Ohmic heating, line tying, and preionization in Hanbit

Abstract

Summary form only given, as follows. Initial attempts have been made at Ohmic (Joule) heating, stabilization, and preionization in Hanbit using an electron-emitting hot cathode in conjunction with a reflex discharge. The hot cathode was constructed using a set of LaB/sub 6/ discs heated internally with current through carbon rods. The cathode was mounted in the cusp section of Hanbit on magnetic field lines connected to the central cell (CC). The reflex discharge was initiated between the cathode and a CC biased limiter. This provided Joule heating of the electrons in the plasma Normally, ion cyclotron resonant heating (ICRH) produces the plasma. In the CC with a slot antenna supplied with power from a 500-kW transmitter at 3.5 MHz. In addition, the reflex discharge could be initiated prior to the ICRH discharge in order to provide a target plasma for the ICRH power. The ICRF power was thus not needed to breakdown the plasma and could be used solely for ion heating. Further experiments have been performed with the heated cathode but, without a reflex discharge to attempt line-tying stabilization of the CC plasma with all electron emitting end wall. The preliminary results for these three experiments will be presented. In addition, the electron-emitting cathode could be used to remove gas on the interior surfaces of the CC by electron impact desorption (EID) when the magnetic fields are arranged to cause the electrons to strike the CC walls arid internal structures. Preliminary results from this experiment will also be presented.