2016 年 26 巻 2 号 p. 80-84
Active focusing schemes of pulsed neutron beams in transverse or longitudinal direction are demonstrated, which are useful for efficient utilizations of precious neutrons. They use the time of flight information for the active controls of the focusing. The modulating permanent magnets can focus the pulse white neutron beams in transverse directions, when the modulation is synchronized with the neutron pulses. Because diffracting lenses have less sensitivities on the alignment tolerances than reflecting devices, the handling of the lenses are fairly easy. Since the magnetic lens has no material on the beam path, no absorption nor scattering disturbs the neutron orbits. Magnifying imaging of electrodes in a Li battery is one of useful applications of the lens. The longitudinal focusing can be achieved by an active control of the RF frequency of a spin flipper with a gradient magnetic field, which accelerates/decelerates neutrons and manipulates the longitudinal distribution of the neutrons. It should be useful for rebunching the longitudinally diffusing neutrons for neutron EDM search or making the wavelength uniform for monochromatic beam applications. Both the active controls of the transverse and longitudinal manipulations of the neutron phase space distribution are useful techniques for better utilization of precious neutrons.
