A positron buncher-cooler

The positron buncher-cooler is a concept for a new compact device whose aim is to produce a high quality pulsed positron beam for use in atomic physics experiments. It is predicted that pulses of at least 8000 positrons (from a 50 mCi source) with an energy spread of 25 meV and a bunch length of <50 ns may be produced at a repetition rate of 10 Hz with a duty cycle of 90%. The operation of the buncher-cooler relies upon a three step process: accumulation and cooling, extraction, and transfer. A slow positron beam is produced by the combination of a 22Na source and a high efficiency W mesh moderator. For the accumulation and cooling step, positrons undergo multiple collisions with high pressure CF4 cooling gas. For the extraction step, the cooled positron cloud is ejected by adjusting the potential. Once the cooled cloud is ejected, the positrons accumulated in the first potential well are transferred into the cooling region and the cycle begins again. This new buncher-cooler is comparable with other experimental apparatus regarding the number of positrons per pulse, but it produces narrower energy spread short pulses