Non-twisted stacks of coated conductors for DC magnets: analysis of inductance and AC losses

In the last 10-15 years, the most common strategy in the development of High Temperature Superconducting (HTS) cable for magnets has been to imitate Low Temperature Superconducting (LTS) cable designs. However, requirements for LTS materials are not valid for HTS materials, which are extremely stable. For example, non-twisted multifilamentary Bi-2223 tapes have been successfully used in several magnets. This paper review stability and analyse inductance and AC losses in non-twisted stack of HTS tapes. Numerical calculations show that twisting has negligible effect on inductance variations in a stack of tapes. Regarding AC losses, any magnet built with coated conductors have larger losses than LTS ones, because of the aspect ratio and large width of the tape. If a wide tape is replaced by a non-twisted stack of narrow tapes, losses and residual magnetisation could be reduced. In contrast with multifilamentary wires, twisting a stack of tapes reduces losses only marginally. Therefore, cables composed of non-twisted stack could be designed to have losses comparable to the one of twisted stack concepts. Few examples of large cables for fusion applications are discussed. Designs based on non-twisted stacks can be simpler, more robust and cost effective than twisted ones.Comment: 20 pages, 10 figures, submitted to Cryogenic

Design and R&D for the DEMO Toroidal Field Coils Based on Nb3Sn React and Wind Method

In 2013, the Swiss Plasma Center proposed a Toroidal Field (TF) layout for the DEMO-EUROfusion tokamak, based on a graded winding made of layers of Nb3Sn (react&wind) and NbTi conductors. The R&D effort led in 2015 to a full size prototype conductor tested up to 82.4 kA at 12.35 T. The test continued in 2016 and new results are presented. In summer 2015 a new reference baseline was issued for the DEMO-EUROfusion tokamak, leading to an update of the TF requirements. The design update is presented in this paper, with the winding pack consisting of 12 single layers of Nb3Sn with "invisible" (no protrusion) inter-layer joints. The high grade Nb3Sn react&wind conductor operates at 63.3 kA, 12.23 T with T-cs > 6.5 K. A new prototype conductor is being manufactured. The main advantages of the graded approach, applied to both the superconductor and the stainless s teel conduit, are a substantial space and cost saving compared to the wind&react approach with pancake winding

Shelf ice-associated cryo-benthos and environmental features

Incidences of cryo-benthic communities beneath ice shelves are rare and recent discoveries. Combined seal- and ROV-borne imagery and novel sampling technologies allowed for a re-assessment and augmentation of earlier findings on a cryo-benthic isopod community (Antarcturus cf. spinacoronatus), being attached head-down to the underside of floating shelf ice at depths of around 80-150m. The shelf ice-associated cryo-benthos was discovered at Drescher Inlet (-72.83667 -19.15300), Riiser-Larsen Ice Shelf (eastern Weddell Sea). The inlet constitutes a 25km long and between 2 and 4km wide crack in the surrounding shelf ice, which is associated with certain environmental features. Here we compile all available local physical, biological, and biogeochemical data and discuss their relevance in the wider regional context for this faunal hotspot. These include data on shelf, sea and platelet ice, seafloor topography, hydrography and water chemistry, as well as associated pelagic and benthic marine life, in particular affinities of the cryo-benthic isopod community to related fauna occurring in nearby seabed communities using molecular barcoding

Physical Properties of High-Temperature Superconductors

A much-needed update on complex high-temperature superconductors, focusing on materials aspects; this timely book coincides with a recent major break-through of the discovery of iron-based superconductors. It provides an overview of materials aspects of high-temperature superconductors, combining introductory aspects, description of new physics, material aspects, and a description of the material properties This title is suitable for researchers in materials science, physics and engineering. Also for technicians interested in the applications of superconductors, e.g. as biomagnet

Fabrication Trials of Round Strands Composed of Coated Conductor Tapes

Various techniques have been proposed in order to assemble coated conductor tapes into high current strands. In this work, the preparation of high current capacity round strands starting from industrial coated conductors has been investigated. Round, twisted strands (about 50 cm long) consisting of stacked tapes sandwiched between two semicircular copper profiles have been assembled following two manufacturing routes: in one case the stack was first soldered to the copper profiles and then twisted; in the second method a twisted strand (stacked tapes between copper profiles) was soldered. The round conductors carry over 400 A at 77 K in self field. Three types of solder alloy were tested: BiSn, InSn, and PbSn. The critical current variation under bending strain was also measured: critical current retention of 99% was observed up to 0.3% peak bending strain. At 0.6% bending strain the strands prepared with PbSn solder exhibit a reversible reduction of the critical current of less than 2%, irrespective of the manufacturing route. Such round strands could be used to manufacture flat cables with conventional cabling methods