Earticle

LMO(LaMnO3) buffer layer of superconducting coated conductor was deposited on IBAD-MgO template in the plasma atmosphere at 650 oC which is relatively low compared with conventional deposition temperature of more than 800 oC. Deposition method of LMO was DC sputtering, and target and deposition chamber were connected to the cathode and anode respectively. When DC voltage was applied between target and chamber, plasma was formed on the surface of target. The tape substrate was located with the distance of 10 cm between target and tape substrate . When anode bias was connected to the tape substrate, electrons were attracted from plasma in target surface to the tape substrate, and only tape substrate was heated by electron bombardment without heating any other zone. The effect of electron bombardment on the surface of substrate was investigated by increasing bias voltage to the substrate. We found out that the sample of electron bombardment had the effect of surface heating and had good texturing at low controlling temperature.

Coated conductors have been developed to increase piece length and critical current for electric power applications. Otherwise, Many efforts were carried out to reduce AC loss of coated conductor for AC applications. Twisting and cabling processes are effective to reduce AC loss but, these processes can not be applied for tape shaped coated conductor. It is inevitable to have thin rectangular shape because coated conductor is fabricated by thin film deposition process on metal substrate. In this study, round shape superconducting wire was first fabricated using coated conductors. First of all, Ag coated conductor was used. coated conductor was slitted to several wires with narrow width below 1mm. 12ea slitted wires were parallel stacked on top of another until making up the square cross-section. The bundle of coated conductors was heat treated to stick on each other by diffusion bonding and then copper plated to make round shape wire. Critical current of round wire was measured 185A at 77K, self field.

We already fabricated a proto-type HTS charging system with photovoltaic (PV) system and obtained design parameters for DC converter and HTS charging system. In order to develop the real scale charging system efficiently, we suggested a maximum power point tracking (MPPT) controller using a perturb and observe (P&O) MPPT algorithm for PV system. In this paper, we designed and simulated the MPPT controller for the real scale HTS charging system. As well as, the PV module has been analyzed by solving solar cell equivalent equations. The simulated and theoretical results presented here are being considered the next study which addresses the design and fabrication parameters.

Shimming, active and/or passive, is indispensable for most MR (magnetic resonance) magnets where homogeneous magnetic fields are required within target spaces. Generally, shimming consists of two steps, field mapping and correcting of fields, and they are recursively repeated until the target field homogeneity is reached. Thus, accuracy of the field mapping is crucial for fast and efficient shimming of MR magnets. For an accurate shimming, a "magnetic" center, which is a mathematical origin for harmonic analysis, must be carefully defined, Although the magnetic center is in general identical to the physical center of a magnet, it is not rare that both centers are different particularly in HTS (high temperature superconducting) magnets of which harmonic field errors, especially high orders, are significantly dependent on a location of the magnetic center. This paper presents a new algorithm, based on a field mapping theory with harmonic analysis, to define the best magnetic center of an MR magnet in terms of minimization of pre-shimming field errors. And the proposed algorithm is tested with simulation under gaussian noise environment.

This paper proposes an insulation coordination and surge arrester design for superconducting power system with SFCL(Superconducting Fault Current Limiter) in Icheon substation. In the aspect of the economic analysis, since the superconducting devices are very expensive, the insulation coordination to prevent the dielectric breakdown caused by the lightning surge should be considered carefully. In this paper, the insulation coordination for real grid including SFCL and the design of the protection devices against lightning surge is verified using PSCAD/EMTDC.

The novel type of cable under consideration is cooled by gaseous Helium at elevated pressure. Helium is known for having poor electric breakdown strength; therefore the dielectric capabilities of this type of cable must be tested under conditions similar to the envisaged operation. In order to study the dielectric performance we have designed and built a novel high pressure cryostat rated at 2.17 MPa which has been used for testing model cables of lengths of up to 1 m. The cryostat is an open system where the gas is not re-circulated. This allows maintaining a high purity of the gas. The target temperature range is between 40 K and 70 K. This substantially increases the critical current density of the HTS compared to 77 K, which is the typical temperature of cables cooled by liquid nitrogen. The cryostat presented allows for adjusting the temperature and keeping it constant for the time necessary to run a complete dielectric characterization test. We give a detailed description of the cryostat. Measurements of partial discharge inception voltages as well as the temperature distribution along the model cables as a function of time are presented.

A double pancake winding method is widely used to make the superconducting magnet, using high temperature superconductor (HTS) tape. In the double pancake winding method, the joints with contact resistances between double pancake coils are inevitably needed. The electrical joule heating on the contacts causes refrigerant loss during operation. And a space outside the winding, for splices and mechanical support, is more than that for its layer-wound equivalent. In this paper, a double pancake winding method in order to reduce the number of the joints was proposed. Both of the double pancake coils using the conventional winding method and the proposed winding method have been fabricated and tested to make the solution technically feasible in the double pancake winding method. Especially, critical-current tests of the fabricated double pancake coils were conducted in order to show the same performance and confirm contact resistances between double pancake coils.

In this paper, configurations and performance of a pulse tube engine (PTE) are investigated. The configuration of PTE is basically designed by using a concept of energy flow. The configurations of PTE are classified as a PTE with two pistons and a PTE with one piston. First, the PTE with two pistons is simulated and the Carnot efficiency is about 41 %. The phase difference of between motion of two pistons located at expander and compressor mainly effects the performance of the PTE. Second, the PTE with one piston is designed. From a concept of analogy, the piston of compressor is replaced by a compliance tube and a resonator. The PTE with one piston is identical with a thermoacousic engine and has the large volume because the compliance tube and resonator are consisted of large volume tubes. Therefore, we will consider each usefulness of the compact PTE with two pistons and the huge PTE with one piston for PTE applications and the judgement of feasibility.

In the extreme conditions of launch vehicle in a space, such as cryogenic temperature and low-gravity environment, the mass gauging of remaining propellants becomes a difficult problem. Pressure–volume -temperature (PVT) method is one of the attractive mass gauging methods under low-gravity due to its simplicity and reliability. PVT gauging experiment with various mass flow rates of helium injection is carried out with the experimental apparatus creating cryogenic homogeneous condition as the condition of low-gravity. Experimental results are analyzed by a novel PVT gauging analysis method which considers all instantaneous changes of pressure and temperature in the ullage volume with small time intervals. It is observed that the gauging error from the novel PVT gauging analysis is –0.11% with 2 slpm mass flow rate of helium injection.

The substantial improvement of the signal-to-noise ratio (SNR) can be achieved with small-size samples or low-field MRI system by high-temperature superconducting(HTS) RF coil. The typical HTS RF coil made of HTS thin film is expensive and is limited the coil geometry to planar surface coil. In this study, commercial Bi-2223 HTS tapes was used as RF coil for a 0.35T permanent MRI system. It has advantages of both much lower cost and easier fabrication over HTS thin film coil. SNR gain of the image obtained from the HTS RF coil over a conventional Cu RF coil at room temperature was about 2.4-fold and 1.9-fold using the spin echo pulse sequence and gradient echo pulse sequence respectively.