High Current Cathodes Without A-K Gap Closure
Agency / Branch:
DOD / USAF
Development of high power microwave (HPM) sources for Air Force applications requires cathodes with long usable lifetimes, negligible anode-cathode (A-K) gap closure, reproducible functioning under high repetition pulsing, uniform current density, and negligible plasma/current production from nearby surfaces. Cathodes must maintain such stable electron beam output characteristics for > 1 nsec. We propose to meet these requirements in an extremely low cost, robust carbon cathode with a matrix of carbon fiber tufts as the emitting surface. Innovations to improve performance include: cesium iodide coating to reduce plasma gap closure and improve current density uniformity; an intermediate electrode to reduce unwanted plasma production from nearby surfaces and increase total current; increased carbon tuft surface density to produce more uniform current density and reduce explosive plasma production; and a ballast resistor array behind the fibers to prevent hot spots of current/plasma production. Cathodes will be produced utilizing these novel features and tested on a crowbarred Marx for 1-2 nsec pulses. Using a corona bushing to eliminate edge effects, 5-cm radius cathodes will be tested with 4-cm A-K gaps up to the 150-200 kV range. Gap closure rates, current density uniformity, and field stress applied to cathode will be determined, and configuration optimized for meeting target performance goals.
Small Business Information at Submission:
Principal Investigator:Donald E. Voss, Ph.d.
416 Washington St. Se Albuquerque, NM 87108
Number of Employees: