Simulations of NBI-ICRF synergy with the full-wave TORIC package

Abstract

Abstract. During the combined plasma heating with neutral beam injection (NBI) and waves in the ion cyclotron (IC) range of frequencies, the NBI fast ions are preferentially accelerated by IC waves close to the IC harmonics, as a consequence of finite Larmor radius (FLR) effects. Since the NBI fast ions are expected to have a strong influence on the wave absorption and propagation, we have implemented a NBI source in the quasilinear Fokker-Planck SSFPQL code, interfaced with the toroidal full-wave TORIC solver. In this implementation the NBI ionization sources are obtained from the output of a Monte Carlo code, such as FAFNER. The numerical scheme adopted in the TORIC-SSFPQL package allows to describe very anisotropic sources, such as NBI, and to iterate the solution of Maxwell's equation taking into account selfconsistently the fast ion tails. As a first application, we present modeling of an ASDEX-Upgrade discharge with combined NBI and ICRF heating. Keywords -Introduction. Neutral beam injection (NBI) and damping of fast waves (FW) inthe ion cyclotron (IC) range of frequencies are the standard methods of ion heating in magnetically confined plasmas. The combination of NBI and IC heating can produce high-energy ion tails. In present day devices, this can be used to address the physics of fast ions [1]. There is a close interplay between the formation of fast-ion tails and the propagation and absorption of IC waves. Numerical simulations of IC heating, therefore, require a self-consistency loop between a wave solver and a solver of the kinetic Fokker-Planck (FP) equation. In view of this, the full wave code TORIC has been recently modified to evaluate the coefficients of the wave equations with the ion distribution functions (DFs) calculated by FP solver SSFPQL, which, in turn, takes into account the quasilinear power source due to the radio-frequency (RF) waves [2]. At IC harmonics (ω = n Ω ci with n ≥ 2) ion heating is a finite Larmor radius (FLR) effect, and, therefore, preferentially accelerates ions with large Larmor radius, ρ k ⊥ > ∼ 1 with k ⊥ the perpendicular wave number, and ρ = v ⊥ /Ω ci . When NBI and harmonic IC heating are simultaneously present, therefore, rather strong synergetic effects can be expected. To simulate this situation, we have now extended SSFPQL to include the NBI source in the FP equation, as we briefly describe in the next section. In the last section we present the results of a first application to an ASDEX-Upgrade (AUG) discharge. -NBI source in SSFPQL.With simultaneous NBI and RF heating the steady-state quasilinear kinetic equation for ion species i is