Radiation damage and the design of beam intercepting devices at CERN

Abstract

In the framework of the High Luminosity LHC project at CERN, the need for further incorporation of evaluation of radiation damage into the design of beam intercepting devices at CERN is described and the risks of radiation damage in high energy applications are summarized. Radiation damage can be an important topic in high energy applications where doses to materials can accumulate up to the point where they start impacting device functionality and lifetime. The context of radiation damage at CERN provides unique circumstances that are not easily investigated experimentally. Simulation is an excellent alternative to study the behavior of particle transport in matter. For the LHC injector upgrade, proton beam energy levels, entering the Proton Synchrotron, are increased from 1.4 to 2 GeV. Using FLUKA Monte Carlo Simulations, the new energy deposition from the protons traversing a 2 cm thick tungsten plate is calculated. The proton beam is not entirely stopped, but the beam is sufficiently diluted to be outside of machine acceptance. Meaning, it can no longer be accelerated further. The energy deposition in the tungsten creates thermal stress waves. To evaluate the suitability of an alternative material, a thermo mechanical design of the plate is made in ANSYS with two different materials. Tungsten and the tungsten heavy alloy Inermet 180 (W-3.5%wt Ni-1.5%wt Cu) interactions with three different proton beams are evaluated. These beams are foreseen for Proton Synchrotron operation during high luminosity LHC. For single beam impact and normal operation mode the maximum temperature is 84 –C. For steady state, accidental impact, temperatures of 430 –C are reached. The maximum stresses are 145 MPa in Inermet 180 and 135 MPa in tungsten. Due to its brittle nature, it is advised to refrain from using tungsten within this stress range. To evaluate the radiation damage, the DPA and gas production are calculated, using the FLUKA Monte Carlo simulations. The peak DPA is 0.0035 and the peak gas production is 3.5 appm for hydrogen and 2.5 appm for helium. The average DPA production shows a clear maximum of DPAs just after the centre of the plate (1.18 cm depth from the surface). The maximum average hydrogen occurs after 1.2 cm and the maximum helium occurs more to the surface (0.2 cm depth). The peak concentrations are not entirely at the same location though this is where there would be higher risk of agglomerate formation just after the cascade. Since the peaks don’t overlap the most critical radiation damage is likely to occur in an intermediate point.