a slow-wave structure in the form of a double corrugated waveguide, lateral tapered input and output couplers, deep X-ray LIGA f...
International Nuclear Information System (INIS)
Mikhailovskii, A.B.
1986-01-01
Some general problems of the theory of Alfven instabilities of a tokamak with high-energy ions are considered. It is assumed that such ions are due to either ionization of fast neutral atoms, injected into the tokamak, or production of them under thermo-nuclear conditions. Small-oscillation equations are derived for the Alfven-type waves, which allow for both destabilizing effects, associated with the high-energy particles, and stabilizing ones, such as effects of shear and bulk-plasm dissipation. A high-energy ion contribution is calculated into the growth rate of the Alfven waves. The author considers the role of trapped-electron collisional dissipation
Theory and simulation of discrete kinetic beta induced Alfven eigenmode in tokamak plasmas
International Nuclear Information System (INIS)
Wang, X; Zonca, F; Chen, L
2010-01-01
It is shown, both analytically and by numerical simulations, that, in the presence of thermal ion kinetic effects, the beta induced Alfven eigenmode (BAE)-shear Alfven wave continuous spectrum can be discretized into radially trapped eigenstates known as kinetic BAE (KBAE). While thermal ion compressibility gives rise to finite BAE accumulation point frequency, the discretization occurs via the finite Larmor radius and finite orbit width effects. Simulations and analytical theories agree both qualitatively and quantitatively. Simulations also demonstrate that KBAE can be readily excited by the finite radial gradients of energetic particles.
Resistive vs. total power depositions by Alfven modes in pre-heated low aspect ratio tokamaks
International Nuclear Information System (INIS)
Cuperman, S.; Bruma, C.; Komoshvili, K.
2004-01-01
The power deposition of fast waves launched by a LFS located antenna in a pre-heated, strongly non-uniform low aspect ratio tokamak (START) is investigated. The rigorous computational results indicate a total power deposition by far larger than that predicted for Alfven continuum eigenmodes in cylindrical plasmas. For toroidal wave numbers |N| > 1, the resistive and total power depositions are almost equal. (author)
Basic physics of Alfven instabilities driven by energetic particles in toroidally confined plasmas
International Nuclear Information System (INIS)
Heidbrink, W. W.
2008-01-01
Superthermal energetic particles (EP) often drive shear Alfven waves unstable in magnetically confined plasmas. These instabilities constitute a fascinating nonlinear system where fluid and kinetic nonlinearities can appear on an equal footing. In addition to basic science, Alfven instabilities are of practical importance, as the expulsion of energetic particles can damage the walls of a confinement device. Because of rapid dispersion, shear Alfven waves that are part of the continuous spectrum are rarely destabilized. However, because the index of refraction is periodic in toroidally confined plasmas, gaps appear in the continuous spectrum. At spatial locations where the radial group velocity vanishes, weakly damped discrete modes appear in these gaps. These eigenmodes are of two types. One type is associated with frequency crossings of counterpropagating waves; the toroidal Alfven eigenmode is a prominent example. The second type is associated with an extremum of the continuous spectrum; the reversed shear Alfven eigenmode is an example of this type. In addition to these normal modes of the background plasma, when the energetic particle pressure is very large, energetic particle modes that adopt the frequency of the energetic particle population occur. Alfven instabilities of all three types occur in every toroidal magnetic confinement device with an intense energetic particle population. The energetic particles are most conveniently described by their constants of motion. Resonances occur between the orbital frequencies of the energetic particles and the wave phase velocity. If the wave resonance with the energetic particle population occurs where the gradient with respect to a constant of motion is inverted, the particles transfer energy to the wave, promoting instability. In a tokamak, the spatial gradient drive associated with inversion of the toroidal canonical angular momentum P ζ is most important. Once a mode is driven unstable, a wide variety of
Excitation of Alfvenic instabilities in spherical tokamaks
International Nuclear Information System (INIS)
McClements, K.G.; Appel, L.C.; Hole, M.J.; Thyagaraja, A.
2003-01-01
Understanding energetic particle confinement in spherical tokamak (STs) is important for optimising the design of ST power plants, and provides a testbed for theoretical modelling under conditions of strong toroidicity and shaping, and high beta. MHD analysis of some recent beam-heated discharges in the MAST ST indicates that high frequency modes observed in these discharges can be identified as toroidal Alfven Eigenmodes (TAEs) and elliptical Alfven Eigenmodes (EAEs). It is possible that such modes could strongly enhance fusion alpha-particle transport in an ST power plant. Computations of TAE growth rates for one particular MAST discharge, made using the HAGIS guiding centre code and benchmarked against analytical estimates, indicate strong drive by sub-Alfvenic neutral beam ions. HAGIS computations using higher mode amplitudes than those observed indicate that whereas co-passing beam ions provide the bulk of he TAE drive, counter-passing ions provide the dominant component of TAE-induced particle losses. Axisymmetric Alfvenic mode activity has been detected during ohmic discharges in MAST. These observations are shown by computational modelling to be consistent with the excitation of global Alfven Eigenmodes (GAEs) with n=0 and low m, driven impulsively by low frequency MHD. (author)
Turbulence and Waves as Sources for the Solar Wind
Cranmer, S. R.
2008-05-01
Gene Parker's insights from 50 years ago provided the key causal link between energy deposition in the solar corona and the acceleration of solar wind streams. However, the community is still far from agreement concerning the actual physical processes that give rise to this energy. It is still unknown whether the solar wind is fed by flux tubes that remain open (and are energized by footpoint-driven wavelike fluctuations) or if mass and energy is input more intermittently from closed loops into the open-field regions. No matter the relative importance of reconnections and loop-openings, though, we do know that waves and turbulent motions are present everywhere from the photosphere to the heliosphere, and it is important to determine how they affect the mean state of the plasma. In this presentation, I will give a summary of wave/turbulence models that seem to succeed in explaining the time-steady properties of the corona (and the fast and slow solar wind). The coronal heating and solar wind acceleration in these models comes from anisotropic turbulent cascade, which is driven by the partial reflection of low-frequency Alfven waves propagating along the open magnetic flux tubes. Specifically, a 2D model of coronal holes and streamers at solar minimum reproduces the latitudinal bifurcation of slow and fast streams seen by Ulysses. The radial gradient of the Alfven speed affects where the waves are reflected and damped, and thus whether energy is deposited below or above Parker's critical point. As predicted by earlier studies, a larger coronal expansion factor gives rise to a slower and denser wind, higher temperature at the coronal base, less intense Alfven waves at 1 AU, and correlative trends for commonly measured ratios of ion charge states and FIP-sensitive abundances that are in general agreement with observations. Finally, I will outline the types of future observations that would be most able to test and refine these ideas.
MHD-Vlasov simulation of the toroidal Alfven eigenmode
International Nuclear Information System (INIS)
Todo, Y.; Sato, T.; Watanabe, K.; Watanabe, T.H.; Horiuchi, R.
1994-11-01
A new simulation method has been developed to investigate the excitation and saturation processes of toroidal Alfven eigenmodes (TAE modes). The background plasma is described by a full-MHD fluid model, while the kinetic evolution of energetic alpha particles is followed by the drift kinetic equation. The magnetic fluctuation of n = 2 mode develops and saturates at the level of 1.8x10 -3 of the equilibrium field when the initial beta of alpha particles is 2% at the magnetic axis. After saturation, the TAE mode amplitude shows an oscillatory behavior with a frequency corresponding to the bounce frequency of the alpha particles trapped by the TEA mode. The decrease of the power transfer rate from the alpha particles to the TAE mode, which is due to the trapped particle effect of a finite-amplitude wave, causes the saturation. From the linear growth rate the saturation level can be estimated. (author)
Low-n shear Alfven spectra in axisymmetric toroidal plasmas
International Nuclear Information System (INIS)
Cheng, C.Z.; Chance, M.S.
1985-11-01
In toroidal plasmas, the toroidal magnetic field is nonuniform over a magnetic surface and causes coupling of different poloidal harmonics. It is shown both analytically and numerically that the toroidicity not only breaks up the shear Alfven continuous spectrum, but also creates new, discrete, toroidicity-induced shear Alfven eigenmodes with frequencies inside the continuum gaps. Potential applications of the low-n toroidicity-induced shear Alfven eigenmodes on plasma heating and instabilities are addressed. 17 refs., 4 figs
Global Alfven Eigenmodes in DIII-D
International Nuclear Information System (INIS)
Turnbull, A.D.; Chu, M.S.; Strait, E.J.; Lao, L.L.; Greene, J.M.; Taylor, T.S.; Heidbrink, W.W.; Duong, H.; Chance, M.S.
1992-06-01
Global Alfven modes, such as the Toroidicity-Induced Alfven Eigenmode (TAE), pose a serious threat for strongly-heated tokamaks since they can result in saturation of the achievable beam β at moderate levels and they may also cause serious α-particle losses in future ignited devices. The DIII-D tokamak has a unique capability for study of the resonant excitation of these instabilities by energetic beam ions. TAE modes have now been observed in DIII-D over a wide range of operating conditions, including both circular cross-section and elongated (κ ∼ 1.8) discharges. Equilibrium reconstructions of several representative discharges, using all available external magnetic and internal profile data, have been done and analyzed in detail. The computed real mode frequencies of the TAE modes are in good agreement with the experimentally observed mode frequencies and differ significantly from the estimated kinetic ballooning mode frequencies. The TAE calculations include coupling to the Alfven and acoustic continuum branches of the MHD spectrum and generally indicate that the simplified circular cross-section, large aspect-ratio assumptions made in analytic calculations are poor approximations to the actual TAE mode structures. In particular, the global TAE modes are almost always coupled to one or more continuum branches by toroidicity, poloidal shaping, and finite β effects. Estimates of the various resonant excitation and damping mechanisms, including continuum damping, have been made and the total is found to be in reasonable agreement with the experimental threshold
On the nature of electromagnetic waves in the vicinity of auroral archs
International Nuclear Information System (INIS)
Volokitin, A.S.; Mordovskaya, V.G.
1988-01-01
Excitation of kinetic Alfven waves by longitudinal current in the vicinity of auroral arcs is considered in the framework of quasilinear theory. It is shown that experimentally observed low-frequency electromagnetic waves with f<2Hz frequency in the vicinity of uniform auroral arcs represent the Alfven waves, excited at altitudes of three Earth radii and above by longitudinal electric current
Electromagnetic internal gravity waves in the Earth's ionospheric E-layer
International Nuclear Information System (INIS)
Kaladze, T.D.; Tsamalashvili, L.V.; Kaladze, D.T.
2011-01-01
In the Earth's ionospheric E-layer existence of the new waves connecting with the electromagnetic nature of internal gravity waves is shown. They represent the mixture of the ordinary internal gravity waves and the new type of dispersive Alfven waves. -- Highlights: ► Existence of electromagnetic internal gravity waves in the ionospheric E-layer is shown. ► Electromagnetic nature of internal gravity waves is described. ► Appearance of the new dispersive Alfven waves is shown.
Alfven Spectroscopy for Advanced Scenarios on JET
Energy Technology Data Exchange (ETDEWEB)
Sharapov, S. E.
2007-07-01
Advanced tokamak scenarios on JET exhibit outstanding quality fusion-grade plasmas, with internal transport barriers (ITBs) capable of supporting gradients {nabla} T{sub i}{approx_equal} 150 keV/m (with T{sub i}(0){approx_equal} 40 keV), and with q(r)-profiles ranging from monotonic to deep shear reversal, including the limiting case of toroidal current holes. It was found experimentally, that in reversed shear JET discharges the ITB start from so-called ITB triggering events, which are seen as increases in electron temperature within, e.g. r/a {<=} 0.4 by {delta} T{sub e}/T{sub e}{approx} 10-30%. If main heating power is applied at this time, an ITB is formed easily. Without an extra-heating power the improved confinement effect is lost in about 100 msec. Here, we investigate the magnetic field topology at the time of the ITB triggering events in JET plasmas. Alfven spectroscopy based on discrete spectrum of Alfven eigenmodes (AEs) excited by ICRH-accelerated and/or NBI-produced energetic ions is used for determining the evolution of the q(r)- profiles. Recently developed interferometry diagnostics of AEs significantly extended time resolution and sensitivity of Alfven spectroscopy on JET and made it possible to perform the ITB triggering event studies with a high accuracy. The ITB triggering events are found to occur when q{sub min} (t) passes values q{sub min} integer (majority of the cases), q{sub min}= half-integer, and when q(r=0)--infinity (current hole is triggered). This experimental data is compared to the density of rational surfaces transport theory. (Author)
Alfven Spectroscopy for Advanced Scenarios on JET
International Nuclear Information System (INIS)
Sharapov, S. E.
2007-01-01
Advanced tokamak scenarios on JET exhibit outstanding quality fusion-grade plasmas, with internal transport barriers (ITBs) capable of supporting gradients ∇ T i ≅ 150 keV/m (with T i (0)≅ 40 keV), and with ) q(r) -profiles ranging from monotonic to deep shear reversal, including the limiting case of toroidal current holes. It was found experimentally, that in reversed shear JET discharges the ITB start from so-called ITB triggering events, which are seen as increases in electron temperature within, e.g. r/a ≤ 0.4 by Δ T e /T e ∼ 10-30%. If main heating power is applied at this time, an ITB is formed easily. Without an extra-heating power the improved confinement effect is lost in about 100 msec. Here, we investigate the magnetic field topology at the time of the ITB triggering events in JET plasmas. Alfven spectroscopy based on discrete spectrum of Alfven eigenmodes (AEs) excited by ICRH-accelerated and/or NBI-produced energetic ions is used for determining the evolution of the q(r)- profiles. Recently developed interferometry diagnostics of AEs significantly extended time resolution and sensitivity of Alfven spectroscopy on JET and made it possible to perform the ITB triggering event studies with a high accuracy. The ITB triggering events are found to occur when q m in (t) passes values q m ininteger (majority of the cases), q m in= half-integer, and when q(r=0)--∞ (current hole is triggered). This experimental data is compared to the idensity of rational surfaces transport theory. (Author)
Watt-Level Continuous-Wave Emission from a Bi-Functional Quantum Cascade Laser/Detector
2017-04-18
cally authorized by the U.S. Government may violate any copyrights that exist in this work. Watt-level continuous- wave emission from a bi- functional ... wave bi- functional devices, opens the perspective of on-chip dual comb spectroscopy. Also for discrete sens- ing setups, one can switch to lasers...seas.harvard.edu Abstract Bi- functional active regions, capable of light generation and detection at the same wavelength, allow a straightforward realization of
Investigation of global Alfven instabilities in TFTR
International Nuclear Information System (INIS)
Wong, K.L.; Paul, S.F.; Fredrickson, E.D.; Nazikian, R.; Park, H.K.; Bell, M.; Bretz, N.L.; Budny, R.; Cheng, C.Z.; Cohen, S.; Hammett, G.W.; Jobes, F.C.; Johnson, L.; Meade, D.M.; Medley, S.S.; Mueller, D.; Nagayama, Y.; Owens, D.K.; Synakowski, E.J.; Roberts, D.R.; Sabbagh, S.
1992-01-01
Toroidal Alfven Eigenmodes (TAE) were excited by the energetic neutral beam ions tangentially injected into TFTR plasmas at low magnetic field such that the injection velocities were comparable to the Alfven speed. The modes were identified by measurements from Mirnov coils and beam emission spectroscopy (BES). TAE modes appear in bursts whose repetition rate increases with beam power. The neutron emission rate exhibits sawtooth-like behavior and the crashes always coincide with TAE bursts. This indicates ejection of fast ions from the plasma until these modes are stabilized. The dynamics of growth and stabilization was investigated at various plasma current and magnetic field. The results indicate that the instability can effectively clamp the number of energetic ions in the plasma. The observed instability threshold is discussed in the light of recent theories. In addition to these TAE modes, intermittent oscillations at three times the fundamental TAE frequency were observed by Mirnov coils, but no corresponding signal was found in BES. It appears that these high frequency oscillations do not have direct effect on the plasma neutron source strength
Driben, Rodislav; Mitschke, Fedor; Zhavoronkov, Nickolai
2010-12-06
The complex mechanism of multiple interactions between solitary and dispersive waves at the advanced stage of supercontinuum generation in photonic crystal fiber is studied in experiment and numerical simulations. Injection of high power negatively chirped pulses near zero dispersion frequency results in an effective soliton fission process with multiple interactions between red shifted Raman solitons and dispersive waves. These interactions may result in relative acceleration of solitons with further collisions between them of quasi-elastic or quasi-plastic kinds. In the spectral domain these processes result in enhancement of certain wavelength regions within the spectrum or development of a new significant band at the long wavelength side of the spectrum.
Energy Technology Data Exchange (ETDEWEB)
Gorelenkov, N.N. [Princeton Plasma Physics Laboratory, Princeton University (United States)], E-mail: ngorelen@pppl.gov; Berk, H.L. [IFS, Austin, Texas (United States); Fredrickson, E. [Princeton Plasma Physics Laboratory, Princeton University (United States); Sharapov, S.E. [Euroatom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire (United States)
2007-10-08
New global MHD eigenmode solutions arising in gaps in the low frequency Alfven-acoustic continuum below the geodesic acoustic mode (GAM) frequency have been found numerically and have been used to explain relatively low frequency experimental signals seen in NSTX and JET tokamaks. These global eigenmodes, referred to here as Beta-induced Alfven-Acoustic Eigenmodes (BAAE), exist in the low magnetic safety factor region near the extrema of the Alfven-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes shifts as the safety factor, q, decreases. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta <2% as well as in NSTX plasmas at relatively high-beta >20%. In contrast to the mostly electrostatic character of GAMs the new global modes also contain an electromagnetic (magnetic field line bending) component due to the Alfven coupling, leading to wave phase velocities along the field line that are large compared to the sonic speed. Qualitative agreement between theoretical predictions and observations are found.
Alfven eigenmodes driven by Alfvenic beam ions in JT-60U
International Nuclear Information System (INIS)
Shinohara, K.; Kusama, Y.; Takechi, M.
2001-01-01
Instabilities with frequency chirping in the frequency range of Alfven eigenmodes have been found in the domain 0.1% h > bparallel /υ A ∼ 1 with high energy neutral beam injection in JT-60U. One instability with a frequency inside the Alfven continuum spectrum appears and its frequency increases slowly to the toroidicity induced Alfven eigenmode (TAE) gap on the timescale of an equilibrium change (∼ 200 ms). Other instabilities appear with a frequency inside the TAE gap and their frequencies change very quickly by 10-20 kHz in 1-5 ms. During the period when these fast frequency sweeping (fast FS) modes occur, abrupt large amplitude events (ALEs) often appear with a drop of neutron emission rate and an increase in fast neutral particle fluxes. The loss of energetic ions increases with a peak fluctuation amplitude of B-tilde θ /B θ . An energy dependence of the loss ions is observed and suggests a resonant interaction between energetic ions and the mode. (author)
Resonant magnetohydrodynamic waves in high-beta plasmas
International Nuclear Information System (INIS)
Ruderman, M. S.
2009-01-01
When a global magnetohydrodynamic (MHD) wave propagates in a weakly dissipative inhomogeneous plasma, the resonant interaction of this wave with either local Alfven or slow MHD waves is possible. This interaction occurs at the resonant position where the phase velocity of the global wave coincides with the phase velocity of either Alfven or slow MHD waves. As a result of this interaction a dissipative layer embracing the resonant position is formed, its thickness being proportional to R -1/3 , where R>>1 is the Reynolds number. The wave motion in the resonant layer is characterized by large amplitudes and large gradients. The presence of large gradients causes strong dissipation of the global wave even in very weakly dissipative plasmas. Very often the global wave motion is characterized by the presence of both Alfven and slow resonances. In plasmas with small or moderate plasma beta β, the resonance positions corresponding to the Alfven and slow resonances are well separated, so that the wave motion in the Alfven and slow dissipative layers embracing the Alfven and slow resonant positions, respectively, can be studied separately. However, when β > or approx. R 1/3 , the two resonance positions are so close that the two dissipative layers overlap. In this case, instead of two dissipative layers, there is one mixed Alfven-slow dissipative layer. In this paper the wave motion in such a mixed dissipative layer is studied. It is shown that this motion is a linear superposition of two motions, one corresponding to the Alfven and the other to the slow dissipative layer. The jump of normal velocity across the mixed dissipative layer related to the energy dissipation rate is equal to the sum of two jumps, one that occurs across the Alfven dissipative layer and the other across the slow dissipative layer.
Resonant interaction of energetic ions with Alfven-like perturbations in stellarators
International Nuclear Information System (INIS)
Karulin, N.; Wobig, H.
1994-04-01
The modification of passing guiding center orbits of 3.5 MeV alpha particles and 45 keV protons in the presence of global Alfven eigenmodes (GAE's) is studied in modular advanced stellarators. It is found that if resonances between particles and waves occur, drift surfaces form a set of island structures. The mode numbers of the perturbations, which are dangerous for the energetic particle confinement, are discussed for two particular stellarators (Helias reactor and Wendelstein 7-AS). The perturbation amplitudes corresponding to the onset of orbit stochasticity are studied numerically. The coefficient of the collisionless stochastic diffusion is estimated using the island width derived analytically. (orig.)
Theory of semicollisional kinetic Alfven modes in sheared magnetic fields
International Nuclear Information System (INIS)
Hahm, T.S.; Chen, L.
1985-02-01
The spectra of the semicollisional kinetic Alfven modes in a sheared slab geometry are investigated, including the effects of finite ion Larmor radius and diamagnetic drift frequencies. The eigenfrequencies of the damped modes are derived analytically via asymptotic analyses. In particular, as one reduces the resistivity, we find that, due to finite ion Larmor radius effects, the damped mode frequencies asymptotically approach finite real values corresponding to the end points of the kinetic Alfven continuum
Directory of Open Access Journals (Sweden)
V. Génot
2004-06-01
Full Text Available Investigating the process of electron acceleration in auroral regions, we present a study of the temporal evolution of the interaction of Alfvén waves (AW with a plasma inhomogeneous in a direction transverse to the static magnetic field. This type of inhomogeneity is typical of the density cavities extended along the magnetic field in auroral acceleration regions. We use self-consistent Particle In Cell (PIC simulations which are able to reproduce the full nonlinear evolution of the electromagnetic waves, as well as the trajectories of ions and electrons in phase space. Physical processes are studied down to the ion Larmor radius and electron skin depth scales. We show that the AW propagation on sharp density gradients leads to the formation of a significant parallel (to the magnetic field electric field (E-field. It results from an electric charge separation generated on the density gradients by the polarization drift associated with the time varying AW E-field. Its amplitude may reach a few percents of the AW E-field. This parallel component accelerates electrons up to keV energies over a distance of a few hundred Debye lengths, and induces the formation of electron beams. These beams trigger electrostatic plasma instabilities which evolve toward the formation of nonlinear electrostatic structures (identified as electron holes and double layers. When the electrostatic turbulence is fully developed we show that it reduces the further wave/particle exchange. This sequence of mechanisms is analyzed with the program WHAMP, to identify the instabilities at work and wavelet analysis techniques are used to characterize the regime of energy conversions (from electromagnetic to electrostatic structures, from large to small length scales. This study elucidates a possible scenario to account for the particle acceleration and the wave dissipation in inhomogeneous plasmas. It would consist of successive phases of acceleration along the magnetic field
Electromagnetic waves in dusty magnetoplasmas using two-potential theory
International Nuclear Information System (INIS)
Zubia, K.; Jamil, M.; Salimullah, M.
2009-01-01
The low-frequency long wavelength electromagnetic waves, viz., shear Alfven waves in a cold dusty plasma, have been examined employing two-potential theory and plasma fluid model. The presence of the unmagnetized dust particles and magnetized plasma components gives rise to a new ion-dust lower hybrid cutoff frequency for the electromagnetic shear Alfven wave propagation. The importance and relevance of the present work to the space dusty plasma environments are also pointed out.
Energy Technology Data Exchange (ETDEWEB)
Eiter, Hans-Martin; Tassini, Leonardo; Muschler, Bernhard; Hackl, Rudi [Walther Meissner Institute, Bavarian Academy of Sciences and Humanities, 85748 Garching (Germany); Lavagnini, Michela; Degiorgi, Leonardo [Laboratorium fuer Festkoerperphysik, ETH - Zuerich, CH-8093 Zuerich (Switzerland); Chu, Jiun-Haw; Ru, Nancy; Fisher, Ian R. [GLAM, Stanford University, CA 94304 (United States)
2010-07-01
We report results of Raman scattering experiments as a function of temperature on the charge-density-wave (CDW) systems DyTe{sub 3} and on LaTe{sub 3} at 6 GPa applied pressure. We clearly identify the unidirectional collective CDW amplitude excitation and follow their temperature dependence in the range from 6 K to 311 K. Surprisingly, we discover that the amplitude mode develops as a succession of two mean-field, BCS-like transitions at two different temperatures. Tri-tellurides with heavier rare-earth atoms (i.e. Tm, Er, Ho, Dy) undergo another phase transition to a bidirectional CDW at low temperatures. In DyTe{sub 3} we find spectroscopic evidence for the amplitude mode excitation associated with the bidirectional CDW occuring below 50 K.
International Nuclear Information System (INIS)
Kirch, J. D.; Chang, C.-C.; Boyle, C.; Mawst, L. J.; Botez, D.; Lindberg, D.; Earles, T.
2015-01-01
Five, 8.36 μm-emitting quantum-cascade lasers (QCLs) have been monolithically phase-locked in the in-phase array mode via resonant leaky-wave coupling. The structure is fabricated by etch and regrowth which provides large index steps (Δn = 0.10) between antiguided-array elements and interelement regions. Such high index contrast photonic-crystal (PC) lasers have more than an order of magnitude higher index contrast than PC-distributed feedback lasers previously used for coherent beam combining in QCLs. Absorption loss to metal layers inserted in the interelement regions provides a wide (∼1.0 μm) range in interelement width over which the resonant in-phase mode is strongly favored to lase. Room-temperature, in-phase-mode operation with ∼2.2 kA/cm 2 threshold-current density is obtained from 105 μm-wide aperture devices. The far-field beam pattern has lobewidths 1.65× diffraction limit (D.L.) and 82% of the light in the main lobe, up to 1.8× threshold. Peak pulsed near-D.L. power of 5.5 W is obtained, with 4.5 W emitted in the main lobe. Means of how to increase the device internal efficiency are discussed
Nonlinear Electromagnetic Waves and Spherical Arc-Polarized Waves in Space Plasmas
Tsurutani, B.; Ho, Christian M.; Arballo, John K.; Lakhina, Gurbax S.; Glassmeier, Karl-Heinz; Neubauer, Fritz M.
1997-01-01
We review observations of nonlinear plasma waves detected by interplanetary spacecraft. For this paper we will focus primarily on the phase-steepened properties of such waves. Plasma waves at comet Giacobini-Zinner measured by the International Cometary Explorer (ICE), at comets Halley and Grigg-Skjellerup measured by Giotto, and interplanetary Alfven waves measured by Ulysses, will be discussed and intercompared.
Dissipation of Alfven waves in compressible inhomogeneous media
Energy Technology Data Exchange (ETDEWEB)
Lepidi, S. [Istituto Nazionale di Geofisica, Rome (Italy); Villante, U. [L`Aquila Univ. (Italy). Dipt. di Fisica; Lazarus, A.J. [MIT Centre for Space Research, Cambridge, MA (United States)
1997-11-01
We examine 33 bow shock crossings by IMP8 and compare different methods to calculate the bow shock normal direction and speed using single spacecraft measurements. We find that the mixed equation by Abraham-Shrauner combined with the mass flux conservation equation and the minimum-variance technique applied to a limited set of the Rankine-Hugoniot conservation equations give very similar results that are in good agreement with theoretical predictions. The solutions obtained by the velocity co planarity theorem are reliable only for nearly perpendicular shocks, while poor results are obtained for such cases from the magnetic co planarity theorem. We also suggest that in some cases the time resolution of plasma measurements (about 60 s) may be too low to resolve the density behaviour close to the bow shock and to allow definite evaluation of the shock parameters.
Covert, Michael
2015-01-01
This book is intended for software developers, system architects and analysts, big data project managers, and data scientists who wish to deploy big data solutions using the Cascading framework. You must have a basic understanding of the big data paradigm and should be familiar with Java development techniques.
Excitation of global Alfven Eigenmodes by RF heating in JET
Energy Technology Data Exchange (ETDEWEB)
Kerner, W; Borba, D; Gormezano, C; Huysmans, G; Porcelli, F; Start, D [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Fasoli, A [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP); Sharapov, S [Kurchatov Institute, Moscow (Russian Federation)
1994-07-01
The alpha-particle confinement of future D-T experiments at JET can be severely degraded by Global Alfven Eigenmodes (AE). Scenarios for the excitation of Alfven Eigenmodes in usual (e.g. D-D) plasmas are proposed, which provide a MHD diagnostic and allow the study of the transport of super-Alfvenic ions. Active studies with separate control of TAE amplitude and energetic particle destabilization, measuring the plasma response, give more information than passive studies, in particular concerning the damping mechanisms. The TAE excitation can be achieved by means of the saddle coil and the ICRH antenna. The experimental method is introduced together with a theoretical model for RF excitation. (authors). 6 refs., 3 figs.
Drift-kinetic Alfven modes in high performance tokamaks
International Nuclear Information System (INIS)
Jaun, A.; Fasoli, A.F.; Testa, D.; Vaclavik, J.; Villard, L.
2001-01-01
The stability of fast-particle driven Alfven eigenmodes is modeled in high performance tokamaks, successively with a conventional shear, an optimized shear and a tight aspect ratio plasma. A large bulk pressure yields global kinetic Alfven eigenmodes that are stabilized by mode conversion in the presence of a divertor. This suggests how conventional reactor scenarii could withstand significant pressure gradients from the fusion products. A large safety factor in the core q 0 >2.5 in deeply shear reversed configurations and a relatively large bulk ion Larmor radius in a low magnetic field can trigger global drift-kinetic Alfven eigenmodes that are unstable in high performance JET, NSTX and ITER plasmas. (author)
Energy Technology Data Exchange (ETDEWEB)
Cuperman, S. [School of Physics and Astronomy, Tel Aviv University, 69978 Tel-Aviv (Israel); Bruma, C. [School of Physics and Astronomy, Tel Aviv University, 69978 Tel-Aviv (Israel) and College of Judea and Samaria, 44837 Ariel (Israel)]. E-mail: edycb@post.tau.ac.il; Komoshvili, K. [School of Physics and Astronomy, Tel Aviv University, 69978 Tel-Aviv (Israel); College of Judea and Samaria, 44837 Ariel (Israel)
2007-03-05
The combined plasma non-uniformity effects on the energy deposition of Alfven waves launched by an external antenna in pre-heated spherical tokamaks are investigated. The following relevant physical processes are here possible: (a) the emergence of gaps in the shear Alfven continuum spectrum and the generation of discrete global Alfven eigenmodes with frequencies inside the gaps; (b) multi-wave interactions, interactions of gaps of the same kind (e.g., toroidicity induced) and of different kinds (toroidicity, ellipticity and triangularity induced) as well as of secondary order gaps arising when a pair of modes is coupled to one or more modes through other coupling parameters; (c) basic wave-plasma interactions as propagation, reflection, mode-conversion, tunneling and deposition. Thus, we solved numerically the full 2D wave equations for the vector and scalar potentials, using a quite general two-fluid resistive tensor-operator, without any geometrical limitations. The results obtained indicate the existence of antenna-launched wave characteristics for which the power is most efficiently coupled in outer regions of plasmas, which is of special interest for low aspect ratio tokamaks, e.g., for the generation of non-inductive current drive as well as for turbulence suppression and transport barriers formation.
Impulsive Alfven coupling between the magnetosphere and ionosphere
International Nuclear Information System (INIS)
Reddy, R.V.; Watanabe, K.; Sato, T.; Watanabe, T.H.
1994-04-01
Basic properties of the impulsive Alfven interaction between the magnetosphere and ionosphere have been studied by means of a three-dimensional self-consistent simulation of the coupled magnetosphere and ionosphere system. It is found that the duration time of an impulsive perturbation at the magnetospheric equator, the latitudinal distribution of the Alfven propagation time along the field lines, and the ratio between the magnetospheric impedance and the ionospheric resistance is the main key factors that determine the propagation dynamics and the ionospheric responses for an impulsive MHD perturbation in the magnetosphere. (author)
KINETIC THEORY OF PLASMA WAVES: Part II: Homogeneous Plasma
Westerhof, E.
2010-01-01
The theory of electromagnetic waves in a homogeneous plasma is reviewed. The linear response of the plasma to the waves is obtained in the form of the dielectric tensor. Waves ranging from the low frequency Alfven to the high frequency electron cyclotron waves are discussed in the limit of the cold
Kinetic theory of plasma waves: Part II homogeneous plasma
Westerhof, E.
2000-01-01
The theory of electromagnetic waves in a homogeneous plasma is reviewed. The linear response of the plasma to the waves is obtained in the form of the dielectric tensor. Waves ranging from the low frequency Alfven to the high frequency electron cyclotron waves are discussed in the limit of the cold
Kinetic theory of plasma waves - Part II: Homogeneous plasma
Westerhof, E.
2008-01-01
The theory of electromagnetic waves in a homogeneous plasma is reviewed. The linear response of the plasma to the waves is obtained in the form of the dielectric tensor. Waves ranging from the low frequency Alfven to the high frequency electron cyclotron waves axe discussed in the limit of the cold
International Nuclear Information System (INIS)
Goree, J.; Ono, M.; Colestock, P.; Horton, R.; McNeill, D.; Park, H.
1985-07-01
Fast wave current drive is demonstrated in the Princeton ACT-I toroidal device. The fast Alfven wave, in the range of high ion-cyclotron harmonics, produced 40 A of current from 1 kW of rf power coupled into the plasma by fast wave loop antenna. This wave excites a steady current by damping on the energetic tail of the electron distribution function in the same way as lower-hybrid current drive, except that fast wave current drive is appropriate for higher plasma densities
Mode structure and continuum damping of high-n toroidal Alfven eigenmodes
International Nuclear Information System (INIS)
Rosenbluth, M.N.; Berk, H.L.; Van Dam, J.W.; Lindberg, D.M.
1992-02-01
An asymptotic theory is described for calculating the mode structure and continuum damping of short wave-length toroidal Alfven eigenmodes (TAE). The formalism somewhat resembles the treatment used for describing low-frequency toroidal modes with singular structure at a rational surface, where an inner solution, which for the TAE mode has toroidal coupling, is matched to an outer toroidally uncoupled solution. A three-term recursion relation among coupled poloidal harmonic amplitudes is obtained, whose solution gives the structure of the global wavefunction and the complex eigenfrequency, including continuum damping. Both analytic and numerical solutions are presented. The magnitude of the damping is essential for determining the thresholds for instability driven by the spatial gradients of energetic particles (e.g., neutral beam-injected ions or fusion-product alpha particles) contained in a tokamak plasma
Symmetries of the triple degenerate DNLS equations for weakly nonlinear dispersive MHD waves
International Nuclear Information System (INIS)
Webb, G. M.; Brio, M.; Zank, G. P.
1996-01-01
A formulation of Hamiltonian and Lagrangian variational principles, Lie point symmetries and conservation laws for the triple degenerate DNLS equations describing the propagation of weakly nonlinear dispersive MHD waves along the ambient magnetic field, in β∼1 plasmas is given. The equations describe the interaction of the Alfven and magnetoacoustic modes near the triple umbilic point, where the fast magnetosonic, slow magnetosonic and Alfven speeds coincide and a g 2 =V A 2 where a g is the gas sound speed and V A is the Alfven speed. A discussion is given of the travelling wave similarity solutions of the equations, which include solitary wave and periodic traveling waves. Strongly compressible solutions indicate the necessity for the insertion of shocks in the flow, whereas weakly compressible, near Alfvenic solutions resemble similar, shock free travelling wave solutions of the DNLS equation
Fan, Xiang
2017-10-01
Concerns central to understanding turbulence and transport include: 1) Dynamics of dual cascades in EM turbulence; 2) Understanding `negative viscosity phenomena' in drift-ZF systems; 3) The physics of blobby turbulence (re: SOL). Here, we present a study of a simple model - that of Cahn-Hilliard Navier-Stokes (CHNS) Turbulence - which sheds important new light on these issues. The CHNS equations describe the motion of binary fluid undergoing a second order phase transition and separation called spinodal decomposition. The CHNS system and 2D MHD are analogous, as they both contain a vorticity equation and a ``diffusion'' equation. The CHNS system differs from 2D MHD by the appearance of negative diffusivity, and a nonlinear dissipative flux. An analogue of the Alfven wave exists in the 2D CHNS system. DNS shows that mean square concentration spectrum Hkψ scales as k - 7 / 3 in the elastic range. This suggests an inverse cascade of Hψ . However, the kinetic energy spectrum EkK scales as k-3 , as in the direct enstrophy cascade range for a 2D fluid (not MHD!). The resolution is that the feedback of capillarity acts only at blob interfaces. Thus, as blob merger progresses, the packing fraction of interfaces decreases, thus explaining the weakened surface tension feedback and the outcome for EkK. We also examine the evolution of scalar concentration in a single eddy in the Cahn-Hilliard system. This extends the classic problem of flux expulsion in 2D MHD. The simulation results show that a target pattern is formed. Target pattern is a meta stable state, since the band merger process continues on a time scale exponentially long relative to the eddy turnover time. Band merger resembles step merger in drift-ZF staircases. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, under Award Number DE-FG02-04ER54738.
International Nuclear Information System (INIS)
Kuperus, M.; Heyvaerts, J.
1980-01-01
The MHD oscillations of the Alfven type running along surfaces of discontinuity generate motions in the discontinuity region which come rapidly out of phase. It is shown how the mathematical theory of this phase detuning predicts that surface wave should suffer dissipationless damping. Real damping is actually achieved by viscosity or kinetic effects. When detuning has grown to a large enough level, however, oscillations must be described by kinetic theory. Kinetic Alfven waves differ from perfect MHD Alfven waves in that they are able to propagate across the field. A theory of kinetic type oscillations in a finite thickness boundary is described, which predicts that surface waves generate intense kinetic Alfven waves in this boundary. The subsequent dissipation of these waves may be a powerful heating mechanism [fr
Characterization of Alfvenic fluctuations in the magnetopause boundary layer
International Nuclear Information System (INIS)
Rezeau, L.; Morane, A.; Perraut, S.; Roux, A.; Schmidt, R.
1989-01-01
The European Space Agency GEOS 2 spacecraft happened to cross the magnetopause several times, at various local times. Intense electric and magnetic fluctuations, in the ultralow-frequency (ULF) range (0-10 Hz) have been detected during each such crossing, with a peak at the magnetopause and still large amplitudes in the adjacent magnetosheath and magnetopause boundary layer. By applying spectral analysis and correlations to the electric and magnetic fluctuations, and a minimum variance analysis to the magnetic fluctuations, the authors investigate the nature of these fluctuations which appear as short-lasting bursts in the spacecraft frame. Having reviewed possible interpretations, they show that the observed electric and magnetic signatures are consistent with small-scale (L ∼ ion Larmor radius) Alfvenic field-aligned structures passing by the spacecraft at high speed. It is suggested that these structures correspond to nonlinear Alfvenic structures
Alfven Eigenmode Stability with Beams in ITER-like Plasma
International Nuclear Information System (INIS)
Gorelenkov, N.N.; Berk, H.L.; Budny, R.V.
2004-01-01
Toroidicity Alfven Eigenmodes (TAE) in ITER can be driven unstable by two groups of energetic particles, the 3.5 MeV α-particle fusion products and the tangentially injected 1MeV beam ions. Stability conditions are established using the perturbative NOVA/NOVA-K codes. A quasi-linear diffusion model is then used to assess the induced redistribution of energetic particles
The effect of compressibility on the Alfven spatial resonance heating
International Nuclear Information System (INIS)
Azevedo, C.A.
1984-01-01
The effect of compressibility of magnetic field line on the damping rate of Alfven spatial resonance heating for a high beta plasma (Kinetic pressure/magnetic pressure) was analysed, using the ideal MHD (Magnetohydrodynamic) model in cylindrical geometry for a diffuse θ-pinch with conducting wall. The dispersion relation was obtained solving the equation of motion in the plasma and vacuum regions together with boundary conditions. (Author) [pt
Non-linear modulation of short wavelength compressional Alfven eigenmodes
Energy Technology Data Exchange (ETDEWEB)
Fredrickson, E. D.; Gorelenkov, N. N.; Podesta, M.; Gerhardt, S. P.; Bell, R. E.; Diallo, A.; LeBlanc, B. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Bortolon, A. [University of California, Irvine, California 92697 (United States); Crocker, N. A. [University of California, Los Angeles, California 90095 (United States); Levinton, F. M.; Yuh, H. [Nova Photonics, Princeton, New Jersey 08543 (United States)
2013-04-15
Most Alfvenic activity in the frequency range between toroidal Alfven eigenmodes and roughly one half of the ion cyclotron frequency on National Spherical Torus eXperiment [Ono et al., Nucl. Fusion 40, 557 (2000)], that is, approximately 0.3 MHz up to Almost-Equal-To 1.2 MHz, are modes propagating counter to the neutral beam ions. These have been modeled as Compressional and Global Alfven Eigenmodes (CAE and GAE) and are excited through a Doppler-shifted cyclotron resonance with the beam ions. There is also a class of co-propagating modes at higher frequency than the counter-propagating CAE and GAE. These modes have been identified as CAE, and are seen mostly in the company of a low frequency, n = 1 kink-like mode. In this paper, we present measurements of the spectrum of these high frequency CAE (hfCAE) and their mode structure. We compare those measurements to a simple model of CAE and present a predator-prey type model of the curious non-linear coupling of the hfCAE and the low frequency kink-like mode.
Wang, Ge; Berk, H. L.
2011-10-01
The frequency chirping signal arising from spontaneous a toroidial Alfven eigenmode (TAE) excited by energetic particles is studied for both numerical and analytic models. The time-dependent numerical model is based on the 1D Vlasov equation. We use a sophisticated tracking method to lock onto the resonant structure to enable the chirping frequency to be nearly constant in the calculation frame. The accuracy of the adiabatic approximation is tested during the simulation which justifies the appropriateness of our analytic model. The analytic model uses the adiabatic approximation which allows us to solve the wave evolution equation in frequency space. Then, the resonant interactions between energetic particles and TAE yield predictions for the chirping rate, wave frequency and amplitudes vs. time. Here, an adiabatic invariant J is defined on the separatrix of a chirping mode to determine the region of confinement of the wave trapped distribution function. We examine the asymptotic behavior of the chirping signal for its long time evolution and find agreement in essential features with the results of the simulation. Work supported by Department of Energy contract DE-FC02-08ER54988.
Energy Technology Data Exchange (ETDEWEB)
Nazarenko, Sergey [Warwick Univ., Coventry (United Kingdom). Mathematics Inst.
2011-07-01
Wave Turbulence refers to the statistical theory of weakly nonlinear dispersive waves. There is a wide and growing spectrum of physical applications, ranging from sea waves, to plasma waves, to superfluid turbulence, to nonlinear optics and Bose-Einstein condensates. Beyond the fundamentals the book thus also covers new developments such as the interaction of random waves with coherent structures (vortices, solitons, wave breaks), inverse cascades leading to condensation and the transitions between weak and strong turbulence, turbulence intermittency as well as finite system size effects, such as ''frozen'' turbulence, discrete wave resonances and avalanche-type energy cascades. This book is an outgrow of several lectures courses held by the author and, as a result, written and structured rather as a graduate text than a monograph, with many exercises and solutions offered along the way. The present compact description primarily addresses students and non-specialist researchers wishing to enter and work in this field. (orig.)
Bursting behaviours in cascaded stimulated Brillouin scattering
International Nuclear Information System (INIS)
Liu Zhan-Jun; He Xian-Tu; Zheng Chun-Yang; Wang Yu-Gang
2012-01-01
Stimulated Brillouin scattering is studied by numerically solving the Vlasov—Maxwell system. A cascade of stimulated Brillouin scattering can occur when a linearly polarized laser pulse propagates in a plasma. It is found that a stimulated Brillouin scattering cascade can reduce the scattering and increase the transmission of light, as well as introduce a bursting behaviour in the evolution of the laser-plasma interaction. The bursting time in the reflectivity is found to be less than half the ion acoustic period. The ion temperature can affect the stimulated Brillouin scattering cascade, which can repeat several times at low ion temperatures and can be completely eliminated at high ion temperatures. For stimulated Brillouin scattering saturation, higher-harmonic generation and wave—wave interaction of the excited ion acoustic waves can restrict the amplitude of the latter. In addition, stimulated Brillouin scattering cascade can restrict the amplitude of the scattered light. (physics of gases, plasmas, and electric discharges)
International Nuclear Information System (INIS)
Breizman, B.N.; Sharapov, S.E.
1994-10-01
The structure of toroidicity-induced Alfven eigenmodes (TAE) and kinetic TAE (KTAE) with large mode numbers is analyzed and the linear power transfer from energetic particles to these modes is calculated in the low shear limit when each mode is localized near a single gap within an interval whose total width Δ out is much smaller than the radius r m of the mode location. Near its peak where most of the mode energy is concentrated, the mode has an inner scalelength Δ in , which is much smaller than Δ out . The scale Δ in is determined by toroidicity and kinetic effects, which eliminate the singularity of the potential at the resonant surface. This work examines the case when the drift orbit width of energetic particles Δ b is much larger than the inner scalelength Δ in , but arbitrary compared to the total width of the mode. It is shown that the particle-to-wave linear power transfer is comparable for the TAE and KTAE modes in this case. The ratio of the energetic particle contributions to the growth rates of the TAE and KTAE modes is then roughly equal to the inverse ratio of the mode energies. It is found that, in the low shear limit the growth rate of the KTAE modes can be larger than that for the TAE modes
Liu, Weimin; Zhu, Liangdong; Fang, Chong
2012-09-15
We demonstrate the simultaneous generation of multicolor femtosecond laser pulses spanning the wavelength range from UV to near IR in a 0.1 mm Type I beta-barium borate crystal from 800 nm fundamental and weak IR super-continuum white light (SCWL) pulses. The multicolor broadband laser pulses observed are attributed to two concomitant cascaded four-wave mixing (CFWM) processes as corroborated by calculation: (1) directly from the two incident laser pulses; (2) by the sum-frequency generation (SFG) induced CFWM process (SFGFWM). The latter signal arises from the interaction between the frequency-doubled fundamental pulse (400 nm) and the SFG pulse generated in between the fundamental and IR-SCWL pulses. The versatility and simplicity of this spatially dispersed multicolor self-compressed laser pulse generation offer compact and attractive methods to conduct femtosecond stimulated Raman spectroscopy and time-resolved multicolor spectroscopy.
Peculiarities of destabilization of Alfven modes by energetic ions in stellarators
International Nuclear Information System (INIS)
Lutsenko, V.V.; Kolesnichenko, Ya.I.; Yakovenko, Yu.V.; Fesenyuk, O.P.; Weller, A.; Werner, A.; Wobig, H.
2003-01-01
Alfven Eigenmodes (AE) associated with the breaking of the axial symmetry in stellarators are considered. Specific calculations are carried out for the Helias reactor HSR4/18. An explanation of the temporal evolution of Alfvenic activity observed in experiments on W7-AS is suggested. (author)
Destabilization of Alfven eigenmodes by fast particles in W7-AS
International Nuclear Information System (INIS)
Zegenhagen, S.
2006-02-01
In the present thesis, a systematic study of beam driven Alfven eigenmodes in high-density and low-temperature plasmas of the W7-AS stellarator is performed. The goal of this thesis is twofold: (I) identification and description of fast particle driven Alfven instabilities in W7-AS, and (II) study of energetic particle losses induced by Alfven instabilities. A total of 133 different Alfven eigenmodes is studied in discharges from different experimental campaigns. The discharges are characterized by high density, n e =5 x 1019 m -3 to 2.5 x 1020 m -3 at relatively low temperatures of T e =T i =150..600 eV. Additional 13 events are found to have frequencies inside the EAE gap and could possibly be EAEs. Evidence for high-frequency Alfven eigenmodes (mirror- and helicity-induced Alfven eigenmodes) is seen, but can not be proven rigorously due to uncertain mode numbers and the complexity of the Alfven continuum. The remaining 41 Alfven eigenmodes can not be classified to be one of the above cases. (orig.)
Destabilization of Alfven eigenmodes by fast particles in W7-AS
Energy Technology Data Exchange (ETDEWEB)
Zegenhagen, S.
2006-02-15
In the present thesis, a systematic study of beam driven Alfven eigenmodes in high-density and low-temperature plasmas of the W7-AS stellarator is performed. The goal of this thesis is twofold: (I) identification and description of fast particle driven Alfven instabilities in W7-AS, and (II) study of energetic particle losses induced by Alfven instabilities. A total of 133 different Alfven eigenmodes is studied in discharges from different experimental campaigns. The discharges are characterized by high density, n{sub e}=5 x 1019 m{sup -3} to 2.5 x 1020 m{sup -3} at relatively low temperatures of T{sub e}=T{sub i}=150..600 eV. Additional 13 events are found to have frequencies inside the EAE gap and could possibly be EAEs. Evidence for high-frequency Alfven eigenmodes (mirror- and helicity-induced Alfven eigenmodes) is seen, but can not be proven rigorously due to uncertain mode numbers and the complexity of the Alfven continuum. The remaining 41 Alfven eigenmodes can not be classified to be one of the above cases. (orig.)
Surface wave propagation in steady ideal Hall-magnetohydrodynamic magnetic slabs
International Nuclear Information System (INIS)
Miteva, Rossitsa; Zhelyazkov, Ivan; Erdelyi, Robert
2003-01-01
This paper studies the dispersion characteristics of sausage and kink surface waves traveling along a plasma layer within the framework of Hall magnetohydrodynamics in steady state. While in a static plasma slab these waves are Alfven ones (their phase velocities are close to the Alfven speed in the layer); in a slab with steady flows they may become super Alfvenic waves. Moreover, there exist two types of waves: forward and backward ones bearing in mind that the flow velocity defines the positive (forward) direction. As a typical representative of a magnetic slab in steady state here is considered a solar wind flux rope with a finite β plasma flow (typically β∼1).The forward sausage surface mode exhibits an increased dispersion at small wave numbers while the forward kink waves become practically non-dispersive. Both backward propagating sausage and kink surface modes show an increased dispersion for large wave numbers
Ofman, Leon; Ozak, Nataly; Vinas, Adolfo F.
2016-01-01
Near the Sun (plasma. The heating and the acceleration of the solar wind ions by turbulent wave spectrum in inhomogeneous plasma is studied using a 2.5D hybrid model. The hybrid model describes the kinetics of the ions, while the electrons are modeled as massless neutralizing fluid in an expanding box approach. Turbulent magnetic fluctuations dominated by power-law frequency spectra, which are evident from in-situ as well as remote sensing measurements, are used in our models. The effects of background density inhomogeneity across the magnetic field on the resonant ion heating are studied. The effect of super- Alfvenic ion drift on the ion heating is investigated. It is found that the turbulent wave spectrum of initially parallel propagating waves cascades to oblique modes, and leads to enhanced resonant ion heating due to the inhomogeneity. The acceleration of the solar wind ions is achieved by the parametric instability of large amplitude waves in the spectrum, and is also affected by the inhomogeneity. The results of the study provide the ion temperature anisotropy and drift velocity temporal evolution due to relaxation of the instability. The non-Maxwellian velocity distribution functions (VDFs) of the ions are modeled in the inhomogeneous solar wind plasma in the acceleration region close to the Sun.
Effect of alpha particles on Toroidal Alfven Eigenmodes
International Nuclear Information System (INIS)
Berk, H.L.
1992-11-01
An overview is given of the analytic structure for the linear theory of the Toroidal Alfven Eigenmode (TAE), where multiple gap structures occur. A discussion is given of the alpha particle drive and the various dissipation mechanisms that can stabilize the system. A self-consistent calculation of the TAE mode, for a low-beta high-aspect-ratio plasma, indicates that though the alpha particle drive is comparable to the dissipation mechanisms, overall stability is still achieved for ignited ITER-like plasma. A brief discussion is given of the nonlinear theory for the TAE mode and how nonlinear alpha particle dynamics can be treated by mapping methods
Parallel inhomogeneity and the Alfven resonance. 1: Open field lines
Hansen, P. J.; Harrold, B. G.
1994-01-01
In light of a recent demonstration of the general nonexistence of a singularity at the Alfven resonance in cold, ideal, linearized magnetohydrodynamics, we examine the effect of a small density gradient parallel to uniform, open ambient magnetic field lines. To lowest order, energy deposition is quantitatively unaffected but occurs continuously over a thickened layer. This effect is illustrated in a numerical analysis of a plasma sheet boundary layer model with perfectly absorbing boundary conditions. Consequences of the results are discussed, both for the open field line approximation and for the ensuing closed field line analysis.
Existence of core localized toroidicity-induced Alfven eigenmode
International Nuclear Information System (INIS)
Fu, G.Y.
1995-02-01
The core-localized toroidicity-induced Alfven eigenmode (TAE) is shown to exist at finite plasma pressure due to finite aspect ratio effects in tokamak plasma. The new critical beta for the existence of the TAE mode is given by α∼ 3ε + 2s 2 , where ε = r/R is the inverse aspect ratio, s is the magnetic shear and α = -Rq 2 dβ/dr is the normalized pressure gradient. In contrast, previous critical α is given by α ∼ s 2 . In the limit of s << √r/R, the new critical α is greatly enhanced by the finite aspect ratio effects
On the stability of shear-Alfven vortices
International Nuclear Information System (INIS)
Jovanovic, D.; Horton, W.
1993-08-01
Linear stability of shear-Alfven vortices is studied analytically using the Lyapunov method. Instability is demonstrated for vortices belonging to the drift mode, which is a generalization of the standard Hasegawa-Mima vortex to the case of large parallel phase velocities. In the case of the convective-cell mode, short perpendicular-wavelength perturbations are stable for a broad class of vortices. Eventually, instability of convective-cell vortices may occur on the perpendicular scale comparable with the vortex size, but it is followed by a simultaneous excitation of coherent structures with better localization than the original vortex
Geometrical and profile effects on toroidicity and ellipticity induced Alfven eigenmodes
International Nuclear Information System (INIS)
Villard, L.; Fu, G.Y.
1992-04-01
The wave structures, eigenfrequencies and damping rates of toroidicity and ellipticity induced Alfven eigenmodes (TAE, EAE) of low toroidal mode numbers (n) are calculated in various axisymmetric ideal MHD equilibria with the global wave finite element code LION. The importance of safety factor (q) and density (ρ) profiles on continuum damping rates is analysed. For realistic profiles several continuum gaps exist in the plasma discharge. Frequency misalignment of these gaps yields continuum damping rates γ/ω of the order of a few percent. Finite β pol lowers the TAE eigenfrequency. For β values below the Troyon limit the TAE enters the continuum and can thus be stabilized. Finite elongation allows the EAE to exist but triangularity can have a stabilizing effect through coupling to the continuum. The localization of TAE and EAE eigenfunctions is found to increase with the shear and with n. Therefore large shear, through enhanced Landau and collisional damping, is a stabilizing factor for TAE and EAE modes. (author) 16 figs., 28 refs
Excitation of beta Alfven eigenmodes in Tore-Supra
International Nuclear Information System (INIS)
Nguyen, C; Garbet, X; Sabot, R; Goniche, M; Maget, P; Basiuk, V; Decker, J; Elbeze, D; Huysmans, G T A; Macor, A; Segui, J-L; Schneider, M; Eriksson, L-G
2009-01-01
Modes oscillating at the acoustic frequency and identified as beta Alfven eigenmodes (BAEs) have been observed in Tore-Supra under ion cyclotron resonant heating. In this paper, the linear excitation threshold of these modes, thought to be driven by suprathermal ions, is calculated and compared with Tore-Supra observations. Similar studies of the linear excitation threshold of energetic particles driven modes were carried out previously for toroidal Alfven eigenmodes or fishbones. In the case of BAEs, the main point is to understand whether the energetic particle drive is able to exceed ion Landau damping, which is expected to be important in the acoustic frequency range. For this, the BAE dispersion relation is computed and simplified in order to derive a tractable excitation criterion suitable for comparison with experiments. The observation of BAEs in Tore-Supra is found to be in agreement with the calculated criterion and confirms the possibility to trigger these modes in the presence of ion Landau damping. Moreover, the conducted analysis clearly puts forward the role of the global tunable parameters which play a role in the BAE excitation (the magnetic field, the density etc), as well as the role of some plasma profiles. In particular, the outcome of a modification of the shear or of the heating localization is found to be non-negligible and it is discussed in the paper.
Waves and discontinuities in relativistic and anisotropic magnetohydrodynamics
International Nuclear Information System (INIS)
Cissoko, Mahdy
1975-01-01
This work is devoted to the relativistic study of a non-dissipative anisotropic fluid diagram of infinite conductivity. Such a fluid diagram is constructed in part one. Starting from a macroscopic viewpoint a hydrothermodynamic study of the fluid diagram considered is carried out and the fundamental differential system of anisotropic magnetohydrodynamics is deduced. Part two concerns the study of characteristic varieties and propagation of waves for a polytropic anisotropic fluid diagram. Three types of characteristic varieties are revealed: entropy waves (or material waves), magnetosonic waves and Alfven waves. The propagation rates of Alfven and magnetosonic waves are situated with respect to each other. The study of wave cones showed up on the one hand certain special features of wave propagation in anisotropic magnetohydrodynamics and on the other hand the hyperbolic nature of differential operators associated with the various waves [fr
Cascade annealing: an overview
International Nuclear Information System (INIS)
Doran, D.G.; Schiffgens, J.O.
1976-04-01
Concepts and an overview of radiation displacement damage modeling and annealing kinetics are presented. Short-term annealing methodology is described and results of annealing simulations performed on damage cascades generated using the Marlowe and Cascade programs are included. Observations concerning the inconsistencies and inadequacies of current methods are presented along with simulation of high energy cascades and simulation of longer-term annealing
International Nuclear Information System (INIS)
Vurgaftman, I; Meyer, J R; Canedy, C L; Kim, C S; Bewley, W W; Merritt, C D; Abell, J; Weih, R; Kamp, M; Kim, M; Höfling, S
2015-01-01
We review the current status of interband cascade lasers (ICLs) emitting in the midwave infrared (IR). The ICL may be considered the hybrid of a conventional diode laser that generates photons via electron–hole recombination, and an intersubband-based quantum cascade laser (QCL) that stacks multiple stages for enhanced current efficiency. Following a brief historical overview, we discuss theoretical aspects of the active region and core designs, growth by molecular beam epitaxy, and the processing of broad-area, narrow-ridge, and distributed feedback (DFB) devices. We then review the experimental performance of pulsed broad area ICLs, as well as the continuous-wave (cw) characteristics of narrow ridges having good beam quality and DFBs producing output in a single spectral mode. Because the threshold drive powers are far lower than those of QCLs throughout the λ = 3–6 µm spectral band, ICLs are increasingly viewed as the laser of choice for mid-IR laser spectroscopy applications that do not require high output power but need to be hand-portable and/or battery operated. Demonstrated ICL performance characteristics to date include threshold current densities as low as 106 A cm −2 at room temperature (RT), cw threshold drive powers as low as 29 mW at RT, maximum cw operating temperatures as high as 118 °C, maximum cw output powers exceeding 400 mW at RT, maximum cw wallplug efficiencies as high as 18% at RT, maximum cw single-mode output powers as high as 55 mW at RT, and single-mode output at λ = 5.2 µm with a cw drive power of only 138 mW at RT. (topical review)
A new formulation of theta pinch implosions - a collisionless wave model
International Nuclear Information System (INIS)
Tsui, K.H.
Previous work in theta pinch implosions is characterized by anomalous resistivity owing its origin to plasma instabilities. A diametrically opposite collisionless model is proposed here that consists of an inhomogeneous wave equation. The electron velocities are solved by guiding center approximation. This model offers qualitative explanations to various effects like experimental Alfven scaling law, Alfven penetration time, sheath thickness, shock formation, shock width, piston thickness, Alfven Mach number. Although collision is not essential, the plasma has an apparent resistivity with an effective collision frequency of roughly the same as those anomalous ones used in turbulent model. (Author) [pt
DEFF Research Database (Denmark)
Ibsen, Lars Bo
2008-01-01
Estimates for the amount of potential wave energy in the world range from 1-10 TW. The World Energy Council estimates that a potential 2TW of energy is available from the world’s oceans, which is the equivalent of twice the world’s electricity production. Whilst the recoverable resource is many...... times smaller it remains very high. For example, whilst there is enough potential wave power off the UK to supply the electricity demands several times over, the economically recoverable resource for the UK is estimated at 25% of current demand; a lot less, but a very substantial amount nonetheless....
Atom localization with double-cascade configuration
International Nuclear Information System (INIS)
Gordeev, Maksim Yu; Rozhdestvensky, Yuri V; Efremova, Ekaterina A
2016-01-01
We investigate the one-dimensional (1D) and two-dimensional (2D) atom localization of a four-level system in a double-cascade configuration. We demonstrate the possibility of 1D localization in the field of a standing wave, 2D localization in the field of two standing waves and 2D localization only in the field of running waves by using different configurations of driven waves on transitions. In addition, for each configuration we reached a high-precision atom localization in one of the states at scales much smaller than the wavelength of the incident optical radiation. (paper)
Strongly nonlinear evolution of low-frequency wave packets in a dispersive plasma
Vasquez, Bernard J.
1993-01-01
The evolution of strongly nonlinear, strongly modulated wave packets is investigated in a dispersive plasma using a hybrid numerical code. These wave packets have amplitudes exceeding the strength of the external magnetic field, along which they propagate. Alfven (left helicity) wave packets show strong steepening for p Schrodinger (DNLS) equation.
Fokker-Planck simulation study of Alfven eigenmode burst
International Nuclear Information System (INIS)
Todo, Y.; Watanabe, T.; Park, Hyoung-Bin; Sato, T.
2001-01-01
Recurrent bursts of toroidicity-induced Alfven eigenmodes (TAEs) are reproduced with a Fokker-Planck-magnetohydrodynamic simulation where a fast-ion source and slowing down are incorporated self-consistently. The bursts take place at regular time intervals and the behaviors of all the TAEs are synchronized. The fast-ion transport due to TAE activity spatially broadens the classical fast-ion distribution and significantly reduces its peak value. Only a small change of the distribution takes place with each burst, leading to loss of a small fraction of the fast ions. The system stays close to the marginal stability state established through the interplay of the fast-ion source, slowing down, and TAE activity. (author)
Recent progress of nonlinear simulation on the toroidal Alfven eigenmode
International Nuclear Information System (INIS)
Todo, Yasushi; Sato, Tetsuya
1998-01-01
Linear and nonlinear particle-magnetohydrodynamic (MHD) simulation codes are developed to study interactions between energetic ions and MHD modes. Energetic alpha particles with a slowing-down distribution are considered and the behavior of n=2 toroidal Alfven eigenmodes (TAE modes) is investigated with the parameters pertinent to the present large tokamaks. The linear simulation reveals the resonance condition between alpha particles and TAE mode. In the nonlinear simulation two n=2 TAE modes are destabilized and alpha particle losses induced by these TAE modes take place. Counter-passing particles are lost when they cross the passing-trapped boundary as a result of the interaction with the TAE modes. They are the major part of lost particles, but trapped particles are also lost appreciably. (author)
Combined Ideal and Kinetic Effects on Reversed Shear Alfven Eigenmodes
International Nuclear Information System (INIS)
Gorelenkov, N.N.; Kramer, G.J.; Nazikian, R.
2011-01-01
A theory of Reversed Shear Alfven Eigenmodes (RSAEs) is developed for reversed magnetic field shear plasmas when the safety factor minimum, qmin, is at or above a rational value. The modes we study are known sometimes as either the bottom of the frequency sweep or the down sweeping RSAEs. We show that the ideal MHD theory is not compatible with the eigenmode solution in the reversed shear plasma with qmin above integer values. Corrected by special analytic FLR condition MHD dispersion of these modes nevertheless can be developed. Large radial scale part of the analytic RSAE solution can be obtained from ideal MHD and expressed in terms of the Legendre functions. The kinetic equation with FLR effects for the eigenmode is solved numerically and agrees with the analytic solutions. Properties of RSAEs and their potential implications for plasma diagnostics are discussed.
Reversed shear Alfven eigenmode stabilization by localized electron cyclotron heating
Energy Technology Data Exchange (ETDEWEB)
Van Zeeland, M A; Hyatt, A W; Lohr, J; Petty, C C [General Atomics, PO Box 85608 San Diego, CA 92186-5608 (United States); Heidbrink, W W [University of California-Irvine, Irvine, CA 92697 (United States); Nazikian, R; Solomon, W M; Gorelenkov, N N; Kramer, G J [Princeton Plasma Physics Laboratory, Princeton, NJ 08543-0451 (United States); Austin, M E [University of Texas-Austin, Austin, TX 78712 (United States); Berk, H L [Institute for Fusion Studies, University of Texas at Austin, Austin, TX 78712 (United States); Holcomb, C T; Makowski, M A [Lawrence Livermore National Laboratory, Livermore, CA (United States); McKee, G R [University of Wisconsin-Madison, Madison, WI 53726 (United States); Sharapov, S E [Euratom/UKAEA Fusion Association, Culham, Abingdon, Oxfordshire, OX14 3DB (United Kingdom); Rhodes, T L [University of California-Los Angeles, Los Angeles, California, 90095 (United States)], E-mail: vanzeeland@fusion.gat.com
2008-03-15
Reversed shear Alfven eigenmode (RSAE) activity in DIII-D is stabilized by electron cyclotron heating (ECH) applied near the minimum of the magnetic safety factor (q{sub min}) in neutral beam heated discharges with reversed-magnetic shear. The degree of RSAE stabilization, fast ion density and the volume averaged neutron production (S{sub n}) are highly dependent on ECH deposition location relative to q{sub min}. While discharges with ECH stabilization of RSAEs have higher S{sub n} and more peaked fast ion profiles than discharges with significant RSAE activity, neutron production remains strongly reduced (up to 60% relative to TRANSP predictions assuming classical fast ion transport) even when RSAEs are stabilized.
Combined ideal and kinetic effects on reversed shear Alfven eigenmodes
International Nuclear Information System (INIS)
Gorelenkov, N. N.; Kramer, G. J.; Nazikian, R.
2011-01-01
A reversed shear Alfven eigenmodes (RSAEs) theory has been developed for reversed magnetic field shear plasmas when the safety factor minimum, q min , is at or above a rational value. The modes we study are known sometimes as either the bottom of the frequency sweep or the down sweeping RSAEs. We show that, strictly speaking, the ideal MHD theory is not compatible with the eigenmode solution in the reversed shear plasma with q min above integer values. Corrected by a special analytic finite Larmor radius (FLR) condition, MHD dispersion of these modes nevertheless can be developed. Numerically, MHD structure can serve as a good approximation for the RSAEs.The large radial scale part of the analytic RSAE solution can be obtained from ideal MHD and expressed in terms of the Legendre functions. The kinetic equation with FLR effects for the eigenmode is solved numerically and agrees with the analytic solutions. Properties of RSAEs and their potential implications for plasma diagnostics are discussed.
High-n helicity-induced shear Alfven eigenmodes
International Nuclear Information System (INIS)
Nakajima, N.; Cheng, C.Z.; Okamoto, M.
1992-05-01
The high-n Helicity-induced shear Alfven Eigenmodes (HAE) are considered both analytically and numerically for the straight helical magnetic system, where n is the toroidal mode number. The eigenmode equation for the high-n HAE modes is derived along the field line and with the aid of the averaging method is shown to reduce to the Mathieu equation asymptotically. The discrete HAE modes are shown to exist inside the continuum spectrum gaps. The continuous spectrum gaps appear around ω 2 = ω A 2 [N(lι-m)/2] 2 for N = 1,2,.., where ω A is the toroidal Alfven transit frequency, and l, m, and ι are the polarity of helical coils, the toroidal pitch number of helical coils, and the rotational transform, respectively. For the same ω A and ι, the frequency of the helical continuum gap is larger than that of the continuum gap in tokamak plasmas by |l-ι -1 m|. The polarity of helical coils l plays a crucial role in determining the spectrum gaps and the properties of the high-n HAE modes. The spectrum gaps near the magnetic axis are created by the helical ripple with circular flux surfaces for l = 1, and ≥ 3 helicals. For l = 2 helical systems, the spectrum gaps are created by the ellipticity of the flux surfaces. These analytical results for the continuum gaps and the existence of the high-n HAE modes in the continuum gaps are confirmed numerically for the l = 2 case, and we find that the HAE modes exist for mode structures with the even and the odd parities. (author)
Alfven. Symphony No 5 in A minor, Op. 54 / Robert Layton
Layton, Robert
1994-01-01
Uuest heliplaadist "Alfven. Symphony No 5 in A minor, Op. 54. The Mountain King - Suite, Gustav II Adolf, Op. 49 - Elegy. Royal Stockholm Philarmonic Orchestra / Neeme Järvi. BIS CD 585 (68 minutes) Recorded in association with Trygg Hansa"
International Nuclear Information System (INIS)
Booker, H.G.
1984-01-01
The book aims to present current knowledge concerning the propagation of electromagnetic waves in a homogeneous magnetoplasma for which temperature effects are unimportant. It places roughly equal emphasis on the radio and the hydromagnetic parts of the electromagnetic spectrum. The dispersion properties of a magnetoplasma are treated as a function both of wave frequency (assumed real) and of ionization density. The effect of collisions is included only in so far as this can be done with simplicity. The book describes how pulses are radiated from both small and large antennas embedded in a homogeneous magnetoplasma. The power density radiated from a type of dipole antenna is studied as a function of direction of radiation in all bands of wave frequency. Input reactance is not treated, but the dependence of radiation resistance on wave frequency is described for the entire electromagnetic spectrum. Also described is the relation between beaming and guidance for Alfven waves. (Auth.)
Simulation study of energetic ion transport due to Alfven eigenmodes in LHD plasma
International Nuclear Information System (INIS)
Todo, Yasushi; Nakajima, Noriyoshi; Osakabe, Masaki; Yamamoto, Satoshi; Spong, Donald A.
2008-01-01
The creation of holes and clumps in an energetic ion energy spectrum associated with Alfven eigenmodes was examined using the neutral particle analyzer (NPA) on the LHD shot no.47645. The difference in slowing-down times between the holes and clumps suggested that the energetic ions were transported over 10% of the plasma minor radius. The spatial profile and frequency of the Alfven eigenmodes were analyzed with the AE3D code. The phase space structures of the energetic ions on the NPA line-of-sight were investigated with Poincare plots, where an oscillating Alfven eigenmode was employed for earth plot. The phase space regions trapped by the Alfven eigenmodes appeared as islands in the Poincare plots. The radial width of the islands corresponded to the transport distance of the energetic ions. Since island width depends on Alfven eigenmode amplitude, it was found that Alfven eigenmodes with amplitude δB r /B - 10 -3 transported energetic ions over 10% of the minor radius. (author)
ENERGY CONTENT AND PROPAGATION IN TRANSVERSE SOLAR ATMOSPHERIC WAVES
Energy Technology Data Exchange (ETDEWEB)
Goossens, M.; Van Doorsselaere, T. [Centre for mathematical Plasma Astrophysics, Mathematics Department, Celestijnenlaan 200B bus 2400, B-3001 Heverlee (Belgium); Soler, R. [Solar Physics Group, Departament de Fisica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Verth, G., E-mail: tom.vandoorsselaere@wis.kuleuven.be [Solar Physics and Space Plasma Research Centre (SP2RC), School of Mathematics and Statistics, University of Sheffield, Hounsfield Road, Hicks Building, Sheffield S3 7RH (United Kingdom)
2013-05-10
Recently, a significant amount of transverse wave energy has been estimated propagating along solar atmospheric magnetic fields. However, these estimates have been made with the classic bulk Alfven wave model which assumes a homogeneous plasma. In this paper, the kinetic, magnetic, and total energy densities and the flux of energy are computed for transverse MHD waves in one-dimensional cylindrical flux tube models with a piecewise constant or continuous radial density profile. There are fundamental deviations from the properties for classic bulk Alfven waves. (1) There is no local equipartition between kinetic and magnetic energy. (2) The flux of energy and the velocity of energy transfer have, in addition to a component parallel to the magnetic field, components in the planes normal to the magnetic field. (3) The energy densities and the flux of energy vary spatially, contrary to the case of classic bulk Alfven waves. This last property has the important consequence that the energy flux computed with the well known expression for bulk Alfven waves could overestimate the real flux by a factor in the range 10-50, depending on the flux tube equilibrium properties.
Fast Particle Interaction With Waves In Fusion Plasmas
International Nuclear Information System (INIS)
Breizman, Boris
2006-01-01
There are two well-known motivations for theoretical studies of fast particle interaction with waves in magnetic confinement devices. One is the challenge of avoiding strong collective losses of alpha particles and beam ions in future burning plasma experiments. The other one is the compelling need to quantitatively interpret the large amount of experimental data from JET, TFTR, JT-60U, DIII-D, and other machines. Such interpretation involves unique diagnostic opportunities offered by MHD spectroscopy. This report discusses how the present theory responds to the stated challenges and what theoretical and computational advances are required to address the outstanding problems. More specifically, this paper deals with the following topics: predictive capabilities of linear theory and simulations; theory of Alfven cascades; diagnostic opportunities based on linear and nonlinear properties of unstable modes; interplay of kinetic and fluid nonlinearities; fast chirping phenomena for non-perturbative modes; and global transport of fast particles. Recent results are presented on some of the listed topics, although the main goal is to identify critical issues for future work
Institute of Scientific and Technical Information of China (English)
ZHOU Nan-run; GONG Li-hua; LIU Ye
2006-01-01
In this letter a cascade quantum teleportation scheme is proposed. The proposed scheme needs less local quantum operations than those of quantum multi-teleportation. A quantum teleportation scheme based on entanglement swapping is presented and compared with the cascade quantum teleportation scheme. Those two schemes can effectively teleport quantum information and extend the distance of quantum communication.
Mechanisms of cascade collapse
International Nuclear Information System (INIS)
Diaz de la Rubia, T.; Smalinskas, K.; Averback, R.S.; Robertson, I.M.; Hseih, H.; Benedek, R.
1988-12-01
The spontaneous collapse of energetic displacement cascades in metals into vacancy dislocation loops has been investigated by molecular dynamics (MD) computer simulation and transmission electron microscopy (TEM). Simulations of 5 keV recoil events in Cu and Ni provide the following scenario of cascade collapse: atoms are ejected from the central region of the cascade by replacement collision sequences; the central region subsequently melts; vacancies are driven to the center of the cascade during resolidification where they may collapse into loops. Whether or not collapse occurs depends critically on the melting temperature of the metal and the energy density and total energy in the cascade. Results of TEM are presented in support of this mechanism. 14 refs., 4 figs., 1 tab
Wave-trains in the solar wind. III
International Nuclear Information System (INIS)
Richter, A.K.
1975-01-01
Applying an Alfven-Wave-Extended-QRH-approximation and the method of characteristics, the equations of motion for outwardly propagating Alfven waves are solved analytically for three different cases of an azimuthal dependence of the background solar wind, (a) for a pure fast-slow stream configuration, (b) for the situation where the high-speed stream originates from a diverging magnetic field, and (c) for the case of (b) and an initially decreasing density configuration ('coronal hole'). The reaction of these waves on the background state as well as mode-mode coupling effects are neglected. These three solar wind models are discussed shortly. For the superimposed Alfven waves it is found, on an average, that there is a strong azimuthal dependence of all relevant parameters which, correlated with the azimuthal distributions of the solar wind variables, leads to good agreements with observations. The signature of high-speed streams and these correlations could clearly indicate solar wind streams originating from 'coronal holes'. Contrary to the purely radial solar wind, where outwardly propagating Alfven waves are exclusively refracted towards the radial direction, a refraction nearly perpendicular to the direction of the interplanetary magnetic field in the compression region and closely towards the magnetic field direction down the trailing edge and in the low-speed regime is found. (Auth.)
Four-dimensional integral equations for the MHD diffraction waves in plasma
International Nuclear Information System (INIS)
Alexandrova, A.A.; Khizhnyak, N.A.
2000-01-01
The superficial analysis of the boundary-value nonstationary problem for Alfven wave has shown the principal possibility of using the method of evolutionary integral equations of non-stationary macroscopic electrodynamical in a case of MHD description of waves in plasma. With the importance of strict mathematical solutions obtained for simple model problems that is the diffraction of one separately taken Alfven wave is that it can be the basis for construction of the approximate solutions of more complex boundary-value problems
Ion stochastic heating by obliquely propagating magnetosonic waves
International Nuclear Information System (INIS)
Gao Xinliang; Lu Quanming; Wu Mingyu; Wang Shui
2012-01-01
The ion motions in obliquely propagating Alfven waves with sufficiently large amplitudes have already been studied by Chen et al.[Phys. Plasmas 8, 4713 (2001)], and it was found that the ion motions are stochastic when the wave frequency is at a fraction of the ion gyro-frequency. In this paper, with test particle simulations, we investigate the ion motions in obliquely propagating magnetosonic waves and find that the ion motions also become stochastic when the amplitude of the magnetosonic waves is sufficiently large due to the resonance at sub-cyclotron frequencies. Similar to the Alfven wave, the increase of the propagating angle, wave frequency, and the number of the wave modes can lower the stochastic threshold of the ion motions. However, because the magnetosonic waves become more and more compressive with the increase of the propagating angle, the decrease of the stochastic threshold with the increase of the propagating angle is more obvious in the magnetosonic waves than that in the Alfven waves.
Finite orbit energetic particle linear response to toroidal Alfven eigenmodes
International Nuclear Information System (INIS)
Berk, H.L.; Ye Huanchun; Breizman, B.N.
1992-01-01
The linear response of energetic particles of the TAE modes is calculated taking into account their finite orbit excursion from the flux surfaces. The general expression reproduces the previously derived theory for small banana width; when the banana width Δ b is much larger than the mode thickness Δ m , we obtain a new compact expression for the linear power transfer. When Δ m /Δ b m /Δ b from that predicted by the narrow orbit theory. A comparison is made of the contribution to the TAE growth rate of energetic particles with a slowing-down distribution arising from an isotropic source, and a balanced-injected beam source when the source speed is close to the Alfven speed. For the same stored energy density, the contribution from the principal resonances (vertical strokev parallel vertical stroke=v A ) is substantially enhanced in the beam case compared to the isotropic case, while the contribution at the higher sidebands (vertical strokev parallel vertical stroke=v A /(2l-1) with l≥2) is substantially reduced. (orig.)
Experimental studies of Alfven modes stability on the JET tokamak
International Nuclear Information System (INIS)
Testa, D.; Fasoli, A.; Borba, D.N.
2002-01-01
The linear stability properties of Alfven modes are studied on JET using an active excitation technique. The Saddle Coils drive low amplitude, vertical bar δB/B vertical bar ∼ 10 -6 , stable plasma modes with toroidal mode number n=0 / 2. The diagnostic technique uses repetitive sweeps of the driving frequency in a pre-defined range, controlled in real-time. The plasma response is extracted from background noise using synchronous detection, and is used to identify in real-time the resonance corresponding to a global mode. When a resonance is found, the real-time controller locks to that frequency and tracks the mode. This provides a direct evaluation of the mode damping rate, γ/ω from the width of the frequency sweep. Two systems are used to measure fast fluctuation data. The KC1F system is a 8-channel, 1MHz/4s continuous digitizer used to analyze magnetic and reflectometry data in the frequency range 5≤f(kHz) ≤500. This system is particularly suitable to follow the time evolution of the instability. The CATS system collects and digitizes a large number of channels generally using short time snapshots. This system is useful to determine the position of the instability using the cross-correlation between the magnetic and other radially localized measurements, such as soft X-rays, reflectometry or electron cyclotron emission
Finite orbit energetic particle linear response to toroidal Alfven eigenmodes
International Nuclear Information System (INIS)
Berk, H.L.; Ye, Huanchun; Breizman, B.N.
1991-07-01
The linear response of energetic particles to the TAE modes is calculated taking into account their finite orbit excursion from the flux surfaces. The general expression reproduces the previously derived theory for small banana width: when the banana width triangle b is much larger than the mode thickness triangle m , we obtain a new compact expression for the linear power transfer. When triangle m /triangle b much-lt 1, the banana orbit effect reduces the power transfer by a factor of triangle m /triangle b from that predicted by the narrow orbit theory. A comparison is made of the contribution to the TAE growth rate of energetic particles with a slowing-down distribution arising from an isotropic source, and a balance-injected beam source when the source speed is close to the Alfven speed. For the same stored energy density, the contribution from the principal resonances (|υ parallel | = υ A is substantially enhanced in the beam case compared to the isotropic case, while the contribution at the higher sidebands (|υ parallel |) = υ A /(2 ell - 1) with ell ≥ 2) is substantially reduced. 10 refs
Shear-Alfven dynamics of toroidally confined plasmas. Part A
International Nuclear Information System (INIS)
Hazeltine, R.D.; Meiss, J.D.
1984-08-01
Recent developments in the stability theory of toroidally confined plasmas are reviewed, with the intention of providing a picture comprehensible to non-specialists. The review considers a class of low-frequency, electromagnetic disturbances that seem especially pertinent to modern high-temperature confinement experiments. It is shown that such disturbances are best unified and understood through consideration of a single, exact fluid moment: the shear-Alfven law. Appropriate versions of this law and its corresponding closure relations are derived - essentially from first principles - and applied in a variety of mostly, but not exclusively, linear contexts. Among the specific topics considered are: flux coordinates (including Hamada coordinates), the Newcomb solubility condition. Shafranov geometry, magnetic island evolution, reduced MHD and its generalizations, drift-kinetic electron response, classical tearing, twisting, and kink instabilities, pressure-modified tearing instability (Δ-critical), collisionless and semi-collisional tearing modes, the ballooning representation in general geometry, ideal ballooning instability, Mercier criterion, near-axis expansions, the second stability region, and resistive and kinetic ballooning modes. The fundamental importance of toroidal topology and curvature is stressed
Magnetospheric pulsations: Models and observations of compressional waves
International Nuclear Information System (INIS)
Zhu, Xiaoming.
1989-01-01
The first part of the dissertation models ultralow frequency (ULF) waves in a simplified geometry in order to understand the physics of the mode coupling between the compressional and shear Alfven waves in an inhomogeneous magnetized plasma. Wave mode coupling occurs when a field line resonant frequency (defined by the shear Alfven mode) matches the global mode frequency (defined by the compressional mode). Large wave amplitudes occur near the resonant field line. Although the wave amplitude of the global mode is small away from resonant field lines, significant wave energy is stored in the wave mode due to its large scale nature. It serves as a reservoir to continuously feed energy to resonant field lines. This mechanism may explain why some field line resonances can last for times longer than that predicted from the ionospheric Joule dissipation. A nonmonotonic Alfven velocity divides the magnetosphere into two or more cavities by the local maxima of the Alfven velocity. The global mode is typically localized in one of the cavities except at some preferred frequencies, the global mode can extend through more than one cavity. This may explain ULF wave excitations in the low latitude magnetosphere. The second part of the dissertation is devoted to study compressional waves in the outer magnetosphere using magnetic field and plasma data. Statistical information on the distribution of compressional Pc 5 waves in the outer magnetosphere is obtained. Large amplitude, long period compressional Pc 5 pulsations are found very common near the magnetic equator. They are polarized mainly in a meridian plane with comparable compressional and transverse amplitudes. Close correlation between compressional wave amplitude and plasma β is also found. Several case studies show that compressional waves are quenched in the region where β < 1
International Nuclear Information System (INIS)
San Martin, Jesus; Rodriguez-Perez, Daniel
2009-01-01
Presented in this work are some results relative to sequences found in the logistic equation bifurcation diagram, which is the unimodal quadratic map prototype. All of the different saddle-node bifurcation cascades, associated with every last appearance p-periodic orbit (p=3,4,5,...), can also be generated from the very Feigenbaum cascade. In this way it is evidenced the relationship between both cascades. The orbits of every saddle-node bifurcation cascade, mentioned above, are located in different chaotic bands, and this determines a sequence of orbits converging to every band-merging Misiurewicz point. In turn, these accumulation points form a sequence whose accumulation point is the Myrberg-Feigenbaum point. It is also proven that the first appearance orbits in the n-chaotic band converge to the same point as the last appearance orbits of the (n + 1)-chaotic band. The symbolic sequences of band-merging Misiurewicz points are computed for any window.
Experimental observations of surface electrostatic wave on KT-5B tokamak
International Nuclear Information System (INIS)
Zhu Shiyao; Han Shensheng
1991-01-01
Shear Alfven waves have been successfully excited in KT-5B small tokamak by means of the one turn longitudinal loop antenna located in the shadow area. The measured antenna loadings show their rich structure, and the loadings are also found to be sensitive to the plasma current. Preliminary evidence of surface electrostatic wave was observed
Learning optimal embedded cascades.
Saberian, Mohammad Javad; Vasconcelos, Nuno
2012-10-01
The problem of automatic and optimal design of embedded object detector cascades is considered. Two main challenges are identified: optimization of the cascade configuration and optimization of individual cascade stages, so as to achieve the best tradeoff between classification accuracy and speed, under a detection rate constraint. Two novel boosting algorithms are proposed to address these problems. The first, RCBoost, formulates boosting as a constrained optimization problem which is solved with a barrier penalty method. The constraint is the target detection rate, which is met at all iterations of the boosting process. This enables the design of embedded cascades of known configuration without extensive cross validation or heuristics. The second, ECBoost, searches over cascade configurations to achieve the optimal tradeoff between classification risk and speed. The two algorithms are combined into an overall boosting procedure, RCECBoost, which optimizes both the cascade configuration and its stages under a detection rate constraint, in a fully automated manner. Extensive experiments in face, car, pedestrian, and panda detection show that the resulting detectors achieve an accuracy versus speed tradeoff superior to those of previous methods.
Theory and observation of compressional Alfven eigenmodes in low aspect ratio plasma
International Nuclear Information System (INIS)
Gorelenkov, N.N.
2002-01-01
A new theory of radially and poloidally localized Compressional Alfven Eigenmodes (CAE) in low aspect ratio plasma is reported. The theory is applied to identify recently observed instabilities in the MHz frequency range in National Spherical Torus experiments (NSTX). The frequency of observed CAEs is correlated with the characteristic Alfven velocity of the plasma. The observed high frequency modes are explained as CAEs driven by energetic beam ions. The CAE frequency is determined by the Alfven frequency at the mode location on the low field side of the plasma and is given approximately by ω CAE v A m=r, where m is the poloidal mode number, and r is the local minor radius. CAEs are destabilized by free energy in the energetic ion velocity space gradient via Doppler shifted cyclotron resonance with beam ions. Properties of the CAE instability driven by different NBI ion distributions are presented. (author)
Nonperturbative effects of energetic ions on Alfven eigenmodes
International Nuclear Information System (INIS)
Todo, Y.; Nakajima, N.; Shinohara, K.; Takechi, M.; Ishikawa, M.; Yamamoto, S.
2005-01-01
Linear properties and nonlinear evolutions of an energetic-ion driven instability in a JT-60U plasma were investigated using a simulation code for magnetohydrodynamics and energetic particles. The spatial profile of the unstable mode peaks near the plasma center where the safety factor profile is flat. The unstable mode is not a toroidal Alfven eigenmode (TAE) because the spatial profile deviates from the expected location of TAE and the spatial profile consists of a single primary harmonic m/n = 2/1 where m, n are poloidal and toroidal mode numbers. The real frequency of the unstable mode is close to the experimental starting frequency of the fast frequency sweeping mode. The simulation results demonstrate that the energetic ion orbit width and the energetic ion pressure significantly broaden radial profile of the unstable mode. For the smallest value among the investigated energetic ion orbit width, the unstable mode is localized within 20% of the minor radius. This gives an upper limit of the spatial profile width of the unstable mode which the magnetohydrodynamic effects alone can induce. For the experimental condition of the JT-60U plasma, the energetic ions broaden the spatial profile of the unstable mode by a factor of 3 compared with the smallest orbit width case. The unstable mode is primarily induced by the energetic particles. It is demonstrated that the frequency shifts both upward and downward in the nonlinear evolution at the rate close to that of the fast frequency sweeping mode. In addition to the energetic particle mode in the JT-60U plasma, an investigation of TAE in an LHD-like plasma using the simulation code for the helical coordinate system is reported. (author)
Nonperturbative effects of energetic ions on Alfven eigenmodes
International Nuclear Information System (INIS)
Todo, Y.; Nakajima, N.; Shinohara, Kouji; Takechi, Manabu; Ishikawa, Masao
2005-01-01
Linear properties and nonlinear evolutions of an energetic-ion driven instability in a JT-60U plasma were investigated using a simulation code for magnetohydrodynamics and energetic particles. The spatial profile of the unstable mode peaks near the plasma center where the safety factor profile is flat. The unstable mode is not a toroidal Alfven eigenmode (TAE) because the spatial profile deviates from the expected location of TAE and the spatial profile consists of a single primary harmonic m/n=2/1 where m, n are poloidal and toroidal mode numbers. The real frequency of the unstable mode is close to the experimental starting frequency of the fast frequency sweeping mode. The simulation results demonstrate that the energetic ion orbit width and the energetic ion pressure significantly broaden radial profile of the unstable mode. For the smallest value among the investigated energetic ion orbit width, the unstable mode is localized within 20% of the minor radius. This gives an upper limit of the spatial profile width of the unstable mode which the magnetohydrodynamic effects alone can induce. For the experimental condition of the JT-60U plasma, the energetic ions broaden the spatial profile of the unstable mode by a factor of 3 compared with the smallest orbit width case. The unstable mode is primarily induced by the energetic particles. It is demonstrated that the frequency shifts both upward and downward in the nonlinear evolution at the rate close to that of the fast frequency sweeping mode. In addition to the energetic particle mode in the JT-60U plasma, an investigation of TAE in an LHD-like plasma using the simulation code for the helical coordinate system is reported. (author)
Linewidth and tuning characteristics of terahertz quantum cascade lasers.
Barkan, A; Tittel, F K; Mittleman, D M; Dengler, R; Siegel, P H; Scalari, G; Ajili, L; Faist, J; Beere, H E; Linfield, E H; Davies, A G; Ritchie, D A
2004-03-15
We have measured the spectral linewidths of three continuous-wave quantum cascade lasers operating at terahertz frequencies by heterodyning the free-running quantum cascade laser with two far-infrared gas lasers. Beat notes are detected with a GaAs diode mixer and a microwave spectrum analyzer, permitting very precise frequency measurements and giving instantaneous linewidths of less than -30 kHz. Characteristics are also reported for frequency tuning as the injection current is varied.
Linear wave propagation in a hot axisymmetric toroidal plasma
International Nuclear Information System (INIS)
Jaun, A.
1995-03-01
Kinetic effects on the propagation of the Alfven wave are studied for the first time in a toroidal plasma relevant for experiments. This requires the resolution of a set of coupled partial differential equations whose coefficients depend locally on the plasma parameters. For this purpose, a numerical wave propagation code called PENN has been developed using either a bilinear or a bicubic Hermite finite element discretization. It solves Maxwell's equations in toroidal geometry, with a dielectric tensor operator that takes into account the linear response of the plasma. Two different models have been implemented and can be used comparatively to describe the same physical case: the first treats the plasma as resistive fluids and gives results which are in good agreement with toroidal fluid codes. The second is a kinetic model and takes into account the finite size of the Larmor radii; it has successfully been tested against a kinetic plasma model in cylindrical geometry. New results have been obtained when studying kinetic effects in toroidal geometry. Two different conversion mechanisms to the kinetic Alfven wave have been described: one occurs at toroidally coupled resonant surfaces and is the kinetic counterpart of the fluid models' resonance absorption. The other has no such correspondence and results directly from the toroidal coupling between the kinetic Alfven wave and the global wavefield. An analysis of a heating scenario suggests that it might be difficult to heat a plasma with Alfven waves up to temperatures that are relevant for a tokamak reactor. Kinetic effects are studied for three types of global Alfven modes (GAE, TAE, BAE) and a new class of kinetic eigenmodes is described which appear inside the fluid gap: it could be related to recent observations in the JET (Joint European Torus) tokamak. (author) 56 figs., 6 tabs., 58 refs
Linear wave propagation in a hot axisymmetric toroidal plasma
Energy Technology Data Exchange (ETDEWEB)
Jaun, A [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP)
1995-03-01
Kinetic effects on the propagation of the Alfven wave are studied for the first time in a toroidal plasma relevant for experiments. This requires the resolution of a set of coupled partial differential equations whose coefficients depend locally on the plasma parameters. For this purpose, a numerical wave propagation code called PENN has been developed using either a bilinear or a bicubic Hermite finite element discretization. It solves Maxwell`s equations in toroidal geometry, with a dielectric tensor operator that takes into account the linear response of the plasma. Two different models have been implemented and can be used comparatively to describe the same physical case: the first treats the plasma as resistive fluids and gives results which are in good agreement with toroidal fluid codes. The second is a kinetic model and takes into account the finite size of the Larmor radii; it has successfully been tested against a kinetic plasma model in cylindrical geometry. New results have been obtained when studying kinetic effects in toroidal geometry. Two different conversion mechanisms to the kinetic Alfven wave have been described: one occurs at toroidally coupled resonant surfaces and is the kinetic counterpart of the fluid models` resonance absorption. The other has no such correspondence and results directly from the toroidal coupling between the kinetic Alfven wave and the global wavefield. An analysis of a heating scenario suggests that it might be difficult to heat a plasma with Alfven waves up to temperatures that are relevant for a tokamak reactor. Kinetic effects are studied for three types of global Alfven modes (GAE, TAE, BAE) and a new class of kinetic eigenmodes is described which appear inside the fluid gap: it could be related to recent observations in the JET (Joint European Torus) tokamak. (author) 56 figs., 6 tabs., 58 refs.
Schlenker, Cody W.
2011-09-27
We demonstrate planar organic solar cells consisting of a series of complementary donor materials with cascading exciton energies, incorporated in the following structure: glass/indium-tin-oxide/donor cascade/C 60/bathocuproine/Al. Using a tetracene layer grown in a descending energy cascade on 5,6-diphenyl-tetracene and capped with 5,6,11,12-tetraphenyl- tetracene, where the accessibility of the π-system in each material is expected to influence the rate of parasitic carrier leakage and charge recombination at the donor/acceptor interface, we observe an increase in open circuit voltage (Voc) of approximately 40% (corresponding to a change of +200 mV) compared to that of a single tetracene donor. Little change is observed in other parameters such as fill factor and short circuit current density (FF = 0.50 ± 0.02 and Jsc = 2.55 ± 0.23 mA/cm2) compared to those of the control tetracene-C60 solar cells (FF = 0.54 ± 0.02 and Jsc = 2.86 ± 0.23 mA/cm2). We demonstrate that this cascade architecture is effective in reducing losses due to polaron pair recombination at donor-acceptor interfaces, while enhancing spectral coverage, resulting in a substantial increase in the power conversion efficiency for cascade organic photovoltaic cells compared to tetracene and pentacene based devices with a single donor layer. © 2011 American Chemical Society.
Energy Technology Data Exchange (ETDEWEB)
Hayden, A. C.; Brown, T. D.
1979-03-15
Combining energy uses in a cascade can result in significant overall reductions in fuel requirements. The simplest applications for a cascade are in the recovery of waste heat from existing processes using special boilers or turbines. Specific applications of more-complex energy cascades for Canada are discussed. A combined-cycle plant at a chemical refinery in Ontario is world leader in energy efficiency. Total-energy systems for commercial buildings, such as one installed in a school in Western Canada, offer attractive energy and operating cost benefits. A cogeneration plant proposed for the National Capital Region, generating electricity as well as steam for district heating, allows the use of a low-grade fossil fuel (coal), greatly improves energy-transformation efficiency, and also utilizes an effectively renewable resource (municipal garbage). Despite the widespread availability of equipment and technology of energy cascades, the sale of steam and electricity across plant boundaries presents a barrier. More widespread use of cascades will require increased cooperation among industry, electric utilities and the various levels of government if Canada is to realize the high levels of energy efficiency potential available.
Schlenker, Cody W.; Barlier, Vincent S.; Chin, Stephanie W.; Whited, Matthew T.; McAnally, R. Eric; Forrest, Stephen R.; Thompson, Mark E.
2011-01-01
We demonstrate planar organic solar cells consisting of a series of complementary donor materials with cascading exciton energies, incorporated in the following structure: glass/indium-tin-oxide/donor cascade/C 60/bathocuproine/Al. Using a tetracene layer grown in a descending energy cascade on 5,6-diphenyl-tetracene and capped with 5,6,11,12-tetraphenyl- tetracene, where the accessibility of the π-system in each material is expected to influence the rate of parasitic carrier leakage and charge recombination at the donor/acceptor interface, we observe an increase in open circuit voltage (Voc) of approximately 40% (corresponding to a change of +200 mV) compared to that of a single tetracene donor. Little change is observed in other parameters such as fill factor and short circuit current density (FF = 0.50 ± 0.02 and Jsc = 2.55 ± 0.23 mA/cm2) compared to those of the control tetracene-C60 solar cells (FF = 0.54 ± 0.02 and Jsc = 2.86 ± 0.23 mA/cm2). We demonstrate that this cascade architecture is effective in reducing losses due to polaron pair recombination at donor-acceptor interfaces, while enhancing spectral coverage, resulting in a substantial increase in the power conversion efficiency for cascade organic photovoltaic cells compared to tetracene and pentacene based devices with a single donor layer. © 2011 American Chemical Society.
Wave driven magnetic reconnection in the Taylor problem
International Nuclear Information System (INIS)
Fitzpatrick, Richard; Bhattacharjee, Amitava; Ma Zhiwei; Linde, Timur
2003-01-01
An improved Laplace transform theory is developed in order to investigate the initial response of a stable slab plasma equilibrium enclosed by conducting walls to a suddenly applied wall perturbation in the so-called Taylor problem. The novel feature of this theory is that it does not employ asymptotic matching. If the wall perturbation is switched on slowly compared to the Alfven time then the plasma response eventually asymptotes to that predicted by conventional asymptotic matching theory. However, at early times there is a compressible Alfven wave driven contribution to the magnetic reconnection rate which is not captured by asymptotic matching theory, and leads to a significant increase in the reconnection rate. If the wall perturbation is switched on rapidly compared to the Alfven time then strongly localized compressible Alfven wave-pulses are generated which bounce backward and forward between the walls many times. Each instance these wave-pulses cross the resonant surface they generate a transient surge in the reconnection rate. The maximum pulse driven reconnection rate can be much larger than that predicted by conventional asymptotic matching theory
International Nuclear Information System (INIS)
Fredrickson, E. D.; Belova, E. V.; Battaglia, D. J.
2017-01-01
In this paper we present data from experiments on the National Spherical Torus Experiment Upgrade, where it is shown for the first time that small amounts of high pitch-angle beam ions can strongly suppress the counterpropagating global Alfven eigenmodes (GAE). GAE have been implicated in the redistribution of fast ions and modification of the electron power balance in previous experiments on NSTX. The ability to predict the stability of Alfven modes, and developing methods to control them, is important for fusion reactors like the International Tokamak Experimental Reactor, which are heated by a large population of nonthermal, super-Alfvenic ions consisting of fusion generated alpha's and beam ions injected for current profile control. We present a qualitative interpretation of these observations using an analytic model of the Doppler-shifted ion-cyclotron resonance drive responsible for GAE instability which has an important dependence on k(perpendicular to rho L). A quantitative analysis of this data with the HYM stability code predicts both the frequencies and instability of the GAE prior to, and suppression of the GAE after the injection of high pitch-angle beam ions.
Hadron cascades produced by electromagnetic cascades
International Nuclear Information System (INIS)
Nelson, W.R.; Jenkins, T.M.; Ranft, J.
1986-12-01
A method for calculating high energy hadron cascades induced by multi-GeV electron and photon beams is described. Using the EGS4 computer program, high energy photons in the EM shower are allowed to interact hadronically according to the vector meson dominance (VMD) model, facilitated by a Monte Carlo version of the dual multistring fragmentation model which is used in the hadron cascade code FLUKA. The results of this calculation compare very favorably with experimental data on hadron production in photon-proton collisions and on the hadron production by electron beams on targets (i.e., yields in secondary particle beam lines). Electron beam induced hadron star density contours are also presented and are compared with those produced by proton beams. This FLUKA-EGS4 coupling technique could find use in the design of secondary beams, in the determination high energy hadron source terms for shielding purposes, and in the estimation of induced radioactivity in targets, collimators and beam dumps
Destabilization of low mode number Alfven modes in a tokamak by energetic or alpha particles
International Nuclear Information System (INIS)
Tsang, K.T.; Sigmar, D.J.; Whitson, J.C.
1980-12-01
With the inclusion of finite Larmor radius effects in the shear Alfven eigenmode equation, the continuous Alfven spectrum, which has been extensively discussed in ideal magnetohydrodynamics, is removed. Neutrally stable, discrete radial eigenmodes appear in the absence of sources of free energy and dissipation. Alpha (or energetic) particle toroidal drifts destabilize these modes, provided the particles are faster than the Alfven speed. Although the electron Landu resonance contributes to damping, a stability study of the parametric variation of the energy and the density scale length of the energetic particles shows that modes with low radial mode numbers remain unstable in most cases. Since the alpha particles are concentrated in the center of the plasma, this drift-type instability suggests anomalous helium ash diffusion. Indeed, it is shown that stochasticity of alpha orbits due to the overlapping of radially neighboring Alfven resonances is induced at low amplitudes, e/sub i//sup approx./phi/T/sub i/ greater than or equal to 0.05, implying a diffusion coefficient D/sub r//sup α/ greater than or equal to 4.4 x 10 3 cm 2 /s
Alfven, Hugo. Die drei Schwedischen Rhapsodien op. 19, 24 und 47 / Andreas Meyer
Meyer, Andreas
1995-01-01
Uuest heliplaadist "Alfven, Hugo. Die drei Schwedischen Rhapsodien op. 19, 24 und 47, En skärgardssägen op. 20, Suite aus Der Berkönig. Königliche Stockholmer Philharmoniker, Neeme Järvi". AD: 1987-1992. BIS?Disco-Center CD 725 (WD: 77'00")
The effect of toroidal plasma rotation on low-frequency reversed shear Alfven eigenmodes in tokamaks
Haverkort, J. W.
2012-01-01
The influence of toroidal plasma rotation on the existence of reversed shear Alfven eigenmodes (RSAEs) near their minimum frequency is investigated analytically. An existence condition is derived showing that a radially decreasing kinetic energy density is unfavourable for the existence of RSAEs.
Alfvenic Instabilities and Fast Ion Transport in the DIII-D Tokamak
International Nuclear Information System (INIS)
Van Zeeland, M.; Heidbrink, W.; Nazikian, R.; Austin, M.; Berk, H.; Gorelenkov, N.; Holcomb, C.; Kramer, G.; Lohr, J.; Luo, Y.; Makowski, M.; McKee, G.; Petty, C.; Prater, R.; Solomon, W.; White, R.
2008-01-01
Neutral beam injection into reversed magnetic shear DIII-D plasmas produces a variety of Alfvenic activity including Toroidicity and Ellipticity induced Alfven Eigenmodes (TAE/EAE, respectively) and Reversed Shear Alfven Eigenmodes (RSAE) as well as their spatial coupling. These modes are typically studied during the discharge current ramp phase when incomplete current penetration results in a high central safety factor and strong drive due to multiple higher order resonances. During this same time period Fast-Ion D α (FIDA) spectroscopy shows that the central fast ion profile is flattened, the degree of which depends on the Alfven eigenmode amplitude. Interestingly, localized electron cyclotron heating (ECH) near the mode location stabilizes RSAE activity and results in significantly improved fast ion confinement relative to discharges with ECH deposition on axis. In these discharges, RSAE activity is suppressed when ECH is deposited near the radius of the shear reversal point and enhanced with deposition near the axis. To simulate the observed neutral beam ion redistribution, NOVA calculations of the 3D eigenmode structures are matched with experimental measurements and used in combination with the ORBIT guiding center following code. For fixed frequency eigenmodes, it is found that ORBIT calculations cannot explain the observed beam ion transport with experimentally measured mode amplitudes. Possible explanations are considered including recent simulation results incorporating eigenmodes with time dependent frequencies
International Nuclear Information System (INIS)
Pitts, J.H.
1985-01-01
Cascade is a concept for an ultrasafe, highly efficient, easily built reactor to convert inertial-confinement fusion energy into electrical power. The Cascade design includes a rotating double-cone-shaped chamber in which a moving, 1-m-thick ceramic granular blanket is held against the reactor wall by centrifugal action. The granular material absorbs energy from the fusion reactions. Accomplishments this year associated with Cascade included improvements to simplify chamber design and lower activation. The authors switched from a steel chamber wall to one made from silicon-carbide (SiC) panels held in compression by SiC-fiber/Al-composite tendons that gird the chamber both circumferentially and axially. The authors studies a number of heat-exchanger designs and selected a gravity-flow cascade design with a vacuum on the primary side. This design allows granules leaving the chamber to be transported to the heat exchangers using their own peripheral speed. The granules transfer their thermal energy and return to the chamber gravitationally: no vacuum locks or conveyors are needed
Energy Technology Data Exchange (ETDEWEB)
Fomenko, Tatiana N [M. V. Lomonosov Moscow State University, Faculty of Computational Mathematics and Cybernetics, Moscow (Russian Federation)
2010-10-22
We find sufficient conditions on a searching multi-cascade for a modification of the set of limit points of the cascade that satisfy an assessing inequality for the distance from each of these points to the initial point to be small, provided that the modifications of the initial point and the initial set-valued functionals or maps used to construct the multi-cascade are small. Using this result, we prove the stability (in the above sense) of the cascade search for the set of common pre-images of a closed subspace under the action of n set-valued maps, n{>=}1 (in particular, for the set of common roots of these maps and for the set of their coincidences). For n=2 we obtain generalizations of some results of A. V. Arutyunov; the very statement of the problem comes from a recent paper of his devoted to the study of the stability of the subset of coincidences of a Lipschitz map and a covering map.
International Nuclear Information System (INIS)
Ilgenfritz, E.M.; Kripfganz, J.; Moehring, H.J.
1977-01-01
The analytical treatment of hadronic decay cascades within the framework of the statistical bootstrap model is demonstrated on the basis of a simple variant. Selected problems for a more comprehensive formulation of the model such as angular momentum conservation, quantum statistical effects, and the immediate applicability to particle production processes at high energies are discussed in detail
MHD waves, reconnection, and plasma transport at the dayside magnetopause
International Nuclear Information System (INIS)
Johnson, J.R.; Cheng, C.Z.
1996-01-01
The magnetic field of the Earth creates a huge cavity in the solar wind known as the magnetosphere. The transition region between the solar wind plasma and magnetosphere plasma is of substantial interest because many magnetospheric processes are governed by the transport of particles, momentum and energy across that boundary. At this boundary, the magnetopause, there is an abrupt decrease in plasma bulk flow, density and pressure, and large increase in temperature and magnetic field. Throughout this region the plasmas is large. Large amplitude compressional waves are nearly always found in the region just outside of the magnetopause. These waves are either intrinsic solar wind fluctuations or they may be global mirror modes which are generated in a localized region of large pressure anisotropy just outside the magnetopause. The substantial background gradients observed at the magnetopause strongly couple the compressional waves with kinetic Alfven waves near the Alfven resonance location, leading to substantial particle transport. Moreover, for a sheared background magnetic field, as is found at times of southward interplanetary magnetic field, the mode converted kinetic Alfven waves can propagate to the location where k parallel = 0 and generate islands in phase space. We present a solution of the kinetic-MHD wave equations for the magnetic field structure based on a realistic steady state profile which includes: a sheared magnetic field; magnetic curvature; and gradients in the background density, pressure and magnetic field. We incorporate wave-particle resonance interactions for electrons and ions to obtain the dissipation. The background magnetic Keld curvature and gradient give rise to drifts which alter the resonance condition for the various particle species (ω - k circ V d - k parallel v parallel ) and reduces the Landau damping of the kinetic Alfven wave, allowing it to propagate to the k parallel = 0 location
Integrated Broadband Quantum Cascade Laser
Mansour, Kamjou (Inventor); Soibel, Alexander (Inventor)
2016-01-01
A broadband, integrated quantum cascade laser is disclosed, comprising ridge waveguide quantum cascade lasers formed by applying standard semiconductor process techniques to a monolithic structure of alternating layers of claddings and active region layers. The resulting ridge waveguide quantum cascade lasers may be individually controlled by independent voltage potentials, resulting in control of the overall spectrum of the integrated quantum cascade laser source. Other embodiments are described and claimed.
The Berk-Breizman Model as a Paradigm for Energetic Particle-driven Alfven Eigenmodes
International Nuclear Information System (INIS)
Lesur, M.
2010-01-01
The achievement of sustained nuclear fusion in magnetically confined plasma relies on efficient confinement of alpha particles, which are high-energy ions produced by the fusion reaction. Such particles can excite instabilities in the frequency range of Alfven Eigenmodes (AEs), which significantly degrade their confinement and threatens the vacuum vessel of future reactors. In order to develop diagnostics and control schemes, a better understanding of linear and nonlinear features of resonant interactions between plasma waves and high-energy particles, which is the aim of this thesis, is required. In the case of an isolated single resonance, the description of AE destabilization by high-energy ions is homothetic to the so-called Berk-Breizman (BB) problem, which is an extension of the classic bump-on-tail electrostatic problem, including external damping to a thermal plasma, and collisions. A semi-Lagrangian simulation code, COBBLES, is developed to solve the initial-value BB problem in both perturbative (δ f) and self-consistent (full-f) approaches. Two collision models are considered, namely a Krook model, and a model that includes dynamical friction (drag) and velocity-space diffusion. The nonlinear behavior of instabilities in experimentally-relevant conditions is categorized into steady-state, periodic, chaotic, and frequency-sweeping (chirping) regimes, depending on external damping rate and collision frequency. The chaotic regime is shown to extend into a linearly stable region, and a mechanism that solves the paradox formed by the existence of such subcritical instabilities is proposed. Analytic and semi-empirical laws for nonlinear chirping characteristics, such as sweeping-rate, lifetime, and asymmetry, are developed and validated. Long-time simulations demonstrate the existence of a quasi-periodic chirping regime. Although the existence of such regime stands for both collision models, drag and diffusion are essential to reproduce the alternation between
Information cascade on networks
Hisakado, Masato; Mori, Shintaro
2016-05-01
In this paper, we discuss a voting model by considering three different kinds of networks: a random graph, the Barabási-Albert (BA) model, and a fitness model. A voting model represents the way in which public perceptions are conveyed to voters. Our voting model is constructed by using two types of voters-herders and independents-and two candidates. Independents conduct voting based on their fundamental values; on the other hand, herders base their voting on the number of previous votes. Hence, herders vote for the majority candidates and obtain information relating to previous votes from their networks. We discuss the difference between the phases on which the networks depend. Two kinds of phase transitions, an information cascade transition and a super-normal transition, were identified. The first of these is a transition between a state in which most voters make the correct choices and a state in which most of them are wrong. The second is a transition of convergence speed. The information cascade transition prevails when herder effects are stronger than the super-normal transition. In the BA and fitness models, the critical point of the information cascade transition is the same as that of the random network model. However, the critical point of the super-normal transition disappears when these two models are used. In conclusion, the influence of networks is shown to only affect the convergence speed and not the information cascade transition. We are therefore able to conclude that the influence of hubs on voters' perceptions is limited.
International Nuclear Information System (INIS)
Hogan, W.J.; Pitts, J.H.
1986-01-01
The double-cone-shaped Cascade reaction chamber rotates at 50 rpm to keep a blanket of ceramic granules in place against the wall as they slide from the poles to the exit slots at the equator. The 1 m-thick blanket consists of layers of carbon, beryllium oxide, and lithium aluminate granules about 1 mm in diameter. The x rays and debris are stopped in the carbon granules; the neutrons are multiplied and moderated in the BeO and breed tritium in the LiAlO 2 . The chamber wall is made up of SiO tiles held in compression by a network of composite SiC/Al tendons. Cascade operates at a 5 Hz pulse rate with 300 MJ in each pulse. The temperature in the blanket reaches 1600 K on the inner surface and 1350 K at the outer edge. The granules are automatically thrown into three separate vacuum heat exchangers where they give up their energy to high pressure helium. The helium is used in a Brayton cycle to obtain a thermal-to-electric conversion efficiency of 55%. Studies have been done on neutron activation, debris recovery, vaporization and recondensation of blanket material, tritium control and recovery, fire safety, and cost. These studies indicate that Cascade appears to be a promising ICF reactor candidate from all standpoints. At the 1000 MWe size, electricity could be made for about the same cost as in a future fission reactor
Energy absorption due to spatial resonance of Alfven waves at continuum tip
Chen, Eugene; Berk, Herb; Breizman, Boris; Zheng, Linjin
2011-10-01
We investigate the response of tokamak plasma to an external driving source. An impedance-like function depending on the driving frequency that is growing at a small rate, is calculated and interpreted with different source profiles. Special attention is devoted to the case where driving frequency approaches that of the TAE continuum tip. The calculation can be applied to the estimation of TAE damping rate by analytically continuing the inverse of the impedance function to the lower half plane. The root of the analytic continuation corresponds to the existence of a quasi-mode, from which the damping rate can be found.
Effects of flow shear and Alfven waves on two-dimensional magnetohydrodynamic turbulence
International Nuclear Information System (INIS)
Douglas, Jamie; Kim, Eun-jin; Thyagaraja, A.
2008-01-01
The suppression of turbulent transport by large scale mean shear flows and uniform magnetic fields is investigated in two-dimensional magnetohydrodynamic turbulence driven by a small-scale forcing with finite correlation time. By numerical integration the turbulent magnetic diffusivity D T is shown to be significantly quenched, with a scaling D T ∝B -2 Ω 0 -5/4 , which is much more severe than in the case of a short or delta correlated forcing typified by white noise, studied in E. Kim and B. Dubrulle [Phys. Plasmas 8, 813 (2001)]. Here B and Ω 0 are magnetic field strength and flow shear rate, respectively. The forcing with finite correlation time also leads to much stronger suppression of momentum transport through the cancellation of the Reynolds stress by the Maxwell stress with a positive small value of turbulent viscosity, ν T >0. While fluctuating kinetic and magnetic energies are unaffected by the magnetic field just as in the case of a delta correlated forcing, they are much more severely quenched by flow shear than in that of a delta correlated forcing. Underlying physical mechanisms for the reduction of turbulent transport and turbulence level by flow shear and magnetic field are discussed
Generation of plasma rotation in a tokamak by ion-cyclotron absorption of fast Alfven waves
International Nuclear Information System (INIS)
Perkins, F.W.; White, R.B.; Bonoli, P.T.; Chan, V.S.
2001-01-01
A mechanism is proposed and evaluated for driving rotation in tokamak plasmas by minority ion-cyclotron heating, even though this heating introduces negligible angular momentum. The mechanism has two elements: First, angular momentum transport is governed by a diffusion equation with a boundary condition at the separatrix. Second, Monte Carlo calculations show that ion-cyclotron energized particles will provide a torque density source which has a zero volume integral but separated positive and negative regions. With such a source, a solution of the diffusion equation predicts that ion-cyclotron heating will cause a rotational shear layer to develop. The corresponding jump in plasma rotation ΔΩ is found to be negative outwards when the ion-cyclotron surface lies on the low-field side of the magnetic axis and positive outwards with the resonance on the high-field side. The magnitude of the jump ΔΩ=(4q max WJ 2 *) (eBR 3 a 2 n e (2π) 2 ) -1 (τ M /τ E ) where |J 2 *|≅2-4 is a nondimensional rotation frequency calculated by the Monte Carlo ORBIT code [R. B. White and M. S. Chance, Phys. Fluids 27, 2455 (1984)]. For a no-slip boundary condition when the resonance lies on the low-field side of the magnetic axis, the sense of predicted axial rotation is co-current and overall agreement with experiment is good. When the resonance lies on the high-field side, the predicted rotation becomes countercurrent for a no-slip boundary while the observed rotation remains co-current. The rotational shear layer position is controllable and of sufficient magnitude to affect microinstabilities
Farrugia, C. J.; Lugaz, N.; Alm, L.; Vasquez, B. J.; Argall, M. R.; Kucharek, H.; Matsui, H.; Torbert, R. B.; Lavraud, B.; Le Contel, O.; Shuster, J. R.; Burch, J. L.; Khotyaintsev, Y. V.; Giles, B. L.; Fuselier, S. A.; Gershman, D. J.; Ergun, R.; Eastwood, J. P.; Cohen, I. J.; Dorelli, J.; Lindqvist, P. A.; Strangeway, R. J.; Russell, C. T.; Marklund, G. T.; Paulson, K.; Petrinec, S.; Phan, T.; Pollock, C.
2017-12-01
We present MMS) observations during two dayside magnetopause crossingsunder hitherto unexamined conditions: (i) when the bow shock is weakening and the solar wind transitioning to sub-Alfvenic flow, and (ii) when it is reforming. Interplanetary conditions consist of a magnetic cloud with (i) a strong B ( 20 nT) pointing south, and (ii) a density profile with episodic decreases to values of 0.3 /cc followed by moderate recovery. During the crossings he magnetosheath magnetic field is stronger than the magnetosphere field by a factor of 2.2. As a result, during the outbound crossing through the ion diffusion region, MMS observed an inversion of relative positions of the X and stagnation (S) lines from that typically the case: the S line was closer to the magnetosheath side. The S-line appears in the form of a slow expansion fan near which most of the energy dissipation is taking place. While in the magnetosphere between the crossings, MMS observed strong field and flow perturbations, which we argue to be due kinetic Alfvén waves.During the reconnection interval, whistler mode waves generated by an electron temperature anisotropy (Tperp>Tpar) were observed. Another aim of the paper isto distinguish bow shock-induced field and flow perturbations from reconnection-related signatures.The high resolution MMS data together with 2D hybrid simulations of bow shock dynamics helped us to distinguish between the two sources. We show examples of bow shock-related effects (such as heating) and reconnection effects such as accelerated flows satisfying the Walen relation.
Lagrangian analysis of nonlinear wave-wave interactions in bounded plasmas
International Nuclear Information System (INIS)
Carr, A.R.
1979-01-01
In a weakly turbulent nonlinear wave-supporting medium, one of the important nonlinear processes which may occur is resonant three-wave interaction. Whitham's averaged Lagrangian method provides a general formulation of wave evolution laws which is easily adapted to nonlinear dispersive media. In this thesis, the strength of nonlinear interactions between three coherent, axisymmetric, low frequency, magnetohydrodynamic (Alfven) waves propagating in resonance along a cold cylindrical magnetized plasma column is calculated. Both a uniform and a parabolic density distribution have been considered. To account for a non-zero plasma temperature, pressure effects have been included. Distinctive features of the work are the use of cylindrical geometry, the presence of a finite rather than an infinite axial magnetic field, the treatment of a parabolic density distribution, and the inclusion of both ion and electron contributions in all expressions. Two astrophysical applications of the presented theory have been considered. In the first, the possibility of resonant three-wave coupling between geomagnetic micropulsations, which propagate as Alfven or magnetosonic waves along the Earth's magnetic field lines, has been investigated. The second case is the theory of energy transport through the solar chromosphere by upward propagating magnetohydrodynamic waves, which may then couple to heavily damped waves in the corona, causing the observed excess heating in that region
Expansion of parameter space for Toroidal Alfven Eigenmode experiments in TFTR
International Nuclear Information System (INIS)
Wong, K.L.; Wilson, J.R.; Chang, Z.Y.; Fredrickson, E.; Hammett, G.W.; Bush, C.; Nazikian, R.; Phillips, C.K.; Snipes, J.; Taylor, G.
1993-05-01
Several techniques were used to excite toroidal Alfven Eigenmodes in the Tokamak Fusion Test Reactor (TFTR) at magnetic fields above 10 kG. These involve pellet injection to raise the plasma density, variation of plasma current to change the energetic ion orbit and the q-profile, and ICRF heating to produce energetic hydrogen ions at velocities comparable to 3.5 MeV alpha particles. These experimental results are presented and relevance to fusion reactors are discussed
Warm-ion drift Alfven turbulence and the L-H transition
International Nuclear Information System (INIS)
Scott, B.
1998-01-01
Computations of fluid drift turbulence treating ions and electrons on equal footing, including both temperatures, are conducted in a model toroidal geometry. The resulting 'ion mixing mode' turbulence bears features of both electron drift-Alfven and ion temperature gradient turbulence, and nonlinear sensitivity to the relative strengths of the density and temperature gradients provides a possible route to the bifurcation needed for the L-H transition. (author)
Wave propagation in a magnetically structured atmosphere. Pt. 2
International Nuclear Information System (INIS)
Roberts, B.
1981-01-01
Magnetic fields may introduce structure (inhomogeneity) into an otherwise uniform medium and thus change the nature of wave propagation in that medium. As an example of such structuring, wave propagation in an isolated magnetic slab is considered. It is supposed that disturbances outside the slab are laterally non-propagating. The effect of gravity is ignored. The field can support the propagation of both body and surface waves. The existence and nature of these waves depends upon the relative magnitudes of the sound speed c 0 and Alfven speed upsilonsub(A) inside the slab, and the sound speed csub(e) in the field-free environment. (orig./WL)
Use of conformal mapping to describe MHD wave propagation
International Nuclear Information System (INIS)
Bulanov, S.V.; Pegoraro, F.
1993-01-01
A method is proposed for finding explicit exact solutions of the magnetohydrodynamic equations describing the propagation of magnetoacoustic waves in a plasma in a magnetic potential that depends on two spatial coordinates. This method is based on the use of conformal mappings to transform the wave equation into an equation describing the propagation of waves in a uniform magnetic field. The basic properties of magnetoacoustic and Alfven waves near the critical points, magnetic separatrices, and in configuration with magnetic islands are discussed. Expressions are found for the dimensionless parameters which determine the relative roles of the plasma pressure, nonlinearity, and dissipation near the critical points. 30 refs
Theory of magnetospheric hydromagnetic waves excited by energetic ring-current protons
International Nuclear Information System (INIS)
Chen, Liu; Hasegawa, Akira.
1987-06-01
A general theoretical formulation, allowing finite ion Larmor radii, general magnetic field geometries and plasma equilibria, has been developed to investigate excitations of magnetohydrodynamic (MHD) Alfven waves within the earth's magnetosphere by the storm-time energetic ring-current protons. In particular, it is found that for adiabatically injected protons, various predicted instability properties are consistent with satellite observations. 8 refs
International Nuclear Information System (INIS)
Podesta, M.; Bell, R.E.; Fredrickson, E.D.; Gorelenkov, N.N.; LeBlanc, B.P.; Crocker, N.A.; Kubota, S.; Heidbrink, W.W.; Yuh, H.
2011-01-01
The National Spherical Torus Experiment (NSTX, (Ono et al 2000 Nucl. Fusion 40 557)) routinely operates with neutral beam injection as the primary system for heating and current drive. The resulting fast ion population is super-Alfvenic, with velocities 1 fast /v Alfven < 5. This provides a strong drive for toroidicity-induced Alfven eigenmodes (TAEs). As the discharge evolves, the fast ion population builds up and TAEs exhibit increasing bursts in amplitude and down-chirps in frequency, which eventually lead to a so-called TAE avalanche. Avalanches cause large (∼<30%) fast ion losses over ∼1 ms, as inferred from the neutron rate. The increased fast ion losses correlate with a stronger activity in the TAE band. In addition, it is shown that a n = 1 mode with frequency well below the TAE gap appears in the Fourier spectrum of magnetic fluctuations as a result of non-linear mode coupling between TAEs during avalanche events. The non-linear coupling between modes, which leads to enhanced fast ion transport during avalanches, is investigated.
International Nuclear Information System (INIS)
Podesta, M.; Bell, R.E.; Crocker, N.A.; Fredrickson, E.D.; Gorelenkov, N.N.; Heidbrink, W.W.; Kubota, S.; LeBlanc, B.P.; Yu, H.
2011-01-01
The National Spherical Torus Experiment (NSTX, (M. Ono et al., Nucl. Fusion 40, 557 (2000))) routinely operates with neutral beam injection as the primary system for heating and current drive. The resulting fast ion population is super-Alfvenic, with velocities 1 fast /v Alfven < 5. This provides a strong drive for toroidicity-induced Alfven eigenmodes (TAEs). As the discharge evolves, the fast ion population builds up and TAEs exhibit increasing bursts in amplitude and down-chirps in frequency, which eventually lead to a so-called TAE avalanche. Avalanches cause large (∼<30%) fast ion losses over ∼ 1 ms, as inferred from the neutron rate. The increased fast ion losses correlate with a stronger activity in the TAE band. In addition, it is shown that a n = 1 mode with frequency well below the TAE gap appears in the Fourier spectrum of magnetic fluctuations as a result of non-linear mode coupling between TAEs during avalanche events. The non-linear coupling between modes, which leads to enhanced fast ion transport during avalanches, is investigated.
Predictions and observations of global beta-induced Alfven-acoustic modes in JET and NSTX
Energy Technology Data Exchange (ETDEWEB)
Gorelenkov, N N [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Berk, H L [Institute for Fusion Studies, University of Texas, Austin, TX 78712 (United States); Crocker, N A [Institute of Plasma and Fusion Research, University of California, Los Angeles, CA 90095-1354 (United States); Fredrickson, E D [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Kaye, S [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Kubota, S [Institute of Plasma and Fusion Research, University of California, Los Angeles, CA 90095-1354 (United States); Park, H [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Peebles, W [Institute of Plasma and Fusion Research, University of California, Los Angeles, CA 90095-1354 (United States); Sabbagh, S A [Department of Applied Physics, Columbia University, New York, NY 10027-6902 (United States); Sharapov, S E [Euroatom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB (United Kingdom); Stutmat, D [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Tritz, K [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Levinton, F M [Nova Photonics, One Oak Place, Princeton, NJ 08540 (United States); Yuh, H [Nova Photonics, One Oak Place, Princeton, NJ 08540 (United States)
2007-12-15
In this paper we report on observations and interpretations of a new class of global MHD eigenmode solutions arising in gaps in the low frequency Alfven-acoustic continuum below the geodesic acoustic mode frequency. These modes have been just reported (Gorelenkov et al 2007 Phys. Lett. 370 70-7) where preliminary comparisons indicate qualitative agreement between theory and experiment. Here we show a more quantitative comparison emphasizing recent NSTX experiments on the observations of the global eigenmodes, referred to as beta-induced Alfven-acoustic eigenmodes (BAAEs), which exist near the extrema of the Alfven-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes may shift as the safety factor, q, profile relaxes. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta <2% as well as in NSTX plasmas at relatively high beta >20%. In NSTX plasma observed magnetic activity has the same properties as predicted by theory for the mode structure and the frequency. Found numerically in NOVA simulations BAAEs are used to explain the observed properties of relatively low frequency experimental signals seen in NSTX and JET tokamaks.
Predications and Observations of Global Beta-induced Alfven-acoustic Modes in JET and NSTX
International Nuclear Information System (INIS)
Gorelenkov, N.N.
2008-01-01
In this paper we report on observations and interpretations of a new class of global MHD eigenmode solutions arising in gaps in the low frequency Alfven-acoustic continuum below the geodesic acoustic mode frequency. These modes have been just reported (Gorelenkov et al 2007 Phys. Lett. 370 70-7) where preliminary comparisons indicate qualitative agreement between theory and experiment. Here we show a more quantitative comparison emphasizing recent NSTX experiments on the observations of the global eigenmodes, referred to as beta-induced Alfven-acoustic eigenmodes (BAAEs), which exist near the extrema of the Alfven-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes may shift as the safety factor, q, profile relaxes. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta 20%. In NSTX plasma observed magnetic activity has the same properties as predicted by theory for the mode structure and the frequency. Found numerically in NOVA simulations BAAEs are used to explain the observed properties of relatively low frequency experimental signals seen in NSTX and JET tokamaks
The Potential for Ambient Plasma Wave Propulsion
Gilland, James H.; Williams, George J.
2016-01-01
A truly robust space exploration program will need to make use of in-situ resources as much as possible to make the endeavor affordable. Most space propulsion concepts are saddled with one fundamental burden; the propellant needed to produce momentum. The most advanced propulsion systems currently in use utilize electric and/or magnetic fields to accelerate ionized propellant. However, significant planetary exploration missions in the coming decades, such as the now canceled Jupiter Icy Moons Orbiter, are restricted by propellant mass and propulsion system lifetimes, using even the most optimistic projections of performance. These electric propulsion vehicles are inherently limited in flexibility at their final destination, due to propulsion system wear, propellant requirements, and the relatively low acceleration of the vehicle. A few concepts are able to utilize the environment around them to produce thrust: Solar or magnetic sails and, with certain restrictions, electrodynamic tethers. These concepts focus primarily on using the solar wind or ambient magnetic fields to generate thrust. Technically immature, quasi-propellantless alternatives lack either the sensitivity or the power to provide significant maneuvering. An additional resource to be considered is the ambient plasma and magnetic fields in solar and planetary magnetospheres. These environments, such as those around the Sun or Jupiter, have been shown to host a variety of plasma waves. Plasma wave propulsion takes advantage of an observed astrophysical and terrestrial phenomenon: Alfven waves. These are waves that propagate in the plasma and magnetic fields around and between planets and stars. The generation of Alfven waves in ambient magnetic and plasma fields to generate thrust is proposed as a truly propellantless propulsion system which may enable an entirely new matrix of exploration missions. Alfven waves are well known, transverse electromagnetic waves that propagate in magnetized plasmas at
Wave-Driven Rotation In Centrifugal Mirrors
International Nuclear Information System (INIS)
Fetterman, Abraham J.; Fisch, Nathaniel J.
2011-01-01
Centrifugal mirrors use supersonic rotation to provide axial confinement and enhanced stability. Usually the rotation is produced using electrodes, but these electrodes have limited the rotation to the Alfven critical ionization velocity, which is too slow to be useful for fusion. Instead, the rotation could be produced using radio frequency waves. A fixed azimuthal ripple is a simple and efficient wave that could produce rotation by harnessing alpha particle energy. This is an extension of the alpha channeling effect. The alpha particle power and efficiency in a simulated devices is sufficient to produce rotation without external energy input. By eliminating the need for electrodes, this opens new opportunities for centrifugal traps.
DEFF Research Database (Denmark)
Damgaard, Mads
2018-01-01
Through a content analysis of 8,800 news items and six months of front pages in three Brazilian newspapers, all dealing with corruption and political transgression, this article documents the remarkable skew of media attention to corruption scandals. The bias is examined as an information...... phenomenon, arising from systemic and commercial factors of Brazil’s news media: An information cascade of news on corruption formed, destabilizing the governing coalition and legitimizing the impeachment process of Dilma Rousseff. As this process gained momentum, questions of accountability were disregarded...
DEFF Research Database (Denmark)
Damgaard, Mads
2018-01-01
Through a content analysis of 8,800 news items and six months of front pages in three Brazilian newspapers, all dealing with corruption and political transgression, this article documents the remarkable skew of media attention to corruption scandals. The bias is examined as an information...... phenomenon, arising from systemic and commercial factors of Brazil’s news media: An information cascade of news on corruption formed, destabilizing the governing coalition and legitimizing the impeachment process of Dilma Rousseff. As this process gained momentum, questions of accountability were disregarded...... by the media, with harmful effects on democracy....
Quantum Cascade Lasers Modulation and Applications
Luzhansky, Edward
The mid-wave IR (MWIR) spectral band, extending from 3 to 5 microns, is considered to be a low loss atmospheric window. There are several spectral sub-bands with relatively low atmospheric attenuation in this region making it popular for various commercial and military applications. Relatively low thermal and solar background emissions, effective penetration through the natural and anthropogenic obscurants and eye safety add to the long list of advantages of MWIR wavelengths. Quantum Cascade Lasers are compact semiconductor devices capable of operating in MWIR spectrum. They are based on inter-subband transitions in a multiple-quantum-well (QW) hetero-structure, designed by means of band-structure engineering. The inter-subband nature of the optical transition has several key advantages. First, the emission wavelength is primarily a function of the QW thickness. This characteristic allows choosing well-understood and reliable semiconductors for the generation of light in a wavelength range of interest. Second, a cascade process in which tens of photons are generated per injected electron. This cascading process is behind the intrinsic high-power capabilities of QCLs. This dissertation is focused on modulation properties of Quantum Cascade Lasers. Both amplitude and phase/frequency modulations were studied including modulation bandwidth, modulation efficiency and chirp linearity. Research was consisted of the two major parts. In the first part we describe the theory of frequency modulation (FM) response of Distributed Feedback Quantum Cascade Lasers (DFB QCL). It includes cascading effect on the QCL's maximum modulation frequency. The "gain levering" effect for the maximum FM response of the two section QCLs was studied as well. In the second part of research we concentrated on the Pulse Position Amplitude Modulation of a single section QCL. The low complexity, low size, weight and power Mid-Wavelength Infra-Red optical communications transceiver concept is
Collins, William
1989-01-01
The magnetohydrodynamic wave emission from several localized, periodic, kinematically specified fluid velocity fields are calculated using Lighthill's method for finding the far-field wave forms. The waves propagate through an isothermal and uniform plasma with a constant B field. General properties of the energy flux are illustrated with models of pulsating flux tubes and convective rolls. Interference theory from geometrical optics is used to find the direction of minimum fast-wave emission from multipole sources and slow-wave emission from discontinuous sources. The distribution of total flux in fast and slow waves varies with the ratios of the source dimensions l to the acoustic and Alfven wavelengths.
Cascade Error Projection Learning Algorithm
Duong, T. A.; Stubberud, A. R.; Daud, T.
1995-01-01
A detailed mathematical analysis is presented for a new learning algorithm termed cascade error projection (CEP) and a general learning frame work. This frame work can be used to obtain the cascade correlation learning algorithm by choosing a particular set of parameters.
International Nuclear Information System (INIS)
Nishiura, M.; Isobe, M.; Yamamoto, S.
2008-10-01
Alfven instabilities induced fast-ion losses have been directly observed for the first time by a newly developed scintillator lost ion probe (SLIP) in the Large Helical Device (LHD). The SLIP can measure the pitch angle and gyro radius of escaped fast ions toward loss region. Neutral beam driven Alfven Eigenmodes (AEs) are excited under the reactor relevant conditions: the ratio of fast ion (beam) speed υ b and Alfven speed υ A is more than 0.3 - 4.0. The beta value for fast ions is considered roughly to be ∼10%. Non-linear phenomena related to Alfven instabilities are observed under such conditions. During repetitive Toroidal Alfven Eigenmode (TAE) bursts, synchronized fast ion losses are observed by SLIP. From the orbit calculation the measured fast ion with pitch angle of 130 degrees and beam energy of 150 keV surely pass through the locations of TAE gaps. The orbit analysis found that the observed fast ions interact strongly with the excited TAEs. This result becomes the first experimental evidence of radial transport of fast ions predicted theoretically during TAE activities. In addition, from the correlation between stored energy degradation and fast-ion loss rate, it is found that fast-ion losses induced by TAE activities with low toroidal mode numbers categorize two phenomena without and with fast- ion loss enhancements, which indicate the fast-ion redistribution and loss. (author)
International Nuclear Information System (INIS)
Fu, G.Y.; Van Dam, J.W.
1989-05-01
The stability of the Global Alfven Eigenmodes is investigated in the presence of super-Alfvenic energetic particles, such as the fusion-product alpha particles in an ignited deuterium-tritium tokamak plasma. Alpha particles tend to destabilize these modes when ω *α > ω A , where ω A is the shear-Alfven modal frequency and ω *α is the alpha particle diamagnetic drift frequency. This destabilization due to alpha particles is found to be significantly enhanced when the alpha particles are modeled with a slowing-down distribution function rather than with a Maxwellian. However, previously neglected electron damping due to the magnetic curvature drift is found to be comparable in magnitude to the destabilizing alpha particle term. Furthermore, the effects of toroidicity are also found to be stabilizing, since the intrinsic toroidicity induces poloidal mode coupling, which enhances the parallel electron damping from the sideband shear-Alfven Landau resonance. In particular, for the parameters of the proposed Compact Ignition Tokamak, the Global Alfven Eigenmodes are found to be completely stabilized by either the electron damping that enters through the magnetic curvature drift or the damping introduced by finite toroidicity. 29 refs., 8 figs., 1 tab
THE EFFECTS OF WAVE ESCAPE ON FAST MAGNETOSONIC WAVE TURBULENCE IN SOLAR FLARES
International Nuclear Information System (INIS)
Pongkitiwanichakul, Peera; Chandran, Benjamin D. G.; Karpen, Judith T.; DeVore, C. Richard
2012-01-01
One of the leading models for electron acceleration in solar flares is stochastic acceleration by weakly turbulent fast magnetosonic waves ( f ast waves ) . In this model, large-scale flows triggered by magnetic reconnection excite large-wavelength fast waves, and fast-wave energy then cascades from large wavelengths to small wavelengths. Electron acceleration by large-wavelength fast waves is weak, and so the model relies on the small-wavelength waves produced by the turbulent cascade. In order for the model to work, the energy cascade time for large-wavelength fast waves must be shorter than the time required for the waves to propagate out of the solar-flare acceleration region. To investigate the effects of wave escape, we solve the wave kinetic equation for fast waves in weak turbulence theory, supplemented with a homogeneous wave-loss term. We find that the amplitude of large-wavelength fast waves must exceed a minimum threshold in order for a significant fraction of the wave energy to cascade to small wavelengths before the waves leave the acceleration region. We evaluate this threshold as a function of the dominant wavelength of the fast waves that are initially excited by reconnection outflows.
Wave and particle evolution downstream of quasi-perpendicular shocks
Mckean, M. E.; Omidi, N.; Krauss-Varban, D.; Karimabadi, H.
1995-01-01
Distributions of ions heated in quasi-perpendicular bow shocks have large perpendicular temperature anisotropies that provide free energy for the growth of Alfven ion cyclotron (AIC) and mirror waves. These modes are often obsreved in the Earth's magnetosheath. Using two-dimensional hybrid simulations, we show that these waves are produced near the shock front and convected downstream rather than being produced locally downstream. The wave activity reduces the proton anisotropy to magnetosheath levels within a few tens of gyroradii of the shock but takes significantly longer to reduce the anisotropy of He(++) ions. The waves are primarily driven by proton anisotropy and the dynamics of the helium ions is controlled by the proton waves. Downstream of high Mach number shocks, mirror waves compete effectively with AIC waves. Downstream of low Mach number shocks, AIC waves dominate.
International Nuclear Information System (INIS)
Damiano, P. A.; Wright, A. N.; McKenzie, J. F.
2009-01-01
The linear wave equation (sixth order in space and time) and the corresponding dispersion relation is derived for Hall magnetohydrodynamic (MHD) waves including electron inertial and finite Larmor radius effects together with several limiting cases for a homogeneous plasma. We contrast these limits with the solution of the full dispersion relation in terms of wave normal (k perpendicular ,k || ) diagrams to clearly illustrate the range of applicability of the individual approximations. We analyze the solutions in terms of all three MHD wave modes (fast, slow, and Alfven), with particular attention given to how the Alfven branch (including the cold ideal field line resonance (FLR) [D. J. Southwood, Planet. Space Sci. 22, 483 (1974)]) is modified by the Hall term and electron inertial and finite Larmor radius effects. The inclusion of these terms breaks the degeneracy of the Alfven branch in the cold plasma limit and displaces the asymptote position for the FLR to a line defined by the electron thermal speed rather than the Alfven speed. For a driven system, the break in this degeneracy implies that a resonance would form at one field line for small k perpendicular and then shift to another as k perpendicular →∞. However for very large ωk perpendicular /V A , Hall term effects lead to a coupling to the whistler mode, which would then transport energy away from the resonant layer. The inclusion of the Hall term also significantly effects the characteristics of the slow mode. This analysis reveals an interesting 'swapping' of the perpendicular root behavior between the slow and Alfven branches.
Observations of neutral beam and ICRF tail ion losses due to Alfven modes in TFTR
International Nuclear Information System (INIS)
Darrow, D.S.; Zweben, S.J.; Chang, Z.
1996-04-01
Fast ion losses resulting from MHD modes at the Alfven frequency, such as the TAE, have been observed in TFTR. The modes have been driven both by neutral beam ions, at low B T , and by H-minority ICRF tail ions at higher B T . The measurements indicate that the loss rate varies linearly with the mode amplitude, and that the fast ion losses during the mode activity can be significant, e.g. up to 10% of the input power is lost in the worst case
Evidence for fast-electron-driven Alfvenic modes in the HSX stellarator
International Nuclear Information System (INIS)
Brower, D.L.; Deng, C.; Spong, D.A.; Abdou, A.; Almagri, A.F.; Anderson, D.T.; Anderson, F.S.B.; Guttenfelder, W.; Likin, K.; Oh, S.; Sakaguchi, V.; Talmadge, J.N.; Zhai, K.
2005-01-01
The helically-symmetric experiment (HSX) stellarator device is the first of a new generation of stellarators that exploit the concept of quasi-symmetric magnetic fields. In HSX, the plasma is both produced and heated by use of electron cyclotron resonance heating (ECRH) at the 2nd harmonic X-mode resonance. This heating configuration generates a nonthermal energetic electron population. Herein, we report on the first experimental evidence for fast-electron-driven Global Alfven Eigenmodes (GAE). This mode has previously been observed in both tokamaks and stellarators but it was always driven by energetic ions, not electrons. Evidence for this instability is obtained from quasi-helically symmetric HSX plasmas. Potential consequences of these measurements are twofold; (1) fast electrons can drive the GAE instability, and (2) quasi-symmetry makes a difference by better confining the particles that drive the instability as compared to the conventional stellarator configuration. We report on several features of this fluctuation. It is a coherent mode that is experimentally observed in the plasma core and edge by external magnetic coils, interferometry, ECE and Langmuir probes diagnostics. Fluctuations are observed in the frequency range of 20-120 kHz and scale with ion mass density according to expectations for Alfvenic modes. The mode is observed to be global with odd poloidal mode number (inferred from interferometry, possibly m=1) and is present in quasi-helically symmetric HSX plasmas. When quasi-helical symmetry is broken, the mode is no longer observed. Theory predicts a GAE mode in the gap below the Alfven continua can be excited in the frequency range of the measured fluctuations. By employing a biased electrode inserted deep into the plasma, flows can be generated. Under these conditions, the Alfvenic mode amplitude can increase and the fluctuation is even observed in the conventional stellarator configuration. Shifts in the measured frequency can be used to
International Nuclear Information System (INIS)
Takechi, M.; Matsunaga, G.; Takagi, S.
1999-09-01
Toroidal Alfven eigenmodes (TAE) destabilized by the pressure gradient of energetic alpha particles may expel the alpha particles before thermalization. TAE is important for tokamaks, and for helical systems (stellarators) as well. In CHS (compact helical system) TAE localized in the plasma core are destabilized when the plasma current is induced by co-injection of neutral beams. The observed TAE exhibits a ballooning nature. The internal structure of TAE was measured with a soft X-ray detector. The soft X-ray fluctuations level for TAE is too low to obtain the radial profiles of fluctuation intensities. (Tanaka, M.)
Inferring network structure from cascades
Ghonge, Sushrut; Vural, Dervis Can
2017-07-01
Many physical, biological, and social phenomena can be described by cascades taking place on a network. Often, the activity can be empirically observed, but not the underlying network of interactions. In this paper we offer three topological methods to infer the structure of any directed network given a set of cascade arrival times. Our formulas hold for a very general class of models where the activation probability of a node is a generic function of its degree and the number of its active neighbors. We report high success rates for synthetic and real networks, for several different cascade models.
Optical Cherenkov radiation in ultrafast cascaded second-harmonic generation
DEFF Research Database (Denmark)
Bache, Morten; Bang, Ole; Zhou, Binbin
2010-01-01
-matching point is located in the absorption region of the crystal, effectively absorbing the generated dispersive wave. By calculating the phase-matching curves for typically used frequency conversion crystals, we point out that the mid-IR absorption in the crystal in many cases automatically will filter away....... The beating between the dispersive wave and the soliton generates trailing temporal oscillations on the compressed soliton. Insertion of a simple short-wave pass filter after the crystal can restore a clean soliton. On the other hand, bandpass filtering around the dispersive wave peak results in near......We show through theory and numerics that when few-cycle femtosecond solitons are generated through cascaded (phase-mismatched) second-harmonic generation, these broadband solitons can emit optical Cherenkov radiation in the form of linear dispersive waves located in the red part of the spectrum...
International Nuclear Information System (INIS)
Barzilov, A.P.; Gulevich, A.V.; Kukharchuk, O.F.
2000-01-01
The technical problem of long-life fission product and minor actinide incineration and production of plutonium fuel in the prospective nuclear systems will arise at significant scales of nuclear power industry development. Subcritical nuclear reactors driven by extemal neutron sources (energy amplifiers) are considered as incinerators of toxicity of complete nuclear industry. In the frames of this concept, the subcritical reactor part consisting of two coupled blanket regions (inner fast neutron spectrum core and outer thermal core) driven by extemal neutron source is discussed. Two types of source are studied: spallation target and 14-MeV fusion bum of micropellets. Liquid metal Pb-Bi is considered as target material and coolant of inner fast core. Thermal core is a heavy-water subcritical reactor of the Candu-type. The fast core is protected from thermal neutrons influence with the boron shield. All reactor technologies used in this concept are tested during years of operation and commercially available. Thus, the cascade energy amplifiers have a set of advantages in comparison with traditional concepts: in energy production, in transmutation efficiency, and in economics. (authors)
A full wave code for ion cyclotron waves in toroidal plasmas
International Nuclear Information System (INIS)
Brambilla, M.
1996-02-01
The code TORIC solves the finite Larmor radius wave equations in the ion cyclotron frequency range in arbitrary axisymmetric toroidal geometry. The model used describes the compressional and torsional Alfven waves (or, depending on the parallel phase velocity, the kinetic counterpart of the latter), and ion Bernstein waves excited by mode conversion near the first ion cyclotron harmonic. In the ion response the broadening of the absorption regions due to the finite width of the cyclotron resonance of individual ions in toroidal geometry is taken into account. The parallel component of the wave electric field is evaluated on the same footing as the transverse ones; the response of the electrons includes Landau damping, Transit Time damping and the mixed term. The numerical approach uses a spectral representation of the solution in the poloidal angle θ, and cubic finite elements in the radial variable ψ. Great flexibility is provided in the way ion Bernstein waves excited by mode conversion are damped when their wavelength becomes comparable with the ion Larmor radius, in the regularization of Alfven resonances, and in the treatment of the outer plasma layers. As an option, we have also implemented the Order Reduction Algorithm, which provides a particularly fast, yet accurate evaluation of the power deposition profiles in toroidal geometry. Thee present report describes the model and its numerical implementation, and provides the information needed to use the code. A few examples illustrating applications of TORIC are also included. (orig.)
Nonlinear pattern formation of Faraday waves
Binks, D.J.; Water, van de W.
1997-01-01
A cascade of surface wave patterns with increasing rotational symmetry ranging from simple square to tenfold quasiperiodic is observed for Faraday waves. The experiment concerns the excitation of subharmonic standing surface waves by oscillating vertical acceleration. Our observation agrees with the
International Nuclear Information System (INIS)
Bruma, C.; Cuperman, S.; Komoshvili, K.
1999-01-01
Some basic aspects of wave-plasma interaction of interest for tight aspect ratio spherical tokamaks are investigated theoretically. The following scenario is considered: A. Fast magnetosonic waves are launched by an external antenna into a simulated spherical Tokamak plasma; these waves are converted to Alfven waves at points (layer) satisfying the Alfven resonance condition. B. The simulated spherical tokamaks-plasma has a circular cross-section and toroidicity effects are simulated by Grad-Shafranov type, radially dependent axial magnetic field and its shear. (J. Actual equilibrium profiles (magnetic field, pressure and current) observed in the low field side (LFS) of spherical tokamaks (viz., START at Culham, UK) are used. D. The study is based on the numerical solution of the full e.m. wave equation which includes a quite general resistive MHD dielectric tensor, with consideration of equilibrium current and neoclassical effects. Two kinds of results will be presented: I. Proofs validating the computational algorithm used and including convergence and energy conservation. II. Exact quantitative results concerning (i) the structure and space dependence of the mode-converted Alfven waves and (ii) the basic features of the deposited p over . The dependence of the results on the launched wave characteristics (wave numbers, frequency and intensity) as well as on those of the equilibrium plasma (equilibrium current, neoclassical resistivity and electron inertia) will be discussed
Ultrarelativistic cascades and strangeness production
Energy Technology Data Exchange (ETDEWEB)
Kahana, D.E. [State Univ. of New York, Stony Brook, NY (United States). Dept. of Physics; Kahana, S.H. [Brookhaven National Lab., Upton, NY (United States). Physics Dept.
1998-08-24
A two-phase cascade code, LUCIFER II, developed for the treatment of ultra high energy-ion-ion collisions is applied to the production of strangeness at SPS energies {radical}(s)=17-20. This simulation is able to simultaneously describe both hard processes such as Drell-Yan and slower, soft processes such as the production of light mesons by separating the dynamics into two steps, a fast cascade involving only the nucleons in the original colliding relativistic ions followed, after an appropriate delay, by a normal multiscattering of the resulting excited baryons and mesons produced virtually in the first step. No energy loss can take place in the short time interval over which the first cascade takes place. The chief result is a reconciliation of the important Drell-Yan measurements with the apparent success of standard cascades to describe the nucleon stopping and meson production in heavy-ion experiments at the CERN SPS. (orig.) 26 refs.
Ultrarelativistic cascades and strangeness production
International Nuclear Information System (INIS)
Kahana, D.E.; Kahana, S.H.
1998-01-01
A two-phase cascade code, LUCIFER II, developed for the treatment of ultra high energy-ion-ion collisions is applied to the production of strangeness at SPS energies √(s)=17-20. This simulation is able to simultaneously describe both hard processes such as Drell-Yan and slower, soft processes such as the production of light mesons by separating the dynamics into two steps, a fast cascade involving only the nucleons in the original colliding relativistic ions followed, after an appropriate delay, by a normal multiscattering of the resulting excited baryons and mesons produced virtually in the first step. No energy loss can take place in the short time interval over which the first cascade takes place. The chief result is a reconciliation of the important Drell-Yan measurements with the apparent success of standard cascades to describe the nucleon stopping and meson production in heavy-ion experiments at the CERN SPS. (orig.)
Ultrarelativistic cascades and strangeness production
International Nuclear Information System (INIS)
Kahana, D.E.; Kahana, S.H.
1998-02-01
A two phase cascade, LUCIFER II, developed for the treatment of ultra high energy Ion-Ion collisions is applied to the production of strangeness at SPS energies. This simulation is able to simultaneously describe both hard processes such as Drell-Yan and slower, soft processes such as the production of light mesons by separating the dynamics into two steps, a fast cascade involving only the nucleons in the original colliding relativistic ions followed, after an appropriate delay, by a normal multiscattering of the resulting excited baryons and mesons produced virtually in the first step. No energy loss can take place in the short time interval over which the first cascade takes place. The chief result is a reconciliation of the important Drell-Yan measurements with the apparent success of standard cascades to describe the nucleon stopping and meson production in heavy ion experiments at the CERN SPS
Cascade redox flow battery systems
Horne, Craig R.; Kinoshita, Kim; Hickey, Darren B.; Sha, Jay E.; Bose, Deepak
2014-07-22
A reduction/oxidation ("redox") flow battery system includes a series of electrochemical cells arranged in a cascade, whereby liquid electrolyte reacts in a first electrochemical cell (or group of cells) before being directed into a second cell (or group of cells) where it reacts before being directed to subsequent cells. The cascade includes 2 to n stages, each stage having one or more electrochemical cells. During a charge reaction, electrolyte entering a first stage will have a lower state-of-charge than electrolyte entering the nth stage. In some embodiments, cell components and/or characteristics may be configured based on a state-of-charge of electrolytes expected at each cascade stage. Such engineered cascades provide redox flow battery systems with higher energy efficiency over a broader range of current density than prior art arrangements.
Stochastic background of atmospheric cascades
International Nuclear Information System (INIS)
Wilk, G.; Wlodarczyk, Z.
1993-01-01
Fluctuations in the atmospheric cascades developing during the propagation of very high energy cosmic rays through the atmosphere are investigated using stochastic branching model of pure birth process with immigration. In particular, we show that the multiplicity distributions of secondaries emerging from gamma families are much narrower than those resulting from hadronic families. We argue that the strong intermittent like behaviour found recently in atmospheric families results from the fluctuations in the cascades themselves and are insensitive to the details of elementary interactions
Computation of inverse magnetic cascades
International Nuclear Information System (INIS)
Montgomery, D.
1981-10-01
Inverse cascades of magnetic quantities for turbulent incompressible magnetohydrodynamics are reviewed, for two and three dimensions. The theory is extended to the Strauss equations, a description intermediate between two and three dimensions appropriate to tokamak magnetofluids. Consideration of the absolute equilibrium Gibbs ensemble for the system leads to a prediction of an inverse cascade of magnetic helicity, which may manifest itself as a major disruption. An agenda for computational investigation of this conjecture is proposed
Kouznetsov, Igor; Lotko, William
1995-01-01
The 'radial' transport of energy by internal ULF waves, stimulated by dayside magnetospheric boundary oscillations, is analyzed in the framework of one-fluid magnetohydrodynamics. (the term radial is used here to denote the direction orthogonal to geomagnetic flux surfaces.) The model for the inhomogeneous magnetospheric plasma and background magnetic field is axisymmetric and includes radial and parallel variations in the magnetic field, magnetic curvature, plasma density, and low but finite plasma pressure. The radial mode structure of the coupled fast and intermediate MHD waves is determined by numerical solution of the inhomogeneous wave equation; the parallel mode structure is characterized by a Wentzel-Kramer-Brillouin (WKB) approximation. Ionospheric dissipation is modeled by allowing the parallel wave number to be complex. For boudnary oscillations with frequencies in the range from 10 to 48 mHz, and using a dipole model for the background magnetic field, the combined effects of magnetic curvature and finite plasma pressure are shown to (1) enhance the amplitude of field line resonances by as much as a factor of 2 relative to values obtained in a cold plasma or box-model approximation for the dayside magnetosphere; (2) increase the energy flux delivered to a given resonance by a factor of 2-4; and (3) broaden the spectral width of the resonance by a factor of 2-3. The effects are attributed to the existence of an 'Alfven buoyancy oscillation,' which approaches the usual shear mode Alfven wave at resonance, but unlike the shear Alfven mode, it is dispersive at short perpendicular wavelengths. The form of dispersion is analogous to that of an internal atmospheric gravity wave, with the magnetic tension of the curved background field providing the restoring force and allowing radial propagation of the mode. For nominal dayside parameters, the propagation band of the Alfven buoyancy wave occurs between the location of its (field line) resonance and that of the
Koch, Peter; Bartschke, Juergen; L'huillier, Johannes A
2015-05-18
We report on the influence of self-focusing and self-defocusing in the phase-mismatched frequency doubling crystal on the third harmonic generation (THG) efficiency in a two crystal frequency tripling scheme. By detuning the temperature of the doubling crystal, the impact of a phase-mismatch in second harmonic generation (SHG) on the subsequent sum frequency mixing process was investigated. It was found that adjusting the temperature not only affected the power ratio of the second harmonic to the fundamental but also the beam diameter of the fundamental beam in the THG crystal, which was caused by self-focusing and self-defocusing of the fundamental beam, respectively. This self-action was induced by a cascaded χ(2) : χ(2) process in the phase-mismatched SHG crystal. Self-defocusing was observable for positive detuning and self-focusing for negative detuning of the phase-matching temperature. Hence, the THG efficiency was not symmetric with respect to the point of optimum phase-matching. Optimum THG was obtained for positive detuning and the resulting self-defocusing in combination with the focusing lens in front of the THG stage was also beneficial for the beam quality of the third harmonic.
National Research Council Canada - National Science Library
Wade, Patrick
2003-01-01
Upstream propagating waves impinging on a cascade of compressor blades were examined in an effort to better understand the influence of downstream components on high cycle fatigue in turbine engines...
International Nuclear Information System (INIS)
Zaitsev, V.V.; Stepanov, A.V.
1982-01-01
It is shown that the existence of a minimum of the Alfven speed in the corona at a height of approx.1R/sub sun/ follows from the characteristics of type II radio bursts. The region of a reduced Alfven speed is a resonator for a fast magnetosonic (FMS) waves. The eigenmodes of the resonator are determined. The period of the fundamental mode has the order of several minutes. In the resonator FMS waves can be excited at the Cherenkov resonance by streams of energetic ions. Modulations of metal solar radio emission with a period of several minutes is explained by the effect of the propagation of radio waves through an oscillating magnetohydrodynamic (MHD) resonator
Electromagnetic Waves and Bursty Electron Acceleration: Implications from Freja
Andersson, Laila; Ivchenko, N.; Wahlund, J.-E.; Clemmons, J.; Gustavsson, B.; Eliasson, L.
2000-01-01
Dispersive Alfven wave activity is identified in four dayside auroral oval events measured by the Freja satellite. The events are characterized by ion injection, bursty electron precipitation below about I keV, transverse ion heating and broadband extremely low frequency (ELF) emissions below the lower hybrid cutoff frequency (a few kHz). The broadband emissions are observed to become more electrostatic towards higher frequencies. Large-scale density depletions/cavities, as determined by the Langmuir probe measurements, and strong electrostatic emissions are often observed simultaneously. A correlation study has been carried out between the E- and B-field fluctuations below 64 Hz (the dc instrument's upper threshold) and the characteristics of the precipitating electrons. This study revealed that the energization of electrons is indeed related to the broadband ELF emissions and that the electrostatic component plays a predominant role during very active magnetospheric conditions. Furthermore, the effect of the ELF electromagnetic emissions on the larger scale field-aligned current systems has been investigated, and it is found that such an effect cannot be detected. Instead, the Alfvenic activity creates a local region of field-aligned currents. It is suggested that dispersive Alfven waves set up these local field-aligned current regions and in turn trigger more electrostatic emissions during certain conditions. In these regions ions are transversely heated, and large-scale density depletions/cavities may be created during especially active periods.
Orthogonal experimental study on high frequency cascade thermoacoustic engine
International Nuclear Information System (INIS)
Hu Zhongjun; Li Qing; Li Zhengyu; Li Qiang
2008-01-01
Orthogonal experiment design and variance analysis were adopted to investigate a miniature cascade thermoacoustic engine, which consisted of one standing wave stage and one traveling wave stage in series, operating at about 470 Hz, using helium as the working gas. Optimum matching of the heater powers between stages was very important for the performance of a cascade thermoacoustic engine, which was obtained from the orthogonal experiments. The orthogonal experiment design considered three experimental factors, i.e. the charging pressure and the heater powers in the two stages, which varied on five different levels, respectively. According to the range analysis and variance analysis from the orthogonal experiments, the charging pressure was the most sensitive factor influencing the dynamic pressure amplitude and onset temperature. The total efficiency and the dynamic pressure amplitude increased when the traveling wave stage heater power increased. The optimum ratio of the heater powers between the traveling wave stage and the standing wave stage was about 1.25, compromising the total efficiency with the dynamic pressure amplitude
Time structure of cascade showers
International Nuclear Information System (INIS)
Nakatsuka, Takao
1984-01-01
Interesting results have been reported on the time structure of the electromagnetic components of air showers which have been obtained by using recent fast electronic circuit technology. However, these analyses and explanations seem not very persuasive. One of the reasons is that there is not satisfactory theoretical calculation yet to explain the delay of electromagnetic components in cascade processes which are the object of direct observation. Therefore, Monte Carlo calculation was attempted for examining the relationship between the altitude at which high energy γ-ray is generated up in the air and the time structure of cascade showers at the level of observation. The investigation of a dominant factor over the delay of electromagnetic components indicated that the delay due to the multiple scattering of electrons was essential. The author used the analytical solution found by himself of C. N. Yang's equation for the study on the delay due to multiple scattering. The results were as follows: The average delay time and the spread of distribution of electromagnetic cascades were approximately in linear relationship with the mass of a material having passed in a thin uniform medium; the rise time of arrival time distribution for electromagnetic cascade showers was very steep under the condition that they were generated up in the air and observed on the ground; the subpeaks delayed by tens of ns in arrival time may sometimes appear due to the perturbation in electromagnetic cascade processes. (Wakatsuki, Y.)
Numerical study of primordial magnetic field amplification by inflation-produced gravitational waves
International Nuclear Information System (INIS)
Kuroyanagi, Sachiko; Tashiro, Hiroyuki; Sugiyama, Naoshi
2010-01-01
We numerically study the interaction of inflation-produced magnetic fields with gravitational waves, both of which originate from quantum fluctuations during inflation. The resonance between the magnetic field perturbations and the gravitational waves has been suggested as a possible mechanism for magnetic field amplification. However, some analytical studies suggest that the effect of the inflationary gravitational waves is too small to provide significant amplification. Our numerical study shows more clearly how the interaction affects the magnetic fields and confirms the weakness of the influence of the gravitational waves. We present an investigation based on the magnetohydrodynamic approximation and take into account the differences of the Alfven speed.
Rescuing Ecosystems from Extinction Cascades
Sahasrabudhe, Sagar; Motter, Adilson
2010-03-01
Food web perturbations stemming from climate change, overexploitation, invasive species, and natural disasters often cause an initial loss of species that results in a cascade of secondary extinctions. Using a predictive modeling framework, here we will present a systematic network-based approach to reduce the number of secondary extinctions. We will show that the extinction of one species can often be compensated by the concurrent removal of a second specific species, which is a counter-intuitive effect not previously tested in complex food webs. These compensatory perturbations frequently involve long-range interactions that are not a priori evident from local predator-prey relationships. Strikingly, in numerous cases even the early removal of a species that would eventually be extinct by the cascade is found to significantly reduce the number of cascading extinctions. Other nondestructive interventions based on partial removals and growth suppression and/or mortality increase are shown to sometimes prevent all secondary extinctions.
Theory of high-n toroidicity-induced shear Alfven eigenmode in tokamaks
International Nuclear Information System (INIS)
Fu, G.Y.; Cheng, C.Z.; Princeton Univ., NJ
1989-07-01
High-n WKB-ballooning mode equation is employed to study toroidicity-induced shear Alfven eigenmodes (TAE) in the δ - α space, where δ = (r/q)(dq/dr) is the magnetic shear, and α = -(2Rq 2 /B 2 )(dp/dr) is the normalized pressure gradient for tokamak plasmas. In the ballooning mode first stability region, TAE modes are found to exist only for α less than some critical value α c . We also find that these TAE modes reappear in the ballooning mode second stability region for bands of α values. The global envelope structures of these TAE modes are studied by WKB method and are found to be bounded radially if the local mode frequency has a maximum in radius. 15 refs., 14 figs
Experimental study of toroidicity-induced Alfven eigenmode (TAE) stability at high q(0)
International Nuclear Information System (INIS)
Batha, S.H.; Levinton, F.M.; Spong, D.A.
1995-07-01
Experiments to destabilize the Toroidicity-induced Alfven Eigenmode (TAE) by energetic alpha particles were performed on the Tokamak Fusion Test Reactor using deuterium and tritium fuel. To decrease the alpha particle pressure instability threshold, discharges with an elevated value of q(0) > 1.5 were used. By raising q(0), the radial location of the low toroidal-mode-number TAE gaps moves toward the magnetic axis and into alignment with the region of maximum alpha pressure gradient, thereby (in theory) lowering the value of β α (0) required for instability. No TAE activity was observed when the central alpha particle β α reached 0.08% in a discharge with fusion power of 2.4 MW. Calculations show that the fusion power is within a factor of 1.5 to 3 of the instability threshold
Fast particle effects on the internal kink, fishbone and Alfven modes
International Nuclear Information System (INIS)
Gorelenkov, N.N.; Bernabei, S.; Cheng, C.Z.; Fu, G.Y.; Hill, K.; Kaye, S.; Kramer, G.J.; Nazikian, R.; Park, W.; Kusama, Y.; Shinokhara, K.; Ozeki, T.
2001-01-01
The issues of linear stability of low frequency perturbative and nonperturbative modes in advanced tokamak regimes are addressed based on recent developments in theory, computational methods, and progress in experiments. Perturbative codes NOVA and ORBIT are used to calculate the effects of TAEs on fast particle population in spherical tokamak NSTX. Nonperturbative analysis of chirping frequency modes in experiments on TFTR and JT-60U is presented using the kinetic code HINST, which identified such modes as a separate branch of Alfven modes - resonance TAE (R-TAE). Internal kink mode stability in the presence of fast particles is studied using the NOVA code and hybrid kinetic-MHD nonlinear code M3D. (author)
Fast Particle Effects on the Internal Kink, Fishbone and Alfven Modes
International Nuclear Information System (INIS)
Gorelenkov, N.N.; Bernabei, S.; Cheng, C.Z.; Fu, G.Y.; Hill, K.; Kaye, S.; Kramer, G.J.; Kusama, Y.; Shinohara, K.; Nazikian, R.; Ozeki, T.; Park, W.
2000-01-01
The issues of linear stability of low frequency perturbative and nonperturbative modes in advanced tokamak regimes are addressed based on recent developments in theory, computational methods, and progress in experiments. Perturbative codes NOVA and ORBIT are used to calculate the effects of TAEs on fast particle population in spherical tokamak NSTX. Nonperturbative analysis of chirping frequency modes in experiments on TFTR and JT-60U is presented using the kinetic code HINST, which identified such modes as a separate branch of Alfven modes - resonance TAE (R-TAE). Internal kink mode stability in the presence of fast particles is studied using the NOVA code and hybrid kinetic-MHD nonlinear code M3D
Electromagnetic transport components and sheared flows in drift-Alfven turbulence
DEFF Research Database (Denmark)
Naulin, V.
2003-01-01
Results from three-dimensional numerical simulations of drift-Alfven turbulence in a toroidal geometry with sheared magnetic field are presented. The simulations show a relation between self-generated poloidal shear flows and magnetic field perturbations. For large values of the plasma beta we ob...... with a folded Gaussian, while the PDFs of the spatially averaged transport are in good agreement with an extreme value distribution. (C) 2003 American Institute of Physics....... related to magnetic flutter is proposed. The characteristics of the ExB flux are investigated using probability density distribution functions (PDFs). Although they are not Gaussian, no signs of algebraic tails in the PDFs are observed. The PDFs of the pointwise transport are found to agree well...
Kinetic-magnetohydrodynamic simulation study of fast ions and toroidal Alfven eigenmodes
International Nuclear Information System (INIS)
Todo, Y.; Sato, T.
2001-01-01
Particle-magnetohydrodynamic and Fokker-Planck-magnetohydrodynamic simulations of fast ions and toroidicity-induced Alfven eigenmodes (TAE modes) have been carried out. Alpha particle losses induced by TAE mode are investigated with particle-magnetohydrodynamic simulations. Trapped particles near the passing-trapped boundary in the phase space are also lost appreciably in addition to the counter-passing particles. In Fokker-Planck-magnetohydrodynamic simulation source and slowing-down of fast ions are considered. A coherent pulsating behavior of multiple TAE modes, which occurs in neutral beam injection experiments, is observed when the slowing-down time is much longer than the damping time of the TAE modes and the fast-ion pressure is sufficiently high. For a slowing-down time comparable to the damping time, the TAE modes reach steady saturation levels. (author)
Kinetic-magnetohydrodynamic simulation study of fast ions and toroidal Alfven eigenmodes
International Nuclear Information System (INIS)
Todo, Y.; Sato, T.
1999-01-01
Particle-magnetohydrodynamic and Fokker-Planck-magnetohydrodynamic simulations of fast ions and toroidicity-induced Alfven eigenmodes (TAE modes) have been carried out. Alpha particle losses induced by TAE mode are investigated with particle-magnetohydrodynamic simulations. Trapped particles near the passing-trapped boundary in the phase space are also lost appreciably in addition to the counter-passing particles. In Fokker-Planck-magnetohydrodynamic simulation source and slowing-down of fast ions are considered. A coherent pulsating behavior of multiple TAE modes, which occurs in neutral beam injection experiments, is observed when the slowing-down time is much longer than the damping time of the TAE modes and the fast-ion pressure is sufficiently high. For a slowing-down time comparable to the damping time, the TAE modes reach steady saturation levels. (author)
Drift-Alfven eigenmodes in inhomogeneous electron-positron-ion plasmas
Energy Technology Data Exchange (ETDEWEB)
Haque, Q; Ahmad, Ali [Theoretical Plasma Physics Division, PINSTECH, PO Nilore, Islamabad (Pakistan); Yamin, S, E-mail: qamar@pinstech.org.pk [Physics Division, PO Nilore, Islamabad (Pakistan)
2011-03-15
An analytical description of drift-Alfven modes in nonuniform bounded magnetized electron-positron-ion plasmas is presented here. In the linear domain, linearized equations are solved by considering the Gaussian density profile in the radial direction. For this bounded plasma, the condition for the quantization of the modes is found. We note that the condition depends upon the density ratios of different plasma species. The full set of nonlinear equations is also solved, yielding stationary rotating solutions in terms of Bessel functions. We also note that the behavior of the nonlinear structures can be affected by the concentration of the positrons in the system. The importance of the present results with respect to astrophysical plasmas is pointed out.
Zonal Flows Driven by Small-Scale Drift-Alfven Modes
International Nuclear Information System (INIS)
Li Dehui; Zhou Deng
2011-01-01
Generation of zonal flows by small-scale drift-Alfven modes is investigated by adopting the approach of parametric instability with the electron polarization drift included. The zonal mode can be excited by primary modes propagating at both electron and ion diamagnetic drift directions in contrast to the assertion in previous studies that only primary modes propagating in the ion diamagnetic drift directions can drive zonal instabilities. Generally, the growth rate of the driven zonal mode is in the same order as that in previous study. However, different from the previous work, the growth rate is no longer proportional to the difference between the diamagnetic drift frequencies of electrons and ions. (magnetically confined plasma)
Hatch, Spencer Mark
The magnetosphere-ionosphere (M-I) transition region is the several thousand-kilometer stretch between the cold, dense and variably resistive region of ionized atmospheric gases beginning tens of kilometers above the terrestrial surface, and the hot, tenuous, and conductive plasmas that interface with the solar wind at higher altitudes. The M-I transition region is therefore the site through which magnetospheric conditions, which are strongly susceptible to solar wind dynamics, are communicated to ionospheric plasmas, and vice versa. We systematically study the influence of geomagnetic storms on energy input, electron precipitation, and ion outflow in the M-I transition region, emphasizing the role of inertial Alfven waves both as a preferred mechanism for dynamic (instead of static) energy transfer and particle acceleration, and as a low-altitude manifestation of high-altitude interaction between the solar wind and the magnetosphere, as observed by the FAST satellite. Via superposed epoch analysis and high-latitude distributions derived as a function of storm phase, we show that storm main and recovery phase correspond to strong modulations of measures of Alfvenic activity in the vicinity of the cusp as well as premidnight. We demonstrate that storm main and recovery phases occur during 30% of the four-year period studied, but together account for more than 65% of global Alfvenic energy deposition and electron precipitation, and more than 70% of the coincident ion outflow. We compare observed interplanetary magnetic field (IMF) control of inertial Alfven wave activity with Lyon-Fedder-Mobarry global MHD simulations predicting that southward IMF conditions lead to generation of Alfvenic power in the magnetotail, and that duskward IMF conditions lead to enhanced prenoon Alfvenic power in the Northern Hemisphere. Observed and predicted prenoon Alfvenic power enhancements contrast with direct-entry precipitation, which is instead enhanced postnoon. This situation
Surface wave propagation in an ideal Hall-magnetohydrodynamic plasma jet in flowing environment
International Nuclear Information System (INIS)
Sikka, Himanshu; Kumar, Nagendra; Zhelyazkov, Ivan
2004-01-01
The behavior of the Hall-magnetohydrodynamic (Hall-MHD) sausage and kink waves is studied in the presence of steady flow. The influence of the flow both inside and outside the plasma slab is taken into account. The plasma in the environment is considered to be cold and moves with the different flow velocity outside the slab. In the limit of parallel propagation, dispersion relation is derived to discuss the propagation of both the modes. Numerical results for the propagation characteristics are obtained for different Alfvenic Mach number ratios inside and outside the slab. It is found that the dispersion curves for both surface modes, namely, the sausage and kink ones in cold plasma show complexities in their behavior in terms of multivalued portions of the curves. These multivalued portions correspond to the different normalized phase velocities for the same value of Alfvenic Mach number. In contrast to the conventional MHD surface waves which are assumed to be pure surface waves or pseudosurface waves, surface waves are obtained which are bulk waves for very small dimensionless wave numbers, then turn to leaky waves and finally transform to pure surface waves for values of dimensionless wave number greater than one
Two-color walking Peregrine solitary waves.
Baronio, Fabio; Chen, Shihua; Mihalache, Dumitru
2017-09-15
We study the extreme localization of light, evolving upon a non-zero background, in two-color parametric wave interaction in nonlinear quadratic media. We report the existence of quadratic Peregrine solitary waves, in the presence of significant group-velocity mismatch between the waves (or Poynting vector beam walk-off), in the regime of cascading second-harmonic generation. This finding opens a novel path for the experimental demonstration of extreme rogue waves in ultrafast quadratic nonlinear optics.
Cascaded resonant bridge converters
Stuart, Thomas A. (Inventor)
1989-01-01
A converter for converting a low voltage direct current power source to a higher voltage, high frequency alternating current output for use in an electrical system where it is desired to use low weight cables and other circuit elements. The converter has a first stage series resonant (Schwarz) converter which converts the direct current power source to an alternating current by means of switching elements that are operated by a variable frequency voltage regulator, a transformer to step up the voltage of the alternating current, and a rectifier bridge to convert the alternating current to a direct current first stage output. The converter further has a second stage series resonant (Schwarz) converter which is connected in series to the first stage converter to receive its direct current output and convert it to a second stage high frequency alternating current output by means of switching elements that are operated by a fixed frequency oscillator. The voltage of the second stage output is controlled at a relatively constant value by controlling the first stage output voltage, which is accomplished by controlling the frequency of the first stage variable frequency voltage controller in response to second stage voltage. Fault tolerance in the event of a load short circuit is provided by making the operation of the first stage variable frequency voltage controller responsive to first and second stage current limiting devices. The second stage output is connected to a rectifier bridge whose output is connected to the input of the second stage to provide good regulation of output voltage wave form at low system loads.
Multiplicity distributions in QCD cascades
International Nuclear Information System (INIS)
Gustafson, G.
1992-03-01
Multiplicity distributions for hadrons and for jets are studied in QCD parton cascades. The colour dipole formalism is used and earlier results in the double log approximation are generalized to include terms which are suppressed by colour factors or factors of ln s. The result is a set of coupled differential equations, together with appropriate boundary conditions
A comparison of methods for cascade prediction
Guo, Ruocheng; Shakarian, Paulo
2016-01-01
Information cascades exist in a wide variety of platforms on Internet. A very important real-world problem is to identify which information cascades can go viral. A system addressing this problem can be used in a variety of applications including public health, marketing and counter-terrorism. As a cascade can be considered as compound of the social network and the time series. However, in related literature where methods for solving the cascade prediction problem were proposed, the experimen...
Computer simulation of displacement cascades in copper
International Nuclear Information System (INIS)
Heinisch, H.L.
1983-06-01
More than 500 displacement cascades in copper have been generated with the computer simulation code MARLOWE over an energy range pertinent to both fission and fusion neutron spectra. Three-dimensional graphical depictions of selected cascades, as well as quantitative analysis of cascade shapes and sizes and defect densities, illustrate cascade behavior as a function of energy. With increasing energy, the transition from production of single compact damage regions to widely spaced multiple damage regions is clearly demonstrated
Dynamics robustness of cascading systems.
Directory of Open Access Journals (Sweden)
Jonathan T Young
2017-03-01
Full Text Available A most important property of biochemical systems is robustness. Static robustness, e.g., homeostasis, is the insensitivity of a state against perturbations, whereas dynamics robustness, e.g., homeorhesis, is the insensitivity of a dynamic process. In contrast to the extensively studied static robustness, dynamics robustness, i.e., how a system creates an invariant temporal profile against perturbations, is little explored despite transient dynamics being crucial for cellular fates and are reported to be robust experimentally. For example, the duration of a stimulus elicits different phenotypic responses, and signaling networks process and encode temporal information. Hence, robustness in time courses will be necessary for functional biochemical networks. Based on dynamical systems theory, we uncovered a general mechanism to achieve dynamics robustness. Using a three-stage linear signaling cascade as an example, we found that the temporal profiles and response duration post-stimulus is robust to perturbations against certain parameters. Then analyzing the linearized model, we elucidated the criteria of when signaling cascades will display dynamics robustness. We found that changes in the upstream modules are masked in the cascade, and that the response duration is mainly controlled by the rate-limiting module and organization of the cascade's kinetics. Specifically, we found two necessary conditions for dynamics robustness in signaling cascades: 1 Constraint on the rate-limiting process: The phosphatase activity in the perturbed module is not the slowest. 2 Constraints on the initial conditions: The kinase activity needs to be fast enough such that each module is saturated even with fast phosphatase activity and upstream changes are attenuated. We discussed the relevance of such robustness to several biological examples and the validity of the above conditions therein. Given the applicability of dynamics robustness to a variety of systems, it
Cascaded Bragg scattering in fiber optics.
Xu, Y Q; Erkintalo, M; Genty, G; Murdoch, S G
2013-01-15
We report on a theoretical and experimental study of cascaded Bragg scattering in fiber optics. We show that the usual energy-momentum conservation of Bragg scattering can be considerably relaxed via cascade-induced phase-matching. Experimentally we demonstrate frequency translation over six- and 11-fold cascades, in excellent agreement with derived phase-matching conditions.
Linear and Nonlinear MHD Wave Processes in Plasmas. Final Report
International Nuclear Information System (INIS)
Tataronis, J. A.
2004-01-01
This program treats theoretically low frequency linear and nonlinear wave processes in magnetized plasmas. A primary objective has been to evaluate the effectiveness of MHD waves to heat plasma and drive current in toroidal configurations. The research covers the following topics: (1) the existence and properties of the MHD continua in plasma equilibria without spatial symmetry; (2) low frequency nonresonant current drive and nonlinear Alfven wave effects; and (3) nonlinear electron acceleration by rf and random plasma waves. Results have contributed to the fundamental knowledge base of MHD activity in symmetric and asymmetric toroidal plasmas. Among the accomplishments of this research effort, the following are highlighted: Identification of the MHD continuum mode singularities in toroidal geometry. Derivation of a third order ordinary differential equation that governs nonlinear current drive in the singular layers of the Alfven continuum modes in axisymmetric toroidal geometry. Bounded solutions of this ODE implies a net average current parallel to the toroidal equilibrium magnetic field. Discovery of a new unstable continuum of the linearized MHD equation in axially periodic circular plasma cylinders with shear and incompressibility. This continuum, which we named ''accumulation continuum'' and which is related to ballooning modes, arises as discrete unstable eigenfrequency accumulate on the imaginary frequency axis in the limit of large mode numbers. Development of techniques to control nonlinear electron acceleration through the action of multiple coherent and random plasmas waves. Two important elements of this program aye student participation and student training in plasma theory
Resonators for magnetohydrodynamic waves in the solar corona: radioemission modulation effect
International Nuclear Information System (INIS)
Zajtsev, V.V.; Stepanov, A.V.
1982-01-01
Data on type 2 solar radio bursts are analyzed in the framework of a model of radio emission production by shock waves. Type 2 solar radio bursts data are shown to suggest the existence of Alfven velocity minimum at a height of the one solar radius in the corona. The domain of a low Alfven velocity is a resonator for the fast magnetosonic waves. The eigenmodes of the resonator are determined. The main mode period is about a few minutes. Fast modes in the resonator can be amplified by energetic ion beams at the Cherenkov resonance. The modulation of meter solar radio emission with a period of about a few minutes can be explained by radiowave propagation through the MHD-resonator
Quantum cascade laser combs: effects of modulation and dispersion.
Villares, Gustavo; Faist, Jérôme
2015-01-26
Frequency comb formation in quantum cascade lasers is studied theoretically using a Maxwell-Bloch formalism based on a modal decomposition, where dispersion is considered. In the mid-infrared, comb formation persists in the presence of weak cavity dispersion (500 fs2 mm-1) but disappears when much larger values are used (30'000 fs2 mm-1). Active modulation at the round-trip frequency is found to induce mode-locking in THz devices, where the upper state lifetime is in the tens of picoseconds. Our results show that mode-locking based on four-wave mixing in broadband gain, low dispersion cavities is the most promising way of achieving broadband quantum cascade laser frequency combs.
Period adding cascades: experiment and modeling in air bubbling.
Pereira, Felipe Augusto Cardoso; Colli, Eduardo; Sartorelli, José Carlos
2012-03-01
Period adding cascades have been observed experimentally/numerically in the dynamics of neurons and pancreatic cells, lasers, electric circuits, chemical reactions, oceanic internal waves, and also in air bubbling. We show that the period adding cascades appearing in bubbling from a nozzle submerged in a viscous liquid can be reproduced by a simple model, based on some hydrodynamical principles, dealing with the time evolution of two variables, bubble position and pressure of the air chamber, through a system of differential equations with a rule of detachment based on force balance. The model further reduces to an iterating one-dimensional map giving the pressures at the detachments, where time between bubbles come out as an observable of the dynamics. The model has not only good agreement with experimental data, but is also able to predict the influence of the main parameters involved, like the length of the hose connecting the air supplier with the needle, the needle radius and the needle length.
Limits to compression with cascaded quadratic soliton compressors
DEFF Research Database (Denmark)
Bache, Morten; Bang, Ole; Krolikowski, Wieslaw
2008-01-01
We study cascaded quadratic soliton compressors and address the physical mechanisms that limit the compression. A nonlocal model is derived, and the nonlocal response is shown to have an additional oscillatory component in the nonstationary regime when the group-velocity mismatch (GVM) is strong....... This inhibits efficient compression. Raman-like perturbations from the cascaded nonlinearity, competing cubic nonlinearities, higher-order dispersion, and soliton energy may also limit compression, and through realistic numerical simulations we point out when each factor becomes important. We find......, the simulations show that reaching single-cycle duration is ultimately inhibited by competing cubic nonlinearities as well as dispersive waves, that only show up when taking higher-order dispersion into account....
International Nuclear Information System (INIS)
Niu, K.
1996-01-01
A shock wave is a discontinuous surface that connects supersonic flow with subsonic flow. After a shock wave, flow velocity is reduced, and pressure and temperature increase; entropy especially increases across a shock wave. Therefore, flow is in nonequilibrium, and irreversible processes occur inside the shock layer. The thickness of a shock wave in neutral gas is of the order of the mean free path of the fluid particle. A shock wave also appears in magnetized plasma. Provided that when the plasma flow is parallel to the magnetic field, a shock wave appears if the governing equation for velocity potential is in hyperbolic type in relation with the Mach number and the Alfven number. When the flow is perpendicular to the magnetic field, the Maxwell stress, in addition to the pressure, plays a role in the shock wave in plasma. When the plasma temperature is so high, as the plasma becomes collision-free, another type of shock wave appears. In a collision-free shock wave, gyromotions of electrons around the magnetic field lines cause the shock formation instead of collisions in a collision-dominant plasma or neutral gas. Regardless of a collision-dominant or collision-free shock wave, the fluid that passes through the shock wave is heated in addition to being compressed. In inertial confinement fusion, the fuel must be compressed. Really, implosion motion performs fuel compression. A shock wave, appearing in the process of implosion, compresses the fuel. The shock wave, however, heats the fuel more intensively, and it makes it difficult to compress the fuel further because high temperatures invite high pressure. Adiabatic compression of the fuel is the desired result during the implosion, without the formation of a shock wave. (Author)
Electromagnetic ion cyclotron waves observed near the oxygen cyclotron frequency by ISEE 1 and 2
Fraser, B. J.; Samson, J. C.; Hu, Y. D.; Mcpherron, R. L.; Russell, C. T.
1992-01-01
The first results of observations of ion cyclotron waves by the elliptically orbiting ISEE 1 and 2 pair of spacecraft are reported. The most intense waves (8 nT) were observed in the outer plasmasphere where convection drift velocities were largest and the Alfven velocity was a minimum. Wave polarization is predominantly left-handed with propagation almost parallel to the ambient magnetic field, and the spectral slot and polarization reversal predicted by cold plasma propagation theory are identified in the wave data. Computations of the experimental wave spectra during the passage through the plasmapause show that the spectral slots relate to the local plasma parameters, possibly suggesting an ion cyclotron wave growth source near the spacecraft. A regular wave packet structure seen over the first 30 min of the event is attributed to the modulation of this energy source by the Pc 5 waves seen at the same time.
Atom-atom collision cascades localization
International Nuclear Information System (INIS)
Kirsanov, V.V.
1980-01-01
The presence of an impurity and thermal vibration influence on the atom-atom collision cascade development is analysed by the computer simulation method (the modificated dynamic model). It is discovered that the relatively low energetic cascades are localized with the temperature increase of an irradiated crystal. On the basis of the given effect the mechanism of splitting of the high energetic cascades into subcascades is proposed. It accounts for two factors: the primary knocked atom energy and the irradiated crystal temperature. Introduction of an impurity also localizes the cascades independently from the impurity atom mass. The cascades localization leads to intensification of the process of annealing in the cascades and reduction of the post-cascade vacancy cluster sizes. (author)
Cascade Chaotic System With Applications.
Zhou, Yicong; Hua, Zhongyun; Pun, Chi-Man; Chen, C L Philip
2015-09-01
Chaotic maps are widely used in different applications. Motivated by the cascade structure in electronic circuits, this paper introduces a general chaotic framework called the cascade chaotic system (CCS). Using two 1-D chaotic maps as seed maps, CCS is able to generate a huge number of new chaotic maps. Examples and evaluations show the CCS's robustness. Compared with corresponding seed maps, newly generated chaotic maps are more unpredictable and have better chaotic performance, more parameters, and complex chaotic properties. To investigate applications of CCS, we introduce a pseudo-random number generator (PRNG) and a data encryption system using a chaotic map generated by CCS. Simulation and analysis demonstrate that the proposed PRNG has high quality of randomness and that the data encryption system is able to protect different types of data with a high-security level.
Cascade reactor: granule fabrication processes
International Nuclear Information System (INIS)
Erlandson, O.D.; Winkler, E.O.; Maya, I.; Pitts, J.H.
1985-01-01
A key feature of Cascade is the granular blanket. Of the many blanket material options open to Cascade, fabrication of Li 2 O granules was felt to offer the greatest challenge. The authors explored available methods for initial Li 2 O granule fabrication. They identified three cost-effective processes for fabricating Li 2 O granules: the VSM drop-melt furnace process, which is based on melting and spheroidizing irregularly shaped Li 2 O feed granules; the LiOH process, which spheroidizes liquefied LiOH and uses GA Technologies' sphere-forming procedures; and the Li 2 CO 3 sol-gel process, used for making spherical fuel particles for the high-temperature gas-cooled reactor (HTGR). Each process is described below
Bankruptcy cascades in interbank markets.
Directory of Open Access Journals (Sweden)
Gabriele Tedeschi
Full Text Available We study a credit network and, in particular, an interbank system with an agent-based model. To understand the relationship between business cycles and cascades of bankruptcies, we model a three-sector economy with goods, credit and interbank market. In the interbank market, the participating banks share the risk of bad debits, which may potentially spread a bank's liquidity problems through the network of banks. Our agent-based model sheds light on the correlation between bankruptcy cascades and the endogenous economic cycle of booms and recessions. It also demonstrates the serious trade-off between, on the one hand, reducing risks of individual banks by sharing them and, on the other hand, creating systemic risks through credit-related interlinkages of banks. As a result of our study, the dynamics underlying the meltdown of financial markets in 2008 becomes much better understandable.
Wave-Number Spectra and Intermittency in the Terrestrial Foreshock Region
International Nuclear Information System (INIS)
Narita, Y.; Glassmeier, K.-H.; Treumann, R. A.
2006-01-01
Wave-number spectra of magnetic field fluctuations are directly determined in the terrestrial foreshock region (upstream of a quasiparallel collisionless shock wave) using four-point Cluster spacecraft measurements. The spectral curve is characterized by three ranges reminiscent of turbulence: energy injection, inertial, and dissipation range. The spectral index for the inertial range spectrum is close to Kolmogorov's slope, -5/3. On the other hand, the fluctuations are highly anisotropic and intermittent perpendicular to the mean magnetic field direction. These results suggest that the foreshock is in a weakly turbulent and intermittent state in which parallel propagating Alfven waves interact with one another, resulting in the phase coherence or the intermittency
Lens Coupled Quantum Cascade Laser
Hu, Qing (Inventor); Lee, Alan Wei Min (Inventor)
2013-01-01
Terahertz quantum cascade (QC) devices are disclosed that can operate, e.g., in a range of about 1 THz to about 10 THz. In some embodiments, QC lasers are disclosed in which an optical element (e.g., a lens) is coupled to an output facet of the laser's active region to enhance coupling of the lasing radiation from the active region to an external environment. In other embodiments, terahertz amplifier and tunable terahertz QC lasers are disclosed.
International Nuclear Information System (INIS)
Lei-Jian, Shen; Chuang-She, Li; Yi-Gang, Du; Cui-Cui, Zuo; Zhi-Qiang, Nie; Yan-Peng, Zhang; Yuan-Yuan, Li; Chen-Li, Gan; Ke-Qing, Lu
2008-01-01
We study the competition between dispersion and absorption of doubly-dressed four-wave mixing (DDFWM) and dressed six-wave mixing. In the case of weak coupling fields limit, we find DDFWM signal is affected by destructive interference between four-wave mixing(FWM) and six-wave mixing as well as constructive interference between FWM and eight-wave mixing. By analysing the difference between two kinds of doubly dressing mechanisms (parallel cascade and nested cascade) in this opening five-level system, we can further understand the generated high-order nonlinear optical signal dressed by multi-fields
Low Frequency Turbulence as the Source of High Frequency Waves in Multi-Component Space Plasmas
Khazanov, George V.; Krivorutsky, Emmanuel N.; Uritsky, Vadim M.
2011-01-01
Space plasmas support a wide variety of waves, and wave-particle interactions as well as wavewave interactions are of crucial importance to magnetospheric and ionospheric plasma behavior. High frequency wave turbulence generation by the low frequency (LF) turbulence is restricted by two interconnected requirements: the turbulence should be strong enough and/or the coherent wave trains should have the appropriate length. These requirements are strongly relaxed in the multi-component plasmas, due to the heavy ions large drift velocity in the field of LF wave. The excitation of lower hybrid waves (LHWs), in particular, is a widely discussed mechanism of interaction between plasma species in space and is one of the unresolved questions of magnetospheric multi-ion plasmas. It is demonstrated that large-amplitude Alfven waves, in particular those associated with LF turbulence, may generate LHW s in the auroral zone and ring current region and in some cases (particularly in the inner magnetosphere) this serves as the Alfven wave saturation mechanism. We also argue that the described scenario can playa vital role in various parts of the outer magnetosphere featuring strong LF turbulence accompanied by LHW activity. Using the data from THEMIS spacecraft, we validate the conditions for such cross-scale coupling in the near-Earth "flow-braking" magnetotail region during the passage of sharp injection/dipolarization fronts, as well as in the turbulent outflow region of the midtail reconnection site.
Energy Technology Data Exchange (ETDEWEB)
Podesta, M; Crocker, N A; Fredrickson, E D; Gorelenkov, N N; Heidbrink, W W; Kubota, S; LeBlanc, B P
2011-04-26
The National Spherical Torus Experiment (NSTX, [M. Ono et al., Nucl. Fusion 40, 557 (2000)]) routinely operates with neutral beam injection as the primary system for heating and current drive. The resulting fast ion population is super-Alfv enic, with velocities 1 < vfast=vAlfven < 5. This provides a strong drive for toroidicity-induced Alfv en eigenmodes (TAEs). As the discharge evolves, the fast ion population builds up and TAEs exhibit increasing bursts in amplitude and down-chirps in frequency, which eventually lead to a so-called TAE avalanche. Avalanches cause large (≤ 30%) fast ion losses over ~ 1 ms, as inferred from the neutron rate. The increased fast ion losses correlate with a stronger activity in the TAE band. In addition, it is shown that a n = 1 mode with frequency well below the TAE gap appears in the Fourier spectrum of magnetic fluctuations as a result of non-linear mode coupling between TAEs during avalanche events. The non-linear coupling between modes, which leads to enhanced fast ion transport during avalanches, is investigated.
Remote control of Alfven eigenmode sensing system on the large helical device
Energy Technology Data Exchange (ETDEWEB)
Ito, T. [Nagoya University, Department of Energy Engineering and Science, Furo-cho, Chikusa-ku, Nagoya City, Aichi (Japan)], E-mail: ito.takafumi@lhd.nifs.ac.jp; Toi, K. [Nagoya University, Department of Energy Engineering and Science, Furo-cho, Chikusa-ku, Nagoya City, Aichi (Japan); National Institute for Fusion Science, 322-6 Oroshicho, Toki, Gifu (Japan); Matsunaga, G. [Japan Atomic Energy Agency, 801-1 Mukouyama, Naka, Ibaraki 311-0193 (Japan)
2008-04-15
An active sensing system of Alfven eigenmodes (AEs), which consists of a set of toroidally distributed loop antennas and several bi-polar power supplies, has been developed in the large helical device (LHD). The power supplies are controlled with a function generator receiving a control pattern of antenna current and the driving frequency from a personal computer (PC) in an LHD control room. This sensing method is based on the analysis of the frequency dependence of a transfer function that is derived by the ratio of the Fourier-transformed magnetic probe signal ('plasma response') to antenna current one ('exciter signal'). Typically, the driving frequency of the antenna current is swept linearly in time from 10 kHz to 500 kHz for 2 s in the LHD experiment. The sensing system is fully controlled through Ethernet LAN with easy extendable GUI. Configuration and control scheme of the active sensing system of AEs are presented in this paper. An initial result of the system operation is also described.
International Nuclear Information System (INIS)
Bergkvist, T.; Hellsten, T.; Johnson, T.
2006-01-01
Alfven eigenmodes (AEs) excited by fusion born α particles can degrade the heating efficiency of a burning plasma and throw out αs. To experimentally study the effects of excitation of AEs and the redistribution of the fast ions, ion cyclotron resonance heating (ICRH) is often used. The distribution function of thermonuclear αs in a reactor is expected to be isotropic and constantly renewed through DT reactions. The distribution function of cyclotron heated ions is strongly anisotropic, and the ICRH do not only renew the distribution function but also provide a strong decorrelation mechanism between the fast ions and the AE. Because of the sensitivity of the AE dynamics on the details of the distribution function, the location of the resonance surfaces in phase space and the extent of the overlapping resonant regions for different AEs, a self-consistent treatment of the AE excitation and the ICRH is necessary. Interactions of fast ions with AEs during ICRH has been implemented in the SELFO code. Simulations are in good agreement with the experimentally observer pitch-fork splitting and rapid damping of the AE as ICRH is turned off. The redistribution of fast ions have been studied in the presence of several driven AEs. (author)
Alfven eigenmode observations on DIII-D via two-colour CO2 interferometry
International Nuclear Information System (INIS)
Zeeland, M A van; Kramer, G J; Nazikian, R; Berk, H L; Carlstrom, T N; Solomon, W M
2005-01-01
Measurements are presented of toroidicity-induced (TAEs) and reverse shear (RSAEs) Alfven eigenmodes made using the standard two-colour CO 2 interferometer on DIII-D modified for increased bandwidth. Typical values of the effective line-integrated density perturbation in DIII-D are found to be d(nL)/nL ∼ 10 -3 , and comparisons are made with NOVA calculations as well as magnetic measurements. There is a strong difference in the measured power spectrum between vertical and radial chords through the plasma. On average, vertical views are characterized by a larger line-integrated density perturbation due to TAEs than radial chords. Radial chords, however, can be used much more reliably than vertical chords to identify the presence of RSAEs in the plasma-a result found to be due to the radially localized nature of these modes. In general, the apparent amplitude of the observed modes for both TAE and RSAE is found to be highly dependent on viewing location. (letter to the editor)
Remote control of Alfven eigenmode sensing system on the large helical device
International Nuclear Information System (INIS)
Ito, T.; Toi, K.; Matsunaga, G.
2008-01-01
An active sensing system of Alfven eigenmodes (AEs), which consists of a set of toroidally distributed loop antennas and several bi-polar power supplies, has been developed in the large helical device (LHD). The power supplies are controlled with a function generator receiving a control pattern of antenna current and the driving frequency from a personal computer (PC) in an LHD control room. This sensing method is based on the analysis of the frequency dependence of a transfer function that is derived by the ratio of the Fourier-transformed magnetic probe signal ('plasma response') to antenna current one ('exciter signal'). Typically, the driving frequency of the antenna current is swept linearly in time from 10 kHz to 500 kHz for 2 s in the LHD experiment. The sensing system is fully controlled through Ethernet LAN with easy extendable GUI. Configuration and control scheme of the active sensing system of AEs are presented in this paper. An initial result of the system operation is also described
Plasmon band gap generated by intense ion acoustic waves
International Nuclear Information System (INIS)
Son, S.; Ku, S.
2010-01-01
In the presence of an intense ion acoustic wave, the energy-momentum dispersion relation of plasmons is strongly modified to exhibit a band gap structure. The intensity of an ion acoustic wave might be measured from the band gap width. The plasmon band gap can be used to block the nonlinear cascading channel of the Langmuir wave decay.
Nonlocal description of X waves in quadratic nonlinear materials
DEFF Research Database (Denmark)
Larsen, Peter Ulrik Vingaard; Sørensen, Mads Peter; Bang, Ole
2006-01-01
We study localized light bullets and X-waves in quadratic media and show how the notion of nonlocality can provide an alternative simple physical picture of both types of multi-dimensional nonlinear waves. For X-waves we show that a local cascading limit in terms of a nonlinear Schrodinger equation...
MCDF calculations of Auger cascade processes
Beerwerth, Randolf; Fritzsche, Stephan
2017-10-01
We model the multiple ionization of near-neutral core-excited atoms where a cascade of Auger processes leads to the emission of several electrons. We utilize the multiconfiguration Dirac-Fock (MCDF) method to generate approximate wave functions for all fine-structure levels and to account for all decays between them. This approach allows to compute electron spectra, the population of final-states and ion yields, that are accessible in many experiments. Furthermore, our approach is based on the configuration interaction method. A careful treatment of correlation between electronic configurations enables one to model three-electron processes such as an Auger decay that is accompanied by an additional shake-up transition. Here, this model is applied to the triple ionization of atomic cadmium, where we show that the decay of inner-shell 4p holes to triply-charged final states is purely due to the shake-up transition of valence 5s electrons. Contribution to the Topical Issue "Atomic and Molecular Data and their Applications", edited by Gordon W.F. Drake, Jung-Sik Yoon, Daiji Kato, Grzegorz Karwasz.
Theoretical Studies of Drift-Alfven and Energetic Particle Physics in Fusion Plasmas
Energy Technology Data Exchange (ETDEWEB)
Liu Chen
2005-07-06
Nonlinear equations for the slow space-time evolution of the radial drift-wave envelope and zonal flow amplitude have been self-consistently derived for a model nonuniform tokamak equilibrium within the coherent four-wave drift wave-zonal flow modulation interaction model of Chen, Lin, and White [Phys. Plasmas 7, 3129 (2000)]. Solutions clearly demonstrate turbulence spreading due to nonlinearly dispersiveness and, consequently, the device-size dependence of the saturated wave intensities and transport coefficients.
Multi-component optical solitary waves
DEFF Research Database (Denmark)
Kivshar, Y. S.; Sukhorukov, A. A.; Ostrovskaya, E. A.
2000-01-01
We discuss several novel types of multi-component (temporal and spatial) envelope solitary waves that appear in fiber and waveguide nonlinear optics. In particular, we describe multi-channel solitary waves in bit-parallel-wavelength fiber transmission systems for highperformance computer networks......, multi-color parametric spatial solitary waves due to cascaded nonlinearities of quadratic materials, and quasiperiodic envelope solitons due to quasi-phase-matching in Fibonacci optical superlattices. (C) 2000 Elsevier Science B.V. All rights reserved....
Abnormal cascading failure spreading on complex networks
International Nuclear Information System (INIS)
Wang, Jianwei; Sun, Enhui; Xu, Bo; Li, Peng; Ni, Chengzhang
2016-01-01
Applying the mechanism of the preferential selection of the flow destination, we develop a new method to quantify the initial load on an edge, of which the flow is transported along the path with the shortest edge weight between two nodes. Considering the node weight, we propose a cascading model on the edge and investigate cascading dynamics induced by the removal of the edge with the largest load. We perform simulated attacks on four types of constructed networks and two actual networks and observe an interesting and counterintuitive phenomenon of the cascading spreading, i.e., gradually improving the capacity of nodes does not lead to the monotonous increase in the robustness of these networks against cascading failures. The non monotonous behavior of cascading dynamics is well explained by the analysis on a simple graph. We additionally study the effect of the parameter of the node weight on cascading dynamics and evaluate the network robustness by a new metric.
Sheared electric field-induced suppression of edge turbulence using externally driven R.F. waves
International Nuclear Information System (INIS)
Craddock, G.G.; Diamond, P.H.
1991-01-01
Here the authors propose a novel method for active control and suppression of edge turbulence by sheared ExB flows driven by externally launched RF waves. The theory developed addresses the problem of open-quotes flow driveclose quotes, which is somewhat analogous to the problem of plasma current drive. As originally demonstrated for the case of spontaneously driven flows, a net difference in the gradient of the fluid and magnetic Reynolds' stresses produced by radially propagating waves can drive the plasma flow. For the prototypical case of the Alfven wave flow drive considered here, ρ 0 r v θ > - r B θ > is proportional to k perpendicular 2 ρ s 2 in the case of the kinetic Alfven wave, and [(ηk perpendicular 2 -vk perpendicular 2 )/ω] 2 in the case of resistive MHD. Both results reflect the dependence of flow drive on the net stress imbalance. The shear layer width is determined by the waves evanescence length (determined by dissipation) that sets the stress gradient scale length, while the direction of the flow is determined by the poloidal orientation of the launched waves. In particular, it should be noted that both positive and negative E r may be driven, so that enhanced confinement need not be accompanied by impurity accumulation, as commonly encountered in spontaneous H-modes. The efficiency is determined by the criterion that the radial electric field shear be large enough to suppress turbulence. For typical TEXT parameters, and unity efficiency, 300 kW of absorbed power is needed to suppress turbulence over 3 cm radially. For DIII-D, 300 kW over 4 cm is needed. Also, direct transport losses induced by RF have been shown to be small. Extensions of the theory to ICRF are underway and are discussed. They also discuss the analogous problem of current drive using kinetic Alfven waves. 2 refs
Diode pumped cascade Er:Y2O3 laser
International Nuclear Information System (INIS)
Sanamyan, T
2015-01-01
A cascade, diode-pumped, continuous wave (CW), dual-wavelength operation in a 0.5% Er 3+ :Y 2 O 3 cryogenic ceramic laser is demonstrated for the first time. The laser operates on cascaded Er ( 4 I 11/2 → 4 I 13/2 → 4 I 15/2 ) transitions and can deliver 24 and 13 W at 1.6 and 2.7 μm, respectively. The overall efficiency with respect to the absorbed ∼980 nm power was 62%. This is, to our best knowledge, the first demonstration of an efficient, high power, cascade, erbium laser achieved in bulk solid-state lasers. The analysis of the output power, the laser’s wavelengths and slope efficiency for each individual laser transition are presented for pure CW operation mode. Also presented are the temporal behaviors of each laser line as a function of pump pulse duration in the quasi-CW regime. (letter)
Disaster Mythology and Availability Cascades
Directory of Open Access Journals (Sweden)
Lisa Grow Sun
2013-04-01
Full Text Available Sociological research conducted in the aftermath of natural disasters has uncovered a number of “disaster myths” – widely shared misconceptions about typical post-disaster human behavior. This paper discusses the possibility that perpetuation of disaster mythology reflects an “availability cascade,” defined in prior scholarship as a “self-reinforcing process of collective belief formation by which an expressed perception triggers a chain reaction that gives the perception increasing plausibility through its rising availability in public discourse.” (Kuran and Sunstein 1999. Framing the spread of disaster mythology as an availability cascade suggests that certain tools may be useful in halting the myths’ continued perpetuation. These tools include changing the legal and social incentives of so-called “availability entrepreneurs” – those principally responsible for beginning and perpetuating the cascade, as well as insulating decision-makers from political pressures generated by the availability cascade. This paper evaluates the potential effectiveness of these and other solutions for countering disaster mythology. Las investigaciones sociológicas realizadas tras los desastres naturales han hecho evidentes una serie de “mitos del desastre”, conceptos erróneos ampliamente compartidos sobre el comportamiento humano típico tras un desastre. Este artículo analiza la posibilidad de que la perpetuación de los mitos del desastre refleje una “cascada de disponibilidad”, definida en estudios anteriores como un “proceso de auto-refuerzo de la formación de una creencia colectiva, a través del que una percepción expresada produce una reacción en cadena que hace que la percepción sea cada vez más verosímil, a través de una mayor presencia en el discurso público” (Kuran y Sunstein 1999. Enmarcar la propagación de los mitos del desastre como una cascada de disponibilidad sugiere que ciertas herramientas pueden ser
Ion-implantation dense cascade data
International Nuclear Information System (INIS)
Winterbon, K.B.
1983-04-01
A tabulation is given of data useful in estimating various aspects of ion-implantation cascades in the nuclear stopping regime, particularly with respect to nonlinearity of the cascade at high energy densities. The tabulation is restricted to self-ion implantation. Besides power-cross-section cascade dimensions, various material properties are included. Scaling of derived quantities with input data is noted, so one is not limited to the values assumed by the author
The parametric decay of dust ion acoustic waves in non-uniform quantum dusty magnetoplasmas
International Nuclear Information System (INIS)
Jamil, M.; Ali, Waris; Shah, H. A.; Shahid, M.; Murtaza, G.; Salimullah, M.
2011-01-01
The parametric decay instability of a dust ion acoustic wave into low-frequency electrostatic dust-lower-hybrid and electromagnetic shear Alfven waves has been investigated in detail in an inhomogeneous cold quantum dusty plasma in the presence of external/ambient uniform magnetic field. The quantum magnetohydrodynamic model of plasmas with quantum effect arising through the Bohm potential and Fermi degenerate pressure has been employed in order to find the linear and nonlinear responses of the plasma particles for three-wave nonlinear coupling in a dusty magnetoplasma. A relatively high frequency electrostatic dust ion acoustic wave has been taken as the pump wave. It couples with two other low-frequency internal possible modes of the dusty magnetoplasma, viz., the dust-lower-hybrid and shear Alfven waves. The nonlinear dispersion relation of the dust-lower-hybrid wave has been solved to obtain the growth rate of the parametric decay instability. The growth rate is at a maximum for a small value of the external magnetic field B 0 . It is noted that the growth rate is proportional to the unperturbed electron number density n oe and is independent of inhomogeneity beyond L e =2 cm. An extraordinary growth rate is observed with the quantum effect.
International Nuclear Information System (INIS)
Takahashi, K.; Higbie, P.R.; Baker, D.N.
1985-01-01
Energetic particle data from the 1977-007 and 1979-053 satellites and magnetic field data from the GOES 2 and 3 satellites have been used to study eight compressional Pc 5 wave events observed at geostationary orbit during 1979. All the events occurred on the dayside, and most of them were observed during the recovery phase of a geomagnetic storm. By using the data from two of the satellites which were close to each other, we measured the azimuthal phase velocity V/sub phi/ and azimuthal wave number m for selected intervals. For all these intervals the waves propagated westward in the spacecraft frame, and we obtained Vertical Bar V/sub phi/ Vertical Bar = 4--14 km/s and Vertical Bar m Vertical Bar = 40--120. In addition, harmonics of a local standing Alfven wave were often present simultaneously with a compressional Pc 5 wave. The frequency of the compressional wave was typically 25% of that of the second harmonic of the Alfven wave. These observed features are discussed in the light of existing theories of instabilities in the ring current plasma
A non-conventional isotope separation cascade without any mixing: net cascade
International Nuclear Information System (INIS)
Zeng Shi; Jiang Dongjun; Ying Zhengen
2012-01-01
A component has different concentrations in the incoming flows at a confluent point in all existing isotope separations cascades for multi-component isotope separation and mixing is inevitable, which results in deterioration of separation performance of the separation cascade. However, realization of no-mixing at a confluent point is impossible with a conventional cascade. A non-conventional isotope separation cascade, net cascade, is found to be able to realize no mixings for all components at confluent points, and its concept is further developed here. No-mixing is fulfilled by requiring symmetrical separation of two specified key components at every stage, and the procedure of realizing no-mixing is presented in detail. Some properties of net cascade are investigated preliminarily, and the results demonstrated the no-mixing property is indeed realized. Net cascade is the only separation cascade that so far possesses the no-mixing property. (authors)
Contingency Analysis of Cascading Line Outage Events
Energy Technology Data Exchange (ETDEWEB)
Thomas L Baldwin; Magdy S Tawfik; Miles McQueen
2011-03-01
As the US power systems continue to increase in size and complexity, including the growth of smart grids, larger blackouts due to cascading outages become more likely. Grid congestion is often associated with a cascading collapse leading to a major blackout. Such a collapse is characterized by a self-sustaining sequence of line outages followed by a topology breakup of the network. This paper addresses the implementation and testing of a process for N-k contingency analysis and sequential cascading outage simulation in order to identify potential cascading modes. A modeling approach described in this paper offers a unique capability to identify initiating events that may lead to cascading outages. It predicts the development of cascading events by identifying and visualizing potential cascading tiers. The proposed approach was implemented using a 328-bus simplified SERC power system network. The results of the study indicate that initiating events and possible cascading chains may be identified, ranked and visualized. This approach may be used to improve the reliability of a transmission grid and reduce its vulnerability to cascading outages.
International Nuclear Information System (INIS)
Arunasalam, V.
1995-08-01
The velocity distribution functions of the newly born (t = 0) charged fusion products of tokamak discharges can be approximated by a monoenergetic ring distribution with a finite v parallel such that v perpendicular ∼ v parallel ∼ v j where (M j V j 2 /2) = E j , the directed birth energy of the charged fusion product species j of mass M j . As the time t progresses these distribution functions will evolve into a Gaussian in velocity with thermal spreadings given by the perpendicular and parallel temperatures T perpendicularj (t) = T parallelj (t) with T j (t) increasing as t increases and finally reaches an isotropic saturation value of T perpendicularj (t ∼ τ j ) = T parallelj (t ∼ τ j ) = T j (t ∼ τ j ) ∼ [M j T d E j /(M j + M)] 1/2 , where T d is the temperature of the background deuterium plasma ions, M is the mass of a triton or a neutron for j = protons and alpha particles, respectively, and τ j ∼ τ sj /4 is the thermalization time of the fusion product species j in the background deuterium plasma and τ sj is the slowing-down time. For times t of the order of τ j their distributions can be approximated by a Gaussian in their total energy. Then for times t ≥ τ sj the velocity distributions of these fusion products will relax towards their appropriate slowing-down distributions. Here the authors will examine the radiative stability of all these distributions. The ion cyclotron emission from energetic ion produced by fusion reactions or neutral beam injection promises to be a useful diagnostic tool
Steinolfson, Richard S.; Davila, Joseph M.
1993-01-01
Numerical simulations of the MHD equations for a fully compressible, low-beta, resistive plasma are used to study the resonance absorption process for the heating of coronal active region loops. Comparisons with more approximate analytic models show that the major predictions of the analytic theories are, to a large extent, confirmed by the numerical computations. The simulations demonstrate that the dissipation occurs primarily in a thin resonance layer. Some of the analytically predicted features verified by the simulations are (a) the position of the resonance layer within the initial inhomogeneity; (b) the importance of the global mode for a large range of loop densities; (c) the dependence of the resonance layer thickness and the steady-state heating rate on the dissipation coefficient; and (d) the time required for the resonance layer to form. In contrast with some previous analytic and simulation results, the time for the loop to reach a steady state is found to be the phase-mixing time rather than a dissipation time. This disagreement is shown to result from neglect of the existence of the global mode in some of the earlier analyses. The resonant absorption process is also shown to behave similar to a classical driven harmonic oscillator.
Plasma waves in the Earth's foreshock, bow shock, and magnetosheath
International Nuclear Information System (INIS)
Onsager, T.G.
1988-01-01
The research presented in this dissertation is a detailed analysis of electrostatic waves in the Earth's foreshock, bow shock, and magnetosheath. The wave modes measured in these regions, the possible generation mechanisms, and the process which drive the plasma to its unstable state are investigated. The measurements used in this study were obtained from the plasma wave receiver, the particle instrument, and the magnetometer on board the Active Magnetospheric Particle Tracer Explorer (AMPTE) Ion Release Module (IRM). Electron beam mode waves have been identified in the Earth's foreshock. A technique is developed which allows the rest frame frequency and wave number of the electron beam mode waves to be determined from the measurements. The experimentally determined values are compared with theoretical predictions, and approximate limits are put on the beam temperatures. It is demonstrated that electrostatic waves are present in the bow shock and magnetosheath with frequencies above the maximum frequency for Doppler shifted ion acoustic waves, yet below the Langmuir frequency. Waves in this frequency range are tentatively identified as electron beam mode waves. This identification is based on the measured frequencies and electric field polarization directions. Data from 45 bow shock crossings are then used to investigate possible correlations between the electron beam mode waves and the near shock plasma parameters. The best correlations are found with Alfven Mach number and electron beta. Possible mechanism which might produce electron beams in the shock and magnetosheath are discussed in terms of the correlation study results
Advances in surface wave methods: Cascaded MASW-SASW
Westerhoff, R.S.; Brouwer, J.H.; Meekes, J.A.C.
2005-01-01
The application of the MASW method in areas that show strong lateral variations in subsurface properties is limited. Traditional SASW may yield a better lateral resolution but the dispersion curves (and thus the subsurface models) obtained with the method may be poor. The joint application of MASW
A Semisupervised Cascade Classification Algorithm
Directory of Open Access Journals (Sweden)
Stamatis Karlos
2016-01-01
Full Text Available Classification is one of the most important tasks of data mining techniques, which have been adopted by several modern applications. The shortage of enough labeled data in the majority of these applications has shifted the interest towards using semisupervised methods. Under such schemes, the use of collected unlabeled data combined with a clearly smaller set of labeled examples leads to similar or even better classification accuracy against supervised algorithms, which use labeled examples exclusively during the training phase. A novel approach for increasing semisupervised classification using Cascade Classifier technique is presented in this paper. The main characteristic of Cascade Classifier strategy is the use of a base classifier for increasing the feature space by adding either the predicted class or the probability class distribution of the initial data. The classifier of the second level is supplied with the new dataset and extracts the decision for each instance. In this work, a self-trained NB∇C4.5 classifier algorithm is presented, which combines the characteristics of Naive Bayes as a base classifier and the speed of C4.5 for final classification. We performed an in-depth comparison with other well-known semisupervised classification methods on standard benchmark datasets and we finally reached to the point that the presented technique has better accuracy in most cases.
Magneto-Hydrodynamic Activity and Energetic Particles - Application to Beta Alfven Eigenmodes
International Nuclear Information System (INIS)
Nguyen, Ch.
2009-12-01
The goal of magnetic fusion research is to extract the power released by fusion reactions and carried by the product of these reactions, liberated at energies of the order of a few MeV. The feasibility of fusion energy production relies on our ability to confine these energetic particles, while keeping the thermonuclear plasma in safe operating conditions. For that purpose, it is necessary to understand and find ways to control the interaction between energetic particles and the thermonuclear plasma. Reaching these two goals is the general motivation for this work. More specifically, our focus is on one type of instability, the Beta Alfven Eigenmode (BAE), which can be driven by energetic particles and impact on the confinement of both energetic and thermal particles. In this work, we study the characteristics of BAEs analytically and derive its dispersion relation and structure. Next, we analyze the linear stability of the mode in the presence of energetic particles. First, a purely linear description is used, which makes possible to get an analytical linear criterion for BAE destabilization in the presence of energetic particles. This criterion is compared with experiments conducted in the Tore-Supra tokamak. Secondly, because the linear analysis reveals some features of the BAE stability which are subject to a strong nonlinear modification, the question is raised of the possibility of a sub-critical activity of the mode. We propose a simple scenario which makes possible the existence of meta-stable modes, verified analytically and numerically. Such a scenario is found to be relevant to the physics and scales characterizing BAEs. (author)
MAGNETOHYDRODYNAMIC WAVES IN A PARTIALLY IONIZED FILAMENT THREAD
International Nuclear Information System (INIS)
Soler, R.; Oliver, R.; Ballester, J. L.
2009-01-01
Oscillations and propagating waves are commonly seen in high-resolution observations of filament threads, i.e., the fine-structures of solar filaments/prominences. Since the temperature of prominences is typically of the order of 10 4 K, the prominence plasma is only partially ionized. In this paper, we study the effect of neutrals on the wave propagation in a filament thread modeled as a partially ionized homogeneous magnetic flux tube embedded in an homogeneous and fully ionized coronal plasma. Ohmic and ambipolar magnetic diffusion are considered in the basic resistive magnetohydrodynamic (MHD) equations. We numerically compute the eigenfrequencies of kink, slow, and Alfven linear MHD modes and obtain analytical approximations in some cases. We find that the existence of propagating modes is constrained by the presence of critical values of the longitudinal wavenumber. In particular, the lower and upper frequency cutoffs of kink and Alfven waves owe their existence to magnetic diffusion parallel and perpendicular to magnetic field lines, respectively. The slow mode only has a lower frequency cutoff, which is caused by perpendicular magnetic diffusion and is significantly affected by the ionization degree. In addition, ion-neutral collision is the most efficient damping mechanism for short wavelengths, while ohmic diffusion dominates in the long-wavelength regime.