A Computational Study Of The Stagnation Phase In Inertial Confinement Fusion

Author : Arijit Bose
Publisher :
ISBN 13 :
Total Pages : 208 pages
Book Rating : 4.:/5 (18 download)

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Download or read book Direct Drive Inertial Confinement Fusion written by Arijit Bose and published by . This book was released on 2017 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Direct laser-driven fusion uses multiple laser beams to symmetrically illuminate a frozen deuterium-tritium shell. The motive is to produce a hot confined central plasma - the core - which would initiate fusion reactions and lead to self-heating by alpha particle energy deposition. The OMEGA laser produces ~25-30 kJ of on-target energy, approximately 1.4% of the energy available on the National Ignition Facility (NIF). Currently, the NIF is not configured to perform symmetric illumination while the 60 beam OMEGA routinely irradiates targets symmetrically. To help motivate NIF to explore direct drive targets in a future symmetric illumination configuration, OMEGA experimental results and their scaling provide a valuable and cost-effective tool. This theoretical and numerical analysis shows that the experiments at the OMEGA [Regan et al., Phys. Rev. Lett. 117, 025001 (2016)] when hydrodynamically scaled to 1.9 MJ would produce several times the fusion energy output than that achieved with the highest performing indirectly driven targets at NIF [Hurricane et al, Nature 506, 343{348 (2014)]. In order to determine the optimal path to thermonuclear ignition, it is necessary to have a metric to estimate implosion performance and the level of alpha heating. A simple model describing the final stage of inertial confinement fusion (ICF) implosions and the performance metric is shown. The Rayleigh-Taylor instability (RTI) produces long- and mid-wavelength distortions of the core, which degrade the implosion performance. A theoretical analysis of the effect of the two types of asymmetries on the implosion hydrodynamics and fusion neutronics is discussed. The experimental observables for the high performing OMEGA implosions were analyzed for investigation of the degradation sources, this is essential for future improvements of the implosion quality. The analysis of several repeats of the cryogenic implosion experiments suggests a systematic degradation mechanism a ecting the implosions. It is found that using a combination of the two types of asymmetries, all of the experimentally observed implosion core conditions could be simultaneously reproduced in simulations. The scaling of the core to NIF required developing a theoretical understanding of the scaling of the deceleration-phase RTI. The scaling of thermal conduction and radiation transport, which mitigate the RTI growth, is shown. It is found that the degradation of implosion performance caused by the RTI is similar for NIF and OMEGA. Using all of these, a general fusion-yield extrapolation procedure has been developed to estimate ICF implosion performance at higher laser energies. The scaling assumes only that the implosion hydrodynamic effciency is unchanged at higher energies, and relies solely on a volumetric scaling of the experimentally observed core conditions. Since the stagnation physics for conventional hot-spot ignition is equivalent for both direct- and indirect-drive, the technique, in general, can be applied to both. Using this, the OMEGA experiments were extrapolated to NIF scale. It is estimated that the current best-performing OMEGA implosion extrapolated to a 1.9 MJ laser driver with the same illumination configuration and laser-target coupling would produce 125 kJ of fusion energy, with similar levels of alpha heating as observed on NIF implosions, but with ~5 times more fusion energy; showing the advantage of direct drive over indirect drive as one approaches the burning plasma regime. Correction of the systematic degradation in the OMEGA implosions - by improving either the low- or mid-mode symmetry - can produce conditions for a burning plasma when scaled to NIF energies."--Pages xi-xiv.