Overview of material choices for HL-LHC collimators

Abstract

In view of the High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN, different materials were investigated for the upgrade of the LHC collimation system. A key objective was to determine how the jaws of the new collimators could be manufactured to meet the demanding requirements of HL-LHC, such as thermo-mechanical robustness and stability, beam coupling impedance, Ultra-High Vacuum (UHV), etc. During the Long-Shutdown 2 (LS2), five primary and ten secondary low-impedance collimators were already produced using novel materials. For LS3, in addition to more secondary collimators, the production and installation of other types of devices, including tertiaries and physics-debris collimators, is planned. This paper details the final mate-rial choices and rationale for each collimator family.

High intensity beam dynamics assessment and challenges for HL-LHC

“…Moreover, two TCP per beam were replaced by higher conductivity MoGr ones (TCPPM) [31]. Furthermore, during LS3, five other secondary collimators in CFC will be exchanged with even lower impedance ones featuring copper-coated isostatic graphite jaws and taperings [33]. The decrease of the total dipolar impedance (horizontal and vertical) after the two successive upgrades is illustrated in figure 6.…”

“…The impedance model was also refined over time, in particular that of individual collimators, which currently contains both the large resistive-wall contribution of the jaws [69], and the impedance of geometric features such as small angle taperings [74], including their resistive-wall contribution [33]. Finally, for low-impedance primaries and secondaries, the geometric impedance now provides a relatively important contribution compared to the resistive-wall part which has been considerably reduced; hence, recently significant effort was made to further refine their model, ultimately using electromagnetic simulations and measurements [75][76][77].…”