arXiv subjects

Brian Appelbe

Publications and source records attributed to Brian Appelbe.

5 recordsLinked to original sources

arXiv2024

Solving the Nonlinear Vlasov Equation on a Quantum Computer

The practical applicability of a recent Carleman-linearization-based quantum algorithm for solving ordinary differential equations (ODEs) with quadratic nonlinearities is investigated for the nonlinear electrostatic Vlasov equation with Krook-type collision operators. The equation is discretized on a (1+1)-dimensional phase-space grid and mapped onto the input of the quantum algorithm. Upper bounds for the query and gate complexities are derived in the limit of large grid sizes and found to be polynomially larger than the time complexity of the corresponding classical algorithms, primarily due to the dimension, sparsity, and norm of the Carleman-linearized evolution matrix. The convergence criteria are shown to impose severe restrictions on physically relevant plasma applications, requiring dissipation levels far exceeding those provided by the Krook operator.

quant-ph↗

arXiv2022

Constraints on Ion Velocity Distributions from Fusion Product Spectroscopy

Recent inertial confinement fusion experiments have shown primary fusion spectral moments which are incompatible with a Maxwellian velocity distribution description. These results show that an ion kinetic description of the reacting ions is necessary. We develop a theoretical classification of non-Maxwellian ion velocity distributions using the spectral moments. At the mesoscopic level, a monoenergetic decomposition of the velocity distribution reveals there are constraints on the space of spectral moments accessible by isotropic distributions. General expressions for the directionally dependent spectral moments of anisotropic distributions are derived. At the macroscopic level, a distribution of fluid element velocities modifies the spectral moments in a constrained manner. Experimental observations can be compared to these constraints to identify the character and isotropy of the underlying reactant ion velocity distribution and determine if the plasma is hydrodynamic or kinetic.

physics.plasm-ph↗

arXiv2020

The Effect of Areal Density Asymmetries on Scattered Neutron Spectra in ICF Implosions

Scattered neutron spectroscopy is a diagnostic technique commonly used to measure areal density in ICF experiments. Deleterious areal density asymmetries modify the shape of the scattered neutron spectrum. In this work a novel analysis is developed which can be used to fit the shape change. This allows scattered neutron spectroscopy to directly infer the amplitude and mode of the areal density asymmetries, with little sensitivity to confounding factors which affect other diagnostics for areal density. The model is tested on spectra produced by a neutron transport calculation with both isotropic and anisotropic primary fusion neutron sources. Multiple lines of sight are required to infer the areal density distribution over the whole sphere -- we investigate the error propagation and optimal detector arrangement associated with this inference.

physics.plasm-ph↗

arXiv2019

Modification of classical electron transport due to collisions between electrons and fast ions

A Fokker-Planck model for the interaction of fast ions with the thermal electrons in a quasi-neutral plasma is developed. When the fast ion population has a net flux (i.e. the distribution of the fast ions is anisotropic in velocity space) the electron distribution function is significantly perturbed from Maxwellian by collisions with the fast ions, even if the fast ion density is orders of magnitude smaller than the electron density. The Fokker-Planck model is used to derive classical electron transport equations (a generalized Ohm's law and a heat flow equation) that include the effects of the electron-fast ion collisions. It is found that these collisions result in a current term in the transport equations which can be significant even when total current is zero. The new transport equations are analyzed in the context of a number of scenarios including $α$ particle heating in ICF and MIF plasmas and ion beam heating of dense plasmas.

physics.plasm-ph↗

arXiv2019

Synthetic Nuclear Diagnostics for Inferring Plasma Properties of Inertial Confinement Fusion Implosions

A suite of synthetic nuclear diagnostics has been developed to post-process radiation hydrodynamics simulations performed with the code Chimera. These provide experimental observables based on simulated capsule properties and are used to assess alternative experimental and data analysis techniques. These diagnostics include neutron spectroscopy, primary and scattered neutron imaging, neutron activation, $γ$-ray time histories and carbon $γ$-ray imaging. Novel features of the neutron spectrum have been analysed to infer plasma parameters. The nT and nD backscatter edges have been shown to provide a shell velocity measurement. Areal density asymmetries created by low mode perturbations have been inferred from the slope of the downscatter spectrum down to 10 MeV. Neutron activation diagnostics showed significant aliasing of high mode areal density asymmetries when observing a capsule implosion with 3D multimode perturbations applied. Carbon $γ$-ray imaging could be used to image the ablator at high convergence ratio. Time histories of both the fusion and carbon $γ$ signals showed a greater time difference between peak intensities for the perturbed case when compared to a symmetric simulation.

physics.plasm-ph↗