25 research outputs found
Time-resolved optical shadowgraphy of solid hydrogen jets as a testbed to benchmark particle-in-cell simulations
Particle-in-cell (PIC) simulations are a superior tool to model
kinetics-dominated plasmas in relativistic and ultrarelativistic laser-solid
interactions (dimensionless vectorpotential ). The transition from
relativistic to subrelativistic laser intensities (), where
correlated and collisional plasma physics become relevant, is reaching the
limits of available modeling capabilities. This calls for theoretical and
experimental benchmarks and the establishment of standardized testbeds. In this
work, we develop such a suitable testbed to experimentally benchmark PIC
simulations using a laser-irradiated micron-sized cryogenic hydrogen-jet
target. Time-resolved optical shadowgraphy of the expanding plasma density,
complemented by hydrodynamics and ray-tracing simulations, is used to determine
the bulk-electron temperature evolution after laser irradiation. As a showcase,
a study of isochoric heating of solid hydrogen induced by laser pulses with a
dimensionless vectorpotential of is presented. The comparison
of the bulk-electron temperature of the experiment with systematic scans of PIC
simulations demostrates that, due to an interplay of vacuum heating and
resonance heating of electrons, the initial surface-density gradient of the
target is decisive to reach quantitative agreement at \SI{1}{\ps} after the
interaction. The showcase demostrates the readiness of the testbed for
controlled parameter scans at all laser intensities of
Efficient laser-driven proton acceleration from cylindrical and planar cryogenic hydrogen jets.
We report on recent experimental results deploying a continuous cryogenic hydrogen jet as a debris-free, renewable laser-driven source of pure proton beams generated at the 150âTW ultrashort pulse laser Draco. Efficient proton acceleration reaching cut-off energies of up to 20âMeV with particle numbers exceeding 109 particles per MeV per steradian is demonstrated, showing for the first time that the acceleration performance is comparable to solid foil targets with thicknesses in the micrometer range. Two different target geometries are presented and their proton beam deliverance characterized: cylindrical (â
5âÎŒm) and planar (20âÎŒmâĂâ2âÎŒm). In both cases typical Target Normal Sheath Acceleration emission patterns with exponential proton energy spectra are detected. Significantly higher proton numbers in laser-forward direction are observed when deploying the planar jet as compared to the cylindrical jet case. This is confirmed by two-dimensional Particle-in-Cell (2D3V PIC) simulations, which demonstrate that the planar jet proves favorable as its geometry leads to more optimized acceleration conditions
Ultra-fast yttrium hydride chemistry at high pressures via non-equilibrium states induced by x-ray free electron laser
Controlling the formation and stoichiometric content of desired phases of
materials has become a central interest for the study of a variety of fields,
notably high temperature superconductivity under extreme pressures. The further
possibility of accessing metastable states by initiating reactions by x-ray
triggered mechanisms over ultra-short timescales is enabled with the
development of x-ray free electron lasers (XFEL). Utilizing the exceptionally
high brilliance x-ray pulses from the EuXFEL, we report the synthesis of a
previously unobserved yttrium hydride under high pressure, along with
non-stoichiometric changes in hydrogen content as probed at a repetition rate
of 4.5\,MHz using time-resolved x-ray diffraction. Exploiting non-equilibrium
pathways we synthesize and characterize a hydride with yttrium cations in an
\textit{A}15 structure type at 125\,GPa, predicted using crystal structure
searches, with a hydrogen content between 4.0--5.75 hydrogens per cation, that
is enthalpically metastable on the convex hull. We demonstrate a tailored
approach to changing hydrogen content using changes in x-ray fluence that is
not accessible using conventional synthesis methods, and reveals a new paradigm
in metastable chemical physics
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Efficient laser-driven proton acceleration from cylindrical and planar cryogenic hydrogen jets
We report on recent experimental results deploying a continuous cryogenic hydrogen jet as a debris-free, renewable laser-driven source of pure proton beams generated at the 150âTW ultrashort pulse laser Draco. Efficient proton acceleration reaching cut-off energies of up to 20âMeV with particle numbers exceeding 109 particles per MeV per steradian is demonstrated, showing for the first time that the acceleration performance is comparable to solid foil targets with thicknesses in the micrometer range. Two different target geometries are presented and their proton beam deliverance characterized: cylindrical (â
5âÎŒm) and planar (20âÎŒmâĂâ2âÎŒm). In both cases typical Target Normal Sheath Acceleration emission patterns with exponential proton energy spectra are detected. Significantly higher proton numbers in laser-forward direction are observed when deploying the planar jet as compared to the cylindrical jet case. This is confirmed by two-dimensional Particle-in-Cell (2D3V PIC) simulations, which demonstrate that the planar jet proves favorable as its geometry leads to more optimized acceleration conditions
Nanoscale subsurface dynamics of solids upon high-intensity laser irradiation observed by femtosecond grazing-incidence x-ray scattering
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 ,
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 subsurface 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 multi-layer (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.Comment: 16 pages, 4 figures. This is the version of the article before peer
review, as submitted by authors. There is a Supplementary Information file in
the Ancillary files director
Scenarios for refurbishment of a hydropower plant equipped with Francis turbines
The energy market imposes new requirements in hydraulic turbines operation. Usually, the old hydraulic turbines are not designed to meet these new requirements. Therefore, the refurbished solutions for hydraulic turbines are expected to be robust and flexible in operation in order to regulate the grid. A methodology is developed for a hydropower plant equipped with Francis turbines. Firstly, the solution available in the hydropower plant is examined. Secondly, two new solutions are designed for the hydraulic passage available in situ. Next, several scenarios from peak load operation to wide range operation are investigated in order to asses the performance of each technical solution. Consequently, the performances are compared proving the best solution for hydropower plant refurbishment
Scenarios for refurbishment of a hydropower plant equipped with Francis turbines
The energy market imposes new requirements in hydraulic turbines operation. Usually, the old hydraulic turbines are not designed to meet these new requirements. Therefore, the refurbished solutions for hydraulic turbines are expected to be robust and flexible in operation in order to regulate the grid. A methodology is developed for a hydropower plant equipped with Francis turbines. Firstly, the solution available in the hydropower plant is examined. Secondly, two new solutions are designed for the hydraulic passage available in situ. Next, several scenarios from peak load operation to wide range operation are investigated in order to asses the performance of each technical solution. Consequently, the performances are compared proving the best solution for hydropower plant refurbishment
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Publisher Correction: Nanoplasmonic electron acceleration by attosecond-controlled forward rescattering in silver clusters (Nature communications (2017) 8 1 (1181))
The original PDF version of this Article contained an error in Equation 1. The original HTML version of this Article contained errors in Equation 2 and Equation 4. These errors have now been corrected in both the PDF and the HTML versions of the Article. The original PDF version of this Article contained an error in Equation 1. A dot over the first occurrence of the variable ri was missing, and incorrectly read: (Formula Presented). The correct form of Equation 1 is as follows: (Formula Presented). This has now been corrected in the PDF version of the Article. The HTML version was correct from the time of publication. The original HTML version of this Article contained errors in Equation 2 and Equation 4. In Equation 2, a circle over the first occurrence of the variable ri replaced the intended dot, and incorrectly read: (Formula Presented). The correct form of Equation 2 is as follows: (Formula Presented). In Equation 4, circles over the first and fifth occurrences of the variable ri replaced the intended dots, and incorrectly read: (Formula Presented). The correct form of Equation 4 is as follows: (Formula Presented). This has now been corrected in the HTML version of the Article. The PDF version was correct from the time of publication
Publisher Correction: Nanoplasmonic electron acceleration by attosecond-controlled forward rescattering in silver clusters
The original PDF version of this Article contained an error in Equation 1. The original HTML version of this Article contained errors in Equation 2 and Equation 4. These errors have now been corrected in both the PDF and the HTML versions of the Article