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Title: Current-Drive Efficiency in a Degenerate Plasma

Abstract

a degenerate plasma, the rates of electron processes are much smaller than the classical model would predict, affecting the efficiencies of current generation by external non-inductive means, such as by electromagnetic radiation or intense ion beams. For electron-based mechanisms, the current-drive efficiency is higher than the classical prediction by more than a factor of 6 in a degenerate hydrogen plasma, mainly because the electron-electron collisions do not quickly slow down fast electrons. Moreover, electrons much faster than thermal speeds are more readily excited without exciting thermal electrons. In ion-based mechanisms of current drive, the efficiency is likewise enhanced due to the degeneracy effects, since the electron stopping power on slow ion beams is significantly reduced.

Authors:
Publication Date:
Research Org.:
Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
934519
Report Number(s):
PPPL-4130
Journal ID: PRLTAO; R&D Project: DOE Research Grant No. DE-FG52-04NA00139; TRN: US0803893
DOE Contract Number:
AC02-76CH0-3073, DE-FG02-05ER54838
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 95; Journal Issue: 22
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; EFFICIENCY; ELECTROMAGNETIC RADIATION; ELECTRON-ELECTRON COLLISIONS; ELECTRONS; FORECASTING; HYDROGEN; ION BEAMS; PLASMA; STOPPING POWER; hydrogen; plasma collision processes; bremsstrahlung; Compton effect; plasma transport processes

Citation Formats

S. Son and N.J. Fisch. Current-Drive Efficiency in a Degenerate Plasma. United States: N. p., 2005. Web. doi:10.1103/PhysRevLett.95.225002.
S. Son and N.J. Fisch. Current-Drive Efficiency in a Degenerate Plasma. United States. doi:10.1103/PhysRevLett.95.225002.
S. Son and N.J. Fisch. Tue . "Current-Drive Efficiency in a Degenerate Plasma". United States. doi:10.1103/PhysRevLett.95.225002. https://www.osti.gov/servlets/purl/934519.
@article{osti_934519,
title = {Current-Drive Efficiency in a Degenerate Plasma},
author = {S. Son and N.J. Fisch},
abstractNote = {a degenerate plasma, the rates of electron processes are much smaller than the classical model would predict, affecting the efficiencies of current generation by external non-inductive means, such as by electromagnetic radiation or intense ion beams. For electron-based mechanisms, the current-drive efficiency is higher than the classical prediction by more than a factor of 6 in a degenerate hydrogen plasma, mainly because the electron-electron collisions do not quickly slow down fast electrons. Moreover, electrons much faster than thermal speeds are more readily excited without exciting thermal electrons. In ion-based mechanisms of current drive, the efficiency is likewise enhanced due to the degeneracy effects, since the electron stopping power on slow ion beams is significantly reduced.},
doi = {10.1103/PhysRevLett.95.225002},
journal = {Physical Review Letters},
number = 22,
volume = 95,
place = {United States},
year = {Tue Nov 01 00:00:00 EST 2005},
month = {Tue Nov 01 00:00:00 EST 2005}
}
  • In a degenerate plasma, the rates of electron processes are much smaller than the classical model would predict, affecting the efficiencies of current generation by external noninductive means, such as by electromagnetic radiation or intense ion beams. For electron-based mechanisms, the current-drive efficiency is higher than the classical prediction by more than a factor of 6 in a degenerate hydrogen plasma, mainly because the electron-electron collisions do not quickly slow down fast electrons. Moreover, electrons much faster than thermal speeds are more readily excited without exciting thermal electrons. In ion-based mechanisms of current drive, the efficiency is likewise enhanced duemore » to the degeneracy effects, since the electron stopping power on slow ion beams is significantly reduced.« less
  • In plasmas with toroidal rotation, the ions are pushed towards the low-field side of the torus by the centrifugal force. An electrostatic potential is set up to maintain charge neutrality which tends to attract electrons towards the low-field side of the torus. Due to this electrostatic potential, the trapped/passing boundary in the electron velocity space changes from a cone for stationary plasmas to an hyperboloid in a rotating plasma. This reduces the phase space for passing electrons. This paper attempts to address rotation effects on the electron cyclotron current drive efficiency. (c) 1999 American Institute of Physics.
  • Using oblique injection of electron-cyclotron (EC) waves, launched from the low field side of the WT-3 tokamak, into a target plasma sustained by lower hybrid current drive (LHCD), the plasma current is ramped up at a rate corresponding to 100 kA/s. The current ramp-up is ascribed to selective EC heating of tail electrons in the LHCD plasma via fundamental EC resonance at an up-shifted frequency due to the Doppler effect.
  • Two-dimensional RF modeling codes use a parameterization (1) of current drive efficiencies to calculate fast wave driven currents. This parameterization assumes a uniform quasi-linear diffusion coefficient and requires {ital a} {ital priori} knowledge of the wave polarizations. These difficulties may be avoided by a direct calculation of the quasilinear diffusion coefficient from the Kennel-Englemann form with the field polarizations calculated by the full wave code, FISIC (2). Current profiles are calculated using the adjoint formulation (3). Comparisons between the two formulations are presented. {copyright} {ital 1996 American Institute of Physics.}
  • In this paper we present results of analytical and numerical studies of the passive cyclotron current drive efficiency in mildly relativistic toroidal plasmas. The problem of linearization and separation of the electron and photon balance equations becomes nontrivial for high-temperature plasmas (e.g., D{endash}{sup 3}He) with low electron pressure ({beta}{sub {ital e}}{lt}0.1) due to the increased effect of radiation friction. The conditions under which this separation is possible is derived in this paper. The linearized problem for the electron distribution is formulated in the form of a standard variational principle, which includes both Coulomb collisions and {open_quote}{open_quote}collisions{close_quote}{close_quote} due to cyclotron radiation.more » The reduced variational principle for the current drive efficiency (generalized Spitzer{endash}H{umlt a}rm function) is derived, as well as its bounce-averaged form for toroidal plasmas. Finally, a convenient form of the passive cyclotron current drive efficiency is introduced, which can be used for a self-consistent modeling of passive cyclotron current generation in tokamaks with the help of fish-scale structures [see the companion paper, W. Kernbichler and S. Kasilov, Phys. Plasmas {bold 3}, 4128 (1996)]. {copyright} {ital 1996 American Institute of Physics.}« less