Metal-as-Insulation HTS coils

In this article, we summarize what we have learned about Metal-as-Insulation (MI) winding behavior and technical challenges. Bailey et al. first proposed the use of Metallic Insulation (MI) for superconducting magnet in 1988 through a U.S. patent. High Temperature Superconductor (HTS) materials are highly thermally stable. This feature compared to classical Low Temperature Superconductor (LTS) enables the use of MI technology to improve the protection against quenches. Gupta was the first to propose the use of a metallic tape in an HTS winding to avoid too much radial currents in No Insulation (NI) in 2011. Hahn et al. presented preliminary results on a pancake sample the same year. We are proposing here to come back on the work done for about 10 years by research groups worldwide and will focus on the turn-to-turn contact resistivity Rct parameter. We will also give details of our LNCMI-CEA-Néel Institute MI HTS insert built in 2018 in the framework of the French National Research Agency (ANR) funding through the NOUGAT project. We tested this magnet many times between 2018 and 2021 and learnt a lot on this technology. This magnet is the first REBCO solenoid of this size using this technology and tested intensively at such high magnetic field (up to 32.5 T) so far. In this magnet, we firstly include a magnetic shielding technology consisting of REBCO NI turns inside the overbanding of each pancake. We give some details and effect of such technology inside an HTS MI insert in case of a fast discharge, a quench or an outsert failure. Finally, we discuss about the self-protection feature of MI coils and we propose a passive protection way for high Rct values.

Activation and transmutation of tungsten boride shields in a spherical tokamak

The FISPACT-II code is used to compute the levels of activation and transmutation of tungsten borides for shielding the central High Temperature Superconductor (HTS) core of a spherical tokamak fusion power plant during operations at 200 MW fusion power for 30 years and after shutting down for 10 years. The materials considered were W2B, WB, W2B5 and WB4 along with a sintered borocarbide B0.329C0.074Cr0.024Fe0.274W0.299, monolithic W and WC. Calculations were made within shields composed of each material, for five reactor major radii from 1400 to 2200 mm, and for six 10B isotope concentrations and at five positions across the shield. The isotopic production and decay in each shield is detailed. The activation of boride materials is lower than for either W or WC and is lowest of all for W2B5. While isotopes from tungsten largely decay within 3 years of shut-down, those from boron have a much longer decay life. An acceptable 70% of the absorbing 10B isotope will remain after 30 years of operations behind the first wall for a 1400 mm radius tokamak. Gaseous production is problematic in boride shields, where 4He in particular is produced in quantities 3 orders of magnitude higher than in W or WC shields. The FISPACT-II displacements per atom (dpa) tend to increase with boron content, although they decrease with increased 10B isotopic content. The dpa ranges of boride shields tend to lie between those of W and WC. Overall, the results confirm that the favourable fusion reaction shielding properties of W2B5 are not seriously challenged by its irradiation and transmutation properties, although helium gas production could be a challenge to its thermal and mechanical properties.

Synthesis of rhombohedral LaCuO3 thin films using oxidation effect of NaClO solution

LaCuO3 is one of the most fundamental cuprate perovskite block which has a similar structure to the cuprate high-temperature superconductor. Therefore, some consider that the study on LaCuO3 is one...

Investigations of proximity-induced superconductivity in the topological insulator Bi2Te3 by microRaman spectroscopy

We used the topological insulator (TI) Bi2Te3 and a high-temperature superconductor (HTSC) hybrid device for investigations of proximity-induced superconductivity (PS) in the TI. Application of the superconductor YBa2Cu3O7-δ (YBCO) enabled us to access higher temperature and energy scales for this phenomenon. The HTSC in the hybrid device exhibits emergence of a pseudogap state for T > Tc that converts into a superconducting state with a reduced gap for T < Tc. The conversion process has been reflected in Raman spectra collected from the TI. Complementary charge transport experiments revealed emergence of the proximity-induced superconducting gap in the TI and the reduced superconducting gap in the HTSC, but no signature of the pseudogap. This allowed us to conclude that Raman spectroscopy reveals formation of the pseudogap state but cannot distinguish the proximity-induced superconducting state in the TI from the superconducting state in the HTSC characterised by the reduced gap. Results of our experiments have shown that Raman spectroscopy is a complementary technique to classic charge transport experiments and is a powerful tool for investigation of the proximity-induced superconductivity in the Bi2Te3.

Viewpoint on the manuscript by Zachary S. Hartwig et al “VIPER: An industrially scalable high current, high temperature superconductor cable” 2020 Supercond. Sci. Technol. 33

HTS tokamak SPARC is under development by the team lead by CFS, Cambridge, MA. The magnet will have toroidal coils operating at 20 T at a current in the 25 to 40 kA range. The ViewPoint describes VIPER, an advanced TSTC-based HTS cable that has a potential to meet all the criteria required for the HTS tokamak. If proven to be successful, the cable approach promises long lengths, hundreds of meters, of the high-performance cable with predictable and repeatable properties.

Mass of Abrikosov vortex in high-temperature superconductor YBa$$_2$$Cu$$_3$$O$$_{7-\delta }$$

For more than four decades, mass of Abrikosov vortices defied experimental observations. We demonstrate a method of its detection in high-temperature superconductors. Similarly to electrons, fluxons circulate in the direction given by the magnetic field, causing circular dichroism. We report the magneto-transmittance of a nearly optimally doped thin YBa$$_2$$ 2 Cu$$_3$$ 3 O$$_{7-\delta }$$ 7 - δ film, measured using circularly polarized submillimeter waves. The circular dichroism emerges in the superconducting state and increases with dropping temperature. Our results confirm the dominant role of quasiparticle states in the vortex core and yield the diagonal fluxon mass of $$2.2 \times 10^8$$ 2.2 × 10 8 electron masses per centimeter at 45 K and zero-frequency limit, and even larger off-diagonal mass of $$4.9 \times 10^8 m_e$$ 4.9 × 10 8 m e /cm.