Exposition

ESA Entrance Slits

Exhibit no. 303

The electrostatic sector analyzer consists of two curved plates of equal and opposite potential. As the plates are finite in size, the electric field lines at the edge of the plates are not straight lines. This is known as edge effects, and the non-uniform fields near the edge are called the fringing fields. The fringing field of an electrostatic analyzer can affect the homogeneity of the inner electric field, and the field strength at the entrance and exit boundaries does not drop sharply to zero outside. The position of the effective sector field boundary is usually adjusted by a fringing field corrector plate also called “Herzog shunt” or “field clamp”, which terminates long tails of the fringing field distribution.

The exhibit is electrostatic analyzer entrance slits, which likely served as field clamps. They are from the MS902 double-focusing mass spectrometer with Nier-Johnson geometry manufactured by AEI Scientific Apparatus Ltd. in 1969.

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