This article describes the configuration and heat loads of the large-scale helium refrigeration system for the superconducting cavities utilized for the TRISTAN and KEKB Factory accelerators. The control system of the refrigeration system is also introduced. The fatal failures of the refrigeration system during the past long-term operation are summarized to entice discussions on future stable operation of the refrigeration system, since the refrigeration system will also be used for the SuperKEKB superconducting cavities
A helium cryogenic system, which a circulates supercritical helium (SHE) flow of 300 g/s at 4.5 K through a string of superconducting magnets for a J-PARC neutrino beam, was constructed in 2008. Subsequently, the cryogenic system has been operated for approximately 24,000 hours over a six-year period without any serious problems, and has contributed to the T2K neutrino experiment. A control system, which is an essential for reliable operation of the cryogenic system, is described in this report. The experiences and problems that occurred in the six years of operation are also summarized.
The Large Helical Device (LHD) is an experimental heliotron-type fusion plasma which consisting of a complete superconducting magnet system cooled by a helium refrigerator having a total equivalent cooling capacity of 9.2 kW@4.4 K. Eighteen plasma experimental campaigns have been performed successfully since 1997, with a high reliability of 99%. Seventeen years have passed since beginning system operation. During the operational history, appropriate improvements have been implemented to prevent serious failures and to pursue further reliability. The operational history of the LHD cryogenic system is reported along with improvements that have been made to the system.
The mission of JT-60SA is to contribute to the early realization of fusion energy by addressing key physics issues relevant for ITER under the Broader Approach activities jointly undertaken by Japan and Europe. JT-60SA is a complete superconducting tokamak capable of 5.5 MA plasmas during 100 s, which is closest to ITER plasma conditions. The cryogenic system for JT-60SA will cool the superconducting magnet system (4.4 K), the high-temperature superconductor (HTS) current leads (50 K) the thermal shields (80 K), and the cryopumps (3.7 K). The cryogenic system including the warm compression station, the gas storage units, the refrigerator cold box (RCB) and the auxiliary cold box (ACB) was manufactured in Europe. It is installed at the JAEA Naka site by 2016.
The Radioactive Isotope Beam Factory (RIBF) is a cyclotron-based accelerator facility capable of providing the world's most intense RI beams over the whole range of atomic masses. The world's first superconducting ring cyclotron (SRC) is the final booster in the RIBF accelerator complex, and is capable of accelerating all-element heavy ions to a velocity of about 70% of the speed of light. The ring cyclotron consists of six major superconducting sector magnets cooled by a helium refrigerator having a total equivalent cooling capacity of 1 kW@4.4 K. The helium cooling system was successfully operated from 2005 for fruitful experimental campaigns with a reliability of 97%, although we experienced two serious problems related to oil contamination and a helium leak that took more than 100 days to repair.
At J-PARC, 3 GeV protons with a power of 1 MW are injected onto a mercury target at a repetition rate of 25 Hz, producing fast neutrons via a spallation reaction. The high-energy neutrons are slowed down to thermal and/or cold neutrons in hydrogen moderators, to which supercritical hydrogen is supplied at 1.5 MPa and below 20 K. The nuclear heating is estimated to be 3.75 kW for a proton beam power of 1 MW. The pulsed cold neutron is suitable for crystal and magnetic structural analyses because it has a narrow full-width-half-maximum of approximately 100 μs and a short tail. We developed a cryogenic hydrogen system in which supercritical para-hydrogen circulates at 190 g/s and have operated it since 2008. It has the largest flow rate in the world and can reduce the moderator temperature fluctuation below 3 K. So far, we encountered several problems, although long-lasting operation for more than three months has been carried out. For example, the Great East Japan Earthquake was experienced in March 2011. The interlocking system was able to shutdown the cryogenic hydrogen system automatically as expected. In this study, we describe the operation characteristics and our experiences with the J-PARC cryogenic hydrogen system. The proton beam power was gradually increased to 500 kW in 2015. The trial of 600-kW proton beam operation was successfully achieved in April 2015. It was confirmed that the heater and accumulator developed can mitigate the pressure rise caused by the sudden heat load at the moderators when the proton beams are turned on and off. The dynamic behavior in the hydrogen loop can be also simulated using our simulation code. The pressure rise for a 1-MW proton beam is predicted to be below the allowable pressure rise of 0.1 MPa. We believe that the pressure control system is effective for use with 1-MW proton beam operation.
Two types of superconducting magnets were installed in the beam interaction region of the KEKB accelerator. One was a QCS superconducting magnets for final focusing of the e- and e+ beams, and the other was a huge superconducting solenoid for the particle detector, Belle. While the two magnets had completely different cold masses, two refrigerators of the same cooling power were used during the long-term 12-year operation for the KEKB physics experiment. This paper briefly describes these two cryogenic systems, and reports the operational problems and development of the cryogenic systems for SuperKEKB.
Acable-in-conduit (CIC) conductor using Nb3Sn strand is applied to an ITER TF coil. The Nb3Sn strand in the conductor is periodically bent due to electromagnetic force, which causes degradation of performance. This degradation should be evaluated to predict conductor critical current performance. In a past study, a numerical simulation model was developed to evaluate the superconductivity of a periodically bent single strand. However, this model is not suitable for application to strands in the conductor because of the extensive calculation time required. The author thus developed a new analytical model with a much shorter calculation time to evaluate the performance of periodically bent strand. This new model uses the classical model concept of a high transverse resistance model (HTRM). The calculated results show good agreement with the test results of a periodically bent Nb3Sn strand in a ends fixed beam model while there was little error in the uniformly bent model under high transverse load due to the difference in bending moment distribution between the two models. However, for both cases, the newly developed model has a much shorter calculation time than that required for numerical simulation. This indicates that a more practical solution can be achieved when evaluating the performance of periodically bent strands. Thus, the model developed in this study can be applied to evaluation of the performance of conductor incorporating many strands.