Mounir Laroussi

Room-temperature atmospheric pressure plasma plume for biomedical applications

As low-temperature nonequilibrium plasmas come to play an increasing role in biomedical applications, reliable and user-friendly sources need to be developed. These plasma sources have to meet stringent requirements such as low temperature (at or near room temperature), no risk of arcing, operation at atmospheric pressure, preferably hand-held operation, low concentration of ozone generation, etc. In this letter, we present a device that meets exactly such requirements. This device is capable of generating a cold plasma plume several centimeters in length. It exhibits low power requirements as shown by its current-voltage characteristics. Using helium as a carrier gas, very little ozone is generated and the gas temperature, as measured by emission spectroscopy, remains at room temperature even after hours of operations. The plasma plume can be touched by bare hands and can be directed manually by a user to come in contact with delicate objects and materials including skin and dental gum without causing any heating or painful sensation.

Dynamics of an atmospheric pressure plasma plume generated by submicrosecond voltage pulses

Nonequilibrium plasmas driven by submicrosecond high voltage pulses have been proven to produce high-energy electrons, which in turn lead to enhanced ionization and excitations. Here, we describe a device capable of launching a cold plasma plume in the surrounding air. This device, “the plasma pencil,” is driven by few hundred nanosecond wide pulses at repetition rates of a few kilohertz. Correlation between current-voltage characteristics and fast photography shows that the plasma plume is in fact a small bulletlike volume of plasma traveling at unusually high velocities. A model based on photoionization is used to explain the propagation kinetics of the plasma bullet under low electric field conditions.

On atmospheric-pressure non-equilibrium plasma jets and plasma bullets

Atmospheric-pressure non-equilibrium plasma jets (APNP-Js), which generate plasma in open space rather than in a confined discharge gap, have recently been a topic of great interest. In this paper, the development of APNP-Js will be reviewed. Firstly, the APNP-Js are grouped based on the type of gas used to ignite them and their characteristics are discussed in detail. Secondly, one of the most interesting phenomena of APNP-Js, the ?plasma bullet?, is discussed and its behavior described. Thirdly, the very recent developments on the behavior of plasma jets when launched in a controlled environment and pressure are also introduced. This is followed by a discussion on the interaction between plasma jets. Finally, perspectives on APNP-J research are presented.

Sterilization of contaminated matter with an atmospheric pressure plasma

The primary methods now used to sterilize contaminated media (infectious waste, tools, liquids, ...) are exposure to UV radiation, incineration, or autoclaving. These methods have recently raised public controversies concerning their environmental effects and other health issues. In an attempt to eliminate these drawbacks, new approaches based on different technologies are being investigated. Irradiation by electron beam is an example of such new sterilization means. This paper describes a new sterilization technique which has recently been developed at the Plasma Science Laboratory of the University of Tennessee. This technique involves the generation and use of a glow discharge plasma at atmospheric pressure. The fact that no pressurized or vacuum system is needed in this apparatus makes this sterilization method practical, economical, and technically very attractive. The plasma, in which the medium to be sterilized is immersed, is generated between two insulated metal plate electrodes powered by a low-frequency RF supply. Inside the plasma, the medium is constantly bombarded by charged particles, active free radicals, and radiation (including UV radiation). It is found that an exposure of a few minutes is sufficient to destroy the microorganisms living in the exposed medium, without damaging the medium itself.

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.

Numerical calculation of the reflection, absorption, and transmission of microwaves by a nonuniform plasma slab

The reflection, absorption, and transmission of microwaves by a magnetized, steady-state, two-dimensional, nonuniform plasma slab is studied. A discussion on the effect of various plasma parameters on the reflected power, absorbed power, and transmitted power is presented. The nonuniform plasma slab is modeled by a series of subslabs. Even though it is assumed that the number density is constant in each subslab, the overall number density profile across the whole slab follows a parabolic function. The partial reflection coefficient at each subslab boundary is computed along with the absorption at each subslab. The total reflected, absorbed, and transmitted powers are then deduced and their functional dependence on the number density, collision frequency, and angle of propagation is studied. >

Effects of nonequilibrium atmospheric pressure plasmas on the heterotrophic pathways of bacteria and on their cell morphology

To date, most research on the interaction of nonequilibrium, atmospheric pressure plasma discharges with bacteria has concentrated on the germicidal effects. Therefore, published results deal mainly with killing efficacy and little attention is given to physical mechanisms and biochemical pathways and their potential alterations when cells of microorganisms are exposed to the plasma. In this letter, an attempt to investigate the effects of plasma exposure on the biochemical pathways of bacteria is presented. In addition, using electron microscopy, we investigate if any gross morphological changes take place when cells are exposed to a lethal dose of plasma. We are testing the hypothesis that disruption of the cell membrane, sometimes to the point of cell lysis, is the mechanism whereby plasma kills cells.

Power consideration in the pulsed dielectric barrier discharge at atmospheric pressure

Nonequilibrium, atmospheric pressure discharges are rapidly becoming an important technological component in material processing applications. Amongst their attractive features is the ability to achieve enhanced gas phase chemistry without the need for elevated gas temperatures. To further enhance the plasma chemistry, pulsed operation with pulse widths in the nanoseconds range has been suggested. We report on a specially designed, dielectric barrier discharge based diffuse pulsed discharge and its electrical characteristics. Two current pulses corresponding to two consecutive discharges are generated per voltage pulse. The second discharge, which occurs at the falling edge of the voltage pulse, is induced by the charges stored on the electrode dielectric during the initial discharge. Therefore, the power supplied to ignite the first discharge is partly stored to later ignite a second discharge when the applied voltage decays. This process ultimately leads to a much improved power transfer to the plasma.

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.

Finite element analysis of ring-shaped emission profile in plasma bullet

In this study, we focus on the mechanisms of ring-shaped emission patterns observed in a plasma bullet.1: Our model is based on a fluid model with the local field approximation in ID cylindrical coordinates, corresponding to a cross-section of a plasma bullet. An expected concentration gradient of humid air is assumed to be present due to diffusion of air into helium gas flow. The current model is almost identical to our previous report2. The major difference is that uniform pulselike electric field is given perpendicular to the simulation domain. The pulse width and repetition rate are determined based on experimental conditions. The magnitude of the electric field was chosen so that a periodic steady state solution can be obtained. We also performed spectroscopic measurements to investigate the structure of the plasma bullets and to compare with the simulation results. Figure 1 shows comparison of spatially-resolved emission profiles from nitrogen second positive systems between experiment and simulation. Light emission from nitrogen clearly shows an off-centered peak (ring-shaped profile) in both experiment and simulation. Our simulation results indicate that diffusion of air (nitrogen) into the helium flow plays a key role. Penning ionization between helium metastables and nitrogen generate the ring-shaped emission profile.