Science Programme

Generally, X-ray FEL beams can be used either as a pump or as a probe. Various X-ray techniques shall be provided at the HED instrument: X-ray diffraction (XRD), small angle X-ray scattering (SAXS), X-ray absorption (XAS), inelastic X-ray scattering (IXS), X-ray self-emission (XES), and X-ray imaging (XI).

Key research projects

Solid-matter properties following extreme excitation

The aim here is to elucidate ultrafast dynamics of optical laser–excited non-equilibrium system using the XFEL probe at sub-picosecond temporal resolution. Possible examples for such studies are investigations of ultrafast phase transitions, like solid–solid transitions, melting, or ablation.

Solid matter in states of extreme pressure and density

Our aim here is to achieve high pressure and temperature regime exceeding what can be achieved using static compression techniques (e.g., diamond anvil cells, DACs). For this purpose users can use a >100-J-class high-energy long pulse optical laser and also dynamic DACs and pulsed laser-heated double stage DACs). Temporal pulse shaping capability of the optical laser allows quasi-isentropic compression of material, to reach off-Hugoniot high pressure states which are seen in planetary interiors.

Schematics of laser shock compression using counter-propagating shocks. The target (which could be a variety of materials including iron, silicates, plastics, aluminium, or even liquid jets) is probed by the XFEL at a given time delay after the ns laser irradiation. The inset at right shows a hydrodynamics simulation of the time-evolution of the mass density, whereas the inset at left shows model cold and plasma scattering patterns.

Complex solids in very high pulsed magnetic fields

The combination of intense magnetic fields and the bright XFEL probe allows one to look at the microscopic structure changes caused by the presence of magnetic field. With the benefit of the very high repetition of the XFEL (220 ns between pulses), one can follow the response of the sample to the ramping of the pulsed magnetic field (max 50–60 Tesla, ~ms ramping time).

Isochoric creation of WDM using XFEL

The short duration and bright XFEL pulses allow producing uniformly heated solid-density plasma states before hydrodynamic expansion occurs. One of the goals is to find an optimized way to create well-defined warm dense matter (WDM), which is defined as partially degenerated, ion-correlated solid-density plasmas. The next step will be to elucidate physical properties of the WDM using either optical diagnostics or XFEL beam. The WDM state is present in many physical environments, such as planetary interiors, laser–matter interaction, and during the implosion of an inertial confinement fusion.

Phase diagram showing the conditions for warm dense matter (WDM, in dark green). Green areas of the diagram are considered high-energy-density (HED) matter (material at pressures exceeding 1 Mbar), while grey areas are not. Thus, WDM is considered a subset of HED matter, with densities nearing solid matter and a temperature around 1 eV. Plasmas below the black line (Γ = 1) are strongly coupled, meaning that the Coulomb energy exceeds the thermal energy.

Plasma physics in the relativistic-electron regime

Using the XFEL as a probe, one can elucidate very complex dynamics of high-density relativistic electron beams inside solids and associated ionization and field structure. To this aim, users can use a 100 TW class short-pulse (~30fs) laser system to produce relativistic electron beams.

Setup of a typical relativistic laser–plasma experiment. The high-intensity short-pulse laser is focused to the target foil by an off-axis parabola (OAP).

Quantum states generated by extremely high-field laser pulses

Using the XFEL beam as a probe, one can measure vacuum birefringence perturbed by optical laser. It requires a beyond petawatt-class laser that will be implemented within a couple of years after the start of operation.

Conceptual Design Report

  • Conceptual Design Report: Scientific Instrument HED