An investigation of a variable geometry orbitron ionization gauge

An investigation of a variable geometry orbitron ionization gauge R Walker,

Editorial

Lecturer,

School

of Physics,

South

Australian

Institute

of Technology,

Adelaide,

South

Australia

note

This paper was originally presented at the Fourth International Vacuum Conference, Manchester, 17-20 April 1968, and will therefore be published shortly as part of the Conference Proceedings. Consequently we are unable to publish this article in Vacuum. We are, however, able to publish the abstract of this paper thus providing as full an account of the First Australian Vacuum Conference as possible.

The “Orbitron” ionization gauge, although still in the development stage, offers an alternative device to the Bayard-Alpert and cold cathode discharge gauges for operation in the high and ultra-high vacuum regions. Its main advantages are: (i) A very low filament operating temperature (with all its associated advantages, eg less chemical pumping, dissociation etc). An emission current of -O.l/iA will produce the same ionization current as for an emission current of -8 mA with the Bayard-Alpert gauge. (ii) Extremely long electron path lengths (-80,000 cm) produced without the aid of a magnetic field, and using only

628

Vacuum/volume

an electrostatic field. Unfortunately its main disadvantage that of severe instabilities in the ion current characteristics.

is

The work carried out by the author was an attempt to relate these instabilities to the geometry of the orbitron. A rubber sheet mode1 of the gauge was also used, and much useful information concerning the orbits of the electrons in the region of the filament was obtained. This information, together with that obtained from the work done with the gauge itself, have enabled the author to suggest the source of these instabilities, and to indicate how they could be eliminated.

18/number

12.

Pergamon

Press

Ltd/Printed

in Great Britain