The vacuum system of the Low Energy Ion Ring at CERN: Requirements, design, and challenges

For the heavy ion program at CERN's Large Hadron Collider, lead-lead collisions with a design luminosity of 10²⁷ cm⁻² s⁻¹ are foreseen. This will be achieved after an upgrade of the ion injector chain where the Low Energy Antiproton Ring (LEAR) is currently converted into a Low Energy Ion Ring (LEIR). Avalanche-like heavy-ion induced molecular desorption, first observed at LEAR and systematically studied at CERN's Heavy Ion Accelerator (LINAC 3), is the major challenge to achieve the required average dynamic pressure of about 4×10⁻¹² mbar in LEIR. The LEIR vacuum requirements, the technical design, the implementation of non-evaporable getter coatings and low-outgassing collimators, and the concept of ion-beam scrubbing are reviewed in this paper.     

He leaks in the CERN LHC beam vacuum chambers operating at cryogenic temperatures

The 27 km long large hadron collider (LHC), currently under construction at CERN, will collide protons beam at 14 TeV in the centre of mass. In the 8 arcs, the superconducting dipoles and quadrupoles of the FODO cells operate with superfluid He at 1.9 K. In the 8 long straight sections, the cold bores of the superconducting magnets are held at 1.9 or 4.5 K. Thus, in the LHC, ∼75% of the beam tube vacuum chamber is cooled with He.In many areas of the machine, He leaks could appear in the beam tube. At cryogenic temperature, the gas condenses onto the cold bores or beam screens, and interacts with the circulating beam. He leaks creates a He front propagating along the vacuum chambers, which might cause magnet quench.We discuss the consequences of He leaks, the possible means of detections, the strategies to localise them and the methods to measure their size.