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Particle-in-Cell Simulations of the Acceleration of Electrons from the Interaction of a Relativistic Laser Reflecting from Solid Density Targets

Ngirmang, Gregory Kodeb
http://rave.ohiolink.edu/etdc/view?acc_num=osu1514985418694386

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Physics.
I present computational simulations of the efficient production of relativistic electron beams from the interaction of an intense, short-pulse laser normally incident on a solid density target in which electrons are accelerated backwards, or counter to the laser incidence direction. This effect, called the standing wave effect, was discovered in an experiment at the Air Force Research Laboratory (AFRL), Dayton OH, with such a laser (780nm wavelength, 1018 W/cm2 intensity, 40 femtosecond pulse) that observed the laser acceleration of backwards directed beams of electrons to MeV energies, an energy exceeding the energy scale for this laser intensity known as the ponderomotive scale. Moreover, this acceleration was observed to have a high laser-to-electron beam energy conversion ratio exceeding one percent (1%) for super-ponderomotive energies. These aspects make this effect attractive as a laser-based electron acceleration scheme. Understanding the laser and plasma physics behind the effect is interesting from a fundamental research perspective; evaluating its effectiveness at other intensity regimes or other target configurations is important to those who seek to employ the effect in electron beam applications, those who study the theory of laser and plasma physics, and for those who perform experiments in regimes where this effect may be of relevance. In this work I present a set of simulations with the Large Scale Plasma code, a Particle-in-Cell code that is apt to model such ultraintense laser interactions, to pursue this end of illuminating the relevant physics of this mechanism. I present the first fully three-dimensional (3D) simulations of the standing wave effect in order to further validate two-dimensional (2D(3v)) simulations performed by the AFRL group, finding that while some characteristics of the accelerated beam differ, the peak electron energy and total energies of beams produced in 2D(3v) are comparable with 3D simulations. After this, I present a suite of 2D(3v) simulations investigating the effect over a wider range of laser energies as well as laser wavelengths, in order to gauge the scaling of electron beam energies with the normalized vector potential, the a0 parameter, which characterizes the momentum of electrons in these interactions. These scans demonstrate that less relativistic lasers with a0<1 show a considerable gain from ponderomotive scale, provided the plasma scale-length on the front of the target is longer than the wavelength, while more relativistic cases a_0>>1 merely match ponderomotive. Finally, the high efficiency has been determined to be due to background plasma density in the target chamber shielding binding electrostatic fields in the target. I present another parameter scan to probe this effect over a range of background densities and find that the high conversion efficiency occurs when the Debye length λd in the background plasma is on the scale of the interaction region, and fails for less relativistic pulses where a0<1. I conclude that the electrons produced in this effect with liquid targets will only be efficient and super-ponderomotive in the just relativistic regime of the AFRL laser pulse at a0~1.
Christopher Orban, Prof. (Advisor)
Enam Chowdhury, Prof. (Committee Member)
Schumacher Douglass, Prof. (Committee Member)
Furnstahl Richard, Prof. (Committee Member)
121 p.
Physics
relativistic laser-plasma interaction; laser; plasma; particle acceleration; electron acceleration; femtosecond; particle-in-cell method; particle-in-cell; high energy density physics;

Recommended Citations

Citations

  • Ngirmang, G. K. (2018). Particle-in-Cell Simulations of the Acceleration of Electrons from the Interaction of a Relativistic Laser Reflecting from Solid Density Targets [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1514985418694386

    APA Style (7th edition)

  • Ngirmang, Gregory. Particle-in-Cell Simulations of the Acceleration of Electrons from the Interaction of a Relativistic Laser Reflecting from Solid Density Targets. 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1514985418694386.

    MLA Style (8th edition)

  • Ngirmang, Gregory. "Particle-in-Cell Simulations of the Acceleration of Electrons from the Interaction of a Relativistic Laser Reflecting from Solid Density Targets." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1514985418694386

    Chicago Manual of Style (17th edition)

osu1514985418694386
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