Success on elimination of pulse shortening of GW-class, 300 nsec HPM sources

Summary form only given, as follows. We have demonstrated two different HPM sources which radiate rf power in excess of 1 GW: the MILO and RKO. The pulse lengths are limited only by the duration of the prime power. Both sources have been operated on the Sandia IMP pulser (500 kV, 5 /spl Omega/, 300 nsec) pulse power driver. While the physics of these sources are different, both have shown rf pulses shorter than the applied electron beam pulse. Following careful investigations both sources now generate rf pulse to the end of the electron beam pulse. This success has been achieved by closely comparing experimental performance and optimized computer simulation. Our results suggest that designing a long pulse HPM source and then being able to make the source operate as desired is usually limited by overlooking subtleties of the actual source operation. While it most certainly is true that stray plasma production may limit pulse length. Stray plasma production in these two sources is a symptom of design errors. We are preparing longer pulse experiments to investigate the next source of pulse shortening.