Development of a high intensity low energy positron beam

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Abstract
The purpose of our project is to greatly increase the moderation efficiency of high energy positrons (several hundred keV) to low energy positrons (a few eV). We will attempt to do this by first efficiently premoderating almost all of the positrons emitted from the radioactive source to energies less than 10 keV. These positrons will be injected in a solid neon moderator which has been shown to have a moderation efficiency of ∼50% at these energies. The immediate objective is to show that confining and guiding electromagnetic fields together with repeated slowing down traversals through a thin solid foil leads to a high efficiency in the premoderation of much of the entire β+ spectrum. We have performed computational simulation of the trajectories of positrons in the premoderation stage, and the point has now been reached where test experiments can be carried out. These will be done in the spring of 1993. We are presently evaluating different positron emitting radioactive sources, and simultaneously considering various extraction mechanisms for removing positrons from a high magnetic field region to a field free space in addition to the originally proposed phase space shifter. Besides a status report of the project, which emphasizes specific research and development work, a discussion will be given of the future steps and their time schedules, and of the planned initial beam experiments.

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