HOT-ELECTRON PLASMA STUDIES IN THE PLUG SECTION OF THE HANBIT TANDEM MIRROR

摘要

Hot electrons have been created in the plug section of the Hanbit tandem mirror in order to allow a test of high-m ballooning stability provided by a high-β hot-electron plasma in a tandem mirror. A rectangular microwave cavity was built to confine the energy from a 2-kW 14-GHz klystron. The cavity was equipped with a diamagnetic loop, a skimmer probe, and bremsstrahlung windows. An end-loss probe has been added in the cusp section in order to study the hot-electron mirror losses from the plug. The end-loss probe contains a Silicon PIN diode that is used to detect the x-rays from fast electrons striking a tantalum radiator. The end-loss probe was scanned radially to determine the radius and radial width of the hot-electron distribution ring for two different magnetic fields. A clear ring is observed for both magnetic fields. Bremsstrahlung measurements have shown the presence of a hot-electron plasma in the plug with an electron temperature in the range of 60 to 120 keV. The temperature with the optimum magnetic field is ～ 100 keV. Diamagnetic measurements give the total stored energy. Stored-energy measurements combined with the radial dimensions determined by the end-loss detector were used to give the value of beta with assumptions on the plasma length. The average beta value is much less than 1% due to the low power and short heating time.