Thermo-mechanical studies of large hadron collimators in accident scenarios

Abstract

The performance of the Large Hadron Collider (LHC) strongly depends on the correct functionality of the LHC collimation system. With a nominal stored beam energy of 362 MJ and a beam momentum of 7 TeV / c, beam accident scenarios must be studied well to assess if the collimator design is robust against possible error scenarios in operation. One of the serious accident scenarios in the LHC is an asynchronous beam dump. While the primary and secondary collimators are designed to withstand such beam impacts, there may be machine conditions that expose the metal-based tertiary collimators (TCTs) and put them at risk of damage. A numerical finite element (FE) model is thus developed in this thesis and applied to investigate the thermo-mechanical response of a TCT in novel jaw error cases derived from an asynchronous beam dump accident. The effectiveness of operating with tilted collimator jaws is identified and it is found that a jaw inclination of -1 mrad can mitigate the damage caused by an accidental beam impact on a TCT. The thermo-mechanical response of TCTs to proton and 208Pb82+ ion beam impacts is also compared and it is concluded that heavy ion operation in the LHC poses no additional challenges on the structural integrity of TCTs during a beam impact. The developed FE model is complemented by the commissioning of thermal and structural characterisation campaigns of the TCT jaw insert material (INERMET® 180) under varying temperature and strain-rate conditions. Moreover, a dedicated beam experiment at the CERN High Radiation to Materials (HiRadMat) facility has successfully validated the reliability of the developed FE model, thus giving confidence in the prediction of damage by such numerical simulations. The work presented in this thesis provides a more thorough understanding of the thermo-mechanical behaviour of TCTs during beam impact in accident scenarios. This is achieved by taking into account all relevant collimator damage limits in a detailed study of various relevant scenarios for the operation of the LHC and its risk optimisation.