Igor Alexeff

Biological decontamination by nonthermal plasmas

Nonthermal gaseous discharges have been found to be effective agents for biological decontamination/sterilization. The ability to generate these discharges at atmospheric pressure makes the decontamination process practical and inexpensive. In addition, the fact that the plasmas generated by such discharges are cold makes their use suitable for applications where medium preservation is desired. To fully understand the biophysical and biochemical processes induced by the interaction of living cells with gaseous discharges, a multidisciplinary approach is required. In this paper, we present two studies on bacteria killing obtained by two different discharges: a glow discharge at atmospheric pressure and an enhanced corona discharge at atmospheric pressure.

Experimental and theoretical results with plasma antennas

This report is a summary of an extensive research program on plasma antennas. We have found that plasma antennas are just as effective as metal antennas. In addition, they can transmit, receive, and reflect lower frequency signals while being transparent to higher frequency signals. When de-energized, they electrically disappear. Plasma noise does not appear to be a problem.

The resistive barrier discharge

Nonequilibrium, atmospheric pressure plasma discharges are increasingly being used in various novel applications. In many of these applications, a nonthermal, large volume, atmospheric pressure discharge, which can be generated in a practical and economical way is sought. We present a novel method to produce such plasma. This method uses a similar configuration to the dielectric barrier discharge. However, instead of a dielectric, a resistive layer is used to cover at least one of the electrodes. This allows the operation of the discharge in either DC or AC (60 Hz) modes.

A computer model

Summary form only given, as follows. Experiments have demonstrated that a plasma filling of a microwave tube can enhance the efficiency by a factor of 8. The plasma filling can neutralize space charge, cause electron beam focusing by ion space charge, and favourably modify the effective dielectric constant. However, the plasma ions can also exhibit an instability, causing frequency and amplitude jitter, and even termination of the electron beam. However, observations on a steady-state, gas-filled Orbitron Maser have demonstrated stable operation. A suggested stabilization effect is that ions are ejected continuously radically from the system before an instability can grow. Analytical models based on the simplified Budker-Buneman instability show that a slow transverse ion flush greatly reduces the growth rate of the instability. In this report, we present computations based on the computer code MAGIC that support the analytical calculations for the Budker-Buneman model. More advanced calculations for a prototype microwave tube are now in progress.

Recent results for plasma antennas

Plasma antennas are just as effective as metal antennas. They can transmit, receive, and reflect radio waves just as well as metal antennas. In addition, plasma generated noise does not appear to be a problem.

Use of atmospheric non-thermal plasma as a disinfectant for objects contaminated with methicillin-resistant Staphylococcus aureus

BACKGROUND Health care-associated infections because of methicillin-resistant strains of Staphylococcus aureus (MRSA) are increasing worldwide despite current infection control measures. Novel methods for disinfection of MRSA would be useful. METHODS We tested the effectiveness of atmospheric, non-thermal plasma discharge at killing S aureus, including USA300 strains, and at disinfecting experimentally contaminated hospital pagers. RESULTS Exposure of S aureus to plasma at different concentrations and for varying lengths of time resulted in up to a 4- to 5-log(10) kill on tryptic soy agar plates within 10 minutes and was not toxic to epithelial cells. USA300 strains of MRSA were more resistant to plasma-based killing than other tested strains. Disinfection of hospital pagers experimentally coated with clinically relevant amounts of MRSA could be achieved in as little as 30 seconds. CONCLUSION Generation of plasma is a promising method for disinfection of objects or surfaces that warrants further study in hospital settings. The USA300 strains of S aureus may be more resistant to disinfection than other strains.

Atmospheric pressure resistive barrier cold plasma for biological decontamination

Steady-state atmospheric pressure nonthermal plasmas can splendidly debilitate bacteria in liquids, gases, and on surfaces, as well as can disintegrate hazardous chemicals. The nonthermal resistive barrier gas discharge at atmospheric pressure is currently investigated for low-temperature sterilization purposes. We have carried out electrical, chemical, optical, and biological studies of the discharge, with the intent of identifying the chemically and biologically active species produced. In this paper, we have demonstrated that effective decontamination can be achieved without causing any damage to the active media.

Reflection and absorption of ion‐acoustic waves in a density gradient

One problem with ion‐acoustic waves is that sometimes they are observed to be reflected from discharge tube walls, and sometimes to be absorbed. Theoretical computation reveals that a velocity gradient produced by a density gradient plays a significant role in the reflection. The velocity gradient produces a subsonic−supersonic transition and long wavelength waves are reflected before reaching the transition while short wavelength waves penetrate over the transition and are absorbed in the supersonic flow plasma.

Linear ion acoustic waves in a density gradient

Both the experimental and theoretical behavior of linear ion acoustic waves in density gradients formed in a collisionless discharge plasma have been studied. The experiment and the theory both show a strong spatial growth of the density perturbation produced by the wave when the wave propagates in the direction of increasing density and a damping when the wave propagates in the direction of decreasing density. Theoretically, the growth and damping rates are found to be proportional to n01/2, where n0 is the local unperturbed density. By using the measured density profile, good agreement is found between experiment and the linearized fluid theory. Although the wave amplitude n1, itself, decreases as the wave propagates into a region of lower density, the relative amplitude n1/n0 increases. This can be expected to lead to wave steepening and shock‐like behavior, as noted previously by others. The work reported here is mainly concerned with the range where the wavelength is smaller than the characteristic l...

The uniform, steady-state atmospheric pressure DC plasma

We have developed and tested a steady-state DC plasma discharge apparatus that operates at atmospheric pressure. The important feature is a ceramic discharge electrode that prevents the diffuse discharge from contracting into an arc. The apparatus has been used successfully in the destruction of microorganisms.