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Title: Observation of rapid frequency chirping instabilities driven by runaway electrons in a tokamak

Abstract

In this work, we report the first observation of chirping instabilities driven by runaway electrons (REs) in a tokamak. The instabilities are accessed during the post-disruption RE beam stage in a low density background plasma (n e < 10 19 m -3) on DIII-D. The chirping instabilities are observed when a decelerating loop voltage is applied to the RE beam. The frequency chirping is detected in two distinct frequency bands: 0.1–10 MHz and 30–80 MHz. The mode frequency increases linearly when the toroidal magnetic field sensed by the RE beam increases. The frequency chirps by 0.3–2.4 MHz on a timescale of 1 ms. Modification of the RE distribution function is directly measured during the chirping in the low-frequency band consistent with the hole–clump model for frequency chirping. The low-frequency instabilities also correlate with an increase of intermittent RE loss from the plasma. Lastly, these observations provide a novel experimental platform for fundamental studies of nonlinear chirping. They also support continued investigation of opportunities to utilize kinetic instabilities for RE mitigation in a tokamak reactor.

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4];  [5]; ORCiD logo [3]; ORCiD logo [5];  [4]; ORCiD logo [3]
  1. Oak Ridge Associated Univ., Oak Ridge, TN (United States)
  2. Univ. of California, Irvine, CA (United States)
  3. General Atomics, San Diego, CA (United States)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  5. Università di Milano-Bicocca, Milan (Italy)
Publication Date:
Research Org.:
Dept. of Energy (DOE), Washington DC (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1569036
Grant/Contract Number:  
FC02-04ER54698
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 59; Journal Issue: 12; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Lvovskiy, A., Heidbrink, W. W., Paz-Soldan, C., Spong, D. A., Dal Molin, A., Eidietis, N. W., Nocente, M., Shiraki, D., and Thome, K. E. Observation of rapid frequency chirping instabilities driven by runaway electrons in a tokamak. United States: N. p., 2019. Web. doi:10.1088/1741-4326/ab4405.
Lvovskiy, A., Heidbrink, W. W., Paz-Soldan, C., Spong, D. A., Dal Molin, A., Eidietis, N. W., Nocente, M., Shiraki, D., & Thome, K. E. Observation of rapid frequency chirping instabilities driven by runaway electrons in a tokamak. United States. doi:10.1088/1741-4326/ab4405.
Lvovskiy, A., Heidbrink, W. W., Paz-Soldan, C., Spong, D. A., Dal Molin, A., Eidietis, N. W., Nocente, M., Shiraki, D., and Thome, K. E. Thu . "Observation of rapid frequency chirping instabilities driven by runaway electrons in a tokamak". United States. doi:10.1088/1741-4326/ab4405.
@article{osti_1569036,
title = {Observation of rapid frequency chirping instabilities driven by runaway electrons in a tokamak},
author = {Lvovskiy, A. and Heidbrink, W. W. and Paz-Soldan, C. and Spong, D. A. and Dal Molin, A. and Eidietis, N. W. and Nocente, M. and Shiraki, D. and Thome, K. E.},
abstractNote = {In this work, we report the first observation of chirping instabilities driven by runaway electrons (REs) in a tokamak. The instabilities are accessed during the post-disruption RE beam stage in a low density background plasma (ne < 1019 m-3) on DIII-D. The chirping instabilities are observed when a decelerating loop voltage is applied to the RE beam. The frequency chirping is detected in two distinct frequency bands: 0.1–10 MHz and 30–80 MHz. The mode frequency increases linearly when the toroidal magnetic field sensed by the RE beam increases. The frequency chirps by 0.3–2.4 MHz on a timescale of 1 ms. Modification of the RE distribution function is directly measured during the chirping in the low-frequency band consistent with the hole–clump model for frequency chirping. The low-frequency instabilities also correlate with an increase of intermittent RE loss from the plasma. Lastly, these observations provide a novel experimental platform for fundamental studies of nonlinear chirping. They also support continued investigation of opportunities to utilize kinetic instabilities for RE mitigation in a tokamak reactor.},
doi = {10.1088/1741-4326/ab4405},
journal = {Nuclear Fusion},
number = 12,
volume = 59,
place = {United States},
year = {2019},
month = {9}
}

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