LHCb - Simulation studies for gas injection into the SMOG2 storage cell at LHCb

The LHCb experiment started during Run 2 a pioneering fixed-target program studying the collisions between LHC protons and gas targets injected into the LHC beam pipe through a system called SMOG. Since the gas was free to spread into the whole beam pipe of LHCb, only noble gases at low pressure where injectable. In the last few years, LHCb went through a complete upgrade of its detectors in preparation for LHC Run 3. In this context, the SMOG apparatus has been upgraded to SMOG2, introducing a storage cell that better confines the gas, allowing higher luminosity with the same injected gas flow and, potentially, the injection of non-noble gases, like Hydrogen and Deuterium. The impact on the performance of the NEG film, the coating that prevents surface emission phenomena when it is hit with accelerated electrons or ions, due to the non-noble gases flowing from the storage cell into the beam pipe must be carefully evaluated before injecting in order to set realistic limits to the flux and injection time; moreover, an accurate simulation of the gas profile inside the storage cell and its flow into the VELO RF foil is fundamental to the luminosity measurement, to take into account any deviation from the ideal profile due to the real geometry and injection system. This poster presents the first results of the gas flow simulation for hydrogen; the results show that the impact on the NEG coating after injecting Hydrogen for 100 hours with an average pressure of 1 × 10−5 mbar in the storage cell is well within the safety limits. A first comparison between the predicted longitudinal gas profile and the one observed in data during the first operation of SMOG2 is also presented.