Ryuji Maekawa

Dynamic Simulation of Sub-Scale ITER CS/STR Cooling Loop

The dynamic simulation of a sub-scale ITER Central Solenoid (CS)/STRucture (STR) cooling loop has been performed to investigate the cryogenic control strategies against pulsating heat loads. HELIOS facility has been modified for this particular study, which consists of a Liquid Helium (LHe) reservoir with two immersed heat exchangers, a circulation pump and an approximately 130 m long piping with three evenly distributed heated sections. The setup provides the equivalent thermo-hydraulic configuration of the ITER CS/STR, cooled by the forced-flow Supercritical Helium (SHe). The dynamic simulator, C-PREST, has been utilized to model the HELIOS test loop and to compare the results with the experimental data sets. This paper presents the dynamic simulation results and discusses the control strategy to minimize the cooling power requirements, to have high reliability.

Characterization of Bonnetless Cryogenic Valves

Publisher Summary This chapter conducts performance evaluation tests of 3 different kinds of BLCV to study the relationship between the respective valve structures and their performance and reliability, as well as the effectiveness of design methods.The Large Helical Device (LHD) is a nuclear fusion test system in which all coils are made superconductive and which requires the guarantee of constant cooling at liquid helium temperature to ensure superconductive action of the coils. Moreover, it is also necessary to accurately control the helium inside the cooling piping to uniformly cool the object material during cool-down operation. Control of liquid helium used for cooling the Large Helical Device (LHD) can be made more effective with Bonnetless Cryogenic Valves (BLCV) , which can be located in the proper places for use inside the helical coil by being constructed in such a way as to be placed inside vacuum insulated vessels, compared with the conventional long-bonnet cryogenic valves, which must be integrally installed in a valve box.

Test Results of Pressure Head Mitigation of Supercritical Helium Across Cold Circulators at KSTAR for the Justification of the ITER Central Solenoid Cooling Circuit Design

The pressure head necessary for the forced convection of supercritical helium (SHe) across the ITER superconducting (SC) magnet system is generated by centrifugal-compressor type cold circulators. From the viewpoint of the cryogenic system, simulation results indicate that the main challenge of the ITER Central Solenoid (CS) operation is the peaking pressure head of SHe across the cold circulator induced during the rapid ramping of electrical current on the coils. Excess variation in pressure head will push the operation point of the rotating machine beyond the surge line in the compressor map which can trip the circulator and in the worst case result in damages. Therefore, in order to avoid the occurrence of a surge, it has been proposed to open adaptively a cryogenic valve, installed in parallel with the CS cooling channels, during the high pressure head instances. Such an action creates an additional flow channel which consequently suppresses the pressure head peak. The proposed strategy has been numerically benchmarked and tests have been performed in existing cryogenic facilities. In this paper, we will present the test results of pressure head mitigation across the cold circulator dedicated to the KSTAR CS and Poloidal Field (PF) coil cooling circuit with the main purpose of demonstrating the safe operation of the ITER CS circulator as well as cooling circuit during plasma shots. The tests were performed by progressively increasing the coil by-pass valve opening during identical PF/CS current shots and monitoring the tendency of the maximum pressure head variation across the cold circulator. Also, preliminary results of pressure head mitigation during real plasma experiments will be introduced.

System identification and robust anti-windup control for a helium liquifier

This paper addresses the system identification and advanced control of a helium (He) liquifier supplying cooling power at liquid helium (LHe) temperatures (-269 °C). To study the dynamic response to heat load variation, a He liquifier simulation model is utilized. The main focus is to regulate the discharge pressure of the compressor station to guarantee stable system operation. System identification is first conducted to obtain plant models, and a two degree of freedom H∞ controller is designed to achieve regulation. Moreover, saturation of the control valve is compensated via an anti-windup technique, which is suitable for regulation problem with disturbance rejection. The effectiveness of the proposed control designs is demonstrated by dynamical simulations in EcosimPro (EA International) software.