Researches on forced convection heat transfer to supercritical helium have been surveyed. Introduction of the recent experiments, discussion on the impairment of heat transfer and the influence of buoyant force on the impairment, and critical review of the available experimental data have been done.
The JT-60 neutral beam injector consists of 14 beamlines. Each beamline has a cryocondensation pump of capacity 1, 400m3/sec. The purpose is to evacuate hydrogen gas of 2-4 Pa·m3/sec from the ion sources, thereby keeping the pressure in the beamline chamber in the order of 10-3 Pa during beam extraction. The cryopump consists of four large modules, two small modules and two phase separators. These modules are divided into three pairs and constitute differential pumping. In each module, liquid helium and liquid nitrogen are supplied from the phase separators by natural circulation based on thermal siphon effect. The cryogenic system for the cryopumps are helium and nitrogen systems. The helium system is a complete closed loop of a refrigerator (cold box, main and pumping compressors), distribution transfer lines, a liquid helium storage dewar and helium gas storage tanks. Design capacity of the refrigerator is 2, 400W at 3.7K. The construction was started in autumn of 1983. Each performance of the 14 cryopumps was tested one by one in the test bed facility with good results. Capacity of helium refrigerator exceeded 2, 500W at 3.6K. Completion of the system is scheduled for July 1986.