The Experts below are selected from a list of 222 Experts worldwide ranked by ideXlab platform
P. Mora - One of the best experts on this subject based on the ideXlab platform.
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thin foil expansion into a vacuum with a two temperature Electron Distribution Function
Physical Review E, 2012Co-Authors: A Diaw, P. MoraAbstract:A kinetic theory of the expansion into a vacuum of a plasma thin foil with initially a hot and a cold Maxwellian Electron population is examined with a one-dimensional kinetic code. Whereas hot Electrons always lose energy to expanding ions, cold Electrons can either gain or lose energy depending on the initial temperature and density ratios and on time. When the cold Electrons' density is not too large, they experience initially an adiabatic compression by the electric field associated with the rarefaction wave. The corresponding temperature increase can be as large as a factor of a few tens. Later on, as expected, the cold Electrons eventually lose energy to the expansion. When cold Electrons are numerically dominant, a rarefaction shock appears during the first phase of the expansion. Hot Electrons cool down faster than cold Electrons, thus reducing the effective temperature ratio. Furthermore, the amplitude of the rarefaction shock and the dip that it causes on the ion velocity spectrum tend to be smoothed out by the expansion.
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rarefaction shock in plasma with a bi maxwellian Electron Distribution Function
Physical Review E, 2011Co-Authors: A Diaw, P. MoraAbstract:The one-dimensional collisionless expansion into a vacuum of a plasma with a bi-Maxwellian Electron Distribution Function and a single ion species is studied both theoretically and numerically. A shock wave occurs when the ratio of the temperatures between the hot and the cold Electrons is larger than 5+{radical}(24)[B. Bezzerides, D. W. Forslund, and E. L. Lindman, Phys. Fluids 21, 2179 (1978)]. The theoretical model presented here gives a coherent and complete description of the rarefaction shock and its effects on the ion acceleration process. Analytical expressions of the characteristics of the shock are given. The analytical findings are compared to the results of a hybrid code describing the plasma expansion, and an excellent agreement is obtained.
A A Kudryavtsev - One of the best experts on this subject based on the ideXlab platform.
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ambipolar field role in formation of Electron Distribution Function in gas discharge plasma
Scientific Reports, 2017Co-Authors: Chengxun Yuan, E A Bogdanov, A A Kudryavtsev, K M Rabadanov, Zhongxiang ZhouAbstract:It is shown that the local approximation for Electron Distribution Function (EDF) determination at plasma periphery, where the ambipolar field is dominant, is not applicable even at high pressures when the characteristic plasma size exceeds the energy relaxation length of the Electrons R > λ e . Therefore, consistent results can be obtained only when solving the complete kinetic equation in both energy and spatial variables (i.e. it is necessary to solve nonlocal kinetic equation).
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the role of the ambipolar field and the local approximation inapplicability in determination of the Electron Distribution Function at high pressures
Technical Physics Letters, 2015Co-Authors: K D Kapustin, Mikhail B Krasilnikov, A A KudryavtsevAbstract:It is demonstrated that the condition for applicability of the local approximation in solving the kinetic equation for Electrons includes not only smallness of the Electron kinetic relaxation length as compared with the characteristic plasma volume, but also smallness of the ambipolar filed as compared with the current (heating) field. Therefore, at the discharge periphery, where the ambipolar field exceeds the longitudinal one, the local approximation cannot be used for calculating the Electron Distribution Function even at high gas pressures.
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fundamental limitations of the local approximation for Electron Distribution Function and fluid model in bounded plasmas
Physics of Plasmas, 2014Co-Authors: Mikhail B Krasilnikov, K D Kapustin, A A KudryavtsevAbstract:It is shown that the local approximation for computing the Electron Distribution Function depends both on the ratio between the energy relaxation length and a characteristic plasma length and on the ratio between heating and ambipolar electric fields. In particular, the local approximation is not valid at the discharge periphery even at high pressure due to the fact that the ambipolar electric field practically always is larger than the heating electric field.
A Diaw - One of the best experts on this subject based on the ideXlab platform.
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Expansion of a plasma into vacuum with a bi-Maxwellian Electron Distribution Function
EPJ Web of Conferences, 2013Co-Authors: A Diaw, Patrick MoraAbstract:A comprehensive theory is developped to describe the expansion of a plasma into a vacuum with a two-temperature Electron Distribution Function. The characteristics of the rarefaction shock which occurs in the plasma when the hot- to the cold-Electron temperature ratio is larger than 9.9 are investigated with a semi-infinite plasma. Furthermore by using a finite plasma foil, a possible heating of the cold Electrons population is evidenced, for a sufficiently large hot- to the cold-Electron density ratio.
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thin foil expansion into a vacuum with a two temperature Electron Distribution Function
Physical Review E, 2012Co-Authors: A Diaw, P. MoraAbstract:A kinetic theory of the expansion into a vacuum of a plasma thin foil with initially a hot and a cold Maxwellian Electron population is examined with a one-dimensional kinetic code. Whereas hot Electrons always lose energy to expanding ions, cold Electrons can either gain or lose energy depending on the initial temperature and density ratios and on time. When the cold Electrons' density is not too large, they experience initially an adiabatic compression by the electric field associated with the rarefaction wave. The corresponding temperature increase can be as large as a factor of a few tens. Later on, as expected, the cold Electrons eventually lose energy to the expansion. When cold Electrons are numerically dominant, a rarefaction shock appears during the first phase of the expansion. Hot Electrons cool down faster than cold Electrons, thus reducing the effective temperature ratio. Furthermore, the amplitude of the rarefaction shock and the dip that it causes on the ion velocity spectrum tend to be smoothed out by the expansion.
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rarefaction shock in plasma with a bi maxwellian Electron Distribution Function
Physical Review E, 2011Co-Authors: A Diaw, P. MoraAbstract:The one-dimensional collisionless expansion into a vacuum of a plasma with a bi-Maxwellian Electron Distribution Function and a single ion species is studied both theoretically and numerically. A shock wave occurs when the ratio of the temperatures between the hot and the cold Electrons is larger than 5+{radical}(24)[B. Bezzerides, D. W. Forslund, and E. L. Lindman, Phys. Fluids 21, 2179 (1978)]. The theoretical model presented here gives a coherent and complete description of the rarefaction shock and its effects on the ion acceleration process. Analytical expressions of the characteristics of the shock are given. The analytical findings are compared to the results of a hybrid code describing the plasma expansion, and an excellent agreement is obtained.
J Demsar - One of the best experts on this subject based on the ideXlab platform.
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tracking the time evolution of the Electron Distribution Function in copper by femtosecond broadband optical spectroscopy
Physical Review Letters, 2020Co-Authors: Manuel Obergfell, J DemsarAbstract:: Multitemperature models are nowadays often used to quantify the ultrafast Electron-phonon (boson) relaxations and coupling strengths in advanced quantum solids. To test their applicability and limitations, we perform systematic studies of carrier relaxation dynamics in copper, a prototype system for which the two-temperature model (TTM) was initially considered. Using broadband time-resolved optical spectroscopy, we study the time evolution of the Electron Distribution Function, f(E), over a large range of excitation densities. Following intraband optical excitation, f(E) is found to be athermal over several 100 fs, with a substantial part of the absorbed energy already being transferred to the lattice. We show, however, that the Electron-phonon coupling constant can still be obtained using the TTM analysis, provided that the data are analyzed over the time window where the Electrons are already quasithermal, and the Electronic temperature is determined experimentally.
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tracking the time evolution of the Electron Distribution Function in copper by femtosecond broadband optical spectroscopy
arXiv: Materials Science, 2019Co-Authors: Manuel Obergfell, J DemsarAbstract:Multi-temperature models are nowadays often used to quantify the ultrafast Electron-phonon (boson) relaxations and coupling strengths in advanced quantum solids. To test their applicability we study the time evolution of the Electron Distribution Function, f(E), in Cu over large range of excitation densities using broadband time-resolved optical spectroscopy. Following intraband optical excitation, f(E) is found to be athermal over several 100 fs, while substantial part of the absorbed energy already being transferred to the lattice. We show, however, that the Electron-phonon coupling constant can still be obtained using the two-temperature model analysis, provided that the data are analyzed over the time-window, when the Electrons are already quasi thermal, and the Electronic temperature is determined experimentally.
Yu. B. Golubovskii - One of the best experts on this subject based on the ideXlab platform.
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Resonant formation of the Electron Distribution Function in striation-like electric fields
Technical Physics Letters, 2008Co-Authors: Yu. B. Golubovskii, V. O. Nekuchaev, A. Yu. SkobloAbstract:The resonant behavior of the Electron Distribution Function (EDF) in spatially periodic striation-like fields is analyzed in application to the discharge in neon at low pressures and small current. Numerical solution of the Boltzmann kinetic equation is interpreted from the standpoint of Tsendin’s analytical theory [3] using decomposition into two factors, one of which depends only on the total energy. Features of the EDF formation are considered for both integer resonances (which follow from theory [3]) and non-integer resonances.
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The structure of the Electron Distribution Function in R striations
Technical Physics Letters, 2007Co-Authors: Yu. B. Golubovskii, A. Yu. SkobloAbstract:The Electron Distribution Function (EDF) in R striations of a low-pressure dc discharge in neon has been measured using probe techniques. The results of measurements satisfactorily agree with calculations performed using a model that describes the EDF formation in R striations as a resonance with the spatial period of two-thirds of the S striation length.
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resonance effects in the Electron Distribution Function formation in spatially periodic fields in inert gases
Physical Review E, 2003Co-Authors: Yu. B. Golubovskii, R Kozakov, J Behnke, C Wilke, V O NekutchaevAbstract:The calculations of the Electron Distribution Function (EDF) in striationlike, sinusoidally modulated electric fields were performed to determine the dependence on spatial period length. The calculations were done for a discharge in neon at pR=2 Torr cm, i/R=5 mA/cm, and electric field E/p=1.9 V cm - 1 Torr - 1 . The presence of the resonances in the EDF and macroscopic parameters has been demonstrated. These resonances correspond to S and P striations observed in experiments. An interpretation of the results is proposed based on an analytical approximation of the numerical solution. Decomposition of EDF into two factors-amplitude and body-is carried out. The amplitude of the EDF is shown to be resonantly dependent on the value of the spatial period. One maximum in the EDF is formed at the value of the spatial period corresponding to the S striation, and two maxima at the value which corresponds to the P striation. The experimental measurements of the EDF in S and P striations with high spatial resolution showed agreement between the theoretical and the experimental results. Resonance effects in the EDF formation are considered based on the linear theory in the weakly modulated electric fields.
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Shaping of the Electron Distribution Function in a striated solution
Technical Physics, 1997Co-Authors: Yu. B. Golubovskii, V. O. Nekuchaev, N. S. Ponomarev, I. A. PorokhovaAbstract:Numerous papers have been devoted to the investigation of striations in inert gases at low pressures ( p ⩽2 Torr) and small currents ( i