H. Rajainmaki

Test results of the ITER PF insert conductor short sample in SULTAN

A short sample of the NbTi cable-in-conduit conductor (CICC) manufactured for the ITER PF insert coil has been tested in the SULTAN facility at CRPP. The short sample consists of two paired conductor sections, identical except for the sub-cable and outer wraps, which have been removed from one of the sections before jacketing. The test program for conductor and joint includes DC performance, cyclic load and AC loss, with a large number of voltage taps and Hall sensors for current distribution. At high operating current, the DC behavior is well below expectations, with temperature margin lower than specified in the ITER design criteria. The conductor without wraps has higher tolerance to current unbalance. The joint resistance is by far higher than targeted.

Vacuum Pressure Impregnation Process in Superconducting Coils: Best Practice

The technology associated with the design and construction of superconducting magnets has evolved dramatically over the last three decades leading to an overall increase in their complexity. Their use has moved from particle physics through medical applications such as MRI to the very large magnets demanded by fusion technology, where the optimal quality of the HV insulation is a critical step in achieving the design performance. The Vacuum Pressure Impregnation (VPI) technique-a particularly refined case of the more widely known Vacuum Assisted Resin Transfer Mould (VARTM)-has become the most common process for the consolidating electrical insulation of large superconducting magnets. To achieve success with the VPI process demands that detailed attention is paid to many steps, namely: coil drying, resin degassing and coil impregnation. Commercial sensitivity has meant that there has not been a well-published exchange of information and therefore many details of the VPI process may vary in different organizations. The present paper aims at filling this gap and will discuss in detail: (1) all required steps with the main risks in each of them, (2) commonly used methods in each of the steps for optimized control of the process and (3) tooling to minimize risk of failure during impregnation.

Status Report of the SULTAN Test Facility

One year of operation and test activity of the SULTAN test facility at CRPP-Villigen, from October 2008 to October 2009 is reviewed. The main improvements of the facility include a new control system for the cryo-plant and a new electric motor for the helium compressor. The range of operation for the SULTAN samples has been improved in terms of cyclic loading rate. The test campaigns from October 2008 to October 2009 include eight ITER TF conductor samples, two JT60SA samples and a number of other developmental samples. The highlights of the test campaign and the statistical data about cool-downs, warm-ups and test duration are reported. For the eight ITER TF samples, more detail is given about the joint development, the standard test program and the data reduction for the assessment of the results. Eventually, an outlook in the next operation period is also discussed.

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.

Implications of NbTi Short-Sample Test Results and Analysis for the ITER Poloidal Field Conductor Insert (PFCI)

As the test of the PFCI is foreseen in 2006 at JAERI Naka, Japan, it is essential to consider in detail the lessons learned from the short NbTi sample tests, as well as the issues left open after them, in order to develop a suitable test program of the PFCI aimed at bridging the extrapolation gap between measured strand and future PF coil performance. Here we consider in particular the following issues: 1) the actual possibility to quench the PFCI conductor in the TCS tests before quenching the intermediate joint, 2) the question of the so-called sudden or premature quench, based on SULTAN sample results, applying a recently developed multi-solid and multi-channel extension of the Mithrandir code to a short sample analysis; 3) the feasibility of the AC losses calorimetry in the PFCI

DESIGN ISSUES OF THE PRE‐COMPRESSION RINGS OF ITER

The pre‐compression system is the keystone of ITER. A centripetal force of ∼30 MN will be applied at cryogenic conditions on top and bottom of each TF coil. It will prevent the ‘breathing effect’ caused by the bursting forces occurring during plasma operation that would affect the machine design life of 30000 cycles. Different alternatives have been studied throughout the years. There are two major design requirements limiting the engineering possibilities: 1) the limited available space and 2) the need to hamper eddy currents flowing in the structures. Six unidirectionally wound glass‐fibre composite rings (∼5 m diameter and ∼300 mm cross section) are the final design choice. The rings will withstand the maximum hoop stresses <500 MPa at room temperature conditions. Although retightening or replacing the pre‐compression rings in case of malfunctioning is possible, they have to sustain the load during the entire 20 years of machine operation. The present paper summarizes the pre‐compression ring R&D carri...

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.

Overview of ITER magnet system and European contribution

The superconducting magnet system of ITER consists of four main sub-systems: Toroidal Field (TF) coils, Central Solenoid (CS) coils; Poloidal Field (PF) coils; and Correction Coils (CC). Like many other ITER systems, the magnet components are supplied in-kind by six Domestic Agencies (DAs). The technical specifications, manufacturing processes and procedures required to fabricate these components are particularly challenging. The management structure and organization to realize this procurement within the tight ITER construction schedule is very complex.

Installation and Test Programme of the ITER Poloidal Field Conductor Insert (PFCI) in the ITER Test Facility at JAEA Naka

ITER PFCI has been manufactured in the Europe and installed into the ITER Test Facility in Naka, Japan. The conductor is NbTi cable-in-conduit conductor with thick square stainless steel jacket and almost identical with the design of the ITER PF coils. The main objective of this test is the characterization of the conductor and joints at the conditions relevant to the ITER PF coil operation. Intermediate joint is located in the winding at relatively high field to examine its performance. The main items in the PFCI test program are thermo-hydraulic test, DC mode test, cyclic test and pulse mode test. The PFCI and CSMC were successfully cooled down to cryogenic temperature within 450 hours. The test of the PFCI was performed from May to August 2008. The key technology of the installation, the test methods and procedures, and some preliminary results of cool-down are described in this paper.

The Electrical Insulation of Large Superconducting Magnets

The latest generation of fusion devices needs large superconducting magnets that have to withstand operational voltages of tens of kV. Their insulation typically targets a dielectric strength of about 10 times the operational voltages to cope with degradation during operation resulting from the high electromagnetic loads with cyclic components, thermal stresses due to cycles from 293 K to 4 K, and ionizing radiation. Degradation of dielectric strength is further mitigated by applying solid polyimide overlapped layers in the insulation. The level of Lorentz forces, together with the large superconducting coil sizes, makes high-voltage tests impossible to realize under exact operational conditions. The fact that insulation is very difficult or even often practically impossible to repair in case of electrical fault, requires sound insulation design to reach utmost quality. In this paper, we will discuss the build-up of the electrical insulation in large superconducting magnets both from the manufacturing and operational point of view. In particular, the impact of the insulation design and manufacturing choices on the quality will be discussed in depth. We will also discuss the implementation and the application of insulation systems.