The Effect of Air Gap Width (S) and the Ratio (P1/D2) on .Minimum Projector Focal Length (Fp)min for the Double Pole-Piece Lens- at Costant Excitation (NI)

Abstract

The  spherical  double pole-piece  electron  lens i§ depend  on some

fact0rs : the-  minimum va}ue-of projector  fo·cal  length (Fp)i:J,Iill  â€¢  the

maximum value of  magnetic flux density (Bm) , the total  hal[ width

,(W)  o'f asyriunetrical   clln'e  of  magnetic field  distribution  [because there are differe_nt values of bore diameter  (D1) • i.                                               the ratio (D)D2) with different values] and the air gap width (S) between tlw iron poles The rat'io (S!Om) is used to represent' this type of lenses and depend  as

a primary factor to desi:gn the lenses . Therefore the effect of  air gap width and; the ratid (D1 /Dx) on the varia_ble-above , especially  (Fp)mili Wi;is studied to obtain  the mos-t favorable design  â€¢. highest  fje)d of view (r) and magnification  (M) of doublet projeetor tens although, the

requirtXI projector lens is about (M=JOO x) .!ll All calculat.ic;ms done by

the finite  element  method  sugges-ted by (Munro, l973)  C2-l   , which is a numerical  method  used to find the magnetic field in electron lenses .