Pumping of methane by a low power hot‐cathode ion pump/gage

摘要

Sealed‐off devices, such as evacuated solar absorbers, with long life spans (about 25 years) frequently require a means of holding down the pressure of gases like methane which are not easily pumped by getters. Required pumping speeds are not high because leak‐up rates are low, but simplicity, low power consumption, together with a means of monitoring the pressure are desirable features. To meet these requirements we have constructed a small hot‐cathode ion pump/gage similar to a small Bayard–Alpert gage and we have subjected it to accelerated life tests in methane. The device consumed less than 1 W of power in operation. After 7×10-2 Torr l of methane had been pumped and with 1 mA of emission current the pumping speed was 2×10-4 l s-1, the equilibrium pressure was 3×10-4 Torr, and the reemission of pumped gas was 6×10-8 Torr l s-1, all quantities being slowly varying functions of the quantity of methane pumped. The sensitivity factor throughout the experiment was 3.3 Torr-1.