Alessandro Bonito-Oliva

Status Report on the Toroidal Field Coils for the ITER Project

The magnet system for ITER comprises 18 Toroidal Field (TF) Coils using Nb3Sn cable-in-conduit superconductor, which operate at 4.5 K in supercritical helium. The procurement of the TF Coils and Structures is amongst the first which have been launched following the creation of the ITER Organization (IO). It is organized in 4 phases. A Procurement Design Readiness Review held in April 2008 confirmed the readiness of the design to proceed with Phases I and II. Procurement Arrangements (PA) were signed with the European and Japanese Domestic Agencies (DA) respectively in June and November 2008. After a brief description of the TF Coils and Structures, the paper gives an overview of the PA showing the milestones towards series production. The procurement strategy of both DA involved is described, in particular the first step which covers pre-production activities: qualification of raw materials, manufacturing trials, mock-ups and full-scale prototype radial plates, impregnation tests and, possibly, winding trials. The work carried out by IO is also presented: optimization of the cover plate welding to satisfy the allowable stress criteria while minimizing the associated distortions, qualification of blends of cyanate ester with epoxy resin for the impregnation of the winding packs and design of the coil terminal region including integration of the needed instrumentation.

Status of the F4E Procurement of Radial Plate Prototypes for the EU ITER TF Coils

This paper reflects the status of the manufacturing of 2 Radial Plate prototypes for the EU ITER TF Coils. The production of these prototypes will supply valuable information for the manufacturing of the total required number of 70 Radial Plates, in terms of manufacturing technologies, optimization of cost, manufacturing time and risks.

The European Procurement of Cold Test and Case Insertion of the ITER Toroidal Field Coils

The International Thermonuclear Experimental Reactor is an international scientific project with the aim of building a tokamak fusion reactor capable of producing at least 10 times more energy than that spent to sustain the reaction. In a tokamak the fusion reaction is magnetically confined and the toroidal field coil system plays a primary role in this confinement. Fusion for Energy, the European Domestic Agency for ITER, is responsible for the supply of 10 out the 19 toroidal field coils. Their procurement has been subdivided in three main work packages: the production of 70 radial plates (the structural components which will house the conductors), the manufacture of 10 winding packs (the core of the magnet) and cold test and insertion into the coil cases of 10 winding packs. The cold test/insertion work package presents significant technological challenges. These include the cold test of the winding packs 14 m high, 9 m wide and weighing 110 t, the welding and inspection of the 316 LN stainless steel coil case, with welded thicknesses of up to 144 mm accessible only from one side combined with the need to minimize the deformation during the welding process (more than 70 m of weld per coil and up to 90 passes to fill the chamfer) and the resin filling of the coil case after insertion of the winding pack (the total volume to be filled up is about one cubic meter per coil). From 2009 up to mid 2011, F4E has carried out an R&D program in order to investigate the most challenging steps of the manufacturing processes associated to this work package, both to meet the demands of the ITER schedule and to minimize technological risks; in this paper an overview of the results obtained is presented.

Electromagnetic Cycling and Strain Effects on

A parametric study has been conducted to quantify the effect in performance of cable-in-conduit conductors (CICCs) to changes in cable and conduit design. Measurements of current sharing temperature and critical current as a function of electromagnetic cycling and longitudinal strain were systematically performed on CICCs with common Nb3Sn internal tin strand. The designs varied in void fraction (0.30 or 0.36), long or short cable twist pitch, cable core patterns (6 around 1 or triplet), and conduit material property (stainless steel 316 or Haynes 242). Measurements were performed at the NHMFL in a test facility for conductor characterization with capability to 12 T, 20 kA, and 250 kN axial tensile load now modified to deliver temperature controlled supercritical helium to the CICC samples.

{\rm Nb}_{3}{\rm Sn}

Transient stability analysis of the superconducting outsert of a 36 T series-connected hybrid (SCH) magnet being developed at the NHMFL is performed. The latest design version of the SCH outsert primary coil will consists of three radial sections, designated as a low-field, a midfield and a high-field ones, each wound with a different superconducting cable-in-conduit conductor (CICC) using a cable of multi-filamentary strands inside a stainless steel jacket that confines slowly flowing supercritical helium (under 3 atm pressure at 4.5 K). There will be also an outer shield coil wound with a CICC that uses NbTi/Cu strands. The outsert cooling system concept delivers helium to all of the winding layers (each layer has an inlet and outlet), aiming to sustain a wide range of duty cycles required by diverse science experiments, conducted with the magnet. The transient stability is discussed in terms of temperature margin, limiting current, and energy margin as well and analyzed for several operation scenarios/duty cycles and situations resulting in different patterns of deposition and evacuation of heat due to AC losses in the outsert sections.

Cable-in-Conduit Conductors With Variations in Cabling Design and Conduit Material Properties

The Iter TF joints are of a twin-box design and the critical parameters of the overall resistance are 1) the contact between cable and termination, and 2) the resistance between two terminations. This paper describes applicability of non-destructive examination (NDE) to these joints. The TFEU joint was adapted to make the joint demountable and the contact area was artificially degraded. The TFEU Joint was measured in the range 30-70 kA, 0-6 T. With no artificial degradation, the resistance of the TFEU Joint was measured to be better than the inter-pancake criterion of 3 nΩ at 2 T, 68 kA. At high fields (6 T) the voltage-current (V I) characteristic of the joint is nonlinear and the resistance is higher than expected. The nonlinearity is worse when the joint is artificially degraded. An FEA model was used to demonstrate that the magneto-resistant coppers contribution to the overall joint resistance is low (<; ~1 nΩ) and does not explain the high field behavior. The nonlinear V I behavior is due to poor current redistribution within the joint, which is related to the resistance of the strand-bundle to copper interface. CRPP is developing a room temperature NDE technique based on resistance profiles to investigate this interface. Resistance measurements at low current and field, or high current and low field, do not guarantee performance at high field; joint tests under the operating conditions are required. Tests on the upper terminations of the TFEU Joint showed that large defects in the contact area between two terminations could be tolerated, when the joint has a good strand-bundle to copper contact resistance and effective current redistribution.

Transient Stability Analysis of the Superconducting Outsert in the NHMFL Series Connected Hybrid Magnet System

In this paper, we will report on the manufacturing of 6 helium inlet mock-ups for the EU ITER TF coils, and on the results of the mock-up tests and other qualification activities carried out in the European industry on this subject.

Applicability of Non-Destructive Examination to Iter TF Joints

A principal part of the ITER fusion reactor is the Toroidal Field magnet system which consists of 18 “D” shaped coils. Fusion for Energy, (F4E), the European Domestic Agency for ITER, is responsible for the procurement of 10 such coils. The completed coils, measuring approximately 14 m × 9 m and weighing 300 tons, comprise an outer structural case into which a “winding pack”, itself made up of 7 conductor double pancake and radial plate assemblies, is inserted. The winding packs will be the largest ever built using Nb3Sn conductor and their manufacture, using a wind, react and transfer process, presents significant technological challenges. In particular, the conductor double pancakes must be wound with high accuracy and their change in dimension during heat treatment correctly predicted in order to facilitate the transfer to their associated radial plates. These processes require novel and sophisticated tooling to be constructed on a large scale. The contract for the manufacture of 10 ITER TF Coil Winding pack was awarded in July 2010 by F4E to a consortium of three main partners-Iberdrola IC, ASG Superconductors and Elytt Energy and in this paper we present the progress made to date. Particular reference is made to the design and procurement of major items of tooling, including the winding line, heat treatment furnace and transfer tool, and the steps taken to minimize risk by design are described.

He-Inlet of the Toroidal Field Coil: Qualification and Manufacturing Status

This paper reflects the status of the manufacturing of 70 radial plates (RPs) for the EU ITER TF Coils. About 3700 t of stainless steel 316 LN have been forged and 240 t of cover plate (CP) raw material bars have been procured for the procurement of the RPs. Each RP is composed of six forged segments welded using local vacuum EB Welding technology for 35 RPs and narrow-gap TIG for the other 35 RPs. All RP plates are finally machined to final dimensions (9 m × 14 m) and tolerances using large portal milling machines. The groove length, planarity, and D-shape form tolerances are the most challenging required tolerances: ±30 ppm for the groove length and 1 mm for both planarity and D-shape form. The main challenges faced and results achieved so far are presented and improvements with respect to the prototype phase are described.