Anode material testing in a vacuum diode
The gas evolved during the operation of a virtual cathode oscillator (vircator), which can be detrimental to the maximum output power, repetition rate, and pulse width was studied. Gases are known to evolve both from processes at the cathode, such as explosive electron emission, and anode processes such as heating by the electron beam. A residual gas analyzer (RGA) and pressure measurements have been used to perform characterization of background gases before and after the operation of the vircator. Multiple anode materials have been tested, with measurements made of both the quantity and types of gases evolved during firing. The test materials include stainless steel, copper tungsten, tantalum, nickel,molybdenum, and oxygen-free high-conductivity copper. For Nickel, two anodes are machined and given different treatments before operation in the sealed vircator. The first being a high temperature bake-out under vacuum (10-7 Torr) followed by an ultrasonic cleaning. The second treatment omits the high temperature bake-out. A low impedance Marx generator, with no intermediate pulse forming apparatus, is used to drive the vircator. For all testing, an aluminum cathode is used. The pressure measurement systems and diagnostics are described, and gas analysis and composition are presented for multiple anode materials.