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Starting Circuit for Hollow Cathode Ion Source

IP.com Disclosure Number: IPCOM000044682D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Cuomo, JJ: AUTHOR [+3]

Abstract

A simplified starting circuit for a hollow cathode in a broad-beam ion source has been developed. The invention utilizes existing ion source power supplies in a different configuration during starting, with the addition of several minor components. This starting circuit eliminates the high voltage negative power supply needed in the past. The ion source in this case starts at high ion energy. An alternative embodiment allows low ion energy starting, again without the previously needed negative high voltage power supply. The actual operation of a hollow cathode electron source has been described in detail elsewhere [1]. Hollow cathodes are often used as electron sources in place of hot, thermionic filaments in broad-beam ion thrusters [2] and various other ion sources [3].

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Starting Circuit for Hollow Cathode Ion Source

A simplified starting circuit for a hollow cathode in a broad-beam ion source has been developed. The invention utilizes existing ion source power supplies in a different configuration during starting, with the addition of several minor components. This starting circuit eliminates the high voltage negative power supply needed in the past. The ion source in this case starts at high ion energy. An alternative embodiment allows low ion energy starting, again without the previously needed negative high voltage power supply. The actual operation of a hollow cathode electron source has been described in detail elsewhere [1]. Hollow cathodes are often used as electron sources in place of hot, thermionic filaments in broad-beam ion thrusters [2] and various other ion sources [3]. Hollow cathodes have the advantage of using less power than a thermionic cathode, heating the surrounding ion source body less, and having a substantially longer lifetime than the equivalent thermionic filament electron emitter. The hollow cathode-driven ion source and the starting and running circuit are shown in Fig. 1. The hollow cathode 12, the keeper 13 and the anodes 14 are all located within the body of the ion source 15. The ion source 15 may have grids 16 at one side through which the ion beam is accelerated in direction 17. Often, within the ion source is a magnetic field 18 which serves to lengthen the path of the electrons before striking the anodes, allowing for increased ionization of the gas within the source. Gas enters the ion source through the hollow cathode 12. An additional source of gas may be added to the source either through another point 19 in the source or through the front grids from the background gas. The ion source is located within a vacuum enclosure. The various power supplies shown are connected to the ion source components by means of vacuum feedthroughs. To start the hollow cathode, the ion source 15 is held at chamber ground potential 28 by turning the ion source power supply 27 to zero, or else removing it. The hollow cathode 12 is biased to a negative high voltage with respect to ground by power supply 20. Both the keeper 13 and the anode 14 are biased to positive voltages with respect to the ion source body 15 with power supplies 21 and 22. With a sufficient flow of an ionizable gas through the hollow cathode 12 a breakdown of gas will occur due to the large negative potential on the hollow cathode. Ions produced in this plasma are accelerated toward the hollow cathode tip. These ions gain sufficient energy due to the high negative potential voltage on the hollow cathode tip compared to the plasma potential to heat the tip to thermionic temperatures. For a 3.5 mm diameter hollow cathode, this heating is accomplished by a current of about 0.5 A at a maximum voltage of about 900-1000 V. At the high temperature reached by the hollow cathode tip, electrons are emitted from the tip...