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Title: The effects of kinetic instabilities on the electron cyclotron emission from runaway electrons

In this paper we show that the kinetic instabilities associated with runaway electron beams play an essential role for the production of high-level non-thermal electron–cyclotron-emission (ECE) radiation. Most of the non-thermal ECE comes from runaway electrons in the low-energy regime with large pitch angle, which are strongly scattered by the excited whistler waves. The power of ECE from runaway electrons is obtained using a synthetic diagnostic model based on the reciprocity method. The electron distribution function is calculated using a kinetic simulation model including the whistler wave instabilities and the quasilinear diffusion effects. Simulations based on DIII-D low-density discharge reproduces the rapid growth of the ECE signals observed in DIII-D experiments. Unlike the thermal ECE where radiation for a certain frequency is strongly localized inside the resonance region, the non-thermal ECE radiation from runaway electrons is nonlocal, and the emission-absorption ratio is higher than that of thermal electrons. The runaway electron tail is more significant for ECE with higher frequencies, and the ECE spectrum becomes flatter as RE population grows. The nonlinear behavior of the kinetic instabilities is illustrated in the oscillations of the ECE waves. In conclusion, the good agreement with the DIII-D experimental observations after including the kineticmore » instabilities clearly illustrate the significance of the scattering effects from wave-particle interactions, which can also be important for runaway electrons produced in disruptions.« less
Authors:
ORCiD logo [1] ;  [2] ; ORCiD logo [1] ;  [3] ; ORCiD logo [4] ; ORCiD logo [5] ;  [6]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Univ. of California, Irvine, CA (United States)
  3. Princeton Univ., NJ (United States)
  4. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Princeton Univ., NJ (United States)
  5. General Atomics, San Diego, CA (United States)
  6. Univ. of Texas, Austin, TX (United States)
Publication Date:
Grant/Contract Number:
AC02-09CH11466; SC0016268; FG02-97ER54415
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 58; Journal Issue: 9; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
OSTI Identifier:
1460952

Liu, Chang, Shi, Lei, Hirvijoki, Eero, Brennan, Dylan P., Bhattacharjee, Amitava, Paz-Soldan, Carlos, and Austin, Max E.. The effects of kinetic instabilities on the electron cyclotron emission from runaway electrons. United States: N. p., Web. doi:10.1088/1741-4326/aacc9b.
Liu, Chang, Shi, Lei, Hirvijoki, Eero, Brennan, Dylan P., Bhattacharjee, Amitava, Paz-Soldan, Carlos, & Austin, Max E.. The effects of kinetic instabilities on the electron cyclotron emission from runaway electrons. United States. doi:10.1088/1741-4326/aacc9b.
Liu, Chang, Shi, Lei, Hirvijoki, Eero, Brennan, Dylan P., Bhattacharjee, Amitava, Paz-Soldan, Carlos, and Austin, Max E.. 2018. "The effects of kinetic instabilities on the electron cyclotron emission from runaway electrons". United States. doi:10.1088/1741-4326/aacc9b.
@article{osti_1460952,
title = {The effects of kinetic instabilities on the electron cyclotron emission from runaway electrons},
author = {Liu, Chang and Shi, Lei and Hirvijoki, Eero and Brennan, Dylan P. and Bhattacharjee, Amitava and Paz-Soldan, Carlos and Austin, Max E.},
abstractNote = {In this paper we show that the kinetic instabilities associated with runaway electron beams play an essential role for the production of high-level non-thermal electron–cyclotron-emission (ECE) radiation. Most of the non-thermal ECE comes from runaway electrons in the low-energy regime with large pitch angle, which are strongly scattered by the excited whistler waves. The power of ECE from runaway electrons is obtained using a synthetic diagnostic model based on the reciprocity method. The electron distribution function is calculated using a kinetic simulation model including the whistler wave instabilities and the quasilinear diffusion effects. Simulations based on DIII-D low-density discharge reproduces the rapid growth of the ECE signals observed in DIII-D experiments. Unlike the thermal ECE where radiation for a certain frequency is strongly localized inside the resonance region, the non-thermal ECE radiation from runaway electrons is nonlocal, and the emission-absorption ratio is higher than that of thermal electrons. The runaway electron tail is more significant for ECE with higher frequencies, and the ECE spectrum becomes flatter as RE population grows. The nonlinear behavior of the kinetic instabilities is illustrated in the oscillations of the ECE waves. In conclusion, the good agreement with the DIII-D experimental observations after including the kinetic instabilities clearly illustrate the significance of the scattering effects from wave-particle interactions, which can also be important for runaway electrons produced in disruptions.},
doi = {10.1088/1741-4326/aacc9b},
journal = {Nuclear Fusion},
number = 9,
volume = 58,
place = {United States},
year = {2018},
month = {7}
}