Experimental Measurements on a 25 Mev Reflexotron

A 25 MeV electron double-pass linac (reflexotron) has been built and tested in a medical-therapy configuration. It uses a 16% ??E/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% duty factor electron accelerator has many attractive features. The 1.6 m on-axis coupled accelerating structure has a ZT2 of 82 M??/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 have been verified by experiment. Therapeutically useful radiation beams are achieved by suitable target and flattener combinations.