<p> Recent advances in the development of intense short pulse lasers are significant. It is available now to access laser with intensity 10<sup> 21</sup> W/cm<sup>2</sup> by focusing a petawatt class laser, at which intensity hot dense plasmas with relativistic electrons, energy greater than 100 MeV, are produced. High energy x-rays, so called γ-rays, are emitted strongly from such plasmas via Bremsstrahlung. </p><p> In a few years the laser intensity is expected to exceed 10<sup>22 </sup> W/cm<sup>2</sup>. In such extreme intense laser-matter interaction, the radiative damping is significant, namely, electrons accelerated by the laser fields lose their energies and emit γ-rays. So that we will see intense γ-ray flash from the laser produced plasmas via two competing processes, Bremsstrahlung and radiative damping. However It is not clearly understood which process is dominant at what laser or what target conditions. My research is focus on making the radiation models to understand the γ-ray emissions and studying the extremely intense laser-matter interaction to optimize the γ-ray emissions under the given laser and target conditions. </p><p> Since these relativistic plasmas are non-thermal and non-equilibriated, it is necessary to develop a kinetic plasma code with the radiation physics. We had developed a collisional particle-in-cell code, PICLS, coupled to a radiation transport module to consider the γ-ray emissions. The emissivities of γ-rays had been derived for the relativistic Bremsstrahlung and the radiative damping. In the radiative damping, especially, not only the first order damping term, but up to 4-th order damping terms had been derived from the Lorentz-Dirac equation for the first time. Especially, the 2nd term is found to be important since it is a damping term of the Lorentz force, indicating the particle acceleration including ions would be much less efficient than that what we expected when the laser intensity become greater than 10<sup> 23</sup> W/cm<sup>2</sup>. </p><p> The laser energy dependence of the γ-ray energy and the intensity dependence of the angular distribution of γ-rays are studied. By solving the emission and transport of γ-ray it was found that the radiative damping is not significant until the laser intensity exceeds 10<sup>23</sup> W/cm<sup>2</sup>. While the Bremsstrahlung is dominant γ-rays emission process, which can also boost by changing the target with higher Z material or increasing the mass (volume) of the target. As an application of γ-ray production, the pair creation, forming a pair plasma, is attractive. The number of positrons via pair creation from the Bethe-Heitler process is also computed in the code. The optimal parameters of laser and target to increase γ-ray yields as well as positrons yields are identified.</p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:3707887 |
| Date | 16 July 2015 |
| Creators | Pandit, Rishi R. |
| Publisher | University of Nevada, Reno |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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