Beam-related machine protection for the CERN Large Hadron Collider experiments

The Large Hadron Collider at CERN, Geneva stores 360 MJ per beam of protons at the top machine energy. This amount of energy storage presents a considerable challenge to the machine protection systems designed to protect both the machine and the six LHC experiments. This paper provides an overview of the machine protection systems relevant to the protection of the experiments, and demon- strates their operation and level of protection through a series of injection and stored beam failure scenarios. We conclude that the systems provide sufficient coverage for the protection of the experiments as far as reasonably possible. 2808 bunches, of 1:15 � 10 11 proton per bunch, in each of the two beams. This results in a beam energy of 362 MJ, which is enough to cause considerable damage to the normal and superconducting elements of the machine. Furthermore, the beam energy density is 3 orders of mag- nitude above currently operating machines, presenting a unique set of operational challenges to the machine and the associated experiments. The LHC beam is prepared by a chain of injectors. A 26 GeV=c beam is extracted from the proton synchrotron (PS), injected into the SPS and accelerated to the LHC injection momentum of 450 GeV=c. When the LHC is filled, 12 batches per beam are transferred to the LHC ring through two transfer lines. The energy stored per batch is around 2 MJ, already exceeds that of an existing accel- erator like the Tevatron, and is above the damage threshold of machine components. When the LHC is filled, the beams are accelerated to 7 TeV=c per beam, with a total stored energy of 360 MJ. The beams now contain an unprecedented amount of energy, and 1 in 10 8 of the top energy beam is enough to quench a superconducting mag- net. To deal with these levels of stored energy, a complex system of machine protection (1) has been designed to protect the machine, including beam loss monitors, current monitors, and quench monitors, which are connected to a beam dump and interlock system. The strategy of these systems is to manage the continuous losses from the beam, and handle failure scenarios over a large range of time scales. This protection system also needs to protect the delicate components of the six experiments of the LHC from accidental beam loss and failure scenarios, a task complicated by the near-beam and movable silicon detec- tors of TOTEM (2) and Large Hadron Collider beauty experiment (LHCb)'s VEtex LOcator (VELO) (3). This paper gives an overview of the LHC machine protection system (MPS) relevant to providing protection to the experiments, with the intention of showing how the elements of the system work together. This will be done with a series of case studies and failure scenarios, which exercises the machine protection systems and demonstrates the degree of protection provided. The intent is to show the level of coverage and protection is sufficient to protect against a range of possible beam scenarios. With this goal in mind, the paper is organized as follows. The systems and strategy of the machine protection systems are discussed in Sec. II, including the injection and dump systems, and the failure scenarios and case studies are presented in Sec. III. A conclusion and summary are presented in Sec. IV.