OPERATION OF AN INVERTED-MAGNETRON GAUGE IN THE PRESSURE RANGE 10⁻³ TO 10⁻¹² MM. Hg

A cold-cathode ionization gauge with axial magnetic field and radial electric field is described which is useful in the pressure range 10 −3 to 10 −12 mm. Hg and has a sensitivity of about 1 amp./mm. Hg. This gauge has the structure of an inverted magnetron with an auxiliary cathode which provides the initial field emission and allows the positive-ion current to be measured independently of the field-emission current. The operation and calibration of the gauge in a dynamic vacuum system is described for the pressure range 10 −3 to 5 × 10 −9 mm. Hg. Pressures ranging from 10 −8 to 10 −12 mm. Hg were obtained in sealed-off systems. Liquid-helium trapping was used for pressures below 10 −10 mm. Hg. It is shown that the gauge gives a reliable indication of pressure below 10 −10 mm. Hg when the pressure is determined by helium diffusion through the envelope.