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${¯}_e$=2×${10}^{13}$ ${\mathrm{cm}}^{\mathrm{-}3}$, while $T_e$=25 eV and $T_i$=15 eV. Strong central peaking occurs and inward pinching is indicated for both density and current.