Performance Tests of the Subcooling System for the LHD Helical Coils

Abstract

Performance tests of the subcooling system for the helical coils in the Large Helical Device (LHD) have been performed. For the performance of the system, it is necessary to supply the helical coils with a subcooled helium mass flow of 50 g/s at 3.2 K. From the test results, the performance was able to fulfill the design requirements of the system. Additionally, the coil temperature has been evaluated with the quasi-one dimensional numerical calculation, in which the numerical model simplifying the helical coil configuration is used. The coil temperature would be 3.6 K under a steady heat load of 100 W from outside of the coil case in the system which maintains the above performance, as the result of the calculation.

Results of the Excitation Test of the LHD Helical Coils Cooled by Subcooled Helium

“…When the temperature of the heat exchanger was lowered to 3.0 K by raising the round speed of the cold compressors, the inlet temperatures of the helical coils were rapidly lowered to 3.2 K with the mass flow of 50 g/s. The outlets were gradually lowered to 3.8 K with the time constant of about 2 hours, which 1051-8223/$25.00 © 2008 IEEE 3. Temperature rises at the outlet of helical coil by excitation, where a is "+1.4 A/s to equivalent 11.1 kA", and b is "+0.7 A/s to equivalent 11.5 kA."…”

“…When the bath temperature of the heat exchanger is 3.0 K and the mass flow is 50 g/s, the inlet and outlet temperatures of the coil were successfully lowered to 3.2 K and 3.8 K, respectively, from the saturated temperature of 4.4 K [2]. The average temperature of the winding is estimated at about 3.6 K [3]. According to the results of stability tests with a model coil cooled by subcooled helium, the helical coils were expected to be excited up to almost 12 kA without propagation of a normal-zone [4].…”