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Determining the Properties of Laser Induced Fast Electrons from Experiments and Simulations

Ovchinnikov, Vladimir Mikhailovich
http://rave.ohiolink.edu/etdc/view?acc_num=osu1316460221

Abstract Details

2011, Doctor of Philosophy, Ohio State University, Physics.
We live in the era of high energy demand. Sooner or later we will exhaust all of our natural resources that are currently being used to make energy most of which are non-renewable. Therefore the quest to find another source of energy is an important one and should be completed within the next few decades. Thermonuclear fusion could become the solution to our energy problem. Currently, there are two main approaches to fusion: Magnetic Confinement Fusion (MCF) and Inertial Confinement Fusion (ICF). This thesis explores the variation of the ICF concept known as the Fast Ignition (FI). The FI concept relies on fast electrons with energies above 1 MeV created from the laser-matter interaction to deposit their energy into the compressed target core and start the fusion burn. Divergence of those electrons is one of the most crucial parameters in FI. If the divergence is found to be too large, then virtually all the anticipated advantages of FI over the conventional hot spot ignition will be lost. Spatially resolved, time-integrated Kα x-ray imagers are frequently used to infer the spatial distribution, and hence the divergence, of fast electrons by looking at the Kα radiation created by those energetic electrons passing through the target. Since any electron with energy above some threshold can produce a Kα photon, the Kα emission distribution can be quite different from that of the fast electrons. This thesis describes the physics behind the formation of Kα images and settles the question of how well those images represent the spatial distributions of the hot electrons that created them. A computational study using the Particle-In-Cell code LSP is presented that shows that a Kα image is not solely determined by the initial population of forward directed hot electrons, but rather also depends upon electrons refluxing off the front, the back and the sides of the target. All these effects create significant features in the Kα time-integrated images making them hard to interpret. To make the Kα image be more representative of the first pass hot electron spatial distribution one needs to eliminate multiple electron refluxing. Attaching a thick layer of a low-Z material to the back of the target (Get-Lost-Layer or GLL) can greatly reduce electron refluxing by slowing them down without significantly attenuating the Kα signal. Two experiments using buried cone targets with a GLL designed to measure the true fast electron divergence were conducted at Titan laser at Lawrence Livermore National Laboratory and are described in this thesis. The experimental results are supported by LSP simulations that prove that the presence of a GLL indeed suppresses electron refluxing. Finally, benchmarking between the experiment and the simulations allows extraction of the correct electron divergence.
Linn Van Woerkom (Advisor)
Richard Freeman (Committee Co-Chair)
Richard Furnstahl (Committee Member)
Fengyuan Yang (Committee Member)
217 p.
Physics; Plasma Physics
Fast Ignition; fast electron divergence; K-alpha imaging; plasma simulations

Recommended Citations

Citations

  • Ovchinnikov, V. M. (2011). Determining the Properties of Laser Induced Fast Electrons from Experiments and Simulations [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316460221

    APA Style (7th edition)

  • Ovchinnikov, Vladimir. Determining the Properties of Laser Induced Fast Electrons from Experiments and Simulations. 2011. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1316460221.

    MLA Style (8th edition)

  • Ovchinnikov, Vladimir. "Determining the Properties of Laser Induced Fast Electrons from Experiments and Simulations." Doctoral dissertation, Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316460221

    Chicago Manual of Style (17th edition)

osu1316460221
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© 2011, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.