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Investigating temperature distributions and thermal conduction effects in laser-heated plasmas relevant to Magnetized Liner Inertial Fusion
AuthorCarpenter, Kyle Richard
AdvisorMancini, Roberto C.
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Laser heating the fuel prior to implosion is a crucial step in Magnetized Liner Inertial Fusion (MagLIF). Experiments investigating this stage have been performed at Sandia National Laboratories. In these experiments, deuterium fuel within a cylindrical pipe, or liner, was heated using 527 nm laser light from the Z Beamlet Laser. The deuterium was doped with a trace amount of Ar and time-integrated spatially resolved spectra and monochromatic x-ray emission images were recorded. Individual analysis of the spatially resolved spectra recovered temperature distributions Te(z) that are resolved along the direction of laser propagation but spatially integrated along the instrument’s line-of-sight . These temperature profiles can be used to assess how different experimental parameters such as an external magnetic field, beam smoothing, and the laser pulse shape, affect the laser heating. Additionally, the spectrum and image data from magnetized and unmagnetized experiments have been included in a multi-objective analysis driven by a Pareto genetic algorithm to further examine the effect of an external axial magnetic field. By simultaneously and self-consistently considering both the spatially resolved spectra and monochromatic x-ray image data, the analysis extracted two-dimensional temperature distributions Te(r,z) . The experimental Te(r,z) profiles show that, by inhibiting thermal conduction in the radial direction, the applied magnetic field increased Te, the axial extent of the laser heating, and the magnitude of the radial temperature gradients. Furthermore, temperature gradient scale lengths extracted from the measured Te(r,z) enabled an assessment of the importance of non-local thermal conduction in both the unmagnetized and magnetized experiments. Lastly, radiation magnetohydrodynamics simulations of these experiments were performed and post-processed to compare the experimental results with simulation predictions and to investigate the impact of thermal conduction on the predicted temperature distributions.  K. R. Carpenter, R. C. Mancini, E. C. Harding, et al, Phys. Plasmas 27, 052704 (2020) K. R. Carpenter, R. C. Mancini, E. C. Harding, et al, Phys. Rev. E 102, 023209 (2020)