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Title: Drift mode growth rates and associated transport

Abstract

Drift mode linear growth rates and quasilinear transport are investigated using the FULL kinetic stability code [Rewoldt {ital et al.}, Phys. Plasmas {bold 5}, 1815 (1998)] and a version of the Weiland transport model [Strand {ital et al.}, Nucl. Fusion {bold 38}, 545 (1998)]. It is shown that the drift mode growth rates (as well as the marginal stability temperature gradient) obtained using the FULL code are dependent on the accuracy of the equilibrium employed. In particular, when an approximate equilibrium model is utilized by the FULL code, the results can differ significantly from those obtained using a more accurate numerical equilibrium. Also investigated are the effects of including full electron physics. It is shown, using both the FULL code and the Weiland model, that the nonadiabatic (e.g., trapped) electron response produces a significant increase in the linear growth rate of the ion-temperature-gradient (ITG) driven branch of the drift instability. Other consequences of the nonadiabatic electron response include a reduction in the marginal temperature gradient for the onset of the ITG mode and an additional contribution to transport due to the excitation of the Trapped Electron Mode (TEM). Physical explanations are given for the sensitivity of the mode growth ratesmore » to the equilibrium and the nonadiabatic electron response. Finally, linear growth rates for the ITG mode computed using the FULL code are compared with growth rates obtained using the Weiland model. {copyright} {ital 1999 American Institute of Physics.}« less

Authors:
; ; ; ;  [1]
  1. Department of Physics, 16 Memorial Drive East, Lehigh University, Bethlehem, Pennsylvania 18015 (United States)
Publication Date:
OSTI Identifier:
335593
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 6; Journal Issue: 4; Other Information: PBD: Apr 1999
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION; CHARGED-PARTICLE TRANSPORT; PLASMA DRIFT; INSTABILITY GROWTH RATES; PLASMA SIMULATION; DRIFT INSTABILITY; COMPUTER CODES

Citation Formats

Redd, A.J., Kritz, A.H., Bateman, G., Rewoldt, G., and Tang, W.M. Drift mode growth rates and associated transport. United States: N. p., 1999. Web. doi:10.1063/1.873360.
Redd, A.J., Kritz, A.H., Bateman, G., Rewoldt, G., & Tang, W.M. Drift mode growth rates and associated transport. United States. doi:10.1063/1.873360.
Redd, A.J., Kritz, A.H., Bateman, G., Rewoldt, G., and Tang, W.M. 1999. "Drift mode growth rates and associated transport". United States. doi:10.1063/1.873360.
@article{osti_335593,
title = {Drift mode growth rates and associated transport},
author = {Redd, A.J. and Kritz, A.H. and Bateman, G. and Rewoldt, G. and Tang, W.M.},
abstractNote = {Drift mode linear growth rates and quasilinear transport are investigated using the FULL kinetic stability code [Rewoldt {ital et al.}, Phys. Plasmas {bold 5}, 1815 (1998)] and a version of the Weiland transport model [Strand {ital et al.}, Nucl. Fusion {bold 38}, 545 (1998)]. It is shown that the drift mode growth rates (as well as the marginal stability temperature gradient) obtained using the FULL code are dependent on the accuracy of the equilibrium employed. In particular, when an approximate equilibrium model is utilized by the FULL code, the results can differ significantly from those obtained using a more accurate numerical equilibrium. Also investigated are the effects of including full electron physics. It is shown, using both the FULL code and the Weiland model, that the nonadiabatic (e.g., trapped) electron response produces a significant increase in the linear growth rate of the ion-temperature-gradient (ITG) driven branch of the drift instability. Other consequences of the nonadiabatic electron response include a reduction in the marginal temperature gradient for the onset of the ITG mode and an additional contribution to transport due to the excitation of the Trapped Electron Mode (TEM). Physical explanations are given for the sensitivity of the mode growth rates to the equilibrium and the nonadiabatic electron response. Finally, linear growth rates for the ITG mode computed using the FULL code are compared with growth rates obtained using the Weiland model. {copyright} {ital 1999 American Institute of Physics.}},
doi = {10.1063/1.873360},
journal = {Physics of Plasmas},
number = 4,
volume = 6,
place = {United States},
year = 1999,
month = 4
}
  • H-mode experiments on Alcator C-Mod [I. H. Hutchinson, R. L. Boivin, F. Bombarda et al., Phys. Plasmas 1, 1511 (1994)], which exhibit an internal transport barrier (ITB), have been examined with gyrokinetic calculations, before barrier formation. Ion temperature gradient (ITG) and electron temperature gradient (ETG) modes are unstable outside the barrier region and not strongly growing in the core; in the barrier region ITG is only weakly unstable. Linear calculations support the picture that ITG and ETG modes drive high transport outside the ITB, and that weakly unstable ITG modes in the barrier region correlate with reduced particle transport andmore » improved thermal confinement even before the ITB is established, without the need for ExB shear stabilization. Long-wavelength mode stability in the barrier region is analyzed in the context of a phase diagram for ion and electron drift waves by varying the temperature and density scale lengths. Results from the gyrokinetic code GS2 [M. Kotschenreuther, G. Rewoldt, W. M. Tang et al., Comput. Phys. Commun. 88, 128 (1995)] are compared to standard threshold models and benchmark successfully against the experiment in the plasma core.« less
  • The linear stability behavior and anomalous transport properties associated with the lower-hybrid-drift instability are studied assuming flute- like perturbations with kcenter-dotBmore » $sub 0$=0. Primary emphasis is placed on the low-drift-velocity regime with V/subE/approximately-less-thanv/subi/ (here, V/ subE/ is the cross-field electron EtimesB drift velocity), which pertains to the late stages of implosion and the post-implosion phase of high-density pinch experiments. Nonlinear estimates of the instantaneous heating rates and rate of momentum transfer are made, and the results are studied numerically to determine the parametric dependence on V/subE//v/subi/ and the level of turbulent field fluctuation energy E/subF/. It is shown that the lower-hybrid-drift instability can result in substantial resistivity and plasma heating for V/subE/approximately- less-thanv/subi/, as well as for the large-drift-velocity regime (V/subE/>v/subi/ ). For example, when T/subi//T/sube/very-much-greater-than1 and $omega$$sup 2$/ subp//sube//$omega$$sup 2$/subc//sube/very-much-greater-than1, the bound on anomalous resistivity for V/subE/approximately-less-thanv/subi/ is n/suba//subn/ )approx. =4$pi$root$pi$/2(V/subE//v/subi/)$sup 2$ $omega$/subL//subH// $omega$$sup 2$/subc//sube/, where $omega$/subL//subH/ = ($omega$/subc//subi/ $omega$/subc//sube/)$sup 1$/$sup 2$ is the lower-hybrid frequency. This large value of resistivity is consistent with observations made during the post- implosion phase of the ZT-1 experiment.« less