Femtosecond X-ray Experiments (FXE): Time-resolved investigations of the dynamics of solids, liquids, gases
The FXE instrument aims at the time-resolved investigation of ultrafast processes in condensed-matter systems (liquids and solids) and possibly also of gaseous samples. Scientific areas of application are chemical dynamics, dynamics of condensed matter and matter under extreme conditions.
The instrument utilizes the ultrashort pulse duration emphasizing pump-probe experiments. The possibility of using optical lasers and X-ray pulses both for pump or probe usage is foreseen. X-ray techniques to be applied are various kinds of diffraction (Bragg, powder, amorphous) and spectroscopy. In spectroscopy the use of X-ray emission spectroscopy (XES) is rather straight forward, while techniques requiring tuning the wavelength of the incident radiation to and around an element-specific absorption edge will require a level of accelerator performance not to be expected for initial operation. This applies to most of the X-ray absorption spectroscopy (XAS) techniques.
Conceptual Design Report
Work package group FXE
FXE workshop 2009
The first FXE workshop took place in Budapest in December 2009. Visit the workshop page for more information including the slides of the given presentations.
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Initial design, TDR-2006 & startup configuration:
- Mounting of samples typically requires a diffractometer to orient and manipulate samples.
- Diffraction techniques require coverage of a large solid angle. This can be achieved by area detectors mounted on a diffractometer arm or a similar device. Due to the horizontal polarization diffraction in the vertical plane needs to be considered. Furthermore small-angle techniques require further definition.
- Absorption spectroscopy techniques will require precise determination of the incident spectrum or wavelength. Eventually dispersion of the incident spectrum behind the sample provides spectral information.
- Emission spectroscopy techniques will require the development of highly efficient spectrometers (large solid angle, high reflectivity) enabling to collect the dispersed plane in a single-shot. This will be very important for normalization of the data using a fluctuating source.
- The use of pump-probe techniques using X-ray and optical laser radiation are fundamental. For the X-ray beam split-and-delay devices will be required. The use of 1st, 3rd and 5th order harmonics in these pump-probe experiments providing appropriate separation and delay needs further definition.
- X-ray beam will be focused to focal spots of ∼1 μm, ∼10 μm and ∼100 μm. Some experiments might require adjusting X-ray flux to prevent sample damage.
- For most diffraction experiments the initial bandwidth might be sufficient. But for spectroscopy and for samples with extremely high crystal perfection the usage of a monochromator (ΔE/E ∼ 10-4) will be of advantage.
- The X-ray beam requires pulse-by-pulse diagnostics of intensity, position, (spot size). Due to expected small signal an accuracy of 10-3-10-4 is needed for measurement of the intensity. Regular measurement of X-ray wavefront and pulse arrival is wishful. Part of this task might be achieved using a specially designed beam stop, others requires intersection of the beam.
- Experiments using solids or liquids can be done at air or He-atmosphere, but vacuum environment might be beneficial for various reasons. Special sample preparation methods are envisaged.
- Methods to visualize the sample (morphology, etc.) might provide insight to sample damage.
- Pump-probe experiments using optical lasers (few 10 fs, mJ, MHz) are foreseen, but only one laser system will be build. This laser has to serve instruments in the opposite ends of the hall.
- Detection will be achieved by use of the newly developed 2D pixel detectors. In the moment the LPD detector with a pixel size of (200-500 μm)2 is foreseen for this instrument. Detector distance is not yet defined. If the detector requires a central hole for the direct beam requires definition. Number of pixels is 1 million.
- Construction of one X-ray hutch is foreseen for this instrument. In addition a control hutch will be built for operation of the instrument.
Beamline design considerations
- Instrument is located at SASE 2 beamline (designed for tunable energy operation from 4 to 12.4 keV, providing horizontal linear polarization).
- Instrument is ∼1000 m from source point.
- Beamline will be designed for optimized transport of ultrashort X-ray pulses.
- Beamline will feature a monochromator allowing a resolution of 10-5–10-4 for definition of bandwidth and intensity per bandwidth element and for spectroscopy.
- Additional capability of transporting spontaneous undulator radiation in the range 20-100 keV.