The 8th Beam Gas Curtain (BGC) Collaboration Meeting was held at CERN in early April.
The two-day meeting, organized by WP13 in collaboration with Cockcroft Institute (CI) and GSI, brought together senior scientists and the collaboration members from these institutions, including a number of young researchers.
It also coincided with the presence of the CI team at CERN to commission the newly delivered v3 (final) prototype of the BGC in preparation for the upcoming installation on the Electron Beam Test Stand.
This device has previously been commissioned at CI as part of the HL-UK in-kind contribution, showing very promising results that were recently published [1]. This prototype will be installed and tested first on the hollow electron beam test stand before being installed in the LHC for tests with protons in an upcoming Year-End Technical Stop.
In the last weeks, commissioning in the LHC has started of a device that uses an existing background gas system which was part of an obsolete beam profile monitor (BGI) to measure beam-gas fluorescence along with its light background in the real machine environment. This will provide essential benchmark data for the BGC as well as providing some preliminary fluorescence measurements – the first ever at this beam energy.
In August 2021, another UK team from the Royal Holloway University of London came across the channel to follow a first beam-test of a prototype of an innovative high bandwidth beam position monitoring system based on Electro-Optical (EO) crystals.
This device is designed to provide beam position measurements in the Hilumi era with a time resolution better than 50 picoseconds, allowing direct monitoring of intra-bunch crabbing as well as fast transverse instabilities.
In such a system, a DC laser and Lithium niobate EO crystals are used to provide a direct optical replica of the beam electrical field. Using a Mach-Zehnder interferometer arrangement to read-out the two crystals that were installed on each side of the beam, the beam position is directly encoded into a laser intensity variation. The large frequency bandwidth of such crystals together with the use of fibre-coupled laser beam would allow an improvement of the time resolution of conventional electromagnetic monitors by more than a factor 5.
A prototype was built, assembled and tested at RHUL in spring 2021, and shipped to CERN in July for installation in the HiRadMat beam line. Beam tests have then been successfully performed starting in August, demostrating for the first time the EO beam position measurement of a 450GeV proton bunch. After these very exciting results, further tests are planned to be done on the CLEAR facility at CERN with shorter electron bunches that will allow precise measurements of the time resolution of the system. Stay tuned!
[1] A. Salehilashkajani et al., Appl. Phys. Lett. 120, 174101 (2022).