A global (volume averaged) model is developed for an argon-acetylene plasma afterglow. The model is used to study the electron and ion densities, electron temperature and densities of argon ...metastable atoms in the afterglow plasma. The calculated time dependence for the electron density is found to be in agreement with the existing experimental data. These calculated plasma characteristics are used to investigate the dust charge distribution function (DCDF) for particles with radii of 10–200 nm. The DCDF is found by solving numerically the master equation describing dust discharging as a one-step stochastic process and is also calculated as a Gaussian distribution with mean dust charge and variance, which are functions of time. The time dependences for mean dust charge, variance and dust charging time are obtained and analysed. If the electronegativity of the plasma in the steady-state is low, negative ions do not affect much discharging of dust particles in the afterglow, while at large electronegativity their role is essential. In the case of low electronegativity, discharging of dust particles is mainly due to deposition of positive ions with small and moderate masses (less than the mass of C 10 H 6 + ions). Increasing electronegativity, the effect of heavy positive ions on dust discharging in the late afterglow is important. Secondary electron emission from dust surface at collisions of metastable atoms appears to be negligible.
Abstract
A global (volume averaged) model is developed for the ionization region (IR) of a gas aggregation source (GAS) plasma. The case of using argon gas and a copper target is considered. The ...model describes the densities of thermal and hot electrons, argon and copper ions, copper atoms and argon atoms in different excited states, the temperature of thermal electrons, the kinetic energies of the ions with which they bombard the target, the sheath width near the target cathode and the energy fluxes by different plasma species to a planar probe in the IR. Also, the fraction of input power is estimated which is dissipated to energize the thermal electrons in the IR. The gas discharge properties are analyzed for different pressures and discharge currents under conditions corresponding to the experimental conditions (Gauter
et al
2018
J. Appl. Phys.
124
073301). The calculated pressure- and current-dependences for the GAS properties are used to explain the measured dependences for the deposition rate and the energy flux. It is found that the deposition rate increases with increasing discharge current because of the growth of currents of copper atoms and ions. With increasing pressure, the rate decreases due to drop of the densities of copper atoms and ions because of decreasing the kinetic energies of the ions with which they bombard the target. The model indicates that in the gas-aggregation-source relevant pressure regime, the energy flux by ions dominates over the energy fluxes of other plasma species.
Dust dynamics during the plasma afterglow Denysenko, I B; Mikikian, M; Azarenkov, N A
Journal of physics. D, Applied physics,
03/2022, Letnik:
55, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Abstract
The charge and dynamics of dust particles in an afterglow plasma are studied using a 1D model in the diffusion approximation, taking into account the transition from ambipolar to free ...diffusion. It is analyzed how external conditions (dust particle size, neutral gas pressure and initial electron density) affect the dust motion. The dust particle dynamics has been examined in microgravity conditions and in presence of gravity. Without gravity, the location of dust particles in plasma volume may change essentially during the afterglow if the dust size and pressure are small (⩽10 nm and ⩽30 mTorr, respectively). At small pressures, in the very beginning of afterglow, small nanoparticles move to the plasma boundary because the ion drag force dominates over the electric force. At afterglow times when the electron temperature becomes time-independent, the ion drag force decreases faster with time than the electric force due to the ion density decrease, and dust particles may move to the slab center. In presence of gravity, the effect of gravity force on dust particles is important only at large afterglow times (
t
⩾ 10 ms), when the electric and ion drag forces are small. The dust dynamics depends essentially on the initial plasma density. If the density is large (∼10
12
cm
−3
), small nanoparticles (⩽10 nm) may deposit on plasma walls in the beginning of plasma afterglow because of an enhancement of the ion drag force.
The properties (densities of electrons and metastable argon atoms, effective electron temperature and dust charge) of argon/dust and pure argon pulsed plasmas are studied using a spatially-averaged ...model. The calculated time-dependencies for the densities of electrons and metastable atoms are compared with the experimental measurements and are found to be in a good qualitative agreement. It is analyzed how the plasma properties depend on the shape of the electron energy probability function (EEPF), the pulsing frequency and the duty cycle for both dust-free and dusty plasma. The analysis reveals that the agreement between theory and experiment is better with Druyvesteyn EEPF than the Maxwellian EEPF. Further, the variation in the pulsing frequency νp differently affects the metastable density nm in a dust-free and in a dusty plasma. For large νp, the metastable density in the dust-free pulsed plasma is larger than in the continuous-wave (CW) discharge, while the opposite is obtained in the presence of dust particles. This difference probably arises because of faster variation in the effective electron temperature in the dusty plasma due to collection of electrons by dust particles. Our calculations also show that dust particles may affect the behavior of electron density in the beginning of the on-period due to an enhancement in electron collection by dust particles.
Modeling of argon-acetylene dusty plasma Denysenko, I B; von Wahl, E; Labidi, S ...
Plasma physics and controlled fusion,
01/2019, Letnik:
61, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The properties of an Ar/C2H2 dusty plasma (ion, electron and neutral particle densities, effective electron temperature and dust charge) in glow and afterglow regimes are studied using a ...volume-averaged model and the results for the glow plasma are compared with mass spectrometry measurements. It is shown that dust particles affect essentially the properties of glow and afterglow plasmas. Due to collection of electrons and ions by dust particles, the effective electron temperature, the densities of argon ions and metastable atoms are larger in the dusty glow plasma comparing with the dust-free case, while the densities of most hydrocarbon ions and acetylene molecules are smaller. Because of a larger density of metastable argon atoms and, as a result, of the enhancement of electron generation in their collisions with acetylene molecules, the electron density in the afterglow dusty plasma can have a peak in its time-dependence. The results of numerical calculations are in a good qualitative agreement with experimental results.
A theoretical model describing the plasma-assisted growth of carbon nanofibres (CNFs) that accounts for the nanostructure heating by ion and etching gas fluxes from the plasma is developed. Using the ...model, it is shown that fluxes from the plasma environment can substantially increase the temperature of the catalyst nanoparticle located on the top of the CNF with respect to the substrate temperature. The difference between the catalyst and the substrate temperatures depends on the substrate width, the length of the CNF, the neutral gas density and temperature as well as the densities of the ions and atoms of the etching gas. In addition to the heating of the nanostructure, the ions and etching gas atoms from the ionized gas environment also strongly affect the CNF growth rates. Due to ion bombardment, the CNF growth rates in plasma enhanced chemical vapour deposition may be much higher than the rates in similar neutral gas-based thermal processes. The CNF growth model, which accounts for the nanostructure heating by the plasma-generated species, provides the growth rates that are in better agreement with the available experimental data on CNF growth than the models in which the heating effects are ignored.
Results on modelling of the plasma-assisted growth of vertically aligned carbon nanostructures and of the energy exchange between the plasma and the growing nanostructures are reviewed. Growth of ...carbon nanofibres and single-walled carbon nanotubes is considered. Focus is made on studies that use the models based on mass balance equations for species, which are adsorbed on catalyst nanoparticles or walls of the nanostructures. It is shown that the models can be effectively used for the study and optimization of nanostructure growth in plasma-enhanced chemical vapour deposition. The results from these models are in good agreement with the available experimental data on the growth of nanostructures. It is discussed how input parameters for the models may be obtained.
A non-invasive diagnostic technique for measurements of ion fluxes and ion densities in low-pressure pulsed radio-frequency (RF) discharges is described. The ion flux towards an electrode is ...determined from the change in electrode dc-bias in the plasma afterglow. The measurements in various gas mixtures (Ar, N2, Ar/C2H2 and Ar with nanoparticles) show an increase in ion flux with the applied RF power. Ion densities are estimated from the ion fluxes and the plasma density at the plasma-sheath boundary, assuming the afterglow electron temperature to be known. Very good agreement between the estimated ion densities and independently measured electron densities is found in the bulk of dust-free plasmas assuming an afterglow electron temperature of 0.05 eV for argon and argon/acetylene plasmas and 0.2 eV for the nitrogen plasma. In dusty plasmas, the ion density at the plasma-sheath boundary can be determined from the measured ion flux and assuming an afterglow electron temperature of 0.05 eV. For the estimation of ion density in the dusty plasma bulk, the ion density distribution, influenced by the negatively charged dust particles, has to be taken into account.
Мета. Оцінити ефективність використання парацетамолу в періопераційному знеболюванні під час ендовідеохірургічних втручань (ЕВХВ) на органах черевної порожнини.
Матеріали і методи. Обстежено 132 ...пацієнти, яким виконували ЕВХВ під загальним знеболюванням. У 1-й (основній) групі (n=66) після індукції наркозу здійснювали внутрішньовенну інфузію 1000 мг парацетамолу. У 2-й (контрольній) групі (n=66) за 20 хв до операції внутрішньовенно вводили декскетопрофен 50 мг. У післяопераційному періоді всі пацієнти отримували внутрішньовенно декскетопрофен 50 мг через 6 - 8 год упродовж трьох діб.
Результати. Рівень кортизолу крові в обох групах зростав, сягаючи максимальних значень на травматичному етапі ЕВХВ: (453 ± 46) нмоль/л - у 1-й групі та (527 ± 43) нмоль/л - у 2-й групі (р < 0,05). Надалі він знижувався, залишаючись вищим у 2-й групі (р < 0,05). Оцінка болю за візуально-аналоговою шкалою (ВАШ) у 1-й групі у порівнянні з 2-ю групою була нижчою через 6 год після операції на 2,1, через 12 год - на 1,4, через 24 год - на 1,6 бала (р < 0,05).
Висновки. Використання парацетамолу в періопераційному знеболюванні ефективне та має переваги над стандартним введенням декскетопрофену перед оперативним втручанням.
PDF
