Steady-state tokamak discharge via dc helicity injection.

A tokamak discharge has been formed and maintained through helicity injection, by use of only an external dc low-energy electron beam. The discharge, in a 5-kG toroidal field, evolved to a steady-state circular cross section with q(a) = 10, q(0) = 4, which was maintained for more than 400 L/R periods, the time (60 msec) limited by the cathode bias supply. The density profile reached a line-averaged n-bar/sub e/ = 2 x 10/sup 13/ cm/sup -3/, while T/sub e/ = 25 eV and T/sub i/ = 15 eV. Strong central peaking occurs and inward pinching is indicated for both density and current.