Naoyuki Amemiya

Numerical electromagnetic field analyses of high Tc superconducting tape in coils were carried out to calculate the magnetic field generated by the shielding (magnetization) current in superconducting tape. The numerical model employs the power law electric field–current density characteristic and the thin strip approximation, in which the current component normal to the wide face of the tape is neglected. The shielding (magnetization) currents lead to non-uniform current distributions in the su

The large cross-sectional aspect ratio of YBCO coated conductors leads to a large magnetization loss in an AC transverse magnetic field. In this work, the magnetization loss of a multifilamentary YBCO coated conductor was studied experimentally. A 100 mm length of striated multifilamentary YBCO coated conductor was prepared where the conductor and filaments were 10 mm wide and 0.4 mm wide, respectively. Striations in the sample were accomplished by laser ablation. The magnetization loss of this

A numerical code for the electromagnetic analysis of high T/sub c/ superconductors by finite element method has been developed. The E-j characteristics of superconductor are represented with the n-value. The equivalent conductivity of superconductor is determined as a function of electric field, and Ohm's law is used as the constitutive equation. First, the current and magnetic flux distributions in the infinite slabs of superconductor exposed to a parallel external magnetic field are analyzed.

We developed a novel model for numerical electromagnetic field analysis of assembled conductors, considering their three-dimensional structure. Since the superconductor layer of a coated conductor is very thin, we applied a thin-strip approximation, where the current flows only in a direction parallel to the wide face of the coated conductor. Although the amount of computation was reduced by the application of the thin-strip approximation, the three-dimensional geometry of each strand was retain

AC losses in power transmission cables composed of coated conductors could be potentially small. A strategy to approach their potentially small AC loss was studied. AC losses in mono-layer conductors for cables were calculated numerically in order to show the principle for AC loss reduction: use of narrower coated conductors and/or decrease in space between conductors reduce the magnetic field component perpendicular to the wide face of coated conductors, and they are effective for AC loss reduc

One of the methods to reduce magnetization loss of YBCO coated conductors in a perpendicular magnetic field is subdividing the YBCO layer into filaments and twisting them as a whole. A 10 mm wide multifilamentary YBCO coated conductor with 200 /spl mu/m wide filaments was prepared by striation using the laser ablation technique. The number of filaments was 40. The sample length was varied from 100 mm to 25 mm, and their magnetization loss was measured at various frequencies. The measured magneti

The three-dimensional structure of Roebel cables consisting of coated conductors influences their ac loss characteristics. Measurements of the ac loss and numerical electromagnetic field analyses were carried out using a six-strand Roebel cable as well as several reference conductors: a single straight coated conductor, a 3 × 1 stack, where three straight coated conductors were stacked, and a 3 × 2 stack, where two 3 × 1 stacks were placed side by side. The measured and calculated ac losses of t

The shielding-current-induced field is a serious concern for the applications of coated conductors to magnets. The striation of the coated conductor is one of the countermeasures, but it is effective only after the decay of the coupling current, which is characterised with the coupling time constant. In a non-twisted striated coated conductor, the coupling time constant is determined primarily by its length and the transverse resistance between superconductor filaments, because the coupling curr

Electromagnetic field analyses were carried out to study the influence of coated-conductor magnetisation, i.e. the screening (shielding) current, on the field quality of a dipole magnet in a rotating gantry for hadron cancer therapy. The analyses were made on the cross section of a cosine-theta dipole magnet in a rotating gantry for carbon ions, which generated 2.90 T of magnetic field. The temporal profile (temporal variation) of the magnet current was determined based on the actual excitation

Using an electro-magnetic method, we measured the total AC loss of a YBCO coated conductor carrying an AC transport current in an AC transverse magnetic field with various orientations. We measured the magnetization loss (energy flow from the external magnetic field) and the transport loss (energy flow from the transport current circuit) independently during simultaneous application of an AC transverse magnetic field and AC transport current. Their sum gave us the total AC loss. The transport lo

To study the influence of coated-conductor magnetization on the field quality of accelerator magnets, we made a small dipole magnet consisting of four racetrack coils wound with GdBCO coated conductors and measured its magnetic field in liquid nitrogen by using rotating pick-up coils. We focused on the dipole and sextupole components (coefficients) of the magnetic field, which vary with time owing to the decay of the magnetization of the coated conductors. About 50 min (3055 s) after the current