In order achieve the HL-LHC goal of running at an average luminosity 5 ×1034 cm-2s-1, the cryogenic infrastructure for the magnet cooling will have to be adapted along several lines.
Generic Underground Cryogenic Distribution: Changes in the accelerator optics layout will impact strongly on the individual magnets installed in the matching sections (MS), requiring as well adaptation of the cryo-line (QRL) and of the remote magnet powering via superconducting links.
Specific cryogenic cooling capacity upgrades: The radio frequency particle accelerating cavities (RF-cavities) function presently at saturated helium temperatures (4.5 K), and draw their cooling from the same refrigerator source as the whole 3.3 km long magnet sector they belong to. When going to high luminosities this sharing of cooling resources can no longer be maintained and a dedicated Cryo-plant for RF in Point 4 of about 5-7 kW @ 4.5 K needs to be installed. The challenge will be to reach an extremely stable vapour pressure by installing a cold-box as close as possible near the RF-cavities in a confined underground space. Additionally studies need to be done for possibly using the same refrigerator for cooling so-called “crab-cavities” which rotate the high energy particle bunches for optimal luminosity.
The high luminosities will increase thermal load on the magnets near the interaction points (IPs). At present these magnets share the cooling resources with the 3.3 km long magnet sector they belong to, a situation which cannot be maintained. Therefore new Cryo-plants in the collision points P1 and P5 of about 2-4 kW per IP need to be installed. Besides the obvious benefit of increased cryogenic power, this will allow complete separation of the cryo-infrastructures of the arc and of the triplet magnets, with big operational advantages (e.g. completely independent cool-down and warm-up).