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Title: Avalanche mechanism for runaway electron amplification in a tokamak plasma

Abstract

The avalanche of runaway electrons is thought to pose a significant obstacle to the success of reactor scale devices such as ITER. As a result, a significant effort has been devoted toward quantifying both the threshold for the initiation of the avalanche of runaway electrons and the efficiency of the avalanche mechanism. In this work, these two quantities are computed utilizing a guiding-center formulation with large-angle collision operators of varying physics fidelity. The use of a guiding-center formulation, while computationally more costly compared to bounce-averaged approaches, provides a conceptually straightforward means of incorporating tokamak geometry. It is found that while the avalanche threshold is only weakly impacted by toroidal geometry for fully ionized low- Z plasmas, it can be significantly impacted if high- Z impurities are present. Furthermore, it is shown that the efficiency of the avalanche mechanism depends sensitively on the impurity content, the charge state of the underlying impurities, and the radial profile of the seed electron population. Lastly, the commonly employed Møller secondary source term used to model the generation of secondary electrons is shown to yield avalanche growth rates and thresholds in good agreement with a more complete conservative large-angle collision operator.

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1512743
Report Number(s):
LA-UR-18-28330
Journal ID: ISSN 0741-3335
Grant/Contract Number:  
89233218CNA000001
Resource Type:
Accepted Manuscript
Journal Name:
Plasma Physics and Controlled Fusion
Additional Journal Information:
Journal Volume: 61; Journal Issue: 5; Journal ID: ISSN 0741-3335
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Magnetic Fusion Energy; runaway electrons; tokamak disruptions; Fokker–Planck equation

Citation Formats

McDevitt, Christopher J., Guo, Zehua, and Tang, Xian -Zhu. Avalanche mechanism for runaway electron amplification in a tokamak plasma. United States: N. p., 2019. Web. doi:10.1088/1361-6587/ab0d6d.
McDevitt, Christopher J., Guo, Zehua, & Tang, Xian -Zhu. Avalanche mechanism for runaway electron amplification in a tokamak plasma. United States. doi:10.1088/1361-6587/ab0d6d.
McDevitt, Christopher J., Guo, Zehua, and Tang, Xian -Zhu. Mon . "Avalanche mechanism for runaway electron amplification in a tokamak plasma". United States. doi:10.1088/1361-6587/ab0d6d.
@article{osti_1512743,
title = {Avalanche mechanism for runaway electron amplification in a tokamak plasma},
author = {McDevitt, Christopher J. and Guo, Zehua and Tang, Xian -Zhu},
abstractNote = {The avalanche of runaway electrons is thought to pose a significant obstacle to the success of reactor scale devices such as ITER. As a result, a significant effort has been devoted toward quantifying both the threshold for the initiation of the avalanche of runaway electrons and the efficiency of the avalanche mechanism. In this work, these two quantities are computed utilizing a guiding-center formulation with large-angle collision operators of varying physics fidelity. The use of a guiding-center formulation, while computationally more costly compared to bounce-averaged approaches, provides a conceptually straightforward means of incorporating tokamak geometry. It is found that while the avalanche threshold is only weakly impacted by toroidal geometry for fully ionized low-Z plasmas, it can be significantly impacted if high-Z impurities are present. Furthermore, it is shown that the efficiency of the avalanche mechanism depends sensitively on the impurity content, the charge state of the underlying impurities, and the radial profile of the seed electron population. Lastly, the commonly employed Møller secondary source term used to model the generation of secondary electrons is shown to yield avalanche growth rates and thresholds in good agreement with a more complete conservative large-angle collision operator.},
doi = {10.1088/1361-6587/ab0d6d},
journal = {Plasma Physics and Controlled Fusion},
number = 5,
volume = 61,
place = {United States},
year = {2019},
month = {4}
}

Journal Article:
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This content will become publicly available on April 1, 2020
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