Cold-Cathode Magnetron Gauge Characteristics

A description of cold cathode magnetrons operating as gauges has been developed in terms of the conditions for establishing a discharge and the effects of space-charge buildup. Pressure response curves for NRC type 552 (Redhead) and GCA model 1410 (Kreisman) gauges were determined by a conductance-regulated, pressure-ratio method using Bayard–Alpert type gauges for upstream pressure reference. Four characteristics of normal magnetrons operated below cutoff are predicted from the discharge mechanism and correlated with test data: (1) an out-of-strike state characterized by a steady pressure-independent gauge reading (about 5×10−14 Torr) due to leakage current; (2) a minimum pressure threshold for operation, 2.7×10−12 Torr for the NRC 552, 1.7×10−10 Torr for the GCA 1410; (3) a range (below 10−9 Torr) of nonlinear pressure-dependent response moderated by space charge buildup; and (4) a range of near linear response corresponding to the region of nearly saturated space charge.