Igor Petrov

Theoretical analysis of achromatic deflectors

An electromagnetic system with matching centers of deflection in any arbitrary direction of charged particle beam is proposed. Analytical expressions for electrostatic and magnetic scalar potential distributions for such systems made of four, six and eight electrodes-poles were obtained in two-dimensional approximation. Values of feeding potential needed for improvement of field homogeneity were found for the six electrode-pole systems. Conditions of the first order achromatism for the deflecting, focusing and correcting systems with the transversal fields have been written in general form. Edge field distribution along optical axis has been calculated numerically for finite length deflectors and empirical formula approximating this distribution has been derived. Beam central trajectory parameters were calculated for electrostatic, magnetic and for systems with common ratio of the electrostatic and magnetic components, providing achromatic deflection in small work region. Other ratios of these components providing expansion of region of the achromatic deflection up to 200-250 and high er degree of the linear deflection were found. Advantages of the proposed deflectors are described.