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

电子冷却方法已广泛应用于原子物理研究和加速器技术中。实验中的冷却时间和最终精度由电子温度决定。电子束最初的能量宽度（或温度）约为100兆电子伏，因为电子是从热阴极发射的。然而，通过在逐渐减小的螺线管场中绝热扩展电子束，可以将电子温度降低到低于阴极温度的水平。这种方法被称为“绝热膨胀法”，电子温度的下降与膨胀系数成反比。基于这一原理，我们将现有的电子系统修改为绝热膨胀型。1996财年，我们设计并建造了一个磁场为3.5 T的超导电子冷却器，在世界上首次实现了膨胀系数100，电子温度达到1 meV。超导磁体不含液氦，结构紧凑，操作简单。该冷却器为超高速光束冷却和高精度实验开辟了道路。在1996-1997财政年度，用这个冷却器进行了高精度的原子碰撞实验。分子离子的解离重组（DR）是高层大气和外层空间的重要过程之一。利用超导电子冷却器在TARN II储存环上产生的1 meV量级的极低温电子束，研究了HeH^+同位素的DR。DR谱在低能区表现出精细的新结构和明显的同位素依赖性。这些特征在基于多通道量子缺陷理论的理论计算中得到了很好的再现。根据该理论，新观察到的结构是一种新的间接机制的证据。这些结果在国内大阪和神户的学术会议上，以及国外温哥华、维也纳和海德堡的学术会议上发表。我们还开始了用新冷却器对许多其他离子进行原子碰撞实验的可行性研究。少

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