Development of a Tomography Camera System with a Doublet Lens Unit for Supersonic Collisional Merging Formation of FRC*)

Collisional merging experiments of field-reversed configurations (FRCs) have been conducted in the FRC Amplification via Translation-Collisional Merging device at Nihon University. Self-organized FRCs have been observed after the dynamic process with destructive disturbance of the collision/merging of plasmoids at super-Alfvenic speeds. A compact and component-based tomography camera (T-cam) has been developed to obtain the internal structure of plasmoids during and after the collisional merging process using a computed tomography technique. The plasmoids radially expand by a factor of 2 within a few microseconds in the collision and merging phases. Because the viewing angle of the T-cam was limited by the inner diameter of the observation port, the field of view was insufficient for the accurate reconstruction of the internal structure. In this study, the incident optical component of the T-cam is improved to provide a sufficient viewing angle to observe the whole process of collision and merging of plasmoids. The newly-built component, comprising a doublet lens with two plano-convex cylindrical lenses at different focal lengths, expands the viewing angle from 60 degrees -100 degrees. Simulation results with dummy data indicate that the internal structure of plasmoids during the dynamic process can be reconstructed with the developed system.