Water in atmospheric-pressure helium rf plasmas

Radio frequency (rf) plasmas operated at atmospheric pressure have received great attention in recent years for their potential use in many scientific and industrial applications. The optical emission profile of these atmospheric pressure rf discharges typically presents two bright layers, one above each of the electrodes. Although in the low-pressure regime bright layers near the electrodes are typically associated with the so-called gamma mode, these layers are observed in the alpha mode at atmospheric pressure and only after a significant increase in current, the transition into the gamma mode takes place. In the gamma mode, the bright layers are found to light up in an alternating fashion, corresponding to the excitation of radiative states by avalanches across the sheaths. On the other hand, in the alpha mode, the bright layers light up simultaneously mostly as a result of the acceleration of bulk electrons in the expanding and retreating sheathbulk boundaries

Water in low-temperature atmospheric-pressure plasmas

pressure plasmas has received growing attention in recent years for the potential use of these plasmas in biomedical applications, air treatment and chemical synthesis. As oxygen, H2O is a good precursor of reactive oxygen species (ROS) and the two can be combined to create cocktails of ROS (O, OH, O3, 1O2, OOH and H2O2) of different compositions. These plasmas tend to be electronegative and display interesting dynamics, particularly when created in small gaps. From a practical point of view, it is important to understand the chemical pathways leading to the production of the biologically relevant ROS, as this will provide guidelines for the optimization of the plasma sources for a particular application

Special Issue on Plenary and Invited Papers From ICOPS 2012

The 39th International Conference on Plasma Science (ICOPS) was held in Edinburgh, Scotland in July 2012. This was the third time that the conference was organized outside North America, the previous ones being in Karlsruhe (Germany) in 2008 and Jeju (S. Korea) in 2003. The technical programme combined seven technical areas of plasma science and technology covering a wide range of topics. The conference featured a wide range of advances in innovative plasma and beam science and applications, and served as a venue for an international community to meet and discuss their ideas and research results. More than 800 abstracts were received in 35 different topical areas, with more than half the papers originating outside the United State. The conference was attended by over 600 delegates and enjoyed the participation of over 200 registered students

Self-organized filaments, striations and other nonuniformities in nonthermal atmospheric microwave excited microdischarges

Self-organized filaments, stationary striations, and spherical nonuniformities have been observed in atmospheric argon microdischarges sustained within a 120-µm gap between two coplanar electrodes. The microdischarges are driven by opposite ends of a half-wave split-ring resonator constructed using microstrip transmission lines. The microdischarge generator operates at 900 MHz using 0.5–2 W of power

Rotational, vibrational, and excitation temperatures of a microwave-frequency microplasma

Integration of microplasma sources in portable systems sets constraints in the amount of power and vacuum levels employed in these plasma sources. Moreover, in order to achieve good power efficiency and prevent physical deterioration of the source, it is desirable to keep the discharge temperature low. In this paper, the thermal characteristics of an atmospheric argon discharge generated with a low-power microwave plasma source are investigated to determine its possible integration in portable systems. The source is based on a microstrip split-ring resonator and is similar to the one reported by Iza and Hopwood, 2003. Rotational, vibrational, and excitation temperatures are measured by means of optical emission spectroscopy. It is found that the discharge at atmospheric pressure presents a rotational temperature of ~300 K, while the excitation temperature is ~0.3 eV (~3500 K). Therefore, the discharge is clearly not in thermal equilibrium. The lowrotational temperature allows for efficient air-cooled operation and makes this device suitable for portable applications including those with tight thermal specifications such as treatment of biological materials

Low-power microwave plasma source based on a microstrip split-ring resonator

Microplasma sources can be integrated into portable devices for applications such as bio-microelectromechanical system sterilization, small-scale materials processing, and microchemical analysis systems. Portable operation, however, limits the amount of power and vacuum levels that can be employed in the plasma source. This paper describes the design and initial characterization of a low-power microwave plasma source based on a microstrip split-ring resonator that is capable of operating at pressures from 0.05 torr (6.7 Pa) up to one atmosphere. The plasma source’s microstrip resonator operates at 900 MHz and presents a quality factor of Q = 335. Argon and air discharges can be self-started with less than 3Win a relatively wide pressure range. An ion density of 1.3 X 10(11) cm-3 in argon at 400 mtorr (53.3 Pa) can be created using only 0.5W. Atmospheric discharges can be sustained with 0.5 W in argon. This low power allows for portable air-cooled operation. Continuous operation at atmospheric pressure for 24 h in argon at 1 W shows no measurable damage to the source

Field emission and lifetime of microcavity plasma

Microplasmas with cylindrical hollow cathode have been studied by means of two-dimensional particle-in-cell/Monte-Carlo collision (PIC/MCC) simulations. For a given input power, the onset of field emission from the cathode surface caused by the strong electric field generated in these discharges leads to a reduction of the discharge voltage and an increase in plasma density. The plasma density profile can be strongly influenced by localized enhancements of the electric field, which in turn will affect the erosion profile of the cathode. The cathode erosion profile is predicted in this work by combining the ion kinetic information obtained from the PIC/MCC simulation with the sputtering yield computed using SRIM [J. F. Ziegler, J. P. Biersack, and M. D. Ziegler, SRIM: The Stopping and Range of Ions in Matter (Lulu, Chester, 2008)]. The entrance of the cathode and the center region are the areas most susceptible to ion-induced damage. The lifetime of the device, however, can be extended by operating the device at high pressure and by reducing the operating voltage by means of field emission and/or additional electron emitting processes from the cathod

Fluorescence probe for determining the ozone dose delivered by plasmas

Plasma composition is typically studied by absorption and emission spectroscopy, mass spectrometry and computational studies. While these techniques provide valuable information about the chemical species in the gas phase, in many applications it is desirable to have a direct measurement of the dose of chemical species delivered to a particular target. In this work, we will use a fluorescent chemical probe in order to characterize actual flux of ozone experienced by a target exposed to plasma

Plasmas for organic synthesis and chemical probes for plasma diagnostics

Although organic chemistry plays a critical role in many plasma applications, there is room for further cross-fertilization between the two disciplines. Here we explore two possible avenues: (1) plasma physics as a new tool for the organic chemist and (2) organic compounds as diagnostics for the plasma physicist

Particle-in-cell Monte Carlo and fluid simulations of argon-oxygen plasma : comparisons with experiments and validations

Particle-in-cell Monte Carlo collision (PIC-MCC) and fluid simulations of argon-oxygen plasmas in capacitively and inductively coupled plasma reactors are presented. Potential profiles and electron/ ion kinetic information such as electron/ion energy distributions and temperatures are compared with experimental data as well as with other analytical and numerical results. One-dimensional PIC-MCC simulations compare favorably with experimental data obtained in capacitively coupled reactors over a wide range of pressure and power. Two-dimensional fluid simulations of capacitive discharges differs from the results of PIC-MCC simulations as nonlocal effects play an important role in these discharges. Fluid simulations as nonlocal inductively coupled plasmas, however, agree favorably with experimental observations