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Title: Effect of electron-to-ion mass ratio on radial electric field generation in tokamak

Abstract

Generation of coherent radial electric fields in plasma by drift-wave turbulence driven by plasma inhomogeneities is ab initio studied using gyro-kinetic particle simulation for conditions of operational tokamaks. In particular, the effect of the electron-to-ion mass ratio epsilon on the entire evolution of the plasma is considered. In conclusion, it is found that the electric field can be increased, and the turbulence-induced particle transport reduced, by making epsilon smaller, in agreement with many existing experimental observations.

Authors:
 [1];  [2];  [1];  [3];  [4]
  1. Zhejiang Univ., Hangzhou (People's Republic of China)
  2. Zhejiang Univ., Hangzhou (People's Republic of China); Southwest Institute of Physics, Chengdu (People's Republic of China)
  3. Zhejiang Univ., Hangzhou (People's Republic of China); Ruhr Univ., Bochum (Germany)
  4. Princeton Univ., Princeton, NJ (United States). Princeton Plasma Physics Lab.
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1414935
Grant/Contract Number:
2013GB104004; 2013GB111004; 2016FZA3003; 11235009; 11374262; 11475147
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 58; Journal Issue: 1; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; radial electric field; tokamak transport; drift-wave turbulence; mass-ratio effects

Citation Formats

Li, Zhenqian, Dong, Jiaqi, Sheng, Zhengmao, Yu, M. Y., and Wang, Weixing. Effect of electron-to-ion mass ratio on radial electric field generation in tokamak. United States: N. p., 2017. Web. doi:10.1088/1741-4326/aa96ba.
Li, Zhenqian, Dong, Jiaqi, Sheng, Zhengmao, Yu, M. Y., & Wang, Weixing. Effect of electron-to-ion mass ratio on radial electric field generation in tokamak. United States. doi:10.1088/1741-4326/aa96ba.
Li, Zhenqian, Dong, Jiaqi, Sheng, Zhengmao, Yu, M. Y., and Wang, Weixing. 2017. "Effect of electron-to-ion mass ratio on radial electric field generation in tokamak". United States. doi:10.1088/1741-4326/aa96ba.
@article{osti_1414935,
title = {Effect of electron-to-ion mass ratio on radial electric field generation in tokamak},
author = {Li, Zhenqian and Dong, Jiaqi and Sheng, Zhengmao and Yu, M. Y. and Wang, Weixing},
abstractNote = {Generation of coherent radial electric fields in plasma by drift-wave turbulence driven by plasma inhomogeneities is ab initio studied using gyro-kinetic particle simulation for conditions of operational tokamaks. In particular, the effect of the electron-to-ion mass ratio epsilon on the entire evolution of the plasma is considered. In conclusion, it is found that the electric field can be increased, and the turbulence-induced particle transport reduced, by making epsilon smaller, in agreement with many existing experimental observations.},
doi = {10.1088/1741-4326/aa96ba},
journal = {Nuclear Fusion},
number = 1,
volume = 58,
place = {United States},
year = 2017,
month =
}

Journal Article:
Free Publicly Available Full Text
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  • Motional Stark effect polarimetry (MSE) is a well established technique for measuring the magnetic field pitch angle in tokamaks. By viewing the Stark emission spectrum from two different angles, this technique can also provide local measurements of the plasma radial electric field, E{sub r} . Simultaneous measurements of the profiles of magnetic field pitch angle and E{sub r} are presented for the first time in a high-performance DIII-D tokamak plasma. Direct measurement of E{sub r} is of great importance in fusion research because the suppression of turbulence through {bold E}{sub r}{times}{bold B} velocity shear provides a mechanism to improve energymore » confinement. {copyright} {ital 1997} {ital The American Physical Society}« less
  • Results are presented from numerical simulations that show that, in a plasma with well-developed turbulence, the radial electric field can be positive in the region where the gradients of the plasma parameters are steep. In a plasma in which the turbulence is suppressed (as is the case with auxiliary lower hybrid heating), the radial electric field is found to exhibit a nearly neoclassical behavior during the formation of a transport barrier and transition to the H-mode.
  • 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 ismore » 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.« less
  • Radial electric fields in tokamaks can be generated by charge accumulation due to a resonant trapped electron pinch effect. The radial field can then drive a toroidal flow. This resonant pinch effect was evaluated for the current-drive scheme that diffused electrons in the direction parallel to the toroidal field. It was found that, for typical tokamak parameters, to generate a radial electric field on the order of 100 kV/m, an rf power density on the order of kW/m{sup 3} is required. This power, absorbed by trapped electrons, is a small fraction of rf power density for current drive which ismore » absorbed by passing electrons. However, according to the Landau resonant mechanism, the fraction of the momentum to trapped electrons decays exponentially with the square of the parallel phase velocity of the wave; therefore, the power absorbed at lower resonant velocities is the key. On the other hand, the redistribution of the current profile, due to rf current, decreases the local poloidal field and may reduce the particle transport significantly. It can relax the requirement of momentum deposited to trapped electrons, and, at the same time, contribute to explain the strongly correlation between the rotation and the driven current observed in experiments.« less
  • Effect of a poloidal electric field on the electron cyclotron current drive is studied in a tokamak geometry. A general discussion of its influence on the electron phase-space dynamics and current drive efficiency is presented. It is shown that the modification to the current drive efficiency increases as the heating location is moved out in the major radius. It is concluded that the modification is only moderate to insignificant (<10% for low magnetic field side heating and <3% for high field side heating) for a poloidal electrostatic potential variation of order inverse aspect ratio under an efficient current drive.