Experimental and Two-Dimensional Computational Study of End Losses from a Theta Pinch

A theoretical and experimental study of axial plasma flow and end losses in a $\theta$ pinch with a collisional 100‐eV plasma with $\beta$ on axis of 0.7 is described. The predictions of a magnetohydrodynamic code which is two‐dimensional in radius and axial length were compared with data from a $\theta$ pinch with a coil 8 m long, which gives stable times of some tens of microseconds and good axial resolution. The radial density distribution was measured at four axial positions and its spatial and temporal evolution during the loss process agreed with the computed results. Rarefaction waves were found numerically, and the propagation velocity on a given flux tube agreed with the analytic expression. The computed and measured line density also agreed, and fell sequentially at different axial positions. The results showed that particle flow on a given flux tube depends on the local values of beta and sound speed. Higher‐β plasma on the axis is lost more slowly than the plasma as a whole.