Dependence of fishbone cycle on energetic particle intensity in EAST low-magnetic-shear plasmas

Abstract

The dependence of fishbone cycle on energetic particle intensity has been investigated in EAST low-magnetic-shear plasmas. It is observed that the fishbone mode growth rate, saturation amplitude as well as fishbone cycle frequency clearly increase with increasing neutral beam injection (NBI) power. Moreover, enhanced electron density and temperature perturbations as well as energetic particle loss were observed with greater injected NBI power. Simulation results using M3D-K code show that as the NBI power increases, the resonant frequency and the energy of the resonant particles become higher, and the saturation amplitude of the mode also changes, due to the non-perturbative energetic particle contribution. The relationship between the calculated energetic particle pressure ratio and fishbone cycle frequency is obtained as ${f_{\textrm{FC}}} = 2.2{(1000{\beta _{\textrm{ep,calc}}} - 0.1)^{5.9 \pm 0.5}}$ . Results consistent with the experimental observations have been achieved based on a predator–prey model.

A simple model for internal transport barrier induced by fishbone in tokamak plasmas

“…1984; Zhu et al. 2020), (2.1) and (2.2). It is shown that there are only five free parameters in this model, , , , and .…”

“…1984; Zhu et al. 2020), where is the average trapped EP beta within the surface, is fishbone amplitude (, the normalised radial perturbed magnetic field), is the deposition rate of trapped EP within the surface, is a measure of the EP loss rate, , , is the fraction of trapped EPs that can be ejected, is the excitation threshold of fishbone, is the resonant drive of trapped EPs and is Heaviside function. The evolution of is periodic with minimum and maximum .…”

“…1984; Zhu et al. 2020). For each burst cycle, the EPs resonantly interact with fishbone and are expelled radially leading to a radial current, and hence a compensating bulk plasma return current.…”

“…With neutral beam injection (NBI) power increasing step by step, the magnitude of each burst of fishbone becomes larger and the burst frequency becomes higher and, accordingly, the ITB becomes stronger (Zhu et al. 2020; Chu et al. 2022).…”

Study of the mechanism of ITB formation and sustainment with optimized q profiles in ELMy H mode discharges on the EAST

“…The energetic particles profile in three typical time slices calculated by TRANSP-NUBEAM [45,46] code in shown in figure 11(e). In these times, the corresponding energetic trapped particle pressure ratio (β ep ) are 0.13%, 0.18% and 0.21% [47]. Shorter intervals between two adjoined fishbones indicate that the state tends to be stable, and the corresponding q profile quickly recovers to the initial state.…”