Electron beam energy
Goldilocks and the Three Bears (and their porridge, beds and chairs) have got nothing on this high voltage design challenge.
Sometimes a client gets into areas of technology that go way over my head, but I manage to pick up a snippet here or there. This is one such case.
The requirement was to create an electron beam for which the beam energy would be precisely known. The measurement technique is diagrammed as follows (Figure 1).
Figure 1 Fairy tales and their application to electron beam energy (if-necessary reference)
Two curved metal channels were arranged in a circular path through which the electron beam was to be directed. Equal but opposite polarity high voltages would be applied as shown. When an electron source was aimed into one end of this structure, the path of that beam, i.e., the beam’s radius of curvature, would vary as a function of the applied high voltages.
By dint of equations that left me in the dust, when the high voltages and beam energy were a proper match, the electron beam would emerge at the output end where it would go on to serve its intended purpose. The beam’s radius of curvature under the electrostatic field would be just right, and the beam energy would be precisely known. If there was a mismatch, the electron beam would impinge instead on one metal plate or the other and not appear at the output.
The high voltage and voltage precision requirements for this thing were quite demanding. The dual power supply we made for this setup went from zero to 25 kV on each side and had a room temperature versus voltage temperature coefficient on the order of 1 ppm per °C.
Happily, it worked very well.
John Dunn is an electronics consultant and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York University (MSEE).
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