Masahiko Kaneyama

Record-High Trapped Magnetic Field by Pulse Field Magnetization Using GdBaCuO Bulk Superconductor

A trapped magnetic field BTP as high as 4.47 T, which is the highest reported using pulse field magnetization to date, has been realized on the surface of a GdBaCuO bulk superconductor by a modified multi pulse technique combined with stepwise cooling. Following an introduction of a small amount magnetic flux into the bulk center by applying lower pulse fields Bex=4.5–4.6 T twice at a higher starting temperature Ts=45–48 K, higher fields of Bex=6.6–6.7 T are applied three times at a lower Ts=28–29 K. The reduction in the temperature rise due to the already existing trapped flux, in addition to the optimization of the higher Bex value at the lower Ts, is a key point in enhancing BTP.

Rise-Time Elongation Effects on Trapped Field and Temperature Rise in Pulse Field Magnetization for High Temperature Superconducting Bulk

Pulse field magnetization (PFM) using a magnetic pulse of Bex=3.83–5.53 T with various rise times tr (=6–20 ms) has been performed for the cryocooled SmBaCuO bulk superconductor starting at the initial temperature of 40 K. The time evolutions of temperature T(t) and local field BLP(t) have been measured on the bulk surface after applying the magnetic pulse. With increasing tr, the temperature rise ΔT and the trapped field BTP increase for Bex≤4.70 T and decrease for Bex=5.53 T. The rise time tr required to realize the optimum BTP has been found to become longer for a smaller pulse field Bex. From the analyses of the generated heat Q after five successive applications of pulses (Nos. 1–5) with the same amplitude, the Q(No. 5) value, which can be regarded as the viscous loss Qv, decreases with increasing tr, due mainly to the decrease in the flux propagation velocity v in the bulk with longer tr.

Effect of metal ring setting outside HTSC bulk disk on trapped field and temperature rise in pulse field magnetizing

In order to enhance the trapped field in cryo-cooled HTSC bulks using pulse field magnetizing (PFM), a metal ring (stainless steel 304 and/or Al) has been tightly set onto the SmBaCuO bulk disk and the relation between the total trapped flux /spl Phi//sub T//sup P/, the trapped field B/sub T//sup P/, and the temperature rise /spl Delta/T, has been investigated as a function of the applied pulse field B/sub ex/. The /spl Phi//sub T//sup P/ and B/sub T//sup P/ values are enhanced about 10 /spl sim/ 20% by the metal ring due to the reduction in the temperature rise /spl Delta/T. These results suggest that a part of the generated heat Q due to the flux motion in the peripheral region promptly transfers to the metal ring and the heat transfer to the cold stage is improved by the ring setting.

Flux motion studies by means of temperature measurement in magnetizing processes for HTSC bulks

The temperature rises /spl Delta/T(t) of cryo-cooled SmBaCuO bulk superconductor have been measured after applying the pulse magnetic field from B/sub ex/ = 3.01 to 5.42 T for various initial stage temperatures (T/sub s/ = 40 K /spl sim/ 70 K). For each T/sub s/ and B/sub ex/, the observed systematic change of /spl Delta/T and the trapped magnetic field B/sub T/ can be explained in terms of the diagram of the maximum temperature measured at the bulk center surface (T/sup 0//sub max/) vs. B/sub T/. The maximum temperature rise /spl Delta/T/sub max/ decreases with increasing T/sub s/ under the identical B/sub ex/.

Heat propagation analysis in HTSC bulks during pulse field magnetization

The time evolutions of the three-dimensional temperature profiles in a superconducting bulk disc have been calculated after applying a pulse field in the pulse field magnetization (PFM) by use of a finite element method (FEM). The total generated heat Q, experimentally estimated using the maximum temperature rise ΔTmax and specific heat C of the bulk, used in the analysis and the distribution of Q in the periphery region of the bulk, is suitably supposed in order that the calculated time evolutions of temperatures T(t) reproduce the measured ones on the bulk surface. From the analysis, the heat generation during PFM takes place under adiabatic conditions because the total Q value is about one or two orders of magnitude larger than the cooling power of the cryocooler used. The enhancement of the total heat capacity by setting a stainless steel ring onto the bulk as a heat reservoir is one of the effective methods to reduce the temperature rise and to enhance the trapped field.