Prototype installation and MD plans for BGC and Coronagraph in LHC

The research and development activities pursued in beam diagnostics within the framework of the High Luminosity LHC project are coming to a crucial phase. Prototype instruments developed over the last 10 years are being finalized and prepared for final validation tests with beams.

The installation of a prototype high bandwidth pick-up using electro-optical waveguide in the Super Proton Synchrotron (SPS) will take place during the next year-end technical stop. This monitor, developed in collaboration with the Royal Holloway University of London, will be commissioned in 2024 and is expected to measure the intra-bunch motion induced by the prototype radiofrequency double quarter-wave crab cavity which is itself under beam tests in the SPS.

Fig 1: Beam Gas Curtain Prototype installed in point 4 of the LHC
Fig 1: Beam Gas Curtain Prototype installed at Point 4 of the LHC

This year, for the first time, two exciting beam diagnostic developments will be tested with protons and heavy ions in the LHC. The first one has been designed to measure transverse beam tails. In order to detect the small amount of charged particles present in those tails, the monitor relies on the imaging of synchrotron light using a masking technique that would block the intense radiation coming from the core of the beam. Initially developed by astronomers to observe the corona of the sun, this ‘coronagraph’ has been studied and redesigned for the synchrotron radiation sources in the LHC at injection and top energies. A prototype has been installed on the Beam 2 synchrotron light monitoring system during the long shutdown in 2020. A series of beam tests are currently planned in 2023 to assess the performance of that instrument and understand its ability to measure beam halo population.

The second prototype instrument that was installed in the LHC early 2023 is the Beam Gas Curtain (BGC) monitor. Built in collaboration with the University of Liverpool and GSI Helmholtzzentrum für Schwerionenforschung, the BGC is a non-invasive beam profile monitor that uses a supersonic gas curtain and beam-induced fluorescence to capture a 2D profile image of a particle beam. A video describing the functioning of the instrument is accessible here. Just before being installed in the LHC, the monitor was successfully transported and then commissioned at CERN and used to measure the beam properties at a dedicated Electron Beam Test Stand (EBTS). Tests with beams in the LHC are currently starting with end of physic fill studies and first beam images have been very recently acquired. Those experimental data shall provide a first measurement of the fluorescence cross-section of different gases (Neon, Nitrogen…) at LHC energies, both from high energy protons and heavy ions. The recorded images should also allow to measure the sensitivity and resolution of the monitor and assess its potential as a non-invasive profile monitor for high energy high intensity particle beams.

The Beam Gas Curtain instrument was developed in framework of the HL-LHC project as an overlap instrument between the circulating proton beam and the hollow electron beam as part of the collimation system. The BGC is the result of the collaboration between the CERN beam instrumentation group, the University of Liverpool/Cockcroft Institute and GSI (Video: CERN).