Time-Dependent Simulations of Fast-Wave Heated High-Non-Inductive-Fraction H-Mode Plasmas in the National Spherical Torus Experiment Upgrade

Abstract

30 MHz fast-wave heating may be an effective tool for non-inductively ramping low-current plasmas to a level suitable for initiating up to 12 MW of neutral beam injection on the National Spherical Tokamak Experiment Upgrade (NSTX-U). Previously on NSTX 30 MHz fast wave heating was shown to efficiently and rapidly heat electrons; at the NSTX maximum axial toroidal magnetic field ( B T (0) ) of 0.55 T, 1.4 MW of 30 MHz heating increased the central electron temperature from 0.2 to 2 keV in 30 ms and generated an H-mode plasma with a non-inductive fraction ( f NI ) ∼ 0.7 at a plasma current ( I p ) of 300 kA. NSTX-U will operate at B T (0) up to 1 T, with up to 4 MW of 30 MHz power ( P rf ). Predictive TRANSP free boundary transport simulations, using the TORIC full wave spectral code to calculate the fast-wave heating and current drive, have been run for NSTX-U I p = 300 kA H-mode plasmas. Favorable scaling of f NI with 30 MHz heating power is predicted, with f NI ≥ 1 for P rf ≥ 2 MW.