Categories: world

A breakthrough in the study of laser / plasma interactions

Large-scale simulations show that chaos is responsible for stochastic heating of dense plasma by intensive laser energy. This image shows a snapshot of electron distribution phase (position / momentum) space from the dense plasma taken from PIC simulations, illustrating the so-called "stretching and folding" mechanism responsible for the onset of chaos in physical systems. Credit: G. Blaclard, CEA Saclay A new 3-D simulation tool, developed by Lawrence Berkeley National Laboratory and CEA Saclay researchers, enables advanced laser / plasma switching simulations that were previously unavailable to standard PIC codes used in plasma research. More detailed understanding of these mechanisms is crucial to the development of ultra-compact particle accelerators and light sources that can solve long-term challenges in medicine, industry and basic science more efficiently and cost effectively. In laser plasma experiments such as at the Berkeley Lab Laser Accelerator (BELLA) Center and at the CEA Saclay an international research facility in France included in the French Atomic Energy Commission – very large electric fields in plasma that accelerate particle beams to high energies over much shorter distances compared to existing accelerator technology. The long-term goal of these laser plasma accelerators (LPAs) is to build a collider for high energy research in one day, but many spin-offs are already being developed. For example, LPA can quickly deposit large amounts of energy into solid materials, create dense plasma and subject this issue to extreme temperatures and pressures. They also have the potential to drive free electron lasers that generate light pulses that…

Large-scale simulations show that chaos is responsible for stochastic heating of dense plasma by intensive laser energy. This image shows a snapshot of electron distribution phase (position / momentum) space from the dense plasma taken from PIC simulations, illustrating the so-called “stretching and folding” mechanism responsible for the onset of chaos in physical systems. Credit: G. Blaclard, CEA Saclay

A new 3-D simulation tool, developed by Lawrence Berkeley National Laboratory and CEA Saclay researchers, enables advanced laser / plasma switching simulations that were previously unavailable to standard PIC codes used in plasma research. More detailed understanding of these mechanisms is crucial to the development of ultra-compact particle accelerators and light sources that can solve long-term challenges in medicine, industry and basic science more efficiently and cost effectively.

In laser plasma experiments such as at the Berkeley Lab Laser Accelerator (BELLA) Center and at the CEA Saclay an international research facility in France included in the French Atomic Energy Commission – very large electric fields in plasma that accelerate particle beams to high energies over much shorter distances compared to existing accelerator technology. The long-term goal of these laser plasma accelerators (LPAs) is to build a collider for high energy research in one day, but many spin-offs are already being developed. For example, LPA can quickly deposit large amounts of energy into solid materials, create dense plasma and subject this issue to extreme temperatures and pressures. They also have the potential to drive free electron lasers that generate light pulses that only hold attosands. Such extremely short pulses can allow researchers to observe the interactions between molecules, atoms and even subatomic particles at extremely short time scales.

Supercomputer simulations have become increasingly important for this research and the Berkeley Labs National Energy Research Scientific Computing Center (NERSC) has become an important resource in this work. By giving researchers access to physical observables such as particle paths and radiated fields that are difficult to come by with experiments with extremely small time and length scales, PIC simulations have played an important role in understanding, modeling and controlling high-intensity physics experiments. But a lack of PIC codes that have enough computational accuracy to model laser-matter interaction at ultra-high intensities has hindered the development of new particles and light sources produced by this interaction.

This challenge led the Berkeley Lab / CEA Saclay team to develop its new simulation tool, called Warp + PXR, an effort started during the first round of the NERSC Exascale Science Applications Program (NESAP). The code combines the widely used 3-D PIC code Warp with the high performance library PICSAR, developed by Berkeley Lab and CEA Saclay. It also utilizes a new type of massively parallel pseudo spectral dissolver developed by Berkeley Lab and CEA Saclay, which dramatically improves the accuracy of the simulations compared to the solvents commonly used in plasma science.

In fact, without this new, highly scalable solver, “the simulations we do now would not be possible,” says Jean-Luc Vay, a senior physicist at Berkeley Lab, who heads the accelerator modeling program in Labs Applied Physics and Accelerator. Technologies Division. “As our team demonstrated in a previous study, this new FFT spectral solver allows much higher precision than can be done with final differential time domain (FDTD) resolver, so we could reach certain parameters that would not have been available with standard FDTD looser. “This new type of spectral solver is also at the heart of the next-generation PIC algorithm with adaptive network refinement that Vay and colleagues are developing in the new Warp-X code as part of the US Department of Energy’s Exascale Computing Project.

2-D and 3-D simulations Both critical

Vay is also co-authored on a paper published March 21 in Physical Review X which reports on the first comprehensive study of laser plasma coupling mechanisms using Warp + PXR. The study combined state-of-the-art experimental measurements conducted at the UHI100 laser plant at CEA Saclay with advanced 2-D and 3-D simulations on the Cori supercomputer at the NERSC and Mira and Theta systems at the Argonne Leadership Computer Facility. at Argonne National Laboratory. These simulations enabled the team to better understand the coupling mechanisms between the ultra-intensive laser light and the dense plasma created, giving new insights on how to optimize ultra-compact particle and light sources. Benchmarks with Warp + PXR showed that the code is scalable up to 400,000 cores on Cori and 800,000 cores at Mira and can accelerate the time to the solution with as much as three orders of magnitude on problems related to ultra-intensity physics experiments.

“We can’t consistently repeat or reproduce what happened in the experiment with 2-D simulations – we need 3-D for this,” says co-author Henri Vincenti, a researcher in the high intensity physics group at CEA Saclay. Vincenti led the theoretical / simulation work for the new study and was Marie Curie’s postdoctoral fellow in Berkeley Lab in Vay’s group where he started working with the new code and solver. “The 3-D simulations were also very important in order to be able to compare the accuracy of the new code with experiments.”

For the experiment described in Physical Review X a 100’s femtosecond laser beam used at CEA’s UHI100 plant, targeting a silica target to create a dense plasma. In addition, two diagnoses – a Lanex scintillation screen and an extreme ultraviolet spectrometer – were applied to study the laser plasma interaction during the experiment. Diagnostic tools presented additional challenges when it comes to studying time and length scales while the experiment was running, which means that the simulations are critical to the researchers’ results.

“Often in this type of experiment you cannot access the time and length scales involved, especially because in the experiments you have a very intense laser field on your target so that you cannot add any diagnostic close to the target,” says Fabien Quéré, a researcher who leads the experimental program at CEA and is a co-author of the PRX paper. “In this kind of experiment, we look at things that are emitted by the target that are far away-10, 20 cm and happen in real time, essentially, while physics is on micron or submicron scale and subfemtosecond scale in time. we need the simulations to decipher what is happening in the experiment. “

” “The first principle simulations we used for this research gave us access to the complex dynamics of the laser field interaction with the solid target level of detail of individual particle paths, so we better understand what happened in the experiment,” added Vincenti. These very large simulations with an ultra-high precision spectral FFT solver were possible thanks to a paradigm shift introduced by Vay and employees in 2013. In a study published in the Journal of Computational Physics, they observed that when solving the time-dependent Maxwell’s equations, standard The FFT parallelization method (which is global and requires communication between processors throughout the simulation domain) is replaced by a domain disintegration with local FFT and communication limited to adjacent processors. In addition to allowing much more favorable strong and weak scaling over a large number of date nodes, the new method is also more energy effective because it reduces communication.

“With standard FFT algorithms, you have to make communication across the machine,” said Vay. “But the new spectral FFT solver enables savings in both computer time and energy, which is a big part for the new supercomputer architectures being introduced.”


Laser “drill” sets a new world record in laser-controlled electron acceleration


More information:
L. Chopineau et al., Identification of coupling mechanisms between ultra intensity light and dense plasmas, Physical Review X (2019). DOI: 10,1103 / PhysRevX.9.011050

Provided by
Lawrence Berkeley National Laboratory

Citation :
A breakthrough in the study of laser / plasma interactions (2019, April 24)
downloaded April 24, 2019
from https://phys.org/news/2019-04-breakthrough-laserplasma-interactions.html

This document is subject to copyright. Except for any fair trade for private study or research, no
Some may be reproduced without written permission. The content is provided for informational purposes only.

Share
Published by
Faela