PLASMA CONTAINMENT IN A QUADRUPOLE CONFIGURATION

The containment times of afterglow plasmas in hydrogen, helium, and neon were measured in a linear quadruple machine (LM-1), where n2. ≤ 2 × 1012, Te ≤ 10 eV, < 1 eV, mean free path λ ≤ 100 cm, connection length ≈ 20 cm, and electron-ion collision time ≈ 10-5 sec. Particle collectors showed the losses to be mainly radial. The plasmas in the ∮ dl, β stable region decayed in times of order a millisecond (about 10 times the Bolm value) which increased with l0, the conductor current, to a roughly constant value, and decreased as Te increased as Te increased. An axial magnetic field which introduced shear (θ ≥ 1,30 rad cm for the main plasma caused negligible change to the containment time in helium, with a slight improvement in neon. Various instabilities were observed. Pronounced variations in probe signals and plasma loss rates at different axial position suggested a convective structture which persisted in the afterglow for some milliseconds. The origin of the radial loss inside the stable region may be due to a low-frequency flutelike mode or possibly to the convective structure in the plasma.