High-Energy Density matter experiments (HED): Investigation of matter under extreme conditions using hard X-ray FEL radiation
The HED instrument aims at the investigation of matter under high energy density conditions. High energy density refers here to about or more than 0.1 mJ of energy stored in a X-ray typical volume of (10 μm)3. Scientific areas of application are plasma physics, planetary physics and matter under extreme conditions.
The instrument utilizes combination of intense, ultrashort X-ray pulses with high-energy optical laser pulses. Generation of HED states can be achieved both by X-ray or optical lasers pulses. Probing using both techniques is foreseen. X-ray techniques to be applied are various kinds of diffraction (Bragg, powder, amorphous), inelastic scattering 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 specific transitions in the plasma will require a level of accelerator performance not to be expected for initial operation.
HED Workshop 2009
The first HED workshop took place in Oxford from 30 March 2009 to 1 April 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 ∼50 μm.
- 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.
- Optical diagnostics (microscopy, interferometry, AFM, etc.) will be important to monitor the sample modification. Also particle detection, e.g. using TOFs, might be applied.
- Pump-probe experiments using optical lasers (100 fs, 1 J, Hz) are foreseen. There had been furthermore the idea to install a kJ-ns laser to drive shocks in materials and investigate those (matter under extreme pressure conditions). These lasers are huge and are currently outside the scope of the project.
- Detection will be achieved by using "standard" CCD detectors. Eventually the pixel detectors developed in the frame of the European XFEL project will provide better performance.
- 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.