High Power Laser Science and Engineering, (2017), Vol. 5, e7, 7 pages.
© The Author 2017. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/
licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
doi:10.1017/hpl.2017.6
Fluid sample injectors for x-ray free electron laser
at SACLA
Kensuke Tono
1,2
1
Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo, Hyogo 679-5198, Japan
2
RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan
(Received 29 October 2016; revised 10 January 2017; accepted 8 February 2017)
Abstract
This paper provides a review on sample injectors which are provided at SPring-8 Angstrom Compact free electron LAser
(SACLA) for conducting serial measurement in a ‘diffract-before-destroy’ scheme using an x-ray free electron laser
(XFEL). Versatile experimental platforms at SACLA are able to accept various types of injectors, among which liquid-
jet, droplet and viscous carrier injectors are frequently utilized. These injectors produce different forms of fluid targets
such as a liquid filament with a diameter in the order of micrometer, micro-droplet synchronized to XFEL pulses, and
slowly flowing column of highly viscous fluid with a rate below 1 µL min
−1
. Characteristics and applications of the
injectors are described.
Keywords: SACLA; sample injector; serial femtosecond crystallography; x-ray free electron laser
1. Introduction
An x-ray free electron laser (XFEL) is a high power x-
ray source which produces laser light with a wavelength
of the order of angstrom. The first two XFEL facilities in
the world, the Linac Coherent Light Source (LCLS) and
SPring-8 Angstrom Compact free electron LAser (SACLA),
provide femtosecond x-ray pulses with peak powers of the
order of tens of GW
[1, 2]
. By focusing the XFEL pulse to
∼1 µm (∼0.05 µm), the intensity reaches as high as ∼10
18
(∼10
20
) W cm
−2
[3, 4]
. These characteristics offer research
opportunities in various fields of science such as structural
biology
[5–9]
, nonlinear x-ray optics
[10, 11]
, ultrafast physics
and chemistry
[12–15]
, and high energy density science
[16]
.
One of the most important targets of XFEL applications is
damage-free structure analysis in a ‘diffract-before-destroy’
scheme
[17, 18]
, in which diffraction events in the sample can
be terminated before structural change is initiated
[19]
. A
diffraction pattern of the sample can be recorded even under
the irradiation of an XFEL pulse with an intensity higher
than the damage threshold. However, as the sample is to
be destroyed after the irradiation, a new sample has to be
delivered before the next x-ray pulse comes to the interaction
point. For this purpose, fluid sample injectors have been
developed.
Correspondence to: K. Tono. XFEL Utilization Division, Japan
Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo, Hyogo 679-
5198, Japan. Email: tono@spring8.or.jp
In the early experiments with XFEL, liquid-jet injectors
using a gas dynamic virtual nozzle (GDVN) were applied
to protein crystallography
[5, 7, 20–23]
. This type of injector
produced a continuous stream of liquid containing 10
8
–
10
9
cm
−3
of protein microcrystals
[20, 21]
. A series of diffrac-
tion patterns from the crystal suspension were recorded with
femtosecond x-ray pulses in a pulse by pulse manner. This
method is called serial femtosecond crystallography (SFX).
Because the liquid-jet injectors worked at a typical flow
rate of the order 10 µL min
−1
, the early SFX experiments
consumed protein crystals in the order of 10–100 mg.
To reduce the sample consumption, different injectors
have been developed primarily for the application to SFX. A
lipidic-cubic-phase (LCP) injector produces a slow flow of
highly viscous lipid containing microcrystals at a flow rate
of 10
−3
–10
−1
µL min
−1
[24–26]
. A typical sample amount
required for collecting a full dataset can be as small as
1 mg. Alternative crystal carriers have been utilized not
only for insoluble proteins but also for soluble ones
[25, 27–29]
.
An electrospun injector produces a liquid jet in an elec-
tric field to deliver a crystal suspension at a low flow
rate of 0.14–3.1 µL min
−1
[30]
. Recently drop-on-demand
injectors have been applied to SFX experiments under the
atmospheric pressure
[31, 32]
. This type of injector delivers
crystal-containing droplets in synchronization with XFEL
pulses. In contrast to the continuous-flow injectors, the
pulsed operation of the injector can help to reduce the sample
consumption.
1