Cryogenic system development and helium behavior study for forced-flow superconducting coils

In Japan Atomic Energy Research Institute (JAERI), cryogenic technology development is propelled to aim at realization of superconducting coil system for fusion experimental reactor (FER). For this purpose, forced-cooling technology which is one of attractive cooling methods and is expected to use for one of large superconducting coils for fusion is being investigated according to the cryogenic technology development program shown in Fig. 1. JAERI has already constructed and tested three forced-flow generating facilities which are named as forced flow generator (FFG), segment test facility (STF) and forced flow test facility (FFTF). The forced flow generator (FFG) which can provide supercritical helium up to 3 g/s with 8 atm and 4.5 K was firstly fabricated for fundamental investigation of forced-cooling coils and coolant. As the second step, STF and FFTF were constructed in order to investigate coolant, supercritical helium, control technique combined with the helium liquefier/refrigerator. They are designed to have the capacities of flow rate up to 20 g/s and 60 g/s with 15 atm and 4.4 K by adding supercritical heat exchanger to the existing 350-l/h and 1.2-kW helium cryogenic system. Using these facilities, several forced-cooled superconducting coils with cable-in-conduit conductor were tested and the stability characteristics and supercritical helium behavior in the conductor were measured. This paper describes design concept and tested performances for the forced flow facilities, and pressure rise Characteristics of supercritical helium in cable-in-conduit conductors.