The XFEL machine produces tens of thousands of X-ray pulses every second. These bursts of pulses arrive in a regular bunch structure giving a rate equivalent to 4.5 million frames a second during the active burst period. At this speed, it is possible to image chemical interactions as they happen or measure chemical structures without crystallising the sample. The challenge for the detector system is to record at this frame rate, read all the data out, and be ready for the next bunch a tenth of a second later. This must all be achieved whilst meeting demanding noise and dynamic range requirements.
Following delivery in 2017, significant efforts have gone into the characterisation and calibration of the LPD, with several corrections required before data is valid for user analysis. When considering LPD has 1M pixels each operating in 3 gain stages across 512 memory cells, a total of more than 1.5 billion gain correction coefficients are required.
Currently, the LPD 1M is fully operational on the Femtosecond X-ray Experiment (FXE) instrument and regularly outputs scientific results. In addition to the 1M, several flavours of the LPD system have been delivered or are currently in development. The LPD mini is a small, portable system, featuring all the capabilities of the 1M version on only 16 ASICs (~8k pixels) and was delivered to the EuXFEL in 2021. The Single SM Housing project is focussed on creating housing for a single LPD super-module (with the 1M the result of a combined 16 super-modules), enabling beamline scientists to remove single super-modules from the 1M housing and reposition them in the FXE experimental hutch as desired.
Alongside continued support for LPD and the provision of spare parts, the STFC detector group are currently undertaking a research program studying the effects of high fluxes on high-Z materials such as CdZnTe, CdTe, and GaAs:Cr with a view to feeding the results into the development of future detectors for second generation FELs.
More information on LPD:
Written by Rhian Mair Wheater, a Detector Development team member.