Superconducting magnet for a cyclotron Rutherford backscattering spectrometry system

We have developed a superconducting magnet for a high-speed and high-resolution Rutherford backscattering spectrometry system that utilizes the ion motion along the cyclotron trajectory in a magnetic field. The superconducting magnet without cryogen consists of a main coil, shim coils, a 4 K refrigerator and pole pieces. It generates a 2 T magnetic field in the spectrometer of ϕ 340 × 750 mm. The shapes of the pole pieces and the coil arrangements are optimized by a magnetic field analysis to generate a uniform field. The magnetic field distribution is made to be so uniform that the scattered ions can pass through a ϕ 1 mm aperture, by ion trajectory calculation. The trajectory of the incident beam is also computed, and the position of a specimen holder is determined so that the incident beam is well focused on the specimen.