The SHERPA project aim is to develop an efficient technique to extract a positron beam from one of the Frascati DAΦNE collider rings, setting up a new beam line able to deliver positron spills of O(ms) length. An excellent beam energy spread and emittance, with a strong reduction of the background and the pile-up for the user experiments, will be achieved. The most common approach to extract from a ring is to use a resonant technique, creating an unstable region in the phase space and then driving the tune towards the separatrix, in order to gradually eject particles from the circulating beam.
SHERPA proposes instead to use coherent processes in bent crystals to kick out positrons from the ring, a cheaper and less complex alternative. This non-resonant technique, already successfully used and still developed mainly in hadron accelerators, will provide a continuous multi-turn extraction with high-efficiency. Realizing this for < GeV leptons is challenging, however will provide the first primary positron beam obtained with crystal extraction. At the DAΦNE Beam Test Facility, < GeV positrons have already been deflected using crystals, proving the technique feasibility.
An immediate application of this new extracted beam line would be the PADME experiment, already running at the BTF, but currently strongly limited by the duty cycle. Using the proposed extraction, PADME could increase the statistics by a factor 104 and its sensitivity by a factor 102, extending the discovery potential at the forefront level. SHERPA could provide a unique new beam test facility, very competitive for performance, construction time and costs, well integrated in the accelerator complex, marking a guideline for the future accelerator technology.