Nonlocal effects in beam generated plasmas for plasma electronics

Abstract

Summary form only given. Given that the development of future plasma energetics depends on the application and control of nonequlibrium, anisotropic electron energy distribution functions (EEDF) in plasmas, the development of methods to measure and control EEDF is of great importance. We present the technique for EEDF measurements with flat one-sided probes in beam plasmas and its application for developing new methods of controlling plasma parameters, based on the nonlocal nature of the electron energy distribution function (EEDF) [Tsendin, L.D., 1995; Kaganovich, V.I., et al., 2009]. When the EEDF is nonlocal, electrons in the plasma form weakly-interacting groups - cold electrons, which are created by inelastic processes in the plasma volume and fast electrons, originating from the cathode and accelerated by the cathode potential fall. In order to demonstrate the possibility of the active EEDF control, a short (without positive column) dc discharge with thermionic cathode and two anodes was designed. One anode (diaphragm) had a hole in the center to allow plasma current to flow to the second anode. Experiments suggest the presence of two dramatically different modes, which are dependent on the diaphragm voltage. In the first mode, the diaphragm current weakly depends on diaphragm voltage, but in the second mode the diaphragm current strongly depends on diaphragm voltage. This characteristic behavior indicates that this device could be potentially used in a power application requiring low-voltage current or voltage stabilization. Through simulations and experimental measurements it is established, that different behavior of groups of fast and cold electrons in the cathodediaphragm and diaphragm-anode regions allows to implement continuous management of the stabilized current.