The LINAC Coherent Light Source (LCLS) fires powerful x-ray laser pulses onto a variety of targets; atoms, molecules, biological structures, etc. Before target destruction, scattered x-ray photons and emitted photons, electrons and ions reveal scales of material structure from microns to Angstroms with dynamics resolved in time from microseconds to attoseconds. Divided into two x-ray photon energy regimes, soft (250 eV to 2 keV) and hard (6 keV to 21 keV) various experimental methods use specialized detectors that readout tremendous amounts of data for every of the 120 x-ray shots fired per second. These detectors are traditionally charged particle detectors (soft x-ray spectroscopies) and photon detectors (both hard and soft x-ray scattering and photon spectroscopy). Such detectors currently produce on the order of TB of raw data per hour.
The upcoming LCLS-II(-HE) will increase the shot rate from 120 pulses per second to 100 thousand or even up to 1 million pulses per second. At these rates, the transfer of raw data, even to local storage farms, is unreasonable if not impossible. The development of ultra-low latency, high-throughput Edge Machine Learning (EdgeML) for use in the LCLS-II Data Reduction Pipeline (DRP) will focus on deploying trained inference networks to FPGAs that are near or ideally directly in the detector electronics. These inference networks will partially analyze the continuous stream of data, generating veto and categorization meta-data that serves as on-the-fly analysis control switches for later stage analysis before it is sent to the local storage farm.
We are using two internally driven R&D projects as exemplars of the EdgeML paradigm: the 2d-TimeTool project which is targeting a spectrogram x-ray/optical relative delay measurement with sub-fs precision and the CookieBox angle resolved electron detector project which is targeting the attosecond scale recovery of x-ray pulse shapes as well as angle resolved photo-electron and Auger electron spectroscopy. Both use case examples are targeting data ingestion rates in the 50 GB/s - 1 TB/s range.
In the hard x-ray regime, detectors with 10s of megapixels collect scattered x-ray photons. If diffraction peaks can be intelligently identified and classified, the subsequent analysis can handle much higher throughput and even use accumulation statistics to decide if image buffers should be aggregated or stored as individual anomalies.