RFP confinement physics studied on the Extrap-T1 device

摘要

Experiments have been performed on the high aspect ratio, high current density Extrap-T1 reversed field pinch to study the response in confinement properties to variations in plasma current and pinch parameter. The study includes measurements of energy and particle confinement times as well as radiated power, impurity concentrations and magnetic fluctuations. The ratio of Spitzer to total input power in these experiments is varied over the wide range 0.4 to 0.8. The operational0value is found to be primarily a function of plasma current and pinch parameter and scales only weakly with density since an increase in density is found to be accompanied by a decrease in temperature. Changes in Te/ne, however, directly affect the dynamo activity. At high Te/ne, the scaling of the energy confinement time is governed by the enhancement of the dynamo activity, which offsets the decrease in Spitzer input power with temperature. On the other hand, the particle confinement time is not deteriorated by enhanced dynamo activity. Instead, particle confinement is degraded at a high fraction of Spitzer input power. In this limit, convection of thermal particles can account for a major part of the total energy loss