A Compact 6 MeV Pulsed Electron Accelerator

Abstract

A compact 6 MeV electron accelerator has been built and tested. The unit uses an axially coupled S-band standing wave structure driven by a magnetron source that delivers a 2 MW peak power, 4 ?s pulse at 300 pps. The structure (including gun and high voltage feedthrough) is 12 cm diameter and 90 cm long. The gun is a novel telefocus design. The electron source is a 5.5 mm diameter loop of carburized thoriated tungsten wire in an electrode-focus coil geometry that produces a 40 keV input beam of s 30 ? mm mrad emittance at 25 mrad convergence half-angle. The gun is rugged, insensitive to mechanical shock, and requires only 7 watts of filament power to achieve 400 mA emission under operating pressures. The whole accelerator-gun package can be baked at 350°C, although a base pressure of 3 × 10-7 Pa is achieved with 24 hours of bakeout at only 150°C. At an output current of 100 mA (peak) in the pulse, the beam produces dose rates of more than 300 RMM+ on axis when uising a 4 mm copper bremsstrahlung target. This roughly translates into a clinical flattened dose rate of 200 RMM over a 35 × 35 cm field. The accelerator package is straightforward to manufacture and could easily be reduced in length for specific applications.