Transient Thermo-Mechanical Analysis of the TPSG4 Beam Diluter

A new extraction channel is being built in the Super Proton Synchrotron (SPS) Long Straight Section 4 (LSS4) to transfer proton beams to the Large Hadron Collider (LHC) and also to the CERN Neutrino to Gran Sasso (CNGS) target. The beam is extracted in a fast mode during a single turn. For this purpose a protection of the MSE copper septum coil, in the form of a beam diluting element placed upstream, will be required to cope with the new failure modes associated with the fast extraction operation. The present analysis focuses on the thermo-mechanical behavior of the proposed TPSG4 diluter element irradiated by a fast extracted beam (up to 4.9 x 10^13 protons per 7.2 mus pulse) from the SPS. The deposited energy densities, estimated from primary and secondary particle simulations using the high-energy particle transport code FLUKA, were converted to internal heat generation rates taken as a thermal load input for the finite-element engineering analyses code ANSYS. According to the time dependence of the extracted beam, the transient solutions were obtained for coupled heat transfer, structural deformation, and shock wave problems. The results are given for the space distribution and the time evolution of temperatures and stresses in the most critical parts of the TPSG4 beam diluting element followed by the MSE copper septum coil. In the worst case of impact of the full LHC ultimate beam, the maximum temperatures remain safely below the melting point. However, the maximum equivalent stresses may slightly exceed the elastic limit in the aluminium section of the diluter. Also, the predicted maximum temperature rise in the MSE septum coil exceeds the design value.