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Title: Perpendicular momentum input of lower hybrid waves and its influence on driving plasma rotation.

Abstract

The mechanism of perpendicular momentum input of lower hybrid waves and its influence on plasma rotation are studied. Discussion for parallel momentum input of lower hybrid waves is presented for comparison. It is found out that both toroidal and poloidal projections of perpendicular momentum input of lower hybrid waves are stronger than those of parallel momentum input. The perpendicular momentum input of lower hybrid waves therefore plays a dominant role in forcing the changes of rotation velocity observed during lower hybrid current drive. Lower hybrid waves convert perpendicular momentum carried by the waves into the momentum of dc electromagnetic field by inducing a resonant-electron flow across flux surfaces therefore charge separation and a radial dc electric field. The dc field releases its momentum into plasma through the Lorentz force acting on the radial return current driven by the radial electric field. Plasma is spun up by the Lorentz force. An improved quasilinear theory with gyro-phase dependent distribution function is developed to calculate the radial flux of resonant electrons. Rotations are determined by a set of fluid equations for bulk electrons and ions, which are solved numerically by applying a finite-difference method. Analytical expressions for toroidal and poloidal rotations are derivedmore » using the same hydrodynamic model.« less

Authors:
 [1]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1355669
DOE Contract Number:
AC02-09CH11466
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; perpendicular momentum; lower hybrid waves; plasma rotation

Citation Formats

Guan, Xiaoyin. Perpendicular momentum input of lower hybrid waves and its influence on driving plasma rotation.. United States: N. p., 2017. Web.
Guan, Xiaoyin. Perpendicular momentum input of lower hybrid waves and its influence on driving plasma rotation.. United States.
Guan, Xiaoyin. 2017. "Perpendicular momentum input of lower hybrid waves and its influence on driving plasma rotation.". United States. doi:.
@article{osti_1355669,
title = {Perpendicular momentum input of lower hybrid waves and its influence on driving plasma rotation.},
author = {Guan, Xiaoyin},
abstractNote = {The mechanism of perpendicular momentum input of lower hybrid waves and its influence on plasma rotation are studied. Discussion for parallel momentum input of lower hybrid waves is presented for comparison. It is found out that both toroidal and poloidal projections of perpendicular momentum input of lower hybrid waves are stronger than those of parallel momentum input. The perpendicular momentum input of lower hybrid waves therefore plays a dominant role in forcing the changes of rotation velocity observed during lower hybrid current drive. Lower hybrid waves convert perpendicular momentum carried by the waves into the momentum of dc electromagnetic field by inducing a resonant-electron flow across flux surfaces therefore charge separation and a radial dc electric field. The dc field releases its momentum into plasma through the Lorentz force acting on the radial return current driven by the radial electric field. Plasma is spun up by the Lorentz force. An improved quasilinear theory with gyro-phase dependent distribution function is developed to calculate the radial flux of resonant electrons. Rotations are determined by a set of fluid equations for bulk electrons and ions, which are solved numerically by applying a finite-difference method. Analytical expressions for toroidal and poloidal rotations are derived using the same hydrodynamic model.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 9
}

Thesis/Dissertation:
Other availability
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  • Plasma heating of a high-density low-temperature linear plasma by the parametric decay instability of lower-hybrid waves excited in a parallel-plate geometry is studied experimentally for ww/sub lh/ = 3 and 10. The electric-field distribution is modeled considering the higher-order modes produced in this geometry. A method of measuring bulk electron temperature in the presence of an oscillating potential is developed and validated. Electron-heating results show that the parametric decay instability in this geometry is strongly driven and strongly convectively damped, resulting in very rapid electron heating that saturates in a time of 20-30w/sup -1/. Bulk electron heating consistent with amore » recent theory of parametric decay of a large-amplitude driver near the lower-hybrid frequency is also observed. Control of the instability by use of a finite-bandwidth driver is also studied, and results show that the threshold of the parametric decay instability in this geometry can be increased by a factor of 3 by a noise-modulated driver with ..delta..ww - .7. These results are contrasted with earlier studies.« less
  • During lower-hybrid current-driven (LHCD) tokamak, discharges with thermal electron temperature T{sub e} {approx} 150 eV, a two-parallel-temperature tail is observed in the electron distribution function. The cold tail extends to parallel energy E{parallel} {approx} 4.5 keV with temperature T {approx} 1.5 keV, and the hot tail extends to E{parallel} {approx} 4.5 keV with T > 40 keV. Fokker-Planck computer simulations suggest the cold tail is created by low power, high N{parallel} sidelobes in the lower-hybrid antenna spectrum, and that these sidelobes bridge the ``spectral gap,`` enabling current drive on small tokamaks such as Versator. During plasma-formation experiments using 28 GHzmore » electron-cyclotron (EC) waves, the plasma is born near the EC layer, then moves toward the upper-hybrid (UH) layer within 100--200{mu}s. Wave power is detected in the plasma with frequency f = 300 MHz, indicating the EC waves decay into ion modes and electron Bernstein waves during plasma formation. Measured turbulent plasma fluctuations are correlated with decay-wave amplitude. Toroidal currents up to I{sub p} {approx} 1 kA are generated, consistent with theory, which predicts asymmetric electron confinement. Electron-cyclotron current-drive (ECCD) is observed with loop voltage V{sub loop} {le} 0 and fully sustained plasma current I{sub p} {approx_lt} 15 kA at densities up to {l_angle}n{sub e}{r_angle} = 2 {times} 10{sup 12} cm{sup {minus}3}. The ECCD efficiency {eta} {equivalent_to} {l_angle}n{sub e}{r_angle}I{sub p}R{sub 0}/P{sub rf} = 0.003, which is 30%--40% of the maximum achievable LHCD efficiency on Versator. The efficiency falls rapidly to zero as the density is raised above {l_angle}n{sub e}{r_angle} = 3 {times} 10{sup 12} cm{sup {minus}3}, suggesting the ECCD depends on low collisionality. X-ray measurements indicate the current is carried primarily by electrons with energies 1 keV {approx_lt} E {approx_lt} 10 keV.« less
  • The combination of the two types of mode conversion when the lower-hybrid turning point is in the vicinity of a cyclotron harmonic requires a sixth-order equation with a quadratic coefficient, for which the usual technique utilizing the Laplace transform has no advantage since the transformed equation is second order and the general solution is not available. Some numerical methods are applied without success. Another type of six-order equation, which has only linear coefficients and represents the three-wave problem marginally, is solved analytically without including the absorption term. Applying the results of this analysis, it is shown that the direct-mode couplingmore » to the ion-Bernstein wave from the incident lower-hybrid wave takes place effectively only when the lower-hybrid turning point is very close to the harmonic resonance such that the distance between their respective turning points is similar in magnitude to the common wave length of the coupling. Finally, the damping and the absorption of the wave are compared for the unmagnetized dispersion relation, the full magnetized dispersion relation, and the mode-conversion analysis as the wave propagates in a magnetically confined plasma with slab geometry.« less
  • Lower-hybrid wave injection into tokamaks has been proposed for use in both bulk plasma heating and current drive schemes. However, experimental investigations show turbulent regions near the outside of tokamak plasmas that will scatter an initially collimated, monochromatic wave in both angle and frequency. Concern here is achieving a theoretical understanding of these processes to explain present results and predict the success of future experiments. In addition, the problem is of interest because of its relevance to other fields and basic physics. Results are related to typical tokamak plasma parameters showing that for most experiments, the majority of the incidentmore » energy is expected to reach the plasma center unless the tokamak plasma is unusually small and dense. However, the initial angular collimation may well be lost, reducing the probability of well defined resonance cones. Although the frequency broadening of the lower-hybrid waves will not significantly affect their propagation, it can be a few to many times the typical frequency of the turbulent density fluctuations - sufficient to account for measured spectral broadening in the Alcator tokamak.« less