Trapped Field Enhancement of a Thin, High-Jc MgB2 Bulk Without Flux Jumps Using Pulsed Field Magnetization With a Split-Type Coil With a Soft Iron Yoke

Abstract

We have investigated the suppression of flux jumps and the enhancement of trapped field on a thin, high-J c MgB 2 bulk (30 mm in diameter and 7 mm in thickness) for the pulsed field magnetization (PFM) using a split-type coil with a soft iron yoke, and compared the results to those magnetized using the split-type coil without a yoke and a solenoid-type coil with a yoke. A maximum-trapped field, B z , of 0.71 T at 14 K was achieved on the bulk surface without flux jumps by using the split coil with yoke. On the other hand, low B z values with flux jumps were observed for the cases using the split-type coil without a soft iron yoke, and the solenoid-type coil with a yoke. These results reproduce previous ones for a thick, high-J c MgB 2 bulk (22 mm in diameter and 15 mm in thickness), for which the trapped field was enhanced to a record high value of B z =1.10 T at 13 K by PFM using the split-type coil with a yoke. Index Terms-MgB 2 bulk, pulsed field magnetization, split coil, flux jump, soft iron yoke. I. INTRODUCTION GB 2 superconducting polycrystalline bulks as trapped field magnets (TFMs) have been intensively investigated due to their merits of being rare-earth-free, lightweight , presenting a symmetric trapped field distribution and their long coherence length [1, 2], which are in clear contrast with REBaCuO bulk magnets (RE: rare earth elements and Y) [3]. MgB 2 polycrystalline bulks with high critical current density, J c , have been fabricated by various methods and activated by field-cooled magnetization (FCM) [4, 5, 6]. A record-high trapped field of B z = 5.4 T has been attained at 12 K on a single MgB 2 bulk disk 20 mm in diameter [7]. To magnetize superconducting bulks, pulsed-field magnetization (PFM) has been also investigated intensively,

Enhancement of trapped field of REBCO bulk in a desktop-type magnet system

“…In the past years, several methods such as IMRA (iteratively magnetizing pulsed-field operation with reducing amplitudes), MPSC (multi-pulse technique with a stepwise cooling), MMPSC (modified MPSC), and so on [14][15][16][17], in which pulsed fields are applied several times with changing an amplitude of magnetic field and temperature, have been employed. Recently, new methods have been developed such as a split coil method and long-pulse method, and so on [18][19][20][21][22]. In the long-pulse method, the bulk is exposed to a magnetic flux for a long time by extending the pulse width.…”