LHC beam dump design study; part 2, thermal analysis; implications for abort repetition and cooling system

This second part of the LHC beam dump design study is devoted to transient and steady state nonlinear heat transfer analysis. Heat generation loads are imported from Part - I: simulation of energy deposition in the graphite by particle cascades induced by the LHC primary protons, and superposition of identical energy distribution from each bunch along positions defined by the beam sweep profile on the upstream face of the core. A parametric finite element model of the dump including graphite core, aluminium frame, base plate with cooling channels, and shielding blocks, is elaborated and resolved by means of the ANSYS Engineering System, providing the transient evolution of internal temperature fields. Steady state analysis is then performed, by means of numerical approximations using a limited number of ANSYS results as an interpolation -- extrapolation base. Only periodic aborts are considered. The first conclusion is that the dump requires several hours of cooling after each beam abort. Influence of natural cooling and thermal contact, and performance of a proposed water cooling system, are considered for single and repetitive beam dumping. At the ultimate intensity of 4.8 \[10^14] protons per beam, the dump assembly needs necessarily to be cooled to permit abort cycles as short as 13 h. At the nominal intensity of 3 \[10^14] protons, periodic aborts once per 5 h can be achieved without cooling. At any intensity, however, water cooling reduces the safe abort period by at least a factor 2. A third part of this study will concern mechanical analyses leading to graphite material specification.