Design of high efficiency supermirror neutron turbine

The supermirror neutron turbine which decelerates very cold neutrons (VCN) to ultracold neutrons (UCN) in the VCN-UCN facility installed in Kyoto Univ. Reactor (KUR) was upgraded with the use of an improved version of polygonal blades made of five supermirrors, in place of the previous three supermirror blades. Since the main reason of the neutron loss is complicated changes of the decelerated neutron trajectories in the turbine rotation, a second step upgrading is performed with the use of a multisections VCN feed guide in a converging type which changes the VCN beam feeding position and direction according to the inlet position and height in the rotating mirror blades in order to cancel the centrifugal force effects. Further, in order to minimize the effect of the Coriolis force, the mirror blades of the turbine are made smaller to diminish the size ratio between the blades and the turbine rotor radius. (author)