A Uniform, Pulsed Magnetic Field Coil for Gigawatt Operation of Relativistic Backward-Wave Oscillator

Guiding magnetic field plays a very important role in the efficient operation of the relativistic backward-wave oscillator (RBWO). Generally, magnetic fields are made using solenoid coils extended behind the cathode region to get the desired magnetic field in the beam-microwave interaction region. Large diameter anodes are required to generate a required electron beam with low radial velocity. This paper presents a pulsed solenoid coil design in which the uniform magnetic field extends just up to the cathode and requires a much lesser volume in which the coil has to be kept and has a lower number of turns. This magnetic field coil setup has been tested for 18-A dc coil current to measure the magnetic field profile. A uniformity of 93.5% is achieved within 460 mm length. This coil setup was further tested with an RBWO setup at 550 kV, 7-kA electron beam parameters to generate 1-GW peak microwave power using a 0.55-T magnetic field at 3.28 GHz.