Investigations leading to large solid frozen-spin polarized HD targets and implementation of such targets for photonuclear spin-physics studies

A new type of solid polarized proton and deuteron target has been developed and placed in operation. The solid HD frozen-spin target consists of about 1.5 moles of solid HD in a 50 mm long, 29 mm diameter region of a 90 mm long cylindrical Kapton$\rm\sp{TM}$ container. It is polarized at 17 Tesla and at temperatures near 15 mK in a dilution refrigerator-superconducting magnet system. Inside a target production cryostat, the target cell is filled with liquid HD which is then solidified. The solid target is then loaded into the dilution refrigerator through a central access of clear bore 40 mm diameter, using a cold-transfer apparatus which operates between 2 and 4K, has its own HTC superconducting holding field solenoid providing 200 G at the target, and has target engaging-disengaging mechanisms. The cold-transfer system permits a cold solid target to be inserted and removed from many cryostats such as the variable temperature HD target production cryostat, the dilution refrigerator polarizing cryostat, the storage cryostat for maintaining highly polarized targets for months, and the in-beam cryostat. The first in-beam cryostat for application of this target to nuclear physics will be at Brookhaven National Laboratory, for a polarized gamma beam produced by back scattering of laser light from the high energy electrons in the synchrotron. The complete polarized target system is described in detail, and a study of Kapitza resistance of solid HD to copper and to gold-coated aluminum cooling wires, essential to control for highest polarizations, is presented. In the first test of this system, H polarization of 51% was achieved at 25 mK and 15T, and following several weeks aging and target cold retrieval, the target\u27s lifetime against depolarization at temperature-field usage conditions of 1.5K and 1T was more than a week. These values resulted from polarizing and aging conditions which were not yet representative of the full capability of the system. No deliberate attempt was made to polarize the D nuclei with our RF dynamic polarization transfer methods, but a D polarization of 11% was nevertheless obtained from relaxation