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Study the negative spherical aberration coefficients for the magnetic lens

Oday A. Hussein, Khalid A. Yahya and Rasha Y. Hamad

A theoretical investigation has been carried out to study the optical properties of a magnetic lens with the aid of analytical method. An analytical expression for paraxial trajectory of an electron in a magnetic lens is used to reach to the negative values of the spherical aberration coefficient. The Glaser's bell-shaped model is adopted to represent the axial flux density distribution of the magnetic lens. The optimization role is achieved by changes some of the effective parameters as the half-width at half maximum (a = 2.01, 2.02, 2.03 and 2.04 mm) and the maximum magnetic flux density (Bm = 0.001, 0.002, 0.003 and 0.004 Tesla). The calculations appear that the values of the negative spherical aberration coefficient are found and these coefficients are very senestive to these effective parameters and one can use this design of the magnetic lens as corrector in the optical systems