Design and operation of magnetron injection guns for a 140 GHz gyrotron

Two magnetron injection electron guns with different electrode geometries have been designed and constructed for use on a 140 GHz gyrotron oscillator. Computer simulations have been performed, detailing the behavior of both designs with variations of all relevant parameters. The first of the two designs has been incorporated into the gyrotron and has been operated up to a beam voltage of 80 kv and a beam current of 7.5 a. With this beam power, the gyrotron has emitted a peak power of 100 kw at 140 GHz, for 1.0 - 1.5 µs pulses. This represents the highest frequency at which a power level of 100 kw has ever been achieved on a gyrotron. In addition to the successful rf results, the gun operates into the highest magnetic mirror ratio (25:1), and the highest cavity and cathode magnetic fields (54 kG and 2.2 kG, respectively) of any magnetron injection guns.