Pietro Testoni

Design and Procurement of the European Dipole (EDIPO) Superconducting Magnet

A 12.5 T superconducting dipole magnet (European DIPOle, EDIPO) has been designed by EFDA and it is now being procured within the framework of the European Fusion Programme in order to be installed in CRPP-PSI. This saddle-shaped magnet is designed to reach 12.5 T in a 100 times 150 mm rectangular bore over a length of about 1.5 m in order to test full size conductor samples that shall be produced during the ITER magnets procurement. The magnet uses Cable In Conduit Conductor (CICC) technology and the cables are made of high Jc (about 2300 A/mm2 at 4.2 K, 12 T) superconducting strands. In this paper the main magnet parameters are given together with the key supporting electromagnetic, mechanical and thermal analyses. An update on the general status of the procurement of the strand, conductors, dipole magnet and facility is also given together with the key results of the on-going supporting R&D.

Status of the F4E Procurement of the EU ITER TF Coils

The ITER magnetic system includes 18 Toroidal Field (TF) Coils using Nb3Sn cable-in-conduit superconductor. Each TF coil, about 300-t in weight, is made by a Winding Pack (WP) composed by 7 Double Pancakes (DP) modules stacked together, impregnated and inserted in stainless steel coil case. Each DP is made by a Radial Plate (RP), a very large D-shaped stainless steel plate with grooves machined on a spiral path on both sides, in which the insulated conductor is inserted after the heat treatment. The procurement of the TF coils will be carried out by Fusion for Energy (the European Domestic Agency (DA)), responsible for 10 coils (including 1 spare coil) and the Japanese DA, responsible for 9 coils. The conductors will be produced by 6 different DAs, while the coil cases only by the Japanese DA. In July 2008 the Procurement Arrangement was signed between the ITER Organization (IO) and F4E defining the scope, technical and management requirements for the procurement of such coils. F4E has developed a procurement strategy aimed to minimize costs and risks, consisting of subdividing the procurement into three main procurement packages, each foreseeing an initial R&D qualification phase. One procurement package is related to the construction of 72 RP (including 2 prototypes), another to the fabrication of the 10 WP and a third to the cold test and coil-case insertion of 10 WP. So far F4E has signed 5 contracts. In 2009, we placed 2 contracts for the procurement of RP prototypes and 1 contract for the development and qualification of the welding and the Ultrasonic Test technologies for the coil case welding. In 2010 1 contract has been placed for the construction of 10 WP and 1 contract for the engineering optimization of the cold test and coil insertion.

Electromagnetic Disruption Loads on ITER Blanket Modules

In this paper we compute the electromagnetic loads (forces, torques, Joule losses) on passive conductors of the international thermonuclear experimental reactor (ITER) fusion device, currently under construction, following a disruption event, i.e., the sudden loss of magnetic confinement. An original integral formulation is used, able to automatically deal with complex topologies like the ones to be studied. Non-isotropic homogenized resistivities are used to take into account fine geometrical details. A suitable inverse problem is solved in order to compute the forcing terms.

Status of the EDIPO Project

The aim of this paper is to present an up to date review of the status of the European DIPOle (EDIPO) project whose objective is to build a new facility to perform both DC and AC tests of large superconductor samples in high magnetic background field (up to 12.5 T). EDIPO was designed by EFDA, is being built by BNG (Babcock-Noell) and, once completed, it shall be installed near the existing SULTAN facility at the Paul-Scherer-Institute, (CRPP, Villigen, Switzerland). The results presented focus on the manufacture of the dummy coil (which is a 1:1 model of one of the EDIPO poles) that was completed in spring 2009. Details are given about the dummy coil winding results, coil reaction heat treatment, impregnation and acceptance tests. Moreover, a progress status is provided about the manufacturing of the other parts of the EDIPO magnet assembly, in particular with respect to the manufacturing of the test-well, AC coils, yoke sheets cutting and assembly, the outer cylinder production and welding (316 LN steel, 35 mm thick) and the coils ends preparation. Some results regarding the R&D studies are also reported about the winding trials carried out to improve the winding accuracy and the numerical simulations made to support coil winding (e.g. conductor spring back).

Magnetically Based Acceptance Procedures for ITER Toroidal Coils: An Assessment of Performance

The Toroidal Field Coils (TFC) are subject to mandatory geometrical tolerances constraints for acceptance by ITER Organization. As a consequence, pre-assembly tests are foreseen to verify if each single coil meets such criteria, including laser tracking, and possibly warm magnetic measurements on each of the finished winding packs. Possible performance limitations of the acceptance tests for the winding pack are assessed in this paper. Since construction details are not presently known, the paper proposes an assessment of the mathematical and numerical tools able to perform the final evaluation of the actual feasibility of magnetic testings and discusses their performance in terms of accuracy and reliability.

Status Report of the EDIPO Project

The aim of this paper is to present an up to date review of the status of the European DIPOle (EDIPO) project whose objective is to build a new facility to perform both DC and AC tests of large superconductor samples in high magnetic background field (up to ~12.5 T). EDIPO was designed by EFDA, is being built by BNG (Babcock-Noell) and, once completed, it shall be installed near the existing SULTAN facility at the Paul-Scherer-Institute, (CRPP, Villigen, Switzerland). The results presented focus on the manufacture of the dummy coil (which is a 1:1 model of one of the EDIPO poles) that was completed in spring 2009. Details are given about the dummy coil winding results, coil reaction heat treatment, impregnation and acceptance tests. Moreover, a progress status is provided about the manufacturing of the other parts of the EDIPO magnet assembly, in particular with respect to the manufacturing of the test-well, AC coils, yoke sheets cutting and assembly, the outer cylinder production and welding (316 LN steel, 35 mm thick) and the coils ends preparation. Some results regarding the R&D studies are also reported about the winding trials carried out to improve the winding accuracy and the numerical simulations made to support coil winding (e.g. conductor spring back).

Characterization of Deformed Magnets From External Magnetic Measurements

Due to the unavoidable construction tolerances and imperfections in the assembly of coils, the actual magnetic field of manufactured magnets differs from the design one. Depending on the consistency and the profile of the field error, a number of problems may arise, especially in high-performance devices, such as magnets for nuclear magnetic resonance or thermonuclear fusion devices. Typical quality insurance procedures can hardly reveal possible winding pack (WP) deformations. In this paper, deformed magnets are characterized by means of a limited set of parameters, providing an equivalent magnetic behavior, and an assessment of limits and possibilities of such a WP characterization from external magnetic field measurement is discussed, including some aspects of the inverse problem resolution.

Magnetic Measurements for Magnets Manufacturing Tolerances Assessment

Superconducting high field magnets are tightly constrained in terms of field quality, since such magnets are usually designed to perform quite demanding tasks, such as focusing particle beams in accelerators, plasma confinement and shaping in fusion devices, and polarizing actions in magnetic resonance. In all these cases, small discrepancies of field map from the design values may strongly impact on device performance. As a consequence, quality insurance procedures are needed to verify if each single coil meets such criteria, e.g., using laser tracking, and possibly warm magnetic measurements. As a matter of fact, external magnetic measurements can be used to estimate the possible deformations of conductors inside the magnet, but this implies inverse problem approaches. The field probes accuracy is therefore critical, and the measurement system must be carefully designed, taking into account the probe characteristics, but also the characteristics of the windings and of the surrounding environment. In this paper, different measurement techniques are compared in terms of sensitivity and accuracy, with reference to various types of sensors and of measurement schemes.

Numerical Model of the Dynamic Response of 3-D Conducting Structures With Magnetic Damping

In this paper, we present a new numerical model for the solution of the classic electromagnetomechanical-coupled problem. The dynamical behavior of conducting structures in the presence of a strong magnetic damping was the subject of a high scientific interest in the past, leading to several computational models with experimental validation, mainly related to thin-shell structures. We extend this approach to the treatment of 3-D conducting structures. To this purpose, we couple a very effective 3-D integral formulation in terms of the current density to the 3-D dynamical model of the conducting structures. The formulation is validated against the experimental results of the TEAM-16 benchmark problem. The importance of the magnetic damping is assessed with reference to the analysis of the dynamic response of the vacuum vessel of a fusion device under the strong Lorentz forces due to the plasma current disruption. The complex geometry of the vacuum vessel represents a real challenging problem in this frame.

Static and Transient Electromagnetic Features of the EFDA Dipole

The EFDA dipole (EDIPO) is a superconducting magnet made of a pair saddle-shaped winding packs enclosed in a circular iron yoke which, in turn, is contained inside an austenitic steel cylinder. In this paper the key electromechanical features of the dipole are presented. As far as the static analysis is concerned, the electromagnetic and mechanical behavior of the whole system has been analyzed by means of finite element models, in order to evaluate, in particular, the peak field on the cables, the stress limit in the jacket and the shear stresses in the insulation. As far as the transient analysis is concerned, the system behavior during a current dump has been simulated by means of a coupled electromagnetic-circuit model that takes into account the non linearity of the ferromagnetic material and the reaction field due to the eddy currents in the steel cylinder. Another important element in the AC analysis consists in the assessment of the conductor losses during AC operation, since they provide the heat loads to be evacuated by the cooling system. The results of this last issue are also presented.