Plasmaphysik Seminar

X-ray Phase-Contrast Imaging for shock-wave studies and Implosion Physics

by Dr. Luca Antonelli (University of York)

Tuesday, December 3, 2019 from to (Europe/Berlin)
at GSI Darmstadt ( SB3 3.170a )
Recent and enormous investment in laser facilities across the world is enabling the exploration of the material properties under extreme conditions. This includes the  study of the materials under high pressure relevant to planetary physics, the generation of ultra-high magnetic fields, particlepair production in high intensity laser fields, Weibel-instability-mediated collisionless shocks and inertial confinement fusion (ICF). Validating theoretical models and numerical simulations requires high quality data and this often demands new diagnostic capabilities. Techniques that combine good spatial and temporal resolution such as X-ray absorption radiography can yield a detailed picture of an experiment, though they are compromised by contrast which limits the range of observable densities. It is possible to extend the density resolution of X-ray imaging by monitoring the phaseshift of the X-ray photons as they pass through the target. Absorption contrast imaging is dependent on the imaginary part of a materials refractive index whilst phase contrast imaging uses the real part of the refractive index. To access the real part it is necessary to ensure the X-ray source has some degree of transverse spatial coherence. This spatial coherence leads to a diagnostic that is particularly sensitive to density gradients perpendicular to the line of sight. It is an ideal technique for studying shock-waves, density filaments and material interfaces, as demonstrated on X-ray free electron lasers where monochromatic intense coherent X-ray beams are available.
We show that phase contrast enhanced imaging is possible on high energy lasers using broadband bremsstrahlung radiation sources. We discuss propagation-based imaging and the key elements for successfully deploying phase contrast imaging on multiple systems such as Phelix-GSI in Germany, Vulcan in the UK and Omega EP in the USA. As an application, we compare absorption and phase contrast imaging with a hybrid technique of phase-contrast enhanced radiography to study a Shock
Ignition Implosion.