Joule-Thomson Hydrogen Refrigerator Target

Abstract

The majority of the hydrogen targets built use liquid hydrogen directly as the cooling medium, requiring a liquid hydrogen storage container which is connected to the target cell. Other condensation targets have been built in which the hydrogen for the target cell is separated from the hydrogen which serves as the cooling medium [1]. This type of target cooling also lends itself to use with deuterium targets. Condensation targets have the advantage that they are relatively simple in construction and can be filled or emptied relatively quickly. The refrigeration capacity can be adjusted to the particular need, the only effect being a different evaporation rate of the hydrogen supply. The disadvantage of this type of system is that strict safety measures for the targets must be exercised because of the large amounts of hydrogen in the system. For this reason other targets were built which use liquid helium as the cooling medium. Targets cooled with helium can generally only be used for small target cells since the high cost of liquid helium makes the operation of larger targets quite expensive. Another problem associated with targets cooled with helium is that liquid helium tends to freeze the hydrogen.