PERSONNEL PROTECTION OF THE CERN SPS NORTH HALL IN FIXED TARGET PRIMARY ION MODE

While CERN's Super Proton Synchrotron (SPS) is able to deliver both secondary proton and primary ion beams to fixed targets in the North Area, the experimental areas (North Hall) are widely accessible during beam. In ion mode all normal safety elements involved in producing secondary beams are removed, so that an accidental extraction of a high-intensity proton beam into the North Hall would expose personnel to a radiation hazard. This has required an injector reconfiguration restricting operation to either ions or protons. However, demands for operational flexibility of CERN accelerators have led to a need to mix within the same SPS super-cycle both highintensity proton cycles for LHC or HiRadMat and ion cycles for the North Area. We present an active interlock designed to mitigate this hazard: Beam Current Transformers are used to measure the beam intensity, and if above a set threshold, pulsing of the extraction septa is vetoed. The safety function is implemented by means of two logically equivalent but diverse and separate interlock chains. This interlock is expected to be in place once the SPS resumes operation after the first Long Shutdown in 2014.