Investigation of the relation between compression, relaxation, and end losses in the late phases of theta pinch discharges by means of a two-dimensional MHD computer programme
A two-dimensional MHD model was developed for the phases after the fast oscillations of theta pinch discharges. This model was tested by comparison with theoretical results and experimental measurements; it turned out that the model aptly describes the quasistationary phases of theta pinches.It is found that the plasma in the late phases is only adiabatically heated.The relaxation of temperature and anisotropy is discussed, particular attention being paid to interaction with heavy impurity ions and to determining the temperature of these ions from Doppler profiles of spectral lines.Finally, on the one hand, the dominant contribution of convection to the end losses is demonstrated by means of a detailed energy balance; on the other, the relevance of thermal conduction to the axial dynamics inside the coil is explained.