Experimental measurements on a 25 MeV reflexotron

A 25 MeV electron double-pass linac (reflexotron) was built and tested in a medical-therapy configuration. It uses a 16 percent ΔE/E reflecting magnet and a pulsed coaxial annular diode gun. The electron beam passes through the S-band accelerating structure twice achieving second pass energies of 5 to 25 MeV depending on the position of the reflecting magnet relative to the accelerating structure. The 0.1 percent duty factor electron accelerator has many attractive features. The 1.6 m on-axis coupled accelerating structure has a ZT2 of 82 MΩ/m and requires less than 2 MW of rf power for energies up to 25 MeV. Calculations of beam transmission, energy variability and double-pass spectra were verified by experiment. Therapeutically useful radiation beams are achieved by suitable target and flattener combinations