Power balance analysis of ion Bernstein wave heating experiments in the Alcator C tokamak

Abstract

Energy and particle transport processes in Alcator C [Phys. Rev. Lett. 60, 298, (1988)] discharges heated by directly launched ion Bernstein waves (IBW) are investigated using the onetwo transport code [Nucl. Fusion 26, 329 (1986)]. The dependence of the observed ion heating rate (ΔTH/Prf) on plasma density is shown to result mainly from the inherent ion energy confinement that is characteristic of these discharges in the Ohmic phase and not on IBW propagation and absorption characteristics. The inferred value of the Ohmic ion thermal conduction exhibits an increasing anomaly with increasing plasma density. At a plasma density of n̄e ≲1×1020 m−3, the inferred ion thermal conduction is nearly equal to the Chang–Hinton neoclassical prediction. However, at a plasma density of n̄e ≳2×1020 m−3, the inferred ion thermal conduction increases to about 5–8 times the Chang–Hinton neoclassical value. This increasing anomaly, which may result from the ion temperature gradient driven instability, can essentially account for the observed ion heating rate behavior during IBW heating. The effect of edge turbulence on IBW propagation is modeled using a Monte Carlo direct sampling simulation. The result is mainly a radial broadening of the calculated power deposition profile with increasing plasma density.