High ion-harmonics fast wave heating in NSTX and CDX-U

Low-aspect-ratio tokamaks (LARTs) have received recent attention because of encouraging results from small scale experiments and because of the LART close-quote s potential for attaining high stable β in next generation devices. For this potential to be realized, efficient methods of non-inductive heating and current drive required to heat and sustain such plasmas must be found. A typical next generation high β LART experiment has an unusually large dielectric ω2pe/Ω2ce∼100, compared to the conventional tokamak value of ∼1. In the high dielectric regime considered here, lower hybrid and electron cyclotron waves have severe accessibility problems. In contrast to these limitations, recent calculations by M. Ono [1] indicate that fast waves in the intermediate frequency regime with ω≅20Ωci<ωLH experience sufficient damping on electrons to consider localized power deposition and have a high ion β accessibility limit. In an attempt to model this regime, ray tracing calculations for NSTX and CDX-U have been performed and modelling results will be presented for cases of interest. copyright 1996 American Institute of Physics