A Beam Interlock System for CERN High Energy Accelerators

The Large Hadron Collider (LHC) at CERN (The European Organisation for Nuclear Research) is one of the largest and most complicated machines envisaged to date. The LHC has been conceived and designed over the course of the last 25 years and represents the cutting edge of accelerator technology with a collision energy of 14TeV, having a stored beam energy over 100 times more powerful than the nearest competitor. Commissioning of the machine is already nderway and operation with beam is intended for Autumn 2007, with 7TeV operation expected in 2008. The LHC is set to answer some of the fundemental questions in theoretical physics, colliding particles with such high energy that the inner workings of the quantum world can be revealed. Colliding particles together at such high energy makes very high demands on machine operation and protection. The specified beam energy requires strong magnetic fields that are made in superconducting dipole magnets, these magnets are kept only around two degrees above absolute zero and there is a high chance of particle impacts causing a magnet to quench, where the magnet becomes normal conducting and has to be switched off before it destroys itself. Losing as little as 10e−8 of the beam into the superconducting magnets will lead to a quench. A loss of 10e−4 of the beam into any part of the machine will cause damage, such as rupturing the machine vacuum, which in the best case results in costly repairs and weeks of downtime, in a worse case the destruction of one or more dipole magnets would mean many weeks of repairs to return the machine to operation. Due to the unprecedented sensitivity of the machine to beam losses, and the high cost of failure, both financially and in terms of inefficiency, a complex Machine Protection System is envisaged, surveilling and diagnosing the operation of the CERN high energy accelerators, ensuring their safe operation. Machine Protection Systems are employed in the LHC, SPS and beam transfer lines, protecting all parts of the accelerator complex that handle beam above damage thresholds. At the heart of each Machine Protection System lies a Beam Interlock System, connecting the many components of the Machine Protection Systems which are located all around the accelerator complex. The LHC is the ultimate application of these protection systems, here the Beam Interlock System is responsible for relaying a command for controlled removal of the beam (Beam Dump) to the LHC Beam Dumping System. The Beam Dumping System is the only part of the accelerator that is capable of withstanding the impact of the full LHC beam without being damaged in the process. The time response of the LHC Beam nterlock System has to be around 100$/mu$s, to protect against the fastest events which lead to beam losses. Each Beam Interlock System is made from sixteen Beam Interlock Controllers. These are distributed around the 27km circumference of the machine, one at the left and one at the right of each Insertion Region, each Controller acts as a local concentrator, monitoring up to 14 User System inputs. Fibre optic links join the sixteen Controllers in so-called beam permit loops, making the high-speed, highly dependable backbone of the Beam Interlock System. This thesis is focussed on the conception, design and realisation of a generic Beam Interlock System used to protect the high energy accelerators at CERN. The Beam Interlock System has been designed to provide the LHC and its injector chain, as well as the SPS and its transfer lines, including the CERN Neutrinos to Gran Sasso project, with an unsurpassed level of protection. In every application the stored beam energy is orders of magnitude above the damage thresholds of the machines.