The accuracy of a position measurement method using the Arago spot is reported for an inertial fusion energy (IFE) target tracking system, where the position of the target is determined by the position of the Arago spot, which is a bright spot appearing in the central portion of the diffraction pattern of a spherical obstacle. We use a He–Ne laser as the light source and a charge-coupled device (CCD) camera with a microscope objective lens to magnify and record the diffraction pattern of a spherical target. We examine two different algorithms to determine the center of the Arago spot in order to compare the measurement performances. The experimental results show that the position of a 5-mm-diameter target can be obtained with a measurement resolution of 1 µm and an rms measurement error of less than 0.2 µm for both algorithms when the distance between the target and the microscope objective lens is 5 cm.

This paper is a complement to our previous work [Jpn. J. Appl. Phys. 46 (2007) 6000] on the accuracy of the position measurement method using an Arago spot for an inertial fusion energy target tracking system and we here report an improvement of the measurement accuracy using a divergent laser beam. By employing divergent beam illumination, we can magnify the displacement of the Arago spot compared with the actual displacement of the target without enlarging the diameter of the Arago spot significantly, allowing us to measure the small displacement of the target with high accuracy over a large measurement range. The experimental results for a 5-mm-diameter target demonstrated that a measurement accuracy of lower than 0.2 mm can be achieved when the distance between the target and a charge-coupled device camera is within the range from 2 to 10 m.

It is proposed that nanosized graphene aggregation could facilitate coherent neutron scattering under particle size conditions similar to nanodiamonds to enhance neutron intensity below cold neutrons. Using the RIKEN accelerator-driven compact neutron source and iMATERIA at J-PARC, we performed neutron measurement experiments, total neutron cross-section, and small-angle neutron scattering on nanosized graphene aggregation. For the first time, the measured data revealed that nanosized graphene aggregation increased the total neutron cross-sections and small-angle scattering in the cold neutron energy region. This is most likely due to coherent scattering, resulting in higher neutron intensities, similar to nanodiamonds.