High Current Cold Cathode Employing Diamond and Related Materials

Thermionic cathodes are in use in an overwhelming majority of vacuum electronics devices, including high-power RF sources used to drive particle accelerators. These cathodes do not operate reliably or have long lifetime if their current density exceeds 5-10 Amperes/cm2. Artificial diamond and related materials, produced by chemical vapor deposition, appear to be an attractive alternative, which could improve performance for high-power RF sources and electron-beam triggered high-power RF switches. Artificial chemical vapor deposition diamond and related material cathodes are prepared with a range of morphologies for evaluation as high current-density cathodes, and as current amplifiers. Tests of these cathodes in high-power RF switches in a two-channel X-band active pulse compressor driven by the Omega-P/NRL magnicon at US Naval Research Laboratory (NRL) are planned. Several recipes and geometries for production of diamond and diamond/graphite cathode films deposited on molybdenum forms were tested, producing up to 300 A, 100 kV pulses. A current amplifier experiment using a thin diamond film in transmission was carried out. Record power gain of 17:1 and peak power values up to 90 MW were obtained using an uncoated cold cathode in RF pulse compression experiments at NRL. Comparison of recipes for creation of cathodes coated with diamond and diamond/graphite composites will continue, with selection based on performance that will best serve for high-power RF switches. Such cathodes will be installed in switches compatible with the dual-chamber X-band active pulse compressor set-up at NRL, and compression studies with cathode currents up to 400 A will be carried out, in the expectation of demonstrating high X-band power gains ~ 20:1, and high peak powers & gt;150 MW. Commercial Applications and Other Benefits: Cathodes are ubiquitous in vacuum-electronics devices used as television transmitters, satellite communications, and radars. Versions of the diamond cathodes to be developed in this project could be built for those devices, allowing improved performance at lower cost and with longer lifetimes. The potential market for such cold diamond cathodes could reach $10s of million annually.