Instrument design

The High Energy Density science (HED) instrument will be a unique platform for experiments combining hard X-ray FEL radiation and the capability to place matter under extreme conditions of pressure, temperature, or electric field using the FEL, high-energy optical lasers, diamond anvil cells, or pulsed magnets.

Full instrument specifications (>2020)

Full instrument specification

Bandwidth ΔE/E

10-3  (SASE FEL source)

10-4  (standard Si-111 monochromator)

10-5  (x-ray self-seeding,, future option)

10-6  (at 7.49 keV, high-resolution Si-533 monochromator)

Photon energy range

5 – 20 keV (3 – 25 keV *)

*Limited in terms of focusing capability, available photon number of sample, quantum efficiency of detectors

Polarization

Linear (horizontal)

Pulse duration

2–100 fs FWHM (depending on bunch charge)

Pulse energy

of order 1 mJ in SASE mode

Beam size on target

Provided by several compound refractive Be lenses (CRLs):

flexible from sub-µm foci to 1 mm collimated beam

Special optics

X-ray Split and delay Line (BMBF contribution)

Standard 4-bounce Si monochromator

High-resolution monochromator at 7.49 keV

Optical lasers

DIPOLE-100X High-energy (100 J-class) long pulse (1-15 ns) laser (HIBEF contribution)
High-intensity (multi-100 TW-class) short pulse (~30 fs) laser (HIBEF contribution)
Pump–probe (mJ to 100 mJ class) short pulse (15 fs – 1 ps) laser

Instrument overview

Here, a broad overview of its components is provided. The subsequent pages will provide more details.

Photon energy and bandwidth

The instrument's working X-ray range is 5-25 keV with nominal bandwidth ΔE/E ~ 10-3. Bandwidths of 10-4 are achieved using a four-bounce Si-(111) monochromator. Tighter bandwidths of order 5×10-6 at a photon energy of 7.5 keV is achieved using a high-resolution Si-(533) monochromator.

Focussing optics

A series of Be compound refractive lenses (CRLs) enables the focussing of X-rays down to 1-200 μm at TCC. There are four sets of lenses: the first two are located in the X-ray tunnel (XTD1/XTD6); the third is in the HED optics hutch (OH); finally, the fourth is found close to the sample position facilitating sub-micron focussing.

Split and delay line

The incoming X-ray pulse can be split into two with independently tunable intensities and a maximum delay separation of 2 ps (at 20 keV) and 23 ps (at 5 keV). Furthermore, pulses can be selected for 10 Hz, 1 Hz, or pulse-on-demand operation using a pulse-picker.
This allows synchronization of X-ray and optical laser delivery to the sample.

Photon diagnostics (OH)

The wings of the X-ray beam can be tailored using power slits in the OH and monitored using a beam-imaging unit. The incident X-ray spectrum is monitored by directing a fraction of the incident beam (using a diamond grating in first order) to a single-pulse spectrometer employing a bent Si crystal. X-ray beam position and intensity are monitored using backscattering from a thin foil (there is a second monitor upstream in the tunnel). Real-time intensity monitoring is possible using a scintillator-coupled fast-frame CCD which collects the other first order diffraction from the diamond grating (above). Beam quality can be further improved by clean-up slits at both high and low photon energies at the downstream end of the optics hutch, close to the experimental hutch (EH).

Experimental hutch (EH)

Schematic

The experimental hutch contains two interaction areas designated IA1 (upstream) and IA2 (downstream). IA1 contains a large (2.6 m × 1.7 m × 1.5 m interior dim.) interaction chamber (IC1) which can accommodate multiple experimental configurations for diffraction, spectroscopy, and inelastic X-ray scattering. The operating vaccuum in IC1 is set at ~10-4 mbar and is separated from the X-ray optics by a differential pumping stage or a diamond window (above 10 keV). In IA2 various setups can be interchanged. A second interaction chamber (IC2) of diameter 1 m can be included and is dedicated to diamond anvil cell (DAC) experiments and high-precision dynamic laser compression experiments in a standardized configuration. Alternatively, a goniometer with a pulsed magnetic coil and a cryogenic sample environment can be placed in IA2.

Note that in IA1 all X-ray and optical laser beams are available, whereas IA2 only has access to the XFEL and nanosecond optical beams only.

Detectors

Requirements for detectors in IC1 include vacuum-compatability, compact dimensions, low-weight, modular assembly, and a repetition rate > 10 Hz. Currently planned detectors include two EIPX100 modules with a 35 mm × 38 mm chip with a pixel-pitch (distance between neighbouring pixels) of 50 μm and a dynamic range of 102 at 8 keV that will be coupled to crystal spectrometers. Further, three EPIX10k modules with the same chip dimensions as above but with a larger pixel-pitch of 100 μm; these offer a dynamic range of 104 by gain switching. Four Jungfrau detectors will be available with a chip size of 40 mm × 80 mm with a 75 μm pixel-pitch and 104 dynamic range at 12 keV. The two sets of gain-switching detectors (EPIX10k and Jungfrau) will be ideally used to record X-ray diffraction.

A detector bench at the end of the EH will offer the possibility to place large area detectors for imaging or small angle X-ray scattering (SAXS) experiments, with variable distances from IA1 or IA2 to the detector. Additionally, the HIBEF consortium intends to integrate an AGIPD 1 M detector, a Perkin-Elmer 4343CT flat-panel large-area detector, and high-resolution CCD cameras for X-ray phase contrast imaging and ptychography applications.

Optical lasers

The all-diode pumped high energy (HE) nanosecond laser DiPOLE-100X laser is developed by STFC CRL (UK) and delivers up to 80 J at 515 nm (2ω) with pulse durations of 2-15 ns, and with a maximum repetition rate of 10 Hz. Its primary use is for shock compression experiments and supports temporally shaped pulses to facilitate isentropic ramp compression techniques.

There will also be a high intensity (HI) multi-100 TW Ti:Sapphire laser currently under construction by Amplitude (France). This will deliver 4-10 J of 800 nm light in ultrashort pulses of less than 25 fs at a repetition rate of 10 Hz. The HI laser can be focussed with an off-axis parabola to spots ~μm2 in order to reach intensities on target of order 1020 W cm-2. This laser will primarily be used for relativistic laser-matter interaction experiments.

Additionally, the standard PP (pump-probe) laser of the European XFEL will be available. Nanosecond pulses are possible in chirped mode.

All three lasers need to be precisely timed and are synchronized with the master oscillator. The PP timing jitter relative to the XFEL is monitored by photon-arrival diagnostics with a precision of a few femtoseconds. Timing between the HI laser and the incident X-rays is realised indirectly by comparing with the characterised PP laser in an optical-optical balanced cross-correlator. Timing between the HE laser and the X-rays is less demanding and achieved via fast photo diodes that detect both X-rays and optical light with a resolution of a few picoseconds.

Other drivers

Matter in magnetic fields up to 60 T can be investigated in a solenoid coil. The field build-up takes 0.6 ms and is well-suited to the length of a 4.5 MHz pulse train from the accelerator.

Further, diamond anvil cells are available for dynamic compression and also as a double stage.

Detailed component lists

Tunnel Components

  • SASE2 undulators
  • beam transport
  • Pop In Monitor
  • Slits
  • Offset Mirror (sends the beam to HED)
  • Split And Delay Line
  • Monochromator (Si-111, 4-bounce)
  • Monochromator (Si-533 high resolution)
  • Compound Refractive Lenses
  • Pop In Monitor
  • X-ray Gas Monitor
  • Pulse Picker Unit
  • Pop In Monitor
  • Safety Shutter at end of tunnel, just before experimental hall

Optical hutch

  • Power Slit
  • Beam Imaging Unit
  • Photon Arrival Monitor
  • Attenuator
  • Compound Refractive Lenses
  • Quarter Wave Plate (later upgrade)
  • Bent Crystal Single Shot Spectrum Analyser
  • I0 Intensity Position Monitor
  • Shutter

Experimental hutch Interaction area 1 (IA1)

General

  • Laser Shutters
  • Instrument Beam Stop
  • Fourier Domain Interferometer
  • Velocity Interferometer System for Any Reflector
  • PP-Laser Transport
  • High Intensity Laser Transport
  • High Energy Laser Transport
  • User Patch panel
  • Vacuum systems

Optical Granite Table

  • Alignment Laser
  • Differential Pumping System
  • Clean Up Slits 1
  • I0 Intensity Position Monitor
  • Clean Up Slits 2

Interaction Area 1

  • Interaction Chamber
  • Fast Solid Sample Scanner in IC1
  • Sample positioner (later upgrade)
  • Inline view microscope (in IC1)
  • Long Distance Microscope 1 (Questar)
  • Long Distance Microscope 2 (Questar)
  • Compound Refractive Lenses (in IC1)
  • X-ray Thompson Scattering Spectrometer (in IC1)
  • X-ray Emission spectrometer (in IC1)
  • 4x Si-533 High Resolution Inelastic X-Ray Scattering Diced analyzers (in IC1)
  • X-Ray Diffraction area detectors (Jungfrau and/or ePIX)
  • Laser Beam transport (Mirrors, aperatures)
The heavy concrete HED-EXP enclosure in October 2014.

Technical Design Report

  • Technical Design Report: Scientific Instrument High Energy Density Physics (HED)

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