RESISTIVE PRESSURE GRADIENT-DRIVEN TURBULENCE AT STELLARATOR PLASMA EDGE

High resolution calculations of resistive pressure gradient-driven tur bulence for the plasma edge parameters of the Advanced Toroidal Facili ty (ATF) [J. F. Lyon et al., Fusion Technol. 10, 179 (1986)] electron cyclotron heated discharges give fluctuation levels, consistent with t he experimental measurements. This turbulence model is also used to si mulate the transition from the low confinement to the high confinement mode. The transition is triggered through the poloidal flow amplifica tion induced by the Reynolds stress. After the transition, the confine ment improvement is relatively low (30%-40%), even for unrealistically low poloidal viscosity. In the high confinement mode, the characteris tic radial scale length of the poloidal flow in the three-dimensional calculations (separation between the lowest-n resonant surfaces) is di fferent from the single helicity results (radial correlation length of the fluctuations). The simple criterion based on the ratio of shearin g rate to the linear growth rate does not;quantitatively account for t he fluctuation reduction. (C) 1997 American Institute of Physics.