Physics Procedia 45 ( 2013 ) 225 – 228

1875-3892 © 2013 The Authors. Published by Elsevier B.V.Selection and/or peer-review under responsibilty of ISS Program Committee. doi: 10.1016/j.phpro.2013.05.008

*Corresponding author. Tel.:+81-29-270-7540; fax: +81-29-270-7579. E-mail address: koizumi.norikiyo@jaea.go.jp. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.

ISS2012

Progress of ITER superconducting magnet procurement

*N. Koizumi

*JAEA, 801-1, Mukoyama, Naka, Ibaraki, 311-0193, Japan Abstract The ITER superconducting magnet system consists of 18 Toroidal Field (TF) coils, 1 Central Solenoid (CS), 6 Poloidal Field (PF) coils and 18 Correction coils (CC). The TF conductors will be manufactured by China (7%), EU (20%), Korea (20%), Japan (25%), Russia (20%) and US (8%), TF coils by EU (10 coils) and Japan (9 coils), in which one spare is included, all TF coil cases by Japan, all CS conductors by Japan, all CS (7 modules including a spare), PF conductor by China (65%), EU (21%) and Russia (14%), PF coils by EU (5 coils) and Russia (1 coil), all CCs by China and all feeder by China, respectively. Since the TF coil manufacture is one of long-lead items, procurement of the TF conductors have been started. More than 40 TF conductors have already been fabricated. Large-scale trials for TF coil manufacture have also been started and successful results were obtained in both EU and Japan, such as manufacture of full-scale radial plates. The trials for PF coil and CC has been done by Russia and China. © 2013 The Authors. Published by Elsevier B.V. Selection and/or peer-review under responsibility of ISS Program Committee. Keywords: Fusion; ITER; LTS; CICC; Large application

1. Introduction

Fusion has the potential to play an important role as part of a future energy without carbon dioxide or other greenhouse gases. International Thermonuclear Experimental Reactor (ITER) [1] is an important step on the road to fusion power plants and being constructed in France under international collaboration by seven parties, China, EU, India, Korea, Japan, Russia and US. In ITER, which is shown in Fig. 1, huge superconducting magnets are used to confine and control plasma. The ITER superconducting magnet system consists of 18 Toroidal Field (TF) coils, 1 Central Solenoid (CS), 6 Poloidal Field (PF) coils and 18 Correction coils (CC) [2], as illustrated in Fig. 2. To supply current to these coils, superconducting feeders are used.

The TF coils are used for charged particle confinement in the plasma and are operated in a steady current. The CS is used to produce inductive fluxes and to induce plasma current. The PF coils are used to control radial position equilibrium of plasma, as well as for plasma shaping and vertical stability. The CCs are used to correct error field harmonics.

Six parties are working for procurement of superconducting magnets as sharing shown in Table 1.

Fig. 1. ITER

Available online at www.sciencedirect.com

© 2013 The Authors. Published by Elsevier B.V.Selection and/or peer-review under responsibilty of ISS Program Committee.

Open access under CC BY-NC-ND license.

Open access under CC BY-NC-ND license.

226 N. Koizumi / Physics Procedia 45 ( 2013 ) 225 – 228

In this paper, status of procurement of ITER magnet is presented. Since it takes the longest time to manufacture TF coils, the procurement of the TF conductors and TF coils proceeds most. Then, status of TF conductors and coils are mainly described in this paper. 2. ITER conductors and their procurement

All ITER magnets are made by using Cable-in-Conduit Conductors (CICC), which is made up of a multi-stage, rope-type cable jacketed into a stainless steel conduit. Nb3Sn strands are used in the TF and CS conductors while NbTi strands are used in the PF and CC conductors. Cross-sectional views and weight of components of these conductors are shown in Fig. 3 and Table 2, respectively.

As an example, configuration and manufacturing procedure of the TF conductor is explained: The TF cable consists of 900 Nb3Sn strands with 0.82 mm diameter and 522 Cu strands. The cable is inserted in straight conduit, which is made by welding TF conduit sections, as shown in Fig. 4. After insertion, conduit with thickness of 2 mm is compacted in a diameter of 43.7 mm. A central channel exists at center of the conductor cross section to reduce pressure drop of forcibly flowed coolant. The conductor length is 760 m or 430 m. Nominal current and field are 68 kA and 11.8 kA.

The conductor production lines are constructed in China, EU, Japan, Russia and US. The production of the TF conductor proceeds well, as described above, and about 75% of the Nb3Sn strands and more than 40 conductor unit lengths (UL), which corresponds to about one-third, have been manufactured. Japan especially advanced and has completed 26 ULs fabrication out of 33ULs.

Since the CS is required to be operated in 30,000 time pulses, cyclic charge of the order of 10,000 was applied in its qualification test, using short conductors. Large degradation was observed after cyclic charge [3] probably due to bucking of strands at the high field zone, whose length is only 45 cm. The mechanism of this degradation was studied [3, 4] and it was thought that such big buckling occurs due to locally applied magnetic field, which does not happen in the CS. To avoid such buckling, cabling is made tighter, namely short twist pitch is selected and the developed conductor was tested, resulting in disappearing large degradation. Thus, the procurement of the CS strands is now ready to start.

3. Procurement of ITER coils

Although some trial activities for the CS, PF coil and CC are going, the most progress is in procurement of the TF coils, because the procurement of the TF should be started first due to its long fabrication period. The major progress in the TF coil procurement is therefore presented.

Fig. 2. ITER superconducting magnet system

24m

18m

CS

PF coil (6)

TF coil (18)

CCs (18)

Table 1 Sharing of ITER magnet procurement

Items CH EU KO JA RU US

TF conductor TF coil TF coil case CS conductor CS PF conductor PF coil CC Feeder

7% - - - -

65% -

18 100%

20%10 - - -

21%5 - -

20% - - - - - - -

25% 9

100% 100%

- - - - -

20%- - - -

14%1 - -

8%- - - - - - - -

TF conductor CS conductor PF conductor CC conductor

Nb3Sn CICC NbTi CICC

Fig. 3. Cross-sectional view of ITER conductors. (Courtesy by A. Devred in IO)

N. Koizumi / Physics Procedia 45 ( 2013 ) 225 – 228 227

The TF coil is composed of Winding Pack (WP) and coil case, as may be seen in Fig. 5. Both EU Domestic Agency (DA) and JADA have responsibility to procure the TF coils and JADA has responsibility to procure all TF coil cases, as shown in Table 1. The manufacturing process of the TF coil, illustrated in Fig. 6, is as follows: 1) A Radial Plate (RP) is fabricated by joining RP sections; 2) the conductor is wound into a D-shaped DP winding; 3) the conductor is heat-treated at 650 oC for approximately 200 hours; 4) the conductor, wrapped in a multilayer glass-polyimide turn insulation, is inserted into the grooves on both surfaces of the RP, which are finally machined to fit the heat treated conductor winding geometry; 5) a Cover Plate (CP) is welded to the RP teeth which extend between grooves in the RP, to fix the conductor; 6) a Double-Pancake (DP) is wrapped in a multilayer glass-polyimide DP insulation, and the DP insulation is vacuum-pressure impregnated together with the turn insulation; 7) 7 DPs are stacked together and vacuum-pressure impregnated to form a rigid WP after an electrical connection is established among adjacent DPs by means of an inter-DP joint; 8) WP is assembled with sub-assemblies of coil cases; 9) sub-assemblies are closure welded; and 10) gap between a WP and case is filled with resin

Prior to manufacture of the first TF coil, sub-scale and full scale trials have been done to establish manufacturing procedure of the TF coil and TF coil case.

Manufacture of RP starts from fabrication of special thick AISI 316LN plate, RP sections are made from these plates by mainly machining, and these RP sections are joined by welding each other. The required tolerance of the RP is a few milli-meters although its height and width is 14 m and 9 m, respectively. Therefore, development of RP manufacturing technique is challenging. EUDA and JADA collaborate in development activities. Since there are a few candidates to each manufacturing step, for example, hot-rolling, forging or hydraulic isotropic pressure (HIP) for thick 316LN plate manufacture, EUDA and JADA agreed to share development work [5] in order to reduce risk and enhance likelihood of success. Thus, three full-scale RPs were fabricated [6]. Figure 7 shows the RP, which was fabricated in JA.

Another critical issue in the TF coil manufacture is insertion of heat-treated conductor into RP groove. The required tolerance is +/-0.023%. Therefore, automatic D-shaped winding technology with high accuracy of the order of 0.01% conductor length is required. JADA developed optical, on-line measurement system of conductor length during automatic winding. The developed system satisfied this requirement. Thus, JADA performed one-third scale D-shaped winding trial to confirm achievability of the above accuracy and applicability of the developed winding system, as shown in Fig. 8. The conductor winding can be successfully done and conductor could be put between pins simulating RP groove. This result justifies that the conductor length is in +/-0.05%. However, it was indicated from 3D optical measurement that the conductor may be elongated due to plastic bending. It was therefore figure out that final machining RP groove is necessary to fit wound, heat-treated conductor geometry.

Table 2 Weight of conductor components.

Coil Total length (km)

SC strand type

Strand weight (ton)

Jacket weight (ton)

TF 88 Nb3Sn 384 185CS 43 Nb3Sn 122 530PF 65 NbTi 224 900CC/Feeder 10.7/3.7 NbTi 21 22

Fig. 4. Fabrication procedure of ITER CICC.

Sub-assemblies of coil case (200ton)

TFWP inboard

Winding pack (WP) (110ton)

Regular double pancake (rDP) (5 sets)

Side DP (sDP) (2 sets)

CP

DP insulation

CP hole to provide resin to turn insulation

Welding between CP and RP teeth Turn insulation

Conductor

RP

RP groove to insert conductor

9m

Inboa

rd

16.5m

A pair of TF coils Winding pack and coil case

Outbo

ar

Fig. 5. ITER TF coil.

228 N. Koizumi / Physics Procedia 45 ( 2013 ) 225 – 228

The trials for PF coil and CC fabrication is successfully performed by RFDA and CNDA. Since PF coil winding will be done on-site due to their huge winding diameter, a building for PF coil fabrication was constructed in the ITER site. 4. Summary

ITER is important step for fusion energy, which is one of candidates of future energies, and ITER project has been started under international collaboration among seven parties. Magnets are first procured because of its long duration for manufacture. The ITER conductor procurement has been started and is the most advanced in ITER. Trials for the TF coil and TF coil case has started and manufacturing procedure to solve technical issues found in trials are being established. These positive results promise success of ITER magnet procurement. References [1] ITER, Project report (On line). Available: http://www.iter. [2] N. Mitchell, D. Bessette, R. Gallix, C. Jong, J. Knaster, P. Libeyre

et al., “The ITER magnet system,” IEEE Trans. Appl. Supercond., 18 (2008) 435-440

[3] T. Hemmi, Y. Nunoya, Y. Nabara, M. Yoshikawa, K. Matsui, H. Kajitani et al., “Test results and investigations of TCS degradation in ITER CS conductor samples, IEEE Trans Appl. Supercond., 22 (2012) 4803305

[4] H. Kajitani, T. Hemmi, H. Murakami, N. Koizumi, “Analytical study of degradation of CIC conductor performance due to strand bending and buckling,” To be published in IEEE Trans. Appl. Supercond., Vol. 23, 2012.

[5] N. Koizumi, K.Matsui, T. Hemmi, K.Takano, Y. Chida, M. Iguchi, et al., “Development of ITER TF Coil in Japan,” 22 (2012) 4200404

[6] E. Barbero Soto, B. Bellesia, A. Bonito Oliva, E. Boter, “Status of the F4E Procurement of the EU ITER TF Coil,” 22 (2012) 4200206 Fig. 6. ITER TF coil manufacturing procedure.

Fig. 7. Full-scale RP made by JADA. Fig. 8. One-third scale DP made by JADA. The conductor put in pins to simulate RP groove.