J.R. Roth

An overview of research using the one atmosphere uniform glow discharge plasma (OAUGDP) for sterilization of surfaces and materials

The medical, food processing, and heating, ventilating, and air conditioning industries are searching for improved pasteurization, disinfection, and sterilization technologies. Candidate techniques must deal with and overcome such problems as thermal sensitivity and destruction by heat, formation of toxic by-products, costs, and inefficiency in performance. We report the results of a plasma source, the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP), which operates at atmospheric pressure in air and produces antimicrobial active species at room temperature, OAUGDP exposures have reduced log numbers of Gram negative and Gram positive bacteria, bacterial endospores, yeast, and bacterial viruses on a variety of surfaces. The nature of the surface influenced the degree of lethality, with microorganisms on polypropylene being most sensitive, followed by glass, and cells embedded in agar. Experimental results showed at least a 5 log/sub 10/ CFU reduction in bacteria within a range of 50-90 s of exposure. After 10-25 s of exposure, macromolecular leakage and bacterial fragmentation were observed. Vulnerability of cell membranes to reactive oxygen species (ROC) is hypothesized. Results from several novel OAUGDP configurations are presented, including a remote exposure reactor (RER) which uses transported active species to sterilize material located more than 20 cm from the plasma generation site, and a second planar electrode configuration developed for air filter sterilization. Applications of these technologies to the healthcare industry, the food industry, and decontaminating surfaces compromised by biological warfare agents are discussed.

The One Atmosphere Uniform Glow Discharge Plasma (OAUGDP)—A Platform Technology for the 21st Century

Representatives from many industrial sectors are searching for more economic and ecologically sound technologies to meet regulatory and competitive pressures. Currently, the majority of industrial plasma processing is done with glow discharges at pressures below 10 torr. This tends to limit such applications to high-value items, as a result of the high capital cost of vacuum systems and the production constraints of batch processing. It has long been recognized that glow discharges would play a much larger industrial role if they could be generated at one atmosphere and in ambient air. A promising platform technology for plasma processing across many industrial sectors is the one atmosphere uniform glow discharge plasma (OAUGDP), a nonthermal normal glow discharge that operates in air (and other gases) at room temperature and atmospheric pressure. It generates active species useful for the sterilization, decontamination, and surface energy enhancement of films, fabrics, air filters, metals, and 3-D workpieces. This paper will survey exploratory research and development at the University of Tennessees Plasma Sciences Laboratory on eight potential industrial applications of the OAUGDP that can be conducted at one atmosphere and at room temperature with air as the working gas

Experimental Generation Of A Steady-state Glow Discharge At Atmospheric Pressure

In industrial plasma engineering, a steady-state atmospheric glow discharge would allow many surface modification and other plasma processing operations to be carried out under atmospheric conditions, rather than in expensive vacuum systems which enforce batch processing. In this paper, we report some encouraging results of an experimental program conceived independently of the work reported by Kanda, et al. (Ref 1). Our experiments were conducted on an experimental apparatus shown schematically in Figure 1. A Parallel Plate plasma reactor with square electrodes 25 cm on a side, covered with an insulating surface (rubber or glass), and with variable spacing, was set up in an enclosed box which made it possible to control the type of working gas used. This reactor was energized by a very specialized RF power supply capable of supplying up to 5 kilowatts of RF power at rms voltages up to 5 kilovolts, and over a frequency range from 1kHz to 100 kHz.

Electrohydrodynamically induced airflow in a one atmosphere uniform glow discharge surface plasma

Summary form only given. The One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) is capable of operating at one atmosphere in air and other gases, and its active species can be used to sterilize and decontaminate surfaces, and to increase the wettability and surface energy of materials. This paper will present the theory of three distinct mechanisms for EHD-induced now acceleration at one atmosphere using the OAUGDP. The first of these mechanisms acts on the net charge density of the OAUGDP, and produces neutral gas flow velocities on the order of one to ten meters per second as the result of a paraelectric effect in which the plasma is accelerated in the direction of an increasing electric field gradient. This phenomenon was observed during wind tunnel tests, in which the paraelectrically induced gas flow was observed to have the predicted linear dependence on the applied voltage, and to be of the correct magnitude. The second mechanism is the result of the momentum transferred to the neutral gas from the mobility drift of ions and electrons in a DC electric field applied to a OAUGDP. The ion momentum transfer dominates the electron momentum transfer, and can produce neutral gas now velocities approaching Mach 1.0 if heating and viscous effects are neglected. The third mechanism is flow induced by peristaltic EHD effects on an OAUGDP, in which a series of strip electrodes are energized by a polyphase low frequency RF power supply, in such a way that a traveling-wave electric field exists along the surface on which the electrodes are mounted. This electric field can accelerate the ions and the neutral gas to velocities of several hundred meters per second.

Schlieren Imaging of the Aerodynamic Flow Field Induced by a Paraelectric Electrohydrodynamic (EHD) Plasma Actuator

Schlieren imaging methods respond to density gradients in gases and are used in aerodynamic research to visualize the structure of atmospheric pressure flow fields. We have used this method to study the flow induced in atmospheric pressure air by electrohydrodynamic body forces generated by a single paraelectric plasma actuator energized in the filamentary mode of operation. The schlieren images show the absence of significant vertical flow and also show an induced boundary layer flow no more than a few millimeters thick.

Absorption and Reflection of Microwaves by a Non‐Uniform Plasma Near the Electron Cyclotron Frequency

In this paper, we report experimental measurements and numerical computations on the absorption and reflection of microwave radiation near the electron cyclotron frequency. In our model the wave is launched in the extraordinary mode into a cold, steady state, weakly ionized, nonuniform two‐dimensional plasma slab with a uniform background magnetic field parallel to the surface. We compare computational and experimentally measured values of the absorption and reflection for selected values of the plasma number density, and collision frequency. These parametric dependences are investigated for normal incidence by computer simulations using cold plasma theory1,2 and compared with recent experimental measurements2 made at normal incidence on a plasma generated by a classical Penning discharge.

Subsonic plasma aerodynamics using paraelectric and peristaltic electrohydrodynamic (EHD) effects

Summary form only given. The recent development of the one atmosphere uniform glow discharge plasma (OAUGDP) has made it possible to cover large areas, including the wings and fuselage of aircraft, with a thin layer of plasma at low energy cost. This plasma layer provides a purely electrohydrodynamic (EHD) coupling between the electric field and the neutral gas in the boundary layer. This coupling is strong enough to accelerate and manipulate the boundary layer and free stream flow, and does not require real currents to flow in a magnetic field, as do magnetohydrodynamic (MHD) approaches. The OAUGDP operates at the Stoletow point, at which the energy cost of an ion-electron pair is the minimum theoretically possible, 81 eV/ion electron pair in air. Other atmospheric plasmas, such as the arcs used for some MHD approaches, require 10,000-50,000 eV/ion electron pair to maintain the plasma. One EHD flow acceleration method is based on paraelectric EHD effects, the electrostatic analog of paramagnetism, in which a plasma is accelerated toward increasing electric field gradients, while dragging the neutral gas with it. In a second approach to flow acceleration, we are conducting experiments in the UT Plasma Sciences Laboratory designed to simultaneously generate a one atmosphere uniform glow discharge plasma (OAUGDP) while effecting peristaltic flow acceleration of atmospheric air.

Industrial applications of the one atmosphere uniform glow discharge plasma

Summary form only given. Over the past six years, we have developed at the UTK Plasma Sciences Laboratory a proprietary (to the UT Research Corporation) and patented technology for generating a one atmosphere uniform glow discharge plasma (OAUGDP), and also for industrial plasma processing applications of this discharge. A OAUGDP in air efficiently generates plasma active species, including ozone and atomic oxygen, without the requirement of a vacuum system or batch processing. The OAUGDP operates in a frequency band determined by the ion trapping mechanism provided that, for air, the electric field is above about 8.5 kV/cm. For proper values of gap distance, RF driving frequency, and rms voltage, the OAUGDP produces a uniform plasma without avalanches, streamers, or filamentary microdischarges. In the OAUGDP, the plasma characteristics, including the electron energy and density, are functions of time. This time dependence has been studied experimentally and by computer modeling for an atmospheric helium plasma.

Optimization of a continuous roll-to-roll reactor for atmospheric plasma surface treatment using a vaiable gap glow discharge plasma

Summary form only given. A new plasma reactor system has been developed to provide controlled and consistent surface treatment of textiles and films. These webs can be continuously and uniformly treated by proper control of gas flow, plasma parameters, fabric speed and tension. A main goal of this research is to relate independently-variable plasma parameters to deposition results. The exposure time required to make the surface wettable (having a contact angle less than 20 degrees) was drastically reduced in order for the fabric to be processed as quickly as possible. This was accomplished using a variable gap curved-to-flat plate geometry in combination with optimized plasma parameters. In this configuration, a one atmosphere uniform glow discharge plasma (OAUGDP)reg exists at the minimum gap, but transitions to a more filamentary glow discharge as the gap widens. This filamentation was minimized by proper gas flow, reducing any negative impact on processing results. The gas flow to the plasma volume was controlled with a porous ceramic diffuser in conjunction with a gas nozzle incorporating three degrees of freedom of motion. With this system, the optimum angle of laminar and axially uniform gas flow into the active volume of the plasma can be achieved. Contact angle measurements and dyeability tests were conducted to confirm proper operation

Flow acceleration in an electrohydrodynamic (EHD) duct using paraelectric and peristaltic effects of a one atmosphere uniform glow discharge plasma

Summary form only given. The plasma generated by a one atmosphere uniform glow discharge plasma (OAUGDP/sup /spl trade//) can be used in aerodynamics for boundary layer flow control, flow re-attachment and flow acceleration. Flow acceleration by an EHD duct can be based on paraelectric effects, in which plasma is accelerated by electric field gradients, and by peristaltic effects, in which the plasma is accelerated by a traveling electrostatic wave, or by a combination of these two mechanisms. In all cases, Lorentzian momentum transport by the plasma ions accelerates the neutral gas flow. Aerodynamic research with paraelectric plasma actuators currently uses a two-dimensional thin plasma layer formed by one or more sets of electrode strips. In this paper, we are conducting experiments to generate a three-dimensional EHD duct using paraelectric or combinations of paraelectric and peristaltic plasma actuators. These EHD duct configurations generate a higher electron and ion number density over a larger volume (as compared to the flat panel plasma actuators), thus transferring more momentum to the neutral gas. This improved momentum transfer accelerates the gas to higher velocities than a flat paraelectric panel. By using two RF power supplies operating at different frequencies, the paraelectrically induced flow velocity can reach more than 9 m/s. Addition of momentum by a peristaltic traveling wave increases the flow velocity still further. The performance of a three-dimensional EHD duct air flow accelerator makes it appealing for several aerodynamic applications.