An ion-imaging detector for high count rates.

The emergence of high-power ionizing light sources with repetition rates greater than 100 kHz promises vastly improved data acquisition times for electron and ion imaging experiments; however, optimal means to record ion images at high average ion flux are challenging. A popular ion imaging detector uses a double (chevron) microchannel plate (MCP) stack operating at high gain (∼106) and a phosphor screen floated to 4 kV while images are recorded using a CCD or CMOS camera. Such imaging detectors tend to exhibit severe inhomogeneity at high incidence ion flux due to saturation effects in the MCP, even when the amplified current is far below the strip-current limit. This inhomogeneity arises from a local loss of gain in channels experiencing a high frequency of ion-amplification events, even when most channels are behaving normally. Here, we describe an alternative ion imaging scheme using a detector based on a single microchannel plate, a phosphor screen that can be floated to 20 kV, and a Timepix3 based event camera and demonstrate its performance in an ion-imaging experiment performed at a repetition rate of 100 kHz. The reduced gain of the single MCP avoids gain inhomogeneity up to higher count-rates, while the high-voltage phosphor helps maintain high single ion detection efficiency. The detector performs well at an ion flux of 107 ions cm-2 s-1.