Abstract
The flux of high-energy protons slow-extracted from the CERN Super Proton Synchrotron (SPS) is limited by the induced radioactivity caused by the beam loss intrinsic to the extraction process. Methods to substantially increase the efficiency of the extraction process are of great interest to fulfill requests for an increasing flux of 400 GeV protons to the present experiments, located in the North Area of the SPS, and also for potential future experiments with very high demanded protons on target. A crystal shadowing technique to significantly reduce the beam scattered and lost on the electrostatic extraction septum during the third-integer resonant slow extraction process has been developed and a prototype system tested with beam. The technique is based on the use of a thin, bent silicon crystal to coherently channel or volume reflect the portion of beam that would otherwise impinge the wire array of the electrostatic septum and instead eject it into the transfer line toward the production targets of the experiments. In this paper, the concept is described and applied to the SPS machine in order to specify the requirements of the prototype crystal shadowing system. Beam dynamics simulations of the prototype system are compared and benchmarked to the results obtained through beam tests, before being exploited to understand the characteristics of the present system and the potential performance reach of an optimized, future operational configuration. The remaining challenges faced to bring the system into operation, the optimization possibilities and other potential applications are discussed.
Highlights
AND MOTIVATIONThe slow extraction of a high intensity and energy proton beam suffers in general from the induced radioactivation of the extraction equipment on which the beam unavoidably impinges
Accurate tracking can be performed whilst significantly reducing the computation time, which was essential for the parametric scans needed to assess the performance of crystal shadowing concept presented in this paper
A new method of substantially reducing the beam loss inherent in the slow extraction process has been developed and tested, exploiting silicon bent crystal technology to coherently deflect the part of the beam that would otherwise strike the blade of the extraction septum
Summary
The slow extraction of a high intensity and energy proton beam suffers in general from the induced radioactivation of the extraction equipment on which the beam unavoidably impinges. At CERN we took on the challenge of aligning the crystal to both a thin electrostatic septum and the separatrix arm of a resonantly slow extracted beam on the third-integer resonance, testing both the channeling and volume reflection schemes. To put the future proton requests for slow extracted protons at the SPS into context, the SHiP experiment [7], which aims to provide experimental proof for the νMSM theory [8], is requesting an unprecedented flux of 400 GeV protons amounting to an integrated value of 2.0 × 1020 on a timescale of 5 years For this purpose, a short machine cycle of 7.2 s is foreseen with 4.0 × 1013 accelerated and extracted at 400 GeV on a flat-top length of 1.2 s.
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