The LHC must be protected in all phases of operation from injection to collisions, which requires a large and highly redundant machine protection system (MPS). For HL-LHC, a number of its components must be improved or renewed.
The impact of new magnets/electrical circuits must be evaluated in terms of reaction time for beam loss monitor response and orbit changes. The criticality of electrical circuits with respect to machine protection depends on circuit time constants (L/R), power converter ramp rates (dI/dt) and on the local optical functions. The local beam optics also has an influence, and the large betatron function of HL-LHC in the region of the triplets enhances the criticality of certain circuits. Collaboration with WP5 will evaluate the aperture limits to ensure their proper protection, in particular for super-conducting elements. The phase space coverage of the collimators must be verified. Coherence of collimation and absorber settings (injection, dump) must be ensured. The failure modes of crab cavities must be studied in detail (time constants, beam excursions etc). Specifications for the speed of interlocks must be given both for internal interlocking of crab cavities and for beam parameter monitoring. The need for upgrades of the LHC beam dumping system must be evaluated, especially if beam intensity will reach the so-called ultimate value or beyond. To protect the LHC against failures occurring over a single turn (injection, extraction) a number of passive protection are installed in the LHC. The need for upgrades of those devices and for additional protection devices must be studied and evaluated. The total intensity and bunch structure changes may require additional diagnostics or interlocks to protect the HL-LHC or to enhance the redundancy of interlocks, in particular in view of the possible installation of fast crab cavities. HL-LHC may require modifications to the safe parameters and flags used for interlocking and may also require modifications of the interlocking logic within one of the protection systems of the LHC.