Chapter 13: Beam instrumentation and long-range beam–beam compensation

Abstract

The extensive array of beam instrumentation with which the LHC is equipped has played a major role in its commissioning, rapid intensity ramp-up and safe and reliable operation. Much of this equipment will need consolidation by the time the LHC enters the High-Luminosity (HL) era, while the upgrade itself brings a number of new challenges. The installation of a completely new final focus system in the two high-luminosity LHC insertions implies the development of new beam position monitors to equip the upgraded quadrupole magnets. As well as replacing the 10 current beam position monitors, six additional beam position monitors will be added per interaction region, to further improve beam control at the collision point. The use of crab cavities for luminosity enhancement implies a need for new instrumentation in order to allow for the optimisation of their performance. This requires intra-bunch measurement of transverse position on a turn-by-turn basis. Several diagnostic systems are being investigated as candidates to perform this task, including very high bandwidth pick-ups and a streak camera installation making use of synchrotron light. The installation of a hollow electron lens for cleaning the beam halo has added to the beam diagnostic challenges of high-luminosity LHC. Not only must the beam halo be measured, but a good concentricity and alignment between the electron and proton beam must be ensured. A coronagraph based on synchrotron light is therefore under study with the aim of being able to image the halo at a level of 10-5 of the core intensity, while a gas curtain monitor is being developed to align the electron and proton beams within the hollow electron lens. The latter will use a high-density, supersonic, gas sheet to allow a two-dimensional image of both beams to be created via luminescence. Upgrading the LHC also provides the opportunity of developing new instrumentation to address areas identified as currently lacking adequate diagnostics. This includes a non-invasive, beam-size measurement system capable of delivering data throughout the LHC acceleration cycle, with a prototype beam gas vertex detector already being tested for this purpose. An upgrade or consolidation is envisaged for several other systems, including the main beam position monitoring system, the beam loss measurement system, the luminosity measurement system, and the synchrotron light monitor. This workpackage also covers the study of possible technologies for long–range beam-beam compensation.