CONFINEMENT OF INJECTED PLASMAS IN STELLARATORS

Plasmas produced by a washer plasma gun have been injected into B-3, which is a twisted figure-eight stellarator, and Etude, which is a racetrack stellarator. Both have l = 3 helical windings. In the injected plasmas n e ≤ 5 < 109, Te ≈ 5-8 eV, and T i is probably greater than Te. The mean free paths for electron collisions were in the range 10-100 machine lengths. The observed confinement times varied with confining field as Bm with 0.6 < m < 1.2 for B ≤ 20 kG in B-3. In Etude, the confinement times varied from the Bohm value at zero rotational transform ι and increased by a factor 20 when ι = 5.43 rad. In B-3 the confinement times varied from about twice the Bohm value when only the geometric transform was present and increased by a factor 30 when t was increased to 19 rad. It was not possible to decide if the increase of confinement time was due to effects of shear or rotational transform.