Characterization and stabilization of atmospheric pressure DC microplasmas and their application to thin film deposition

Ph.D., Mechanical Engineering -- Drexel University, 200

Electron-wall interaction in Hall thrusters

Electron-wall interaction effects in Hall thrusters are studied through measurements of the plasma response to variations of the thruster channel width and the discharge voltage. The discharge voltage threshold is shown to separate two thruster regimes. Below this threshold, the electron energy gain is constant in the acceleration region and therefore, secondary electron emission (SEE) from the channel walls is insufficient to enhance electron energy losses at the channel walls. Above this voltage threshold, the maximum electron temperature saturates. This result seemingly agrees with predictions of the temperature saturation, which recent Hall thruster models explain as a transition to space-charge saturated regime of the near-wall sheath. However, in the experiment, the maximum saturation temperature exceeds by almost three times the critical value estimated under the assumption of a Maxwellian electron energy distribution function. The channel narrowing, which should also enhance electron-wall collisions, causes unexpectedly larger changes of the plasma potential distribution than does the increase of the electron temperature with the discharge voltage. An enhanced anomalous crossed-field mobility (near wall or Bohm-type) is suggested by a hydrodynamic model as an explanation to the reduced electric field measured inside a narrow channel. We found, however, no experimental evidence of a coupling between the maximum electron temperature and the location of the accelerating voltage drop, which might have been expected due to the SEE-induced near-wall conductivity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87763/2/057104_1.pd

Characterization of plasma in a Hall thruster operated at high discharge voltage

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77205/1/AIAA-2005-4404-466.pd

An Open Access Policy at Texas A&M University

An information sheet on a proposed open access policy at Texas A&MOpen access scholarly literature is “digital, online, free-of-charge, and free of most copyright and licensing restrictions”1. An Open Access Policy reserves Open access policies directly support the mission of land grant universities by making publically supported research openly available. Universities around the world have created Open access policies to share their research so that society has equitable access to published scholarship. These policies generally allow authors to archive a copy of their publication in an institutional repository or published in an open access journal, in ways that help address both the price barriers and the permission barriers that undermine global access to the products of a university’s scholarly and creative work. Over six hundred universities and research institutions worldwide, including more than half of our peer institutions (as defined by Vision 2020), have an open access policy2. The Faculty Senate Research sub-committee recommends that TAMU adopt an Open Access Policy. An open access policy at TAMU would be managed by the TAMU Libraries, who would provide the support to TAMU authors so they can archive an open access copy of their publication in our institutional repository so that the burden on the authors would be minimal. We are proposing the Faculty Senate as a whole vote on a resolution to recommend that the President’s office implement such a policy.Texas A&M Faculty Senat

Ultrafast X-ray Phase Contrast Imaging of High Repetition Rate Shockwaves

High-repetition-rate plasma-induced shockwaves in liquid have been observed using ultrafast X-ray phase contrast imaging (PCI) for the first time. Using a laser-triggered nanosecond-pulsed plasma device in heptane at ambient conditions, it is demonstrated that these well-timed weak shocks can be generated at an unprecedented repetition rate (>3 per minute), significantly faster than that of more commonly-used dynamic targets (exploding wire, gas gun). This simple portable target can easily be adapted to study discharges in different media (water, oils, solids) at comparably high repetition rates and over a wide range of possible input energies. Compared to previously PCI-imaged shocks, these shocks are relatively weak (1 < Mach number < 1.4), which advances the resolution and sensitivity limits of this high-speed imaging diagnostic. Numeric solutions of a Fresnel-Kirchhoff diffraction model are used to estimate post-shock thermodynamic conditions, the results of which show good agreement with expectations based on Rankine-Hugoniot normal shock thermodynamic relations. A comparison in shock imaging sensitivity between LYSO and LuAG scintillators is also discussed, showing that the short decay tail of LYSO brings the shock profile above the detectability limit for this implementation of PCI.Comment: 6 pages, 7 figure

Ultrafast X-ray imaging of pulsed plasmas in water

Pulsed plasmas in liquids exhibit complex interaction between three phases of matter (liquids, gas, plasmas) and are currently used in a wide range of applications across several fields, however significant knowledge gaps in our understanding of plasma initiation in liquids hinder additional application and control; this area of research currently lacks a comprehensive predictive model. To aid progress in this area experimentally, here we present the first-known ultrafast (50 ps) X-ray images of pulsed plasma initiation processes in water (+25 kV, 10 ns, 5 mJ), courtesy of the X-ray imaging techniques available at Argonne National Laboratory's Advanced Photon Source (APS), with supporting nanosecond optical imaging and a computational X-ray diffraction model. These results clearly resolve narrow (~10 µm) low-density plasma channels during initiation timescales typically obscured by optical emission (<100 ns), a well-known and difficult problem to plasma experiments without access to state-of-the-art X-ray sources such as the APS synchrotron. Images presented in this work speak to several of the prevailing plasma initiation hypotheses, supporting electrostriction and bubble deformation as dominant initiation phenomena. We also demonstrate the plasma setup used in this work as a cheap (<US$100k), compact, and repeatable benchmark imaging target (29.1 km/s, 1 TW/cm^2) useful for the development of next-generation ultrafast imaging of high-energy-density physics (HEDP), as well as easier integration of HEDP research into synchrotron-enabled facilities

Dataset for: Plasma Generated Ozone and Reactive Oxygen Species for Point of Use PPE Decontamination System

This is a dataset for a paper. Plasma Generated Ozone and Reactive Oxygen Species for Point of Use PPE Decontamination System Article published in PLOS One: DOI: 10.1371/journal.pone.0262818This is a dataset for a paper. This paper reports a plasma reactive oxygen species (ROS) method for decontamination of PPE (N95 respirators and gowns) using a surface DBD source to meet the increased need of PPE due to the COVID-19 pandemic. A system is presented consisting of a mobile trailer (35 m3) along with several Dielectric barrier discharge sources installed for generating a plasma ROS level to achieve viral decontamination. The plasma ROS treated respirators were evaluated at the CDC NPPTL, and additional PPE specimens and material functionality testing were performed at Texas A&M. The effects of decontamination on the performance of respirators were tested using a modified version of the NIOSH Standard Test Procedure TEB-APR-STP-0059 to determine particulate filtration efficiency. The treated Prestige Ameritech and BYD brand N95 respirators show filtration efficiencies greater than 95% and maintain their integrity. The overall mechanical and functionality tests for plasma ROS treated PPE show no significant variations