Attempt to Generate a Strong and Uniform Magnetic Field by Face-to-face HTS Bulk Elements in a Magnet System

Abstract

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 30K by applyinga pulsed magnetic field up to 7 T, and positioned face-to-face with gaps less than 70mm. The uniformity of the magnetic field required for detecting the NMR signals isless than 1,500ppm at more than 0.3 T in the cross sectional plane of 2 x 2 mm2. After thepreliminary trials whichrevealed auniformity of 5,421ppm at 0.44 T in a70mm 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 358ppm at 1.11 T was obtained at 9mm distance from the iron plate surface in a gap of 30mm. It is stated that the concave magnetic field distribution was compensated by the counter conical-shape field, resulting in the uniform field plane.