Journal
NUCLEAR FUSION
Volume 61, Issue 12, Pages -Publisher
IOP Publishing Ltd
DOI: 10.1088/1741-4326/ac26a0
Keywords
MHD; AE; stability; EIC; non linear; optimization; LHD
Categories
Funding
- Comunidad de Madrid [2019-T1/AMB-13648]
- Comunidad de Madrid
- UC3M ('Excelencia para el Profesorado Universitario'-EPUC3M14)-Fifth regional research plan 2016-2020
- [NIFS07KLPH004]
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The study aimed to analyze the saturation regime of the energetic ion-driven resistive interchange mode in LHD plasma. Nonlinear simulations were conducted to reproduce the experimental observations of 1/1 EIC saturation phases, showing enhancement of the resistive interchange modes as EP beta increases and triggering burst events. The study also revealed inward propagation and stabilization phases of the 1/1 EIC due to the nonlinear destabilization of energetic particle modes.
The aim of the present study is to analyze the saturation regime of the energetic-ion-driven resistive interchange mode (EIC) in the LHD plasma. A set of nonlinear simulations are performed by the FAR3d code that uses a reduced MHD model for the thermal plasma coupled with a gyrofluid model for the energetic particle (EP) species. The hellically trapped EP component is introduced through a modification of the averaged drift velocity operator to include their precessional drift. The nonlinear simulation results show similar 1/1 EIC saturation phases with respect to the experimental observations, reproducing the enhancement of the n/m = 1/1 resistive interchange modes (RIC) amplitude and width as the EP beta increases, the EP beta threshold for the 1/1 EIC excitation, the further destabilization of the 1/1 EIC as the population of the helically trapped EP increases and the triggering of burst events. The frequency of the 1/1 EIC calculated during the burst event is 9.4 kHz and the 2/2 and 3/3 overtones are destabilized, consistent with the frequency range and the complex mode structure measured in the experiment. In addition, the simulation shows the inward propagation of the 1/1 EIC due to the nonlinear destabilization of the 3/4 and 2/3 energetic particle modes, leading to the partial overlapping between resonances during the burst event. Finally, the analysis of the 1/1 EIC stabilization phase shows the excitation of the 1/1 RIC as soon as the flattening induced by the 1/1 EIC in the pressure profile vanishes, leading to the retrieval of the pressure gradient at the plasma periphery and the overcoming of the RIC stability limit.
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