T-REXX: a new endstation for serial time-resolved crystallography

by David von Setten (EMBL)

Tuesday, February 25, 2020 from to (Europe/Berlin)
at 25b ( 109 )
EMBL operates two beamlines (P13 and P14) for macromolecular 
crystallography at the PETRA-III synchrotron. A second endstation 
(‘P14.EH2’, ‘T-REXX’) for serial time-resolved crystallography is in 
operation in a second hutch at the far end of P14 since October 2018. 
For this endstation, the P14 X-ray beam is refocussed with a compound 
refractive lens (CRL) transfocator to provide a 15x10 μm2 beam with a 
flux of about 2e12 photons/s at 12.7 keV. To be able to accommodate 
different microcrystal sample delivery systems suitable for serial 
crystallography, T-REXX is not equipped with a goniometer, but instead 
with a beam shaping device (BSD) that provides an on-axis viewer, beam 
shaping apertures, a fully motorized beamstop, and a scintillator for 
visualisation of the X-ray beam. For time-resolved pump/probe 
experiments, a laser system (355 nm) for initiating reactions is built 
into the setup, such that the laser and X-ray beams are almost parallel 
at the sample position, which facilitates alignment of the beams using 
the on-axis viewer. First experiments have yielded promising results 
using different sample delivery systems, such as microfluidic flow cells 
as well as patterned silicon chips (Mehrabi et al., Nature Methods 16, 
979 (2019)). In the future, the Hadamard technique (Yorke et al., Nature 
Methods 11, 1131 (2014)) will be employed to reach sub-millisecond 
timescales in time-resolved experiments, either by gating the detector 
or alternatively by modulating the X-ray beam.