Highly efficient conversion of laser energy to hard X-rays in high intensity laser-solid simulations

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Submitted by Stuart_Morris

Feb. 8, 2022, 2:44 p.m.

Highly efficient conversion of laser energy to hard X-rays in high intensity laser-solid simulations

S. Morris, A. Robinson, C. Ridgers
Morris, S., Robinson, A. and Ridgers, C., 2021. Highly efficient conversion of laser energy to hard x-rays in high-intensity laser–solid simulations. Physics of Plasmas, 28(10), p.103304.
DOI:  10.1063/5.0055398          

Brief Description
A novel hybrid-PIC code has been developed to model high energy X-rays produced when intense laser-pulses strike solid targets. This provides a significant speed boost over traditional PIC codes, and allowed 3D modelling of the full X-ray emission. This paper found that the emission lasted much longer than previous campaigns considered, and so significantly more X-rays were produced than were expected.

The code is built on the framework of the EPOCH-PIC code (FORTRAN, MPI), with several new physics routines added to model solid targets. Documentation and input decks for the paper results have been provided in the DOI, and the code is available on GitHub; however, the MATLAB scripts used to create the figures from the output SDF files have not been included.

When attempting to reproduce for ReproHack, the ReproHacker should use the SDF scripts present in EPOCH to extract data from the SDF files, which can then be used to recreate the paper figures. The ReproHacker should note that PIC codes use "macro-particles", which represent many real particles (this is the macro-particle "weight"). This will be important for "total-energy" calculations.

The results of Section IIIA should be the easiest to reproduce, as these describe normal hybrid-PIC simulations. The code on GitHub does not have the capability of producing the Section IIIB results - these were from direct-code-output (e.g. print-statements) that were added to the code. To do this correctly would require a good understanding of the hybrid scripts, and so this should be considered a challenge section (sum the energy lost from each process by saving the particle energy before and after the process, output at the end). Section IIIC was done using a standard PIC code, and requires extensive post-processing - this is well beyond the scope of a 1-week project, and should not be attempted.
Why should we reproduce your paper?
There are many applications to multi-MeV X-rays. Their penetrative properties make them good for scanning dense objects for industry, and their ionising properties can destroy tumours in radiotherapy. They are also around the energy of nuclear transitions, so they can trigger nuclear reactions to break down nuclear waste into medical isotopes, or to reveal smuggled nuclear-materials for port security. Laser-driven X-ray generation offers a compact and efficient way to create a bright source of X-rays, without having to construct a large synchrotron. To fully utilise this capability, work on optimising the target design and understanding the underlying X-ray mechanisms are essential. The hybrid-PIC code is in a unique position to model the full interaction, so its ease-of-use and reproducibility are crucial for this field to develop.
What should reviewers focus on?
Section IIIA - this is the most important section, and shows the X-ray properties (energy spectra, angular distribution, temporal emission, total efficiency). This should be the focus. Section IIIB - will require additions to the GitHub code to reproduce. I do not expect the ReproHacker to attempt this. Section IIIC - this section does not contain results from the hybrid-PIC code, and requires extensive post-processing. The ReproHacker should not attempt this, as this is beyond the scope of a 1-week project.


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