Browsing by Author "CHEN, K"

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ANISOTROPIC AC-SUSCEPTIBILITY RESPONSE OF A MELT-TEXTURED YBCO SUPERCONDUCTOR
(1991-12-01)
CHEN, YC
;
CHEN, K
;
HSU, SW
;
TSENG, TY
;
LU, SW
We report on low field measurements of the out-of-plane (c-axis parallel-to H) and in-plane (c-axis perpendicular-to H) ac susceptibilities of a melt-textured YBa2Cu3Ox superconductor with high transport J(c). With the field parallel to the ab-plane of the sample, an obvious second peak appears in the imaginary part of chi(ac) at T almost-equal-to 81 K with a width of 2-4 K depending on the ac field amplitude, which may be due to the interlayer weak-links in the melt-textured samples.
ENHANCEMENT OF MAGNETIC-FIELDS GENERATED BY HIGH-T(C) SUPERCONDUCTING COILS
(1993-12-01)
CHEN, K
;
HORNG, L
;
TAI, CH
;
WEI, JC
;
YANG, TJ
High-T(c) superconducting pancake coils wound by Ag-sheathed Bi-based tapes have been placed in between ring-shaped mu metal sheets. The central magnetic field B0 of a single coil was found to be enhanced by 60 % at liquid nitrogen temperature 77 K, and increased approximately 26 % for a four-coil stacked magnet. Critical currents of these coils were decreased. B0 was also increased when the magnet was wrapt by a mu metal sheet. This indicates that the well-designed high permeability materials can significantly enhance the magnetic fields generated by high-T(c) superconducting magnets.
MAGNETIC-RELAXATION IN A AG-SHEATHED HIGH-JC BI-PB-SR-CA-CU-O SUPERCONDUCTING TAPE
(1991-12-01)
CHEN, K
;
LEE, WH
;
HORNG, L
;
YANG, TJ
;
電子物理學系
The magnetic relaxation and magnetization curves were studied on the Ag-sheathed and highly c-axis oriented Bi-Pb-Sr-Ca-Cu-O tape with transport J(c) > 10(4) A/cm2 at 77 K. Zero-field-cooled (ZFC) in-field relaxation for applied field perpendicular to the sample a-b plane was investigated. It was found that the field-dependent relaxation rate had a maximum in the certain applied field at various temperatures. The applied field at this maximum was greater than H*, the first field for which currents flow through the entire volume of the sample in the Bean's critical state model. Pinning energies were estimated at the maximal relaxation rate in a series of temperatures.
MECHANICAL-PROPERTIES OF AG-SHEATHED BI-BASED SUPERCONDUCTING TAPES
(1993-12-01)
HORNG, L
;
CHEN, K
;
LEE, WD
;
WEI, JC
;
YANG, TJ
Flexible Ag-sheathed Bi-based superconducting tapes have fabricated by powder-in-tube technique. The critical current density (J(c)) does not varied when the bending radius is larger than the critical bending radius R0, bending radius without deteriorating transport properties. The bending tests were studied under magnetic field up to 5,000 G. The critical bending radius R0 (or Critical bending strain epsilon(b0)) was found to be independent of magnetic field from 0 to 5,000 G. The J(c)(B)/J(c)(0) curves are super-imposed in the same curve, i.e., the transport behavior of a tape at magnetic field is not affected by bending. It implies that the intrinsic pinning properties of a bent tape are unchanged in magnetic field. The results are useful for making a react-and-wind magnets and cables.
NONLOGARITHMIC MAGNETIC-RELAXATION IN A HIGHLY ORIENTED BI-BASED SUPERCONDUCTING TAPE
(1993-12-01)
WEI, JC
;
HORNG, L
;
YANG, TJ
;
CHEN, K
;
電子物理學系
Magnetic Relexation was studied at a wide range of temperatures and magnetic fields for a Ag-sheathed Bi-based superconducting tape with highly-c-axis orientation and high critical current density (J(c) > 10(4) A/cm2 at 77 K and 0 T). Under certain conditions, it is found that the magnetization data varies nonlinearly with ln(t) for entire period of time (t > 10(4) s). The curves can be divided into two relaxation rate (dM/dln(t)) in different period of time. It was observed that the lower the temperature is, the higher the magnetic field needs to bend a logarithmic line into a curve with two different relaxation rate (dM/dln(t)) in different region of time. The diagram of temperature and magnetic field was obtained from the experiment.