Current control in ITER steady state plasmas with neutral beam steering

Abstract

Predictions of quasisteady state DT plasmas in ITER [R. Aymar et al., Nucl. Fusion 41, 1301 (2001)] are generated using the PTRANSP code [R. V. Budny, Nucl. Fusion 49, 085008 (2009)]. The plasma temperatures, densities, boundary shape, and total current (9–10 MA) anticipated for ITER steady state plasmas are specified. Current drive by negative ion neutral beam injection, lower-hybrid, and electron cyclotron resonance are calculated. Four modes of operation with different combinations of current drive are studied. For each mode, scans with the negative ion neutral beam injection aimed at differing heights in the plasma are performed to study their effects on current control on the q profile. The time-evolution of the currents and q are calculated, and long-duration transients (up to ≃1500 s) are predicted. Effects of the beam and alpha ion pressures on the magnetohydrodynamic equilibrium are predicted to significantly alter the bootstrap current. The TEQ equilibrium solver [L. Degtyarev and V. Drozdov, Comput. Phys. Rep. 46, 481 (1985)] in PTRANSP is found to be much more accurate than the VMEC solver [S. P. Hirshman et al., J. Comput. Phys. 87, 396 (1990)]. Quasisteady state, strongly reversed q profiles are predicted for some beam injection angles when the current drive and bootstrap currents are sufficiently large.