A. Anemona

Design of an Industrially Feasible Twisted-Stack HTS Cable-in-Conduit Conductor for Fusion Application

Taking advantage of the large experience of the ENEA Superconducting Laboratory in the manufacture and characterization of large scale superconducting systems, a project was launched, aimed at using High Temperature Superconductor (HTS) 2G wires for the manufacture of a cable-in-conduit conductor (CICC). In particular, the main aim was the definition of a conductor design fully compatible with existing cabling technologies, to be promptly transferred to an industrial scale production. The considered layout is based on 150 HTS tapes, arranged as five layered structures of twisted tapes wound on a helically slotted core with external round jacket. All manufacturing steps (slotted core production, tape stacking and insertion into the ducts, external wrapping and jacketing) are fulfilled by using equipments and technologies available at TRATOS Cavi S.p.A. These CICCs are intended for operation using forced flow of Helium. A 2D local thermal model has been developed for the optimization of the cooling configuration. This conductor is designed to target 20 kA at 4.2 K and 15 T (or, alternatively, higher temperature, in self-field and LN2 cooling) corresponding to a Je of about 55 A/mm2. The production of a short dummy sample revealed that the exploited industrial production process is very promising for the development of HTS CICC.

Design of Large Size, Force Flow Superconductors for DEMO TF Coils

The DEMO plant will demonstrate by mid-century the feasibility of electric power generation by nuclear fusion. In the scope of design studies coordinated by the European Commission, CRPP and ENEA are developing two force flow conductor layouts as candidates for the toroidal field (TF) coils of DEMO. The operating conditions include 82 kA operating current and 13.5 T peak field, placing the DEMO TF conductor at substantially higher performance compared to the ITER TF (68 kA/11.5 T). The innovative winding layout is graded, layer wound with Nb3Sn/NbTi hybridization for both conductor designs, aiming at minimizing the size and the cost of the superconductor: one of the conductors is a wind and react cable-in-conduit conductor with reduced void fraction and has a rectangular shape. The other conductor is a react and wind flat cable with copper segregation and thick conduit assembled by longitudinal weld. The conductor designs were first drafted in 2012 and reviewed in 2013 based on a first round of assessments and on an updated requirements catalog. The manufacture of full-size prototypes is planned in 2014.

Electrical Characterization of ENEA High Temperature Superconducting Cable

ENEA is currently involved in the design and manufacture of a fully high temperature superconductor (HTS) cable in the cable-in-conduit conductor (CICC) configuration exploiting commercial second generation ReBaCuO (Re: Rare Earth and Y) coated-conductors. The final cable will be composed of five slots obtained in a helically twisted aluminum central core and filled with 2G tape stacks. This conductor is designed to operate above 10 kA in 12 T background field at 4.2 K or at about 10 kA in self-field at 77 K. A first sample of about 1-m length with one fully superconductive slot has been manufactured using 15 tapes provided by Superpower, Inc. and 12 tapes from the SuNAM Company grouped in two sub-stacks divided by a Kapton foil. Each tape of the stack has been characterized individually by measuring critical current values Ic at 77 K (liquid N2 bath) in self-field and n-index. Results revealed that the tapes showed no degradation of critical current values when compared with suppliers specifications confirming that the proposed manufacturing process is fully compatible with commercial coated-conductors. Inter-tape resistance(Rinter) has also been measured and the observed dependence of Rinter on the tape position in the stack has been put in correlation with transverse stress distribution calculated by finite element models. A second sample with a full superconducting slot has been manufactured using 18 SuNAM tapes. Preliminary results on the stack transport measurements performed at 77 K in self-field will be presented and discussed. All the samples were manufactured by using already existing industrial equipments at Tratos Cavi SpA.

Design, Manufacture, and Test of an 80 kA-Class Nb3Sn Cable-In-Conduit Conductor With Rectangular Geometry and Distributed Pressure Relief Channels

Within the frame of the R&D activities carried out in Europe for the toroidal field coils of the nuclear fusion device DEMO, a fundamental milestone was considered to be the demonstration of Nb3Sn cable-in-conduit conductors (CICC) performance in the demanding range of interest for DEMO. Among the different technological solutions envisaged, the present paper deals with a wind & react CICC solution, with rectangular geometry, thick steel jacket, and distributed pressure relief channel, designed to operate at 82 kA in a magnetic field of 13 T and with a current sharing temperature Tcs > 6.5 ,K. The main manufacturing steps of the prototype conductor are described in the present paper, carried out within industrial environment, partly using the facilities and procedures available for the manufacture of ITER conductors. A sample was designed for the EDIPO facility at the Swiss Plasma Center, Switzerland, in the configuration usually adopted for the test of ITER poloidal field conductors, where the two straight conductor legs are part of the same cable length, with a continuous transition through a bottom hairpin-type joint, thus avoiding any resistive connection. The conductor has been characterized in terms of dc performance at relevant operating conditions and the absence of any performance degradation with electro-magnetic load cycles has been verified, thus, qualifying the proposed technological solution. AC losses and thermo-hydraulic tests have also been carried out, providing relevant information for further coil design.

Overview of Conductor Production for ITER Toroidal Field Magnet in Korea

The ITER toroidal field (TF) conductor is made up of superconducting Nb3Sn and copper strands assembled into a multistage, rope-type cable inserted into a conduit of butt-welded stainless steel jacket sections. For the ITER Project, the Korean Domestic Agency (KODA) took the responsibility of the procurement of 27 superconducting conductors for the ITER TF magnets. After concluding the Procurement Arrangement (PA) with the ITER International Organization in May 2008, KODA has been implementing the PA through four major industrial contracts: (1) Nb3Sn strand, (2) cable, (3) stainless steel jacket sections, and (4) jacketing. Prior to the production of conductors required for the TF coils, one 760-m-long copper dummy conductor and one 100-m-long superconducting conductor were fabricated for manufacturing process qualification. As of June 2013, 16 TF conductors were successfully manufactured. The full-size conductor performance tests in the SULTAN facility yielded very high performance. This article describes the technical requirements of the TF conductor and how KODA has been manufacturing the conductors with a high-level quality assurance/quality control system. It also presents the results of acceptance tests, including those of the SULTAN test.

Assessment Studies and Manufacturing Trials for the Conductors of DEMO TF Coils

This paper reports the main outcomes of the 2013 design activities for the toroidal field magnet of the European nuclear fusion reactor DEMOnstration Power Plant (DEMO). Within the current project plan, the manufacture of full-size conductor prototypes during 2014 and their test during 2015 are foreseen, aimed at the assessment of the proposed cable-in-conduit-conductor technologies. Industrial partners have been thus already involved at this early stage, and the preliminary cabling trials performed are illustrated here. As far as the coil design assessment is concerned, one of the main aspects to be investigated is the mechanical performance of the magnet, considering its large size and the high electromagnetic forces involved. An overall 3-D finite-element model of the coil has been set up, and mechanical stress analysis has been carried out for a selected instant of the plasma scenario after the computation of the electromagnetic loads within a full 3-D system model, including central solenoid and poloidal field coil contributions. The resulting loads have been mapped on the finite-element-method model, making use of a novel mesh-independent interpolator based on radial basis functions. The results reported here highlight a quite high level of stress, which is close to the acceptance limits, in some regions of the steel casing. Further investigations and assessments are required, but the most critical areas are clearly identified.

The DRYSMES4GRID project: development of a cryogen free cooled SMES demonstrator based on MgB2

A three-year research project, called DRYSMES4GRID, was recently funded by the Italian Minister of Economic Development, Italy. The project, which involves five Italian partners (companies, universities, and research institutes), is aimed to demonstrate the feasibility of cost-competitive SMES based on magnesium diboride (MgB2 ) with a cryogen-free cooling by means of the manufacturing and the testing of a demonstrator with an objective rating of 500 kJ/200 kW. This rating is deemed suitable for disclosing the critical technological aspects of all components in view of practical applications. A further goal of the project is the assessment of the technical and economic benefits that the SMES can bring to real-world electric grids. The general outline and technical objectives of the project are presented in this paper. Preliminary design assumptions and results concerning the MgB2 coil and the power condition system are also discussed.