Microwave emission from pulsed, relativistic <i>e</i>-beam diodes. I. The smooth-bore magnetron

Abstract

Measurements of intense magnetron oscillations in pulsed, field-emission diodes (∼350 kV, 30 nsec) subjected to crossed externally applied fields (≲16 kG) are reported. The oscillations set in as soon as the magnetic field exceeds the critical field necessary for cutting off the diode current. The oscilations are diagnosed by the microwave emission which is studied in the range from 7 to 40 GHz. The radiation is emitted in broad frequency bands, it is strongly polarized, and can be tuned by the magnetic field; the power levels are typically 1 to 5 kW. The observations are consistent with the onset of the slipping stream instability in the Brillouin space charge flow of the electron cloud.