Research on pulse shortening of GW class HPM sources

Summary form only given. During the previous year we have demonstrated two fundamentally different HPM sources which radiate rf power in excess of 1 GW: the MILO and Injection Locked RKO. While the fundamental physics of these sources are different, they both show an rf pulse shorter than the applied electron beam pulse. In the MILO experiments, data typically showed beam modulation for longer times than the radiated pulse, however breakdown in the slow wave circuit was observed. In the RKO experiments the resonance for the instability requires limited variation in the electron beam impedance, the limited impedance range was exceeded due to the emission criteria of our metal cathode. We report on experiments investigating techniques to overcome these pulse shortening issues. A new MILO has been designed and fabricated using conventional tube techniques. The design and preliminary data comparing performance with the existing MILO will be presented. A new cathode was designed for the RKO which allows better electron emission, and operates at a more constant impedance. Comparison of the rf pulse generation with the original metal cathode will be made. Initial work on multi-pulse conditioning are investigated and the preliminary results will be shown. Finally, data from an optical Stark Broadening diagnostic will be shown. This diagnostic allows determination of the local electric field and identification of the emitting material.