Studies on an electrical isolator cum thermal conductor for a superconducting quadrapole magnet at IUAC

IUAC has recently commissioned a superconducting quadrupole doublet magnet cryostat with zero boil off technology using 2 number of GM cryocooler each having refrigeration capacity 1.5 watt @ 4.2 K. Both the magnets are designed to be operated up to 84 Ampere for the required magnetic field gradient. To reduce the heat load to the 2^nd stage of the cryocooler 4 number of high temperature superconductor (HTS) leads have been used to power the magnet in the cryostat. Each HTS lead requires two thermal stations cum electrical isolator for its efficient functioning. In the first design Aluminum Nitride (AlN) was used as electrical isolator cum thermal conductor. In the recently conducted cold test of the magnet, we have observed a temperature rise in the 2^nd stage joint during current charging (From 4.4 K to 6.7 K). The quantum of temperature rise is not acceptable for the stable operation. To minimize the temperature rise in the 2^nd stage an experimental study was conducted to select a design having better thermal conductivity. In the new design the thermal conductivity ratio improved by four times compared to the 1^st design and when implemented the base temperature reduced from 4.4 K to 3.4 K. This paper will highlight the effort made to realize a better electrical isolator cum thermal conductor at low temperature and its implementation in the existing cryostat. (author)