Kiyoshi Yoda

Minimum quench energy measurement of NbTi wires using a small ceramic heater

A small ceramic chip resistor is proposed as a possible ideal point heater for transient stability measurements of superconductors. Preliminary results were obtained using a 1-mm*1.5-mm*0.5-mm ceramic resistor and NbTi wires whose copper-to-superconductor (Cu/SC) ratios were 1 and 2, having the same SC areas. The resistor was soldered on the NbTi wire to minimize the thermal resistance between the resistor and the wire. The minimum quench energy of the Cu/SC ratio 2 wire was approximately twice as large as that of the Cu/SC ratio 1 wire, under the same background magnetic field and with the same ratio of the operating current to its critical current.

Numerical analysis of low-frequency electromagnetic scattering from axially symmetric bodies using an inductance matrix

We have proposed a numerical method for calculating low-frequency electromagnetic scattering from axially symmetric conducting bodies with and without apertures. The surface of the perfectly conducting scatterer is modeled by a set of inductively coupled coil elements, and the current in each coil element is computed by solving an inductance matrix equation. A disadvantage of a conventional method for a scatterer with apertures is discussed. Scattering from various axially symmetric conducting bodies with or without apertures is calculated and the resulting fields are in good agreement with those obtained by finite-element method.

Low-Frequency Electromagnetic Scattering From A Perfectly Conducting Scatterer With Apertures Using a T-Omega Finite Element Method

We have found that a T-Omega finite element method results in an inaccurate low frequency scattered field distribution when the system includes a perfect conductor with an aperture. A simple model shows that Faradays law does not hold on the aperture

Numerical Analysis of Low-Frequency Electromagnetic Scattering From Three-Dimensional Arbitrarily Shaped Conducting Bodies Using an Inductance Matrix

We have proposed a numerical method for calculating low-frequency electromagnetic scattering from three-dimensional arbitrarily shaped perfectly conducting bodies using an inductance matrix. The surface of the perfectly conducting scatterer and its apertures are modeled by a set of triangular patches. The current on each patch is computed by solving a coupled inductance matrix equation. Scattering from various conducting bodies with apertures is calculated to compare with the other methods. The proposed method well agrees with finite element method in electromagnetic field distribution

Shape estimation of radioactive spent resins in a storage tank using the sampled pattern matching

A method for estimating the shape of accumulated radioactive spent resins in a storage tank has been proposed using the sampled pattern matching. In a two-dimensional simulation model, several kinds of the resin shapes are assumed, and the radiation fields outside the tank are calculated. The resin shapes were estimated using the simulated radiation field data and compared to the assumed shapes, resulting in reasonable agreements between them.

A wavelet transform approach to inverse problems of Vandermonde type systems

Inverse problems of Vandermonde type systems have been solved using the discrete wavelet transform. The inverse matrices of the transformed subsystems were calculated, thereby locating the largest well-conditioned submatrix. The reduced system was solved and the solution was inversely transformed. Results were compared between two different wavelet basis functions, indicating that Daubechies-4 wavelets lead to much more accurate solutions than Haar wavelets. Three simple techniques for eliminating another systematic noise are also proposed to further improve the accuracy of the final solution.

Calculation of optimum Cu/SC ratio to maximize superconductor stability

Optimum copper to superconductor ratio (Cu/SC ratio) to maximize the superconductor composites stability is calculated for a given current and cross section of the composite using L. Dresners minimum quench energy formula. The optimum Cu/SC ratio was plotted as a function of the composite current density (20-420 A/mm2), while background magnetic fields varied from 4-8 T. It is shown that the optimum value decreases when the current density or background magnetic field increases. >

Direct design optimization using approximate algebra

Unknown vector components of a system matrix equation are expressed as series expansions with respect to symbolic design parameters in the matrix. Calculation of unknown coefficients of the series expansions gives the vector components that are functions of the design parameters, resulting in a direct design optimization procedure. Preliminary results are shown. >