LHC Beam Dump Design Study - Part III : Off-normal operating conditions

The LHC beam dump design study has been preliminarily substantiated by energy deposition simulations (Part I) and heat transfer analyses (Part II). The present report is devoted to the abnormal operating conditions induced by a malfunction of the beam diluters. A general approach to the analysis of off-normal operation is presented, which is derived from standard design norms adopted in the nuclear industry. Attention is focused mainly on the carbon core, which is longitudinally split into segments of different density in order to better distribute the deposited energy. The maximum energy density it absorbs decreases by at least 33%, compared to a uniform standard density carbon core. This structure may sustain any partial sweep failure without major damage, up to the ultimate beam intensity and energy. To minimise the risks inherent in a fully unswept beam, a sacrificial graphite mandrel will be placed on the core axis, surrounded by a thick high strength carbon-carbon composite tube. With this arrangement, structural damage will be avoided in the event of total sweep failure, during LHC commissioning and probably up to nominal beam intensity. However, severe damage may still occur at the ultimate beam intensity; in this respect, further analyses of mass-transport phenomena is required. Potential long term improvements are considered.The next and last part of this study will be devoted to the structural analysis of the main aluminium-graphite dump under normal operating conditions.