Optics interlock system for the CERN LHC: Implementation and operational experience

In 2016 the luminosity reach of the Large Hadron Collider (LHC) was increased by reducing the β-function in the main collision points below the design value to β*=40 cm. This was possible thanks to a specially matched betatron phase advance between the extraction kickers and some sensitive machine elements that would otherwise risk to be damaged by miskicked beam in case of an asynchronous beam dump. This method imposed the demand to guarantee the phase advance always stays within an acceptable tolerance, including operational actions like tune adjustments. Therefore, a new interlock system on the quadrupole magnet currents was put in place to safeguard the stability of the phase advance. This paper describes the technical implementation of this power-converter interlock (PcInterlock) and the strategies used to derive appropriated tolerances to allow sufficient protection without risking false beam dump triggers. The experience with the new PcInterlock settings in 2016-18 are discussed.