Apparatus for removing ions from an electron beam

Details Apparatus for removing ions from an electron beam Apparatus for removing ions from an electron beam

1995-10-04

1997-04-01

Berman, Jack I.

Radiant energy

Ionic separation or analysis

Static field-type ion path-bending selecting means

250396R, H01J 4948

Patent

active

056169205

ABSTRACT:
Purely electrical or magnetic deflection systems are usually utilized in the probe-shaping part of modern electron beam tomographs in order to remove the gas ions generated in the evacuated drift tube by electron impact from the beam. The known deflection systems, however, cause an offset of the electron beam, so that this enters extra-axially into the lens element following the deflection system. In the apparatus for removing ions from an electron beam disclosed herein, a deflection unit (Wien filter) generates an E.times.B field oriented perpendicular to the beam axis that exerts strong shearing forces only on the positively charged gas ions, but does not influence the electrons. The deflection unit is essentially composed of two tube electrodes lying at a constant potential, of an electrostatic octopole deflector, and two saddle coil pairs annularly surrounding the octopole deflector. The apparatus is useful for fast electron beam tomographs, including x-ray scanners.

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