PERFORMANCE OF THE COLD-CATHODE GAUGES IN A HIGH AND MISALIGNED MAGNETIC-FIELD

Cold cathode gauge tubes without their permanent magnets will be used to monitor the vacuum systems of a muon storage ring, presently under construction at Brookhaven. The fringe field of the storage ring's sup erconducting magnet will be used to sustain the gauge discharge. Three commercial cold cathode gauges, a Penning type, a grounded Penning an d an inverted magnetron, have been studied for their suitability under this high and misaligned magnetic field. Using an electromagnet, the discharge intensities of these gauges have been measured at pressures from 10(-8) to 10(-5) Torr, magnetic fields from a few hundred Gauss t o 15 kG, and alignment angles from 0-degrees to 50-degrees. The discha rge intensity of the Penning gauge increases with increasing magnetic field misalignment and decreases gradually with increasing pressure an d magnetic field. At small misalignment, the discharge intensity of th e grounded Penning decreases with increasing magnetic field, and if th e misalignment is large, it drops off abruptly at high magnetic field. The discharge intensity of the grounded Penning peaks around 1 X 10(- 6) Torr if the magnetic field is low; and at a high magnetic field, it drops off gradually with increasing pressure. At lower pressures, the discharge intensity of the inverted magnetron gauge remains fairly co nstant with an increasing magnetic field, but decreases with increasin g magnetic field at higher pressure ranges. Its discharge intensity al so decreases rapidly with increasing misalignment.