The spatial extent of gain depression for MCP-based photon detectors

We describe a technique to measure the spatial extent and magnitude of gain depression in the quiescent pores surrounding an active region of an MCP and present preliminary results. We find that significant gain depression occurs up to 1.5 mm from the center of the active region. The magnitude of the reduction in gain decreases linearly with radius and is proportional to the count rate. We evaluate two possible mechanisms for gain depression. We find that the pore deactivating model in which the electric field from the discharging of a pore distorts the electric fields in surrounding pores is more successful than the transfer of charge from quiescent pores.