Conveners
Collective Phenomena (Alfven and Low Frequency Modes)
- Huishan Cai (University of Science and Technology of China)
Linear wave properties of the low-frequency Alfven modes (LFAMs) observed in the DIII-D tokamak experiments with reversed magnetic shear [Nucl. Fusion 61, 016029 (2021)] are theoretically studied and delineated based on the general fishbone-like dispersion relation. By adopting the representative experimental equilibrium parameters, it is found that, in the absence of energetic ions, the LFAM...
We present results of simulation study of low-frequency Alfvenic modes in sub-TAE (Toroidal Alfven Eigenmodes) range in DIII-D, in particular, BAE (Beta-induced AE) and LFM (low-frequency mode) [1-3]. Using the Gyrokinetic Toroidal Code (GTC) [4], we have performed gyrokinetic simulations of BAE and LFM in DIII-D plasmas and identified LFM by comparing its properties to those of BAE [5]. Fast...
Operation in the quiescent regime with a large number of energetic particles (EEs) in specific energy range (~ 150–250 keV) have been achieved during the flattop of EAST low-density Ohmic discharges. Toroidal Alfvén eigenmodes (TAEs) excited by EEs are well demonstrated both in the deuterium plasmas and the helium plasmas. The resonance condition for EEs to drive TAEs is discussed and well...
Energetic particles (EPs), especially alpha particles, can excite collective shear Alfvén wave (SAW) instability in tokamak plasmas，and in turn affects the behavior of EPs, resulting in EPs transport loss. Notably, reversed shear Alfvén eigenmodes (RSAE) can be preferentially excited by core localized EPs [1], with their frequency and radial localization directly determined by local safety...
Quasi-axisymmetric (QA) device combines the advantages of both tokamak and stellarator, and thus, it can be considered as a disruption-free tokamak and it excites the interests of the fusion community. Alfvén eigenmode (AE) is an important issue for magnetic confinement fusion because it enhances energetic particle (EP) transport and degrades heating performance. Nowadays, a QA device named...
The long time-scale nonlinear simulation of energetic particle (EP) instabilities is critical to studies of fast ion transport since this allows inclusion of mode-coupling induced zonal flows/currents, and transfers of energy to longer and shorter scales. These processes, which are important in evaluating the impact of EP instabilities on heating efficiency, can evolve over much longer...
We present recent measurements and analyses of Alfven Eigenmode (AE) stability in JET D and T plasmas. Stable AEs are resonantly excited by an array of eight in-vessel, toroidally-spaced antennas with independent power and phasing. Databases of stable AE frequencies, net damping rates $\gamma < 0$, and toroidal mode numbers have been assembled for various isotope mixes, and trends are...
The seeming coupling between fast upwards frequency sweeping modes and tornado modes in a set of JET sawtoothing discharges was investigated. The frequency sweeping modes were identified as near-axis Alfvén cascade eigenmodes associated with a very flat yet strictly monotonic q-profile near the axis, in contrast with the common reversed-shear scenarios. The evolution of the modes’ frequency...
Spatial channelling (SC) is a phenomenon of the transfer of the energy and momentum across the magnetic field by destabilized eigenmodes [1-3]. Energy transfer deteriorates or improves plasma confinement, depending on the energy flux direction. In particular, inward SC of alpha-particle energy by fast magnetoacoustic modes (FMM) may have played a role in the improved confinement and...
The energetic particle-induced geodesic acoustic mode (EGAM) causes loss of injected beam ions on DIII-D [1, 2]. The EGAM is a global [3] n=0, m=0 predominantly electrostatic mode with typical fundamental frequencies between 20-40 kHz. (n and m are toroidal and poloidal mode numbers.) While EGAMs commonly appear in amplitude bursts, they can be continuous, sweep in frequency, or oscillate in...
