A compact positron source using a microtron accelerator

The microtron accelerator developed at AT and T Bell Laboratories currently produces macropulses with charge slightly greater than 1 μC at energies of 19-20 MeV. The measured vertical emittance at the exit of the microtron is (8±4)π mm mrad while the horizontal emittance is much smaller. In normal operations, a current of approximately 30 μA cw is delivered to a positron moderator in 16 μs pulses at 30 Hz. The accelerator is being used to study stimulated emission in a helical undulator for a free electron laser and to form a pulse train of 105 positrons/pulse for various solid state experiments and for laser measurements on positronium atoms. Several important microtron improvements including a LaB6 cathode, electron beam extraction, better vacuum, a new cavity design, and rf pulse envelope flattening will be discussed. (orig.)