Commissioning of the CNGS Extraction in SPS LSS4

The CNGS project (CERN Neutrino to Gran Sasso) aims at directly detecting νμ - ντ oscillations. For this purpose an intense νμ beam is generated at CERN and directed towards LNGS (Laboratori Nazionali del Gran Sasso) in Italy, about 730 km from CERN. The neutrinos are generated from the decay of pions and kaons which are produced by 400 GeV protons hitting a graphite target. The protons are extracted from the SPS straight section 4 (LSS4) in two 10.5 s batches, nominally 2.4 Ñ 1013 protons each, at an interval of 50 ms. The high intensity extracted beam can cause damage to equipment if lost in an uncontrolled way, with the extraction elements particularly at risk. In addition, the beam losses at extraction must be very well controlled to avoid unacceptably high levels of radiation. To guarantee safe operation and limit radiation, the LSS4 extraction system was thoroughly commissioned with beam during the CNGS commissioning in summer 2006. The obtained results in terms of aperture in the extraction channel, longitudinal loss patterns, extraction losses and radiation during nominal operation are summarised in this note.