At the front of the electron multiplier, photons kick out electrons which move into a maze of curved metal plates.
Each new plate is biased about a hundred volts more positive then the last. Electrons which are kicked out of the first plate (at low energy) thus accelerate into the second plate where they each kick out multiple electrons. This multiplication process continues downward in much the same way that an avalanche grows. As a result, a single photon can produce millions of electrons.
The blue wires carry the necessary ladder of voltages to the plates.
