Theoretical Study of the Spatial Resolution Characteristics of Magnetic Focusing Framing Tubes

Abstract

Three magnetic focusing framing tubes are designed based on short magnetic lenses, long magnetic lenses, and hybrid lenses consisting of short and long magnetic lenses, and the spatial resolution characteristics of these framing tubes are theoretically studied. The excitation current of the short magnetic lenses is 0.15 A, the imaging magnification ratio is 1:1, and the spatial resolution is better than 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> . The spatial resolution difference is 23.08% within the 30-mm off-axis. The spatial resolution of the long magnetic lens framing tube is better than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~\mu \text{m}$ </tex-math></inline-formula> , and the spatial resolution difference is 10.71%. However, the long magnetic lenses require a large excitation current of 26.25 A. For the hybrid magnetic lenses, the excitation current of 0.15 A is used to achieve a spatial resolution of better than 20 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> and a spatial resolution difference of 8.11%. The simulation results show that the hybrid magnetic lenses are the best imaging method among these three lenses. A high spatial resolution and spatial resolution uniformity can be simultaneously obtained by using a small excitation current in the hybrid magnetic lens framing tube.