M.I. Surin

The background magnets of the Samsung Superconductor Test Facility (SSTF)

The background magnet system of SSTF (Samsung Superconductor Test Facility) for KSTAR (Korea Superconducting Tokamak Advanced Research) is now under design. The main coil (MC) is split solenoids and the gap can be changed from 0 to 750 mm. The ID of MC is 750 mm. It will be wound using a CICC (cable-in-conduit conductor) designed for the central solenoid of KSTAR. The central field is 8 T at 22.5 kA when the gap is 250 mm. The ramp rate of MC is 3 T/s. A pair of blip coils will simulate (during the discharge) 1 T amplitude and 20 T/s rate electromagnetic disturbances expected from the KSTAR operation. To compensate the inductive interaction between MC and blip coils during the discharge of the blip coils, a pair of cancellation coils is foreseen. Both blip and cancellation coils (BCC) are fed in series and generate 1 T central field at 7 kA and 250 mm gap. The BCC are wound with CICC and cooled internally and externally.

Development of superconducting solenoids from multifilamentary niobiumtin wires without stabilizing matrix and analysis of their thermal stability

Abstract Experience in developing superconducting solenoids from multifilamentary niobium-tin wires without stabilizing copper is presented. Such wires are the components of the conductor of the Tokamak 15 magnetic system. The heat treatment of the wire was carried out after winding the solenoid. Tests showed that currents close to the critical values for short samples can be achieved in the solenoids in fields of up to 12.3 T. The calculated stabilities of the NbTi and Nb 3 Sn wires under local pulse disturbances were compared to explain the results. The NbTi wires were shown to be more stable in low fields due to the presence of copper. In high fields the Nb 3 Sn wires proved to be more stable even without a stabilizing matrix.

The superconducting transformer of the Samsung Superconductor Test Facility (SSTF)

In the frames of designing the SSTF (Samsung Superconductor Test Facility) for the KSTAR (Korea Superconducting Tokamak Advanced Research), the 50 kA transformer charging a CICC (cable-in-conduit conductor) short sample for one second is now under design. The primary winding conductor consists of six NbTi and six stainless steel strands tabled around a low RRR rectangular copper core, which was used by Kurchatov Institute in small SMES (superconducting magnetic energy storage) windings. The secondary winding consists of 24 subcables wrapped around and soldered to a low RRR copper strip. Each subcable consists of six NbTi strands cabled around a copper strand. The strands for primary and secondary windings are 0.85 mm diameter NbTi wires with six micrometer 8910 filaments. Both primary and secondary conductors have large current and temperature margins to ensure a reliable operation of the superconducting transformer. The primary coil is placed in a cylindrical LHe vessel. The four secondary turns are glued to the outer surface of the LHe vessel. The joints between the transformer and the sample are described.

The design and development of high-current leads on the basis of 2G HTS conductors

The feasibility of creating high-current leads on the basis of second-generation (2G) high-temperature superconductors (HTSs) was demonstrated. A method for graded soldering of 2G HTS tape stacks is proposed. It allows one to avoid negative effects that are related to an inhomogeneous current sharing between parallel HTS conductors. A prototype of HTS-coated current leads (CLs) was designed, manufactured, and tested; its critical current exceeds 18 kА. Prototypes of HTS CLs for the superconducting magnetic system of the Nuclotron accelerator (a part of the NICA collider) with an operating current of 6 kA were developed, manufactured, and tested in liquid helium (the overcurrent was 9 kA).

A prototype of a superconducting magnet for a 170-GHz gyrotron

Within the framework of the “International Thermonuclear Experimental Reactor” (ITER) program, a prototype of a superconducting magnet for a 170-GHz gyrotron has been developed, manufactured, and tested. The operating induction value (7.1 T at the center of a 219-mm-diameter cold hole and 8.1 T on the winding) is reached at a current of 185.2 A. In the final version of the magnet, the required induction value was reached without aging. Special requirements are imposed on the distribution of the magnetic field along the axis, including an abrupt field decrease on both sides of the magnet. Axial forces are additionally taken by a special device. The magnet’s sections are wound with multifiber conductors based on niobium-tin and niobium-titanium alloys. Seventeen resistive shunts are provided for protecting sections during their transition to the normal state. The magnet is equipped with a device for removing a part of energy from the sections. Mechanical stresses in the magnet’s sections and the structure’s power elements have been measured during tests.

The comparison of active and passive cancellation coils for SSTF

The Samsung superconductor test facility (SSTF) at SAIT (Samsung Advanced Institute of Technology, Taejon, Korea) is to be equipped with a 740 mm inner diameter superconducting split magnet (MC), which provides the background field B/sub 0/ = 8 T with ramp rate up to 3 T/s at 250 mm gap between the magnet halves. A smaller superconducting split magnet (BC) with the diameter 400 mm will be installed coaxially inside of MC to produce an additional fast variation of magnetic field with ramp rate up to 20 T/s and amplitude /spl plusmn/1 T. In order to reduce the coupling between MC and BC magnets and to avoid the MC disturbance by the fast changing stray field from BC a cancellation coil (CC) is to be provided. The comparison of an active superconducting CC charged in series with BC and a passive cryoresistive, LHe cooled CC (PCC) of which the current is induced during the fast BC discharge only has been made. The advantages of the PCC concept are discussed. The amount of LHe evaporated by PCC (charged for a short time) is estimated to be 3 to 5 liter/pulse. Recovering time for PCC is 5 to 10 min.

The conductors of the 50 kA superconducting transformer for SSTF

The 50 kA transformer for Samsung Superconductor Test Facility (SSTF), which will charge the Korean Superconducting Tokamak Advanced Research cable-in-conduit conductor samples for 1 s is under design. The NbTi based conductors for primary and secondary windings are described. The primary winding conductor consists of six NbTi and six stainless steel strands cabled around rectangular copper core. Such a design was previously used by Kurchatov Institute in small SMES windings. The secondary winding conductor consists of 24 subcables wrapped around and soldered to a copper strip. Each subcable consists of six NbTi strands cabled around one copper strand. NbTi strands for both primary and secondary windings are 0.85 mm in diameter. NbTi wires have 8910 6-μm filaments. Both primary and secondary winding conductors have large current and temperature margins to ensure a reliable operation of the superconducting transformer.

Results of preliminary testing of blip and cancellation coils for the Samsung Superconductor Test Facility (SSTF)

The background magnet system of SSTF (Samsung Superconductor Test Facility) for KSTAR (Korea Superconducting Tokamak Advanced Research) will be equipped with a pair of main coils (MC) and a pair of blip coils (BC). The main goal of the BC is to simulate electromagnetic disturbances (1 T amplitude and 20 T/s discharge rate), expected from the KSTAR operation. The coupling losses and magnetic interaction between MC and BC will be decreased by resistive cancellation coils (CC) wound onto a fiberglass bobbin. The BC is wound with a cable in conduit conductor (CICC) packed with Nb/sub 3/Sn strands. A set of BC and CC was tested in an open type cryostat. The BC is cooled with both boiling LHe in a container and pressurized helium passing through the CICC. The BC was charged up to 6.7 kA and discharged in 50 ms. During the discharge, the maximum field variation rate corresponds to 28 T/s in the BC center and 53 T/s on the BC conductor. No quench was observed and the BC was recharged in less than 1 minute. The measured shielding current in the CC is in a good agreement with the calculated value.