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Plasma, Volume 2, Issue 1 (March 2019)

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Open AccessArticle
A Computationally Assisted Ar I Emission Line Ratio Technique to Infer Electron Energy Distribution and Determine Other Plasma Parameters in Pulsed Low-Temperature Plasma
Plasma 2019, 2(1), 65-76; https://doi.org/10.3390/plasma2010007
Received: 11 February 2019 / Revised: 7 March 2019 / Accepted: 14 March 2019 / Published: 21 March 2019
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Abstract
In the post-transient stage of a 1-Torr pulsed argon discharge, a computationally assisted diagnostic technique is demonstrated for either inferring the electron energy distribution function (EEDF) if the metastable-atom density is known (i.e., measured) or quantitatively determining the metastable-atom density if the EEDF [...] Read more.
In the post-transient stage of a 1-Torr pulsed argon discharge, a computationally assisted diagnostic technique is demonstrated for either inferring the electron energy distribution function (EEDF) if the metastable-atom density is known (i.e., measured) or quantitatively determining the metastable-atom density if the EEDF is known. This technique, which can be extended to be applicable to the initial and transient stages of the discharge, is based on the sensitivity of both emission line ratio values to metastable-atom density, on the EEDF, and on correlating the measurements of metastable-atom density, electron density, reduced electric field, and the ratio of emission line pairs (420.1–419.8 nm or 420.1–425.9 nm) for a given expression of the EEDF, as evidenced by the quantitative agreement between the observed emission line ratio and the predicted emission line ratio. Temporal measurement of electron density, metastable-atom density, and reduced electric field are then used to infer the transient behavior of the excitation rates describing electron-atom collision-induced excitation in the pulsed positive column. The changing nature of the EEDF, as it starts off being Druyvesteyn and becomes more Maxwellian later with the increasing electron density, is key to interpreting the correlation and explaining the temporal behavior of the emission line ratio in all stages of the discharge. Similar inferences of electron density and reduced electric field based on readily available diagnostic signatures may also be afforded by this model. Full article
(This article belongs to the Special Issue Latest Developments in Pulsed Low-Temperature Plasmas)
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Open AccessFeature PaperReview
Experiments Designed to Study the Non-Linear Transition of High-Power Microwaves through Plasmas and Gases
Plasma 2019, 2(1), 51-64; https://doi.org/10.3390/plasma2010006
Received: 31 January 2019 / Revised: 28 February 2019 / Accepted: 4 March 2019 / Published: 8 March 2019
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Abstract
The interaction of powerful sub-picosecond timescale lasers with neutral gas and plasmas has stimulated enormous interest because of the potential to accelerate particles to extremely large energies by the intense wakefields formed and without being limited by high accelerating gradients as in conventional [...] Read more.
The interaction of powerful sub-picosecond timescale lasers with neutral gas and plasmas has stimulated enormous interest because of the potential to accelerate particles to extremely large energies by the intense wakefields formed and without being limited by high accelerating gradients as in conventional accelerator cells. The interaction of extremely high-power electromagnetic waves with plasmas is though, of general interest and also to plasma heating and wake-field formation. The study of this subject has become more accessible with the availability of sub-nanosecond timescale GigaWatt (GW) power scale microwave sources. The interaction of such high-power microwaves (HPM) with under-dense plasmas is a scale down of the picosecond laser—dense plasma interaction situation. We present a review of a unique experiment in which such interactions are being studied, some of our results so far including results of our numerical modeling. Such experiments have not been performed before, self-channeling of HPM through gas and plasma and extremely fast plasma electron heating to keV energies have already been observed, wakefields resulting from the transition of HPM through plasma are next and more is expected to be revealed. Full article
(This article belongs to the Special Issue High-Power Microwave and Plasma Interactions)
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Open AccessArticle
Influence of the On-time on the Ozone Production in Pulsed Dielectric Barrier Discharges
Plasma 2019, 2(1), 39-50; https://doi.org/10.3390/plasma2010005
Received: 12 January 2019 / Revised: 22 February 2019 / Accepted: 25 February 2019 / Published: 4 March 2019
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Abstract
Understanding the production mechanisms of ozone and other reactive species in atmospheric pressure dielectric barrier discharges (DBDs) has become increasingly important for the optimization and commercial success of these plasma devices in emerging applications, such as plasma medicine, plasma agriculture, and plasma catalysis. [...] Read more.
Understanding the production mechanisms of ozone and other reactive species in atmospheric pressure dielectric barrier discharges (DBDs) has become increasingly important for the optimization and commercial success of these plasma devices in emerging applications, such as plasma medicine, plasma agriculture, and plasma catalysis. In many of these applications, input power modulation is exploited as a means to maintain a low gas temperature. Although the chemical pathways leading to ozone production/destruction and their strong temperature dependence are relatively well understood, the effect of the on-time duration on the performance of these modulated DBDs remains largely unexplored. In this study, we use electrical and optical diagnostics, as well as computational methods, to assess the performance of a modulated DBD device. The well-established Lissajous method for measuring the power delivered to the discharge is not suitable for modulated DBDs because the transients generated at the beginning of each pulse become increasingly important in short on-time modulated plasmas. It is shown that for the same input power and modulation duty-cycle, shorter on-time pulses result in significantly enhanced ozone production, despite their operation at slightly higher temperatures. The key underpinning mechanism that causes this counter-intuitive observation is the more efficient net generation rate of ozone during the plasma on-time due to the lower accumulation of NO2 in the discharge volume. Full article
(This article belongs to the Special Issue Latest Developments in Pulsed Low-Temperature Plasmas)
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Open AccessArticle
Generators of Atmospheric Pressure Diffuse Discharge Plasma and Their Use for Surface Modification
Plasma 2019, 2(1), 27-38; https://doi.org/10.3390/plasma2010004
Received: 29 January 2019 / Revised: 25 February 2019 / Accepted: 26 February 2019 / Published: 28 February 2019
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Abstract
Studies of the properties of runaway electron preionized diffuse discharges (REP DDs) and their possible use have been carried out for more than 15 years. Three experimental setups generating a low-temperature atmospheric-pressure plasma and differing in the geometry of a discharge gap were [...] Read more.
Studies of the properties of runaway electron preionized diffuse discharges (REP DDs) and their possible use have been carried out for more than 15 years. Three experimental setups generating a low-temperature atmospheric-pressure plasma and differing in the geometry of a discharge gap were developed. They allow the treatment of surfaces of different materials with an area of several tens of square centimeters. A diffuse discharge plasma was formed in the pulse–periodic mode by applying negative voltage pulses with an amplitude of several tens of kilovolts and a duration of 4 ns to a discharge gap with sharply non-uniform electric field strength distribution. This paper presents experimental results of the study of the surface layer microstructure of copper and steel specimens of different sizes after treatment with the REP DD plasma in nitrogen flow mode and nitrogen circulation mode in the discharge chamber. It was shown that after 105 discharge pulses, the carbon concentration decreases and a disoriented surface layer with a depth of up to 200 nm is formed. Moreover, the results of X-ray phase analysis did not reveal changes in the phase composition of the surface of copper specimens. However, as a result of surface treatment with the REP DD plasma, the copper lattice becomes larger and the microstress increases. Full article
(This article belongs to the Special Issue High-Power Microwave and Plasma Interactions)
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Open AccessArticle
Radial Kick in High-Efficiency Output Structures
Plasma 2019, 2(1), 15-26; https://doi.org/10.3390/plasma2010003
Received: 14 January 2019 / Revised: 28 January 2019 / Accepted: 19 February 2019 / Published: 22 February 2019
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Abstract
We have developed an analytical approach that predicts radial oscillation near the aperture of a pillbox cavity. In addition, it provides natural criteria for the design of a tapered guiding magnetic field in the output section of a relativistic klystron amplifier, as well [...] Read more.
We have developed an analytical approach that predicts radial oscillation near the aperture of a pillbox cavity. In addition, it provides natural criteria for the design of a tapered guiding magnetic field in the output section of a relativistic klystron amplifier, as well as that of a travelling wave tube, in a method that is self-consistent with the dynamics of the electrons. Full article
(This article belongs to the Special Issue High-Power Microwave and Plasma Interactions)
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Open AccessEditorial
Acknowledgement to Reviewers of Plasma in 2018
Published: 18 January 2019
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Abstract
Rigorous peer-review is the corner-stone of high-quality academic publishing [...] Full article
Open AccessArticle
Gyroton with the Corrugated Resonator
Plasma 2019, 2(1), 1-13; https://doi.org/10.3390/plasma2010001
Received: 23 November 2018 / Revised: 27 December 2018 / Accepted: 3 January 2019 / Published: 11 January 2019
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Abstract
A new type of high-power electronic device—a gyroton with a corrugated resonator—is described and investigated. Spatial bunching of the electron beam does not occur in this device, however, highly efficient electron beam power conversion into the rotating electromagnetic field power is possible. The [...] Read more.
A new type of high-power electronic device—a gyroton with a corrugated resonator—is described and investigated. Spatial bunching of the electron beam does not occur in this device, however, highly efficient electron beam power conversion into the rotating electromagnetic field power is possible. The rectilinear electron beam deviates from the axis by the slow TM11 wave, then it gives up longitudinal energy to the same wave with more than 78% efficiency, and an output power up to 30 MW. The developed mathematical model of the interaction of the relativistic electron beam with an irregular circular waveguide and resonator fields presented in this article can be used to calculate and optimize the processes occurring in various microwave electronic devices, such as gyrotrons, gyrotons, TWT, Gyro-TWT, and BWT. Full article
(This article belongs to the Special Issue High-Power Microwave and Plasma Interactions)
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