Katsutoshi Takano

Progress of the ITER central solenoid model coil programme

The worlds largest pulsed superconducting coil was successfully tested by charging up to 13 T and 46 kA with a stored energy of 640 MJ. The ITER central solenoid (CS) model coil and CS insert coil were developed and fabricated through an international collaboration, and their cooldown and charging tests were successfully carried out by international test and operation teams. In pulsed charging tests, where the original goal was 0.4 T/s up to 13 T, the CS model coil and the CS insert coil achieved ramp rates to 13 T of 0.6 T/s and 1.2 T/s, respectively. In addition, the CS insert coil was charged and discharged 10 003 times in the 13 T background field of the CS model coil and no degradation of the operational temperature margin directly coming from this cyclic operation was observed. These test results fulfilled all the goals of CS model coil development by confirming the validity of the engineering design and demonstrating that the ITER coils can now be constructed with confidence.

First test results for the ITER central solenoid model coil

Abstract The largest pulsed superconducting coils ever built, the Central Solenoid (CS) Model Coil and Central Solenoid Insert Coil were successfully developed and tested by international collaboration under the R&D activity of the International Thermonuclear Experimental Reactor (ITER), demonstrating and validating the engineering design criteria of the ITER Central Solenoid coil. The typical achievement is to charge the coil up to the operation current of 46 kA, and the maximum magnetic field to 13 T with a swift rump rate of 0.6 T/s without quench. The typical stored energy of the coil reached during the tests was 640 MJ that is 21 times larger than any other superconducting pulsed coils ever built. The test have shown that the high current cable in conduit conductor technology is indeed applicable to the ITER coils and could accomplish all the requirements of current sharing temperature, AC losses, ramp rate limitation, quench behavior and 10 000-cycle operation.

Development of low carbon and boron added 22Mn-13Cr-9Ni-1Mo-0.24N steel (JK2LB) for jacket which undergoes Nb/sub 3/Sn heat treatment

Japan Atomic Energy Research Institute has developed a low carbon and boron added 0.03C-22Mn-13Cr-9Ni-1Mo-0.24N-0.003B steel (JK2LB) for a conductor jacket of the central solenoid for the International Thermonuclear Experimental Reactor in collaboration with Kobe Steel Ltd. The feature of JK2LB is to have enough ductility and toughness after reaction heat treatment to produce Nb/sub 3/Sn. Tensile properties, fracture toughness, and fatigue crack propagation rate were measured at 4 K by using samples taken from an intermediate billet and the final jacket of JK2LB, which were produced with a mass production line. The average elongation and fracture toughness at 4 K after the heat treatment are 33% and 93 MPa/spl radic/m for the final jacket, and 30% and 121MPa/spl radic/m for the intermediate billet, respectively. The mechanical properties of weld metals were also evaluated and all data satisfied the ITER targets. It was also clarified that improvement of ductility and toughness were caused by reduction of chromium carbide precipitations due to low carbon and boron addition.

Test of the NbAl insert and ITER central solenoid model coil

The Central Solenoid Model Coil (CSMC) was designed and built by an ITER collaboration in 1993-2001. Three heavily instrumented Inserts have been also built for testing in the background field of the CSMC. The Nb/sub 3/Al Insert was designed and built by Japan to explore the feasibility of an alternative to Nb/sub 3/Sn superconductor for fusion magnets. The Nb/sub 3/Al Insert coil was tested in the CSMC Test Facility at the Japan Atomic Energy Research Institute, Naka, Japan in March-May 2002. It was the third Insert tested in this facility under this program. The Nb/sub 3/Al Insert coil was charged successfully without training in the background field of the CSMC to the design current of 46 kA at 13 T peak field and later was successfully charged up to 60 kA in 12.5 T field. This paper presents the test results overview.

Demonstration of JK2LB Jacket Fabrication for ITER Central Solenoid

The Japan Atomic Energy Research Institute developed a jacket material called JK2LB (0.03C-22Mn-13Cr-9Ni-1Mo-0.2N-B) for the Central Solenoid (CS) conductor in the International Thermonuclear Experimental Reactor (ITER). To demonstrate production feasibility of CS conductor jacket, trial fabrication of a full size jacket using hot extrusion followed by cold drawing of the JK2LB billets was performed. As a result of dimensional measurement, the ITER dimensional requirement for circle-in-square jacket has been achievable. We achieved the requirement of 0.2% yield strength >1000 MPa and KIC(J)ges130 MParadicm for solution treated + aged jacket. It has been observed that applied cold work strongly affects the toughness of jacket before and after aging. We estimate that C and N reduction will be required to achieve the required strength and fracture toughness for ITER CS jacket. The fabrication R&D has prepared us for mass production of jacket for the ITER CS conductor procurement

Development of high strength austenitic stainless steel for conduit of Nb3Al conductor

Japan Atomic Energy Research Institute (JAERI) started developing new austenitic stainless steel for a conduit (1–2 mm) of a Nb3Al conductor in collaboration with Nippon Steel Corporation (NSC). A high strength austenitic stainless steel is required for a conduit of a Nb3Al conductor to make the best use of superconducting properties of a Nb3Al conductor. JAERI and NSC successfully developed the high strength austenitic stainless steel, JN1 (YS = 1,300 MPa, KIc = 200 MPavm at 4K) for magnet structures having thick section. However, JN1 is not suitable for a conduit material because elongation of JN1 decreases to less than 10 % due to sensitization during reaction heat treatment for Nb3Al. Therefore, modification of JN1 was performed as a first step to develop a new conduit material which withstands Nb3Al reaction heating. Small trial lots heat-treated at 973 – 1173 K for 2 – 200 hours were prepared and evaluated by Charpy impact test and tensile test at 77 K and 4K. A material having yield strength of 1,390 MPa and elongation of 34 % after aging at 973 K × 200 h are developed up to now. This paper describes requirements on the mechanical properties and status of the development work. In addition, empirical equations to predict 4K yield strength, elongation, and Charpy absorbed energy from 77K data are proposed in this paper.

Diagnosis of ITER's large scale superconducting coils using acoustic emission techniques

In 2000, Japan Atomic Energy Research Institute (JAERI) and its collaboration team accomplished many kinds of experiments under the magnetic field of 13 T for the ITER Project. The target coils are the central solenoid (CS) model coil and the CS insert coil. In 2001, the test using both the CS model coil and the toroidal field (TF) insert coil was carried out and successfully finished. During the experiment, we have measured the change in the amount of mechanical disturbances inside the coil using acoustic emission (AE) technology. In this paper, we report the general trend of AE characteristics obtained in the experiments for two years. That is to say, as for the CS model coil, we investigated the training characteristics of the CS model coil that experienced one cooling cycle from 4.2 K to room temperature. As a result, we confirmed the training effect of the CS model coil wound by forced flow CIC conductors. On the other hand, as for the insert coil, some peculiar AE signals were observed during the CS insert coil cyclic test. On this matter, a re-examination was carried out.

Acoustic emission during DC operations of the ITER Central Solenoid model coil

Acoustic emission (AE) signals from the Central Solenoid (CS) model coil developed in ITER program were studied during direct current (DC) operation. Estimation of the AE energy from the coil indicates close correlation between the AE energy and AC losses in the cable-in-conduit (CIC) conductor. This correlation comes from motions of the cables and dc-bonding of strands in the CIC conductors during repeated charging of the coil. The AE measurements clearly indicated the existence of mechanical disturbances even in the cases where the voltage spikes observed in the balance voltages were comparable to the noise level. In the case of the CS model coil, the locations of the mechanical disturbances could be determined using AE signals in combination with information from voltage spikes correlated with the AE signals.

Development of a 13T-46kA Nb3Sn conductor and central solenoid model coils for ITER

Abstract Japan Atomic Energy Research Institute (JAERI) is developing the outer module of the central solenoid (CS) model coils. The Nb3Sn strands and cables for the outer module were almost completed. The winding and the heat treatment technique were established by the trial fabrication. The design of the conductor joint was already finalized by the full size sample test. The first layer of the 8-layer module was wound with enough accuracy by using a two-conductor-in-hand technique. The CS model coil will be completed and tested in 1998.

Evaluation of critical current performance of 13 T–46 kA steel-jacketed Nb3Al conductor

A 13 T-46 kA Nb3Al conductor with steel jacket has been developed in the framework of ITER-EDA. The thermal strain will appear on the Nb3Al strands after heat treatment, when the steel jacket is used because of difference in their thermal expansion. The conductor critical current performance is degraded by this process. The critical current performance of this conductor was then studied to verify no degradation during the fabrication and small deterioration in the critical current performance even when the steel jacket is used. The thermal strain is evaluated to be 2001 Elsevier Science B.V. All rights reserved.