Large superconductors and joints for fusion magnets: From conceptual design to testing at full scale

Abstract

A new kind of superconductor, using the cable-in-conduit concept, is emerging, mainly in the context of fusion activity. At present no large Nb3Sn magnet in the world is operating using this concept. The difficulty of this technology, which has now been studied for 20 years, is that it requires major advances in several interconnected new fields, such as handling a large number (1000) of superconducting strands, high current conductors (50 kA), forced flow cryogenics, Nb3Sn technology, low loss conductors in pulsed operation, high current connections and high voltage insulation (10 kV), as well as demonstration of its economical and industrial feasibility. CEA has been very much involved, during the past ten years, in this development, which took place in the framework of the NET and ITER technological programmes. One major milestone was reached in 1998-1999 with the successful tests by Euratom-CEA of three full size conductor and connection samples in the SULTAN facility in Switzerland.

Analysis of Microcomposite Cu-Nb Conductors Characteristics and Possibility of Their Joining / Mikrokompozitinių Cu-Nb Laidininkų Ypatumų Ir Jų Sujungimo Galimybių Analizė

“…Analogiškos problemos bus ir taikant šiuos laidus didelės galios elektros linijose, kur taip pat kils poreikis patikimai sujungi laidų galus. Kompozitinių laidininkų struktūra, sujungiant juos lydomo suvirinimo būdu, iš dalies pažeidžiama arba modifikuojama (Ciazynski et al 2001). Todėl dauguma tradicinių lydomojo suvirinimo metodų nepritaikoma kompozitinėms medžiagoms, nes iš-silydant matricai vyksta negrįžtamieji struktūros pokyčiai.…”

“…Taip pat atliekami moksliniai tyrimai bei bandymai pritaikyti ir kitas specialias technologijas mikrokompozitiniams laidininkams sujungti. Šiuo metu jau galima rasti informacijos apie superlaidžių NbSn, NbTi ir kitų analogiškų mikrokompozitinių laidininkų litavimo su PbSn lydmetaliu ir elektronpluoščio suvirinimo bandymų rezultatus bei šių technologijų taikymą ITER projekte (Ciazynski et al 2001). Bandymai, siekiant atlikti Cu-Nb mikrokompozitinių laidininkų kontaktinį suvirinimą ir litavimą, buvo daromi ir Lietuvoje (Višniakov et al 2011).…”

Joint Design for the EDIPO

“…2): I) after removing the jacket from the two conductor ends to be joined for at least one twist pitch (TP) length, all the last-but-one cabling stage bundles are separated by each other and cut at different complementary lengths; II) all the strand coating is removed and then one single cable is re-constituted matching head-to-head and re-twisting the two trimmed cables; III) a metallic tube (preferentially Cu) is pulled over the joint area and here compacted in order to lower inter-strand contact resistance (and supply additional thermo-electrical stabilization), which improves the overall electrical joint conductivity; IV) jacket is rebuilt by welding a new conduit to the ends of the original ones. The joint has a size just slightly larger than original conductor (depending on conduit dimensions used for jacket rebuilding) and the concept of interpenetrating the two cables has been chosen mainly to avoid complicated bonding procedure and/or big room occupancy, as for example it is in the so-called "Twin-box" Joint [3], currently adopted for ITER coils.…”

Electrical and thermal designs and analyses of joints for the ITER PF coils

“…The twin-box concept developed by CEA has been chosen not only because of its capability to be really dismountable, but also because of the long experience gained on this type of joint (at subsize and full-size scales) in Europe [2], [3].…”