Beam Scraping in the SPS for LHC Injection

The Large Hadron Collider (LHC) at CERN will be the world's most powerful accelerator when it is commissioned in fall 2008. Operation of the LHC will require injection of very high intensity beams. Fast transverse beam scrapers have been installed in the Super Proton Synchrotron (SPS) injector to detect and, if necessary, remove transverse beam tails. This will help to both diagnose and prevent beam quenches in the LHC. Scraping of a high intensity beam at top energy can potentially damage the scraper jaws. This has been studied with Monte Carlo simulations to find energy deposition and limits for hardware damage. Loss maps from scraping have been generated both with machine studies and tracking simulations. Time dependent Beam Loss Monitor (BLM) measurements have shown several interesting details about the beam. An analytical model of time dependent losses is compared with beam measurements and demonstrates that beam scraping can be used to estimate the beam size. Energy deposition simulations also give the time dependence of scraping, and are compatible with measurements in this respect. Several machine studies have been conducted to investigate transverse beam tails and possible uses of the beam scrapers. These have shown that the beam scrapers in combination with BLMs are very sensitive detectors of transverse beam tails. Measurements with coasting beam have shown that tails repopulate after some time. The most recent resul ts from machine studies are discussed, in light of possible sources of tail repopulation.