Highly homogeneous superconducting magnet for photocathode pattern transfer system

A superconducting magnet, which is used as a focusing magnet for a photocathode pattern transfer system, has been developed. The focusing magnet requires highly homogeneous and stable magnetic field to attain high resolution capability. The magnet is Helmholtz type with 880 mm average winding diameter. Each coil is placed in a cryostat which has 620 mm diameter bore. In order to obtain the field homogeneity, the relative position of two cryostats is made adjustable. Field homogeneity was 6 × 10-5over the 90 mm diameter after adjustment. This value was measured by nuclear magnetic resonance (NMR) method. 3k Gauss magnetic field was obtained at 188 A/mm2excitation current density. Superconducting persistent current was maintained for 10-4/hour in decreasing ratio. Consequently, the photocathode pattern transfer system with this superconducting magnet successfully transferred VLSI patterns of 0.5 μm geometry.