Abstract. A new type of fast ionization gauge is described to measure neutral particle densities in the presence of a plasma in a magnetic field. The gauge has a sensitivity of 6.5m Torr^-1 for nitrogen over the pressure range 70 n Torr to 0.3m Torr. The notable features of the gauge are its small volume, 2.2 cm³, low emission current, 1 mu A, and power dissipation, 2W. With the appropriate choice of electrode potentials the sensitivity changes by no more than 20% when the magnetic field intensity is varied in the range 1.8-3.0 kG. The gauge may be rotated so that its axis makes and angle of +or-15 degrees with the direction of the magnetic field before the sensitivity changes by +or-10%. Its speed of response to a fast rising pulse of gas is less than 300 mu s. A venetian blind type of structure is used to shield the gauge from charged plasma particles. The gauge has been used to monitor the neutral particle density in the PROTO-CLEO stellarator during the plasma confinement period.

Print publication: Issue 6 (June 1974)