Readout electronics of a prototype time-of-flight ion composition analyzer for space plasma

Readout electronics is developed for a prototype time-of-flight (TOF) ion composition spectrometer for in situ measurement of the mass/charge distributions of major ion species from 200 to 100 keV/e in space plasma. By utilizing a constant fraction discriminator (CFD) and time-to-digital converter (TDC), challenging dynamic range measurements were performed with high time resolution and event rates. CFD was employed to discriminate the TOF signals from the micro-channel plate and channel electron multipliers. TDC based on the combination of counter and OR-gate delay chain was designed in a high reliability flash field programmable gate array. Owing to the non-uniformity of the delay chain, a correction algorithm based on integral nonlinearity compensation was implemented to reduce the time uncertainty. The test results showed that the electronics achieved a low timing error of < 200 ps in the input range from 35 to 500 mV for the CFD, and a time resolution of 550 ps with time uncertainty < 180 ps after correction and a time range of 6.4 vis for the TDC. The TOF spectrum from an electron beam experiment of the impacting N-2 gas further indicated the good performance of this readout electronic.