A NEGATIVE BIASING EXPERIMENT TO TEST NUMERICAL-CALCULATIONS BASED ONA NEOCLASSICAL L-H TRANSITION MODEL IN STELLARATORS

Numerical calculations based on Shiang's L-H transition theory in stel larators [1] and performed by Dabi et al. [2] determine viscosity as a function of ion flow speed in the interchangeable module stellarator (IMS) [3]. The calculations predict local maximums in viscosity at flo ws corresponding to Mach numbers -2 and -10, but not elsewhere. The lo cal peaks manifest themselves as jumps in flow speed, and as regions o f high radial electric field (E(r)) shear. By inducting flows swept be tween Mach numbers +/-5, an electron injection biasing probe revealed a jump at -2, but none at +2, in agreement with the numerical results. A series of flow profiles at constant bias confirmed this result. Alt ogether, these data agree well with the numerical calculations and pro vide support for Shaing's L-H transition model as applied to stellarat ors.