Attempt to generate a strong and uniform magnetic field by face-to-face HTS bulk elements in a magnet system

A unique experimental attempt aiming to obtain a uniform magnetic field space as required for NMR has been carried out with use of HTS bulk magnets. The magnetic poles were activated as 1.8 T ( North) and 1.4 T ( South) at 30 K by applying a pulsed magnetic field up to 7 T, and positioned face-to-face with gaps less than 70 mm. The uniformity of the magnetic field required for detecting the NMR signals is less than 1,500 ppm at more than 0.3 T in the cross sectional plane of 2 x 2 mm(2). After the preliminary trials which revealed a uniformity of 5,421 ppm at 0.44 T in a 70 mm gap, we attached a ferromagnetic iron plate to a magnetic pole surface to change the magnetic field distribution to be concave. The best uniformity of 358 ppm at 1.11 T was obtained at 9 mm distance from the iron plate surface in a gap of 30 mm. It is stated that the concave magnetic field distribution was compensated by the counter conical-shape field, resulting in the uniform field plane. (C) 2015 The Authors. Published by Elsevier B.V.