APPROACH TO IGNITION CONDITIONS IN A 2-FLUID SPHEROMAK WITH DIRECT ION HEATING

The spheromak, as a compact toroidal magnetic fusion device, offers su bstantial advantages as a fusion reactor concept over larger, more com plicated, and more costly devices such as the tokamak. The very defini te advantages associated with the simply closed geometry, minimized ex ternal coil requirements and the possibility of ohmic ignition in the spheromak, represent a substantial improvement over conventional magne tic fusion reactor designs. Furthermore, recent successes in improving confinement parameters (T-e similar to 400 eV, T-i similar to 1 keV, n(e) similar to 5 x 10(14) cm(-3), B similar to 1T) have renewed inter est in advancing this concept to a proof of principle, reactor prototy pe stage. Herein, the initial work by Fowler et al. (Comments Plasma P hys. Control. Fusion 16 (1994) 91), indicating the possibility of ohmi c ignition in spheromaks, is extended to a two fluid model that includ es direct ion heating. Non-ohmic magnetic dissipation, contributing to direct ion heating, and confinement scaling are quantified through co mparison with the latest results from the gun driven Compact Torus Exp eriment (CTX) spheromak (Phys. Fluids B 2 (1990) 1342). Excellent agre ement is demonstrated between experimentally measured plasma parameter s and our model predictions. Extrapolation to ignition experiments and reactor relevant conditions is discussed, indicating the possibility of reaching these conditions by gun driven ohmic heating alone and ill ustrating the merits of direct ion heating. Conservative to pessimisti c confinement estimates are used throughout so as to ensure that the p romise offered by this concept does not presume unrealizable improveme nts in energy containment.