835 research outputs found
Quantitative Shape-Classification of Misfitting Precipitates during Cubic to Tetragonal Transformations: Phase-Field Simulations and Experiments
The effectiveness of the mechanism of precipitation strengthening in metallic alloys de-pends on the shapes of the precipitates. Two different material systems are considered: tetragonal γ′′ precipitates in Ni-based alloys and tetragonal θ′ precipitates in Al-Cu-alloys. The shape formation and evolution of the tetragonally misfitting precipitates was investigated by means of experiments and phase-field simulations. We employed the method of invariant moments for the consistent shape quantification of precipitates obtained from the simulation as well as those obtained from the experiment. Two well-defined shape-quantities are proposed: (i) a generalized measure for the particles aspect ratio and (ii) the normalized λ2, as a measure for shape deviations from an ideal ellipse of the given aspect ratio. Considering the size dependence of the aspect ratio of γ′′ precipitates, we find good agreement between the simulation results and the experiment. Further, the precipitates’ in-plane shape is defined as the central 2D cut through the 3D particle in a plane normal to the tetragonal c-axes of the precipitate. The experimentally observed in-plane shapes of γ′′-precipitates can be quantitatively reproduced by the phase-field model. © 2021 by the authors. Licensee MDPI, Basel, Switzerland
Evolution of the electric fields induced in high intensity laser-matter interactions
Multi MeV protons \cite{snavely2000intense} and heavier ions are emitted by
thin foils irradiated by high-intensity lasers, due to the huge accelerating
fields, up to several teraelectronvolt per meter, at sub-picosecond timescale
\cite{dubois2014target}. The evolution of these huge fields is not well
understood till today. Here we report, for the first time, direct and
temporally resolved measurements of the electric fields produced by the
interaction of a short-pulse high-intensity laser with solid targets. The
results, obtained with a sub- fs temporal diagnostics, show that such
fields build-up in few hundreds of femtoseconds and lasts after several
picoseconds
Recent studies on single-shot diagnostics for plasma accelerators at SPARC_LAB
Plasma wakefield acceleration is the most promising acceleration technique
for compact and cheap accelerators, thanks to the high accelerating gradients
achievable. Nevertheless, this approach still suffers of shot-to-shot
instabilities, mostly related to experimental parameters fluctuations.
Therefore, the use of single shot diagnostics is needed to properly understand
the acceleration mechanism. In this work, we present two diagnostics to probe
electron beams from laser-plasma interactions, one relying on Electro Optical
Sampling (EOS) for laser-solid matter interactions, the other one based on
Optical Transition Radiation (OTR) for single shot measurements of the
transverse emittance of plasma accelerated electron beams, both developed at
the SPARC_LAB Test Facility
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