V. Tomarchio

Recent Progress of the Design Activity for the Poloidal Field Coil System in JT-60SA

PA (procurement arrangement) for poloidal field (PF) coil system, which consists of the central solenoid (CS) and the equilibrium field (EF) coils, was agreed between Japan and EU. During this activity, design of PF coils system was continued to be modified. For CS, material for the jacket of this conductor was changed into stainless steel (316LN) to make providing easier. In the modified material, maximum stress at the jacket was kept within the allowable limit. Accompanying this modification, the amount of pre-compress had to be re-estimated. Therefore, it was clarified that designs of pre-compression and tie plates need not to be major modification. For EF coils, positions and the number of turns were modified since the progress of the research for the plasma operations required in JT-60SA. Due to this optimization, total amount of superconducting material was reduced. The detail designs of PF coils were also performed to reduce the materials of supports and to evaluate the mechanical strength considering the various events. Thickness of clamp plate of the EF coil which received relatively small electromagnetic force was able to be reduced. Regarding the design of support legs with flexible plate, deformation of toroidal field (TF) coil was considered that should be included the evaluation of stress at this parts because this parts are directly attached on the TF coil case. Therefore, the revised designs of supports with sufficient mechanical strength were obtained for EF1 and EF4.

A Global Structural and Electromagnetic Finite Element Model for the Prediction of the Mechanical Behavior of the JT-60SA Superconducting Magnet System

The JT-60SA is a fusion experiment designed to contribute to the early realization of fusion energy by providing support to the operation of ITER; by addressing key physics issues for ITER and DEMO; and by investigating how best to optimize the operation of the next fusion devices that will be built after ITER. It is a combined project of the JA-EU Satellite Tokamak Program under the Broader Approach (BA) Program and JAEAs Program for National Use, and it is to be built in Naka, Japan, using the infrastructure of the existing JT-60U experiment. The superconducting magnet system of JT-60SA consists of a Central Solenoid, six Equilibrium Field coils and eighteen Toroidal Field coils. The systems are connected to each other by means of flexible and kinematic mechanical attachments, with the Toroidal Field magnet acting as the structural backbone of the whole magnet system. This is then supported to the cryostat base of the machine through a series of gravity supports. A detailed finite element model, representing a 40 degree sector of the superconducting magnet system of JT-60SA, has been developed with particular focus on the mechanical connections between the different coil systems. A complete set of analyses were carried out to obtain the electromagnetic force distribution on the three magnet sub-systems during all operational scenarios and consequently to predict the corresponding stresses and deformations. By doing this the integrity of the system and the performance of its bolted and pinned connections were verified against the applicable codes and standards. This paper illustrates the details of the modeling strategy which lead to the production of the finite element model and provides a comprehensive report and a critical analysis of the most relevant results obtained to date.

The JT-60SA Toroidal Field Magnet—Design for Assembly

The JT-60SA experiment will be the worlds largest superconducting tokamak when it is assembled in Naka, Japan (R = 3 m, a = 1.2 m). This paper describes the approach taken to define appropriate manufacturing tolerances and metrology points for each toroidal field (TF) coil and in particular the proposed procedure for the final assembly of the TF magnet system.

Qualification of the Fastening Components of the Outer Intercoil Structure of the JT-60 SA Tokamak

The 18 toroidal field coils of the JT-60SA are mechanically linked by the so called “Outer Intercoil Structure” (OIS). Each OIS is bolted to its neighbors by five splice plates: this presents the double advantage of facilitating the assembly of the structure as well as ensuring an efficient electrical insulation by the insertion of an epoxy-glass sheet between the clamping stainless-steel parts. Since strong electromagnetic loads are carried by these OIS, the bolting requires a high preload to provide a significant contact pressure and thus prevent the slippage of the splice plates. We identified some critical issues that are associated with this bolted joint: the sliding behavior at the cryogenic temperature, the risk of creep of the epoxy-glass spacers during the long period of the assembly phase, and the high stress levels developed in the bolting. In this paper, we present the results of the qualification tests for several components of the fastening parts of the OIS. Two mockups of the connection were tested at room temperature and at 4 K to measure the sliding coefficient between the stainless steel and the glass-epoxy faying surfaces. The loss of preload in the bolts due to the hydraulic tightening process has also been measured on different scaled mockups. The effectiveness of the titanium washers used to compensate the loss of preload due to the difference in the thermal shrinkage between the steel and the glass-epoxy components has also been validated. Finally, the creep behavior of the insulation has been investigated by testing the glass-epoxy samples on a specially designed testing device.

Experimental and Analytical Approaches on JT—60SA TF Strand and TF Conductor Quality Control During Qualification and Production Manufacture Stages

In the framework of the JT-60SA project, aiming at upgrading the present JT-60U tokamak, Europe as part of its in-kind contribution within the Broader Approach agreement, will provide the full Toroidal Field (TF) magnet system. For this purpose, Fusion for Energy is committed to procure about 27 km of TF conductor. The TF conductor is cable-in-conduit type and includes 486 strands (2/3 NbTi-1/3 copper) wrapped with a thin stainless steel foil and embedded into a rectangular stainless steel jacket. The procurement is split into two main contracts: one for strand manufacturing and the other for cabling and jacketing. After having successfully passed the qualification stage, strand and conductor are now in mass production stage. In the present paper, we emphasize on the scientific and quality control approaches of both TF strand and TF conductor productions. For the NbTi strand, the focus is on design and measurement of performance critical aspects (CuNi barrier design optimization, AC losses, TCS performance, etc.). For Cu strand the main issue is RRR. For the TF conductor, the topics presented cover hydraulic correlation validation measurements (pressure drop tests), geometrical advanced controls, and electromagnetic behavior (hotspot checks and mainly the experimental results of the TF conductor full-size samples tested in SULTAN facility). The article presents comparisons of numerical simulation and experimental results used to confirm the design and the manufacturing processes.

Analysis of Maximum Voltage Transient of JT-60SA Toroidal Field Coils in Case of Fast Discharge

The voltage transient appearing across and inside the toroidal field (TF) coils of JT-60SA in case of fast voltage variation, such as a safety discharge operated by the quench protection circuit (QPC), can be significantly high. In fact, the voltage distribution between coils and inside the winding can be not uniform during fast transient, being influenced by the presence of parasitic capacitances. A simplified electrical model of the TF coils has been developed to investigate this aspect. Its robustness has been proved by means of parametric sensitivity analysis, and the impact of the included simplifications has been evaluated. The obtained model has been used in conjunction with an electrical model of the TF circuit elements, including a simplified model of the QPC able to reproduce the voltage appearing across its terminals as observed during experimental operation of the QPC prototype. The worst case in terms of transient voltage applied to the winding has been identified, corresponding to a fault to ground occurring just after QPC operation. It has been verified that the resulting voltage is largely inside the coil insulation capability defined by performed insulation voltage tests.

Manufacturing of the first toroidal field coil for the JT-60SA magnet system

In the framework of the Broader Approach Agreement for the construction of the JT-60SA tokamak, ENEA is in charge to provide 9 of the 18 Toroidal Field (TF) coils. The 9 coils are being manufactured by ASG superconductors in Genoa under the supervision of ENEA in collaboration with the JT-60SA European home team. The winding line, which is the core of the project, has been assembled and will be used to wind the first set of Double Pancakes (DPs). The functional tests of the winding line and the tooling required for the DP manufacture is reported and the associated inspections to assess the compliance to the design tolerances are described. Successive steps in the Winding Pack (WP) coil manufacturing are the DP insulation, stacking of up to 6 DPs, insulation of the WP, electrical joints assembly and final impregnation using a D-shape impregnation mould. In this paper a description of the winding line installation and an overview of the principal equipment used during the manufacture of the first DP are presented.

Construction Status of the Superconducting Magnet System for JT-60SA

The construction of the JT-60SA tokamak is one of the three projects of the Broader Approach activities being undertaken jointly by Japan and Europe. The superconducting magnet system for JT-60SA consists of 18 toroidal field coils, a central solenoid with four modules, six equilibrium field coils, superconducting feeders, high-temperature-superconductor current leads, thermal shields, and the cryogenic system. This paper shows the latest construction activities of the superconducting magnet system.

Status of the JT-60SA magnet system

The JT-60SA experiment will be the worlds largest superconducting tokamak when it is assembled in 2019 in Naka, Japan (R=3m, a=1.2m). The superconducting magnet system includes 18 D-shaped toroidal field coils, each 7m high and 4.5m wide, 6 pulsed equilibrium field coils up to 12m in diameter and 4 central solenoid modules. Manufacturing of the superconducting magnets for JT-60SA is well established in Japan and in Europe. Conductor manufacturing is almost complete, half of the superconducting coils have been wound and the first cold test results for production coils will be available later in 2015. Challenges remain to integrate the coils with their mechanical structures and to assembly them into the tokamak.

Manufacturing Status of JT-60SA Toroidal Field Coils

The 18 D-shaped Nb-Ti toroidal field (TF) coils for the JT-60SA tokamak will each be 7 m high and 4.5 m wide. Together they will generate an on-axis field of 2.25 T. All the main contracts for their manufacture are now in place, with manufacturing split primarily between sites in Japan (superconducting strand), Italy (conductor cabling and jacketing, casings fabrication and coil winding, and integration), and France (support structures, coil winding and integration, and final coil cold testing). This paper will summarize the key aspects of the design of the coils and the current status of manufacture on each area of the manufacture of the TF coils. A simple overview of the overall schedule for their completion is included.