Thermal design of an ejector-supported cycle using krypton for cooling of particle detector accelerators

According to the High-Luminosity plan (HL-LHC) the Large Hadron Collider will be upgraded to further extend physics discoveries (2033–2034). The increase of the luminosity is followed by an increase of the radiation damage on the silicon sensors used to detect those particles, which they must be preserved from the thermal runaway after which the sensors reach electrical breakdown. The future upgrade will require to the cooling system temperature levels ranging from -60 to -80 °C, currently unattainable by the CO₂ cooling technology (2PACL). From a previous study the noble gas krypton was selected for the thermal management of future detectors as working medium. To meet the requirements of the new generation of particle accelerators, a new ejector-supported cooling system was proposed.

In this work, thermal design of the innovative ejector cycle was carried out starting from the detector. The semi-passive detector loop was first designed to ensure optimal working conditions of the detector. Liquid krypton is supplied to the detector by the ejector, maintaining a constant pressure lift independently of the operating temperature, with a flow variation not exceeding 4.3 % of the design value. The boundary conditions expressed by pressure, density and flow rates will serve as inputs for the design of the adjustable geometry ejector. To verify the thermal stability along the detectors, development of a control strategy to handle setpoint changes and sudden change in the cooling power is also addressed. The off-design case with fluctuating heat loads shows an offset in the evaporating temperature below 0.3 K.