Abstract
Losses and component activation are limiting performance factors for slow extraction with high-power applications, and new techniques of loss-reduction, such as bent crystals, require a stable and narrow separatrix angular spread. Conventional tune-sweep slow extraction results in an optics change and an accompanying separatrix rotation through the spill. This can be compensated by a dynamic closed-orbit bump, but requires a high level of complexity for setting up and monitoring. For the Super Proton Synchrotron (SPS), a simpler and powerful new extraction technique has been developed and deployed, providing a mechanism to fix the machine optics and hence separatrix completely through the spill. The technique with the name constant optics slow extraction (COSE) relies on high chromaticity and scaling all machine settings with beam rigidity following the momentum distribution of the beam. In this paper we describe the new COSE concept and its successful operational deployment in the SPS during the 2018 run.
Highlights
The method of slow extraction allows to extract beam from circular accelerators in long spills of seconds by exploiting the separatrices of the third order resonance
The optics is changed during the slow extraction process and with it the presentation of the beam separatrix at the electrostatic septum, which is detrimental for various loss mitigation schemes
constant optics slow extraction (COSE) relies on an accelerator control system based on higher level physics parameters and sufficient reproducibility of the machine to control the slow extracted spill in feed-forward
Summary
The method of slow extraction allows to extract beam from circular accelerators in long spills of seconds by exploiting the separatrices of the third order resonance. Slow extraction beam losses are in the order of a few % at the SPS ES [1] Methods of reducing these losses and mitigating their effects are an active study topic for CERN’s Physics Beyond Colliders program [2]. Various promising techniques to reduce slowextraction losses by means of, for example, bent silicon crystals [3], diffusers [4] or phase space folding with multipoles [5] have been proposed All these benefit in efficiency from a constant phase space representation, i.e., constant separatrix angle, throughout the spill or constant optics in the case of exploiting multipoles for loss reduction. During the 2018 SPS run the authors developed an elegant and operationally inexpensive method with the name constant optics slow extraction to fix the optics and the separatix angle at the septum throughout the SPS slowextracted spill, without the complication of controlling and setting up dynamic bumps or other means of correction and without the need for additional hardware or electronics in the accelerator
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