Cable Twist Pitch Variation in $\hbox{Nb}_{3}\hbox{Sn}$ Conductors for ITER Toroidal Field Coils in Japan

174

118

Taking the relay of the Large Hadron Collider (LHC) at CERN, ITER has become the largest project in applied superconductivity. In addition to its technical complexity, ITER is also a management challenge as it relies on an unprecedented collaboration of 7 partners, representing more than half of the world population, who provide 90% of the components as in-kind contributions. The ITER magnet system has a stored energy of 51 GJ and involves 6 of the ITER partners. The coils are wound from Cable-In-Conduit Conductors (CICCs) made up of superconducting and copper strands assembled into a fully transposed, rope-type cable, inserted into a conduit of butt-welded austenitic steel tubes. The conductors for the Toroidal Field (TF) and Central Solenoid (CS) coils require about 500 tons of Nb 3 Sn strands while the Poloidal Field (PF) and Correction Coil (CC) and busbar conductors need around 250 tons of Nb-Ti strands. The required amount of Nb 3 Sn strands far exceeds pre-existing industrial capacity and has called for a significant worldwide production scale up. The TF conductors are the first ITER components to be mass produced and are more than 50% complete. During its life time, the CS coil will have to sustain several tens of thousands of electromagnetic (EM) cycles to high current and field conditions, way beyond anything a large Nb 3 Sn coil has ever experienced. Following a comprehensive R&D program, a technical solution has been found for the CS conductor, which ensures stable performance versus EM and thermal cycling. Productions of PF, CC and busbar conductors are also underway. After an introduction to the ITER project and magnet system, we describe the ITER conductor procurements and the Quality Assurance/Quality Control programs that have been implemented to ensure production uniformity across numerous suppliers. Then, we provide examples of technical challenges that have been encountered and we present a status of ITER conductor production worldwide.

Section: Twist Pitch Elongationmentioning

confidence: 76%

Challenges and status of ITER conductor production

Devred

Backbier

Bessette

et al. 2014

174

118

“…Also very important is the outer cable steel wrapping, usually applied to protect the external strands from damage due to friction during the cable insertion into the jacket assembly, and also to withstand possible cable deformations (e.g. elongation and change of last stage twist pitch [166]) caused by the pulling force. The choice of the wrap thickness and of the tension applied is therefore very important.…”

Section: Cablingmentioning

confidence: 99%

“…For the case of the JT-60SA TF conductor, the cable unit length of 240 m, characterized by a full weight of about 5.4 kN, is typically inserted in the jacket assembly through a gap of about 1.5 mm, with a maximum pulling force of about 6 kN. For the case of the ITER cables, the very high values of pulling force have been demonstrated to cause a deformation of the cable for the first few meters at the pulling head, through the elongation of its last stage twist pitch [92,166].…”

Section: Jacketingmentioning

confidence: 99%

Cable-in-conduit conductors: lessons from the recent past for future developments with low and high temperature superconductors

Muzzi

Marzi

Zenobio

et al. 2015

We review progress in the design of high field superconducting cable-in-conduit conductors (CICCs) for fusion applications, with special attention to the results of recent key experiments, leading to the state-of-the-art CICC technology: the ITER Toroidal Field and Central Solenoid programs, the EFDA Dipole conductor development program, the NHFML Hybrid Magnet project, the EU-TF Alt conductor demonstration, and the CRPP React & Wind flat cable test. For these projects, the main CICC design driver was the mitigation of Nb 3 Sn conductor performance degradation with electro-magnetic loading cycles. This was achieved by proper choice of cable layout and of conductor geometry, depending on the specific operating conditions and project requirements. In all cases, the necessity to limit cable movements inside the conductor jacket was identified to be of crucial importance. The main aspects of CICC manufacture are also discussed here, at least for what is the experience gained by the authors in both CICC jacketing and cabling processes. Finally, the state of the art of high-temperature superconducting (HTS) cables is discussed: at present, this technology is still in its infancy, but it is highly likely that major technological improvements could eventually lead to a widespread use of HTS CICCs.

“…The varied twist pitch measured at high performance magnetic (HPM) for ITER TF changed from 420 to 525 mm along the full cable length (760 m), which increased by 25% [12]. In JAEA, the cable twist pitch of ITER TF and CS increased by about 15% and 20% along the conductor length (TF-760 m, CS-918 m), respectively [13,14]. In Russian Scientific R&D Cable Institute (VNIIKP), the cable twist pitch of ITER TF increased by about 9% [15].…”

Section: Introductionmentioning

confidence: 99%

“…The cable twist pitches in CICCs should be well controlled in the required range. In order to better understand the untwisting and final stage twist pitches, experiments have been performed at HPM (USA), JAEA (Japan), VNIIKP (Russia), and ASIPP (China) to evaluate the cable rotation of their ITER TF or CS cables [12][13][14][15]20], shown in figure 2. They developed devices to monitor the cable rotation during insertion and tested some short cable samples under tension.…”

Section: Introductionmentioning

confidence: 99%

Rotation analysis on large complex superconducting cables based on numerical modeling and experiments

Qin

Yue

Zhang

et al. 2017

The conductors used in large fusion reactors, e.g. ITER, CFETR and DEMO, are made of cable-inconduit conductor (CICC) with large diameters up to about 50 mm. The superconducting and copper strands are cabled around a central spiral and then wrapped with stainless-steel tape of 0.1 mm thickness. The cable is then inserted into a jacket under tensile force that increases with the length of insertion. Because the cables are long and with a large diameter, the insertion force could reach values of about 40 kN. The large tensile force could lead to significant rotation forces. This may lead to an increase of the twist pitch, especially for the final one. Understanding the twist pitch variation is very important; in particular, the twist pitch of a cable inside a CICC strongly affects its properties, especially for Nb 3 Sn conductors. In this paper, a simplified numerical model was used to analyze the cable rotation, including material properties, cabling tension as well as wrap tension. Several rotation experiments with tensile force have been performed to verify the numerical results for CFETR CSMC cables. The results show that the numerical analysis is consistent with the experiments and provides the optimal cabling conditions for large superconducting cables.