1,721,676 research outputs found
Author’s reply to the letter to the editor of Journal of the Korean Association of Oral and Maxillofacial Surgeons
No full textNonlocal collisionless power absorption using effective viscosity model in inductively coupled plasma discharges
No full textEffective viscosity model for inductively coupled plasma (ICP) discharges has been used to calculate the power absorbed inside ICP discharges. It is found that it can be used to calculate collisionless heating, which is a warm plasma effect. The validity of effective viscosity model has been checked by comparing it with kinetic model for warm ICP discharges. For very small plasma lengths, the results of both models are the same. At intermediate lengths where bounce resonance heating is important, results of the two models are not the same. Bounce resonance length given by effective viscosity model does not match very well with that given by the kinetic model. It shows that bounce resonance heating cannot be taken care of accurately using the effective viscosity model. For large plasma length, when driving frequencies are low, power absorbed calculated using the kinetic model is more than that calculated by the effective viscosity model. For high driving frequencies, power absorbed calculated using the kinetic model is less than that calculated by the effective viscosity model. The best match between the results of two models (for large plasma length) is obtained if the combination of plasma density, electron temperature, driving frequency, and speed of light is such that the relation K=omega(p)v(th)/omega c similar or equal to 1 holds. It is concluded that computationally less extensive effective viscosity model can be used to estimate power absorption in ICP discharges by calibrating it with the help of computationally intensive kinetic model. Once calibration is done a lot of computational effort can be avoided by using effective viscosity model instead of kinetic model.open1132sciescopu
Striation phenomenon in the plasma display panel
No full textA detailed analysis, based on kinetic and fluid simulations, of striation phenomenon in the plasma display panel cell has been presented. Numerical studies indicate that the phenomenon of striation occurs primarily due to the accumulation of space charge near the anode electrode. These space charges locally create multiple-layer potential distribution near the anode region. The ion density in the vicinity of this region groups up due to ionization processes, which are caused by electron species. However, the electrons are further attracted by the anode. Well-like deformations occur in the anode potential distribution, which confine electrons and produce density humps. On the contrary, cathode plasma density depends on the secondary-electron emission by ions that are attracted to the anode dielectric surface. (C) 2001 American Institute of Physics.open1139sciescopu
Growth rate calculation and one-dimensional simulation of an electromagnetically pumped FEL
No full textThe dispersion relation of the scattered electromagnetic wave for an electromagnetically pumped free-electron laser is numerically solved. In addition, one-dimensional coupled Maxwell-lorentz equations are derived, and a particle simulation of the performance of the FEL amplifier in the long-pulse limit is performed for various pump conditions. The effect of the axial guide field, the beam energy and energy spread, and the pump strength on the system are investigated. Finally, the requirements on the electron beam quality and the parameter region of practical interest are discussed.X11sci
Mode transition induced by low-frequency current in dual-frequency capacitive discharges
No full textThe mode transition induced by varying the low-frequency current in low-pressure dual-frequency discharges in argon is found through particle-in-cell or Monte Carlo simulations. As the low-frequency (2 MHz) current increases for the fixed high-frequency (27 MHz) current, the electron distribution function (EDF) changes from Druyvesteyn to bi-Maxwellian (in alpha mode) or Maxwellian-type (in gamma mode), along with the significant drop in the effective electron temperature. It is shown that this EDF evolution is attributed to the transition from collisional to collisionless property (but not stochastic heating) of the low-energy electrons as well as the alpha-gamma transition.open11110sciescopu
Moment conserving method for modelling multiple collisions in particle simulations
No full textA statistical procedure for modelling the cumulative effect of multiple collisions in particle simulations is presented. The procedure approximates the probability density function (PDF) of the final scattering angle and that of the particle net displacement by parametric functions. Formulae for determining the moments of the exact PDFs as a function of the statistics of a sin-le collision event are derived. Using these formulae, the parametric functions can be fitted to yield the same first moments as the real distributions. Therefore, in contrast to other approaches where after one iteration the error in the first moments depends on the number of collisions modelled, the present model provides always the right moments. Correlation between the scattering angle and the displacement of the particle is also considered and enforced by means of a Gaussian copula.X111sciescopu
Mode transition and nonlinear self-oscillations in the beam-driven collisional discharge plasma
No full textNonlinear dynamics and self-oscillations in a de beam-driven collisional discharge are investigated with particle-in-cell simulation and theoretical estimation. Three different modes, anode-glow, temperature-limited, and double-layer modes, are observed in the system. A theory for the critical voltage of mode transition between temperature-limited and anode-glow modes is in good agreement with the simulation results,The mechanism of low frequency self-oscillation in the double layer mode is examined along with period-doubling and chaotic oscillations. (C) 1998 American Institute of Physics.open1113sciescopu
The bounce resonance heating of low-energy electrons in capacitively coupled discharges
No full textLow-energy electrons are confined in the bulk plasma by the ambipolar potential and are typically heated inefficiently due to their low collisionality and the weak rf electric field present in the bulk when their mean-free path is much larger than the system length in capacitively coupled discharges. It is shown in this study, however, that electrons in the bulk that bounce inside the electrostatic potential well with a frequency equal to the rf excitation frequency are efficiently heated by coherent interaction with the rf field. This resonant heating manifests itself as a plateau in the electron energy probability function and is observed in a wide range of pressures from 25 mTorr to 1 Torr while decreasing the gap distance. The weak transverse magnetic field significantly influences the bounce frequency of the low-energy electrons. As a result, the electrons not in the resonant condition in the absence of a magnetic field can be led to satisfy the resonant condition, becoming effectively heated in the presence of a weak transverse magnetic field.X115sciescopu
Formation of quasistationary vortex and transient hole patterns through vortex merger
No full textCollection of point-like intense vortices arranged symmetrically outside of a uniform circular vortex patch, both enclosed in a free-slip circular boundary, are numerically time evolved for up to 10-15 patch turnover times. These patterns are found to merge with the patch by successively inducing nonlinear dispersive modes (V-states) on the surface of the patch, draw off fingers of vorticity (filamentation), trap the irrotational regions as the fingers symmetrize under the shear flow of the patch and point-like vortices (wave breaking) followed by the vortex-hole capture. While the hole patterns are observed to break up over several turnover periods the vortex patterns appear to evolve into quasistationary patterns for some cases of an initial number of point-like vortices N-pv. The bounded V-states, filamentation, and vortex (hole) pattern formation are discussed in some detail and their possible connection to recently observed vortex "crystals" is pointed out. (C) 2002 American Institute of Physics.open1121sciescopu
Dual radio-frequency discharges: Effective frequency concept and effective frequency transition
No full textA concept of effective frequency is introduced to study dual-frequency (DF) capacitively coupled plasmas (CCP) which can be analyzed in a fashion similar to single-frequency (SF) CCP driven with effective parameters. Effective frequencies can be defined quantitatively for ion bombardment energy distribution functions and rf discharge parameters by analyzing ion dynamics in ion-collisionless dual rf sheaths and a homogeneous plasma model for dual rf discharges, respectively. Unlike the driving frequency in SF CCP, the effective frequency in DF CCP is dependent on the ratio of two driving voltages or currents. This characteristic makes it possible to control the ion flux and ion bombardment energy independently. The abrupt transition of the effective frequency leads to several physical phenomena unique in DF CCP (c) 2005 American Vacuum Society.open112727sciescopu
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