Abstract
The slow high-efficiency extraction from a ring positron accelerator (SHERPA) project's aim is to develop an efficient technique to extract a positron beam from one of the accelerator rings composing the $\mathrm{DA}\mathrm{\ensuremath{\Phi}}\mathrm{NE}$ complex at the Frascati National Laboratory of INFN, setting up a new beam line able to deliver positron spills of O(ms) length, excellent beam energy spread and emittance. The most common approach to slowly extract from a ring is to increase betatron oscillations approaching the third order tune resonance to gradually eject particles from the circulating beam. SHERPA proposes a paradigm change for lepton machines using coherent processes in bent crystals to kick out positrons from the ring, a cheaper and less complex alternative. A description of this innovative nonresonant extraction technique is reported in this manuscript, including its performance preliminary estimation.
Highlights
The positron annihilation into dark matter experiment (PADME) [1,2] has been designed to search for a new kind of dark sector light particle, like a “dark photon” or an axionlike mediator, seen as a peak in the missing mass spectrum of monophoton events in eþe− → γX annihilations of positrons on target
Very high luminosity is achieved in a fixed-target collision scheme, albeit at the price of a reduced center-ofmass energy below 20 MeV, exploiting the positron beam coming from the LINAC [3] of the DAΦNE complex
The crystal extraction solutions proposed here have to be optimized in terms of injection and optics parameter, rf tuning, crystal position and septum features to obtain the best result in terms of extracted beam quality
Summary
The positron annihilation into dark matter experiment (PADME) [1,2] has been designed to search for a new kind of dark sector light particle, like a “dark photon” or an axionlike mediator, seen as a peak in the missing mass spectrum of monophoton events in eþe− → γX annihilations of positrons on target. From 2018 to 2020, PADME has taken data using secondary and primary positrons in the BTF-1 beam line; the main limitation to the sensitivity of the experiment comes from the maximum tolerable rate in the veto detectors, requiring to increase the positron beam bunch length as much as possible. The maximum tolerable rate for the PADME detectors is of the order of 102 positrons= ns, so that with 300 ns long pulses the maximum positron population cannot exceed 3 × 104 positrons/pulse With such a positron beam density, a maximum of 1.5 × 1013 positrons on target (POT) can be reached in one year of operation, given the LINAC maximum repetition rate of 50 Hz. In order to get a significant increase in the reach of the experiment, it would be necessary to further extend the duration of the LINAC pulses. Different options have been studied, considering technical and practical aspects aiming at the design of a realistic and efficient implementation
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