History and future of the relativistic magnetron

The relativistic cavity magnetron is one of the most mature of all high-power (>100 MW) sources. The operational mechanism is robust; it is relatively compact, has been operated at frequencies 1-8 GHz. From 1976-present, research teams have explored the full range of operational parameters: single-source output in excess of 4 GW; multiple phase-locked sources output of 3 GW total output; repetitive, near-GW peak powers at pulse repetition rates up to 1 kHz, and long-pulse operation with energy per pulse of about 1 kJ. This magnetron is the most tunable high-power source, with a 30% tunable range by mechanical means, and can be tuned while firing repetitively. Experiments have clarified the major issues of upper limits of achievable repetition rates and energies per pulse. Theoretically, the basic design process derives from the 1940s, and modern computer simulation techniques have sped understanding and the process of design changes. Major practical issues of fielding a magnetron-based system have been addressed in the Orion facility, a transportable outdoor microwave effects test system built in the US and operating in the UK since 1996. The MILO (for magnetically-insulated line oscillator), a linear-magnetron variant, has dual attractions of not using an externally applied magnetic field and producing high power at low impedance, so that it couples well to lower-voltage, compact power supplies. Both tunable relativistic cavity magnetrons and MILOs are commercially available.