Relativistic electron beam current drive in the Macrotor tokamak

Relativistic electron beam current drive experiments in the Macrotor tokamak achieved current drive levels (increases in the toroidal current) which were consistent with the zero-dimensional theory. Injection of a 2-4 kJ relativistic electron beam into Macrotor produced an additional toroidal current of 4.5-7.5 kA, which persisted for more than 800 μs. The beam-induced increase in toroidal current was observed to be independent, to first order, of the initial tokamak plasma current, Isub(p), and the number density, nsub(p), over the entire range of plasma parameters available in Macrotor (3 kA<Isub(p)<60 kA; 5x1012<nsub(p)<2x1013). The 1 μs rise-time of the current implied an enhanced plasma collision frequency of 102-103 over classical. Comparison of co- and counter-injection data demonstrated that the initial increase in current was entirely due to beam-driven currents while later in time the increased current was sustained by the OH system. (author)