Modeling of beam-induced damage of the LHC tertiary collimators

Abstract

Modern hadron machines with high beam intensity may suffer from material damage in the case of large beam losses and even beam-intercepting devices, such as collimators, can be harmed. A systematic method to evaluate thresholds of damage owing to the impact of high energy particles is therefore crucial for safe operation and for predicting possible limitations in the overall machine performance. For this, a three-step simulation approach is presented, based on tracking simulations followed by calculations of energy deposited in the impacted material and hydrodynamic simulations to predict the thermomechanical effect of the impact. This approach is applied to metallic collimators at the CERN Large Hadron Collider (LHC), which in standard operation intercept halo protons, but risk to be damaged in the case of extraction kicker malfunction. In particular, tertiary collimators protect the aperture bottlenecks, their settings constrain the reach in β Ã and hence the achievable luminosity at the LHC experiments. Our calculated damage levels provide a very important input on how close to the beam these collimators can be operated without risk of damage. The results of this approach have been used already to push further the performance of the present machine. The risk of damage is even higher in the upgraded high-luminosity LHC with higher beam intensity, for which we quantify existing margins before equipment damage for the proposed baseline settings.

Collimation-induced experimental background studies at the CERN Large Hadron Collider

“…The fact that the TCT setting is not constrained by beamhalo background does, however, not mean that it can be arbitrarily tight. Other constraints from protection of the triplet magnets and the TCT itself, in particular during accidental losses, are the present limitation at the LHC for further reductions of β Ã [34,59], although they have been relaxed through the use of a specially matched optics [3].…”

Dynamic Response of Advanced Materials Impacted by Particle Beams: The MultiMat Experiment

“…If the deposited power density is sufficiently high, dynamic responses will be induced, principally because the thermal expansion of the impacted material is initially prevented by its inertia, giving rise to isochoric (constant-volume) heating [21]. This can be the case, for instance, of accidental beam impacts on collimators [10], as opposed to nominal operating conditions, which typically lead to slow transient or quasi-static responses. From a thermomechanical standpoint, the problem can be reduced to the study of a body subjected to a non-uniform, quasi-instantaneous heat generation lasting the time of the beam interaction τ: this deposition time is of the order of few microseconds, thus generally much shorter than both the period T of the waves generated by the impact and the heat diffusion time t d [22].…”

“…The experiment profited of the experience of previous tests carried out at the CERN HiRadMat facility. In HRMT09 [9], carried out in 2012, a full LHC collimator, with a tungsten alloy as absorbing material, was tested to observe the effects of accidental direct beam impacts, benchmark simulations and derive acceptable limits for this absorbing material [10]. In HRMT14 [11], also performed in 2012, specimens of simple geometry, extensively instrumented, were impacted with particle beams to benchmark the numerical results obtained with different FE codes (namely, ANSYS [12], Autodyn [13] and LS-Dyna [14]).…”

Design, construction, and beam tests of a rotatable collimator prototype for high-intensity and high-energy hadron accelerators

“…Therefore, these rotatable collimators would be installed in these locations in the LHC. This scenario has been revised since then (see e.g., [6][7][8]) by more realistic models, but is still relevant for design specifications of IR7 collimators.…”