| 摘要 |
A stigmator assembly capable of correcting even three-fold astigmatism without increasing the size of an electron microscope or the like in which the assembly is mounted. Values indicating control parameters A3 and thetah are set with control knobs and entered into a first arithmetic circuit. Values indicating control parameters A2 and thetaq are set with control knobs and input into a second arithmetic circuit. The first arithmetic circuit calculates current values for producing a corrective hexapole field, using the entered control parameters A3 and thetah. The second arithmetic circuit calculates current values for producing a corrective quadrupole field, using the entered control parameters A2 and thetaq. An adder circuit supplies control currents into coils, respectively, the control currents corresponding to the sums of the values calculated by the arithmetic circuits.
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