Time-resolved Langmuir Probing of a New Lanthanum Hexaboride (LaB6) Hollow Cathode.

摘要

A new laboratory model lanthanum hexaboride (LaB6) hollow cathode sized for a 20 A HET discharge has been developed. The cathode design is based on previous high current LaB6 cathodes. The cathode s heating element, which is used to bring the insert to thermionic emission temperatures, is usually the most likely to break down. In this new LaB6 cathode, the heater has been redesigned to address various fail mechanisms such as the fusion of the heating element to other critical elements of the cathode, and the high-cost of replacing this component of the cathode. This relatively low-cost, and robust cathode was designed for use in experiments to aid in the contemporary modeling of electron dynamics in Hall-effect Thrusters (HETs), and for use in experiments to aid in the development of methods for electron energy distribution function (EEDF) control in HETs. In preparation for these experiments, this cathode was run in triode mode with an annular anode, and stable operation was achieved for various operating conditions. Various plasma parameters were calculated from Langmuir probe (LP) data at a point downstream in the plasma plume. The EEDF was also determined from this data and is best described by a Maxwellian distribution function with a velocity shift.