The CMS detector is built from several different layers, surrounding the beam pipe in which the LHC beams collide. The subdetector that is closest to the collisions is the pixel detector. It has a functionality similar to a digital camera taking 40 million snapshots of particle trajectories every second. The pixel detector components surround the CMS beam pipe like bracelets. Therefore, both components (CMS pixel detector and the beam pipe) need to be compatible with each other.
Complete replacement of the CMS beam pipe is planned during the recently started two year maintenance period, called Long Shutdown 2 (LS2), and the key motivation is to make it compatible with the geometry of the future CMS pixel detector. The cylindrical section of the beam pipe will be extended opening more space for the Phase-2 pixel detector that will be installed during Long Shutdown 3 (LS3, scheduled for 2024). The new layout will also be compatible with other foreseen engineering changes of the detector and the LHC accelerator during the upgrade phase of High-Luminosity LHC in LS3.
Although the central cylindrical section will, as now, be made of beryllium (for maximum transparency to particles) the material used in outer sections of the beam pipe is being changed from stainless steel to aluminium alloy, with the aim of reducing activation by a factor 5.
Last week the beam pipe was successfully removed from the heart of CMS, following the pixel extraction a week before. Production of different beam pipe components is now ongoing with foreseen installation in 2020.