Study of the Ultracold and Ultrafast Beam-Cooling with a Superconducting Electron Cooler

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An electron cooling method has widely been used in the atomic physics research as well as accelerator technology. The cooling time and the final accuracy in experiments are determined by the electron temperature. The electron beam has initially an energy width (or temperature) of about 100 meV,since electrons are emitted from a hot cathode. However, electron temperature can be reduced to a level less than the cathode temperature by expanding the electron beam adiabatically in a gradually decreasing solenoid field. This method is called 'adiabatic expansion method' and the electron temperature decreases in inverse proportion to an expansion factor. Based on this principle, we modified the existing electron system to the adiabatic expansion type. In the fiscal 1996, we designed and constructed an superconducting electron cooler with a magnetic field of 3.5 T and realized an expansion factor of 100 resulting in an electron temperature of 1 meV for the first time in the world. The supercon … More ducting magnet is liquid-helium free, which realized a compact design and a simple operation. The cooler opened the way to the super-fast beam cooling and extremely high-accuracy experiments. In the fiscal 1996-1997, highly accurate atomic collision experiments have been performed with this cooler. Dissociative recombination (DR) of molecular ions is one of the important processes in the upper atmosphere and the outer space. The DR of HeH^+ isotopes were studied with the extremely low-temperature electron beam of the order of 1 meV produced by the superconducting electron cooler at the storage ring TARN II.The DR spectra show a fine new structure and a clearisotope dependence in the low energy region. Those features are well reproduced by the theoretical calculations based on a multichannel quantum-defect theory. According to the theory, the newly observed structure is an evidence of a new indirect mechanism. These results on the cooler and the physics experiments have been presented at the domestic conferences in Osaka and at Kobe, and the foreign conferences in Vancouver, Vienna and Heidelberg. We also started the feasibility study of atomic collision experiments with the new cooler on many other ions. Less