Simulation study of neutron focusing effect on a pulsed sextupole magnetic lens using PHITS code

We have performed various simulation calculations for a pulsed sextupole magnetic lens to look for the best condition of focusing experiments, assuming conditions of the pulse magnetic lens now under construction. Here, we placed a slit between the pulsed neutron moderator and the neutron lens, in order to see the focusing effect clearly. For the simulation, we used PHITS code to know influences of the position of the slit on the intensity of focused neutron beam, the focal point, and the broadening of the focal point. Increase of the distance of the slit from the source resulted in the decrease of the peak intensity of neutron beam at the focal point. Full-width at half-maximum of the neutron distribution along the incident beam direction around the focal point, broadened with increasing the distance, and the focal distance also became longer. The intensity ratios defined by (intensity with magnetic field)/(intensity without magnetic field) also increased with decreasing the distance. Therefore, it is better to set a slit near the moderator.