Session RR1: Plasmas at Special Conditions

Early Formation of Uranium Monoxide in Laser-Ablated Plasmas: Constraints on the Rate Coefficients from Ultrafast Spectrometry and Plasma-Chemistry Models

The mechanisms regulating uranium chemical fractionation in post-detonation nuclear debris are not well understood. The fractionation process alters the chemistry of the nuclear debris so that it no longer reflects the chemistry of the source weapon. We have measured time-resolved vibronic emission spectra of uranium monoxide (UO) formed after laser ablation of the metal in gaseous oxygen. Tests with different oxygen isotopes of $^{\mathrm{238}}$U$^{\mathrm{16}}$O and $^{\mathrm{238}}$U$^{\mathrm{18}}$O have allowed to uniquely identify a convenient molecular emission line that can be tracked over time to characterize the kinetics of UO formation in the cooling plasma plume. Comparison with a Monte-Carlo Plasma Chemistry model including a detailed thermochemistry of uranium combustion has allowed for the first time to constrain the rate coefficients and highlight the dominant reaction pathways of UO formation in oxygen atmospheres.   

Sound generated by small perturbations of power in high-pressure arcs

We propose a simple analytical theory to describe the sound generated by small periodic perturbations of a cylindrical dc arc in a dense gas. Theoretical analysis was done within the framework of the conventional channel arc model with an effective channel radius and a given fluctuating Joule's heat. The arc channel model was supplemented with time-dependent gas dynamic equations. Estimation formulas for the generated sound intensity in the near field were obtained. In the peripheral region of an arc with graphite electrodes burning in a high pressure inert gas, a large number of microscopic soot particles are produced together with nanoparticles. Experimental studies have shown that exposure of the peripheral region of the arc to intense ultrasounds (\textasciitilde 100 - 120 dB) lead to a noticeable increase in the efficiency of the synthesis of nanoparticles and to the reduction in the yield of soot [1]. It was shown in [2] that ultrasounds, acting on the suspension of soot microparticles and nanoparticles in gas result in the coagulation of soot particles, without noticeably affecting the small-scale nanoparticles. Our estimates show that relatively small perturbations of the power in a high-pressure arc (at the level of several percent) can be a source of high-intensity sound comparable to that used in experiments [1]. 1. G.N. Churilov, Nanotubes and Carbon Nanostructures, 16,5-6, 395 (2008) 2. M.N. Shneider, AIAA 2016-1693, San Diego, CA, 2016   

Hydrodynamic approach to modeling of plasma processes under the action of pulsed electron beam

The investigation is devoted to the mathematical modeling of action of pulsed high intensity pulse electron beam (HIPEB) on one-component molecular gas. The characteristic parameters of HIPEB are: energy of electrons is 300-500 keV, current density is 500-1000 A/ñm$^{\mathrm{2}}$, pulse duration is 100 nsec, and gas pressure is varied from 10 to 100 kPa. Under the action of PHPEB on gas the nonequlibrium plasma is formed. Because the beam energy is transferred to the gas through the electronic component the electron and ion temperatures vary significantly. The time for alignment of the temperatures is very large because of the relatively small pressures. The theoretical investigation of the plasma processes under the action of HIPEB has performed within the framework of one-liquid two-temperature hydrodynamic model. Because of the electron and ion temperatures vary significantly we use the separate equations for thermal balance. As a result of the numerical modeling the main channel of energy dissipation of electron beam is revealed. The energy pumping from electron to ion subsystem is also discussed.   

Analytical model of cold-cathode breakdown in helium at extremely high electric field and low pressure

An analytical model is developed for gas ionization breakdown at extremely high values of reduced electric field (the ratio $E/n$ of electric field to gas density) between parallel-plate electrodes in helium. The value of $E/n$ under investigation \quad varies in the range of 70--6600 kTd (1~kTd $=$ 10$^{\mathrm{-18}}$ Vm$^{\mathrm{-2}})$ for \textit{pd }\textasciitilde \quad 0.5 Torr-cm, where $p$ is the gas pressure and $d$ is the electrode separation. The model includes anisotropic scattering for all species and fast neutral atom backscattering at electrodes, as well as fast-neutral impact ionization. The results are compared to those from a detailed Particle-In-Cell/Monte Carlo (PIC/MCC) simulation (Liang Xu et. al., “Investigation of the Paschen Curve for Helium in 100-1000 kV Range”), and to experimental measurements. Analytical model results are sufficiently accurate for $E$/$n$ \textasciitilde 1000~kTd if the model treats the electrons as a single beam and assumes that charge exchange is the dominant collision process which determines the local distributions of ions and fast neutral atoms.   

Overview of DOE/FES program activities for low temperature plasma science research

TBA   

Overview of NSF plasma physics and low temperature plasma science and engineering programs

TBA   

NSF Low Temperature Plasma Workshop on Sustainability: Process, Findings, Path forward

The workshop "Science Challenges in Low Temperature Plasma Science and Engineering: Enabling a Future Based on Electricity through Non-Equilibrium Plasma Chemistry", sponsored by the National Science Foundation and Army Research Office, was held August 2016 with the goal of defining the research challenges and the role of low temperature plasmas in sustainability. The workshop report, available at \underline {http://mipse.umich.edu/nsfworkshop/}, broadly discusses challenges across the discipline, with emphasis on the focus areas of multiphase plasma systems, energy and the environment, biotechnology and food cycle, and synthesis and modification of materials. In this talk, the process and motivation for holding the workshop and the workshop findings will be discussed. The talk will encourage community wide strategic discussion, advocacy for a path forward, and engagement of Federal agencies in this initiative.