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Sample records for loss-driven h-mode transition

  1. Change of transport at L- and H-mode transition

    International Nuclear Information System (INIS)

    Itoh, Sanae-I; Itoh, Kimitaka.

    1990-01-01

    A new refined model of the L-mode and H-mode transition in tokamaks is presented based on the bifurcation of the radial electric field, E r , near edge. The radial gradient of E r is newly introduced to explain the sudden change of fluctuations as well as plasma fluxes at the onset of transition. This model predicts that the L-to H-mode transition is associated with the decrease of dE r /dr causing reduction of particle and energy fluxes at critical gradient. (author)

  2. Transition to H-mode by energetic electrons

    International Nuclear Information System (INIS)

    Itoh, Kimitaka; Itoh, Sanae.

    1992-07-01

    Effect of the electron loss due to the toroidal ripple on an H-mode transition is studied. When energetic electrons exist in tokamaks, e.g., in the case of the current drive by lower hybrid (LH) waves, the edge electric field can show the bifurcation to the more positive value. In this state, both the electron loss and ion loss (such as loss cone loss) are reduced. The criterion for the transition is derived. Comparison with H-mode in JT-60 LH plasma shows a qualitative agreement. (author)

  3. LH transition theories and theory of H-mode

    International Nuclear Information System (INIS)

    Ward, D.J.

    1996-01-01

    Recent developments in H-mode theory are discussed with earlier work described to put new theories in context. Much of the recent work concerns the development of the radial electric field near the plasma edge and its impact on transport driven by fluctuations, and is the main topic discussed. (author)

  4. Observation of precursor magnetic oscillations to the H-mode transition of ASDEX

    International Nuclear Information System (INIS)

    Toi, K.; Gernhardt, J.; Klueber, O.; Kornherr, M.

    1988-05-01

    Precursor oscillations to the H-mode transition are identified in magnetic fluctuations of the ASDEX H-mode discharges initiated without a sawtooth. This precursor is m=4/n=1 mode, rotating with f ≅ 10 kHz in the opposite direction to co-injected neutral beams. Time behaviour of the amplitude suggests that the H-mode transition is caused, not by the edge electron temperature, but by the edge current density. (orig.)

  5. Observation of inverse hysteresis in the E to H mode transitions in inductively coupled plasmas

    International Nuclear Information System (INIS)

    Lee, Min-Hyong; Chung, Chin-Wook

    2010-01-01

    An inverse hysteresis is observed during the E mode to H mode transition in low pressure argon inductively coupled plasmas. The transition is accompanied by an evolution of electron energy distribution from the bi-Maxwellian to the Maxwellian distribution. The mechanism of this inversion is not clear. However, we think that the bi-Maxwellian electron energy distribution in E mode, where the proportion of high energy electron is much higher than the Maxwellian distribution, would be one of the reasons for the observed inverse hysteresis. As the gas pressure increases, the inverse hysteresis disappears and the E to H mode transition follows the scenario of usual hysteresis.

  6. The influence of gas pressure on E↔H mode transition in argon inductively coupled plasmas

    Science.gov (United States)

    Zhang, Xiao; Zhang, Zhong-kai; Cao, Jin-xiang; Liu, Yu; Yu, Peng-cheng

    2018-03-01

    Considering the gas pressure and radio frequency power change, the mode transition of E↔H were investigated in inductively coupled plasmas. It can be found that the transition power has almost the same trend decreasing with gas pressure, whether it is in H mode or E mode. However, the transition density increases slowly with gas pressure from E to H mode. The transition points of E to H mode can be understood by the propagation of electromagnetic wave in the plasma, while the H to E should be illustrated by the electric field strength. Moreover, the electron density, increasing with the pressure and power, can be attributed to the multiple ionization, which changes the energy loss per electron-ion pair created. In addition, the optical emission characteristics in E and H mode is also shown. The line ratio of I750.4 and I811.5, taken as a proxy of the density of metastable state atoms, was used to illustrate the hysteresis. The 750.4 nm line intensity, which has almost the same trend with the 811.5 nm line intensity in H mode, both of them increases with power but decreases with gas pressure. The line ratio of 811.5/750.4 has a different change rule in E mode and H mode, and at the transition point of H to E, it can be one significant factor that results in the hysteresis as the gas pressure change. And compared with the 811.5 nm intensity, it seems like a similar change rule with RF power in E mode. Moreover, some emitted lines with lower rate constants don't turn up in E mode, while can be seen in H mode because the excited state atom density increasing with the electron density.

  7. Critical edge parameters for H-mode transition in DIII-D

    International Nuclear Information System (INIS)

    Groebner, R.J.; Carlstrom, T.N.

    1997-11-01

    Measurements in DIII-D of edge ion and electron temperatures (T i and T e ) just prior to the transition to H-mode are presented. A fitting model based on a hyperbolic tangent function is used in the analysis. The edge temperatures are observed to increase during the L-phase with the application of auxiliary heating. The temperature rise is small if the H-mode power threshold is close to the Ohmic power level in the absence of auxiliary heating and is large if the H-mode threshold is well above the Ohmic power level. The edge temperatures just prior to the transition are approximately proportional to the toroidal magnetic field Bt for the field either in the reversed or forward direction. However, for the reversed magnetic field, the temperatures are at least a factor of two higher than for the forward direction

  8. L to H mode transitions and associated phenomena in divertor tokamaks

    International Nuclear Information System (INIS)

    Punjabi, A.

    1990-09-01

    This is the final report for the research project titled ''L to H Mode Transitions and Associated Phenomena in Divertor Tokamaks.'' The period covered by this project is the fiscal year 1990. This report covers the development of Advanced Two Chamber Model

  9. Reciprocating Probe Measurements of L-H Transition in LHCD H-mode on EAST

    DEFF Research Database (Denmark)

    Peng, Liu; Guosheng, Xu; Huiqian, Wang

    2013-01-01

    that the power loss P loss was comparable during the L-H transition, by comparing the adjacent L-mode and H-mode discharge. The Dα emission, Te and ne decreased rapidly in the time scale of about 1 ms, and the radial electric field Er turned positive in this process near the last closed flux surface. Multiple L......-H-L transitions were observed during a single shot when the applied LHW power was marginal to the threshold. The floating potential (Vf) had negative spikes corresponding with the Dα signal, and Er oscillation evolved into several intermittent negative spikes just before the L-H transition. In some shots......, dithering was observed just before the L-H transition....

  10. Study of the conditions for spontaneous H-mode transitions in DIII-D

    International Nuclear Information System (INIS)

    Carlstrom, T.N.; Groebner, R.J.

    1996-01-01

    A series of scaling studies attempting to correlate the H(high)-mode power threshold (P TH ) with global parameters have been conducted. Data from these discharges is also being used to look for dependence of P TH on local edge parameters and to test theories of the transition. Boronization and better operational techniques have resulted in lower power thresholds and weaker density scaling. Neon impurity injection experiments show that radiation also plays a role in determining P TH . A low density threshold for the L(low)-H(high) transition has been linked with the locked mode low density limit, and can be reduced with the use of an error field correcting coil. Highly developed edge diagnostics, with spatial resolution as low as 5 mm, are used to evaluate how the power threshold depends on local edge conditions. Preliminary analysis of local edge conditions for parameter scans of n e , B T , and I p in single-null discharges, and the X-point imbalance in double-null discharges-show that, just before the transition to H-mode, the edge temperatures near the separatrix are approximately constant at 100 i e *i , varied from 2 to 17, demonstrating that a transition condition as simple as v *i = constant is inconsistent with the data. The local edge parameters of n e , T e , and T i do not always follow the same global scaling as P TH . Therefore, theories of the L-H transition need not be constrained by these scalings

  11. H-mode physics

    International Nuclear Information System (INIS)

    Itoh, Sanae.

    1991-06-01

    After the discovery of the H-mode in ASDEX ( a tokamak in Germany ) the transition between the L-mode ( Low confinement mode ) and H-mode ( High confinement mode ) has been observed in many tokamaks in the world. The H-mode has made a breakthrough in improving the plasma parameters and has been recognized to be a universal phenomena. Since its discovery, the extensive studies both in experiments and in theory have been made. The research on H-mode has been casting new problems of an anomalous transport across the magnetic surface. This series of lectures will provide a brief review of experiments for explaining H-mode and a model theory of H-mode transition based on the electric field bifurcation. If the time is available, a new theoretical model of the temporal evolution of the H-mode will be given. (author)

  12. E-H mode transition in low-pressure inductively coupled nitrogen-argon and oxygen-argon plasmas

    International Nuclear Information System (INIS)

    Lee, Young Wook; Lee, Hye Lan; Chung, T. H.

    2011-01-01

    This work investigates the characteristics of the E-H mode transition in low-pressure inductively coupled N 2 -Ar and O 2 -Ar discharges using rf-compensated Langmuir probe measurements and optical emission spectroscopy (OES). As the ICP power increases, the emission intensities from plasma species, the electron density, the electron temperature, and the plasma potential exhibit sudden changes. The Ar content in the gas mixture and total gas pressure have been varied in an attempt to fully characterize the plasma parameters. With these control parameters varying, the changes of the transition threshold power and the electron energy distribution function (EEDF) are explored. In N 2 -Ar and O 2 -Ar discharges at low-pressures of several millitorr, the transition thresholds are observed to decrease with Ar content and pressure. It is observed that in N 2 -Ar plasmas during the transition, the shape of the EEDF changes from an unusual distribution with a flat hole near the electron energy of 3 eV in the E mode to a Maxwellian distribution in the H mode. However, in O 2 -Ar plasmas, the EEDFs in the E mode at low Ar contents show roughly bi-Maxwellian distributions, while the EEDFs in the H mode are observed to be nearly Maxwellian. In the E and H modes of O 2 -Ar discharges, the dissociation fraction of O 2 molecules is estimated using optical emission actinometry. During the E-H mode transition, the dissociation fraction of molecules is also enhanced.

  13. A model for a scrape-off-layer low-high (L-H) mode transition

    International Nuclear Information System (INIS)

    Cohen, R.H.; Xu, X.

    1995-01-01

    Increasing the radial mode number has a stabilizing effect on the conducting-wall and curvature-driven interchange modes in a tokamak scrape-off layer (SOL), arising from the increased polarization response. Such an effect is naturally imposed as the SOL width is decreased, and for a narrow-enough SOL, the stabilizing effect is stronger than the increase in the instability drives. By combining a mixing-length estimate for the thermal diffusivity with energy conservation and heat conduction equations and the condition of continuity of the heat flux at the separatrix, it is found that the resultant turbulence-transport system admits two solutions, one stable and one unstable, at different SOL widths; the inclusion of additional physics can add a second stable root at lower width. These roots are plausibly identified with SOL behavior in low (L) and high (H) modes. Particularly when a model is introduced for finite-β, finite-k parallel effects on the modes, a power threshold for transition to the narrower root is obtained, suggesting a possible L-H transition mechanism. The non-monotonic dependence of the turbulent heat flux vs SOL width and the possibility of multiple solutions for the equilibrium SOL width are verified with nonlinear simulations. copyright 1995 American Institute of Physics

  14. Role of zonal flow predator-prey oscillations in triggering the transition to H-mode confinement.

    Science.gov (United States)

    Schmitz, L; Zeng, L; Rhodes, T L; Hillesheim, J C; Doyle, E J; Groebner, R J; Peebles, W A; Burrell, K H; Wang, G

    2012-04-13

    Direct evidence of zonal flow (ZF) predator-prey oscillations and the synergistic roles of ZF- and equilibrium E×B flow shear in triggering the low- to high-confinement (L- to H-mode) transition in the DIII-D tokamak is presented. Periodic turbulence suppression is first observed in a narrow layer at and just inside the separatrix when the shearing rate transiently exceeds the turbulence decorrelation rate. The final transition to H mode with sustained turbulence and transport reduction is controlled by equilibrium E×B shear due to the increasing ion pressure gradient.

  15. H-mode transition physics close to DN on MAST and its applications to other tokamaks

    International Nuclear Information System (INIS)

    Meyer, H.

    2004-01-01

    Full text: ELMy H-mode is the base-line operating scenario for the next step fusion device ITER. To improve active and passive pedestal control a deeper understanding of H- mode physics is desirable. MAST contributes towards this understanding with good edge diagnostics, and by accessing extreme parameter regimes. The first inter-machine comparisons with respect to the influence of the magnetic topology on the power threshold with ASDEX-Upgrade and NSTX reveal a reduction of the power threshold in true double null (C-DN) configuration opening new operation regimes in both devices. The 30% reduction in threshold power close to C-DN observed on ASDEX-Upgrade, though significant, is less than the factor of two or more observed in both large spherical tokamaks, MAST and NSTX. This points towards the importance of field line curvature for this effect. The power thresholds measured in C-DN on MAST and NSTX are very similar. Despite this strong effect on the power threshold, changes in most edge parameters in L-mode due to the different magnetic configurations are small. However, significant changes are seen in the toroidal impurity flow velocity, related to the radial electric field, and in the scrape-off-layer temperature decay length at the high field side. The statistical comparison of MAST data with various H-mode theories suggests that different instabilities need to be stabilised at different spatial positions in the region where the pedestal forms to access H-mode. Pedestal temperatures observed on MAST are two to five times lower than in MAST equivalent discharges at ASDEX-Upgrade. However, the pedestal densities are similar. The differences in L-mode are less significant. The usual DN operating regime with co current NBI in MAST has been extended to include single null (SN) configurations, to provide more direct comparisons with conventional tokamaks. The plasma edge in SN on MAST is more stable to ELMs and the typical type-III ELMs, often observed in C-DN, are

  16. Measurement of peripheral electron temperature by electron cyclotron emission during the H-mode transition in JFT-2M tokamak

    International Nuclear Information System (INIS)

    Hoshino, Katsumichi; Yamamoto, Takumi; Kawashima, Hisato

    1987-01-01

    Time evolution and profile of peripheral electron temperature during the H-mode like transition in a tokamak plasma is measured using the second and third harmonic of electron cyclotron emission (ECE). The so called ''H-mode'' state which has good particle/energy confinement is characterized by sudden decrease in the spectral line intensity of deuterium molecule. Such a sudden decrease in the line intensity of D α with good energy confinement is found not only in divertor discharges, but also in limiter dischargs in JFT-2M tokamak. It is found by the measurement of ECE that the peripheral electron temperature suddenly increases in both of such phases. The relation between H-transition and the peripheral electron temperature or its profile is investigated. (author)

  17. New features of L-H transition in limiter H-modes of JIPP T-IIU

    International Nuclear Information System (INIS)

    Toi, K.; Morita, S.; Kawahata, K.

    1992-09-01

    In limiter H-modes of JIPP T-IIU, a new type of L-H transition preceded by an ELM is observed. The preceding ELM (pre-ELM) appears just prior to the L-H transition. This type of transition is usually observed in H-modes of JIPP T-IIU. The L-H transition without the pre-ELM is triggered only in the case when a sufficiently large rapid current ramp down is emploied. In H-modes with constant q(a)∼3.5-4.5, coherent magnetic oscillations with m=3/n=1 destabilized during L-phase are further enhanced at the pre-ELM, and suppressed suddenly at the transition. This mode is situated in the region of the transport barrier. Propagation frequency of the m=3/n=1 mode, which may be affected by plasma mass rotation, rises appreciably (by ∼ 10 %) during H-phase with frequent ELMs, but remains unchanged for at least 200 μs after the transition. Behaviours of the m=3/n=1 and m=2/n=1 modes are well explained by quasi-linear resistive tearing mode analysis for modelled toroidal current density profiles slightly detached from the limiter. These experimental results suggest that the transition is controlled by the change of a magnetic field structure relating to the modification of a toroidal current density profile near the edge. The possibility for the development of edge radial electric field as a consequence of the transition is discussed. (author)

  18. Physics of the L-mode to H-mode transition in tokamaks

    International Nuclear Information System (INIS)

    Burrell, K.H.; Carlstrom, T.N.; Gohil, P.; Groebner, R.J.; Kim, J.; Osborne, T.H.; St. John, H.; Stambaugh, R.D.; Doyle, E.J.; Moyer, R.A.; Rettig, C.L.; Peebles, W.A.; Rhodes, T.L.; Finkenthal, D.; Hillis, D.L.; Wade, M.R.; Matsumoto, H.; Watkins, J.G.

    1992-07-01

    Combined theoretical and experimental work has resulted in the creation of a paradigm which has allowed semi-quantitative understanding of the edge confinement improvement that occurs in the H-mode. Shear in the E x B flow of the fluctuations in the plasma edge can lead to decorrelation of the fluctuations, decreased radial correlation lengths and reduced turbulent transport. Changes in the radial electric field, the density fluctuations and the edge transport consistent with shear stabilization of turbulence have been seen in several tokamaks. The purpose of this paper is to discuss the most recent data in the light of the basic paradigm of electric field shear stabilization and to critically compare the experimental results with various theories

  19. First HIBP Measurement of Plasma Potential During the H-Mode Transition on the TUMAN-3M Tokamak

    International Nuclear Information System (INIS)

    Askinazi, L.G.; Golant, V.E.; Kornev, V.A.; Lebedev, S.V.; Shevkin, E.A.; Tukachinsky, A.S.; Zhubr, N.A.; Chmyga, A.A.; Dreval, N.B.; Khrebtov, S.M.; Komarov, A.S.; Krupnik, L.I.; Oost, G. van; Tendler, M.

    2003-01-01

    The difficulty of Heavy Ion Beam Probe (HIBP) application on the TUMAN-3M (R=0.53m, a=0.22m, BT=0.8T, Ip=140kA, Te=0.5keV, n<4 1019m-3) -- significant toroidal shift of beam trajectory -- is caused by high ratio of poloidal field to toroidal one. Strong UV radiation from the plasma loads the energy analyzer's detector and complicates the problem even more. This paper presents the results of first measurement of plasma potential evolution in the discharges performed in ohmic H-mode using 80 keV K+ beam and a Proca-Green secondary ion energy analyzer. Spatial region covered by the diagnostic in the experiments discussed was 0< r<0.6a. Spatial scan was performed utilizing the toroidal field decrease due to capacity power supply battery discharge. The change in plasma potential of the order of 100V has been measured during the H-mode formation. The potential in core plasma (r<0.6a) starts to change simultaneously with L-H transition, and than changes during ∼6-8ms after the transition. Thus, the potential changes rather slowly in a comparison with L-H transition timescale (∼2ms for TUMAN-3M ohmic H-mode). Possible explanation to the slow change in central plasma potential may be a formation of potential well structure at the plasma edge, in which radial electric field changes direction. This kind of structure is beneficial for the edge turbulent transport suppression because of high |∂Er/∂r|, but not necessary requires a strong change in central plasma potential to occur immediately. The results from microwave reflectometry support this hypothesis

  20. Dimensionally similar studies of confinement and H-mode transition in ASDEX Upgrade and JET

    International Nuclear Information System (INIS)

    Ryter, F.; Stober, J.; Suttrop, W.

    2001-01-01

    Joint experiments on confinement and L-H transition were performed in ASDEX Upgrade and JET. The confinement experiments suggest that the invariance principle is not always fulfilled at high density. For the L-H transition studies, the dimensionless variables taken at the plasma edge can be in general only made identical per pair, due to the condition imposed by the L-H transition. This new approach to investigate the L-H physics suggests a weak dependence of the L-H transition mechanism on collisionality. (author)

  1. Dimensionally similar studies of confinement and H-mode transition in ASDEX Upgrade and JET

    International Nuclear Information System (INIS)

    Ryter, F.; Stober, J.; Suttrop, W.

    1999-01-01

    Joint experiments on confinement and L-H transition were performed in ASDEX Upgrade and JET. The confinement experiments suggest that the invariance principle is not always fulfilled at high density. For the L-H transition studies, the dimensionless variables taken at the plasma edge can be in general only made identical per pair, due to the condition imposed by the L-H transition. This new approach to investigate the L-H physics suggests a weak dependence of the L-H transition mechanism on collisionality. (author)

  2. On L to H-mode transitions of the tokamak and entropy reduction

    Directory of Open Access Journals (Sweden)

    Rastović Danilo

    2006-01-01

    Full Text Available In an ideal case, it is assumed that the models for tokamak and stellarator plasma behaviour lead to the theory of invariant manifolds by Rastović [Chaos, Solitons & Fractals, 2007]. But, at the present state of knowledge a more realistic concept for describing L to H transitions and edge localized modes is the reduction of entropy and appropriate methods.

  3. Explanation of L→H mode transition based on gradient stabilization of edge thermal fluctuations

    International Nuclear Information System (INIS)

    Stacey, W.M.

    1996-01-01

    A linear analysis of thermal fluctuations, using a fluid model which treats the large radial gradient related phenomena in the plasma edge, leads to a constraint on the temperature and density gradients for stabilization of edge temperature fluctuations. A temperature gradient, or conductive edge heat flux, threshold is identified. It is proposed that the L→H transition takes place when the conductive heat flux to the edge produces a sufficiently large edge temperature gradient to stabilize the edge thermal fluctuations. The consequences following from this mechanism for the L→H transition are in accord with observed phenomena associated with the L→H transition and with the observed parameter dependences of the power threshold. First, a constraint is established on the edge temperature and density gradients that are sufficient for the stability of edge temperature fluctuations. A slab approximation for the thin plasma edge and a fluid model connected to account for the large radial gradients present in the plasma edge are used. Equilibrium solutions are characterized by the value of the density and of its gradient L n -1 double-bond - n -1 , etc. Temperature fluctuations expanded about the equilibrium value are then used in the energy balance equation summed over plasma ions, electrons and impurities to obtain, after linearization, an expression for the growth rate ω of edge localized thermal fluctuations. Thermal stability of the equilibrium solution requires ω ≤ 0, which establishes a constraint that must be satisfied by L n -1 and L T -1 . The limiting value of the constraint (ω = 0) leads to an expression for the minimum value of that is sufficient for thermal stability, for a given value of L T -1. It is found that there is a minimum value of the temperature gradient, (L T -1 ) min that is necessary for a stable solution to exist for any value of L n -1

  4. Dynamics of the Plasma Edge during the L-H Transition and H-mode in MAST

    Energy Technology Data Exchange (ETDEWEB)

    Scannell, R.; Meyer, H.; Cunningham, G.; Field, A.; Kirk, A.; Samuli, S.; Patel, A., E-mail: rory.scannell@ccfe.ac.uk [EURATOM /CCFE Fusion Association, Culham Science Centre, Abingdon (United Kingdom); Dunai, D.; Zoletnik, S. [KFKI-RMKI, EURATOM Association, Budapest (Hungary)

    2012-09-15

    Full text: The evolution of the MAST plasma during the L-H transition has been studied in the density range 1.5 - 3.0 x 10{sup 19} m{sup -3}. A dithering transition phase, the duration of which depends on the plasma density, is observed before the transition to ELMy or ELM free H-mode. A range of new diagnostic data has been taken during these periods, showing a spin-up of the perpendicular He{sup +} flow correlated with changes in the Da emission. In this density range the power threshold increases with increasing density. As well as the expected power threshold dependency on absolute density, the threshold power is observed to depend on the density evolution prior to the transition. Small changes in fuelling location, plasma current, toroidal field and plasma shape can lead to changes in the power threshold by a factor of two, significantly larger than hose predicted by the scaling. The pedestal evolution between typical type I ELMs in connected double null configuration on MAST show increasing pedestal pressure and width as function time through the ELM cycle. This results in an expanding high pressure gradient region with little increase in peak pressure gradient within this region. It has been shown that the triggering of these ELMs is caused by decreasing stability limit as the transport barrier moves inwards. Application of n = 6 resonant magnetic perturbations to the plasma causes ELM mitigation, with smaller but much more frequent ELMs. The pressure gradients in this mitigated period are significantly less than those observed during non-mitigated type I ELMs. This reduction in pressure gradient, which indicates a different stability limit, results from both a decrease in pedestal height and increase in pedestal width. (author)

  5. H-mode transition physics close to double null on MAST and its applications to other tokamaks

    International Nuclear Information System (INIS)

    Meyer, H.; Carolan, P.G.; Cunningham, G.; Kirk, A.; Lloyd, B.; Saarelma, S.; Wilson, H.R.; Conway, G.D.; Horton, L.D.; Ryter, F.; Schirmer, J.; Suttrop, W.; Maingi, R.

    2005-01-01

    By accessing extreme parameter regimes combined with well diagnosed edge MAST data contribute towards the understanding of H-mode physics. The first inter-machine comparisons with respect to the influence of the magnetic topology on the power threshold with ASDEX Upgrade and NSTX reveal a reduction of the power threshold in true double null (C-DN) configuration opening new operation regimes in both devices. In L-mode, the negative radial electric field close to the separatrix was found to be more negative in C-DN than in single null (SN), whilst most of the other edge parameters are similar. Pedestal temperatures in MAST are lower than in ASDEX Upgrade in MAST-equivalent discharges, whereas the pedestal densities can be similar, although in long inter ELM periods the MAST density pedestal is higher than on ASDEX Upgrade. In order to test four leading H-mode theories MAST data are compared statistically to their H-mode access criteria. The usual DN operating regime with co current NBI in MAST has been extended to include single null (SN) configurations, to provide more direct comparisons with conventional tokamaks. The plasma edge in SN on MAST is more stable to ELMs and the typical type-III ELMs, often observed in C-DN, are absent, despite input powers close to the H-mode threshold power. In this respect, the stability of measured plasma edge profiles in SN and DN against ideal peeling-ballooning modes will be discussed. (author)

  6. Investigation of peeling-ballooning stability prior to transient outbursts accompanying transitions out of H-mode in DIII-D

    Energy Technology Data Exchange (ETDEWEB)

    Eldon, D., E-mail: deldon@princeton.edu [University of California San Diego, 9500 Gilman Dr., La Jolla, California 92093-0964 (United States); Princeton University, Princeton, New Jersey 08543 (United States); Boivin, R. L.; Groebner, R. J.; Osborne, T. H.; Snyder, P. B.; Turnbull, A. D.; Burrell, K. H. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Tynan, G. R.; Boedo, J. A. [University of California San Diego, 9500 Gilman Dr., La Jolla, California 92093-0964 (United States); Kolemen, E. [Princeton University, Princeton, New Jersey 08543 (United States); Schmitz, L. [University of California Los Angeles, Los Angeles, California 90095-7099 (United States); Wilson, H. R. [University of York, Heslington, York YO10 5DD (United Kingdom)

    2015-05-15

    The H-mode transport barrier allows confinement of roughly twice as much energy as in an L-mode plasma. Termination of H-mode necessarily requires release of this energy, and the timescale of that release is of critical importance for the lifetimes of plasma facing components in next step tokamaks such as ITER. H-L transition sequences in modern tokamaks often begin with a transient outburst which appears to be superficially similar to and has sometimes been referred to as a type-I edge localized mode (ELM). Type-I ELMs have been shown to be consistent with ideal peeling ballooning instability and are characterized by significant (up to ∼50%) reduction of pedestal height on short (∼1 ms) timescales. Knowing whether or not this type of instability is present during H-L back transitions will be important of planning for plasma ramp-down in ITER. This paper presents tests of pre-transition experimental data against ideal peeling-ballooning stability calculations with the ELITE code and supports those results with secondary experiments that together show that the transient associated with the H-L transition is not triggered by the same physics as are type-I ELMs.

  7. H-mode study in CHS

    International Nuclear Information System (INIS)

    Toi, K.; Morisaki, T.; Sakakibara, S.

    1995-02-01

    In CHS rapid H-mode transition is observed in NBI heated deuterium and hydrogen plasmas without obvious isotope effect, when a net plasma current is ramped up to increase the external rotational transform. The H-mode of CHS has many similarities with those in tokamaks. Recent measurement with fast response Langmuir probes has revealed that the rapid change in floating potential occurs at the transition, but the change follows the formation of edge transport barrier. The presence of ι/2π = 1 surface near the edge and sawtooth crash triggered by internal modes may play an important role for determining the H-mode transition in CHS. (author)

  8. The role of electric field shear stabilization of turbulence in the H-mode to VH-mode transition in DIII-D

    International Nuclear Information System (INIS)

    Burrell, K.H.; Osborne, T.H.; Groebner, R.J.; Rettig, C.L.

    1993-01-01

    VH-mode plasma exhibit energy confinement times up to 2.4 times the DIII-D/JET H-mode scaling relation and up to 3.9 times the value given by ITER89-P L-mode scaling. If this confinement improvement can be exploited in reactor plasmas, smaller prototype reactors with significantly lower unit cost can be produced. Accordingly, understanding and optimizing the confinement improvement is of significant interest. One of the possible explanations for this bulk confinement improvement is stabilization of turbulence by shear in the radial electric field, similar to the present explanation for the confinement improvement at the extreme plasma edge at the L to H transition. Preliminary measurements have shown that the region of the plasma where the electric field gradient is steepest broadens when the plasma goes from H-mode to VH-mode. More recent measurements have confirmed this broadening and have shown that the change in the electric field gradient occurs prior to the change in the thermal transport. In addition, transport analysis shows that the electric field shear increases in the same region between magnetic flux coordinate p=0.6 and 0.9 where the local thermal transport decreases. Furthermore, far infra-red (FIR) scattering measurements have detected density fluctuations in the region around p=0.8 which could be responsible for enhanced transport and which disappear at the time that the electric shear increases. These fluctuations appear as bursts of density fluctuations in the 0.5 to 1.5 MHz range. The time between bursts increases as the electric field shear increases. Once these bursts disappear, the major change in confinement takes place in most discharges. When isolated bursts occur, the heat and angular momentum pulse connected with the burst are detectable on the plasma profile diagnostics. (author) 13 refs., 4 figs

  9. The H-mode operational window as determined from the ITER H-mode database

    International Nuclear Information System (INIS)

    Ryter, F.; Kardaun, O.J.W.F.; Stroth, U.

    1994-01-01

    The H-mode is a promising regime for fusion reactors and it is essential to be able to predict its operational window in future devices. The 'H-Mode Database Working Group' started in 1992 to gather, analyze and compare H-mode threshold data from several divertor tokamaks so that predictions could be made. The database and first results were presented and the threshold database has been improved and extended since. The work has two objectives: 1) to predict the minimum heating power necessary to reach the H-mode in future devices, 2) to contribute to physics studies of the L-H transition. (author) 11 refs., 2 figs

  10. Limiter H-mode experiments on TFTR

    Energy Technology Data Exchange (ETDEWEB)

    Bush, C [Oak Ridge National Lab., TN (USA); Bretz, N L; Fredrickson, E D; McGuire, K M; Nazikian, R; Park, H K; Schivell, J; Taylor, G; Bitter, B; Budny, R; Cohen, S A; Kilpatrick, S J; LeBlanc, B; Manos, D M; Meade, D; Paul, S F; Scott, S D; Stratton, B C; Synakowski, E J; Towner, H H; Weiland, R M; Arunasalam, V; Bateman, G; Bell, M G; Bell, R; Boivin, R; Cavallo, A; Cheng, C Z; Chu, T K; Cowl,

    1990-12-15

    Limiter H-modes with centrally peaked density profiles have been obtained in TFTR using a highly conditioned graphite limiter. The transition to these centrally peaked H-modes takes place from the supershot to the H-mode rather than the usual L- to H-mode transition observed on other tokamaks. Bi-directional beam heating is required to induce the transition. Density peaking factors, n{sub e}(0)/{l angle}n{sub e}{r angle}, >2.3 are obtained and at the same time the H-mode characteristics are similar to those of limiter H-modes on other tokamaks and the global confinement, {tau}{sub E}, can be >2.5 times L-mode scaling. The TRANSP analysis shows that transport in these H-modes is similar to that of supershots within the inner 60 cm of the plasma, but the stored electron energy (calculated using measured values of T{sub e} and n{sub e}) is higher for the H-mode at the plasma edge. Microwave scattering near the edge shows broad spectra at k = 5.5 cm{sup {minus}1} which begin at the drop in D{sub {alpha}} radiation and are strongly shifted in the electron diamagnetic drift direction. At the same time beam emission spectroscopy shows a coherent mode near the boundary with m = 15--20 at 20--30 kHz which is propagating in the ion direction. During an ELM event these apparent rotations cease and Mirnov fluctuations in the 50--500 kHz increase in intensity.

  11. The H-mode of ASDEX

    International Nuclear Information System (INIS)

    1989-01-01

    The paper is a review of investigations of the H-mode on ASDEX performed since its discovery in 1982. The topics discussed are: (1) the development of the plasma profiles, with steep gradients in the edge region and flat profiles in the bulk plasma, (2) the MHD properties resulting from the profile changes, including an extensive stability analysis, (3) the impurity development, with special emphasis on the MHD aspects and on neoclassical impurity transport effects in quiescent H-phases, and (4) the properties of the edge plasma, including the evidence of three-dimensional distortions at the edge. The part on confinement includes scaling studies and the results of transport analysis. The power threshold of the H-mode is found to depend weakly on the density, but there is probably no dependence on the toroidal field or the current. For the operational range of the H-mode, new results for the limiter H-mode on ASDEX and the development of the H-mode under beam current drive conditions are included. A number of experiments are described which demonstrate the crucial role of the edge electron temperature in the L-H transition. New results of magnetic and density fluctuation studies at the plasma edge within the edge transport barrier are presented. Finally, the findings on ASDEX are compared with results obtained on other machines and are used to test various H-mode theories. (author). 131 refs, 103 figs, 1 tab

  12. Physics of the H-mode

    International Nuclear Information System (INIS)

    Hinton, F.L.; Chu, M.S.; Dominguez, R.R.

    1985-01-01

    A theoretical picture of the H-mode is proposed which explains some of the most important features of this good confinement mode in neutral beam heated plasmas with divertors. From consideration of the transport through the separatrix and along the open field lines outside the separatrix, as well as the stability of the plasma inside the separatrix, we show that a bifurcation in the operating parameters is possible. At high edge temperatures, very large particle confinement times are possible because of the Ware pinch. The transport of particles and heat along the open field lines to the divertor region depends on temperature in a non-monotonic way, and the bifurcation of the thermal equilibrium which is implied may correspond to the L- to H-mode transition. The improvement of the interior confinement in the H-mode, when the edge temperature is higher, is shown to follow from the tearing mode stability properties of current profiles with pedestals. (author)

  13. ELM Dynamics in TCV H-modes

    Science.gov (United States)

    Degeling, A. W.; Martin, Y. R.; Lister, J. B.; Llobet, X.; Bak, P. E.

    2003-06-01

    TCV (Tokamak à Configuration Variable, R = 0.88 m, a limited and diverted plasmas, with the primary aim of investigating the effects of plasma shape and current profile on tokamak physics and performance. L-mode to H-mode transitions are regularly obtained in TCV over a wide range of configurations. Under most conditions, the H-mode is ELM-free and terminates in a high density disruption. The conditions required for a transition to an ELMy H-mode were investigated in detail, and a reliable gateway in parameter space for the transition was identified. Once established, the ELMy H-mode is robust to changes in plasma current, elongation, divertor geometry and plasma density over ranges that are much wider than the size of the gateway in these parameters. There exists marked irregularity in the time interval between consecutive ELMs. Transient signatures in the time-series revealing the existence of an underlying chaotic dynamical system are repeatedly observed in a sizable group of discharges [1]. The properties of these signatures (called unstable periodic orbits, or UPOs) are found to vary systematically with parameters such as the plasma current, density and inner plasma — wall gap. A link has also been established between the dynamics of ELMs and sawteeth in TCV: under certain conditions a clear preference is observed in the phase between ELMs and sawtooth crashes, and the ratio of the ELM frequency (felm) to sawtooth frequency (fst) is found to prefer simple rational values (e.g. 1/1, 2/1 or 1/2). An attempt to control the ELM dynamics was made by applying a perturbation signal to the radial field coils used for vertical stabilisation. Phase synchronisation was found with the external perturbation, and felm was found to track limited scans in the driver frequency about the unperturbed value, albeit with intermittent losses in phase lock.

  14. ELM Dynamics in TCV H-modes

    International Nuclear Information System (INIS)

    Degeling, A.W.; Martin, Y.R.; Lister, J.B.; Llobet, X.; Bak, P.E.

    2003-01-01

    TCV (Tokamak a Configuration Variable, R = 0.88 m, a < 0.25 m, BT < 1.54 T) is a highly elongated tokamak, capable of producing limited and diverted plasmas, with the primary aim of investigating the effects of plasma shape and current profile on tokamak physics and performance. L-mode to H-mode transitions are regularly obtained in TCV over a wide range of configurations. Under most conditions, the H-mode is ELM-free and terminates in a high density disruption. The conditions required for a transition to an ELMy H-mode were investigated in detail, and a reliable gateway in parameter space for the transition was identified. Once established, the ELMy H-mode is robust to changes in plasma current, elongation, divertor geometry and plasma density over ranges that are much wider than the size of the gateway in these parameters. There exists marked irregularity in the time interval between consecutive ELMs. Transient signatures in the time-series revealing the existence of an underlying chaotic dynamical system are repeatedly observed in a sizable group of discharges [1]. The properties of these signatures (called unstable periodic orbits, or UPOs) are found to vary systematically with parameters such as the plasma current, density and inner plasma -- wall gap. A link has also been established between the dynamics of ELMs and sawteeth in TCV: under certain conditions a clear preference is observed in the phase between ELMs and sawtooth crashes, and the ratio of the ELM frequency (felm) to sawtooth frequency (fst) is found to prefer simple rational values (e.g. 1/1, 2/1 or 1/2). An attempt to control the ELM dynamics was made by applying a perturbation signal to the radial field coils used for vertical stabilisation. Phase synchronisation was found with the external perturbation, and felm was found to track limited scans in the driver frequency about the unperturbed value, albeit with intermittent losses in phase lock

  15. Scaling of the H-mode power threshold for ITER

    International Nuclear Information System (INIS)

    1998-01-01

    Analysis of the latest ITER H-mode threshold database is presented. The power necessary for the transition to H-mode is estimated for ITER, with or without the inclusion of radiation losses from the bulk plasma, in terms of the main engineering variables. The main geometrical variables (aspect ratio ε, elongation κ and average triangularity δ) are also included in the analysis. The H-mode transition is also considered from the point of view of the local edge variables, and the electron temperature at 90% of the poloidal flux is expressed in terms of both local and global variables. (author)

  16. Ohmic H-mode studies in TUMAN-3

    International Nuclear Information System (INIS)

    Lebedev, S.V.; Andrejko, M.V.; Askinazi, L.G.; Golant, V.E.; Kornev, V.A.; Levin, L.S.; Tukachinsky, A.S.; Tendler, M.

    1994-01-01

    The spontaneous transition from Ohmically heated limiter discharges into the regime with improved confinement termed as ''Ohmic H-mode'' has been investigated in ''TUMAN-3''. The typical signatures of H-mode in tokamaks with powerful auxiliary heating have been observed: sharp drop of D α radiation with simultaneous increase in the electron density and stored energy, suppression of the density fluctuations and establishing the steep gradient near the periphery. The crucial role of the radial electric field in the L-H transition was found in the experiments with boundary biasing. The possibility of initiating the H-mode using single pellet injection was demonstrated. In Ohmic H-mode strong dependencies of τ E on plasma current and on input power and weak dependence on density were found. Thermal energy confinement time enhanced by a factor of 10 compared to predictions of Neo-Alcator scaling. Longest energy confinement time (30 ms) was obtained in the small tokamak TUMAN-3. Absolute values of the energy confinement time are in agreement with scaling proposed for description of the ELM-free H-modes in devices with powerful auxiliary heating (''DIII-D/JET H-mode'' scaling). (author)

  17. H-mode pedestal characteristics on MAST

    International Nuclear Information System (INIS)

    Kirk, A; Counsell, G F; Arends, E; Meyer, H; Taylor, D; Valovic, M; Walsh, M; Wilson, H

    2004-01-01

    The H-mode pedestal characteristics on the mega ampere spherical tokamak (MAST) are measured in a variety of disconnected double null discharges and the effect of edge localized modes (ELMs) on the pedestal is presented. The edge density pedestal width in spatial co-ordinates is similar on both the inboard and outboard sides. Neutral penetration may be able to explain the density pedestal width but it alone cannot explain the characteristics of the temperature pedestal. The data from MAST can be used to improve temperature pedestal width scalings by extending the ranges in pedestal collisionality, magnetic field, elongation and aspect ratio studied by other machines. Convective transport is found to dominate energy losses during ELMs and the fractional loss of pedestal energy during an ELM on MAST correlates better with SOL ion transit time than with pedestal collisionality

  18. Characteristics of the First H-mode Discharges in NSTX

    International Nuclear Information System (INIS)

    Maingi, R.; Bell, M.G.; Bell, R.E.; Bush, C.E.; Fredrickson, E.D.; Gates, D.A.; Kaye, S.M.; Kugel, H.W.; LeBlanc, B.P.; Menard, J.E.; Mueller, D.; Sabbagh, S.A.; Stutman, D.; Taylor, G.; Johnson, D.W.; Kaita, R.; Maqueda, R.J.; Ono, M.; Paoletti, F.; Peng, Y-K.M.; Roquemore, A.L.; Skinner, C.H.; Soukhanovskii, V.A.; Synakowski, E.J.

    2001-01-01

    We report observations of the first low-to-high (L-H) confinement mode transitions in the National Spherical Torus Experiment (NSTX). The H-mode energy confinement time increased over reference L-mode discharges transiently by 100-300%, as high as ∼150 ms. This confinement time is ∼1.8-2.3 times higher than predicted by a multi-machine ELM-free H-mode scaling. This achievement extends the H-mode window of fusion devices down to a record low aspect ratio (R/a) ∼ 1.3, challenging both confinement and L-H power thresholds scalings based on conventional aspect ratio tokamaks

  19. Improved H-mode access in connected DND in MAST

    International Nuclear Information System (INIS)

    Meyer, H; Carolan, P G; Conway, N J; Counsell, G F; Cunningham, G; Field, A R; Kirk, A; McClements, K G; Price, M; Taylor, D

    2005-01-01

    In the Mega-Amp Spherical Tokamak, MAST, the formation of the edge transport barrier leading to the high-confinement (H-mode) regime is greatly facilitated by operating in a double null diverted (DND) configuration where both X-points are practically on the same flux surface. Ohmic H-modes are presently only obtained in these connected double null diverted (CDND) configurations. The ease of H-mode access is lost if the two flux surfaces passing through the X-points are radially separated by more than one ion Larmor radius (ρ i ∼ 6 mm) at the low-field-side mid-plane. The change of the magnetic configuration from disconnected to CDND is accompanied by a change in the radial electric field of about ΔE ψ ∼ -1 kV m -1 and a reduction of the electron temperature decay length in the high-field-side scrape-off-layer. Other parameters at the plasma edge, in particular those affecting the H-mode access criteria of common L/H transition theories, are not affected by the slight changes to the magnetic configuration. It is believed that the observed change in E ψ , which may result from differences in ion orbit losses, leads to a higher initial E x B flow shear in CDND configurations which could lead to the easier H-mode access

  20. Phenomenological model for H-mode

    International Nuclear Information System (INIS)

    Ohyabu, N.

    1985-08-01

    A phenomenological model has been developed to clarify the role of the boundary configuration in the heat transport of the H-mode regime. We assume that the dominant mechanism of heat loss at the edge of the plasma is convection and that the diffusion coefficient (D/sub edge/) at the edge of the plasma increases rapidly with plasma pressure, but drops to a low value when the temperature exceeds a certain threshold value. When particle refueling takes place without time delay, as in the case of a limiter discharge, the unfavorable temperature dependence of the D/sub edge/ prohibits even a modest rise of the edge temperature. In a divertor discharge, the particles lost from the closed surface are kept away from the edge region for a time comparable to or longer than the energy transport time in the edge region. Thus, rapid increase in the heat flux allows an excursion of the edge temperature to a higher value thereby reaching the threshold value of the H-transition

  1. An emerging understanding of H-mode discharges in tokamaks

    International Nuclear Information System (INIS)

    Groebner, R.J.

    1992-12-01

    A remarkable degree of consistency of experimental results from tokamaks throughout the world has developed with regard to the phenomenology of the transition from L-mode to H-mode confinement in tokamaks. The transition is initiated in a narrow layer at the plasma periphery where density fluctuations are suppressed and steep gradients of temperature and density form in a region with large first and second radial derivatives in the υ E → = (E x B)/B 2 flow velocity. These results are qualitatively consistent with theories which predict suppression of fluctuations by shear or curvature in υE. The required υE flow is generated very rapidly when the magnitude of the heating power or of an externally imposed radial current exceed threshold values and several theoretical models have been developed to explain the observed changes in the υE flow. After the transition occurs, the altered boundary conditions enable the development of improved confinement in the plasma interior on a confinement time scale. The resulting H-mode discharge has typically twice the confinement of L-mode discharges and regimes of further improved confinement have been obtained in some H-mode scenarios

  2. 'Snowflake' H Mode in a Tokamak Plasma

    International Nuclear Information System (INIS)

    Piras, F.; Coda, S.; Duval, B. P.; Labit, B.; Marki, J.; Moret, J.-M.; Pitzschke, A.; Sauter, O.; Medvedev, S. Yu.

    2010-01-01

    An edge-localized mode (ELM) H-mode regime, supported by electron cyclotron heating, has been successfully established in a 'snowflake' (second-order null) divertor configuration for the first time in the TCV tokamak. This regime exhibits 2 to 3 times lower ELM frequency and 20%-30% increased normalized ELM energy (ΔW ELM /W p ) compared to an identically shaped, conventional single-null diverted H mode. Enhanced stability of mid- to high-toroidal-mode-number ideal modes is consistent with the different snowflake ELM phenomenology. The capability of the snowflake to redistribute the edge power on the additional strike points has been confirmed experimentally.

  3. Statistical study of TCV disruptivity and H-mode accessibility

    International Nuclear Information System (INIS)

    Martin, Y.; Deschenaux, C.; Lister, J.B.; Pochelon, A.

    1997-01-01

    Optimising tokamak operation consists of finding a path, in a multidimensional parameter space, which leads to the desired plasma characteristics and avoids hazards regions. Typically the desirable regions are the domain where an L-mode to H-mode transition can occur, and then, in the H-mode, where ELMs and the required high density< y can be maintained. The regions to avoid are those with a high rate of disruptivity. On TCV, learning the safe and successful paths is achieved empirically. This will no longer be possible in a machine like ITER, since only a small percentage of disrupted discharges will be tolerable. An a priori knowledge of the hazardous regions in ITER is therefore mandatory. This paper presents the results of a statistical analysis of the occurrence of disruptions in TCV. (author) 4 figs

  4. Overview of H-mode studies in DIII-D

    International Nuclear Information System (INIS)

    Groebner, R.J.; Baker, D.R,; Allen, S.L.

    1994-01-01

    A major portion of the DIII-D program includes studies of the L-H transition, of the VH-mode, of particle transport and control and of the power-handling capability of a diverter. Significant progress has been made in all of these areas and the purpose of this paper is to summarize the major results obtained during the last two years. An increased understanding of the origin of improved confinement in H-mode and in VH-mode discharges has been obtained, good impurity control has been achieved in several operating scenarios, studies of helium transport provide encouraging results from the point of view of reactor design, an actively pumped diverter chamber has controlled the density in H-mode discharges and a radiative diverter is a promising technique for controlling the heat flux from the main plasma

  5. H-mode development in TEXT-U limiter plasmas

    International Nuclear Information System (INIS)

    Roberts, D.R.; Bravenec, R.V.; Bengtson, R.D.

    1996-01-01

    H-mode transitions in TEXT-U limiter plasmas have been observed at q a ∼ 3 and I p ∼ 250 kA (P OH ∼ 300 kW) with at least 300 kW of central electron-cyclotron heating (ECH). These are dithering transitions which are induced by sawtooth crashes and display the typical signatures of H-modes (D α drop, spontaneous density increase, evidence of a transport barrier). However, they show only a slight improvement over L-mode energy confinement. The vessel walls are boronized and conditioned prior to experiments to achieve low-impurity influx and particle recycling. Discharges which undergo transitions are fuelled almost entirely on residual recycling. Transitions are observed when limited on a toroidally localized top or bottom limiter and, more often, when the limiter surface is 'fresh', which is achieved by alternating between top and bottom limiters on successive shots. No strong dependence upon the distance from the low-field-side limiter has been found. Transitions are not yet observed when limited on the high-field-side wall tiles or in the case of TEXT-U diverted configurations. Preliminary measurements with the 2 MeV heavy-ion beam probe (HIBP) (in the core) and Langmuir probes (in the edge) indicate that the plasma potential drops outside the q = 1 radius while only small changes are observed in the density fluctuations level. (author)

  6. L to H-mode Power Threshold and Confinement Characteristics of H-modes in KSTAR

    Energy Technology Data Exchange (ETDEWEB)

    Kim, H. S.; Na, Y.S., E-mail: ftwalker.hyuns@gmail.com [Seoul National University, Seoul (Korea, Republic of); Ahn, J. W. [Oak Ridge National Laboratory, Oak Ridge (United States); Jeon, Y. M.; Yoon, S. W.; Lee, K. D.; Ko, W. H.; Bae, Y. S.; Kim, W. C.; Kwak, J. G. [National Fusion Research Institute, Daejeon (Korea, Republic of)

    2012-09-15

    Full text: Since KSTAR has obtained the H-mode in 2010 campaign, H-mode plasmas were routinely obtained with combined heating of NBI with maximum power of 1.5 MW and ECRH with maximum power of {approx} 0.3 MW and {approx} 0.6 MW for 110 GHz and 170 GHz, respectively. The L- to H-mode power threshold and confinement properties of KSTAR H-modes are investigated in this work. Firstly, the L- to H-mode power threshold and the power loss to the seperatrix are calculated by power balance analysis for about collected 400 shots. As a result, a trend of roll-over is observed in the power threshold of KSTAR H-mode compared with the multi-machine power threshold scaling in the low density regime. Dependence of the power threshold on other parameters are also investigated such as the X-point position and shaping parameters like as triangularity and elongation. In addition, the reason of reduction of power threshold in 2011 campaign compared with that in 2010 is addressed. Secondly, the confinement enhancement factors are calculated to evaluate the performance of KSTAR H-modes. The calculated H{sub 89-p} and H{sub 98} (y, 2) represent that the confinement is enhanced in most KSTAR H-mode discharges. Interestingly, even in L-mode phases, confinement is observed to be enhanced against the multi-machine scalings. H{sub exp} factor is newly introduced to evaluate the amount of confinement improvement in the H-mode phase compared with the L-mode phase in a single discharge. H{sub exp} exhibits that the global energy confinement time of the H-mode phase is improved about 1.3 - 2.0 times compared with that of the L-mode phase. Finally, interpretive and predictive numerical simulations are carried out using the ASTRA code for typical KSTAR H-mode discharges. The Weiland model and the GLF23 model are employed for calculating the anomalous contributions of both electron and ion heat transport in predictive simulations. For the H-mode phase, the Weiland model reproduces the experiment

  7. H-modes studies in PDX

    International Nuclear Information System (INIS)

    Fonck, R.J.; Beirsdorfer, P.; Bell, M.

    1984-07-01

    A regime of enhanced energy confinement during neutral beam heating has been obtained routinely in the PDX tokamak after modifications to form a closed divertor geometry. Plasma density profiles were broad and the electron temperature at the plasma edge reached values of approx. 400 eV in the H-mode phase of a discharge. A comparison of closed divertor discharges with moderate and intense gas puffing indicates that a requirement for obtaining high confinement times is the localization of the plasma fueling source in the divertor throat region. While high confinement was attained at moderate injected powers (P/sub INJ/ less than or equal to 3 MW), confinement was degraded at higher powers due to both increased edge instabilities and, especially, the intense gas puffing needed to prevent disruptions. Initial results with a particle scoop limiter indicate high particle confinement times and energy confinement times approaching those of diverted H-mode plasmas

  8. Effect of Gas Fueling Location on H-mode Access in NSTX

    International Nuclear Information System (INIS)

    Maingi, R.; Bell, M.; Bell, R.; Biewer, T.; Bush, C.; Chang, C.S.; Gates, D.; Kaye, S.; Kugel, H.; LeBlanc, B.; Maqueda, R.; Menard, J.; Mueller, D.; Raman, R.; Sabbagh, S.; Soukhanovskii, V.

    2003-01-01

    The dependence of H-mode access on the poloidal location of the gas injection source has been investigated in the National Spherical Torus Experiment (NSTX). We find that gas fueling from the center stack midplane area produces the most reproducible H-mode access with generally the lowest L-H threshold power in lower single-null configuration. The edge toroidal rotation velocity is largest (in direction of the plasma current) just before the L-H transition with center stack midplane fueling, and then reverses direction after the L-H transition. Simulation of these results with a 2-D guiding-center Monte Carlo neoclassical transport code is qualitatively consistent with the trends in the measured velocities. Double-null discharges exhibit H-mode access with gas fueling from either the center stack midplane or center stack top locations, indicating a reduced sensitivity of H-mode access on fueling location in that shape

  9. H-mode edge rotation in W7-AS

    International Nuclear Information System (INIS)

    Hirsch, M.; Baldzuhn, J.; Ehmler, H.; Grigull, P.; Maassberg, H.; McCormick, K.; Wagner, F.; Wobig, H.

    2005-01-01

    In W7-AS three regimes of improved confinement exist which base on negative radial electric fields at the plasma edge resulting there from ion-root conditions of the ambipolar radial fluxes. Experimental control besides the magnetic configuration is given via the edge density profile i.e. the recycling and fuelling conditions. However, the ordering element seems to be the radial electric field profile (respectively its shear) and its interplay with the gradients of ion temperature and density. At low to medium densities the so called optimum confinement regime occurs with maximum density gradients located well inside the plasma boundary and large negative values of E r extending deep in the bulk plasma. For a large inner fraction of the bulk the ion temperature can be sufficiently high that ion transport conditions already can be explained by neoclassics. This regime delivers maximum values of T i , τ e and n τ e T i . Density gradients located right inside the plasma boundary result in the classical H-mode phenomena reminiscent to other toroidal devices with the capability of an edge layer with nearly complete suppression of turbulence either quasi stationary (in a quiescent H-mode) or intermittently (in between ELMs). At even higher densities and highly collisional plasmas with the maximum of ∇n shifted to or even out of the plasma boundary the High Density H-mode (HDH) opens access to steady state conditions with no measurable impurity accumulation. These improved confinement regimes are accessed and left via significant transitions of the transport properties albeit these transitions occur on rather different timescales. A comprehensive picture of improved edge confinement regimes in W7-AS is drawn based on the assumption that a weak edge bounded transport barrier resulting from the ion root conditions (thus E r <0) is the ground state of the (turbulent) edge plasma and already behaves as a barrier for anomalous transport. On top of that the classical H-mode

  10. Evidence of Zonal-Flow-Driven Limit-Cycle Oscillations during L-H Transition and at H-mode Pedestal of a New Small-ELM Regime in EAST

    DEFF Research Database (Denmark)

    Xu, G.; Wang, H.; Guo, H.

    Small-amplitude edge localized oscillations have been observed, for the first time, in EAST preceding the L-H transition at marginal input power, which manifest themselves as dithering in the divertor D signals at a frequency under 4 kHz, much lower than the GAM frequency. Detailed measurements...... edge turbulence in the range of 30 100 kHz and low-frequency Er oscillations. Just prior to the L-H transition, the Er oscillations often evolve into intermittent negative Er spikes. The Er oscillations, as well as the Er spikes, are strongly correlated with the turbulence driven Reynolds stress, thus...... providing a direct evidence of the zonal flows for the L-H transition at marginal input power. Furthermore, near the transition threshold sawtooth heat pulses appear to periodically enhance the dithering, finally triggering the L-H transition after a big sawtooth crash. The zonal flow induced limit...

  11. Progress in quantifying the edge physics of the H mode regime in DIII-D

    International Nuclear Information System (INIS)

    Groebner, R.J.; Baker, D.R.; Burrell, K.H.

    2001-01-01

    Edge conditions in DIII-D are being quantified in order to provide insight into the physics of the H mode regime. Several studies show that electron temperature is not the key parameter that controls the L-H transition. Gradients of edge temperature and pressure are much more promising candidates for elements of such parameters. They systematically increase during the L phases of discharges which make a transition to H mode, and these increases are typically larger than the increases in the underlying quantities. The quality of H mode confinement is strongly correlated with the height of the H mode pedestal for the pressure. The gradient of the pressure is limited by MHD modes, in particular by ideal kink ballooning modes with finite mode number n. For a wide variety of discharges, the width of the barrier for electron pressure is well described by a relationship that is proportional to (β p ped ) 1/2 . A new regime of confinement, called the quiescent H mode, which provides steady state operation with no ELMs, low radiated power and normal H mode confinement, has been discovered. A coherent edge MHD mode provides adequate particle transport to control the plasma density while permitting the pressure pedestal to remain almost identical to that observed in ELMing discharges. (author)

  12. Bifurcation to Enhanced Performance H-mode on NSTX

    Science.gov (United States)

    Battaglia, D. J.; Chang, C. S.; Gerhardt, S. P.; Kaye, S. M.; Maingi, R.; Smith, D. R.

    2015-11-01

    The bifurcation from H-mode (H98 Performance (EP)H-mode (H98 = 1.2 - 2.0) on NSTX is found to occur when the ion thermal (χi) and momentum transport become decoupled from particle transport, such that the ion temperature (Ti) and rotation pedestals increase independent of the density pedestal. The onset of the EPH-mode transition is found to correlate with decreased pedestal collisionality (ν*ped) and an increased broadening of the density fluctuation (dn/n) spectrum in the pedestal as measured with beam emission spectroscopy. The spectrum broadening at decreased ν*ped is consistent with GEM simulations that indicate the toroidal mode number of the most unstable instability increases as ν*ped decreases. The lowest ν*ped, and thus largest spectrum broadening, is achieved with low pedestal density via lithium wall conditioning and when Zeff in the pedestal is significantly reduced via large edge rotation shear from external 3D fields or a large ELM. Kinetic neoclassical transport calculations (XGC0) confirm that Zeff is reduced when edge rotation braking leads to a more negative Er that shifts the impurity density profiles inward relative to the main ion density. These calculations also describe the role kinetic neoclassical and anomalous transport effects play in the decoupling of energy, momentum and particle transport at the bifurcation to EPH-mode. This work was sponsored by the U.S. Department of Energy.

  13. H-mode and confinement studies in ASDEX Upgrade

    International Nuclear Information System (INIS)

    Suttrop, W.; Ryter, F.; Mertens, V.; Gruber, O.; Murmann, H.; Salzmann, H.; Schweinzer, J.

    2001-01-01

    H-mode operational boundaries and H-mode confinement are investigated on ASDEX Upgrade. The local edge parameter threshold for H-mode holds independent of divertor geometry and changes little with ion mass. The deviation of the H-mode power threshold at densities near the Greenwald limit can be understood as a consequence of a confinement deterioration, caused by 'stiff' temperature profiles and lack of core density gradients in gas puff fuelled discharges. Ion and electron temperature profiles can be described by a lower limit of gradient length L T =T/T'. (author)

  14. H-Mode Turbulence, Power Threshold, ELM, and Pedestal Studies in NSTX

    International Nuclear Information System (INIS)

    Maingi, R.; Bush, C.E.; Fredrickson, E.D.; Gates, D.A.; Kaye, S.M.; LeBlanc, B.P.; Menard, J.E.; Meyer, H.; Mueller, D.; Nishino, N.; Roquemore, A.L.; Sabbagh, S.A.; Tritz, K.; Zweben, S.J.; Bell, M.G.; Bell, R.E.; Biewer, T.; Boedo, J.A.; Johnson, D.W.; Kaita, R.; Kugel, H.W.; Maqueda, R.J.; Munsat, T.; Raman, R.; Soukhanovskii, V.A.; Stevenson, T.; Stutman, D.

    2004-01-01

    High-confinement mode (H-mode) operation plays a crucial role in NSTX [National Spherical Torus Experiment] research, allowing higher beta limits due to reduced plasma pressure peaking, and long-pulse operation due to high bootstrap current fraction. Here, new results are presented in the areas of edge localized modes (ELMs), H-mode pedestal physics, L-H turbulence, and power threshold studies. ELMs of several other types (as observed in conventional aspect ratio tokamaks) are often observed: (1) large, Type I ELMs, (2) ''medium'' Type II/III ELMs, and (3) giant ELMs which can reduce stored energy by up to 30% in certain conditions. In addition, many high-performance discharges in NSTX have tiny ELMs (newly termed Type V), which have some differences as compared with ELM types in the published literature. The H-mode pedestal typically contains between 25-33% of the total stored energy, and the NSTX pedestal energy agrees reasonably well with a recent international multi-machine scaling. We find that the L-H transition occurs on a ∼100 (micro)sec timescale as viewed by a gas puff imaging diagnostic, and that intermittent quiescent periods precede the final transition. A power threshold identity experiment between NSTX and MAST shows comparable loss power at the L-H transition in balanced double-null discharges. Both machines require more power for the L-H transition as the balance is shifted toward lower single null. High field side gas fueling enables more reliable H-mode access, but does not always lead to a lower power threshold e.g., with a reduction of the duration of early heating. Finally the edge plasma parameters just before the L-H transition were compared with theories of the transition. It was found that while some theories can separate well-developed L- and H-mode data, they have little predictive value

  15. Energy confinement in Ohmic H-mode in TUMAN-3M

    International Nuclear Information System (INIS)

    Andrejko, M.V.; Askinazi, L.G.; Golant, V.E.; Kornev, V.A.; Lebedev, S.V.; Levin, L.S.; Tukachinsky, A.S.

    1997-01-01

    The spontaneous transition from Ohmically heated limiter discharges into the regime with improved confinement termed as ''Ohmic H-mode'' has been investigated in ''TUMAN-3''. The typical signatures of H-mode in tokamaks with powerful auxiliary heating have been observed: sharp drop of D α radiation with simultaneous increase in the electron density and stored energy, suppression of the density fluctuations and establishing the steep gradient near the periphery. In 1994 new vacuum vessel had been installed in TUMAN-3 tokamak. The vessel has the same sizes as old one (R 0 =0.55 m, a 1 =0.24 m). New vessel was designed to reduce mechanical stresses in the walls during B T ramp phase of a shot. Therefore modified device - TUMAN-3M is able to produce higher B T and I p , up to 2 T and 0.2 MA respectively. During first experimental run device was operated in Ohmic Regime. In these experiments the possibility to achieve Ohmic H-mode was studied. The study of the parametric dependencies of the energy confinement time in both OH and Ohmic H-mode was performed. In Ohmic H-mode strong dependencies of τ E on plasma current and on input power and weak dependence on density were found. Energy confinement time in TUMAN-3/TUMAN-3M Ohmic H-mode has revealed good agreement with JET/DIII-D/ASDEX scaling for ELM-free H-mode, resulting in very long τ E at the high plasma current discharges. (author)

  16. ELM triggering conditions for the integrated modeling of H-mode plasmas

    International Nuclear Information System (INIS)

    Pankin, A.Y.; Schnack, D.D.; Bateman, G.; Kritz, A.H.; Brennan, D.P.; Snyder, P.B.; Voitsekhovitch, I.; Kruger, S.; Janeschitz, G.; Onjun, T.; Pacher, G.W.; Pacher, H.D.

    2005-01-01

    Recent advances in the integrated modeling of ELMy H-mode plasmas are presented. A new model for the H-mode pedestal and for the triggering of ELMs predicts the height, width, and shape of the H-mode pedestal and the frequency and width of ELMs. The model for the pedestal and ELMs is used in the ASTRA integrated transport code to follow the time evolution of tokamak discharges from L-mode through the transition from L-mode to H-mode, with the formation of the H-mode pedestal, and, subsequently, to the triggering of ELMs. Turbulence driven by the ion temperature gradient mode, resistive ballooning mode, trapped electron mode, and electron temperature gradient mode contributes to the anomalous thermal transport at the plasma edge in this model. Formation of the pedestal and the L-H transition is the direct result of E(vector) r x B(vector) flow shear suppression of anomalous transport. The periodic ELM crashes are triggered by MHD instabilities. Two mechanisms for triggering ELMs are considered: ELMs are triggered by ballooning modes if the pressure gradient exceeds the ballooning threshold or by peeling modes if the edge current density exceeds the peeling mode threshold. The BALOO, DCON, and ELITE ideal MHD stability codes are used to derive a new parametric expression for the peeling-ballooning threshold. The new dependence for the peeling-ballooning threshold is implemented in the ASTRA transport code. Results of integrated modeling of DIII-D like discharges are presented and compared with experimental observations. The results from the ideal MHD stability codes are compared with results from the resistive MHD stability code NIMROD. (author)

  17. Intermittency in the Scrape-off Layer of the National Spherical Torus Experiment During H-mode Confinement

    International Nuclear Information System (INIS)

    Maqueda, R.J.; Stotler, D.P.; Zweben, S.J.

    2010-01-01

    A gas puff imaging diagnostic is used in the National Spherical Tokamak Experiment (M. Ono, et al., Nucl. Fusion 40, 557 (2000)) to study the edge turbulence and intermittency present during H-mode discharges. In the case of low power Ohmic H-modes the suppression of turbulence/blobs is maintained through the duration of the (short lived) H-modes. Similar quiescent edges are seen during the early stages of H-modes created with the use of neutral beam injection. Nevertheless, as time progresses following the L-H transition, turbulence and blobs reappear although at a lower level than that typically seen during L-mode confinement. It is also seen that the time-averaged SOL emission profile broadens, as the power loss across the separatrix increases. These broad profiles are characterized by a large level of fluctuations and intermittent events.

  18. Plasma current dependence of the edge pedestal height in JET ELM-free H-modes

    International Nuclear Information System (INIS)

    Nave, M.F.F; Lomas, P.; Gowers, C.; Guo, H.; Hawkes, N.; Huysmans, G.T.A.; Jones, T.; Parail, V.V.; Rimini, F.; Schunke, B.

    2000-01-01

    Some models for the suppression of turbulence in the L to H transition, suggest that the width of the H-mode edge barrier is either proportional or is of the order of the thermal or the fast-ion poloidal Larmor radius. This would require that the width of the edge barrier should depend on the plasma current. This dependence has been clearly verified at JET in experiments designed to control the edge MHD stability of ELM-free hot-ion H-mode plasmas. The effects of isotopic mass and the applicability of several edge barrier models to the hot-ion H-mode plasmas were analysed in (Guo H Y et al 2000 Edge transport barrier in JET hot-ion H-modes Nucl. Fusion 40 69) using a large database containing both deuterium-only and deuterium-tritium plasmas. This database has now been enlarged to include discharges from a plasma shape scan, allowing one to study the dependence of the pedestal height on the edge shear. In addition, the range of plasma currents was extended up to 6 MA. It is shown that the edge data are best described by a model where the edge barrier width is determined by the fast ions weighted towards the components with largest poloidal Larmor radii. However, it is not possible to conclusively eliminate the thermal ion model. (author)

  19. Progress in qualifying the edge physics of the H-mode regime in DIII-D

    International Nuclear Information System (INIS)

    Groebner, R.J.; Baker, D.R.; Boedo, J.A.

    2001-01-01

    Edge conditions in DIII-D are being quantified in order to provide insight into the physics of the H-mode regime. Electron temperature is not the key parameter that controls the L-H transition. Gradients of edge temperature and pressure are much more promising candidates for such parameters. The quality of H-mode confinement is strongly correlated with the height of the H-mode pedestal for the pressure. The gradient of the pressure appears to be controlled by MHD modes, in particular by kink-ballooning modes with finite mode number n. For a wide variety of discharges, the width of the barrier is well described with a relationship that is proportional to (β p ped ) 1/2 . An attractive regime of confinement has been discovered which provides steady-state operation with no ELMs, low impurity content and normal H-mode confinement. A coherent edge MHD-mode evidently provides adequate particle transport to control the plasma density and impurity content while permitting the pressure pedestal to remain almost identical to that observed in ELMing discharges. (author)

  20. On global H-mode scaling laws for JET

    International Nuclear Information System (INIS)

    Kardaun, O.; Lackner, K.; Thomsen, K.; Christiansen, J.; Cordey, J.; Gottardi, N.; Keilhacker, M.; Smeulders, P.

    1989-01-01

    Investigation of the scaling of the energy confinement time τ E with various plasma parameters has since long been an interesting, albeit not uncontroversial topic in plasma physics. Various global scaling laws have been derived for ohmic as well as (NBI and/or RF heated) L-mode discharges. Due to the scarce availability of computerised, extensive and validated H-mode datasets, systematic statistical analysis of H-mode scaling behaviour has hitherto been limited. A common approach is to fit the available H-mode data by an L-mode scaling law (e.g., Kaye-Goldston, Rebut-Lallia) with one or two adjustable constant terms. In this contribution we will consider the alternative approach of fitting all free parameters of various simple scaling models to two recently compiled datasets consisting of about 140 ELM-free and 40 ELMy H-mode discharges, measured at JET in the period 1986-1988. From this period, approximately all known H-mode shots have been included that satisfy the following criteria: D-injected D + discharges with no RF heating, a sufficiently long (≥300 ms) and regular P NBI flat-top, and validated main diagnostics. (author) 13 refs., 1 tab

  1. Analysis of the H-mode density limit in the ASDEX upgrade tokamak using bolometry

    Energy Technology Data Exchange (ETDEWEB)

    Bernert, Matthias

    2013-10-23

    The high confinement mode (H-mode) is the operational scenario foreseen for ITER, DEMO and future fusion power plants. At high densities, which are favourable in order to maximize the fusion power, a back transition from the H-mode to the low confinement mode (L-mode) is observed. This H-mode density limit (HDL) occurs at densities on the order of, but below, the Greenwald density. In this thesis, the HDL is revisited in the fully tungsten walled ASDEX Upgrade tokamak (AUG). In AUG discharges, four distinct operational phases were identified in the approach towards the HDL. First, there is a stable H-mode, where the plasma density increases at steady confinement, followed by a degrading H-mode, where the core electron density is fixed and the confinement, expressed as the energy confinement time, reduces. In the third phase, the breakdown of the H-mode and transition to the L-mode, the overall electron density is fixed and the confinement decreases further, leading, finally, to an L-mode, where the density increases again at a steady confinement at typical L-mode values until the disruptive Greenwald limit is reached. These four phases are reproducible, quasi-stable plasma regimes and provide a framework in which the HDL can be further analysed. Radiation losses and several other mechanisms, that were proposed as explanations for the HDL, are ruled out for the current set of AUG experiments with tungsten walls. In addition, a threshold of the radial electric field or of the power flux into the divertor appears to be responsible for the final transition back to L-mode, however, it does not determine the onset of the HDL. The observation of the four phases is explained by the combination of two mechanisms: a fueling limit due to an outward shift of the ionization profile and an additional energy loss channel, which decreases the confinement. The latter is most likely created by an increased radial convective transport at the edge of the plasma. It is shown that the

  2. Analysis of the H-mode density limit in the ASDEX upgrade tokamak using bolometry

    International Nuclear Information System (INIS)

    Bernert, Matthias

    2013-01-01

    The high confinement mode (H-mode) is the operational scenario foreseen for ITER, DEMO and future fusion power plants. At high densities, which are favourable in order to maximize the fusion power, a back transition from the H-mode to the low confinement mode (L-mode) is observed. This H-mode density limit (HDL) occurs at densities on the order of, but below, the Greenwald density. In this thesis, the HDL is revisited in the fully tungsten walled ASDEX Upgrade tokamak (AUG). In AUG discharges, four distinct operational phases were identified in the approach towards the HDL. First, there is a stable H-mode, where the plasma density increases at steady confinement, followed by a degrading H-mode, where the core electron density is fixed and the confinement, expressed as the energy confinement time, reduces. In the third phase, the breakdown of the H-mode and transition to the L-mode, the overall electron density is fixed and the confinement decreases further, leading, finally, to an L-mode, where the density increases again at a steady confinement at typical L-mode values until the disruptive Greenwald limit is reached. These four phases are reproducible, quasi-stable plasma regimes and provide a framework in which the HDL can be further analysed. Radiation losses and several other mechanisms, that were proposed as explanations for the HDL, are ruled out for the current set of AUG experiments with tungsten walls. In addition, a threshold of the radial electric field or of the power flux into the divertor appears to be responsible for the final transition back to L-mode, however, it does not determine the onset of the HDL. The observation of the four phases is explained by the combination of two mechanisms: a fueling limit due to an outward shift of the ionization profile and an additional energy loss channel, which decreases the confinement. The latter is most likely created by an increased radial convective transport at the edge of the plasma. It is shown that the

  3. Pellet fuelling and ELMy H-mode physics at JET

    International Nuclear Information System (INIS)

    Horton, L.D.

    2001-01-01

    As the reference operating regime for ITER, investigations of the ELMy H-mode have received high priority in the JET experimental programme. Recent experiments have concentrated in particular on operation simultaneously at high density and high confinement using high field side (HFS) pellet launch. The enhanced fuelling efficiency of HFS pellet fuelling is found to scale favourably to a large machine such as JET. The achievable density of ELMy H-mode plasmas in JET has been significantly increased using HFS fuelling although at the expense of confinement degradation back to L-mode levels. Initial experiments using control of the pellet injection frequency have shown that density and confinement can simultaneously be increased close to the values necessary for ITER. The boundaries of the available ELMy H-mode operational space have also been extensively explored. The power necessary to maintain the high confinement normally associated with ELMy H-mode operation is found to be substantially higher than the H-mode threshold power. The compatibility of ELMy H-modes with divertor operation acceptable for a fusion device has been studied. Narrow energy scrape-off widths are measured which place stringent limits on divertor power handling. Deuterium and tritium codeposition profiles are measured to be strongly in/out asymmetric. Successful modelling of these profiles requires the inclusion of the (measured) scrape-off layer flows and of the production in the divertor of hydrocarbon molecules with sticking coefficients below unity. Helium exhaust and compression are found to be within the limits sufficient for a reactor. (author)

  4. Collisional drift waves in the H-mode edge

    International Nuclear Information System (INIS)

    Sen, S.

    1994-01-01

    The stability of the collisional drift wave in a sheared slab geometry is found to be severely restricted at the H-mode edge plasma due to the very steep density gradient. However, a radially varying transverse velocity field is found to play the key role in stability. Velocity profiles usually found in the H-mode plasma stabilize drift waves. On the other hand, velocity profiles corresponding to the L-mode render collisional drift waves unstable even though the magnetic shear continues to play its stabilizing role. (author). 24 refs

  5. Edge ion dynamics in H-mode discharges in DIII-D

    International Nuclear Information System (INIS)

    Groebner, R.J.; Burrell, K.H.; Gohil, P.; Kim, J.; Seraydarian, R.P.

    1992-05-01

    The goal of this paper is to present detailed measurements of T i and E r at the plasma edge in L- and H-mode with high spatial resolution in order the study the edge ion dynamics. Of primary interest is the relationship between T i and E r and the behavior of the edge T i profile in H-mode. The principle findings are: there appears to be a threshold temperature for T i required for the transition to occur with T i at the LCFS in the range of 0.2--0.3 keV at the transition; a correlation between the edge E r profile and the edge T i profile has been observed; and values of T i of 2--3 keV within a few cm of the LCFS and of dT i /dr of up to 1 keV/cm are observed in the transport barrier in H-mode, with the scale length for T i being of the order of a poloidal gyroradius

  6. Coupling of an ICRF compact loop antenna to H-mode plasmas in DIII-D

    International Nuclear Information System (INIS)

    Mayberry, M.J.; Baity, F.W.; Hoffman, D.J.; Luxon, J.L.; Owens, T.L.; Prater, R.

    1987-01-01

    Low power coupling tests have been carried out with a prototype ICRF compact loop antenna on the DIII-D tokamak. During neutral-beam-heated L-mode discharges the antenna loading is typically R≅1-2Ω for an rf frequency of 32 MHz (B/sub T/ = 21 kG, ω = 2Ω/sub D/(0)). When a transition into the H-mode regime of improved confinement occurs, the loading drops to R≅0.5-1.0Ω. During ELMs, transient increases in loading up to several Ohms are observed. The apparent sensitivity of ICRF antenna coupling to changes in the edge plasma profiles associated with the H-mode regime could have important implications for the design of future high power systems

  7. The physics of transport barrier formation in the PBX-M H-mode

    International Nuclear Information System (INIS)

    Tynan, G.R.; Schmitz, L.; Blush, L.

    1994-01-01

    Measurements of edge profiles, turbulence, and turbulent-driven transport were made inside the last-closed flux surface (LCFS) and in the scrape-off layer (SOL) of PBX-M L-mode and H-mode plasmas using a fast reciprocating Langmuir probe diagnostic. Direct measurements of the potential profile confirm the generation of a strong inward radial electric field (E r ∼ -100 V/cm) just inside the LCFS in H-mode. Density and potential fluctuations levels are reduced at the L-H transition, resulting in significantly lower turbulent transport. The reduction in turbulent transport occurs across the LCFS and SOL regions and is not localized to the region of strong radial electric field. (author)

  8. Papers presented at the 6th H-mode workshop (Seeon, Germany)

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-10-01

    The 6th H-mode workshop was held at Kloster Seeon (Germany) during the period of September 22-24, 1997. Contribution to this workshop is reported. Reports include. 1. Role of Nonuniform Superthermal Ions for Internal Transport Barriers. 2. Electric Field Bifurcation and Transition in the Core Plasma of CHS. 3. Formation and Termination of High Ion Temperature Mode in Heliotron/torsatron Plasmas. 4. Transition to an Enhanced Internal Transport Barrier. 5. Physics of Collapses - Probabilistic Occurrence of ELMs and Crashes -. (J.P.N.)

  9. Offset linear scaling for H-mode confinement

    International Nuclear Information System (INIS)

    Miura, Yukitoshi; Tamai, Hiroshi; Suzuki, Norio; Mori, Masahiro; Matsuda, Toshiaki; Maeda, Hikosuke; Takizuka, Tomonori; Itoh, Sanae; Itoh, Kimitaka.

    1992-01-01

    An offset linear scaling for the H-mode confinement time is examined based on single parameter scans on the JFT-2M experiment. Regression study is done for various devices with open divertor configuration such as JET, DIII-D, JFT-2M. The scaling law of the thermal energy is given in the MKSA unit as W th =0.0046R 1.9 I P 1.1 B T 0.91 √A+2.9x10 -8 I P 1.0 R 0.87 P√AP, where R is the major radius, I P is the plasma current, B T is the toroidal magnetic field, A is the average mass number of plasma and neutral beam particles, and P is the heating power. This fitting has a similar root mean square error (RMSE) compared to the power law scaling. The result is also compared with the H-mode in other configurations. The W th of closed divertor H-mode on ASDEX shows a little better values than that of open divertor H-mode. (author)

  10. Ballooning mode stability for self-consistent pressure and current profiles at the H-mode edge

    International Nuclear Information System (INIS)

    Miller, R.L.; Lin-Liu, Y.R.; Osborne, T.H.; Taylor, T.S.

    1997-11-01

    The edge pressure gradient (H-mode pedestal) for computed equilibria in which the current density profile is consistent with the bootstrap current may not be limited by the first regime ballooning limit. The transition to second stability is easier for: higher elongation, intermediate triangularity, larger ratio, pedestal at larger radius, narrower pedestal width, higher q 95 , and lower collisionality

  11. H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Moda)

    Science.gov (United States)

    Hubbard, A. E.; Hughes, J. W.; Bespamyatnov, I. O.; Biewer, T.; Cziegler, I.; LaBombard, B.; Lin, Y.; McDermott, R.; Rice, J. E.; Rowan, W. L.; Snipes, J. A.; Terry, J. L.; Wolfe, S. M.; Wukitch, S.

    2007-05-01

    This paper reports on studies of the edge transport barrier and transition threshold of the high confinement (H) mode of operation on the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)], over a wide range of toroidal field (2.6-7.86T) and plasma current (0.4-1.7MA). The H-mode power threshold and edge temperature at the transition increase with field. Barrier widths, pressure limits, and confinement are nearly independent of field at constant current, but the operational space at high B shifts toward higher temperature and lower density and collisionality. Experiments with reversed field and current show that scrape-off-layer flows in the high-field side depend primarily on configuration. In configurations with the B ×∇B drift away from the active X-point, these flows lead to more countercurrent core rotation, which apparently contributes to higher H-mode thresholds. In the unfavorable case, edge temperature thresholds are higher, and slow evolution of profiles indicates a reduction in thermal transport prior to the transition in particle confinement. Pedestal temperatures in this case are also higher than in the favorable configuration. Both high-field and reversed-field results suggest that parameters at the L-H transition are influencing the evolution and parameters of the H-mode pedestal.

  12. ELM triggering conditions for the integrated modeling of H-mode plasmas

    International Nuclear Information System (INIS)

    Pankin, A.Y.; Schnack, D.D.; Bateman, G.; Kritz, A.H.; Brennan, D.P.; Snyder, P.B.; Voitsekhovitch, I.; Kruger, S.; Janeschitz, G.; Onjun, T.; Pacher, G.W.; Pacher, H.D.

    2004-01-01

    Recent advances in the integrated modeling of ELMy (edge localized mode) H-mode plasmas are presented. A model for the H-mode pedestal and for the triggering of ELMs predicts the height, width, and shape of the H-mode pedestal and the frequency and width of ELMs. Formation of the pedestal and the L-H transition is the direct result of E r x B flow shear suppression of anomalous transport. The periodic ELM crashes are triggered by either the ballooning or peeling MHD instabilities. The BALOO, DCON, and ELITE ideal MHD stability codes are used to derive a new parametric expression for the peeling-ballooning threshold. The new dependence for the peeling-ballooning threshold is implemented in the ASTRA transport code. Results of integrated modeling of DIII-D like discharges are presented and compared with experimental observations. The results from the ideal MHD stability codes are compared with results from the resistive MHD stability code NIMROD. (authors)

  13. Operational limits of high density H-modes in ASDEX Upgrade

    International Nuclear Information System (INIS)

    Mertens, V.; Borrass, K.; Kaufmann, M.; Lang, P.T.; Lang, R.; Mueller, H.W.; Neuhauser, J.; Schneider, R.; Schweinzer, J.; Suttrop, W.

    2001-01-01

    Systematic investigations of H-mode density limit (H→L-mode back transition) plasmas with gas fuelling and alternatively with additional pellet injection from the magnetic high-field-side HFS are being performed in the new closed divertor configuration DV-II. The resulting database covering a wide range of the externally controllable plasma parameters I p , B t and P heat confirms that the H-mode threshold power exceeds the generally accepted prediction P L→H heat ∝B-bar t dramatically when one approaches Greenwald densities. Additionally, in contrast to the Greenwald scaling a moderate B t -dependence of the H-mode density limit is found. The limit is observed to coincide with divertor detachment and a strong increase of the edge thermal transport, which has, however, no detrimental effect on global τ E . The pellet injection scheme from the magnetic high-field-side HFS, developed recently on ASDEX Upgrade, leads to fast particle drifts which are, contrary to the standard injection from the low-field-side, directed into the plasma core. This improves markedly the pellet particle fuelling efficiency. The responsible physical mechanism, the diamagnetic particle drift of the pellet ablatant was successfully verified recently. Other increased particle losses on respectively different time scales after the ablation process, however, still persist. Generally, a clear gain in achievable density and plasma stored energy is achieved with stationary HFS pellet injection compared to gas-puffing. (author)

  14. Plasma current dependence of the edge pedestal height in JET ELM-free H-modes

    International Nuclear Information System (INIS)

    Nave, M.; Lomas, P.; Gowers, C.

    2000-01-01

    Models for the suppression of turbulence in the L to H transition, suggest that the width of the H-mode edge barrier is either proportional or is of the order of the ion poloidal Larmor radius. This would require that the width of the edge barrier should depend on the plasma current. This dependence has been clearly verified at JET in experiments designed to control the edge MHD stability of ELM-free hot-ion H-mode plasmas. The effects of isotopic mass and the applicability of several edge barrier models to the hot-ion H-mode plasmas were analysed in using a large database containing both Deuterium-only (DD) and Deuterium-Tritium (DT) plasmas. This database has now been enlarged to include discharges from a plasma shape scan, allowing to study the dependence of the pedestal height on the edge shear. In addition the range of plasma currents was extended up to 6 MA. It is shown that the edge data is best described by a model where the edge barrier width is determined by the fast ions weighted towards the components with largest poloidal Larmor radii. However, it is not possible to eliminate conclusively the thermal ion model. (author)

  15. Coherent edge fluctuation measurements in H-mode discharges on JFT-2M

    International Nuclear Information System (INIS)

    Nagashima, Y; Shinohara, K; Hoshino, K; Ejiri, A; Tsuzuki, K; Ido, T; Uehara, K; Kawashima, H; Kamiya, K; Ogawa, H; Yamada, T; Shiraiwa, S; Ohara, S; Takase, Y; Asakura, N; Oyama, N; Fujita, T; Ide, S; Takenaga, H; Kusama, Y; Miura, Y

    2004-01-01

    Results of coherent edge fluctuation measurements using three diagnostics (a reciprocating Langmuir probe, a two channel O-mode reflectometer, and fast magnetic probes) in H-mode discharges on JFT-2M are presented. In discharges in which a high recycling steady (HRS) H-mode phase is obtained through a transient phase with slightly enhanced D α intensity, two types of coherent fluctuations are observed. The higher frequency mode (around 300 kHz) is the high frequency mode (HFM) observed in the HRS H-mode (Kamiya K et al 2003 9th IAEA Tech. Meeting H-mode Workshop Topic B-14). The lower frequency mode has a frequency of around 80 kHz. The HFM is detected by a Langmuir probe over a wide region in the SOL, as well as by the reflectometer and magnetic probes. However, the HFM is not detected by the higher frequency (38 GHz) channel of the reflectometer after the HRS transition, suggesting that the HFM is not located deeply inside the plasma. The 80 kHz mode is detected by both channels of the reflectometer and by a Langmuir probe, but not by magnetic probes, suggesting that it is an electrostatic mode. In contrast to the HFM, the 80 kHz mode is detected by the Langmuir probe only near the separatrix during the transient phase, which leads to either the HRS phase or the ELMy phase, and is similar to the fluctuations reported in Shinohara K et al (1998 J. Plasma Fusion Res. 74 607)

  16. Operational conditions and characteristics of ELM-events during H-mode plasmas in the stellarator W7-AS

    International Nuclear Information System (INIS)

    Hirsch, M.; Grigull, P.; Wobig, H.; Kisslinger, J.; McCormick, K.; Anton, M.; Baldzuhn, J.; Fiedler, S.; Fuchs, Ch.; Geiger, J.; Giannone, L.; Hartfuss, H.-J.; Holzhauer, E.; Hirsch, M.; Jaenicke, R.; Kick, M.; Maassberg, H.; Wagner, F.; Weller, A.

    2000-01-01

    H-mode operation in the low-shear stellarator W7-AS is achieved for specific plasma edge topologies characterized by three 'operational windows' of the edge rotational transform. An explanation for this strong influence of the magnetic configuration could be the increase of viscous damping if rational surfaces and thus island structures occur within the relevant plasma edge layer, thereby impeding the development of an edge transport barrier. Prior to the final transition to a quiescent state, the plasma edge passes a rich phenomenology of dynamic behaviour such as dithering and ELMs. Plasma edge parameters indicate that a quiescent H-mode occurs if a certain edge pressure is achieved. (author)

  17. High temperature L- and H-mode confinement in JET

    International Nuclear Information System (INIS)

    Balet, B.; Boyd, D.A.; Campbell, D.J.

    1990-01-01

    The energy confinement properties of low density, high ion temperature L- and H-mode plasmas are investigated. For L-mode plasmas it is shown that, although the global confinement is independent of density, the energy confinement in the central region is significantly better at low densities than at higher densities. The improved confinement appears to be associated with the steepness of the density gradient. For the H-mode phase, although the confinement at the edge is dramatically improved, which is once again associated with the steep density gradient in the edge region, the central confinement properties are essentially the same as for the standard L-mode. The results are compared in a qualitative manner with the predictions of the ion temperature gradient instability theory and appear to be in disagreement with some aspects of this theory. (author). 13 refs, 15 figs

  18. Theory of anomalous transport in H-mode plasmas

    International Nuclear Information System (INIS)

    Itoh, S.; Itoh, K.; Fukuyama, A.; Yagi, M.

    1993-05-01

    Theory of the anomalous transport is developed, and the unified formula for the L- and H-mode plasmas is presented. The self-sustained ballooning-mode turbulence is solved in the presence of the inhomogeneous radial electric field, E r . Reductions in transport coefficients and the amplitude and decorrelation length of fluctuations due to E r ' are quantitatively analyzed. Combined with the E r -bifurcation model, the thickness of the transport barrier is simultaneously determined. (author)

  19. Study of H-mode threshold conditions in DIII-D

    International Nuclear Information System (INIS)

    Groebner, R.J.; Carlstrom, T.N.; Burrell, K.H.

    1996-10-01

    Studies have been conducted in DIII-D to determine the dependence of the power threshold P lh for the transition to the H-mode regime and the threshold P hl for the transition from H-mode to L-mode as functions of external parameters. There is a value of the line-averaged density n e at which P lh has a minimum and P lh tends to increase for lower and higher values of n e . Experiments conducted to separate the effect of the neutral density n 0 from the plasma density n e give evidence of a strong coupling between n 0 and n e . The separate effect of neutrals on the transition has not been determined. Coordinated experiments with JET made in the ITER shape show that P lh increases approximately as S 0.5 where S is the plasma surface area. For these discharges, the power threshold in DIII-D was high by normal standards, thus suggesting that effects other than plasma size may have affected the experiment. Studies of H-L transitions have been initiated and hysteresis of order 40% has been observed. Studies have also been done of the dependence of the L-H transition on local edge parameters. Characterization of the edge within a few ms prior to the transition shows that the range of edge temperatures at which the transition has been observed is more restrictive than the range of densities at which it occurs. These results suggest that some temperature function is important for controlling the transition

  20. Behaviour of impurities during the H-mode in JET

    International Nuclear Information System (INIS)

    Gianella, R.; Behringer, K.; Denne, B.; Gottardi, N.; Hellermann, M. von; Morgan, P.D.; Pasini, D.; Stamp, M.F.

    1989-01-01

    In additionally-heated tokamak discharges, the H-mode phases are reported to display, together with a better energy confinement, a longer global containment time for particles. In particular, steep gradients of electron density and temperature are sustained in the outer region of the plasma column. This enhanced performance is observed especially in discharges in which the activity of edge localized modes (ELMs) is low or absent. High confinement and accumulation of metallic impurities, which quickly give raise to terminal disruptions have been described under similar conditions. In JET H-modes very long impurity confinement times are also observed. However the experimental condition is somewhat more favourable since quiescent H-modes are obtained lasting much longer than the energy confinement times and the radiation from metals is generally negligible. The dominant impurities are normally carbon and oxygen, the latter generally accounting for half or more of the power radiated from the bulk plasma. During the X-point operation the effective influx of carbon into the discharge, which is normally in close correlation with that of deuterium, is substantially reduced while the influx of oxygen, whose production mechanisms is believed to be of a chemical nature, does not show significant variations. (author) 5 refs., 4 figs

  1. VH mode accessibility and global H-mode properties in previous and present JET configurations

    Energy Technology Data Exchange (ETDEWEB)

    Jones, T T.C.; Ali-Arshad, S; Bures, M; Christiansen, J P; Esch, H P.L. de; Fishpool, G; Jarvis, O N; Koenig, R; Lawson, K D; Lomas, P J; Marcus, F B; Sartori, R; Schunke, B; Smeulders, P; Stork, D; Taroni, A; Thomas, P R; Thomsen, K [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking

    1994-07-01

    In JET VH modes, there is a distinct confinement transition following the cessation of ELMs, observed in a wide variety of tokamak operating conditions, using both NBI and ICRF heating methods. Important factors which influence VH mode accessibility such as magnetic configuration and vessel conditions have been identified. The new JET pumped divertor configuration has much improved plasma shaping control and power and particle exhaust capability and should permit exploitation of plasmas with VH confinement properties over an even wider range of operating regimes, particularly at high plasma current; first H-modes have been obtained in the 1994 JET operating period and initial results are reported. (authors). 7 refs., 6 figs.

  2. Rotation characteristics of main ions and impurity ions in H-mode tokamak plasma

    International Nuclear Information System (INIS)

    Kim, J.; Burrell, K.H.; Gohil, P.; Groebner, R.J.; Kim, Y.; St. John, H.E.; Seraydarian, R.P.; Wade, M.R.

    1994-01-01

    Poloidal and toroidal rotation of the main ions (He 2+ ) and the impurity ions (C 6+ and B 5+ ) in H-mode helium plasmas have been measured via charge exchange recombination spectroscopy in the DIII-D tokamak. It was discovered that the main ion poloidal rotation is in the ion diamagnetic drift direction while the impurity ion rotation is in the electron diamagnetic drift direction, in qualitative agreement with the neoclassical theory. The deduced radial electric field in the edge is of the same negative-well shape regardless of which ion species is used, validating the fundamental nature of the electric field in L-H transition phenomenology

  3. Simulation of electron thermal transport in H-mode discharges

    International Nuclear Information System (INIS)

    Rafiq, T.; Pankin, A. Y.; Bateman, G.; Kritz, A. H.; Halpern, F. D.

    2009-01-01

    Electron thermal transport in DIII-D H-mode tokamak plasmas [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] is investigated by comparing predictive simulation results for the evolution of electron temperature profiles with experimental data. The comparison includes the entire profile from the magnetic axis to the bottom of the pedestal. In the simulations, carried out using the automated system for transport analysis (ASTRA) integrated modeling code, different combinations of electron thermal transport models are considered. The combinations include models for electron temperature gradient (ETG) anomalous transport and trapped electron mode (TEM) anomalous transport, as well as a model for paleoclassical transport [J. D. Callen, Nucl. Fusion 45, 1120 (2005)]. It is found that the electromagnetic limit of the Horton ETG model [W. Horton et al., Phys. Fluids 31, 2971 (1988)] provides an important contribution near the magnetic axis, which is a region where the ETG mode in the GLF23 model [R. E. Waltz et al., Phys. Plasmas 4, 2482 (1997)] is below threshold. In simulations of DIII-D discharges, the observed shape of the H-mode edge pedestal is produced when transport associated with the TEM component of the GLF23 model is suppressed and transport given by the paleoclassical model is included. In a study involving 15 DIII-D H-mode discharges, it is found that with a particular combination of electron thermal transport models, the average rms deviation of the predicted electron temperature profile from the experimental profile is reduced to 9% and the offset to -4%.

  4. Ohmic H-mode and confinement in TCV

    International Nuclear Information System (INIS)

    Moret, J.-M.; Anton, M.; Barry, S.

    1995-01-01

    The unique flexibility of TCV for the creation of a wide variety of plasma shapes has been exploited to address some aspects of tokamak physics for which the shape may play an important role. The electron energy confinement time in limited ohmic L-mode plasmas whose elongation and triangularity have been varied (κ = 1.3 - 1.9, δ 0.1 - 0.7) has been observed to improve with elongation as κ 0.5 but to degrade with triangularity as (1 - 0.8 δ), for fixed safety factor. Ohmic H-modes have been obtained in several diverted and limited configurations, with some of the diverted discharges featuring large ELMs whose effects on the global confinement have been quantified. These effects depend on the configuration: in double null (DN) equilibria, a single ELM expels on average 2%, 6% and 2.5% of the particle, impurity and thermal energy content respectively, whilst in single null (SN) configurations, the corresponding numbers are 3.5%, 7% and 9%, indicative of larger ELM effects. The presence of absence of large ELMs in DN discharges has been actively controlled in a single discharge by alternately forcing one or other of the two X-points to lie on the separatrix, permitting stationary density and impurity content (Z eff ∼ 1.6) in long H-modes (1.5 s). (Author)

  5. Ohmic H-mode and confinement in TCV

    International Nuclear Information System (INIS)

    Moret, J.M.; Anton, M.; Barry, S.

    1995-01-01

    The unique flexibility of TCV for the creation of a wide variety of plasma shapes has been exploited to address some aspects of tokamak physics for which the shape may play an important role. The electron energy confinement time in limited ohmic L-mode plasmas whose elongation and triangularity have been varied, has been observed to improve with elongation as κ 0.5 but to degrade with triangularity as (1-0.8 δ), for fixed safety factor. Ohmic H-modes have been obtained in several diverted and limited configurations, with some of the diverted discharges featuring large ELMs whose effects on the global confinement have been quantified. These effects depend on the configuration: in double null (DN) equilibria, a single ELM expels on average 2%, 6% and 2.5% of the particle, impurity and thermal energy content respectively, whilst in single null (SN) configurations, the corresponding numbers are 3.5%, 7% and 9%, indicative of larger ELM effects. The presence or absence of large ELMs in DN discharges has been actively controlled in a single discharge by alternately forcing one or other of the two X-points to lie on the separatrix, permitting stationary density and impurity content (Z eff ≅1.6) in long H-modes (1.5 s). (author) 9 figs., 9 refs

  6. JET Radiative Mantle Experiments in ELMy H-Mode

    International Nuclear Information System (INIS)

    Budny, R.; Coffey, I.; Dumortier, P.; Grisolia, C.; Strachan, J.D.

    1999-01-01

    Radiative mantle experiments were performed on JET ELMy H-mode plasmas. The Septum configuration was used where the X-point is embedded into the top of the Septum. Argon radiated 50% of the input power from the bulk plasma while Z eff rose from an intrinsic level of 1.5 to about 1.7 due to the injected Argon. The total energy content and global energy confinement time decreased 15% when the impurities were introduced. In contrast, the effective thermal diffusivity in the core confinement region (r/a = .4--.8) decreased by 30%. Usually, JET ELMy H-mode plasmas have confinement that is correlated to the edge pedestal pressure. The radiation lowered the edge pedestal and consequently lowered the global confinement. Thus the confinement was changed by a competition between the edge pedestal reduction lowering the confinement and the weaker RI effect upon the core transport coefficients raising the confinement. The ELM frequency increased from 10 Hz Type I ELMs, to 200 Hz type III ELMs. The energy lost by each ELM reduced to 0.5% of the plasma energy content

  7. Transport of impurities during H-mode pulses in JET

    International Nuclear Information System (INIS)

    Giannella, R.; Gottardi, N.; Mompean, F.; Mori, H.; Pasini, D.; Stork, D.; Barnsley, R.; Hawkes, N.C.; Lawson, K.

    1990-01-01

    The transport of impurities during the H-mode is very different from that observed in the other regimes. This is clearly evident in the quiescent discharges where the confinement time of impurities τ I are measured in all the quiescent H-mode discharges in spite of the variety of impurity behavior observed corresponding to different plasma parameters and operating scenarios. The condition of the machine has an influence on the role played by the various impurities, but this does not seem to affect the flow patterns of these ions substantially. In particular oxygen, which was often detected as the dominant radiator, can be reduced to a negligible fraction by He conditioning of the carbon X-point tiles or limiters or by evaporating beryllium in the vacuum vessel. Nevertheless the behaviour of the residual impurities in otherwise similar discharges remains substantially unchanged. The transport patterns appear in fact to be affected by the plasma parameters and their profiles. In particular, two extreme transport regimes are presented in the following. These discharges have been modelled with the aid of a recently developed fully time-dependent impurity transport code using heuristic profiles for the impurity diffusion D and the convection velocity v. (author) 4 refs., 5 figs

  8. Overview of long pulse H-mode operation on EAST

    Science.gov (United States)

    Gong, X.; Garofalo, A. M.; Wan, B.; Li, J.; Qian, J.; Li, E.; Liu, F.; Zhao, Y.; Wang, M.; Xu, H.; EAST Team

    2017-10-01

    The EAST research program aims to demonstrate steady-state long-pulse high-performance H-mode operations with ITER-like poloidal configuration and RF-dominated heating schemes. In the recent experimental campaign, a long pulse fully non-inductive H-mode discharge lasting over 100 seconds using the upper ITER-like tungsten divertor has been achieved in EAST. This scenario used only RF heating and current drive, but also benefitted from an integrated control of the wall conditioning, plasma configuration, divertor heat flux, particle exhaust, impurity management and superconducting coils safety. Maintaining effective coupling of multiple RF heating and current drive sources on EAST is a critical ingredient. This long pulse discharge had good energy confinement, H98,y2 1.1-1.2, and all of the plasma parameters reach a true steady-state. Power balance indicates that the confinement improvement is due partly to a significantly reduced core electron transport inside minor radius rho<0.4. This work was supported by the National Magnetic Confinement Fusion Program of China Contract No. 2015GB10200 and the US Department of Energy Contract No. DE-SC0010685.

  9. Dependence of H-mode power threshold on global and local edge parameters

    International Nuclear Information System (INIS)

    Groebner, R.J.; Carlstrom, T.N.; Burrell, K.H.

    1995-12-01

    Measurements of local electron density n e , electron temperature T e , and ion temperature T i have been made at the very edge of the plasma just prior to the transition into H-mode for four different single parameter scans in the DIII-D tokamak. The means and standard derivations of n e , T e , and T i under these conditions for a value of the normalized toroidal flux of 0.98 are respectively, 1.5 ± 0.7 x 10 19 m -3 , 0.051 ± 0.016 keV, and 0.14 ± 0.03 keV. The threshold condition for the transition is more sensitive to temperature than to density. The data indicate that the dependence is not as simple as a requirement for a fixed value of the ion collisionality

  10. Ballooning stability analysis of JET H-mode discharges

    International Nuclear Information System (INIS)

    O'Brien, D.P.; Galvao, R.; Keilhacker, M.; Lazzaro, E.; Watkins, M.L.

    1989-01-01

    Previous studies of the stability of a large aspect ratio model equilibrium to ideal MHD ballooning modes have shown that across the bulk of the plasma there exist two marginally stable values of the pressure gradient parameter α. These define an unstable zone which separates the first (small α) stable region from the second (large α) stable region. Close to the separatrix, however, the first and second regions can coalesce when the surface averaged current density, Λ, exceeds a critical value. The plasma in this region is then stable to ballooning modes at all values of the pressure gradient. In this paper we extend these results to JET H-mode equilibria using a finite aspect ratio ballooning formalism, and assess the relevance of ideal ballooning stability in these discharges. In particular we analyse shot 15894 at time 56 sec. which is 1.3 s into the H-phase. (author) 4 refs., 4 figs

  11. ELMs and the H-mode pedestal in NSTX

    International Nuclear Information System (INIS)

    Maingi, R.; Sabbagh, S.A.; Bush, C.E.; Fredrickson, E.D.; Menard, J.E.; Stutman, D.; Tritz, K.; Bell, M.G.; Bell, R.E.; Boedo, J.A.; Gates, D.A.; Johnson, D.W.; Kaita, R.; Kaye, S.M.; Kugel, H.W.; LeBlanc, B.P.; Mueller, D.; Raman, R.; Roquemore, A.L.; Soukhanovskii, V.A.; Stevenson, T.

    2005-01-01

    We report on the behavior of ELMs in NBI-heated H-mode plasmas in NSTX. It is observed that the size of Type I ELMs, characterized by the change in plasma energy, decreases with increasing line-average density, as observed at conventional aspect ratio. It is also observed that the Type I ELM size decreases as the plasma equilibrium is shifted from a symmetric double-null toward a lower single-null configuration. Type II/III ELMs have also been observed in NSTX, as well as a high-performance regime with small ELMs which we designate Type V. The Type V ELMs are characterized by an intermittent n 1 magnetic pre-cursor oscillation rotating counter to the plasma current; the mode vanishes between Type V ELMs crashes. Without active pumping, the density rises continuously through the Type V phase, albeit at a slower rate than ELM-free discharges

  12. H-mode profile parametrization for extrapolation and control

    International Nuclear Information System (INIS)

    Imre, K.; Riedel, K.S.; Schissel, D.P.; Schunke, B.

    1996-01-01

    A steady-state ELMy H-mode profile data set of 68 DIII-D discharges and 74 JET discharges is fitted with an error of 7-8%. The advantages of a parametrization of the plasma profiles in terms of a semi-parametric representation, T(ρ, I p , n-bar, B t , P L , R), are described. The shape of the temperature profile depends almost exclusively upon the size, R and q 95 , with a secondary dependence on the heating power. The density profile depends primarily upon q95 with a secondary dependence on n-bar. The line-average temperature T-bar e scales as n-bar -0.31 instead of T-bar∼''n-bar'' -1.0 . The predicted ITER temperature is T-bar = 17.1 keV. (Author)

  13. Accounting of the Power Balance for Neutral-beam heated H-Mode Plasmas in NSTX

    International Nuclear Information System (INIS)

    Paul, S.F.; Maingi, R.; Soukhanovskii, V.; Kaye, S.M.; Kugel, H.

    2004-01-01

    A survey of the dependence of power balance on input power, shape, and plasma current was conducted for neutral-beam-heated plasmas in the National Spherical Torus Experiment (NSTX). Measurements of heat to the divertor strike plates and divertor and core radiation were taken over a wide range of plasma conditions. The different conditions were obtained by inducing a L-mode to H-mode transition, changing the divertor configuration [lower single null (LSN) vs. double-null (DND)] and conducting a NBI power scan in H-mode. 60-70% of the net input power is accounted for in the LSN discharges with 20% of power lost as fast ions, 30-45% incident on the divertor plates, up to 10% radiated in the core, and about 12% radiated in the divertor. In contrast, the power accountability in DND is 85-90%. A comparison of DND and LSN data show that the remaining power in the LSN is likely to be directed to the upper divertor

  14. Fuel ion rotation measurement and its implications on H-mode theories

    International Nuclear Information System (INIS)

    Kim, J.; Burrell, K.H.; Gohil, P.; Groebner, R.J.; Hinton, F.L.; Kim, Y.B.; Seraydarian, R.; Mandl, W.

    1993-10-01

    Poloidal and toroidal rotation of the fuel ions (He 2+ ) and the impurity ions (C 6+ and B 5+ ) in H-mode helium plasmas have been investigated in the DIII-D tokamak by means of charge exchange recombination spectroscopy, resulting in the discovery that the fuel ion poloidal rotation is in the ion diamagnetic drift direction while the impurity ion rotation is in the electron diamagnetic drift direction. The radial electric field obtained from radial force balance analysis of the measured pressure gradients and rotation velocities is shown to be the same regardless of which ion species is used and therefore is a more fundamental parameter than the rotation flows in studying H-mode phenomena. It is shown that the three contributions to the radial electric field (diamagnetic, poloidal rotation, and toroidal rotation terms) are comparable and consequently the poloidal flow does not solely represent the E x B flow. In the high-shear edge region, the density scale length is comparable to the ion poloidal gyroradius, and thus neoclassical theory is not valid there. In view of this new discovery that the fuel and impurity ions rotate in opposite sense, L-H transition theories based on the poloidal rotation may require improvement

  15. The H-mode power threshold in JET

    Energy Technology Data Exchange (ETDEWEB)

    Start, D F.H.; Bhatnagar, V P; Campbell, D J; Cordey, J G; Esch, H P.L. de; Gormezano, C; Hawkes, N; Horton, L; Jones, T T.C.; Lomas, P J; Lowry, C; Righi, E; Rimini, F G; Saibene, G; Sartori, R; Sips, G; Stork, D; Thomas, P; Thomsen, K; Tubbing, B J.D.; Von Hellermann, M; Ward, D J [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking

    1994-07-01

    New H-mode threshold data over a range of toroidal field and density values have been obtained from the present campaign. The scaling with n{sub e} B{sub t} is almost identical with that of the 91/92 period for the same discharge conditions. The scaling with toroidal field alone gives somewhat higher thresholds than the older data. The 1991/2 database shows a scaling of P{sub th} (power threshold) with n{sub e} B{sub t} which is approximately linear and agrees well with that observed on other tokamaks. For NBI and carbon target tiles the threshold power is a factor of two higher with the ion {Nu}B drift away from the target compared with the value found with the drift towards the target. The combination of ICRH and beryllium tiles appears to be beneficial for reducing P{sub th}. The power threshold is largely insensitive to plasma current, X-point height and distance between the last closed flux surface and the limiter, at least for values greater than 2 cm. (authors). 3 refs., 6 figs.

  16. Scaling studies of the H-mode pedestal

    International Nuclear Information System (INIS)

    Groebner, R.J.; Osborne, T.H.

    1998-01-01

    The structure and scaling of the H-mode pedestal are examined for discharges in the DIII-D tokamak. For typical conditions, the pedestal values of the ion and electron temperatures T i and T e are comparable. Measurements of main ion and C 6+ profiles indicate that the ion pressure gradient in the barrier is 50%--100% of the electron pressure gradient for deuterium plasmas. The magnitude of the pressure gradient in the barrier often exceeds the predictions of infinite-n ballooning mode theory by a factor of two. Moreover, via the bootstrap current, the finite pressure gradient acts to entirely remove ballooning stability limits for typical discharges. For a large dataset, the width of the pressure barrier δ is best described by the dimensionless scaling δ/R ∝ (β pol ped ) 0.4 where (β pol ped ) is the pedestal value of poloidal beta and R is the major radius. Scalings based on the poloidal ion gyroradius or the edge density gradient do not adequately describe overall trends in the data set and the propagation of the pressure barrier observed between edge-localized modes. The width of the T i barrier is quite variable and is not a good measure of the width of the pressure barrier

  17. Suppression of tungsten accumulation during ELMy H-mode by lower hybrid wave heating in the EAST tokamak

    Directory of Open Access Journals (Sweden)

    L. Zhang

    2017-08-01

    Full Text Available EAST tokamak has been equipped with upper tungsten divertor since 2014. The tungsten accumulation has been often observed in NBI-heated H-mode discharges suggesting deleterious tungsten confinement in the plasma core. It causes not only H-L back transition but also plasma disruption in several discharges. Suppression of the tungsten accumulation is therefore the most important issue in EAST to achieve a long pulse H-mode discharge. In order to study the tungsten behavior in the long pulse discharge, tungsten spectra have been measured at 20–140Å. The tungsten density, nw, is evaluated from the intensity of tungsten unresolved transition array (W-UTA in a wavelength range of 45–70Å which is composed of several ionization stages of tungsten, e.g. W27+-W45+ at Te0∼2.5keV. It is found that the tungsten accumulation can be suppressed when the 4.6GHz LHW with PLHW∼0.8MW is superimposed on the NBI phase (PNBI= 1.9MW. During the superimposed phase the ELM frequency, fELM, increases from ∼30Hz to ∼60Hz and the tungsten density is halved compared to the NBI-heated discharge. The H-mode discharge can be thus steadily sustained for longer period. It is found that the nw is a large function of the ratio of LHW power to the total injection power, PLHW/(PLHW+PNBI, and the nw can be reduced, at least, in an order of magnitude smaller than that in NBI-heated discharges at PLHW/(PLHW+PNBI≥0.8. The result strongly suggests a possible way toward the steady H-mode discharge.

  18. H-mode threshold power scaling and the ∇B drift effect

    International Nuclear Information System (INIS)

    Carlstrom, T.N.; Burrell, K.H.; Groebner, R.J.; Staebler, G.M.

    1997-06-01

    One of the largest influences on the H-mode power threshold (P TH ) is the direction of the ion ∇B drift relative to the X-point location, where factors of 2--3 increase in P TH are observed for the ion ∇B drift away from the X-point. It is proposed that the threshold power scaling observed in single-null configurations with the ion ∇B drift toward the X-point location (P TH ∼ nB, where n is the plasma density, and B is the toroidal field) is due to the scaling of the magnitude of the ∇B drift effect. Hinton and later Hinton and Stebler have modeled this effect as neoclassical cross field fluxes of both heat and particles driven by poloidal temperature gradients on the open field lines in the scrape-off layer (SOL). The ∇B drift effect influences the power threshold by affecting the edge conditions needed for the L-H transition. It is not essential for the L-H transition itself since transitions are observed with either direction of B. Predictions of this model include saturation of the B scaling of P TH at high field, 1/B scaling of P TH with reverse B, and no B scaling of P TH in balanced double-null configurations. This last prediction is consistent with the observed scaling of p TH in double-null plasma sin DIII-D

  19. Development of ITER 15 MA ELMy H-mode Inductive Scenario

    International Nuclear Information System (INIS)

    C. E. Kessel, D. Campbell, Y. Gribov, G. Saibene, G. Ambrosino, T. Casper, M. Cavinato, H. Fujieda, R. Hawryluk, L. D. Horton, A. Kavin, R. Kharyrutdinov, F. Koechl, J. Leuer, A. Loarte, P. J. Lomas, T. Luce, V. Lukash, M. Mattei, I.Nunes, V. Parail, A. Polevoi, A. Portone, R. Sartori, A.C.C. Sips, P. R. Thomas, A. Welander and J. Wesley

    2008-01-01

    The poloidal field (PF) coil system on ITER, which provides both feedforward and feedback control of plasma position, shape, and current, is a critical element for achieving mission performance. Analysis of PF capabilities has focused on the 15 MA Q = 10 scenario with a 300-500 s flattop burn phase. The operating space available for the 15 MA ELMy H-mode plasma discharges in ITER and upgrades to the PF coils or associated systems to establish confidence that ITER mission objectives can be reached have been identified. Time dependent self-consistent free-boundary calculations were performed to examine the impact of plasma variability, discharge programming, and plasma disturbances. Based on these calculations a new reference scenario was developed based upon a large bore initial plasma, early divertor transition, low level heating in L-mode, and a late H-mode onset. Equilibrium analyses for this scenario indicate that the original PF coil limitations do not allow low li (<0.8) operation or lower flux states, and the flattop burn durations were predicted to be less than the desired 400 s. This finding motivates the expansion of the operating space, considering several upgrade options to the PF coils. Analysis was also carried out to examine the feedback current reserve required in the CS and PF coils during a series of disturbances and a feasibility assessment of the 17 MA scenario was undertaken. Results of the studies show that the new scenario and modified PF system will allow a wide range of 15 MA 300-500 s operation and more limited but finite 17 MA operation

  20. The 13th International Workshop on H-mode Physics and Transport Barriers (Oxford, UK, 2011) The 13th International Workshop on H-mode Physics and Transport Barriers (Oxford, UK, 2011)

    Science.gov (United States)

    Saibene, G.

    2012-11-01

    The 13th International Workshop on H-mode Physics and Transport Barriers, held in Lady Margaret Hall College in Oxford in October 2011 continues the tradition of bi-annual international meetings dedicated to the study of transport barriers in fusion plasmas. The first meeting of this series took place in S Diego (CA, US) in 1987, and since then scientists in the fusion community studying the formation and effects of transport barriers in plasmas have been meeting at this small workshop to discuss progress, new experimental evidence and related theoretical studies. The first workshops were strongly focussed on the characterization and understanding of the H-mode plasma, discovered in ASDEX in 1982. Tokamaks throughout the entire world were able to reproduce the H-mode transition in the following few years and since then the H-mode has been recognised as a pervasive physics feature of toroidally confined plasmas. Increased physics understanding of the H-mode transition and of the properties of H-mode plasmas, together with extensive development of diagnostic capabilities for the plasma edge, led to the development of edge transport barrier studies and theory. The H-mode Workshop reflected this extension in interest, with more and more contributions discussing the phenomenology of edge transport barriers and instabilities (ELMs), L-H transition and edge transport barrier formation theory. In the last 15 years, in response to the development of fusion plasma studies, the scientific scope of the workshop has been broadened to include experimental and theoretical studies of both edge and internal transport barriers, including formation and sustainment of transport barriers for different transport channels (energy, particle and momentum). The 13th H-mode Workshop was organized around six leading topics, and, as customary for this workshop, a lead speaker was selected for each topic to present to the audience the state-of-the-art, new understanding and open issues, as well

  1. Investigation of the hydrogen fluxes in the plasma edge of W7-AS during H-mode discharges

    International Nuclear Information System (INIS)

    Langer, U.; Taglauer, E.; Fischer, R.

    2001-01-01

    In the stellarator W7-AS the H-mode is characterized by an edge transport barrier which is localized within a few centimeters inside the separatrix. The corresponding L-H transition shows well-known features such as the steepening of the temperature and density profiles in the region of the separatrix. With a so-called sniffer probe the temporal development of the hydrogen and deuterium fluxes has been studied in the plasma edge during different H-mode discharges with deuterium gas puffing. Prior to the transition a significant reduction of the deuterium and also the hydrogen fluxes can be observed. This fact confirms the assumption that the steepening of the density profiles starts at the outermost edge of the plasma. Moreover, sniffer probe measurements in the plasma edge could therefore identify a precursor for the L-H transition. The analysis of the hydrogen neutral gases shows a distinct change of the hydrogen isotope ratio during the transition. This observation is in agreement with the change in the particle fluxes onto the targets and can also be seen in the reduced H α signals from the limiters. It is further demonstrated that significant improvement in the time resolution of the measured data can be obtained by deconvolution of the data with the apparatus function using Bayesian probability theory and the Maximum Entropy method with adaptive kernels

  2. Predictive modelling of edge transport phenomena in ELMy H-mode tokamak fusion plasmas

    International Nuclear Information System (INIS)

    Loennroth, J.-S.

    2009-01-01

    This thesis discusses a range of work dealing with edge plasma transport in magnetically confined fusion plasmas by means of predictive transport modelling, a technique in which qualitative predictions and explanations are sought by running transport codes equipped with models for plasma transport and other relevant phenomena. The focus is on high confinement mode (H-mode) tokamak plasmas, which feature improved performance thanks to the formation of an edge transport barrier. H-mode plasmas are generally characterized by the occurrence of edge localized modes (ELMs), periodic eruptions of particles and energy, which limit confinement and may turn out to be seriously damaging in future tokamaks. The thesis introduces schemes and models for qualitative study of the ELM phenomenon in predictive transport modelling. It aims to shed new light on the dynamics of ELMs using these models. It tries to explain various experimental observations related to the performance and ELM-behaviour of H-mode plasmas. Finally, it also tries to establish more generally the potential effects of ripple-induced thermal ion losses on H-mode plasma performance and ELMs. It is demonstrated that the proposed ELM modelling schemes can qualitatively reproduce the experimental dynamics of a number of ELM regimes. Using a theory-motivated ELM model based on a linear instability model, the dynamics of combined ballooning-peeling mode ELMs is studied. It is shown that the ELMs are most often triggered by a ballooning mode instability, which renders the plasma peeling mode unstable, causing the ELM to continue in a peeling mode phase. Understanding the dynamics of ELMs will be a key issue when it comes to controlling and mitigating the ELMs in future large tokamaks. By means of integrated modelling, it is shown that an experimentally observed increase in the ELM frequency and deterioration of plasma confinement triggered by external neutral gas puffing might be due to a transition from the second to

  3. Investigation of EBW Thermal Emission and Mode Conversion Physics in H-Mode Plasmas on NSTX

    International Nuclear Information System (INIS)

    Diem, S.J.; Taylor, G.; Efthimion, P.C.; Kugel, H.W.; LeBlanc, B.P.; Phillips, C.K.; Caughman, J.B.; Wilgen, J.B.; Harvey, R.W.; Preinhaelter, J.; Urban, J.; Sabbagh, S.A.

    2008-01-01

    High β plasmas in the National Spherical Torus Experiment (NSTX) operate in the overdense regime, allowing the electron Bernstein wave (EBW) to propagate and be strongly absorbed/emitted at the electron cyclotron resonances. As such, EBWs may provide local electron heating and current drive. For these applications, efficient coupling between the EBWs and electromagnetic waves outside the plasma is needed. Thermal EBW emission (EBE) measurements, via oblique B-X-O double mode conversion, have been used to determine the EBW transmission efficiency for a wide range of plasma conditions on NSTX. Initial EBE measurements in H-mode plasmas exhibited strong emission before the L-H transition, but the emission rapidly decayed after the transition. EBE simulations show that collisional damping of the EBW prior to the mode conversion (MC) layer can significantly reduce the measured EBE for T e < 20 eV, explaining the observations. Lithium evaporation was used to reduce EBE collisional damping near the MC layer. As a result, the measured B-X-O transmission efficiency increased from < 10% (no Li) to 60% (with Li), consistent with EBE simulations.

  4. Edge operational space for high density/high confinement ELMY H-modes in JET

    International Nuclear Information System (INIS)

    Sartori, R.; Saibene, G.; Loarte, A.

    2002-01-01

    This paper discusses how the proximity to the L-H threshold affects the confinement of ELMy H-modes at high density. The largest reduction in confinement at high density is observed at the transition from the Type I to the Type III ELMy regime. At medium plasma triangularity, δ≅0.3 (where δ is the average triangularity at the separatrix), JET experiments show that by increasing the margin above the L-H threshold power and maintaining the edge temperature above the critical temperature for the transition to Type III ELMs, it is possible to avoid the degradation of the pedestal pressure with density, normally observed at lower power. As a result, the range of achievable densities (both in the core and in the pedestal) is increased. At high power above the L-H threshold power the core density was equal to the Greenwald limit with H97≅0.9. There is evidence that a mixed regime of Type I and Type II ELMs has been obtained at this intermediate triangularity, possibly as a result of this increase in density. At higher triangularity, δ≅0.5, the power required to achieve similar results is lower. (author)

  5. Papers presented at the IAEA technical committee meeting on H-mode physics

    International Nuclear Information System (INIS)

    TCV team

    1995-11-01

    The two papers contained in this report deal with ohmic H-modes and effect on confinement of edge localized modes in the TCV tokamak. They were presented by the TCV team at the 1995 IAEA technical committee meeting on H-mode physics. figs., tabs., refs

  6. Comparison of hybrid and baseline ELMy H-mode confinement in JET with the carbon wall

    NARCIS (Netherlands)

    Beurskens, M. N. A.; Frassinetti, L.; Challis, C.; Osborne, T.; Snyder, P. B.; Alper, B.; Angioni, C.; Bourdelle, C.; Buratti, P.; Crisanti, F.; Giovannozzi, E.; Giroud, C.; Groebner, R.; Hobirk, J.; Jenkins, I.; Joffrin, E.; Leyland, M. J.; Lomas, P.; Mantica, P.; McDonald, D.; Nunes, I.; Rimini, F.; Saarelma, S.; Voitsekhovitch, I.; P. de Vries,; Zarzoso, D.

    2013-01-01

    The confinement in JET baseline type I ELMy H-mode plasmas is compared to that in so-called hybrid H-modes in a database study of 112 plasmas in JET with the carbon fibre composite (CFC) wall. The baseline plasmas typically have beta(Nu) similar to 1.5-2, H-98 similar to 1, whereas the hybrid

  7. The H-mode Pedestal and Edge Localized Modes in NSTX

    International Nuclear Information System (INIS)

    Maingi, R.; Fredrickson, E.D.; Menard, J.E.; Nishino, N.; Roquemore, A.L.; Sabbagh, S.A.; Tritz, K.

    2004-01-01

    The research program of the National Spherical Torus Experiment (NSTX) routinely utilizes the H-mode confinement regime to test and extend beta and pulse length limits. As in conventional aspect ratio tokamaks, NSTX observes a variety of edge localized modes (ELMs) in H-mode. Hence a significant part of the research program is dedicated to ELMs studies

  8. Investigation of lower hybrid current drive during H-mode in EAST tokamak

    International Nuclear Information System (INIS)

    Li Miao-Hui; Ding Bo-Jiang; Kong Er-Hua; Zhang Lei; Zhang Xin-Jun; Qian Jin-Ping; Yan Ning; Han Xiao-Feng; Shan Jia-Fang; Liu Fu-Kun; Wang Mao; Xu Han-Dong; Wan Bao-Nian

    2011-01-01

    H-mode discharges with lower hybrid current drive (LHCD) alone are achieved in EAST divertor plasma over a wide parameter range. These H-mode discharges are characterized by a sudden drop in D α emission and a spontaneous rise in main plasma density. Good lower hybrid (LH) coupling during H-mode is obtained by putting the plasma close to the antenna and by injecting D 2 gas from a pipe near the grill mouse. The analysis of lower hybrid current drive properties shows that the LH deposition profile shifts off axis during H-mode, and current drive (CD) efficiency decreases due to the increase in density. Modeling results of H-mode discharges with a general ray tracing code GENRAY are reported. (physics of gases, plasmas, and electric discharges)

  9. Results of the H-mode experiments with JT-60 outer and lower divertors

    International Nuclear Information System (INIS)

    Nakamura, Hiroo; Tsuji, Shunji; Nagami, Masayuki

    1989-08-01

    In JT-60, hydrogen H-mode experiments with outer and lower divertors were performed. In the outer divertor, H-mode were obtained, similar to the ones observed in the other lower/upper divertors. Its threshold absorbed power and electron density were 16 MW and 1.8 x 10 19 m -3 . In the two combined heatings with NB+ICRF and NB+LHRF, H-mode discharges are also obtained. Moreover, in new configuration of lower divertor, H-mode phases without and with ELM are obtained. Typical results of the lower divertor are shown to compare the H-mode characteristics between the two configurations. Improvement of the energy confinement time in the two divertors was limited to 10 %. Analyses on ballooning/interchange instabilities were carried out with precise equlibria of JT-60. These results showed that the both modes were enough stable. (author)

  10. Discriminant analysis to predict the occurrence of ELMs in H-mode discharges

    International Nuclear Information System (INIS)

    Kardaun, O.J.W.F.; Itoh, S.; Itoh, K.; Kardaun, J.W.P.F.

    1993-08-01

    After an exposition of its theoretical background, discriminant analysis is applied to the H-mode confinement database to find the region in plasma parameter space in which H-mode with small ELMs (Edge Localized Modes) is likely to occur. The boundary of this region is determined by the condition that the probability of appearance of such a type of H-mode, as a function of the plasma parameters, should be (1) larger than some threshold value and (2) larger than the corresponding probability for other types of H-mode (i.e., H-mode without ELMs or with giant ELMs). In practice, the discrimination has been performed for the ASDEX, JET and JFT-2M tokamaks (a) using four instantaneous plasma parameters (injected power P inj , magnetic field B t , plasma current I p and line averaged electron density (n-bar e ) and (b) taking also memory effects of the plasma and the distance between the plasma and the wall into account, while using variables that are normalised with respect to machine size. Generally speaking, it is found that there is a substantial overlap between the region of H-mode with small ELMs and the region of the two other types of H-mode. However, the ELM-free and the giant ELM H-modes relatively rarely appear in the region, that, according to the analysis, is allocated to small ELMs. A reliable production of H-mode with only small ELMs seems well possible by choosing this regime in parameter space. In the present study, it was not attempted to arrive at a unified discrimination across the machines. So, projection from one machine to another remains difficult, and a reliable determination of the region where small ELMs occur still requires a training sample from the device under consideration. (author) 53 refs

  11. Application of divertor cryopumping to H-mode density control in DIII-D

    International Nuclear Information System (INIS)

    Mahdavi, M.A.; Ferron, J.R.; Hyatt, A.W.

    1993-11-01

    In this paper we describe the method and the results of experiments where a unique in-vessel cryopump-baffle system was used to control density of H-mode plasmas. We were able to independently regulate current and density of ELMing H-mode plasmas, each over a range of factor two, and measure the H-mode confinement scaling with plasma density and current. With a modest pumping speed of ∼40 kl/s, particle exhaust rates as high as 2 x 10 22 atom/s -1 have been observed

  12. Effect of ripple-induced transport on H-mode performance in tokamaks

    International Nuclear Information System (INIS)

    Parail, V.; Vries, P. de; Lonnroth, J.; Kiviniemi, T.; Johnson, T.; Loarte, A.; Saibene, G.; Hatae, T.; Kamada, Y.; Konovalov, S.; Oyama, N.; Shinohara, K.; Tobita, K.; Urano, H.

    2005-01-01

    A number of experiments have shown that ripple-induced transport influences performance of ELMy H-modes in the tokamak. A noticeable difference in confinement, ELM frequency and amplitude was found between JET (with ripple amplitude δ∼0.1%) and JT-60U (with δ∼1%) in otherwise identical discharges. It was previously shown in JET experiments with enhanced ripple that a gradual increase in the ripple amplitude first leads to a modest improvement in plasma confinement, which is followed by the degradation of edge pedestal and further transition to the L-mode regime if δ increases further. The DIII-D team recently reported a marginal increase in confinement in experiments with an edge transport enhanced by the externally driven resonant magnetic perturbation. Numerical predictive modelling of the dynamics of ELMy H-mode JET plasma relevant to a JET/JT-60U similarity experiment has been conducted taking into account ripple-induced ion transport, which was computed using the orbit following code ASCOT. This predictive modelling reveals that, depending on plasma parameters, ripple amplitude and localisation (the latter depending on the toroidal coil design), this additional transport can either improve global plasma confinement or reduce it. These controlled ripple losses might be used as an effective tool for ELM mitigation and may provide an explanation for the difference between JET and JT-60U observed in the similarity experiments. A detailed comparison between ripple- induced transport and the alternative method of ELM mitigation by an externally driven edge magnetic perturbation is discussed. The fact that ripple losses mainly increase ion transport, while a stochastic magnetic layer increases electron transport indicates that it might be beneficial to use a combination of both methods in future experiments. This work was funded partly by the United Kingdom Engineering and Physical Sciences Research Council and by the European Communities under the contract of

  13. W transport and accumulation control in the termination phase of JET H-mode discharges and implications for ITER

    Science.gov (United States)

    Köchl, F.; Loarte, A.; de la Luna, E.; Parail, V.; Corrigan, G.; Harting, D.; Nunes, I.; Reux, C.; Rimini, F. G.; Polevoi, A.; Romanelli, M.; Contributors, JET

    2018-07-01

    Tokamak operation with W PFCs is associated with specific challenges for impurity control, which may be particularly demanding in the transition from stationary H-mode to L-mode. To address W control issues in this phase, dedicated experiments have been performed at JET including the variation of the decrease of the power and current, gas fuelling and central ion cyclotron heating (ICRH), and applying active ELM control by vertical kicks. The experimental results obtained demonstrate the key role of maintaining ELM control to control the W concentration in the exit phase of H-modes with slow (ITER-like) ramp-down of the neutral beam injection power in JET. For these experiments, integrated fully predictive core+edge+SOL transport modelling studies applying discrete models for the description of transients such as sawteeth and ELMs have been performed for the first time with the JINTRAC suite of codes for the entire transition from stationary H-mode until the time when the plasma would return to L-mode focusing on the W transport behaviour. Simulations have shown that the existing models can appropriately reproduce the plasma profile evolution in the core, edge and SOL as well as W accumulation trends in the termination phase of JET H-mode discharges as function of the applied ICRH and ELM control schemes, substantiating the ambivalent effect of ELMs on W sputtering on one side and on edge transport affecting core W accumulation on the other side. The sensitivity with respect to NB particle and momentum sources has also been analysed and their impact on neoclassical W transport has been found to be crucial to reproduce the observed W accumulation characteristics in JET discharges. In this paper the results of the JET experiments, the comparison with JINTRAC modelling and the adequacy of the models to reproduce the experimental results are described and conclusions are drawn regarding the applicability of these models for the extrapolation of the applied W

  14. Operational range and transport barrier of the H-mode in the stellarator W7-AS

    International Nuclear Information System (INIS)

    Hirsch, M.; Amadeo, P.; Anton, M.; Baldzuhn, J.; Brakel, R.; Bleuel, J.; Fiedler, S.; Geist, T.; Grigull, P.; Hartfuss, H.J.; Jaenicke, R.; Kick, M.; Kisslinger, J.; Koponen, J.; Wagner, F.; Weller, A.; Wobig, H.; Zoletnik, S.; Holzhauer, E.

    1998-01-01

    In W7-AS the H-mode is characterized by an edge transport barrier localized in the first 3-4 cm inside the separatrix. In the ELMy H-mode preceding the quiescent state ELMs appear as a sudden breakdown of the edge transport barrier in coincidence with bursts of fluctuations. Between ELMs fluctuations are identical to those of the quiescent H-mode. The operational range of the quiescent H-mode is determined by narrow windows of the edge rotational transform and a threshold edge electron density. In contrast, ELM-like events are observed for a variety of plasma conditions by far exceeding the narrow operational windows for the quiescent state. (author)

  15. Ion orbit loss and pedestal width of H-mode tokamak plasmas in limiter geometry

    International Nuclear Information System (INIS)

    Xiao Xiaotao; Liu Lei; Zhang Xiaodong; Wang Shaojie

    2011-01-01

    A simple analytical model is proposed to analyze the effects of ion orbit loss on the edge radial electric field in a tokamak with limiter configuration. The analytically predicted edge radial electric field is consistent with the H-mode experiments, including the width, the magnitude, and the well-like shape. This model provides an explanation to the H-mode pedestal structure. Scaling of the pedestal width based on this model is proposed.

  16. Study of density fluctuation in L-mode and H-mode plasmas on JFT-2M by microwave reflectometer

    International Nuclear Information System (INIS)

    Shinohara, Kouji

    1997-08-01

    We propose the model which can explain the runaway phase. The model takes account of the scattered wave which is caused by the density fluctuation near the cut-off layer. We should take a new approach instead of the conventional phase measurement in order to derive the information of the density fluctuation from the data with the runaway phase. The complex spectrum and the rotary spectrum analyses are useful tools to analyze such data. The density fluctuation in L-mode and H-mode plasmas is discussed by using this new approach. We have observed that the reduction of the density fluctuation is localized in the edge region where the sheared electric field is produced. The fluctuations in the range of frequency lower than 100 kHz are mainly reduced. Two interesting features have been observed. One is the detection of the coherent mode around 100 kHz in H-mode. This mode appears about 10 ms after L to H transition. The timing corresponds to the formation of a steep density and temperature gradient in the edge region. The other is the enhancement of the fluctuations with the frequency higher than 300 kHz in H-mode in contrast to the reduction of the fluctuations with the frequency lower than 100 kHz. The Doppler shift is observed in the complex auto-power spectrum of the reflected wave when the plasma is actively moved. We have confirmed that the movement of the plasma is appropriately measured by using the low pass filter. The reflectometer can be used to measure the density profile by using a low pass filter even when the runaway phase phenomenon occurs. (author). 150 refs

  17. Enhancement of mode-converted electron Bernstein wave emission during National Spherical Torus Experiment H-mode plasmas

    International Nuclear Information System (INIS)

    Taylor, G.; Efthimion, P.C.; Jones, B.; Le Blanc, B.P.; Maingi, R.

    2002-01-01

    A sudden, threefold increase in emission from fundamental electrostatic electron Bernstein waves (EBW) which mode convert and tunnel to the electromagnetic X-mode has been observed during high energy and particle confinement (H-mode) transitions in the National Spherical Torus Experiment (NSTX) plasma [M. Ono, S. Kaye, M. Peng et al., in Proceedings of the 17th IAEA Fusion Energy Conference (IAEA, Vienna, Austria, 1999), Vol. 3, p. 1135]. The mode-converted EBW emission viewed normal to the magnetic field on the plasma midplane increases when the density profile steepens in the vicinity of the mode conversion layer, which is located in the plasma scrape off. The measured conversion efficiency during the H-mode is consistent with the calculated EBW to X-mode conversion efficiency derived using edge density data. Calculations indicate that there may also be a small residual contribution to the measured X-mode electromagnetic radiation from polarization-scrambled, O-mode emission, converted from EBWs

  18. Local Physics Basis of Confinement Degradation in JET ELMy H-Mode Plasmas and Implications for Tokamak Reactors

    International Nuclear Information System (INIS)

    Budny, R.V.; Alper, B.; Borba, D.; Cordey, J.G.; Ernst, D.R.; Gowers, C.

    2001-01-01

    First results of gyrokinetic analysis of JET [Joint European Torus] ELMy [Edge Localized Modes] H-mode [high-confinement modes] plasmas are presented. ELMy H-mode plasmas form the basis of conservative performance predictions for tokamak reactors of the size of ITER [International Thermonuclear Experimental Reactor]. Relatively high performance for long duration has been achieved and the scaling appears to be favorable. It will be necessary to sustain low Z(subscript eff) and high density for high fusion yield. This paper studies the degradation in confinement and increase in the anomalous heat transport observed in two JET plasmas: one with an intense gas puff and the other with a spontaneous transition between Type I to III ELMs at the heating power threshold. Linear gyrokinetic analysis gives the growth rate, gamma(subscript lin) of the fastest growing modes. The flow-shearing rate omega(subscript ExB) and gamma(subscript lin) are large near the top of the pedestal. Their ratio decreases approximately when the confinement degrades and the transport increases. This suggests that tokamak reactors may require intense toroidal or poloidal torque input to maintain sufficiently high |gamma(subscript ExB)|/gamma(subscript lin) near the top of the pedestal for high confinement

  19. PREFACE: 11th IAEA Technical Meeting on H-mode Physics and Transport Barriers

    Science.gov (United States)

    Takizuka, Tomonori

    2008-07-01

    This volume of Journal of Physics: Conference Series contains papers based on invited talks and contributed posters presented at the 11th IAEA Technical Meeting on H-mode Physics and Transport Barriers. This meeting was held at the Tsukuba International Congress Center in Tsukuba, Japan, on 26-28 September 2007, and was organized jointly by the Japan Atomic Energy Agency and the University of Tsukuba. The previous ten meetings in this series were held in San Diego (USA) 1987, Gut Ising (Germany) 1989, Abingdon (UK) 1991, Naka (Japan) 1993, Princeton (USA) 1995, Kloster Seeon (Germany) 1997, Oxford (UK) 1999, Toki (Japan) 2001, San Diego (USA) 2003, and St Petersburg (Russia) 2005. The purpose of the eleventh meeting was to present and discuss new results on H-mode (edge transport barrier, ETB) and internal transport barrier, ITB, experiments, theory and modeling in magnetic fusion research. It was expected that contributions give new and improved insights into the physics mechanisms behind high confinement modes of H-mode and ITBs. Ultimately, this research should lead to improved projections for ITER. As has been the tradition at the recent meetings of this series, the program was subdivided into six topics. The topics selected for the eleventh meeting were: H-mode transition and the pedestal-width Dynamics in ETB: ELM threshold, non-linear evolution and suppression, etc Transport relations of various quantities including turbulence in plasmas with ITB: rotation physics is especially highlighted Transport barriers in non-axisymmetric magnetic fields Theory and simulation on transport barriers Projections of transport barrier physics to ITER For each topic there was an invited talk presenting an overview of the topic, based on contributions to the meeting and on recently published external results. The six invited talks were: A Leonard (GA, USA): Progress in characterization of the H-mode pedestal and L-H transition N Oyama (JAEA, Japan): Progress and issues in

  20. Pedestal characteristics and MHD stability of H-mode plasmas in TCV

    International Nuclear Information System (INIS)

    Pitzschke, A.

    2011-01-01

    temperature profile during the ELM cycle, the low repetition rate of the lasers used for Thomson scattering is a limiting. Although the system on TCV comprises 3 laser units that may be triggered in sequence with time separations down to 1 ms, time evolution over longer periods can only be reconstructed from repetitive events. In this context, an adjustment of the laser trigger to improve the synchronization with the ELM event is an advantage. A method was developed and implemented to generate a synchronizing trigger sequence, by a real-time monitoring of the D-alpha emission, which provides a marker for the ELM event. Recently, a ‘snowflake’ (SF) divertor configuration, proposed as a possible solution to reduce the plasma-wall interaction by changing the divertor’s poloidal magnetic field topology, was generated, for the first time, in TCV. A numerical code (KINX), based on a magnetohydrodynamic model (ideal MHD), was used to investigate the stability limits of this configuration under H-mode conditions and compare them with a similar standard single-null equilibrium. In a series of experiments, improved energy confinement was found and explained by improved stability of the edge region in the SF configuration. The influence of the pedestal structure in ELMy H-mode plasmas on the energy confinement and on ELM energy losses was investigated. The different ELM regimes found in TCV were analyzed, in particular the transition between type-III to type-I ELMs. The operational boundary of each ELM regime was characterized and verified by ideal MHD stability simulations for the ETB region. Recent studies on the scaling of the pedestal width with normalized poloidal pressure were confirmed. Using the capabilities of TCV, the influence of plasma shaping on pedestal parameters and MHD stability limits was investigated. In the past, models were developed to describe the onset of type-I ELMs, which are associated with modes in the ETB region arising from a coupling of pressure- and

  1. Gyrokinetic Stability Studies of the Microtearing Mode in the National Spherical Torus Experiment H-mode

    International Nuclear Information System (INIS)

    Baumgaertel J.A., Redi M.H., Budny R.V., Rewoldt G., Dorland W.

    2005-01-01

    Insight into plasma microturbulence and transport is being sought using linear simulations of drift waves on the National Spherical Torus Experiment (NSTX), following a study of drift wave modes on the Alcator C-Mod Tokamak. Microturbulence is likely generated by instabilities of drift waves, which cause transport of heat and particles. Understanding this transport is important because the containment of heat and particles is required for the achievement of practical nuclear fusion. Microtearing modes may cause high heat transport through high electron thermal conductivity. It is hoped that microtearing will be stable along with good electron transport in the proposed low collisionality International Thermonuclear Experimental Reactor (ITER). Stability of the microtearing mode is investigated for conditions at mid-radius in a high density NSTX high performance (H-mode) plasma, which is compared to the proposed ITER plasmas. The microtearing mode is driven by the electron temperature gradient, and believed to be mediated by ion collisions and magnetic shear. Calculations are based on input files produced by TRXPL following TRANSP (a time-dependent transport analysis code) analysis. The variability of unstable mode growth rates is examined as a function of ion and electron collisionalities using the parallel gyrokinetic computational code GS2. Results show the microtearing mode stability dependence for a range of plasma collisionalities. Computation verifies analytic predictions that higher collisionalities than in the NSTX experiment increase microtearing instability growth rates, but that the modes are stabilized at the highest values. There is a transition of the dominant mode in the collisionality scan to ion temperature gradient character at both high and low collisionalities. The calculations suggest that plasma electron thermal confinement may be greatly improved in the low-collisionality ITER

  2. Essential elements of the high density H-mode on W7-AS

    International Nuclear Information System (INIS)

    McCormick, K.; Burhenn, R.; Grigull, P.

    2003-01-01

    The High Density H-Mode (HDH), discovered during the run-in phase of W7-AS divertor operation/1-3/, rapidly became the workhorse of the divertor program, combining optimal core behavior along with edge parameters necessary for successful operation of an Island Divertor. Its unique properties of high energy confinement along with low impurity retention and radiation localized at the edge under ELM-free steady-state conditions at high densities (to 4 x 10 20 m -3 ) and heating powers (to 1.7 MWm -3 ) make the HDH H-mode ideal for a reactor scenario, given it can be extended to higher temperatures in a larger machine. Hence, considerable effort has been invested to understand the nature of the HDH-mode in order to be able to extrapolate to next generation devices. To this end the present paper reports on experiments where two globally-similar ELM-free H-modes are compared: the classic quiescent H-mode H* where both impurity and density control are a severe problem and the HDH-mode with its contrasting steady-state behavior. Through modeling of the temporal behavior of laser-ablated aluminum spectral lines, as well as that of background impurities, it is concluded that a principle difference between the two H-modes is that of enhanced impurity diffusion in the edge gradient region of the HDH-mode. However, no direct indicators of enhanced diffusion have yet been identified. (orig.)

  3. Turbulence at the transition to the high density H-mode in Wendelstein 7-AS plasmas

    DEFF Research Database (Denmark)

    Basse, N.P.; Zoletnik, S.; Baumel, S.

    2003-01-01

    Recently a new improved confinement regime was found in the Wendelstein 7-AS (W7-AS) stellarator (Renner H. et al 1989 Plasma Phys. Control. Fusion 31 1579). The discovery of this high density high confinement mode (HDH-mode) was facilitated by the installation of divertor modules. In this paper,...

  4. Comparison of L- and H-mode plasma edge fluctuations in MAST

    International Nuclear Information System (INIS)

    Dudson, B D; Dendy, R O; Kirk, A; Meyer, H; Counsell, G F

    2005-01-01

    Edge turbulence measurements from a reciprocating Langmuir probe in MAST are presented. A comparison of the range/standard deviation (R/S), growth of range, first moment and differencing and rescaling methods for calculating the Hurst exponent is made. The differencing and rescaling method is found to be the most useful for identifying scaling over long time-periods. A comparison is made between L-mode, dithering H-mode and H-mode plasma edge turbulence and evidence for self-similarity is found. Tests are performed and it is demonstrated that the results are due to properties of the data, and are not artefacts of the methods. A comparison of Hurst exponent methods with the autocorrelation function and power spectrum is used to demonstrate the presence of long-time correlation in L-mode data, and the absence of long-time correlation in the case of dithering H-mode

  5. Expression for the thermal H-mode energy confinement time under ELM-free conditions

    International Nuclear Information System (INIS)

    Ryter, F.; Gruber, O.; Kardaun, O.J.W.F.; Menzler, H.P.; Wagner, F.; Schissel, D.P.; DeBoo, J.C.; Kaye, S.M.

    1992-07-01

    The design of future tokamaks, which are supposed to reach ignition with the H-mode, requires a reliable scaling expression for the H-mode energy confinement time. In the present work, an H-mode scaling expression for the thermal plasma energy confinement time has been developed by combining data from four existing divertor tokamaks, ASDEX, DIII-D, JET and PBX-M. The plasma conditions, which were as similar as possible to ensure a coherent set of data, were ELM-free deuterium discharges heated by deuterium neutral beam injection. By combining four tokamaks, the parametric dependence of the thermal energy confinement on the main plasma parameters, including the three main geometrical variables, was determined. (orig./WL)

  6. Gyrokinetic Calculations of Microturbulence and Transport for NSTX and Alcator-CMOD H-modes

    International Nuclear Information System (INIS)

    Redi, M.H.; Dorland, W.; Bell, R.; Bonoli, P.; Bourdelle, C.; Candy, J.; Ernst, D.; Fiore, C.; Gates, D.; Hammett, G.; Hill, K.; Kaye, S.; LeBlanc, B.; Menard, J.; Mikkelsen, D.; Rewoldt, G.; Rice, J.; Waltz, R.; Wukitch, S.

    2003-01-01

    Recent H-mode experiments on NSTX [National Spherical Torus Experiment] and experiments on Alcator-CMOD, which also exhibit internal transport barriers (ITB), have been examined with gyrokinetic simulations with the GS2 and GYRO codes to identify the underlying key plasma parameters for control of plasma performance and, ultimately, the successful operation of future reactors such as ITER [International Thermonuclear Experimental Reactor]. On NSTX the H-mode is characterized by remarkably good ion confinement and electron temperature profiles highly resilient in time. On CMOD, an ITB with a very steep electron density profile develops following off-axis radio-frequency heating and establishment of H-mode. Both experiments exhibit ion thermal confinement at the neoclassical level. Electron confinement is also good in the CMOD core

  7. Origin of the various beta dependences of ELMy H-mode confinement properties

    International Nuclear Information System (INIS)

    Takizuka, T; Urano, H; Takenaga, H; Oyama, N

    2006-01-01

    Dependence of the energy confinement in ELMy H-mode tokamak on the beta has been investigated for a long time, but a common conclusion has not been obtained so far. Recent non-dimensional transport experiments in JT-60U demonstrated clearly the beta degradation. A database for JT-60U ELMy H-mode confinement was assembled. Analysis of this database is carried out, and the strong beta degradation consistent with the above experiments is confirmed. Two subsets of ASDEX Upgrade and JET data in the ITPA H-mode confinement database are analysed to find the origin of the various beta dependences. The shaping of the plasma cross section, as well as the fuelling condition, affects the confinement performance. The beta dependence is not identical for different devices and conditions. The shaping effect, as well as the fuelling effect, is a possible candidate for causing the variation of beta dependence

  8. MHD-activity in ohmic, diverted and limited H-mode plasmas in TCV

    International Nuclear Information System (INIS)

    Pochelon, A.; Anton, M.; Buehlmann, F.; Dutch, M.J.; Duval, B.P.; Hirt, A.; Hofmann, F.; Joye, B.; Lister, J.B.; Llobet, X.; Martin, Y.; Moret, J.M.; Nieswand, C.; Pietrzyk, A.Z.; Tonetti, G.; Weisen, H.

    1994-01-01

    During its first year of operation the TCV tokamak has produced a variety of plasma configurations with currents in the range 150 to 800 kA and elongations in the range of 1.0 to 2.05. Ohmic H-modes have been obtained in diverted discharges and discharges limited on the graphite tiles inner wall. After boronisation in May 1994 H-modes with line average densities up to 1.7x10 20 m -3 , corresponding to a Murakami parameter of 10, were obtained. (author) 5 figs., 2 refs

  9. The role of MHD instabilities in the improved H-mode scenario

    International Nuclear Information System (INIS)

    Flaws, Asher

    2009-01-01

    Recently a regime of tokamak operation has been discovered, dubbed the improved H-mode scenario, which simultaneously achieves increased energy confinement and stability with respect to standard H-mode discharges. It has been suggested that magnetohydrodynamic (MHD) instabilities play some role in establishing this regime. In this thesis MHD instabilities were identified, characterised, and catalogued into a database of improved H-mode discharges in order to statistically examine their behaviour. The onset conditions of MHD instabilities were compared to existing models based on previous H-mode studies. Slight differences were found, most notably a reduced β N onset threshold for the frequently interrupted regime for neoclassical tearing modes (NTM). This reduced threshold is due to the relatively low magnetic shear of the improved H-mode regime. This study also provided a first-time estimate for the seed island size of spontaneous onset NTMs, a phenomenon characteristic of the improved H-mode scenario. Energy confinement investigations found that, although the NTM impact on confinement follows the same model applicable to other operating regimes, the improved H-mode regime acts to mitigate the impact of NTMs by limiting the saturated island sizes for NTMs with toroidal mode number n ≥ 2. Surprisingly, although a significant loss in energy confinement is observed during the sawtooth envelope, it has been found that discharges containing fishbones and low frequency sawteeth achieve higher energy confinement than those without. This suggests that fishbone and sawtooth reconnection may indeed play a role in establishing the high confinement regime. It was found that the time evolution of the central magnetic shear consistently locks in the presence of sawtooth and fishbone reconnection. Presumably this is due to the periodic redistribution of the central plasma current, an effect which is believed to help establish and maintain the characteristic current profile

  10. H-mode confinement properties close to the power threshold in ASDEX Upgrade

    International Nuclear Information System (INIS)

    Ryter, F; Fuchs, J; Schneider, W; Sips, A; Staebler, A; Stober, J

    2008-01-01

    Confinement properties close to the H-mode power threshold are studied in the ASDEX Upgrade tokamak. The results show that good confinement can be obtained close to the threshold with Type-I ELMs. The existence of Type-I ELMs does not necessarily require the heating power to be higher than the H-Mode power threshold, but it requires collisionality to be low enough. At higher collisionality Type-III ELMs replace the Type-I ELMs and confinement time is reduced by about 20%

  11. The role of MHD instabilities in the improved H-mode scenario

    Energy Technology Data Exchange (ETDEWEB)

    Flaws, Asher

    2009-02-16

    Recently a regime of tokamak operation has been discovered, dubbed the improved H-mode scenario, which simultaneously achieves increased energy confinement and stability with respect to standard H-mode discharges. It has been suggested that magnetohydrodynamic (MHD) instabilities play some role in establishing this regime. In this thesis MHD instabilities were identified, characterised, and catalogued into a database of improved H-mode discharges in order to statistically examine their behaviour. The onset conditions of MHD instabilities were compared to existing models based on previous H-mode studies. Slight differences were found, most notably a reduced {beta}{sub N} onset threshold for the frequently interrupted regime for neoclassical tearing modes (NTM). This reduced threshold is due to the relatively low magnetic shear of the improved H-mode regime. This study also provided a first-time estimate for the seed island size of spontaneous onset NTMs, a phenomenon characteristic of the improved H-mode scenario. Energy confinement investigations found that, although the NTM impact on confinement follows the same model applicable to other operating regimes, the improved H-mode regime acts to mitigate the impact of NTMs by limiting the saturated island sizes for NTMs with toroidal mode number n {>=} 2. Surprisingly, although a significant loss in energy confinement is observed during the sawtooth envelope, it has been found that discharges containing fishbones and low frequency sawteeth achieve higher energy confinement than those without. This suggests that fishbone and sawtooth reconnection may indeed play a role in establishing the high confinement regime. It was found that the time evolution of the central magnetic shear consistently locks in the presence of sawtooth and fishbone reconnection. Presumably this is due to the periodic redistribution of the central plasma current, an effect which is believed to help establish and maintain the characteristic current

  12. High performance H-mode plasmas at densities above the Greenwald limit

    International Nuclear Information System (INIS)

    Mahdavi, M.A.; Osborne, T.H.; Leonard, A.W.

    2001-01-01

    Densities up to 40 percent above the Greenwald limit are reproducibly achieved in high confinement (H ITER89p =2) ELMing H-mode discharges. Simultaneous gas fueling and divertor pumping were used to obtain these results. Confinement of these discharges, similar to moderate density H-mode, is characterized by a stiff temperature profile, and therefore sensitive to the density profile. A particle transport model is presented that explains the roles of divertor pumping and geometry for access to high densities. Energy loss per ELM at high density is a factor of five lower than predictions of an earlier scaling, based on data from lower density discharges. (author)

  13. Poloidal rotation and the evolution of H-mode and VH-mode profiles

    International Nuclear Information System (INIS)

    Hinton, F.L.; Staebler, G.M.; Kim, Y.B.

    1993-12-01

    The physics which determines poloidal rotation, and its role in the development of profiles during H- and VH-modes, is discussed. A simple phenomenological transport model, which incorporates the rvec E x rvec B flow shear suppression of turbulence, is shown to predict profile evolution similar to that observed experimentally during H-mode and VH-mode

  14. Ubiquity of non-diffusive momentum transport in JET H-modes

    NARCIS (Netherlands)

    Weisen, H.; Camenen, Y.; Salmi, A.; Versloot, T. W.; de Vries, P. C.; Maslov, M.; Tala, T.; Beurskens, M.; Giroud, C.; JET-EFDA Contributors,

    2012-01-01

    A broad survey of the experimental database of neutral beam heated baseline H-modes and hybrid scenarios in the JET tokamak has established the ubiquity of non-diffusive momentum transport mechanisms in rotating plasmas. As a result of their presence, the normalized angular frequency gradient R

  15. New Edge Coherent Mode Providing Continuous Transport in Long Pulse H-mode Plasmas

    DEFF Research Database (Denmark)

    Wang, H.Q.; Xu, G.S.; Wan, B.N.

    2014-01-01

    An electrostatic coherent mode near the electron diamagnetic frequency (20–90 kHz) is observed in the steep-gradient pedestal region of long pulse H-mode plasmas in the Experimental Advanced Super-conducting Tokamak, using a newly developed dual gas-puff-imaging system and diamond-coated reciproc...

  16. Comparison of fusion alpha performance in JET advanced scenario and H-mode plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Asunta, O; Kurki-Suonio, T; Tala, T; Sipilae, S; Salomaa, R [JET-EFDA, Culham Science Centre, OX14 3DB, Abingdon (United Kingdom)], E-mail: Otto.Asunta@tkk.fi

    2008-12-15

    Currently, plasmas with internal transport barriers (ITBs) appear the most likely candidates for steady-state scenarios for future fusion reactors. In such plasmas, the broad hot and dense region in the plasma core leads to high fusion gain, while the cool edge protects the integrity of the first wall. Economically desirable large bootstrap current fraction and low inductive current drive may, however, lead to degraded fast ion confinement. In this work the confinement and heating profile of fusion alphas were compared between H-mode and ITB plasmas in realistic JET geometry. The work was carried out using the Monte Carlo-based guiding-center-following code ASCOT. For the same plasma current, the ITB discharges were found to produce four to eight times more fusion power than a comparable ELMy H-mode discharge. Unfortunately, also the alpha particle losses were larger ({approx}16%) compared with the H-mode discharge (7%). In the H-mode discharges, alpha power was deposited to the plasma symmetrically around the magnetic axis, whereas in the current-hole discharge, the power was spread out to a larger volume in the plasma center. This was due to wider particle orbits, and the magnetic structure allowing for a broader hot region in the centre.

  17. The Effect of Plasma Shape on H-Mode Pedestal Characteristics on DIII-D

    International Nuclear Information System (INIS)

    T.H. Osborne; J.R. Ferron; R.J. Groebner; L.L. Lao; A.W. Leonard; R. Maingi; R.L. Miller; A.D. Turnbull; M.R. Wade; J.G. Watkins

    1999-01-01

    The characteristics of the H-mode are studied in discharges with varying triangularity and squareness. The pressure at the top of the H-mode pedestal increases strongly with triangularity primarily due to an increase in the margin by which the edge pressure gradient exceeds the ideal ballooning mode first stability limit. Two models are considered for how the edge may exceed the ballooning mode limit. In one model [1], access to the ballooning mode second stable regime allows the edge pressure gradient and associated bootstrap current to continue to increase until an edge localized, low toroidal mode number, ideal kink mode is destabilized. In the second model [2], the finite width of the H-mode transport barrier, and diamagnetic effects raise the pressure gradient limit above the ballooning mode limit. We observe a weak inverse dependence of the width of the H-mode transport barrier, Δ, on triangularity relative to the previously obtained [3] scaling Δ ∞ (β P PED ) 1/2 . The energy loss for Type I ELMs increases with triangularity in proportion to the pedestal energy increase. The temperature profile is found to respond stiffly to changes in T PED at low temperature, while at high temperature the response is additive. The response of the density profile is also found to play a role in the response of the total stored energy to changes in the W PED

  18. Comparison between dominant NB and dominant IC heated ELMy H-mode discharges in JET

    NARCIS (Netherlands)

    Versloot, T.W.; Sartori, R.; de Vries, P.C.; et al, [No Value

    2011-01-01

    Abstract The experiment described in this paper is aimed at characterization of ELMy H-mode discharges with varying momentum input, rotation, power deposition profiles and ion to electron heating ratio obtained by varying the proportion between ion cyclotron (IC) and neutral beam (NB) heating. The

  19. Comparison between dominant NB and dominant IC heated ELMy H-mode discharges in JET

    NARCIS (Netherlands)

    Versloot, T. W.; Sartori, R.; Rimini, F.; de Vries, P. C.; Saibene, G.; Parail, V.; Beurskens, M. N. A.; Boboc, A.; Budny, R.; Crombe, K.; de la Luna, E.; Durodie, F.; Eich, T.; Giroud, C.; Kiptily, V.; Johnson, T.; Mantica, P.; Mayoral, M. L.; McDonald, D. C.; Monakhov, I.; Nave, M. F. F.; Voitsekhovitch, I.; Zastrow, K. D.

    2011-01-01

    The experiment described in this paper is aimed at characterization of ELMy H-mode discharges with varying momentum input, rotation, power deposition profiles and ion to electron heating ratio obtained by varying the proportion between ion cyclotron (IC) and neutral beam (NB) heating. The motivation

  20. CORRELATION OF H-MODE BARRIER WIDTH AND NEUTRAL PENETRATION LENGTH

    International Nuclear Information System (INIS)

    GROEBNER, R.J.; MAHDAVI, M.A.; LEONARD, A.W.; OSBORNE, T.H.; WOLF, N.S.; PORTER, G.D.; STANGEBY, P.C.; BROOKS, N.H.; COLCHIN, R.J.; HEIDBRINK, W.W.; LUCE, T.C.; MCKEE, G.R.; OWEN, L.W.; WANG, G.; WHYTE, D.G.

    2002-01-01

    OAK A271 CORRELATION OF H-MODE BARRIER WIDTH AND NEUTRAL PENETRATION LENGTH. Pedestal studies in DIII-D find a good correlation between the width of the H-mode density barrier and the neutral penetration length. These results are obtained by comparing experimental density profiles to the predictions of an analytic model for the profile, obtained from the particle continuity equations for electrons and deuterium atoms. In its range of validity (edge temperature between 40-500 eV), the analytic model quantitatively predicts the observed decrease of the width as the pedestal density increases, the observed strong increase of the gradient of the density as the pedestal density increases and the observation that L-mode and H-mode profiles with the same pedestal density have very similar shapes. The width of the density barrier, measured from the edge of the electron temperature barrier, is the lower limit for the observed width of the temperature barrier. These results support the hypothesis that particle fueling provides the dominant control for the size of the H-mode transport barrier

  1. CORRELATION OF H-MODE BARRIER WIDTH AND NEUTRAL PENTRATION LENGTH

    International Nuclear Information System (INIS)

    GROEBNER, R.J.; MAHDAVI, M.A.; LEONARD, A.W.; OSBORNE, T.H.; WOLF, N.S.; PORTER, G.D.; STANGEBY, P.C.; BROOKS, N.H.; COLCHIN, R.J.; HEIDBRINK, W.W.; LUCE, T.C.; MCKEE, G.R.; OWEN, L.W.; WANG, G.; WHYTE, D.G.

    2002-01-01

    OAK A271 CORRELATION OF H-MODE BARRIER WIDTH AND NEUTRAL PENTRATION LENGTH. Pedestal studies in DIII-D find a good correlation between the width of the region of steep gradient in the H-mode density and the neutral penetration length. These results are obtained by comparing experimental density profiles to the predictions of an analytic model for the profile, obtained from the particle continuity equations for electrons and deuterium atoms. In its range of validity (edge temperature between 40-500 eV), the analytic model quantitatively predicts the observed decrease of the width as the pedestal density increases, the observed strong increase of the gradient of the density as the pedestal density increases and the observation that L-mode and H-mode profiles with the same pedestal density have very similar shapes. The width of the density barrier, measured from the edge of the electron temperature barrier, is the lower limit for the observed width of the temperature barrier. These results support the hypothesis that particle fueling provides a dominant control for the size of the H-mode transport barrier

  2. Radiative type-III ELMy H-mode in all-tungsten ASDEX Upgrade

    NARCIS (Netherlands)

    Rapp, J.; Kallenbach, A.; Neu, R.; Eich, T.; Fischer, R.; Herrmann, A.; Potzel, S.; van Rooij, G. J.; Zielinski, J. J.; ASDEX Upgrade team,

    2012-01-01

    The type-III ELMy H-mode might be the solution for an integrated ITER operation scenario fulfilling the fusion power amplification factor (output fusion power to input heating power) of Q = 10 with simultaneous acceptable steady-state and transient power loads to the plasma-facing components. This

  3. Dependence of the L- to H-mode Power Threshold on Toroidal Rotation and the Link to Edge Turbulence Dynamics

    International Nuclear Information System (INIS)

    McKee, G.; Gohil, P.; Schlossberg, D.; Boedo, J.; Burrell, K.; deGrassie, J.; Groebner, R.; Makowski, M.; Moyer, R.; Petty, C.; Rhodes, T.; Schmitz, L.; Shafer, M.; Solomon, W.; Umansky, M.; Wang, G.; White, A.; Xu, X.

    2008-01-01

    The injected power required to induce a transition from L-mode to H-mode plasmas is found to depend strongly on the injected neutral beam torque and consequent plasma toroidal rotation. Edge turbulence and flows, measured near the outboard midplane of the plasma (0.85 < r/a < 1.0) on DIII-D with the high-sensitivity 2D beam emission spectroscopy (BES) system, likewise vary with rotation and suggest a causative connection. The L-H power threshold in plasmas with the ion (del)B drift away from the X-point decreases from 4-6 MW with co-current beam injection, to 2-3 MW with near zero net injected torque, and to <2 MW with counter injection. Plasmas with the ion (del)B drift towards the X-point exhibit a qualitatively similar though less pronounced power threshold dependence on rotation. 2D edge turbulence measurements with BES show an increasing poloidal flow shear as the L-H transition is approached in all conditions. At low rotation, the poloidal flow of turbulent eddies near the edge reverses prior to the L-H transition, generating a significant poloidal flow shear that exceeds the measured turbulence decorrelation rate. This increased poloidal turbulence velocity shear may facilitate the L-H transition. No such reversal is observed in high rotation plasmas. The poloidal turbulence velocity spectrum exhibits a transition from a Geodesic Acoustic Mode zonal flow to a higher-power, lower frequency, zero-mean-frequency zonal flow as rotation varies from co-current to balanced during a torque scan at constant injected neutral beam power, perhaps also facilitating the L-H transition. This reduced power threshold at lower toroidal rotation may benefit inherently low-rotation plasmas such as ITER

  4. Observation of a new turbulence-driven limit-cycle state in H-modes with lower hybrid current drive and lithium-wall conditioning in the EAST superconducting tokamak

    DEFF Research Database (Denmark)

    Wang, H.Q.; Xu, G.S.; Guo, H.Y.

    2012-01-01

    The first high confinement H-mode plasma has been obtained in the Experimental Advanced Superconducting Tokamak (EAST) with about 1 MW lower hybrid current drive after wall conditioning by lithium evaporation and real-time injection of Li powder. Following the L–H transition, a small-amplitude, low...

  5. Energy confinement and transport of H-mode plasmas in tokamak

    International Nuclear Information System (INIS)

    Urano, Hajime

    2005-02-01

    A characteristic feature of the high-confinement (H-mode) regime is the formation of a transport barrier near the plasma edge, where steepening of the density and temperature gradients is observed. The H-mode is expected to be a standard operation mode in a next-step fusion experimental reactor, called ITER-the International Thermonuclear Experimental Reactor. However, energy confinement in the H-mode has been observed to degrade with increasing density. This is a critical constraint for the operation domain in the ITER. Investigation of the main cause of confinement degradation is an urgent issue in the ITER Physics Research and Development Activity. A key element for solving this problem is investigation of the energy confinement and transport properties of H-mode plasmas. However, the influence of the plasma boundary characterized by the transport barrier in H-modes on the energy transport of the plasma core has not been examined sufficiently in tokamak research. The aim of this study is therefore to investigate the energy confinement properties of H-modes in a variety of density, plasma shape, seed impurity concentration, and conductive heat flux in the plasma core using the experimental results obtained in the JT-60U tokamak of Japan Atomic Energy Research Institute. Comparison of the H-mode confinement properties with those of other tokamaks using an international multi-machine database for extrapolation to the next step device was also one of the main subjects in this study. Density dependence of the energy confinement properties has been examined systematically by separating the thermal stored energy into the H-mode pedestal component determined by MHD stability called the Edge Localized Modes (ELMs) and the core component governed by gyro-Bohm-like transport. It has been found that the pedestal pressure imposed by the destabilization of ELM activities led to a reduction in the pedestal temperature with increasing density. The core temperature for each

  6. Scaling of H-mode pedestal characteristics in DIII-D and C-Mod

    International Nuclear Information System (INIS)

    Granetz, R.S.; Boivin, R.L.; Osborne, T.H.

    1999-01-01

    Since the H-mode edge pedestal effectively sets the boundary conditions for energy transport throughout the core, a better understanding of the pedestal region is necessary in order to fully predict H-mode performance. Pedestal characteristics in the DIII-D and Alcator C-Mod tokamaks are described, and scalings of the pedestal width with various plasma parameters are shown. The pedestal width in both tokamaks varies in an inverse sense with plasma current, and is independent of toroidal field. Other similarities, as well as differences, are discussed. It is also found that the pedestal widths of the various physical quantities involved (T e , T i , n e , n i ) may be different. (author)

  7. New fluctuation phenomena in the H-mode regime of PDX tokamak plasmas

    International Nuclear Information System (INIS)

    Slusher, R.E.; Surko, C.M.; Valley, J.F.; Crowley, T.; Mazzucato, E.; McGuire, K.

    1984-05-01

    A new kind of quasi-coherent fluctuation is observed near the edge of plasmas in the PDX tokamak during H-mode operation. (The H-mode occurs in neutral beam heated divertor plasmas and is characterized by improved energy containment as well as large density and temperature gradients near the plasma edge.) These fluctuations are evidenced as VUV and density fluctuation bursts at well-defined frequencies (Δω/ω less than or equal to 0.1) in the frequency range between 50 and 180 kHz. They affect the edge temperature-density product, and therefore they may be important for understanding the relationship between the large edge density and temperature gradients and the improved energy confinement

  8. Parameter dependences of the separatrix density in nitrogen seeded ASDEX Upgrade H-mode discharges

    Science.gov (United States)

    Kallenbach, A.; Sun, H. J.; Eich, T.; Carralero, D.; Hobirk, J.; Scarabosio, A.; Siccinio, M.; ASDEX Upgrade Team; EUROfusion MST1 Team

    2018-04-01

    The upstream separatrix electron density is an important interface parameter for core performance and divertor power exhaust. It has been measured in ASDEX Upgrade H-mode discharges by means of Thomson scattering using a self-consistent estimate of the upstream electron temperature under the assumption of Spitzer-Härm electron conduction. Its dependence on various plasma parameters has been tested for different plasma conditions in H-mode. The leading parameter determining n e,sep was found to be the neutral divertor pressure, which can be considered as an engineering parameter since it is determined mainly by the gas puff rate and the pumping speed. The experimentally found parameter dependence of n e,sep, which is dominated by the divertor neutral pressure, could be approximately reconciled by 2-point modelling.

  9. Correlation of the tokamak H-mode density limit with ballooning stability at the separatrix

    Science.gov (United States)

    Eich, T.; Goldston, R. J.; Kallenbach, A.; Sieglin, B.; Sun, H. J.; ASDEX Upgrade Team; Contributors, JET

    2018-03-01

    We show for JET and ASDEX Upgrade, based on Thomson-scattering measurements, a clear correlation of the density limit of the tokamak H-mode high-confinement regime with the approach to the ideal ballooning instability threshold at the periphery of the plasma. It is shown that the MHD ballooning parameter at the separatrix position α_sep increases about linearly with the separatrix density normalized to Greenwald density, n_e, sep/n_GW for a wide range of discharge parameters in both devices. The observed operational space is found to reach at maximum n_e, sep/n_GW≈ 0.4 -0.5 at values for α_sep≈ 2 -2.5, in the range of theoretical predictions for ballooning instability. This work supports the hypothesis that the H-mode density limit may be set by ballooning stability at the separatrix.

  10. Effect of low density H-mode operation on edge and divertor plasma parameters

    International Nuclear Information System (INIS)

    Maingi, R.; Mioduszewski, P.K.; Cuthbertson, J.W.

    1994-07-01

    We present a study of the impact of H-mode operation at low density on divertor plasma parameters on the DIII-D tokamak. The line-average density in H-mode was scanned by variation of the particle exhaust rate, using the recently installed divertor cryo-condensation pump. The maximum decrease (50%) in line-average electron density was accompanied by a factor of 2 increase in the edge electron temperature, and 10% and 20% reductions in the measured core and divertor radiated power, respectively. The measured total power to the inboard divertor target increased by a factor of 3, with the major contribution coming from a factor of 5 increase in the peak heat flux very close to the inner strike point. The measured increase in power at the inboard divertor target was approximately equal to the measured decrease in core and divertor radiation

  11. Chapter 7: High-Density H-Mode Operation in ASDEX Upgrade

    International Nuclear Information System (INIS)

    Stober, Joerg Karl; Lang, Peter Thomas; Mertens, Vitus

    2003-01-01

    Recent results are reported on the maximum achievable H-mode density and the behavior of pedestal density and central density peaking as this limit is approached. The maximum achievable H-mode density roughly scales as the Greenwald density, though a dependence on B t is clearly observed. In contrast to the stiff temperature profiles, the density profiles seem to allow more shape variation and especially with high-field-side pellet-injection, strongly peaked profiles with good confinement have been achieved. Also, spontaneous density peaking at high densities is observed in ASDEX Upgrade, which is related to the generally observed large time constants for the density profile equilibration. The equilibrated density profile shapes depend strongly on the heat-flux profile in the sense that central heating leads to significantly flatter profiles

  12. Influence of the wall material on the H-mode performance

    International Nuclear Information System (INIS)

    Itoh, K.; Itoh, S.

    1994-06-01

    Theory on the influence of the wall material on the level of the enhanced confinement in H-mode is discussed. When the high-Z material is employed as the wall, the reflection of the neutral particles causes the higher neutral particle density in the plasma. The increased neutral particles lead to the loss of the ion momentum, decrease the radial electric field and degrade the confinement improvement. (author)

  13. Tungsten transport in JET H-mode plasmas in hybrid scenario, experimental observations and modelling

    Czech Academy of Sciences Publication Activity Database

    Angioni, C.; Mantica, P.; Pütterich, T.; Valisa, M.; Baruzzo, M.; Belli, A.E.; Belo, P.; Casson, F.J.; Challis, C.; Drewelow, P.; Giroud, C.; Hawkes, N.; Hender, T.C.; Hobirk, J.; Koskela, T.; Lauro Taroni, L.; Maggi, C.F.; Mlynář, Jan; Odstrčil, T.; Reinke, M.L.; Romanelli, M.

    2014-01-01

    Roč. 54, č. 8 (2014), 083028-083028 ISSN 0029-5515 Institutional support: RVO:61389021 Keywords : heavy impurity transport * H-mode hybrid scenario * neoclassical and turbulent transport Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.062, year: 2014 http://iopscience.iop.org/0029-5515/54/8/083028/pdf/0029-5515_54_8_083028.pdf

  14. Observation of internal transport barrier in ELMy H-mode plasmas on the EAST tokamak

    Science.gov (United States)

    Yang, Y.; Gao, X.; Liu, H. Q.; Li, G. Q.; Zhang, T.; Zeng, L.; Liu, Y. K.; Wu, M. Q.; Kong, D. F.; Ming, T. F.; Han, X.; Wang, Y. M.; Zang, Q.; Lyu, B.; Li, Y. Y.; Duan, Y. M.; Zhong, F. B.; Li, K.; Xu, L. Q.; Gong, X. Z.; Sun, Y. W.; Qian, J. P.; Ding, B. J.; Liu, Z. X.; Liu, F. K.; Hu, C. D.; Xiang, N.; Liang, Y. F.; Zhang, X. D.; Wan, B. N.; Li, J. G.; Wan, Y. X.; EAST Team

    2017-08-01

    The internal transport barrier (ITB) has been obtained in ELMy H-mode plasmas by neutron beam injection and lower hybrid wave heating on the Experimental Advanced Superconducting Tokamak (EAST). The ITB structure has been observed in profiles of ion temperature, electron temperature, and electron density within ρ safety factor q(0) ˜ 1. Transport coefficients are calculated by particle balance and power balance analysis, showing an obvious reduction after the ITB formation.

  15. Correlation of H-mode barrier width and neutral penetration length

    International Nuclear Information System (INIS)

    Groebner, R.J.; Mahdavi, M.A.; Leonard, A.W.

    2003-01-01

    Pedestal studies in DIII-D find a good correlation between the width of the H-mode density barrier and the neutral penetration length. These results are obtained by comparing experimental density profiles to the predictions of an analytic model for the profile, obtained from the particle continuity equations for electrons and deuterium atoms. In its range of validity (edge temperature between 40-500 eV), the analytic model quantitatively predicts the observed decrease of the width as the pedestal density increases, the observed strong increase of the gradient of the density as the pedestal density increases and the observation that L-mode and H-mode profiles with the same pedestal density have very similar shapes. The width of the density barrier, measured from the edge of the electron temperature barrier, is the lower limit for the observed width of the temperature barrier. These results support the hypothesis that particle fueling provides the dominant control for the size of the H-mode transport barrier. (author)

  16. Comparison of H-mode barrier width with a model of neutral penetration length

    International Nuclear Information System (INIS)

    Groebner, R.J.; Mahdavi, M.A.; Leonard, A.W.; Osborne, T.H.; Brooks, N.S.; Wolf, N.S.; Porter, G.D.; Stangeby, P.C.; Colchin, R.J.; Owen, L.W.

    2004-01-01

    Pedestal studies in DIII-D find that the width of the region of steep gradient in the H-mode density is comparable with the neutral penetration length, as computed from a simple analytic model. This model has analytic solutions for the edge plasma and neutral density profiles, which are obtained from the coupled particle continuity equations for electrons and deuterium atoms. In its range of validity (edge temperature between 40 and 500 eV), the analytic model quantitatively predicts the observed decrease in the width as the pedestal density increases and the observed strong increase in the gradient of the density as the pedestal density increases. The model successfully predicts that L-mode and H-mode profiles with the same pedestal density have gradients that differ by less than a factor of 2. The width of the density barrier, measured from the edge of the electron temperature barrier, is the lower limit for the observed width of the temperature barrier. These results support the hypothesis that particle fuelling is an important part of the physics that determines the structure of the H-mode transport barrier. (author)

  17. Density fluctuation measurements via reflectometry on DIII-D during L- and H-mode operation

    International Nuclear Information System (INIS)

    Doyle, E.J.; Lehecka, T.; Luhmann, N.C. Jr.; Peebles, W.A.; Philipona, R.

    1990-01-01

    The unique ability of reflectometers to provide radial density fluctuation measurements with high spatial resolution (of the order of ≤ centimeters, is ideally suited to the study of the edge plasma modifications associated with H-mode operation. Consequently, attention has been focused on the study of these phenomena since an improved understanding of the physics of H-mode plasmas is essential if a predictive capability for machine performance is to be developed. In addition, DIII-D is ideally suited for such studies since it is a major device noted for its robust H-mode operation and excellent basic plasma profile diagnostic information. The reflectometer system normally used for fluctuation studies is an O-mode, homodyne, system utilizing 7 discrete channels spanning 15-75 GHz, with corresponding critical densities of 2.8x10 18 to 7x10 19 m -3 . The Gunn diode sources in this system are only narrowly tunable in frequency, so the critical densities are essentially fixed. An X-mode system, utilizing a frequency tunable BWO source, has also been used to obtain fluctuation data, and in particular, to 'fill in the gaps' between the discrete O-mode channels. (author) 12 refs., 5 figs

  18. EDITORIAL: Special issue containing papers presented at the 12th International Workshop on H-mode Physics and Transport Barriers Special issue containing papers presented at the 12th International Workshop on H-mode Physics and Transport Barriers

    Science.gov (United States)

    Hahm, T. S.

    2010-06-01

    The 12th International Workshop on H-mode Physics and Transport Barriers was held at the Princeton Plasma Physics Laboratory, Princeton, New Jersey, USA between September 30 and October 2, 2009. This meeting was the continuation of a series of previous meetings which was initiated in 1987 and has been held bi-annually since then. Following the recent tradition at the last few meetings, the program was sub- divided into six sessions. At each session, an overview talk was presented, followed by two or three shorter oral presentations which supplemented the coverage of important issues. These talks were followed by discussion periods and poster sessions of contributed papers. The sessions were: Physics of Transition to/from Enhanced Confinement Regimes, Pedestal and Edge Localized Mode Dynamics, Plasma Rotation and Momentum Transport, Role of 3D Physics in Transport Barriers, Transport Barriers: Theory and Simulations and High Priority ITER Issues on Transport Barriers. The diversity of the 90 registered participants was remarkable, with 22 different nationalities. US participants were in the majority (36), followed by Japan (14), South Korea (7), and China (6). This special issue of Nuclear Fusion consists of a cluster of 18 accepted papers from submitted manuscripts based on overview talks and poster presentations. The paper selection procedure followed the guidelines of Nuclear Fusion which are essentially the same as for regular articles with an additional requirement on timeliness of submission, review and revision. One overview paper and five contributed papers report on the H-mode pedestal related results which reflect the importance of this issue concerning the successful operation of ITER. Four papers address the rotation and momentum transport which play a crucial role in transport barrier physics. The transport barrier transition condition is the main focus of other four papers. Finally, four additional papers are devoted to the behaviour and control of

  19. A two term model of the confinement in Elmy H-modes using the global confinement and pedestal databases

    International Nuclear Information System (INIS)

    2003-01-01

    Two different physical models of the H-mode pedestal are tested against the joint pedestal-core database. These models are then combined with models for the core and shown to give a good fit to the ELMy H-mode database. Predictions are made for the next step tokamaks ITER and FIRE. (author)

  20. Particle and power deposition on divertor targets in EAST H-mode plasmas

    International Nuclear Information System (INIS)

    Wang, L.; Xu, G.S.; Guo, H.Y.; Chen, R.; Ding, S.; Gan, K.F.; Gao, X.; Gong, X.Z.; Jiang, M.; Liu, P.; Liu, S.C.; Luo, G.N.; Ming, T.F.; Wan, B.N.; Wang, D.S.; Wang, F.M.; Wang, H.Q.; Wu, Z.W.; Yan, N.; Zhang, L.

    2012-01-01

    The effects of edge-localized modes (ELMs) on divertor particle and heat fluxes were investigated for the first time in the Experimental Advanced Superconducting Tokamak (EAST). The experiments were carried out with both double null and lower single null divertor configurations, and comparisons were made between the H-mode plasmas with lower hybrid current drive (LHCD) and those with combined ion cyclotron resonance heating (ICRH). The particle and heat flux profiles between and during ELMs were obtained from Langmuir triple-probe arrays embedded in the divertor target plates. And isolated ELMs were chosen for analysis in order to reduce the uncertainty resulting from the influence of fast electrons on Langmuir triple-probe evaluation during ELMs. The power deposition obtained from Langmuir triple probes was consistent with that from the divertor infra-red camera during an ELM-free period. It was demonstrated that ELM-induced radial transport predominantly originated from the low-field side region, in good agreement with the ballooning-like transport model and experimental results of other tokamaks. ELMs significantly enhanced the divertor particle and heat fluxes, without significantly broadening the SOL width and plasma-wetted area on the divertor target in both LHCD and LHCD + ICRH H-modes, thus posing a great challenge for the next-step high-power, long-pulse operation in EAST. Increasing the divertor-wetted area was also observed to reduce the peak heat flux and particle recycling at the divertor target, hence facilitating long-pulse H-mode operation. The particle and heat flux profiles during ELMs appeared to exhibit multiple peak structures, and were analysed in terms of the behaviour of ELM filaments and the flux tubes induced by modified magnetic topology during ELMs. (paper)

  1. H-mode regimes and observators of central toroidal rotation in Alcator C-Mod

    International Nuclear Information System (INIS)

    Greenwald, M.; Rice, J.; Boivin, R.

    1999-01-01

    The Enhanced D α or EDA H-mode regime in Alcator C-Mod has been investigated and compared in detail to ELM-free plasmas. (In this paper, ELM-free will refer to discharges with no type I ELMs and with no sign of EDA, though technically, most EDA plasmas are ELM-free as well.) EDA discharges have only slightly lower energy confinement than comparable ELM-free ones, but show markedly reduced impurity confinement. Thus EDA discharges do not accumulate impurities and typically have a lower fraction of radiated power. EDA plasmas are seen to be more likely at low plasma current (q > 3.7 - 4), for moderate plasma shaping (0.35 - 0.55), and for high neutral pressures. No obvious trends were observed with input power or pressure (β). In both H-mode regimes, and in ICRF heated L-modes, central impurity toroidal rotation has been deduced, from the Doppler shifts of argon x-ray lines. Rotation velocities up to 1.3 x 10 5 m/s in the co-current direction have been observed in H-mode discharges that had no direct momentum input. There is a strong correlation between the increase in the central impurity rotation velocity and the increase in the plasma stored energy, induced by ICRF heating. In otherwise similar discharges with the same stored energy increase, plasmas with lower current rotate faster. The ion pressure gradient is an unimportant contributor to the central impurity rotation and the presence of a substantial core radial electric field is inferred during the ICRF pulse. An inward shift of ions induced by ICRF waves could give rise to a non-ambipolar electric field in the plasma core. Comparisons with a neo-classical ion orbit shift model show good agreement with the observations, both in magnitude, and in the scaling with plasma current. (author)

  2. Density profile analysis during an ELM event in ASDEX Upgrade H-modes

    International Nuclear Information System (INIS)

    Nunes, I.; Manso, M.; Serra, F.; Horton, L.D.; Conway, G.D.; Loarte, A.

    2005-01-01

    This paper reports results on measurements of the density profiles. Here we analyse the behaviour of the electron density for a set of experiments in type I ELMy H-mode discharges in ASDEX Upgrade where the plasma current, plasma density, triangularity and input power were varied. Detailed measurements of the radial extent of the perturbation on the density profiles caused by the edge localized mode (ELM) crash (ELM affected depth), the velocity of the radial propagation of the perturbation as well as the width and gradient of the density pedestal are determined. The effect of a type I ELM event on the density profiles affects the outermost 20-40% of the plasma minor radius. At the scrape-off layer (SOL) the density profile broadens while in the pedestal region the density decreases resulting in a smaller density gradient. This change in the density profile defines a pivot point around which the density profile changes. The average radial velocity at the SOL is in the range 125-150 ms -1 and approximately constant for all the density layers far from the pivot point. The width of the density pedestal is approximately constant for all the ELMy H-mode discharges analysed, with values between 2 and 3.5 cm. These results are then compared with an analytical model where the width of the density is predominantly set by ionization (neutral penetration model). The width of the density profiles for L-mode discharges is included, since L- and H-mode have different particle transport. No agreement between the experimental results and the model is found

  3. Ball-Pen Probe Measurements in L-Mode and H-Mode on ASDEX Upgrade

    Czech Academy of Sciences Publication Activity Database

    Adámek, Jiří; Horáček, Jan; Müller, H. W.; Rohde, V.; Ionita, C.; Schrittwieser, R.; Mehlmann, F.; Kurzan, B.; Stöckel, Jan; Dejarnac, Renaud; Weinzettl, Vladimír; Seidl, Jakub; Peterka, M.

    2010-01-01

    Roč. 50, č. 9 (2010), s. 854-859 ISSN 0863-1042. [International Workshop on Electric Probes in Magnetized Plasmas/8th./. Innsbruck, 21.09.2009-24.09.2009] R&D Projects: GA AV ČR KJB100430901; GA ČR GA202/09/1467 Institutional research plan: CEZ:AV0Z20430508 Keywords : Tokamak * ball- pen probe * electron temperature * L-mode * H-mode * ELMs Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 1.006, year: 2010 http://onlinelibrary.wiley.com/doi/10.1002/ctpp.201010145/pdf

  4. Crossbar H-mode drift-tube linac design with alternative phase focusing for muon linac

    Science.gov (United States)

    Otani, M.; Futatsukawa, K.; Hasegawa, K.; Kitamura, R.; Kondo, Y.; Kurennoy, S.

    2017-07-01

    We have developed a Crossbar H-mode (CH) drift-tube linac (DTL) design with an alternative phase focusing (APF) scheme for a muon linac, in order to measure the anomalous magnetic moment and electric dipole moment (EDM) of muons at the Japan Proton Accelerator Research Complex (J-PARC). The CH-DTL accelerates muons from β = v/c = 0.08 to 0.28 at an operational frequency of 324 MHz. The design and results are described in this paper.

  5. Confinement improvement in H-mode-like plasmas in helical systems

    International Nuclear Information System (INIS)

    Itoh, K.; Sanuki, H.; Itoh, S.; Fukuyama, A.; Yagi, M.

    1993-06-01

    The reduction of the anomalous transport due to the inhomogeneous radial electric field is theoretically studied for toroidal helical plasmas. The self-sustained interchange-mode turbulence is analysed for the system with magnetic shear and magnetic hill. For the system with magnetic well like conventional stellarators, the ballooning mode turbulence is studied. Influence of the radial electric field inhomogeneity on the transport coefficients and fluctuations are quantitatively shown. Unified theory of the transport coefficients in the L-mode and H-mode-like plasmas are presented. (author)

  6. Transport simulation of EAST long-pulse H-mode discharge with integrated modeling

    Science.gov (United States)

    Wu, M. Q.; Li, G. Q.; Chen, J. L.; Du, H. F.; Gao, X.; Ren, Q. L.; Li, K.; Chan, Vincent; Pan, C. K.; Ding, S. Y.; Jian, X.; Zhu, X.; Lian, H.; Qian, J. P.; Gong, X. Z.; Zang, Q.; Duan, Y. M.; Liu, H. Q.; Lyu, B.

    2018-04-01

    In the 2017 EAST experimental campaign, a steady-state long-pulse H-mode discharge lasting longer than 100 s has been obtained using only radio frequency heating and current drive, and the confinement quality is slightly better than standard H-mode, H98y2 ~ 1.1, with stationary peaked electron temperature profiles. Integrated modeling of one long-pulse H-mode discharge in the 2016 EAST experimental campaign has been performed with equilibrium code EFIT, and transport codes TGYRO and ONETWO under integrated modeling framework OMFIT. The plasma current is fully-noninductively driven with a combination of ~2.2 MW LHW, ~0.3 MW ECH and ~1.1 MW ICRF. Time evolution of the predicted electron and ion temperature profiles through integrated modeling agree closely with that from measurements. The plasma current (I p ~ 0.45 MA) and electron density are kept constantly. A steady-state is achieved using integrated modeling, and the bootstrap current fraction is ~28%, the RF drive current fraction is ~72%. The predicted current density profile matches the experimental one well. Analysis shows that electron cyclotron heating (ECH) makes large contribution to the plasma confinement when heating in the core region while heating in large radius does smaller improvement, also a more peaked LHW driven current profile is got when heating in the core. Linear analysis shows that the high-k modes instability (electron temperature gradient driven modes) is suppressed in the core region where exists weak electron internal transport barriers. The trapped electron modes dominates in the low-k region, which is mainly responsible for driving the electron energy flux. It is found that the ECH heating effect is very local and not the main cause to sustained the good confinement, the peaked current density profile has the most important effect on plasma confinement improvement. Transport analysis of the long-pulse H-mode experiments on EAST will be helpful to build future experiments.

  7. Status of the COMPASS tokamak and characterization of the first H-mode

    Czech Academy of Sciences Publication Activity Database

    Pánek, Radomír; Adámek, Jiří; Aftanas, Milan; Bílková, Petra; Böhm, Petr; Brochard, F.; Cahyna, Pavel; Cavalier, Jordan; Dejarnac, Renaud; Dimitrova, Miglena; Grover, O.; Harrison, J.; Háček, Pavel; Havlíček, Josef; Havránek, Aleš; Horáček, Jan; Hron, Martin; Imríšek, Martin; Janky, Filip; Kirk, A.; Komm, Michael; Kovařík, Karel; Krbec, Jaroslav; Kripner, Lukáš; Markovič, Tomáš; Mitošinková, Klára; Mlynář, Jan; Naydenkova, Diana; Peterka, Matěj; Seidl, Jakub; Stöckel, Jan; Štefániková, Estera; Tomeš, Matěj; Urban, Jakub; Vondráček, Petr; Varavin, Mykyta; Varju, Jozef; Weinzettl, Vladimír; Zajac, Jaromír

    2016-01-01

    Roč. 58, č. 1 (2016), č. článku 014015. ISSN 0741-3335 R&D Projects: GA MŠk(CZ) LM2011021; GA ČR(CZ) GAP205/12/2327; GA ČR(CZ) GA15-10723S Institutional support: RVO:61389021 Keywords : COMPASS * ELM * tokamak * H-mode Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 2.392, year: 2016

  8. Quiescent H-mode plasmas with strong edge rotation in the cocurrent direction.

    Science.gov (United States)

    Burrell, K H; Osborne, T H; Snyder, P B; West, W P; Fenstermacher, M E; Groebner, R J; Gohil, P; Leonard, A W; Solomon, W M

    2009-04-17

    For the first time in any tokamak, quiescent H-mode (QH-mode) plasmas have been created with strong edge rotation in the direction of the plasma current. This confirms the theoretical prediction that the QH mode should exist with either sign of the edge rotation provided the magnitude of the shear in the edge rotation is sufficiently large and demonstrates that counterinjection and counteredge rotation are not essential for the QH mode. Accordingly, the present work demonstrates a substantial broadening of the QH-mode operating space and represents a significant confirmation of the theory.

  9. Initial results of H-mode edge pedestal turbulence evolution with quadrature reflectometer measurements on DIII-D

    Energy Technology Data Exchange (ETDEWEB)

    Wang, G. [University of California, Los Angeles, CA 90095 (United States)]. E-mail: wangg@fusion.gat.com; Peebles, W.A. [University of California, Los Angeles, CA 90095 (United States); Doyle, E.J. [University of California, Los Angeles, CA 90095 (United States); Rhodes, T.L. [University of California, Los Angeles, CA 90095 (United States); Zeng, L. [University of California, Los Angeles, CA 90095 (United States); Nguyen, X. [University of California, Los Angeles, CA 90095 (United States); Osborne, T.H. [General Atomics, San Diego, CA 92186-5608 (United States); Snyder, P.B. [General Atomics, San Diego, CA 92186-5608 (United States); Kramer, G.J. [Princeton Plasma Physics Laboratory, Princeton, NJ 08543 (United States); Nazikian, R. [Princeton Plasma Physics Laboratory, Princeton, NJ 08543 (United States); Groebner, R.J. [General Atomics, San Diego, CA 92186-5608 (United States); Burrell, K.H. [General Atomics, San Diego, CA 92186-5608 (United States); Leonard, A.W. [General Atomics, San Diego, CA 92186-5608 (United States); Fenstermacher, M.E. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Strait, E.J. [General Atomics, San Diego, CA 92186-5608 (United States)

    2007-06-15

    High-resolution quadrature reflectometer measurements of density fluctuation levels have been obtained on DIII-D for H-mode edge pedestal studies. Initial results are presented from the L-H transition to the first ELM for two cases: (i) a low pedestal beta discharge, in which density turbulence in the pedestal has little change during the ELM-free phase, and (ii) a high pedestal beta discharge in which both density and magnetic turbulence are observed to increase before the first ELM. These high beta data are consistent with the existence of electromagnetic turbulence suggested by some transport models. During Type-I ELM cycles, when little magnetic turbulence can be observed, pedestal turbulence increases just after an ELM crash and then decreases before next ELM strikes, in contrast to a drop after ELM crash and then it re-grows when strong magnetic turbulence shows similar behavior. Clear ELM precursors are observed on {<=}20% of Type-I ELMs observed to date.

  10. A Comparison of Plasma Performance Between Single-Null and Double-Null Configurations During Elming H-Mode

    International Nuclear Information System (INIS)

    Petrie, T.W.; Fenstermacher, M.E.; Allen, S.L.; Carlstrom, T.N.; Gohil, P.; Groebner, R.J.; Greenfield, C.M.; Hyatt, A.W.; Lasnier, C.J.; La Haye, R.J.; Leonard, A.W.; Mahdavi, M.A.; Osborne, T.H.; Porter, G.D.; Rhodes, T.L.; Thomas, D.M.; Watkins, J.G.; West, W.P.; Wolf, N.S.

    1999-01-01

    Tokamak plasma performance generally improves with increased shaping of the plasma cross section, such as higher elongation and higher triangularity. The stronger shaping, especially higher triangularity, leads to changes in the magnetic topology of the divertor. Because there are engineering and divertor physics issues associated with changes in the details of the divertor flux geometry, especially as the configuration transitions from a single-null (SN) divertor to a marginally balanced double-null (DN) divertor, we have undertaken a systematic evaluation of the plasma characteristics as the magnetic geometry is varied, particularly with respect to (1) energy confinement, (2) the response of the plasma to deuterium gas fueling, (3) the operational density range for the ELMing H-mode, and (4) heat flux sharing by the diverters. To quantify the degree of divertor imbalance (or equivalently, to what degree the shape is double-null or single-null), we define a parameter DRSEP. DRSEP is taken as the radial distance between the upper divertor separatrix and the lower divertor separatrix, as determined at the outboard midplane. For example, if DRSEP=O, the configuration is a magnetically balanced DN; if DRSEP = +1.0 cm, the divertor configuration is biased toward the upper divertor. Three examples are shown in Fig. 1. In the following discussions, VB drift is directed toward the lower divertor

  11. Status of the COMPASS tokamak and characterization of the first H-mode

    Science.gov (United States)

    Pánek, R.; Adámek, J.; Aftanas, M.; Bílková, P.; Böhm, P.; Brochard, F.; Cahyna, P.; Cavalier, J.; Dejarnac, R.; Dimitrova, M.; Grover, O.; Harrison, J.; Háček, P.; Havlíček, J.; Havránek, A.; Horáček, J.; Hron, M.; Imríšek, M.; Janky, F.; Kirk, A.; Komm, M.; Kovařík, K.; Krbec, J.; Kripner, L.; Markovič, T.; Mitošinková, K.; Mlynář, J.; Naydenkova, D.; Peterka, M.; Seidl, J.; Stöckel, J.; Štefániková, E.; Tomeš, M.; Urban, J.; Vondráček, P.; Varavin, M.; Varju, J.; Weinzettl, V.; Zajac, J.; the COMPASS Team

    2016-01-01

    This paper summarizes the status of the COMPASS tokamak, its comprehensive diagnostic equipment and plasma scenarios as a baseline for the future studies. The former COMPASS-D tokamak was in operation at UKAEA Culham, UK in 1992-2002. Later, the device was transferred to the Institute of Plasma Physics of the Academy of Sciences of the Czech Republic (IPP AS CR), where it was installed during 2006-2011. Since 2012 the device has been in a full operation with Type-I and Type-III ELMy H-modes as a base scenario. This enables together with the ITER-like plasma shape and flexible NBI heating system (two injectors enabling co- or balanced injection) to perform ITER relevant studies in different parameter range to the other tokamaks (ASDEX-Upgrade, DIII-D, JET) and to contribute to the ITER scallings. In addition to the description of the device, current status and the main diagnostic equipment, the paper focuses on the characterization of the Ohmic as well as NBI-assisted H-modes. Moreover, Edge Localized Modes (ELMs) are categorized based on their frequency dependence on power density flowing across separatrix. The filamentary structure of ELMs is studied and the parallel heat flux in individual filaments is measured by probes on the outer mid-plane and in the divertor. The measurements are supported by observation of ELM and inter-ELM filaments by an ultra-fast camera.

  12. BURNING PLASMA PROJECTIONS USING DRIFT WAVE TRANSPORT MODELS AND SCALINGS FOR THE H-MODE PEDESTAL

    International Nuclear Information System (INIS)

    KINSEY, J.E.; ONJUN, T.; BATEMAN, G.; KRITZ, A.; PANKIN, A.; STAEBLER, G.M.; WALTZ, R.E.

    2002-01-01

    OAK-B135 The GLF23 and Multi-Mode (MM95) transport models are used along with a model for the H-mode pedestal to predict the fusion performance for the ITER, FIRE, and IGNITOR tokamak designs. The drift-wave predictive transport models reproduce the core profiles in a wide variety of tokamak discharges, yet they differ significantly in their response to temperature gradient (stiffness). Recent gyro-kinetic simulations of ITG/TEM and ETG modes motivate the renormalization of the GLF23 model. The normalizing coefficients for the ITG/TEM modes are reduced by a factor of 3.7 while the ETG mode coefficient is increased by a factor of 4.8 in comparison with the original model. A pedestal temperature model is developed for type I ELMy H-mode plasmas based on ballooning mode stability and a theory-motivated scaling for the pedestal width. In this pedestal model, the pedestal density is proportional to the line-averaged density and the pedestal temperature is inversely related to the pedestal density

  13. Gyrokinetic Calculations of Microinstabilities and Transport During RF H-Modes on Alcator C-Mod

    International Nuclear Information System (INIS)

    Redi, M.H.; Fiore, C.; Bonoli, P.; Bourdelle, C.; Budny, R.; Dorland, W.D.; Ernst, D.; Hammett, G.; Mikkelsen, D.; Rice, J.; Wukitch, S.

    2002-01-01

    Physics understanding for the experimental improvement of particle and energy confinement is being advanced through massively parallel calculations of microturbulence for simulated plasma conditions. The ultimate goal, an experimentally validated, global, non-local, fully nonlinear calculation of plasma microturbulence is still not within reach, but extraordinary progress has been achieved in understanding microturbulence, driving forces and the plasma response in recent years. In this paper we discuss gyrokinetic simulations of plasma turbulence being carried out to examine a reproducible, H-mode, RF heated experiment on the Alcator CMOD tokamak3, which exhibits an internal transport barrier (ITB). This off axis RF case represents the early phase of a very interesting dual frequency RF experiment, which shows density control with central RF heating later in the discharge. The ITB exhibits steep, spontaneous density peaking: a reduction in particle transport occurring without a central particle source. Since the central temperature is maintained while the central density is increasing, this also suggests a thermal transport barrier exists. TRANSP analysis shows that ceff drops inside the ITB. Sawtooth heat pulse analysis also shows a localized thermal transport barrier. For this ICRF EDA H-mode, the minority resonance is at r/a * 0.5 on the high field side. There is a normal shear profile, with q monotonic

  14. Characteristics of edge localized mode in JFT-2M H-mode

    International Nuclear Information System (INIS)

    Matsumoto, Hiroshi; Funahashi, Akimasa; Goldston, R.J.

    1989-03-01

    Characteristics of edge localized mode (ELM/ERP) during H-mode plasma of JFT-2M were investigated. It was found that ELM/ERP is mainly a density fluctuation phenomena in the edge, and electron temperature in the edge except just near the separatrix is not very much perturbed. Several experimental conditions to controll ELM/ERP are, plasma density, plasma ion species, heating power, and plasma current ramping. ELM/ERPs found in low density deuterium discharge are suppressed by raising the density. ELM/ERPs are pronounced in hydrogen plasma compared with deuterium plasma. ELM/ERPs seen in hydrogen plasma or in near marginal H-mode conditions are suppressed by increasing the heating power. ELM/ERPs are found to be suppressed by plasma current ramp down, whereas they are enhanced by current ramp up. MHD aspect of ELM/ERP was investigated. No clear MHD features of ELM/ERP were found. However, reversal of mode rotation seen imediately after ELM/ERP suggests the temporal return to L-mode during the ELM/ERP event. (author)

  15. Methane penetration in DIII-D ELMing H-mode plasmas

    International Nuclear Information System (INIS)

    West, W.P.; Lasnier, C.J.; Whyte, D.G.; Isler, R.C.; Evans, T.E.; Jackson, G.L.; Rudakov, D.; Wade, M.R.; Strachan, J.

    2003-01-01

    Carbon penetration into the core plasma during midplane and divertor methane puffing has been measured for DIII-D ELMing H-mode plasmas. The methane puffs are adjusted to a measurable signal, but global plasma parameters are only weakly affected (line average density, e > increases by E , drops by 6+ density profiles in the core measured as a function of time using charge exchange recombination spectroscopy. The methane penetration factor is defined as the difference in the core content with the puff on and puff off, divided by the carbon confinement time and the methane puffing rate. In ELMing H-mode discharges with ion ∇B drift direction into the X-point, increasing the line averaged density from 5 to 8x10 19 m -3 dropped the penetration factor from 6.6% to 4.6% for main chamber puffing. The penetration factor for divertor puffing was below the detection limit (<1%). Changing the ion ∇B drift to away from the X-point decreased the penetration factor by more than a factor of five for main chamber puffing

  16. Pedestal Temperature Model for Type III ELMy H-mode Plasma

    International Nuclear Information System (INIS)

    Buangam, W.; Suwanna, S.; Onjun, T.; Poolyarat, N.; Picha, R.; Singhsomroje, W.

    2009-07-01

    Full text: It is widely known that the improved performance of H-mode plasma results mainly from a formation of the pedestal, which is a narrow region of strong pressure gradient near the edge of plasma. A predictive capability for the conditions at the top of the pedestal is important, especially for predictive simulations of future experiments. New models for predicting the temperature values at the top of the pedestal for type III ELMy H-mode plasma are developed by using two different approaches: a theory-based approaches and an empirical approach. For a theory-based approach, a model is developed based on the calculation of thermal energy in the pedestal region and on accepted scaling laws of energy confinement time. For an empirical model, a scaling law for pedestal temperature in terms of plasma controlled parameters, such as plasma current, magnetic field, heating power, is deduced from experimental data. Predictions from these models are compared with experimental data from the Pedestal International Database. Statistical quantities, such as Root-Mean Square Error (RMSE) and offset values, are computed to quantify the predictive capability of the models. It is found that the theory-based model predicts the pedestal temperature values moderately well yielding RMSE between 30% and 40%. The IPB98(y,3) scaling law yields with best agreement with RMSE of 30.4%. The empirical model predicts the pedestal temperature value with better agreement, yield RMSE of 25.9%

  17. Correlation of H-mode density barrier width and neutral penetration length

    International Nuclear Information System (INIS)

    Groebner, R.J.

    2002-01-01

    Pedestal studies in DIII-D find a good correlation between the width of the H-mode particle barrier width(ne) and the neutral penetration length. These results are obtained by comparing experimental n e profiles to the predictions of an analytic model for the density profile, obtained from a solution of the particle continuity equations for electrons and deuterium atoms. Initial bench-marking shows that the model is consistent with the fluid neutrals model of the UEDGE code. In its range of validity (edge temperature between 0.02-0.3 keV), the model quantitatively predicts the observed values of width(ne), the observed decrease of width(ne) as the pedestal density n e,ped increases, the observed increase of the gradient of n e with the square of n e,ped , and the observation that L-mode and H-mode profiles with the same n e,ped have very similar widths. In the model, width(ne) depends on the fuelling source and on the plasma transport. Thus, these results provide evidence that the width of the particle barrier depends on both plasma physics and atomic physics. (author)

  18. Drift-based Model for Power Scrape-off Width in Low-Gas-Puff H-mode Plasmas: Theory and Implications

    Energy Technology Data Exchange (ETDEWEB)

    Goldston, R., E-mail: rgoldston@pppl.gov [Princeton Plasma Physics Laboratory, Princeton (United States)

    2012-09-15

    . The strong parallel flows and plasma charging implied by this model suggest a mechanism for H-mode transition, consistent with the observation that LSN divertors have lower power threshold and the JT-60 divertor did not accommodate H-mode. These results suggest that ITER may need to operate at least transiently in the low SOL regime presented here in order to achieve H-mode transition. (author)

  19. A quantitative analysis of the effect of ELMs on H-mode thermal energy confinement in DIII-D

    International Nuclear Information System (INIS)

    Schissel, D.P.; Osborne, T.H.; Carlstrom, T.N.; Zohm, H.

    1992-06-01

    The desire to reach ignition in future tokamaks the energy confinement time critical parameter. The most promising enhanced (over L-mode) confinement regime is the H-mode, discovered on ASDEX with neutral beam heating, and then confirmed with various auxiliary heating sources on numerous machines. The knowledge of how H-mode τ E depends on different parameters is of chemical importance to the performance predictions for next generation devices. Inter-machine H-mode total and thermal energy confinement (τ th ) scalings, which are being utilized to predict ITER thermal energy confinement, have been created for discharges where the Edge Localized Mode (ELM) instability has not been present. Confinement scaling research hm concentrated on this ELM-free H-mode phase mostly owing to the difficulty of characterizing ELM behavior. To date, long pulse H-mode operation has only been achieved by utilizing ELMs to flush out unpurities and prevent radiative collapse of the discharge. Unfortunately, accompanying the ELMS is a decrease of the plasma stored energy due to the expulsion of particles near the edge of the discharge resulting in a reduction of the steep edge electron density gradient. In order to predict ITER's H-mode τ th in the presence of ELMS, an estimated 25% confinement degradation factor has been applied to the ELM-free predictions. Our work, summarized in this paper, indicates that this 25% reduction factor is too large and instead a value of approximately 15% would be more appropriate

  20. ROLE OF NEUTRALS IN CORE FUELING AND PEDESTAL STRUCTURE IN H-MODE DIII-D DISCHARGES

    International Nuclear Information System (INIS)

    WOLF, NS; PETRIE, TW; PORTER, GD; ROGNLIEN, TD; GROEBNER, RJ; MAKOWSKI, MA

    2002-01-01

    OAK A271 ROLE OF NEUTRALS IN CORE FUELING AND PEDESTAL STRUCTURE IN H-MODE DIII-D DISCHARGES. The 2-D fluid code UEDGE was used to analyze DIII-D experiments to determine the role of neutrals in core fueling, core impurities, and also the H-mode pedestal structure. The authors compared the effects of divertor closure on the fueling rate and impurity density of high-triangularity, H-mode plasmas. UEDGE simulations indicate that the decrease in both deuterium core fueling (∼ 15%-20%) and core carbon density (∼ 15%-30%) with the closed divertor compared to the open divertor configuration is due to greater divertor screening of neutrals. They also compared UEDGE results with a simple analytic model of the H-mode pedestal structure. The model predicts both the width and gradient of the transport barrier in n e as a function of the pedestal density. The more sophisticated UEDGE simulations of H-mode discharges corroborate the simple analytic model, which is consistent with the hypothesis that fueling processes play a role in H-mode transport barrier formation

  1. Exploration of the Super H-mode regime on DIII-D and potential advantages for burning plasma devices

    Energy Technology Data Exchange (ETDEWEB)

    Solomon, W. M., E-mail: solomon@fusion.gat.com; Bortolon, A.; Grierson, B. A.; Nazikian, R.; Poli, F. [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Snyder, P. B.; Burrell, K. H.; Garofalo, A. M.; Groebner, R. J.; Leonard, A. W.; Meneghini, O.; Osborne, T. H.; Petty, C. C. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Loarte, A. [ITER Organization, Route de Vinon-sur-Verdon - CS 90 046, 13067 St Paul Lez Durance Cedex (France)

    2016-05-15

    A new high pedestal regime (“Super H-mode”) has been predicted and accessed on DIII-D. Super H-mode was first achieved on DIII-D using a quiescent H-mode edge, enabling a smooth trajectory through pedestal parameter space. By exploiting Super H-mode, it has been possible to access high pedestal pressures at high normalized densities. While elimination of Edge localized modes (ELMs) is beneficial for Super H-mode, it may not be a requirement, as recent experiments have maintained high pedestals with ELMs triggered by lithium granule injection. Simulations using TGLF for core transport and the EPED model for the pedestal find that ITER can benefit from the improved performance associated with Super H-mode, with increased values of fusion power and gain possible. Similar studies demonstrate that the Super H-mode pedestal can be advantageous for a steady-state power plant, by providing a path to increasing the bootstrap current while simultaneously reducing the demands on the core physics performance.

  2. QUIESCENT H-MODE, AN ELM-FREE HIGH-CONFINEMENT MODE ON DIII-D WITH POTENTIAL FOR STATIONARY STATE OPERATION

    International Nuclear Information System (INIS)

    WEST, WP; BURRELL, KH; DeGRASSIE, JS; DOYLE, EJ; GREENFIELD, CM; LASNIER, CJ; SNYDER, PB; ZENG, L.

    2003-01-01

    OAK-B135 The quiescent H-mode (QH-mode) is an ELM-free and stationary state mode of operation discovered on DIII-D. This mode achieves H-mode levels of confinement and pedestal pressure while maintaining constant density and radiated power. The elimination of edge localized modes (ELMs) and their large divertor loads while maintaining good confinement and good density control is of interest to next generation tokamaks. This paper reports on the correlations found between selected parameters in a QH-mode database developed from several hundred DIII-D counter injected discharges. Time traces of key plasma parameters from a QH-mode discharge are shown. On DIII-D the negative going plasma current (a) indicates that the beam injection direction is counter to the plasma current direction, a common feature of all QH-modes. The D α time behavior (c) shows that soon after high powered beam heating (b) is applied, the discharge makes a transition to ELMing H-mode, then the ELMs disappear, indicating the start of the QH period that lasts for the remainder of the high power beam heating (3.5 s). Previously published work showing density and temperature profiles indicates that long-pulse, high-triangularity QH discharges develop an internal transport barrier in combination with the QH edge barrier. These discharges are known as quiescent, double-barrier discharges (QDB). The H-factor (d) and stored energy (c) rise then saturate at a constant level and the measured axial and minimum safety factors remain above 1.0 for the entire QH duration. During QDB operation the performance of the plasma can be very good, with β N *H 89L product reaching 7 for > 10 energy confinement times. These discharges show promise that a stationary state can be achieved

  3. QUIESCENT H-MODE, AN ELM-FREE HIGH-CONFINEMENT MODE ON DIII-D WITH POTENTIAL FOR STATIONARY STATE OPERATION

    Energy Technology Data Exchange (ETDEWEB)

    WEST,WP; BURRELL,KH; deGRASSIE,JS; DOYLE,EJ; GREENFIELD,CM; LASNIER,CJ; SNYDER,PB; ZENG,L

    2003-08-01

    OAK-B135 The quiescent H-mode (QH-mode) is an ELM-free and stationary state mode of operation discovered on DIII-D. This mode achieves H-mode levels of confinement and pedestal pressure while maintaining constant density and radiated power. The elimination of edge localized modes (ELMs) and their large divertor loads while maintaining good confinement and good density control is of interest to next generation tokamaks. This paper reports on the correlations found between selected parameters in a QH-mode database developed from several hundred DIII-D counter injected discharges. Time traces of key plasma parameters from a QH-mode discharge are shown. On DIII-D the negative going plasma current (a) indicates that the beam injection direction is counter to the plasma current direction, a common feature of all QH-modes. The D{sub {alpha}} time behavior (c) shows that soon after high powered beam heating (b) is applied, the discharge makes a transition to ELMing H-mode, then the ELMs disappear, indicating the start of the QH period that lasts for the remainder of the high power beam heating (3.5 s). Previously published work showing density and temperature profiles indicates that long-pulse, high-triangularity QH discharges develop an internal transport barrier in combination with the QH edge barrier. These discharges are known as quiescent, double-barrier discharges (QDB). The H-factor (d) and stored energy (c) rise then saturate at a constant level and the measured axial and minimum safety factors remain above 1.0 for the entire QH duration. During QDB operation the performance of the plasma can be very good, with {beta}{sub N}*H{sub 89L} product reaching 7 for > 10 energy confinement times. These discharges show promise that a stationary state can be achieved.

  4. The role of the radial electric field in confinement and transport in H-mode and VH-mode discharges in the DIII-D tokamak

    International Nuclear Information System (INIS)

    Gohil, P.; Burrell, K.H.; Groebner, R.J.; Osborne, T.H.; Doyle, E.J.; Rettig, C.L.

    1993-08-01

    Measurements of the radial electric field, E r , with high spatial and high time resolution in H-mode and VH-mode discharges in the DIII-D tokamak have revealed the significant influence of the shear in E r on confinement and transport in these discharges. These measurements are made using the DIII-D Charge Exchange Recombination (CER) System. At the L-H transition in DIII-D plasmas, a negative well-like E r profile develops just within the magnetic separatrix. A region of shear in E r results, which extends 1 to 2 cm into the plasma from the separatrix. At the transition, this region of sheared E r exhibits the greatest increase in impurity ion poloidal rotation velocity and the greatest reduction in plasma fluctuations. A transport barrier is formed in this same region of E x B velocity shear as is signified by large increases in the observed gradients of the ion temperature, the carbon density, the electron temperature and electron density. The development of the region of sheared E r , the increase in impurity ion poloidal rotation, the reduction in plasma turbulence, and the transport barrier all occur simultaneously at the L-H transition. Measurements of the radial electric field, plasma turbulence, thermal transport, and energy confinement have been performed for a wide range of plasma conditions and configurations. The results support the supposition that the progression of improving confinement at the L-H transition, into the H-mode and then into the VH-mode can be explained by the hypothesis of the suppression of plasma turbulence by the increasing penetration of the region of sheared E x B velocity into the plasma interior

  5. Modification of H-Mode Pedestal Instabilities in the DIII-D Tokamak

    International Nuclear Information System (INIS)

    J.R. Ferron; M.S. Chu; G.L. Jackson; L.L. Lao; R.L. Miller; T.H. Osborne; P.B. Snyder; E.J. Strait; T.S. Taylor; A.D. Turnbull; A.M. Garofalo; M.A. Makowski; B.W. Rice; M.S. Chance; L.R. Baylor; M. Murakami; M.R. Wade

    1999-01-01

    Through comparison of experiment and ideal magnetohydrodynamic (MHD) theory, modes driven in the edge region of tokamak H-mode discharges [Type I edge-localized modes (ELMs)] are shown to result from low toroidal mode number (n) instabilities driven by pressure gradient and current density. The mode amplitude and frequency are functions of the discharge shape. Reductions in mode amplitude are observed in discharge shapes with either high squareness or low triangularity where the low-n stability threshold in the edge pressure gradient is predicted to be reduced and the most unstable mode is expected to have higher values of n. The importance of access to the ballooning mode second stability regime is demonstrated through the changes in the ELM character that occur when second regime access is not available. An edge stability model is presented that predicts that there is a threshold value of n for second regime access and that the most unstable mode has n near this threshold

  6. Characteristics of edge pedestals in LHW and NBI heated H-mode plasmas on EAST

    Science.gov (United States)

    Zang, Q.; Wang, T.; Liang, Y.; Sun, Y.; Chen, H.; Xiao, S.; Han, X.; Hu, A.; Hsieh, C.; Zhou, H.; Zhao, J.; Zhang, T.; Gong, X.; Hu, L.; Liu, F.; Hu, C.; Gao, X.; Wan, B.; the EAST Team

    2016-10-01

    By using the recently developed Thomson scattering diagnostic, the pedestal structure of the H-mode with neutral beam injection (NBI) or/and lower hybrid wave (LHW) heating on EAST (Experimental Advanced Superconducting Tokamak) is analyzed in detail. We find that a higher ratio of the power of the NBI to the total power of the NBI and the lower hybrid wave (LHW) will produce a large and regular different edge-localized mode (ELM), and a lower ratio will produce a small and irregular ELM. The experiments show that the mean pedestal width has good correlation with β \\text{p,\\text{ped}}0.5 , The pedestal width appears to be wider than that on other similar machines, which could be due to lithium coating. However, it is difficult to draw any conclusion of correlation between ρ * and the pedestal width for limited ρ * variation and scattered distribution. It is also found that T e/\

  7. Tokamak fluidlike equations, with applications to turbulence and transport in H mode discharges

    International Nuclear Information System (INIS)

    Kim, Y.B.; Biglari, H.; Carreras, B.A.; Diamond, P.H.; Groebner, R.J.; Kwon, O.J.; Spong, D.A.; Callen, J.D.; Chang, Z.; Hollenberg, J.B.; Sundaram, A.K.; Terry, P.W.; Wang, J.F.

    1990-01-01

    Significant progress has been made in developing tokamak fluidlike equations which are valid in all collisionality regimes in toroidal devices, and their applications to turbulence and transport in tokamaks. The areas highlighted in this paper include: the rigorous derivation of tokamak fluidlike equations via a generalized Chapman-Enskog procedure in various collisionality regimes and on various time scales; their application to collisionless and collisional drift wave models in a sheared slab geometry; applications to neoclassical drift wave turbulence; i.e. neoclassical ion-temperature-gradient-driven turbulence and neoclassical electron-drift-wave turbulence; applications to neoclassical bootstrap-current-driven turbulence; numerical simulation of nonlinear bootstrap-current-driven turbulence and tearing mode turbulence; transport in Hot-Ion H mode discharges. 20 refs., 3 figs

  8. ELM suppression in low edge collisionality H-mode discharges using n = 3 magnetic perturbations

    Energy Technology Data Exchange (ETDEWEB)

    Burrell, K H [General Atomics, PO Box 85608, San Diego, CA 92186-9784 (United States); Evans, T E [General Atomics, PO Box 85608, San Diego, CA 92186-9784 (United States); Doyle, E J [University of California, Los Angeles, California (United States); Fenstermacher, M E [Lawrence Livermore National Laboratory, Livermore, California (United States); Groebner, R J [General Atomics, PO Box 85608, San Diego, CA 92186-9784 (United States); Leonard, A W [General Atomics, PO Box 85608, San Diego, CA 92186-9784 (United States); Moyer, R A [University of California, San Diego, California (United States); Osborne, T H; Schaffer, M J; Snyder, P B [General Atomics, PO Box 85608, San Diego, CA 92186-9784 (United States); Thomas, P R [CEA Cadarache EURATOM Association, Cadarache (France); West, W P [General Atomics, PO Box 85608, San Diego, CA 92186-9784 (United States); Boedo, J A [University of California, San Diego, California (United States); Garofalo, A M [Columbia University, New York, New York (United States); Gohil, P; Jackson, G L; La Haye, R J [General Atomics, PO Box 85608, San Diego, CA 92186-9784 (United States); Lasnier, C J [Lawrence Livermore National Laboratory, Livermore, California (United States); Reimerdes, H [Columbia University, New York, New York (United States); Rhodes, T L [University of California, Los Angeles, California (United States); Scoville, J T [General Atomics, PO Box 85608, San Diego, CA 92186-9784 (United States); Solomon, W M [Princeton Plasma Physics Laboratory, Princeton, New Jersey (United States); Thomas, D M [General Atomics, PO Box 85608, San Diego, CA 92186-9784 (United States); Wang, G [University of California, Los Angeles, California (United States); Watkins, J G [Sandia National Laboratories, Albuquerque, New Mexico (United States); Zeng, L [University of California, Los Angeles, California (United States)

    2005-12-15

    Using resonant magnetic perturbations with toroidal mode number n = 3, we have produced H-mode discharges without edge localized modes (ELMs) which run with constant density and radiated power for periods up to about 2550 ms (17 energy confinement times). These ELM suppression results are achieved at pedestal collisionalities close to those desired for next step burning plasma experiments such as ITER and provide a means of eliminating the rapid erosion of divertor components in such machines which could be caused by giant ELMs. The ELM suppression is due to an enhancement in the edge particle transport which reduces pedestal current density and maximum edge pressure gradient below the threshold for peeling-ballooning modes. These n = 3 magnetic perturbations provide a means of active control of edge plasma transport.

  9. Transport modeling of L- and H-mode discharges with LHCD on EAST

    Science.gov (United States)

    Li, M. H.; Ding, B. J.; Imbeaux, F.; Decker, J.; Zhang, X. J.; Kong, E. H.; Zhang, L.; Wei, W.; Shan, J. F.; Liu, F. K.; Wang, M.; Xu, H. D.; Yang, Y.; Peysson, Y.; Basiuk, V.; Artaud, J.-F.; Yuynh, P.; Wan, B. N.

    2013-04-01

    High-confinement (H-mode) discharges with lower hybrid current drive (LHCD) as the only heating source are obtained on EAST. In this paper, an empirical transport model of mixed Bohm/gyro-Bohm for electron and ion heat transport was first calibrated against a database of 3 L-mode shots on EAST. The electron and ion temperature profiles are well reproduced in the predictive modeling with the calibrated model coupled to the suite of codes CRONOS. CRONOS calculations with experimental profiles are also performed for electron power balance analysis. In addition, the time evolutions of LHCD are calculated by the C3PO/LUKE code involving current diffusion, and the results are compared with experimental observations.

  10. ELM suppression in low edge collisionality H-mode discharges using n = 3 magnetic perturbations

    International Nuclear Information System (INIS)

    Burrell, K H; Evans, T E; Doyle, E J; Fenstermacher, M E; Groebner, R J; Leonard, A W; Moyer, R A; Osborne, T H; Schaffer, M J; Snyder, P B; Thomas, P R; West, W P; Boedo, J A; Garofalo, A M; Gohil, P; Jackson, G L; La Haye, R J; Lasnier, C J; Reimerdes, H; Rhodes, T L; Scoville, J T; Solomon, W M; Thomas, D M; Wang, G; Watkins, J G; Zeng, L

    2005-01-01

    Using resonant magnetic perturbations with toroidal mode number n = 3, we have produced H-mode discharges without edge localized modes (ELMs) which run with constant density and radiated power for periods up to about 2550 ms (17 energy confinement times). These ELM suppression results are achieved at pedestal collisionalities close to those desired for next step burning plasma experiments such as ITER and provide a means of eliminating the rapid erosion of divertor components in such machines which could be caused by giant ELMs. The ELM suppression is due to an enhancement in the edge particle transport which reduces pedestal current density and maximum edge pressure gradient below the threshold for peeling-ballooning modes. These n = 3 magnetic perturbations provide a means of active control of edge plasma transport

  11. Nonlinear theory of trapped electron temperature gradient driven turbulence in flat density H-mode plasmas

    International Nuclear Information System (INIS)

    Hahm, T.S.

    1990-12-01

    Ion temperature gradient turbulence based transport models have difficulties reconciling the recent DIII-D H-mode results where the density profile is flat, but χ e > χ i in the core region. In this work, a nonlinear theory is developed for recently discovered ion temperature gradient trapped electron modes propagating in the electron diamagnetic direction. This instability is predicted to be linearly unstable for L Ti /R approx-lt κ θ ρ s approx-lt (L Ti /R) 1/4 . They are also found to be strongly dispersive even at these long wavelengths, thereby suggesting the importance of the wave-particle-wave interactions in the nonlinear saturation phase. The fluctuation spectrum and anomalous fluxes are calculated. In accordance with the trends observed in DIII-D, the predicted electron thermal diffusivity can be larger than the ion thermal diffusivity. 17 refs., 3 figs

  12. SOLPS5 modelling of the type III ELMing H-mode on TCV

    International Nuclear Information System (INIS)

    Gulejova, B.; Pitts, R.A.; Wischmeier, M.; Behn, R.; Coster, D.; Horacek, J.; Marki, J.

    2007-01-01

    Although ohmic H-modes have long been produced on TCV and the effects of ELMs at the divertor target studied in some detail, no attempt has yet been made to model the scrape-off layer (SOL) in these plasmas. This paper describes details of the first such efforts in which simulations of the inter-ELM phases using the coupled fluid-Monte Carlo SOLPS5 code (without drifts) are constrained by careful upstream Thomson scattering and Langmuir probe profiles. Simulated divertor profiles are compared with Langmuir probes and fast IR camera measurements at the targets. To account for the very differing transport rates in the edge pedestal and main SOL regions, radial variation of edge transport coefficients has been introduced in the simulations. Similarly, it is found that transport in the main chamber and divertor regions must be separately adjusted to provide an acceptable code-experiment match

  13. Dependence of helium transport on plasma current and ELM frequency in H-mode discharges in DIII-D

    International Nuclear Information System (INIS)

    Wade, M.R.; Hillis, D.L.; Hogan, J.T.; Finkenthal, D.F.; West, W.P.; Burrell, K.H.; Seraydarian, R.P.

    1993-05-01

    The removal of helium (He) ash from the plasma core with high efficiency to prevent dilution of the D-T fuel mixture is of utmost importance for future fusion devices, such as the International Thermonuclear Experimental Reactor (ITER). A variety of measurements in L-mode conditions have shown that the intrinsic level of helium transport from the core to the edge may be sufficient to prevent sufficient dilution (i.e., τ He /τ E < 5). Preliminary measurements in biased-induced, limited H-mode discharges in TEXTOR suggest that the intrinsic helium transport properties may not be as favorable. If this trend is shown also in diverted H-mode plasmas, then scenarios based on ELMing H-modes would be less desirable. To further establish the database on helium transport in H-mode conditions, recent studies on the DIII-D tokamak have focused on determining helium transport properties in H-mode conditions and the dependence of these properties on plasma current and ELM frequency

  14. Predictive modelling of the impact of argon injection on H-mode plasmas in JET with the RITM code

    International Nuclear Information System (INIS)

    Unterberg, B; Kalupin, D; Tokar', M Z; Corrigan, G; Dumortier, P; Huber, A; Jachmich, S; Kempenaars, M; Kreter, A; Messiaen, A M; Monier-Garbet, P; Ongena, J; Puiatti, M E; Valisa, M; Hellermann, M von

    2004-01-01

    Self-consistent modelling of energy and particle transport of the plasma background and impurities has been performed with the code RITM for argon seeded high density H-mode plasmas in JET. The code can reproduce both the profiles in the plasma core and the structure of the edge pedestal. The impact of argon on core transport is found to be small; in particular, no significant change in confinement is observed in both experimental and modelling results. The same transport model, which has been used to reproduce density peaking in the radiative improved mode in TEXTOR, reveals a flat density profile in Ar seeded JET H-mode plasmas in agreement with the experimental observations. This behaviour is attributed to the rather flat profile of the safety factor in the bulk of H-mode discharges

  15. H-mode-like discharge under the presence of 1/1 rational surface at ergodic layer in LHD

    International Nuclear Information System (INIS)

    Morita, Shigeru; Morisaki, Tomohiro; Tanaka, Kenji

    2004-01-01

    H-mode-like discharge was found in LHD with a full B t field of 2.5T at an outwardly shifted configuration of R ax = 4.00 m where the m/n = 1/1 rational surface is located at the ergodic layer. The H-mode-like discharge was triggered by changing the P NBI from 9MW to 5 MW in a density range of 4-8 x 10 13 cm -3 , followed by a clear density rise, ELM-like H α bursts, and a reduction of magnetic fluctuation. These H-mode-like features vanished with a small radial movement of the 1/1 surface. (author)

  16. Experimental study of the β-limit in ohmic H-mode in the TUMAN-3M tokamak

    International Nuclear Information System (INIS)

    Lebedev, S.V.; Andreiko, M.V.; Askinazi, L.G.; Golant, V.E.; Kornev, V.A.; Krikunov, S.V.; Levin, L.S.; Rozhdestvensky, V.V.; Tukachinsky, A.S.; Yaroshevich, S.P.

    1998-01-01

    Because of its high confinement properties, the H-mode provides good opportunities to achieve high beta values in a tokamak. In this paper the results of an experimental study of β T and β N limits in the H-mode, obtained in a circular cross section tokamak without auxiliary heating are presented. The experiments were performed in the TUMAN-3M tokamak. The device has the following parameters: R 0 =0.53m, a s =0.22m (limiter configuration), B T ≤1.2T, I p ≤175kA, n-bar e ≤6.2x10 19 m -3 . The stored energy was measured using diamagnetic loops and compared with W calculated from kinetic data obtained by Thomson scattering and microwave interferometry. Measurements of the stored energy and of the β were performed in the ohmic H-mode before and after boronization and in the scenario with fast current ramp-down in ohmic H-mode. A maximum value of β T of 2.0% and β N of 2.0 were achieved. The β N limit achieved reveals itself as a 'soft' (non-disruptive) limit. The stored energy slowly decays after the current ramp-down. No correlation was found between beta restriction and MHD phenomena. Internal transport barrier (ITB) formation was observed in ohmic H-mode. An enhancement factor of 2.0 over ITER93H(ELM-free) was found in the ohmic H-mode with ITB. (author)

  17. First observation of a new zonal-flow cycle state in the H-mode transport barrier of the experimental advanced superconducting Tokamak

    DEFF Research Database (Denmark)

    Xu, G.S.; Wang, H. Q.; Wan, B. N.

    2012-01-01

    A new turbulence-flow cycle state has been discovered after the formation of a transport barrier in the H-mode plasma edge during a quiescent phase on the EAST superconducting tokamak. Zonal-flow modulation of high-frequency-broadband (0.05-1MHz) turbulence was observed in the steep-gradient region...... leading to intermittent transport events across the edge transport barrier. Good confinement (H-98y,H-2 similar to 1) has been achieved in this state, even with input heating power near the L-H transition threshold. A novel model based on predator-prey interaction between turbulence and zonal flows...... reproduced this state well. © 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769852]...

  18. H-mode edge stability of Alcator C-mod plasmas

    International Nuclear Information System (INIS)

    Mossessian, D.A.; Hubbard, A.; Hughes, J.W.; Greenwald, M.; LaBombard, B.; Snipes, J.A.; Wolfe, S.; Snyder, P.; Wilson, H.; Xu, X.; Nevins, W.

    2003-01-01

    For steady state H-mode operation, a relaxation mechanism is required to limit build-up of the edge gradient and impurity content. C-Mod sees two such mechanisms - EDA and grassy ELMs, but not large type I ELMs. In EDA the edge relaxation is provided by an edge localized quasi coherent electromagnetic mode that exists at moderate pedestal temperature T 3.5 and does not limit the build up of the edge pressure gradient. The mode is not observed in the ideal MHD stability analysis, but is recorded in the nonlinear real geometry fluctuations modeling based on fluid equations and is thus tentatively identified as a resistive ballooning mode. At high edge pressure gradients and temperatures the mode is replaced by broadband fluctuations (f< 50 kHz) and small irregular ELMs are observed. Based on ideal MHD calculations that include the effects of edge bootstrap current, these ELMs are identified as medium n (10 < n < 50) coupled peeling/ballooning modes. The stability thresholds, its dependence on the plasma shape and the modes structure are studied experimentally and with the linear MHD stability code ELITE. (author)

  19. The influence of gas fuelling location on H-mode access in the MAST spherical tokamak

    International Nuclear Information System (INIS)

    Field, A R; Carolan, P G; Conway, N J; Counsell, G F; Cunningham, G; Helander, P; Meyer, H; Taylor, D; Tournianski, M R; Walsh, M J

    2004-01-01

    The observation that high-field side (HFS) gas puff refuelling facilitates access to the improved confinement (H-mode) regime on the COMPASS-D and MAST tokamaks prompted a theoretical investigation of the role of the neutral gas dynamics in controlling the edge plasma rotation and radial E-field, E r . Within the framework of neo-classical theory, higher edge plasma flow, and hence E r , are predicted when fuelling from the HFS-rather than from the more usual low-field side (LFS)-provided neutral viscosity dominates the transport of toroidal angular momentum. Here, these predictions are compared with experiments on MAST, where the influence of the gas-puff location on the edge E r profile is measured spectroscopically. An increase in E r is indeed observed with HFS refuelling in the region where the edge transport barrier forms, provided the neutral density at the LFS is sufficiently low so as not to damp the toroidal flow

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

    International Nuclear Information System (INIS)

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

    1999-01-01

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

  1. H-mode pedestal characteristics in ITER shape discharges on DIII-D

    International Nuclear Information System (INIS)

    Osborne, T.H.; Burrell, K.H.; Groebner, R.J.

    1998-09-01

    Characteristics of the H-mode pedestal are studied in Type 1 ELM discharges with ITER cross-sectional shape and aspect ratio. The scaling of the width of the edge step gradient region, δ, which is most consistent with the data is with the normalized edge pressure, (β POL PED ) 0.4 . Fits of δ to a function of temperature, such as ρ POL , are ruled out in divertor pumping experiments. The edge pressure gradient is found to scale as would be expected from infinite n ballooning mode theory; however, the value of the pressure gradient exceeds the calculated first stable limit by more than a factor of 2 in some discharges. This high edge pressure gradient is consistent with access to the second stable regime for ideal ballooning for surfaces near the edge. In lower q discharges, including discharges at the ITER value of q, edge second stability requires significant edge current density. Transport simulations give edge bootstrap current of sufficient magnitude to open second stable access in these discharges. Ideal kink analysis using current density profiles including edge bootstrap current indicate that before the ELM these discharges may be unstable to low n, edge localized modes

  2. Review of DIII-D H-Mode Density Limit Studies

    International Nuclear Information System (INIS)

    Maingi, R.; Mahdavi, M.A.

    2005-01-01

    Density limit studies over the past 10 yr on DIII-D have successfully identified several processes that limit plasma density in various operating modes. The recent focus of these studies has been on maintenance of the high-density operational window with good H-mode level energy confinement. We find that detachment and onset of multifaceted axisymmetric radiation from the edge (MARFE), fueling efficiency, particle confinement, and magnetohydrodynamic activity can impose density limits in certain regimes. By studying these processes, we have devised techniques with either pellets or gas fueling and divertor pumping to achieve line average density above Greenwald scaling, relying on increasing the ratio of pedestal to separatrix density, as well as density profile peaking. The scaling of several of these processes to next-step devices (e.g., the International Thermonuclear Experimental Reactor) has indicated that sufficiently high pedestal density can be achieved with conventional fueling techniques while ensuring divertor partial detachment needed for heat flux reduction. One density limit process requiring further study is neoclassical tearing mode (NTM) onset, and techniques for avoidance/mitigation of NTMs need additional development in present-day devices operated at high density

  3. Development of superconducting crossbar-H-mode cavities for proton and ion accelerators

    Directory of Open Access Journals (Sweden)

    F. Dziuba

    2010-04-01

    Full Text Available The crossbar-H-mode (CH structure is the first superconducting multicell drift tube cavity for the low and medium energy range operated in the H_{21} mode. Because of the large energy gain per cavity, which leads to high real estate gradients, it is an excellent candidate for the efficient acceleration in high power proton and ion accelerators with fixed velocity profile. A prototype cavity has been developed and tested successfully with a gradient of 7  MV/m. A few new superconducting CH cavities with improved geometries for different high power applications are under development at present. One cavity (f=325  MHz, β=0.16, seven cells is currently under construction and studied with respect to a possible upgrade option for the GSI UNILAC. Another cavity (f=217  MHz, β=0.059, 15 cells is designed for a cw operated energy variable heavy ion linac application. Furthermore, the EUROTRANS project (European research program for the transmutation of high level nuclear waste in an accelerator driven system, 600 MeV protons, 352 MHz is one of many possible applications for this kind of superconducting rf cavity. In this context a layout of the 17 MeV EUROTRANS injector containing four superconducting CH cavities was proposed by the Institute for Applied Physics (IAP Frankfurt. The status of the cavity development related to the EUROTRANS injector is presented.

  4. X-Divertor Geometries for Deeper Detachment Without Degrading the DIII-D H-Mode

    Science.gov (United States)

    Covele, Brent; Kotschenreuther, M. T.; Valanju, P. M.; Mahajan, S. M.; Leonard, A. W.; Hyatt, A. W.; McLean, A. G.; Thomas, D. M.; Guo, H. Y.; Watkins, J. G.; Makowski, M. A.; Hill, D. N.

    2015-11-01

    Recent DIII-D experiments comparing the standard divertor (SD) and X-Divertor (XD) geometries show heat and particle flux reduction at the divertor target plate. The XD features large poloidal flux expansion, increased connection length, and poloidal field line flaring, quantified by the Divertor Index. Both SD and XD were pushed deep into detachment with increased gas puffing, until core energy confinement and pedestal pressure were substantially reduced. As expected, outboard target heat fluxes are significantly reduced in the XD compared to the SD under similar upstream plasma conditions, even at low Greenwald fraction. The high-triangularity (floor) XD cases show larger reduction in temperature, heat, and particle flux relative to the SD in all cases, while low-triangularity (shelf) XD cases show more modest reductions over the SD. Consequently, heat flux reduction and divertor detachment may be achieved in the XD with less gas puffing and higher pedestal pressures. Further causative analysis, as well as detailed modeling with SOLPS, is underway. These initial experiments suggest the XD as a promising candidate to achieve divertor heat flux control compatible with robust H-mode operation. Work supported by US DOE under DE-FC02-04ER54698, DE-AC52-07NA27344, DE-FG02-04ER54754, and DE-FG02-04ER54742.

  5. Plasma interaction with tungsten samples in the COMPASS tokamak in ohmic ELMy H-modes

    International Nuclear Information System (INIS)

    Dimitrova, M; Weinzettl, V; Matejicek, J; Dejarnac, R; Stöckel, J; Havlicek, J; Panek, R; Popov, Tsv; Marinov, S; Costea, S

    2016-01-01

    This paper reports experimental results on plasma interaction with tungsten samples with or without pre-grown He fuzz. Under the experimental conditions, arcing was observed on the fuzzy tungsten samples, resulting in localized melting of the fuzz structure that did not extend into the bulk. The parallel power flux densities were obtained from the data measured by Langmuir probes embedded in the divertor tiles on the COMPASS tokamak. Measurements of the current-voltage probe characteristics were performed during ohmic ELMy H-modes reached in deuterium plasmas at a toroidal magnetic field B T = 1.15 T, plasma current I p = 300 kA and line-averaged electron density n e = 5×10 19 m -3 . The data obtained between the ELMs were processed by the recently published first-derivative probe technique for precise determination of the plasma potential and the electron energy distribution function (EEDF). The spatial profile of the EEDF shows that at the high-field side it is Maxwellian with a temperature of 5 -- 10 eV. The electron temperatures and the ion-saturation current density obtained were used to evaluate the radial distribution of the parallel power flux density as being in the order of 0.05 -- 7 MW/m 2 . (paper)

  6. Comparison of H-mode pedestals in different confinement regimes in DIII-D

    Energy Technology Data Exchange (ETDEWEB)

    Groebner, R J [General Atomics, PO Box 85608, San Diego, California, 92186-5608 (United States); Leonard, A W [General Atomics, PO Box 85608, San Diego, California, 92186-5608 (United States); Luce, T C [General Atomics, PO Box 85608, San Diego, California, 92186-5608 (United States); Fenstermacher, M E [Lawrence Livermore National Laboratory, Livermore, California (United States); Jackson, G L [General Atomics, PO Box 85608, San Diego, California, 92186-5608 (United States); Osborne, T H [General Atomics, PO Box 85608, San Diego, California, 92186-5608 (United States); Thomas, D M [General Atomics, PO Box 85608, San Diego, California, 92186-5608 (United States); Wade, M R [General Atomics, PO Box 85608, San Diego, California, 92186-5608 (United States)

    2006-05-15

    A survey of global performance parameters and their correlation with pedestal parameters is performed for standard H-mode, QH-mode and the enhanced confinement regimes of VH-mode, hybrid and advanced tokamak in the DIII-D tokamak. This study shows that there is a trend for global confinement quality or global beta to increase as the pedestal electron pressure or beta increases. However, there are also improvements in core confinement and beta, observed at fixed pedestal pressure or beta, which indicate that factors other than pedestal parameters also contribute to the best core performance. Several other pedestal structure parameters are found to be similar among these regimes. The scale lengths for electron pressure in the pedestal are in the range 0.8-1.6 cm at the outer midplane, most {eta}{sub e} values are in the range 1-3 in the middle of the T{sub e} pedestal and the T{sub e} and n{sub e} pedestals tend to penetrate the same distance into the plasma.

  7. Global gyrokinetic simulations of the H-mode tokamak edge pedestal

    Energy Technology Data Exchange (ETDEWEB)

    Wan, Weigang; Parker, Scott E.; Chen, Yang [Department of Physics, University of Colorado, Boulder, Colorado 80309 (United States); Groebner, Richard J. [General Atomics, Post Office Box 85068, San Diego, California 92186 (United States); Yan, Zheng [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Pankin, Alexei Y.; Kruger, Scott E. [Tech-X Corporation, 5621 Arapahoe Ave., Boulder, Colorado 80305 (United States)

    2013-05-15

    Global gyrokinetic simulations of DIII-D H-mode edge pedestal show two types of instabilities may exist approaching the onset of edge localized modes: an intermediate-n, high frequency mode which we identify as the “kinetic peeling ballooning mode (KPBM),” and a high-n, low frequency mode. Our previous study [W. Wan et al., Phys. Rev. Lett. 109, 185004 (2012)] has shown that when the safety factor profile is flattened around the steep pressure gradient region, the high-n mode is clearly kinetic ballooning mode and becomes the dominant instability. Otherwise, the KPBM dominates. Here, the properties of the two instabilities are studied by varying the density and temperature profiles. It is found that the KPBM is destabilized by density and ion temperature gradient, and the high-n mode is mostly destabilized by electron temperature gradient. Nonlinear simulations with the KPBM saturate at high levels. The equilibrium radial electric field (E{sub r}) reduces the transport. The effect of the parallel equilibrium current is found to be weak.

  8. Structure, stability and ELM dynamics of the H-mode pedestal in DIII-D

    International Nuclear Information System (INIS)

    Fenstermacher, M.E.; Leonard, A.W.; Osborne, T.H.

    2005-01-01

    Experiments are described that have increased understanding of the transport and stability physics that set the H-mode edge pedestal width and height, determine the onset of Type-I edge localized modes (ELMs), and produce the nonlinear dynamics of the ELM perturbation in the pedestal and scrape-off layer (SOL). Predictive models now exist for the n e pedestal profile and the p e height at the onset of Type-I ELMs, and progress has been made toward predictive models of the T e pedestal width and nonlinear ELM evolution. Similarity experiments between DIII-D and JET suggested that neutral penetration physics dominates in the relationship between the width and height of the n e pedestal while plasma physics dominates in setting the T e pedestal width. Measured pedestal conditions including edge current at ELM onset agree with intermediate-n peeling-ballooning (P-B) stability predictions. Midplane ELM dynamics data show the predicted (P-B) structure at ELM onset, large rapid variations of the SOL parameters, and fast radial propagation in later phases, similar to features in nonlinear ELM simulations. (author)

  9. Metal impurity transport control in JET H-mode plasmas with central ion cyclotron radiofrequency power injection

    DEFF Research Database (Denmark)

    Valisa, M.; Carraro, L.; Predebon, I.

    2011-01-01

    The scan of ion cyclotron resonant heating (ICRH) power has been used to systematically study the pump out effect of central electron heating on impurities such as Ni and Mo in H-mode low collisionality discharges in JET. The transport parameters of Ni and Mo have been measured by introducing...

  10. H-mode pedestal characteristics, ELMs, and energy confinement in ITER shape discharges on DIII-D

    International Nuclear Information System (INIS)

    Osborne, T.H.; Groebner, R.J.; Lao, L.L.; Leonard, A.W.; Miller, R.L.; Thomas, D.M.; Waltz, R.E.; Maingi, R.; Porter, G.D.

    1997-12-01

    The H-mode confinement enhancement factor, H, is found to be strongly correlated with the height of the edge pressure pedestal in ITER shape discharges. In discharges with Type I ELMs the pedestal pressure is set by the maximum pressure gradient before the ELM and the width of the H-mode transport barrier. The pressure gradient before Type I ELMs is found to scale as would be expected for a stability limit set by ideal ballooning modes, but with values significantly in excess of that predicted by stability code calculations. The width of the H-mode transport barrier is found to scale equally well with pedestal P(POL)(2/3) or B(POL)(1/2). The improved H value in high B(POL) discharges may be due to a larger edge pressure gradient and wider H-mode transport barrier consistent with their higher edge ballooning mode limit. Deuterium puffing is found to reduce H consistent with the smaller pedestal pressure which results from the reduced barrier width and critical pressure gradient. Type I ELM energy loss is found to be proportional to the change in the pedestal energy

  11. Differences in the H-mode pedestal width of temperature and density

    International Nuclear Information System (INIS)

    Schneider, P A; Wolfrum, E; Günter, S; Kurzan, B; Lackner, K; Zohm, H; Groebner, R J; Osborne, T H; Ferron, J R; Snyder, P B; Beurskens, M N A; Dunne, M G

    2012-01-01

    A pedestal database was built using data from type-I ELMy H-modes of ASDEX Upgrade, DIII-D and JET. ELM synchronized pedestal data were analysed with the two-line method. The two-line method is a bilinear fit which shows better reproducibility of pedestal parameters than a modified hyperbolic tangent fit. This was tested with simulated and experimental data. The influence of the equilibrium reconstruction on pedestal parameters was investigated with sophisticated reconstructions from CLISTE and EFIT including edge kinetic profiles. No systematic deviation between the codes could be observed. The flux coordinate system is influenced by machine size, poloidal field and plasma shape. This will change the representation of the width in different coordinates, in particular, the two normalized coordinates Ψ N and r/a show a very different dependence on the plasma shape. The scalings derived for the pedestal width, Δ, of all machines suggest a different scaling for the electron temperature and the electron density. Both cases show similar dependence with machine size, poloidal magnetic field and pedestal electron temperature and density. The influence of ion temperature and toroidal magnetic field is different on each of Δ T e and Δ n e . In dimensionless form the density pedestal width in Ψ N scales with ρ 0.6 i* , the temperature pedestal width with β p,ped 0.5 . Both widths also show a strong correlation with the plasma shape. The shape dependence originates from the coordinate transformation and is not visible in real space. The presented scalings predict that in ITER the temperature pedestal will be appreciably wider than the density pedestal. (paper)

  12. Quiescent H-mode operation using torque from non-axisymmetric, non-resonant magnetic fields

    International Nuclear Information System (INIS)

    Burrell, K.H.; Garofalo, A.M.; Osborne, T.H.; Snyder, P.B.; Solomon, W.M.; Park, J.-K.; Fenstermacher, M.E.; Orlov, D.M.

    2013-01-01

    Quiescent H-mode (QH-mode) sustained by magnetic torque from non-axisymmetric magnetic fields is a promising operating mode for future burning plasmas including ITER. Using magnetic torque from n = 3 fields to replace counter-I p torque from neutral beam injection, we have achieved long duration, counter-rotating QH-mode operation with neutral beam injection (NBI) torque ranging continuously from counter-I p up to co-I p values of about 1 N m. This co-I p torque is about 3 times the scaled torque that ITER will have. This range also includes operation at zero net NBI torque, applicable to rf wave heated plasmas. These n = 3 fields have been created using coils either inside or, most recently, outside the toroidal coils. Experiments utilized an ITER-relevant lower single-null plasma shape and were done with ITER-relevant values ν ped * ∼0.08, β T ped ∼ 1%$ and β N = 2. Discharges have confinement quality H 98y2 = 1.3, exceeding the value required for ITER. Initial work with low q 95 = 3.4 QH-mode plasmas transiently reached fusion gain values of G = β N H 89 /q 95 2 =0.4, which is the desired value for ITER; the limits on G have not yet been established. This paper also includes the most recent results on QH-mode plasmas run without n = 3 fields and with co-I p NBI; these shots exhibit co-I p plasma rotation and require NBI torque ⩾2 N m. The QH-mode work to date has made significant contact with theory. The importance of edge rotational shear is consistent with peeling–ballooning mode theory. We have seen qualitative and quantitative agreement with the predicted torque from neoclassical toroidal viscosity. (paper)

  13. First-wall heat-flux measurements during ELMing H-mode plasma

    International Nuclear Information System (INIS)

    Lasnier, C.J.; Allen, S.L.; Hill, D.N.; Leonard, A.W.; Petrie, T.W.

    1994-01-01

    In this report we present measurements of the diverter heat flux in DIII-D for ELMing H-mode and radiative diverter conditions. In previous work we have examined heat flux profiles in lower single-null diverted plasmas and measured the scaling of the peak heat flux with plasma current and beam power. One problem with those results was our lack of good power accounting. This situation has been improved to better than 80--90% accountability with the installation of new bolometer arrays, and the operation of the entire complement of 5 Infrared (IR) TV cameras using the DAPS (Digitizing Automated Processing System) video processing system for rapid inter-shot data analysis. We also have expanded the scope of our measurements to include a wider variety of plasma shapes (e.g., double-null diverters (DND), long and short single-null diverters (SND), and inside-limited plasmas), as well as more diverse discharge conditions. Double-null discharges are of particular interest because that shape has proven to yield the highest confinement (VH-mode) and beta of all DIII-D plasmas, so any future diverter modifications for DIII-D will have to support DND operation. In addition, the proposed TPX tokamak is being designed for double-null operation, and information on the magnitude and distribution of diverter heat flux is needed to support the engineering effort on that project. So far, we have measured the DND power sharing at the target plates and made preliminary tests of heat flux reduction by gas injection

  14. Pellet injection into H-mode ITER plasma with the presence of internal transport barriers

    Science.gov (United States)

    Leekhaphan, P.; Onjun, T.

    2011-04-01

    The impacts of pellet injection into ITER type-1 ELMy H-mode plasma with the presence of internal transport barriers (ITBs) are investigated using self-consistent core-edge simulations of 1.5D BALDUR integrated predictive modeling code. In these simulations, the plasma core transport is predicted using a combination of a semi-empirical Mixed B/gB anomalous transport model, which can self-consistently predict the formation of ITBs, and the NCLASS neoclassical model. For simplicity, it is assumed that toroidal velocity for ω E× B calculation is proportional to local ion temperature. In addition, the boundary conditions are predicted using the pedestal temperature model based on magnetic and flow shear stabilization width scaling; while the density of each plasma species, including both hydrogenic and impurity species, at the boundary are assumed to be a large fraction of its line averaged density. For the pellet's behaviors in the hot plasma, the Neutral Gas Shielding (NGS) model by Milora-Foster is used. It was found that the injection of pellet could result in further improvement of fusion performance from that of the formation of ITB. However, the impact of pellet injection is quite complicated. It is also found that the pellets cannot penetrate into a deep core of the plasma. The injection of the pellet results in a formation of density peak in the region close to the plasma edge. The injection of pellet can result in an improved nuclear fusion performance depending on the properties of pellet (i.e., increase up to 5% with a speed of 1 km/s and radius of 2 mm). A sensitivity analysis is carried out to determine the impact of pellet parameters, which are: the pellet radius, the pellet velocity, and the frequency of injection. The increase in the pellet radius and frequency were found to greatly improve the performance and effectiveness of fuelling. However, changing the velocity is observed to exert small impact.

  15. Temporal evolution of H-mode pedestal in DIII-D

    International Nuclear Information System (INIS)

    Groebner, R.J.; Osborne, T.H.; Leonard, A.W.; Fenstermacher, M.E.

    2009-01-01

    The temporal evolution of pedestal parameters is examined in the initial edge localized mode (ELM)-free phase and inter-ELM phases of H-mode discharges in the DIII-D tokamak. These discharges are heated by deuterium neutral beam injection and achieve type-I ELMing conditions. Pedestal parameters exhibit qualitatively similar behaviour in both the ELM-free and inter-ELM phases. There is a trend for the widths and heights of pedestals for electron density, temperature and pressure to increase during these phases; the increase in width is most pronounced in the density and least pronounced in electron temperature. Near the separatrix, the ion temperature achieves higher values but a flatter profile as compared with the electron temperature. Higher heating powers lead to a faster evolution of the pedestal and to a shorter period until the onset of an ELM. For sufficiently long ELM-free or inter-ELM periods, some parameters, particularly gradients, approach a steady state. However, a simultaneous steady state in all parameters is not observed. The simultaneous increase in density width and pedestal density is opposite to the predictions of a simple model, which predicts that the density width is set by neutral penetration. Thus, additional physics must be added to the simple model to provide a more general description of pedestal behaviour. However, the barrier growth is qualitatively consistent with time-dependent theoretical models that predict a self-consistent temporal growth of the pedestal due to E x B shearing effects. In addition, an approximate linear correlation is observed between the density width and the square root of the pedestal ion temperature and also between the density width and the square root of the pedestal beta poloidal. These pedestal studies suggest that a complete model of the pedestal width in type-I ELMing discharges must be time dependent, include transport physics during inter-ELM periods and include the limits to pedestal evolution

  16. Tungsten Transport in the Core of JET H-mode Plasmas, Experiments and Modelling

    Science.gov (United States)

    Angioni, Clemente

    2014-10-01

    The physics of heavy impurity transport in tokamak plasmas plays an essential role towards the achievement of practical fusion energy. Reliable predictions of the behavior of these impurities require the development of realistic theoretical models and a complete understanding of present experiments, against which models can be validated. Recent experimental campaigns at JET with the ITER-like wall, with a W divertor, provide an extremely interesting and relevant opportunity to perform this combined experimental and theoretical research. Theoretical models of both neoclassical and turbulent transport must consistently include the impact of any poloidal asymmetry of the W density to enable quantitative predictions of the 2D W density distribution over the poloidal cross section. The agreement between theoretical predictions and experimentally reconstructed 2D W densities allows the identification of the main mechanisms which govern W transport in the core of JET H-mode plasmas. Neoclassical transport is largely enhanced by centrifugal effects and the neoclassical convection dominates, leading to central accumulation in the presence of central peaking of the density profiles and insufficiently peaked ion temperature profiles. The strength of the neoclassical temperature screening is affected by poloidal asymmetries. Only around mid-radius, turbulent diffusion offsets neoclassical transport. Consistently with observations in other devices, ion cyclotron resonance heating in the plasma center can flatten the electron density profile and peak the ion temperature profile and provide a means to reverse the neoclassical convection. MHD activity may hamper or speed up the accumulation process depending on mode number and plasma conditions. Finally, the relationship of JET results to a parallel modelling activity of the W behavior in the core of ASDEX Upgrade plasmas is presented. This project has received funding from the European Union's Horizon 2020 research and innovation

  17. Power requirements for superior H-mode confinement on Alcator C-Mod: experiments in support of ITER

    International Nuclear Information System (INIS)

    Hughes, J.W.; Reinke, M.L.; Terry, J.L.; Brunner, D.; Greenwald, M.; Hubbard, A.E.; LaBombard, B.; Lipschultz, B.; Ma, Y.; Wolfe, S.; Wukitch, S.J.; Loarte, A.

    2011-01-01

    Power requirements for maintaining sufficiently high confinement (i.e. normalized energy confinement time H 98 ≥ 1) in H-mode and its relation to H-mode threshold power scaling, P th , are of critical importance to ITER. In order to better characterize these power requirements, recent experiments on the Alcator C-Mod tokamak have investigated H-mode properties, including the edge pedestal and global confinement, over a range of input powers near and above P th . In addition, we have examined the compatibility of impurity seeding with high performance operation, and the influence of plasma radiation and its spatial distribution on performance. Experiments were performed at 5.4 T at ITER relevant densities, utilizing bulk metal plasma facing surfaces and an ion cyclotron range of frequency waves for auxiliary heating. Input power was scanned both in stationary enhanced D α (EDA) H-modes with no large edge localized modes (ELMs) and in ELMy H-modes in order to relate the resulting pedestal and confinement to the amount of power flowing into the scrape-off layer, P net , and also to the divertor targets. In both EDA and ELMy H-mode, energy confinement is generally good, with H 98 near unity. As P net is reduced to levels approaching that in L-mode, pedestal temperature diminishes significantly and normalized confinement time drops. By seeding with low-Z impurities, such as Ne and N 2 , high total radiated power fractions are possible, along with substantial reductions in divertor heat flux (>4x), all while maintaining H 98 ∼ 1. When the power radiated from the confined versus unconfined plasma is examined, pedestal and confinement properties are clearly seen to be an increasing function of P net , helping to unify the results with those from unseeded H-modes. This provides increased confidence that the power flow across the separatrix is the correct physics basis for ITER extrapolation. The experiments show that P net /P th of one or greater is likely to lead to H

  18. Pedestal structure and stability in H-mode and I-mode: a comparative study on Alcator C-Mod

    International Nuclear Information System (INIS)

    Hughes, J.W.; Walk, J.R.; Davis, E.M.; LaBombard, B.; Baek, S.G.; Churchill, R.M.; Greenwald, M.; Hubbard, A.E.; Lipschultz, B.; Marmar, E.S.; Reinke, M.L.; Rice, J.E.; Theiler, C.; Terry, J.; White, A.E.; Whyte, D.G.; Snyder, P.B.; Groebner, R.J.; Osborne, T.; Diallo, A.

    2013-01-01

    New experimental data from the Alcator C-Mod tokamak are used to benchmark predictive modelling of the edge pedestal in various high-confinement regimes, contributing to greater confidence in projection of pedestal height and width in ITER and reactors. ELMy H-modes operate near stability limits for ideal peeling–ballooning modes, as shown by calculations with the ELITE code. Experimental pedestal width in ELMy H-mode scales as the square root of β pol at the pedestal top, i.e. the dependence expected from theory if kinetic ballooning modes (KBMs) were responsible for limiting the pedestal width. A search for KBMs in experiment has revealed a short-wavelength electromagnetic fluctuation in the pedestal that is a candidate driver for inter-edge localized mode (ELM) pedestal regulation. A predictive pedestal model (EPED) has been tested on an extended set of ELMy H-modes from C-Mod, reproducing pedestal height and width reasonably well across the data set, and extending the tested range of EPED to the highest absolute pressures available on any existing tokamak and to within a factor of three of the pedestal pressure targeted for ITER. In addition, C-Mod offers access to two regimes, enhanced D-alpha (EDA) H-mode and I-mode, that have high pedestals, but in which large ELM activity is naturally suppressed and, instead, particle and impurity transport are regulated continuously. Pedestals of EDA H-mode and I-mode discharges are found to be ideal magnetohydrodynamic (MHD) stable with ELITE, consistent with the general absence of ELM activity. Invocation of alternative physics mechanisms may be required to make EPED-like predictions of pedestals in these kinds of intrinsically ELM-suppressed regimes, which would be very beneficial to operation in burning plasma devices. (paper)

  19. Plasma dynamics with second and third-harmonic ECRH and access to quasi-stationary ELM-free H-mode on TCV

    International Nuclear Information System (INIS)

    Porte, L.; Coda, S.; Alberti, S.; Arnoux, G.; Blanchard, P.; Bortolon, A.; Fasoli, A.; Goodman, T.P.; Klimanov, Y.; Martin, Y.; Maslov, M.; Scarabosio, A.; Weisen, H.

    2007-01-01

    Intense electron cyclotron resonance heating (ECRH) and electron cyclotron current drive (ECCD) are employed on the Tokamak a Configuration Variable (TCV) both in second- and third-harmonic X-mode (X2 and X3). The plasma behaviour under such conditions is driven largely by the electron dynamics, motivating extensive studies of the heating and relaxation phenomena governing both the thermal and suprathermal electron populations. In particular, the dynamics of suprathermal electrons are intimately tied to the physics of X2 ECCD. ECRH is also a useful tool for manipulating the electron distribution function in both physical and velocity space. Fundamental studies of the energetic electron dynamics have been performed using periodic, low-duty-cycle bursts of ECRH, with negligible average power injection, and with electron cyclotron emission (ECE). The characteristic times of the dynamical evolution are clearly revealed. Suprathermal electrons have also been shown to affect the absorption of X3 radiation. Thermal electrons play a crucial role in high density plasmas where indirect ion heating can be achieved through ion-electron collisions. In recent experiments ∼ 1.35 MW of vertically launched X3 ECRH was coupled to a diverted ELMy H-mode plasma. In cases where ≥ 1.1 MW of ECRH power was coupled, the discharge was able to transition into a quasi-stationary ELM-free H-mode regime. These H-modes operated at β N ∼ 2, n-bar e /n G approx. 0.25 and had high energy confinement, H IPB98(y,2) up to ∼ 1.6. Despite being purely electron heated and having no net particle source these discharges maintained a density peaking factor (n e,o /(n e ) ∼ 1.6). They also exhibited spontaneous toroidal momentum production in the co-current direction. The momentum production is due to a transport process as there is no external momentum input. This process supports little or no radial gradient of the toroidal velocity

  20. Transition to ELM-free Improved H-mode by Lithium Deposition on NSTX Graphite Divertor Surfaces

    International Nuclear Information System (INIS)

    Mansfield, D.K.; Kugel, H.W.; Maingi, R.; Bell, M.G.; Bell, R.; Kaita, R.; Kallman, J.; Kaye, S.; LeBlanc, B.; Mueller, D.; Paul, S.; Raman, R.; Roquemore, L.; Sabbagh, S.; Schneider, H.; Skinner, C.H.; Soukhanovskii, V.; Timberlake, J.; Wilgen, J.; Zakharov, L.

    2009-01-01

    Lithium evaporated onto plasma facing components in the NSTX lower divertor has made dramatic improvements in discharge performance. As lithium accumulated, plasmas previously exhibiting robust Type 1 ELMs gradually transformed into discharges with intermittent ELMs and finally into continuously evolving ELM-free discharges. During this sequence, other discharge parameters changed in a complicated manner. As the ELMs disappeared, energy confinement improved and remarkable changes in edge and scrape-off layer plasma properties were observed. These results demonstrate that active modification of plasma surface interactions can preempt large ELMs.

  1. ELMy-H mode as limit cycle and chaotic oscillations in tokamak plasmas

    International Nuclear Information System (INIS)

    Itoh, Sanae; Itoh, Kimitaka; Fukuyama, Atsushi.

    1991-06-01

    A model of Edge Localized Modes (ELMs) in tokamaks is presented. A limit cycle solution is found in time-dependent Ginzburg Landau type model equation of L/H transition, which has a hysteresis curve between the plasma gradient and flux. The oscillation of edge density appears near the L/H transition boundary. Spatial structure of the intermediate state (mesophase) is obtained in the edge region. Chaotic oscillation is predicted due to random neutrals and external oscillations. (author)

  2. Pellet injection into H-mode ITER plasma with the presence of internal transport barriers

    Energy Technology Data Exchange (ETDEWEB)

    Leekhaphan, P. [Thammasat University, School of Bio-Chemical Engineering and Technology, Sirindhorn International Institute of Technology (Thailand); Onjun, T. [Thammasat University, School of Manufacturing Systems and Mechanical Engineering, Sirindhorn International Institute of Technology (Thailand)

    2011-04-15

    The impacts of pellet injection into ITER type-1 ELMy H-mode plasma with the presence of internal transport barriers (ITBs) are investigated using self-consistent core-edge simulations of 1.5D BALDUR integrated predictive modeling code. In these simulations, the plasma core transport is predicted using a combination of a semi-empirical Mixed B/gB anomalous transport model, which can self-consistently predict the formation of ITBs, and the NCLASS neoclassical model. For simplicity, it is assumed that toroidal velocity for {omega}{sub E Multiplication-Sign B} calculation is proportional to local ion temperature. In addition, the boundary conditions are predicted using the pedestal temperature model based on magnetic and flow shear stabilization width scaling; while the density of each plasma species, including both hydrogenic and impurity species, at the boundary are assumed to be a large fraction of its line averaged density. For the pellet's behaviors in the hot plasma, the Neutral Gas Shielding (NGS) model by Milora-Foster is used. It was found that the injection of pellet could result in further improvement of fusion performance from that of the formation of ITB. However, the impact of pellet injection is quite complicated. It is also found that the pellets cannot penetrate into a deep core of the plasma. The injection of the pellet results in a formation of density peak in the region close to the plasma edge. The injection of pellet can result in an improved nuclear fusion performance depending on the properties of pellet (i.e., increase up to 5% with a speed of 1 km/s and radius of 2 mm). A sensitivity analysis is carried out to determine the impact of pellet parameters, which are: the pellet radius, the pellet velocity, and the frequency of injection. The increase in the pellet radius and frequency were found to greatly improve the performance and effectiveness of fuelling. However, changing the velocity is observed to exert small impact.

  3. A new boundary control scheme for simultaneous achievement of H-mode and radiative cooling (SHC boundary)

    International Nuclear Information System (INIS)

    Ohyabu, N.

    1995-05-01

    We have proposed a new boundary control scheme (SHC boundary), which could allow simultaneous achievement of the H-mode type confinement improvement and radiative cooling with wide heat flux distribution. In our proposed configuration, a low m island layer sharply separates a plasma confining region from an open 'ergodic' boundary. The degree of openness in the ergodic boundary must be high enough to make the plasma pressure constant along the field line, which in turn separates low density plasma just outside the plasma confining region (the key external condition for achieving a good H-mode discharge) from very high density, cold radiative plasma near the wall (required for effective edge radiative cooling). Examples of such proposed SHC boundaries for Heliotron typed devices and tokamaks are presented. (author)

  4. Characterisation of the ELM synchronized H-mode edge pedestal in ASDEX upgrade and DIII-D

    Energy Technology Data Exchange (ETDEWEB)

    Schneider, Philip A.; Wolfrum, Elisabeth; Guenter, Sibylle; Kurzan, Bernd; Zohm, Hartmut [Max Planck Institut fuer Plasmaphysik, EURATOM Association, Garching (Germany); Groebner, Rich; Osborne, Tom H.; Ferron, John; Snyder, Philip B. [General Atomics, San Diego, CA (United States); Dunne, Mike G. [Department of Physics, University College Cork, Association Euratom-DCU, Cork (Ireland); Collaboration: ASDEX Upgrade Team; DIII-D Team

    2011-07-01

    The results of a large database of edge pedestal data from type-I ELMy H-mode discharges from ASDEX Upgrade and DIII-D are presented. The data from high resolution edge diagnostics of both devices is analysed with the same analysis code in order to avoid systematic differences. Furthermore, sophisticated equilibrium reconstructions are used to asses uncertainties which arise during mapping from 2D real space coordinates to 1D flux coordinates. ELM synchronization allows the study of the pedestal structure at the ELM stability boundary. The pedestal is characterized by its top value, the gradient and the width. A large parameter range is covered by the two devices. Over this parameter range the profile shape of edge electron density differs from that of the temperature, irrespective of the device. However, the resulting electron pressure profile shape remains similar for all analysed H-Mode discharges.

  5. Scaling of ELM and H-mode pedestal characteristics in ITER shape discharges in the DIII-D tokamak

    International Nuclear Information System (INIS)

    Osborne, T.H.; Groebner, R.J.; Lao, L.L.; Leonard, A.W.; Miller, R.L.; Thomas, D.M.; Waltz, R.E.; Maingi, R.; Porter, G.D.

    1997-07-01

    The authors have shown a correlation between the H-mode pressure pedestal height and the energy confinement enhancement in ITER shape discharges on DIII-D which is consistent with the behavior of H in different ELM classes. The width of the steep gradient region was found to equally well fit the scalings δ/R ∝ (ρ POL /R) 2/3 and δ/R ∝ (β POL PED /R) 1/2 . The normalized pressure gradient α MHD was found to be relatively constant just before a type I ELM. An estimate of T PED for ITER gave 1 to 5 keV. They also estimate ΔE ELM ≅ 26 MJ for ITER. They identified a distinct class of type III ELM at low density which may play a role in setting H at powers near the H-mode threshold power

  6. H-mode access during plasma current ramp-up in TCV

    International Nuclear Information System (INIS)

    Martin, Y.; Behn, R.; Furno, I.; Labit, B.; Reimerdes, H.

    2014-01-01

    A recent TCV experiment has investigated the dependence of the L–H transition threshold power on the plasma current ramp-rate and the X-point height above the divertor target, which both have previously been seen to affect the transition behaviour. Systematic scans in ohmically heated plasmas do not show any dependence on the plasma current ramp-up rate. In contrast, the threshold power is found to increase by a factor of two while the X-point is moved from about 10 cm up to 35 cm above the vessel floor. However, further increase, up to 60 cm, does not lead to any further increase of the required power. The Fundamenski et al model is tested against the measurements. Estimates of the Wagner number (Wa) at L–H transitions are generally close to unity, in accordance with the model. In contrast, estimates of Wa before the L–H transition, i.e. in L-mode, do not show the expected evolution towards unity. (paper)

  7. One-dimensional modelling of limit-cycle oscillation and H-mode power scaling

    DEFF Research Database (Denmark)

    Wu, Xingquan; Xu, Guosheng; Wan, Baonian

    2015-01-01

    To understand the connection between the dynamics of microscopic turbulence and the macroscale power scaling in the L-I-H transition in magnetically confined plasmas, a new time-dependent, one-dimensional (in radius) model has been developed. The model investigates the radial force balance equati...

  8. Application of the H-Mode, a Design and Interaction Concept for Highly Automated Vehicles, to Aircraft

    Science.gov (United States)

    Goodrich, Kenneth H.; Flemisch, Frank O.; Schutte, Paul C.; Williams, Ralph A.

    2006-01-01

    Driven by increased safety, efficiency, and airspace capacity, automation is playing an increasing role in aircraft operations. As aircraft become increasingly able to autonomously respond to a range of situations with performance surpassing human operators, we are compelled to look for new methods that help us understand their use and guide their design using new forms of automation and interaction. We propose a novel design metaphor to aid the conceptualization, design, and operation of highly-automated aircraft. Design metaphors transfer meaning from common experiences to less familiar applications or functions. A notable example is the "Desktop metaphor" for manipulating files on a computer. This paper describes a metaphor for highly automated vehicles known as the H-metaphor and a specific embodiment of the metaphor known as the H-mode as applied to aircraft. The fundamentals of the H-metaphor are reviewed followed by an overview of an exploratory usability study investigating human-automation interaction issues for a simple H-mode implementation. The envisioned application of the H-mode concept to aircraft is then described as are two planned evaluations.

  9. Effect of Wave Accessibility on Lower Hybrid Wave Current Drive in Experimental Advanced Superconductor Tokamak with H-Mode Operation

    International Nuclear Information System (INIS)

    Li Xin-Xia; Xiang Nong; Gan Chun-Yun

    2015-01-01

    The effect of the wave accessibility condition on the lower hybrid current drive in the experimental advanced superconductor Tokamak (EAST) plasma with H-mode operation is studied. Based on a simplified model, a mode conversion layer of the lower hybrid wave between the fast wave branch and the slow wave branch is proved to exist in the plasma periphery for typical EAST H-mode parameters. Under the framework of the lower hybrid wave simulation code (LSC), the wave ray trajectory and the associated current drive are calculated numerically. The results show that the wave accessibility condition plays an important role on the lower hybrid current drive in EAST plasma. For wave rays with parallel refractive index n ‖ = 2.1 or n ‖ = 2.5 launched from the outside midplane, the wave rays may penetrate the core plasma due to the toroidal geometry effect, while numerous reflections of the wave ray trajectories in the plasma periphery occur. However, low current drive efficiency is obtained. Meanwhile, the wave accessibility condition is improved if a higher confined magnetic field is applied. The simulation results show that for plasma parameters under present EAST H-mode operation, a significant lower hybrid wave current drive could be obtained for the wave spectrum with peak value n ‖ = 2.1 if a toroidal magnetic field B T = 2.5 T is applied. (paper)

  10. Study on H-mode access at low density with lower hybrid current drive and lithium-wall coatings on the EAST superconducting tokamak

    DEFF Research Database (Denmark)

    Xu, G.S.; Wan, B.N.; Li, J.G.

    2011-01-01

    The first high-confinement mode (H-mode) with type-III edge localized modes at an H factor of HIPB98(y,2) ~ 1 has been obtained with about 1 MW lower hybrid wave power on the EAST superconducting tokamak. The first H-mode plasma appeared after wall conditioning by lithium (Li) evaporation before ...

  11. Magnetic perturbation experiments on MAST L- and H-mode plasmas using internal coils

    Czech Academy of Sciences Publication Activity Database

    Kirk, A.; Liu, Y.Q.; Nardon, E.; Tamain, P.; Cahyna, Pavel; Chapman, I.; Denner, P.; Meyer, H.; Mordijck, S.; Temple, D.

    2011-01-01

    Roč. 53, č. 6 (2011), 065011-065011 ISSN 0741-3335 R&D Projects: GA ČR GAP205/11/2341 Institutional research plan: CEZ:AV0Z20430508 Keywords : Resonant magnetic perturbations * L-H transition * spherical tokamaks * edge localized modes Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.425, year: 2011 http://dx.doi.org/10.1088/0741-3335/53/6/065011

  12. ELMy-H mode as limit cycle and chaotic oscillations in tokamak plasmas

    International Nuclear Information System (INIS)

    Itoh Sanae, I.; Itoh, Kimitaka; Fukuyama, Atsushi; Miura, Yukitoshi.

    1991-05-01

    A model of Edge Localized Modes (ELMs) in tokamak plasmas is presented. A limit cycle solution is found in the transport equation (time-dependent Ginzburg-Landau type), which a has hysteresis curve between the gradient and flux. Periodic oscillation of the particle outflux and L/H intermediate state are predicted near the L/H transition boundary. A mesophase in spatial structure appears near edge. Chaotic oscillation is also predicted. (author)

  13. TRANSIT

    Indian Academy of Sciences (India)

    First page Back Continue Last page Overview Graphics. TRANSIT. SYSTEM: DETERMINE 2D-POSITION GLOBALLY BUT INTERMITTENT (POST-FACTO). IMPROVED ACCURACY. PRINCIPLE: POLAR SATELLITES WITH INNOVATIONS OF: GRAVITY-GRADIENT ATTITUDE CONTROL; DRAG COMPENSATION. WORKS ...

  14. Validation of neoclassical bootstrap current models in the edge of an H-mode plasma.

    Science.gov (United States)

    Wade, M R; Murakami, M; Politzer, P A

    2004-06-11

    Analysis of the parallel electric field E(parallel) evolution following an L-H transition in the DIII-D tokamak indicates the generation of a large negative pulse near the edge which propagates inward, indicative of the generation of a noninductive edge current. Modeling indicates that the observed E(parallel) evolution is consistent with a narrow current density peak generated in the plasma edge. Very good quantitative agreement is found between the measured E(parallel) evolution and that expected from neoclassical theory predictions of the bootstrap current.

  15. Transport analysis of the edge zone of H-mode plasmas by computer simulation

    International Nuclear Information System (INIS)

    Becker, G.; Murmann, H.

    1988-01-01

    Local transport and ideal ballooning stability in the L-phase and ELM-free H-phase in ASDEX are analysed by computer modelling. It is found that the diffusivities χ e and D at the edge are reduced by a factor of six a few milliseconds after the H-transition. Local transport in the inner plasma improves at an early stage by a typical factor of two. A change in the collisionality regime of electrons and ions does not take place. During the L-phase and the quiescent H-phase ideal ballooning modes are found to be stable. Computer experiments further show that a significant reduction in the particle flux at the separatrix takes place which is closely connected with the H-transition process. This explains the observed buildup of a density shoulder on a millisecond time-scale and the drop of the particle flow into the divertor. A strong decrease of the electron heat conduction flux at the separatrix is, however, ruled out in ELM-free periods. On the assumption of electrostatic turbulence induced transport, these results are consistent with measured density fluctuation levels near the separatrix. (author). 20 refs, 9 figs

  16. Thermo-mechanical and damage analyses of EAST carbon divertor under type-I ELMy H-mode operation

    Energy Technology Data Exchange (ETDEWEB)

    Li, W.X. [School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230026 (China); Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Song, Y.T. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230026 (China); Ye, M.Y. [School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230026 (China); Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Peng, X.B., E-mail: pengxb@ipp.ac.cn [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Wu, S.T. [School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230026 (China); Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Qian, X.Y.; Zhu, C.C. [School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230026 (China)

    2016-04-15

    Highlights: • Type-I ELMy H-mode is one of the most severe operating environment in tokamak. • An actual time-history heat load has been used in thermo-mechanical analysis. • The analysis results are time-dependent during the whole discharge process. • The analysis could be very useful in evaluating the operational capability of the divertor. - Abstract: The lower carbon divertor has been used since 2008 in EAST, and many significant physical results, like the 410 s long pulse discharge and the 32 s H-mode operation, have been achieved. As the carbon divertor will still be used in the next few years while the injected auxiliary heating power would be increased gradually, it’s necessary to evaluate the operational capability of the carbon divertor under the heat loads during future operation. In this paper, an actual time-history heat load during type-I ELMy H-mode from EAST experiment, as one of the most severe operating environment in tokamak, has been used in the calculation and analysis. The finite element (FE) thermal and mechanical calculations have been carried out to analysis the stress and deformation of the carbon divertor during the heat loads. According to the results, the main impact on the overall temperature comes from the relative stable phase before and after the type-I ELMs and local peak load, and the transient thermal load such as type-I ELMy only has a significant effect on the surface temperature of the graphite tiles. The carbon divertor would work with high stress near the screw bolts in the current operational conditions, because of high preload and conservative frictional coefficient between the bolts and heatsink. For the future operation, new plasma facing materials (PFM) and divertor technology should be developed.

  17. Long sustainment of quasi-steady-state high βp H mode discharges in JT-60U

    International Nuclear Information System (INIS)

    Isayama, A.; Kamada, Y.; Ozeki, T.; Ide, S.; Fujita, T.; Oikawa, T.; Suzuki, T.; Neyatani, Y.; Isei, N.; Hamamatsu, K.; Ikeda, Y.; Takahashi, K.; Kajiwara, K.

    2001-01-01

    Quasi-steady-state high β p H mode discharges performed by suppressing neoclassical tearing modes (NTMs) are described. Two operational scenarios have been developed for long sustainment of the high β p H mode discharge: NTM suppression by profile optimization, and NTM stabilization by local electron cyclotron current drive (ECCD)/electron cyclotron heating (ECH) at the magnetic island. Through optimization of pressure and safety factor profiles, a high β p H mode plasma with H 89PL = 2.8, HH y,2 = 1.4, β p ∼ 2.0 and β N ∼ 2.5 has been sustained for 1.3 s at small values of collisionality ν e* and ion Larmor radius ρ i* without destabilizing the NTMs. Characteristics of the NTMs destabilized in the region with central safety factor above unity are investigated. The relation between the beta value at the mode onset β N on and that at the mode disappearance β N off can be described as β N off /β N on =0.05-0.4, which shows the existence of hysteresis. The value of β N /ρ i* at the onset of an m/n = 3/2 NTM has a collisionality dependence, which is empirically given by β N /ρ i* ∝ ν e* 0.36 . However, the profile effects such as the relative shapes of pressure and safety factor profiles are equally important. The onset condition seems to be affected by the strength of the pressure gradient at the mode rational surface. Stabilization of the NTM by local ECCD/ECH at the magnetic island has been attempted. A 3/2 NTM has been completely stabilized by EC wave injection of 1.6 MW. (author)

  18. Role of Density Gradient Driven Trapped Electron Modes in the H-Mode Inner Core with Electron Heating

    Science.gov (United States)

    Ernst, D.

    2015-11-01

    We present new experiments and nonlinear gyrokinetic simulations showing that density gradient driven TEM (DGTEM) turbulence dominates the inner core of H-Mode plasmas during strong electron heating. Thus α-heating may degrade inner core confinement in H-Mode plasmas with moderate density peaking. These DIII-D low torque quiescent H-mode experiments were designed to study DGTEM turbulence. Gyrokinetic simulations using GYRO (and GENE) closely match not only particle, energy, and momentum fluxes, but also density fluctuation spectra, with and without ECH. Adding 3.4 MW ECH doubles Te /Ti from 0.5 to 1.0, which halves the linear TEM critical density gradient, locally flattening the density profile. Density fluctuations from Doppler backscattering (DBS) intensify near ρ = 0.3 during ECH, displaying a band of coherent fluctuations with adjacent toroidal mode numbers. GYRO closely reproduces the DBS spectrum and its change in shape and intensity with ECH, identifying these as coherent TEMs. Prior to ECH, parallel flow shear lowers the effective nonlinear DGTEM critical density gradient 50%, but is negligible during ECH, when transport displays extreme stiffness in the density gradient. GS2 predictions show the DGTEM can be suppressed, to avoid degradation with electron heating, by broadening the current density profile to attain q0 >qmin > 1 . A related experiment in the same regime varied the electron temperature gradient in the outer half-radius (ρ ~ 0 . 65) using ECH, revealing spatially coherent 2D mode structures in the Te fluctuations measured by ECE imaging. Fourier analysis with modulated ECH finds a threshold in Te profile stiffness. Supported by the US DOE under DE-FC02-08ER54966 and DE-FC02-04ER54698.

  19. Low-n magnetohydrodynamic edge instabilities in quiescent H-mode plasmas with a safety-factor plateau

    International Nuclear Information System (INIS)

    Zheng, L.J.; Kotschenreuther, M.T.; Valanju, P.

    2013-01-01

    Low-n magnetohydrodynamic (MHD) modes in the quiescent high confinement mode (H-mode) pedestal are investigated in this paper. Here, n is the toroidal mode number. The low collisionality regime is considered, so that a safety-factor plateau arises in the pedestal region because of the strong bootstrap current. The JET-like (Joint European Torus) equilibria of quiescent H-mode discharges are generated numerically using the VMEC code. The stability of this type of equilibria is analysed using the AEGIS code, with subsonic rotation effects taken into account. The current investigation extends the previous studies of n = 1 modes to n = 2 and 3 modes. The numerical results show that the MHD instabilities in this type of equilibria have characteristic features of the infernal mode. We find that this type of mode tends to prevail when the safety-factor value in the shear-free region is slightly larger than an integer. In this case the frequencies (ω n ) of modes with toroidal mode number n roughly follow the rule ω n ∼ −nΩ p , where Ω p is the local rotation frequency where the infernal harmonic prevails. Since the infernal mode tends to develop near the pedestal top, where pressure driving is strong but magnetic shear stabilization is weak, this local rotation frequency tends to be close to the pedestal top value. These typical mode features bear close resemblance to the edge harmonic oscillations (or outer modes) at the quiescent H-mode discharges observed experimentally. (paper)

  20. MHD-induced Energetic Ion Loss during H-mode Discharges in the National Spherical Torus Experiment (NSTX)

    Energy Technology Data Exchange (ETDEWEB)

    S.S. Medley; N.N. Gorelenkov; R. Andre; R.E. Bell; D.S. Darrow; E.D. Fredrickson; S.M. Kaye; B.P. LeBlanc; A.L. Roquemore; and the NSTX Team

    2004-03-15

    MHD-induced energetic ion loss in neutral-beam-heated H-mode [high-confinement mode] discharges in NSTX [National Spherical Torus Experiment] is discussed. A rich variety of energetic ion behavior resulting from magnetohydrodynamic (MHD) activity is observed in the NSTX using a horizontally scanning Neutral Particle Analyzer (NPA) whose sightline views across the three co-injected neutral beams. For example, onset of an n = 2 mode leads to relatively slow decay of the energetic ion population (E {approx} 10-100 keV) and consequently the neutron yield. The effect of reconnection events, sawteeth, and bounce fishbones differs from that observed for low-n, low-frequency, tearing-type MHD modes. In this case, prompt loss of the energetic ion population occurs on a time scale of less than or equal to 1 ms and a precipitous drop in the neutron yield occurs. This paper focuses on MHD-induced ion loss during H-mode operation in NSTX. After H-mode onset, the NPA charge-exchange spectrum usually exhibits a significant loss of energetic ions only for E > E(sub)b/2 where E(sub)b is the beam injection energy. The magnitude of the energetic ion loss was observed to decrease with increasing tangency radius, R(sub)tan, of the NPA sightline, increasing toroidal field, B(sub)T, and increasing neutral-beam injection energy, E(sub)b. TRANSP modeling suggests that MHD-induced ion loss is enhanced during H-mode operation due to an evolution of the q and beam deposition profiles that feeds both passing and trapped ions into the region of low-n MHD activity. ORBIT code analysis of particle interaction with a model magnetic perturbation supported the energy selectivity of the MHD-induced loss observed in the NPA measurements. Transport analysis with the TRANSP code using a fast-ion diffusion tool to emulate the observed MHD-induced energetic ion loss showed significant modifications of the neutral- beam heating as well as the power balance, thermal diffusivities, energy confinement times

  1. MHD-induced Energetic Ion Loss during H-mode Discharges in the National Spherical Torus Experiment (NSTX)

    International Nuclear Information System (INIS)

    Medley, S.S.; Gorelenkov, N.N.; Andre, R.; Bell, R.E.; Darrow, D.S.; Fredrickson, E.D.; Kaye, S.M.; LeBlanc, B.P.; Roquemore, A.L.

    2004-01-01

    MHD-induced energetic ion loss in neutral-beam-heated H-mode [high-confinement mode] discharges in NSTX [National Spherical Torus Experiment] is discussed. A rich variety of energetic ion behavior resulting from magnetohydrodynamic (MHD) activity is observed in the NSTX using a horizontally scanning Neutral Particle Analyzer (NPA) whose sightline views across the three co-injected neutral beams. For example, onset of an n = 2 mode leads to relatively slow decay of the energetic ion population (E ∼ 10-100 keV) and consequently the neutron yield. The effect of reconnection events, sawteeth, and bounce fishbones differs from that observed for low-n, low-frequency, tearing-type MHD modes. In this case, prompt loss of the energetic ion population occurs on a time scale of less than or equal to 1 ms and a precipitous drop in the neutron yield occurs. This paper focuses on MHD-induced ion loss during H-mode operation in NSTX. After H-mode onset, the NPA charge-exchange spectrum usually exhibits a significant loss of energetic ions only for E > E(sub)b/2 where E(sub)b is the beam injection energy. The magnitude of the energetic ion loss was observed to decrease with increasing tangency radius, R(sub)tan, of the NPA sightline, increasing toroidal field, B(sub)T, and increasing neutral-beam injection energy, E(sub)b. TRANSP modeling suggests that MHD-induced ion loss is enhanced during H-mode operation due to an evolution of the q and beam deposition profiles that feeds both passing and trapped ions into the region of low-n MHD activity. ORBIT code analysis of particle interaction with a model magnetic perturbation supported the energy selectivity of the MHD-induced loss observed in the NPA measurements. Transport analysis with the TRANSP code using a fast-ion diffusion tool to emulate the observed MHD-induced energetic ion loss showed significant modifications of the neutral- beam heating as well as the power balance, thermal diffusivities, energy confinement times, and

  2. Evaluation of Particle Pinch and Diffusion Coefficients in the Edge Pedestal of DIII-D H-mode Discharges

    Science.gov (United States)

    Stacey, W. M.; Groebner, R. J.

    2009-11-01

    Momentum balance requires that the radial particle flux satisfy a pinch-diffusion relationship. The pinch can be evaluated in terms of measurable quantities (rotation velocities, Er, etc.) by the use of momentum and particle balance [1,2], the radial particle flux can be determined by momentum balance, and then the diffusion coefficient can be evaluated from the pinch diffusion relation using the measured density gradient. Applications to several DIII-D H-mode plasmas are presented. 6pt [1] W.M. Stacey, Contr. Plasma Phys. 48, 94 (2008). [2] W.M. Stacey and R.J. Groebner, Phys. Plasmas 15, 012503 (2008).

  3. Studies of Turbulence and Transport in Alcator C-Mod H-Mode Plasmas with Phase Contrast Imaging and Comparisons with GYRO

    Science.gov (United States)

    Porkolab, M.; Lin, L.; Edlund, E. M.; Rost, J. C.; Fiore, C. L.; Greenwald, M.; Mikkelsen, D.

    2008-11-01

    We present recent experimental measurements of turbulence and transport in C-Mod H-Mode plasmas with and without internal transport barriers (ITB) using the phase contrast imaging (PCI) diagnostic and compare the results with GYRO predictions. In plasmas without ITB, the fluctuation above 300 kHz observed by PCI agrees with ITG in GYRO simulation, including the direction of propagation, wavenumber spectrum, and absolute intensity within experimental uncertainly (+/-75%). After transition to ITBs, the observed overall fluctuation intensity increases. GYRO simulation in the core shows that ITG dominates in ITBs but its intensity is lower than the overall experimental measurements which may also include contributions from the plasma edge. These results, as well as the impact of varying ∇Ti, ∇n, and ExB shear on turbulence will be discussed. C.L. Fiore et al., Fusion Sci. Technol., 51, 303 (2007). M. Porkolab et al., IEEE Trans. Plasma Sci. 34, 229 (2006). J. Candy et al., Phys. Rev. Lett., 91, 045001 (2003).

  4. Heuristic Drift-based Model of the Power Scrape-off width in H-mode Tokamaks

    International Nuclear Information System (INIS)

    Goldston, Robert J.

    2011-01-01

    An heuristic model for the plasma scrape-off width in H-mode plasmas is introduced. Grad B and curv B drifts into the SOL are balanced against sonic parallel flows out of the SOL, to the divertor plates. The overall particle flow pattern posited is a modification for open field lines of Pfirsch-Shlueter flows to include sinks to the divertors. These assumptions result in an estimated SOL width of ∼ 2αρ p /R. They also result in a first-principles calculation of the particle confinement time of H-mode plasmas, qualitatively consistent with experimental observations. It is next assumed that anomalous perpendicular electron thermal diffusivity is the dominant source of heat flux across the separatrix, investing the SOL width, defined above, with heat from the main plasma. The separatrix temperature is calculated based on a two-point model balancing power input to the SOL with Spitzer-Haerm parallel thermal conduction losses to the divertor. This results in a heuristic closed-form prediction for the power scrape-off width that is in reasonable quantitative agreement both in absolute magnitude and in scaling with recent experimental data from deuterium plasmas. Further work should include full numerical calculations, including all magnetic and electric drifts, as well as more thorough comparison with experimental data.

  5. Effect of variation in equilibrium shape on ELMing H-mode performance in DIII-D diverted plasmas

    International Nuclear Information System (INIS)

    Fenstermacher, M.E.; Osborne, T.H.; Petrie, T.W.

    2001-01-01

    The changes in the performance of the core, pedestal, scrape-off-layer (SOL), and divertor plasmas as a result of changes in triangularity, δ, up/down magnetic balance, and secondary divertor volume were examined in shape variation experiments using ELMing H mode plasmas on DIII-D. In moderate density, unpumped plasmas, high δ∼0.7 increased the energy in the H mode pedestal and the global energy confinement of the core, primarily due to an increase in the margin by which the edge pressure gradient exceeded the value which would have been expected had it been limited by infinite-n ideal ballooning modes. In addition, a nearly balanced double-null (DN) shape was effective for sharing the peak heat flux in the divertor in these attached plasmas. For detached plasmas good heat flux sharing was obtained for a substantial range of unbalanced DN shapes. Finally, the presence of a second X-point in unbalanced DN shapes did not degrade the plasma performance if it was sufficiently far inside the vacuum vessel. These results indicate that a high δ unbalanced DN shape has some advantages over a single null shape for future high power tokamak operation. (author)

  6. Ion thermal conductivity and convective energy transport in JET hot-ion regimes and H-modes

    International Nuclear Information System (INIS)

    Tibone, F.; Balet, B.; Cordey, J.G.

    1989-01-01

    Local transport in a recent series of JET experiments has been studied using interpretive codes. Auxiliary heating, mainly via neutral beam injection, was applied on low-density target plasmas confined in the double-null X-point configuration. This has produced two-component plasmas with high ion temperature and neutron yield and, above a threshold density, H-modes characterised by peak density and power deposition profiles. H-mode confinement was also obtained for the first time with 25 MW auxiliary power, of which 10 MW was from ion cyclotron resonance heating. We have used profile measurements of electron temperature T e from electron cyclotron emission and LIDAR Thomson scattering, ion temperature T i from charge-exchange recombination spectroscopy (during NBI), electron density n e from LIDAR and Abel-inverted interferometer measurements. Only sparse information is, however, available to date concerning radial profiles of effective ionic charge and radiation losses. Deuterium depletion due to high impurity levels is an important effect in these discharges, and our interpretation of thermal ion energy content, neutron yield and ion particle fluxes needs to be confirmed using measured Z eff -profiles. (author) 4 refs., 4 figs

  7. An Heuristic Drift-Based Model of the Power Scrape-Off Width in H-Mode Tokamaks

    International Nuclear Information System (INIS)

    Goldston, Robert J.

    2011-01-01

    An heuristic model for the plasma scrape-off width in H-mode plasmas is introduced. Grad B and curv B drifts into the SOL are balanced against sonic parallel flows out of the SOL, to the divertor plates. The overall mass flow pattern posited is a modification for open field lines of Pfirsch-Shlueter flows to include sinks to the divertors. These assumptions result in an estimated SOL width of 2αρ p /R. They also result in a first-principles calculation of the particle confinement time of H-mode plasmas, qualitatively consistent with experimental observations. It is next assumed that anomalous perpendicular electron thermal diffusivity is the dominant source of heat flux across the separatrix, investing the SOL width, defined above, with heat from the main plasma. The separatrix temperature is calculated based on a two-point model balancing power input to the SOL with Spitzer-Haerm parallel thermal conduction losses to the divertor. This results in an heuristic closed-form prediction for the power scrape-off width that is in remarkable quantitative agreement both in absolute magnitude and in scaling with recent experimental data. Further work should include full numerical calculations, including all magnetic and electric drifts, as well as more thorough comparison with experimental data.

  8. Effects of triangularity on confinement, density limit and profile stiffness of H-modes on ASDEX upgrade

    International Nuclear Information System (INIS)

    Stober, J.; Gruber, O.; Kallenbach, A.; Mertens, V.; Ryter, F.; Staebler, A.; Suttrop, W.; Treutterer, W.

    2000-01-01

    At ASDEX Upgrade the influence of triangularity on the H-mode performance has been studied intensively. It has been found that confinement increases with δ for a fixed line-averaged density. Though confinement decreases with increasing density for all analysed values of δ, H-factors (ITERH-98P) at the Greenwald density could be raised to 1 for the highest δ values achieved so far. The H-mode density limit could be increased by approx. 20%. There is a scatter of about 30% on the confinement data, which is anti-correlated to the average density in the scrape-off layer or the neutral fluxes outside the plasma. For nearly all discharges analysed so far, the temperature profiles are self-similar. This indication of profile stiffness could be verified by changing the heat-flux profile by changing the beam-voltage of the neutral-beam injection (NBI) at high density. At low density, first results indicate a deviation from this stiff behaviour. (author)

  9. Stabilizing effect of resistivity towards ELM-free H-mode discharge in lithium-conditioned NSTX

    Science.gov (United States)

    Banerjee, Debabrata; Zhu, Ping; Maingi, Rajesh

    2017-07-01

    Linear stability analysis of the national spherical torus experiment (NSTX) Li-conditioned ELM-free H-mode equilibria is carried out in the context of the extended magneto-hydrodynamic (MHD) model in NIMROD. The purpose is to investigate the physical cause behind edge localized mode (ELM) suppression in experiment after the Li-coating of the divertor and the first wall of the NSTX tokamak. Besides ideal MHD modeling, including finite-Larmor radius effect and two-fluid Hall and electron diamagnetic drift contributions, a non-ideal resistivity model is employed, taking into account the increase of Z eff after Li-conditioning in ELM-free H-mode. Unlike an earlier conclusion from an eigenvalue code analysis of these equilibria, NIMROD results find that after reduced recycling from divertor plates, profile modification is necessary but insufficient to explain the mechanism behind complete ELMs suppression in ideal two-fluid MHD. After considering the higher plasma resistivity due to higher Z eff, the complete stabilization could be explained. A thorough analysis of both pre-lithium ELMy and with-lithium ELM-free cases using ideal and non-ideal MHD models is presented, after accurately including a vacuum-like cold halo region in NIMROD to investigate ELMs.

  10. The H-mode pedestal, ELMs and TF ripple effects in JT-60U/JET dimensionless identity experiments

    International Nuclear Information System (INIS)

    Saibene, G.; Oyama, N.; Loennroth, J.; Andrew, Y.; Luna, E. de la; Giroud, C.; Huysmans, G.T.A.; Kamada, Y.; Kempenaars, M.A.H.; Loarte, A.; Donald, D. Mc; Nave, M.M.F.; Meiggs, A.; Parail, V.; Sartori, R.; Sharapov, S.; Stober, J.; Suzuki, T.; Takechi, M.; Toi, K.; Urano, H.

    2007-01-01

    This paper summarizes results of dimensionless identity experiments in JT-60U and JET, aimed at the comparison of the H-mode pedestal and ELM behaviour in the two devices. Given their similar size, dimensionless matched plasmas are also similar in their dimensional parameters (in particular, the plasma minor radius a is the same in JET and JT-60U). Power and density scans were carried out at two values of I p , providing a q scan (q 95 = 3.1 and 5.1) with fixed (and matched) toroidal field. Contrary to initial expectations, a dimensionless match between the two devices was quite difficult to achieve. In general, p ped in JT-60U is lower than in JET and, at low q, the pedestal pressure of JT-60U with a Type I ELMy edge is matched in JET only in the Type III ELM regime. At q 95 = 5.1, a dimensionless match in ρ*, ν* and β p,ped is obtained with Type I ELMs, but only with low power JET H-modes. These results motivated a closer investigation of experimental conditions in the two devices, to identify possible 'hidden' physics that prevents obtaining a good match of pedestal values over a large range of plasmas parameters. Ripple-induced ion losses of the medium bore plasma used in JT-60U for the similarity experiments are identified as the main difference with JET. The magnitude of the JT-60U ripple losses is sufficient to induce counter-toroidal rotation in co-injected plasma. The influence of ripple losses was demonstrated at q 95 = 5.1: reducing ripple losses by ∼2 (from 4.3 to 1.9 MW) by replacing positive with negative neutral beam injection at approximately constant P in resulted in an increased p ped in JT-60U, providing a good match to full power JET H-modes. At the same time, the counter-toroidal rotation decreased. Physics mechanisms relating ripple losses to pedestal performance are not yet identified, and the possible role of velocity shear in the pedestal stability, as well as the possible influence of ripple on thermal ion transport are briefly

  11. Edge radial electric field structure in quiescent H-mode plasmas in the DIII-D tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Burrell, K H [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); West, W P [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Doyle, E J [University of California, Los Angeles, CA 90095-1597 (United States); Austin, M E [University of Texas at Austin, Austin, TX 78712 (United States); DeGrassie, J S [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Gohil, P [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Greenfield, C M [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Groebner, R J [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Jayakumar, R [Lawrence Livermore National Laboratory, Livermore, CA 94551-9900 (United States); Kaplan, D H [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Lao, L L [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Leonard, A W [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Makowski, M A [Lawrence Livermore National Laboratory, Livermore, CA 94551-9900 (United States); McKee, G R [University of Wisconsin, Madison, WI 53706-1687 (United States); Solomon, W M [Princeton Plasma Physics Laboratory, Princeton, NJ 08543-0451 (United States); Thomas, D M [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Rhodes, T L [University of California, Los Angeles, CA 90095-1597 (United States); Wade, M R [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Wang, G [University of California, Los Angeles, CA 90095-1597 (United States); Watkins, J G [Sandia National Laboratories, Albuquerque, NM 87185 (United States); Zeng, L [University of California, Los Angeles, CA 90095-1597 (United States)

    2004-05-01

    H-mode operation is the choice for next step tokamak devices based on either conventional or advanced tokamak physics. This choice, however, comes at a significant cost for both the conventional and advanced tokamaks because of the effects of edge localized modes (ELMs). ELMs can produce significant erosion in the divertor and can affect the {beta} limit and reduced core transport regions needed for advanced tokamak operation. Experimental results from DIII-D over the past four years have demonstrated a new operating regime, the quiescent H-mode (QH-mode) regime, that solves these problems. QH-mode plasmas have now been run for over 4 s (>30 energy confinement times). Utilizing the steady-state nature of the QH-mode edge allows us to obtain unprecedented spatial resolution of the edge ion profiles and the edge radial electric field, E{sub r}, by sweeping the edge plasma slowly past the view points of the charge exchange spectroscopy system. We have investigated the effects of direct edge ion orbit loss on the creation and sustainment of the QH-mode. Direct loss of ions injected into the velocity-space loss cone at the plasma edge is not necessary for creation or sustainment of the QH-mode. The direct ion orbit loss has little effect on the edge E{sub r} well. The E{sub r} at the bottom of the well in these cases is about -100 kV m{sup -1} compared with -20 to -30 kV m{sup -1} in the standard H-mode. The well is about 1 cm wide, which is close to the diameter of the deuteron gyro-orbit. We also have investigated the effect of changing edge triangularity by changing the plasma shape from upwardly biased single null to magnetically balanced double null. We have now achieved the QH-mode in these double-null plasmas. The increased triangularity allows us to increase pedestal density in QH-mode plasmas by a factor of about 2.5 and overall pedestal pressure by a factor of 2. Pedestal {beta} and {nu}{sup *} values matching the values desired for ITER have been achieved. In

  12. Kinetic equilibrium reconstruction for the NBI- and ICRH-heated H-mode plasma on EAST tokamak

    Science.gov (United States)

    Zhen, ZHENG; Nong, XIANG; Jiale, CHEN; Siye, DING; Hongfei, DU; Guoqiang, LI; Yifeng, WANG; Haiqing, LIU; Yingying, LI; Bo, LYU; Qing, ZANG

    2018-04-01

    The equilibrium reconstruction is important to study the tokamak plasma physical processes. To analyze the contribution of fast ions to the equilibrium, the kinetic equilibria at two time-slices in a typical H-mode discharge with different auxiliary heatings are reconstructed by using magnetic diagnostics, kinetic diagnostics and TRANSP code. It is found that the fast-ion pressure might be up to one-third of the plasma pressure and the contribution is mainly in the core plasma due to the neutral beam injection power is primarily deposited in the core region. The fast-ion current contributes mainly in the core region while contributes little to the pedestal current. A steep pressure gradient in the pedestal is observed which gives rise to a strong edge current. It is proved that the fast ion effects cannot be ignored and should be considered in the future study of EAST.

  13. Characteristics of heat flux and particle flux to the divertor in H-mode of JT-60U

    International Nuclear Information System (INIS)

    Itami, K.; Hosogane, N.; Asakura, N.; Kubo, H.; Tsuji, S.; Shimada, M.

    1995-01-01

    Heat flux and particle flux behavior in H-mode is studied in a comparative manner. It was confirmed that the multiple peak structure of heat flux during ELM activity has a role in reducing the average value of a peak heat flux at the divertor. In order to characterize heat and particle flux during ELM activity, the ELM part and the steady state part of heat flux and particle flux were determined and statistically analyzed. A large in-out asymmetry of peak ELM heat flux density was found. The asymmetry is almost unaffected by the ion grad-B drift direction. In-out asymmetry of both ELM and steady-state parts of the particle flux were found to be similar. ((orig.))

  14. Formation of an internal transport barrier in the ohmic H-mode in the TUMAN-3M tokamak

    International Nuclear Information System (INIS)

    Andrejko, M.V.; Askinazi, L.G.; Golant, V.E.; Zhubr, N.A.; Kornev, V.A.; Krikunov, S.V.; Lebedev, S.V.; Levin, L.S.; Razdobarin, G.T.; Rozhdestvensky, V.V.; Smirnov, A.I.; Tukachinsky, A.S.; Yaroshevich, S.P.

    2000-01-01

    In experiments on studying the ohmic H-mode in the TUMAN-3M tokamak, it is found that, in high-current (I p ∼ 120-170 kA) discharges, a region with high electron-temperature and density gradients is formed in the plasma core. In this case, the energy confinement time τ E attains 9-18 ms, which is nearly twice as large as that predicted by the ELM-free ITER-93H scaling. This is evidence that the internal transport barrier in a plasma can exist without auxiliary heating. Calculations of the effective thermal diffusivity by the ASTRA transport code demonstrate a strong suppression of heat transport in the region where the temperature and density gradients are high

  15. High resolution main-ion charge exchange spectroscopy in the DIII-D H-mode pedestal.

    Science.gov (United States)

    Grierson, B A; Burrell, K H; Chrystal, C; Groebner, R J; Haskey, S R; Kaplan, D H

    2016-11-01

    A new high spatial resolution main-ion (deuterium) charge-exchange spectroscopy system covering the tokamak boundary region has been installed on the DIII-D tokamak. Sixteen new edge main-ion charge-exchange recombination sightlines have been combined with nineteen impurity sightlines in a tangentially viewing geometry on the DIII-D midplane with an interleaving design that achieves 8 mm inter-channel radial resolution for detailed profiles of main-ion temperature, velocity, charge-exchange emission, and neutral beam emission. At the plasma boundary, we find a strong enhancement of the main-ion toroidal velocity that exceeds the impurity velocity by a factor of two. The unique combination of experimentally measured main-ion and impurity profiles provides a powerful quasi-neutrality constraint for reconstruction of tokamak H-mode pedestals.

  16. High-frequency coherent edge fluctuations in a high-pedestal-pressure quiescent H-mode plasma.

    Science.gov (United States)

    Yan, Z; McKee, G R; Groebner, R J; Snyder, P B; Osborne, T H; Burrell, K H

    2011-07-29

    A set of high frequency coherent (HFC) modes (f=80-250 kHz) is observed with beam emission spectroscopy measurements of density fluctuations in the pedestal of a strongly shaped quiescent H-mode plasma on DIII-D, with characteristics predicted for kinetic ballooning modes (KBM): propagation in the ion-diamagnetic drift direction; a frequency near 0.2-0.3 times the ion-diamagnetic frequency; inferred toroidal mode numbers of n∼10-25; poloidal wave numbers of k(θ)∼0.17-0.4 cm(-1); and high measured decorrelation rates (τ(c)(-1)∼ω(s)∼0.5×10(6) s(-1)). Their appearance correlates with saturation of the pedestal pressure. © 2011 American Physical Society

  17. H-mode WEST tungsten divertor operation: deuterium and nitrogen seeded simulations with SOLEDGE2D-EIRENE

    Directory of Open Access Journals (Sweden)

    G. Ciraolo

    2017-08-01

    Full Text Available Simulations of WEST H-mode divertor scenarios have been performed with SOLEDGE2D-EIRENE edge plasma transport code, both for pure deuterium and nitrogen seeded discharge. In the pure deuterium case, a target heat flux of 8 MW/m2 is reached, but misalignment between heat and the particle outflux yields 50 eV plasma temperature at the target plates. With nitrogen seeding, the heat and particle outflux are observed to be aligned so that lower plasma temperatures at the target plates are achieved together with the required high heat fluxes. This change in heat and particle outflux alignment is analysed with respect to the role of divertor geometry and the impact of vertical vs horizontal target plates on neutrals spreading.

  18. Effect of progressively increasing lithium conditioning on edge transport and stability in high triangularity NSTX H-modes

    Energy Technology Data Exchange (ETDEWEB)

    Maingi, R., E-mail: rmaingi@pppl.gov [Princeton Plasma Physics Laboratory, 100 Stellarator Road, Princeton, NJ 08543 (United States); Canik, J.M. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); Bell, R.E. [Princeton Plasma Physics Laboratory, 100 Stellarator Road, Princeton, NJ 08543 (United States); Boyle, D.P. [Princeton University, Princeton, NJ (United States); Diallo, A.; Kaita, R.; Kaye, S.M.; LeBlanc, B.P. [Princeton Plasma Physics Laboratory, 100 Stellarator Road, Princeton, NJ 08543 (United States); Sabbagh, S.A. [Columbia University, New York, NY (United States); Scotti, F.; Soukhanovskii, V.A. [Lawrence Livermore National Laboratory, Livermore, CA (United States)

    2017-04-15

    A sequence of H-mode discharges with increasing levels of pre-discharge lithium evaporation (‘dose’) was conducted in high triangularity and elongation boundary shape in NSTX. Energy confinement increased, and recycling decreased with increasing lithium dose, similar to a previous lithium dose scan in medium triangularity and elongation plasmas. Data-constrained SOLPS interpretive modeling quantified the edge transport change: the electron particle diffusivity decreased by 10–30x. The electron thermal diffusivity decreased by 4x just inside the top of the pedestal, but increased by up to 5x very near the separatrix. These results provide a baseline expectation for lithium benefits in NSTX-U, which is optimized for a boundary shape similar to the one in this experiment.

  19. The quiescent H-mode regime for high performance edge localized mode-stable operation in future burning plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Garofalo, A. M., E-mail: garofalo@fusion.gat.com; Burrell, K. H.; Meneghini, O.; Osborne, T. H.; Paz-Soldan, C.; Smith, S. P.; Snyder, P. B.; Turnbull, A. D. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Eldon, D.; Grierson, B. A.; Solomon, W. M. [Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States); Hanson, J. M. [Columbia University, 2960 Broadway, New York, New York 10027-6900 (United States); Holland, C. [University of California San Diego, 9500 Gilman Dr., La Jolla, California 92093-0417 (United States); Huijsmans, G. T. A.; Liu, F.; Loarte, A. [ITER Organization, Route de Vinon sur Verdon, 13067 St Paul Lez Durance (France); Zeng, L. [University of California Los Angeles, P.O. Box 957099, Los Angeles, California 90095-7099 (United States)

    2015-05-15

    For the first time, DIII-D experiments have achieved stationary quiescent H-mode (QH-mode) operation for many energy confinement times at simultaneous ITER-relevant values of beta, confinement, and safety factor, in an ITER-like shape. QH-mode provides excellent energy confinement, even at very low plasma rotation, while operating without edge localized modes (ELMs) and with strong impurity transport via the benign edge harmonic oscillation (EHO). By tailoring the plasma shape to improve the edge stability, the QH-mode operating space has also been extended to densities exceeding 80% of the Greenwald limit, overcoming the long-standing low-density limit of QH-mode operation. In the theory, the density range over which the plasma encounters the kink-peeling boundary widens as the plasma cross-section shaping is increased, thus increasing the QH-mode density threshold. The DIII-D results are in excellent agreement with these predictions, and nonlinear magnetohydrodynamic analysis of reconstructed QH-mode equilibria shows unstable low n kink-peeling modes growing to a saturated level, consistent with the theoretical picture of the EHO. Furthermore, high density operation in the QH-mode regime has opened a path to a new, previously predicted region of parameter space, named “Super H-mode” because it is characterized by very high pedestals that can be more than a factor of two above the peeling-ballooning stability limit for similar ELMing H-mode discharges at the same density.

  20. Integrated simulations of H-mode operation in ITER including core fuelling, divertor detachment and ELM control

    Science.gov (United States)

    Polevoi, A. R.; Loarte, A.; Dux, R.; Eich, T.; Fable, E.; Coster, D.; Maruyama, S.; Medvedev, S. Yu.; Köchl, F.; Zhogolev, V. E.

    2018-05-01

    ELM mitigation to avoid melting of the tungsten (W) divertor is one of the main factors affecting plasma fuelling and detachment control at full current for high Q operation in ITER. Here we derive the ITER operational space, where ELM mitigation to avoid melting of the W divertor monoblocks top surface is not required and appropriate control of W sources and radiation in the main plasma can be ensured through ELM control by pellet pacing. We apply the experimental scaling that relates the maximum ELM energy density deposited at the divertor with the pedestal parameters and this eliminates the uncertainty related with the ELM wetted area for energy deposition at the divertor and enables the definition of the ITER operating space through global plasma parameters. Our evaluation is thus based on this empirical scaling for ELM power loads together with the scaling for the pedestal pressure limit based on predictions from stability codes. In particular, our analysis has revealed that for the pedestal pressure predicted by the EPED1  +  SOLPS scaling, ELM mitigation to avoid melting of the W divertor monoblocks top surface may not be required for 2.65 T H-modes with normalized pedestal densities (to the Greenwald limit) larger than 0.5 to a level of current of 6.5–7.5 MA, which depends on assumptions on the divertor power flux during ELMs and between ELMs that expand the range of experimental uncertainties. The pellet and gas fuelling requirements compatible with control of plasma detachment, core plasma tungsten accumulation and H-mode operation (including post-ELM W transient radiation) have been assessed by 1.5D transport simulations for a range of assumptions regarding W re-deposition at the divertor including the most conservative assumption of zero prompt re-deposition. With such conservative assumptions, the post-ELM W transient radiation imposes a very stringent limit on ELM energy losses and the associated minimum required ELM frequency. Depending on

  1. Impurity transport model for the normal confinement and high density H-mode discharges in Wendelstein 7-AS

    International Nuclear Information System (INIS)

    Ida, K; Burhenn, R; McCormick, K; Pasch, E; Yamada, H; Yoshinuma, M; Inagaki, S; Murakami, S; Osakabe, M; Liang, Y; Brakel, R; Ehmler, H; Giannone, L; Grigull, P; Knauer, J P; Maassberg, H; Weller, A

    2003-01-01

    An impurity transport model based on diffusivity and the radial convective velocity is proposed as a first approach to explain the differences in the time evolution of Al XII (0.776 nm), Al XI (55 nm) and Al X (33.3 nm) lines following Al-injection by laser blow-off between normal confinement discharges and high density H-mode (HDH) discharges. Both discharge types are in the collisional regime for impurities (central electron temperature is 0.4 keV and central density exceeds 10 20 m -3 ). In this model, the radial convective velocity is assumed to be determined by the radial electric field, as derived from the pressure gradient. The diffusivity coefficient is chosen to be constant in the plasma core but is significantly larger in the edge region, where it counteracts the high local values of the inward convective velocity. Under these conditions, the faster decay of aluminium in HDH discharges can be explained by the smaller negative electric field in the bulk plasma, and correspondingly smaller inward convective velocity, due to flattening of the density profiles

  2. Experimental evidence for the suitability of ELMing H-mode operation in ITER with regard to core transport of helium

    International Nuclear Information System (INIS)

    Wade, M.R.; Hillis, D.L.; Burrell, K.H.

    1996-09-01

    Studies have been conducted in DIII-D to assess the viability of the ITER design with regard to helium ash removal, including both global helium exhaust studies and detailed helium transport studies. With respect to helium ash accumulation, the results are encouraging for successful operation of ITER in ELMing H-mode plasmas with conventional high-recycling divertor operation. Helium can be removed from the plasma core with a characteristic time constant of ∼ 8 energy confinement times, even with a central source of helium. Furthermore, the exhaust rate is limited by the pumping efficiency of the system and not by transport of helium within the plasma core. Helium transport studies have shown that D He /X eff ∼ 1 in all confinement regimes studied to date and there is little dependence of D He /X eff on normalized gyroradius in dimensionless scaling studies, suggesting that D He /X eff will be ∼ 1 in ITER. These observations suggest that helium transport within the plasma core should be sufficient to prevent unacceptable fuel dilution in ITER. However, helium exhaust is also strongly dependent on many factors (e.g., divertor plasma conditions, plasma and baffling geometry, flux amplification, pumping speed, etc.) that are difficult to extrapolate. Studies have revealed the helium diffusivity decreases as the plasma density increases, which is unfavorable to ITER's extremely high density operation

  3. Analysis of performance degradation in an electron heating dominant H-mode plasma after ECRH termination in EAST

    Science.gov (United States)

    Du, Hongfei; Ding, Siye; Chen, Jiale; Wang, Yifeng; Lian, Hui; Xu, Guosheng; Zhai, Xuemei; Liu, Haiqing; Zang, Qing; Lyu, Bo; Duan, Yanmin; Qian, Jinping; Gong, Xianzu

    2018-06-01

    In recent EAST experiments, significant performance degradation accompanied by a decrease of internal inductance is observed in an electron heating dominant H-mode plasma after the electron cyclotron resonance heating termination. The lower hybrid wave (LHW) deposition and effective electron heat diffusivity are calculated to explain this phenomenon. Analysis shows that the changes of LHW heating deposition rather than the increase of transport are responsible for the significant decrease in energy confinement (). The reason why the confinement degradation occurred on a long time scale could be attributed to both good local energy confinement in the core and also the dependence of LHW deposition on the magnetic shear. The electron temperature profile shows weaker stiffness in near axis region where electron heating is dominant, compared to that in large radius region. Unstable electron modes from low to high k in the core plasma have been calculated in the linear GYRO simulations, which qualitatively agree with the experimental observation. This understanding of the plasma performance degradation mechanism will help to find ways of improving the global confinement in the radio-frequency dominant scenario in EAST.

  4. Plasma-edge gradients in L-mode and ELM-free H-mode JET plasmas

    International Nuclear Information System (INIS)

    Breger, P.; Zastrow, K.-D.; Davies, S.J.; K ig, R.W.T.; Summers, D.D.R.; Hellermann, M.G. von; Flewin, C.; Hawkes, N.C.; Pietrzyk, Z.A.; Porte, L.

    1998-01-01

    Experimental plasma-edge gradients in JET during the edge-localized-mode (ELM) free H-mode are examined for evidence of the presence and location of the transport barrier region inside the magnetic separatrix. High spatial resolution data in electron density is available in- and outside the separatrix from an Li-beam diagnostic, and in electron temperature inside the separatrix from an ECE diagnostic, while outside the separatrix, a reciprocating probe provides electron density and temperature data in the scrape-off layer. Ion temperatures and densities are measured using an edge charge-exchange diagnostic. A comparison of observed widths and gradients of this edge region with each other and with theoretical expectations is made. Measurements show that ions and electrons form different barrier regions. Furthermore, the electron temperature barrier width (3-4 cm) is about twice that of electron density, in conflict with existing scaling laws. Suitable parametrization of the edge data enables an electron pressure gradient to be deduced for the first time at JET. It rises during the ELM-free phase to reach only about half the marginal pressure gradient expected from ballooning stability before the first ELM. Subsequent type I ELMs occur on a pressure gradient contour roughly consistent with both a constant barrier width model and a ballooning mode envelope model. (author)

  5. Radial transport in the far scrape-off layer of ASDEX upgrade during L-mode and ELMy H-mode

    DEFF Research Database (Denmark)

    Ionita, C.; Naulin, Volker; Mehlmann, F.

    2013-01-01

    The radial turbulent particle flux and the Reynolds stress in the scrape-off layer (SOL) of ASDEX Upgrade were investigated for two limited L-mode (low confinement) and one ELMy H-mode (high confinement) discharge. A fast reciprocating probe was used with a probe head containing five Langmuir...

  6. Edge Pedestal Control in Quiescent H-Mode Discharges in DIII-D Using Co Plus Counter Neutral Beam Injection

    International Nuclear Information System (INIS)

    Burrell, K.H.; Osborne, T.H.; Snyder, P.B.; West, W.P.; Chu, M.S.; Fenstermacher, M.E.; Gohil, P.; Solomon, W.M.

    2008-01-01

    We have made two significant discoveries in our recent studies of quiescent H-mode (QH-mode) plasmas in DIII-D. First, we have found that we can control the edge pedestal density and pressure by altering the edge particle transport through changes in the edge toroidal rotation. This allows us to adjust the edge operating point to be close to, but below the ELM stability boundary, maintaining the ELM-free state while allowing up to a factor of two increase in edge pressure. The ELM boundary is significantly higher in more strongly shaped plasmas, which broadens the operating space available for QH-mode and leads to improved core performance. Second, for the first time on any tokamak, we have created QH-mode plasmas with strong edge co-rotation; previous QH-modes in all tokamaks had edge counter rotation. This result demonstrates that counter NBI and edge counter rotation are not essential conditions for QH-mode. Both these investigations benefited from the edge stability predictions based on peeling-ballooning mode theory. The broadening of the ELM-stable region with plasma shaping is predicted by that theory. The theory has also been extended to provide a model for the edge harmonic oscillation (EHO) that regulates edge transport in the QH-mode. Many of the features of that theory agree with the experimental results reported either previously or in the present paper. One notable example is the prediction that co-rotating QH-mode is possible provided sufficient shear in the edge rotation can be created

  7. Towards cooperative guidance and control of highly automated vehicles: H-Mode and Conduct-by-Wire.

    Science.gov (United States)

    Flemisch, Frank Ole; Bengler, Klaus; Bubb, Heiner; Winner, Hermann; Bruder, Ralph

    2014-01-01

    This article provides a general ergonomic framework of cooperative guidance and control for vehicles with an emphasis on the cooperation between a human and a highly automated vehicle. In the twenty-first century, mobility and automation technologies are increasingly fused. In the sky, highly automated aircraft are flying with a high safety record. On the ground, a variety of driver assistance systems are being developed, and highly automated vehicles with increasingly autonomous capabilities are becoming possible. Human-centred automation has paved the way for a better cooperation between automation and humans. How can these highly automated systems be structured so that they can be easily understood, how will they cooperate with the human? The presented research was conducted using the methods of iterative build-up and refinement of framework by triangulation, i.e. by instantiating and testing the framework with at least two derived concepts and prototypes. This article sketches a general, conceptual ergonomic framework of cooperative guidance and control of highly automated vehicles, two concepts derived from the framework, prototypes and pilot data. Cooperation is exemplified in a list of aspects and related to levels of the driving task. With the concept 'Conduct-by-Wire', cooperation happens mainly on the guidance level, where the driver can delegate manoeuvres to the automation with a specialised manoeuvre interface. With H-Mode, a haptic-multimodal interaction with highly automated vehicles based on the H(orse)-Metaphor, cooperation is mainly done on guidance and control with a haptically active interface. Cooperativeness should be a key aspect for future human-automation systems. Especially for highly automated vehicles, cooperative guidance and control is a research direction with already promising concepts and prototypes that should be further explored. The application of the presented approach is every human-machine system that moves and includes high

  8. Reactor-relevant quiescent H-mode operation using torque from non-axisymmetric, non-resonant magnetic fields

    International Nuclear Information System (INIS)

    Burrell, K. H.; Garofalo, A. M; Osborne, T. H.; Schaffer, M. J.; Snyder, P. B.; Solomon, W. M.; Park, J.-K.; Fenstermacher, M. E.

    2012-01-01

    Results from recent experiments demonstrate that quiescent H-mode (QH-mode) sustained by magnetic torque from non-axisymmetric magnetic fields is a promising operating mode for future burning plasmas. Using magnetic torque from n=3 fields to replace counter-I p torque from neutral beam injection (NBI), we have achieved long duration, counter-rotating QH-mode operation with NBI torque ranging from counter-I p to up to co-I p values of 1-1.3 Nm. This co-I p torque is 3 to 4 times the scaled torque that ITER will have. These experiments utilized an ITER-relevant lower single-null plasma shape and were done with ITER-relevant values of ν ped * and β N ped . These discharges exhibited confinement quality H 98y2 =1.3, in the range required for ITER. In preliminary experiments using n=3 fields only from a coil outside the toroidal coil, QH-mode plasmas with low q 95 =3.4 have reached fusion gain values of G=β N H 89 /q 95 2 =0.4, which is the desired value for ITER. Shots with the same coil configuration also operated with net zero NBI torque. The limits on G and co-I p torque have not yet been established for this coil configuration. QH-mode work to has made significant contact with theory. The importance of edge rotational shear is consistent with peeling-ballooning mode theory. Qualitative and quantitative agreements with the predicted neoclassical toroidal viscosity torque is seen.

  9. Parametric dependencies of the experimental tungsten transport coefficients in ICRH and ECRH assisted ASDEX Upgrade H-modes

    Science.gov (United States)

    Sertoli, M.; Angioni, C.; Odstrcil, T.; ASDEX Upgrade Team; Eurofusion MST1 Team

    2017-11-01

    The profiles of the W transport coefficients have been experimentally calculated for a large database of identical ASDEX Upgrade H-mode discharges where only the radio-frequency (RF) power characteristics have been varied [Angioni et al., Nucl. Fusion 57, 056015 (2017)]. Central ion cyclotron resonance heating (ICRH) in the minority heating scheme has been compared with central and off-axis electron cyclotron resonance heating (ECRH), using both localized and broad heat deposition profiles. The transport coefficients have been calculated applying the gradient-flux relation to the evolution of the intrinsic W density in-between sawtooth cycles as measured using the soft X-ray diagnostic. For both ICRH and ECRH, the major player in reducing the central W density peaking is found to be the reduction of inward pinch and, in the case of ECRH, the rise of an outward convection. The impurity convection increases, from negative to positive, almost linearly with RF-power, while no appreciable changes are observed in the diffusion coefficient, which remains roughly at neoclassical levels independent of RF power or background plasma conditions. The ratio vW/DW is consistent with the equilibrium ∇ n W / n W prior to the sawtooth crash, corroborating the separate estimates of diffusion and convection. These experimental findings are slightly different from previous results obtained analysing the evolution of impurity injections over many sawtooth cycles. Modelling performed using the drift-kinetic code NEO and the gyro-kinetic code GKW (assuming axisymmetry) overestimates the diffusion coefficient and underestimates the experimental positive convection. This is a further indication that magneto-hydrodynamic/neoclassical models accounting for 3D effects may be needed to characterize impurity transport in sawtoothing tokamak plasmas.

  10. Simulations of particle and heat fluxes in an ELMy H-mode discharge on EAST using BOUT++ code

    Science.gov (United States)

    Wu, Y. B.; Xia, T. Y.; Zhong, F. C.; Zheng, Z.; Liu, J. B.; team3, EAST

    2018-05-01

    In order to study the distribution and evolution of the transient particle and heat fluxes during edge-localized mode (ELM) bursts on the Experimental Advanced Superconducting Tokamak (EAST), the BOUT++ six-field two-fluid model is used to simulate the pedestal collapse. The profiles from the EAST H-mode discharge #56129 are used as the initial conditions. Linear analysis shows that the resistive ballooning mode and drift-Alfven wave are two dominant instabilities for the equilibrium, and play important roles in driving ELMs. The evolution of the density profile and the growing process of the heat flux at divertor targets during the burst of ELMs are reproduced. The time evolution of the poloidal structures of T e is well simulated, and the dominant mode in each stage of the ELM crash process is found. The studies show that during the nonlinear phase, the dominant mode is 5, and it changes to 0 when the nonlinear phase goes to saturation after the ELM crash. The time evolution of the radial electron heat flux, ion heat flux, and particle density flux at the outer midplane (OMP) are obtained, and the corresponding transport coefficients D r, χ ir, and χ er reach maximum around 0.3 ∼ 0.5 m2 s‑1 at ΨN = 0.9. The heat fluxes at outer target plates are several times larger than that at inner target plates, which is consistent with the experimental observations. The simulated profiles of ion saturation current density (j s) at the lower outboard (LO) divertor target are compared to those of experiments by Langmuir probes. The profiles near the strike point are similar, and the peak values of j s from simulation are very close to the measurements.

  11. Study of the phase transition dynamics of the L to H transition

    International Nuclear Information System (INIS)

    Moyer, R.A.; Rhodes, T.L.; Rettig, C.L.

    1997-12-01

    A highly radiating zone (MARFE) just above the divertor X-point has been used to access the marginal transition regime P sep ∼ P thres to study the existence of a critical point for the L to H transition. Phase transition models predict that at the critical point, the transition duration increases and the plasma parameters vary continuously between L-mode and H-mode. In these experiments, the L to H transition duration increased 50--100 times over fast transitions. However, the evolution of E r shear, edge density gradient, H-mode pedestal, and fluctuations is essentially unchanged from that in fast transitions. The only difference is in the speed with which and the degree to which the fluctuation amplitudes are transiently reduced. This difference is understandable in terms of the time scales for fluctuation amplitude reduction (≤ 100 micros) and edge pressure gradient increase (several ms), provided the edge fluctuations are pressure-gradient driven

  12. Impact of E × B flow shear on turbulence and resulting power fall-off width in H-mode plasmas in experimental advanced superconducting tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Q. Q., E-mail: yangqq@ipp.ac.cn; Zhong, F. C., E-mail: gsxu@ipp.ac.cn, E-mail: fczhong@dhu.edu.cn; Jia, M. N. [College of Science, Donghua University, Shanghai 201620 (China); Xu, G. S., E-mail: gsxu@ipp.ac.cn, E-mail: fczhong@dhu.edu.cn; Wang, L.; Wang, H. Q.; Chen, R.; Yan, N.; Liu, S. C.; Chen, L.; Li, Y. L.; Liu, J. B. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)

    2015-06-15

    The power fall-off width in the H-mode scrape-off layer (SOL) in tokamaks shows a strong inverse dependence on the plasma current, which was noticed by both previous multi-machine scaling work [T. Eich et al., Nucl. Fusion 53, 093031 (2013)] and more recent work [L. Wang et al., Nucl. Fusion 54, 114002 (2014)] on the Experimental Advanced Superconducting Tokamak. To understand the underlying physics, probe measurements of three H-mode discharges with different plasma currents have been studied in this work. The results suggest that a higher plasma current is accompanied by a stronger E×B shear and a shorter radial correlation length of turbulence in the SOL, thus resulting in a narrower power fall-off width. A simple model has also been applied to demonstrate the suppression effect of E×B shear on turbulence in the SOL and shows relatively good agreement with the experimental observations.

  13. Measurement of deuterium density profiles in the H-mode steep gradient region using charge exchange recombination spectroscopy on DIII-D.

    Science.gov (United States)

    Haskey, S R; Grierson, B A; Burrell, K H; Chrystal, C; Groebner, R J; Kaplan, D H; Pablant, N A; Stagner, L

    2016-11-01

    Recent completion of a thirty two channel main-ion (deuterium) charge exchange recombination spectroscopy (CER) diagnostic on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] enables detailed comparisons between impurity and main-ion temperature, density, and toroidal rotation. In a H-mode DIII-D discharge, these new measurement capabilities are used to provide the deuterium density profile, demonstrate the importance of profile alignment between Thomson scattering and CER diagnostics, and aid in determining the electron temperature at the separatrix. Sixteen sightlines cover the core of the plasma and another sixteen are densely packed towards the plasma edge, providing high resolution measurements across the pedestal and steep gradient region in H-mode plasmas. Extracting useful physical quantities such as deuterium density is challenging due to multiple photoemission processes. These challenges are overcome using a detailed fitting model and by forward modeling the photoemission using the FIDASIM code, which implements a comprehensive collisional radiative model.

  14. Electron Bernstein wave heating of over-dense H-mode plasmas in the TCV tokamak via O-X-B double mode conversion

    International Nuclear Information System (INIS)

    Pochelon, A.; Mueck, A.; Curchod, L.; Camenen, Y.; Coda, S.; Duval, B.P.; Goodman, T.P.; Klimanov, I.; Laqua, H.P.; Martin, Y.; Moret, J.-M.; Porte, L.; Sushkov, A.; Udintsev, V.S.; Volpe, F.

    2007-01-01

    This paper reports on the first demonstration of electron Bernstein wave heating (EBWH) by double mode conversion from ordinary (O-) to Bernstein (B-) via the extraordinary (X-) mode in an over-dense tokamak plasma, using low field side launch, achieved in the TCV tokamak H-mode, making use of its naturally generated steep density gradient. This technique offers the possibility of overcoming the upper density limit of conventional EC microwave heating. The sensitive dependence of the O-X mode conversion on the microwave launching direction has been verified experimentally. Localized power deposition, consistent with theoretical predictions, has been observed at densities well above the conventional cut-off. Central heating has been achieved, at powers up to two megawatts. This demonstrates the potential of EBW in tokamak H-modes, the intended mode of operation for a reactor such as ITER

  15. Transition physics and scaling overview

    International Nuclear Information System (INIS)

    Carlstrom, T.N.

    1996-01-01

    This paper presents an overview of recent experimental progress towards understanding H-mode transition physics and scaling. Terminology and techniques for studying H-mode are reviewed and discussed. The model of shear E x B flow stabilization of edge fluctuations at the L-H transition is gaining wide acceptance and is further supported by observations of edge rotation on a number of new devices. Observations of poloidal asymmetries of edge fluctuations and dephasing of density and potential fluctuations after the transition pose interesting challenges for understanding H-mode physics. Dedicated scans to determine the scaling of the power threshold have now been performed on many machines. A clear B t dependence is universally observed but dependence on the line averaged density is complicated. Other dependencies are also reported. Studies of the effect of neutrals and error fields on the power threshold are under investigation. The ITER threshold database has matured and offers guidance to the power threshold scaling issues relevant to next-step devices. (author)

  16. Transition physics and scaling overview

    International Nuclear Information System (INIS)

    Carlstrom, T.N.

    1995-12-01

    This paper presents an overview of recent experimental progress towards understanding H-mode transition physics and scaling. Terminology and techniques for studying H-mode are reviewed and discussed. The model of shear E x B flow stabilization of edge fluctuations at the L-H transition is gaining wide acceptance and is further supported by observations of edge rotation on a number of new devices. Observations of poloidal asymmetries of edge fluctuations and dephasing of density and potential fluctuations after the transition pose interesting challenges for understanding H-mode physics. Dedicated scans to determine the scaling of the power threshold have now been performed on many machines. A dear B t dependence is universally observed but dependence on the line averaged density is complicated. Other dependencies are also reported. Studies of the effect of neutrals and error fields on the power threshold are under investigation. The ITER threshold database has matured and offers guidance to the power threshold scaling issues relevant to next-step devices

  17. Direct measurements of the plasma potential in ELMy H-mode plasma with ball-pen probes on ASDEX Upgrade tokamak

    Czech Academy of Sciences Publication Activity Database

    Adámek, Jiří; Stöckel, Jan; Brotánková, Jana; Horáček, Jan; Rohde, V.; Müller, H. W.; Herrmann, A.; Schrittwieser, R.; Mehlmann, F.; Ionita, C.

    390-391, - (2009), s. 1114-1117 ISSN 0022-3115. [International Conference on Plasma-Surface Interactions in Controlled Fusion Device/18th./. Toledo, 26.05.2008-30.05.2008] R&D Projects: GA AV ČR KJB100430601 Institutional research plan: CEZ:AV0Z20430508 Keywords : Edge plasma * Electric field * ELMs * H-mode * ASDEX-Upgrade Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 1.933, year: 2009 http://dx.doi.org/10.1016/j.jnucmat.2009.01.286

  18. Direct measurements of the plasma potential in ELMy H-mode plasma with ball-pen probes on ASDEX Upgrade tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Adamek, J., E-mail: adamek@ipp.cas.c [Institute of Plasma Physics, Association EURATOM/IPP.CR, Prague, Za Slovankou 3, 182 00, Prague 8 (Czech Republic); Rohde, V.; Mueller, H.W.; Herrmann, A. [Institute of Plasma Physics, Association EURATOM/IPP, Garching (Germany); Ionita, C.; Schrittwieser, R.; Mehlmann, F. [Institute for Ion Physics and Applied Physics, University of Innsbruck, Association EURATOM/OAW (Austria); Stoeckel, J.; Horacek, J.; Brotankova, J. [Institute of Plasma Physics, Association EURATOM/IPP.CR, Prague, Za Slovankou 3, 182 00, Prague 8 (Czech Republic)

    2009-06-15

    Experimental investigations of the plasma potential and electric field were performed for ELMy H-mode plasmas in the vicinity of the limiter shadow of ASDEX Upgrade. A fast reciprocating probe with a probe head containing four ball-pen probes (BPPs) [J. Adamek et al., Czech. J. Phys. 54 (2004) C95 - C99.] was used on the midplane manipulator. Different gradients of the plasma potential were observed during ELMs and in between them. The temporal resolution of the direct plasma potential measurements with BPP was determined by using power-spectra analysis.

  19. Helium Exhaust Studies in H-Mode Discharges in the DIII-D Tokamak Using an Argon-Frosted Divertor Cryopump

    International Nuclear Information System (INIS)

    Wade, M.R.; Hillis, D.L.; Hogan, J.T.; Mahdavi, M.A.; Maingi, R.; West, W.P.; Brooks, N.H.; Burrell, K.H.; Groebner, R.J.; Jackson, G.L.; Klepper, C.C.; Laughon, G.; Menon, M.M.; Mioduszewski, P.K.

    1995-01-01

    The first experiments demonstrating exhaust of thermal helium in a diverted, H-mode deuterium plasma have been performed on the DIII-D tokamak. The helium, introduced via gas puffing, is observed to reach the plasma core, and then is readily removed from the plasma with a time constant of ∼10--20 energy-confinement times by an in-vessel cryopump conditioned with argon frosting. Detailed analysis of the helium profile evolution suggests that the exhaust rate is limited by the exhaust efficiency of the pump (∼5%) and not by the intrinsic helium-transport properties of the plasma

  20. Characteristics of H-mode-like discharges and ELM activities in the presence of {iota}/2{pi} = 1 surface at the ergodic layer in LHD

    Energy Technology Data Exchange (ETDEWEB)

    Morita, S [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Morisaki, T [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Tanaka, K [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Masuzaki, S [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Goto, M [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Sakakibara, S [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Michael, C [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Narihara, K [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Ohdachi, S [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Sakamoto, R [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Sanin, A [Budker Institute of Nuclear Physics, 630090, Novosibirsk (Russian Federation); Toi, K [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Tokuzawa, T [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan); Vyacheslavov, L N [Budker Institute of Nuclear Physics, 630090, Novosibirsk (Russian Federation); Watanabe, K Y [National Institute for Fusion Science, Toki 509-5292, Gifu (Japan)

    2006-05-15

    Magnetic configurations of LHD are characterized by the presence of chaotic magnetic field, the so-called ergodic layer, surrounding the core plasma. H-mode-like discharges have been obtained at an outwardly shifted configuration of R{sub ax} = 4.00 m with a thick ergodic layer, where the {iota}/2{pi} = 1 position is located in the middle of the ergodic layer. A clear density rise and a reduction of magnetic fluctuation were observed. ELM-like H{alpha} bursts also appeared with a radial propagation of density bursts. These H-mode-like discharges can be triggered by changing P{sub NBI}(<12 MW) from three beams to two beams in a density range (4-8) x 10{sup 13} cm{sup -3}. The ELM-like bursts vanished with a small change of the edge rotational transform. A precise profile measurement of the edge density bursts confirmed that ELM-like bursts occur at the {iota}/2{pi} = 1 position.

  1. Heuristic drift-based model of the power scrape-off width in low-gas-puff H-mode tokamaks

    International Nuclear Information System (INIS)

    Goldston, R.J.

    2012-01-01

    A heuristic model for the plasma scrape-off width in low-gas-puff tokamak H-mode plasmas is introduced. Grad B and curv B drifts into the scrape-off layer (SOL) are balanced against near-sonic parallel flows out of the SOL, to the divertor plates. The overall particle flow pattern posited is a modification for open field lines of Pfirsch–Schlüter flows to include order-unity sinks to the divertors. These assumptions result in an estimated SOL width of ∼2aρ p /R. They also result in a first-principles calculation of the particle confinement time of H-mode plasmas, qualitatively consistent with experimental observations. It is next assumed that anomalous perpendicular electron thermal diffusivity is the dominant source of heat flux across the separatrix, investing the SOL width, derived above, with heat from the main plasma. The separatrix temperature is calculated based on a two-point model balancing power input to the SOL with Spitzer–Härm parallel thermal conduction losses to the divertor. This results in a heuristic closed-form prediction for the power scrape-off width that is in reasonable quantitative agreement both in absolute magnitude and in scaling with recent experimental data. Further work should include full numerical calculations, including all magnetic and electric drifts, as well as more thorough comparison with experimental data.

  2. Three-dimensional simulation of H-mode plasmas with localized divertor impurity injection on Alcator C-Mod using the edge transport code EMC3-EIRENE

    International Nuclear Information System (INIS)

    Lore, J. D.; Reinke, M. L.; Lipschultz, B.; Brunner, D.; LaBombard, B.; Terry, J.; Pitts, R. A.; Feng, Y.

    2015-01-01

    Experiments in Alcator C-Mod to assess the level of toroidal asymmetry in divertor conditions resulting from poloidally and toroidally localized extrinsic impurity gas seeding show a weak toroidal peaking (∼1.1) in divertor electron temperatures for high-power enhanced D-alpha H-mode plasmas. This is in contrast to similar experiments in Ohmically heated L-mode plasmas, which showed a clear toroidal modulation in the divertor electron temperature. Modeling of these experiments using the 3D edge transport code EMC3-EIRENE [Y. Feng et al., J. Nucl. Mater. 241, 930 (1997)] qualitatively reproduces these trends, and indicates that the different response in the simulations is due to the ionization location of the injected nitrogen. Low electron temperatures in the private flux region (PFR) in L-mode result in a PFR plasma that is nearly transparent to neutral nitrogen, while in H-mode the impurities are ionized in close proximity to the injection location, with this latter case yielding a largely axisymmetric radiation pattern in the scrape-off-layer. The consequences for the ITER gas injection system are discussed. Quantitative agreement with the experiment is lacking in some areas, suggesting potential areas for improving the physics model in EMC3-EIRENE

  3. Detailed study of spontaneous rotation generation in diverted H-mode plasma using the full-f gyrokinetic code XGC1

    Science.gov (United States)

    Seo, Janghoon; Chang, C. S.; Ku, S.; Kwon, J. M.; Yoon, E. S.

    2013-10-01

    The Full-f gyrokinetic code XGC1 is used to study the details of toroidal momentum generation in H-mode plasma. Diverted DIII-D geometry is used, with Monte Carlo neutral particles that are recycled at the limiter wall. Nonlinear Coulomb collisions conserve particle, momentum, and energy. Gyrokinetic ions and adiabatic electrons are used in the present simulation to include the effects from ion gyrokinetic turbulence and neoclassical physics, under self-consistent radial electric field generation. Ion orbit loss physics is automatically included. Simulations show a strong co-Ip flow in the H-mode layer at outside midplane, similarly to the experimental observation from DIII-D and ASDEX-U. The co-Ip flow in the edge propagates inward into core. It is found that the strong co-Ip flow generation is mostly from neoclassical physics. On the other hand, the inward momentum transport is from turbulence physics, consistently with the theory of residual stress from symmetry breaking. Therefore, interaction between the neoclassical and turbulence physics is a key factor in the spontaneous momentum generation.

  4. The back transition and hysteresis effects in DIII-D

    International Nuclear Information System (INIS)

    Thomas, D.M.; Groebner, R.J.; Burrell, K.H.; Osborne, T.H.; Carlstrom, T.N.

    1997-09-01

    The back transition from H-mode to L-mode has been studied on DIII-D as a part of the investigation of the L-H transition power threshold scaling. Based on a density-dependent scaling for the H-mode power threshold, ITER will require substantial hysteresis in this parameter to remain in H-mode as n e rises. Defining the hysteresis in terms of the ratio of sustaining to threshold power, P HL /P LH may need to be as small as 50% for ITER. Operation of DIII-D at injection powers slightly above the H-mode threshold results in an oscillatory behavior with multiple forward-backward transitions in the course of a discharge. These discharges represent a unique system for studying various control parameters that may influence the H↔L state transition. Careful analysis of the power flow through the edge gives values for the sustaining power which are well below the corresponding threshold powers (P HL /P LH = 35--70%), indicating substantial hysteresis can be achieved in this parameter. Studies of other control parameter candidates such as edge temperature during the back transitions are less clear: the amount of hysteresis seen in these parameters, if any, is primarily dependent on the nature (ELMing, ELM-free) of the parent H-state

  5. Edge harmonic oscillations at the density pedestal in the H-mode discharges in CHS Heliotron measured using beam emission spectroscopy and magnetic probe

    Energy Technology Data Exchange (ETDEWEB)

    Kado, S. [High Temperature Plasma Center, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8568 (Japan)]. E-mail: kado@q.t.u-tokyo.ac.jp; Oishi, T. [School of Engineering, University of Tokyo, Bunkyo-ku, Tokyo 113-8656 (Japan); Yoshinuma, M. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Ida, K. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Takeuchi, M. [Department of Energy Engineering and Science, Nagoya University, Nagoya 464-8603 (Japan); Toi, K. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Akiyama, T. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Minami, T. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Nagaoka, K. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Shimizu, A. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Okamura, S. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Tanaka, S. [School of Engineering, University of Tokyo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2007-06-15

    Edge harmonic oscillations (EHO) offer the potential to relax the H-mode pedestal in a tokamak, thus avoiding edge localised modes (ELM). The mode structure of the EHO in CHS was investigated using a poloidal array of beam emission spectroscopy (BES) and a magnetic probe array. The EHO exhibited a peculiar characteristic in which the first, second and third harmonics show the same wavenumber, suggesting that the propagation velocities are different. Change in the phase of higher harmonics at the time when that of the first harmonic is zero can be described as a variation along the (m, n) = (-2, 1) mode structure, though the EHO lies on the {iota} = 1 surface. This behavior leads to an oscillation that exhibits periodic dependence of shape on spatial position.

  6. Stability of Microturbulent Drift Modes during Internal Transport Barrier Formation in the Alcator C-Mod Radio Frequency Heated H-mode

    International Nuclear Information System (INIS)

    Redi, M.H.; Fiore, C.L.; Dorland, W.; Mikkelsen, D.R.; Rewoldt, G.; Bonoli, P.T.; Ernst, D.R.; Rice, J.E.; Wukitch, S.J.

    2003-01-01

    Recent H-mode experiments on Alcator C-Mod [I.H. Hutchinson, et al., Phys. Plasmas 1 (1994) 1511] which exhibit an internal transport barrier (ITB), have been examined with flux tube geometry gyrokinetic simulations, using the massively parallel code GS2 [M. Kotschenreuther, G. Rewoldt, and W.M. Tang, Comput. Phys. Commun. 88 (1995) 128]. The simulations support the picture of ion/electron temperature gradient (ITG/ETG) microturbulence driving high xi/ xe and that suppressed ITG causes reduced particle transport and improved ci on C-Mod. Nonlinear calculations for C-Mod confirm initial linear simulations, which predicted ITG stability in the barrier region just before ITB formation, without invoking E x B shear suppression of turbulence. Nonlinear fluxes are compared to experiment, which both show low heat transport in the ITB and higher transport within and outside of the barrier region

  7. Effect of ion orbit loss on the structure in the H-mode tokamak edge pedestal profiles of rotation velocity, radial electric field, density, and temperature

    International Nuclear Information System (INIS)

    Stacey, Weston M.

    2013-01-01

    An investigation of the effect of ion orbit loss of thermal ions and the compensating return ion current directly on the radial ion flux flowing in the plasma, and thereby indirectly on the toroidal and poloidal rotation velocity profiles, the radial electric field, density, and temperature profiles, and the interpretation of diffusive and non-diffusive transport coefficients in the plasma edge, is described. Illustrative calculations for a high-confinement H-mode DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] plasma are presented and compared with experimental results. Taking into account, ion orbit loss of thermal ions and the compensating return ion current is found to have a significant effect on the structure of the radial profiles of these quantities in the edge plasma, indicating the necessity of taking ion orbit loss effects into account in interpreting or predicting these quantities

  8. Comparing 1.5D ONETWO and 2D SOLPS analyses of inter-ELM H-mode plasma in DIII-D

    International Nuclear Information System (INIS)

    Owen, Larry W.; Canik, John; Groebner, R.; Callen, J.D.; Bonnin, X.; Osborne, T.H.

    2010-01-01

    A DIII-D inter-ELM H-mode plasma that is in approximate transport equilibrium is analysed with the 1.5D ONETWO core code and the 2D SOLPS code. In order to investigate the importance of core-edge coupling and 2D effects, including divertor fuelling across the X-point and poloidal asymmetries that are not explicitly included in ONETWO, the domain of SOLPS is extended to very near the magnetic axis. Two principal objectives are (1) to determine whether poloidal asymmetries in the plasma distributions are large enough to vitiate a core-type interpretive plasma transport analysis and (2) to determine whether the interpretive transport coefficients and neutral beam power and particle sources from ONETWO, when used in 2D SOLPS full plasma simulations, yield the same quality fits to the measured upstream density and temperature profiles as obtained with ONETWO. Results show that only a small increase in the separatrix value of the particle diffusion coefficient, and no change in the thermal diffusivities from ONETWO was needed to get excellent agreement of the upstream SOLPS density and temperature profiles and the Thomson scattering and CER data. Good agreement of the ONETWO and SOLPS flux surface averaged distributions of the core electron and D+ densities and temperatures are also obtained. Likewise the C6+ density, with a simple chemical sputtering model based on a constant fraction of the divertor D+ flux, the core heat and particle fluxes and the neutral density reveal no 2D effects in the core/pedestal region that would vitiate a 1.5D treatment of the inter-ELM H-mode plasma.

  9. Predictive transport modelling of type I ELMy H-mode dynamics using a theory-motivated combined ballooning-peeling model

    International Nuclear Information System (INIS)

    Loennroth, J-S; Parail, V; Dnestrovskij, A; Figarella, C; Garbet, X; Wilson, H

    2004-01-01

    This paper discusses predictive transport simulations of the type I ELMy high confinement mode (H-mode) with a theory-motivated edge localized mode (ELM) model based on linear ballooning and peeling mode stability theory. In the model, a total mode amplitude is calculated as a sum of the individual mode amplitudes given by two separate linear differential equations for the ballooning and peeling mode amplitudes. The ballooning and peeling mode growth rates are represented by mutually analogous terms, which differ from zero upon the violation of a critical pressure gradient and an analytical peeling mode stability criterion, respectively. The damping of the modes due to non-ideal magnetohydrodynamic effects is controlled by a term driving the mode amplitude towards the level of background fluctuations. Coupled to simulations with the JETTO transport code, the model qualitatively reproduces the experimental dynamics of type I ELMy H-mode, including an ELM frequency that increases with the external heating power. The dynamics of individual ELM cycles is studied. Each ELM is usually triggered by a ballooning mode instability. The ballooning phase of the ELM reduces the pressure gradient enough to make the plasma peeling unstable, whereby the ELM continues driven by the peeling mode instability, until the edge current density has been depleted to a stable level. Simulations with current ramp-up and ramp-down are studied as examples of situations in which pure peeling and pure ballooning mode ELMs, respectively, can be obtained. The sensitivity with respect to the ballooning and peeling mode growth rates is investigated. Some consideration is also given to an alternative formulation of the model as well as to a pure peeling model

  10. H-L transition caused by irregular probe insertion in the JFT-2M tokamak

    International Nuclear Information System (INIS)

    Hanada, K.; Hasegawa, M.; Shinohara, K.

    1996-01-01

    A pair of probe pins whose lengths differ by 5 mm are inserted into the separatrix of H-mode plasmas. When the long pin is biased positively against the short one, the H-L transition takes place and the current through the resistor making a connection between these pins increases for 10 μs and the potential of the pin increases for 100 μs. The energy dissipated by the resistor during the H-L transition is comparable to the energy of the radial electric field in H-mode plasma. When the long pin is biased negatively, the H-L transition also occurs; however, it takes 1 ms to change the potential of the pin and the plasma returns to H-mode after the extraction of the probe. (author)

  11. Theory of Rapid Formation of Pedestal and Pedestal width due to Anomalous Particle Pinch in the Edge of H-mode Discharges

    Energy Technology Data Exchange (ETDEWEB)

    Kaw, P.K., E-mail: kaw@ipr.res.in [Institute for Plasma Research, Bhat (India); Singh, R. [Institute for Plasma Research, Bhat (India); ITER Organization, Saint Paul-lez-Durance [France; Nordman, H. [Chamlers Institute of Technology, Goteborg (Sweden); Garbet, X.; Bourdelle, C. [CEA, Saint Paul-lez-Durance (France); Campbell, D.; Loarte, A.; Bora, D. [ITER Organization, Saint Paul-lez-Durance (France)

    2012-09-15

    Full text: A theory based on a turbulent particle pinch is proposed to explain the rapid formation of sharp density gradients in tokamak edge plasmas, in particular the pedestal region. The inward radial particle flux in the pedestal results from the interaction between small scale electron temperature gradient driven (ETG) turbulence and self-consistently formed 'electron geodesic acoustic modes' (el-GAMs). To address this phenomenon, the el-GAM modulational instability driven by the ETG turbulence background is studied. The ETG level of fluctuations and particle pinch are estimated through the back reaction of eGAMs on ETG turbulence. It is found that the particle pinch is quite sensitive to magnetic shear, safety factor, ratio of electron to ion temperatures and atomic mass number. In the absence of particle source in the pedestal, the density gradient length scale, of the order of the pedestal width, is estimated. It is shown that it is proportional to the major radius, up to some dependence on the poloidal beta. Moreover it does not depend on the normalized gyro-radius. This scaling agrees with DIII-D and JET similarity experiments. This dependence is favorable when extrapolated to the pedestal width in ITER in spite of its low normalized gyro radius. It is also shown that the density scale length becomes sharper by increasing the magnetic shear. A new H-mode pedestal pressure scaling is derived assuming that the pressure gradient is limited by the ballooning instability. (author)

  12. A statistical methodology to derive the scaling law for the H-mode power threshold using a large multi-machine database

    International Nuclear Information System (INIS)

    Murari, A.; Lupelli, I.; Gaudio, P.; Gelfusa, M.; Vega, J.

    2012-01-01

    In this paper, a refined set of statistical techniques is developed and then applied to the problem of deriving the scaling law for the threshold power to access the H-mode of confinement in tokamaks. This statistical methodology is applied to the 2010 version of the ITPA International Global Threshold Data Base v6b(IGDBTHv6b). To increase the engineering and operative relevance of the results, only macroscopic physical quantities, measured in the vast majority of experiments, have been considered as candidate variables in the models. Different principled methods, such as agglomerative hierarchical variables clustering, without assumption about the functional form of the scaling, and nonlinear regression, are implemented to select the best subset of candidate independent variables and to improve the regression model accuracy. Two independent model selection criteria, based on the classical (Akaike information criterion) and Bayesian formalism (Bayesian information criterion), are then used to identify the most efficient scaling law from candidate models. The results derived from the full multi-machine database confirm the results of previous analysis but emphasize the importance of shaping quantities, elongation and triangularity. On the other hand, the scaling laws for the different machines and at different currents are different from each other at the level of confidence well above 95%, suggesting caution in the use of the global scaling laws for both interpretation and extrapolation purposes. (paper)

  13. Intra-ELM phase modelling of a JET ITER-like wall H-mode discharge with EDGE2D-EIRENE

    Energy Technology Data Exchange (ETDEWEB)

    Harting, D.M., E-mail: Derek.Harting@ccfe.ac.uk [CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Wiesen, S. [Institute of Energy and Climate Research – IEK4, Association EURATOM-FZJ, D-52425 Jülich (Germany); Groth, M. [Aalto University, Association EURATOM-Tekes, Espoo (Finland); Brezinsek, S. [Institute of Energy and Climate Research – IEK4, Association EURATOM-FZJ, D-52425 Jülich (Germany); Corrigan, G.; Arnoux, G. [CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Boerner, P. [Institute of Energy and Climate Research – IEK4, Association EURATOM-FZJ, D-52425 Jülich (Germany); Devaux, S.; Flanagan, J. [CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Järvinen, A. [Aalto University, Association EURATOM-Tekes, Espoo (Finland); Marsen, S. [Max-Planck-Institut für Plasmaphysik, EURATOM-Association, D-17491 Greifswald (Germany); Reiter, D. [Institute of Energy and Climate Research – IEK4, Association EURATOM-FZJ, D-52425 Jülich (Germany)

    2015-08-15

    We present the application of an improved EDGE2D-EIRENE SOL transport model for the ELM phase utilizing kinetic correction of the sheath-heat-transmission coefficients and heat-flux-limiting factors used in fluid SOL modelling. With a statistical analysis over a range of similar type-I ELMy H-mode discharges performed at the end of the first JET ITER-like wall campaign, we achieved a fast (Δt = 200 μs) temporal evolution of the outer midplane n{sub e} and T{sub e} profiles and the target-heat and particle-flux profiles, which provides a good experimental data set to understand the characteristics of an ELM cycle. We will demonstrate that these kinetic corrections increase the simulated heat-flux-rise time at the target to experimentally observed times but the power-decay time at the target is still underestimated by the simulations. This longer decay times are potentially related to a change of the local recycling coefficient at the tungsten target plate directly after the heat pulse.

  14. Modification of adhered dust on plasma-facing surfaces due to exposure to ELMy H-mode plasma in DIII-D

    Directory of Open Access Journals (Sweden)

    I. Bykov

    2017-08-01

    Full Text Available Transient heat load tests have been conducted in the lower divertor of DIII-D using DiMES manipulator in order to study the behavior of dust on tungsten Plasma Facing Components (PFCs during ELMy H-mode discharges. Samples with pre-adhered, pre-characterized dust have been exposed at the outer strike point (OSP in a series of discharges with varied intra-(inter- ELM heat fluxes. We used C dust because of its high sublimation temperature and non-metal properties. Al dust as a surrogate for Be and W dust were employed as relevant to that in the ITER divertor. The poor initial thermal contact between the substrate and the particles led to overheating, sublimation and shrinking of the carbon dust, and wetting induced coagulation of Al dust. Little modification of the W dust was observed. An enhanced surface adhesion and improvement of the thermal contact of C and Al dust were the result of exposure. A post mortem “adhesive tape” sampling showed that 70% of Al, <5% of W and C particles could not be removed from the surface owing to the improved adhesion. Al and C but not W particles that could be lifted had W inclusions indicating damage to the substrate. This suggests that non destructive methods may be inefficient for removal of dust in ITER.

  15. Mean and oscillating plasma flows and turbulence interactions across the L-H confinement transition.

    Science.gov (United States)

    Conway, G D; Angioni, C; Ryter, F; Sauter, P; Vicente, J

    2011-02-11

    A complex interaction between turbulence driven E × B zonal flow oscillations, i.e., geodesic acoustic modes (GAMs), the turbulence, and mean equilibrium flows is observed during the low to high (L-H) plasma confinement mode transition in the ASDEX Upgrade tokamak. Below the L-H threshold at low densities a limit-cycle oscillation forms with competition between the turbulence level and the GAM flow shearing. At higher densities the cycle is diminished, while in the H mode the cycle duration becomes too short to sustain the GAM, which is replaced by large amplitude broadband flow perturbations. Initially GAM amplitude increases as the H-mode transition is approached, but is then suppressed in the H mode by enhanced mean flow shear.

  16. Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas

    Science.gov (United States)

    Wynn, A.; Lipschultz, B.; Cziegler, I.; Harrison, J.; Jaervinen, A.; Matthews, G. F.; Schmitz, J.; Tal, B.; Brix, M.; Guillemaut, C.; Frigione, D.; Huber, A.; Joffrin, E.; Kruzei, U.; Militello, F.; Nielsen, A.; Walkden, N. R.; Wiesen, S.; Contributors, JET

    2018-05-01

    The low temperature boundary layer plasma (scrape-off layer or SOL) between the hot core and the surrounding vessel determines the level of power loading, erosion and implantation of material surfaces, and thus the viability of tokamak-based fusion as an energy source. This study explores mechanisms affecting the formation of flattened density profiles, so-called ‘density shoulders’, in the low-field side (LFS) SOL, which modify ion and neutral fluxes to surfaces—and subsequent erosion. We find that increases in SOL parallel resistivity, Λdiv (=[L || ν eiΩi]/c sΩe), postulated to lead to shoulder growth through changes in SOL turbulence characteristics, correlates with increases in SOL shoulder amplitude, A s, only under a subset of conditions (D2-fuelled L-mode density scans with outer strike point on the horizontal target). Λdiv fails to correlate with A s for cases of N2 seeding or during sweeping of the strike point across the horizontal target. The limited correlation of Λdiv and A s is also found for H-mode discharges. Thus, while it may be necessary for Λdiv to be above a threshold of ~1 for shoulder formation and/or growth, another mechanism is required. More significantly, we find that in contrast to parallel resistivity, outer divertor recycling, as quantified by the total outer divertor Balmer D α emission, I-D α , does scale with A s where Λdiv does and even where Λdiv does not. Divertor recycling could lead to SOL density shoulder formation through: (a) reducing the parallel to the field flow (loss) of ions out of the SOL to the divertor; and (b) changes in radial electric fields which lead to E  ×  B poloidal flows as well as potentially affecting SOL turbulence birth characteristics. Thus, changes in divertor recycling may be the sole process involved in bringing about SOL density shoulders or it may be that it acts in tandem with parallel resistivity.

  17. Discovery of stationary operation of quiescent H-mode plasmas with net-zero neutral beam injection torque and high energy confinement on DIII-D

    Energy Technology Data Exchange (ETDEWEB)

    Burrell, K. H.; Chen, X.; Garofalo, A. M.; Groebner, R. J.; Muscatello, C. M.; Osborne, T. H.; Petty, C. C.; Snyder, P. B. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Barada, K.; Rhodes, T. L.; Zeng, L. [University of California-Los Angeles, Los Angeles, California 90024 (United States); Solomon, W. M. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Yan, Z. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

    2016-05-15

    Recent experiments in DIII-D [J. L. Luxon et al., in Plasma Physics and Controlled Nuclear Fusion Research 1996 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] have led to the discovery of a means of modifying edge turbulence to achieve stationary, high confinement operation without Edge Localized Mode (ELM) instabilities and with no net external torque input. Eliminating the ELM-induced heat bursts and controlling plasma stability at low rotation represent two of the great challenges for fusion energy. By exploiting edge turbulence in a novel manner, we achieved excellent tokamak performance, well above the H{sub 98y2} international tokamak energy confinement scaling (H{sub 98y2} = 1.25), thus meeting an additional confinement challenge that is usually difficult at low torque. The new regime is triggered in double null plasmas by ramping the injected torque to zero and then maintaining it there. This lowers E × B rotation shear in the plasma edge, allowing low-k, broadband, electromagnetic turbulence to increase. In the H-mode edge, a narrow transport barrier usually grows until MHD instability (a peeling ballooning mode) leads to the ELM heat burst. However, the increased turbulence reduces the pressure gradient, allowing the development of a broader and thus higher transport barrier. A 60% increase in pedestal pressure and 40% increase in energy confinement result. An increase in the E × B shearing rate inside of the edge pedestal is a key factor in the confinement increase. Strong double-null plasma shaping raises the threshold for the ELM instability, allowing the plasma to reach a transport-limited state near but below the explosive ELM stability boundary. The resulting plasmas have burning-plasma-relevant β{sub N} = 1.6–1.8 and run without the need for extra torque from 3D magnetic fields. To date, stationary conditions have been produced for 2 s or 12 energy confinement times, limited only by external hardware constraints

  18. Repetitive 'snakes' and their damping effect on core toroidal rotation in EAST plasmas with multiple H-L-H transitions

    International Nuclear Information System (INIS)

    Xu Liqing; Hu Liqun

    2015-01-01

    Repetitive impurity snake-modes have been observed after H-L mode transitions (high to low confinement modes) in EAST plasmas exhibiting multiple H-L-H transitions. Such snake-modes have been observed to lower the core plasma toroidal rotation. A critical impurity strength factor associated with snake-mode formation has been estimated to be as high as α_Z_,_c =n_Z_,_cZ"2 / n_e ∼0.75. These observations have implications for ITER H-mode sustainability when the heating power is only slightly above the H-mode power threshold. (author)

  19. L-H transition in the mega-Amp spherical tokamak

    DEFF Research Database (Denmark)

    Akers, R.J.; Counsell, G.F.; Sykes, A.

    2002-01-01

    H-mode plasmas have been achieved on the MAST spherical tokamak at input power considerably higher than predicted by conventional threshold scalings. Following L-H transition, a clear improvement in energy confinement is obtained, exceeding recent international scalings even at densities approach...

  20. Edge stability and performance of the ELM-free quiescent H-mode and the quiescent double barrier mode on DIII-D

    International Nuclear Information System (INIS)

    West, W.P.; Burrell, K.H.; Snyder, P.B.; Gohil, P.; Lao, L.L.; Leonard, A.W.; Osborne, T.H.; Thomas, D.M.; Casper, T.A.; Lasnier, C.J.; Doyle, E.J.; Wang, G.; Zeng, L.; Nave, M.F.F.

    2005-01-01

    The quiescent H (QH) mode, an edge localized mode (ELM)-free, high-confinement mode, combines well with an internal transport barrier to form quiescent double barrier (QDB) stationary state, high performance plasmas. The QH-mode edge pedestal pressure is similar to that seen in ELMing phases of the same discharge, with similar global energy confinement. The pedestal density in early ELMing phases of strongly pumped counter injection discharges drops and a transition to QH-mode occurs, leading to lower calculated edge bootstrap current. Plasmas current ramp experiment and ELITE code modeling of edge stability suggest that QHmodes lie near an edge current stabilty boundary. At high triangularity, QH-mode discharges operate at higher pedestal density and pressure, and have achieved ITER level values of β PED and ν*. The QDB achieves performance of β N H 89 ∼ 7 in quasi-stationary conditions for a duration of 10 τ E , limited by hardware. Recently we demonstrated stationary state QDB discharges with little change in kinetic and q profiles (q 0 > 1) for 2 s, comparable to ELMing 'hybrid scenarios', yet without the debilitating effects of ELMs. Plasma profile control tools, including electron cyclotron heating and current drive and neutral beam heating, have been demonstrated to control simultaneously the q profile development, the density peaking, impurity accumulation and plasma beta. (author)

  1. The EPED pedestal model and edge localized mode-suppressed regimes: Studies of quiescent H-mode and development of a model for edge localized mode suppression via resonant magnetic perturbations

    Energy Technology Data Exchange (ETDEWEB)

    Snyder, P. B.; Osborne, T. H.; Burrell, K. H.; Groebner, R. J.; Leonard, A. W.; Wade, M. R. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Nazikian, R. [Princeton Plasma Physics Laboratory, Princeton, New Jersey (United States); Orlov, D. M. [University of California-San Diego, San Diego, California 92093 (United States); Schmitz, O. [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, Association FZJ-EURATOM, Juelich (Germany); Wilson, H. R. [York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD (United Kingdom)

    2012-05-15

    The EPED model predicts the H-mode pedestal height and width based upon two fundamental and calculable constraints: (1) onset of non-local peeling-ballooning modes at low to intermediate mode number, (2) onset of nearly local kinetic ballooning modes at high mode number. We present detailed tests of the EPED model in discharges with edge localized modes (ELMs), employing new high resolution measurements, and finding good quantitative agreement across a range of parameters. The EPED model is then applied for the first time to quiescent H-mode (QH), finding a similar level of agreement between predicted and observed pedestal height and width, and suggesting that the model can be used to predict the critical density for QH-mode operation. Finally, the model is applied toward understanding the suppression of ELMs with 3D resonant magnetic perturbations (RMP). Combining EPED with plasma response physics, a new working model for RMP ELM suppression is developed. We propose that ELMs are suppressed when a 'wall' associated with the RMP blocks the inward penetration of the edge transport barrier. A calculation of the required location of this 'wall' with EPED is consistent with observed profile changes during RMP ELM suppression and offers an explanation for the observed dependence on safety factor (q{sub 95}).

  2. Tokamak turbulence in self-regulated differentially rotating flow and L-H transition dynamics

    International Nuclear Information System (INIS)

    Terry, P.W.; Carreras, B.A.; Sidikman, K.

    1992-01-01

    An analytical study of turbulence in the presence of turbulently generated differentially rotating flow is presented as a paradigm for fluctuation dynamics in L- and H-mode plasmas. Using a drift wave model, the role of both flow shear and flow curvature (second radial derivative of the poloidal ExB flow) is detailed in linear and saturated turbulence phases. In the strong turbulence saturated state, finite amplitude-induced modification of the fluctuation structure near low order rational surfaces strongly inhibits flow shear suppression. Suppression by curvature is not diminished, but it occurs through a frequency shift. A description of L-H mode transition dynamics based on the self-consistent linking of turbulence suppression by differentially rotating flow and generation of flow by turbulent momentum transport is presented. In this model, rising edge temperature triggers a transition characterized by spontaneous generation of differentially rotating flow and decreasing turbulence intensity

  3. Energy exchange dynamics across L-H transitions in NSTX

    Science.gov (United States)

    Diallo, A.; Banerjee, S.; Zweben, S. J.; Stoltzfus-Dueck, T.

    2017-06-01

    We studied the energy exchange dynamics across the low-to-high-confinement (L-H) transition in NSTX discharges using the gas-puff imaging (GPI) diagnostic. The investigation focused on the energy exchange between flows and turbulence to help clarify the mechanism of the L-H transition. We applied this study to three types of heating schemes, including a total of 17 shots from the NSTX 2010 campaign run. Results show that the edge fluctuation characteristics (fluctuation levels, radial and poloidal correlation lengths) measured using GPI do not vary just prior to the H-mode transition, but change after the transition. Using a velocimetry approach (orthogonal-dynamics programming), velocity fields of a 24× 30 cm GPI view during the L-H transition were obtained with good spatial (˜1 cm) and temporal (˜2.5 μs) resolutions. Analysis using these velocity fields shows that the production term is systematically negative just prior to the L-H transition, indicating a transfer from mean flows to turbulence, which is inconsistent with the predator-prey paradigm. Moreover, the inferred absolute value of the production term is two orders of magnitude too small to explain the observed rapid L-H transition. These discrepancies are further reinforced by consideration of the ratio between the kinetic energy in the mean flow to the thermal free energy, which is estimated to be much less than 1, suggesting again that the turbulence depletion mechanism may not play an important role in the transition to the H-mode. Although the Reynolds work therefore appears to be too small to directly deplete the turbulent free energy reservoir, order-of-magnitude analysis shows that the Reynolds stress may still make a non-negligible contribution to the observed poloidal flows.

  4. Transitional Justice

    DEFF Research Database (Denmark)

    Gissel, Line Engbo

    This presentation builds on an earlier published article, 'Contemporary Transitional Justice: Normalising a Politics of Exception'. It argues that the field of transitional justice has undergone a shift in conceptualisation and hence practice. Transitional justice is presently understood to be th...... to be the provision of ordinary criminal justice in contexts of exceptional political transition.......This presentation builds on an earlier published article, 'Contemporary Transitional Justice: Normalising a Politics of Exception'. It argues that the field of transitional justice has undergone a shift in conceptualisation and hence practice. Transitional justice is presently understood...

  5. Causal impact of magnetic fluctuations in slow and fast L–H transitions at TJ-II

    Energy Technology Data Exchange (ETDEWEB)

    Milligen, B. Ph. van; Estrada, T.; Ascasíbar, E.; Hidalgo, C.; Pastor, I.; Fontdecaba, J. M. [Laboratorio Nacional de Fusion, CIEMAT, Avda. Complutense 40, 28040 Madrid (Spain); Carreras, B. A. [BACV Solutions, 110 Mohawk Road, Oak Ridge, Tennessee 37830 (United States); Balbín, R. [Instituto Español de Oceanografía, Centro Oceanográfico de Baleares, Muelle de Poniente s/n, 07015 Palma de Mallorca (Spain)

    2016-07-15

    This work focuses on the relationship between L–H (or L–I) transitions and MHD activity in the low magnetic shear TJ-II stellarator. It is shown that the presence of a low order rational surface in the plasma edge (gradient) region lowers the threshold density for H-mode access. MHD activity is systematically suppressed near the confinement transition. We apply a causality detection technique (based on the Transfer Entropy) to study the relation between magnetic oscillations and locally measured plasma rotation velocity (related to Zonal Flows). For this purpose, we study a large number of discharges in two magnetic configurations, corresponding to “fast” and “slow” transitions. With the “slow” transitions, the developing Zonal Flow prior to the transition is associated with the gradual reduction of magnetic oscillations. The transition itself is marked by a strong spike of “information transfer” from magnetic to velocity oscillations, suggesting that the magnetic drive may play a role in setting up the final sheared flow responsible for the H-mode transport barrier. Similar observations were made for the “fast” transitions. Thus, it is shown that magnetic oscillations associated with rational surfaces play an important and active role in confinement transitions, so that electromagnetic effects should be included in any complete transition model.

  6. Comparison of L-H transition measurements with physics models

    International Nuclear Information System (INIS)

    Carlstrom, T.N.; Burrell, K.H.; Carreras, B.A.

    1999-01-01

    Sawteeth and neutrals are found to have a significant influence on the H-mode power threshold scaling. The ion ∇B drift direction has only a small effect on the edge plasma conditions measured near the plasma midplane but a large effect on the divertor plasma. Since the power threshold changes dramatically with the direction of the ion ∇B drift, this implies that phenomena in the divertor region are critical for the L-H transition. Local conditions at the plasma edge are consistent with several theories of the L-H transition that use edge gradients in their formulation of a critical threshold parameter. However, scatter in the database is too large to distinguish between conditions that lead to an L-H transition and those that remain in L-mode. (author)

  7. Comparison of L-H transition measurements with physics models

    International Nuclear Information System (INIS)

    Carlstrom, T.N.; Burrell, K.H.; Groebner, R.J.

    2001-01-01

    Sawteeth and neutrals are found to have a significant influence on the H-mode power threshold scaling. The ion ∇B drift direction has only a small effect on the edge plasma conditions measured near the plasma midplane but a large effect on the divertor plasma. Since the power threshold changes dramatically with the direction of the ion ∇B drift, this implies that phenomena in the divertor region are critical for the L-H transition. Local conditions at the plasma edge are consistent with several theories of the L-H transition that use edge gradients in their formulation of a critical threshold parameter. However, scatter in the database is too large to distinguish between conditions that lead to an L-H transition and those that remain in L-mode. (author)

  8. Supporting Transition

    Science.gov (United States)

    Qureshi, Asima; Petrucco, James

    2018-01-01

    Meadowbrook Primary School has explored the use of The Teacher Assessment in Primary Science (TAPS) to support transition, initially for transfer to secondary school and now for transition from Early Years Foundation Stage (EYFS) into Key Stage 1 (ages 5-7). This article will consider an example of a secondary transition project and discuss the…

  9. Simulations of the L-H transition on experimental advanced superconducting Tokamak

    International Nuclear Information System (INIS)

    Weiland, Jan

    2014-01-01

    We have simulated the L-H transition on the EAST tokamak [Baonian Wan, EAST and HT-7 Teams, and International Collaborators, “Recent experiments in the EAST and HT-7 superconducting tokamaks,” Nucl. Fusion 49, 104011 (2009)] using a predictive transport code where ion and electron temperatures, electron density, and poloidal and toroidal momenta are simulated self consistently. This is, as far as we know, the first theory based simulation of an L-H transition including the whole radius and not making any assumptions about where the barrier should be formed. Another remarkable feature is that we get H-mode gradients in agreement with the α – α d diagram of Rogers et al. [Phys. Rev. Lett. 81, 4396 (1998)]. Then, the feedback loop emerging from the simulations means that the L-H power threshold increases with the temperature at the separatrix. This is a main feature of the C-mod experiments [Hubbard et al., Phys. Plasmas 14, 056109 (2007)]. This is also why the power threshold depends on the direction of the grad B drift in the scrape off layer and also why the power threshold increases with the magnetic field. A further significant general H-mode feature is that the density is much flatter in H-mode than in L-mode

  10. Radiation loss driven instabilities in laser heated plasmas

    International Nuclear Information System (INIS)

    Evans, R.G.

    1985-01-01

    Any plasma in which a significant part of the power balance is due to optically thin radiative losses may be subject to a radiation cooling instability. A simple analytical model gives the dispersion relation for the instability and inclusion of a realistic radiation loss term in a two dimensional hydrodynamic simulation shows that ''jet'' like features form in moderate to high Z plasmas

  11. Transition radiation and transition scattering

    International Nuclear Information System (INIS)

    Ginzburg, V.L.

    1982-01-01

    Transition radiation is a process of a rather general character. It occurs when some source, which does not have a proper frequency (for example, a charge) moves at a constant velocity in an inhomogeneous and (or) nonstationary medium or near such a medium. The simplest type of transition radiation takes place when a charge crosses a boundary between two media (the role of one of the media may be played by vacuum). In the case of periodic variation of the medium, transition radiation possesses some specific features (resonance transition radiation or transition scattering). Transition scattering occurs, in particular, when a permittivity wave falls onto an nonmoving (fixed) charge. Transition scattering is closely connected with transition bremsstrahlung radiation. All these transition processes are essential for plasma physics. Transition radiation and transition scattering have analogues outside the framework of electrodynamics (like in the case of Vavilov-Cherenkov radiation). In the present report the corresponding range of phenomena is elucidated, as far as possible, in a generally physical aspect. (Auth.)

  12. Phase transitions

    CERN Document Server

    Sole, Ricard V; Solé, Ricard V; Solé, Ricard V; Sol, Ricard V; Solé, Ricard V

    2011-01-01

    Phase transitions--changes between different states of organization in a complex system--have long helped to explain physics concepts, such as why water freezes into a solid or boils to become a gas. How might phase transitions shed light on important problems in biological and ecological complex systems? Exploring the origins and implications of sudden changes in nature and society, Phase Transitions examines different dynamical behaviors in a broad range of complex systems. Using a compelling set of examples, from gene networks and ant colonies to human language and the degradation of diverse ecosystems, the book illustrates the power of simple models to reveal how phase transitions occur. Introductory chapters provide the critical concepts and the simplest mathematical techniques required to study phase transitions. In a series of example-driven chapters, Ricard Solé shows how such concepts and techniques can be applied to the analysis and prediction of complex system behavior, including the origins of ...

  13. Transit transparency.

    Science.gov (United States)

    2012-07-01

    Public transit agencies have employed intelligent systems for determining : schedules and routes and for monitoring the real-time location and status of their : vehicle fleets for nearly two decades. But until recently, the data generated by : daily ...

  14. Energy Exchange Dynamics across L-H transitions in NSTX

    Science.gov (United States)

    Diallo, Ahmed

    2017-10-01

    H-mode is planned for future devices such as ITER, and is preceded by a low (L) to high (H) transition. A key question remains. What is the mechanism behind the L-H transition? Most theoretical descriptions of the L-H transition are based on the shear of the radial electric field and coincident ExB poloidal flow shear, which is thought to be responsible for the onset of the anomalous transport suppression that leads to the L-H transition. This talk will focus on the analysis of the flow dynamics across the L-H transition in NSTX. We analyze the L-H transition dynamics using the velocimetry of 2D edge turbulence data from gas-puff imaging (GPI). We determine the velocity components at the edge across the L-H transition for 17 discharges with three types of heating power (NBI, ohmic, and RF). Using a reduced model equation of edge flows and turbulence, the energy transfer dynamics is compared with the turbulence depletion hypothesis of the predator-prey model. In order for Reynolds work to suppress the turbulence, it must deplete the total turbulent free energy, including the thermal free-energy term. For this to occur, the increase in kinetic energy in the mean flow over the L-H transition must be comparable to the pre-transition thermal free energy. However, this ratio was found to be of order 10-2. Although there are significant simplifications in the theoretical model, they are unlikely to cause inaccuracy by two orders of magnitude, suggesting that direct turbulence depletion by the Reynolds work may not be large enough to explain the L-H transition on NSTX, contrary to the predator-prey model. This work is supported by the US DOE Contract No. DE-AC02-09CH11466.

  15. Turbulence simulations of X point physics on the L-H transitions

    International Nuclear Information System (INIS)

    Xu, X.Q.; Cohen, R.H.; Nevins, W.M.

    2001-01-01

    We show that the resistive X-point mode is the dominant mode in boundary plasmas in X-point divertor geometry. The poloidal fluctuation phase velocity from the simulation results of the resistive X-point turbulence shows experimentally measured structure across separatrix in many fusion devices. The fluctuation phase velocity is larger than ExB velocity both in L and H mode phases. We also demonstrate that there is a strong poloidal asymmetry of particle flux in the proximity of the separatrix. Turbulence suppression in the L-H transition results when sources of energy and particles drive sufficient gradients as in the experiments. (author)

  16. Transit space

    DEFF Research Database (Denmark)

    Raahauge, Kirsten Marie

    2008-01-01

    This article deals with representations of one specific city, Århus, Denmark, especially its central district. The analysis is based on anthropological fieldwork conducted in Skåde Bakker and Fedet, two well-off neighborhoods. The overall purpose of the project is to study perceptions of space...... and the interaction of cultural, social, and spatial organizations, as seen from the point of view of people living in Skåde Bakker and Fedet. The focus is on the city dwellers’ representations of the central district of Århus with specific reference to the concept of transit space. When applied to various Århusian...

  17. Transition region

    International Nuclear Information System (INIS)

    Jordan, C.

    1977-01-01

    The Glossary is designed to be a technical dictionary that will provide solar workers of various specialties, students, other astronomers and theoreticians with concise information on the nature and the properties of phenomena of solar and solar-terrestrial physics. Each term, or group of related terms, is given a concise phenomenological and quantitative description, including the relationship to other phenomena and an interpretation in terms of physical processes. The references are intended to lead the non-specialist reader into the literature. This section deals with: transition region; di-electronic recombination; intersystem or intercombination lines; satellite lines; grazing-incidence optics; and crystal spectrometers. (B.R.H.)

  18. Transitional issues

    International Nuclear Information System (INIS)

    1998-01-01

    This discussion paper, the fifth in the series developed at the IPPSO Market Design Conference, addressed the issue of the need to prevent Ontario Hydro from taking unfair advantage of independent producers and other stakeholders through activities and investments in new power generating capacity in the transitional period leading up to deregulation. The need for controls is predicated on the assumption that the short-term actions and investments of Ontario Hydro could seriously compromise the position of independent generators, and that without such controls the level playing field essential to the operation of a competitive market, does not exist. Various actual and potential actions of Ontario Hydro were discussed, all of which point to the need for strict controls over Ontario Hydro exercising its dominant market power in an unfair way. It was recommended that as a minimum, the provincial government should no longer provide guarantees for Ontario Hydro capital projects, and that Ontario Hydro be instructed to defer any investment on new or returning generating capacity until the new market is in place. Limits could also be placed on Ontario Hydro's marketing efforts to enter into contracts during the transition period, and Ontario Hydro and municipal utilities should be required to keep separate accounts of their commercial preparation, and to settle such accounts separate from ratepayer revenue

  19. Energy transition

    International Nuclear Information System (INIS)

    Anon.

    2013-01-01

    The yearly environmental conference will hold on September 2013 to evaluate the negotiations led at the national and local levels for december 2012. The government will have then to decide of an energy programming bill which will be submitted to the Parliament at the beginning of the year 2014. 30 main propositions have emerged of the decentralised debates. One of them is the ecological taxation which raise the question of the gas oil and petrol taxation. The current environmental taxes are for almost three quarters of them taxes on energy consumptions and mainly on fossil energies. The Economic, Social and Environmental Council, gives his opinion on the way to find resources to ensure the ecological and energy transition while reducing the public deficit of the State. (O.M.)

  20. The simulation of L-H transition in tokamak plasma using MMM95 transport model

    International Nuclear Information System (INIS)

    Intharat, P; Poolyarat, N; Chatthong, B; Onjun, T; Picha, R

    2015-01-01

    BALDUR integrative predictive modelling code together with a Multimode (MMM95) anomalous transport model is used to simulate the evolution profiles, including plasma current, temperature, density and energy in a tokamak reactor. It is found that a self - transition from low confinement mode (L-mode) to high confinement mode (H-mode) regimes can be achieved once a sufficient auxiliary heating applied to the plasma is reached. The result agrees with experimental observations from various tokamaks. A strong reduction of turbulent transport near the edge of plasma is also observed, which is related to the formation of steep radial electric field near the edge regime. From transport analysis, it appears that the resistive ballooning mode is the dominant term near the plasma edge regime, which is significantly reduced during the transition. (paper)

  1. Locality effects on bifurcation paradigm of L-H transition in tokamak plasmas

    Directory of Open Access Journals (Sweden)

    Boonyarit Chatthong

    2015-12-01

    Full Text Available The locality effects on bifurcation paradigm of L-H transition phenomenon in magnetic confinement plasmas are investigated. One dimensional thermal transport equation with both neoclassical and anomalous transports effects included is considered, where a flow shear due to pressure gradient component is included as a transport suppression mechanism. Three different locally driven models for anomalous transport are considered, including a constant transport model, pressure gradient driven transport model, and critical pressure gradient threshold transport model. Local stability analysis shows that the transition occurs at a threshold flux with hysteresis nature only if ratio of anomalous strength over neoclassical transport exceeds a critical value. The depth of the hysteresis loop depends on both neoclassical and anomalous transports, as well as the suppression strength. The reduction of the heat flux required to maintain H-mode can be as low as a factor of two, which is similar to experimental evidence.

  2. Comparison of a low- to high-confinement transition theory with experimental data from DIII-D.

    Science.gov (United States)

    Guzdar, P N; Kleva, R G; Groebner, R J; Gohil, P

    2002-12-23

    From our recent theory based on the generation of shear flow and field in finite beta plasmas, the criterion for bifurcation from low to high confinement mode yields a critical parameter proportional to T(e)/square root (L(n)), where T(e) is the electron temperature and L(n) is the density scale length. The predicted threshold shows very good agreement with edge measurements on discharges undergoing low-to-high transitions in DIII-D. The observed differences in the transitions with the reversal of the toroidal magnetic field are reconciled in terms of this critical parameter. The theory also provides an explanation for pellet injection H modes in DIII-D, thereby unifying unconnected methods for accomplishing the transition.

  3. Numerical modeling of the transition from low to high confinement in magnetically confined plasma

    International Nuclear Information System (INIS)

    Rasmussen, J Juul; Nielsen, A H; Madsen, J; Naulin, V; Xu, G S

    2016-01-01

    The transition dynamics from low (L) to high (H) mode confinement in magnetically confined plasmas is investigated using a four-field drift fluid model—HESEL (Hot Edge-Sol-Electrostatic). The model includes profile evolution and is solved in a 2D domain at the out-board mid-plane of a tokamak including both open and closed field lines. The results reveal different types of L–H-like transitions in response to ramping up the input power by increasing the ion temperature in the edge region. For a fast rising input power we obtain an abrupt transition, and for a slow rising power we obtain a L–I–H transition with an intermediate I-phase displaying limit-cycle oscillations (LCO). The model recovers the power threshold for the L–H transition, the scaling of the threshold with the density and with the loss-rate in the SOL, indicating a decrease in power threshold when switching from single to double null configuration. The results hold promises for developing full predictive modeling of the L–H transition, which is an essential step in understanding and optimizing fusion devices. (paper)

  4. Particle transport in JET and TCV-H mode plasmas

    International Nuclear Information System (INIS)

    Maslov, M.

    2009-10-01

    Understanding particle transport physics is of great importance for magnetically confined plasma devices and for the development of thermonuclear fusion power for energy production. From the beginnings of fusion research, more than half a century ago, the problem of heat transport in tokamaks attracted the attention of researchers, but the particle transport phenomena were largely neglected until fairly recently. As tokamak physics advanced to its present level, the physics community realized that there are many hurdles to the development of fusion power beyond the energy confinement. Particle transport is one of the outstanding issues. The aim of this thesis work is to study the anomalous (turbulence driven) particle transport in tokamaks on the basis of experiments on two different devices: JET (Joint European Torus) and TCV (Tokamak à Configuration Variable). In particular the physics of particle inward convection (pinch), which causes formation of peaked density profiles, is addressed in this work. Density profile peaking has a direct, favorable effect on fusion power in a reactor, we therefore also propose an extrapolation to the international experimental reactor ITER, which is currently under construction. To complete the thesis research, a comprehensive experimental database was created on the basis of data collected on JET and TCV during the duration of the thesis. Improvements of the density profile measurements techniques and careful analysis of the experimental data allowed us to derive the dependencies of density profile shape on the relevant plasma parameters. These improved techniques also allowed us to dispel any doubts that had been voiced about previous results. The major conclusions from previous work on JET and other tokamaks were generally confirmed, with some minor supplements. The main novelty of the thesis resides in systematic tests of the predictions of linear gyrokinetic simulations of the ITG (Ion Temperature Gradient) mode against the experimental observations. The simulations were performed with the GS2 code. The parameter dependencies of plasma density gradient, as observed on JET, are a good agreement with those from the simulations over a wide range. The simulations done for the TCV case, which are in a different physics parameter domain, are also in partial agreement with the experiment. Complete agreement is not out of the question, but will remain a goal for the future, when measurements of one of the most important parameters will be available. The good agreement between the experiment and the simulations suggests that the ITG instability may be responsible for the majority of the anomalous inward particle convection observed in tokamaks. Both the simulations and the empirical data extrapolations predicting a peaked density profile in ITER plasma conditions, instead of a flat one, as was assumed during the concept design period. (author)

  5. Kinetic neoclassical transport in the H-mode pedestal

    Energy Technology Data Exchange (ETDEWEB)

    Battaglia, D. J.; Chang, C. S.; Ku, S.; Grierson, B. A. [Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08540 (United States); Burrell, K. H.; Grassie, J. S. de [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)

    2014-07-15

    Multi-species kinetic neoclassical transport through the QH-mode pedestal and scrape-off layer on DIII-D is calculated using XGC0, a 5D full-f particle-in-cell drift-kinetic solver with self-consistent neutral recycling and sheath potentials. Quantitative agreement between the flux-driven simulation and the experimental electron density, impurity density, and orthogonal measurements of impurity temperature and flow profiles is achieved by adding random-walk particle diffusion to the guiding-center drift motion. The radial electric field (E{sub r}) that maintains ambipolar transport across flux surfaces and to the wall is computed self-consistently on closed and open magnetic field lines and is in excellent agreement with experiment. The E{sub r} inside the separatrix is the unique solution that balances the outward flux of thermal tail deuterium ions against the outward neoclassical electron flux and inward pinch of impurity and colder deuterium ions. Particle transport in the pedestal is primarily due to anomalous transport, while the ion heat and momentum transport are primarily due to the neoclassical transport. The full-f treatment quantifies the non-Maxwellian energy distributions that describe a number of experimental observations in low-collisionallity pedestals on DIII-D, including intrinsic co-I{sub p} parallel flows in the pedestal, ion temperature anisotropy, and large impurity temperatures in the scrape-off layer.

  6. Studies of energy transport in Jet H-modes

    International Nuclear Information System (INIS)

    Keilhacker, M.; Balet, B.; Cordey, J.; Gottardi, N.; Muir, D.; Thomsen, K.; Watkins, M.

    1989-01-01

    The local heat transport properties in the interior of ohmic, L- and H-phases of 2MA discharges, are determined. Time dependent energy balance code, TRANSP, and timeslice code, QFLUX are used. The global confinement properties of higher current discharges (≤ 3.8MA) are analyzed. The results indicate that during the L-phase of JET single null X-point discharges, the total heat transport coefficient in the plasma decreases to a level close to the ohmic value. Moreover, confinement during the H-phase continues to improve with current (up to 3.8MA), but degrades with increasing neutral beam power

  7. Ohmic H-mode and confinement in TCV

    Czech Academy of Sciences Publication Activity Database

    Moret, J. M.; Anton, M.; Barry, S.; Behn, R.; Besson, G.; Buhlmann, F.; Burri, A.; Chavan, R.; Corboz, M.; Deschenaux, C.; Dutch, M. J.; Duval, B. P.; Fasel, A.; Favre, A.; Franke, S.; Hirt, A.; Hofmann, F.; Hollenstein, C.; Isoz, P. F.; Joye, B.; Lister, J. B.; Llobet, X.; Magnin, J. C.; Mandrin, P.; Marletaz, B.; Marmillod, P.; Martin, Y.; Mayor, J. M.; Moravec, Jaroslav; Nieswand, C.; Paris, P. J.; Perez, A.; Pietrzyk, Z. A.; Piffl, Vojtěch; Pitts, R. A.; Pochelon, A.; Sauter, O.; Toledo van, W.; Tonetti, G.; Tran, M. Q.; Troyon, F.; Ward, D. J.; Weisen, H.

    1995-01-01

    Roč. 37, 11A (1995), s. A215-A226 ISSN 0741-3335. [EPS Conference on Controlled Fusion and Plasma Physics /22./. Bournemouth, 03.07.1995-07.07.1995] R&D Projects: GA AV ČR IAA1043501 Impact factor: 2.020, year: 1995

  8. Numerical modeling of the transition from low to high confinement in magnetically confined plasma

    DEFF Research Database (Denmark)

    Rasmussen, Jens Juul; Nielsen, Anders Henry; Madsen, Jens

    2016-01-01

    The transition dynamics from low (L) to high (H) mode confinement in magnetically confined plasmas is investigated using a four-field drift fluid model—HESEL (Hot Edge-Sol-Electrostatic). The model includes profile evolution and is solved in a 2D domain at the out-board mid-plane of a tokamak......–I–H transition with an intermediate I-phase displaying limit-cycle oscillations (LCO). The model recovers the power threshold for the L–H transition, the scaling of the threshold with the density and with the loss-rate in the SOL, indicating a decrease in power threshold when switching from single to double null...... including both open and closed field lines. The results reveal different types of L–H-like transitions in response to ramping up the input power by increasing the ion temperature in the edge region. For a fast rising input power we obtain an abrupt transition, and for a slow rising power we obtain a L...

  9. Rapid change of ion energy distribution and floating potential at L/H transition in the JFT-2M tokamak

    International Nuclear Information System (INIS)

    Miura, Y.; Nagashima, K.; Okano, F.

    1994-01-01

    Rapid changes of the main ion energy distribution at transitions from L-to-H, H-to-L and during ELMs are studied with the time of flight neutral measurement in the JFT-2M tokamak. The change of the main ion energy distribution after sawtooth crash during an L-mode phase is also studied. The change of the ion energy distribution just after sawtooth crash is the same as that at L/H-transition. The floating potential measured in the SOL also shows the rapid jump to more positive just after the sawtooth crash (at the same time of the change of an ion energy distribution). This shows the increase of ion outflux in the SOL and might correspond to the change of the ion energy distribution. This may be the reason why most of H-modes are triggered by a sawtooth. (author)

  10. Biodiesel Mass Transit Demonstration

    Science.gov (United States)

    2010-04-01

    The Biodiesel Mass Transit Demonstration report is intended for mass transit decision makers and fleet managers considering biodiesel use. This is the final report for the demonstration project implemented by the National Biodiesel Board under a gran...

  11. Public Transit Stations

    Data.gov (United States)

    Department of Homeland Security — fixed rail transit stations within the Continental United States, Alaska, Hawaii, the District of Columbia, and Puerto Rico. The modes of transit that are serviced...

  12. Neoclassical transport, poloidal rotation and radial electric field at the L-H transition

    International Nuclear Information System (INIS)

    Minardi, E.; Gervasini, G.; Lazzaro, E.

    1993-01-01

    The transition to a high confinement regime in tokamaks operating with a magnetic divertor configuration is accompanied by the strong steepening of the edge temperature profile and the onset of a large positive poloidal mass rotation associated with a negative radial electric field. The latter phenomena are signatures of a neoclassical transport mechanism. We address the question of establishing whether neoclassical transport is indeed sufficient to establish high edge gradients and drive poloidal rotation under strong auxiliary heating. The heat transport equation is solved numerically in a narrow edge layer interfaced to the plasma body through heat flux continuity, but allowing for heat conductivity discontinuity. The results compared with recent experimental measurements support the assumption that a highly sheared neoclassical poloidal velocity profile can suppress the anomalous part of the heat transport, and that the neoclassical residual transport, characterizes the plasma behaviour at the edge during H modes. (author) 3 refs., 4 figs

  13. Morphological transition of ZnO nanostructures influenced by magnesium doping

    International Nuclear Information System (INIS)

    Premkumar, T.; Zhou, Y.S.; Gao, Y.; Baskar, K.; Jiang, L.; Lu, Y.F.

    2012-01-01

    Wurtzite zinc oxide (ZnO) nanochains have been synthesized through high-pressure pulsed laser deposition. The chain-like ZnO nanostructures were obtained from magnesium (Mg) doped ZnO targets, whereas vertically aligned nanorods were obtained from primitive ZnO targets. The Mg doping has influenced the morphological transition of ZnO nanostructures from nanorods to nanochains. The field emission scanning electron microscope images revealed the growth of beaded ZnO nanochains. The ZnO nanochains of different diameters 40 and 120 nm were obtained. The corresponding micro-Raman spectra showed strong E 2H mode of ZnO, which confirmed the good crystallinity of the nanochains. In addition to near band edge emission at 3.28 eV, ZnO nanochains show broad deep level emission at 2.42 eV than that of ZnO nanorods.

  14. Quantum phase transitions

    International Nuclear Information System (INIS)

    Sachdev, S.

    1999-01-01

    Phase transitions are normally associated with changes of temperature but a new type of transition - caused by quantum fluctuations near absolute zero - is possible, and can tell us more about the properties of a wide range of systems in condensed-matter physics. Nature abounds with phase transitions. The boiling and freezing of water are everyday examples of phase transitions, as are more exotic processes such as superconductivity and superfluidity. The universe itself is thought to have passed through several phase transitions as the high-temperature plasma formed by the big bang cooled to form the world as we know it today. Phase transitions are traditionally classified as first or second order. In first-order transitions the two phases co-exist at the transition temperature - e.g. ice and water at 0 deg., or water and steam at 100 deg. In second-order transitions the two phases do not co-exist. In the last decade, attention has focused on phase transitions that are qualitatively different from the examples noted above: these are quantum phase transitions and they occur only at the absolute zero of temperature. The transition takes place at the ''quantum critical'' value of some other parameter such as pressure, composition or magnetic field strength. A quantum phase transition takes place when co-operative ordering of the system disappears, but this loss of order is driven solely by the quantum fluctuations demanded by Heisenberg's uncertainty principle. The physical properties of these quantum fluctuations are quite distinct from those of the thermal fluctuations responsible for traditional, finite-temperature phase transitions. In particular, the quantum system is described by a complex-valued wavefunction, and the dynamics of its phase near the quantum critical point requires novel theories that have no analogue in the traditional framework of phase transitions. In this article the author describes the history of quantum phase transitions. (UK)

  15. Cosmological phase transitions

    International Nuclear Information System (INIS)

    Kolb, E.W.

    1993-10-01

    If modern ideas about the role of spontaneous symmetry breaking in fundamental physics are correct, then the Universe should have undergone a series of phase transitions early in its history. The study of cosmological phase transitions has become an important aspect of early-Universe cosmology. In this lecture I review some very recent work on three aspects of phase transitions: the electroweak transition, texture, and axions

  16. Modeling for transition management

    NARCIS (Netherlands)

    Chappin, E.J.L.; Dijkema, G.P.J.

    2015-01-01

    A framework for the modeling and simulation of transitions is presented. A transition, “substantial change in the state of a socio-technical system”, typically unfolds over a long timespan. We therefore suggest to use simulation to inform transition managers on the effect of their decisions.

  17. Modeling for Transition Management

    NARCIS (Netherlands)

    Chappin, Emile J L; Dijkema, Gerard P.J.

    2015-01-01

    A framework for the modeling and simulation of transitions is presented. A transition, “substantial change in the state of a socio-technical system”, typically unfolds over a long timespan. We therefore suggest to use simulation to inform transition managers on the effect of their decisions.

  18. Microwave stability at transition

    International Nuclear Information System (INIS)

    Holt, J.A.; Colestock, P.L.

    1995-05-01

    The question of microwave stability at transition is revisited using a Vlasov approach retaining higher order terms in the particle dynamics near the transition energy. A dispersion relation is derived which can be solved numerically for the complex frequency in terms of the longitudinal impedance and other beam parameters. Stability near transition is examined and compared with simulation results

  19. Transit manager's handbook.

    Science.gov (United States)

    2011-09-01

    This handbook provides an overview of public transit in Iowa and how to do business with the Iowa Department of Transportation (Iowa DOT) Office of Public Transit (OPT). It is intended to be a tool to assist transit managers navigate through the many...

  20. Transit labor relations guide

    Science.gov (United States)

    2001-09-01

    This report is designed as a guide for those involved in labor relations in the transit industry. It begins with a history of transit labor relations. The economic, political, and legal environment of transit relations is then discussed. A section fo...

  1. Transition: Preschool to Kindergarten

    Science.gov (United States)

    Arizona Department of Education, 2007

    2007-01-01

    Transition is movement or change without interruption. It should be a smooth flow from one place or condition to another. While the transition plan for a student receiving special education services is designed to prepare him or her for life after high school, transition can start when a child enters preschool. The second of six distinct stages of…

  2. Transition Theory – Sustainable Transition of Socio-Technical Systems

    DEFF Research Database (Denmark)

    Søndergård, Bent; Holm, Jesper; Stauning, Inger

    2015-01-01

    Theories of transition management, transition studies and social practise theory Applied to studies of hosuing and construction......Theories of transition management, transition studies and social practise theory Applied to studies of hosuing and construction...

  3. Gifts from Exoplanetary Transits

    Science.gov (United States)

    Narita, Norio

    2009-08-01

    The discovery of transiting extrasolar planets has enabled us to do a number of interesting studies. Transit photometry reveals the radius and the orbital inclination of transiting planets, which allows us to learn the true mass and density of the respective planets by the combined information from radial velocity (RV) measurements. In addition, follow-up observations of transiting planets, looking at such things as secondary eclipses, transit timing variations, transmission spectroscopy, and the Rossiter-McLaughlin effect, provide us information about their dayside temperatures, unseen bodies in systems, planetary atmospheres, and the obliquity of planetary orbits. Such observational information, which will provide us a greater understanding of extrasolar planets, is available only for transiting planets. Here, I briefly summarize what we can learn from transiting planets and introduce previous studies.

  4. A statistical method for model extraction and model selection applied to the temperature scaling of the L–H transition

    International Nuclear Information System (INIS)

    Peluso, E; Gelfusa, M; Gaudio, P; Murari, A

    2014-01-01

    Access to the H mode of confinement in tokamaks is characterized by an abrupt transition, which has been the subject of continuous investigation for decades. Various theoretical models have been developed and multi-machine databases of experimental data have been collected. In this paper, a new methodology is reviewed for the investigation of the scaling laws for the temperature threshold to access the H mode. The approach is based on symbolic regression via genetic programming and allows first the extraction of the most statistically reliable models from the available experimental data. Nonlinear fitting is then applied to the mathematical expressions found by symbolic regression; this second step permits to easily compare the quality of the data-driven scalings with the most widely accepted theoretical models. The application of a complete set of statistical indicators shows that the data-driven scaling laws are qualitatively better than the theoretical models. The main limitations of the theoretical models are that they are all expressed as power laws, which are too rigid to fit the available experimental data and to extrapolate to ITER. The proposed method is absolutely general and can be applied to the extraction or scaling law from any experimental database of sufficient statistical relevance. (paper)

  5. Workers in transition

    OpenAIRE

    Rutkowski, Michael

    1995-01-01

    After Central and Eastern European and Central Asian economies abandoned central planning, nearly 195 million workers had to adjust to new rules of work and life. Most transition economies have not yet fully committed themselves to the rules of the market place. A few that have are already enjoying growth in wages and employment; in other countries, labor income growth is still to come. Reform has not been so well accepted in countries that were forced to enter the transition. Transition brou...

  6. Transition and Social networks

    OpenAIRE

    Raghavan, Raghu; Pawson, N.

    2011-01-01

    School leavers with learning disabilities often face difficulties in making a smooth transition from school to college, employment or more broadly, to adult life. The transition phase is traumatic for the young person with learning disabilities and their families as it often results in the loss of friendships, relationships and social networks. The aim of this chapter is to explore the issues of transition from adolescence to adulthood for young people with learning disabilities and its effe...

  7. Thermodynamics of phase transitions

    International Nuclear Information System (INIS)

    Cofta, H.

    1972-01-01

    The phenomenology of the phase transitions has been considered. The definitions of thermodynamic functions and parameters, as well as those of the phase transitions, are given and some of the relations between those quantities are discussed. The phase transitions classification proposed by Ehrenfest has been described. The most important features of phase transitions are discussed using the selected physical examples including the critical behaviour of ferromagnetic materials at the Curie temperature and antiferromagnetic materials at the Neel temperature. Some aspects of the Ehrenfest's equations, that have been derived, for the interfacial lines and surfaces are considered as well as the role the notion of interfaces. (S.B.)

  8. The Energy Transition Chronicles

    International Nuclear Information System (INIS)

    Cappelletti, Floriane; Vallar, Jean-Pierre; Wyssling, Julia

    2015-01-01

    Energy Cities provides local authorities with support for implementing their own energy transition process. The Proposals for the energy transition of cities and towns (www.energy-cities.eu/30proposals) are illustrated with around a hundred of inspirational examples from all over Europe. In this document composed of five case reports, Energy Cities goes further and tells the tale of energy transition success stories. Because it is important to show that energy transition is 'possible'. Why, how, with whom, for what results? We interviewed local players and decision-makers to find out more. Here are their stories

  9. Transit Benefit Program Data -

    Data.gov (United States)

    Department of Transportation — This data set contains information about any US government agency participating in the transit benefits program, funding agreements, individual participating Federal...

  10. Eigenstate Phase Transitions

    Science.gov (United States)

    Zhao, Bo

    Phase transitions are one of the most exciting physical phenomena ever discovered. The understanding of phase transitions has long been of interest. Recently eigenstate phase transitions have been discovered and studied; they are drastically different from traditional thermal phase transitions. In eigenstate phase transitions, a sharp change is exhibited in properties of the many-body eigenstates of the Hamiltonian of a quantum system, but not the thermal equilibrium properties of the same system. In this thesis, we study two different types of eigenstate phase transitions. The first is the eigenstate phase transition within the ferromagnetic phase of an infinite-range spin model. By studying the interplay of the eigenstate thermalization hypothesis and Ising symmetry breaking, we find two eigenstate phase transitions within the ferromagnetic phase: In the lowest-temperature phase the magnetization can macroscopically oscillate by quantum tunneling between up and down. The relaxation of the magnetization is always overdamped in the remainder of the ferromagnetic phase, which is further divided into phases where the system thermally activates itself over the barrier between the up and down states, and where it quantum tunnels. The second is the many-body localization phase transition. The eigenstates on one side of the transition obey the eigenstate thermalization hypothesis; the eigenstates on the other side are many-body localized, and thus thermal equilibrium need not be achieved for an initial state even after evolving for an arbitrary long time. We study this many-body localization phase transition in the strong disorder renormalization group framework. After setting up a set of coarse-graining rules for a general one dimensional chain, we get a simple "toy model'' and obtain an almost purely analytical solution to the infinite-randomness critical fixed point renormalization group equation. We also get an estimate of the correlation length critical exponent nu

  11. Transitivity of Preferences

    Science.gov (United States)

    Regenwetter, Michel; Dana, Jason; Davis-Stober, Clintin P.

    2011-01-01

    Transitivity of preferences is a fundamental principle shared by most major contemporary rational, prescriptive, and descriptive models of decision making. To have transitive preferences, a person, group, or society that prefers choice option "x" to "y" and "y" to "z" must prefer "x" to…

  12. Alaska Community Transit

    Science.gov (United States)

    Grant Information Human Services Funding 5310 5316 (Repealed) 5317 (Repealed) Alaska Mental Health Trust Department of Transportation & Public Facilities/ Alaska Community Transit Search DOT&PF State of Alaska Photo banner DOT&PF> Program Development > Alaska Community Transit Home About Us

  13. Distance-transitive graphs

    NARCIS (Netherlands)

    Cohen, A.M.; Beineke, L.W.; Wilson, R.J.; Cameron, P.J.

    2004-01-01

    In this chapter we investigate the classification of distance-transitive graphs: these are graphs whose automorphism groups are transitive on each of the sets of pairs of vertices at distance i, for i = 0, 1,.... We provide an introduction into the field. By use of the classification of finite

  14. Towards Transition Theory

    NARCIS (Netherlands)

    J. de Haan (Hans)

    2010-01-01

    textabstractThis thesis is a treatise on a theory for societal transitions: pillar theory. Societal transitions are complex processes taking place in complex systems, large-scale, long-term processes in which societal systems radically change the way they are composed and function. Since we all are

  15. Matter in transition

    International Nuclear Information System (INIS)

    Anderson, Lara B.; Gray, James; Raghuram, Nikhil; Taylor, Washington

    2016-01-01

    We explore a novel type of transition in certain 6D and 4D quantum field theories, in which the matter content of the theory changes while the gauge group and other parts of the spectrum remain invariant. Such transitions can occur, for example, for SU(6) and SU(7) gauge groups, where matter fields in a three-index antisymmetric representation and the fundamental representation are exchanged in the transition for matter in the two-index antisymmetric representation. These matter transitions are realized by passing through superconformal theories at the transition point. We explore these transitions in dual F-theory and heterotic descriptions, where a number of novel features arise. For example, in the heterotic description the relevant 6D SU(7) theories are described by bundles on K3 surfaces where the geometry of the K3 is constrained in addition to the bundle structure. On the F-theory side, non-standard representations such as the three-index antisymmetric representation of SU(N) require Weierstrass models that cannot be realized from the standard SU(N) Tate form. We also briefly describe some other situations, with groups such as Sp(3), SO(12), and SU(3), where analogous matter transitions can occur between different representations. For SU(3), in particular, we find a matter transition between adjoint matter and matter in the symmetric representation, giving an explicit Weierstrass model for the F-theory description of the symmetric representation that complements another recent analogous construction.

  16. Transitional Employment Programs.

    Science.gov (United States)

    Dulle, Paul J.; And Others

    The paper examines the need and implementation of transitional employment programs for handicapped youth. Effects on the handicapped of future automation are considered along with the need for school-business cooperation to prepare for the future. The importance of initial success in any innovation is noted. A Chicago transitional employment…

  17. Transitive probabilistic CLIR models.

    NARCIS (Netherlands)

    Kraaij, W.; de Jong, Franciska M.G.

    2004-01-01

    Transitive translation could be a useful technique to enlarge the number of supported language pairs for a cross-language information retrieval (CLIR) system in a cost-effective manner. The paper describes several setups for transitive translation based on probabilistic translation models. The

  18. Bridging the Transition Gap

    Science.gov (United States)

    2013-05-23

    period and provide recommendations to guide future research and policy development. 4 DEFINING THE TRANSITIONAL SECURITY GAP There have been...BRIDGING THE TRANSITION GAP A Monograph by MAJ J.D. Hansen United States Army School of Advanced Military Studies United States Army...suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704

  19. Transition probabilities for atoms

    International Nuclear Information System (INIS)

    Kim, Y.K.

    1980-01-01

    Current status of advanced theoretical methods for transition probabilities for atoms and ions is discussed. An experiment on the f values of the resonance transitions of the Kr and Xe isoelectronic sequences is suggested as a test for the theoretical methods

  20. Contemporary Transitional Justice

    DEFF Research Database (Denmark)

    Gissel, Line Engbo

    2017-01-01

    This article studies the contemporary expression of transitional justice, a field of practice through which global governance is exercised. It argues that transitional justice is being normalised, given the normative and empirical de-legitimisation of its premise of exceptionalism. The article...... theorises exceptionalism and normalcy in transitional justice and identifies three macro-level causes of normalisation: the legalisation, internationalisation, and professionalization of the field. This argument is illustrated by a study of Uganda’s trajectory of transitional justice since 1986. Across five...... phases of transitional justice, processes of legalisation, internationalisation, and professionalization have contributed to the gradual dismantling of the country’s exceptional justice. The case demonstrates, further, that normalization is a contested and incomplete process....

  1. Coordination of IVI and transit signal priority on transit evacuations.

    Science.gov (United States)

    2011-02-01

    During an emergency evacuation, execution time is always critical to the evacuees who are : transit dependent. Transit Signal Priority (TSP) can speed up the transit services by prioritizing : the approaching bus at a signalized intersection. With th...

  2. Cosmological phase transitions

    International Nuclear Information System (INIS)

    Kolb, E.W.

    1987-01-01

    If the universe stated from conditions of high temperature and density, there should have been a series of phase transitions associated with spontaneous symmetry breaking. The cosmological phase transitions could have observable consequences in the present Universe. Some of the consequences including the formation of topological defects and cosmological inflation are reviewed here. One of the most important tools in building particle physics models is the use of spontaneous symmetry breaking (SSB). The proposal that there are underlying symmetries of nature that are not manifest in the vacuum is a crucial link in the unification of forces. Of particular interest for cosmology is the expectation that are the high temperatures of the big bang symmetries broken today will be restored, and that there are phase transitions to the broken state. The possibility that topological defects will be produced in the transition is the subject of this section. The possibility that the Universe will undergo inflation in a phase transition will be the subject of the next section. Before discussing the creation of topological defects in the phase transition, some general aspects of high-temperature restoration of symmetry and the development of the phase transition will be reviewed. 29 references, 1 figure, 1 table

  3. Milestoning with transition memory

    Science.gov (United States)

    Hawk, Alexander T.; Makarov, Dmitrii E.

    2011-12-01

    Milestoning is a method used to calculate the kinetics and thermodynamics of molecular processes occurring on time scales that are not accessible to brute force molecular dynamics (MD). In milestoning, the conformation space of the system is sectioned by hypersurfaces (milestones), an ensemble of trajectories is initialized on each milestone, and MD simulations are performed to calculate transitions between milestones. The transition probabilities and transition time distributions are then used to model the dynamics of the system with a Markov renewal process, wherein a long trajectory of the system is approximated as a succession of independent transitions between milestones. This approximation is justified if the transition probabilities and transition times are statistically independent. In practice, this amounts to a requirement that milestones are spaced such that trajectories lose position and velocity memory between subsequent transitions. Unfortunately, limiting the number of milestones limits both the resolution at which a system's properties can be analyzed, and the computational speedup achieved by the method. We propose a generalized milestoning procedure, milestoning with transition memory (MTM), which accounts for memory of previous transitions made by the system. When a reaction coordinate is used to define the milestones, the MTM procedure can be carried out at no significant additional expense as compared to conventional milestoning. To test MTM, we have applied its version that allows for the memory of the previous step to the toy model of a polymer chain undergoing Langevin dynamics in solution. We have computed the mean first passage time for the chain to attain a cyclic conformation and found that the number of milestones that can be used, without incurring significant errors in the first passage time is at least 8 times that permitted by conventional milestoning. We further demonstrate that, unlike conventional milestoning, MTM permits

  4. Martensitic phase transitions

    International Nuclear Information System (INIS)

    Petry, W.; Neuhaus, J.

    1996-01-01

    Many elements transform from a high temperature bcc phase to a more dense packed temperature phase. The great majority of these transitions are of 1st order, displacive and reconstructive. The lattice potentials which govern these martensitic transitions can be probed by inelastic neutron scattering, thereby answering fundamental questions like : Will the transition be announced by dynamical or static fluctuations? What are the trajectories for the displacements needed for the transformation? Does the vibrational entropy stabilize the high temperature phase? Are the unusual transport properties in these materials related to their ability to transform? (author) 17 figs., 1 tab., 46 refs

  5. Variational Transition State Theory

    Energy Technology Data Exchange (ETDEWEB)

    Truhlar, Donald G. [Univ. of Minnesota, Minneapolis, MN (United States)

    2016-09-29

    This is the final report on a project involving the development and applications of variational transition state theory. This project involved the development of variational transition state theory for gas-phase reactions, including optimized multidimensional tunneling contributions and the application of this theory to gas-phase reactions with a special emphasis on developing reaction rate theory in directions that are important for applications to combustion. The development of variational transition state theory with optimized multidimensional tunneling as a useful computational tool for combustion kinetics involved eight objectives.

  6. Martensitic phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Petry, W; Neuhaus, J [Techn. Universitaet Muenchen, Physik Department E13, Munich (Germany)

    1996-11-01

    Many elements transform from a high temperature bcc phase to a more dense packed temperature phase. The great majority of these transitions are of 1st order, displacive and reconstructive. The lattice potentials which govern these martensitic transitions can be probed by inelastic neutron scattering, thereby answering fundamental questions like : Will the transition be announced by dynamical or static fluctuations? What are the trajectories for the displacements needed for the transformation? Does the vibrational entropy stabilize the high temperature phase? Are the unusual transport properties in these materials related to their ability to transform? (author) 17 figs., 1 tab., 46 refs.

  7. The energy transition

    International Nuclear Information System (INIS)

    Passalacqua, Arnaud; Billes-Garabedian, Laurent; Jancovici, Jean-Marc; Arnoux, Mathieu; Auverlot, Dominique; Leguet, Benoit; Grandjean, Alain; Morel, Julien; Lambert, Quentin; Tranie, Jean-Pascal; Bureau, Dominique; Dron, Dominique; Beeker, Etienne

    2013-01-01

    This special dossier about energy transition is made of 10 contributions dealing with: thousands of years of energy transition (Jean-Marc Jancovici); a recurring problem after a thousand years of fight (Mathieu Arnoux); urban mobility: another energy story (Arnaud Passalacqua); an opportunity subjected to conditions for the French competitiveness (Dominique Auverlot, Benoit Leguet); Germany: an energy utopia or a role model? (Etienne Beeker); environment: the financing stakes (Dominique Dron); reconciling the economical, social and ecological stakes (Alain Grandjean); Sweden in the face of transportation challenge (Julien Morel, Quentin Lambert); India and China with a commitment to global warming (Jean-Pascal Tranie); training the energy transition managers (Dominique Bureau)

  8. BEAM-LOSS DRIVEN DESIGN OPTIMIZATION FOR THE SPALLATION NEUTRON SOURCE (SNS) RING.

    Energy Technology Data Exchange (ETDEWEB)

    WEI,J.; BEEBE-WANG,J.; BLASKIEWICZ,M.; CAMERON,P.; DANBY,G.; GARDNER,C.J.; JACKSON,J.; LEE,Y.Y.; LUDEWIG,H.; MALITSKY,N.; RAPARIA,D.; TSOUPAS,N.; WENG,W.T.; ZHANG,S.Y.

    1999-03-29

    This paper summarizes three-stage design optimization for the Spallation Neutron Source (SNS) ring: linear machine design (lattice, aperture, injection, magnet field errors and misalignment), beam core manipulation (painting, space charge, instabilities, RF requirements), and beam halo consideration (collimation, envelope variation, e-p issues etc.).

  9. Beam-Loss Driven Design Optimization for the Spallation Neutron Source (SNS) Ring

    International Nuclear Information System (INIS)

    Wei, J.

    1999-01-01

    This paper summarizes three-state design optimization for the Spallation Neutron Source (SNS) ring: linear machine design (lattice, aperture, injection, magnet field errors and misalignment), beam core manipulation (painting, space charge, instabilities, RF requirements), and beam halo consideration (collimation, envelope variation, e-p issues etc.)

  10. Rural transit emergency planning guidance.

    Science.gov (United States)

    2008-07-01

    Providing safe, reliable transportation has long been a priority at all levels of the transit industry including the Federal Transit Administration (FTA), California Department of Transportation (Caltrans) and individual transit providers. Over the l...

  11. Transit ridership, reliability, and retention.

    Science.gov (United States)

    2008-10-01

    This project explores two major components that affect transit ridership: travel time reliability and rider : retention. It has been recognized that transit travel time reliability may have a significant impact on : attractiveness of transit to many ...

  12. Modeling Metropolitan Detroit transit.

    Science.gov (United States)

    2010-10-01

    "The seven-county Southeast Michigan region, that encompasses the Detroit Metropolitan Area, : ranks fifth in population among top 25 regions in the nation. It also ranks among bottom five in : the transit service provided, measured in miles or hours...

  13. Generalizing smooth transition autoregressions

    DEFF Research Database (Denmark)

    Chini, Emilio Zanetti

    We introduce a variant of the smooth transition autoregression - the GSTAR model - capable to parametrize the asymmetry in the tails of the transition equation by using a particular generalization of the logistic function. A General-to-Specific modelling strategy is discussed in detail, with part......We introduce a variant of the smooth transition autoregression - the GSTAR model - capable to parametrize the asymmetry in the tails of the transition equation by using a particular generalization of the logistic function. A General-to-Specific modelling strategy is discussed in detail......, with particular emphasis on two different LM-type tests for the null of symmetric adjustment towards a new regime and three diagnostic tests, whose power properties are explored via Monte Carlo experiments. Four classical real datasets illustrate the empirical properties of the GSTAR, jointly to a rolling...

  14. Oligocyclopentadienyl transition metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    de Azevedo, Cristina G.; Vollhardt, K. Peter C.

    2002-01-18

    Synthesis, characterization, and reactivity studies of oligocyclopentadienyl transition metal complexes, namely those of fulvalene, tercyclopentadienyl, quatercyclopentadienyl, and pentacyclopentadienyl(cyclopentadienyl) are the subject of this account. Thermal-, photo-, and redox chemistries of homo- and heteropolynuclear complexes are described.

  15. Phase transitions modern applications

    CERN Document Server

    Gitterman, Moshe

    2014-01-01

    This book provides a comprehensive review of the theory of phase transitions and its modern applications, based on the five pillars of the modern theory of phase transitions i.e. the Ising model, mean field, scaling, renormalization group and universality. This expanded second edition includes, along with a description of vortices and high temperature superconductivity, a discussion of phase transitions in chemical reaction and moving systems. The book covers a close connection between phase transitions and small world phenomena as well as scale-free systems such as the stock market and the Internet. Readership: Scientists working in different fields of physics, chemistry, biology and economics as well as teaching material for undergraduate and graduate courses.

  16. Transit management certificate program.

    Science.gov (United States)

    2012-07-01

    TTI worked closely with the Landscape Architecture and Urban Planning Department : (LAUP) of Texas A&M University (TAMU) to develop a transit management certificate : focus for the current Graduate Certificate in Transportation Planning (CTP) housed ...

  17. Slow-transit Constipation.

    Science.gov (United States)

    Bharucha, Adil E.; Philips, Sidney F.

    2001-08-01

    Idiopathic slow-transit constipation is a clinical syndrome predominantly affecting women, characterized by intractable constipation and delayed colonic transit. This syndrome is attributed to disordered colonic motor function. The disorder spans a spectrum of variable severity, ranging from patients who have relatively mild delays in transit but are otherwise indistinguishable from irritable bowel syndrome to patients with colonic inertia or chronic megacolon. The diagnosis is made after excluding colonic obstruction, metabolic disorders (hypothyroidism, hypercalcemia), drug-induced constipation, and pelvic floor dysfunction (as discussed by Wald ). Most patients are treated with one or more pharmacologic agents, including dietary fiber supplementation, saline laxatives (milk of magnesia), osmotic agents (lactulose, sorbitol, and polyethylene glycol 3350), and stimulant laxatives (bisacodyl and glycerol). A subtotal colectomy is effective and occasionally is indicated for patients with medically refractory, severe slow-transit constipation, provided pelvic floor dysfunction has been excluded or treated.

  18. Superconductivity in transition metals.

    Science.gov (United States)

    Slocombe, Daniel R; Kuznetsov, Vladimir L; Grochala, Wojciech; Williams, Robert J P; Edwards, Peter P

    2015-03-13

    A qualitative account of the occurrence and magnitude of superconductivity in the transition metals is presented, with a primary emphasis on elements of the first row. Correlations of the important parameters of the Bardeen-Cooper-Schrieffer theory of superconductivity are highlighted with respect to the number of d-shell electrons per atom of the transition elements. The relation between the systematics of superconductivity in the transition metals and the periodic table high-lights the importance of short-range or chemical bonding on the remarkable natural phenomenon of superconductivity in the chemical elements. A relationship between superconductivity and lattice instability appears naturally as a balance and competition between localized covalent bonding and so-called broken covalency, which favours d-electron delocalization and superconductivity. In this manner, the systematics of superconductivity and various other physical properties of the transition elements are related and unified. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  19. Transition to turbulence

    International Nuclear Information System (INIS)

    Pomeau, Y.

    1981-07-01

    In this work it is reviewed a few known types of transition to turbulence, as the cascade of period doubling and the intermittent transition. This happens in dynamical systems with a few degrees of freedom, as modelled by the iteration of non linear maps. Then it is presented specific transitions for systems with many degrees of freedom. It is condidered first the occurence of a low frequency broadband noise in large cells at the onset of Rayleigh-Benard convection; then the transition by intermittent bursts in parallel flows. In this last case, one is concerned with localized and finite amplitude perturbations. Simple geometric arguments show that these fluctuations, when they are isolated and with a well definite relative speed, exist for a single value of the Reynolds number only [fr

  20. Symptomatic lumbosacral transitional vertebra

    DEFF Research Database (Denmark)

    Holm, Emil Kongsted; Bünger, Cody; Foldager, Casper Bindzus

    2017-01-01

    Bertolotti's syndrome (BS) refers to the possible association between the congenital malformation lumbosacral transitional vertebra (LSTV), and low back pain (LBP). Several treatments have been proposed including steroid injections, resections of the LSTV, laminectomy, and lumbar spinal fusion...

  1. Criminal Justice Transitions

    OpenAIRE

    McAra, Lesley; McVie, Susan

    2007-01-01

    This report explores transitions into the adult criminal justice system amongst a large cohort of young people who were involved in the Edinburgh Study of Youth Transitions and Crime. It includes: a description of patterns of criminal convictions and disposals for young people up to age 19 (on average); an examination of the characteristics and institutional histories of cohort members with a criminal record as compared with youngsters with no such record; and an exploration of the profile of...

  2. The WFCAM Transit Survey

    Directory of Open Access Journals (Sweden)

    Hodgkin S.

    2011-02-01

    Full Text Available The WFCAM Transit Survey (WTS has been obtaining data on the United Kingdom Infrared Telescope since 2007. The WTS targets about 8,000 M dwarfs over several square degrees of sky, and aims to find low-mass eclipsing binaries and planets, down to the size of the Earth, transiting M dwarf stars with periods up to a few days.

  3. Facility transition instruction

    International Nuclear Information System (INIS)

    Morton, M.R.

    1997-01-01

    The Bechtel Hanford, Inc. facility transition instruction was initiated in response to the need for a common, streamlined process for facility transitions and to capture the knowledge and experience that has accumulated over the last few years. The instruction serves as an educational resource and defines the process for transitioning facilities to long-term surveillance and maintenance (S and M). Generally, these facilities do not have identified operations missions and must be transitioned from operational status to a safe and stable configuration for long-term S and M. The instruction can be applied to a wide range of facilities--from process canyon complexes like the Plutonium Uranium Extraction Facility or B Plant, to stand-alone, lower hazard facilities like the 242B/BL facility. The facility transition process is implemented (under the direction of the US Department of Energy, Richland Operations Office [RL] Assistant Manager-Environmental) by Bechtel Hanford, Inc. management, with input and interaction with the appropriate RL division and Hanford site contractors as noted in the instruction. The application of the steps identified herein and the early participation of all organizations involved are expected to provide a cost-effective, safe, and smooth transition from operational status to deactivation and S and M for a wide range of Hanford Site facilities

  4. Metal-insulator transitions

    Science.gov (United States)

    Imada, Masatoshi; Fujimori, Atsushi; Tokura, Yoshinori

    1998-10-01

    Metal-insulator transitions are accompanied by huge resistivity changes, even over tens of orders of magnitude, and are widely observed in condensed-matter systems. This article presents the observations and current understanding of the metal-insulator transition with a pedagogical introduction to the subject. Especially important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by the correlation effects is categorized as the Mott Insulator. Near the transition point the metallic state shows fluctuations and orderings in the spin, charge, and orbital degrees of freedom. The properties of these metals are frequently quite different from those of ordinary metals, as measured by transport, optical, and magnetic probes. The review first describes theoretical approaches to the unusual metallic states and to the metal-insulator transition. The Fermi-liquid theory treats the correlations that can be adiabatically connected with the noninteracting picture. Strong-coupling models that do not require Fermi-liquid behavior have also been developed. Much work has also been done on the scaling theory of the transition. A central issue for this review is the evaluation of these approaches in simple theoretical systems such as the Hubbard model and t-J models. Another key issue is strong competition among various orderings as in the interplay of spin and orbital fluctuations. Experimentally, the unusual properties of the metallic state near the insulating transition have been most extensively studied in d-electron systems. In particular, there is revived interest in transition-metal oxides, motivated by the epoch-making findings of high-temperature superconductivity in cuprates and colossal magnetoresistance in manganites. The article reviews the rich phenomena of anomalous metallicity, taking as examples Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Ru compounds. The diverse phenomena include strong spin and

  5. Examining hydrogen transitions.

    Energy Technology Data Exchange (ETDEWEB)

    Plotkin, S. E.; Energy Systems

    2007-03-01

    This report describes the results of an effort to identify key analytic issues associated with modeling a transition to hydrogen as a fuel for light duty vehicles, and using insights gained from this effort to suggest ways to improve ongoing modeling efforts. The study reported on here examined multiple hydrogen scenarios reported in the literature, identified modeling issues associated with those scenario analyses, and examined three DOE-sponsored hydrogen transition models in the context of those modeling issues. The three hydrogen transition models are HyTrans (contractor: Oak Ridge National Laboratory), MARKAL/DOE* (Brookhaven National Laboratory), and NEMS-H2 (OnLocation, Inc). The goals of these models are (1) to help DOE improve its R&D effort by identifying key technology and other roadblocks to a transition and testing its technical program goals to determine whether they are likely to lead to the market success of hydrogen technologies, (2) to evaluate alternative policies to promote a transition, and (3) to estimate the costs and benefits of alternative pathways to hydrogen development.

  6. Phase transitions in nuclear physics

    Energy Technology Data Exchange (ETDEWEB)

    Moretto, L.G.; Phair, L.; Wozniak, G.J.

    1997-08-01

    A critical overview of the low energy phase transitions in nuclei is presented with particular attention to the 2nd (1st) order pairing phase transitions, and to the 1st order liquid-vapor phase transition. The role of fluctuations in washing out these transitions is discussed and illustrated with examples. A robust indicator of phase coexistence in multifragmentation is presented.

  7. Phase transitions in nuclear physics

    International Nuclear Information System (INIS)

    Moretto, L.G.; Phair, L.; Wozniak, G.J.

    1997-08-01

    A critical overview of the low energy phase transitions in nuclei is presented with particular attention to the 2nd (1st) order pairing phase transitions, and to the 1st order liquid-vapor phase transition. The role of fluctuations in washing out these transitions is discussed and illustrated with examples. A robust indicator of phase coexistence in multifragmentation is presented

  8. Transition to the Cloud

    DEFF Research Database (Denmark)

    Hedman, Jonas; Xiao, Xiao

    2016-01-01

    The rising of cloud computing has dramatically changed the way software companies provide and distribute their IT product and related services over the last decades. Today, most software is bought offthe-shelf and distributed over the Internet. This transition is greatly influencing how software...... companies operate. In this paper, we present a case study of an ERP vendor for SMB (small and mediumsize business) in making a transition towards a cloud-based business model. Through the theoretical lens of ecosystem, we are able to analyze the evolution of the vendor and its business network as a whole......, and find that the relationship between vendor and Value-added-Reseller (VAR) is greatly affected. We conclude by presenting critical issues and challenges for managing such cloud transition....

  9. Citizens in sustainable transitions

    DEFF Research Database (Denmark)

    Hoffmann, Birgitte; Agger, Annika

    2013-01-01

    The paper explores how local public authorities can support and facilitate citizens’ participa-tion and learning in sustainable transition in urban neighbourhoods, by supporting local in-termediaries. The role of intermediaries can be performed by a variety of actors such as public housing...... associations; NGO´s, or semi public institutions. Our claim is that intermediary actors have the potential to facilitate new platforms for citizens’ participation in urban sustainable transition due to their particular role in between public authorities and civil society. The key question of the paper is how...... the intermediary actors facilitate citizens' participatory processes in sustainable urban transitions, and the paper explores the concept of institutional capacity building as a way to develop learning processes and new practises? The aim is to analyse approaches of creating platforms for involving citizens...

  10. To finance the transition

    International Nuclear Information System (INIS)

    Regnier, Yannick; Maciel, Guillaume; Zeroual, Bouchra; Leca, Christel; Guillou, Maelle; Mossalgue, Marc; Raguet, Alex; Sabot, Guillaume; Coton, Patrice; Olesen, Gunnar Boye; Friggens, Sam; Pouyet, Regis; Blanc, Nicolas; Laurent, Pierre; Ruedinger, Andreas

    2013-01-01

    A set of brief articles illustrates the emergence of innovating and operational financing tools aimed at supporting energy transition in France and in Europe. As far as France is concerned, different examples are evoked: raising local savings, crowd-funding for renewable energies, citizen investment, cooperation between industries, communities and citizens, a semi-public company with citizen participation, the case of the Nancy urban community, a joint experience by a local public company and an investment fund. As far as Europe is concerned, the following topics or examples are evoked: local policies as lever for European financing, the Danish example of citizen-based financing, crowd-funding in the UK, the European emergence of cooperatives. As far as banks and institutions are concerned, the following topics are addressed: tools implemented by the Caisse des Depots for energy transition, the roles of banks and of public institutions in the financing of energy transition

  11. Electroweak phase transitions

    International Nuclear Information System (INIS)

    Anderson, G.W.

    1991-01-01

    An analytic treatment of the one Higgs doublet, electroweak phase transition is given. The phase transition is first order, occurs by the nucleation of thin walled bubbles and completes at a temperature where the order parameter, left-angle φ right-angle T is significantly smaller than it is when the origin becomes absolutely unstable. The rate of anomalous baryon number violation is an exponentially function of left-angle φ right-angle T . In very minimal extensions of the standard model it is quite easy to increase left-angle φ right-angle T so that anomalous baryon number violation is suppressed after completion of the phase transition. Hence baryogenesis at the electroweak phase transition is tenable in minimal of the standard model. In some cases additional phase transitions are possible. For a light Higgs boson, when the top quark mass is sufficiently large, the state where the Higgs field has a vacuum expectation value left-angle φ right-angle = 246 GeV is not the true minimum of the Higgs potential. When this is the case, and when the top quark mass exceeds some critical value, thermal fluctuations in the early universe would have rendered the state left-angle φ right-angle = 246 GeV unstable. The requirement that the state left-angle φ right-angle = 246 GeV is sufficiently long lived constrains the masses of the Higgs boson and the top quark. Finally, we consider whether local phase transitions can be induced by heavy particles which act as seeds for deformations in the scalar field

  12. Parametric modal transition systems

    DEFF Research Database (Denmark)

    Beneš, Nikola; Křetínský, Jan; Larsen, Kim Guldstrand

    2011-01-01

    Modal transition systems (MTS) is a well-studied specification formalism of reactive systems supporting a step-wise refinement methodology. Despite its many advantages, the formalism as well as its currently known extensions are incapable of expressing some practically needed aspects in the refin......Modal transition systems (MTS) is a well-studied specification formalism of reactive systems supporting a step-wise refinement methodology. Despite its many advantages, the formalism as well as its currently known extensions are incapable of expressing some practically needed aspects...

  13. Successive Transitions in Ecodesign

    DEFF Research Database (Denmark)

    Boks, Casper; McAloone, Tim C.

    2008-01-01

    In the past 15 years, stimulated by a growing environmental concern and awareness in the media, ecodesign, or design for environment, has expanded considerably as a scientific research area; from a group of opportunistic eco-pathfinders trying to optimise a product’s recyclability......, into acknowledged scientific research regarding technology transfer and commercialisation. This paper proposes that this maturing process took place through a number of transitions; this is illustrated by discussing characteristic aspects of each transition, together providing a historic account of how academic...

  14. Pinocchio: Geppetto's transitional object

    Directory of Open Access Journals (Sweden)

    Gabriele Zeloni

    2015-01-01

    Full Text Available The literature has been considered by Freud and others after him, a form of unaware exploration of mind that can leads to discoveries similar to psychoanalysis’s discoveries. From this perspective, the author puts forward the following hypothesis: Pinocchio is a puppet who comes to life and is therefore, from a child's perception, a transitional object according to Winnicott. Consequently Geppetto is nothing more than the involuntary representation of any child interacting with the transitional object. The author explains the results of the analysis of the text in support of the hypothesis and reflects on the impact of The adventure of Pinocchio on the reader.

  15. European countries in transition

    International Nuclear Information System (INIS)

    Gautier, Celia; Pescia, Dimitri; Ferreira, Francisco; Antunes, Rita; Claustre, Raphael; Priesner, Goerg C.; Pidous, Blandine; Dufour, Manon; Zuloaga, Francisco

    2014-01-01

    From the Atlantic Ocean to the Baltic Sea, from Portugal to Poland through UK, Germany or Austria, energy transition is in progress everywhere in Europe, but at different rhythms and in various conditions from one country to the other. How does the European framework promote the energy transition at the local and regional scales? What advantages the most advanced countries are relying on? How do citizens and local projects take over slow or retrograde governmental policies? This dossier gives some elements of answer through an overview of some energy policy scenarios under implementation in some European countries (Germany, Portugal, Denmark, Austria, UK, Spain)

  16. A programme in transition

    International Nuclear Information System (INIS)

    Dean, S.O.

    1992-01-01

    Fusion is beginning its transition from a scientific research programme to that of an engineering development programme aimed at practical applications. This transition is likely to last a decade or more because many scientific questions remain and because of the magnitude and cost of the engineering issues. This article reviews briefly the encouraging results produced at the Joint European Torus (JET) where 1.7 MW of fusion power was generated for 2 seconds in experiments in November 1991, the remaining scientific issues, the role of near-term experimental reactors like the International Thermonuclear Experimental reactor (ITER) and other approaches to a demonstration power plant. (author)

  17. Electronic phase transitions

    CERN Document Server

    Kopaev, YuV

    1992-01-01

    Electronic Phase Transitions deals with topics, which are presently at the forefront of scientific research in modern solid-state theory. Anderson localization, which has fundamental implications in many areas of solid-state physics as well as spin glasses, with its influence on quite different research activities such as neural networks, are two examples that are reviewed in this book. The ab initio statistical mechanics of structural phase transitions is another prime example, where the interplay and connection of two unrelated disciplines of solid-state theory - first principle ele

  18. The simultaneous measurements of core and outer core density fluctuations in L-H transition using CO2 laser collective scattering diagnostic in the EAST superconducting tokamak

    International Nuclear Information System (INIS)

    Cao, G.M.; Li, Y.D.; Zhang, X.D.; Sun, P.J.; Hu, L.Q.; Li, J.G.; Wu, G.J.

    2013-01-01

    The H-mode is the projected basic operation scenario for the ITER tokamak. The turbulence de-correlation by the synergistic effect of zonal flow and equilibrium ExB flow shear is believed to be the reason for L-H transition, however, the detailed physical mechanism has not been identified so far. Tangential multi-channel CO 2 laser collective scattering diagnostic system (mainly k r measurement) was first installed to investigate electron density fluctuations on EAST tokamak. The measurements in a spontaneous dithering L-H transition show that in core plasma (0 < r/a < 0.5) the low-frequency fluctuations strengthen greatly before L-H transition; meanwhile in outer core plasma (0.2 < r/a < 1) the low-frequency fluctuations strengthen slightly. Bispectral analysis reveals that the coupling strength between low- and high-frequency fluctuations in both core and outer core plasma strengthens greatly before the transition, but the latter is greater than the former. The results indicate that the low-frequency fluctuations of the core and outer core plasma play active, but different, roles in the spontaneous L-H transition. (author)

  19. Investigation of the critical edge ion heat flux for L-H transitions in Alcator C-Mod and its dependence on B T

    Science.gov (United States)

    Schmidtmayr, M.; Hughes, J. W.; Ryter, F.; Wolfrum, E.; Cao, N.; Creely, A. J.; Howard, N.; Hubbard, A. E.; Lin, Y.; Reinke, M. L.; Rice, J. E.; Tolman, E. A.; Wukitch, S.; Ma, Y.; ASDEX Upgrade Team; Alcator C-Mod Team

    2018-05-01

    This paper presents investigations on the role of the edge ion heat flux for transitions from L-mode to H-mode in Alcator C-Mod. Previous results from the ASDEX Upgrade tokamak indicated that a critical value of edge ion heat flux per particle is needed for the transition. Analysis of C-Mod data confirms this result. The edge ion heat flux is indeed found to increase linearly with density at given magnetic field and plasma current. Furthermore, the Alcator C-Mod data indicate that the edge ion heat flux at the L-H transition also increases with magnetic field. Combining the data from Alcator C-Mod and ASDEX Upgrade yields a general expression for the edge ion heat flux at the L-H transition. These results are discussed from the point of view of the possible physics mechanism of the L-H transition. They are also compared to the L-H power threshold scaling and an extrapolation for ITER is given.

  20. Military Lives: Coaching Transitions

    Science.gov (United States)

    Beech, Nick; Gold, Jeff; Beech, Susan

    2017-01-01

    Purpose: The purpose of this paper is to first consider how veterans use talk to shape interpretations of personal and social identity. Second, this paper seeks to gain an understanding of how veterans see themselves in a civilian world, their ability to re-conceptualise and realign their perspective on life to support their transition in to a…

  1. Afghanistan in Transition

    Science.gov (United States)

    2010-01-01

    These include: Afghanistan is the graveyard of empires ; efforts to centralize power in Afghanistan provoke local resistance; and Afghanistan is an...ethnically fragmented and decentralized country inca - pable of forming a unified state. Afghanistan in Transition Autumn 2010 7 The realities

  2. Transition to Adulthood

    Science.gov (United States)

    ... equality of opportunity, full participation, independent living, and economic self-sufficiency for individuals with disabilities.” [20 U.S. ... a lot of ground to cover! But it’s essential ground, if the student’s transition to the adult ...

  3. Boundaries, transitions and passages

    NARCIS (Netherlands)

    Koenderink, Jan; van Doorn, Andrea J.; Pinna, Baingio; Wagemans, Johan

    2016-01-01

    Many pictures are approximately piecewise uniform quilts. The patches meet in transitional areas that have a vague, ribbon-like geometry. These borders may occasionally get lost and sometimes pick up again, creating a 'passage' that partly blends adjacent patches. This type of structure is widely

  4. paraelectric phase transition

    Indian Academy of Sciences (India)

    The ferroelectric phase transition is diffuse in nature and broadening of the peak increases with La content. Keywords. PLZT ... Marssi et al (1998) concluded the PLZTs x/65/35 as a model. ∗ ... by analysing field cooled (FC) and zero field cooled (ZFC) dielectric ... material are fitted with universal dielectric behaviour within.

  5. Families in Transition .

    Science.gov (United States)

    Bundy, Michael L., Ed.; Gumaer, James, Ed.

    1984-01-01

    Focuses on disrupted families and the role of the school counselor in helping children adjust. Describes characteristics of healthy families, and discusses the transition to the blended family, effects of divorce groups on children's classroom behavior, counseling children in stepfamilies, single-parent families, and parenting strengths of single…

  6. Transition and Financial Collapse

    NARCIS (Netherlands)

    Uhlig, H.F.H.V.S.

    1995-01-01

    One of the many problems facing the countries in transition from socialism to capitalism after the initial phase of privatization and restructuring is the lack of proven entrepreneurial talent in addition to a low initial level of capital. New entrepreneurs might find it hard to finance their

  7. Lost in Transit

    DEFF Research Database (Denmark)

    Lange, Ida Sofie Gøtzsche; Laursen, Lea Louise Holst; Lassen, Claus

    how a town primarily characterized by ferry transit is being challenged on its capacity to be a 'place' of meaning and social importance to its inhabitants. The paper raises the key question: Can a place become too well connected and this in such a manner that its identity and key character becomes...

  8. Singing Smoothes Classroom Transitions

    Science.gov (United States)

    Mathews, Sarah E.

    2012-01-01

    Just as humming a merry tune helped Snow White and her furry animal friends to quickly clean a filthy cottage in the movie "Snow White and the Seven Dwarfs" (Disney & Cottrell, 1937), singing can be an effective way to help keep young children fully engaged during classroom transitions. The purposes of this article are to: (1) consider why…

  9. Understanding of hysteresis behaviors at the L-H-L transitions in tokamak plasma based on bifurcation concept

    Energy Technology Data Exchange (ETDEWEB)

    Chatthong, B. [Department of Physics, Faculty of Science, Prince of Songkla University, Hat Yai, Songkla (Thailand); Onjun, T. [School of Manufacturing Systems and Mechanical Engineering, Sirindhorn International Institute of Technology, Thammasat University, Pathum Thani (Thailand)

    2016-08-15

    The hysteresis behaviour at the L-H-L transitions in tokamak plasma is investigated based on bifurcation concept. The formation of an edge transport barrier (ETB) is modeled via thermal and particle transport equations with the flow shear suppression effect on anomalous transport included. The anomalous transport is modeled based on critical gradients threshold and the flow shear is calculated from the force balance equation, couples the two transport equations leading to a non-linear behaviour. Analytical investigation reveals that the fluxes versus gradients space exhibits bifurcation behaviour with s -curve soft bifurcation type. Apparently, the backward H-L transition occurs at lower values than that of the forward L-H transition, illustrating hysteresis behaviour. The hysteresis properties, i.e. locations of threshold fluxes, gradients and their ratios are analyzed as a function of neoclassical and anomalous transport values and critical gradients. It is found that the minimum heat flux for maintaining H -mode depends on several plasma parameters including the strength of anomalous transport and neoclassical transport. In particular, the hysteresis depth becomes larger when neoclassical transport decreases or anomalous transport increases. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  10. Caltrans : transit funding manual : managing the delivery of transit projects

    Science.gov (United States)

    2001-05-01

    This manual attempts to provide a step by step transit funding process. Included in this manual : is an overview of Caltrans Division of Mass Transportation, roles and responsibilities in : assisting local agencies to deliver transit projects. Transi...

  11. The Mongolia experience: transitioning within transition.

    Science.gov (United States)

    MacKenzie, Richard G

    2009-12-01

    Although Mongolia has a long and distinguished history, as a new and emerging democracy it is experiencing the pains of transition-one that is moving the country from its pastoral and nomadic past into the 21st century. Confounded by its previous dependence on socialist Soviet Russia, the concept of a market economy seems opportunistic for some, while for those living within the traditional lifestyle of the herdsman in the countryside it is confusing and threatening to family structure and values. Adolescents and young adults are caught at the interface-not only of their own development, but by the disparities between tradition and Western values, new technology, and freedoms granted by the emerging democracy, and by the civic practice of democracy itself. Conceptually the new belongs to the young, and yet limited health and educational resources are available to modulate and focus both threats and opportunities. Using the analogy of the spirit banner of the warrior, it is the young as the warriors of the 21st century who have the energy and investment in the future that will be needed to shepherd this change. Both personal and public health, within the context of development, the psychobiological model, and the political and social ecology will be strong determinants of success. It is a parallel investment in both youth and the ideals they represent that will ensure success for the new Mongolia.

  12. Hypocritical transitions? The challenge of urban sustainable mobility transition

    DEFF Research Database (Denmark)

    Vogel, Nina

    of a sustainable mobility discourse can be traced in the policy documents, how mobility is framed, and which arguments are used to legitimate or envision strategies and planning practices. Is Fredericia performing a transition towards low-carbon mobility? The paper will draw on concepts from transition theory...... urban complexity within transition processes. Transitions are always taking place, but the question is which direction they take and if these directions are in line with a planning approach for sustainable mobility....

  13. Jamming transitions in cancer

    Science.gov (United States)

    Oswald, Linda; Grosser, Steffen; Smith, David M.; Käs, Josef A.

    2017-12-01

    The traditional picture of tissues, where they are treated as liquids defined by properties such as surface tension or viscosity has been redefined during the last few decades by the more fundamental question: under which conditions do tissues display liquid-like or solid-like behaviour? As a result, basic concepts arising from the treatment of tissues as solid matter, such as cellular jamming and glassy tissues, have shifted into the current focus of biophysical research. Here, we review recent works examining the phase states of tissue with an emphasis on jamming transitions in cancer. When metastasis occurs, cells gain the ability to leave the primary tumour and infiltrate other parts of the body. Recent studies have shown that a linkage between an unjamming transition and tumour progression indeed exists, which could be of importance when designing surgery and treatment approaches for cancer patients.

  14. Energy transition in France

    International Nuclear Information System (INIS)

    Grandjean, Alain

    2014-01-01

    After having recalled the main issues and stakes addressed by the French national debate on energy transition (strategic stakes, priority to a reduction of French energy consumption, options for the evolution of the French energy mix), the author comments the possible evolution of energy prices and of the energy taxing policy (evolution of oil prices, carbon price). In a second part, the author addresses the issue of financing of building and housing renovation. He shows that this operation cannot be only based on financial markets which are not efficient. This means that a public intervention is required, and different solutions are then possible. Some of them seem difficult to implement (creation of money by the central Bank, creation of a public bank which could lend money to private actors), and some others need to be further examined (creation of a financing company for energy transition, use of national savings, simplified circuits for a financing of local projects by local savings, and so on)

  15. Online Community Transition Detection

    DEFF Research Database (Denmark)

    Tan, Biying; Zhu, Feida; Qu, Qiang

    2014-01-01

    communities over time. How to automatically detect the online community transitions of individual users is a research problem of immense practical value yet with great technical challenges. In this paper, we propose an algorithm based on the Minimum Description Length (MDL) principle to trace the evolution......Mining user behavior patterns in social networks is of great importance in user behavior analysis, targeted marketing, churn prediction and other applications. However, less effort has been made to study the evolution of user behavior in social communities. In particular, users join and leave...... of community transition of individual users, adaptive to the noisy behavior. Experiments on real data sets demonstrate the efficiency and effectiveness of our proposed method....

  16. Jamming transitions in cancer

    International Nuclear Information System (INIS)

    Oswald, Linda; Grosser, Steffen; Käs, Josef A; Smith, David M

    2017-01-01

    The traditional picture of tissues, where they are treated as liquids defined by properties such as surface tension or viscosity has been redefined during the last few decades by the more fundamental question: under which conditions do tissues display liquid-like or solid-like behaviour? As a result, basic concepts arising from the treatment of tissues as solid matter, such as cellular jamming and glassy tissues, have shifted into the current focus of biophysical research. Here, we review recent works examining the phase states of tissue with an emphasis on jamming transitions in cancer. When metastasis occurs, cells gain the ability to leave the primary tumour and infiltrate other parts of the body. Recent studies have shown that a linkage between an unjamming transition and tumour progression indeed exists, which could be of importance when designing surgery and treatment approaches for cancer patients. (topical review)

  17. Vacancies in transition metals

    International Nuclear Information System (INIS)

    Allan, G.; Lannoo, M.

    1976-01-01

    A calculation of the formation energy and volume for a vacancy in transition metals is described. A tight-binding scheme is used for the d band and a Born-Mayer type potential to account for the repulsive part of the energy at small distances. The results show that the relaxation energy is small in all cases, less than 0.1 eV. This seems to be coherent with the good agreement obtained for the theoretical and experimental values of the formation energy Esub(F)sup(V) of the vacancy, without including relaxation. The center of the transitional series is found to give a contraction (Formation volume of order -0.4 at.vol.) whereas the edges are found to produce dilations. (author)

  18. Pays en transition

    International Development Research Centre (IDRC) Digital Library (Canada)

    Les périodes de transformation risquent de provoquer le chaos, mais elles sont également porteuses de rapides progrès sur le plan social et économique. Le CRDI est intervenu dans quelque 25 pays ayant amorcé une transition de la guerre à la paix, de la dictature à la démocratie ou d'une économie fermée à une.

  19. Eccentricity from transit photometry

    DEFF Research Database (Denmark)

    Van Eylen, Vincent; Albrecht, Simon

    2015-01-01

    and can be described by a Rayleigh distribution with $\\sigma$ = 0.049 $\\pm$ 0.013. This is in full agreement with solar system eccentricities, but in contrast to the eccentricity distributions previously derived for exoplanets from radial velocity studies. Our findings are helpful in identifying which...... (TTVs), and we present some previously unreported TTVs. Finally transit durations help distinguish between false positives and true planets and we use our measurements to confirm six new exoplanets....

  20. DARK Technology Transition Plan

    Science.gov (United States)

    1990-04-01

    handicap in violation of Title VI of the Civil Rights Act of 1964. Title IX of the Educational Amendments of 1972 and Section 504 of the...to make productive use of the technology. Note that, for those technologies where commercialisation would be a prerequisite for institutionalisation...leverage, and nurture the ensuing transition activities (e.g., as a resource) as much as possible. This is where commercialisation would give a boost

  1. Stimulated coherent transition radiation

    International Nuclear Information System (INIS)

    Hung-chi Lihn.

    1996-03-01

    Coherent radiation emitted from a relativistic electron bunch consists of wavelengths longer than or comparable to the bunch length. The intensity of this radiation out-numbers that of its incoherent counterpart, which extends to wavelengths shorter than the bunch length, by a factor equal to the number of electrons in the bunch. In typical accelerators, this factor is about 8 to 11 orders of magnitude. The spectrum of the coherent radiation is determined by the Fourier transform of the electron bunch distribution and, therefore, contains information of the bunch distribution. Coherent transition radiation emitted from subpicosecond electron bunches at the Stanford SUNSHINE facility is observed in the far-infrared regime through a room-temperature pyroelectric bolometer and characterized through the electron bunch-length study. To measure the bunch length, a new frequency-resolved subpicosecond bunch-length measuring system is developed. This system uses a far-infrared Michelson interferometer to measure the spectrum of coherent transition radiation through optical autocorrelation with resolution far better than existing time-resolved methods. Hence, the radiation spectrum and the bunch length are deduced from the autocorrelation measurement. To study the stimulation of coherent transition radiation, a special cavity named BRAICER is invented. Far-infrared light pulses of coherent transition radiation emitted from electron bunches are delayed and circulated in the cavity to coincide with subsequent incoming electron bunches. This coincidence of light pulses with electron bunches enables the light to do work on electrons, and thus stimulates more radiated energy. The possibilities of extending the bunch-length measuring system to measure the three-dimensional bunch distribution and making the BRAICER cavity a broadband, high-intensity, coherent, far-infrared light source are also discussed

  2. Kondo-Anderson transitions

    Science.gov (United States)

    Kettemann, S.; Mucciolo, E. R.; Varga, I.; Slevin, K.

    2012-03-01

    Dilute magnetic impurities in a disordered Fermi liquid are considered close to the Anderson metal-insulator transition (AMIT). Critical power-law correlations between electron wave functions at different energies in the vicinity of the AMIT result in the formation of pseudogaps of the local density of states. Magnetic impurities can remain unscreened at such sites. We determine the density of the resulting free magnetic moments in the zero-temperature limit. While it is finite on the insulating side of the AMIT, it vanishes at the AMIT, and decays with a power law as function of the distance to the AMIT. Since the fluctuating spins of these free magnetic moments break the time-reversal symmetry of the conduction electrons, we find a shift of the AMIT, and the appearance of a semimetal phase. The distribution function of the Kondo temperature TK is derived at the AMIT, in the metallic phase, and in the insulator phase. This allows us to find the quantum phase diagram in an external magnetic field B and at finite temperature T. We calculate the resulting magnetic susceptibility, the specific heat, and the spin relaxation rate as a function of temperature. We find a phase diagram with finite-temperature transitions among insulator, critical semimetal, and metal phases. These new types of phase transitions are caused by the interplay between Kondo screening and Anderson localization, with the latter being shifted by the appearance of the temperature-dependent spin-flip scattering rate. Accordingly, we name them Kondo-Anderson transitions.

  3. LES PAYS EN TRANSITION

    International Development Research Centre (IDRC) Digital Library (Canada)

    Cathy Egan

    En 2002, une certaine paix sociale avait été rétablie, bien qu'elle fut instable et souvent entachée de violence. Le pays amorçait le ... mieux comprendre comment il recueille et diffuse l'information destinée ... transition) et les technologies de l'information et de la communication (TIC). Les étapes suivantes ont consisté à ...

  4. Energy transition. Selective bibliography

    International Nuclear Information System (INIS)

    2015-10-01

    At the occasion of the promulgation on August 17, 2015 of law no. 2015-992 relative to energy transition, this bibliography reviews the legal, economical and political aspects of the recent evolutions in the energy domain. Basic and synthetic documents are listed first. Then follow documents dealing with: general data, energy models, sustainable agriculture, green technologies, energy conservation, waste processing, renewable energy sources, sustainable cities and buildings. The bibliography ends with a selection of relevant web sites

  5. Army Leader Transitions Handbook

    Science.gov (United States)

    2008-01-01

    The courseware allows users to tailor training materials to specific needs. Users access this at the CAL AKO website or Army eLearning https...usarmy.skillport.com/ skillportfe/login/usarmylogin.cfm. New users must register with eLearning . Then login, select “Army Custom Curricula” and scroll to...challenges of your transition. Patience, flexibility and a good understanding of influence techniques on your part will help make any needed realignment a

  6. Strategic Transit Automation Research Plan

    Science.gov (United States)

    2018-01-01

    Transit bus automation could deliver many potential benefits, but transit agencies need additional research and policy guidance to make informed deployment decisions. Although funding and policy constraints may play a role, there is also a reasonable...

  7. Nav Status & Daily Transit Report -

    Data.gov (United States)

    Department of Transportation — Displays a breakdown of vessel transit through Eisenhower lock in Massena, NY by different types of vessels and comparing current year transits to the year previous....

  8. 2008 Enterprise Transition Plan (ETP)

    National Research Council Canada - National Science Library

    England, Gordon

    2008-01-01

    The Enterprise Transition Plan (ETP) is the Department of Defense's integrated business transformation plan, which incorporates the transition plans of the Military Services, Components and the DoD Enterprise...

  9. The energy transition

    International Nuclear Information System (INIS)

    Defeuilley, Christophe

    2014-01-01

    In a first part, the author proposes an analysis of energy transition and of its consequences on the competitive environment. He recalls the main characteristics of energy transition and more particularly focuses on two aspects: the development of renewable energies and the management of demand. Thus, the author discusses the following issues: the relationship between the struggle against climate change and the low carbon economy, the development of renewable energies, the evolution and main actors of photovoltaic array and of wind turbine production, the distribution of photovoltaic and wind energy installed production among countries, and some key figures about the main renewable energy operators in Europe. He discusses how to manage consumptions, and operations performed. In a second part, the author addresses the impact of the German energy transition (Energiewende) on the business models of the main German energy operators (RWE and E.On). He recalls and comments the objective of this energy policy, presents the German electric and gas sector, comments the evolution of the electric utilities since 1998, more presently presents and discusses the activities of RWE and E.On, the evolution of their main financial indicators, and the levels of installed power with respect of energy sources

  10. Energy systems in transition

    International Nuclear Information System (INIS)

    Haefele, W.

    1989-01-01

    The principal point of the author was to discuss energy systems (ES) in transition, transition addresses the next 10-25 years, and strategy of the transition. He considers different scenarios of future development of ES. Further he presents considerations elaborated during the last years on the concept of novel horizontally integrated ES which gives promise to be at least an approximation to the desired object of no emissions. The main ideas of the concept are: to decompose and thereby clean all the primary inputs before they are brought to combustion; to develop a network combining all the primary inputs to an integrated supply structure of high absorption, buffer, and storage capacity that resembles in some way the supply and utility functions of the well established electric grid but completes it at best on the basis of mass flows; to achieve a high flexibility in supplying the final energy. The author considers the long run perspective of hydrogen, solar, and nuclear energy with respect to alternative energy sources. 6 refs, 24 figs

  11. Economic Growth Models Transition

    Directory of Open Access Journals (Sweden)

    Coralia Angelescu

    2006-03-01

    Full Text Available The transitional recession in countries of Eastern Europe has been much longer than expected. The legacy and recent policy mistakes have both contributed to the slow progress. As structural reforms and gradual institution building have taken hold, the post-socialist economics have started to recover, with some leading countries building momentum toward faster growth. There is a possibility that in wider context of globalization several of these emerging market economies will be able to catch up with the more advanced industrial economies in a matter of one or two generations. Over the past few years, most candidate countries have made progress in the transition to a competitive market economy, macroeconomic stabilization and structural reform. However their income levels have remained far below those in the Member States. Measured by per capita income in purchasing power standards, there has been a very limited amount of catching up over the past fourteen years. Prior, the distinctions between Solow-Swan model and endogenous growth model. The interdependence between transition and integration are stated in this study. Finally, some measures of macroeconomic policy for sustainable growth are proposed in correlation with real macroeconomic situation of the Romanian economy. Our study would be considered the real convergence for the Romanian economy and the recommendations for the adequate policies to achieve a fast real convergence and sustainable growth.

  12. Economic Growth Models Transition

    Directory of Open Access Journals (Sweden)

    Coralia Angelescu

    2006-01-01

    Full Text Available The transitional recession in countries of Eastern Europe has been much longer than expected. The legacy and recent policy mistakes have both contributed to the slow progress. As structural reforms and gradual institution building have taken hold, the post-socialist economics have started to recover, with some leading countries building momentum toward faster growth. There is a possibility that in wider context of globalization several of these emerging market economies will be able to catch up with the more advanced industrial economies in a matter of one or two generations. Over the past few years, most candidate countries have made progress in the transition to a competitive market economy, macroeconomic stabilization and structural reform. However their income levels have remained far below those in the Member States. Measured by per capita income in purchasing power standards, there has been a very limited amount of catching up over the past fourteen years. Prior, the distinctions between Solow-Swan model and endogenous growth model. The interdependence between transition and integration are stated in this study. Finally, some measures of macroeconomic policy for sustainable growth are proposed in correlation with real macroeconomic situation of the Romanian economy. Our study would be considered the real convergence for the Romanian economy and the recommendations for the adequate policies to achieve a fast real convergence and sustainable growth.

  13. Economic Reforms and Constitutional Transition

    OpenAIRE

    Jeffrey D. Sachs; Wing Thye Woo; Xiaokai Yang

    2000-01-01

    This paper investigates the relationship between economic reforms and constitutional transition, which has been neglected by many transition economists. It is argued that assessment of reform performance might be very misleading if it is not recognized that economic reforms are just a small part of large scale of constitutional transition. Rivalry and competition between states and between political forces within each country are the driving forces for constitutional transition. We use Russia...

  14. Discrete dynamics in transitional economies

    Directory of Open Access Journals (Sweden)

    J. Barkley Rosser, Jr.

    1998-01-01

    Full Text Available This paper traces the transition from planned command socialism to market capitalism and the accompanying complex non-linear dynamics involved. Long wave chaotic hysteretic investment cycles emerge under socialism leading to crisis and breakdown. Macroeconomic collapse occurs with bifurcations of coordination structures during transition. During recovery, transitional cobweb labor market dynamics exhibit chaos, fractal basin boundaries between coexisting non-chaotic attractors, discontinuous phase transitions, strange attractors, and cascades of infinitely many period-doubling bifurcations.

  15. Reconstructing Transition Knowledge in Taiwan

    Science.gov (United States)

    Cheng, Chen-chen

    2012-01-01

    Taking a post-colonial stand and using school to work transition as an example, the author re-examines the special education discourses in Taiwan and attempts to construct alternate understandings of transition from sociological and cultural perspectives. A review of past transition literature and a survey of the educational background of the…

  16. Alameda-Contra Costa Transit District (AC Transit) Fuel Cell Transit Buses: Preliminary Evaluation Results

    Energy Technology Data Exchange (ETDEWEB)

    Chandler, K.; Eudy, L.

    2007-03-01

    This report provides an evaluation of three prototype fuel cell-powered transit buses operating at AC Transit in Oakland, California, and six baseline diesel buses similar in design to the fuel cell buses.

  17. Role of radial electric field in LH transition triggered by counter-NBI at low plasma density in the TUMAN-3M tokamak

    International Nuclear Information System (INIS)

    Tukachinsky, A.S.; Askinazi, L.G.; Chernyshev, F.V. and others; Krupnik, L.I.; Rushkevich, A.A.

    2008-01-01

    Threshold power needed to attain H-mode in a tokamak is a critical parameter for designing of future devices and in particular fusion reactor ITER [1]. According to commonly accepted scaling [2] the threshold power P t hr increases with average density n e when the density exceeds some n em in at which P t hr is minimal. An increase in the P t hr towards low density was observed in many experiments [3-6], prevents the transition at lower n e as well. Physics of the threshold power increase at low ne is not well understood. Since the radial electric field E r and E r xB sheared flow play important roles in the LH transition one could expect these quantities effect the low n-bar e transitions. Toroidal rotation and radial electric field generation during counter-NBI have been studied in [7] and recently reconsidered theoretically in [8]. Thus, motivation for the presented study is to analyze effect of counter-NBI on the LH transition at low density

  18. Evolution of the Turbulence Radial Wavenumber Spectrum near the L-H Transition in NSTX Ohmic Discharges

    Energy Technology Data Exchange (ETDEWEB)

    Kubota, S.; Peebles, W.A., E-mail: skubota@ucla.edu [UCLA, Los Angeles (United States); Bush, C. E.; Maingi, R. [Oak Ridge National Laboratory, Oak Ridge (United States); Zweben, S. J.; Bell, R.; Crocker, N.; Diallo, A.; Kaye, S.; LeBlanc, B. P.; Park, J. K.; Ren, Y. [Princeton Plasma Physics Laboratory, Princeton University, Princeton (United States); Maqueda, R. J. [Nova Photonics, Princeton (United States); Raman, R. [University of Washington, Seattle (United States)

    2012-09-15

    Full text: The measurement of radially extended meso-scale structures such as zonal flows and streamers, as well as the underlying microinstabilities driving them, is critical for understanding turbulence-driven transport in plasma devices. In particular, the shape and evolution of the radial wavenumber spectrum indicate details of the nonlinear spectral energy transfer, the spreading of turbulence, as well as the formation of transport barriers. In the National Spherical Torus Experiment (NSTX), the FMCW backscattering diagnostic is used to probe the turbulence radial wavenumber spectrum (k{sub r} = 0 - 22 cm-1 ) across the outboard minor radius near the L- to H-mode transition in Ohmic discharges. During the L-mode phase, a broad spectral component (k{sub r} {approx} 2 - 10 cm{sup -1} ) extends over a significant portion of the edge-core from R = 120 to 155 cm ({rho} = 0.4 - 0.95). At the L-H transition, turbulence is quenched across the measurable k{sub r} range at the ETB location, where the radial correlation length drops from {approx} 1.5 - 0.5 cm. The k{sub r} spectrum away from the ETB location is modified on a time scale of tens of microseconds, indicating that nonlocal turbulence dynamics are playing a strong role. Close to the L-H transition, oscillations in the density gradient and edge turbulence quenching become highly correlated. These oscillations are also present in Ohmic discharges without an L-H transition, but are far less frequent. Similar behavior is also seen near the L-H transition in NB-heated discharges. (author)

  19. Phase Transitions in Geomorphology

    Science.gov (United States)

    Ortiz, C. P.; Jerolmack, D. J.

    2015-12-01

    Landscapes are patterns in a dynamic steady-state, due to competing processes that smooth or sharpen features over large distances and times. Geomorphic transport laws have been developed to model the mass-flux due to different processes, but are unreasonably effective at recovering the scaling relations of landscape features. Using a continuum approximation to compare experimental landscapes and the observed landscapes of the earth, one finds they share similar morphodynamics despite a breakdown of classical dynamical similarity between the two. We propose the origin of this effectiveness is a different kind of dynamic similarity in the statistics of initiation and cessation of motion of groups of grains, which is common to disordered systems of grains under external driving. We will show how the existing data of sediment transport points to common signatures with dynamical phase transitions between "mobile" and "immobile" phases in other disordered systems, particularly granular materials, colloids, and foams. Viewing landscape evolution from the lens of non-equilibrium statistical physics of disordered systems leads to predictions that the transition of bulk measurements such as particle flux is continuous from one phase to another, that the collective nature of the particle dynamics leads to very slow aging of bulk properties, and that the dynamics are history-dependent. Recent results from sediment transport experiments support these predictions, suggesting that existing geomorphic transport laws may need to be replaced by a new generation of stochastic models with ingredients based on the physics of disordered phase transitions. We discuss possible strategies for extracting the necessary information to develop these models from measurements of geomorphic transport noise by connecting particle-scale collective dynamics and space-time fluctuations over landscape features.

  20. Gardner Transition in Physical Dimensions

    Science.gov (United States)

    Hicks, C. L.; Wheatley, M. J.; Godfrey, M. J.; Moore, M. A.

    2018-06-01

    The Gardner transition is the transition that at mean-field level separates a stable glass phase from a marginally stable phase. This transition has similarities with the de Almeida-Thouless transition of spin glasses. We have studied a well-understood problem, that of disks moving in a narrow channel, which shows many features usually associated with the Gardner transition. We show that some of these features are artifacts that arise when a disk escapes its local cage during the quench to higher densities. There is evidence that the Gardner transition becomes an avoided transition, in that the correlation length becomes quite large, of order 15 particle diameters, even in our quasi-one-dimensional system.

  1. Transition in synthetic jets

    Czech Academy of Sciences Publication Activity Database

    Tesař, Václav; Kordík, Jozef

    2012-01-01

    Roč. 187, NOV 2012 (2012), s. 105-117 ISSN 0924-4247 R&D Projects: GA TA ČR(CZ) TA02020795; GA ČR(CZ) GPP101/12/P556; GA ČR(CZ) GCP101/11/J019 Institutional research plan: CEZ:AV0Z20760514 Keywords : turbulence * synthetic jet * transition * velocity spectra Subject RIV: BK - Fluid Dynamics Impact factor: 1.841, year: 2012 http://www. science direct.com/ science /article/pii/S0924424712005031

  2. Chain transitivity in hyperspaces

    International Nuclear Information System (INIS)

    Fernández, Leobardo; Good, Chris; Puljiz, Mate; Ramírez, Ártico

    2015-01-01

    Given a non-empty compact metric space X and a continuous function f: X → X, we study the dynamics of the induced maps on the hyperspace of non-empty compact subsets of X and on various other invariant subspaces thereof, in particular symmetric products. We show how some important dynamical properties transfer across induced systems. These amongst others include, chain transitivity, chain (weakly) mixing, chain recurrence, exactness by chains. From our main theorem we derive an ε-chain version of Furstenberg’s celebrated 2 implies n Theorem. We also show the implications our results have for dynamics on continua.

  3. Transitioning to digital radiography

    Energy Technology Data Exchange (ETDEWEB)

    Miranda, F., E-mail: Francisco.Miranda@pwc.ca [Pratt & Whitney Canada, Longueuil, Quebec (Canada)

    2015-09-15

    This article provides insight on the technical and business considerations necessary to implement or to transition to digital radiography Continued refinements in digital radiography technology have resulted in significant improvements in image quality and detectability of indications. These improvements have resulted in the acceptance of the technology by users and aerospace primes for final product inspection and disposition. Digital radiography has also been identified as an interesting cost reduction initiative with the potential of providing gains in productivity through increased throughput and decreased inspection lead-times and resulting costs. (author)

  4. Global transition i sundhed

    DEFF Research Database (Denmark)

    Bygbjerg, Ib Christian; Meyrowitsch, Dan W

    2006-01-01

    , and by degenerative, and man-made diseases in ageing populations. Omran could not foresee the HIV/AIDS pandemic or the dramatic fall in longevity and fertility in, for example, Russia. But his model remains of value for health planners and politicians. We advocate for research in the interplay between diseases......Global epidemiological transition reflected in changed patterns of death and diseases was first described by Omran; decreasing death and disease rates from infectious diseases, particularly in children and the young, are followed by decreased fertility rate and increased longevity...

  5. ALICE Transition Radiation Detector

    CERN Multimedia

    Pachmayer, Y

    2013-01-01

    The Transition Radiation Detector (TRD) is the main electron detector in ALICE. In conduction with the TPC and the ITS, it provides the necessary electron identification capability to study: - Production of light and heavy vector mesons as well as the continuum in the di-electron channel, - Semi leptonic decays of hadrons with open charm and open beauty via the single-electron channel using the displaced vertex information provided by the ITS, - Correlated DD and BB pairs via coincidences of electrons in the central barrel and muons in the forward muon arm, - Jets with high Pτ tracks in one single TRD stack.

  6. Sexuality in transit

    DEFF Research Database (Denmark)

    Heinskou, Marie Bruvik

    2015-01-01

    such an approach, the complexities of sexual assault, changing power relations and unstable narratives of gender and sexuality are illuminated. The analysis shows that the traditional divide between public and private has dissolved and that public spaces of pop culture are drawn into spaces of intimacy and thereby......Through an investigation of a reported rape, this article suggests that we conceive sexuality as a transitional object that changes and transforms depending on space and temporality. This makes sexuality difficult to grasp within specific and stable frames of gender and power analysis. Applying...

  7. Tiber Personal Rapid Transit

    Directory of Open Access Journals (Sweden)

    Diego Carlo D'agostino

    2011-02-01

    Full Text Available The project “Tiber Personal Rapid Transit” have been presented by the author at the Rome City Vision Competition1 2010, an ideas competition, which challenges architects, engineers, designers, students and creatives individuals to develop visionary urban proposals with the intention of stimulating and supporting the contemporary city, in this case Rome. The Tiber PRT proposal tries to answer the competition questions with the definition of a provocative idea: a Personal Rapid transit System on the Tiber river banks. The project is located in the central section of the Tiber river and aims at the renewal of the river banks with the insertion of a Personal Rapid Transit infrastructure. The project area include the riverbank of Tiber from Rome Transtevere RFI station to Piazza del Popolo, an area where main touristic and leisure attractions are located. The intervention area is actually no used by the city users and residents and constitute itself a strong barrier in the heart of the historic city.

  8. 309 Building transition plan

    International Nuclear Information System (INIS)

    Graves, C.E.

    1994-01-01

    The preparation for decontamination and decommissioning (transition) of the 309 Building is projected to be completed by the end of the fiscal year (FY) 1998. The major stabilization and decontamination efforts include the Plutonium Recycle Test Reactor (PRTR), fuel storage and transfer pits, Transfer Waste (TW) tanks and the Ion Exchange Vaults. In addition to stabilizing contaminated areas, equipment, components, records, waste products, etc., will be dispositioned. All nonessential systems, i.e., heating, ventilation, and air conditioning (HVAC), electrical, monitoring, fluids, etc., will be shut down and drained/de-energized. This will allow securing of the process, laboratory, and office areas of the facility. After that, the facility will be operated at a level commensurate with its surveillance needs while awaiting D ampersand D. The implementation costs for FY 1995 through FY 1998 for the transition activities are estimated to be $1,070K, $2,115K, $2,939K, and $4,762K, respectively. Costs include an assumed company overhead of 20% and a 30% out year contingency

  9. Variational transition state theory

    International Nuclear Information System (INIS)

    Truhlar, D.G.

    1986-01-01

    This project is concerned with the development and applications of generalized transition state theory and multidimensional tunneling approximations to chemical reaction rates. They have developed and implemented several practical versions of variational transition state theory (VTST), namely canonical variational theory (CVT), improved canonical variational theory (ICVT), and microcanonical variational theory (μVT). They have also developed and implemented several accurate multidimensional semiclassical tunneling approximations, the most accurate of which are the small-curvature semiclassical adiabatic (SCSA), large-curvature version-3 (LC3), and least-action (LA) approximations. They have applied the methods to thermal rate constants, using transmission coefficients based on ground-state tunneling, and they have also presented and applied adiabatic and diabatic extensions to calculated rate constants for vibrationally excited reactants. Their general goal is to develop accurate methods for calculating chemical reaction rate constants that remain practical even for reasonably complicated molecules. The approximations mentioned above yield rate constants for systems whose potential energy surface is known or assumed. Thus a second, equally important aspect of their work is the determination or modeling, semi-empirically and/or from electronic structure calculations, of potential energy surfaces

  10. Physical education in transition

    Directory of Open Access Journals (Sweden)

    Đokić Zoran

    2017-01-01

    Full Text Available The consequences of physical inactivity and insufficient education about its importance are affecting not only the length and the quality of life, but also the economic aspects, such as health care costs caused by the reduction in labour productivity of the Serbian population. Based on previous experiences of countries in transition and those that have well-arranged systems of education, in terms of teaching of physical education programmes, there are possibilities for the necessary reform of the curriculum, adapted to our abilities and needs. These are primarily related to the objectives of education - proper development and creation of positive habits regarding physical activity and health. So far, the reforms of physical education in Serbia have not produced results. The reform should be the transition from education focused on the program to education focused on the ultimate goals (knowledge, skills, and attitudes towards physical activity, i.e. the lifelong values. The objectives and outcomes of teaching physical education should be individualized according to the psychosomatic status and specific dimensions of that status. Therefore, the role and responsibility of teachers change and it is necessary to reform their education. Of course, government is very involved in all of this, at all levels - throughout strategies and campaigns to raise awareness of the nation and its knowledge about the importance of physical activity through all forms of education.

  11. Invariant probabilities of transition functions

    CERN Document Server

    Zaharopol, Radu

    2014-01-01

    The structure of the set of all the invariant probabilities and the structure of various types of individual invariant probabilities of a transition function are two topics of significant interest in the theory of transition functions, and are studied in this book. The results obtained are useful in ergodic theory and the theory of dynamical systems, which, in turn, can be applied in various other areas (like number theory). They are illustrated using transition functions defined by flows, semiflows, and one-parameter convolution semigroups of probability measures. In this book, all results on transition probabilities that have been published by the author between 2004 and 2008 are extended to transition functions. The proofs of the results obtained are new. For transition functions that satisfy very general conditions the book describes an ergodic decomposition that provides relevant information on the structure of the corresponding set of invariant probabilities. Ergodic decomposition means a splitting of t...

  12. Subsequence Automata with Default Transitions

    DEFF Research Database (Denmark)

    Bille, Philip; Gørtz, Inge Li; Skjoldjensen, Frederik Rye

    2016-01-01

    of states and transitions) of the subsequence automaton is O(nσ) and that this bound is asymptotically optimal. In this paper, we consider subsequence automata with default transitions, that is, special transitions to be taken only if none of the regular transitions match the current character, and which do...... not consume the current character. We show that with default transitions, much smaller subsequence automata are possible, and provide a full trade-off between the size of the automaton and the delay, i.e., the maximum number of consecutive default transitions followed before consuming a character......(nσ) and delay O(1), thus matching the bound for the standard subsequence automaton construction. The key component of our result is a novel hierarchical automata construction of independent interest....

  13. Subsequence automata with default transitions

    DEFF Research Database (Denmark)

    Bille, Philip; Gørtz, Inge Li; Skjoldjensen, Frederik Rye

    2017-01-01

    of states and transitions) of the subsequence automaton is O(nσ) and that this bound is asymptotically optimal. In this paper, we consider subsequence automata with default transitions, that is, special transitions to be taken only if none of the regular transitions match the current character, and which do...... not consume the current character. We show that with default transitions, much smaller subsequence automata are possible, and provide a full trade-off between the size of the automaton and the delay, i.e., the maximum number of consecutive default transitions followed before consuming a character......(1), thus matching the bound for the standard subsequence automaton construction. Finally, we generalize the result to multiple strings. The key component of our result is a novel hierarchical automata construction of independent interest....

  14. Phase transition in finite systems

    International Nuclear Information System (INIS)

    Chomaz, Ph.; Duflot, V.; Duflot, V.; Gulminelli, F.

    2000-01-01

    In this paper we present a review of selected aspects of Phase transitions in finite systems applied in particular to the liquid-gas phase transition in nuclei. We show that the problem of the non existence of boundary conditions can be solved by introducing a statistical ensemble with an averaged constrained volume. In such an ensemble the microcanonical heat capacity becomes negative in the transition region. We show that the caloric curve explicitly depends on the considered transformation of the volume with the excitation energy and so does not bear direct informations on the characteristics of the phase transition. Conversely, partial energy fluctuations are demonstrated to be a direct measure of the equation of state. Since the heat capacity has a negative branch in the phase transition region, the presence of abnormally large kinetic energy fluctuations is a signal of the liquid gas phase transition. (author)

  15. Place in Transition

    DEFF Research Database (Denmark)

    Mikkelsen, Jacob Bjerre; Lange, Ida Sofie Gøtzsche

    from the 'Everyday World'. Within mobilities studies, research has focused on different aspects and consequences of the post-oil society (see Dennis & Urry 2009, Urry 2013). This paper discusses the conception of place within the enclosed 'Oil World' with point of departure in relocation...... and redefinition of oil rigs from an urban design perspective. The paper constitutes a theoretical basis for future design scenarios - exemplified through visionary urban design proposals for a specific site in the city of Esbjerg, Denmark. Relocating rigs to an urban context initiates discussions of conception...... of 'Place' questioning the fixity of 'Place' (Jensen 2010). Scoped through a relational sense of place (Massey 1993) and the potential of exploring new relations between places (Burns & Kahn 2005), the paper challenges the notion of 'Place as God' (Hvattum 2010). These places in transition contest...

  16. Transitions in Secondary Education

    DEFF Research Database (Denmark)

    Larsen, Britt Østergaard; Jensen, Leif; Pilegaard Jensen, Torben

    2014-01-01

    statistical model of educational progression. By using this method, we parcel educational attainment into a series of transitions and the model is able to control for educational selection and unobserved heterogeneity. We apply counterfactual analyses to allow a formal decomposition of the effects of social......The purpose of this article is to investigate educational choices and attainment of children who experience social problems during their upbringing. The study explores the extent to which social problems can help explain the gaps in entry and dropout rates in upper secondary education in Denmark...... between students from different socioeconomic backgrounds. Population-based registers are used to include information on family upbringing, e.g. alcohol abuse, criminality, use of psychopharmaca and out-of-home placement. We estimate a parsimonious version of Cameron and Heckman's (2001) dynamic...

  17. Hybrid Electric Transit Bus

    Science.gov (United States)

    Viterna, Larry A.

    1997-01-01

    A government, industry, and university cooperative is developing an advanced hybrid electric city transit bus. Goals of this effort include doubling the fuel economy compared to current buses and reducing emissions to one-tenth of current EPA standards. Unique aspects of the vehicle's power system include the use of ultra-capacitors as an energy storage system, and a planned natural gas fueled turbogenerator developed from a small jet engine. Power from both the generator and energy storage system is provided to a variable speed electric motor attached to the rear axle. At over 15000 kg gross weight, this is the largest vehicle of its kind ever built using ultra-capacitor energy storage. This paper describes the overall power system architecture, the evolution of the control strategy, and its performance over industry standard drive cycles.

  18. Radioisotope esophageal transit test

    International Nuclear Information System (INIS)

    Miyazono, Kazuhiro; Fukuda, Kazuo; Toyonaga, Atsushi

    1982-01-01

    A new technique employed sup(99m)Tc-MAA for the study of esophageal dysfunction and its clinical implication were evaluated in the patients with achalasia, progressive systemic sclerosis, reflux esophagitis and 10 normal controls. To investigate esophageal emptying and gastroesophageal reflux, a homogeneous bolus of sup(99m)Tc-MAA in 15ml of water was swallowed in the upright and supine positions under the collimeter of a gamma camera linked to nuclear medicine data analyser (Shimazu Scinti Pack 1200). This radionuclide transit studies made a quantitative evaluation of the esophageal dysfunction possible in all cases. Comparing the conventional esophageal function test procedures, this test is a safe, noninvasive and more physiological and sensitive in detecting abnormal esophageal emptying and gastroesophageal reflux. (author)

  19. Energy transition in action

    International Nuclear Information System (INIS)

    2014-07-01

    By presenting examples and experiments implemented in France, this publication illustrates the various ways to translate the objectives of energy transition into practical actions. A first part addresses the building sector and shows how to better renovate buildings: exemplary rehabilitations, techniques of construction to decrease energy consumption and equipment to control it, insulation by vegetal fibres, control of consumption decrease. The second part addresses the development of renewable energies: a heat network for household heating, innovative use of biogas, production of hot water by using solar energy, a waste incineration plant, heating by using waste waters. The third part addresses the promotion of circular economy: a recycling project, an optics-based glass sorting system, the commitment of Parisian restaurateurs for waste valorisation, a plant for waste sorting and valorisation

  20. Transit spectroscopy with GTC

    Directory of Open Access Journals (Sweden)

    Osorio M.R. Zapatero

    2013-04-01

    Full Text Available Thanks to different ground-based surveys and space missions, nowadays we have a fairly large sample of discovered extra-solar planets to study and, without a doubt, this number will increase in the future. One of the most succesful techniques that allows us to prove the physical properties and atmospheric composition of these exoplanets is transmission spectroscopy. The level of precision that is require to measure these effects provides a technical challenge that is solved by using big telescopes and stable instruments to reach low noise levels. In this article, we will discuss the use of the 10m class telescope GTC to observed planetary transits in spectroscopic mode and some of the results that we are currently obtaining.

  1. Strategic planning in transition

    DEFF Research Database (Denmark)

    Olesen, Kristian; Richardson, Tim

    2012-01-01

    In this paper, we analyse how contested transitions in planning rationalities and spatial logics have shaped the processes and outputs of recent episodes of Danish ‘strategic spatial planning’. The practice of ‘strategic spatial planning’ in Denmark has undergone a concerted reorientation...... style of ‘strategic spatial planning’ with its associated spatial logics is continuously challenged by a persistent regulatory, top-down rationality of ‘strategic spatial planning’, rooted in spatial Keynesianism, which has long characterised the Danish approach. The findings reveal the emergence...... of a particularly Danish approach, retaining strong regulatory aspects. However this approach does not sit easily within the current neoliberal political climate, raising concerns of an emerging crisis of ‘strategic spatial planning’....

  2. Nonadiabatic transition path sampling

    International Nuclear Information System (INIS)

    Sherman, M. C.; Corcelli, S. A.

    2016-01-01

    Fewest-switches surface hopping (FSSH) is combined with transition path sampling (TPS) to produce a new method called nonadiabatic path sampling (NAPS). The NAPS method is validated on a model electron transfer system coupled to a Langevin bath. Numerically exact rate constants are computed using the reactive flux (RF) method over a broad range of solvent frictions that span from the energy diffusion (low friction) regime to the spatial diffusion (high friction) regime. The NAPS method is shown to quantitatively reproduce the RF benchmark rate constants over the full range of solvent friction. Integrating FSSH within the TPS framework expands the applicability of both approaches and creates a new method that will be helpful in determining detailed mechanisms for nonadiabatic reactions in the condensed-phase.

  3. Transition to electronic publishing

    Science.gov (United States)

    Bowning, Sam

    Previous communications have described some of the many changes that will occur in the next few months as AGU makes the transition to fully electronic publishing. With the advent of the new AGU electronic publishing system, manuscripts will be submitted, edited, reviewed, and published in electronic formats. This piece discusses how the electronic journals will differ from the print journals. Electronic publishing will require some adjustments to the ways we currently think about journals from our perspective of standard print versions. Visiting the Web site of AGU's Geochemistry, Geophysics, Geosystems (G-Cubed) is a great way to get familiar with the look and feel of electronic publishing. However, protocols, especially for citations of articles, are still evolving. Some of the biggest changes for users of AGU publications may be the lack of page numbers, the use of a unique identifier (DOI),and changes in citation style.

  4. Are transition economy workers underpaid?

    OpenAIRE

    Adamchik, Vera A.; Brada, Josef C.; King, Arthur E.

    2009-01-01

    We examine the extent to which workers in transition and developed market economies are able to obtain wages that fully reflect their skills and labor force characteristics. We find that workers in two transition economies, the Czech Republic and Poland, are able to better attain the maximum wage available than are workers in a sample of developed market economies. This greater wage-setting efficiency in the transition economies ap-pears to be more the result of social and demographic charact...

  5. Transition densities with electron scattering

    International Nuclear Information System (INIS)

    Heisenberg, J.

    1985-01-01

    This paper reviews the ground state and transition charge densities in nuclei via electron scattering. Using electrons as a spectroscopic tool in nuclear physics, these transition densities can be determined with high precision, also in the nuclear interior. These densities generally ask for a microscopic interpretation in terms of contributions from individual nucleons. The results for single particle transitions confirm the picture of particle-phonon coupling. (Auth.)

  6. Intermultiplet transitions using neutron spectroscopy

    International Nuclear Information System (INIS)

    Osborn, R.; Lovesey, S.W.; Taylor, A.D.; Balcar, E.

    1989-12-01

    Neutron inelastic scattering is used here to attempt to obtain optical spectra for lanthanide metals and compounds. Intermultiplet spectroscopy provides information about transitions from different electronic configurations and hybridisation of the 4f shell. This report discusses the relatively limited contribution that neutron scattering has played in intermultiplet spectroscopy, and covers spin-orbit transitions and coulomb transitions Racah algebra is developed in calculating the scattering cross sections. (author)

  7. Transition Complexity of Incomplete DFAs

    Directory of Open Access Journals (Sweden)

    Yuan Gao

    2010-08-01

    Full Text Available In this paper, we consider the transition complexity of regular languages based on the incomplete deterministic finite automata. A number of results on Boolean operations have been obtained. It is shown that the transition complexity results for union and complementation are very different from the state complexity results for the same operations. However, for intersection, the transition complexity result is similar to that of state complexity.

  8. Nuclear regulation in transition

    International Nuclear Information System (INIS)

    Tomain, J.P.

    1986-01-01

    The current state of nuclear regulations in the USA is examined. Since Three Mile Island the regulation of the nuclear power industry has been undergoing a noticeable transition. It will be argued here that the transition is characterized by two indicia. First, the primary focus of state and federal regulators has been on the financial aspects of the industry: this is best seen in the context of decisions allocating the costs of nuclear plant cancellations. Second, decisionmaking power has been decentralized: although the regulatory history of nuclear power demonstrates the tradition of centralized decisionmaking power (i.e., formerly the primary decisionmaking body was the Atomic Energy Commission), now States share decisionmaking power with the Nuclear Regulatory Commission. In Section 1 a brief legislative history of nuclear regulation is presented to establish the assertion that nuclear regulation, both de jure and de facto, was centralized. Next, Section 2 canvasses recent United States Supreme Court opinions regarding nuclear regulation. The Court frequently acts as policymaker through the consequences of its opinions, if not by its intent. In the area of nuclear policymaking, the Court has paid allegiance recently both to the tradition of centralization and to the movement toward decentralization. This dualism is reflected in other federal court decisions as well which will be briefly mentioned. Continuing the analysis of Federal regulation, Section 3 examines the current reform efforts of the NRC. Section 4 presents an examination of State responses to nuclear plant cancellations. In this section, State administrative agency and court decisions will be examined and recent State legislation will be discussed. (author)

  9. Nuclear regulation in transition

    Energy Technology Data Exchange (ETDEWEB)

    Tomain, J.P. (Cincinnati Univ., OH, US. Coll. of Law)

    1986-01-01

    The current state of nuclear regulations in the USA is examined. Since Three Mile Island the regulation of the nuclear power industry has been undergoing a noticeable transition. It will be argued here that the transition is characterized by two indicia. First, the primary focus of state and federal regulators has been on the financial aspects of the industry: this is best seen in the context of decisions allocating the costs of nuclear plant cancellations. Second, decisionmaking power has been decentralized: although the regulatory history of nuclear power demonstrates the tradition of centralized decisionmaking power (i.e., formerly the primary decisionmaking body was the Atomic Energy Commission), now States share decisionmaking power with the Nuclear Regulatory Commission. In Section 1 a brief legislative history of nuclear regulation is presented to establish the assertion that nuclear regulation, both de jure and de facto, was centralized. Next, Section 2 canvasses recent United States Supreme Court opinions regarding nuclear regulation. The Court frequently acts as policymaker through the consequences of its opinions, if not by its intent. In the area of nuclear policymaking, the Court has paid allegiance recently both to the tradition of centralization and to the movement toward decentralization. This dualism is reflected in other federal court decisions as well which will be briefly mentioned. Continuing the analysis of Federal regulation, Section 3 examines the current reform efforts of the NRC. Section 4 presents an examination of State responses to nuclear plant cancellations. In this section, State administrative agency and court decisions will be examined and recent State legislation will be discussed.

  10. Cyclotron transitions of bound ions

    Science.gov (United States)

    Bezchastnov, Victor G.; Pavlov, George G.

    2017-06-01

    A charged particle in a magnetic field possesses discrete energy levels associated with particle rotation around the field lines. The radiative transitions between these levels are the well-known cyclotron transitions. We show that a bound complex of particles with a nonzero net charge displays analogous transitions between the states of confined motion of the entire complex in the field. The latter bound-ion cyclotron transitions are affected by a coupling between the collective and internal motions of the complex and, as a result, differ from the transitions of a "reference" bare ion with the same mass and charge. We analyze the cyclotron transitions for complex ions by including the coupling within a rigorous quantum approach. Particular attention is paid to comparison of the transition energies and oscillator strengths to those of the bare ion. Selection rules based on integrals of collective motion are derived for the bound-ion cyclotron transitions analytically, and the perturbation and coupled-channel approaches are developed to study the transitions quantitatively. Representative examples are considered and discussed for positive and negative atomic and cluster ions.

  11. Connecticut Transit (CTTRANSIT) Fuel Cell Transit Bus: Preliminary Evaluation Results

    Energy Technology Data Exchange (ETDEWEB)

    Chandler, K.; Eudy, L.

    2008-10-01

    This report provides preliminary results from a National Renewable Energy Laboratory evaluation of a protoptye fuel cell transit bus operating at Connecticut Transit in Hartford. Included are descriptions of the planned fuel cell bus demonstration and equipment; early results and agency experience are also provided.

  12. Innovation policy for the Dutch energy transition Operationalising transition management?

    NARCIS (Netherlands)

    D.A. Loorbach (Derk); R. Kemp (René)

    2005-01-01

    textabstractThe term transition is a key term of the fourth national environmental policy plan (NMP4, 2001), which put forward transition management (Rotmans et al, 2000) as a new policy approach for dealing with persistent and highly complex societal problems such as climate change, loss of

  13. Lost in Transition: Examining Transitions in Psychotherapy Training.

    Science.gov (United States)

    Tan, Adrienne; Philipp, Diane; Malat, Jan; Feder, Victor; Kulkarni, Chetana; Lawson, Andrea; So, Vivien; Ravitz, Paula

    2015-10-01

    Disruptions are inevitable during psychiatry residency training and can affect resident learning and patient care. This exploratory study examined the nature and impact of transitions in psychotherapy training. PGY2-5 residents (45/150; 30% response rate) and psychotherapy supervisors (46/247; 18.6% response rate) were surveyed about transitional events during residency training in psychotherapy. Supervisors and residents ranked the frequency of occurrence of transitional events and their impact very similarly, as well as the "feed forward" items when transitioning to a new supervisor. Residents feeling confused or overwhelmed with the balancing of learning differing models with differing levels of comfort or knowledge was ranked as the issue that occurred most frequently by both supervisors and residents. This study highlights issues that arise at transitions during psychotherapy training in psychiatry residency. Strategies for managing these periods are discussed, with a focus on resident learning and improved continuity of patient care.

  14. Dynamic investigation of mode transition in inductively coupled plasma with a hybrid model

    International Nuclear Information System (INIS)

    Zhao Shuxia; Gao Fei; Wang Younian

    2009-01-01

    Industrial inductively coupled plasma (ICP) sources are always operated in low gas pressure 10-100 mTorr, therefore in order to accurately investigate the mode transition of ICP, we developed our pure fluid model (2009 J. Appl. Phys. 105 083306) into a hybrid fluid/Monte Carlo (MC) model, where the MC part is exploited to take in more dynamic characteristics of electrons and self-consistently calculate the rate coefficients and electron temperature used in the fluid module, and more crucially to study the electron energy distribution function (EEDF) evolution with mode transition. Due to the introduction of the nonlocal property of the electrons at relatively low pressures, the dependences of the plasma density on the coil current, including the mode transitions, are distinctly different at low and high pressures when simulated by this improved hybrid model (HM), while the trends for different pressures obtained from the original pure fluid model (PFM) are the same in all cases. Furthermore, the computed peaks of the electron density profile by the HM shift from the discharge centre in the E mode to the intense inductive field heating area (about half of the radius of the reaction chamber under the dielectric window) in H mode. In addition, the electron temperature profiles of two modes under different pressures simulated by HM are totally higher than the results of PFM. When the pressure is low, there is a minimum exhibited in the bulk plasma of the electron temperature profiles of the E mode, and along with the mode transition the distribution area of low temperature is substantially reduced. Moreover, this phenomenon disappears when the gas pressure is increased. Accompanied by this, the calculated EEDF of the E mode in the low pressure also demonstrates an absolutely dominant low energy electron fraction (about ≤5 eV); while transforming to the H discharge most of the electrons carry an energy of 1-10 eV. The tendencies of the calculated EEDF evolution with

  15. Molecular-nuclear transitions

    International Nuclear Information System (INIS)

    Belyaev, V.B.; Miller, M.B.

    2007-01-01

    Full text: The spectra in some light nuclei have one interesting property. For example, in the closed vicinity of some resonance states of such nuclei as 5 He, 8 Be, 18 F, 18 Ne the thresholds exist for two- or three-body decay of those nuclei. Let us consider the lightest of the above nuclei, 5 He. The energy threshold for 5 He > d+t decay is ∼50 keV lower than the energy of 3/2 + state of 5 He nucleus. However, due to a rather large width of this state, ∼70 keV, the nuclear capture of deuterons by tritons in dtm-molecule is highly enhanced in comparison with the process of dd capture in the ddm molecule. The physical reason for the enhancement of the probability of the capture into the resonant state can be associated with a long tail of wave function of the resonant state and, accordingly, with the large value of the overlap integral determining in general the probability of the transition between two systems. Thus, one can expect the enhancement of the molecular-nuclear transitions, and this was indeed observed experimentally for the case of dtm molecule. Now, let us consider some other molecular-nuclear combinations: 18 Ne - H 2 O, 18 F - 17 OH, and 8 Be - 6 LiD molecule. With the high accuracy the energies of the above molecular systems coincide with the energies of the resonant states in the appropriate nuclei. Due to the uncertainty in the experimental nuclear data it is not known at present whether the energies of these thresholds are lower or higher of the corresponding energies of the nuclear resonances. Let us assume that the molecular energy is few keV over the energy of the nuclear resonance. Then, we will deal with a very interesting phenomenon: the molecular-nuclear complex constitutes a two level system, which in some sense is analogous to the two-level atomic system, as in a laser. The crucial difference between this one and the two-level atomic systems consists in a fact that in the molecular-nuclear case no special procedure of pumping up

  16. Mean shear flows, zonal flows, and generalized Kelvin-Helmholtz modes in drift wave turbulence: A minimal model for L→H transition

    International Nuclear Information System (INIS)

    Kim, Eun-jin; Diamond, P.H.

    2003-01-01

    The dynamics of and an interplay among structures (mean shear flows, zonal flows, and generalized Kelvin-Helmholtz modes) are studied in drift wave turbulence. Mean shear flows are found to inhibit the nonlinear generation of zonal flows by weakening the coherent modulation response of the drift wave spectrum. Based on this result, a minimal model for the L→H (low- to high-confinement) transition is proposed, which involves the amplitude of drift waves, zonal flows, and the density gradient. A transition to quiescent H-mode sets in as the profile becomes sufficiently steep to completely damp out drift waves, following an oscillatory transition phase where zonal flows regulate drift wave turbulence. The different roles of mean flows and zonal flows are elucidated. Finally, the effect of poloidally nonaxisymmetric structures (generalized Kelvin-Helmholtz mode) on anomalous transport is investigated, especially in reference to damping of collisionless zonal flows. Results indicate that nonlinear excitation of this structure can be potentially important in enhancing anomalous transport as well as in damping zonal flows

  17. Transition management: origin, evolution, critique

    NARCIS (Netherlands)

    J. Rotmans (Jan); D.A. Loorbach (Derk); R. Kemp (René)

    2007-01-01

    textabstractTransition management has rapidly emerged over the past few years as a new approach to dealing with complex societal problems and governance in the context of these problems. In the Netherland, UK and Belgium, serious efforts have been and are being undertaken to develop transition

  18. Phenomenology of cosmic phase transitions

    International Nuclear Information System (INIS)

    Kaempfer, B.; Lukacs, B.; Paal, G.

    1989-11-01

    The evolution of the cosmic matter from Planck temperature to the atomic combination temperature is considered from a phenomenological point of view. Particular emphasis is devoted to the sequence of cosmic phase transitions. The inflationary era at the temperature of the order of the grand unification energy scale and the quantum chromodynamic confinement transition are dealt with in detail. (author) 131 refs.; 26 figs

  19. Transitivity and partial screening off

    NARCIS (Netherlands)

    Peijnenburg, Jeanne; Atkinson, David

    2013-01-01

    The notion of probabilistic support is beset by well-known problems. In this paper we add a new one to the list: the problem of transitivity. Tomoji Shogenji has shown that positive probabilistic support, or confirmation, is transitive under the condition of screening off. However, under that same

  20. Transition Planning for Foster Youth

    Science.gov (United States)

    Geenen, Sarah J.; Powers, Laurie E.

    2006-01-01

    The study evaluated the IEPs/Individualized Transition Plans of 45 students who were in special education and foster care, and compared them to the plans of 45 students who were in special education only. Results indicate that the transition plans of foster youth with disabilities were poor in quality, both in absolute terms and in comparison to…

  1. Generalized definitions of phase transitions

    International Nuclear Information System (INIS)

    Chomaz, Ph.; Gulminelli, F.

    2001-09-01

    We define a first order phase transition as a bimodality of the event distribution in the space of observations and we show that this is equivalent to a curvature anomaly of the thermodynamical potential and that it implies the Yang Lee behavior of the zeros of the partition sum. Moreover, it allows to study phase transitions out of equilibrium. (authors)

  2. Transition: Intended and unintended processes

    NARCIS (Netherlands)

    Ellman, M.

    2005-01-01

    An analysis of the relationship between transition as that was intended by the international financial institutions and transition as it actually happened. Attention is paid to what has been learned by experience about stabilisation, liberalisation and privatisation. Attention is also given to the

  3. STYLIZED ECONOMIC FACTS OF TRANSITION

    Directory of Open Access Journals (Sweden)

    NATASHA TRAJKOVA-NAJDOVSKA

    2017-12-01

    Full Text Available In the course of transition, former socialistic countries moved from planned to market economy. This journey typically started with sharp falls in economic activity in all transition countries, accompanied by deterioration of various social indicators. Hence, their main objective was the recovery of economic activity, i.e. increasing the economic growth rate, which in addition was supposed to enable catching up with the European developed economies. This growth movement is usually described by famous U-curve of transition. However, in spite of the efforts and reforms, all transition economies recorded various paces of recovery. This study discusses that difference, through various GDP indicators, - real GDP path, GDP growth rates path, the height of the GDP index achieved and the volatility of growth rates. Analysed in concert, these indicators suggest several other variations of the transition Ucurve, such as: the rapid-J group, the wide-U group and the L-curve group. Namely, almost three decades after the start of the transition, the differences persist, suggesting that some transition economies has not moved significantly towards catching up with the successful transition countries, or with the developed economies.

  4. Philosophical explorations on energy transition

    NARCIS (Netherlands)

    Geerts, Robert-Jan

    2017-01-01

    This dissertation explores energy transition from a philosophical perspective. It puts forward the thesis that energy production and consumption are so intimately intertwined with society that the transition towards a sustainable alternative will involve more than simply implementing novel

  5. Partnership Transitions and Maternal Parenting

    Science.gov (United States)

    Beck, Audrey N.; Cooper, Carey E.; McLanahan, Sara; Brooks-Gunn, Jeanne

    2010-01-01

    We use data from the Fragile Families and Child Wellbeing Study (N = 1,975) to examine the association between mothers' partnership changes and parenting behavior during the first 5 years of their children's lives. We compare coresidential with dating transitions and recent with more distal transitions. We also examine interactions between…

  6. Transition Metal Complexes and Catalysis

    Indian Academy of Sciences (India)

    approaches towards the study of bonding in transition metal complexes. Despite .... industrial scale reactions for the production of organic compounds using transition ..... It has found several applications as an engineering thermoplastic. .... and processes of interest to the company, that is, applied research. It is this very ...

  7. Weak transitions in 44Ca

    International Nuclear Information System (INIS)

    Tauhata, L.; Marques, A.

    1972-01-01

    Energy levels and gamma radiation transitions of Ca 44 are experimentally determined, mainly the weak transition at 564 KeV and 728 KeV. The decay scheme and the method used (coincidence with Ge-Li detector) are also presented [pt

  8. Non-equilibrium phase transitions

    CERN Document Server

    Henkel, Malte; Lübeck, Sven

    2009-01-01

    This book describes two main classes of non-equilibrium phase-transitions: (a) static and dynamics of transitions into an absorbing state, and (b) dynamical scaling in far-from-equilibrium relaxation behaviour and ageing. The first volume begins with an introductory chapter which recalls the main concepts of phase-transitions, set for the convenience of the reader in an equilibrium context. The extension to non-equilibrium systems is made by using directed percolation as the main paradigm of absorbing phase transitions and in view of the richness of the known results an entire chapter is devoted to it, including a discussion of recent experimental results. Scaling theories and a large set of both numerical and analytical methods for the study of non-equilibrium phase transitions are thoroughly discussed. The techniques used for directed percolation are then extended to other universality classes and many important results on model parameters are provided for easy reference.

  9. Gauge theory of glass transition

    International Nuclear Information System (INIS)

    Vasin, Mikhail

    2011-01-01

    A new analytical approach for the description of the glass transition in a frustrated system is suggested. The theory is based on the non-equilibrium dynamics technique, and takes into account the interaction of the local order field with the massive gauge field, which describes frustration-induced plastic deformation. The glass transition is regarded as a phase transition interrupted because of the premature critical slowing-down of one of the degrees of freedom caused by the frustrations. It is shown that freezing of the system appears when the correlation length and relaxation time of the gauge field diverge. The Vogel–Fulcher–Tammann relation for the transition kinetics and the critical exponent for the nonlinear susceptibility, 2.5∼ t correlation function dependence on time, and explains the boson peak appearance on this curve. In addition, the function of the glass transition temperature value with cooling rate is derived; this dependence fully conforms with known experimental data

  10. Narratives about labour market transitions

    DEFF Research Database (Denmark)

    Cort, Pia; Thomsen, Rie

    2014-01-01

    on flexicurity and its implications for labour market transitions, little attention has been paid to the views and experiences of the individuals concerned. The aim of this article is to connect the grand narrative with individual narratives about labour market transitions in the Danish flexicurity system....... On the basis of narrative interviews with skilled workers, this article explores how labour market transitions are experienced by the individual and the role played by national support structures in the individual narratives. The article shows how, for the individual, a transition may prove to be a valuable...... learning experience during which radical career decisions are taken, and how support structures may work to the detriment of such learning and of the principles behind flexicurity. The article points to a reconceptualisation of transitions as important learning opportunities during which (more) adequate...

  11. Vacuum transitions in dual models

    International Nuclear Information System (INIS)

    Pashnev, A.I.; Volkov, D.V.; Zheltukhin, A.A.

    1976-01-01

    The investigation is continued of the spontaneous vacuum transition problem in the Neview-Schwartz dual model (NSDM). It is shown that vacuum transitions allow disclosing of supplementary degeneration in the resonance state spectrum. The dual amplitudes possess an internal structure corresponding to the presence of an infinite number of quarks with increasing masses and retained charges. The Adler principle holds. Analytic continuation on the constant of induced vacuum transitions makes it possible to establish the existence of spontaneous vacuum transitions in the NSDM. The consequence of this fact is the exact SU(2) symmetry of π, rho meson trajectories and the Higgs mechanism in the model. In this case the ratios of masses of particles leading trajectories are analogous to those obtained in the current algebra. It is shown that in the NSDM there arises chiral SU(2) x SU(2) x U(1) x U(1) x ... symmetry resulting from spontaneous vacuum transitions

  12. Variational transition-state theory

    International Nuclear Information System (INIS)

    Truhlar, D.G.; Garrett, B.C.

    1980-01-01

    A general introduction to and some results from studies of a procedure called variational transition-state theory are presented. A fundamental assumption of this theory is that the net rate of forward reaction at equilibrium equals the equilibrium flux in the product direction through the transition state where the transition state is a surface in phase space dividing reactants from products. Classical generalized-transition-state-theory calculations for nine collinear systems are compared to classical trajectory calculations. This new technique should provide useful insight into the successes and failures of the conventional theory and useful quantitative estimates of possible errors on the predictions of conventional transition-state theory. This should also contribute to a more accurate theory now available for the practical calculations of chemical reaction rates and thermochemical and structural interpretations of rate processes

  13. Energy transition, is it now?

    International Nuclear Information System (INIS)

    Combe, Matthieu; Thouverez, Pierre

    2016-06-01

    As French energy policy is now defined for energy transition, the contributions of this publication discuss implemented measures, what new laws will change, and what will be the consequences for industry. A first set of articles thus comments evolutions related to the implementation of energy transition in the building sector, how energy transition wants to get rid of wastage, how energy transition will impact the transport sector (public transports, car-pool and car sharing, bicycle, retail sector, airfields), and outline that President Hollande has fulfilled (nearly) all his commitments. The next article comments changes and critics made by the French constitutional Council on the law for energy transition. The next set of articles comments the results of an ADEME's study on bicycle kilometre allowance, discusses the issue of energy safety, and comments statements made by candidates to the French President election of 2012 on nuclear energy after the Fukushima accident

  14. Energy: Transitions and Reshaping

    International Nuclear Information System (INIS)

    Hache, Emmanuel; Mazzucchi, Nicolas; Alex, Bastien; Tchung-Ming, Stephane; Meritet, Sophie; Mignon, Valerie; Fischer-Herzog, Claude; Baccarini, Luca; Karbuz, Sohbet; Carcanague, Samuel; Noreng, Oesteyn; Luciani, Giacomo; Criqui, Patrick

    2016-01-01

    This issue of 'Revue internationale et strategique' from Winter 2016 presents a special dossier about the geopolitics of energy in a transitional and reshaping market. Content: Introduction: A New Age for Energy Markets? (Emmanuel Hache); National vs International Oil Companies: Toward a New Balance (Nicolas Mazzucchi); Can OPEC Survive Oil Abundance? (Emmanuel Hache); Dutch Disease and Low Oil Prices: From Economic Bankruptcy to (geo)political Reshaping (Bastien Alex, Stephane Tchung-Ming); Is Energy a Driving Force in American Foreign Policy? (Sophie Meritet); Oil Prices and U.S. Dollar: Two Sides of the Same Power? (Valerie Mignon ); The EU's Energy Union: What Energy Security for Europe? (Claude Fischer-Herzog); Natural Gas Discoveries and the Future of the Eastern Mediterranean Region (Luca Baccarini, Sohbet Karbuz); The Two Years that Changed the Caspian Sea region (Samuel Carcanague); On Oil and Islam (Oeystein Noreng); Middle East: clean energy sources and the diversification of the oil economies? (Giacomo Luciani); After the Paris Agreement, the New Geopolitics of Energy Innovations (Patrick Criqui)

  15. Inverse transition radiation

    International Nuclear Information System (INIS)

    Steinhauer, L.C.; Romea, R.D.; Kimura, W.D.

    1997-01-01

    A new method for laser acceleration is proposed based upon the inverse process of transition radiation. The laser beam intersects an electron-beam traveling between two thin foils. The principle of this acceleration method is explored in terms of its classical and quantum bases and its inverse process. A closely related concept based on the inverse of diffraction radiation is also presented: this concept has the significant advantage that apertures are used to allow free passage of the electron beam. These concepts can produce net acceleration because they do not satisfy the conditions in which the Lawson-Woodward theorem applies (no net acceleration in an unbounded vacuum). Finally, practical aspects such as damage limits at optics are employed to find an optimized set of parameters. For reasonable assumptions an acceleration gradient of 200 MeV/m requiring a laser power of less than 1 GW is projected. An interesting approach to multi-staging the acceleration sections is also presented. copyright 1997 American Institute of Physics

  16. Social costs of transition

    Directory of Open Access Journals (Sweden)

    Pavlović Dušan

    2006-01-01

    Full Text Available The risk of political and economic transformation in Central and East Europe after 1990 was based on the presumption that the reforms will collapse when the citizens realize that the cost they have to pay for them is too high. The classical claim was that democracy will be destroyed by democratic means-namely, that the losers in the transition will vote the way back to the authoritarian regime. The article offers an explanation as to the regress to the authoritarian regime will not be a consequence of the economic reforms. The article is divided in six section. Section 1 considers the general context of the start of the economic transformation in the light of the debate about the choice between the expert government and the significance of democratic procedures for economic reforms. Section 2 defines the context of Serbia within which economic transformation started out after 2000. Sections 4-5 consider economic policy of the two post-Milosevic government. The major finding is that it was the economic policy that was highly socially sensible that prevented social uprising and undermining democracy by democratic means. Section 6 concludes by applying the concept of equilibrium of partial reforms.

  17. Energy transition and legal transition: renewable energies development in France

    International Nuclear Information System (INIS)

    Darson, Alice

    2015-01-01

    The way to an energy transition will be reached with an integration of renewable energies in our energy mix. This development includes a legal transition because the current legal context that applies to green energies is not efficient and does not contribute to this emergency. Changing the legal frame becomes a necessity and particularly the way these energies are governed, planned and supported. It's also important that administrative procedures that regulate the implantation of energies production system are set. At last, this legal transition will have to conciliate imperatives linked to the development of renewable energies with those governing the protection of surroundings, all aiming to a sustainable development. (author) [fr

  18. 22 CFR 41.71 - Transit aliens.

    Science.gov (United States)

    2010-04-01

    ... 22 Foreign Relations 1 2010-04-01 2010-04-01 false Transit aliens. 41.71 Section 41.71 Foreign... NATIONALITY ACT, AS AMENDED Transit Aliens § 41.71 Transit aliens. (a) Transit aliens—general. An alien is classifiable as a nonimmigrant transit alien under INA 101(a) (15) (C) if the consular officer is satisfied...

  19. Selenophene transition metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    White, Carter James [Iowa State Univ., Ames, IA (United States)

    1994-07-27

    This research shows that selenophene transition metal complexes have a chemistry that is similar to their thiophene analogs. Selenophene coordination has been demonstrated and confirmed by molecular structure in both the η5- and the η1(Se)-coordination modes. The reaction chemistry of selenophene complexes closely resembles that of the analogous thiophene complexes. One major difference, however, is that selenophene is a better donor ligand than thiophene making the selenophene complexes more stable than the corresponding thiophene complexes. The 77Se NMR chemical shift values for selenophene complexes fall within distinct regions primarily depending on the coordination mode of the selenophene ligand. In the final paper, the C-H bond activation of η1(S)-bound thiophenes, η1(S)-benzothiophene and η1(Se)-bound selenophenes has been demonstrated. The deprotonation and rearrangement of the η1(E)-bound ligand to the carbon bound L-yl complex readily occurs in the presence of base. Reprotonation with a strong acid gives a carbene complex that is unreactive towards nucleophilic attack at the carbene carbon and is stable towards exposure to air. The molecular structure of [Cp(NO)(PPh3)Re(2-benzothioenylcarbene)]O3SCF3 was determined and contains a Re-C bond with substantial double bond character. Methyl substitution for the thienylcarbene or selenylcarbene gives a carbene that rearranges thermally to give back the η1(E)-bound complex. Based on these model reactions, a new mechanism for the H/D exchange of thiophene over the hydrodesulfurization catalyst has been proposed.

  20. Connecticut Transit (CTTRANSIT) Fuel Cell Transit Bus Preliminary Evaluation Results

    Science.gov (United States)

    2008-10-16

    This report describes operations at Connecticut Transit (CTTRANSIT) in Hartford for one prototype fuel cell bus and three new diesel buses operating from the same location. The report discusses the planned fuel cell bus demonstration and equipment us...