J. Reece Roth

Aerodynamic flow acceleration using paraelectric and peristaltic electrohydrodynamic effects of a One Atmosphere Uniform Glow Discharge Plasma

The development of the One Atmosphere Uniform Glow Discharge Plasma has made it possible to cover the wings and fuselage of aircraft with a thin layer of glow discharge plasma at low energy cost. This plasma layer provides, through Lorentzian collisions, a purely electrohydrodynamic coupling between an electric field and the neutral gas in the boundary layer. This coupling is strong enough to cause aerodynamically significant acceleration and manipulation of the boundary layer and free stream flow, including re-attachment of flow to an airfoil at high angles of attack, and the peristaltic induction of neutral gas flow by a traveling electrostatic wave on the surface of a flat plate.

The physics and phenomenology of One Atmosphere Uniform Glow Discharge plasma (OAUGDP) reactors for surface treatment applications

In this paper, we present data on the physics and phenomenology of plasma reactors based on the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP™) that are useful in optimizing the conditions for plasma formation, uniformity and surface treatment applications. It is shown that the real (as opposed to reactive) power delivered to a reactor is divided between dielectric heating of the insulating material and power delivered to the plasma available for ionization and active species production. A relationship is given for the dielectric heating power input as a function of the frequency and voltage at which the OAUGDP™ discharge is operated.

Use of a one atmosphere uniform glow discharge plasma to kill a broad spectrum of microorganisms

The medical, industrial, and food processing industries are constantly in search of new technologies to provide improved methods of sterilization and pasteurization. Proposed techniques must deal with such problems as thermal sensitivity and destruction by heat, formation of toxic by-products, cost, and inefficiency in performance. We report results from a newly invented plasma source, a one atmosphere uniform glow discharge plasma (OAUGDP), which is capable of operating at atmospheric pressure in air and providing antimicrobial active species at room temperature. OAUGDP exposures have reduced log numbers of bacteria (Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa), bacterial endospores (Bacillus subtilis and Bacillus pumilus), and various yeast and bacterial viruses on a variety of surfaces. These surfaces included polypropylene, filter paper, paper strips, solid culture media, and glass. Experimental results showed at least a ⩾5 log10 colony forming units (CFU) reduction in bacteria...

Sterilization and plasma processing of room temperature surfaces with a one atmosphere uniform glow discharge plasma (OAUGDP)

A technique for generating active species with the one atmosphere uniform glow discharge plasma (OAUGDP) has been developed and tested in a wide range of potential plasma processing applications, including the sterilization and decontamination of surfaces. The OAUGDP is a non-thermal plasma with the classical characteristics of a low pressure DC normal glow discharge that operates in air (and other gases) at atmospheric pressure. In addition to directly exposing webs and workpieces to active species by immersion or at the plasma boundary of a parallel-plate reactor, we have shown that active species capable of sterilization can be convected at near room temperature to a remote exposure chamber. No vacuum system or batch processing is necessary, and a wide range of applications can be accommodated. This technology is simple, cost-effective and suitable for online treatment of webs and such three-dimensional workpieces as medical instruments. We will report the use of an air OAUGDP to sterilize a broad range of microorganisms on a variety of surfaces, and in several distinct applications. These include a remote exposure reactor to sterilize large workpieces 20 cm or more from the plasma-generating region, and a sterilizable air filter.

Surface Modification of Fabrics Using a One-Atmosphere Glow Discharge Plasma to Improve Fabric Wettability

In industrial applications, a steady-state glow discharge capable of operating at one atmosphere would allow many plasma-related surface modification processes to be done on the production line, rather than in expensive vacuum systems that force batch processing. In this paper, we report some encouraging results from the plasma surface treatment of polypropylene meltblown nonwovens in the UTK one-atmosphere glow discharge plasma reactor. This reactor generates a large volume (up to 2.4 liters), low power (less than 150 watts), uniform glow discharge plasma in a parallel plate configuration with oval electrodes of 213 cm2 face area, the lower electrode being covered with a 3.2 mm thick insulating Pyrex surface. The plates are set up in an enclosed box that makes it possible to control the working gas used, and the spacing between the plates can be varied. This reactor is energized by a custom-made high impedance kilohertz power supply capable of supplying up to 5 kilowatts of kilohertz power at RMS voltages up to 10 kV, and over a frequency range from 1 to 100 kHz. Exposing a wide variety of polymer fabrics reveals that the wettability, wickability, printability, and surface contact angle of the materials are significantly changed in a direction that may lead to new uses for these materials.

Potential industrial applications of the one atmosphere uniform glow discharge plasma operating in ambient air

The majority of industrial plasma processing is conducted with glow discharges at pressures below 10 Torr. This tends to limit such applications to high value workpieces, 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 1 atm and in air. The one atmosphere uniform glow discharge plasma (OAUGDP®) has these capabilities. As a normal glow discharge, the OAUGDP® can operate with maximum electrical efficiency at the Stoletow point, where the energy input per ion-electron pair is a minimum. This paper will survey exploratory investigations at the University of Tennessee’s Plasma Sciences Laboratory of seven potential industrial applications of the OAUGDP® which can be conducted at 1 atm and at room temperature with air as the working gas.

FLOW FIELD MEASUREMENTS OF PARAELECTRIC, PERISTALTIC, AND COMBINED PLASMA ACTUATORS BASED ON THE ONE ATMOSPHERE UNIFORM GLOW DISCHARGE PLASMA (OAUGDP)

The EHD approaches tested in the past included drag reduction from the ion wind associated with atmospheric corona discharges, but the induced velocity was small, of the order of one meter per second, and the drag reduction effect weak 5, 6 . In this paper, we extend previous results to document with Pitot tube measurements the flow fields associated with both paraelectric and peristaltic plasma actuators, and with a combination of both in which paraelectric flow acceleration provides a boost to increase the peristaltic plasma flow velocity. We have found that the flow field of the plasma actuators can be modeled as a classical Glauert wall jet, and have compared the plasma actuator flow field to that of the Glauert wall jet. In addition to documenting these EHD flow fields, we report on exploratory research designed to improve the electrode configuration of both peristaltic and paraelectric plasma actuators, and to make the induced flow velocities laminar rather than turbulent. Finally, we report tests made on a 25x25 cm panel covered with plasma actuator electrode strips to determine the effects on the actuator plasma of water spray, walking on the actuator panel, and direct contact (touching) with the panel while energized. The development of the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) 7, 8 has made it possible to install on the wings and fuselage of aircraft mechanically robust glow discharge plasma actuators that require only a few watts per linear foot. These actuators can provide, through Lorentzian collisions, a purely electrohydrodynamic (EHD) coupling between the electric field in the plasma and the neutral gas in the boundary layer

Back-scattering cross-section of a cylindrical uniform plasma column

In monostatic radar applications it is the signal back to the source that is responsible for target detection. The back-scattering cross-section allows one to calculate the amount of power reflected back in the direction of incidence. In this paper, we develop theoretically and calculate computationally the back-scattering cross-section of a cylindrical column of magnetized plasma with a uniform number density. The effect of the plasma number density and of the collision frequency are investigated.

Strength, surface energy, and ageing of meltblown and electrospun nylon and polyurethane (PU) fabrics treated by a one atmosphere uniform glow discharge plasma (OAUGDP)

The One Atmosphere Uniform Glow Discharge Plasma (OAUGDP™) generates a normal glow electrical discharge at 1 atmosphere in air and other gases. This plasma has been used to treat meltblown and electrospun nylon and polyurethane (PU) fabrics, and has produced an increase in the surface energy/wettability in all cases. Nylon and polyurethane (PU) nanofiber fabrics can be exposed to the OAUGDP™ for up to 10 seconds, long enough to greatly increase their surface energy without significant degradation of strength. After 10 seconds of plasma exposure, the electrospun (but not the meltblown) fabric strength and color degrade to a noticeable extent. It was found that prior to plasma exposure, the strength per unit areal weight of electrospun nanofiber fabrics was (for nylon) up to ten times that of the meltblown material. We also found that the surface energy of meltblown nylon could be increased to 70 dynes cm 1 by 5 seconds of OAUGDP™ exposure, that it was durable at this level for 6 months, and that the surface energy dropped from 70 to 64 dynes cm 1 only after more than 1 year post-exposure. We also report the effects of OAUGDP™ exposure on three surface characteristics of meltblown nylon and PU fabrics: (1) the strength of the fabric as a function of the plasma exposure time; (2) the surface energy of the fabric as a function of the plasma exposure time; and (3) the surface energy/wettability of the fabric as a function of time after exposure (ageing effect). We also describe the treatment of nanofiber fabrics using recent improvements in OAUGDP™ reactor technology

Paired Comparison Tests of the Relative Signal Detected by Capacitive and Floating Langmuir Probes in Turbulent Plasma from 0.2 to 10 MHz

Paired comparison measurements of the spectrum of electrostatic potential fluctuations in a steady state turbulent plasma confined in a magnetic mirror geometry have been made with capacitive and floating Langmuir probes over the frequency range from 0.2 to 10.0 MHz. For the experimental conditions investigated (5×107≤ne≤5×108/cm3, 8≤Te≤38 eV, 350≤Ti≤930 eV, Bmax=1.0 T), no significant difference in the relative frequency response was observed below 4.0 MHz. At about this frequency, however, the signal detected by the floating Langmuir probe dropped off relative to that of the capacitive probe. The source resistance of the turbulent fluctuations sensed by the Langmuir probe was about 400 Ω. At higher frequencies (from 7.0 to 10.0 MHz) a signal was detected by the floating Langmuir probe that was not detected by the capacitive probe. This spurious signal may be confused with the turbulent fluctuations of the plasma in the absence of paired comparison tests.