This paper describes the measurement of the plasma parameters in an 8-metre long theta pinch. The plasma in the midplane is found to be free of end effects and energy loss for some tens of microseconds and is characterized by electron densities of 2 - 5 × 1016 electrons/cm3 and temperatures of 100 - 300 eV. The measured radial distributions of temperature and density and their dependence on voltage and filling pressure were in agreement with MHD code calculations using an anomalous resistivity previously shown to account for the diffusion in the early stages.

A theoretical and experimental study of axial plasma flow and end losses in a θ pinch with a collisional 100-eV plasma with β 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 θ 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.

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