First operation of the superconducting electron cooler at the storage ring TARN II

A superconducting electron cooler with an adiabatic expansion factor of 100 was designed and constructed at the TARN II ring for high-precision experiments and high speed cooling. The gun solenoid is a liquid-helium-free superconducting magnet with a 20-cm room-temperature bore, which can produce a high magnetic field of up to 3.5 T. An electron beam is expanded from a diameter of 5 mm to 50 mm in a gradually decreasing solenoid field from 3.5 T to 0.035 T. With this cooler it can be expected to reach an electron temperature on the order of 1 meV. The cooler first came into operation in November, 1996. The spectrum of the dissociative recombination, /sup 3/HeH/sup +/+e/spl rarr//sup 3/He+H, clearly showed a dramatic decrease in the electron-beam temperature compared with our previous data measured at an expansion factor of 10 with a normal-conducting solenoid.