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 ( 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. 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.

Lvovskiy, A., Heidbrink, W., Paz-Soldan, C., Spong, D., Dal Molin, A., Eidietis, N., et al. (2019). Observation of rapid frequency chirping instabilities driven by runaway electrons in a tokamak. NUCLEAR FUSION, 59(12) [10.1088/1741-4326/ab4405].

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

Dal Molin, A.;Nocente, M.;
2019

Abstract

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 ( 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. 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.
Si
Articolo in rivista - Articolo scientifico
Scientifica
runaway electrons; frequency chirping; kinetic instabilities
English
Lvovskiy, A., Heidbrink, W., Paz-Soldan, C., Spong, D., Dal Molin, A., Eidietis, N., et al. (2019). Observation of rapid frequency chirping instabilities driven by runaway electrons in a tokamak. NUCLEAR FUSION, 59(12) [10.1088/1741-4326/ab4405].
Lvovskiy, A; Heidbrink, W; Paz-Soldan, C; Spong, D; Dal Molin, A; Eidietis, N; Nocente, M; Shiraki, D; Thome, K
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/10281/246464
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