Dual Ion Beam Irradiation System for In situ Observation with Electron Microscope

Abstract

We have developed a new in situ observation system for dynamic processes under dual ion beam irradiation. The system consists of a modified 400 keV analytical electron microscope (JEOL, JEM-4000FX) and two 40 kV ion beam accelerators. This system allows evaluation of microscopic changes of structure and chemical bonding state of materials in the dynamic processes under two kinds of ion beam irradiations, that is required for the simulation test of the first wall of nuclear fusion reactors onto which He⁺, H⁺, and H₂⁺ ions are irradiated simultaneously. These two ion accelerators were equipped symmetrically both sides of the electron microscope and individually controlled. Each ion beam extracted from a duo-plasmatron ion gun is bent downward by an angle of 30° with a mass-separating magnet, and introduced into specimen chamber of the electron microscope. Inside the specimen chamber the beam is deflected again by an angle of 30° with an electrostatic prism so as to be incident on the specimen surface. Finally, two ion beams from both side are incident on the specimen surface at an angle of 60°. The maximum ion current density of helium is more than 250 μA/cm² at the specimen at an ion energy of 17 keV. Images of the electron microscope during dual ion beam irradiation are observed through a TV camera and recorded with a VTR.