Evaluation and Minimization of Aberrations for a Solenoid Lens

Relativistically correct computer simulations of transporting a beam of charged particles through a solenoid lens were used to study nonlinear focusing effects of this lens type. Input beams with both zero and nonzero emittance can be studied. The magnetic field is specified either by a Fourier-Bessel function-type expansion of the vector potential at a suitably chosen radius or by a direct interpolation of the fields calculated by the magnet design code POISSON. As an area in phase space, the dependence of nonlinear effects on field strength and beam radius was determined for a few magnetic field distributions. Attempts to tailor the field to minimize spherical aberrations are discussed.