Apertures in the Lhc Beam Dump System and Beam Losses during Beam Abort

The LHC beam dumping system (LBDS) is used to dispose accelerated protons and ions in a wide energy range from 450 GeV up to 7 TeV. An abort gap of 3 μs is foreseen to avoid sweeping particles through the LHC ring aperture. This paper gives a brief overview of the critical apertures in the extraction region and the two beam dump lines. MAD-X tracking studies have been made to investigate the impact of particles swept through the aperture due to extraction kicker failures or the presence of particles within the abort gap. The issue of failures during beam abort is a major concern for machine protection as well as a critical factor for safe operation of the experiments and their detectors. THE LHC BEAM DUMPING SYSTEM The LHC Beam Dumping System (LBDS) [1] is designed to fast extract beam from the LHC in a loss free way. For each beam a system of 15 horizontal kicker magnets (MKD), 15 vertically deflecting magnetic septa (MSD) and 10 diluter magnets (MKB) are installed. After the MKD the beam sees an additional deflection when traversing the Q4 quadrupole. The MSD put the beam in the vertical plane above the LHC machine before it is further deflected in the horizontal and vertical planes in a spiral shape by the MKB kickers, Fig. 1. After several 100 m of beam dump line the beam is absorbed by the dump block (TDE). To protect the septa from miss-kicked beams a special fixed 8 m long graphite protection device (TCDS) is placed just in front of the MSD. Figure 1: Diluted beam sweep on the TDE. Blue: nominal particles, red: particles in filled abort gap. For nominal operations the MKD rise time should always be accurately synchronised with the 3 μs abort gap, so that no beam is swept through the aperture. However some failures can occur which lead to an “asynchronous” dump, and in addition some stray particles may also be present in the abort gap [2]. To protect the LHC aperture from these eventualities, a movable single-jawed 6 m long graphite protection device (TCDQ) is installed upstream of Q4, supplemented by a two-jaw 1 m long graphite secondary collimator (TCSG) and a 2 m long fixed iron mask (TCDQM).