In Japan, 9 ITER TF coils for Japan and 10 TF coil cases (CCs) for EU are procured from two suppliers. In the second manufacturing line (ML), some of manufacturing procedures were optimized and/or ...rationalized from lessons learned from the experiences in the first ML. These efforts contributed to simplification and acceleration of the fabrication of the ITER TF coil in the second ML and then, the first ITER TF coil has been completed in May 2021 in the second ML. In addition, the most challenging processes in TF coil fabrication such as very accurate current center line positioning and proper gap between a winding pack (WP) and CC, more than 4 mm were achieved in assembly of WP and CC, as well as the first ML. These results justified the validity of the optimized and rationalized manufacturing procedure in the second ML. Therefore, we can say that manufacturing in both first and second MLs in Japan has become stable. Actually, four and two TF coils have been completed in the first and second MLs in Japan, respectively.
Small magnets using 18-m class mono-core (Ba,Na)Fe 2 As 2 and seven-core (Ba,K)Fe 2 As 2 round wires were constructed. Wires used in these magnets were fabricated using powder-in-tube method followed ...by hot isostatic pressing process. Both magnets show zero resistivity at low currents, and strong increase in resistance shows up at 47-53 A. Generated magnetic fields at these currents were 3.1 kOe and 2.7 kOe for magnets using mono-core (Ba,Na)Fe 2 As 2 and seven-core (Ba,K)Fe 2 As 2 round wires, respectively. Short pieces of the long wires used for the magnets were evaluated independently after disassembling the magnets. It turns out that critical current ( I c ) varies significantly along the length of the wire, and the largest I c reaches 160 A in mono-core (Ba,Na)Fe 2 As 2 wire. X-ray tomography observations of the wires revealed severe sausaging effect even in a few mm length scale, which could be the reason for the large variation of I c along the entire length of the wire. We also evaluated the effect of bending strain on mono-core and multi-core (Ba,Na)Fe 2 As 2 wires. Effects of bending strain turns out to be modest, and more than 60% of I c was sustained even at the bending strain of 0.5%.
Abstract
Characterizations of round wires of iron-based superconductors were performed by using two different X-ray techniques. The core of the round wire turns out to be concentrically textured. The ...texturing parameter (
r
) defined by
r
=
I
(002)/
I
(103) has a clear correlation with the value of the critical current density (
J
c
) of the wire. Using ~18 m-long (Ba,
A
)Fe
2
As
2
(
A
: K, Na) wires, small magnets was constructed and successfully generated a magnetic field as large as 3.1 kOe at
I
= 53 A. The wire for the magnet was carefully cut and local variation of the critical current (
I
c
) was evaluated. Variation of the core area was also measured by using X-ray tomography for the segments with the largest and smallest
I
c
. Obtained images demonstrates that the core has a certain degree of sausaging effect and it has good correlation with
I
c
of the wire. Using the largest value of measured
I
c
and the minimum core area of that segment, record-high value of
J
c
= 71 kA/cm
2
at 100 kOe has been achieved.
Abstract
Joint sample tests have been carried out as a qualification test for ITER Toroidal Field (TF) coils. The joint sample comprises two short TF conductors that have “twin-box” joint terminals ...at both ends. The lower joint is a testing part that is a full size joint of the TF coils. Hall probes are attached on the lower joint box at around the center of the external field coil of the test facility. The magnetic field induced by shielding currents in the joint can be estimated from the difference between the measured magnetic field strength and the magnetic field generated by the external field coil. The magnetic field by the shielding currents during shut-off of the external field coil from -1.0 T is evaluated for six samples. The decay time constants of the shielding currents are gradually elongated with decrease of the shielding currents in all the samples. In comparison with simulation results, it is considered that the main shielding current flows in superconducting cables in the two conductors with crossing the jointed plane and that the joint resistance is decreased at low total current.
We fabricated superconducting coils using 10-20 m-class round wires of 122-type iron-based superconductors (IBSs). Round wires and coils are fabricated by powder-in-tube method and ...hot-isostatic-press technique. Transport critical current (Ic) of the whole (Ba,K)Fe2As2 coil is 46 A under the self-field at 4.2 K, and magnetic field at the center of the coil reaches 0.3 T. Although the edge of the long wire in the coil is damaged, the rest of the part is relatively homogeneous. Furthermore, the largest transport critical current density (Jc) and Ic in (Ba,K)Fe2As2 wires picked up from the coil reach 49 kAcm−2 and 44 A at 4.2 K under a magnetic field of 10 T, respectively. This value exceeds the previous highest transport Jc of (Ba,K)Fe2As2 round wires. We also fabricated a (Ba,Na)Fe2As2 coil using long round wire with large superconducting core by react and wind method. Transport Ic of the coil is significantly low due to cracks perpendicular to electric current flow direction, although magnetic Jc in the round wire picked up from the coil reaches 40 kAcm−2 at 4.2 K under 4 T.
We fabricated round wires and tapes of (Ba,Na)Fe2As2 using hot isostatic press (HIP) process, and evaluated their critical current density (Jc). Polycrystalline powders were synthesized by two ...methods by mixing raw materials in a planetary ball mill or by using pre-synthesized precursors (BaAs, NaAs, Fe2As). Transport Jc of best wire reached 95 kA/cm2 under self-field and 40 kA/cm2 at 100 kOe. We also fabricated HIP tapes using the same powder and discuss their detailed characterizations. In particular, X-ray diffraction is extensively applied to the evaluation of the degree of texturing of the tape, and discuss its relationship with Jc.
We have fabricated round wires of Baa0.6Na0.4Fe2As2 using powder-in-tube technique and hot isostatic press (HIP) treatment. Transport Jc was measured at 4.2 K of two Ba0.6Na0.4Fe2As2 round wires with ...Ag/Cu double sheath which were processed at 700 °C for 4 h at 175 MPa. Transport Jc of one of the wires reached 76 kA/cm2 and 24 kA/cm2 at self-field and 100 kOe, respectively, while Jc of another wire is slightly larger at low fields. It means that Jc of Ba0.6Na0.4Fe2As2 wire is resilient against large magnetic field, which demonstrates very promising characteristics of this material. Detailed characterizations of wires using X-ray diffraction and compositional mapping by EDX are also presented. We also explore the better condition for synthesis of Ba0.6Na0.4Fe2As2 by changing the reaction temperature.
We report the fabrication and characterizations of KCa2Fe4As4F2 round wires for the first time. Polycrystalline KCa2Fe4As4F2 powder was prepared by solid-state reaction. Superconducting wires were ...fabricated by powder-in-tube (PIT) method followed by hot-isostatic-press (HIP) technique. The self-field Jc of the KCa2Fe4As4F2 HIP wires fabricated at 700 and 740°C at a high pressure of 9 MPa for 0.5 h, reached 10 kAcm−2. Although high-pressure sintering at high temperatures enhanced the Jc and density of the core of the wires, X-ray diffraction and scanning electron microscopy-energy-dispersive X-ray spectroscopy analyses indicated that impurity phases were present both in the polycrystalline powder and in the core of the wire.
•Series production of double-pancakes (DPs) for TF coil is in process.•Winding of 17 DPs, heat treatment of 16 DPs, fabrication of 15 radial plates (RP), transfer of 11 DPs, cover plate (CP) welding ...of 9 DPs and DP impregnation of 6 DPs were finished and acceptance tests of 5 DPs were successfully completed before end of September, 2016.•In addition, tight tolerances, such as ±0.01% accuracy in conductor length for winding, 1mm flatness in RP fabrication, about 2.5mm (2.1–2.6mm) flatness after 1.5km CP welding and 2mm flatness of completed DP, could be achieved.•These results justify that series production of TF coil DP in Japan is going well.
National Institutes for Quantum and Radiological Science and Technology, (QST), as Japan Domestic Agency, has responsibility to procure 9 ITER Toroidal Field (TF) coils. QST completed proto double-pancake (DP) trials aiming at qualification and optimization of manufacturing procedure of TF coil in 2015. Series production of DPs then started and winding of 17 DPs, heat treatment of 16 DPs, fabrication of 15 radial plates (RP), transfer of 11 DPs and cover plate (CP) welding of 9 DPs were completed by end of Sep. 2016. Challenging tight tolerances in conductor length, ±0.01%, was achieved to enable transfer of heat-treated conductor into RP groove. 1mm flatness was achieved in RP, whose height and width are 13m and 9m. In addition, about 2.5mm flatness was achieved after CP welding by optimizing welding sequence. The DP insulation and impregnation were successfully completed on 5 DPs. The flatness of 2mm could be achieved for all DPs completed so far and this makes DP stacking easier. These results justify that series production of TF coil DP in Japan is going well.
We report the fabrication of 10 m-class (Ba, Na)Fe2As2 long round wires and coils using these round wires. Round wires are fabricated by powder-in-tube (PIT) method and hot-isostatic-press (HIP) ...technique. To increase Ic keeping the diameter of the wire constant, the cross section area of the superconducting core is enlarged by changing the dimensions of metal sheaths. At 4.2 K under a high field of 100 kOe, Jc of a short segment of HIP wire reaches 42 kAcm-2, which is comparable to the highest Jc of IBS round wires of 44 kAcm-2. Furthermore, Ic of the HIP wire at 4.2 K under 10 kOe and 100 kOe reaches 95 A and 54 A, respectively, which is about twice the value of the previous report. We also fabricated a small demonstration superconducting coil using 12.5 m long PIT wires by HIP method. Ic of the whole coil is ∼60 A under the self-field, and magnetic field at the center of the coil reaches 2.6 kOe. The coil generated the magnetic field of 43 Oe/A, which is almost consistent with the calculated field from the coil dimensions.
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