Design of a magnetic lens doublet for a Mott polarimeter

Two equal iron magnetic lenses forming a high-aperture doublet have been constructed. Their axial and radial magnetic fields have been determined both experimentally and numerically with sufficient agreement. As long as fringing fields and saturation effects in the iron are negligible, a computer simulation of this lens doublet is practicable. A constant distance z0 = 100 cm is assumed between a point source at z1 = 0 cm in the center of lens 1 and a detector plane, perpendicular to the optical axis z. The position of lens 2 is variable within 15 cm ≤ z2 ≤ 100 cm. The currents I1 and I2 in the lenses 1 and 2 are varied until a minimum of the spherical aberration is achieved in the detector plane. This is repeated for different values of the transmission and angular magnification. Results are summarized in a table and graphic design. Topic theoretical results in the longitudinal electron polarization of RaE are outlined and further measurements are proposed.