| 1. |
- Bao, Yupan, et al.
(författare)
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Single-shot 3D imaging of hydroxyl radicals in the vicinity of a gliding arc discharge
- 2021
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Ingår i: Plasma Sources Science and Technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 30:4
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Tidskriftsartikel (refereegranskat)abstract
- Chemical processing by plasma is utilized in many applications. Plasma-related studies, however, are challenging to carry out due to plasmas' transient and unpredictable behavior, excessive luminosity emission, 3D complexity and aggressive chemistry and physiochemical interactions that are easily affected by external probing. Laser-induced fluorescence is a robust technique for non-intrusive investigations of plasma-produced species. The hydroxyl radical (OH) is an interesting molecule to target, as it is easily produced by plasmas in humid air. In this letter, we present 3D distributions of ground state OH radicals in the vicinity of a glow-type gliding arc plasma. Such radical distributions, with minimal plasma emission, are captured instantaneously in one single camera acquisition by combining structured laser illumination and a lock-in based imaging analysis method called FRAME. The orientation of the plasma discharge can be reconstructed from the 3D data matrix, which can then be used to calculate 2D distributions of ground state OH radicals in a plane perpendicular to the orientation of the plasma channel. Our results indicate that OH distributions around a gliding arc are strongly affected by gas dynamics. We believe that the ability to instantaneously capture 3D transient molecular distributions in a plasma discharge, with minimal plasma emission interference, will have a strong impact on the plasma community for in-situ investigations of plasma-induced chemistry and physics.
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| 2. |
- Cont-Bernard, Davide Del, et al.
(författare)
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Femtosecond two-photon laser-induced fluorescence imaging of atomic hydrogen in a laminar methane-air flame assisted by nanosecond repetitively pulsed discharges
- 2020
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Ingår i: Plasma Sources Science and Technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 29:6
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Tidskriftsartikel (refereegranskat)abstract
- Sustainable and low-emission combustion is in need of novel schemes to enhance combustion efficiency and control to meet up with new emission standards and comply with varying quality of renewable fuels. Plasma actuation is a promising candidate to achieve this goal but few detailed experiments have been carried out that target how specific combustion and plasma related species are affected by the coupling of plasma and combustion chemistry. Atomic hydrogen is such a species that here is imaged by using the two-photon absorption laser induced fluorescence (TALIF) technique as an atmospheric pressure methane-air flame is actuated by nanosecond repetitively pulsed (NRP) discharges. Atomic hydrogen is observed both in the flame and in the discharge channel and plasma actuation results in a wide modification of the flame shape. A local 50% increase of fluorescence occurs at the flame front where it is crossed by the discharge. Atomic hydrogen in the discharge channel in the fresh-gases is found to decay with a time constant of about 2.4 μs. These results provide new insights on the plasma flame interaction at atmospheric pressure that can be further used for cross-validation of numerical calculations.
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| 3. |
- Brenning, Nils, et al.
(författare)
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A unified treatment of self-sputtering, process gas recycling, and runaway for high power impulse sputtering magnetrons
- 2017
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Ingår i: Plasma sources science & technology. - : Institute of Physics (IOP). - 0963-0252 .- 1361-6595. ; 26:12
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Tidskriftsartikel (refereegranskat)abstract
- The combined processes of self-sputter (SS)-recycling and process gas recycling in high power impulse magnetron sputtering (HiPIMS) discharges are analyzed using the generalized recycling model (GRM). The study uses experimental data from discharges with current densities from the direct current magnetron sputtering range to the HiPIMS range, and using targets with self-sputter yields Y-SS from approximate to 0.1 to 2.6. The GRM analysis reveals that, above a critical current density of the order of J(crit) approximate to 0.2 A cm(-2), a combination of self-sputter recycling and gas-recycling is generally the case. The relative contributions of these recycling mechanisms, in turn, influence both the electron energy distribution and the stability of the discharges. For high self-sputter yields, above Y-SS approximate to 1, the discharges become dominated by SS-recycling, contain few hot secondary electrons from sheath energization, and have a relatively low electron temperature T-e. Here, stable plateau values of the discharge current develop during long pulses, and these values increase monotonically with the applied voltage. For low self-sputter yields, below Y-SS approximate to 0.2, the discharges above J(crit) are dominated by process gas recycling, have a significant sheath energization of secondary electrons and a higher T-e, and the current evolution is generally less stable. For intermediate values of YSS the discharge character gradually shifts between these two types. All of these discharges can, at sufficiently high discharge voltage, give currents that increase rapidly in time. For such cases we propose that a distinction should be made between 'unlimited' runaway and 'limited' runaway: in unlimited runaway the current can, in principle, increase without a limit for a fixed discharge voltage, while in limited runaway it can only grow towards finite, albeit very high, levels. For unlimited runway Y-SS > 1 is found to be a necessary criterion, independent of the amount of gas-recycling in the discharge.
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| 4. |
- Gudmundsson, Jon Tomas, 1965-, et al.
(författare)
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Foundations of DC plasma sources
- 2017
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Ingår i: Plasma sources science & technology. - : Institute of Physics (IOP). - 0963-0252 .- 1361-6595. ; 26:12
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Tidskriftsartikel (refereegranskat)
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| 5. |
- Brenning, Nils, et al.
(författare)
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HiPIMS optimization by using mixed high-power and low-power pulsing
- 2021
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Ingår i: Plasma sources science & technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 30:1
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Tidskriftsartikel (refereegranskat)abstract
- The possibility to optimize a high-power impulse magnetron sputtering (HiPIMS) discharge through mixing two different power levels in the pulse pattern is investigated. Standard HiPIMS pulses are used to create the ions of the film-forming material. After each HiPIMS pulse an off-time follows, during which no voltage (or, optionally, a reversed voltage) is applied, letting the remaining ions in the magnetic trap escape towards the substrate. After these off-times, a long second pulse with lower amplitude, in the dc magnetron sputtering range, is applied. During this pulse, which is continued up to the following HiPIMS pulse, mainly neutrals of the film-forming material are produced. This pulse pattern makes it possible to achieve separate optimization of the ion production, and of the neutral atom production, that constitute the film-forming flux to the substrate. The optimization process is thereby separated into two sub-problems. The first sub-problem concerns minimizing the energy cost for ion production, and the second sub-problem deals with how to best split a given allowed discharge power between ion production and neutral production. The optimum power split is decided by the lowest ionized flux fraction that gives the desired film properties for a specific application. For the first sub-problem we describe a method where optimization is achieved by the selection of five process parameters: the HiPIMS pulse amplitude, the HiPIMS pulse length, the off-time, the working gas pressure, and the magnetic field strength. For the second sub-problem, the splitting of power between ion and neutral production, optimization is achieved by the selection of the values of two remaining process parameters, the HiPIMS pulse repetition frequency and the discharge voltage of the low-power pulse.
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| 6. |
- Proto, A., et al.
(författare)
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Electron power absorption in radio frequency driven capacitively coupled chlorine discharge
- 2021
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Ingår i: Plasma sources science & technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 30:6
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Tidskriftsartikel (refereegranskat)abstract
- Particle-in-cell Monte Carlo collision simulations and Boltzmann term analysis are applied to study the origination and properties of the electric field and the electron power absorption within the electronegative core of a capacitively coupled discharge in chlorine as the pressure is varied from 1 to 50 Pa. The capacitively coupled chlorine discharge exhibits high electronegativity and high electric field develops within the electronegative core. It is found that the electron power absorption increases and the ion power absorption decreases as the pressure is increased. At 1 Pa the electron power absorption is due to both the pressure and ohmic terms. At the higher pressures >10 Pa the ohmic term dominates and all the other contributions to the electron power absorption become negligible. Therefore, the discharge becomes increasingly ohmic with increased pressure and eventually behaves as a resistive load.
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Huang, Shuo, et al.
(författare)
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Dual frequency capacitively coupled chlorine discharge
- 2015
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Ingår i: Plasma sources science & technology. - : Institute of Physics (IOP). - 0963-0252 .- 1361-6595. ; 24:1
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the control parameters of both high and low frequency sources on a dual-frequency capacitively coupled chlorine discharge is systematically investigated using a hybrid approach, which consists of a particle-in-cell/Monte Carlo simulation and a volume-averaged global model. The high frequency current density is varied from 20 to 80Am-2, the driving high frequency is varied from 27.12 to 100MHz, and the driving low frequency is varied from 1 to 13.56MHz, while the low frequency current density is kept at 1Am-2. The discharge pressure is maintained at 10mTorr. Key plasma parameters (including the electron heating rate, the electron energy probability function, the ion flux, the ion energy, and angular distributions) are explored and their variations with the control parameters are analyzed and compared with other discharge chemistries. As the high frequency current increases, the electron heating is enhanced in the sheath region and is diminished in the bulk region, showing a transition of the electron heating from the drift-ambipolar mode to the α mode. The fluxes of ions and high-energy Cl2 molecules reaching the surface decrease with an increase in the driving high frequency, and the average sheath potential is approximately inversely proportional to the driving high frequency. The electron heating rate, the fluxes of and Cl+ ions reaching the surface, and the average sheath potential show little dependence on the driving low frequency, while the profile of the ion energy distribution evolves from a broad bimodal profile to a narrow single-peak profile as the driving low frequency increases, which corresponds to the transition of the discharge from the intermediate frequency regime to the high frequency regime.
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