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A superconducting electron cooler with an adiabatic expansion factor of 100 was designed 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 magnetic field of up to 3.5 T. An electron beam is expanded from a diameter of 5 to 50 mm in a gradually decreasing solenoid field from 3.5 T to 35 mT. With this cooler, a transverse electron temperature on the order of 1 meV was attained. The longitudinal cooling force was measured with an induction accelerator as functions of the ion and electron currents, and the expansion factor. The longitudinal cooling force does not depend much on the expansion factor.

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.