Workshop on SAXS@XFELs and HI & HE laser driven matter

Europe/Berlin
Helmholtz-Zentrum Dresden-Rossendorf

Helmholtz-Zentrum Dresden-Rossendorf

Bautzner Landstraße 400 01328 Dresden
Description

This workshop follows the recent commissioning of HIBEF at European XFEL that brought together different communities that want to use SAXS to probe the interaction of high intensity lasers or high energy lasers with matter. Together with LCLS and SACLA we expect great new applications of SAXS in this area in the future.
With this workshop we wish to facilitate an informal and open exchange about the state of the art of data collection and analysis. Participants are encouraged to bring their own problems, methods, data etc. and to consider tutorial-style talks.

To continue exchange in the fields and foster collaborations and joint activities which have suffered during the pandemic in many cases we will organize the meeting in Dresden as a hybrid event. We want to encourage especially young researchers to consider on-site presence and want to highlight the fully unproblematic travel and accomodation conditions for vaccinated or recovered people. Current Covid regulations in Dresden allow for a fruitful meeting, but may of course be subject to changes.
Workshop attendance is free of charge.

Topics of the workshop include:

• Small Angle X-Ray Scattering at XFELs and/or laser driven samples
• Grazing-Incidence X-Ray Scattering at XFELs and/or laser driven samples
• Experimental results, experiment ideas
• novel developments and links to neighboring techniques, e.g. WAXS, PCI or spectroscopy
• advanced methods including holography, photon correlation spectroscopy, prospects of AI etc
• Reconstruction methods, both classical and based on ML and AI
• High performance file formats and meta-data collection
• Neutron scattering contributions welcome, too!

Registration is free of charge. However, please register so that we can estimate the necessary resources both on-site and online! More information about the scientific program will follow soon.

Registration
Registration
Thomas Kluge
• Thursday, 4 November
• 15:00 17:30
Talks
• 15:00
Surface dynamics of warm dense plasmas upon high-intensity laser irradiation investigated by grazing-incidence x-ray surface scattering 35m

Observing ultrafast laser-induced structural changes in nanoscale systems is essential for understanding the dynamics of intense light-matter interactions. For laser intensities on the order of $10^{14}$W/cm$^2$, highly-collisional plasmas are generated at and below the surface. Subsequent transport processes such as heat conduction, electron-ion thermalization, surface ablation and resolidification occur at picosecond and nanosecond time scales. Imaging methods, e.g. using x-ray free-electron lasers (XFEL), were hitherto unable to measure the depth-resolved sub-surface dynamics of laser-solid interactions with appropriate temporal and spatial resolution. Here we demonstrate picosecond grazing-incidence small-angle x-ray scattering (GISAXS) from laser-produced plasmas using XFEL pulses. Using multilayer (ML) samples, both the surface ablation and subsurface density dynamics are measured with nanometer depth resolution. Our experimental data challenges the state-of-the-art modeling of matter under extreme conditions and opens new perspectives for laser material processing and high-energy density science.

Speaker: Lisa Randolph (Universität Siegen)
• 15:35
Using GISAXS to observe Density Oscillation in Multi Layer Targets 25m

Presenting results of simulations showing the density oscillation. The density oscillation describes the oscillation of the single layers in width and density in a multi layer target. We will see how the the GISAXS method allows to observe this dynmamic.

Speaker: Franziska-Luise Paschke-Bruehl
• 16:00
Break 20m
• 16:20
Machine Learning in GISAXS reconstruction 20m
Speaker: Yichao Liu
• 16:40
Reconstruction of SAXS Data using Neural Networks 20m

We aim to simplify the process of reconstructing electron densities from SAXS images by employing a special Neural Network architecture, the conditional Invertible Neural Network (cINN). The only requirement is a simulation from electron density to diffraction image to generate a training dataset. Once trained, it can make accurate and fast (ms range) predictions on simulated and experimental data and furthermore resolve ambiguities resulting from the phase problem. Some challenges remain though, since we cannot differentiate between accurate predictions and false predictions from experimental data not covered by the training dataset (out-of-distribution data) as the output does not convey the degree of certainty of the prediction made by the cINN.

Speaker: Erik Thiessenhusen (HZDR)
• 17:00
OpenPMD (unconfirmed) 20m
Speaker: Axel Hübl (LLNL)
• Friday, 5 November
• 09:00 17:00
Talks
• 09:00
Targetry for revealing laser-driven nanostructures in SAXS and GISAXS experiments with high repetition rate 20m

The first experiments with ultrafast SAXS and GISAXS using
free-electron lasers have shown effects such as plasma expansion from
micro- or nanostructured targets, for example clusters, gratings, wires
or multilayers. These targets produce pronounced features in the SAXS
and GISAXS signal due to their geometry. For investigating plasma
instabilities or surface plasma waves, which have very subtle SAXS
signatures, targetry with smooth planar geometry would be advantageous.
High repetition rate targetry, for example liquid leaf targets and tape
targets are discussed, which can facilitate parametric scans in SAXS and
GISAXS experiments.

• 09:20
Targets for SAXS experiments 20m
Speaker: Irene Prencipe
• 09:40
SAXS mirror 20m

In recent years, a HAPG crystal was designed, tested, and used at HED, XFEL to deflect the SAXS signal from the XFEL beampath, in order to allow shielding of the detector for SAXS signal. In this talk we present the design overview, basic parameters & first results of this instrument.

Speaker: Michal Smid (HZDR)
• 10:00
Break 20m
• 10:20
Diamond formation kinetics in shock-compressed C-H-O samples via small angle X-ray scattering and X-ray diffraction 20m

Icy giant planets such as Neptune and Uranus are abundant in our galaxy. The interiors of these celestial objects are thought to be mainly composed of a dense fluid mixture of water, methane and ammonia[1]. Due to the high pressure and high temperature conditions deep inside the planet, this material mixture will likely undergo chemical reactions and structural transitions[2]. An example of these reactions is the possible dissociation of hydrocarbons, and subsequent phase separation, allowing the formation of diamonds. Laser shock experiments in combination with an XFEL allowed us to address these questions.[3-5] Due to the presence of water and therefore large amounts of oxygen inside the ice giants, ínvestigating C-H-O samples provides a more realistic scenario than studying pure hydrocarbon systems.
As an ultra-sensitive diagnostic technique, small angle X-ray scattering (SAXS)[6] can explore feature sizes in the order of nanometers by recording their scattering at small angles (typically 0.1-10°), allowing us to obtain deeper insights into the question how diamonds are formed, what grain sizes are achieved and how many grains are formed.
Experiments were carried out at the MEC end station of the LCLS XFEL in December 2020. Three oxygenated polymers with different carbon to H2O ratios, polyethylene terephthalate (PET, C10H8O4), polylactic acid (PLA, C3H4O2) and cellulose acetate (CA, C10H16O8) were compressed to planetary interior states ranging from 50 GPa to 150 GPa and 2000K to 7000K by laser-driven single shocks. The compressed samples were probed utilizing in situ X-ray diffraction (XRD) and SAXS.
The diamond formation kinetics in presence of oxygen in these three materials have been observed. SAXS shows more sensitive information than XRD, revealing that the diamond fraction first increases and then decreases with increasing of pressure and the growth of particles with time in the medium pressure regime (~110 GPa). The observed particle radius of diamond is between 1.5 nm and 3 nm. In addition, the proportion of carbon in the initial sample materials also shows a correlation with the observed diamond fraction. Ongoing simulations aim to explain these phenomena in order to improve the theory of planetary formation and evolution.
[1]T. Guillot, Annu. Rev. Earth Planet. Sci. 33, (2005).
[2]M. Ross, Nature 292, (1981).
[3]D. Kraus, J. Vorberger, A. Pak, et al., Nature Astronomy 1, (2017).
[4]D. Kraus, N. Hartley, S. Frydrych, et al., Phys. Plasmas 25, (2018).
[5]A. Schuster, N. Hartley, J. Vorberger, et al., Phys. Rev. B 101, (2020).
[6]O. Glatter, O. Kratky and H. Kratky, Small angle X-ray scattering (Academic press, 1982).

Speaker: Zhiyu He (Helmholtz-Zentrum Dresden-Rossendorf)
• 10:40
SAXS @ the SACLA HI laser facility (unconfirmed) 20m
Speaker: Masato Ota (Osaka University)
• 11:00
SAXS @ DESY (unconfirmed) 20m
Speaker: Stephan Kuschel (DESY)
• 11:20
Autonomous experiments (unconfirmed) 20m
Speaker: Parente
• 11:40
Break 1h
• 12:40
Probing ultrafast plasma expansion using SAXS 20m
Speaker: Thomas Kluge (HZDR)
• 13:00
Synthetic probing of ionization dynamics in the solid density plasmas driven by relativistic laser pulses using resonant SAXS 20m

Understanding the ionization dynamics is fundamentally important in the interaction of a relativistic laser pulse with a solid density target. In this talk, firstly we present the particle-in-cell (PIC) simulations with various collisional ionization and potential models, showing the target heating, magnetic instabiltiy and plasma resistivity are highly model-dependent \cite{Huang2016,Huang2017}. Secondly, we propose to probe the evolution of ionic density at specific bound-bound resonances by scanning the XFEL photon energy via established SAXS method, which is cable to access the spatial–temporal resolution down to few nanometers and femtoseconds simultaneously. The plasma opacity plays a key role of the XFEL absorption, which in turn affects the resonant SAXS pattern contributed by the imaginary part of ionic scattering form factor\cite{Kluge2016}. We present the calculation of plasma opacity using the atomic collisional-radiative code SCFLY and further simulate the synthetic resonant SAXS imaging pattern which shows strong asymmetric feature. Our recently performed experiment reveals the connection of the temporal evolution of the asymmetry signal and ionization dynamics \cite{Gaus2020}.

[1] L. G. Huang, T. Kluge, and T. E. Cowan, Physics of Plasmas23, 063112 (2016).[2] L. G. Huang, H. P. Schlenvoigt, H. Takabe, and T. E. Cowan, Physics of Plasmas24, 103115 (2017).
[3] T. Kluge, M. Bussmann, H.-K. Chung, C. Gutt, L. G. Huang, M. Zacharias, U. Schramm, and T. E.Cowan, Physics of Plasmas23, 033103 (2016).
[4] L. Gaus, L. Bischoff, M. Bussmann, E. Cunningham, C. B. Curry, E. Galtier, M. Gauthier, A. L.Garc ́ıa, M. Garten, S. Glenzer, J. Grenzer, C. Gutt, N. J. Hartley, L. Huang, U. H ̈ubner, D. Kraus,H. J. Lee, E. E. McBride, J. Metzkes-Ng, B. Nagler, M. Nakatsutsumi, J. Nikl, M. Ota, A. Pelka,I. Prencipe, L. Randolph, M. R ̈odel, Y. Sakawa, H.-P. Schlenvoigt, M.ˇSm ́ıd, F. Treffert, K. Voigt,K. Zeil, T. E. Cowan, U. Schramm, and T. Kluge, “Probing ultrafast laser plasma processes insidesolids with resonant small-angle x-ray scattering,” (2020), arXiv:2012.07922 [physics.plasm-ph].

Speaker: Lingen Huang (Helmholtz-Zentrum Dresden-Rossendorf)
• 13:20
Combined single-shot Small Angle X-Ray Scattering and Phase Contrast Imaging in ultra-intense laser-matter interactions at euXFEL 20m

The High Energy Density (HED) instrument at the European XFEL provides a platform to study hot and warm dense matter. The Helmholtz International Beamline for Extreme Fields (HiBEF) is the User Consortium supplying HED with two laser systems (the high-intensity ReLaX laser, by Amplitude Technologies, and the high-energy Dipole-100X laser, by STFC), Diamond Anvil Cells setup and high-pulsed magnetic fields. These tools in combination with the XFEL beam enable the investigation of relativistic laser plasmas, strong-field QED phenomena, high-pressure astro- and planetary physics as well as magnetic phenomena in condensed matter.
The commissioning of the ultra-short pulse high-intensity relativistic laser at XFEL, ReLaX, provides new unique opportunities in the plasma and high-field physics fields. ReLaX is a double CPA Ti:Sa laser delivering 100 TW pulses on target, reaching intensities up to 10$^{20}$ W/cm$^{2}$.
Small-Angle X-Ray Scattering (SAXS) without the need of a beamstop was first commissioned at HED in September 2019. Two high-annealed pyrolytic graphite (HAPG) crystals were used to reflect the SAXS photons onto a detector while allowing the main XFEL beam to go through. In April and May 2021, Small-Angle X-Ray Scattering (SAXS) and Phase Contrast Imaging (PCI) were simultaneously demonstrated in pump-probe experiments at HED.
In this talk, we discuss the challenges on combining these X-Ray techniques in the harsh environment generated by the laser-matter interaction. We will also show results on the combined SAX and PCI measurements of hole boring in wire targets.

Speaker: Alejandro Laso Garcia (HZDR)
• 13:40
Considerations for single-pulse phase contrast imaging at HED 20m
Speaker: Johannes Hagemann
• 14:00
Break 20m
• 14:20
X-ray radiation transport in GPU accelerated Particle In Cell simulations 20m

Ultra-high-intensity laser pulse interactions with solid density targets are of central importance for modern accelerator physics, Inertial Confinement Fusion(ICF) and astrophysics.

In order to meet the requirements of real-world applications, a deeper understanding of the underlying plasma dynamics, including plasma instabilities and acceleration mechanisms, is needed.

Due to high electron density, the over-dense target bulk is impenetrable to probes in the optical range.
Hence, several X-ray diagnostics, such as small-angle X-ray scattering (SAXS) and X-ray polarimetry, were proposed by the community.

Therefore, we bring a Monte Carlo based X-ray radiation transport module into our Particle In Cell simulation framework PIConGPU. Among others, this allows for Thompson scattering, e.g. for SAXS, and Faraday effect calculation for polarimetry - as online, in-situ diagnostics.

Speaker: Pawel Ordyna
• 14:40
Asymmetries in resonant SAXS 20m
Speaker: Thomas Kluge (HZDR)
• 15:00
Probing laser-solid interactions with Resonant Small-Angle X-ray Scattering 20m

SAXS has been applied in two beam times at LCLS (2014, 2018) in order to study the plasma expansion dynamics following the interaction of solid-density samples with an ultrahigh intensity laser. The first experiment demonstrated, that SAXS in combination with nanostructured grating targets enables to measure the plasma surface expansion with fs and nm resolution [Kluge et al., Phys. Rev. X 8, 031068 (2018)]. In the follow-up experiment, the pump laser intensity reached the relativistic intensity regime and allowed for the generation of highly ionized plasma states. In this scenario, probing at resonant X-ray energies has shown to give new insight into the ionization process, plasma opacity and density dynamics by studying asymmetries in SAXS patterns [Gaus et al., arXiv: 2012.07922 (under review)]. This talk aims to give an overview on the experimental results from these experiments with respect to resonant SAXS.

Speaker: Lennart Gaus (HZDR)
• 15:20
openPMD 20m
Speaker: Franz Pöschel (CASUS)
• 15:40
Wrap up, summary & closing remarks 20m