Production of slow positron bunches using a microtron accelerator

The microtron accelerator at Bell Laboratories presently produces 16-μs-long, 40-mA pulses of 18.5-MeV electrons at a repetition rate of 30 Hz. Energetic positron-electron pairs are produced at a 4-mm-thick W beam dump. The positrons are moderated to a few electron volts energy by a 9-mm-diam W(110) single crystal and bunched by a parabolic potential accelerator to 14-ns full width at half maximum bursts containing (7±1)×104 positrons. The collection efficiency of the buncher is 63%. With the buncher turned off, the positron production efficiency is 4×10−8 positrons per electron.