1 FIP/1-4Rb Research, Development and Production of ITER Toroidal - - PDF document

1

FIP/1-4Rb Research, Development and Production of ITER Toroidal Field Conductors and Poloidal Field Cables in Russia

V.S. Vysotsky, K.A. Shutov, A.V. Taran, I.F. Chensky, L. V. Potanina, D.S. Kaverin, and G.G. Svalov Russian Scientific R&D Cable Institute, 111024, Moscow, Russia E-mail contact of V.S. Vysotsky: vysotsky@ieee.org

• Abstract. Russian Scientific Research and Development Cable Institute (known by Russian abbreviation as

VNIIKP) have been participating in ITER project since 1993 both at the early stage of Research and Development (R&D) and at the following stage of Engineering Design Activity (EDA). Tests of several short samples at Sultan test facility were crowned by successful testing of Toroidal Field and Poloidal Field insert coils performed in Japan in 2001 and 2008 correspondingly. Now VNIIKP is actively implementing the final production and delivery stage. After completion in 2009 of the full technological complex to produce PF cables for both the Russian Federation and European parts and TF conductors for RF part VNIIKP passed all qualification and certification procedure demanded by Procurement Arrangements. Right now the production and delivery of PF cables and TF conductors are in the full steam and going to be concluded in 2015. We are presenting the development of technology; results of R&D accompanied developments and the results of production and delivery of the cables and conductors for magnet system of ITER.

• 1. Introduction

Since 1993 Russian Scientific Research and Development Cable Institute (VNIIKP) has been participating in ITER project. During R&D at EDA stage we developed several types of multi- strand cables and Cable-In-Conduit Conductors (CICC) and tested full size Toroidal Field (TF) and Poloidal Field (PF) insert coils. [1]-[6]. The experience gained during R&D stages permitted eventually to develop the industrial technology complex for regular manufacturing

• f the TF conductors and PF cables. Some details about technology complex were presented

earlier in [7]-[9]. The general technology route for PF cables and TF conductors is as follows: According to the RF Domestic Agency (DA) internal cooperation, the bare NbTi and Nb3Sn strands for cables and conductors are produced by Chepetsk Mechanical Plant (ChMP) in Glasov city and then delivered to VNIIKP. Before cabling the NbTi strands have to be coated by nickel and Nb3Sn strands have to be coated by chromium. Copper wires used for fabrication of PF and TF dummy cables and in TF cables have to be coated by chromium as

• well. Then basic wires are moved to the cabling workshop for the five stage cabling. After

cabling the PF cables are delivered to International Consortium of Superconductivity (ICAS) facility in Chivasso city in Italy for jacketing to a rectangular jacket. ICAS is the sub- contractor for Fusion for Energy which is European Domestic Agency for ITER. TF cables are delivered to VNIIKP jacketing line located at the Institute for High Energy Physics in Protvino city [7], [9]. When TF conductors are produced and wound in a transport solenoid with 4 m in diameter, they are delivered to NRC “Kurchatov Institute” for final leak test [9]. After leak test the TF conductors are delivered to ASG Company in La Spezia, Italy for production of TF coils. Before we came over to the production stage the heavy qualification procedures have been

• passed. All technology procedures and processes were verified by independent experts,

2

FIP/1-4Rb

described and approved by International organization (IO) of ITER as it is demanded by our Procurement arrangements (PA) [10]. The staff working in sensitive Quality Assurance areas like welding, X-ray check, vacuum check, etc. passed examinations and certifications from independent experts nominated by IO as well. Also 5 dummy PF cables and 2 TF conductors were produced and delivered as part of qualification procedures. Only after all qualifications and certifications were passed, we were allowed to start regular production and delivery of both PF cables and TF conductors in 2011. Besides development of new technologies and production of superconducting cables and conductors we are performing several R&D studies. Particularly, study of Residual Resistance Ratio (RRR) changes during production processes [11], [12], untwisting of cables during their insertion to a jacket [13], [14], study of microstructure of Nb3Sn strands after their test at SULTAN test facility [15], etc. In this review we present the current data on the cables and conductors production state. Some results from our R&D are presented as well.

• 2. Strands coating

In accordance with PAs before cabling the NbTi strands have to be coated by nickel and Nb3Sn strands have to be coated by chromium. Copper wires used for fabrication of PF and TF dummy cables and in TF cables have to be coated as well. Before this, strands and wires should be cleaned to prepare their surface for high quality coating. The two stage coating technology is described in details in [7], [8]. Two electro-chemical cleaning line has been installed to increase the cleaning efficiency. Entire production capacity permits now to clean up to 45 km of Cu wires and superconducting strands per day. One line for Ni coating (Fig.1 a) and three lines for Cr coating (Fig.1 b) were developed and installed. The linear capacity of Ni-coating line is ~100 m/min; the capacity of a single Cr-coating line is ~30-40 m/min. The tightly adjusted chemical coating processes developed in VNIIKP together with fully qualified verification procedures ensure the required quality of plated strands, i.e. clean surface free of any defects before plating, thickness of layer within 1.5-2.0 µm, good cohesion

• f plating without any flaking, designed diameter tolerance. Entire technological route has

initial, intermediate and final check points for verification and confirmation the quality of strands demanded. The quality of plated strands is shown in Fig. 1. Up to October 2014 about 33 600 km of Ni-coated NbTi strands and about 27 400 km of Cr – coated Nb3Sn strands have been produced. a b

Fig.1. a - Ni-plating facility and nickeled NbTi strand; b - Cr-plating facility and chromed Nb3Sn strand

We have to note that our coating processes are based on a soft technology, consuming not more than 100 liters of distilled water for a fourteen hours working day, and have no leakages

• r discharge to a main drain.

3

FIP/1-4Rb

• 3. Cabling

The general cabling route of TF ITER cable is illustrated in Fig.2 as an example. One can see that cables have inner spiral, five stages twisting and stainless steel tape wrapping at the fourth and fifth stages. To complete all these process the spiral production and the cabling workshop have been arranged in VNIIKP. 3.1 Spiral production Both PF and TF cables contain central cooling spirals. The special spiral making machine has been developed to produce long length spirals with diameters from 8 to 14 mm [9]. The photos of the spirals produced are shown in Fig.2. By the October 2014 we have produced in total more than ~45 km of spirals for our own needs, and ~15 km of TF spiral were delivered for USA DA and ICAS teams.

Fig.2. General view of the TF five-stage cabling process. PF cables have similar five stage cabling process but without copper strands. Fig.3 Spirals for ITER: PF cable spiral (up) and TF cable spiral (below)

3.2 Cabling machines Our cabling workshop is equipped by two high speed tubular machines for the first and the second stages twisting. Two planetary machines with wrappers for the third and the fourth stages twisting can produce up to 10 km of third stage sub-cables a day and up to 1.5 km of fourth stage sub-cables a day. The final twisting is being performed at the large planetary machine with wrapper that is able to perform final twisting of ~800 m cable during 3-5 days. This machine is equipped with three special multi – rollers compacting calibers to provide exact diameter and the required density of a cable pack before jacketing. The photos of our cabling machines are shown in

• Fig. 4.

3.3 PF Cabling Status In accordance with agreement between European Union (EU) and Russian Federation, RF produces all NbTi cables for PF1 and PF6 poloidal field coils, while EU performs jacketing of all cables for the coils mentioned. In total VNIIKP has to produce 41 unit lengths of PF cables (including 5 dummy cables) with lengths 414 m and 734 m for both PF6 and PF1 poloidal

• coils. Right now the production of PF cables in VNIIKP is going in a full steam. Our cabling

process has successfully passed all qualification procedures. In Fig. 5 the photo of PF cable sample consisting of 6 sub-cables is shown before final wrapping by stainless steel tape and in Fig.6 PF cables produced and ready for delivery are shown.

4

FIP/1-4Rb

By the October 2014 we produced 28 PF cables of 41 necessary. 19 cables have been delivered to ICAS facility in Chivasso and jacketing process for PF6 and PF1 conductors has been started there. a b c

Fig.4. Cabling machines at VNIIKP cabling workshop. a – high speed tubular machines for 1 and 2 stages; b – medium planetary machine for 3 and 4 stages, c – large planetary machine for 4 and 5 stages

• Fig. 5. PF cable sample consisting of

6 sub-cables (“petals”) before final wrapping by SS tape.

• Fig. 6 PF cables on drums prepared for delivery (left) and

loading them to deliver to ICAS (right).

3.4 TF Cabling Status We have successfully passed the TF cabling qualification and preproduction phases II and III

• f PA. The 760 m long Cu dummy cable and 120 m superconducting dummy cable have been

fabricated in 2010 and sent to the jacketing line. Every unit length of cables underwent to destructive examination for checking the conformity

• f cable components and twist pitches. Samples were cut from a head and a tail of every
• cable. After these examinations we can say, that all cables, which were manufactured in

VNIIKP, fully comply with the PA specification. Also we can say that throughout the entire length a cable design and twist pitches were kept without deviating from the values specified in PA. Up to now 24 TF cables (including two dummies) of 28 cables necessary have been produced and sent to jacketing line.

• 4. Jacketing and TF Conductor Status

The jacketing line to produce the TF CICC is located at Institute for High Energy Physics territory in Protvino-city ~100 km south from Moscow and consists of a gallery with ~900 m length shown in Fig. 7 and a workshop where the equipment for welding, testing, compaction and coiling is placed. A view of the workshop with automatic welding machine, X-ray

5

FIP/1-4Rb

camera, vacuum test camera, TV equipment for internal checking of tubes and other production and testing equipment is shown in Fig.8.

Welding line Compacting line X-ray camera

• Fig. 7. View of the 900 m gallery with stainless

steel tubes prepared for TF cable insertion and compaction.

• Fig. 8. A view of the workshop of the jacketing

line located at IHEP in Protvino.

Welding is one of the most time consuming procedure in jacketing, because in accordance with demands of ITER International Organization there should be performed five tests after butt welding of tubes. They are: go-no-go caliber, internal visual test by TV camera, vacuum test, X-ray test and dye penetrant test. Some tools used for the welding and the check and marking following are shown in Fig. 9. To increase the production capacity we have separated welding line from jacketing and compaction lines. Now we can perform welding independently of other processes and in the non-stop mode. a b c d

Fig.9. The tools used for the welding and checking of a conduit for a TF conductor. a – welding camera; d - TV camera for visual check, c vacuum check, d – X-ray camera

In 2010-2011 we passed all welding qualification procedures, including vacuum, TV, X-ray and dye penetrant tests. Also the compaction, winding and packing – unpacking procedures were developed and qualified. A TF conductor should be delivered to a TF coil winding facility at ASG Company in La Spezia, Italy as a 4 m transport solenoid coil. The winder has been developed to prepare transport solenoids. The winder is equipped by bending device synchronizing with compacting device. After several technological updates we will be able to achieve mutual misalignments of turns about ±3-6 mm. It is much better than specified in PA ±30 mm

• misalignment. The winder and winding process is shown in Fig. 10

a b c

Fig.10. The winding of a TF conductor to a 4 m transport solenoid. a – the winder; b – the bending machine; c – finally winded TF conductor

6

FIP/1-4Rb

To assure the safe delivery to Europe of our TF conductors, we developed the special stainless steel shells to pack the conductors that protect them well during transportation. The packing procedure is shown in Fig. 11, 12. Besides stainless steel shells we are using vacuumed plastic shells and outer protecting plastic bag.

Fig.11. Packaging of a TF conductor into stainless steel shells and its rotation form horizontal to vertical position.

a b c

• Fig. 12. Transport solenoid of a TF conductor packaged into inner vacuumed plastic bag (a), in outer

plastic protection bag (b), and TF conductors in NRC “KI” awaiting shipment to Europe (c).

The global leak test is being performed in collaboration with National Research Center “Kurchatov Institute” (NRC “KI”) where the vacuum chamber used previously for testing of T-15 superconducting coils was renovated [9]. The vacuum chamber with 4.8 m in inner diameter and about 5 m in total height is equipped by high production vacuum pumps and instrumented with high accuracy measuring devices for the measurements of pressure, temperature, He flow, He leak as well as a mass spectrometer to measure gases’ composition in a chamber. This set permits to perform careful global leak test [9]. The transport solenoids

• f TF conductors in NRC “KI” awaiting shipment to Europe and loaded to a track are shown

in Fig.12. In total in our jacketing line we could produce ~7-8 TF conductors a year. By October 2014 24 TF conductors of 28 necessary have been produced. 23 already passed the final global leak test in NRC “Kurchatov Institute”. 16 unit lengths of TF conductors have been delivered to ASG facility in La Spezia for TF coils production. Six different 5 m TF conductor samples, including three pieces from 760 m conductors, of different manufacturing phases such as R&D, qualification and mass production have been tested in the SULTAN facility [16]. Every conductor section showed very good stability of DC performance within one test. There was no degradation observed during electromagnetic cycling and warm-up/cool-down procedure. All the tested conductors meet the ITER Tcs requirement of 5.8 K with some margin. At the same time the results obtained show a very good agreement between all the samples both in AC and DC condition. Such stable conductor performance is obtained due to a strict quality control system at all steps of the manufacturing process from the Nb3Sn superconducting strand to the final CICC. One of the possible reasons

• f the stable behavior is the frictional property of the Cr plating made in VNIIKP, which may

promote the sliding at the strand crossovers and mitigate the local strand bending [17].

7

FIP/1-4Rb

• 5. Researches

During all ITER works several R&D studies have been performed. We would like to mention some important ones. During insertion of a cable into a jacket, a cable head, to which the pulling force is applied, starts to rotate in a direction opposite to a cable twisting. The untwisting leads to change of such major parameters as twist pitch and cable diameter. Those parameters should be strongly controlled in accordance with QA requirements and their values should be within

• specification. A model of cable rotation during insertion into jacket and twist pitch changes

has been developed. The calculations and the experimental data for the full cable length are in a good agreement [14]. This model can be applied for other ITER cables, after determination

• f specific coefficients for each type of cable, using short cable samples. Based on this model

the method of compensation of cable untwisting has been proposed. The residual resistance ratio (RRR) is an important parameter affecting the stability of superconductors and the quench protection properties of magnets. During the manufacture of cable-in-conduit-conductors (CICC’s) based on Nb3Sn strands, RRR may change noticeably. We studied the RRR of strands in as-received condition and at different stages of the TF conductor manufacturing (cleaning and Cr-plating of strands, cabling and final compaction). It has been found that the statistical average RRR degradation by 33 % takes place during Cr- plating and the production of TF conductor. Then, the advantage of Cycle B (100 hours instead of 200 hours at 650 C) heat treatment from the strands RRR point of view has been confirmed statistically [11]. Similar researches were done with NbTi strands also. The study of defects generated in superconducting filaments of Nb3Sn strands under electromagnetic and thermal cycling was carried out for the TFRF3 cable-in-conduit- conductor (CICC) sample passed final testing at the SULTAN test facility. The strand samples were taken from different locations in cross–section of TFRF3 and different positions along its axis in relation to background magnetic field. Qualitative and quantitative analysis of defects were carried out using metallographic images obtained by Laser Scanning Microscope. It was found that well distributed Nb3Sn bronze strands (with higher number of sub-elements) seem more convenient for CICC manufacture due to their resistance against bending. Non- uniform distribution of voids in bronze matrix (in particular, clustering of large voids) can result in additional filament damage because most of filament cracks are void-induced [15].

• 6. Conclusion

Passing of the entire technological route with trial and dummy conductors allows VNIIKP to demonstrate that entire facilities for the production of TF conductors are qualified and ready for delivery of regular unit lengths for the ITER magnet system. In parallel some R&D studies are performed on cable rotations during insertion, state of Nb3Sn filaments during production and after high field tests of witness samples, RRR changes during production, etc. These studies permitted to update and to improve the technologies on all stages of production. Now the regular production of cables and conductors is underway and about 75% of cables and conductors (as of October 2014) are ready to be delivered to Europe. References [1]

• V. E. SYTNIKOV, I. B. PESHKOV, et al, "RF jacketing line for manufacturing ITER

cable-in-conduit conductor," in Proc. of ICEC16/ICMC, Japan, 1996, pp. 799-802.

8

FIP/1-4Rb

[2]

• V. E. SYTNIKOV, et al, "Development and manufacturing of superconducting cable-in-

conduit conductor for ITER," IEEE Trans. Appl. Superc., vol. 7, pp. 1364-1367, 1997. [3]

• V. E. SYTNIKOV, et al, "Jacketing of 860 m ITER dummy CICC”, in Proc. of 15th
• Inter. Conf. on Magnet Technology, Part 2, Beijing, China, 1997, p. 1152-1155.

[4]

• V. E. SYTNIKOV, A. V. TARAN, et al, "The long length line for jacketing cable-in

conduit conductors," Fusion Engineering and Design, vol. 45, pp. 209-214, 1999. [5]

• N. MARTOVETSKY, et al, "Test of the ITER TF insert and Central Solenoid Model

Coil", IEEE Trans. Appl. Supercond., V.13 , No 2, pp. 1441 - 1446, 2003 [6]

• D. BESSETTE, et al, "Test Results From the PF Conductor Insert Coil for the ITER PF

System", IEEE Trans. Appl. Supercond., V.19 , No 3, pp. 1525 - 1531, 2009 [7] A.V. TARAN, et al, "New Technology Complex for ITER TF and PF Cables and TF Conductors Production", IEEE Trans. Appl. Supercon., Vol.20, No3, pp. 394-397, 2010 [8] YU.P. IPATOV "Improvement of Cr- and Ni-coating technology for ITER conductors' production", IEEE Trans. Appl. Supercond., Vol.23, N3, , 2012, (4804204) [9] V.S. VYSOTSKY, et al, «Status and Achievements in Production of ITER TF Conductors and PF Cables», IEEE Trans. Appl. Superc., Vol.23, 2012, (4200505) [10] Procurement Arrangement 1.1P6C.RF.01.0 and 1.1P6A.RF.01.0 [11] S.S. FETISOV, et al, “Resistance Residual Ratio in Nb3Sn Strands During ITER TF Conductor Manufacture and after SULTAN test”, IEEE Trans. Appl. Supercond., Vol.24, №3, 2014 , (8800305) [12] S.S. FETISOV, et al, “Resistance Residual Ratio in NbTi strands extracted from the ITER PF1/6 conductor sample after SULTAN tests”, Paper 4MPo2A-04 at ASC-2014, USA, Aug. 2014 [13] D.S. KAVERIN, V.V. ZUBKO, et al, “VNIIKP RF TF Cable Twisting and Stretching Under Tensile Force”, IEEE Trans. Appl. Supercond., Vol.24, №3, 2014, (4801104) [14] D.S. KAVERIN, et al, “A Model of ITER TF Cable Rotation during Insertion into Jacket”, Paper 3LPo2C-05 presented at ASC-2014, Charlotte, USA, August 2014 [15] D. S. KAVERIN, et al, “Analysis of Nb3Sn strand microstructure after full-size «SULTAN» test of ITER TF conductor sample”, presented at ICEC25 - ICMC-2014, Twente University, the Netherlands, July 2014, poster available at: https://indico.cern.ch/event/244641/session/45/contribution/37/material/poster/0.pdf ) [16] V. TRONZA, S. LELEKHOV, et al, “Test Results of RF ITER TF Conductors in the SULTAN Test Facility”, IEEE Trans. Appl. Supercond., Vol.24, №3, 2014 , (4801905) [17] P. BRUZZONE, B. STEPANOV, K. SEDLAK,et al, Summary of the Test Results of ITER Conductors in SULTAN, Paper FIP/1-4Ra, this conference