End loss from a collision dominated theta pinch plasma

The plasma parameters and end loss in a collision-dominated theta pinch plasma have been investigated photographically, interferometrically, with axially arrayed diamagnetic probes and with a local pressure sensitive diagnostic. The compressed plasma (n_emax∼10¹⁷ cm^-3, T_e=T_i∼45 eV) is highly stable for a period of approximately 9 μsec; the end-loss process is examined over this time interval. The development of a plasma throat region has been identified at an axial position of approximately one coil diameter within the theta pinch coil ends. The existence of inward propagating rarefaction waves is indicated from the plasma temperature time history. The plasma end-loss rate derived from local pressure measurements indicates an initial period of rapid particle loss followed by a period of gradual decay in the loss rate. The experimentally observed end-loss time is in excellent agreement with the prediction of a recent numerical magnetohydrodynamic computation.