Modification of lower-hybrid current ramp-up by runaways

Runaway effects on lower-hybrid current ramp-up are studied numerically using a two-dimensional Fokker–Planck analysis and a nonlinear circuit equation. Runaway contribution to the inductance is shown to be important in limiting the magnitude of the induced electric field. This tends to reduce the current ramp-up efficiency. However, for a range of ωp/Ω, the anomalous Doppler instability can be excited and the runaway production rate as well as the associated inductance is significantly reduced when that happens. This allows the ramp-up efficiency to be further increased.