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An Office of Science User Facility

Coherent X-ray Imaging  (CXI)

This site is OBSOLETE as of 30 Oct. 2017
Please go to the new CXI site
 

 

 

CXI Standard Configuration for Run 16

Types of Experiments

With this standard configuration, CXI will be able to support Serial Femtosecond Crystallography (SFX) experiments with or without a pump laser and Small Angle and Wide Angle X-ray Scattering (SAXS/WAXS) with or without a pump laser using a wide variety of sample delivery methods, either LCLS-owned or supplied by the user groups. Two full size CSPADs can be available, one for high angle close to the sample with a second detector downstream if absolutely necessary.

X-ray Focus

CXI will be configured to use the 1 micron KB focus. This provides a ~1 micron (FWHM) beam that is not adjustable in size.

Sample Environment

The CXI 1 micron Sample Chamber will be used. It provides a large volume to support devices inside vacuum, including the following which will be supported in this standard configuration.

Liquid Jet Mechanical System

The liquid jet mechanical system is installed on top of the sample chamber. It consists of an XYZ stage to position a shroud in which the sample is delivered. This shroud is part of a load-lock system which allows long nozzle rods to be inserted and removed without venting the sample chamber. Any sample delivery system which is compatible with this mechanical system, this load-lock and the standard nozzle rods will be supported. This included Gas Dynamic Virtual Nozzle (GDVN), Lipidic Cubic Phase (LCP), the Microfluidic Electrokinetic Sample Holder (MESH) or other viscous extrusion systems, many types of mixing nozzles and any other system that can be mounted on the nozzle rod. Contact the CXI scientists for details on the nozzle rod and the injector mechanical system.

On-axis Sample Viewing System

The CXI sample chamber will be equipped with an on-axis jet viewing system. This system provides a ~3 micron resolution view of the jet from the perspective of what the x-ray beam sees. This provides a rough alignment of the jet without any detailed information about the sample content or jet size and speed.

Perpendicular High Resolution Jet Imaging System

A high resolution jet imaging system will be installed to provide a perpendicular view of the jet. A continuous illumination LED will be used to provide the necessary illumination. This LED is currently available at 520nm, 617 nm or 850 nm.

Post-Sample Attenuator

A post-sample attenuator mount will be available. This consists of an XYZ stage on which user-supplied foils or filters with a central hole can be mounted and aligned with the beam. This can allow attenuating the scattered beam. It can also allow in principle with a properly design attenuator to attenuate parts of the scattered signal, for example, attenuating the low angles and not the high angles. Such attenuators would have to be supplied by the users and matching the existing CXI mounting brackets. Contact the CXI scientists for information on the details of this post-sample attenuator mounting.

Pump Lasers

Time-resolved experiments employing tunable nanosecond and/or femtosecond pulses will be supported under this standard configuration. In the case that both nanosecond and femtosecond lasers are desired, the chosen wavelength will need to be compatible with the same optics set and should not require reconfiguration of the optical setup. While it is should not be expected that two lasers can be supported during a single experiment, a minimum required condition for this would be using only one of them at a time and switching between them during an off-shift if optics do not need to be modified.

Nanosecond laser

An Opolette HR 355 will be available for <8 ns pump laser pulses over a wide tunability range (410-2200 nm). This laser will be fiber-coupled then propagated in free-space into the sample chamber and combined collinearly with the x-ray, with in-coupling ~250 mm upstream of the sample and with the focusing lens ~350mm away from the sample. Note that the efficiency of the optics and the performance of the laser will not be the same for the entire wavelength range. The maximum achievable power density will be determined by the existing optical system and will not be modified. Contact the CXI scientists to discuss specific needs and determine if they can be achieved using this standard configuration of the laser. The expected performance at the source is shown below (the energy on target will be substantially lower due to transport losses). The CXI system will have the following options:  


Femtosecond laser

The fundamental (800 nm) or second harmonic (400 nm) of the CXI, ~50-150fs Ti:Sapphire laser will be available, delivered to the sample collinearly with the x-rays, with in-coupling ~250 mm upstream of the sample and with the focusing lens ~350mm away from the sample. The system can also be used with a TOPAS-Prime Optical Parametric Amplifier (OPA) capable of 480-2400 nm wavelengths. Again, note that the efficiency of the optics and the performance of the laser and the OPA will not be the same for the entire wavelength range. The achievable peak intensity/fluence will be determined by the existing optical system and will not be modified. Contact the CXI scientists to discuss specific needs and to confirm whether they can be achieved in this standard configuration of the laser. The expected performance at the source is shown below. The approximate on target energy is shown below.


 

Timing diagnostics

For the nanosecond laser, a fast diode will be available to verify the time overlap of the laser and the x-rays.

For the femtosecond laser, the CXI time tool will be available to record single shot arrival times that can be post-sorted. Time zero at the sample can be obtained to better than 200 fs using a CXI-supplied target to measure the index of refraction change induced by the x-ray beam.

CSPADs

Two full size CSPADs can be available, one for high angle close to the sample with a second detector downstream if absolutely necessary. The second CSPAD will typically be used for Protein Crystal Screening (PCS) by another group parasitically using the beam passing through the whole in the front detector. Users of the standard configuration at CXI should expect PCS beamtime running at the same time and their beamtime. The front CSPAD can be positioned from 70 to 580 mm from the sample. The back CSPAD can be positioned between ~2300 and ~2600 mm.

CXI Instrument Staff

Mark Hunter, Sergio Carbajo, Andy Aquila, Alex Batyuk, TJ Lane, Meng Liang, Matt Seaberg, Ray Sierra, Sebastien Boutet

Parameter Table

To be considered for scheduling in this standard configuration, users will be required to include a table in the proposal that lists the specific experimental parameters to ensure compatibility with these configurations. If the experimental parameters are not compatible with the standard configuration or if the table of parameters is incomplete, the proposal will be reviewed and considered for scheduling as general user proposal. Please see the  table of required parameters. No fundamental changes to the standard configurations will occur, but some details of the configuration may be updated in response to inquiries, so users should recheck the website before submitting your proposal to confirm that you have the latest information. Address any questions to the instrument staff.
 
 
LCLS proposals are submitted through the User Portal.



SLAC SLAC National Accelerator Laboratory, Menlo Park, CA
Operated by Stanford University for the U.S. Dept. of Energy