Experimental studies of spheromak formation

Studies in the PS‐1 spheromak configuration can be effectively formed by a combined z‐ and θ‐pinch technique on both a fast (τformation≂τAlfvén) and a much slower timescale. The gross tilt and shift instability of the toroid can be suppressed by a combination of conduction walls, shaping the separatrix by externally applied fields, and the use of ‘‘figure‐eight’’ coils. Optimum stabilty is obtained for almost spherical toroids. Maximum field‐reversal times for stable, well‐confined toroids are ≥40 /μsec, consistent with resistive decay. Temperatures during the stable decay are 5–10 eV; impurity radiation is an important energy‐loss mechanism.