Experimental investigation of kinetic instabilities driven by runaway electrons in the EXL-50 spherical torus

In this study, the first observation of high-frequency instabilities driven by runaway electrons has been reported in the EXL-50 spherical torus using a high-frequency magnetic pickup coil. The central frequency of these instabilities is found to be exponentially dependent on the plasma density, sim...

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Bibliographic Details
Published inarXiv.org
Main Authors Wang, Mingyuan, Tan, Mingsheng, Shi, Yuejiang, Wang, Ziqi, Dong, Jiaqi, Liu, Adi, Zhuang, Ge, Li, Songjian, Song, Shaodong, Yuan, Baoshan, Y-K, Martin Peng
Format Paper
LanguageEnglish
Published Ithaca Cornell University Library, arXiv.org 13.07.2023
Subjects
Electron density
Excitation
Frequency stability
Pickup coils
Plasma
Plasma density
Toruses
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Summary:In this study, the first observation of high-frequency instabilities driven by runaway electrons has been reported in the EXL-50 spherical torus using a high-frequency magnetic pickup coil. The central frequency of these instabilities is found to be exponentially dependent on the plasma density, similar to the dispersion relation of the whistler wave. The instability frequency displays chirping characteristics consistent with the Berk-Breizman model of beam instability. Theoretically, the excitation threshold of the instability driven by runaway electrons is related to the ratio of the runaway electron density to the background plasma density, and such a relationship is first demonstrated experimentally in this study. The instability can be stabilized by increasing the plasma density, consistent with the wave-particle resonance mechanism. This investigation demonstrates the controlled excitation of chirping instabilities in a tokamak plasma and reveals new features of these instabilities, thereby advancing the understanding of the mechanisms for controlling and mitigating runaway electrons.
ISSN:2331-8422