Performance of NEG getter materialin a sealed reflex-triode vircator at 225 A/cm2

Summary form only given. This study focuses on the use of non-evaporable getter (NEG) materials in a high power microwave (HPM) virtual-cathode oscillator (vircator). The vircator has a background pressure in the low 10^-9 torr range with a vacuum volume of 5 L backed by a small 20 L/s ion pump. Presently, the source is driven by an 80 J, 300 kV Marx generator with a current density of 225 A/cm² and pulse width of 100 ns. Initial current pulses increases the chamber pressure to the low 10^-6 torr range desorbing approximately 10¹⁴ particles^1,2. Reduction in the number of particles desorbed decreases an order of magnitude after approximately 2,000 current pulses, with no further noticeable decrease after 10,000 pulses³. The HPM system will eventually be modified to operate at 500 Hz with a pulse width between 10-20 ns. In first order approximations, a pumping speed of 2500 L/s will be needed to pump 10¹⁴ particles within 2 ms from a 5 L volume. This corresponds to a surface area of approximately 2400 cm² for a zirconium-vanadium-iron (ZrVFe) getter material. An introduction of NEG materials into the vacuum chamber will aid in achieving repetitive operation; and preliminary results on the use of the NEG material in the vacuum environment will be presented. A residual gas analyzer (RGA) and an inverted-magnetron cold cathode vacuum sensor are used for the gas diagnostics and are rated to survive the 300°C, 72 hour vircator bake out process.