Multiple Alfvén eigenmodes induced by energetic electrons and nonlinear mode couplings in EAST radio-frequency heated H-mode plasmas

Abstract

Multiple electromagnetic coherent modes with frequencies f ∼ 20–300 kHz and toroidal mode numbers n = 1 and n = 2 have been observed and investigated in radio-frequency heated H-mode plasmas of the EAST tokamak. The experimental results show that the two main branches of these coherent modes are driven by energetic electrons (EEs), which are produced in the processes of radio-frequency current drive and heating. Bicoherence analysis indicates that there are strong nonlinear mode interactions between the two branches (mother waves), i.e. one is in the low-frequency range of f ∼ 20–50 kHz and the other one is in the high-frequency range of f ∼ 120–250 kHz, and their nonlinear couplings can generate many harmonics (daughter waves). Both coherent modes propagate poloidally along the electron diamagnetic drift direction. The gyrokinetic eigenvalue simulations support the view that both the low-frequency and the high-frequency coherent modes observed in EAST are Alfvén eigenmode (AE) type, and the kinetic effects of background plasmas and EEs are responsible for the formation and excitation of AEs, respectively. The low-frequency coherent mode is identified as the kinetic beta-induced Alfvén eigenmode located in the edge, and the high-frequency coherent mode is radially global, which is characterized by a toroidal Alfvén eigenmode (TAE) in the core and also has the components of a kinetic TAE and ellipticity-induced Alfvén eigenmode in the outer region due to the large downshift of the Alfvén continuum gap from the core to the edge in H-mode discharges.

Verification and validation of linear gyrokinetic and kinetic-MHD simulations for internal kink instability in DIII-D tokamak

“…In current progress, the MHD module in GAM-solver builds on the reduced ideal MHD model using slow sound approximation [41] and the drift and resistive MHD model with full plasma compressibility [41], which have been verified with Alfvén eigenmode, kink mode and kinetic ballooning mode physics [41]. The gyrokinetic module in GAM-solver is based on well-circulating and deeply trapped approximations, which has been successfully applied to explain the energetic electron excitation of Alfvén eigenmodes observed in EAST experiments recently [40]. For the simulation results of ideal kink mode in present work, the fully ideal MHD model in GAMsolver is used to be consistent with other codes on ideal kink mode physics, which includes the MHD vorticity equation with geodesic compressibility [39], and the parallel sound wave compressibility effect [41], while the diamagnetic and resistive effects are removed.…”

“…In this work, we initiate a verification and validation (V & V) study [33] for gyrokinetic and kinetic-MHD simulations of the current-driven internal kink instability in a real tokamak experiment. The verification focuses on a benchmark between a gyrokinetic turbulence code GTC [24,34], two kinetic-MHD initial value codes M3D-C1 [17,35,36] and XTOR-K [16,37,38], and two kinetic-MHD eigenvalue codes GAM-solver [39][40][41] and NOVA-K [42,43]. The validation focuses on comparing the linear global simulation results of the current-driven instability with the experimental measurements in the DIII-D discharge #141216.…”

Dynamics between toroidal Alfvén eigenmode evolution and turbulence suppression under resonant magnetic perturbations on EAST

“…TAEs could be excited in deuterium plasma discharge with lower hybrid wave (LHW) heating in EAST [38]. In the plasma core of EAST, the energetic electrons included TAEs show the frequency characteristics 120 kHz < f < 280 kHz and the typical toroidal mode number n = 1 or n = 2 [38]. EAST discharge No.…”

Verification and validation of gyrokinetic and kinetic-MHD simulations for internal kink instability in DIII-D tokamak

“…In current progress, the MHD module in GAM-solver builds on the reduced ideal MHD model using slow sound approximation [41] and the drift and resistive MHD model with full plasma compressibility [41], which have been verified with Alfvén eigenmode, kink mode and kinetic ballooning mode physics [41]. The gyrokinetic module in GAM-solver is based on well-circulating and deeply trapped approximations, which has been successfully applied to explain the energetic electron excitation of Alfvén eigenmodes observed in EAST experiments recently [40]. For the simulation results of ideal kink mode in present work, the fully ideal MHD model in GAM-solver is used to be consistent with other codes on ideal kink mode physics, which includes the MHD vorticity equation with geodesic compressibility [39], and the parallel sound wave compressibility and effect [41], while the diamagnetic and resistive effects are removed.…”