The purity of niobium for a superconducting cavity refined using an electron-beam melting method was explained from RRR measurement, gas analysis and GDMS analysis. Metallic purity notation generally refers to the value obtained by subtracting the total of metal impurities other than gas components from100%. For example, it is 3N at 99.9% and 4N at 99.99%. In the case of niobium, since tantalum containing tens to hundreds of ppm is the majority of the impurities, it is 3N or 2N8 in a normal purity notation. However, with the agreement of customers, when tantalum, tungsten and molybdenum are excluded from the target elements, purity corresponding to 6N - 7N is obtained. Tantalum is not removed by electron-beam melting, so we select and purchase less tantalum at the raw materials stage.
High-purity Nb as a superconducting cavity material for accelerators is investigated. In order to carry out Nb purification, a 600-kW electron beam furnace procured by our company. This has made stable refining for cavity applicationgrade material possible by optimizing the melting conditions. The change in hardness achieved by processing in high-purity Nb is definitely different from that of low-purity Nb. High-purity Nb requires considerably high processing power to induce sufficient strain hardening. We believe that the key point of fine forming in high-purity Nb is the homogenization of crystal grain size using a strong process. Trial manufacturing of two single-cell cavities using our high-purity Nb ingot was performed. An accelerating gradient of 35 M/m was achieved using these cavities. Additionally, we succeeded in the fabrication of a seamless tube for a three-cell cavity in a scale-up study. Since the average grain size in the tube for a three-cell cavity is smaller than that for a singlecell cavity, it is expected that a smoother surface will obtained after the hydroforming process.
We have been studying the characteristics of ice as a dielectric or electrical insulation material at cryogenic temperature. IceXI, ferroelectric ice, exists at cryogenic temperature. It is very difficult to make iceXI. We applied direct-currentvoltage to ordinary ice at 253 K and cooled it to 77 K to obtain a polarized ice similar to iceXI. In this procedure, the protons move towards the cathode side under an electric field. The protons were stopped on the cathode side by cooling to 77 K, resulting in ice polarization. This polarized ice is called “ice electret”. We have previously reported the amount of electrical charge calculated from an integral of the ice electret depolarization current observed. The amount of charge increased as voltage and application time increased. In this paper, the effect of voltage, application time and temperature on depolarization current properties of the ice electret is reported. The depolarization current of the ice electret was examined in detail. Two peaks were observed in the depolarization current. One peak appeared around 270 K. But this peak did not occur in the specimen with a voltage of 140 K applied. The other peak was observed around 130 K in any specimen. The electrical charge calculated from this 130 K peak increased only when a voltage was applied, and did not increase as time and temperature increased when voltage was applied.
For the medical application of superconducting magnets, we investigated a new magnetic drug delivery system that utilizes a rotating magnetic field. To improve the efficiency of drug treatment, a technique that can accumulate the drug in a targeted area is needed. Recently, utilizing a magnetic field by combining ferromagnetic particles and the drugs (ferromagnetic drugs) and applying the magnetic field has been investigated (i.e., Magnetic Drug Delivery System: MDDS). In conventional MDDS, however, the drug can be accumulated only near the body surface because the magnetic field is applied from outside of the body. This indicates that it is difficult to accumulate the drug to a deep target inside the body. We aim to resolve this problem by means of MDDS utilizing a Rotating Magnetic Field (RMF) with superconducting magnets. With this technique it is possible to accumulate a drug selectively in a targeted area, preventing drug accumulation outside of the target by rotating the magnetic field around the central axis of the targeted area. As a fundamental study, we used multiple electromagnets in order to rotate a magnetic field inside the body by controlling the electric current. As a result, we established a fundamental technique to accumulate ferromagnetic particles (a model ferromagnetic drug) at the central axis of the RMF. The feasibility of the technique to accumulate ferromagnetic drugs selectively deep inside the body using the strong magnetic field of superconducting magnets was proven.
The synthetic processes of organic compounds need the process for separating structural isomers which is formed coincidentally with an objective substance. The existing separation methods of isomers are extraction, recrystallization and distillation. However, the environmental burden of existing methods is large because they require large space and energy. In this study, a separation method of structural isomers using a Magneto-Archimedes method that can separate the substance with a smaller device and lower energy was examined. This is a method to separate the materials by applying the difference of magnetic levitation positions depending on their magnetic properties. Powders of 1,6-DDA (1,6-Decanedicarboxylic Acid, C12H22O4) and 1,10-DDA (1,10-Decanedicarboxylic Acid) were used as an example of structural isomers that have different industrial applications. In the Magneto-Archimedes method, particle aggregation makes selective magnetic separation difficult, thus the type and concentration of the medium was controlled based on the zeta potentials of the particles so as to disperse the aggregates. Then a magnetic field was designed based on specific gravities and magnetic properties of the separation targets and selected medium. The levitation positions of particle was calculated from the relation between the distance from the magnet surface and the magnetic field product in the vertical direction, which suggested that the two structural isomers can be separated. The experiment based on the calculation confirmed the possibility of separating the 1,6-DDA and 1,10-DDA isomers. Finally, a suitable superconducting solenoidal magnet that can separate structural isomers efficiently was examined.