Full wave simulations of fast wave mode conversion and lower hybrid wave propagation in tokamaks

Abstract

Fast wave (FW) studies of mode conversion (MC) processes at the ion–ion hybrid layer in toroidal plasmas must capture the disparate scales of the FW and mode converted ion Bernstein and ion cyclotron waves. Correct modeling of the MC layer requires resolving wavelengths on the order of k⊥ρi∼1 which leads to a scaling of the maximum poloidal mode number, Mmax, proportional to 1/ρ* (ρ*≡ρi/L). The computational resources needed scale with the number of radial (Nr), poloidal (Nθ), and toroidal (Nφ) elements as Nr * Nφ * Nθ3. Two full wave codes, a massively-parallel-processor (MPP) version of the TORIC-2D finite Larmor radius code [M. Brambilla, Plasma Phys. Controlled Fusion 41, 1 (1999)] and also an all orders spectral code AORSA2D [E. F. Jaeger et al., Phys. Plasmas 9, 1873 (2002)], have been developed which for the first time are capable of achieving the resolution and speed necessary to address mode conversion phenomena in full two-dimensional (2-D) toroidal geometry. These codes have been used in conjunction with theory and experimental data from the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] to gain new understanding into the nature of FWMC in tokamaks. The massively-parallel-processor version of TORIC is also now capable of running with sufficient resolution to model planned lower hybrid range of frequencies experiments in the Alcator C-Mod.