Slow extraction at the SPS: extraction efficiency and loss reduction studies

Elevated activation levels in LSS2 were first reported dur-ing an intervention on the SPS extraction septum (ZS) inSeptember 2015. The increase was attributed to higher in-tensity Fixed Target (FT) operation and poorer extractionefficiency, and reported to the IEFC [1]. Since this eventthe awareness of the impact of slow extraction losses on theoperation and maintenance of the SPS has been heightened.This is particularly pertinent in light of tightening limits ondose to personnel and recent requests for increased intensi-ties, as well as ambitious future experimental proposals inthe North Area (NA), such as the SPS Beam Dump Facility(BDF) [2]. To follow up these issues the SPS Losses andActivation Working Group (SLAWG) was formed.The MD programme for 2016 was originally foreseen totest the faster spill on a 1.2 second flat-top for the BDF andbenchmarksimulationsoftheextractionprocess, butthiswasnot possible due to the restrictions imposed by the TIDVG.Nevertheless, during operational set-up and re-alignmentof the electrostatic septum (ZS) the extraction efficiencycould be studied parasitically. The first re-alignment of theZS actually took place during dedicated MD time in May,before moving to physics time.The application of bent crystals used in different configu-rations and modes of operation for slow extraction is beingstudied [3,4]. Bent crystals offer promising solutions forreducing the activation of the SPS LSS2 extraction regionthat is induced by the small fraction of beam that unavoid-ably impinges the ZS during the conventional resonant slowextraction process. In 2016, the slow extraction of a lowintensity coasting 270 GeV proton beam into the TT20 ex-traction line towards the NA of the SPS was demonstratedin dedicated MDs using the extraction septa in LSS2 and abent crystal, provided by the UA9 collaboration as part oftheir experimental installation in LSS5.