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The optimization of the heat treatment of \Nb3\Sn conductors for toroidal field coils in ITER was attempted to improve the current sharing temperatures (Tcs). Using the strand, we chose the pattern at 570  ^\circ\C for 250 h and 650  ^\circ\C for 100 h as the best, which increased the critical current and maintained the residual resistivity ratio higher than 100. The behavior of the critical current of the strand vs. the magnetic field, temperature, and strain was also improved. This pattern was used on two conductors, and their performances were tested. Tcs was evaluated over 1000 electromagnetic cycles and one thermal cycle. A sharp Tcs degradation occurred at 50 cycles. Then Tcs decreased linearly. Although this tendency was similar to the conductors that were heat treated with the original pattern, the degradation rates were improved. The ac losses (Q) before cycling were approximately 10% lower than those of the original pattern. Q after cycling became almost equivalent between two patterns. The conductor was inspected after the test, which showed that the conductor under the high-magnetic-field zone had contracted by approximately 600 ppm during the test. Some clearly deformed strands were observed under the high-magnetic-field zone, which could degrade Tcs. [ABSTRACT FROM PUBLISHER]

The performance of four \Nb3\Sn conductors for the ITER central solenoids was tested. The current sharing temperatures (Tcs) were measured over approximately 9000 electromagnetic cycles, including two or three thermal cycles between 4.2 K and room temperature. Tcs increased and became almost constant through the cycling. The gradient of the electric field against the temperature gradually decreased against cycling. The degradations caused by the electromagnetic force of the short twist pitch conductors were smaller than that of the original twist pitch conductor. The ac losses of short twist pitch conductors were several times higher than that of original twist pitch conductor. The dents and the removals of the Cr plating on the strands, which were formed during cabling, decreased the electric resistance between strands, which may cause the observed high ac loss. Inspection of the cable showed neither a clear bias of cable in the cross-sectional surface nor distorted strands in the lateral face. The high rigidity of the short twist pitch cable could prevent these plastic deformations, caused by the Lorentz force. [ABSTRACT FROM PUBLISHER]

The performances of six Nb3Sn conductors for the ITER Toroidal Field coils were tested. Four of them showed similar degradation rates of their current sharing temperatures Tcs over 1,000 electromagnetic cycles. By contrast, two of them showed sharp Tcs degradations at 50 cycles, after which their slopes became similar to those of the other four conductors. These two cables seemed to shrink under high magnetic fields during the first 50 cycles, which caused the sharp Tcs degradation. This shrinkage might arise from a decline in cable rigidity due to, for example, the deformation of strands or the breakage of the Nb3Sn filaments. The four mass-produced conductors had roughly the same AC loss before cycling. After 1,000 cycles, the AC losses of all the conductors decreased markedly to less than half of those before cycling, and the values became approximately the same. After the test campaign, the destructive inspection of two of the conductors made it clear that the conductor had shrunk by about 520 ppm under the high magnetic field during the test. It was also clarified that some strands were visibly deformed under the high magnetic field, whereas those under the low magnetic field did not look distorted. This plastic deformation of the strands could be one of the major reasons for the Tcs degradation with cyclic operation. [ABSTRACT FROM PUBLISHER]

A new generation of ITER TF conductor samples has been assembled and tested in SULTAN in 2007 following a common procedure agreed among the ITER parties. The test results of six SULTAN samples, made of twelve conductor sections manufactured in Europe, Japan, Korea and Russia, are reported here. The conductor layout reflects the ITER TF conductor design, with minor differences for the Nb3 Sn strand characteristics, void fraction and twist pitch. The object of the test is a straight comparison with the ITER requirement of 5.7 K current sharing temperature at 68 kA current and 11.3 T field. A broad range of behavior is observed. [ABSTRACT FROM AUTHOR]

In this paper we discuss the predictive analysis performed in support of the test program of the International Thermonuclear Experimental Reactor (ITER) Poloidal Field Conductor Insert (PFCI). A subset of the test program items was considered, with particular emphasis on DC performance and AC losses. The results and implications of the comparison of selected predictions from different laboratories will be presented. [ABSTRACT FROM AUTHOR]

Cryogen-free superconducting magnets are becoming popular due to their simple operation compared with the conventional liquid Helium cooled magnet. However, for higher fields such as those greater than 14 T, the cryogen-free magnet has not become popular yet, because it is difficult to design and manufacture since the critical current is markedly reduced at higher fields and higher temperatures. We have developed two types of 15 T cryogen-free superconducting magnets, which will be among the highest field magnets in operation as cryogen-free with a GM cryocooler. One magnet has a 52 mm room temperature bore with overall dimensions of 820 mm in diameter and 680 mm in height. This magnet is designed so as to be simple in both operation and installation. Therefore, the magnet is cooled with a single 1 W GM cryocooler. Also, all coils are connected in series and charged with a single power supply. The magnet was successfully charged up to 15 T in 30 minutes and then charged slowly to 16 T without quench. The other magnet has a 170 mm room temperature bore with overall dimensions of 980 mm in diameter and 1015 mm in height. This magnet is designed so as to be used with temperature controlled sample cryostats with an outer diameter of 168 mm. The magnet is cooled with four 1 W GM cryocoolers and charged with a single power supply. The magnet was successfully charged up to 15 T in 90 minutes. Both magnets will enable high magnetic field research or application with very easy operation. [ABSTRACT FROM AUTHOR]

Abstract: We have proposed a new cryocooler system for the high temperature superconducting (HTS) bulk magnet. In this system, the cyclic temperature variations are generated. A change of magnetic trapped flux under the cyclic temperature variation is examined in detail. As a result, it has been found that the trapped flux mainly deteriorates at the first temperature rise, but it has been kept almost constant after the first temperature descent and following thermal cycles when the bulk is excited at 100mT. Moreover it has been found that the change of the trapped flux at the excitation of 130mT becomes same as the case of 100mT. The deterioration at the first temperature rise can be explained by the Bean model, but we can find a difference between calculated results by the Bean model and experimental trapped flux distributions near the center of the bulk. Therefore, we take into consideration a two dimensional invasion of the magnetic field to explain the difference. Consequently calculated distributions of the trapped flux become in goal accordance with experimental ones. [Copyright &y& Elsevier]

Higher magnetic field of a Toroidal field (TF) coil in a tokamak fusion reactor can offer better performance of the reactor. Therefore, fusion magnet development always drives a new superconductor to be used in a large magnet on an industrial basis. Magnets for the International Thermonuclear Experimental Reactor (ITER) use Nb3Sn in order to generate a peak magnetic field of 13 T. Technologies for Nb3Sn superconductor has made a significant progress through the extensive development in ITER including the manufacture of model coils. A next generation superconductor, Nb3Al, has outstanding features of large critical current density at higher field and smaller degradation of the critical current due to a strain compared to Nb3Sn. High temperature superconductor (HTS) is another candidate, and if it becomes available, a magnetic filed above 20 T can be realized in a large magnet. These materials have the possibility of being used for high performance fusion reactors. [Copyright &y& Elsevier]

Development of Nb3Sn cable-in-conduit (CIC) conductors with stainless steel (SS) jackets for the central solenoid (CS) and divertor coil of the superconducting tokamak called JT-60SC, is presented. Full-size and subsize conductors were manufactured using two types of high-copper-ratio and high-Jc strands made by different processes (bronze and internal-tin). Use of a SS jacket causes decrease of critical current of the conductor because compression strain due to difference of the thermal contraction between the SS jacket and Nb3Sn cable is generated. The strains are estimated from the results of critical current measurements using short full-size samples which were pool-cooled. In order to investigate Jc - B - T characteristics of a CIC conductor, a novel apparatus, which can control the temperature and magnetic field, has been developed. This apparatus makes it possible to measure directly the critical current and temperature of a subsize conductor, which is composed of two superconducting strands, one copper wire and a SS jacket. Strains of the subsize conductors are estimated from the results of the J3 - B - T characteristic measurements. By comparison of the estimated strains between the full-size and subsize samples, we concluded that the characteristics of the full-size conductor can be predicted by measuring of J3 -. B - T characteristics of subsize conductors. Finally, the strain of the actual conductor under the operational condition is estimated. The result confirms that the developed conductors are applicable to CS and divertor coil of JT-60SC. [ABSTRACT FROM AUTHOR]

The ITER Central Solenoid (CS) is 12 m high and 4 m in diameter. The CS consists of a stack of 6 electrically independent modules to allow control of plasma shape. The modules are compressed vertically by a p re-compression structure to maintain contact between modules. The CS conductor is CIC conductor with Nb3 S ii strands and a steel conduit. The CS model coil and insert coil test results have shown that the conductor design must be modified to achieve an operation margin. This required either to increase the cable diameter or to use strand with a higher current capability. A bronze-process (NbTi)3Sn strand is proposed to achieve a higher critical magnetic field. A square conduit with a high Mn stainless steel is proposed as it can satisfy fatigue requirements. The inlets are in the high stress region and any stress intensification there must be minimized. The preload structure is composed of a set of tie-plates, flanges, buffer plates, and wedges. These design proposals satisfy all ITER operational requirements. [ABSTRACT FROM AUTHOR]

Cable-in-conduit conductors (CICC) consisting of about 1000 Nb3 Sn strands with an outer diameter of about 0.8 mm, have been designed for the TF and CS coils of the ITER. The rated currents of these coils are 68 and 40 kA, respectively. Two joint types (Butt and Lap) were developed during the CS Model Coil project. The performance of these joints was evaluated during the operating tests and satisfactory results were obtained. The joints of the TF coils are located outside of the winding in a region where the magnetic field is about 2.1 T, a very low value as compared to the maximum field of 11.81 at the winding. The CS joints are located at the coil outer diameter and embedded within the winding pack to minimize the space occupied around the coil. The maximum fields at the CS joint and winding are 3.5 and 13 T, respectively. For the TF coils and the CS, the joints are cooled in series with the conductor at the outlet. The maximum allowable temperature increase due to the joule heating in the joints is 0.15 K to reduce the heat load on the refrigerator. The stability of these joints at the ITER operating condition was analyzed by using the experimental data. The analysis shows that both joint types are applicable to the full size ITER coils. [ABSTRACT FROM AUTHOR]

In 2000, Japan Atomic Energy Research Institute (JAERI) and its collaboration team accomplished many kinds of experiments under the magnetic field of 13T 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 of 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. [ABSTRACT FROM AUTHOR]

Abstract: Modern scanning magnetic microscopes have the potential for fine-scale magnetic investigations of rocks. Observations at high spatial resolution produce large volumes of data, and the interpretation of these data is a nontrivial task. We have developed software using an efficient magnetic inversion technique that explicitly constructs the spatially localized Backus–Gilbert averaging kernel. Our approach, using the subtractive optimally localized averages (SOLA) method (Pijpers, R.P., Thompson, M.J., 1992. Faster formulations of the optimally localized averages method for helioseismic inversions. Astronomy and Astrophysics 262, L33–L36), yield a unidirectional magnetization. The averaging kernel expresses the spatial resolution of the inversion and is valuable for paleomagnetic application of the scanning magnetic microscope. Inversion examples for numerical magnetization patterns are provided to exhibit the performance of the method. Examples of actual magnetic field data collected from thin sections of natural rocks measured with a magnetoimpedance (MI) magnetic microscope are also provided. Numerical tests suggest that the data-independent averaging kernel is desirable for a point-to-point comparison among multiple data. Contamination by vector magnetization components can be estimated by the averaging kernel. We conclude that the SOLA method is a useful technique for paleomagnetic and rock magnetic investigations using scanning magnetic microscopy. [Copyright &y& Elsevier]

Abstract: A design study of the TF coil for the fusion DEMO plant at JAERI is in progress. A major issue is to estimate the maximum fields generated by the TF coils for three tokamak options and two conductor options. Three tokamak options are proposed varying the aspect ratio and the role of the CS coil. Two kinds of conductors using advanced superconducting materials are candidates for the TF coils: Nb3Al and high temperature superconductor (HTS). In order to evaluate achievable magnetic fields, a simple method was adopted to calculate mechanical properties. The estimated maximum fields are 17–20T by the HTS conductor and 16–17T by the Nb3Al conductor. There is a possibility of a 0.7T enhancement using grading of Nb3Al winding. [Copyright &y& Elsevier]

Abstract: Research and trials by the Japan Atomic Energy Agency (JAEA) focus on the remaining technical issues in the ITER TF coil winding pack (WP) manufacturing process. Specific issues include the feasibility of automatically measuring conductor length during automatic winding with a high degree of accuracy (±0.02%) and a fabrication process to comply with the demanding tolerances (up to 1mm distortion in flatness and 1.5mm in-plane shrinkage) of the radial plate (RP) due to cover plate (CP) welding. The authors developed a new technique to measure conductor length very accurately by combining an ordinary encoder and a newly developed optical system. A simulation based on test results of CP welding using a RP mock-up indicates that a flatness of 1mm is achievable, but the in-plane shrinkage of the RP is approximately 5mm. One possible solution is to fabricate the RP larger than required to allow for in-plane shrinkage. Another solution is to reduce the thickness or length of the welding. The feasibility of these solutions to most of the major technical issues suggests that it is time for full qualification testing of the fabrication process in a dummy double-pancake trial. [Copyright &y& Elsevier]

Abstract: Nb3Al has advantages of better tolerance to strain/stress and a higher critical magnetic field (30T at 4.2K) for stoichiometric composition over Nb3Sn. The rapid-heating, quenching and transformation annealing (RHQT) process enables to form a stoichiometric Nb3Al with fine grain structures via metastable bcc supersaturated-solid-solution. As a result a large critical current density of Nb3Al is achieved over the whole range of magnetic fields without trading off the excellent strain tolerance. A long-length of RHQ processing has been established, and a rectangular but Cu stabilized Nb3Al strand is about be commercially available for NMR uses. Ag or Cu internal stabilization and Cu ion-plating/electroplating techniques have been also developed to enable the stabilized round wire for accelerator and fusion magnets. Successfully energized test coils that were manufactured with a wind-and-react technique have demonstrated that a long piece of Cu stabilized RHQT Nb3Al wire is really available for practical applications. [Copyright &y& Elsevier]

Abstract: In order to clarify the limitation of bending strain in conductor to fabricate the toroidal field coils of DEMO reactor by react-and-wind (R&W) method, the effect of bending strain on the critical currents (I c) of Nb3Al cable-in-conduit (CIC) conductor was investigated using the newly developed apparatus which can bend cooled sample from outside of cryostat. The Nb3Al strand manufactured by jelly roll process was 0.74mm in diameter with the copper/non-copper ratio of 4.0. The CIC conductor sample which consisted of 54 Nb3Al strands and 27 copper wires inserted into a stainless steel conduit was 12.4mm in diameter and 2.3m in length. The CIC conductor was wound into a torsion coil spring shape with 4.5 turns and 150mm in diameter. The bending strain and external magnetic field ranges for I c measurement were from 0% to 0.6% and from 9.2T to 11.3T, respectively. It was clearly shown that the I c decrease of the CIC conductor by bending is considerably low compared with that of strand, indicating the relaxation of intrinsic strain in Nb3Al filaments in CIC conductor due to the cabling effect. The I c was not decreased up to 0.4% in bending strain and slightly decreased to 96% of initial I c at 0.55% in bending strain. This indicates that the R&W method with bending strain of 0.6% is fully applied to the coil fabrication method. The furnace size for heat-treatment for R&W method becomes half of wind-and-react (W&R) method. [Copyright &y& Elsevier]

The Poloidal Field (PF) coils of ITER (International Thermonuclear Experimental Reactor) will supply the necessary magnetic field to initiate, shape, control and shutdown burning plasmas. The PF coils use NbTi cable-in-conduit superconductors, which operate at maximum currents of the order of 45–60 kA and experience large variations of current and magnetic fields. In order to test full-scale NbTi superconductors at operational conditions similar to ITER, the European Team has been asked to design and manufacture a PF conductor insert (PFCI). The cable has been provided by the Russian Federation. The Insert will be tested in 2004 in the Central Solenoid Model Coil (CSMC) facility at JAERI Naka, Japan. [Copyright &y& Elsevier]