SangGap Lee

Effect of Resistive Metal Cladding of HTS Tape on the Characteristic of No-Insulation Coil

This paper presents experimental and theoretical studies of the no-insulation (NI) winding method of second-generation high-temperature superconducting (HTS) wire. We compared two single pancake coils wound by two different HTS wires. One pancake coil is made of a normal HTS wire with an electroplated copper stabilizer. The other pancake coil is made of the same HTS wire with the only difference in an additional outermost layer made of stainless steel. We employed an equivalent circuit model to evaluate our experimental results. We tested both coils by the same simple operating procedure consisting of two steps: first, ramping up of current from zero to holding current (IH) and second, keeping the IH at minimum 500 s. We also tested the stability of the coil wound by an HTS wire with an additional layer of stainless steel by applying a current exceeding a critical current of the coil. We observed a charging time of the metal-cladding HTS coil reduced to a quarter of copper-electroplated HTS coil.

400-MHz/60-mm All-REBCO Nuclear Magnetic Resonance Magnet: Magnet Design

We present a design of a 400-MHz/60-mm all-REBCO nuclear magnetic resonance (NMR) magnet (H400) that consists of a stack of 56 double-pancake (DP) coils. With the multiwidth no-insulation technique incorporated, DP coils were wound with REBCO tapes of five different widths, i.e., 4.1, 5.1, 6.1, 7.1, and 8.1 mm; DP coils placed at and near the magnet midplane were wound with the narrowest (4.1 mm wide) REBCO tapes, whereas those with progressively wider tapes were placed toward the top and bottom of the magnet, where the “perpendicular field B⊥” is at its peak within the magnet. The magnet was designed to be operated under a conduction cooling environment at 20 K. Once successfully completed, the magnet will be installed as an NMR user facility in the Korea Basic Science Institute. Basic magnet performances and major technical challenges were discussed.

Feasibility Study of the Impregnation of a No-Insulation HTS Coil Using an Electrically Conductive Epoxy

This paper reports the feasibility of the impregnation of no-insulation (NI) high-temperature superconducting (HTS) coils using an electrically conductive epoxy resin. Recently, several studies of HTS coils without turn-to-turn insulation have been reported for field coils used in rotating machines such as motors and generators. The NI winding technique enhances the thermal stability of the HTS coil without requiring complicated protection techniques because the quench current is automatically bypassed through the turn-to-turn contacts within the HTS coil. Nevertheless, there is still a question as to whether the NI technique can be applied to rotating machines. To utilize an HTS coil under high mechanical loads such as field coils for rotating machines, the HTS tapes must be stabilized mechanically. For HTS field coils intended for use in rotating machines, epoxy impregnation is generally necessary to protect the HTS field coil from mechanical disturbances caused by the magnetic field and rotational vibration of the rotor to enhance the mechanical stability [1], [2] . However, the NI HTS coil cannot be fabricated by wet winding using epoxy resin because epoxy resins such as Stycast 2850 FT and CTD 521 are electrically insulating materials. This study examines the electrical stability of an NI HTS coil impregnated with an epoxy resin containing electrically conductive particles. The results are likely to present useful data for the application of electrically conductive epoxy impregnated NI HTS coils to rotating machines.

Three-Dimensional Numerical Simulation Employing Normal Zone Propagation Velocity on Heat Propagation of LTS Magnet Under Quench Process

Because low-temperature superconducting (LTS) magnets can conduct large electric current and generate intense magnetic fields under cryogenic conditions, such magnets are used in many applications such as MRI, nuclear magnetic resonance spectrometers, and mass spectrometers. However, an abnormal termination called “quench” disturbs the normal operation and increases the magnet temperature. To protect the LTS magnet from excessive heat, the maximum temperature of a magnet under the quench process should be calculated. The design of a superconducting magnet protection system is performed according to the calculated maximum temperature. This is why accurate estimation of magnet temperature is important. The quench process of a superconducting magnet involves complex physical mechanisms, which requires a thermal–electrical simulation using computational analysis. We propose a highly efficient and reliable three-dimensional quench calculation method that can calculate the magnet temperature in the quench process. The LTS magnet is divided into many unit nodes; multiphysics analysis at each node is carried out with respect to the elapsed time. To verify the feasibility of the simulation, LTS magnet quench experimental results were compared with the simulation results. This study has the potential to develop a computational method for heat propagation analysis of a superconducting magnet.