Speaker
Description
Laser-driven implosions are used in several fields, from laboratory astrophysics to energy application (e.g. inertial confinement fusion). In all these fields, the researchers make a big effort to develop dedicated diagnostics to observe and characterize the implosion driven by a laser.
The development and deployment of a diagnostic is not only a practical matter, but it requires the use of a dedicated numerical tool to mimic the diagnostic. In this case we talk of synthetic diagnostics. A synthetic diagnostic has two main applications: first it helps the community develop the “real” diagnostic and provides support to prepare and design the experiment, second the analysis of the experimental data. The simulation codes used to reproduce the laser-matter interactions (hydrodynamic, particle-in-cell code, etc.) give as output quantities (density, temperature, etc.) that most of the time are not directly measurable in a indepent way.
For example, the signal acquired from imaging diagnostics is a function of the temperature and density spatial distribution of the observed target. A synthetic diagnostic provides the link between the simulated phenomenon and the real one.
Our work focused on the development of X-ray imaging synthetic diagnostics. In particular we have developed one code for X-ray radiography, called PhaseX [1] and one for X-ray emission imaging, called EmXI. PhaseX simulates X-ray radiography diagnostics working both in absorption mode and phase-contrast mode [2]. Whereas, EmXI simulates diagnostics based on the X-rays emitted from the target, like as framing cameras and streak cameras.
In the present work we show the two codes applied to the study of the dynamic shell formation for laser direct-drive fusion [3]. Goncharov et al. [4] proposed a new target design without a precast shell. The shell will be created by the laser itself, with a specific pulse shape, before the compression phase. The concept will be tested in a proof-of-principle experiment at OMEGA laser facility in LLE (Rochester, USA). We simulated the X-ray imaging diagnostics to be employed in the experiment.
Figure 1. Synthetic diagnostics applied to dynamic shell formation; the “Absorption Image” is generated with a photon energy of 1.85 keV; the “Emission Image” and “Streak” are obtained by integrating the emission between 0.5 keV and 10 keV.
Figure 1 shows the outputs of three synthetic diagnostics. The first one shows a comparison between a X-ray phase-contrast image (XPCI) and X-ray absorption-contrast image (XACI). The two images are generated with PhaseX by using a monochromatic source with photon energy equal to 1.85 keV (silicon back-lighter). The last two images are generated with EmXI. The “Emission Image” shows the emission that can be acquired from a framing camera. The emission is integrated over the photon energy range 0.5 keV - 10 keV. The last plot (“Streak”) shows the emission along the x-axis, integrated on the same photon energy range specified before, versus time. The absorption and emission images both show the formation of the shell, at 3.90 ns after the laser interaction, as predicted from the hydrodynamic simulation.
We will also present application of the above codes to non-symmetric implosions, resulting from non uniform irradiation and/or from target deviation from perfect sphericity. All the targets, used as input for the synthetic diagnostics, are simulated with the hydrodynamic code DUED [5].
References
1. F. Barbato, et al. “PhaseX: an X-ray phase-contrast imaging simulation code for matter under extreme conditions.” Optics Express 30.3 (2022): 3388-3403.
2. F. Barbato, et al. “Quantitative phase contrast imaging of a shock-wave with a laser-plasma based X-ray source.” Scientific reports 9.1 (2019): 1-11.
3. L. Savino, et al. “Studies on dynamical shell formation for direct-drive laser fusion”. Il Nuovo Cimento C. (In publication).
4. V. N. Goncharov, et al. “Novel Hot-Spot Ignition Designs for Inertial Confinement Fusion with Liquid-Deuterium-Tritium Spheres.” Physical Review Letters 125.6 (2020): 065001.
5. S. Atzeni, et al. "Fluid and kinetic simulation of inertial confinement fusion plasmas." Computer physics communications 169.1-3 (2005): 153-159.
Acknowledgements
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. The involved teams have operated within the framework of the Enabling Research Project: ENR-IFE.01.CEA “Advancing shock ignition for direct-drive inertial fusion”.
