Page "Photomultiplier" Paragraph 28
The electrons leave the photocathode, having the energy of the incoming photon ( minus the work function of the photocathode ).
As the electrons move toward the first dynode, they are accelerated by the electric field and arrive with much greater energy.
Upon striking the first dynode, more low energy electrons are emitted, and these electrons in turn are accelerated toward the second dynode.
The geometry of the dynode chain is such that a cascade occurs with an ever-increasing number of electrons being produced at each stage.
Finally, the electrons reach the anode, where the accumulation of charge results in a sharp current pulse indicating the arrival of a photon at the photocathode.