This is a very simple simulation of Secondary Electron Emission Bistability.
(150 kb java applet)

(The user can pulse the eyelet by moving the mouse cursor over the black buttons and left-clicking the mouse.)

Pulsing the eyelet negatively (upwards) lowers the energy of the incoming electrons. If the energy is too low (the potential difference between electron and target too small) the electrons will be deflected.

Pulsing the eyelet positively (larger potential difference) far enough, the electrons become so energetic that they will "kick out" extra secondary electrons, and the eyelet then loses net charge. This increases the potential differences between the eyelet and the incoming electrons. If sufficient secondaries are ejected, the potential of the eyelet becomes so large that electrons are accelerated through the hole in the center and impinge upon a phosphor grain.

Note that this model demonstrates bi-stability: it has two stable operating points, charged and discharged. It has memory. By applying an appropriate pulse, the eyelet will, when released, "float" to a stable potential and either pass or reject electrons. In the physical device the mode can be set or reset by application of the appropriate voltage waveform to an electrode capacitively coupled to the eyelet.