New method to correct eddy current in magnetic focusing-deflection system

摘要

Analysis and new structure is introduced to correct eddy current in electron beam focusing-deflection system. Maximum errors caused by eddy current are computed by changing permeability of the conductive materials at time t_0 (t_0 = 0, μ = 0) and t_∞ (t_0 = ∞, μ = μ_r) with the aid of Munro's software. The new double ferrite structure includes outer-and inner-layer ferrite rings which are spaced by ceramic spacer uniformly and staggered each other in radial direction. Basic principle for eddy current correction in this paper is that ferrite materials prevent the flow of magnetic flux from the deflection coil to the polepiece without perturbing the lens field. Magnetic flux of various lens structures and magnetic scalar equipotential lines of various deflectors illustrate the principle. Correction and performance versus the values of the gap (G) and the space (S) between the ferrite rings are considered. The new double ferrite structure not only corrects the eddy current, but also increases the sensitivity of the deflection without decreasing the performance.