Thermal hydraulic characteristics of superconducting coil cooled by subcooled He I

Superconducting magnets of helical coils for the Large Helical Device (LHD) have been operated by saturated helium at 4.4 K and plasma experiments have been carried out at less than 3 T successfully. Now, it is considered that the subcooled He I are used to improve the operating condition of the superconducting magnets of the LHD helical coils. To use subcooled He I as a coolant for the superconducting magnets of the LHD helical coils, we need to investigate the cooling characteristics and the stability of a superconducting coil in the subcooled He I. So, an R & D coil, wound with superconductors for the LHD helical coils, was cooled with the subcooled and saturated helium, and then stability tests of the coil were carried out. Subcooled and saturated He I was supplied from the bottom of the coil and flowed out to a bath of current leads at the pressure of 120 kPa. The temperature of the supplied He I was 3.1, 3.5 (subcooled He I) and 4.4 K (saturated He I) at the outlet of the heat exchanger. In the present experiment, the helium temperature distribution in the cooling channels of the R & D coil was measured under steady state conditions and the transient helium temperature change in the channels was observed in stability tests. This paper discusses the thermal hydraulic characteristics of the R & D coil from these results.