High power neutral beam heating experimentson TFTR with balanced and unbalanced momemtum input

Abstract

New long-pulse ion sources have been employed to extend the neutral beam pulse on TFTR from 0.5sec to 2.0 sec. This made it possible to study the long-term evolution of supershots at constantcurrent and to perform experiments in which the plasma current was ramped up during the heatingpulse. Experiments were conducted with co and counter injection as well as with nearly balancedinjection of deuterium beams up to a total power of 20 MW. The best results, i.e., central iontemperatures Tio > 25 keV and neo τE Tio values of 3 × 1020 keV sec m-3, were obtained withnearly balanced injection. The central toroidal plasma rotation velocity scales in a linear-offset fashion with beam power and density. The scaling of the inferred global momentumconfinement time with plasma parameters is inconsistent with the predictions of the neoclassicaltheory of gyroviscous damping. An interesting plasma regime with properties similar to the H-modehas been observed for limiter plasmas with edge qa just above 3 and 2.5.