Pulse simulations and heat flow measurements for the ATLAS Forward Calorimeter under high-luminosity conditions

The high luminosity phase of the Large Hadron Collider at CERN is an important step for further and more detailed studies of the Standard Model of particle physics as well as searches for new physics. The necessary upgrade of the ATLAS detector is a challenging task as the increased luminosity entails many problems for the different detector parts. The liquid-argon Forward Calorimeter suffers signal-degradation effects and a high voltage drop of the supply potential under high-luminosity conditions. It is possible that the argon starts to boil due to the large energy depositions. The effect of the high-luminosity environment on the liquid-argon Forward Calorimeter has been simulated in order to investigate the level of signal degradation. The results show a curvature of the triangular pulse shape that appears prolonged when increasing the energy deposit. This effect is caused by the drop in the electric potential that produces a decrease in the electric field across the liquid-argon gap in the Forward Calorimeter. The magnitude of this voltage drop is determined as a function of the energy deposit. In order to examine the heat flow and potential boiling of the liquid argon, a mockup of a section of the end-cap cryostat of the ATLAS detector has been constructed. Temperature differences and thermal conductivities have been measured under different conditions and are compared with simulations. The behaviour of the measured temperatures between various mock-up settings was shown to be in agreement with the simulations while the values of the temperatures differ.