Timing in a FLASH

A segmented Fast Light Acquiring Start Hodoscope (FLASH) prototype was constructed and tested at the Mainz Microtron (MAMI). Its working principle is based on the detection of Cherenkov light, produced inside radiator bars made of synthetic fused silica, by fast Micro-Channel Plate PMTs (MCP-PMTs). The bars are inclined with respect to the particle trajectory to match the Cherenkov angle to mininmize reflections off the radiator surfaces.

The segmentation allows determining a coarse impact position (~few mm) and also repeatedly measuring the arrival time so that an averaging procedure can be used to improve the timing precision. The FLASH protoype is built around the PLANACON 64-channel MCP-PMT with a pore size of 10 micron. The radiator bars (5 x 5.5 x 140 mm^3) are arranged in an 8 x 8 matrix so that each radiator bar matches a pixel on the MCP-PMT. The MCP-PMTs are equipped with NINO-based frontend electronics providing leading edge time and Time-over-Threshold (ToT). The frontend electronics is read out with modified TRB boards where the DC/DC converters were taken off.

Two such units were tested using the 855 MeV electron beam of MAMI. The detector response was investigated and the basic characteristics were extracted. The timing performance was studied and the ToT information was used to perform walk corrections. The best timing precision achieved was ~50 ps per FLASH unit. The results are also published here: http://dx.doi.org/10.1016/j.nima.2017.02.080