Properties of energetic-particle continuum modes destabilized by energetic ions with beam-like velocity distributions

Abstract

Properties of energetic-particle continuum modes ͑EPMs͒ destabilized by energetic ions in tokamak plasmas were investigated using a hybrid simulation code for magnetohydrodynamics and energetic particles. The energetic ions are assumed to have beam-like velocity distributions for the purpose of clarifying the dependence on energetic ion velocity. It was found that for beam velocities lower than the Alfvén velocity, the unstable modes are EPMs while the toroidal Alfvén eigenmodes are unstable for the beam velocities well above the Alfvén velocity. The EPMs destabilized by the copassing energetic ions and those destabilized by the counterpassing energetic ions differ in primary poloidal harmonics and spatial locations. The frequencies of the EPMs are located close to the shear Alfvén continuous spectrum when they are compared at the spatial peak locations of the primary poloidal harmonic or compared at the spatial tails if the primary poloidal harmonic is m = 1. The frequencies of the EPMs were carefully compared with the energetic-ion orbital frequencies. It was found that the frequencies of the EPMs are in good agreement with the energetic-ion orbital frequencies with a correction for the toroidal circulation frequency. This demonstrates that the energetic-ion orbital frequency determines the EPM frequency.

Full-field drift Hamiltonian particle orbits in 3D geometry

“…The background distribution function F 0 is most conveniently, but not necessarily, expressed as a function of the constants of the motion so as to represent an equilibrium distribution. Thus, in axisymmetric or nearly axisymmetric systems F 0 = F 0 (P ϕ , , µ) the evolution of the weights w of each marker particle can be expressed as [13,21,22] …”

Global particle-in-cell simulations of fast-particle effects on shear Alfvén waves

“…The EPM modes have been studied analytically [10,19] within the ballooning formulation using the multiple scale asymptotic technique. Numerically, the EPM instabilities have been simulated using the hybrid-MHD approach [20,21]. In this approach, the background plasma is treated within the magnetohydrodynamic (MHD) theory whereas the fast-particle dynamics is gyrokinetic.…”

Radial Transport Characteristics of Fast Ions Due to Energetic-Particle Modes inside the Last Closed-Flux Surface in the Compact Helical System

“…EPMs often show nonlinear phenomena such as periodic burst and frequency chirping, which are considered to be related to fast-ion behavior, for example, change of fast-ion profile. The investigation of EPM properties and interaction with fast ions is still in progress [3,10,11].…”

“…EPMs often show nonlinear phenomena such as periodic burst and frequency chirping, which are considered to be related to fast-ion behavior, for example, change of fast-ion profile. The investigation of EPM properties and interaction with fast ions is still in progress [3,10,11].Recently, a directional Langmuir probe (DLP) method was applied to plasmas heated by a neutral beam (NB) for fast-ion measurement, and fast-ion behavior inside the last closed-flux surface (LCFS) can be measured with high time and spatial resolutions [12]. In this Letter, we focus on the experimental studies on the fast-ion-behavior interacting with bursting EPMs.…”