Target System
The Target system serves to liquefy hydrogen or deuterium into the target cell. The target cell is placed at the centre of the BGO ball. The alignment of the target with respect to the beam is provided by a mechanical system, which enables displacements and tilts both in the vertical and horizontal directions. The whole target construction including the cryostat can be moved in and out of the beam position using a dedicated rail system both along and perpendicular to the beam.
Cryogenic System
The cryogenerator is made of a helium compressor (with a 100 l external helium buffer tank), a two-stages cold head (working at the nominal temperatures of 70 K and 20 K) and a cryostat (Quantum Technology Corp.). The cryostat 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 in a closed system is cooled down by the helium through heat exchangers and liquefied inside the cell. The gases are stored in a buffer tank each (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.
Target Cell
The target cell is a 4 cm diameter aluminum cylinder with Mylar end caps. It is contained in a vacuum pipe, which guarantees the thermal insulation. Two different lengths of the cell are available (6 and 11 cm). The target cell can be filled either with liquid Hydrogen (H2) or Deuterium (D2). When the cell is filled up, the working temperature of the liquid Hydrogen or Deuterium is about 18 K and 21 K, respectively.
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.