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The residual gases present in a DC-705 oil-diffusion-pump uhv system have been determined as a function of various trapping conditions. The system was equipped with a metal 2-in. oil-diffusion pump in series with a specially designed trap in which zeolite was used. The configuration of the trap permitted the trapping zone to be immersed in cryogenic liquids, e.g., LN2. The effectiveness of the trap was determined as a function of temperature. A comparison of the residual gases is made for six conditions, including three trapping temperatures, while operating with zeolite and without zeolite.

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.

The performance of a modified buried collector gauge was determined over a (helium) pressure range 10−13–10−4 Torr. Optimum operating parameters were empirically chosen. With 5.0-mA emission current and 100-V grid to filament potential, the x-ray photoelectron current of the gauge was estimated to be 5.2×10−13 A. By subtracting the measured background current, linear response was obtained between 6×10−13 and 3×10−4 Torr (He) with a gauge sensitivity of 0.015 A/Torr (He). Variations of gauge sensitivity as a function of filament geometry are discussed.

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