Challenges and status of ITER conductor production

Abstract

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.

Electromagnetic behaviors of superconducting Nb3Sn wire under a time-dependent current injection

“…1 Under the consideration of functionality and stability of CICC, performance degradation and AC loss are the key issues in the design of the magnet system. 2 In recent years, attempts have been made to study the electromagnetic behaviors of some superconductors by numerical simulation. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] As for finite element modelling (FEM), the extreme complexity of hierarchical geometry and structure of Nb 3 Sn strand and CICC requires a special concern for the modelling of the strand entity.…”

Comparisons of internal self-field magnetic flux densities between recent Nb3Sn fusion magnet CICC cable designs

“…2, indicate different fundamental behavior between STP and original design cable with EM loading [6]. This strongly suggests that the improvement in conductor performance is not sensitive to minor variation in a cable parameter but an indication of a significant change, kin to a phase transition.…”

“…The main problem with the magnet was that the Nb 3 Sn based Cable-In-Conduit Conductor (CICC) that makes up each module was not performing to requirements during early tests. Specifically, CICC samples subjected to high background field were showing lower and lower current sharing temperature (T cs ) without stabilization, with repeated electromagnetic (EM) loading from current cycling [4][5][6][7]. The minimum T cs was set at 5.2 K and this requirement was being breached, sometimes after several thousand current cycles, with the original CICC design.…”

“…The ITER International Organisation (IO) which is responsible for the design of ITER led a study that uncovered a solution to the problem in the form of a design change to the CICC cable, which brought about a return to shorter sub-cable twist pitches [6,7,12,13]. Additional investigation with different CICC samples confirmed the improved performance from the changed design [6], [13][14][15][16]. The new design, referred to as short twist pitch (STP), has since been adopted as the new baseline for ITER CS conductor [17].…”

Doping-Induced Isotopic Mg11B2 Bulk Superconductor for Fusion Application

“…A high and steady magnetic field needs to be produced to confine the deuterium (D)-tritium (T) burning plasma inside the ITER Tokamak nuclear fusion reactor. According to the previous ITER plan, hundreds of tons of superconducting cables made from NbTi and Nb3Sn strands have been fabricated to assemble 18 Nb3Sn toroidal field (TF) coils, a 6-module Nb3Sn central solenoid (CS) coil, six Nb-Ti poloidal field (PF) coils, and nine pairs of Nb-Ti correction coils (CC) [1][2][3]. ITER is aimed at demonstrating the feasibility of fusion energy, but for the next step, the development of a commercial fusion reactior there is a concern that, after irradiation, 93 Nb be transformed into the long-lived nuclide 94 Nb with a half-life of about 20,000 years [4,5].…”