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.