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The superconducting magnets of the tokamak JT-60SA are cooled by means of forced flows of supercritical helium at 4.4 K and 0.5 MPa. The closed loops transfer heat from the magnets to the refrigerator through heat exchangers immersed into a saturated liquid helium bath. An experimental loop was designed to represent a 1/20 scaled down mock-up of JT-60SA central solenoid cooling circuits. This design for keeping the same transit times in the helium circuits, aims at observing the thermally induced transients in the closed loop. Indeed, heated section simulates the variable loads coming from the magnet circuits. A series of experiments was performed with pulsed loads in an isochoric configuration of the loop. The cold circulator has been characterized under pulsed operation and its performances are addressed. Mass flow regulations at the interface of the refrigerator were tested to smooth the pulsed loads with the saturated liquid bath acting as a thermal buffer. Knowledge of the pulsed loads effects on the cryogenic components is important in view of a safe operation of the cryogenic system. [ABSTRACT FROM AUTHOR]

The ITER cryogenic system will have to cope with substantial dynamic heat loads due to the magnetic field variation and the production of neutrons generated by the fusion reactions. This will induce large pressure variations in the primary cooling loop of the superconducting coils, which results in the large power variation to the helium refrigerator. The HELIOS test facility, developed at CEA-Grenoble, and initially designed to study the pulse mitigation of the JT-60SA central solenoid cooling circuit (in order to smooth the pulsed load and test components), was adapted to the ITER cooling loop requirements. This paper presents the experimental results concerning the specific ITER analysis. We reproduce experimentally the pressure variation of the Central Solenoid (CS) loop predicted by a numerical model, and observe the behaviour of the circulating pump in these conditions. The investigations of the heat load smoothing methods, using the circuit of Toroidal Field Structures, such as the pulse mitigation by temporary by-pass of the flow of the Structure cooling loop, and variation of the speed of the cold circulating pump, are also presented. [ABSTRACT FROM AUTHOR]