Koh Agatsuma

Design and Test of Filter of High Gradient Magnetic Separation System for Trapping Immunoglobulin in Serum

Recently, affinity magnetic beads have been widely used in immunomagnetic cell sorting (IMCS) technology. Today, we can easily sort and analyze DNA and antibodies (immunoglobulin) using various types of affinity magnetic beads available in the market. The diameters of these affinity magnetic beads used in immunomagnetic cell sorting are limited to above approximately 1 mum because of the low magnetic fields induced by permanent magnets. Now, nano-sized affinity magnetic beads are strongly desired to achieve high resolutions. We have been studying and attempting to develop a high-gradient magnetic separation (HGMS) system that employs a superconducting magnet to induce a considerably higher magnetic field than that induced by a permanent magnet in order to trap smaller nano-sized affinity magnetic beads by a filter made of fine stainless steel wool. In this study, we constructed a prototype of a desktop-type HGMS system using a cryocooler-cooled LTS magnet and conducted preliminary experiments on trapping the nano-sized magnetic particles. Furthermore, we investigated the magnetic field distribution and magnetic force around a magnetic wire in the filter by means of a numerical simulation.

Fiber-reinforced-superconductors for a 15 T-class high-field pulsed magnet and their conceptual design

The authors are developing a novel type of Nb/sub 3/Sn superconductor with high elastic modulus fibers for application to high field pulsed superconducting magnets, called the fiber-reinforced superconductor (FRS). They describe the conceptual design of a conductor for a pulsed magnet using FRSs and present superconducting characteristics for monofilamentary FRS samples. Each monofilamentary FRS supports hoop stress under operation of the magnet. Short lengths of monofilamentary FRSs using tungsten fiber were prepared by RF-magnetron sputtering. Critical current measurement up to 15 T and a uniaxial strain test at 10 T have been carried out. The data support the conceptual design of the 15-T-class pulsed superconducting magnet using FRSs.<<ETX>>

Stability Analysis of HTS Power Cable With Fault Currents

We numerically calculated the transient temperature distribution of flowing subcooled liquid nitrogen in a high-Tc superconducting (HTS) model cable when faults occur. The coolant and cable core temperatures were calculated by numerically solving the heat equation using the finite difference method. In the calculation, we assume that the heat transfer coefficient between the flowing subcooled liquid nitrogen and the cable core surface is described by the Dittus-Boelter correlation. The calculation results reveal that the coolant temperature increases even after the fault has been removed and that it continues increasing until fresh coolant arrives from the inlet. The calculated temperature profile of the coolant agrees well with measured data obtained by conducting over-current tests on a model HTS cable. Using our computational code, we also evaluated the maximum HTS cable lengths that ensure that the coolant remains in the liquid phase for certain fault currents for an HTS model cable.

Improvement of a High-Gradient Magnetic Separation System for Trapping Immunoglobulin in Serum

Recently, affinity magnetic beads have been widely used in immunomagnetic cell sorting (IMCS) technology. Today, we can easily sort and analyse DNA and antibodies (immunoglobulin) using various types of affinity magnetic beads available in the market. The diameters of the affinity magnetic beads used in immunomagnetic cell sorting are above approximately 1 ¿m because of the low magnetic fields induced by permanent magnets. At present, nanosized affinity magnetic beads are strongly desired to achieve high resolutions. We have been studying and attempting to develop a high-gradient magnetic separation (HGMS) system that employs a superconducting magnet to induce a considerably higher magnetic field than that induced by a permanent magnet. The objective is to trap smaller nanosized affinity magnetic beads using a filter made of fine stainless steel wool. In a previous study, we constructed a prototype of a desktop-type HGMS system using a cryocooler-cooled LTS magnet; we conducted preliminary experiments on trapping nanosized magnetic particles and investigated the magnetic field distribution and magnetic force around a magnetic wire in the filter by means of a numerical simulation. In this study, we succeeded in producing prototype nanobeads covered with the biosurfactant of a high-affinity ligand system for immunoglobulin G and M. Furthermore, we attempted to improve the recovery of nanobeads by adding a resonance circuit to the HGMS system. In practice, the trapped nanobeads attract one another and agglomerate due to their remaining magnetization when the magnetic field is decreased to 0 T. Therefore, the nanobeads and wire are demagnetized in the AC magnetic field by the resonance circuit, making good use of the superconducting magnet of the HGMS system.

Mechanical properties of a niobium-tin superconductor reinforced by tantalum cores

We have been developing fiber-reinforced type of niobium-tin superconductor for large scale high field magnets. In this conductor, each niobium-tin filament has a tantalum core. Tantalum is selected as material for the core since it has good ductility with mechanical strength and hence a conventional drawing method can be applied to fabricate a conductor. Stress-strain characteristics and the irreversible strain limits of the conductor with different heat-treatment conditions are measured. Combining these results, discussions about the mechanical properties of the conductor are presented.

Properties of fiber-reinforced niobium-tin superconductor fabricated by bronze process

We are developing a fiber reinforced type of superconductor for large scale, high-field magnets. Formerly we used the sputtering process to develop a niobium-tin conductor reinforced with a tungsten fiber and showed that this type of conductor has excellent stress tolerance. For practical applications however, a conventional fabrication process like bronze process is desirable. Hence we have tried to fabricate a fiber-reinforced type niobium-tin conductor utilizing tantalum fiber as the reinforcing member, In this conductor, each niobium-tin filament has a tantalum core of about 20-/spl mu/m diameter, We adopted tantalum as the core material since it has both good ductility and mechanical strength comparable to stainless steel, This conductor showed a reasonable critical field of about 22 T and good mechanical strength compared to a niobium-tin conductor fabricated by the conventional bronze process.

Properties of

Since MgB2 superconductor was discovered by Akimitsu, many scientists has been studied this new intermediate temperature superconductor material. Recently Dou reported the critical current density and flux pinning of MgB2 is enhanced by doping of SiC nano powder, and Fujii reported MgB2 superconductor made by the powder-in-tube in-situ process using MgH2 as a precursor powder enhanced the critical current density especially under high magnetic field. Also Matsumoto reported the irreversibility field of MgB 2 tape prepared by the in-situ powder in tube process using MgH2 as a precursor powder increased to 23 T by the SiC doping. These results show MgB2 has high potential as a strong candidate for a practical use. We study the effects of doping nano carbon impurity because graphite has the same structure as the hexagonal Boron structure in MgB2. We added carbon impurities of graphite, C60, and open-ended carbon nano tube respectively to MgB2 conductors made by powder in tube ex-situ process

rm MgB_2

A computer simulation has been developed to estimate the transient temperature and pressure distributions in a high-temperature superconducting (HTS) power cable cooled by a forced flow of subcooled LN2. This simulation is critical for assessing the effects of short-circuit accidents in practical HTS power cables. When a fault occurs, an excessive current of 31.5 kA may flow in a cable for 2 s, and it is important to understand the temperature and pressure profiles in a cable cooled by the forced flow of LN2 when these faults occur until the disturbance flows out from a cable. The temperature profile of the LN2 coolant and the cable cores was analyzed by solving heat conduction and heat transfer equations using the finite-difference method. The Cryodata GASPAK software package was used to estimate the fluid properties. The simulation results show a fairly good agreement with the experimental results. By employing a new model of the induction refrigeration system and the circulation pump, a small discrepancy is resolved in pressures between simulation and experiment. The analysis results show that the pressure in the cable significantly changes depending on the initial gas volumes in the terminals and the volume of the LN2 gas that evaporates from the copper former in the cable.

Superconductor by Doping Impurity of SiC, Graphite,

We have been developing an active magnetic levitation system, which is composed of a field-cooled disk-shaped or sphere-shaped high-temperature superconducting bulks (HTS bulks) and vertically piled ring-shaped electromagnets without an iron core. We suppose that this active magnetic levitation system can be applied to inertial nuclear fusion. In inertial nuclear fusion, one of the most important issues is to achieve high-accuracy position control of the fusion fuel, which consists of deuterium and tritium in order to evenly illuminate the entire surface of the target. Therefore, active magnetic levitation is applied to the levitation and position control of a sphere-shaped superconducting capsule containing nuclear fusion fuel. In this study, we designed and constructed a three-coil position control system in order to achieve the stable levitation of the sphere-shaped HTS bulk with a diameter of 5 mm by using the numerical simulation based on the hybrid finite element and boundary element analysis. Then, we carried out the experiments on the position control and restoring force characteristics of the sphere-shaped HTS bulk in the constructed levitation system.

rm C_60

We have been developing tantalum-fiber-reinforced bronze process niobium-tin wires for use in large-scale high field magnets. They are fabricated by conventional drawing. We manufactured two kinds of the wires with different geometries but similar volume ratios. We have investigated their characteristics and have clarified that there are some differences in their superconducting critical current, critical magnetic field, critical temperature, and the influence of their heat-treatment conditions.