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Wien filter

 

 

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WIEN FILTER


according to K. Tsuno and J. Rouse, J. Electron Micr. 45 (1996) 417.

 

The electrons slowed down to energy E=60 eV enter crossed electrostatic and magnetic dipole fields Ex and Dy and an additional quadrupole field Q. The dipole field is generated by 8-pole electrodes that are 40 mm long. The dipole fields must fulfill the Wien condition Ex=v*Dy, where v is the velocity of electron, and the quadrupole field fulfills the condition Q=e*Ex*Ex/E/8 where e is the elementary charge. Dy is about 1.93 mT. The extent of the field is limited with magnetic clamps.

 

To document the accuracy of our ray tracing programs, the aberrations in several image plane are shown as the next example.

The axial dipole and quadrupole fields were computed with the help of EMD program, the trajectories with TRASYS. The results were shown with the help of SGPLOT. The Wien filter than acts approximately as a rotationally symmetric lens with energy dispersion in x plane. This is shown in the two figures below for angles up to 2 degrees with the axis.

 

 

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Last modified: 17/03/02 15:35