Figure 2
(click on image for figure alone)
Fig. 2 The beam is injected against a negatively biased grid.
When the bias voltage is slightly larger than the cathode
voltage most of the beam is reflected but a few electrons are
transmitted. Note that the equipotential surface near the grid
is not plane but convex. This causes an angular spread of the
reflected electrons. Electrons in the center of the beam are
normal to the sheath and can pass the grid when their energy
exceeds the potential energy of the sheath.
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Last Revision: 25 January 2000.