XFEL Hub at Diamond

The XFEL Hub at Diamond is funded by the Wellcome Trust and the Biotechnology and Biological Research council (BBSRC) to provide expertise and support to the UK community engaged in XFEL-related research in the life sciences. This includes all aspects of various XFEL experiments from conception to beamtime proposals through sample preparations and testing, to XFEL data collection, analysis and publication.

Over the past year, members of the XFEL Hub have visited and/or conducted serial femtosecond crystallographic (SFX) and time-resolved SFX (tr-SFX) experiments at all five XFEL facilities: i) the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory in Menlo Park, California, USA; ii) SPring-8 Angstrom Compact free electron LAser, (SACLA) in Hyogo, Japan; iii) the European XFEL in Schenefeld Germany; iv) The Pohang Accelerator Laboratory XFEL (PAL-XFEL) in Pohang Korea; and v) The Swiss FEL at the Paul Scherrer Institute in Villigen PSI Switzerland. Six out of eight, and eight out of 11 experiments conducted at either LCLS, SACLA or the European XFEL included UK research groups in 2017 and the first half of 2018, respectively. The XFEL Hub also provided travel awards to several UK research groups that were granted XFEL beamtime at these three facilities.

The XFEL Hub continues methods R&D to support on-demand acoustic sample delivery methods for SFX and tr-SFX. These complement fixed target strategies developed by the I24 and I23 teams at Diamond. We have also formed a new Beamtime Access Group (BAG) at Diamond titled, 'Dynamic Structural Biology at Diamond & XFELs', which emphasises serial data collection strategies at ambient temperature and pressure using slurries of microcrystals. The new BAG uses some of Diamond’s MX beamlines I24, I04, and VMXi.

The European XFEL delivers X-ray pulses in a discontinuous train structure that repeats at 10 Hz and with a 'dark period' or 'idle time' between each train. For example, a 600 ms pulse train is followed by a 99.4 ms gap. The maximum intra-train repetition rate is 4.5 MHz with 2700 X-ray pulses per train, but it can also operate slower by integer divisions. During the user-assisted commissioning studies, the facility delivered 60 ms pulse trains at 10 Hz with an intra-train frequency of 1.1 MHz.

 The XFEL Hub, through its membership in the SFX Consortium, is working to supply an on-demand droplet sample injector for the downstream interaction region of the SPB/SFX instrument. One of our goals is to support SFX and tr-SFX by delivering ~30 picolitre droplets of microcrystal slurries directly into and synchronized with the XFEL beam pulses. At the end of this year or early next year, we anticipate testing sample delivery at 10 kHz within each pulse train to yield a 60 Hz overall data collection rate. Longer-term goals include 100 kHz sample delivery within a pulse train, which will produce SFX data at 600 Hz overall. Although MHz sample delivery rates are likely to require fast jets, an advantage of on-demand acoustic methods is that they are more efficient with samples since none is wasted in the gap between the X-ray trains.