Improving the properties of cryogenic targets for COSY experiments

A very light liquid hydrogen/deuterium target has been constructed for the use in intermediate energy experiments with phase space cooled particle beams in the external COSY experiments. The target cell is 6 mm in diameter and 4 mm long at the end of a gravity assisted heat pipe system of 45 mm length and less than 400 mg weight. There are very thin windows of 0.9 y.m Mylar foils for the beam passage. For cooling the target from room temperature to liquid hydrogen/deuterium temperatures until recently metallic heat conductors were used between cooling machine and target region. The performances (thermal conductivity and heat capacity) of copper, aluminum and Silver heat conductors have been compared. Resulting cool down times will be shown. Recently, the short gravity assisted heat pipe has been converted to much longer length. The target liquid is used as transport medium as before. The combination of long heat pipe and thin target cell provides better working conditions with minimum density variation and minimizes inactive materials to less than 10 gm in the 32 cm long standard setup compared with 600 gm in the previous copper conductor system. These heat pipes with a nominal diameter of 16 mm combined with the target cell are routinely used with H2/D2/CH4/N2. A comparison of the operating conditions for the new long heat pipe-target cell combination and the old solid heat conductors will be shown. The cool-down time is much shorter than that with solid heat conductors. Heat pipes up to 2 m length with a common diameter of 16 mm have already worked. A 2 m long heat pipe was developed for future Time of Flight Spectrometer (TOF) experiments. It works safely