The Central Solenoid (CS) Model Coil project was started in 1992 as one of the most important R & D programs in the International Thermal Experimental Reactor (ITER) Engineering Design Activity (EDA). The purpose is to confirm the design criteria and performance of the ITER conductor, to develop and verify manufacturing tooting and processes, and to verify material performance following fabrication processes. The CS model coil was fabricated by using full-size ITER CS conductor and consisted of an inner module of 10 layers and an outer module of 8 layers. The coil, which has an inner diameter of 1.58m, an outer module of 3.6m, and a height of 2.78m, including two 0.5m lead regions. The coil was completed in 1999 and tested at the CS model coil test facility in JAERI in 2000. It achieved successfully 13T at 46kA under the pulsed operation condition of 0.4T/s for a ramp-up rate and 1.2T/s for a ramp-down rate, which is targeted as development. And the CS insert, which was a one-layer solenoid to investigate the performance of the ITER conductor in detail, was constructed and tested by being installed inside the CS model coil. The inset was operated up to 13T with a ramp-up rate of 1.2T/s.

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To demonstrate the superconducting magnet technology applicable for the construction of the International Thermonuclear Experimental Reactor (ITER), a model coil simulating the ITER central solenoid coil has been fabricated. In this way, the world's largest superconducting pulse coil with supercritical helium forced-flow cooling was realized. To test the model coil, the Japan Atomic Energy Research Institute has developed and constructed a large superconducting coil test facility named the CS model coil test facility. This facility has a large power supply system with a maximum capacity of 225MVA and a 5kW helium cryogenic system with a 1.0kg supercritical helium circulation system, which is the world's largest superconducting test facility. Design features, specifications, and performances of the CS model coil test facility are described.

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In International Thermonuclear Experimental Reactor (ITER) Engineering Design Activities, the Central Solenoid Model Coil (CSMC) and the CS Insert Coil (CSIC) have been fabricated, and installed into the ITER CSMC test facility at Naka Fusion Establishment, Japan Atomic Energy Research Institute (JAERI). The CSMC and CSIC conductors are applied to the cable-in-conduit conductors cooled by forced-flow supercritical helium (SHe) at 4.5K. There are 48 parallel cooling channels for the CSMC, the CSIC and the structures. In the CSMC experiment, the cool-down and the warm-up were finished successfully. The cool-down time was within 480 hours. The steady head load without coil current was measured and evaluated.

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International Thermonuclear Experimental Reactor (ITER) Engineering Design Activities (EDA) have been performed in collaboration with Japan, the European Union, the Russian Federation, and the United States of America. In ITER EDA, the Central Solenoid Model Coil (CSMC) and CS insert coil have been fabricated to demonstrate the realization of ITER superconducting magnet. The conductor used in the CSMC and CS insert coil is a forced flow cable-in-conduit conductor (CICC) cooled by supercritical helium. For CICC, a pressure drop characteristic is one item of important information from the viewpoint of understanding of heat transfer in the conductor and thermodynamics design of a cryogenic system with a helium circulation pump for coil cooling. The ITER conductor has a central channel made of a spiral tube of thin stainless steel tape and a spring tube made of INCONEL in the bundle having about 1, 100 superconducting strands. The helium gas flow into the bundle and central channel in parallel and the pressure drop characteristic are determined from flow balance between the bundle region and the central channel because of different flow friction factor characteristics of both. In the past, pressure drop measurement for various bundle types of CICC composed of a few hundreds strands, such as Demo Poloidal Coil (DPC), has been well performed at 4-K supercritical helium. Recently, the friction factors of the bundle region and the central channel of the ITER conductor have been measured at room temperature. The pressure drop characteristics of an ITER relevant sub size conductor, such as QUELL have been measured at 4K. However, there are no measurement results in the practical coil operation conditions (4-K supercritical helium condition) for an ITER full-size conductor. In a CSMC experiment, the pressure drop characteristic of ITER full size conductor has been measured in a practical operation condition for the first time at an ITER CS model coil test facility in the Naka Fusion Research Establishment, Japan Atomic Energy Research Institute (JAERI).

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Central Solenoid (CS) model coil program is a backbone activity of International Thermonuclear Experimental Reactor (ITER) Engineering Design Activities (EDA). The CS model coil has been developed to demonstrate the ITER real CS coil by international collaborations. The first charge test of the CS model coil and CS insert coil was carried out from April to August 2000 success. It achieved 13T of the maximum magnetic flux density with DC and pulse operation. A performance test of the CS model coil and CS insert was done under relevant conditions of real ITER coils. The mechanical performance of the CS model coil and the CS insert coil is discussed. And the temperature rise during coil charge is also reported.

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Acoustic emission (AE) signals induced from the Central Solenoid Model Coil (CSMC) and the Central Solenoid Insert Coil (CSIC) of the International Thermonuclear Experimental Reactor (ITER) are described. Two kinds of AE data acquisition methods for the AE signals are adopted during series of energizing, i.e., one is the whole waveform recording, and the other is the AE envelope recording. It can be estimated that the AE signals are mainly induced by motion of a superconductor because the AE signals synchronize with the voltage spikes, especially in the virgin current region. The multi channel measurement provided us with information about the spatial distribution of disturbances by the AE sensors at each installed point in CSMC. The observation of AE with high-time resolution shows that the disturbances in CSMC decrease with the iteration number of excitation, judging from instantaneous AE levels, AE energies, and AE event count. Meanwhile, under the background field of 13T by CSMC, charging and discharging tests of the CSIC at the rate of 5kA/s from 0kA to 40kA were repeated 10, 003 times. We monitored the disturbances in CSIC and in CSMC during this cyclic test by using envelope signals of an AE sensor installed near the bottom of the innermost layer of CSMC. The detected AE signals were large, in the range of 1, 000 to 2, 000 times and 3, 000 to 4, 000 times. And after that, the AE signals were very small, until 10, 003 times. From 3, 000 through 4, 000 times, we monitored strange AE behaviors that can be attributed to the loosening of bolts.

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Critical current (I_C) and sharing temperature (T_CS) measurement of the ITER-CS insert coil were performed. The coil is Nb₃Sn superconducting coil and is installed inside the ITER-CS model coil. Voltage behavior related to normal state transition of a conductor during I_C or T_CS measurement has not been well understood, especially in such a large cable as this coil, which has more than 1, 000 strands, because the magnetic field, which makes much effect against superconduting property, is not constant inside of a cable. The authors analyzed voltage behavior of the conductor during the measurement and found that an averaging electric field gives reasonable clues to evaluate I_C or T_CS value, considering the twist pitch of the cables which is less than the range of the field variation in this case. The obtained result showed a lower T_CS value than the expected value from the strand by 0.2-0.4K.

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The ITER Central Solenoid (CS) model coil and the CS insert coil were fabricated, and the test was carried out. The AC loss measurement of the coils is one of the most important tests to determine coil performance. The AC loss of a short sample conductor for the CS insert coil was measured by using the calorimetric method, and the coupling time constants of the conductor were estimated to be 30ms and 20ms for pulse and discharge tests, respectively. The AC loss of the CS insert coil was measured by using the calorimetric method for pulse and discharge tests. The coupling time constant estimated from the result of the pulse tests was 34ms and almost equal to that of the short sample. The coupling time constant for the discharge test was estimated to be 140ms and about 4 times that of the pulse test.

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Pulse charge tests of an ITER Central Solenoid (CS) Model Coil and a CS Insert Coil, hereafter referred to as CSIC, have been carried out in the CS Model Coil experiment, which was conducted by Japan Atomic Energy Research Institute in 2000. Both coils were successfully operated up to 13T with the designed ramp rate of 0.4T/s. Also, ramp rate limitation (RRL) tests were performed for both coils. The RRL test results of CSIC are reported in this paper since the AC loss and critical current evaluation of this coil has been almost completed. The results indicate that CSIC quenches at lower currents than those that were expected to be the critical current, taking into account the temperature rise by the AC losses in the much faster pulse operation than the designed. Moreover, the ratio between the quench and critical currents decreases with increasing ramp rate.

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The Central Solenoid (CS) insert coil and the CS model coil (CSMC) have been developed in the Engineering Design Activity (EDA) for the International Thermonuclear Experimental Reactor (ITER). They are wound with the ITER CS conductor. The CSMC is composed of 18 layer windings, whose most important object is to generate 13-T magnetic field at 46-kA current, so the coil does not have instrumentation in winding. The CS insert coil is a single layer coil and was tested under a field generated by CSMC. This coil was fabricated to study its performance when wound with the ITER CS conductor, so the coil has much instrumentation in winding. Both coils are very stable and achieved their rated condition without quench. To study the quench characteristics, we made artificial quenches by heating the coils. Many data about quench behavior of CS insert coil were obtained from the experiment. The results of quench property, propagation velocity, pressure rise, and temperature rise are reported and compared with the calculation results.

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The CS model coil cryogenic system had experienced many transient disturbances because of AC losses and quenches during the coil experiment. The cryogenic system adopted a forced-flow circulating loop to refrigerate the coil system by supercritical helium, and it was observed how the disturbances affected the refrigeration loop. When the disturbance occurred, the loop pressure suddenly increased such as an adiabatic-compression phenomenon in an incompressible fluid loop. Thermal disturbance, however, generated and grew in the coil-cooling channels and moved with the coolant velocity. Through the observation of disturbance, a cryogenic-system operation method that could control the influence because of disturbance was developed. The method functioned by 25 times of the transient disturbance and did not cause the cryogenic system to stop.

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