Lanthanum hexaboride hollow cathode for dense plasma production

Abstract

A hollow tube cathode using lanthanum hexaboride as the electron emitter has been designed and constructed. Tests in both argon and hydrogen indicate that this cathode is capable of producing over 800 A of electron current continuously, corresponding to over 25 A/cm(2) from the LaB(6). The cathode has been operated for over 300 h and exposed to air more than 100 times with no deterioration in emission. Projected lifetime is in excess of 3500 h for the sintered LaB(6) piece tested in this configuration. Construction details, performance characteristics, and discussions of space charge limits on emission are described.

High-current electron beam generation in a diode with a multicapillary dielectric cathode

“…For instance, the LaB 6 thermionic cathode used for ignition of the hollow cathode discharge emission current of ϳ800 A and current density of ϳ25 A / cm 2 , described in Ref. 44, requires a heater with a power supply of 1 kW. An improved version of this electron source, 46 which operates at a vacuum Ͻ10 −4 Torr, requires a thermionic heater of 4.5 kW.…”

“…In the case of MCDC with the FPS igniter, the required energy is hundreds of times less than in the case of thermionic cathode. 44,45 The compatibility of the cathodes with the high vacuum requirement is one of the key issues in diode operation at a high repetition rate. The deterioration of the background pressure during MCDC operation was studied using a calibrated Penning probe.…”

“…A review concerning active plasma sources was already published 30 years ago by Kreindel,32 and recently a textbook 33 by Oks summarized the progress achieved for the past decades in research, development, and application of different types of plasma cathode. As examples of such plasma sources one can consider pulsed arc plasma sources, [34][35][36][37] hollow cathode operating in steady state [38][39][40][41][42] and pulsed [43][44][45][46] modes, hollow-anode plasma source, [47][48][49] and a ferroelectric plasma source ͑FPS͒. 50,51 Developed active plasma sources show long lifetime ͑Ͼ10 6 pulses͒, they operate at moderate vacuum ͑10 −4 Torr͒, and in general these sources are not sensitive to pollution.…”

“…Let us note that some important applications require pulsed electron beams with a large cross-sectional area and current densities of several A / cm 2 . 18,33,36,57,58 Arc, 34,36 magnetron, 39,43 Penning, 33,36,39 and thermionic [40][41][42][44][45][46] sources were used for ignition of high-current hollow cathode plasma sources which can produce electron beams with a current density up to several tens of A / cm 2 under the application of an accelerating pulse with an amplitude up to several hundreds of kilovolts. However, all these methods of hollow cathode discharge ignition require relatively powerful power supplies.…”

An ionization pressure gauge with LaB6 emitter for long-term operation in strong magnetic fields

“…LaB 6 is known to have a comparably lower work function and is widely used as a thermionic emitter in many situations, not only in vacuum (e.g. in electron guns or electron microscopes) but also in hydrogen for plasma or neutral beam generation [6,7,8,9,10]. For hydrogen, which is also used in nuclear fusion experiments, there is no cathode poisoning of LaB 6 emitters [11].…”