Jung Bin Song

Joint Characteristics of YBCO Coated Conductor by Removing a Metallic Stabilizer

This paper presents the development status of joint method between the superconducting YBCO coated conductors (YBCO CC). In general, the YBCO-CC tape consists of an upper stabilizer, substrate, buffer, YBCO and a bottom stabilizer. It is suggested that the stabilizer between the two YBCO-CC tapes need to be removed, in order to improve the characteristics of the joints. The removing process was conducted by using heat and partial etching. The resistance and critical current of the joints were measured from the curve. The optical micrographs were analyzed for microstructures between the joint areas. After several times of over current test, the critical currents of the various types of joint samples were examined for applying to the high temperature superconducting magnet system.

Effect of Winding Tension on Electrical Behaviors of a No-Insulation ReBCO Pancake Coil

This paper presents a study on the effects of winding tension on the characteristic resistance of a no-insulation (NI) coil. Two ReBCO NI test pancake coils, having the same winding i.d. (60 mm), o.d. (67.6 mm), and number of turns (60), were sequentially prepared in a way that the first test coil was wound with a winding tension of 12-N, tested, and then rewound with a new winding tension of 20-N for the same tests. In each test, the test coil was energized at a target current, the power supply was “suddenly” disconnected, and then the temporal decay of the coil center field was measured, from which the time constant of the test coil and the consequent characteristic resistance were obtained. To check the reproducibility of experimental data, each test was repeated four times and each time the test coil was unwound and rewound with a given winding tension. The experimental results were analyzed with equivalent circuit analyses. Correlation between the winding tension and the characteristic resistance was discussed in detail.

Thermal Quench Behaviors of No-Insulation Coils Wound Using GdBCO Coated Conductor Tapes With Various Lamination Materials

This paper presents the quench initiation and propagation characteristics of no-insulation racetrack coils wound using three types of Cu-stabilized GdBCO coated conductors (CCs), with SUS and brass laminations, and without lamination. The test results show that the minimum quench energy values of the brass-laminated GdBCO CC coil were larger than those of the SUS-laminated one. Moreover, the normal zone propagation velocities of the brass-laminated GdBCO CC coil were greater than those of the SUS-laminated one due to the higher thermal conductivity of brass. Moreover, the nonlaminated GdBCO CC coil exhibited greatly improved thermal stability compared to the brass/SUS-laminated GdBCO CC coils, because the local heat in the event of quenching was easily dissipated due to the absence of lamination.

Dynamic Response of No-Insulation and Partial-Insulation Coils for HTS Wind Power Generator

In this paper, we present results, experimental and numerical, of the electromagnetic interaction forces between pairs of racetrack coils under time-varying conditions. Three turn-to-turn insulation designs were applied to wind three racetrack coils with GdBCO coated conductor: 1) no insulation (NI); 2) partial insulation (PI) of a polyimide layer every eight turns; and 3) insulation (INS) of a polyimide layer between each, i.e., NI, PI, and INS racetracks. Two racetrack pairs, namely, NI-INS and PI-INS, were tested for their interaction forces, measured with load cell under current-ramping conditions in a bath of liquid nitrogen at 77 K. Good experimental and simulation results validate our equivalent circuit model to compute interaction forces of PI-INS racetrack pair. Overcurrent test of NI and PI coils, where each racetrack coil was charged above critical current (Ic), was also performed to compare coil stability. This result implies that, although the PI winding technique improves the dynamic response, stability will be somewhat compromised.

High-

This paper presents recent progress in the fabrication and test of a 3 T/60 mm room temperature bore high- Tc superconducting high gradient magnetic separator (HGMS) using a solid nitrogen (SN2) cooling system. The aim of the study was to develop an inexpensive, compact, and stable superconducting HGMS for the purification of chemical-mechanical-planarization wastewater in the semiconductor industry. The HGMSs magnet, which was cooled by SN2, was comprised of an assembly of 18 GdBCO double pancake coils, each of which was wound without turn-to-turn insulation. Cooling test results showed that the thermal stability of the high-Tc superconducting-HGMS magnet with SN2 was enhanced due to the large heat capacity of SN2. Moreover, in the filtration tests, the suspended solids value of filtrated wastewater at 2 T in a flow rate of 400 ml/min decreased to 1.6 mg/L, resulting in a 99.6% reduction in SS value compared to raw wastewater.

T_{\rm c}

This paper presents experimental and analytical results of electromagnetic forces between no-insulation (NI) and insulation (INS) coils under time-varying conditions for NI coils that may be used in wind power generator. Three test pancake coils, one NI and the others INS, of the identical winding i.d., bore size, and number of turns, are wound with GdBCO coated tape. To determine an electric circuit model of the NI coil, the coil was charged-and-discharged at different ramping rates. The data were used to compute a characteristic resistance of a parallel inductor/resistor circuit model. In force measurement, two sets of pancake pairs were tested, NI-INS and INS-INS, the later for comparison. The coils were tested in a bath of liquid nitrogen at 77 K. The dynamic force response of the NI-INS pair was compared with that of INS-INS. The analysis based on the circuit model was tested with the experimental results. Analysis agrees well with experiment, validating our technique to analyze the time-varying forces between the NI-INS pair.

Superconducting High Gradient Magnetic Separator Using Solid Nitrogen Cooling System for Purification of CMP Wastewater

This paper proposes a numerical approach to calculate the characteristic resistance (Rc) of partial-insulation (PI) and no-insulation (NI) high-temperature superconductor pancake coils with the nonuniform current path in such coils taken into consideration. Recently, an analytic approach has been proposed to estimate (Rc) of an NI coil, where the coil current is assumed to be “uniform” over the entire coil. This model, however, is not effective to explain the increase of (Rc) when a coil is modified from NI to PI. In this paper, we first introduce our numerical approach based on a finite element analysis. Then, the charging characteristics of selected PI and NI coils that we had previously reported are analyzed by the proposed approach. Reasonable agreement between the measured and calculated data validates the proposed approach to estimate (Rc) of a PI as well as an NI coil.

HTS Wind Power Generator: Electromagnetic Force Between No-Insulation and Insulation Coils Under Time-Varying Conditions

It is well known that HTS (high temperature superconductor) is promising for magnet applications, but it has been almost impossible so far to apply them to magnets in persistent current mode because of poor qualities of their superconducting joints at higher current as well as their lower index values. To get rid of the non-superconducting joints from an HTS superconducting magnet, a wind-and-flip technique for demonstrating a persistent current mode operation of HTS magnet using YBCO coated conductors had been suggested. This paper presents experimental results of measured drift of a persistent current in the YBCO pancake coil which was made by using the wind-and-flip technique. The pancake coil was wound by YBCO coated conductor with a width of 12 mm, which was slit longitudinally at the center of the conductor along the conductor by a specially designed slitter. A stainless steel heater was attached on the one end of the YBCO conductor as a persistent current switch to energize the pancake coil. A temporal stability of the magnetic field was analyzed by monitoring the long-term drift of the magnetic field at 77.3 K by Hall sensors.

Characteristic Resistance of No-Insulation and Partial-Insulation Coils With Nonuniform Current Distribution

This study examined the purification of wastewater from the chemical mechanical polishing (CMP) process via a superconducting high gradient magnetic separation (HGMS) system. To remove silica, the main contaminant in CMP wastewater, the optimal coagulation process of silica-magnetite-ferric hydroxide aggregates was empirically determined. Filtration tests via superconducting HGMS system with optimal coagulation process were conducted with respect to the magnetic field and wastewater flow rate. The turbidity and Si concentration of the wastewater filtered at 2 T and 400 mL/min were in accordance with the grey water standard and reverse osmosis (RO) feed water requirement, which demonstrated the feasibility of the superconducting HGMS system for the purification of CMP wastewater.

Magnetic Field Stability of a Small YBCO Magnet in Persistent Current Mode

The quench and recovery characteristics of two GdBCO-coated conductor racetrack coils, one wound onto a high-strength aluminum (AL 6061-T6) bobbin and the other wound onto an oxygen-free high-conductivity (OFHC) copper bobbin, were evaluated to investigate the effect of bobbin material on the thermal stability of the HTS racetrack coil. The test results show that the minimum quench energy values of the coil wound onto the OFHC copper bobbin were larger than those of the coil wound onto the AL 6061-T6 bobbin. Furthermore, in the case of the coil wound onto the OFHC copper bobbin, the voltage signals increased more slowly compared to the coil wound onto the AL bobbin, and the recovery time was much shorter after a hot spot was generated by a heater. Overall, the coil wound onto the OFHC copper bobbin exhibited better thermal stability due to its superior thermal diffusivity.