HPM investigation of gas breakdown

Summary form only given. One of the fundamental parameters of HPM technology in question is the relationship between the electric field pulse, gas pressure, and pulse length. As HPM sources have increased in power this relationship is crucial to properly design antennas and radomes to remove the generated microwave pulse. To investigate this relationship we are in the process of reassembling the Injection-Locked Relativistic Klystron Oscillator. The initial experiments focus on techniques to reduce the rate of change of the emitted beam current. Recall we have previously published that the microwave pulse length was experimentally observed to be limited to a finite change in the beam current. We will be presenting results of these experiments and the experimental changes employed to control the rate of change of the current. Once the current ramp is within acceptable limits, we will transition to the gas breakdown experiments. We have designed and assembled double belljar system with a Vlasov antenna to allow adjustment of the gas pressure between the belljars. This pressure control allows determination of the Paschen breakdown curve in a microwave only environment. Because the microwave radiating structure is more than 25 feet from electron beam source, we know there are no X-ray sources beyond the background level. Also, the antenna does not contain any field distortion features to initiate the breakdown. We intend to investigate several gases for the E/p versus pt relationship; where E is the microwave electric field in the gas region between the belljar (<30 kV/cm calculated with 1.5 GW of power generated), p is the neutral gas pressure prior to breakdown (10 Torr - 760 Torr), and t is full-width at half-maximum (FWHM) microwave pulse width (< 500 nsec) limited by the pulsed power system available.