Division of systems engineering

The liquid targets of the MINOS project have been used as part of an international collaboration (12 countries) in Riken, Japan since May 2014. Four experiments of three weeks each were carried out using the MINOS device associated with detection systems belonging to the host laboratory. The cryostat has been designed to provide the space required for detection, particularly for the MINOS time projection chamber (TPC).

The cryostat (pictured above), used to obtain liquid hydrogen (picture on the right), is equipped with a commercial cryocooler with cold head power of 15 W (at 20 K). The choice of this cryocooler (compressor and cold head) was motivated by the simplicity of its use (requiring only water and electricity). The absence of a cryogenic infrastructure in the host laboratory (no liquid helium available) and the lack of specialist personnel were two factors that were also decisive. Finally, the compact size of the cold head is a perfect response to detection constraints.

The cryogenic cycle begins by cooling the system without hydrogen for 12 hours. The liquefaction phase begins by transferring gaseous hydrogen from its storage tank, at an initial absolute pressure of 1.5 bars, to the cryostat via a cryogenic bay. The hydrogen liquefies at a temperature of 20.4 K at atmospheric pressure in the one-liter condenser mounted on the second stage of the cold head. The condenser gradually feeds the target with liquid hydrogen by gravity flow. The resulting cold vapor returns to the condenser via a closed loop and is then liquefied. To complete the operation, during temperature-controlled heating, the liquid hydrogen vaporizes and returns to its dedicated storage tank through the check valves. This cryogenic system design minimizes the quantity of hydrogen used (120 g at normal pressure and temperature) and ensures the safety of the system, which uses an explosive fluid under cryogenic conditions.