The commercially available high temperature superconductors (HTS) tapes and wires (BSSCO and REBCO) are introduced and the past and present projects to build fusion devices using HTS based magnets are reviewed. The main design options for high current, high field conductors are presented with the related R&D and the open issues. Depending on the material, the cable layout and the application specific needs, the challenges for HTS magnet technology are different, ranging from the anisotropic properties of the REBCO tapes, to the large volume heat treatment under high pressure for Bi-2212, to the ability to withstand the large transverse loads, to the optimization of the electrical connections for segmented coil assembly, to the ambitious target of fully demountable TF coils for tokamaks. For the generation of magnetic fields larger than 18–20 T, the HTS represents the enabling technology. The use of the expensive HTS can be better justified for applications, which are out of range for conventional, low temperature superconductors (LTS). Eventually, a roadmap for future R&D is sketched focusing on medium term technology milestones, e.g. addressing the issue of quench protection in HTS large magnets, the industrial manufacture of robust high current HTS cables and the engineering design/demonstration of demountable winding packs.

https://iopscience.iop.org/article/10.1088/1741-4326/aad835/pdf

High temperature superconductors for fusion magnets

/pdf/a-review-of-commercial-high-temperature-superconducting-2o02lszkmx.pdf

A review of commercial high temperature superconducting materials for large magnets: from wires and tapes to cables and conductors

Rare-Earth-barium–copper–oxide tapes are now available from several industrial manufacturers and are very promising conductors in high field applications. Due to diverging materials and deposition processes, these manufacturers' tapes can be expected to differ in their electro-mechanical and mechanical properties. For magnets designers, these are together with the conductors' in-field critical current performance of the highest importance in choosing a suitable conductor. In this work, the strain and stress dependence of the current carrying capabilities as well as the stress and strain correlation are investigated for commercial coated conductors from Bruker HTS, Fujikura, SuNAM, SuperOx and SuperPower at 77 K, self-field and 4.2 K, 19 T.

http://iopscience.iop.org/article/10.1088/0953-2048/28/4/045011/pdf

Electro-mechanical properties of REBCO coated conductors from various industrial manufacturers at 77 K, self-field and 4.2 K, 19 T

Rare-earth-barium-copper-oxide (REBCO) tapes are now available from several industrial manufacturers and are very promising conductors in high field applications. Due to diverging materials and deposition processes, these manufacturers' tapes can be expected to differ in their electro-mechanical and mechanical properties. For magnets designers, these are together with the conductors' in-field critical current performance of the highest importance in choosing a suitable conductor. In this work, the strain and stress dependence of the current carrying capabilities as well as the stress and strain correlation are investigated for commercial coated conductors from Bruker HTS, Fujikura, SuNAM, SuperOx and SuperPower at 77 K, self-field and 4.2 K, 19 T.

Helical reactor design FFHR-d1 and c1 for steady-state DEMO

Feasibility studies on applying high-temperature superconductors (HTS) to the heliotron-type fusion energy reactor FFHR are being carried out. Using HTS, we consider that the three-dimensional helical coils with a ~40 m diameter can be constructed without preparing a huge winding machine. A practical method for realizing this concept is proposed. The electromagnetic stress inside the helical coil packs is examined using an FEM analysis for double-pancake windings. The effect of error magnetic field generated by the shielding currents in HTS tapes is also examined.

Design Progress on the High-Temperature Superconducting Coil Option for the Heliotron-Type Fusion Energy Reactor FFHR

Negative ion beam extraction in ROBIN

Impedance matching circuit between radio frequency (RF) generator and the plasma load, placed between them, determines the RF power transfer from RF generator to the plasma load. The impedance of plasma load depends on the plasma parameters through skin depth and plasma conductivity or resistivity. Therefore, for long pulse operation of inductively coupled plasmas, particularly for high power (∼100 kW or more) where plasma load condition may vary due to different reasons (e.g., pressure, power, and thermal), online tuning of impedance matching circuit is necessary through feedback. In fusion grade ion source operation, such online methodology through feedback is not present but offline remote tuning by adjusting the matching circuit capacitors and tuning the driving frequency of the RF generator between the ion source operation pulses is envisaged. The present model is an approach for remote impedance tuning methodology for long pulse operation and corresponding online impedance matching algorithm based on RF coil antenna current measurement or coil antenna calorimetric measurement may be useful in this regard.

/pdf/online-tuning-of-impedance-matching-circuit-for-long-pulse-3nr3iqx30e.pdf

Online tuning of impedance matching circuit for long pulse inductively coupled plasma source operation—An alternate approach

Large-current capacity high-temperature superconducting (HTS) conductors suitable for high-field large-scale DC magnets, such as of helical-type fusion reactor FFHR, are being designed by employing YBCO tapes. As the first step of R&D of such an HTS conductor, we have fabricated short conductor samples using Bi-2223/Ag tapes. The HTS conductor was made by simply stacking and soldering Bi-2223/Ag tapes inside a copper sheath. The HTS conductor sample was fabricated in a hair-pin configuration and was tested under a bias magnetic field of 8 T. The conductor was thermally insulated by epoxy and GFRP and was conduction-cooled by liquid helium from the ends. Resistive heaters attached to the surface of the GFRP-insulated conductor were used to increase the temperature of the conductor for testing at elevated temperatures up to 30 K. The critical currents of the HTS conductor at 4.2 K, 10 K, 20 K, and 30 K were measured in a bias magnetic field of 8 T. The stability margin of the HTS conductor was examined in conduction-cooled conditions at different temperatures. The conductor was found to be very stable even at high currents closer to the critical currents.

Experimental Results of Large-Current Capacity HTS Conductors

The technique of surface production of negative ions using cesium, Cs, has been efficiently exploited over the years for producing negative ion beams with increased current densities from negative ion sources used on neutral beam lines. Deposition of Cs on the source walls and the plasma grid lowers the work function and therefore enables a higher yield of H−, when hydrogen particles (H and/or Hx+) strike these surfaces.A single driver RF based (100 kW, 1 MHz) negative ion source test bed, ROBIN, is being set up at IPR under a technical collaboration between IPR and IPP, Germany. The optimization of the Cs oven design to be used on this facility as well as multidriver sources is underway. The characterization experiments of such a Cs delivery system with a 1 g Cs inventory have been carried out using surface ionization technique. The experiments have been carried by delivering Cs into a vacuum chamber without plasma. The linear motion of the surface ionization detector, SID, attached with a linear motion ...

Cesium Delivery System for Negative Ion Source at IPR

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