High-speed position readout for microchannel plate-based space plasma instruments

Position sensitive micro-channel plate (MPC) detectors are attractive for space plasma instruments but have a number of limitations. Most of the techniques have limited global rate handling and require the MCP to run at high gain with MCP lifetime implications. In addition, available mass and power resources limit the number of channels of readout electronics. A fast position sensing technique was developed that is well suited for MCP-based space plasma applications. The output charge from the MCP falling on an anode pixel is capacitively split into two separate channels of readout electronics. Choosing an appropriate readout pattern, the charge is forced to split unequally, introducing a time walk between the signals from the following leading edge discriminator. Identifying the active channels and the order of their arrival time provides unique identification of the position of the incoming event. The pixels are interleaved so that each readout channel can be connected to several pixels, reducing the total number of readout channels. The timing logic and signal processing is carried out within an FPGA with additional processor/spacecraft interfaces also built in. The system dead time within the FPGA has been simulated and found to be less than 100 ns. The performance of the system can be optimised depending on the resolution, rate handling and lifetime requirements of the instrument. Details of the readout technique and its implementation in a space plasma analyser are presented.