MCP: Stacking

MCP stacking is a technique of using two or more MCPs in series to increase the gain and the performance of the MCP detector. By stacking MCPs, the output electrons from the first MCP are used as the input for the second MCP, and so on, creating a cascade of electron multiplication.
However, stacking MCPs also has some issues compared to using a single MCP, such as:

• Stacking MCPs increases the complexity and the cost of the detector, as it requires more components, such as spacers, connectors, and power supplies.
• Stacking MCPs reduces the spatial resolution and the uniformity of the detector, as it introduces more variations and distortions in the electron trajectories and the output images.
• Stacking MCPs increases the noise and the background of the detector, as it amplifies the dark counts, the ion feedback, and the electronic interference from the MCPs and the anodes.

There are usually two or three stages for MCP stacking, depending on the application and the desired gain.

• Two-stage MCP (Chevron): This is an assembly of two microchannel plates with channels aligned in a V shape. The two MCPs can either be pressed together to preserve spatial resolution or have a small gap between them to spread the charge across multiple channels, which further increases the gain. A two-stage MCP can have a gain of up to 10 million.
• Three-stage MCP (Z-Stack): This is an assembly of three microchannel plates with channels aligned in a Z shape. The three MCPs are separated by small gaps to spread the charge and increase the gain. A three-stage MCP can have a gain of more than 10 million.