The target cell and the cryogenic system will be located directly behind the beam dump along the beam direction. The cell is contained in a vacuum pipe, which guarantees the thermal insulation and it is surrounded hermetically by the BGO Ball.
The target cell (see fig. 1 and 2) is a 4 cm diameter aluminum cylinder, closed by thin mylar windows at the two sides. Two different lengths of the cell are available (6 and 11 cm) in order to fulfill different experimental requirements. The target cell can be filled either with liquid Hydrogen (H2) or Deuterium (D2).
The cryogenerator is made of: a) a helium compressor (with a 100 l external helium buffer tank); b) a two-stages cold head (working at the nominal temperatures of 70 K and 20 K); c) a cryostat (Quantum Technology Corp.). The cryostat (see fig. 3) is a closed-cycle refrigerator, working with high purity helium gas: inside the cryostat the temperature of the refrigerating helium is cooled down via two Gifford-McMahon (G-M) cycles with helium gas pressure cycled isothermally from 17 bar relative (250 psig) to 5 bar relative (70 psig). The hydrogen/deuterium gas is cooled down by the helium through heat exchangers and liquefied inside the cell.
The target temperature is constantly monitored by three probes and stabilized by a heating resistor. One of the probes is connected with a security system which automatically stops the compressor in order to avoid freezing of the liquid inside the cell.
When the cell is filled up, the working temperature of the liquid Hydrogen or Deuterium is about 17 K and 22 K, respectively.
The hydrogen and deuterium gas is stored in two tanks (454 l), connected in parallel to the same distribution panel, so that the change from Hydrogen to Deuterium target (or vice-versa) can be made by simply switching from one tank to another, after a purge and pump procedure.
The alignement of the target with respect to the beam will be provided by a regulation system, with displacements and tilts both in the vertical and horizontal directions. The frame containing the target pipe and the cryostat will move on rails for the extraction of the whole system along a direction perpendicular to the beam.
A remote control system will allow the constant monitoring of the target temperatures and pressure.
In fig. 4, the configuration of the target and the cryostat in the experimental area is shown.