A general solution condition for collisionless sheaths

A general solution condition for collisionless sheaths is developed. Previous work has assumed that the Bohm criterion or the generalized Bohm criterion ensures a self-consistent sheath solution. This paper shows that for nonmonotonic collisionless sheath structures, such as double sheaths containing trapped ions, the generalized Bohm criterion is a necessary but not a sufficient condition. The general solution condition developed is always sufficient and the generalized Bohm criterion is shown to be special case of it. The general solution condition is applied to a double emitter sheath containing trapped ions. First, it is shown that the low-energy part of the plasma ion distribution coming into the sheath cannot be neglected as claimed in some analyses, because the shift in mean ion velocity through the pre-sheath (generalized Bohm speed) depends strongly on low-energy ions. Second, it is shown that the presence of trapped ions moves the point of critical self-consistency away from the collisionless sheath-neutral plasma asymptotic match and into the collisionless sheath. Consequently, both the sheath structure and the generalized Bohm speed depend on the amount of trapped ions. Thus collisional effects may dominate the structure of a presumably collisionless sheath through the trapping mechanism and the collisional pre-sheath which determines the low-energy ion component entering the collisionless sheath.

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The Spacecraft Potential’s Influence on the FOV of Rosetta-ICA at Low Ion Energies

10.5194/egusphere-egu2020-6871 ◽

2020 ◽

Author(s):

Sofia Bergman ◽

Gabriella Stenberg Wieser ◽

Martin Wieser ◽

Fredrik Johansson ◽

Anders Eriksson

Keyword(s):

Debye Length ◽

Low Energy ◽

In Situ Techniques ◽

Positive Ions ◽

Spacecraft Potential ◽

Energy Part ◽

Ion Energies ◽

Low Energies ◽

Composition Analyzer ◽

Low Energy Ions

Low-energy ions play important roles in many processes in the environments around various bodies in the solar system. At comets, they are, for example, important for the understanding of the interaction of the cometary particles with the solar wind, including the formation of the diamagnetic cavity. Unfortunately, spacecraft charging makes low-energy ions difficult to measure using in-situ techniques. The charged spacecraft surface will attract or repel the ions prior to detection, affecting both their trajectories and energy. The affected trajectories will change the effective FOV of the instrument. A negatively charged spacecraft will focus incoming positive ions, enlarging and distorting the FOV.We model the low-energy FOV distortion of the Ion Composition Analyzer (ICA) on board Rosetta. ICA is an ion spectrometer measuring positive ions with an energy range of a few eV to 40 keV. Rosetta was commonly charged to a negative potential throughout the mission, and consequently the positive ions were accelerated towards the spacecraft before detection. This distorted the low-energy part of the data. We use the Spacecraft Plasma Interaction Software (SPIS) to simulate the environment around the spacecraft and backtrace particles from the instrument. We then compare the travel direction of the ions at detection and infinity, and draw conclusions about the resulting FOV distortion. We investigate the distortion for different spacecraft potentials and Debye lengths of the surrounding plasma. The results show that the effective FOV of ICA is severely distorted at low energies, but the distortion varies between different viewing directions of the instrument. It is furthermore sensitive to changes in the Debye length and we observe a small non-linearity in the relation between FOV distortion, ion energy and spacecraft potential. Generally, the FOV is not significantly affected when the energy of the ions is above twice the spacecraft potential.

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Electrostatic interaction between Interball-2 and the ambient plasma. 2. Influence on the low energy ion measurements with Hyperboloid

Annales Geophysicae ◽

10.5194/angeo-20-377-2002 ◽

2002 ◽

Vol 20 (3) ◽

pp. 377-390 ◽

Cited By ~ 7

Author(s):

M. Hamelin ◽

M. Bouhram ◽

N. Dubouloz ◽

M. Malingre ◽

S. A. Grigoriev ◽

...

Keyword(s):

Spatial Scales ◽

Low Energy ◽

Solar Panels ◽

Ion Distribution ◽

Energy Channel ◽

Ambient Plasma ◽

Ion Distributions ◽

Wind Events ◽

Low Energy Ions ◽

Satellite Potential

Abstract. The measurement of the thermal ion distributions in space is always strongly influenced by the ion motion through the complex 3D electrostatic potential structure built around a charged spacecraft. In this work, we study the related aberrations of the ion distribution detected on board, with special application to the case of the Hyperboloid instrument borne by the Interball-2 auroral satellite. Most of the time, the Interball-2 high altitude auroral satellite is charged at some non-negligible positive potential with respect to the ambient plasma, as shown in part 1; in consequence, the measurement of magnetospheric low energy ions (< 80 eV) with the Hyperboloid instrument can be disturbed by the complex electric potential environment of the satellite. In the case of positive charging, as in previous experiments, a negative bias is applied to the Hyperboloid structure in order to reduce this effect and to keep as much as possible the opportunity to detect very low energy ions. Then, the ions reaching the Hyperboloid entrance windows would have travelled across a continuous huge electrostatic lens involving various spatial scales from ~ 10 cm (detector radius) to ~ 10 m (satellite antennas). Neglecting space charge effects, we have computed the ion trajectories that are able to reach the Hyperboloid windows within their acceptance angles. There are three main results: (i) for given values of the satellite potential, and for each direction of arrival (each window), we deduced the related energy cutoff; (ii) we found that all ions in the energy channel, including the cutoff, can come from a large range of directions in the unperturbed plasma, especially when the solar panels or antennas act as electrostatic mirrors; (iii) for higher energy channels, the disturbances are reduced to small angular shifts. Biasing of the aperture is not very effective with the Hyperboloid instrument (as on previous missions with instruments installed close to the spacecraft body) because the potential environment is driven by effects from the spacecraft. Our results are used to explain some unexpected features of the low energy ion measurements, especially during polar wind events recorded by Hyperboloid. In conclusion, knowing the satellite potential from IESP measurements, we were able to reject any low energy doubtful data and to perform angular corrections for all higher energy ion data. Then the selected and corrected data are a reliable basis for interpretation and estimation of the thermal ion distributions.Key words. Space plasma physics (charged particle motion and acceleration; numerical simulation studies; spacecraft sheaths, wakes, charging)

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Analysis of Experimental Data for Neutralization of Low-Energy Ions at a Solid Surface.

10.21236/ada163205 ◽

1986 ◽

Author(s):

Hai-Woong Lee ◽

Thomas F. George

Keyword(s):

Experimental Data ◽

Solid Surface ◽

Low Energy ◽

Low Energy Ions

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Ion-Assisted Surface Processing of Electronic Materials

MRS Bulletin ◽

10.1557/s0883769400041476 ◽

1992 ◽

Vol 17 (6) ◽

pp. 52-57 ◽

Cited By ~ 6

Author(s):

S.T. Picraux ◽

E. Chason ◽

T.M. Mayer

Keyword(s):

Plasma Etching ◽

Electronic Materials ◽

Low Energy ◽

Surface Processing ◽

Wave Guides ◽

Side Walls ◽

Wet Chemical ◽

Low Energy Ions ◽

Metal Layers ◽

Defect Densities

Why are low-energy ions relevant to the surface processing of electronic materials? The answer lies in the overriding trend of miniaturization in microelectronics. The achievement of these feats in ultrasmall architecture has required surface processing capabilities that allow layer addition and removal with incredible precision. The resulting benefits of greater capacity and speed at a plummeting cost per function are near legendary.The ability of low-energy ions to enhance the precision of surface etching, cleaning, and deposition/growth processes (Figure 1) provides one basis for the interest in ion-assisted processes. Low-energy ions are used, for example, to enhance the sharpness of side walls in plasma etching and to improve step coverage by metal layers in sputter deposition. Emerging optoelectronic applications such as forming ridges for wave-guides and ultrasmooth vertical surfaces for lasers further extend piesent requirements, and low-energy ions again provide one tool to help in this area of ultraprecise materials control. Trends associated with the decreased feature size include the movement from wet chemical processing to dry processing, the continuing need for reductions in defect densities, and the drive toward reduced temperatures and times in process steps.How do the above trends focus interest on studies of low-energy ion-assisted processes? In current applications, these trends are driving the need for increased atomic-level understanding of the ion-enhancement mechanisms, for example, in reactive ion etching to minimize defect production and enhance surface chemical reactions.

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A method to estimate a contribution of Ge(n,n′) reaction to the low-energy part of gamma spectra of HPGe detectors

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment ◽

10.1016/j.nima.2012.12.122 ◽

2013 ◽

Vol 709 ◽

pp. 8-11 ◽

Cited By ~ 9

Author(s):

M. Krmar ◽

J. Hansman ◽

N. Jovančević ◽

N. Lalović ◽

J. Slivka ◽

...

Keyword(s):

Low Energy ◽

Energy Part ◽

Hpge Detectors ◽

Gamma Spectra

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Modelling Interaction Cross Sections for Intermediate and Low Energy Ions

Radiation Protection Dosimetry ◽

10.1093/oxfordjournals.rpd.a006837 ◽

2002 ◽

Vol 99 (1) ◽

pp. 49-51 ◽

Cited By ~ 1

Author(s):

L. H. Toburen ◽

J. L. Shinpaugh ◽

E. L. B. Justiniano

Keyword(s):

Cross Sections ◽

Low Energy ◽

Low Energy Ions ◽

Interaction Cross Sections

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Epitaxy and Chemical Reactions During Thin Film Formation from Low Energy Ions New Kinetic Pathways, New Phases and New Properties

MRS Proceedings ◽

10.1557/proc-236-287 ◽

1991 ◽

Vol 236 ◽

Cited By ~ 1

Author(s):

Nicole Herbots ◽

O.C. Hellman ◽

O. Vancauwenberghe

Keyword(s):

Thin Film ◽

Chemical Reactions ◽

Degrees Of Freedom ◽

Film Growth ◽

Film Formation ◽

Chemical Reactivity ◽

Ion Beam ◽

Low Energy ◽

Low Energy Ions ◽

Beam Deposition

AbstractThree important effects of low energy direct Ion Beam Deposition (IBD) are the athermal incorporation of material into a substrate, the enhancement of atomic mobility in the subsurface, and the modification of growth kinetics it creates. All lead to a significant lowering of the temperature necessary to induce epitaxial growth and chemical reactions. The fundamental understanding and new applications of low temperature kinetics induced by low energy ions in thin film growth and surface processing of semiconductors are reviewed. It is shown that the mechanism of IBD growth can be understood and computed quantitatively using a simple model including ion induced defect generation and sputtering, elastic recombination, thermal diffusion, chemical reactivity, and desorption The energy, temperature and dose dependence of growth rate, epitaxy, and chemical reaction during IBD is found to be controlled by the net recombination rate of interstitials at the surface in the case of epitaxy and unreacted films, and by the balance between ion beam decomposition and phase formation induced by ion beam generated defects in the case of compound thin films. Recent systematic experiments on the formation of oxides and nitrides on Si, Ge/Si(100), heteroepitaxial SixGe1−x/Si(100) and GaAs(100) illustrate applications of this mechanism using IBD in the form of Ion Beam Nitridation (IBN), Ion Beam Oxidation (IBO) and Combined Ion and Molecular beam Deposition (CIMD). It is shown that these techniques enable (1) the formation of conventional phases in conditions never used before, (2) the control and creation of properties via new degrees of freedom such as ion energy and lowered substrate temperatures, and (3) the formation of new metastable heterostructures that cannot be grown by pure thermal means.

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The Uniform Flexure of an Incomplete Tore

Australian Journal of Chemistry ◽

10.1071/ch9490469 ◽

1949 ◽

Vol 2 (4) ◽

pp. 469

Author(s):

W Freiberger ◽

RCT Smith

Keyword(s):

General Solution ◽

Cross Section ◽

Harmonic Functions ◽

Rectangular Cross Section ◽

Three Dimensional ◽

Elasticity Problems ◽

Three Dimensional Elasticity ◽

Derivatives Of ◽

Special Case

In this paper we discuss the flexure of an incomplete tore in the plane of its circular centre-line. We reduce the problem to the determination of two harmonic functions, subject to boundary conditions on the surface of the tore which involve the first two derivatives of the functions. We point out the relation of this solution to the general solution of three-dimensional elasticity problems. The special case of a narrow rectangular cross-section is solved exactly in Appendix II.

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