Cold cathode ionisation gauges for the measurement of low pressures

Abstract Cold cathode ionisation gauges in which the discharge is maintained in an axial magnetic field provide a convenient and rapid means of measuring pressure in the range 10 −2 to 10 −7 mm. Hg. These instruments are simple to make and operate and it is virtually impossible to damage them. With such a gauge, measurement of pressure is effected by a robust pivot-meter which measures a current of ions formed by electron bombardment. Primary electrons are released by cold emission from a pair of cathodes and many secondary electrons are generated by the ions themselves. The magnetic field causes the electrons to move in tight spirals to and fro between the two cathode plates. In this way the number of ions per electron, between initial emission and eventual escape from the discharge to the anode, is much increased. A review is given of the construction, characteristics and performance of various types of cold cathode gauge. The influence is reported of size and shape of the electrodes, of applied voltage, of magnetic field and of the nature of the gas. Reference is made to the performance at relatively high pressures (10 −2 to 10 −3 mm. Hg.). Attention is drawn to the generation of radio frequencies by cold cathode gauges.