The effects of secondary electron emission on the operation of position sensitive anodes

Secondary electron emission plays a crucial role in the operation of position sensing anodes used in imaging microchannel plate (MCP) intensifiers. Secondary electrons emitted from the anode strongly influence both the size and shape of the collected charge cloud distribution and also mediate charge redistribution between the anode electrodes. The performance of position readouts using charge division can be severely limited by these mechanisms. We describe experiments designed to study the secondary electron emission process from a charge division position readout. An intermediate grid between the MCP and anode is used to establish an electric field above the anode to control the trajectories of the secondaries without disturbing the operation of the MCP. Tuning of the grid and anode voltages allows the measurement of a variety of physical processes occurring within the detector. We present measurements of the secondary emission coefficients of anode and grid materials, and show how both the initial spatial and energy distribution of primary electrons from the MCP may be measured. The usefulness of controlling secondary electrons to improve imaging performance is demonstrated.