A superconducting solenoid lens for spin selection and focusing of hydrogen atoms

Results from a novel variation on the Stern--Gerlach method for magnetic separation are presented. A superconducting solenoid lens for spin selection and focusing of a cold atomic hydrogen beam has been built and tested at Brookhaven National Laboratory. The solenoid consists of three coils connected in series, with the current in the outer two coils counter to the current in the middle coil, resulting in a large magnetic field (up to 5.2 T) with strong gradients. Beam density enhancement (focusing) of up to a factor of 10 was achieved. Excellent qualitative agreement exists with ray-tracing calculations. Quantitatively, the experimental results show a lens performance which is a factor of at least 3 better than what these calculations predict