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velocity distribution function of Na released by photons from planetary surfaces

PLANETARY AND SPACE SCIENCE 2018年 159卷 97-104页

作者： Gamborino, D. Wurz, P. Univ Bern Phys Inst Sidlerstr 5 CH-3012 Bern Switzerland

In most surface-bound exospheres Na has been observed at altitudes above what is possible by thermal release. Photon stimulated desorption of adsorbed Na on solid surfaces has been commonly used to explain observations at high altitudes. We investigate three model velocity distribution functions (VDF) that have been previously used in several studies to describe the desorption of atoms from a solid surface either by electron or by photon bombardment, namely: the Maxwell-Boltzmann (M-B) distribution, the empirical distribution proposed by [1] for PSD, and the Weibull distribution. We use all available measurements reported by [2, 3] to test these distributions and determine which one fits best (statistically) and we discuss their physical validity. Our results show that the measured VDF of released Na atoms are too narrow compared to Maxwell-Boltzmann fits with supra-temperatures as suggested by [3]. We found that a good fit with M-B is only achieved with a speed offset of the whole distribution to higher speeds and a lower temperature, with the offset and the fit temperature not showing any correlation with the surface temperature. From the three distributions we studied, we find that the Weibull distribution provides the best fits using the temperature of the surface, though an offset towards higher speeds is required. This work confirms that Electron-Stimulated Desorption (ESD) and Photon-Stimulated Desorption (PSD) should produce non-thermal velocity (or energy) distributions of the atoms released via these processes, which is expected from surface physics. We recommend to use the Weibull distribution with the shape parameter kappa = 1.7, the speed offset v(0) = 575 m/s, and the surface temperature to model PSD distributions at planetary bodies.

关键词： Mercury Exosphere Sodium velocity distribution function

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Analytical Model of Ablation Using Bimodal velocity distribution function in Knudsen Layer

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2009年第3期23卷 479-488页

作者： Pekker, L. ERC Inc Edwards AFB CA 93524 USA

An analytical model of the Knudsen layer at ablative surfaces has been developed that takes into account the temperature gradient in the bulk gas and rebound of gas particles by the ablative wall back into the gas region. This model uses a bimodal velocity distribution function, which preserves the laws of conservation of mass, momentum, and energy within the Knudsen layer and converges to the Chapman-Enskog velocity distribution function at the outer boundary of the Knudsen layer. The region of validity of this model and effects of the temperature gradient, diffusive reflection, and specular reflection on the Knudsen layer properties are calculated.

关键词： velocity distribution function Conservation of Mass Ablation Condensation Thermal Conduction Thermodynamic Equilibrium Direct Simulation Monte Carlo Numerical Simulation Thermal Conductivity Energy Conservation

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Diagnostics Method for 2-D velocity distribution function of Beam Deuterons Using Visible Light of Energetic ³He in Deuterium Plasmas

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IEEE TRANSACTIONS ON PLASMA SCIENCE 2021年第10期49卷 3142-3148页

作者： Kimura, Kento Matsuura, Hideaki Itoh, Chujo Kyushu Univ Dept Appl Quantum Phys & Nucl Engn Fukuoka 8190395 Japan

In high-temperature plasmas, fast ion diagnostics is one of the important components for plasma heating. Therefore, it is important for fusion research to confirm and understand the physics of fast ions in experimental devices. Although conventional spectroscopy measurements have excellent energy resolution, it is difficult to measure fast deuterons with MeV order energy. The energy resolutions for neutron and gamma-ray measurements are low and need to be improved. A diagnostics method using the visible light (VIS) spectrum of He-3 produced by the deuteron-deuteron reaction has been proposed. The previous studies did not consider the measurement line-of-sight (LOS) in the actual device. In this article, the observability of the proposed method is evaluated considering the spatial distribution of the temperature and density and the direction of ion motion in the deuterium beam-injected ITER deuterium plasma. It is shown that the change of the Doppler broadening of the VIS spectrum due to the formation of beam deuteron tails (non-Maxwell component) is sufficiently larger than the resolution of the spectrometer, it is strongly dependent on the LOS. The ratios of emissivity to bremsstrahlung are 40%-50% in the vertical LOS and 4%-7% in the tangential LOS.

关键词： Ions Plasmas Pollution measurement distribution functions Deuterium velocity measurement Plasma measurements Charge-exchange spectroscopy deuterium plasma velocity distribution function visible light (VIS) spectra

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Impact of Initial Non-Maxwellian Electron velocity distribution function on Electric Propulsion Beam Expansion: Grid-Based Vlasov Simulations

Impact of Initial Non-Maxwellian Electron Velocity Distribut...

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AIAA SciTech Forum

作者： Cui, Chen Wang, Joseph Univ Southern Calif Los Angeles CA 90089 USA Univ Southern Calif Dept Astronaut Engn Los Angeles CA 90089 USA Mississippi State Univ Dept Aerosp Engn Mississippi State MS 39762 USA

ISBN: (数字)9781624107115

ISBN: (纸本)9781624107115

This study investigates the impact of initial non-Maxwellian electron velocity distribution functions (eVDFs) on beam expansion in electric propulsion devices, using grid-based Vlasov simulations. The study primarily focuses on understanding the influence of augmented high-energy electrons which are represented by the Kappa distribution in this work on ion acceleration and electron thermodynamics during the beam expansion process. Kappa distribution function is used to mimic the augmented high-energy electrons in this study. A near-constant acceleration ratio for different degrees of enhanced high-energy electrons at different time moments is found in this study. An anomalous electron temperature enhancement is found in the beam expansion process when starting with an initial Kappa velocity distribution. Furthermore, the electron heat flux characteristics appear similar for both initial Maxwellian and Kappa velocity distribution electrons but their magnitudes differ. This study reveals that the simplified polytropic relationship fails to accurately represent electron thermodynamics in these scenarios, necessitating the use of a complete set of energy equations.

关键词： Electric Propulsion velocity distribution function Heat Flux Electron Temperature Boltzmann's Constant Ion Beam Kinetic Energy Advection Finite Element Method Electric Potential

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Ring-averaged ion velocity distribution function probe for laboratory magnetized plasma experiment

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REVIEW OF SCIENTIFIC INSTRUMENTS 2017年第10期88卷 103507-103507页

作者： Kawamori, Eiichirou Chen, Jinting Lin, Chiahsuan Lee, Zongmau Natl Cheng Kung Univ Inst Space & Plasma Sci Tainan 70101 Taiwan

Ring-averaged velocity distribution function of ions at a fixed guiding center position is a fundamental quantity in the gyrokinetic plasma physics. We have developed a diagnostic tool for the ring averaged velocity distribution function of ions for laboratory plasma experiments, which is named as the ring-averaged ion distribution function probe (RIDFP). The RIDFP is a set of ion collectors for different velocities. It is designed to be immersed in magnetized plasmas and achieves momentum selection of incoming ions by the selection of the ion Larmor radii. To nullify the influence of the sheath potential surrounding the RIDFP on the orbits of the incoming ions, the electrostatic potential of the RIDFP body is automatically adjusted to coincide with the space potential of the target plasma with the use of an emissive probe and a voltage follower. The developed RIDFP successfully measured the equilibrium ring-averaged velocity distribution function of a laboratory magnetized plasma, which was in accordance with the Maxwellian distribution having an ion temperature of 0.2 eV. Published by AIP Publishing.

关键词： diagnostic tool Probes velocity distribution function Plasma physics Ion velocity Ions distribution function space potential Ion temperature

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Measurement of fast electron velocity distribution function in a reversed field pinch plasma

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JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 1996年第7期35卷 4064-4072页

作者： Yagi, Y Hirano, Y Shimada, T Maejima, Y Electrotechnical Laboratory Agency of Industrial Science and Technology MITI 1-1-4 Umezono Tsukuba-shi Ibaraki 305 Japan

Fast electrons in the edge region of the reversed field pinch (RFP) device, TPE-1RM20 are studied using an a electron energy analyzer (EEA) in the energy range below 1 keV. Results show that the fast electron velocity distribution function can be approximated either by a drift Maxwellian distribution function or two asymmetric half-Maxwellian distribution functions. The fast electron temperature is comparable to or slightly less than the central electron temperature depending on the fitting functions. The temperature obtained using the EEA is more than one order of magnitude lower than the characteristic fast electron energy estimated from soft X-ray emissions from the inserted materials at 2-8 keV. These observations indicate that fast electrons mainly have a Maxwellian distribution function with a temperature comparable to the central electron temperature-and that the distribution function may have a higher energy tail in the keV region.

关键词： reversed field pinch electron energy analyzer fast electron velocity distribution function

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velocity distribution functions and reactivity of D-T fusion plasma with spin-polarized fuel

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FUSION ENGINEERING AND DESIGN 2001年第4期55卷 467-475页

作者： Takahashi, T Nakao, Y Gunma Univ Dept Elect Engn Kiryu Gumma 3768515 Japan Kyushu Univ Dept Appl Quantum Phys & Nucl Engn Fukuoka 8128581 Japan

velocity distribution functions and the reactivity are calculated for D-T fusion plasma with spin-polarized fuel. The distribution functions are classified by spin states. Binary collisions and the resonance with waves are taken into account as depolarization mechanisms in plasmas. Spin-orbit interactions are shown to have no deleterious effect. However, lower hybrid heating and current drive using GHz waves resonant with the spin precession frequency are found to cause complete depolarization, when deltaB/B-0, (the ratio of the amplitude of the fluctuating magnetic field to the external field) exceeds 10(-5). Thus electron heating may increase the retention of polarization. Other depolarization mechanisms in plasmas will be also discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

关键词： spin-polarized fusion velocity distribution function thermonuclear reactivity depolarization

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Direct coupling between molecular dynamics and lattice Boltzmann method based on velocity distribution functions for steady-state isothermal flow

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2017年第PartA期115卷 544-555页

作者： Tong, Zi-Xiang Li, Ming-Jia Chen, Xi He, Ya-Ling Xi An Jiao Tong Univ Sch Energy & Power Engn Key Lab Thermofluid Sci & Engn Minist Educ 28 Xianning West Rd Xian 710049 Shaanxi Peoples R China Columbia Univ Dept Earth & Environm Engn New York NY 10027 USA

The direct coupling scheme between the molecular dynamics (MD) and lattice Boltzmann method (LBM) is established in this paper. Different from the existing coupling schemes which are based on the exchange of the density and velocities, the proposed coupling scheme is based on the velocity distribution functions. Firstly, the relations between the discrete velocity distribution functions of LBM and the continuous velocity distribution functions of MD are derived based on the Hermite expansions. Then, the coupling schemes between MD and LBM are proposed. The inconsistency between the equation of states of MD and LBM is specially treated and the deviatoric stresses are exchanged. The coupling simulations of the Poiseuille flow and Couette flow demonstrate that both the velocity and stress can be well exchanged by the coupling scheme. The coupling simulation of the flow past a nanotube shows that the proposed method can be further used in the study of microscopic fluid flow problems. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Hybrid Coupling simulation Lattice Boltzmann method Molecular dynamics velocity distribution function Hermite expansions

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NUMERICAL-SIMULATION OF INTENSE HELICAL ELECTRON-BEAMS WITH THE CALCULATION OF THE velocity distribution-functionS

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INTERNATIONAL JOURNAL OF INFRARED AND MILLIMETER WAVES 1995年第2期16卷 363-376页

作者： LYGIN, VK Institute of Applied Physics Russian Academy of Science Nizhny Novgorod Russia

The method of calculation of intense helical electron beams which allows to find the distribution function of electrons with respect to their transverse (oscillatory) and longitudinal velocities is developed. The initial velocity distribution function can be arbitrary. The data obtained in numerical simulation and experimental measurements for beams with various topologies are compared. The evolution of the transverse velocity distribution function with the beam current growth is traced. It is found that the transformation of the velocity distribution function may indicate a possible instability in a real beam.

关键词： MAGNETRON-INJECTION GUNS HELICAL ELECTRON BEAMS velocity distribution function velocity SPREAD

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Electron velocity distribution functions in a sputtering magnetron discharge for the ExB direction

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JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS 1998年第4期16卷 2173-2176页

作者： Sheridan, TE Goeckner, MJ Goree, J Univ Iowa Dept Phys & Astron Iowa City IA 52242 USA

The electron velocity distribution function is measured for the E x B (azimuthal) direction in a cylindrically symmetric, planar, sputtering magnetron discharge as a function of height above the cathode. Near the cathode, the distribution function is approximately a warm Maxwellian (T-e approximate to 2 eV) shifted in the E x B direction, indicating a strong azimuthal drift. Farther above the cathode, the distribution function is characterized by a cold (T-e approximate to 0.5 eV), Maxwellian bulk with energetic, asymmetric tails. (C) 1998 American Vacuum Society. [S0734-2101(98)05304-4].

关键词： Cathodes velocity distribution function Discharge (fluid mechanics) Patient Discharge Dismissal discharge Electron velocity distribution distribution function Sputtering

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