| 1. |
- Baránková, Hana, et al.
(författare)
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Conversion of Nitrogen and Carbon Oxides by the Atmospheric Hollow Cathode Discharges
- 2012
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 40:5, s. 1324-1328
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Tidskriftsartikel (refereegranskat)abstract
- We have successfully tested the fused hollow cathode with aerodynamic stabilization as a 100% oxidation catalyst in conversion of NOx in air mixtures. Plasma chemical kinetics and the processing window width are controlled by plasma characteristics. Results show that, besides the plasma source design itself, the material of the electrodes plays a crucial role. It was found that, by using graphite electrodes, a 100% removal of NO from the air mixtures is possible without necessity of adding hydrocarbons. This paper presents results of oxygen screening, discusses the mechanisms of the process, and reports also on the CO2 reduction in some discharge regimes.
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| 2. |
- Bozhko, Igor, et al.
(författare)
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Corona discharge to water surface and its transition to a spark
- 2011
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 36:5, s. 1228-1233
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Tidskriftsartikel (refereegranskat)abstract
- Impulse corona discharge in atmospheric air to the surface of a water layer with different electric conductivities isstudied. The discharge was initiated from a corona electrode consisting of a metallic disk with evenly distributed corona needles.The dependences of the magnitudes of the measured impulse currents on the polarity of the corona electrode as well as the parameters of the gas gap and liquid layer were obtained. An equivalent electric circuit of the discharge system was proposed,allowing for explanations of the regularities in the measured currents and also the role of the water layer as a factor affecting the transition of the corona discharge to a spark.
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| 3. |
- Eriksson, Anders, et al.
(författare)
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Influence of Ar and N2 Pressure on Plasma Chemistry, Ion Energy, and Thin Film Composition during Filtered Arc Deposition from Ti3SiC2 Cathodes
- 2014
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Ingår i: IEEE Transactions on Plasma Science. - : IEEE Press. - 0093-3813 .- 1939-9375. ; 42:11, s. 3498-3507
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Tidskriftsartikel (refereegranskat)abstract
- Arc plasma from Ti3SiC2 compound cathodes used in a filtered dc arc system has been characterized with respect to plasma chemistry and charge-state resolved ion energies. In vacuum, the plasma composition is dominated by Ti ions, with concentrations of 84.3, 9.3, and 6.4 at% for Ti, Si, and C ions, respectively. The reduced amount of Si and most notably C compared with the cathode composition is confirmed by analysis of film composition in corresponding growth experiments. The deposition of light-element deficient films is thus related to plasma generation or filter transport. The ion energy distributions in vacuum range up to 140, 90, and 70 eV for Ti, Si, and C, respectively. Corresponding average ion energies of 48, 36, and 27 eV are reduced upon introduction of gas, down to around 5 eV at 0.6 Pa Ar or 0.3 Pa N2 for all species. In vacuum, the charge state distributions of Si and C are shifted to higher values compared with corresponding elemental cathodes, likely caused by changed effective electron temperature of the plasma stemming from compound cathode material and/or by electron impact ionization in the filter. The average ion charge states are reduced upon addition of Ar, ranging between 1.97 and 1.48 for Ti, 1.91 and 1.46 for Si, and 1.25 and 1.02 for C. Similar effects are observed upon introduction of N2, though with more efficient charge state reduction with pressure. It is conceivable that the pressure-induced changes in ion energy and charge state are crucial for the film synthesis from a microstructure evolution point of view, as they affect the ion-surface interactions through supply of energy, especially when substrate biasing is employed during arc deposition from a compound cathode.
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| 4. |
- Huang, Shuo, et al.
(författare)
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Ion Energy and Angular Distributions in a Dual-frequency Capacitively Coupled Chlorine Discharge
- 2014
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Ingår i: IEEE Transactions on Plasma Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0093-3813 .- 1939-9375. ; 42:10, s. 2854-2855
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Tidskriftsartikel (refereegranskat)abstract
- Ion energy distributions (IEDs) and ion angular distributions (IADs) of Cl2 + and Cl+ ions in a dual-frequency capacitively coupled chlorine discharge are obtained through a particle-in-cell/Monte Carlo simulation. Since the ion transit time is less than the low-frequency period, the ions respond to the instantaneous electric field in the sheath region, which leads to bimodal IEDs for Cl2 + and Cl+ ions. When transiting the sheath, the Cl+ ions experience a more collisional sheath than the Cl2 + ions. The IADs of Cl2 + and Cl+ ions at the surface are almost anisotropic. However, a secondary peak is found in the IAD of Cl+ ions, which can be ascribed to dissociative ionization reactions.
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| 5. |
- Höök, Josef, et al.
(författare)
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An Adaptive delta f Monte Carlo Method
- 2010
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 38:9, s. 2190-2197
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Tidskriftsartikel (refereegranskat)abstract
- A new adaptive delta f Monte Carlo method is presented with an application to radio frequency heating and transport in fusion plasmas. The method is suitable when an initial zeroth-order approximation of the distribution function is known. The difference between our method and earlier delta f methods is that we model the source term, obtained from the delta f ansatz, by adding particles. The rate of particles is defined by the inhomogeneous term in the Fokker-Planck equation. We develop an adaptive scheme for modifying the unperturbed part G(x) such that the number of particles used in the simulation for a fixed weight is minimized. This implicitly reduces the variance and improves computational efficiency. The method is tested on a one-dimensional Fokker-Planck model for RF-heating and compared against the analytical stationary solution.
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| 6. |
- Mukhtar, Qaisar, et al.
(författare)
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On Solving Singular Diffusion Equations With Monte Carlo Methods
- 2010
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 38:9, s. 2185-2189
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion equations in one, two, or three dimensions with inhomogeneous diffusion coefficients are usually solved with finite-difference or finite-element methods. For higher dimensional problems, Monte Carlo solutions to the corresponding stochastic differential equations can be more effective. The inhomogeneities of the diffusion constants restrict the time steps. When the coefficient in front of the highest derivative of the corresponding differential equation goes to zero, the equation is said to be singular. For a 1-D stochastic differential equation, this corresponds to the diffusion coefficient that goes to zero, making the coefficient strongly inhomogeneous, which, however, is a natural condition when the process is limited to a region in phase space. The standard methods to solve stochastic differential equations near the boundaries are to reduce the time step and to use reflection. The strong inhomogeneity at the boundary will strongly limit the time steps. To allow for longer time steps for Monte Carlo codes, higher order methods have been developed with better convergence in phase space. The aim of our investigation is to find operators producing converged results for large time steps for higher dimensional problems. Here, we compare new and standard algorithms with known steady-state solutions.
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| 7. |
- Murphy, GC, et al.
(författare)
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Multidimensional Simulations of Magnetic Field Amplification and Electron Acceleration to Near-Energy Equipartition With Ions by a Mildly Relativistic Quasi-Parallel Plasma Collision
- 2010
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 38:10, s. 2985-2992
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Tidskriftsartikel (refereegranskat)abstract
- The energetic electromagnetic eruptions observed during the prompt phase of gamma-ray bursts are attributed to synchrotron emissions. The internal shocks moving through the ultrarelativistic jet, which is ejected by an imploding supermassive star, are the likely source of this radiation. Synchrotron emissions at the observed strength require the simultaneous presence of powerful magnetic fields and highly relativistic electrons. We explore with 1-D and 3-D relativistic particle-in-cell simulations the transition layer of a shock, which evolves out of the collision of two plasma clouds at a speed 0.9$c$ and in the presence of a quasi-parallel magnetic field. The cloud densities vary by a factor of 10. The number densities of ions and electrons in each cloud, which have the mass ratio 250, are equal. The peak Lorentz factor of the electrons is determined in the 1-D simulation, as well as the orientation and the strength of the magnetic field at the boundary of the two colliding clouds. The relativistic masses of the electrons and ions close to the shock transition layer are comparable as in previous work. The 3-D simulation shows rapid and strong plasma filamentation behind the transient precursor. The magnetic field component orthogonal to the initial field direction is amplified in both simulations to values that exceed those expected from the shock compression by over an order of magnitude. The forming shock is quasi-perpendicular due to this amplification. The simultaneous presence of highly relativistic electrons and strong magnetic fields will give rise to significant synchrotron emissions.
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| 8. |
- Möller, Cecilia, et al.
(författare)
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Experimental Studies of the Influence of a Resonance Cavity in an Axial Vircator
- 2010
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 38:6, s. 1318-1324
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Tidskriftsartikel (refereegranskat)abstract
- Experiments on an axial virtual-cathode oscillator (vircator) with a resonance cavity enclosing the virtual cathode are reported. The vircator is driven by a repetitive Marx generator operating in a single-shot mode. To be able to separate different radiation mechanisms, the design of the vircator allows adjustment of the cavity depth as well as the way microwave radiation is extracted. The microwave radiation is measured with a pair of free-field B-dot sensors. The maximum field strengths were registered when the bandwidth was very narrow.
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| 9. |
- Möller, Cecilia, et al.
(författare)
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Proof of Principle Experiments on Direct Generation of the TE11 Mode in a Coaxial Vircator
- 2010
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 38:1, s. 26-31
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Tidskriftsartikel (refereegranskat)abstract
- Experiments on a coaxial vircator with a sectioned emitter are reported. The emitting area is sectioned to form two opposing emitters in order to favor growth of the TE11 mode and inhibit growth of the TM01 mode that is usually excited in a coaxial vircator. Experiments are performed using a compact 320-J 400-kV Marx generator and a compact coaxial vircator built in a standard 8 '' vacuum tube. The radiated magnetic-field strength is measured by means of four free-field (B-dot) probes, and experiments show that sectioning the emitter does, in fact, lead to generation of the TE11 mode.
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| 10. |
- Olofsson, Erik, et al.
(författare)
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Closed-Loop System Identification and Controller Reconfiguration for EXTRAP T2R Reversed-Field Pinch
- 2010
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 38:3, s. 365-370
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Tidskriftsartikel (refereegranskat)abstract
- We first briefly summarize a supposedly efficient novel method for measuring the external plasma response as applied to the inherently unstable reversed-field pinch EXTRAP T2R. Second, the set of parameters estimated with this particular method is harvested and fed as input to a discrete-time fixed-order fast-Fourier-transform-decoupled multi-input-multioutput controller synthesis. The thus reconfigured feedback system is implemented and experimentally tested on the real plant T2R. The recorded first-deployment results are encouraging. The overall methodology followed throughout this paper is emphasized and strongly exemplifies applied process control thinking for the stabilization of magnetically confined toroidal plasmas.
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