A relativistic magnetron with a thermionic cathode

The design and development of a relativistic magnetron are described. Target pulse lengths of one microsecond and mean pulse powers of one gigawatt were selected and an oxide cathode was chosen because the space-charge should inhibit vacuum dc breakdown between the anode and cathode, thus allowing longer pulses than are achieved with other relativistic designs employing cold, field-emitting cathodes. A high power tube was nonrelativistically scaled to an operating voltage of 500 kilovolts. The resulting anode has twelve resonators and was operated with one end short-circuited to rf. An impregnated tungsten matrix cathode and a coated cathode were tested. The coated cathode, which was found to be more tolerant of the poor vacuum, emitted successfully. A rf measurement technique provided simultaneous power and frequency information during each pulse. The magnetron operated in the desired mode at power levels of about 20 megawatts for pulse lengths of about 35 nanoseconds.