At non-relativistic energies, single particles generally produce effects too small to enable their direct detection. The microchannel plate functions as a particle amplifier, turning a single impinging particle into a cloud of electrons. By applying a strong electric field across the MCP, each individual microchannel becomes a continuous-dynode electron multiplier.
A particle or photon that enters one of the channels through a small orifice is guaranteed to hit the wall of the channel, due to the channel being at an angle to the plate. The impact starts a cascade of electrons that propagates through the channel, amplifying the original signal by several orders of magnitude, depending on the electric field strength and the geometry of the microchannel plate. After the cascade, the microchannel takes time to recover (or recharge) before it can detect another signal.
The electrons exit the channels on the opposite side of the plate, where they are collected on an anode. Some anodes are designed to allow spatially resolved ion collection, producing an image of the particles or photons incident on the plate.
Although in many cases the collecting anode functions as the detecting element, the MCP itself can also be used as a detector. The discharging and recharging of the plate produced by the electron cascade, can be decoupled from the high voltage applied to the plate and measured, to directly produce a signal corresponding to a single particle or photon.
The gain of an MCP is very noisy, meaning that two identical particles detected in succession will often produce wildly different signal magnitudes. The temporal jitter resulting from the peak height variation can be removed by using a constant fraction discriminator. Thusly employed, MCPs are capable of measuring particle arrival times with high resolution, making them ideal detectors for mass spectrometers.