Volt-second saving by lower hybrid current drive in JT-60

Abstract
The volt-second consumption of the Ohmic primary circuit is reduced by lower hybrid current drive during the current rise phase. Most of the lower hybrid power is consumed in compensating the resistive voltage of typically 0.8 V. Up to 2.5 V s of flux is saved by 2 MW × 2.5 s of lower hybrid power, which could be projected to several tens of volt-seconds in ITER class reactors. In most cases, for lower hybrid assisted current ramp-up discharges the safety factor q can pass the value qa = 3 without causing any disastrous MHD instabilities leading to a major disruption.