NONLINEAR VISCOSITY IN THE INTERCHANGEABLE MODULE STELLARATOR

The experimental observation of nonlinear parallel viscosity in the In terchangeable Module Stellarator is reported. The damping of plasma fl ows, by poloidal viscosity and ion-neutral collisions, is determined f rom the dependence of the radial current on the radial electric field in the plasma. At low neutral density, the radial current drops and a jump in the radial electric field occurs at a poloidal Mach number in the range -10 to -15, in reasonable agreement with a model based on no nlinear viscosity. The nonlinearity of viscosity diminishes as the neu tral density is increased.