X-band magnicon amplifier experiment

Summary form only given. A prototype 50-MW, 11.4-GHz frequency-doubling magnicon amplifier tube driven by a /spl sim/480-kV, 210-A ultrahigh-convergence electron gun, was put into operation in July, 1999. RF conditioning of the magnicon circuit was carried out over the next several months of daily operation. Following /spl sim/3 months and /spl sim/2.5/spl times/10/sup 6/ pulses, the conditioning of the 5.7-GHz gain and penultimate cavities appeared to be completed. At that time, output powers as high as 5 MW were observed via calorimetry, and the operating frequency was measured using a heterodyne diagnostic. However, the maximum output power was limited by a problem with the drive-cavity input coupler, which limited the available drive power to /spl sim/15 W compared to the 75-150 MW required to drive the magnicon to saturation. The limited drive power required operating the magnicon in a magnetic field configuration that produced higher gain, but low output efficiency. As a result, the decision was made to bring the magnicon up to atmospheric pressure to repair the input coupler. The repair was carried out in late October, and conditioning resumed in early November. Shortly thereafter, the tube suffered an abrupt loss of vacuum due to the formation of a sub-millimeter-diameter hole through the back of the copper collector cone and into the collector water jacket, apparently due to cumulative damage resulting from ion focusing of the electron beam. This paper will describe the experimental progress prior to the collector failure, the cause of the failure, the redesign of the collector to prevent repetition of this occurrence, and the steps being taken to rehabilitate the gun, cavities, and waveguide components to prepare for the resumption of magnicon testing.