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Advanced Simulations and Optimization of Intense Laser Interactions

Smith, Joseph Richard Harrison
http://orcid.org/0000-0002-5978-6840
http://rave.ohiolink.edu/etdc/view?acc_num=osu1589302684037632

Abstract Details

2020, Doctor of Philosophy, Ohio State University, Physics.
This work uses computer simulations to investigate intense laser-plasma interactions. First, we use two-dimensional particle-in-cell (PIC) simulations and simple analytic models to investigate the laser-plasma interaction known as ponderomotive steepening. When normally incident laser light reflects at the critical surface of a plasma, the resulting standing electromagnetic wave modifies the electron density profile via the ponderomotive force, which creates peaks in the electron density separated by approximately half of the laser wavelength. What is less well studied is how this charge imbalance accelerates ions towards the electron density peaks, modifying the ion density profile of the plasma. Idealized PIC simulations with an extended underdense plasma shelf are used to isolate the dynamics of ion density peak growth for a 42 fs pulse from an 800 nm laser with an intensity of 1018 W cm-2. These simulations exhibit sustained longitudinal electric fields of 200 GV m-1, which produce counter-steaming populations of ions reaching a few keV in energy. We compare these simulations to theoretical models, and we explore how ion energy depends on factors such as the plasma density and the laser wavelength, pulse duration, and intensity. We also provide relations for the strength of longitudinal electric fields and an approximate timescale for the density peaks to develop. These conclusions may be useful for investigating the phenomenon of ponderomotive steepening as advances in laser technology allow shorter and more intense pulses to be produced at various wavelengths. We also discuss the parallels with other work studying the interference from two counter-propagating laser pulses. Next we investigate the development of ultra-intense laser-based sources of high energy ions, which is an important goal, with a variety of potential applications. One of the barriers to achieving this goal is the need to maximize the conversion efficiency from laser energy to ion energy. We apply a new approach to this problem, in which we use an evolutionary algorithm to optimize conversion efficiency by exploring variations of the target density profile with thousands of one-dimensional PIC simulations. We then compare this “optimal” target identified by the one-dimensional PIC simulations to more conventional choices, such as with an exponential scale length pre-plasma, with fully three-dimensional PIC simulations. The optimal target outperforms the conventional targets in terms of maximum ion energy by 20% and shows a significant enhancement of conversion efficiency to high energy ions. This target geometry enhances laser coupling to the electrons, while still allowing the laser to strongly reflect from an effectively thin target. These results underscore the potential of this statistics-driven approach for optimizing laser-plasma simulations and experiments. Finally, we present computational fluid dynamic simulations that model the formation of thin liquid targets. These simulations allow us to explore new types of targets that may be beneficial for high repetition rate laser plasma interactions.
Chris Orban, PhD (Advisor)
Enam Chowdhury, PhD (Committee Member)
Douglass Schumacher, PhD (Committee Member)
Richard Furnstahl, PhD (Committee Member)
111 p.
Physics
laser-plasma interactions; particle-in-cell simulations; ion acceleration; high energy density physics; optimization; high repetition rate targets; ponderomotive force

Recommended Citations

Citations

  • Smith, J. R. H. (2020). Advanced Simulations and Optimization of Intense Laser Interactions [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1589302684037632

    APA Style (7th edition)

  • Smith, Joseph. Advanced Simulations and Optimization of Intense Laser Interactions. 2020. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1589302684037632.

    MLA Style (8th edition)

  • Smith, Joseph. "Advanced Simulations and Optimization of Intense Laser Interactions." Doctoral dissertation, Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1589302684037632

    Chicago Manual of Style (17th edition)

osu1589302684037632
403
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