Tatsuya Tateiwa

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.

New Type Superconducting Bulk Magnet by Pulse Field Magnetizing With Usable Surface on Both Sides in Open Space

A new-type of magnet system using high-Tc superconducting bulks has been developed, in which two aligned bulk disks are cooled down from the side face by thermal conduction and are magnetized along the c-axis in turn employing a split-type pulse coil. The temperature rise DeltaT due to the magnetic flux intrusion is relatively small and the trapped field BT P is enhanced in comparison with the conventional bulk magnet system based on a solenoid-type pulse coil. BT P=3.20 T on the SmBaCuO bulk surface at 50 K and BT 4mm =1.97 T vacuum sheath, 4 mm above the bulk surface, have been attained. This type of magnet system, consisting of multi-bulks, with usable surfaces on both sides in open space, can be realized only by use of a split-type pulse coil and has a potential for new application fields

Enhancement of trapped field and total trapped flux on high temperature bulk superconductor by a new pulse-field magnetization method

A higher trapped field BTP and larger total trapped flux ΦT have been achieved on a SmBaCuO bulk superconductor ( 45 mm) by a modified multipulse technique with stepwise cooling (MMPSC) and a subsequent iterative magnetizing operation with gradually reduced pulse field amplitude (IMRA). BTP=4.33 T has been realized at the center of the bulk surface by the MMPSC method, which is higher than that attained by a single-pulse application (BTP=3.3 T). After the IMRA process, ΦT (5 mm) = 1.55 mWb was achieved 5 mm above the bulk surface, which is about 35% larger than that after the MMPSC process. The MMPSC method combined with the IMRA process (MMPSC-IMRA) is demonstrated to be a universal and promising pulse-field magnetization technique for enhancing both BTP and ΦT on any superconducting bulks.

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.