A closed loop system to control transverse deformations in LHC collimators

This work presents a novel closed-loop control system for the detection and control of thermal deformations integrated in the secondary collimators of the Large Hadron Collider (LHC). Interactions between spurious particles lost transversally from the circulating beam core and the collimator jaws that make up the active area of the collimator will result in thermally induced deformations in those jaws. This interaction can push the jaw's straightness out of the tolerance and force the jaw either into the beam core or away from it. This action can result in reductions in beam cleaning efficiency and increases in impedance on the beam. Whilst deformations in either direction are to be avoided, deformations into the beam are considered more of an issue as too much deformation can provoke beam dumps if beam losses are too high. To minimize this unavoidable thermal effect a novel adaptive closed-loop monitoring and actuation system, comprising of multiple intrinsic Fabry–Pérot interferometric (IFPI) optical sensors, and several integrated piezoelectric stack actuators, has been developed. When operating, this system can transiently monitor the jaws straightness and when required correct for deformations up to 500μm. In addition, subsequent steps to use this system as an active damper to reduce vibratory response, as experienced when the jaw undergoes a direct beam impact, are also discussed.