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Sample records for plasma sheath obliquely

  1. Dust-Plasma Sheath in an Oblique Magnetic Field

    SciTech Connect

    Foroutan, G.; Mehdipour, H.

    2008-09-07

    Using numerical simulations of the multi fluid equations the structure of the magnetized sheath near a plasma boundary is studied in the presence of charged dust particles. The dependence of the electron, ion, and dust densities as well as the electrostatic potential, dust charge, and ion normal velocity, on the magnetic field strength and the edge dust number density is investigated.

  2. Effect of electron reflection on magnetized plasma sheath in an oblique magnetic field

    SciTech Connect

    Wang, Ting-Ting; Ma, J. X. Wei, Zi-An

    2015-09-15

    Magnetized plasma sheaths in an oblique magnetic field were extensively investigated by conventionally assuming Boltzmann relation for electron density. This article presents the study of the magnetized sheath without using the Boltzmann relation but by considering the electron reflection along the magnetic field lines caused by the negative sheath potential. A generalized Bohm criterion is analytically derived, and sheath profiles are numerically obtained, which are compared with the results of the conventional model. The results show that the ion Mach number at the sheath edge normal to the wall has a strong dependence on the wall potential, which differs significantly from the conventional model in which the Mach number is independent of the wall potential. The floating wall potential is lower in the present model than that in the conventional model. Furthermore, the sheath profiles are appreciably narrower in the present model when the wall bias is low, but approach the result of the conventional model when the wall bias is high. The sheath thickness decreases with the increase of ion-to-electron temperature ratio and magnetic field strength but has a complex relationship with the angle of the magnetic field.

  3. Radio frequency sheaths in an oblique magnetic field

    DOE PAGESBeta

    Myra, James R.; D'Ippolito, Daniel A.

    2015-06-01

    The physics of radio-frequency (rf) sheaths near a conducting surface is studied for plasmas immersed in a magnetic field that makes an oblique angle θ with the surface. A set of one-dimensional equations is developed that describe the dynamics of the time-dependent magnetic presheath and non-neutral Debye sheath. The model employs Maxwell-Boltzmann electrons, and the magnetization and mobility of the ions is determined by the magnetic field strength, and wave frequency, respectively. The angle, θ assumed to be large enough to insure an electron-poor sheath, is otherwise arbitrary. Concentrating on the ion-cyclotron range of frequencies, the equations are solved numericallymore » to obtain the rectified (dc) voltage, the rf voltage across the sheath and the rf current flowing through the sheath. As an application of this model, the sheath voltage-current relation is used to obtain the rf sheath impedance, which in turn gives an rf sheath boundary condition for the electric field at the sheath-plasma interface that can be used in rf wave codes. In general the impedance has both resistive and capacitive contributions, and generalizes previous sheath boundary condition models. The resistive part contributes to parasitic power dissipation at the wall.« less

  4. Radio frequency sheaths in an oblique magnetic field

    SciTech Connect

    Myra, James R.; D'Ippolito, Daniel A.

    2015-06-01

    The physics of radio-frequency (rf) sheaths near a conducting surface is studied for plasmas immersed in a magnetic field that makes an oblique angle θ with the surface. A set of one-dimensional equations is developed that describe the dynamics of the time-dependent magnetic presheath and non-neutral Debye sheath. The model employs Maxwell-Boltzmann electrons, and the magnetization and mobility of the ions is determined by the magnetic field strength, and wave frequency, respectively. The angle, θ assumed to be large enough to insure an electron-poor sheath, is otherwise arbitrary. Concentrating on the ion-cyclotron range of frequencies, the equations are solved numerically to obtain the rectified (dc) voltage, the rf voltage across the sheath and the rf current flowing through the sheath. As an application of this model, the sheath voltage-current relation is used to obtain the rf sheath impedance, which in turn gives an rf sheath boundary condition for the electric field at the sheath-plasma interface that can be used in rf wave codes. In general the impedance has both resistive and capacitive contributions, and generalizes previous sheath boundary condition models. The resistive part contributes to parasitic power dissipation at the wall.

  5. Radio frequency sheaths in an oblique magnetic field

    SciTech Connect

    Myra, J. R.; D'Ippolito, D. A.

    2015-06-15

    The physics of radio-frequency (rf) sheaths near a conducting surface is studied for plasmas immersed in a magnetic field that makes an oblique angle θ with the surface. A set of one-dimensional equations is developed that describes the dynamics of the time-dependent magnetic presheath and non-neutral Debye sheath. The model employs Maxwell-Boltzmann electrons, and the magnetization and mobility of the ions is determined by the magnetic field strength, and wave frequency, respectively. The angle θ, assumed to be large enough to insure an electron-poor sheath, is otherwise arbitrary. Concentrating on the ion-cyclotron range of frequencies, the equations are solved numerically to obtain the rectified (dc) voltage, the rf voltage across the sheath, and the rf current flowing through the sheath. As an application of this model, the sheath voltage-current relation is used to obtain the rf sheath impedance, which in turn gives an rf sheath boundary condition for the electric field at the sheath-plasma interface that can be used in rf wave codes. In general, the impedance has both resistive and capacitive contributions, and generalizes previous sheath boundary condition models. The resistive part contributes to parasitic power dissipation at the wall.

  6. Radio frequency sheaths in an oblique magnetic field

    NASA Astrophysics Data System (ADS)

    Myra, J. R.; D'Ippolito, D. A.

    2015-06-01

    The physics of radio-frequency (rf) sheaths near a conducting surface is studied for plasmas immersed in a magnetic field that makes an oblique angle θ with the surface. A set of one-dimensional equations is developed that describes the dynamics of the time-dependent magnetic presheath and non-neutral Debye sheath. The model employs Maxwell-Boltzmann electrons, and the magnetization and mobility of the ions is determined by the magnetic field strength, and wave frequency, respectively. The angle θ, assumed to be large enough to insure an electron-poor sheath, is otherwise arbitrary. Concentrating on the ion-cyclotron range of frequencies, the equations are solved numerically to obtain the rectified (dc) voltage, the rf voltage across the sheath, and the rf current flowing through the sheath. As an application of this model, the sheath voltage-current relation is used to obtain the rf sheath impedance, which in turn gives an rf sheath boundary condition for the electric field at the sheath-plasma interface that can be used in rf wave codes. In general, the impedance has both resistive and capacitive contributions, and generalizes previous sheath boundary condition models. The resistive part contributes to parasitic power dissipation at the wall.

  7. Communication through plasma sheaths

    SciTech Connect

    Korotkevich, A. O.; Newell, A. C.; Zakharov, V. E.

    2007-10-15

    We wish to transmit messages to and from a hypersonic vehicle around which a plasma sheath has formed. For long distance transmission, the signal carrying these messages must be necessarily low frequency, typically 2 GHz, to which the plasma sheath is opaque. The idea is to use the plasma properties to make the plasma sheath appear transparent.

  8. Plasma-Sheath Model

    NASA Astrophysics Data System (ADS)

    Riemann, Karl-Ulrich

    2012-10-01

    In typical gas discharges a quasineutral plasma is shielded from a negativ absorbing wall by a thin positive sheath that is nearly planar and collision-free. The subdivision of ``plasma'' and ``sheath'' was introduced by Langmuir and is based on a small ratio of the electron Debye lenghth λD to the dominant competing characteristic plasma length l. Depending on the special conditions, l may represent, e.g., the plasma extension, the ionization length, the ion mean free path, the ion gyro radius, or a geometric length. Strictly speaking, this subdivion is possible only in the asymptotic limit λD/l->0. The asymptotic analysis results in singularities at the ``sheath edge'' closely related to the ``Bohm criterion.'' Due to these singularities a direct smooth matching of the separate plasma and sheath soltions is not possible. To obtain a consistent smooth transition, the singular sheath edge must be bridged by an additinal narrow ``intermediate'' model zone accounting both for plasma processes (e.g., collisions) and for the first build up of space charge. Due to this complexity and to different interpretations of the ``classical'' papers by Langmuir and Bohm, the asymptotic plasma-sheath concept and the definition of the sheath edge were questioned and resulted in controversies during the last two decades. We discuss attempts to re-define the sheath edge, to account for finite values of λD/l in the Bohm criterion, and demonstrate the consistent matching of plasma and sheath. The investigations of the plasma-sheath transition discussed so far are based on a simplified fluid analysis that cannot account for the essential inhomogeneity of the boundary layer and for the dominant role of slow ions in space charge formation. Therefore we give special emphasis to the kinetic theory of the plasma-sheath transition. Unfortunately this approach results in an additional mathematical difficulty caused by ions with zero velocity. We discuss attempts to avoid this singularity by

  9. The plasma drag and dust motion inside the magnetized sheath

    SciTech Connect

    Pandey, B. P.; Vladimirov, S. V.; Samarian, A.

    2011-05-15

    The motion of micron size dust inside the sheath in the presence of an oblique magnetic field is investigated by self-consistently calculating the charge and various forces acting on the dust. It is shown that the dust trajectory inside the sheath, which is like an Archimedean spiral swinging back and forth between the wall and the plasma-sheath boundary, depends only indirectly on the orientation of the magnetic field. When the Lorentz force is smaller than the collisional momentum exchange, the dust dynamics is insensitive to the obliqueness of the magnetic field. Only when the magnetic field is strong enough, the sheath structure and, thus, the dust dynamics are significantly affected by the field orientation. Balance between the plasma drag, sheath electrostatic field, and gravity plays an important role in determining how far the dust can travel inside the sheath. The dust equilibrium point shifts closer to the wall in the presence of gravity and plasma drag. However, in the absence of plasma drag, dust can sneak back into the plasma if acted only by gravity. The implication of our results to the usability of dust as a sheath probe is discussed.

  10. Sheath energy transmission in a collisional plasma with collisionless sheath

    SciTech Connect

    Tang, Xian-Zhu Guo, Zehua

    2015-10-15

    Sheath energy transmission governs the plasma energy exhaust onto a material surface. The ion channel is dominated by convection, but the electron channel has a significant thermal conduction component, which is dominated by the Knudsen layer effect in the presence of an absorbing wall. First-principle kinetic simulations reveal a robustly supersonic sheath entry flow. The ion sheath energy transmission and the sheath potential are accurately predicted by a sheath model of truncated bi-Maxwellian electron distribution. The electron energy transmission is further enhanced by a parallel heat flux of the perpendicular degrees of freedom.

  11. Plasma sheath driven targets

    NASA Astrophysics Data System (ADS)

    Brownell, J. H.; Freeman, B. L.

    1980-02-01

    Plasma focus driven target implosions are simulated using hydrodynamic-burn codes. Support is given to the idea that the use of a target in a plasma focus should allow 'impedance matching' between the fuel and gun, permitting larger fusion yields from a focus-target geometry than the scaling laws for a conventional plasma focus would predict.

  12. Computed tomography in the evaluation of Brown syndrome of the superior oblique tendon sheath

    SciTech Connect

    Mafee, M.F.; Folk, E.R.; Langer, B.G.; Miller, M.T.; Lagouros, P.; Mittleman, D.

    1985-03-01

    Computed tomographic (CT) findings in 4 patients with superior oblique tendon sheath syndrome (congenital or acquired Brown syndrome) are described. When the inferior oblique muscle moves the eye upward, the superior oblique muscle normally relaxes, while its tendon lengthens and slides freely through the trochlea. In Brown syndrome this process is somehow restricted, which is most apparent during attempts at elevation when the eye is adducted, resulting in an apparent inferior oblique palsy (pseudopalsy). CT is a valuable tool in understanding the pathophysiology and management of acquired Brown syndrome, showing thickening and inflammatory changes of the reflected portion of the superior oblique tendon.

  13. Optical properties of nonextensive inhomogeneous plasma sheath

    NASA Astrophysics Data System (ADS)

    Mousavi, A.; Esfandiari-Kalejahi, A.; Akbari-Moghanjoughi, M.

    2016-07-01

    Propagation of electromagnetic wave through an inhomogeneous magnetized nonextensive plasma sheath is numerically examined for a realistic density profile of a reentry problem around a hypersonic vehicle. The effect of nonextensivity and inhomogeneity on radio wave communication is studied parametrically. Variation of reflection and transmission coefficients, total attenuation, and total phase shift over the plasma sheath with respect to the strength of applied magnetic field are derived and compared for different values of q-nonextensive parameter. The obtained results for inhomogeneous plasma sheath are compared with previously obtained results of authors for homogeneous plasma sheath. The comparison shows that radio communication in the inhomogeneous plasma sheath is more advantageous than that in the homogeneous case. The transmission coefficient of a plasma sheath with superthermal electrons ( /1 3 < q < 1 ) has larger value compared to that with q > 1. Moreover, for ω c e > ω , the minimum value of total attenuation corresponds to the range /1 3 < q < 1 . An interesting result is that nonextensivity effect on wave propagation in plasma sheath depends on the strength of the ambient magnetic field. The effect of nonextensivity on attenuation coefficient is found to be negligible for ω c e < ω while it is significant for ω c e > ω .

  14. Modeling of dynamic bipolar plasma sheaths

    NASA Astrophysics Data System (ADS)

    Grossmann, J. M.; Swanekamp, S. B.; Ottinger, P. F.

    1992-01-01

    The behavior of a one-dimensional plasma sheath is described in regimes where the sheath is not in equilibrium because it carries current densities that are either time dependent, or larger than the bipolar Child-Langmuir level determined from the injected ion flux. Earlier models of dynamic bipolar sheaths assumed that ions and electrons evolve in a series of quasiequilibria. In addition, sheath growth was described by the equation Zen0ẋs=‖ ji‖-Zen0u0, where ẋs is the velocity of the sheath edge, ji is the ion current density, n0u0 is the injected ion flux density, and Ze is the ion charge. In this paper, a generalization of the bipolar electron-to-ion current density ratio formula is derived to study regimes where ions are not in equilibrium. A generalization of the above sheath growth equation is also developed, which is consistent with the ion continuity equation and which reveals new physics of sheath behavior associated with the emitted electrons and their evolution. Based on these findings, two new models of dynamic bipolar sheaths are developed. Larger sheath sizes and potentials than those of earlier models are found. In certain regimes, explosive sheath growth is predicted.

  15. Theory and simulation of plasma sheath waves

    SciTech Connect

    Xu, X.Q.; DiPeso, G.; Vahedi, V.; Birdsall, C.K.

    1992-12-15

    Sheath waves have been investigated analytically and with particle simulation for an unmagnetized two dimensional plasma slab with periodic boundary conditions in y and conducting walls at x = 0, L{sub x}. Analytically treating the sheath as a vacuum layer, the sheath wave bears a resemblance to plasma vacuum surface waves. The simulations are in agreement with the theory for both bulk Bohm Grow waves and edge sheath waves, with some unanswered questions. Some waves that were expected did not show up, at least, where we thought they should be. Hence, improvements were made in the initialization (a better quiet start), in the diagnostics (especially the spectra in frequency), and in the excitation (ability to pulse). It has become clear that this problem, seeking both sheath (or surface) and body waves in a bounded system, needs far more attention, in analysis (non-uniform density included) and in simulation, especially in diagnostics. Hence, this report is to be treated as a start on the problem. The problem is not dropped, as the understanding of such waves (in 2d and 3d) is very important, for both basic sheath understanding and for applications, such as plasma control via excitation of sheath or pre-sheath waves.

  16. How to Patch Active Plasma and Collisionless Sheath: Practical Guide

    SciTech Connect

    Kaganovich, Igor D.

    2002-08-22

    Most plasmas have a very thin sheath compared with the plasma dimension. This necessitates separate calculations of the plasma and sheath. The Bohm criterion provides the boundary condition for calculation of plasma profiles. To calculate sheath properties, a value of electric field at the plasma-sheath interface has to be specified in addition to the Bohm criterion. The value of the boundary electric field and robust procedure to approximately patch plasma and collisionless sheath with a very good accuracy are reported.

  17. Multidimensional Plasma Sheaths over Electrically Inhomogeneous Surfaces

    NASA Astrophysics Data System (ADS)

    Economou, Demetre

    2004-09-01

    Multidimensional plasma sheaths are encountered in a number of applications including plasma immersion ion implantation, extraction of ions (or plasma) through grids, MEMS fabrication, neutral beam sources, and plasma in contact with internal reactor parts (e.g., wafer chuck edge). The sheath may be multidimensional when: (a) plasma is in contact with surface topography, and the size of the topographical features is comparable to or larger than the plasma sheath thickness, or (b) the surface is flat but inhomogeneous, i.e., a conducting surface next to an insulating surface. In either case, the flux, energy and angular distributions of energetic species incident on the substrate are of primary importance. These quantities depend critically on the shape of the meniscus (plasma-sheath boundary) formed over the surface. A two-dimensional fluid/Monte Carlo simulation model was developed to study multidimensional sheaths. The radio frequency (RF) sheath potential evolution, and ion density and flux profiles over the surface were predicted with a self-consistent fluid simulation. The trajectories of ions and energetic neutrals (resulting by ion neutralization on surfaces or charge exchange collisions in the gas phase) were then followed with a Monte Carlo simulation. Ion flow and energy and angular distributions of ions bombarding a flat but electrically inhomogeneous surface will be reported in detail. Ion flow over trenches and holes will also be reported. Work supported by the NSF, Sandia National Laboratories and NIST.

  18. Revisiting the plasma sheath—dust in plasma sheath

    NASA Astrophysics Data System (ADS)

    Das, G. C.; Deka, R.; Bora, M. P.

    2016-04-01

    In this work, we have considered the formation of warm plasma sheath in the vicinity of a wall in a plasma with considerable presence of dust particles. As an example, we have used the parameters relevant in case of plasma sheath formed around surfaces of various solid bodies in space, though the results obtained in this work can be applied to any other physical situation such as laboratory plasma. In the ion-acoustic time scale, we neglect the dust dynamics. The dust particles affect the sheath dynamics by affecting the Poisson equation which determines the plasma potential in the sheath region. It is important to note that our calculations are valid only when the amount of dust particles is not sufficient so as to affect the plasma dynamics in the dust-acoustic time scale, but enough to affect the plasma sheath. We have assumed the current to a dust particle to be balanced throughout the analysis. This makes the grain potential dependent on plasma potential, which is then incorporated into the Poisson equation. The resultant numerical model becomes an initial value problem, which is described by a 1-D integro-differential equation, which is then solved self-consistently by incorporating the change in plasma potential caused by inclusion of the dust potential in the Poisson equation.

  19. Effects of plasma sheath on solar power satellite array

    NASA Technical Reports Server (NTRS)

    Parker, L. W.

    1979-01-01

    The structure of the plasma sheath and equilibrium voltage distribution of a high-power solar array governs various kinds of plasma-interaction phenomena and array losses. Sheath effects of a linearly-connected array are investigated for GEO. Although the array may be large, the thin-sheath-limit analysis may be invalid, necessitating numerical methods. Three-dimensional computer calculations show that potential barriers and over-lapping sheaths can occur, i.e., structures not predictable under the thin-sheath-limit analysis, but nevertheless controlling the distribution of plasma currents impacting on the array.

  20. Oblique shock dynamics in nonextensive magnetized plasma

    NASA Astrophysics Data System (ADS)

    Bains, A. S.; Tribeche, M.

    2014-05-01

    A study is presented for the oblique propagation of low-frequency ion-acoustic ( IA) shock waves in a magnetized plasma having cold viscous ion fluid and nonextensively distributed electrons. A weakly nonlinear analysis is carried out to derive a Korteweg de-Vries-Burger like equation. Dependence of the shock wave characteristics (height, width and nature) on plasma parameters is then traced and studied in details. We hope that our results will aid to explain and interpret the nonlinear oscillations occurring in magnetized space plasmas.

  1. Simulations of plasma sheaths using continuum kinetic models

    NASA Astrophysics Data System (ADS)

    Srinivasan, Bhuvana; Hakim, Ammar

    2015-11-01

    Understanding plasma sheath physics is important for the performance of devices such as Hall thrusters due to the effect of energetic particles on electrode erosion. Plasma sheath physics is studied using kinetic and multi-fluid models with relevance to secondary electron emissions and plasma-surface interactions. Continuum kinetic models are developed to directly solve the Vlasov-Poisson equation using the discontinuous Galerkin method for each of the ion and electron species. A steady-state sheath is simulated by including a simple model for a neutral fluid. Multi-fluid simulations for the plasma sheath are also performed using the discontinuous Galerkin method to solve a complete set of fluid equations for each of the ion and electron species. The kinetic plasma sheath is compared to a multi-fluid plasma sheath. Supported by Air Force Office of Scientific Research.

  2. Modelling of Charged Particle Dynamics in the Sheath and Plasma-facing Surface Sputtering

    NASA Astrophysics Data System (ADS)

    Borodkina, I. E.; Tsvetkov, I. V.

    In this work a useful analytical approximation for the electric potential profile in the presence of an oblique magnetic field is suggested. It describes the potential profile dependence on the magnitude and angle of a magnetic field and plasma parameters in the Debye sheath and the magnetic pre-sheath. It is in good agreement with the Chodura and Stangeby solutions and respective PIC simulations performed with the SPICE2 code. The influence of the magnetic field inclination angle on the angle and energy distributions of ions which reach the wall, and thus on the effective sputtering, is analyzed for various first wall materials.

  3. Fluid model of the sheath in front of a floating electrode immersed in a magnetized plasma with oblique magnetic field: Some comments on ion source terms and ion temperature effects

    NASA Astrophysics Data System (ADS)

    Gyergyek, T.; Kovačič, J.

    2015-04-01

    A one-dimensional fluid model of the magnetized plasma-wall transition region in front of a floating electrode immersed in a magnetized plasma with oblique magnetic field is presented. The Boltzmann relation is assumed for the electrons, while the positive ions obey the ion continuity and momentum exchange equation. The ions are assumed to be isothermal. By comparison with a two-fluid model, it is shown that assuming the Boltzmann relation for the electrons implies that there is no creation or annihilation of the electrons. Consequently, there should not be any creation and annihilation of the positive ions either. The models that assume the Boltzmann relation for the electrons and a non-zero ion source term at the same time are therefore inconsistent, but such models have nevertheless been used extensively by many authors. So, in this work, an extensive comparison of the results obtained using the zero source term on one hand and three different non-zero source terms on the other hand is made. Four different ion source terms are considered in total: the zero source term and three different non-zero ion source terms. When the zero source term is used, the model becomes very sensitive to the boundary conditions, and in some cases, the solutions exhibit large amplitude oscillations. If any of the three non-zero ion source terms is used, those problems are eliminated, but also the consistency of the model is broken. The model equations are solved numerically in the entire magnetized plasma-wall transition region. For zero ion temperature, the model can be solved even if a very small ion velocity is selected as a boundary condition. For finite ion temperature, the system of equations becomes stiff, unless the ion velocity at the boundary is increased slightly above the ion thermal velocity. A simple method how to find a solution with a very small ion velocity at the boundary also for finite ion temperature in the entire magnetized plasma-wall transition region is

  4. Fluid model of the sheath in front of a floating electrode immersed in a magnetized plasma with oblique magnetic field: Some comments on ion source terms and ion temperature effects

    SciTech Connect

    Gyergyek, T.; Kovačič, J.

    2015-04-15

    A one-dimensional fluid model of the magnetized plasma-wall transition region in front of a floating electrode immersed in a magnetized plasma with oblique magnetic field is presented. The Boltzmann relation is assumed for the electrons, while the positive ions obey the ion continuity and momentum exchange equation. The ions are assumed to be isothermal. By comparison with a two-fluid model, it is shown that assuming the Boltzmann relation for the electrons implies that there is no creation or annihilation of the electrons. Consequently, there should not be any creation and annihilation of the positive ions either. The models that assume the Boltzmann relation for the electrons and a non-zero ion source term at the same time are therefore inconsistent, but such models have nevertheless been used extensively by many authors. So, in this work, an extensive comparison of the results obtained using the zero source term on one hand and three different non-zero source terms on the other hand is made. Four different ion source terms are considered in total: the zero source term and three different non-zero ion source terms. When the zero source term is used, the model becomes very sensitive to the boundary conditions, and in some cases, the solutions exhibit large amplitude oscillations. If any of the three non-zero ion source terms is used, those problems are eliminated, but also the consistency of the model is broken. The model equations are solved numerically in the entire magnetized plasma-wall transition region. For zero ion temperature, the model can be solved even if a very small ion velocity is selected as a boundary condition. For finite ion temperature, the system of equations becomes stiff, unless the ion velocity at the boundary is increased slightly above the ion thermal velocity. A simple method how to find a solution with a very small ion velocity at the boundary also for finite ion temperature in the entire magnetized plasma-wall transition region is

  5. Kinetic model for the collisionless sheath of a collisional plasma

    NASA Astrophysics Data System (ADS)

    Tang, Xian-Zhu; Guo, Zehua

    2016-08-01

    Collisional plasmas typically have mean-free-path still much greater than the Debye length, so the sheath is mostly collisionless. Once the plasma density, temperature, and flow are specified at the sheath entrance, the profile variation of electron and ion density, temperature, flow speed, and conductive heat fluxes inside the sheath is set by collisionless dynamics, and can be predicted by an analytical kinetic model distribution. These predictions are contrasted here with direct kinetic simulations, showing good agreement.

  6. Charge separation in a magnetized plasma-sheath-lens

    NASA Astrophysics Data System (ADS)

    Stamate, Eugen

    2009-10-01

    Most of plasma processing technologies are based on radical-assisted ion-induced surface-modification where ions accumulate energy in the sheath, and then strike the surface modifying its properties in a desirable way. Plasma-sheath-lens is a three-dimensional potential distribution of customized shape, formed by the space charge surrounding a biased electrode-insulator interface. The discrete and modal focusing effects have been reveled for this type of electrostatic structures formed in plasma [1] and several applications including sheath thickness evaluation, negative ion detection and extraction of positive or negative ion beams have been developed. A non-magnetized plasma-sheath-lens act as a kinetic energy separator, but it is not mass sensitive. However, a magnetized plasma-sheath-lens exhibits mass separation, so that ions of different mass will impact the electrode at different locations on the biased electrode surface. The mass spectrum can be measured as the radial distribution of the ion current density over the plasma-sheath-lens's electrode. Relevant fluid and particles simulations of the magnetized plasma-sheath-lens structures and ion trajectories within them are presented for different plasma parameters and magnetic filed configurations. Practical aspects linked to the development of a new type of mass spectrometers are also investigated.[0pt] [1] E. Stamate and H. Sugai, Phys. Rev. Lett. (2005) 94, 125004

  7. Space charge sheath in plasma-neutral gas interaction

    NASA Astrophysics Data System (ADS)

    Venkataramani, N.; Mattoo, S. K.

    1986-04-01

    A space charge sheath is found to be formed whenever a high-velocity magnetized plasma stream penetrates a gas cloud. The sheath is always located at the head of the plasma stream, and its thickness is very small compared to the length of the plasma stream. Soon after the sheath is formed it quickly slows down to the Alfven critical velocity. The plasma behind the sheath continues to move at higher velocity until the whole plasma stream is retarded to the critical velocity. In the interaction at gas density of about 10 to the 19th/cu cm, the sheaths are observed to be accompanied by a single loop of current with current density of about 10,000 A/sq m. Maximum potential in the sheath ranges between 50 and 200 V. Presently available models for the sheath may explain the initiation of the sheath formation. Physical processes like heating of the electrons and ionization of the gas cloud which come into play at a later stage of the interaction are not included in these models. These processes considerably alter the potential structure in the sheath region. A schematic model of the observed sheath is presented. Experiments reveal a threshold value of the magnetic field for plasma retardation to occur. This seems to correspond to the threshold condition for excitation of the modified two-stream instability, which can lead to the electron heating. The observed currents are found sufficient to account for the plasma retardation at a gas density of about 10 to the 17th/cu m.

  8. Anode Sheath Switching in a Carbon Nanotube Arc Plasma

    SciTech Connect

    Abe Fetterman, Yevgeny Raitses, and Michael Keidar

    2008-04-08

    The anode ablation rate is investigated as a function of anode diameter for a carbon nanotube arc plasma. It is found that anomalously high ablation occurs for small anode diameters. This result is explained by the formation of a positive anode sheath. The increased ablation rate due to this positive anode sheath could imply greater production rate for carbon nanotubes.

  9. Plasma sheath multipath analysis and its effect on GNSS navigation

    NASA Astrophysics Data System (ADS)

    Du, Yongxing; Xi, Xiaoli; Song, Zhongguo; Liu, Jiangfan

    2015-11-01

    When hypersonic vehicle reenters the Earth's atmosphere, the plasma sheath will be generated by its collision with ambient air that would affect global navigation satellite system (GNSS). In order to understand such effects, the transmission coefficient of the plasma sheath has been investigated using the numerical method before. But this is found to be insufficient, for besides the attenuation on the signal energy, the multipath effect between the plasma sheath and the vehicle surface is also a serious factor, which may result in errors in pseudorange measurement and carrier phase measurement of GNSS receiver and finally affect the positioning accuracy. The multipath of the plasma sheath is analyzed by finite-difference time-domain method combined with further signal processing, and a simulation platform is established to verify this effects on positioning performance. Simulation results indicate the degradation of positioning performance when these multipath signals were present, causing position error with several meters to tens of meters.

  10. Effects of emitted electron temperature on the plasma sheath

    SciTech Connect

    Sheehan, J. P.; Kaganovich, I. D.; Wang, H.; Raitses, Y.; Sydorenko, D.; Hershkowitz, N.

    2014-06-15

    It has long been known that electron emission from a surface significantly affects the sheath surrounding that surface. Typical fluid theory of a planar sheath with emitted electrons assumes that the plasma electrons follow the Boltzmann relation and the emitted electrons are emitted with zero energy and predicts a potential drop of 1.03T{sub e}/e across the sheath in the floating condition. By considering the modified velocity distribution function caused by plasma electrons lost to the wall and the half-Maxwellian distribution of the emitted electrons, it is shown that ratio of plasma electron temperature to emitted electron temperature significantly affects the sheath potential when the plasma electron temperature is within an order of magnitude of the emitted electron temperature. When the plasma electron temperature equals the emitted electron temperature the emissive sheath potential goes to zero. One dimensional particle-in-cell simulations corroborate the predictions made by this theory. The effects of the addition of a monoenergetic electron beam to the Maxwellian plasma electrons were explored, showing that the emissive sheath potential is close to the beam energy only when the emitted electron flux is less than the beam flux.

  11. An analytic expression for the sheath criterion in magnetized plasmas with multi-charged ion species

    NASA Astrophysics Data System (ADS)

    Hatami, M. M.

    2015-04-01

    The generalized Bohm criterion in magnetized multi-component plasmas consisting of multi-charged positive and negative ion species and electrons is analytically investigated by using the hydrodynamic model. It is assumed that the electrons and negative ion density distributions are the Boltzmann distribution with different temperatures and the positive ions enter into the sheath region obliquely. Our results show that the positive and negative ion temperatures, the orientation of the applied magnetic field and the charge number of positive and negative ions strongly affect the Bohm criterion in these multi-component plasmas. To determine the validity of our derived generalized Bohm criterion, it reduced to some familiar physical condition and it is shown that monotonically reduction of the positive ion density distribution leading to the sheath formation occurs only when entrance velocity of ion into the sheath satisfies the obtained Bohm criterion. Also, as a practical application of the obtained Bohm criterion, effects of the ionic temperature and concentration as well as magnetic field on the behavior of the charged particle density distributions and so the sheath thickness of a magnetized plasma consisting of electrons and singly charged positive and negative ion species are studied numerically.

  12. An analytic expression for the sheath criterion in magnetized plasmas with multi-charged ion species

    SciTech Connect

    Hatami, M. M.

    2015-04-15

    The generalized Bohm criterion in magnetized multi-component plasmas consisting of multi-charged positive and negative ion species and electrons is analytically investigated by using the hydrodynamic model. It is assumed that the electrons and negative ion density distributions are the Boltzmann distribution with different temperatures and the positive ions enter into the sheath region obliquely. Our results show that the positive and negative ion temperatures, the orientation of the applied magnetic field and the charge number of positive and negative ions strongly affect the Bohm criterion in these multi-component plasmas. To determine the validity of our derived generalized Bohm criterion, it reduced to some familiar physical condition and it is shown that monotonically reduction of the positive ion density distribution leading to the sheath formation occurs only when entrance velocity of ion into the sheath satisfies the obtained Bohm criterion. Also, as a practical application of the obtained Bohm criterion, effects of the ionic temperature and concentration as well as magnetic field on the behavior of the charged particle density distributions and so the sheath thickness of a magnetized plasma consisting of electrons and singly charged positive and negative ion species are studied numerically.

  13. Radio-frequency sheath-plasma interactions with magnetic field tangency points along the sheath surface

    SciTech Connect

    Kohno, H.; Myra, J. R.; D'Ippolito, D. A.

    2013-08-15

    Computer simulations of radio-frequency (RF) waves propagating across a two-dimensional (2D) magnetic field into a conducting boundary are described. The boundary condition for the RF fields at the metal surface leads to the formation of an RF sheath, which has previously been studied in one-dimensional models. In this 2D study, it is found that rapid variation of conditions along the sheath surface promote coupling of the incident RF branch (either fast or slow wave) to a short-scale-length sheath-plasma wave (SPW). The SPW propagates along the sheath surface in a particular direction dictated by the orientation of the magnetic field with respect to the surface, and the wave energy in the SPW accumulates near places where the background magnetic field is tangent to the surface.

  14. Micro-Particles as Electrostatic Probes for Plasma Sheath Diagnostic

    SciTech Connect

    Wolter, Matthias; Haass, Moritz; Ockenga, Taalke; Kersten, Holger; Blazec, Joseph; Basner, Ralf

    2008-09-07

    An interesting aspect in the research of complex (dusty) plasmas is the experimental study of the interaction of micro-particles of different sizes with the surrounding plasma for diagnostic purpose. In the plasma micro-disperse particles are negatively charged and confined in the sheath. The particles are trapped by an equilibrium of gravity, electric field force and ion drag force. From the behavior, local electric fields can be determined, e.g. particles are used as electrostatic probes. In combination with additional measurements of the plasma parameters with Langmuir probes and thermal probes as well as by comparison with an analytical sheath model, the structure of the sheath can be described. In the present work we focus on the behavior of micro-particles of different sizes and several plasma parameters e.g. the gas pressure and the rf-power.

  15. Collector and source sheaths of a finite ion temperature plasma

    SciTech Connect

    Schwager, L.A.; Birdsall, C.K. )

    1990-05-01

    The region between a Maxwellian plasma source and an absorbing surface is described theoretically with a static, kinetic plasma--sheath model and modeled numerically with a dynamic, electrostatic particle simulation. In the kinetic theory, Poisson's equation and Vlasov equations govern the non-Maxwellian velocity distribution of the ions and electrons. The results in this paper for collector potential and plasma transport agree with the bounded model of Emmert {ital et} {ital al}. (Phys. Fluids {bold 23}, 803 (1980)). However, this approach differs from those using traditional Bohm sheath analysis by {plus minus}0.25 (in units of electron temperature) for potential drop through the collector sheath of a hydrogen plasma. In both the theory and simulation, the plasma source injects equal fluxes of ions and electrons with half-Maxwellian velocities and various mass and temperature ratios and is assumed to have a zero electric field. The potential change within a spatially distributed, full Maxwellian source region is represented with the source sheath potential drop that depends primarily on temperature ratio. This source sheath evolves over a few Debye lengths from the source to neutralize the injected plasma. The plasma flows to an electrically floating collector where the more familiar electron-repelling collector sheath appears. The collector potential {psi}{sub {ital C}} and source sheath potential drop {psi}{sub {ital P}} (in units of electron temperature) are evaluated as a function of mass and temperature ratio. The velocity moments of density, drift velocity, temperature, kinetic energy flux, and heat flux are also derived as a function of {psi}{sub {ital C}} and {psi}{sub {ital P}}. Comparisons with electrostatic particle simulations are shown for the ion/electron mass ratios of 40 and 100 and temperature ratios of 0.1, 1, and 10.

  16. Multiple ion species plasmas with thermal ions in an oblique magnetic field

    SciTech Connect

    Hatami, M. M.

    2013-08-15

    Using a three-fluid model, the combined effects of an oblique magnetic field and finite temperature of positive ion species on the characteristics of the sheath region of multi-component plasmas are investigated numerically. It is assumed that the ion species are singly charged and have different masses. In the presence of an external magnetic field, it is shown that the density distribution of positive ion species (especially the lighter ion species) begins to fluctuate and does not decrease monotonically towards the wall. Also, it is shown that by increasing the magnetic field, the amplitude of fluctuation increases and its position moves towards the sheath edge. Moreover, it is illustrated that the presence of the magnetic field affects the sheath width and by increasing the magnetic field, the sheath width decreases. In addition, the results show that in the presence of the magnetic field, the increase of temperature of positive ion species has an infinitesimal effect on the sheath width and density distribution of positive ion species.

  17. Wave rectification in plasma sheaths surrounding electric field antennas

    NASA Technical Reports Server (NTRS)

    Boehm, M. H.; Carlson, C. W.; Mcfadden, J. P.; Clemmons, J. H.; Ergun, R. E.; Mozer, F. S.

    1994-01-01

    Combined measurements of Langmuir or broadband whistler wave intensity and lower-frequency electric field waveforms, all at 10-microsecond time resolution, were made on several recent sounding rockets in the auroral ionosphere. It is found that Langmuir and whistler waves are partically rectified in the plasma sheaths surrounding the payload and the spheres used as antennas. This sheath rectification occurs whenever the high frequency (HF) potential across the sheath becomes of the same order as the electron temperature or higher, for wave frequencies near or above the ion plasma frequency. This rectification can introduce false low-frequency waves into measurements of electric field spectra when strong high-frequency waves are present. Second harmonic signals are also generated, although at much lower levels. The effect occurs in many different plasma conditions, primarily producing false waves at frequencies that are low enough for the antenna coupling to the plasma to be resistive.

  18. Formation of pre-sheath boundary layers in electronegative plasmas

    SciTech Connect

    Vitello, P., LLNL

    1998-05-01

    In electronegative plasmas Coulomb scattering between positive and negative ions can lead to the formation of a pre-sheath boundary layer containing the bulk of the negative ions. The negative ion boundary layer forms when momentum transfer from positive to negative ions dominates the negative ion acceleration from the electric field. This condition is met in Inductively Coupled Plasma reactors that operate at low pressure and high plasma density. Simulations of the GEC reactor for Chlorine and Oxygen chemistries using the INDUCT95 2D model are presented showing the pre-sheath boundary layer structure as a function of applied power and neutral pressure.

  19. Nonextensive statistics and the sheath criterion in collisional plasmas

    SciTech Connect

    Hatami, M. M.

    2015-01-15

    The Bohm criterion in an electropositive plasma containing nonextensively distributed electrons and warm ions is investigated by using a steady state two-fluid model. Taking into account the ion-neutral collisions and finite temperature of ions, a modified Bohm criterion is derived which limits both maximum and minimum allowable velocity of ions at the sheath edge (u{sub 0i}). It is found that the degree of nonextensivity of electrons (q) and temperature of positive ions (T{sub i}) affect only the lower limit of the entrance velocity of ions into the sheath while the degree of ion collisionality (α) influences both lower and upper limits of the ion velocities at the sheath edge. In addition, depending on the value of q, it is shown that the minimum velocity of positive ions at the sheath edge can be greater or smaller than its Maxwellian counterpart. Moreover, it is shown that, depending on the values of α and T{sub i}, the positive ions with subsonic velocity may enter the sheath for either q > 1 or −1 < q < 1. Finally, as a practical application, the density distribution of charged particles in the sheath region is studied for different values of u{sub 0i}, and it is shown that monotonical reduction of the positive ion density distribution occurs only when the velocity of positive ions at the sheath edge lies between two above mentioned limits.

  20. High-frequency instability of the sheath-plasma resonance

    NASA Technical Reports Server (NTRS)

    Stenzel, R. L.

    1989-01-01

    Coherent high frequency oscillations near the electron plasma frequency (omega approx. less than omega sub p) are generated by electrodes with positive dc bias immersed in a uniform Maxwellian afterglow plasma. The instability occurs at the sheath-plasma resonance and is driven by a negative RF sheath resistance associated with the electron inertia in the diode-like electron-rich sheath. With increasing dc bias, i.e., electron transit time, the instability exhibits a hard threshold, downward frequency pulling, line broadening and copious harmonics. The fundamental instability is a bounded oscillation due to wave evanescence, but the harmonics are radiated as electromagnetic waves from the electrodes acting like antennas. Wavelength and polarization measurements confirm the emission process. Electromagnetic waves are excited by electrodes of various geometries (planes, cylinders, spheres) which excludes other radiation mechanisms such as orbitrons or beam-plasma instabilities. The line broadening mechanism was identified as a frequency modulation via the electron transit time by dynamic ions. Ion oscillations at the sheath edge give rise to burst-like RF emissions. These laboratory observations of a new instability are important for antennas in space plasmas, generation of coherent beams with diodes, and plasma diagnostics.

  1. Effect of secondary electron emission on the plasma sheath

    SciTech Connect

    Langendorf, S. Walker, M.

    2015-03-15

    In this experiment, plasma sheath potential profiles are measured over boron nitride walls in argon plasma and the effect of secondary electron emission is observed. Results are compared to a kinetic model. Plasmas are generated with a number density of 3 × 10{sup 12} m{sup −3} at a pressure of 10{sup −4} Torr-Ar, with a 1%–16% fraction of energetic primary electrons. The sheath potential profile at the surface of each sample is measured with emissive probes. The electron number densities and temperatures are measured in the bulk plasma with a planar Langmuir probe. The plasma is non-Maxwellian, with isotropic and directed energetic electron populations from 50 to 200 eV and hot and cold Maxwellian populations from 3.6 to 6.4 eV and 0.3 to 1.3 eV, respectively. Plasma Debye lengths range from 4 to 7 mm and the ion-neutral mean free path is 0.8 m. Sheath thicknesses range from 20 to 50 mm, with the smaller thickness occurring near the critical secondary electron emission yield of the wall material. Measured floating potentials are within 16% of model predictions. Measured sheath potential profiles agree with model predictions within 5 V (∼1 T{sub e}), and in four out of six cases deviate less than the measurement uncertainty of 1 V.

  2. Effect of secondary electron emission on the plasma sheath

    NASA Astrophysics Data System (ADS)

    Langendorf, S.; Walker, M.

    2015-03-01

    In this experiment, plasma sheath potential profiles are measured over boron nitride walls in argon plasma and the effect of secondary electron emission is observed. Results are compared to a kinetic model. Plasmas are generated with a number density of 3 × 1012 m-3 at a pressure of 10-4 Torr-Ar, with a 1%-16% fraction of energetic primary electrons. The sheath potential profile at the surface of each sample is measured with emissive probes. The electron number densities and temperatures are measured in the bulk plasma with a planar Langmuir probe. The plasma is non-Maxwellian, with isotropic and directed energetic electron populations from 50 to 200 eV and hot and cold Maxwellian populations from 3.6 to 6.4 eV and 0.3 to 1.3 eV, respectively. Plasma Debye lengths range from 4 to 7 mm and the ion-neutral mean free path is 0.8 m. Sheath thicknesses range from 20 to 50 mm, with the smaller thickness occurring near the critical secondary electron emission yield of the wall material. Measured floating potentials are within 16% of model predictions. Measured sheath potential profiles agree with model predictions within 5 V (˜1 Te), and in four out of six cases deviate less than the measurement uncertainty of 1 V.

  3. Anode sheath contributions in plasma thrusters

    NASA Astrophysics Data System (ADS)

    Riggs, John F.

    1994-03-01

    Contributions of the anode to Magnetoplasmadynamic (MPD) thruster performance are considered. High energy losses at this electrode, surface erosion, and sheath/ionization effects must be controlled in designs of practical interest. Current constriction or spotting at the anode, evolving into localized surface damage and considerable throat erosion, is shown to be related to the electron temperature's T(sub e) rise above the gas temperature T(sub o). An elementary one-dimensional description of a collisional sheath which highlights the role of T(sub e) is presented. Computations to model the one-dimensional sheath are attempted using a set of five coupled first-order, nonlinear differential equations describing the electric field, as well as the species current and number densities. For a large temperature nonequilibrium (i.e., T(sub e) greater than T(sub o)), the one-dimensional approach fails to give reasonable answers and a multidimensional description is deemed necessary. Thus, anode spotting may be precipitated by the elevation of T sub e among other factors. A review of transpiration cooling as a means of recouping some anode power is included. Active anode cooling via transpiration cooling would result in (1) quenching T(sub e), (2) adding 'hot' propellant to exhaust, and (3) reducing the local electron Hall parameter.

  4. Collector and source sheaths of a finite ion temperature plasma

    SciTech Connect

    Schwager, L.A.; Birdsall, C.K.

    1988-04-13

    The region between a Maxwellian plasma source and an absorbing surface is modeled with an electrostatic particle simulation and with a kinetic plasma-sheath model. In the kinetic model, Poisson's equation and Vlasov equations govern the velocity distribution of the ions and electrons. Our numerical and theoretical results for collector potential and plasma transport agree with the bounded model of Emmert et al., but differ somewhat from those using traditional Bohm sheath analysis. The plasma source injects equal fluxes of half-Maxwellian ions and electrons with specified mass and temperature ratios and is assumed to have a zero electric field. Representing the potential change within a distributed full-Maxwellian source region, the source potential drop depends primarily on temperature ratio and evolves a few Debye lengths from the source to neutralize the injected plasma. The plasma flows to an electrically floating collector where the more familiar electron-repelling collector sheath appears. Profiles of potential, density, drift velocity, temperature, kinetic energy flux, and heat flux are shown from simulation; all compare very well with theory. 24 refs., 7 figs., 1 tab.

  5. Modeling a planar sheath in dust-containing plasmas

    SciTech Connect

    Chung, T. H.

    2014-01-15

    One-dimensional fluid model is utilized to describe the sheath at a dust-containing plasma-wall boundary. The model equations are solved on the scale of the electron Debye length. The spatial distributions of electric potential and of the velocities and densities of charged species are calculated in a wide range of control parameters. The dust charge number, electric force, and ion drag force are also investigated. The impacts of Havnes parameter, the electron to ion temperature ratio, the ion collisionality, and the ionization on the spatial distributions of the plasma species and the incident fluxes of the ions to the wall (or to the probe) are investigated. With increase of Havnes parameter, the sheath thickness and the ion flux to the wall are reduced, whereas the ion drift velocity is increased. Enhanced ion thermal motion causes the ion flux to the wall to increase. An increase in ion collisionality with neutrals causes both the sheath thickness and the ion flux to the wall to decrease. With increase of the ionization rate, the sheath thickness is found to decrease and the ion flux collected by a probe increases. The localization of dust particles above the electrode is intensified by the increases in Havnes parameter, the electron to ion temperature ratio, collisionality, and ionization rate.

  6. Radio-frequency Plasma Sheath Studies

    NASA Astrophysics Data System (ADS)

    Hicks, Nathaniel

    2015-09-01

    The response of ion-electron plasma as well as two-component plasma to RF fields is studied via PIC simulation. In each case, the light species responds strongly to the RF and the heavy species does not. By varying the external electrode geometry, RF waveform, and driving voltage and frequency, light species of certain charge-to-mass ratios may experience a trapping effect within the RF structure. The space charge of this species creates a potential well for the oppositely-charged, heavy species. Simulation results are presented, as well as plans for experimental investigation of the same effect. Applications to plasma processes in which a plasma boundary is subjected to external RF fields are discussed.

  7. Plasma-wall interaction in an electrostatic sheath of plasma containing a monoenergetic electron beam

    NASA Astrophysics Data System (ADS)

    Ou, Jing; Zhao, Xiaoyun; Gan, Chunyun

    2016-04-01

    The plasma-wall interaction in the presence of a monoenergetic electron beam has been studied by taking into account the self-consistency among plasma transport in a collisionless electrostatic sheath, deposited energy flux at the wall and material thermal response for carbon and tungsten as wall materials. The variations of the potential drop across the sheath, ion velocity at the sheath edge, and surface temperature of material as a function of electron beam flux are explored in the presence of the electron emission. It is found that when electron beam does not dominate the sheath, potential drop across the sheath depends strongly on the material properties due to the impact of electron emission while the surface temperature of material shows monotonic variation. In the case of carbon wall, the electron beam may dominate the sheath at a certain electron beam concentration or energy. Under this circumstance, both the potential drop across the sheath and surface temperature of material demonstrate the sharp increasing transition. The development of local hot spot on the plasma facing material is caused by the enhanced ion energy flux instead of the electron beam energy flux. If the electron emission is not taken into account, as a smaller electron beam flux, both the potential drop across the sheath and surface temperature of material display the significant change and then it may be easier to develop for the local hot spot on the plasma facing material.

  8. Unified Model of the rf Plasma Sheath, Part II

    NASA Astrophysics Data System (ADS)

    Riley, Merle

    1996-10-01

    By developing an approximation to the first integral of the Poisson equation, one can obtain solutions for the current-voltage characteristics of an rf plasma sheath that are valid over the whole range of inertial response of the ions to an imposed rf voltage or current. (M.E.Riley, 1995 GEC, abstract QA5, published in Bull. Am. Phys. Soc., 40, 1587 (1995).) The theory has been shown to adequately reproduce current-voltage characteristics of two extreme cases (M.A. Lieberman, IEEE Trans. Plasma Sci. 16, 638 (1988). A. Metze, D.W. Ernie, and H.J.Oskam, J.Appl.Phys., 60, 3081 (1986).) of ion response. In this work I show the effect of different conventions for connecting the sheath model to the bulk plasma. Modifications of the Mach number and a finite electric field at the Bohm point are natural choices. The differences are examined for a sheath in a high density Ar plasma and are found to be insignificant. A theoretical argument favors the electric field modification. *Work performed at Sandia National Labs and supported by US DoE under contract DE-AC04-94AL85000.

  9. Nonextensivity effect on radio-wave transmission in plasma sheath

    NASA Astrophysics Data System (ADS)

    Mousavi, A.; Esfandiari-Kalejahi, A.; Akbari-Moghanjoughi, M.

    2016-04-01

    In this paper, new theoretical findings on the application of magnetic field in effective transmission of electromagnetic (EM) waves through a plasma sheath around a hypersonic vehicle are reported. The results are obtained by assuming the plasma sheath to consist of nonextensive electrons and thermal ions. The expressions for the electric field and effective collision frequency are derived analytically in the framework of nonextensive statistics. Examination of the reflection, transmission, and absorption coefficients regarding the strength of the ambient magnetic field shows the significance of q-nonextensive parameter effect on these entities. For small values of the magnetic field, the transmission coefficient increases to unity only in the range of - 1 < q < 1 . It is also found that the EM wave transmission through the nonextensive plasma sheath can take place using lower magnetic field strengths in the presence of superthermal electrons compared with that of Maxwellian ones. It is observed that superthermal electrons, with nonextensive parameter, q < 1, play a dominant role in overcoming the radio blackout for hypersonic flights.

  10. Dust Particles Alignments and Transitions in a Plasma Sheath

    SciTech Connect

    Stokes, J. D. E.; Samarian, A. A.; Vladimirov, S. V.

    2008-09-07

    The alignments and transitions of two dust particles in a plasma sheath have been investigated. It is shown that the Hamiltonian description of a non-Hamiltonian system can be used to predict qualitative features of possible equilibria in a variety of confinement potentials and can provide useful plasma diagnostics. The results compare favorably with simulation and are used to create new experimental hypotheses. In particular, the symmetry breaking transition of the particles as they leave the horizontal plane admits a Hamiltonian description which is used to elucidate the wake parameter.

  11. Microparticles deep in the plasma sheath: Coulomb 'explosion'

    SciTech Connect

    Antonova, T.; Du, C.-R.; Ivlev, A. V.; Hou, L.-J.; Thomas, H. M.; Morfill, G. E.; Annaratone, B. M.

    2012-09-15

    A cloud of microparticles was trapped deep in the sheath of a radio-frequency (rf) discharge, very close to the lower (grounded) electrode of the plasma chamber. This was achieved by employing a specifically designed rf-driven segment integrated in the lower electrode, which provided an additional confinement compressing the cloud to a very high density. After switching the rf-driven segment off, the cloud 'exploded' due to mutual interparticle repulsion. By combining a simple theoretical model with different numerical simulation methods, some basic properties of complex plasmas in this highly non-equilibrium regime were determined.

  12. Measurement of effective sheath width around cutoff probe in low-pressure plasmas

    SciTech Connect

    Kim, D. W.; Oh, W. Y.; You, S. J. Kim, J. H.; Chang, H. Y.

    2014-05-15

    Previous studies indicated that the measurement results of microwave probes can be improved by applying the adequate sheath width to their measurement models, and consequently the sheath width around the microwave probe tips has become very important information for microwave probe diagnostics. In this paper, we propose a method for measuring the argon plasma sheath width around the cutoff probe tips by applying the circuit model to the cutoff probe phase spectrum. The measured sheath width of the cutoff probe was found to be in good agreement with the floated sheath width calculated from the Child-Langmuir sheath law. The physical reasons for a discrepancy between the two measurements are also discussed.

  13. Measurement of effective sheath width around cutoff probe in low-pressure plasmas

    NASA Astrophysics Data System (ADS)

    Kim, D. W.; You, S. J.; Kim, J. H.; Chang, H. Y.; Oh, W. Y.

    2014-05-01

    Previous studies indicated that the measurement results of microwave probes can be improved by applying the adequate sheath width to their measurement models, and consequently the sheath width around the microwave probe tips has become very important information for microwave probe diagnostics. In this paper, we propose a method for measuring the argon plasma sheath width around the cutoff probe tips by applying the circuit model to the cutoff probe phase spectrum. The measured sheath width of the cutoff probe was found to be in good agreement with the floated sheath width calculated from the Child-Langmuir sheath law. The physical reasons for a discrepancy between the two measurements are also discussed.

  14. The modeling and simulation of plasma sheath effect on GNSS system

    NASA Astrophysics Data System (ADS)

    Song, Zhongguo; Liu, Jiangfan; Du, Yongxing; Xi, Xiaoli

    2015-11-01

    Plasma sheath can potentially degrade global navigation satellite system (GNSS) through signal attenuation as well as phase noise when a hypersonic vehicle reenters the Earth's atmosphere. Modeling and simulation method of GNSS system disturbed by plasma sheath is introduced in this paper by means of electromagnetic wave propagation theory combined with the satellite signal simulation technique. The transmission function of the plasma sheath with stratified model is derived utilizing scattering matrix method. The effects of the plasma sheath on GPS signal reception and positioning performance are examined. Experimental results are presented and discussed, partly supporting the validity of the analytical method proposed.

  15. Precession of cylindrical dust particles in the plasma sheath

    SciTech Connect

    Banu, N.; Ticoş, C. M.

    2015-10-15

    The vertical precession of cylindrical dust particles levitated in the sheath of an rf plasma is experimentally investigated. Typically, the dust particles have two equilibrium positions depending on the orientation of their longitudinal axis: horizontal and vertical. A transition between these two states is induced by rapidly increasing the neutral gas pressure in the plasma chamber. During this transition, the cylindrical dust particles make an angle with the horizontal and rotate about their center of mass. The rotation speed increases as the dust rods aligned with the vertical axis. All dust particles will eventually end up in the vertical state while spinning fast about their longitudinal axis. Dust-dust interaction and the attracting ion wakes are possible mechanisms for inducing the observed dust precession.

  16. Bounded multi-scale plasma simulation: Application to sheath problems

    SciTech Connect

    Parker, S.E. ); Friedman, A.; Ray. S.L. ); Birdsall, C.K. )

    1993-08-01

    In our previous paper we introduced the multi-scale method, a self-consistent plasma simulation technique that allowed particles to have independent timesteps. Here we apply the method to one-dimensional electrostatic bounded plasma problems and demonstrate a significant reduction in computing time. We describe a technique to allow for variable grid spacing and develop consistent boundary conditions for the direct implicit method. Also discussed are criteria for specifying timestep size as a function of position in phase space. Next, an analytically solvable sheath problem is presented, and a comparison to simulation results in made. Finally, we show results for an ion acoustic shock front propagating toward a conducting wall. 20 refs., 16 figs., 2 tabs.

  17. Electron inertia effects on the planar plasma sheath problem

    SciTech Connect

    Duarte, V. N.; Clemente, R. A.

    2011-04-15

    The steady one-dimensional planar plasma sheath problem, originally considered by Tonks and Langmuir, is revisited. Assuming continuously generated free-falling ions and isothermal electrons and taking into account electron inertia, it is possible to describe the problem in terms of three coupled integro-differential equations that can be numerically integrated. The inclusion of electron inertia in the model allows us to obtain the value of the plasma floating potential as resulting from an electron density discontinuity at the walls, where the electrons attain sound velocity and the electric potential is continuous. Results from numerical computation are presented in terms of plots for densities, electric potential, and particles velocities. Comparison with results from literature, corresponding to electron Maxwell-Boltzmann distribution (neglecting electron inertia), is also shown.

  18. Dusty Plasma Modeling of the Fusion Reactor Sheath Including Collisional-Radiative Effects

    SciTech Connect

    Dezairi, Aouatif; Samir, Mhamed; Eddahby, Mohamed; Saifaoui, Dennoun; Katsonis, Konstantinos; Berenguer, Chloe

    2008-09-07

    The structure and the behavior of the sheath in Tokamak collisional plasmas has been studied. The sheath is modeled taking into account the presence of the dust{sup 2} and the effects of the charged particle collisions and radiative processes. The latter may allow for optical diagnostics of the plasma.

  19. Analysis of Particle Detectors in Plasma Sheaths on Sounding Rockets and in Laboratory Plasmas

    NASA Astrophysics Data System (ADS)

    Fisher, Lisa; Lynch, Kristina

    2013-10-01

    The influence of plasma sheaths on particle measurements is a well-known problem. Improvements in computational speed and memory have made the use of particle-in-cell codes, attainable on a laptop. These codes can calculate complex sheath structures and include most of the relevant physics. We will discuss how the use of one such code, SPIS, has been integrated into our data processing for the MICA sounding rocket. This inclusion of sheath physics has allowed us to describe the current-voltage signature of an ion retarding potential analyzer, called the PIP, to measure the ambient ionospheric temperature, as well as to examine the possibility of ion upflow. These results will be compared with the other instrumentation on MICA, which use traditional thin-sheath approximations. This comparison will emphasize the strengths and weaknesses of these other data analysis methods and call attention to the need to include sheath physics when measuring very low energy populations. Additionally, these instruments have also been tested in the Dartmouth College plasma facility. This provides another set of plasma conditions for testing and extrapolating our method to a future low-orbit mission.

  20. Iterative methods for plasma sheath calculations: Application to spherical probe

    NASA Technical Reports Server (NTRS)

    Parker, L. W.; Sullivan, E. C.

    1973-01-01

    The computer cost of a Poisson-Vlasov iteration procedure for the numerical solution of a steady-state collisionless plasma-sheath problem depends on: (1) the nature of the chosen iterative algorithm, (2) the position of the outer boundary of the grid, and (3) the nature of the boundary condition applied to simulate a condition at infinity (as in three-dimensional probe or satellite-wake problems). Two iterative algorithms, in conjunction with three types of boundary conditions, are analyzed theoretically and applied to the computation of current-voltage characteristics of a spherical electrostatic probe. The first algorithm was commonly used by physicists, and its computer costs depend primarily on the boundary conditions and are only slightly affected by the mesh interval. The second algorithm is not commonly used, and its costs depend primarily on the mesh interval and slightly on the boundary conditions.

  1. The magnetized sheath of a dusty plasma with grains size distribution

    SciTech Connect

    Ou, Jing Gan, Chunyun; Lin, Binbin; Yang, Jinhong

    2015-05-15

    The structure of a plasma sheath in the presence of dust grains size distribution (DGSD) is investigated in the multi-fluid framework. It is shown that effect of the dust grains with different sizes on the sheath structure is a collective behavior. The spatial distributions of electric potential, the electron and ion densities and velocities, and the dust grains surface potential are strongly affected by DGSD. The dynamics of dust grains with different sizes in the sheath depend on not only DGSD but also their radius. By comparison of the sheath structure, it is found that under the same expected value of DGSD condition, the sheath length is longer in the case of lognormal distribution than that in the case of uniform distribution. In two cases of normal and lognormal distributions, the sheath length is almost equal for the small variance of DGSD, and then the difference of sheath length increases gradually with increase in the variance.

  2. Plasma sheath effects and voltage distributions of large high-power satellite solar arrays

    NASA Technical Reports Server (NTRS)

    Parker, L. W.

    1979-01-01

    Knowledge of the floating voltage configuration of a large array in orbit is needed in order to estimate various plasma-interaction effects. The equilibrium configuration of array voltages relative to space depends on the sheath structure. The latter dependence for an exposed array is examined in the light of two finite-sheath effects. One effect is that electron currents may be seriously underestimated. The other is that a potential barrier for electrons can occur, restricting electron currents. A conducting surface is assumed on the basis of a conductivity argument. Finite-sheath effects are investigated. The results of assuming thin-sheath and thick-sheath limits on the floating configuration of a linearly connected array are studied. Sheath thickness and parasitic power leakage are estimated. Numerically computed fields using a 3-D code are displayed in the thick-sheath limit.

  3. The positive ion temperature effect in magnetized electronegative plasma sheath with two species of positive ions

    SciTech Connect

    Shaw, A. K.; Kar, S.; Goswami, K. S.

    2012-10-15

    The properties of a magnetized multi-component (two species of positive ions, negative ions and electrons) plasma sheath with finite positive ion temperature are studied. By using three fluid hydrodynamic model and some dimensionless variables, the ion (both lighter and heavier positive ions, and negative ions) densities, the ion (only for positive ions) velocities, and electric potential inside the sheath are investigated. In addition, the absence and presence of magnetic field and the orientation of magnetic field are considered. It is noticed that, with increase of positive ion temperature, the lighter positive ion density peaks increase only at the sheath edge and shift towards the sheath edge for both absence and presence of magnetic field. For heavier positive ions, in the absence of magnetic field, the density peaks increase at the sheath edge. But in the presence of magnetic field, the density fluctuations increase at the sheath edge. For both the cases, the density peaks shift towards the sheath edge.

  4. 3D Particle-In-Cell (PIC) simulations of plasma sheath formation above lunar craters

    NASA Astrophysics Data System (ADS)

    Likhanskii, A.; Poppe, A. R.; Piquette, M.; Amyx, K.; Messmer, P.; Horanyi, M.

    2010-12-01

    Comprehensive investigation of plasma sheath formation and consequent dust levitation on lunar surface is important for interpretation of results of future lunar missions (such as LADEE and ARTEMIS). Until recently, most of such studies were done in experimental laboratories at reduced scales. Due to the complexity and nonlinearity of the problem, only simplified theories, describing this effect, were developed. However, recent progress in high-performance kinetic plasma simulations allowed tackling the problem of plasma sheath formation numerically. In this poster we will present the simulation results of plasma sheath formation above the lunar craters in presence of solar wind and photoelectron emission. These results were obtained using 3D Particle-In-Cell (PIC) code VORPAL. In the simulations we considered plasma sheath formation for normal, 45 and 90 degree incidence solar wind. Sample distribution of electric field in plasma sheath is shown in Figure 1. In the second part of the poster, we will present results of simulations of the LASP (Laboratory for Atmospheric and Space Physics at University of Colorado) experiments on study of plasma sheath formation above hemispherical isolated dimple. Figure 1. Electric field distribution in the plasma sheath above the lunar crater

  5. Obliquely Propagating Electromagnetic Waves in Magnetized Kappa Plasmas

    NASA Astrophysics Data System (ADS)

    Gaelzer, R.

    2015-12-01

    The effects of velocity distribution functions (VDFs) that exhibit a power-law dependence on the high-energy tail have been the subjectof intense research by the space plasma community. Such functions, known as kappa or superthermal distributions, have beenfound to provide a better fitting to the VDF measured by spacecraft in the solar wind. One of the problems that is being addressed on this new light is the temperature anisotropy of solar wind protons and electrons. An anisotropic kappa VDF contains a large amount of free energy that can excite waves in the solar wind. Conversely, the wave-particle interaction is important to determine the shape of theobserved particle distributions.In the literature, the general treatment for waves excited by (bi-)Maxwellian plasmas is well-established. However, for kappa distributions, either isotropic or anisotropic, the wave characteristics have been studied mostly for the limiting cases of purely parallel or perpendicular propagation. Contributions for the general case of obliquely-propagating electromagnetic waves have been scarcely reported so far. The absence of a general treatment prevents a complete analysis of the wave-particle interaction in kappa plasmas, since some instabilities, such as the firehose, can operate simultaneously both in the parallel and oblique directions.In a recent work [1], we have obtained expressions for the dielectric tensor and dispersion relations for the low-frequency, quasi-perpendicular dispersive Alfvén waves resulting from a kappa VDF. In the present work, we generalize the formalism introduced by [1] for the general case of electrostatic and/or electromagnetic waves propagating in a kappa plasma in any frequency range and for arbitrary angles.We employ an isotropic distribution, but the methods used here can be easily applied to more general anisotropic distributions,such as the bi-kappa or product-bi-kappa. [1] R. Gaelzer and L. F. Ziebell, Journal of Geophysical Research 119, 9334

  6. Obliquely propagating electromagnetic waves in magnetized kappa plasmas

    NASA Astrophysics Data System (ADS)

    Gaelzer, R.; Ziebell, L. F.

    2016-02-01

    Velocity distribution functions (VDFs) that exhibit a power-law dependence on the high-energy tail have been the subject of intense research by the plasma physics community. Such functions, known as kappa or superthermal distributions, have been found to provide a better fitting to the VDFs measured by spacecraft in the solar wind. One of the problems that is being addressed on this new light is the temperature anisotropy of solar wind protons and electrons. In the literature, the general treatment for waves excited by (bi-)Maxwellian plasmas is well-established. However, for kappa distributions, the wave characteristics have been studied mostly for the limiting cases of purely parallel or perpendicular propagation, relative to the ambient magnetic field. Contributions to the general case of obliquely propagating electromagnetic waves have been scarcely reported so far. The absence of a general treatment prevents a complete analysis of the wave-particle interaction in kappa plasmas, since some instabilities can operate simultaneously both in the parallel and oblique directions. In a recent work, Gaelzer and Ziebell [J. Geophys. Res. 119, 9334 (2014)] obtained expressions for the dielectric tensor and dispersion relations for the low-frequency, quasi-perpendicular dispersive Alfvén waves resulting from a kappa VDF. In the present work, the formalism is generalized for the general case of electrostatic and/or electromagnetic waves propagating in a kappa plasma in any frequency range and for arbitrary angles. An isotropic distribution is considered, but the methods used here can be easily applied to more general anisotropic distributions such as the bi-kappa or product-bi-kappa.

  7. Numerical model of the plasma sheath generated by the plasma source instrument aboard the Polar satellite

    NASA Astrophysics Data System (ADS)

    Singh, N.; Leung, W. C.; Moore, T. E.; Craven, P. D.

    2001-09-01

    The plasma sheath generated by the operation of the Plasma Source Instrument (PSI) aboard the Polar satellite is studied by using a three-dimensional particle-in-cell (PIC) code. When the satellite passes through the region of low-density plasma, the satellite charges to positive potentials as high as 40-50 V, owing to the photoelectron emission. In such a case, ambient core ions cannot accurately be measured or detected. The goal of the onboard PSI is to reduce the floating potential of the satellite to a sufficiently low value so that the ions in the polar wind become detectable. When the PSI is operated, ion-rich xenon plasma is ejected from the satellite, such that the floating potential of the satellite is reduced and is maintained at ~2 V. Accordingly, in our three-dimensional PIC simulation we considered that the potential of the satellite is 2 V as a fixed bias. Considering the relatively high density of the xenon plasma in the sheath (-10-103cm-3), the ambient plasma of low density (<1 cm-3) is neglected. In the simulations the electric fields and plasma dynamics are calculated self-consistently. We found that an ``apple''-shape positive potential sheath forms surrounding the satellite. In the region near the PSI emission a high positive potential hill develops. Near the Thermal Ion Dynamics Experiment detector away from the PSI, the potentials are sufficiently low for the ambient polar wind ions to reach it. In the simulations it takes only about a couple of tens of electron gyroperiods for the sheath to reach a quasi steady state. This time is approximately the time taken by the heavy Xe+ ions to expand up to about one average Larmor radius of electrons from the satellite surface. After this time the expansion of the sheath in directions transverse to the ambient magnetic field slows down because the electrons are magnetized. Using the quasi steady sheath, we performed trajectory calculations to characterize the detector response to a highly supersonic

  8. Numerical Model of the Plasma Sheath Generated by the Plasma Source Instrument Aboard the Polar Satellite

    NASA Technical Reports Server (NTRS)

    Singh, N.; Leung, W. C.; Moore, T. E.; Craven, P. D.

    2001-01-01

    The plasma sheath generated by the operation of the Plasma Source Instrument (PSI) aboard the Polar satellite is studied by using a three-dimensional particle-in-cell (PIC) code. When the satellite passes through the region of low-density plasma, the satellite charges to positive potentials as high as 40-50 V, owing to the photoelectron emission. In such a case, ambient core ions cannot accurately be measured or detected. The goal of the onboard PSI is to reduce the floating potential of the satellite to a sufficiently low value so that the ions in the polar wind become detectable. When the PSI is operated, ion-rich xenon plasma is ejected from the satellite, such that the floating potential of the satellite is reduced and is maintained at approximately 2 V. Accordingly, in our three-dimensional PIC simulation we considered that the potential of the satellite is 2 V as a fixed bias. Considering the relatively high density of the xenon plasma in the sheath (10-10(exp 3)/cc), the ambient plasma of low density (<1/cc) is neglected. In the simulations the electric fields and plasma dynamics are calculated self-consistently. We found that an 'apple'-shape positive potential sheath forms surrounding the satellite. In the region near the PSI emission a high positive potential hill develops. Near the Thermal Ion Dynamics Experiment detector away from the PSI, the potentials are sufficiently low for the ambient polar wind ions to reach it. In the simulations it takes only about a couple of tens of electron gyroperiods for the sheath to reach a quasi steady state. This time is approximately the time taken by the heavy Xe(+) ions to expand up to about one average Larmor radius of electrons from the satellite surface. After this time the expansion of the sheath in directions transverse to the ambient magnetic field slows down because the electrons are magnetized. Using the quasi steady sheath, we performed trajectory calculations to characterize the detector response to a

  9. High voltage plasma sheath analysis related to TSS-1

    NASA Technical Reports Server (NTRS)

    Sheldon, John W.

    1990-01-01

    On the first mission of the Tethered Satellite System (TSS-1), a 1.8 m diameter spherical satellite will be deployed a distance of 20 km above the Space Shuttle Orbiter on an insulated conducting tether. The satellite will be held at electric potentials up to 5000 volts positive with respect to the ambient plasma. Due to the passage of the conducting tether through the Earth's magnetic field, an electromagnetic field (EMF) will be created, driving electrons down the tether to the Orbiter, out through an electron gun into the ionosphere and back into the positive-biased satellite. The main problem addressed here is the current-voltage characteristics of the ionospheric interaction with the satellite. The first problem is that while the satellite will be capable of measuring charged particle flow to the surface at several locations, the detectors have a limited range of acceptance angle. The second problem is that the angle of incidence of the incoming electrons will have to be relative to the local normal. This will be important in order to predict the magnitude of the detectable current at each detector location so the detector gain can be pre-set to the correct range. The plasma sheath was analyzed mathematically, and subroutines were written to solve relevant finite element, Taylor-Vlasov, and Poisson equations.

  10. Self-consistent simulation of high-frequency driven plasma sheaths

    NASA Astrophysics Data System (ADS)

    Shihab, Mohammed; Eremin, Denis; Mussenbrock, Thomas; Brinkmann, Ralf

    2011-10-01

    Low pressure capacitively coupled plasmas are widely used in plasma processing and microelectronics industry. Understanding the dynamics of the boundary sheath is a fundamental problem. It controls the energy and angular distribution of ions bombarding the electrode, which in turn affects the surface reaction rate and the profile of microscopic features. In this contribution, we investigate the dynamics of plasma boundary sheaths by means of a kinetic self-consistent model, which is able to resolve the ion dynamics. Asymmetric sheath dynamics is observed for the intermediate RF regime, i.e., in the regime where the ion plasma frequency is equal to the driving frequency. The ion inertia causes an additional phase difference between the expansion and the contraction phase of the plasma sheath and an asymmetry for the ion energy distribution bimodal shape. A comparison with experimental results and particle in cell simulations is performed. Low pressure capacitively coupled plasmas are widely used in plasma processing and microelectronics industry. Understanding the dynamics of the boundary sheath is a fundamental problem. It controls the energy and angular distribution of ions bombarding the electrode, which in turn affects the surface reaction rate and the profile of microscopic features. In this contribution, we investigate the dynamics of plasma boundary sheaths by means of a kinetic self-consistent model, which is able to resolve the ion dynamics. Asymmetric sheath dynamics is observed for the intermediate RF regime, i.e., in the regime where the ion plasma frequency is equal to the driving frequency. The ion inertia causes an additional phase difference between the expansion and the contraction phase of the plasma sheath and an asymmetry for the ion energy distribution bimodal shape. A comparison with experimental results and particle in cell simulations is performed. The financial support from the Federal Ministry of Education and Research within the frame of

  11. The spatiotemporal oscillation characteristics of the dielectric wall sheath in stationary plasma thrusters

    SciTech Connect

    Zhang Fengkui; Yu Daren; Ding Yongjie; Li Hong

    2011-03-14

    A two-dimensional particle in cell model is used to simulate the sheath oscillation in stationary plasma thrusters. The embedded secondary electron emission (SEE) submodel is based on that of Morozov but improved by considering the electron elastic reflection effect. The simulation results show that when the SEE coefficient is smaller than one due to the relative low electron temperature, one-dimensional static sheath can be found; as the electron temperature increase, the SEE coefficient approaches to one and temporal oscillation sheath appears; when the electron temperature increases so high that the SEE coefficient is beyond one, the sheath oscillates not only in time but also in space.

  12. Sheath and presheath in ion-ion plasmas via particle-in-cell simulation

    SciTech Connect

    Meige, A.; Leray, G.; Raimbault, J.-L.; Chabert, P.

    2008-02-11

    A full particle-in-cell simulation is developed to investigate electron-free plasmas constituted of positive and negative ions under the influence of a dc bias voltage. It is shown that high-voltage sheaths following the classical Child-law sheaths form within a few microseconds (which corresponds to the ion transit time) after the dc voltage is applied. It is also shown that there exists the equivalent of a Bohm criterion where a presheath accelerates the ions collected at one of the electrodes up to the sound speed before they enter the sheath. From an applied perspective, this leads to smaller sheaths than one would expect.

  13. Three dimensional space charge model for large high voltage satellites. [plasma sheath

    NASA Technical Reports Server (NTRS)

    Cooks, D.; Parker, L. W.; Mccoy, J. E.

    1980-01-01

    High power solar arrays for satellite power systems with dimensions of kilometers, and with tens of kilovolts distributed over their surface face many plasma interaction problems that must be properly anticipated. In most cases, the effects cannot be adequately modeled without detailed knowledge of the plasma sheath structure and space charge effects. Two computer programs were developed to provide fully self consistent plasma sheath models in three dimensions as a result of efforts to model the experimental plasma sheath studies at NASA/JSC. Preliminary results indicate that for the conditions considered, the Child-Langmuir diode theory can provide a useful estimate of the plasma sheath thickness. The limitations of this conclusion are discussed. Some of the models presented exhibit the strong ion focusing observed in the JSC experiments.

  14. Numerical Model of the Plasma Sheath Generated by the Plasma Source Instrument Aboard the Polar Satellite

    NASA Technical Reports Server (NTRS)

    Leung, Wing C.; Singh, Nagendra; Moore, Thomas E.; Craven, Paul D.

    2000-01-01

    The plasma sheath generated by the operation of the Plasma Source Instrument (PSI) aboard the POLAR satellite is studied by using a 3-dimensional Particle-In-Cell (PIC) code. When the satellite passes through the region of low density plasma, the satellite charges to positive potentials as high as 4050Volts due to the photoelectrons emission. In such a case, ambient core ions cannot accurately be measured or detected. The goal of the onboard PSI is to reduce the floating potential of the satellite to a sufficiently low value so that the ions in the polar wind become detectable. When the PSI is operated, an ion-rich Xenon plasma is ejected from the satellite, such that the floating potential of the satellite is reduced and is maintained at about 2Volts. Accordingly, in our 3-dimensional PIC simulation, we considered that the potential of the satellite is 2Volts as a fixed bias. Considering the relatively high density of the Xenon plasma in the sheath (approx. 10 - 10(exp 3)/cc), the ambient plasma of low density (less than 1/cc) is neglected. In the simulations, the electric fields and plasma dynamics are calculated self-consistently. We found that an "Apple" shape positive potential sheath forms surrounding the satellite. In the region near the PSI emission, a high positive potential hill develops. Near the Thermal Ion Detection Experiment (TIDE) detector away from the PSI, the potentials are sufficiently low for the ambient polar wind ions to reach it. In the simulations, it takes about a hundred electron gyroperiods for the sheath to reach a quasi-steady state. This time is approximately the time taken by the heavy Xe(+) ions to expand up to about one average Larmor radius of electrons from the satellite surface. Using the steady state sheath, we performed trajectory calculations to characterize the detector response to a highly supersonic polar wind flow. The detected ions' velocity distribution shows significant deviations from a shifted Maxwellian in the

  15. Oblique solitary waves in a five component plasma

    SciTech Connect

    Sijo, S.; Manesh, M.; Sreekala, G.; Venugopal, C.; Neethu, T. W.; Renuka, G.

    2015-12-15

    We investigate the influence of a second electron component on oblique dust ion acoustic solitary waves in a five component plasma consisting of positively and negatively charged dust, hydrogen ions, and hotter and colder electrons. Of these, the heavier dust and colder photo-electrons are of cometary origin while the other two are of solar origin; electron components are described by kappa distributions. The K-dV equation is derived, and different attributes of the soliton such as amplitude and width are plotted for parameters relevant to comet Halley. We find that the second electron component has a profound influence on the solitary wave, decreasing both its amplitude and width. The normalized hydrogen density strongly influences the solitary wave by decreasing its width; the amplitude of the solitary wave, however, increases with increasing solar electron temperatures.

  16. An oblique pulsar magnetosphere with a plasma conductivity

    NASA Astrophysics Data System (ADS)

    Cao, Gang; Zhang, Li; Sun, Sineng

    2016-09-01

    An oblique pulsar magnetosphere with a plasma conductivity is studied by using a pseudo-spectral method. In the pseudo-spectral method, the time-dependent Maxwell equations are solved, both electric and magnetic fields are expanded in terms of the vector spherical harmonic functions in spherical geometry and the divergencelessness of magnetic field is analytically enforced by a projection method. The pulsar magnetospheres in infinite (i.e., force free approximation) and finite conductivities are simulated and a family of solutions that smoothly transition from the Deutsch vacuum solution to the force-free solution are obtained. The sin2α dependence of the spin-down luminosity on the magnetic inclination angle α in which the full electric current density are taken into account is retrieved in the force-free regime.

  17. Computational study on reliability of sheath width measurement by the cutoff probe in low pressure plasmas

    NASA Astrophysics Data System (ADS)

    Kim, D.-W.; You, S.-J.; Kim, J.-H.; Seong, D.-J.; Chang, H.-Y.; Oh, W.-Y.

    2015-11-01

    Recently, the technique for measurement of the sheath width by using the cutoff probe and its equivalent circuit model was proposed and conducted experimentally. In this study, we investigate the reliability of this technique based on the computational simulation. The simulation of three-dimensional Finite-Difference Time-Domain reproduces the transmission spectrum of the cutoff probe with an input parameter of sheath width. We measure the sheath width by using the circuit model and calculate the discrepancy between them under various input plasma densities and sheath widths. The results show the acceptable discrepancy under all of the conditions we studied (the largest discrepancy is about 45%). This indicates that the technique for measurement of sheath width around the floating tip of cutoff probe is robust and reliable. A shorter version of this contribution is due to be published in PoS at: 1st EPS conference on Plasma Diagnostics

  18. Sheath structure in plasmas with nonextensively distributed electrons and thermal ions

    SciTech Connect

    Hatami, M. M.

    2015-02-15

    Sheath region of an electropositive plasma consisting of q-nonextensive electrons and singly charged positive ions with finite temperature is modeled. Using Sagdeev's pseudo potential technique to derive the modified sheath formation criterion, it is shown that the velocity of ions at the sheath edge is directly proportional to the ion temperatures and inversely proportional to the degree of nonextensivity of electrons (q-parameter). Using the modified Bohm criterion, effect of degree of nonextensivity of electrons and temperature of positive ions on the characteristics of the sheath region are investigated numerically. It is shown that an increase in the ion temperature gives rise to an increase in the electrostatic potential and the velocity of ions in the sheath regardless of the value of q. Furthermore, it is seen that the sheath width and the density distribution of the charged particles decrease by increasing the temperature of positive ions. In addition, it is found that the positive ion temperature is less effective on the sheath structure for higher values of the q-parameter. Finally, the results obtained for a thermal plasma with nonextensively distributed electrons are compared with the results of a cold plasma with nonextensive electrons and an extensive (Maxwellian) plasma with thermal ions.

  19. Effect of two-temperature electrons distribution on an electrostatic plasma sheath

    NASA Astrophysics Data System (ADS)

    Ou, Jing; Xiang, Nong; Gan, Chunyun; Yang, Jinhong

    2013-06-01

    A magnetized collisionless plasma sheath containing two-temperature electrons is studied using a one-dimensional model in which the low-temperature electrons are described by Maxwellian distribution (MD) and high-temperature electrons are described by truncated Maxwellian distribution (TMD). Based on the ion wave approach, a modified sheath criterion including effect of TMD caused by high-temperature electrons energy above the sheath potential energy is established theoretically. The model is also used to investigate numerically the sheath structure and energy flux to the wall for plasmas parameters of an open divertor tokamak-like. Our results show that the profiles of the sheath potential, two-temperature electrons and ions densities, high-temperature electrons and ions velocities as well as the energy flux to the wall depend on the high-temperature electrons concentration, temperature, and velocity distribution function associated with sheath potential. In addition, the results obtained in the high-temperature electrons with TMD as well as with MD sheaths are compared for the different sheath potential.

  20. Ion sheath effects on RF plasma probes - Experimental results in laboratory plasmas

    NASA Technical Reports Server (NTRS)

    Kist, R.

    1977-01-01

    Laboratory work dealing with the frequency characteristic of the plasma impedance of spherical and cylindrical electrode systems is reported. The influence of the ion sheath on various features of the impedance characteristic is emphasized. Those features are the series and parallel resonance as well as additional resonances due to the excitation of electroacoustic and cyclotron harmonic waves. The dependence of the series and parallel resonances on dc biasing leads to a method of determining the ion sheath capacity for a cylindrical electrode system. The obtained values agree fairly well with those obtained from a theoretical model for the density and potential distribution in the sheath of a cylindrical sensor aligned with a supersonic plasma flow. The amplitude of resonances due to excitation of longitudinal plasma waves (electroacoustic and cyclotron harmonic) is reduced or even vanishes for sufficiently negative dc bias. Positive bias first leads to an increased amplitude up to a certain dc bias value above which, however, the amplitude decreases again due to electron absorption at the sensor surface.

  1. Plasma sheath physics and dose uniformity in enhanced glow discharge plasma immersion ion implantation and deposition

    SciTech Connect

    Li Liuhe; Li Jianhui; Kwok, Dixon T. K.; Chu, Paul K.; Wang Zhuo

    2009-07-01

    Based on the multiple-grid particle-in-cell code, an advanced simulation model is established to study the sheath physics and dose uniformity along the sample stage in order to provide the theoretical basis for further improvement of enhanced glow discharge plasma immersion ion implantation and deposition. At t=7.0 mus, the expansion of the sheath in the horizontal direction is hindered by the dielectric cage. The electron focusing effect is demonstrated by this model. Most of the ions at the inside wall of the cage are implanted into the edge of the sample stage and a relatively uniform ion fluence distribution with a large peak is observed at the end. Compared to the results obtained from the previous model, a higher implant fluence and larger area of uniformity are disclosed.

  2. Sheath-limited unipolar induction in the solar wind. [plasma interactions with solar system bodies

    NASA Technical Reports Server (NTRS)

    Srnka, L. J.

    1975-01-01

    A model of the steady-state interaction between the solar wind and an electrically conducting body having neither an atmosphere nor an intrinsic magnetic field sufficient enough to deflect the plasma flow is presented which considers some effects of a plasma surface sheath on unipolar induction. The Sonett-Colburn (1967, 1968) unipolar dynamo model is reviewed, and it is noted that the unipolar dynamo response of an electrically conducting body in the solar wind's motional field can be controlled by sheath effects in certain cases where the body radius is less than a certain critical value. It is shown that sheath effects do not limit the unipolar response of the moon or Mercury since their body radii are much larger than their critical radii. Sheath effects are also considered for asteroids, the Martian satellites, the irregular Jovian satellites, the outer satellites of Saturn, and meteorite parent bodies in a primordial enhanced solar wind.

  3. Quantitative modeling of ICRF antennas with integrated time domain RF sheath and plasma physics

    NASA Astrophysics Data System (ADS)

    Smithe, David N.; D'Ippolito, Daniel A.; Myra, James R.

    2014-02-01

    Significant efforts have been made to quantitatively benchmark the sheath sub-grid model used in our time-domain simulations of plasma-immersed antenna near fields, which includes highly detailed three-dimensional geometry, the presence of the slow wave, and the non-linear evolution of the sheath potential. We present both our quantitative benchmarking strategy, and results for the ITER antenna configuration, including detailed maps of electric field, and sheath potential along the entire antenna structure. Our method is based upon a time-domain linear plasma model [1], using the finite-difference electromagnetic Vorpal/Vsim software [2]. This model has been augmented with a non-linear rf-sheath sub-grid model [3], which provides a self-consistent boundary condition for plasma current where it exists in proximity to metallic surfaces. Very early, this algorithm was designed and demonstrated to work on very complicated three-dimensional geometry, derived from CAD or other complex description of actual hardware, including ITER antennas. Initial work with the simulation model has also provided a confirmation of the existence of propagating slow waves [4] in the low density edge region, which can significantly impact the strength of the rf-sheath potential, which is thought to contribute to impurity generation. Our sheath algorithm is based upon per-point lumped-circuit parameters for which we have estimates and general understanding, but which allow for some tuning and fitting. We are now engaged in a careful benchmarking of the algorithm against known analytic models and existing computational techniques [5] to insure that the predictions of rf-sheath voltage are quantitatively consistent and believable, especially where slow waves share in the field with the fast wave. Currently in progress, an addition to the plasma force response accounting for the sheath potential, should enable the modeling of sheath plasma waves, a predicted additional root to the dispersion

  4. Quantitative modeling of ICRF antennas with integrated time domain RF sheath and plasma physics

    SciTech Connect

    Smithe, David N.; D'Ippolito, Daniel A.; Myra, James R.

    2014-02-12

    Significant efforts have been made to quantitatively benchmark the sheath sub-grid model used in our time-domain simulations of plasma-immersed antenna near fields, which includes highly detailed three-dimensional geometry, the presence of the slow wave, and the non-linear evolution of the sheath potential. We present both our quantitative benchmarking strategy, and results for the ITER antenna configuration, including detailed maps of electric field, and sheath potential along the entire antenna structure. Our method is based upon a time-domain linear plasma model, using the finite-difference electromagnetic Vorpal/Vsim software. This model has been augmented with a non-linear rf-sheath sub-grid model, which provides a self-consistent boundary condition for plasma current where it exists in proximity to metallic surfaces. Very early, this algorithm was designed and demonstrated to work on very complicated three-dimensional geometry, derived from CAD or other complex description of actual hardware, including ITER antennas. Initial work with the simulation model has also provided a confirmation of the existence of propagating slow waves in the low density edge region, which can significantly impact the strength of the rf-sheath potential, which is thought to contribute to impurity generation. Our sheath algorithm is based upon per-point lumped-circuit parameters for which we have estimates and general understanding, but which allow for some tuning and fitting. We are now engaged in a careful benchmarking of the algorithm against known analytic models and existing computational techniques to insure that the predictions of rf-sheath voltage are quantitatively consistent and believable, especially where slow waves share in the field with the fast wave. Currently in progress, an addition to the plasma force response accounting for the sheath potential, should enable the modeling of sheath plasma waves, a predicted additional root to the dispersion, existing at the

  5. Investigation of compression of puffing neon by deuterium current and plasma sheath in plasma focus discharge

    NASA Astrophysics Data System (ADS)

    Kubes, P.; Paduch, M.; Cikhardt, J.; Cikhardtova, B.; Rezac, K.; Klir, D.; Kravarik, J.; Kortanek, J.; Zielinska, E.

    2015-06-01

    This paper presents the results of the research of the influence of compressed neon, injected by the gas-puff nozzle in front of the anode axis by the deuterium current and plasma sheath on the evolution of the pinch, and neutron production at the current of 2 MA. The intense soft X-ray emission shows the presence of neon in the central region of the pinch. During the implosion and stopping of the plasma sheath, the deuterium plasma penetrates into the internal neon layer. The total neutron yield of 1010-1011 has a similar level as in the pure deuterium shots. The neutron and hard X-ray pulses from fusion D-D reaction are as well emitted both in the phase of the stopping implosion and during the evolution of instabilities at the transformation of plasmoidal structures and constrictions composed in this configuration from both gases. The fast deuterons can be accelerated at the decay of magnetic field of the current filaments in these structures.

  6. Investigation of compression of puffing neon by deuterium current and plasma sheath in plasma focus discharge

    SciTech Connect

    Kubes, P.; Cikhardt, J.; Cikhardtova, B.; Rezac, K.; Klir, D.; Kravarik, J.; Kortanek, J.; Paduch, M.; Zielinska, E.

    2015-06-15

    This paper presents the results of the research of the influence of compressed neon, injected by the gas-puff nozzle in front of the anode axis by the deuterium current and plasma sheath on the evolution of the pinch, and neutron production at the current of 2 MA. The intense soft X-ray emission shows the presence of neon in the central region of the pinch. During the implosion and stopping of the plasma sheath, the deuterium plasma penetrates into the internal neon layer. The total neutron yield of 10{sup 10}–10{sup 11} has a similar level as in the pure deuterium shots. The neutron and hard X-ray pulses from fusion D-D reaction are as well emitted both in the phase of the stopping implosion and during the evolution of instabilities at the transformation of plasmoidal structures and constrictions composed in this configuration from both gases. The fast deuterons can be accelerated at the decay of magnetic field of the current filaments in these structures.

  7. Plasma sheath in the presences of non-Maxwellian energetic electrons and secondary emission electrons

    NASA Astrophysics Data System (ADS)

    Ou, Jing; Lin, Binbin; Zhao, Xiaoyun; Yang, Youlei

    2016-07-01

    The formation of a sheath in front of a carbon or tungsten material plane immersed in a plasma containing non-Maxwellian energetic electrons and secondary emission electrons is studied using a 1D model. In the model, energetic electrons are described by the electron energy distribution function (EEDF) and secondary electron emission (SEE) is produced by the electrons impinging on the wall. It is found that SEE coefficient depends on not only the sheath potential but also the EEDF profile of energetic electrons when a non-Maxwellian energetic electron component is present. The energetic electrons and associated secondary emission electrons can strongly modify ion velocity at sheath edge, floating potential and I–V probe characteristic. Due to the interdependence between SEE coefficient originating from the impact of non-Maxwellian energetic electrons on the wall and the sheath potential, with the increase in the energy of energetic electrons, a sudden jump phenomenon can be found in the profiles of SEE coefficient and other quantities such as floating potential and ion velocity at the sheath edge for tungsten wall, while for carbon wall they are the continuous variation. To begin with, the energetic electron component does not dominate the sheath, and I–V probe characteristic depends on both the EEDF profile of energetic electrons and material properties. Once the energetic electron component dominates the sheath, the analysis of I–V probe characteristic will yield the energy of energetic electrons.

  8. Fine structure of modal focusing effect in a three dimensional plasma-sheath-lens formed by disk electrodes

    SciTech Connect

    Stamate, Eugen; Yamaguchi, Masahito

    2015-08-31

    Modal and discrete focusing effects associated with three-dimensional plasma-sheath-lenses show promising potential for applications in ion beam extraction, mass spectrometry, plasma diagnostics and for basic studies of plasma sheath. The ion focusing properties can be adjusted by controlling the geometrical structure of the plasma-sheath-lens and plasma parameters. The positive and negative ion kinetics within the plasma-sheath-lens are investigated both experimentally and theoretically and a modal focusing ring is identified on the surface of disk electrodes. The focusing ring is very sensitive to the sheath thickness and can be used to monitor very small changes in plasma parameters. Three dimensional simulations are found to be in very good agreement with experiments.

  9. Plasma sheath properties in a magnetic field parallel to the wall

    NASA Astrophysics Data System (ADS)

    Moritz, J.; Faudot, E.; Devaux, S.; Heuraux, S.

    2016-06-01

    Particle in cell simulations were carried out with a plasma bounded by two absorbing walls and a magnetic field applied parallel to them. Both the sheath extent and the potential drop in it were derived from simulations for different plasma parameters, such as the electron and ion temperature Ti, particle density, and ion mass. Both of them exhibit a power law dependent on the Larmor to plasma ion pulsation ratio Ωi. For increasing values of the magnetic field, the potential drop within the sheath decreases from a few Ti/e down to zero, where e stands for the electron charge. The space charge extent increases with Ωi and saturates to 2.15 ion Larmor radius. A simple model of sheath formation in such a magnetic field configuration is presented. Assuming strongly magnetized electrons, and neglecting collisions and ionizations, a new typical length is evidenced, which depends on the ratio Ωi. The charge separation sheath width is theoretically found to increase from a combination of the electron gyroradius and the ion Debye length for low Ωi ratios up to several ion gyroradii for strongly magnetized ions. Both the calculated sheath extent and plasma potential show a fair agreement with the numerical simulations.

  10. Fully kinetic plasma-sheath theory for a cold-electron emitting surface

    NASA Astrophysics Data System (ADS)

    Ordonez, C. A.

    1992-04-01

    The fully kinetic, one-dimensional, plasma-sheath theory by Schwager and Birdsall [Phys. Fluids B 2, 1057 (1990)] is further developed. A cold-electron emitting surface is included and a three-dimensional plasma is considered. The sheath potential is not assumed to equal the floating potential so that the theory applies to a current-carrying sheath. Appropriate values are found for higher-order moments of the velocity distribution which depend on the three-dimensional velocity distribution width. Distribution functions in terms of energy and angle are derived. The (effective) temperature, the total energy flux, and the heat flux are evaluated in terms of exact analytic functions. The normalized magnitude of the floating potential for a deuterium plasma with equal ion and electron temperatures is calculated to be ψf=3.2 for δ=0 and ψf=1.8 for δ=0.75 where δ is the electron emission coefficient. The normalized magnitude of the sheath potential for the same plasma (with δ=0) is calculated to be ψs=3.9 for γ=0.02 and ψs=2.8 for γ=-0.02 where γ is the normalized current density. A self-consistent integral solution for the electrostatic potential profile within the sheath is derived.

  11. Modeling of Sheath Ion-Molecule Reactions in Plasma Enhanced Chemical Vapor Deposition of Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Hash, David B.; Govindan, T. R.; Meyyappan, M.

    2004-01-01

    In many plasma simulations, ion-molecule reactions are modeled using ion energy independent reaction rate coefficients that are taken from low temperature selected-ion flow tube experiments. Only exothermic or nearly thermoneutral reactions are considered. This is appropriate for plasma applications such as high-density plasma sources in which sheaths are collisionless and ion temperatures 111 the bulk p!asma do not deviate significantly from the gas temperature. However, for applications at high pressure and large sheath voltages, this assumption does not hold as the sheaths are collisional and ions gain significant energy in the sheaths from Joule heating. Ion temperatures and thus reaction rates vary significantly across the discharge, and endothermic reactions become important in the sheaths. One such application is plasma enhanced chemical vapor deposition of carbon nanotubes in which dc discharges are struck at pressures between 1-20 Torr with applied voltages in the range of 500-700 V. The present work investigates The importance of the inclusion of ion energy dependent ion-molecule reaction rates and the role of collision induced dissociation in generating radicals from the feedstock used in carbon nanotube growth.

  12. Sheath effects observed on a 10 meter high voltage panel in simulated low earth orbit plasma

    NASA Technical Reports Server (NTRS)

    Mccox, J. E.; Konradi, A.

    1979-01-01

    A large (1m x 10m) flat surface of conductive material was biased to high voltage (+ or - 3000 V) to simulate the behavior of a large solar array in low earth orbit. The model array was operated in a plasma environment of 1,000 to 1,000,000/cu cm, with sufficient free space around it for the resulting plasma sheaths to develop unimpeded for 5-10 meters into the surrounding plasma. Measurements of the resulting sheath thickness were obtained. The observed thickness varied approximately as V to the 3/4 power and N to the 1/2 power. This effect appears to limit total current leakage from the test array until sheath dimensions exceed about 1 meter. Total leakage current was also measured with the array.

  13. Sheath and boundary conditions for plasma simulations of a Hall thruster discharge with magnetic lenses

    SciTech Connect

    Keidar, Michael; Beilis, Isak I.

    2009-05-11

    The effect of magnetic lens configuration on sheath in a Hall thruster discharge channels is considered. A model of the plasma-wall transition is developed in the case of large magnetic field incidence angle with respect to the wall. Peculiarity of such case consists in that the potential drop across the magnetic field is set externally. In this case, standard boundary conditions at the sheath edge for plasma simulations fail and a new formulation for those boundary conditions is proposed. The results obtained demonstrate importance of the effect of the magnetic field incidence angle on the sheath boundary conditions for plasma simulations as well as on the energy balance in the Hall thruster discharge.

  14. A matching approach to communicate through the plasma sheath surrounding a hypersonic vehicle

    SciTech Connect

    Gao, Xiaotian; Jiang, Binhao

    2015-06-21

    In order to overcome the communication blackout problem suffered by hypersonic vehicles, a matching approach has been proposed for the first time in this paper. It utilizes a double-positive (DPS) material layer surrounding a hypersonic vehicle antenna to match with the plasma sheath enclosing the vehicle. Analytical analysis and numerical results indicate a resonance between the matched layer and the plasma sheath will be formed to mitigate the blackout problem in some conditions. The calculated results present a perfect radiated performance of the antenna, when the match is exactly built between these two layers. The effects of the parameters of the plasma sheath have been researched by numerical methods. Based on these results, the proposed approach is easier to realize and more flexible to the varying radiated conditions in hypersonic flight comparing with other methods.

  15. The magnetized sheath of a dusty plasma with nanosize dust grains

    SciTech Connect

    Mehdipour, H.; Foroutan, G.

    2010-08-15

    The magnetized sheath of a dusty plasma is investigated via numerical simulations of stationary multifluid equations by taking into account the electric, magnetic, gravitational, ion drag, neutral drag, and thermophoretic forces. Dependence of the sheath properties on the characteristics of the magnetic field and plasma parameters is explored. The sheath dynamics is mainly governed by the electric and ion drag forces and the effect of gravitation is negligible. The sheath demonstrates a nonmonotonic behavior against variations of the magnetic intensity and its angle of incidence. The sheath thickness and the maximum of dust density distribution decrease with increasing the ion to electron density ratio at the sheath edge, but increase with growing electron temperature and the positive temperature gradient of the neutrals. The effects of ion drag are similar to those of the gravitational force as both of them accelerate the dust to the wall. By a suitable configuration of the temperature gradient in the neutral gas, thermophoretic force can be utilized to deposit the building units of nanostructures on a substrate or remove any unwanted contaminant from its neighborhood.

  16. Simulation of the plasma sheath dynamics in a spherical plasma focus

    NASA Astrophysics Data System (ADS)

    Ay, Yasar; Abd Al-Halim, Mohamed A.; Bourham, Mohamed A.

    2015-09-01

    A two concentric electrodes spherical plasma focus device is simulated using a snow plow model, depending on the momentum, circuit and shock wave equations. In the spherical plasma focus, the magnetic pressure for constant discharge current is higher at the system antipodal point as compared to that at the equator. The simulation phases include a run down phase with expansion from the first antipodal to the equator, then a compression from the equator point to the second antipodal point, and finally a reflection of the shock wave on the axis. The results show that the spherical plasma focus model is in good agreement with published experimental results of the plasma parameters such as the discharge current and current derivative. Plasma parameters and the effect of the variation in the gas pressure and discharge voltage were obtained for hydrogen, deuterium and tritium. The energy deposited into the plasma sheath and the power deposited into the plasma focus tube are calculated. The basic calculation of the current fraction is also included in this study.

  17. Kelvin-Helmholtz vortex formation and particle transport in a cross-field plasma sheath

    SciTech Connect

    Theilhaber, K.; Birdsall, C.K.

    1989-02-13

    The time-dependent behavior of a magnetized, two-dimensional plasma-wall sheath has been studied through particle simulations, whcih have shown that the cross-field sheath develops into a turbulent boundary layer, driven by the Kelvin-Helmholtz instability. The sheath acquires an equilibrium thickness l/sub x/approx.5rho/sub i/, and maintains long-lived vortices, with amplitudes deltaphiapprox.-2T/sub i//e, which drift parallel to the wall at half the ion thermal velocity. A central simulation result is that for ..omega../sub ..pi../greater than or equal to2..omega../sub ci/, the anomalous particle transport in the sheath scales like Bohn diffusion.

  18. PIC Simulation of RF Plasma Sheath Formation and Initial Validation of Optical Diagnostics using HPC Resources

    NASA Astrophysics Data System (ADS)

    Icenhour, Casey; Exum, Ashe; Martin, Elijah; Green, David; Smithe, David; Shannon, Steven

    2014-10-01

    The coupling of experiment and simulation to elucidate near field physics above ICRF antennae presents challenges on both the experimental and computational side. In order to analyze this region, a new optical diagnostic utilizing active and passive spectroscopy is used to determine the structure of the electric fields within the sheath region. Parallel and perpendicular magnetic fields with respect to the sheath electric field have been presented. This work focuses on the validation of these measurements utilizing the Particle-in-Cell (PIC) simulation method in conjunction with High Performance Computing (HPC) resources on the Titan supercomputer at Oak Ridge National Laboratory (ORNL). Plasma parameters of interest include electron density, electron temperature, plasma potentials, and RF plasma sheath voltages and thicknesses. The plasma is modeled utilizing the VSim plasma simulation tool, developed by the Tech-X Corporation. The implementation used here is a two-dimensional electromagnetic model of the experimental setup. The overall goal of this study is to develop models for complex RF plasma systems and to help outline the physics of RF sheath formation and subsequent power loss on ICRF antennas in systems such as ITER. This work is carried out with the support of Oak Ridge National Laboratory and the Tech-X Corporation.

  19. Oblique collision of dust acoustic solitons in a strongly coupled dusty plasma

    SciTech Connect

    Boruah, A.; Sharma, S. K. Bailung, H.; Nakamura, Y.

    2015-09-15

    The oblique collision between two equal amplitude dust acoustic solitons is observed in a strongly coupled dusty plasma. The solitons are subjected to oblique interaction at different colliding angles. We observe a resonance structure during oblique collision at a critical colliding angle which is described by the idea of three wave resonance interaction modeled by Kadomtsev-Petviashvili equation. After collision, the solitons preserve their identity. The amplitude of the resultant wave formed during interaction is measured for different collision angles as well as for different colliding soliton amplitudes. At resonance, the maximum amplitude of the new soliton formed is nearly 3.7 times the initial soliton amplitude.

  20. Effect of the q-nonextensive electron velocity distribution on a magnetized plasma sheath

    SciTech Connect

    Safa, N. Navab Ghomi, H.; Niknam, A. R.

    2014-08-15

    In this work, a sheath model has been developed to investigate the effect of the q-nonextensive electron velocity distribution on the different characteristics of a magnetized plasma. By using Segdeev potential method, a modified Bohm criterion for a magnetized plasma with the nonextensive electron velocity distribution is derived. The sheath model is then used to analyze numerically the sheath structure under different q, the parameter quantifying the nonextensivity degree of the system. The results show that as the q-parameter decreases, the floating potential becomes more negative. The sheath length increases at the lower values of the q-parameter due to the increase in the electron population at the high-energy tail of the distribution function. As q-parameter decreases, the effective temperature of the electrons increases which results in a more extended plasma sheath. The ion velocity and density profiles for the different nonextensivity degrees of the system reflect the gyro-motion of the ions in the presence of the magnetic field. Furthermore, the results coincide with those given by the Maxwellian electron distribution function, when q tends to 1.

  1. Excitation of the lower oblique resonance by an artificial plasma jet in the ionosphere

    NASA Astrophysics Data System (ADS)

    Thiel, J.; Storey, L. R. O.; Bauer, O. H.; Jones, D.

    1984-04-01

    Aboard the Porcupine rockets, bursts of noise were detected in the electron whistler range during the operation of a xenon plasma gun on a package ejected from the main payload. These observations can be interpreted in terms of excitation of the lower oblique resonance by instabilities associated with the motion of the xenon ion beam through the ionospheric plasma.

  2. Measurements of the asymmetric, dynamic sheath around a pulse biased sphere immersed in flowing metal plasma

    SciTech Connect

    Anders, Andre; Wu, Hongchen; Anders, Andre

    2008-06-13

    A long-probe technique was utilized to record the expansion and retreat of the dynamic sheath around a spherical substrate immersed in pulsed cathode arc metal plasma. Positively biased, long cylindrical probes were placed on the side and downstream of a negatively pulsed biased stainless steel sphere of 1" (25.4 mm) diameter. The amplitude and width of the negative high voltage pulses (HVP) were 2 kV, 5 kV, 10 kV, and 2 mu s, 4 mu s, 10 mu s, respectively. The variation of the probe (electron) current during the HVP is a direct measure for the sheath expansion and retreat. Maximum sheath sizes were determined for the different parameters of the HVP. The expected rarefaction zone behind the biased sphere (wake) due to the fast plasma flow was clearly established and quantified.

  3. Fluid simulation of an electrostatic plasma sheath with two species of positive ions and charged nanoparticles

    SciTech Connect

    Foroutan, G.

    2010-12-15

    One-dimensional fluid simulations are used to study the dynamics of an electrostatic plasma sheath containing nanosized dust grains and two species of positive ions, i.e., He{sup +} and Ar{sup +}. The impacts of the concentration of each species, the velocity at the sheath edge of the ions, and the bias voltage of the substrate, on the spatial distribution of the velocity and number density of the plasma particles, and the incident fluxes of the ions on the substrate, are investigated. The numerical results show that the sheath thickness increases with increasing {sigma}, the density ratio of He{sup +} ions to Ar{sup +} ions at the sheath edge. For nanosized dust particles considered in this work, the dominant forces are the ion drag and the electric force and the effects of the neutral drag and gravity are negligible. Due to enhancement of the ion drag force and the electric force, the dust velocity increases and, consequently, the dust number density decreases as the concentration at the sheath edge of Ar{sup +} ions is increased. For the same velocity and number density at the sheath edge, the number density of Ar{sup +} ions near the wall is larger than that of He{sup +} ions, but their incident fluxes are the same. The maximum in the dust number density increases with the velocity of Ar{sup +} ions at the sheath edge, but it weakly changes with the Mach number of He{sup +} ions, except for large values of {sigma}. The position of the maximum dust number density initially decreases very quickly with increasing the velocity at the sheath edge of the ions from small values, but then at larger values it changes quite slowly. The differences in the sheath parameters for different values of {sigma} disappear at some values of the velocity at the sheath edge of the ions and dust particles. The incident flux of the ions are independent of the bias voltage of the substrate, but their kinetic energy is equal to the bias potential.

  4. Modeling the ITER ICRF Antenna with Integrated Time Domain RF Sheath and Plasma Physics

    NASA Astrophysics Data System (ADS)

    Smithe, David; D'Ippolito, Daniel; Myra, James; CSWPI Collaboration

    2014-10-01

    We present results from computer simulations of detailed 3D models of the ICRF launcher assembly, including straps, Faraday Shields, and vessel wall. These simulations provide exquisite detail of the antenna near fields, and the sheaths between plasma and the metallic components of the launcher. Significant work has been done to create a sheath model that allows us to estimate local values of sheath potential everywhere on the 3D structure, so that we can estimate RF rectified plasma potential. Those potentials are in turn a likely source of sputtering and impurity creation, when the antennas are operating, and we discuss ongoing work to quantify these effects. Additional study of the antenna near fields also investigates slow waves which can exist in the low density scrape-off layer, and may impact power balance, and also sheath amplitudes. Movies of the 3D field and sheath oscillations will be shown. Supported by DOE Grants DE-08ER54953 and DE-FG02-09ER55006.

  5. Scaling of the plasma sheath in a magnetic field parallel to the walla)

    NASA Astrophysics Data System (ADS)

    Krasheninnikova, Natalia S.; Tang, Xianzhu; Roytershteyn, Vadim S.

    2010-05-01

    Motivated by the magnetized target fusion [R. E. Siemon et al., Comments Plasma Phys. Controlled Fusion 18, 363 (1999)] experiment, a systematic investigation of the scaling of a one-dimensional plasma sheath with a magnetic field parallel to the wall was carried out using analytical theory and the particle-in-cell code VPIC [K. J. Bowers et al., Phys. Plasmas 15, 055703 (2008)]. Starting with a uniform Maxwellian distribution in three-dimensional velocity space, plasma consisting of collisionless electrons, and ions of the same temperature interacts with a perfectly absorbing wall. A much larger ion Larmor radius causes the wall to be charged positively, creating an electric field that tends to repel the ions and attract the electrons, which is the opposite of the conventional Bohm sheath [D. Bohm, Characteristics of Electrical Discharges in Magnetic Fields (McGraw-Hill, New York, 1949)]. This manifests in the form of gyro-orbit modification by this spatially varying electric field, the degree of which is found to intricately depend on the relation between three parameters: electron and ion thermal Larmor radii and plasma Debye length: ρthe, ρthi, and λD. Furthermore, the study of the sheath width scaling through the analysis of the full width at half max of electric field, xEh, elucidates three distinct types of behavior of xEh, corresponding to three different regimes: ρthi<λD, ρthe<λD<ρthi, and λD<ρthe. In addition to the sheath width, the scaling of the wall potential ϕWall, as well as the role of the ion mass and charge Z are investigated. The results of this analytical and computational approach can also be useful in studying the plasma sheath in the conventional magnetic confinement devices, in particular at the first wall of tokamaks.

  6. Investigation on oblique shock wave control by arc discharge plasma in supersonic airflow

    SciTech Connect

    Wang Jian; Li Yinghong; Xing Fei

    2009-10-01

    Wedge oblique shock wave control by arc discharge plasma in supersonic airflow was investigated theoretically, experimentally, and numerically in this paper. Using thermal choking model, the change in oblique shock wave was deduced, which refer that the start point of shock wave shifts upstream, the shock wave angle decreases, and its intensity weakens. Then the theoretical results were validated experimentally in a Mach 2.2 wind tunnel. On the test conditions of arc discharge power of approx1 kW and arc plasma temperature of approx3000 K, schlieren photography and gas pressure measurements indicated that the start point of shock wave shifted upstream of approx4 mm, the shock wave angle decreased 8.6%, and its intensity weakened 8.8%. The deduced theoretical results match the test results qualitatively, so thermal mechanism and thermal choking model are rational to explain the problem of oblique shock wave control by arc discharge plasma. Finally, numerical simulation was developed. Based on thermal mechanism, the arc discharge plasma was simplified as a thermal source term that added to the Navier-Stokes equations. The simulation results of the change in oblique shock wave were consistent with the test results, so the thermal mechanism indeed dominates the oblique shock wave control process.

  7. Measurement of electric field and gradient in the plasma sheath using clusters of floating microspheres.

    PubMed

    Sheridan, T E; Katschke, M R; Wells, K D

    2007-02-01

    A method for measuring the time-averaged vertical electric field and its gradient in the plasma sheath using clusters with n = 2 or 3 floating microspheres of known mass is described. The particle charge q is found by determining the ratio of the breathing frequency to the center-of-mass frequency for horizontal (in-plane) oscillations. The electric field at the position of the particles is then calculated using the measured charge-to-mass ratio, and the electric-field gradient is determined from the vertical resonance frequency. The Debye length is also found. Experimental results are in agreement with a simple sheath model. PMID:17578108

  8. Calculation of two-dimensional plasma sheath with application to radial dust oscillations

    SciTech Connect

    Sheridan, T.E.

    2005-07-15

    Dust particles are often confined radially in a plasma potential well above a cylindrical depression in an otherwise flat electrode. The structure of the two-dimensional, time-independent sheath is computed for this geometry using cold, collisionless ions and Boltzmann electrons. A depression with a radius of 16 Debye lengths and a depth of 2 Debye lengths is modeled for negative electrode biases from 6 to 32 times the electron temperature. The normalized radial oscillation frequency for a dust particle in the well is computed from the sheath potential structure. The model results agree qualitatively with the experimental measurements.

  9. General cause of sheath instability identified for low collisionality plasmas in devices with secondary electron emission.

    PubMed

    Campanell, M D; Khrabrov, A V; Kaganovich, I D

    2012-06-01

    A condition for sheath instability due to secondary electron emission (SEE) is derived for low collisionality plasmas. When the SEE coefficient of the electrons bordering the depleted loss cone in energy space exceeds unity, the sheath potential is unstable to a negative perturbation. This result explains three different instability phenomena observed in Hall thruster simulations including a newly found state with spontaneous ∼20  MHz oscillations. When instabilities occur, the SEE propagating between the walls becomes the dominant contribution to the particle flux, energy loss and axial transport. PMID:23003962

  10. General Cause of Sheath Instability Identified for Low Collisionality Plasma in Devices with Secondary Electron Emission

    SciTech Connect

    M.C. Campanell, A. Khrabrov and I Kaganovich

    2012-05-11

    A condition for sheath instability due to secondary electron emission (SEE) is derived for low collisionality plasmas. When the SEE coefficient of the electrons bordering the depleted loss cone in energy space exceeds unity, the sheath potential is unstable to a negative perturbation. This result explains three different instability phenomena observed in Hall thruster simulations including a newly found state with spontaneous ~20MHz oscillations. When instabilities occur, the SEE propagating between the walls becomes the dominant contribution to the particle flux, energy loss and axial transport.

  11. Sheath expansion and plasma dynamics in the presence of electrode evaporation: Application to a vacuum circuit breaker

    SciTech Connect

    Sarrailh, P.; Garrigues, L.; Hagelaar, G. J. M.; Boeuf, J. P.; Sandolache, G.; Rowe, S.

    2009-09-01

    During the postarc dielectric recovery phase in a vacuum circuit breaker, a cathode sheath forms and expels the plasma from the electrode gap. The success or failure of current breaking depends on how efficiently the plasma is expelled from the electrode gap. The sheath expansion in the postarc phase can be compared to sheath expansion in plasma immersion ion implantation except that collisions between charged particles and atoms generated by electrode evaporation may become important in a vacuum circuit breaker. In this paper, we show that electrode evaporation plays a significant role in the dynamics of the sheath expansion in this context not only because charged particle transport is no longer collisionless but also because the neutral flow due to evaporation and temperature gradients may push the plasma toward one of the electrodes. Using a hybrid model of the nonequilibrium postarc plasma and cathode sheath coupled with a direct simulation Monte Carlo method to describe collisions between heavy species, we present a parametric study of the sheath and plasma dynamics and of the time needed for the sheath to expel the plasma from the gap for different values of plasma density and electrode temperatures at the beginning of the postarc phase. This work constitutes a preliminary step toward understanding and quantifying the risk of current breaking failure of a vacuum arc.

  12. Sheath structure in plasma with two species of positive ions and secondary electrons

    NASA Astrophysics Data System (ADS)

    Xiao-Yun, Zhao; Nong, Xiang; Jing, Ou; De-Hui, Li; Bin-Bin, Lin

    2016-02-01

    The properties of a collisionless plasma sheath are investigated by using a fluid model in which two species of positive ions and secondary electrons are taken into account. It is shown that the positive ion speeds at the sheath edge increase with secondary electron emission (SEE) coefficient, and the sheath structure is affected by the interplay between the two species of positive ions and secondary electrons. The critical SEE coefficients and the sheath widths depend strongly on the positive ion charge number, mass and concentration in the cases with and without SEE. In addition, ion kinetic energy flux to the wall and the impact of positive ion species on secondary electron density at the sheath edge are also discussed. Project supported by the National Natural Science Foundation of China (Grant Nos. 11475220 and 11405208), the Program of Fusion Reactor Physics and Digital Tokamak with the CAS “One-Three-Five” Strategic Planning, the National ITER Program of China (Grant No. 2015GB101003), and the Higher Education Natural Science Research Project of Anhui Province, China (Grant No. 2015KJ009).

  13. Numerical analysis of radio-frequency sheath-plasma interactions in the ion cyclotron range of frequencies

    SciTech Connect

    Kohno, H.; Myra, J. R.; D'Ippolito, D. A.

    2012-01-15

    A new finite element numerical scheme for analyzing self-consistent radio-frequency (RF) sheath-plasma interaction problems in the ion cyclotron range of frequencies is applied to various problems represented by simplified models for the tokamak scrape-off layer. The present code incorporates a modified boundary condition, which is called a sheath boundary condition, that couples the radio-frequency waves and sheaths at the material boundaries by treating the sheath as a thin vacuum layer. A series of numerical analyses in one- and two-dimensional domains show several important physical properties, such as the existence of multiple roots, hysteresis effects, presence and characteristics of the sheath-plasma waves, and the phase shift of a reflected slow wave, some of which are newly identified by introducing a spatially varying plasma density and background magnetic field.

  14. Self-consistent modeling of the tokamak RF antennas, edge plasma, and sheath voltages

    NASA Astrophysics Data System (ADS)

    Smithe, David; Jenkins, Tom; Austin, Travis; Loverich, John; Stoltz, Peter

    2012-10-01

    We model the 24-strap ITER RF antenna with a time-domain electromagnetic simulation package [1] that faithfully represents the 3D complexity of the launcher geometry. The simulations include a cold-plasma fluid model of the edge plasma [2], with an RF sheath sub-grid model which allows for realistic behavior of plasma in contact with metallic structures, such as Faraday shields [3]. Interestingly, localized short wavelength modes, likely slow waves, have been observed in the vicinity of the launcher, and are very sensitive to density. We investigate the effect on these waves for varying density, density profile, and magnetic shear. We further investigate the contribution to high sheath potentials such waves might have. We also present status and additional highlights of the continuing evolution of the overall model. This includes studies to benchmark the nonlinear sheath width and loss parameters, and more diagnostics aimed towards better characterizing energy balance. It also includes application of the analysis on larger problem domain size, with scaling-study results. Finally, we review recent work to improve the model for warm plasma, and nonlinear effects. Work supported by US. DOE Grants DE-FG02-09ER55006 and DE-FC02-08ER54953.[4pt] [1] Nieter, C. and Cary, J. R., JCP 196 (2004) 448-473.[0pt] [2] Smithe, D., Physics of Plasmas 14, 056104 (2007).[0pt] [3] Myra and D'Ippolito, PRL 101, 195004 (2008).

  15. Investigating the Structure of the Wake of a Dust Particle in the Plasma Sheath

    NASA Astrophysics Data System (ADS)

    Jung, Hendrik; Greiner, Franko; Piel, Alexander

    2015-11-01

    Due to the deflection of the ambient streaming ions, a negatively charged dust particle in the plasma sheath forms a wake with a net positive space charge in downstream direction. The wake is characterized by attractive, non-reciprocal forces between negatively charged particles and a charge reduction of a particle in the wake of another particle. In this contribution a two-particle system is used to investigate the ion wake structure behind a dust particle in the plasma sheath of an rf discharge. For this purpose, we have used the phase-resolved resonance method that evaluates the dynamic response of the particle system to small external, sinusoidal perturbations, which allows to measure the wake induces characteristics. Plasma inherent etching processes are used to achieve an increasing levitation height of the lower particle, so that the structure of the wake of the upper particle, which is nearly unaffected by etching, can be probed. In good agreement with theoretical predictions, a significant modification in the plasma sheath to one long potential tail is observed. The presented method is used to investigate the influence of a strong magnetic field on the formation and spatial structure of the wake. Funded by DFG under contract SFB TR-24/A2.

  16. Investigations of the Sheath Effect on the Resultant Magnetic Field of a Cylindrical Monopole Plasma Antenna

    NASA Astrophysics Data System (ADS)

    Moses, E. Emetere

    2015-02-01

    The functionality of the plasma antenna has been narrowed to types and brand names only. The physics of its operation has been neglected and has stagnated technological innovations. The magnetic field in the sheath and plasma were investigated. Notable specifications were worked out in the proposed improved cylindrical monopole plasma antenna. The occurrence of femto spin demagnetization was discovered between the duration of switch on and switch off of the antenna. This phenomenon seems transient because magnetization is highest at the switch on/off point.

  17. Oblique firehose instability in hot collisionless plasmas - interplay between protons and electrons

    NASA Astrophysics Data System (ADS)

    Maneva, Yana; Lazar, Marian; Vinas, Adolfo; Poedts, Stefaan

    2016-04-01

    We solve the linearized kinetic Vlasov-Maxwell dispersion relation for oblique wave propagation in a homogeneous highly anisotropic hot electron-proton plasma. We assume bi-Maxwellian velocity distributions for both species, charge neutrality and current conservation, and consider no differential streaming between the ions and the electrons. We calculate the growth rate of the parallel and oblique proton firehose instabilities for various angles of wave propagation and varios electron plasma properties. We study the transition from stable to unstable scales with increasing electron temperature and temperature anisotropies. We find that for highly anisotropic hot plasma both the oscillatory parallel and the aperiodic oblique proton firehose branches may easily couple to the parallel and oblique electron firehose branches. In other words our work demonstrates the interplay between the proton and electron firehose instabilities, whose scales become fully mixed in hot collisionless plasma when the protons and the electrons are simultaneously anisotropic. In the case of parallel wave propagation both left and right-hand polarized waves are simultaneously excited. As we increase the angle of propagation the electron firehose starts to dominate with excitation of large-amplitude aperiodic fluctuations over a large range of wave-numbers, starting at the protons scales and extending up to the smaller electron scales. Whereas the maximum growth rate of the parallel proton firehose branch remains always at the proton scales, the maximum growth rate for the oblique proton firehose extends down to the electron scales. The observed electron-proton scale mixing can have significant implications for the observed plasma properties and instability thresholds in hot colissionless solar wind streams.

  18. Oblique modulation of ion-acoustic waves and envelope solitons in electron-positron-ion plasma

    SciTech Connect

    Jehan, Nusrat; Salahuddin, M.; Mirza, Arshad M.

    2009-06-15

    The effect of oblique modulation on the amplitude dynamics of ion-acoustic wave propagating in a collisionless electron-positron-ion plasma is investigated. Using Krylov-Bogoliubov-Mitropolsky (KBM) perturbation method, a nonlinear Schroedinger (NLS) equation is derived which governs the evolution of obliquely modulated ion-acoustic envelope excitations. It is found that the presence of positron component significantly modifies the stability domains for small angles of propagation with the direction of modulation. The stationary solutions of NLS equation, i.e., bright and dark envelope solitons, become narrower as the concentration of positron component increases.

  19. Shear flow instability in a partially-ionized plasma sheath around a fast-moving vehicle

    SciTech Connect

    Sotnikov, V. I.; Mudaliar, S.; Genoni, T. C.; Rose, D. V.; Oliver, B. V.; Mehlhorn, T. A.

    2011-06-15

    The stability of ion acoustic waves in a sheared-flow, partially-ionized compressible plasma sheath around a fast-moving vehicle in the upper atmosphere, is described and evaluated for different flow profiles. In a compressible plasma with shear flow, instability occurs for any velocity profile, not just for profiles with an inflection point. A second-order differential equation for the electrostatic potential of excited ion acoustic waves in the presence of electron and ion collisions with neutrals is derived and solved numerically using a shooting method with boundary conditions appropriate for a finite thickness sheath in contact with the vehicle. We consider three different velocity flow profiles and find that in all cases that neutral collisions can completely suppress the instability.

  20. Obliquely propagating cnoidal waves in a magnetized dusty plasma with variable dust charge

    SciTech Connect

    Yadav, L. L.; Sayal, V. K.

    2009-11-15

    We have studied obliquely propagating dust-acoustic nonlinear periodic waves, namely, dust-acoustic cnoidal waves, in a magnetized dusty plasma consisting of electrons, ions, and dust grains with variable dust charge. Using reductive perturbation method and appropriate boundary conditions for nonlinear periodic waves, we have derived Korteweg-de Vries (KdV) equation for the plasma. It is found that the contribution to the dispersion due to the deviation from plasma approximation is dominant for small angles of obliqueness, while for large angles of obliqueness, the dispersion due to magnetic force becomes important. The cnoidal wave solution of the KdV equation is obtained. It is found that the frequency of the cnoidal wave depends on its amplitude. The effects of the magnetic field, the angle of obliqueness, the density of electrons, the dust-charge variation and the ion-temperature on the characteristics of the dust-acoustic cnoidal wave are also discussed. It is found that in the limiting case the cnoidal wave solution reduces to dust-acoustic soliton solution.

  1. Studies of sheath characteristics in a double plasma device with a negatively biased separating grid and a magnetic filter field

    SciTech Connect

    Das, B. K.; Chakraborty, M.; Bandyopadhyay, M.

    2012-09-15

    A double plasma device has two regions: Source region and target region. These two regions are divided by a magnetic filter field. A grid is placed coplanar to the magnetic filter. To study the sheath structure in the target region, a metallic plate is placed at the center, which can be biased with respect to the chamber (ground) potential. Plasma is created in the source region by filament discharge technique. Plasma diffusing from the source region to the target region is subjected to the magnetic filter field and also an electric field applied on the grid. Plasma thus obtained in the target region forms a sheath on the biased plate. The influence of both the magnetic filter field and the electric field, applied between the grid and the chamber wall, on the sheath structure formed on the biased plate is studied. It is found that the magnetic filter field and the electric field change the sheath structure in different ways.

  2. Influences of Turbulent Reentry Plasma Sheath on Wave Scattering and Propagation

    NASA Astrophysics Data System (ADS)

    Liu, Zhiwei; Bao, Weimin; Li, Xiaoping; Shi, Lei; Liu, Donglin

    2016-06-01

    The randomness of turbulent reentry plasma sheaths can affect the propagation and scattering properties of electromagnetic waves. This paper developed algorithms to estimate the influences. With the algorithms and typical reentry data, influences of GPS frequency and Ka frequency are studied respectively. Results show that, in terms of wave scattering, the scattering loss caused by the randomness of the turbulent plasma sheath increases with the increase of the ensemble average electron density, ensemble average collision frequency, electron density fluctuation and turbulence integral scale respectively. Also the scattering loss is much smaller than the dielectric loss. The scattering loss of Ka frequency is much less than that of the GPS frequency. In terms of wave propagation, the randomness arouses the fluctuations of amplitude and phase of waves. The fluctuations change with altitudes that when the altitude is below 30 km, fluctuations increase with altitude increasing, and when the altitude is above 30 km, fluctuations decrease with altitude increasing. The fluctuations of GPS frequency are strong enough to affect the tracking, telemetry, and command at appropriate conditions, while the fluctuations of Ka frequency are much more feeble. This suggests that the Ka frequency suffers less influences of the randomness of a turbulent plasma sheath. supported by the National Basic Research Program of China (No. 2014CB340205) and National Natural Science Foundation of China (Nos. 61301173 and 61473228)

  3. Propagation and oblique collision of ion-acoustic solitary waves in a magnetized dusty electronegative plasma

    SciTech Connect

    El-Labany, S. K.; Behery, E. E.; El-Shamy, E. F.

    2013-12-15

    The propagation and oblique collision of ion-acoustic (IA) solitary waves in a magnetized dusty electronegative plasma consisting of cold mobile positive ions, Boltzmann negative ions, Boltzmann electrons, and stationary positive/negative dust particles are studied. The extended Poincaré-Lighthill-Kuo perturbation method is employed to derive the Korteweg-de Vries equations and the corresponding expressions for the phase shifts after collision between two IA solitary waves. It turns out that the angle of collision, the temperature and density of negative ions, and the dust density of opposite polarity have reasonable effects on the phase shift. Clearly, the numerical results demonstrated that the IA solitary waves are delayed after the oblique collision. The current finding of this work is applicable in many plasma environments having negative ion species, such as D- and F-regions of the Earth's ionosphere and some laboratory plasma experiments.

  4. Oblique Propagation of Ion Acoustic Solitons in Magnetized Superthermal Plasmas

    NASA Astrophysics Data System (ADS)

    Devanandhan, S.; Sreeraj, T.; Singh, S.; Lakhina, G. S.

    2015-12-01

    Small amplitude ion-acoustic solitons are studied in a magnetized plasma consisting of protons, doubly charged helium ions and superthermal electrons. The Korteweg-de-Vries-Zakharov-Kuznetsov (KdV-ZK) is derived to examine the properties of ion acoustic solitary structures observed in space plasmas. Our model is applicable for weakly magnetized plasmas. The results will be applied to the satellite observations in the solar wind at 1 AU where magnetized ion acoustic waves with superthermal electrons can exist. The effects of superthermality, temperature and densities on these solitary structures will be discussed.

  5. Nonlinear surface plasma wave induced target normal sheath acceleration of protons

    SciTech Connect

    Liu, C. S.; Tripathi, V. K. Shao, Xi; Liu, T. C.

    2015-02-15

    The mode structure of a large amplitude surface plasma wave (SPW) over a vacuum–plasma interface, including relativistic and ponderomotive nonlinearities, is deduced. It is shown that the SPW excited by a p-polarized laser on a rippled thin foil target can have larger amplitude than the transmitted laser amplitude and cause stronger target normal sheath acceleration of protons as reported in a recent experiment. Substantial enhancement in proton number also occurs due to the larger surface area covered by the SPW.

  6. Investigation Of The Dust Particles Trapping In Electrostatic Sheaths Of Plasma Discharge

    SciTech Connect

    Tahraoui; Zaham, B.; Annou, R.; Bougdira, J.; Hugon, R.

    2008-09-23

    In this work, a 1D steady state model to study the dynamics along with trapping of dust grains in a plasma sheath over the lower electrode in a plasma reactor, is proposed. Electron and negative ions density distributions are taken Boltzmannian whereas positive ions are described by a cold fluid model. Numerous forces acting on dust grains are taken into account, viz, electric force, gravity force, ion drag force, neutral drag force, etc. It is found that trapping is grain size dependent, and it affects only negatively charged grains. The trapping position is determined and the physical parameters controlling the later are discussed.

  7. Calculation of sheath and wake structure about a pillbox-shaped spacecraft in a flowing plasma

    NASA Technical Reports Server (NTRS)

    Parker, L. W.

    1977-01-01

    A computer program was used for studies of the disturbed zones around bodies in flowing plasmas, particularly spacecraft and their associated sheaths and wakes. The program solved a coupled Poisson-Vlasov system of nonlinear partial differential integral equations to obtain distributions of electric potential and ion and electron density about a finite length cylinder in a plasma flow at arbitrary ion Mach numbers. The approach was applicable to a larger range of parameters than other available approaches. In sample calculations, bodies up to 100 Debye lengths in radius were treated, that is, larger than any previously treated realistically. Applications were made to in-situ satellite experiments.

  8. High voltage plasma sheath analysis related to TSS-1

    NASA Technical Reports Server (NTRS)

    Sheldon, John W.

    1991-01-01

    On the first mission of the Tethered Satellite System (TSS-1), a 1.8 m diameter spherical satellite will be deployed a distance of 20 km above the space shuttle Orbiter on an insulated conducting tether. The satellite will be held at electric potentials up to 5000 volts positive with respect to the ambient plasma. Due to the passage of the conducting tether through the Earth's magnetic field, an emf will be created, driving electrons down the tether to the orbiter, out through an electron gun into the ionosphere and back into the positive biased satellite. Instrumentation on the satellite will measure electron flow to the surface at several locations, but these detectors have a limited range of acceptance angle. The problem addressed herein is the determination of the electron current distribution over the satellite surface and the angle of incidence of the incoming electrons relative to the surface normal.

  9. Oblique surface Josephson plasma waves in layered superconductors

    NASA Astrophysics Data System (ADS)

    Averkov, Yu. O.; Yakovenko, V. M.; Yampol'skii, V. A.; Nori, Franco

    2013-02-01

    We have theoretically studied oblique surface waves (OSWs) which propagate along the interface between a dielectric and a layered superconductor. We assume that this interface is perpendicular to the superconducting layers, and OSWs at the interface can propagate at an arbitrary angle with respect to them. The electromagnetic field of the OSWs in a layered superconductor is a superposition of an ordinary wave (with its electric field parallel to the layers) and an extraordinary wave (with its magnetic field parallel to the layers). We have derived the dispersion equation for the OSWs and shown that the dispersion curves have end points where the extraordinary mode transforms from evanescent wave to bulk wave, propagating deep into the superconductor. In addition, we have analytically solved the problem of the resonance excitation of the OSWs by the attenuated-total-reflection method using an additional dielectric prism. Due to the strong current anisotropy in the boundary of the superconductor, the excitation of the OSWs is accompanied by an additional important phenomenon: The electromagnetic field component with the orthogonal polarization appears in the wave reflected from the bottom of the prism. We show that, for definite optimal combinations of the problem parameters (the wave frequency, the direction of the incident wave vector, the thickness of the gap between dielectric prism and superconductor, etc.), there is a complete suppression of the reflected wave with its polarization coinciding with the polarization of the incident wave. Contrary to the isotropic case, this phenomenon can be observed even in the dissipationless limit. In such a regime, the complete transformation of the incident wave into a reflected wave with orthogonal polarization can be observed.

  10. The effect of a dust size distribution on electrostatic sheaths in unmagnetized dusty plasmas

    SciTech Connect

    Benlemdjaldi, D.; Tahraoui, A.; Hugon, R.; Bougdira, J.

    2013-04-15

    In this work, the structure of plasma sheaths in presence of dust particles with different sizes is investigated numerically in a multifluid framework, where the dust size distribution is modeled by Gauss' law. For this, we have established a 1D, stationary, unmagnetized, and weakly collisional electronegative dusty plasma sheath model. The electrons and negative ions are considered in a local thermodynamic equilibrium, therefore, described by a Boltzmann distribution. On the other hand, positive ions and dust grains are described by fluid equations. The charging process is described by the orbit motion limited model. It is shown that taking into account dust grains with different sizes reduces considerably the sheath thickness. The behavior of dust surface potential is not affected, but the dust charge number is reduced, as well as the electrostatic force. It results in a decrease of layered structure. The presence of negative ions makes the structure of the electrostatic potential more oscillatory. The other physical parameters are also analyzed and discussed.

  11. Telemetry Channel Capacity Assessment for Reentry Vehicles in Plasma Sheath Environment

    NASA Astrophysics Data System (ADS)

    Shi, Lei; Zhao, Lei; Yao, Bo; Li, Xiaoping

    2015-12-01

    Channel capacity is the prerequisite and basis for the design of a communication system. To assess the impact of a harsh plasma environment on the communication system of reentry vehicles, Shannon's information theory is used to evaluate the channel capacity through the estimation results of the signal-to-noise ratio obtained by the communication link budget method. First, the attenuation caused by the plasma sheath is calculated with a stratified medium finite-difference time-domain method for typical S, C and Ka telemetry frequencies in a typical reentry plasma environment. Thereafter, typical telemetry transceiver parameters are considered to estimate the channel capacity. Results show that the S-band channel capacity is almost zero at the altitude of 30-40 km and the plasma attenuation at the C-band is slightly better. However, the blackout phenomenon remains obvious. The Ka-band signal can penetrate the plasma sheath layer with the smallest attenuation, thus significantly increasing the capacity of the channel and it may thus adequately meet telemetry needs. supported by the National Program on Key Basic Research Project of China (No. 2014CB340205) and National Natural Science Foundation of China (Nos. 61301173 and 61473228)

  12. Spatio-temporal behavior of microwave sheath-voltage combination plasma source

    NASA Astrophysics Data System (ADS)

    Kar, Satyananda; Kousaka, Hiroyuki; Raja, Laxminarayan L.

    2015-05-01

    Microwave sheath-Voltage combination Plasma (MVP) is a high density plasma source and can be used as a suitable plasma processing device (e.g., ionized physical vapor deposition). In the present report, the spatio-temporal behavior of an argon MVP sustained along a direct-current biased Ti rod is investigated. Two plasma modes are observed, one is an "oxidized state" (OS) at the early time of the microwave plasma and the other is "ionized sputter state" (ISS) at the later times. Transition of the plasma from OS to ISS results a prominent change in the visible color of the plasma, resulting from a significant increase in the plasma density, as measured by a Langmuir probe. In the OS, plasma is dominated by Ar ions, and the density is in amplitude order of 1011 cm-3. In the ISS, metal ions from the Ti rod contribute significantly to the ion composition, and higher density plasma (1012 cm-3) is produced. Nearly uniform high density plasma along the length of the Ti rod is produced at very low input microwave powers (around 30 W). Optical emission spectroscopy measurements confirm the presence of sputtered Ti ions and Ti neutrals in the ISS.

  13. Ion velocity distributions in the sheath and presheath of a biased object in plasma

    SciTech Connect

    Miloch, W. J.; Gulbrandsen, N.; Mishra, L. N.; Fredriksen, A.

    2011-08-15

    Ion velocity distributions in the vicinity of a spherical object with a negative potential with respect to collisionless, source-free plasma are studied with three-dimensional numerical simulations. The ion dynamics around the object leads to distorted radial velocity distributions in the presheath and the sheath edge region. Far in the sheath, an increase in the thermal velocity in the radial direction is observed. Different potentials of the object, ion temperatures, and ion masses are considered, as well as the role of spatial and temporal resolutions in laboratory measurements of ion velocity distributions. The simulations are carried out with the DiP3D, a three-dimensional particle-in-cell numerical code.

  14. Understanding the evolution and propagation of coronal mass ejections and associated plasma sheaths in interplanetary space

    NASA Astrophysics Data System (ADS)

    Hess, Phillip

    A Coronal Mass Ejection (CME) is an eruption of magnetized plasma from the Coronaof the Sun. Understanding the physical process of CMEs is a fundamental challenge in solarphysics, and is also of increasing importance for our technological society. CMEs are knownthe main driver of space weather that has adverse effects on satellites, power grids, com-munication and navigation systems and astronauts. Understanding and predicting CMEs is still in the early stage of research. In this dissertation, improved observational methods and advanced theoretical analysis are used to study CMEs. Unlike many studies in the past that treat CMEs as a single object, this study divides aCME into two separate components: the ejecta from the corona and the sheath region thatis the ambient plasma compressed by the shock/wave running ahead of the ejecta; bothstructures are geo-effective but evolve differently. Stereoscopic observations from multiplespacecraft, including STEREO and SOHO, are combined to provide a three-dimensionalgeometric reconstruction of the structures studied. True distances and velocities of CMEs are accurately determined, free of projection effects, and with continuous tracking from the low corona to 1 AU.To understand the kinematic evolution of CMEs, an advanced drag-based model (DBM) is proposed, with several improvements to the original DBM model. The new model varies the drag parameter with distance; the variation is constrained by thenecessary conservation of physical parameters. Second, the deviation of CME-nose from the Sun-Earth-line is taken into account. Third, the geometric correction of the shape of the ejecta front is considered, based on the assumption that the true front is a flattened croissant-shaped flux rope front. These improvements of the DBM model provide a framework for using measurement data to make accurate prediction of the arrival times of CME ejecta and sheaths. Using a set of seven events to test the model, it is found that the evolution

  15. Influence of residual plasma drift velocity on the post-arc sheath expansion of vacuum circuit breakers

    NASA Astrophysics Data System (ADS)

    Mo, Yongpeng; Shi, Zongqian; Bai, Zhibin; Jia, Shenli; Wang, Lijun

    2016-05-01

    The residual plasma in the inter-contact region of a vacuum circuit breaker moves towards the post-arc cathode at current zero, because the residual plasma mainly comes from the cathode spots during the arc burning process. In the most previous theoretical researches on the post-arc sheath expansion process of vacuum circuit breakers, only the thermal motion of residual plasma was taken into consideration. Alternately, the residual plasma was even assumed to be static at the moment of current zero in some simplified models. However, the influence of residual plasma drift velocity at current zero on the post-arc sheath expansion process was rarely investigated. In this paper, this effect is investigated by a one-dimensional particle-in-cell model. Simulation results indicate that the sheath expands slower with higher residual plasma drift velocity in the initial sheath expansion stage. However, with the increase of residual plasma drift velocity, the overall plasma density in the inter-contact region decreases faster, and the sheath expansion velocity increases earlier. Consequently, as a whole, it needs shorter time to expel the residual plasma from the inter-contact region. Furthermore, if the residual plasma drift velocity is high enough, the sheath expansion process ceases before it develops to the post-arc anode. Besides, the influence of the collisions between charges and neutrals is investigated as well in terms of the density of metal vapor. It shows that the residual plasma drift velocity takes remarkable effect only if the density of the metal vapor is relatively low, which corresponds to the circumstance of low-current interruptions.

  16. Oblique shock waves in a two electron temperature superthermally magnetized plasma

    NASA Astrophysics Data System (ADS)

    Bains, A. S.; Panwar, A.; Ryu, C. M.

    2015-11-01

    A study is presented for the oblique propagation of low-frequency ion acoustic ( IA) shock waves in a magnetized plasma consisting of cold ions and two temperature superthermally distributed electrons. A nonlinear Korteweg de-Vries-Burger ( KdV-Burger) equation is obtained by using the reductive perturbation method (RPM) which governs the dynamics of the IA shock wave. Using the solution of KdV-Burger equation, the characteristics of the IA shock wave have been studied for various plasma parameters. The combined effects of the cold to hot electron temperature ratio (σ), the density ratio of hot electrons to ions (f), the superthermality of cold and hot electrons (κc, κh), the strength of the magnetic field (ω_{ci}), and the obliqueness (θ), significantly influence the profile of the shock wave. The findings in the present study could be important for the electrostatic wave structures in the Saturn's magnetosphere, where two temperature electrons exist with a kappa distribution.

  17. Two-region model for positive and negative plasma sheaths and its application to Hall thruster metallic anodes

    SciTech Connect

    Ahedo, E.; Escobar, D.

    2008-03-15

    An asymptotic presheath/sheath model for positive and negative sheaths in front of a conducting electrode, with a continuous parametric transition at the no-sheath case, is presented. Key aspects of the model are as follows: full hydrodynamics of both species in the presheath; a kinetic formulation with a truncated distribution function for the repelled species within the sheath; and the fulfillment of the marginal Bohm condition at the sheath edge, in order to match the two formulations of the repelled species. The sheath regime depends on the ratios of particle fluxes and sound speeds between the two species. The presheath model includes the effect of a magnetic field parallel to the wall on electrons. An asymptotic, parametric study of the anode presheath is carried out in terms of the local ion-to-electron flux ratio and Hall parameter. The drift-diffusive model of magnetized electrons fails in a parametric region that includes parts of the negative sheath regime. In the case of the Hall parameter vanishing near the electrode and a weakly collisional plasma, a quasisonic, quasineutral plateau forms next to the sheath edge.

  18. Analytical solutions and particle simulations of cross-field plasma sheaths

    SciTech Connect

    Gerver, M.J. . Plasma Fusion Center); Parker, S.E.; Theilhaber, K. . Electronics Research Lab.)

    1989-08-30

    Particles simulations have been made of an infinite plasma slab, bounded by absorbing conducting walls, with a magnetic field parallel to the walls. The simulations have been either 1-D, or 2-D, with the magnetic field normal to the simulation plane. Initially, the plasma has a uniform density between the walls, and there is a uniform source of ions and electrons to replace particles lost to the walls. In the 1-D case, there is no diffusion of the particle guiding centers, and the plasma remains uniform in density and potential over most of the slab, with sheaths about a Debye length wide where the potential rises to the wall potential. In the 2-D case, the density profile becomes parabolic, going almost to zero at the walls, and there is a quasineutral presheath in the bulk of the plasma, in addition to sheaths near the walls. Analytic expressions are found for the density and potential profiles in both cases, including, in the 2-D case, the magnetic presheath due to finite ion Larmor radius, and the effects of the guiding center diffusion rate being either much less than or much grater than the energy diffusion rate. These analytic expressions are shown to agree with the simulations. A 1-D simulation with Monte Carlo guiding center diffusion included gives results that are good agreement with the much more expensive 2-D simulation. 17 refs., 10 figs.

  19. Emissive sheath measurements in the afterglow of a radio frequency plasma

    SciTech Connect

    Sheehan, J. P. Hershkowitz, N.; Barnat, E. V.; Weatherford, B. R.; Kaganovich, I. D.

    2014-01-15

    The difference between the plasma potential and the floating potential of a highly emissive planar surface was measured in the afterglow of a radio frequency discharge. A Langmuir probe was used to measure the electron temperature and an emissive probe was used to measure the spatial distribution of the potential using the inflection point in the limit of zero emission technique. Time-resolved measurements were made using the slow-sweep method, a technique for measuring time-resolved current-voltage traces. This was the first time the inflection point in the limit of zero emission was used to make time-resolved measurements. Measurements of the potential profile of the presheath indicate that the potential penetrated approximately 50% farther into the plasma when a surface was emitting electrons. The experiments confirmed a recent kinetic theory of emissive sheaths, demonstrating that late in the afterglow as the plasma electron temperature approached the emitted electron temperature, the emissive sheath potential shrank to zero. However, the difference between the plasma potential and the floating potential of a highly emissive planar surface data appeared to be much less sensitive to the electron temperature ratio than the theory predicts.

  20. Bounds imposed on the sheath velocity of a dense plasma focus by conservation laws and ionization stability condition

    SciTech Connect

    Auluck, S. K. H. E-mail: skauluck@barc.gov.in

    2014-09-15

    Experimental data compiled over five decades of dense plasma focus research are consistent with the snowplow model of sheath propagation, based on the hypothetical balance between magnetic pressure driving the plasma into neutral gas ahead and “wind pressure” resisting its motion. The resulting sheath velocity, or the numerically proportional “drive parameter,” is known to be approximately constant for devices optimized for neutron production over 8 decades of capacitor bank energy. This paper shows that the validity of the snowplow hypothesis, with some correction, as well as the non-dependence of sheath velocity on device parameters, have their roots in local conservation laws for mass, momentum, and energy coupled with the ionization stability condition. Both upper and lower bounds on sheath velocity are shown to be related to material constants of the working gas and independent of the device geometry and capacitor bank impedance.

  1. Bounds imposed on the sheath velocity of a dense plasma focus by conservation laws and ionization stability condition

    NASA Astrophysics Data System (ADS)

    Auluck, S. K. H.

    2014-09-01

    Experimental data compiled over five decades of dense plasma focus research are consistent with the snowplow model of sheath propagation, based on the hypothetical balance between magnetic pressure driving the plasma into neutral gas ahead and "wind pressure" resisting its motion. The resulting sheath velocity, or the numerically proportional "drive parameter," is known to be approximately constant for devices optimized for neutron production over 8 decades of capacitor bank energy. This paper shows that the validity of the snowplow hypothesis, with some correction, as well as the non-dependence of sheath velocity on device parameters, have their roots in local conservation laws for mass, momentum, and energy coupled with the ionization stability condition. Both upper and lower bounds on sheath velocity are shown to be related to material constants of the working gas and independent of the device geometry and capacitor bank impedance.

  2. Plasma-sheath instability in Hall thrusters due to periodic modulation of the energy of secondary electrons in cyclotron motion

    SciTech Connect

    Sydorenko, D.; Smolyakov, A.; Kaganovich, I.; Raitses, Y.

    2008-05-15

    Particle-in-cell simulation of Hall thruster plasmas reveals a plasma-sheath instability manifesting itself as a rearrangement of the plasma sheath near the thruster channel walls accompanied by a sudden change of many discharge parameters. The instability develops when the sheath current as a function of the sheath voltage is in the negative conductivity regime. The major part of the sheath current is produced by beams of secondary electrons counter-streaming between the walls. The negative conductivity is the result of nonlinear dependence of beam-induced secondary electron emission on the plasma potential. The intensity of such emission is defined by the beam energy. The energy of the beam in crossed axial electric and radial magnetic fields is a quasiperiodical function of the phase of cyclotron rotation, which depends on the radial profile of the potential and the thruster channel width. There is a discrete set of stability intervals determined by the final phase of the cyclotron rotation of secondary electrons. As a result, a small variation of the thruster channel width may result in abrupt changes of plasma parameters if the plasma state jumps from one stability interval to another.

  3. Plasma-Sheath Instability in Hall Thrusters Due to Periodic Modulation of the Energy of Secondary Electrons in Cyclotron Motion

    SciTech Connect

    Sydorenko, D.; Smolyakov, A.; Kaganovich, I.; Raitses, Y.

    2008-04-23

    Particle-in-cell simulation of Hall thruster plasmas reveals a plasma-sheath instability manifesting itself as a rearrangement of the plasma sheath near the thruster channel walls accompanied by a sudden change of many discharge parameters. The instability develops when the sheath current as a function of the sheath voltage is in the negative conductivity regime. The major part of the sheath current is produced by beams of secondary electrons counter-streaming between the walls. The negative conductivity is the result of nonlinear dependence of beam-induced secondary electron emission on the plasma potential. The intensity of such emission is defined by the beam energy. The energy of the beam in crossed axial electric and radial magnetic fields is a quasi-periodical function of the phase of cyclotron rotation, which depends on the radial profile of the potential and the thruster channel width. There is a discrete set of stability intervals determined by the final phase of the cyclotron rotation of secondary electrons. As a result, a small variation of the thruster channel width may result in abrupt changes of plasma parameters if the plasma state jumps from one stability interval to another.

  4. A Numerical Characterization of the Gravito-Electrostatic Sheath Equilibrium Structure in Solar Plasma

    NASA Astrophysics Data System (ADS)

    Karmakar, Pralay Kumar

    This article describes the equilibrium structure of the solar interior plasma (SIP) and solar wind plasma (SWP) in detail under the framework of the gravito-electrostatic sheath (GES) model. This model gives a precise definition of the solar surface boundary (SSB), surface origin mechanism of the subsonic SWP, and its supersonic acceleration. Equilibrium parameters like plasma potential, self-gravity, population density, flow, their gradients, and all the relevant inhomogeneity scale lengths are numerically calculated and analyzed as an initial value problem. Physical significance of the structure condition for the SSB is discussed. The plasma oscillation and Jeans time scales are also plotted and compared. In addition, different coupling parameters, and electric current profiles are also numerically studied. The current profiles exhibit an important behavior of directional reversibility, i.e., an electrodynamical transition from negative to positive value. It occurs beyond a few Jeans lengths away from the SSB. The virtual spherical surface lying at the current reversal point, where the net current becomes zero, has the property of a floating surface behavior of the real physical wall. Our investigation indicates that the SWP behaves as an ion current-carrying plasma system. The basic mechanism behind the GES formation and its distinctions from conventional plasma sheath are discussed. The electromagnetic properties of the Sun derived from our model with the most accurate available inputs are compared with those of others. These results are useful as an input element to study the properties of the linear and nonlinear dynamics of various solar plasma waves, oscillations and instabilities.

  5. A model of plasma current through a hole of Rogowski probe including sheath effects

    NASA Astrophysics Data System (ADS)

    Furui, H.; Ejiri, A.; Nagashima, Y.; Takase, Y.; Sonehara, M.; Tsujii, N.; Yamaguchi, T.; Shinya, T.; Togashi, H.; Homma, H.; Nakamura, K.; Takeuchi, T.; Yajima, S.; Yoshida, Y.; Toida, K.; Takahashi, W.; Yamazaki, H.

    2016-04-01

    In TST-2 Ohmic discharges, local current is measured using a Rogowski probe by changing the angle between the local magnetic field and the direction of the hole of the Rogowski probe. The angular dependence shows a peak when the direction of the hole is almost parallel to the local magnetic field. The obtained width of the peak was broader than that of the theoretical curve expected from the probe geometry. In order to explain this disagreement, we consider the effect of sheath in the vicinity of the Rogowski probe. A sheath model was constructed and electron orbits were numerically calculated. From the calculation, it was found that the electron orbit is affected by E × B drift due to the sheath electric field. Such orbit causes the broadening of the peak in the angular dependence and the dependence agrees with the experimental results. The dependence of the broadening on various plasma parameters was studied numerically and explained qualitatively by a simplified analytical model.

  6. Description of plasma focus current sheath as the Turner relaxed state of a Hall magnetofluid

    SciTech Connect

    Auluck, S. K. H.

    2009-12-15

    The central mystery of plasma focus research is the two orders-of-magnitude-higher-than-thermal fusion reaction rate and the fact that both the space-resolved neutron spectra and space-resolved reaction proton spectra show features which can be ascribed only to a rotational motion of the center-of-mass of the reacting deuteron population. It has been suggested earlier [S. K. H. Auluck, IEEE Trans. Plasma Sci. 25, 37 (1997)] that this and other experimental observations can be consistently explained in terms of a hypothesis involving rotation of the current carrying plasma annulus behind the imploding gas-dynamic shock. Such rotation (more generally, mass flow) is an in-built feature of relaxed state of a two-fluid plasma [R. N. Sudan, Phys. Rev. Lett. 42, 1277 (1979)]. Relaxation in the 'Hall magnetofluid' approximation, in which the generalized Ohm's law includes the Hall effect term and the magnetic convection term but omits the contributions to the electric field from resistive dissipation, electron pressure gradient, thermoelectric effect, electron inertia, etc., has been extensively studied by many authors. In the present paper, Turner's [IEEE Trans. Plasma Sci. PS-14, 849 (1986)] degenerate solution for the relaxed state of the Hall magnetohydrodynamic plasma has been adapted to the case of an infinitely long annular current carrying plasma, a tractable idealization of the current sheath of a plasma focus. The resulting model is consistent with experimental values of ion kinetic energy and observation of predominantly radially directed neutron emission in good shots.

  7. Dusty plasma sheath-like structure in the region of lunar terminator

    NASA Astrophysics Data System (ADS)

    Popel, S. I.; Zelenyi, L. M.; Atamaniuk, B.

    2015-12-01

    The main properties of the dusty plasma layer near the surface over the illuminated and dark parts of the Moon are described. They are used to realize dusty plasma behaviour and to determine electric fields over the terminator region. Possibility of the existence of a dusty plasma sheath-like structure in the region of lunar terminator is shown. The electric fields excited in the terminator region are demonstrated to be on the order of 300 V/m. These electric fields can result in rise of dust particles of the size of 2-3 μm up to an altitude of about 30 cm over the lunar surface that explains the effect of "horizon glow" observed at the terminator by Surveyor lunar lander.

  8. Dusty plasma sheath-like structure in the region of lunar terminator

    SciTech Connect

    Popel, S. I.; Zelenyi, L. M.; Atamaniuk, B.

    2015-12-15

    The main properties of the dusty plasma layer near the surface over the illuminated and dark parts of the Moon are described. They are used to realize dusty plasma behaviour and to determine electric fields over the terminator region. Possibility of the existence of a dusty plasma sheath-like structure in the region of lunar terminator is shown. The electric fields excited in the terminator region are demonstrated to be on the order of 300 V/m. These electric fields can result in rise of dust particles of the size of 2–3 μm up to an altitude of about 30 cm over the lunar surface that explains the effect of “horizon glow” observed at the terminator by Surveyor lunar lander.

  9. A fully kinetic, self-consistent particle simulation model of the collisionless plasma--sheath region

    SciTech Connect

    Procassini, R.J.; Birdsall, C.K.; Morse, E.C. )

    1990-12-01

    A fully kinetic particle-in-cell (PIC) model is used to self-consistently determine the steady-state potential profile in a collisionless plasma that contacts a floating, absorbing boundary. To balance the flow of particles to the wall, a distributed source region is used to inject particles into the one-dimensional system. The effect of the particle source distribution function on the source region and collector sheath potential drops, and particle velocity distributions is investigated. The ion source functions proposed by Emmert {ital et} {ital al}. (Phys. Fluids {bold 23}, 803 (1980)) and Bissell and Johnson (Phys. Fluids {bold 30}, 779 (1987)) (and various combinations of these) are used for the injection of both ions {ital and} electrons. The values of the potential drops obtained from the PIC simulations are compared to those from the theories of Emmert {ital et} {ital al}., Bissell and Johnson, and Scheuer and Emmert (Phys. Fluids {bold 31}, 3645 (1988)), all of which assume that the electron density is related to the plasma potential via the Boltzmann relation. The values of the source region and total potential drop are found to depend on the choice of the electron source function, as well as the ion source function. The question of an infinite electric field at the plasma--sheath interface, which arises in the analyses of Bissell and Johnson and Scheuer and Emmert, is also addressed.

  10. The effect of magnetic flux expansion on plasma sheath/presheath

    NASA Astrophysics Data System (ADS)

    Guo, Z. H.; Tang, X. Z.; Berk, H.

    2010-11-01

    Significant magnetic flux expansion can help spread the plasma heat load over a greater area of tokamak divertor plate. It also appears in the expander of an axisymmetric magnetic mirror, which for its favorable magnetic curvature, helps stabilize the global interchange modes in the central cell. For a weakly collisional plasma, the flux expansion introduces a mirror force accelerating the electron and ion flows downstream, which likely induces an ambipolar parallel electric field. This is in addition to the conventional presheath electric field which accelerates the ion to satisfy the Bohm criteria near the wall. We perform kinetic simulations in two spatial and three velocity dimensions to understand (1) the role of mirror force in the parallel and perpendicular thermal energy transfer, and (2) the combined role of mirror-acceleration and parallel electric field on the parallel flow acceleration in the presheath and sheath. The detailed sheath/presheath plasma profiles and the ambipolar electric field will be investigated. Worked supported by OFES.

  11. The polarized Debye sheath effect on Kadomtsev-Petviashvili electrostatic structures in strongly coupled dusty plasma

    SciTech Connect

    Shahmansouri, M.; Alinejad, H.

    2015-04-15

    We give a theoretical investigation on the dynamics of nonlinear electrostatic waves in a strongly coupled dusty plasma with strong electrostatic interaction between dust grains in the presence of the polarization force (i.e., the force due to the polarized Debye sheath). Adopting a reductive perturbation method, we derived a three-dimensional Kadomtsev-Petviashvili equation that describes the evolution of weakly nonlinear electrostatic localized waves. The energy integral equation is used to study the existence domains of the localized structures. The analysis provides the localized structure existence region, in terms of the effects of strong interaction between the dust particles and polarization force.

  12. LIF measurements of the ion distribution function in the sheath and pre-sheath of a biased capacitively coupled plasma reactor

    NASA Astrophysics Data System (ADS)

    Gekelman, Walter

    2011-10-01

    The time-dependent argon ion energy distribution function (IEDF) above and within the plasma sheath of a radio frequency (rf) biased substrate has been measured using laser induced fluorescence (LIF) in a commercial plasma processing tool. The measurements were acquired at eight different phases of the 2.2 MHz rf waveform and show the ion dynamics to vary dramatically throughout a cycle. Discharge parameters were such that the rf bias period was on the order of the ion transit time through the sheath (tion/trf = 0.435). The first experiments measured the IEDF along a line parallel to the normal of the wafer with spatial resolution (dy = 88 um). These measurements have been extended to an x-y plane (y is the height above the wafer) which includes the wafer edge so that f(r,v,t) can be measured within a sheet of light. These measurements include the option for multiple bias voltages (2.2, 60 MHz). A patented technology, which enables rapidly switching either bias or ICP source without a match circuit allows for time sequencing in any combination with (tpulse > 50 usec). The heat flux and plasma flow is derived from the ion distribution function. This work embodies the first time resolved measurement of ion velocity distribution functions (IVDFs) within an rf biased sheath over a large area (30 cm diameter) substrate. Additional probe measurements of the plasma parameters above the wafer will be presented as well. Comparisons will be made to ion energy and velocity distributions obtained from computer modeling. Work supported by the NSF and done at The Basic Plasma Science Facility at UCLA (supported by NSF and DOE) and the University of Michigan.

  13. Plasma effects on fast pair beams. III. Oblique electrostatic growth rates for perpendicular Maxwellian pair beams

    SciTech Connect

    Supsar, Markus; Schlickeiser, Reinhard E-mail: rsch@tp4.rub.de

    2014-03-10

    The distant universe is opaque to γ radiation from blazars due to gamma-gamma attenuation with extragalactic background light. This process produces electron-positron pair beams that interact with the intergalactic medium and are unstable to linear instabilities, particularly the electrostatic and Weibel instabilities. The electrostatic instability grows faster and so determines the dissipation of the free energy of the beam. Here, we generalize the calculation of the electrostatic growth rate to a beam plasma system with a Maxwellian perpendicular momentum spread and allow for oblique propagation directions. We show that the growth rate for the oblique electrostatic mode has a maximum value that is even higher than for a cold beam or for one with a constant perpendicular momentum spread.

  14. Laser-induced fluorescence measurements of argon and xenon ion velocities near the sheath boundary in 3 ion species plasmas

    NASA Astrophysics Data System (ADS)

    Yip, Chi-Shung; Hershkowitz, Noah; Severn, Greg; Baalrud, Scott D.

    2016-05-01

    The Bohm sheath criterion is studied with laser-induced fluorescence in three ion species plasmas using two tunable diode lasers. Krypton is added to a low pressure unmagnetized DC hot filament discharge in a mixture of argon and xenon gas confined by surface multi-dipole magnetic fields. The argon and xenon ion velocity distribution functions are measured at the sheath-presheath boundary near a negatively biased boundary plate. The potential structures of the plasma sheath and presheath are measured by an emissive probe. Results are compared with previous experiments with Ar-Xe plasmas, where the two ion species were observed to reach the sheath edge at nearly the same speed. This speed was the ion sound speed of the system, which is consistent with the generalized Bohm criterion. In such two ion species plasmas, instability enhanced collisional friction was demonstrated [Hershkowitz et al., Phys. Plasmas 18(5), 057102 (2011).] to exist which accounted for the observed results. When three ion species are present, it is demonstrated under most circumstances the ions do not fall out of the plasma at their individual Bohm velocities. It is also shown that under most circumstances the ions do not fall out of the plasma at the system sound speed. These observations are also consistent with the presence of the instabilities.

  15. Kelvin--Helmholtz vortex formation and particle transport in a cross-field plasma sheath. II. Steady state

    SciTech Connect

    Theilhaber, K.; Birdsall, C.K. )

    1989-11-01

    The steady-state behavior of the magnetized plasma--wall sheath has been studied through two-dimensional particle simulations, which have shown that the sheath maintains itself in a strongly nonlinear, turbulent equilibrium, continuously driven by the edge Kelvin--Helmholtz instability. The sheath assumes a thickness of order {ital l}{sub {ital x}}{similar to}5{rho}{sub {ital i}}, and maintains large, long-lived vortices, with amplitudes {delta}{phi}{similar to}2.5{ital T}{sub {ital i}}/{ital e}, which drift parallel to the wall at half the ion thermal velocity. The sheath also maintains a large, spatially averaged potential drop from the wall to the plasma with {Delta}{phi}{approx}{minus}2{ital T}{sub {ital i}}/{ital e}, opposite in sign to that of the unmagnetized sheath. Accompanying the long-wavelength vortices are shorter-wavelength fluctuations, which induce an anomalous cross-field transport, scaling in accordance to Bohm diffusion when {omega}{sub {ital pi}}{ge}2{omega}{sub {ital ci}}. At lower densities, {omega}{sub {ital pi}}{lt}2{omega}{sub {ital ci}}, the diffusion coefficient has an additional factor, proportional to the density. These results permit the modeling of the cross-field sheath by a simple effective boundary condition.

  16. Numerical investigation of the ion temperature effect in magnetized plasma sheath with two species of positive ions

    SciTech Connect

    Shaw, A. K.; Goswami, K. S.; Saikia, B. J.; Kar, S.

    2012-01-15

    The effect of ion temperature, magnitude of magnetic field and its orientation on a magnetized plasma sheath consisting of electrons and two species of positive ions are investigated. Using three-fluid hydrodynamic model and some dimensionless variables, the dimensionless equations are obtained and solved numerically. It is found that with the increase of the ion temperature and magnetic field strength there is a significant change in ion densities and energies in the sheath. It is also noticed that increase of magnetic field angle enhances the ion density near the sheath edge for a constant ion temperature. With increase in ion temperature and magnetic field angle, the lighter ion density near the sheath edge enhances and reverses for the heavier ion species.

  17. Spin effect on parametric decay of oblique Langmuir wave in degenerate magneto-plasmas

    SciTech Connect

    Shahid, M.; Murtaza, G.

    2013-08-15

    The electron spin −1/2 effects on the parametric decay instability of oblique Langmuir wave into low-frequency electromagnetic shear Alfven wave and Left-Handed Circularly Polarized wave (LHCP) has been investigated in detail, in an electron-ion quantum plasma immersed in the uniform external magnetic field. Incorporating the quantum effects due to electron spin, Fermi pressure and Bohm potential term, the quantum magneto-hydrodynamic (QMHD) model has been used to investigate the linear and nonlinear response of the plasma species for three-wave coupling interaction in a quantum magneto-plasmas. Nonlinear dispersion relations and growth rate of the problem have been derived analytically. It has been shown that the spin of electrons has considerable effect on the growth rate of parametric instability problem even when the external magnetic field B{sub 0} is below the quantum critical magnetic field strength B{sub Q}=4.4138×10{sup 13}G.

  18. Oblique propagation of ion-acoustic solitary waves in a magnetized electron-positron-ion plasma

    SciTech Connect

    Ferdousi, M.; Sultana, S.; Mamun, A. A.

    2015-03-15

    The properties of obliquely propagating ion-acoustic solitary waves in the presence of ambient magnetic field have been investigated theoretically in an electron-positron-ion nonthermal plasma. The plasma nonthermality is introduced via the q-nonextensive distribution of electrons and positrons. The Korteweg-de Vries (K-dV) and modified K-dV (mK-dV) equations are derived by adopting reductive perturbation method. The solution of K-dV and modified K-dV equation, which describes the solitary wave characteristics in the long wavelength limit, is obtained by steady state approach. It is seen that the electron and positron nonextensivity and external magnetic field (obliqueness) have significant effects on the characteristics of solitary waves. A critical value of nonextensivity is found for which solitary structures transit from positive to negative potential. The findings of this investigation may be used in understanding the wave propagation in laboratory and space plasmas where static external magnetic field is present.

  19. Experimental evidence for collisional shock formation via two obliquely merging supersonic plasma jets

    SciTech Connect

    Merritt, Elizabeth C. Adams, Colin S.; Moser, Auna L.; Hsu, Scott C. Dunn, John P.; Miguel Holgado, A.; Gilmore, Mark A.

    2014-05-15

    We report spatially resolved measurements of the oblique merging of two supersonic laboratory plasma jets. The jets are formed and launched by pulsed-power-driven railguns using injected argon, and have electron density ∼10{sup 14} cm{sup −3}, electron temperature ≈1.4 eV, ionization fraction near unity, and velocity ≈40 km/s just prior to merging. The jet merging produces a few-cm-thick stagnation layer, as observed in both fast-framing camera images and multi-chord interferometer data, consistent with collisional shock formation [E. C. Merritt et al., Phys. Rev. Lett. 111, 085003 (2013)].

  20. Obliquely propagating electrostatic waves in a magnetized plasma for different types of anisotropic kappa distribution

    NASA Astrophysics Data System (ADS)

    Bashir, M. F.; Yoon, P. H.; Murtaza, G.; Aqeel, D.; Javed, S.; Zahra, M.

    2015-12-01

    By using the kinetic theory, the dispersion relation of obliquely propagating electrostatic waves are discussed for three types of kappa distribution function: 1) loss-cone-bi-kappa-Maxwellian distribution, 2) current carrying Bi-kappa-Maxwellian distribution and 3) product-bi-kappa distribution. The effects of kappa-index, loss-cone index, streaming velocity and the temperature anisotropy on the Harris instability is highlighted for their possible application to explain the banded emissions observed in the terrestrial magnetosphere and in the magnetospheres of other planets, e.g., Jupiter, Saturn, Uranus, and in Io's plasma torus.

  1. Formation of collisional sheath in electronegative plasma with two species of positive ions

    SciTech Connect

    Moulick, R. Goswami, K. S.

    2015-03-15

    Sheath formation is investigated for electronegative plasma in presence of two species of positive ions in collisional environment. The gas under consideration is a mixture of oxygen and argon. Argon is the considered as having fixed volume and impact of collision is studied with increasing pressure of oxygen. Fluid equations are solved for three species namely, the two positive ions and a negative ion. Electrons are considered to follow Boltzmann distribution. Collision is modeled by constant mean free path model and has been used as a parameter. It has been found that collision enhances the sheath formation. The negative ion core is nearly unaffected by the presence of collision and is governed by the electric potential. The negative flux field is, however, affected by the presence of collision and shows a steady behavior in front of the wall. The two positive ions are heavily affected by the presence of collision and the modeling is such that their equilibrium densities can be estimated by solving simultaneous cubic equations.

  2. Formation of collisional sheath in electronegative plasma with two species of positive ions

    NASA Astrophysics Data System (ADS)

    Moulick, R.; Goswami, K. S.

    2015-03-01

    Sheath formation is investigated for electronegative plasma in presence of two species of positive ions in collisional environment. The gas under consideration is a mixture of oxygen and argon. Argon is the considered as having fixed volume and impact of collision is studied with increasing pressure of oxygen. Fluid equations are solved for three species namely, the two positive ions and a negative ion. Electrons are considered to follow Boltzmann distribution. Collision is modeled by constant mean free path model and has been used as a parameter. It has been found that collision enhances the sheath formation. The negative ion core is nearly unaffected by the presence of collision and is governed by the electric potential. The negative flux field is, however, affected by the presence of collision and shows a steady behavior in front of the wall. The two positive ions are heavily affected by the presence of collision and the modeling is such that their equilibrium densities can be estimated by solving simultaneous cubic equations.

  3. A suitable boundary condition for bounded plasma simulation without sheath resolution

    SciTech Connect

    Parker, S.E.; Procassini, R.J.; Birdsall, C.K. ); Cohen, B.I. )

    1993-01-01

    We have developed a technique that allows for a sheath boundary layer without having to resolve the inherently small space and time scales of the sheath region. We refer to this technique as the logical sheath boundary condition. This boundary condition, when incorporated into a direct-implicit particle code, permits large space- and time-scale simulations of bounded systems, which would otherwise be impractical on current supercomputers. The lack of resolution of the collector sheath potential drop obtained from conventional implicit simulations at moderate values of [omega][sub pe][Delta]t and [Delta]z/[lambda][sup De] provides the motivation for the development of the logical sheath boundary condition. The algorithm for use of the logical sheath boundary condition in a particle simulation is presented. Results from simulations which use the logical sheath boundary condition are shown to compare reasonably well with those from an analytic theory and simulations in which the sheath is resolved.

  4. Dusty plasma sheath-like structure in the lunar terminator region

    NASA Astrophysics Data System (ADS)

    Popel, Sergey; Zelenyi, Lev; Atamaniuk, Barbara

    2016-07-01

    The main properties of the dusty plasma layer near the surface over the illuminated and dark parts of the Moon are described. They are used to realize dusty plasma behaviour and to determine electric fields over the terminator region. Possibility of the existence of a dusty plasma sheath-like structure [1] in the region of lunar terminator is shown. The electric fields excited in the terminator region are demonstrated to be on the order of 300 V/m. These electric fields can result in rise of dust particles of the size of a few micrometers up to an altitude of about 30 cm over the lunar surface that explains the effect of ``horizon glow" observed at the terminator by Surveyor lunar lander. This work was supported in part by the Presidium of the Russian Academy of Sciences (under Fundamental Research Program No. 7, ``Experimental and Theoretical Study of the Solar System Objects and Stellar Planet Systems. Transient Explosion Processes in Astrophysics" and the Russian Foundation for Basic Research (Project No. 15-02-05627-a). [1] S. I. Popel, L. M. Zelenyi, and B. Atamaniuk, Phys. Plasmas 22, 123701 (2015); doi: 10.1063/1.4937368.

  5. Dual-role plasma absorption probe to study the effects of sheath thickness on the measurement of electron density

    NASA Astrophysics Data System (ADS)

    Li, Bin; Li, Hong; Chen, Zhipeng; Xie, Jinlin; Liu, Wandong

    2010-08-01

    A sensitive plasma absorption probe (PAP) is reported for measuring electron density in processing plasmas. The sheath formed around the probe tip is important for the resonance of surface waves. For determining the absolute electron density from the absorption frequency of the sensitive PAP, a proper value of sheath thickness relative to the Debye length is required to be assigned in the data processing. In this paper, a dual-role PAP has been proposed to study the effects of sheath thickness on the measurement of electron density. It is used as a Langmuir probe and a sensitive PAP simultaneously. Based on these two functions, the sheath thickness is calibrated before the measurement of electron density. The calibrated value is assigned in the data processing to replace the fitting coefficient used in the previous work. Therefore, the measurement error caused by an inaccurately assigned sheath thickness can be minimized effectively. Because of the bi-functional characteristic, the dual-role PAP is an independent diagnostic tool.

  6. Transverse conductivity of a relativistic plasma in oblique electric and magnetic fields

    NASA Technical Reports Server (NTRS)

    Melia, Fulvio; Fatuzzo, Marco

    1991-01-01

    Resistive tearing in a primary candidate for flares occurring in stressed magnetic fields. Its possible application to the strongly magnetized environments (Hz about 10 to the 12th G) near the surface of neutron stars, particularly as a mechanism for generating the plasma heating and particle acceleration leading to gamma-ray bursts, has motivated a quantum treatment of this process, which requires knowledge of the electrical conductivity sigma of a relativistic gas in a new domain (i.e., that of a low-density n/e/) plasma in oblique electric and magnetic fields. This paper discusses the mathematical formalism for calculating sigma and present numerical results for a wide range of parameter values. The results indicate that sigma depends very strongly on both the applied electric and magnetic fields.

  7. Gravitoelectromagnetic sheath

    NASA Astrophysics Data System (ADS)

    Goutam, H. P.; Karmakar, P. K.

    2015-06-01

    In this paper we propose a gravito-electro-magnetic sheath (GEMS) model to explore the equilibrium properties of the solar plasma system. It describes the solar interior plasma (SIP) on the bounded scale and the solar wind plasma (SWP) on the unbounded scale from the viewpoint of plasma-based theory. This differs from the previously reported gravito-electrostatic sheath (GES) model employed to precisely define the solar surface boundary (SSB) on the fact that the present investigation incorporates variable temperature, magnetic field and collisional processes on the solar plasma flow dynamics. We show that the included parameters play important roles in the solar plasma dynamics. We demonstrate that the SSB location shifts outward as a result of the magnetic field by 14 % in comparison with that predicted by the GES model. As a consequence of the interaction of the plasma with magnetic field, the width of the sheath broadens by 25 % in comparison with the GES model predicted value. This physically means that the magnetic field decreases the distribution of the tiny (inertialess) electrons relative to the massive (inertial) ions, which in turn increases the confining wall potential value resulting in the increased width. Besides, the sonic point moves inward by 8 % as a result of collisions in the SIP that leads to rapid acceleration. Here, collisional dynamics plays an important role in the conversion process of the electron thermal energy into the bulk plasma flow energy. An interesting feature of continuous and smooth transition of the electric current density from the SIP to the SWP (with finite positive divergence on both the scales) through the SSB under inhomogeneous temperature distribution is also reported. Finally, the analyses may be applied to understand the realistic equilibrium dynamics of stellar plasmas never addressed before within the earlier GES framework like establishment of current-field correlation, properties of the slow solar wind and its

  8. Experimental Investigation of RF Sheath Rectification in ICRF and LH Heated Plasmas on Alcator C-Mod

    SciTech Connect

    Ochoukov, R.; Whyte, D. G.; Faust, I.; LaBombard, B.; Lipschultz, B.; Meneghini, O.; Wallace, G.; Wukitch, S.; Myra, J.

    2011-12-23

    Radio frequency (RF) rectification of the plasma sheath is being actively studied on C-Mod as a likely mechanism that leads to prohibitively high molybdenum levels in the plasma core of ion cyclotron RF (ICRF) heated discharges. We installed emissive, ion sensitive, Langmuir, and 3-D B-dot probes to quantify the plasma potentials ({Phi}{sub P}) in ICRF and lower hybrid (LH) heated discharges. Two probe sets were mounted on fixed limiter surfaces and one set of probes was mounted on a reciprocating (along the major radius) probe. Initial results showed that RF rectification is strongly dependent on the local plasma density and not on the local RF fields. The RF sheaths had a threshold-like appearance at the local density of {approx}10{sup 16} m-{sup 3}. Radial probe scans revealed that the RF sheaths peaked in the vicinity of the ICRF limiter surface, agreeing with a recent theory. The highest {Phi}{sub P}'s were observed on magnetic field lines directly mapped to the active ICRF antenna. Measurements in LH heated plasmas showed a strong {Phi}{sub P} dependence on the parallel index of refraction n{sub ||} of the launched LH waves: {Phi}{sub P} is greater at lower n{sub ||}. Little dependence was observed on the local plasma density.

  9. Stability analysis of the Gravito-Electrostatic Sheath-based solar plasma equilibrium

    NASA Astrophysics Data System (ADS)

    Karmakar, P. K.; Goutam, H. P.; Lal, M.; Dwivedi, C. B.

    2016-08-01

    We present approximate solutions of non-local linear perturbational analysis for discussing the stability properties of the Gravito-Electrostatic Sheath (GES)-based solar plasma equilibrium, which is indeed non-uniform on both the bounded and unbounded scales. The relevant physical variables undergoing perturbations are the self-solar gravity, electrostatic potential and plasma flow along with plasma population density. We methodologically derive linear dispersion relation for the GES fluctuations, and solve it numerically to identify and characterize the existent possible natural normal modes. Three distinct natural normal modes are identified and named as the GES-oscillator mode, GES-wave mode and usual (classical) p-mode. In the solar wind plasma, only the p-mode survives. These modes are found to be linearly unstable in wide-range of the Jeans-normalized wavenumber, k. The local plane-wave approximation marginally limits the validity or reliability of the obtained results in certain radial- and k-domains only. The phase and group velocities, time periods of these fluctuation modes are investigated. It is interesting to note that, the oscillation time periods of these modes are 3-10 min, which match exactly with those of the observed helio-seismic waves and solar surface oscillations. The proposed GES model provides a novel physical view of the waves and oscillations of the Sun from a new perspective of plasma-wall interaction physics. Due to simplified nature of the considered GES equilibrium, it is a neonatal stage to highlight its applicability in the real Sun. The proposed GES model and subsequent fluctuation analysis need further improvements to make it more realistic.

  10. Generalised model of a sheath of a plasma bubble excited by a short laser pulse or by a relativistic electron bunch in transversely inhomogeneous plasma

    NASA Astrophysics Data System (ADS)

    Golovanov, A. A.; Kostyukov, I. Yu; Pukhov, A. M.; Thomas, J.

    2016-04-01

    An analytical model of a plasma bubble (a wake wave in the strongly nonlinear regime) in transversely inhomogeneous plasma is generalised to an arbitrary profile of an electron sheath at its boundary. Within the framework of this generalisation we have found the potential within the bubble and shown that its envelope is described by a second-order equation, similar to the equation of a less general theory. We have also determined the domain of parameters at which this equation is considerably simplified and no longer depends on the profile of the electron sheath.

  11. End-boundary sheath potential, electron and ion energy distribution in the low-pressure non-ambipolar electron plasma

    NASA Astrophysics Data System (ADS)

    Chen, Lee; Chen, Zhiying; Funk, Merritt

    2013-12-01

    The end-boundary floating-surface sheath potential, electron and ion energy distribution functions (EEDf, IEDf) in the low-pressure non-ambipolar electron plasma (NEP) are investigated. The NEP is heated by an electron beam extracted from an inductively coupled electron-source plasma (ICP) through a dielectric injector by an accelerator located inside the NEP. This plasma's EEDf has a Maxwellian bulk followed by a broad energy continuum connecting to the most energetic group with energies around the beam energy. The NEP pressure is 1-3 mTorr of N2 and the ICP pressure is 5-15 mTorr of Ar. The accelerator is biased positively from 80 to 600 V and the ICP power range is 200-300 W. The NEP EEDf and IEDf are determined using a retarding field energy analyser. The EEDf and IEDf are measured at various NEP pressures, ICP pressures and powers as a function of accelerator voltage. The accelerator current and sheath potential are also measured. The IEDf reveals mono-energetic ions with adjustable energy and it is proportionally controlled by the sheath potential. The NEP end-boundary floating surface is bombarded by a mono-energetic, space-charge-neutral plasma beam. When the injected energetic electron beam is adequately damped by the NEP, the sheath potential is linearly controlled at almost a 1 : 1 ratio by the accelerator voltage. If the NEP parameters cannot damp the electron beam sufficiently, leaving an excess amount of electron-beam power deposited on the floating surface, the sheath potential will collapse and become unresponsive to the accelerator voltage.

  12. Impact of plasma sheath on rocket-based E-region ion measurements

    NASA Astrophysics Data System (ADS)

    Imtiaz, Nadia; Burchill, Johnathan; Marchand, Richard

    2015-01-01

    We model the particle velocity distribution functions around the entrance window of the Suprathermal Ion Imager (SII). The SII sensor was mounted on a 1 m boom carried by the scientific payload of NASA rocket 36.234 as part of Joule II mission to investigate Joule heating in the E-region ionosphere. The rocket flew above Northern Alaska on 19 January 2007. The payload was spin-stabilized with a period of 1.6 s, giving an apparent rotation of the ion flow velocity in the frame of reference of the payload. The SII sensor is an electrostatic analyzer that measures two dimensional slices of the distribution of the kinetic energies and arrival-angles of low energy ions. The study is concerned with the interpretation of data obtained from the SII sensor. For this purpose, we numerically investigate ram velocity effects on ions velocity distributions in the vicinity of the SII sensor aperture at an altitudes of approximately 150 km. The electrostatic sheath profiles surrounding the SII sensor, boom and payload are calculated numerically with the PIC code PTetra. It is observed that the direction of the ion flow velocity modifies the plasma sheath potential profile. This in turn impacts the velocity distributions of NO+ and ions at the aperture of the particle sensor. The velocity distribution functions at the sensor aperture are calculated by using test-particle modeling. These particle distribution functions are then used to inject particles in the sensor, and calculate the fluxes on the sensor microchannel plate (MCP), from which comparisons with the measurements can be made.

  13. Characterization of the ionization degree evolution of the PF-400J plasma sheath by means of time resolved optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Avaria, G.; Cuadrado, O.; Moreno, J.; Pavez, C.; Soto, L.

    2016-05-01

    Spectral measurements in the visible range of the plasma sheath ionization degree evolution on the plasma focus device PF-400J are presented. The measurements were done with temporal and spatial resolution in a plasma focus device of low stored energy: PF-400J (176-539 J, 880 nF, 20-35 kV, quarter period ∼ 300ns) [1]. An ICCD was attached to a 0.5 m focal length visible spectrometer, which enabled the acquisition of time resolved spectrum with 20 ns integration time throughout the whole current pulse evolution. The spatial resolution was attained using a set of lenses which allowed the focusing of a small volume of the plasma sheath in different positions of the inter-electrode space. Discharges were carried out in mixtures of Hydrogen with gases in different proportions: 5% Neon, 5% Krypton and 2% Nitrogen. Discharges using Neon as an impurity showed no ionization of the gas, just a very low intensity emission of Ne I at times much larger than the maximum current. Nitrogen, on the other hand, showed a high ionization reaching N V (N 4+) at the end of the axial phase, with a distinctive evolution of the ionization degree as the plasma sheath moved towards the end of the electrodes. A mixed result was found when using Krypton, since the ionization degree only reached levels around Kr II/III, even though it has an ionization potential lower than Neon.

  14. Vortex dynamics and transport to the wall in a crossed-field plasma sheath

    SciTech Connect

    Theilhaber, K.; Birdsall, C.K.

    1987-04-10

    Results of numerical simulations of the time-dependent behavior of a transversely magnetized plasma-wall sheath are presented. These simulations have been conducted with the aim of modelling plasma behavior in the vicinity of the limiters and walls of a fusion device. The two-dimensional, bounded particle simulation code ''ES2'' has been used as a tool for the investigation of these edge effects, in an idealized geometry which retains, however, the essential features of the physics of the edge plasma. The simulations have revealed that the bounded plasma is subject to the so-called ''Kelvin-Helmholtz'' instability, an instability maintained by the non-uniform electric field which is induced by the presence of the material walls. This instability is seen to saturate into large and stable vortices, with e phi/T/sub i/ approx. 1, which exist in the vicinity of the walls, and drift parallel to their surfaces. An important feature of these structures is that they continuously convect particles to the walls, at an ''anomalous'' rate much greater than that induced by collisional diffusion, a feature which seems tied to the mutual interaction of the vortices. In the code ''ES2'', volume ionization of neutrals has been modelled by a uniform electron-ion pair creation in the simulation region, and this results in a steady state, in which the linear edge instability, the nonlinear fluid dynamics of the vortices, and the nonlinear dynamics of the particles scattered by the vortices all balance each other. This steady-state but non-equilibrium configuration, which is a first model of the edge behavior induced by the boundaries, is conceptually analogous to Rayleigh-Benard convection.

  15. Observations of interplanetary plasma waves, spacecraft noise, and sheath phenomena on Imp 7

    NASA Technical Reports Server (NTRS)

    Scarf, F. L.; Fredricks, R. W.; Green, I. M.; Crook, G. M.

    1974-01-01

    The Imp 7 plasma wave instrument measures electric and magnetic wave components of plasma oscillations over the frequency range from 10 Hz to 100 kHz. The instrumentation and relevant external characteristics of the spacecraft that appear to be responsible for some in-flight disturbance effects are briefly described. It is shown that as each one of the 16 solar panel flats rotates into shadow or sunlight, the array transients produce fluctuating magnetic fields that are detected on the magnetic loop mounted 3.4 m from the spacecraft. These transients occur 16 times per spin period, and the corresponding magnetic noise has a high frequency on the rapidly spinning Imp 7 spacecraft. The analysis suggests that some Imp magnetic threshold levels measured 3-4 m from the spacecraft are determined by the solar array current transient effects associated with the discrete 16-sided geometry of the spacecraft. The geometry also influences the response of the electric dipole antenna by modulating the sheath.

  16. Current sheath formation dynamics and structure for different insulator lengths of plasma focus device

    SciTech Connect

    Seng, Y. S.; Lee, P.; Rawat, R. S.

    2014-11-15

    The breakdown phase of the UNU-ICTP plasma focus (PF) device was successfully simulated using the electromagnetic particle in cell method. A clear uplift of the current sheath (CS) layer was observed near the insulator surface, accompanied with an exponential increase in the plasma density. Both phenomena were found to coincide with the surge in the electric current, which is indicative of voltage breakdown. Simulations performed on the device with different insulator lengths showed an increase in the fast ionization wave velocity with length. The voltage breakdown time was found to scale linearly with the insulator length. Different spatial profiles of the CS electron density, and the associated degree of uniformity, were found to vary with different insulator lengths. The ordering, according to the degree of uniformity, among insulator lengths of 19, 22, and 26 mm agreed with that in terms of soft X-ray radiation yield observed from experiments. This suggests a direct correlation between CS density homogeneity near breakdown and the radiation yield performance. These studies were performed with a linearly increasing voltage time profile as input to the PF device.

  17. Simulation of the influence high-frequency (2 MHz) capacitive gas discharge and magnetic field on the plasma sheath near a surface in hypersonic gas flow

    SciTech Connect

    Schweigert, I. V.

    2012-08-15

    The plasma sheath near the surface of a hypersonic aircraft formed under associative ionization behind the shock front shields the transmission and reception of radio signals. Using two-dimensional kinetic particle-in-cell simulations, we consider the change in plasma-sheath parameters near a flat surface in a hypersonic flow under the action of electrical and magnetic fields. The combined action of a high-frequency 2-MHz capacitive discharge, a constant voltage, and a magnetic field on the plasma sheath allows the local electron density to be reduced manyfold.

  18. Obliquely propagating ion-acoustic solitons and supersolitons in four-component auroral plasmas

    NASA Astrophysics Data System (ADS)

    Rufai, O. R.; Bharuthram, R.; Singh, S. V.; Lakhina, G. S.

    2016-02-01

    Arbitrary amplitude nonlinear low frequency electrostatic soliton and supersoliton structures are studied in magnetized four-component auroral plasmas composed of a cold singly charged oxygen-ion fluid, Boltzmann distribution of hot protons and two distinct group of electron species. Using the Sagdeev pseudo-potential technique, the characteristics of obliquely propagating nonlinear structures are investigated analytically and numerically. The model supports the evolution of soliton and supersoliton structures in the auroral acceleration region. Depending on the parametric region, the positive and negative potential solitons coexists at lower Mach numbers, but at higher Mach numbers only negative potential solitons and supersolitons can exist. The presence of hot protons restricted the Mach number of the nonlinear structures to exist only at the subsonic region. The present investigation concurs with the Swedish Viking satellite observations in the auroral region.

  19. Obliquely propagating dust-density waves

    NASA Astrophysics Data System (ADS)

    Piel, A.; Arp, O.; Klindworth, M.; Melzer, A.

    2008-02-01

    Self-excited dust-density waves are experimentally studied in a dusty plasma under microgravity. Two types of waves are observed: a mode inside the dust volume propagating in the direction of the ion flow and another mode propagating obliquely at the boundary between the dusty plasma and the space charge sheath. The dominance of oblique modes can be described in the frame of a fluid model. It is shown that the results fom the fluid model agree remarkably well with a kinetic electrostatic model of Rosenberg [J. Vac. Sci. Technol. A 14, 631 (1996)]. In the experiment, the instability is quenched by increasing the gas pressure or decreasing the dust density. The critical pressure and dust density are well described by the models.

  20. Multidimensional Plasma Sheath Modeling Using The Three Fluid Plasma Model in General Geometries

    NASA Astrophysics Data System (ADS)

    Lilly, Robert; Shumlak, Uri

    2012-10-01

    There has been renewed interest in the use of plasma actuators for high speed flow control applications. In the plasma actuator, current is driven through the surrounding weakly ionized plasma to impart control moments on the hypersonic vehicle. This expanded general geometry study employs the three-fluid (electrons, ions,neutrals) plasma model as it allows the capture of electron inertial effects, as well as energy and momentum transfer between the charged and neutral species. Previous investigations have typically assumed an electrostatic electric field. This work includes the full electrodynamics in general geometries. Past work utilizing the research code WARPX (Washington Approximate Riemann Problem) employed cartesian grids. In this work, the problem is expanded to general geometries with the euler fluid equations employing Braginskii closure. In addition, WARPX general geometry grids are generated from Cubit or CAD files. Comparisons are made against AFRL magnetized plasma actuator experiments.

  1. Difference in chemical reactions in bulk plasma and sheath regions during surface modification of graphene oxide film using capacitively coupled NH{sub 3} plasma

    SciTech Connect

    Lee, Sung-Youp; Kim, Chan; Kim, Hong Tak

    2015-09-14

    Reduced graphene oxide (r-GO) films were obtained from capacitively coupled NH{sub 3} plasma treatment of spin-coated graphene oxide (GO) films at room temperature. Variations were evaluated according to the two plasma treatment regions: the bulk plasma region (R{sub bulk}) and the sheath region (R{sub sheath}). Reduction and nitridation of the GO films began as soon as the NH{sub 3} plasma was exposed to both regions. However, with the increase in treatment time, the reduction and nitridation reactions differed in each region. In the R{sub bulk}, NH{sub 3} plasma ions reacted chemically with oxygen functional groups on the GO films, which was highly effective for reduction and nitridation. While in the R{sub sheath}, physical reactions by ion bombardment were dominant because plasma ions were accelerated by the strong electrical field. The accelerated plasma ions reacted not only with the oxygen functional groups but also with the broken carbon chains, which caused the removal of the GO films by the formation of hydrocarbon gas species. These results showed that reduction and nitridation in the R{sub bulk} using capacitively coupled NH{sub 3} plasma were very effective for modifying the properties of r-GO films for application as transparent conductive films.

  2. Kelvin--Helmholtz vortex formation and particle transport in a cross-field plasma sheath. I. Transient behavior

    SciTech Connect

    Theilhaber, K.; Birdsall, C.K. )

    1989-11-01

    The time-dependent behavior of a transversely magnetized, two-dimensional plasma--wall sheath has been studied through particle simulations, with the aim of modeling plasma behavior in the vicinity of the limiters and walls of magnetized plasma devices. The model assumes a magnetic field perfectly parallel to the confining surfaces. The simulations have shown that the cross-field sheath between a wall and a plasma is a self-sustaining turbulent boundary layer, with strong potential fluctuations and anomalous particle transport. The driving mechanism for this turbulence is the Kelvin--Helmholtz instability, which arises from the sheared particle drifts created near the wall. In this paper, the transient behavior leading to the turbulent steady state is presented, and the processes of linear growth, vortex saturation, and vortex coalescence are examined. An analytic model for the boundary Kelvin--Helmholtz instability is derived and shown to correctly predict the growth rates of the long-wavelength modes. In a companion paper, the steady-state structure and behavior of the cross-field sheath will be discussed in detail.

  3. Effect of particles attachment to multi-sized dust grains present in electrostatic sheaths of discharge plasmas

    SciTech Connect

    Zaham, B.; Tahraoui, A. Chekour, S.; Benlemdjaldi, D.

    2014-12-15

    The loss of electrons and ions due to their attachment to a Gauss-distributed sizes of dust grains present in electrostatic sheaths of discharge plasmas is investigated. A uni-dimensional, unmagnetized, and stationary multi-fluid model is proposed. Forces acting on the dust grain along with its charge are self-consistently calculated, within the limits of the orbit motion limited model. The dynamic analysis of dust grains shows that the contribution of the neutral drag force in the net force acting on the dust grain is negligible, whereas the contribution of the gravity force is found considerable only for micrometer particles. The dust grains trapping is only possible when the electrostatic force is balanced by the ion drag and the gravity forces. This trapping occurs for a limited radius interval of micrometer dust grains, which is around the most probable dust grain radius. The effect of electron temperature and ion density at the sheath edge is also discussed. It is shown that the attachment of particles reduces considerably the sheath thickness and induces dust grain deceleration. The increase of the lower limit as well as the upper limit of the dust radius reduces also the sheath thickness.

  4. Parameteric studies of nonlinear oblique magnetosonic waves in two-ion-species plasmas

    SciTech Connect

    Toida, Mieko; Kondo, Yuichi

    2011-06-15

    The study of the effects of ion composition on perpendicular magnetosonic waves in two-ion-species plasmas [M. Toida, H. Higashino, and Y. Ohsawa, J. Phys. Soc. Jpn. 76, 104052 (2007)] is extended to include oblique waves. First, the conditions necessary for KdV equations for low- and high-frequency modes to be valid are analytically obtained. The upper limit of the amplitude of the low-frequency-mode pulse is expressed as a function of the propagation angle {theta}, density ratio, and cyclotron frequency ratio of the two ion species. Next, with electromagnetic particle simulations, the nonlinear evolution of a long-wavelength low-frequency-mode disturbance is examined for various {theta}s in two plasmas with different ion densities and cyclotron frequency ratios, and the theory for the low-frequency-mode pulse is confirmed. It is also shown that if the pulse amplitude exceeds the theoretical value of the upper limit of the amplitude, then shorter-wavelength low- and high-frequency-mode waves are generated.

  5. Oblique ion-acoustic cnoidal waves in two temperature superthermal electrons magnetized plasma

    SciTech Connect

    Panwar, A. Ryu, C. M.; Bains, A. S.

    2014-12-15

    A study is presented for the oblique propagation of ion acoustic cnoidal waves in a magnetized plasma consisting of cold ions and two temperature superthermal electrons modelled by kappa-type distributions. Using the reductive perturbation method, the nonlinear Korteweg de-Vries equation is derived, which further gives the solutions with a special type of cnoidal elliptical functions. Both compressive and rarefactive structures are found for these cnoidal waves. Nonlinear periodic cnoidal waves are explained in terms of plasma parameters depicting the Sagdeev potential and the phase curves. It is found that the density ratio of hot electrons to ions μ significantly modifies compressive/refractive wave structures. Furthermore, the combined effects of superthermality of cold and hot electrons κ{sub c},κ{sub h}, cold to hot electron temperature ratio σ, angle of propagation and ion cyclotron frequency ω{sub ci} have been studied in detail to analyze the height and width of compressive/refractive cnoidal waves. The findings in the present study could have important implications in understanding the physics of electrostatic wave structures in the Saturn's magnetosphere where two temperature superthermal electrons are present.

  6. Study of obliquely propagating dust acoustic solitary waves in magnetized tropical mesospheric plasmas with effect of dust charge variations and rotation of the plasma

    SciTech Connect

    Mushtaq, A.; Shah, H.A.; Rubab, N.; Murtaza, G.

    2006-06-15

    The characteristics of obliquely propagating Dust Acoustic Waves (DAWs) in rotating and magnetized dusty plasma in the dayside tropical mesosphere are examined by incorporating adiabatic dust charge fluctuations. A Korteweg-de Vries equation is derived, which may support a nonlinear dust acoustic wave on a very slow time scale. The meteoritic dust in mesospheric plasmas on the dayside is charged positively due to photo- and thermionic emissions. The dynamics of the DAW with electronic, ionic, thermionic, and photoelectric currents along with obliqueness and effective gyrofrequency are studied. It is observed that the amplitude of the soliton depends directly on the obliqueness {theta} and dust charge variation, respectively, while the width is modified inversely with these parameters. It is also observed that the effective gyrofrequency modifies the width inversely.

  7. Laser-Plasma Interaction in Presence of an Obliquely External Magnetic Field: Application to Laser Fusion without Radioactivity

    NASA Astrophysics Data System (ADS)

    Mobaraki, M.; Jafari, S.

    2016-08-01

    In this paper, the nonlinear interaction of ultra-high power laser beam with fusion plasma at relativistic regime in the presence of obliquely external magnetic Geld has been studied. Imposing an external magnetic Geld on plasma can modify the density profile of the plasma so that the thermal conductivity of electrons reduces which is considered to be the decrease of the threshold energy for ignition. To achieve the fusion of Hydrogen-Boron (HB) fuel, the block acceleration model of plasma is employed. Energy production by HB isotopes can be of interest, since its reaction does not generate radioactive tritium. By using the inhibit factor in the block model acceleration of plasma and Maxwell's as well as the momentum transfer equations, the electron density distribution and dielectric permittivity of the plasma medium are obtained. Numerical results indicate that with increasing the intensity of the external magnetic field, the oscillation of the laser magnetic field decreases, while the dielectric permittivity increases. Moreover, the amplitude of the electron density becomes highly peaked and the plasma electrons are strongly bunched with increasing the intensity of external magnetic field. Therefore, the magnetized plasma can act as a positive focusing lens to enhance the fusion process. Besides, we find that with increasing θ-angle (from oblique external magnetic field) between 0 and 90°, the dielectric permittivity increases, while for θ between 90° and 180°, the dielectric permittivity decreases with increasing θ.

  8. Efficient gamma-ray generation by ultra-intense laser pulses obliquely incident on a planar plasma layer

    NASA Astrophysics Data System (ADS)

    Serebryakov, D. A.; Nerush, E. N.

    2016-04-01

    We have carried out numerical simulations of oblique incidence of a laser pulse with an intensity of I = 1.33 × 1023 W cm-2 on a planar plasma layer and found the plasma density and the angle of incidence of p-polarised laser pulses that correspond to the highest gamma-ray generation efficiency and high gamma-ray directivity. The shape of the plasma surface has been determined by simulation and conditions have been considered that lead to an increase in generation efficiency.

  9. PLASMA SPRAYED FUNCTIONALLY GRADED AND LAYERED MoSi2-A1203 COMPOSITES FOR HIGH TEMPERATURE SENSOR SHEATH APPLICATION

    SciTech Connect

    R. VAIDYA; ET AL

    2001-01-01

    Protective sensor sheaths are required in the glass industry for sensors that are used to measure various properties of the melt. Molten glass presents an extremely corrosive elevated temperature environment, in which only a few types of materials can survive. Molybdenum disilicide (MoSi{sub 2}) has been shown to possess excellent corrosion resistance in molten glass, and is thus a candidate material for advanced sensor sheath applications. Plasma spray-forming techniques were developed to fabricate molybdenum dilicide-alumina (Al{sub 2}O{sub 3}) laminate and functionally graded composite tubes with mechanical properties suitable for sensor sheath applications. These functionally graded materials (FGMs) were achieved by manipulating the powder hoppers and plasma torch translation via in-house created computer software. Molybdenum disilicide and alumina are thermodynamically stable elevated temperature materials with closely matching thermal expansion coefficients. Proper tailoring of the microstructure of these MoSi{sub 2}-Al{sub 2}O{sub 3} composites can result in improved strength, toughness, and thermal shock resistance. This study focuses on the mechanical performance of these composite microstructures.

  10. Pre-sheath density drop induced by ion-neutral friction along plasma blobs and implications for blob velocities

    SciTech Connect

    Furno, I.; Chabloz, V.; Fasoli, A.; Loizu, J.; Theiler, C.

    2014-01-15

    The pre-sheath density drop along the magnetic field in field-aligned, radially propagating plasma blobs is investigated in the TORPEX toroidal experiment [Fasoli et al., Plasma Phys. Controlled Fusion 52, 124020 (2010)]. Using Langmuir probes precisely aligned along the magnetic field, we measure the density n{sub se} at a poloidal limiter, where blobs are connected, and the upstream density n{sub 0} at a location half way to the other end of the blobs. The pre-sheath density drop n{sub se}/n{sub 0} is then computed and its dependence upon the neutral background gas pressure is studied. At low neutral gas pressures, the pre-sheath density drop is ≈0.4, close to the value of 0.5 expected in the collisionless case. In qualitative agreement with a simple model, this value decreases with increasing gas pressure. No significant dependence of the density drop upon the radial distance into the limiter shadow is observed. The effect of reduced blob density near the limiter on the blob radial velocity is measured and compared with predictions from a blob speed-versus-size scaling law [Theiler et al., Phys. Rev. Lett. 103, 065001 (2009)].

  11. Wall current closure effects on plasma and sheath fluctuations in Hall thrusters

    SciTech Connect

    Frias, Winston Smolyakov, Andrei I.; Kaganovich, Igor D.; Raitses, Yevgeny

    2014-06-15

    The excitation of negative energy, ion sound type modes driven by the E × B drift and the reactive/dissipative response of the wall sheath interface is analyzed for conditions typical in a Hall thruster. Such sheath impedance modes are sensitive to the dielectric properties of the thruster wall material, which therefore may have direct influence (other than via the secondary electron emission) on fluctuations and transport. Our results predict mode frequencies consistent with the frequencies of fluctuations observed experimentally.

  12. Kinetic theory of electromagnetic plane wave obliquely incident on bounded plasma slab

    SciTech Connect

    Angus, J. R.; Krasheninnikov, S. I.; Smolyakov, A. I.

    2010-10-15

    The effects of electromagnetic plane waves obliquely incident on a warm bounded plasma slab of finite length L are studied by solving the coupled Vlasov-Maxwell set of equations. It is shown that the solution can be greatly simplified in the limit where thermal effects are most important by expanding in small parameters and introducing self-similar variables. These solutions reveal that the coupling of thermal effects with the angle of incidence is negligible in the region of bounce resonance and anomalous skin effect. In the region of the anomalous skin effect, the heating is shown to scale linearly with the anomalous skin depth {delta}{sub a} when {delta}{sub a}<>L, the heating is shown to decay with 1/{delta}{sub a}{sup 3}. The transmission is found to be exponentially larger than that predicted from a local theory in the appropriate region of the anomalous skin effect.

  13. Oblique propagation of electrostatic waves in a magnetized electron-positron-ion plasma with superthermal electrons

    SciTech Connect

    Alinejad, H.; Mamun, A. A.

    2011-11-15

    A theoretical investigation is carried out to understand the basic features of linear and nonlinear propagation of ion-acoustic (IA) waves subjected to an external magnetic field in an electron-positron-ion plasma which consists of a cold magnetized ion fluid, Boltzmann distributed positrons, and superthermal electrons. In the linear regime, the propagation of two possible modes (fast and slow) and their evolution are investigated. It is shown that the electron superthermality and the relative fraction of positrons cause both modes to propagate with smaller phase velocities. Also, two special cases of dispersion relation are found, which are related to the direction of the wave propagation. In the nonlinear regime, the Korteweg-de Vries (KdV) equation describing the propagation of fast and slow IA waves is derived. The latter admits a solitary wave solution with only negative potential in the weak amplitude limit. It is found that the effects of external magnetic field (obliqueness), superthermal electrons, positron concentration, and temperature ratio significantly modify the basic features of solitary waves.

  14. Extremely Nonsinusoidal Emissions from Strong Laser Pulses Obliquely P-Incident on Sharp-Edged Plasmas

    NASA Astrophysics Data System (ADS)

    Tyshetskiy, Y.; Nikolic, L.; Johnston, T. W.; Vidal, F.

    2006-10-01

    Extremely high laser harmonics emissions [1] emerge from the Vulcan petawatt laser's sub-picosecond laser pulses obliquely incident on slab targets with extremely low pre-pulse energy. Similar studies are to be made using the ALLS 200 TW Ti-Saph laser (24 fs at 10 Hz with 10-10 contrast even without plasma mirrors). We discuss our 2-D PIC simulations using the OSIRIS code with a view to (a) understanding the basic mechanism(s) for the production of the harmonics and (b) establishing the effect of density gradients. Typical results resemble those of Naumova et al. [2], including the presence of a very large and asymmetric electromagnetic ``spikes'' which account for the high harmonic content. [1] B. Dromey, M. Zepf, A. Gopal, K. Lancaster, M. S. Wei, K. Krushelnick, M. Tatarakis, N. Vakakis, S. Moustaizis, R. Kodama, M. Tampo, C. Stoeckl, R. Clarke, H. Habara, D. Neely, S. Karsch and P. Norreys, Nature Phys. Lett., 2, 456-459 (2006) [2] N. Naumova, I. Sokolov, J. Nees,1 A. Maksimchuk, V. Yanovsky, and G. Mourou Phys. Rev. Lett. 93, 195003 (2004)

  15. Oblique propagation of ion acoustic shock waves in weakly and highly relativistic plasmas with nonthermal electrons and positrons

    NASA Astrophysics Data System (ADS)

    Hafez, M. G.; Roy, N. C.; Talukder, M. R.; Hossain Ali, M.

    2016-09-01

    This work investigates the oblique nonlinear propagation of ion acoustic (IA) shock waves for both weakly and highly relativistic plasmas composed of nonthermal electrons and positrons with relativistic thermal ions. The KdVB-like equation, involving dispersive, weakly transverse dispersive, nonlinearity and dissipative coefficients, is derived employing the well known reductive perturbation method. The integration of this equation is carried out by the {tanh} method taking the stable shock formation condition into account. The effects of nonthermal electrons and positrons, nonthermal electrons with isothermal positrons, isothermal electrons with nonthermal positrons, and isothermal electrons and positrons on oblique propagation of IA shock waves in weakly relativistic regime are described. Furthermore, the effects of plasma parameters on oblique propagation of IA shock waves in highly relativistic regime are discussed and compared with weakly relativistic case. It is seen that the plasma parameters within certain limits significantly modify the structures of the IA shock waves in both cases. The results may be useful for better understanding of the interactions of charged particles with extra-galactic jets as well as astrophysical compact objects.

  16. RF Sheath Models

    NASA Astrophysics Data System (ADS)

    D'Ippolito, D. A.; Myra, J. R.

    2007-11-01

    RF sheath formation on the antennas and walls in ICRF-heated experiments can reduce the heating efficiency, limit the coupled power, and cause damage to plasma-facing structures. The sheaths are driven by a slow wave component of the rf field due to a mismatch between the magnetic field and the boundary (antenna or wall). Quantitative modeling of the highly nonlinear sheaths may now be feasible for the first time in massively-parallel-processing (MPP) codes developed in the RF SciDAC project. Recently, a new approach to sheath modeling was proposed,ootnotetextD.A. D'Ippolito and J.R. Myra, Phys. Plasmas 13, 102508 (2006). in which the sheath physics is incorporated into the RF wave computation by using a modified boundary condition (BC) on the RF fields in both wave propagation and antenna codes. Here, we illustrate the use of the sheath BC for near-field sheaths by a model calculation that includes electromagnetic effects and a simple antenna coupling model. Properties of the model (such as the role of sheath-plasma waves) and implications for antenna codes such as TOPICAootnotetextV. Lancellotti et al., Nucl. Fusion 46, S476 (2006). will be discussed.

  17. Re-entry communication through a plasma sheath using standing wave detection and adaptive data rate control

    NASA Astrophysics Data System (ADS)

    Xie, Kai; Yang, Min; Bai, Bowen; Li, Xiaoping; Zhou, Hui; Guo, Lixin

    2016-01-01

    Radio blackout during the re-entry has puzzled the aerospace industry for decades and has not yet been completely resolved. To achieve a continuous data link in the spacecraft's re-entry period, a simple and practicable communication method is proposed on the basis that (1) the electromagnetic-wave backscatter of the plasma sheath affects the voltage standing wave ratio (VSWR) of the antenna, and the backscatter is negatively correlated to transmission components, and (2) the transmission attenuation caused by the plasma sheath reduces the channel capacity. We detect the voltage standing wave ratio changes of the antenna and then adjust the information rate to accommodate the varying channel capacity, thus guaranteeing continuous transmission (for fewer critical data). The experiment was carried out in a plasma generator with an 18-cm-thick and 30-cm-diameter hollow propagation path, and the adaptive communication was implemented using spread spectrum frequency, shift key modulation with a variable spreading factor. The experimental results indicate that, when the over-threshold of VSWR was detected, the bit rate reduced to 250 bps from 4 Mbps automatically and the tolerated plasma density increased by an order of magnitude, which validates the proposed scheme. The proposed method has little additional cost, and the adaptive control does not require a feedback channel. The method is therefore applicable to data transmission in a single direction, such as that of a one-way telemetry system.

  18. Second harmonic generation by propagation of a p-polarized obliquely incident laser beam in underdense plasma

    SciTech Connect

    Jha, Pallavi; Agrawal, Ekta

    2014-05-15

    An analytical study of second harmonic generation due to interaction an intense, p-polarized laser beam propagating obliquely in homogeneous underdense plasma, in the mildly relativistic regime, has been presented. The efficiency of the second harmonic radiation as well as its detuning length has been obtained and their variation with the angle of incidence is analyzed. It is shown that, for a given plasma electron density, the second harmonic efficiency increases with the angle of incidence while the detuning length decreases. The second harmonic amplitude vanishes at normal incidence of the laser beam.

  19. Oblique propagation of ion acoustic soliton-cnoidal waves in a magnetized electron-positron-ion plasma with superthermal electrons

    SciTech Connect

    Wang, Jian-Yong; Cheng, Xue-Ping; Tang, Xiao-Yan; Yang, Jian-Rong; Ren, Bo

    2014-03-15

    The oblique propagation of ion-acoustic soliton-cnoidal waves in a magnetized electron-positron-ion plasma with superthermal electrons is studied. Linear dispersion relations of the fast and slow ion-acoustic modes are discussed under the weak and strong magnetic field situations. By means of the reductive perturbation approach, Korteweg-de Vries equations governing ion-acoustic waves of fast and slow modes are derived, respectively. Explicit interacting soliton-cnoidal wave solutions are obtained by the generalized truncated Painlevé expansion. It is found that every peak of a cnoidal wave elastically interacts with a usual soliton except for some phase shifts. The influence of the electron superthermality, positron concentration, and magnetic field obliqueness on the soliton-cnoidal wave are investigated in detail.

  20. A comparison of parametric decay of oblique Langmuir wave in high and low density magneto-plasmas

    SciTech Connect

    Shahid, M.; Hussain, A.; Murtaza, G.

    2013-09-15

    The parametric decay instability of an obliquely propagating Langmuir wave into the low-frequency electromagnetic shear Alfven wave and the Left-Handed Circularly Polarized wave has been investigated in an electron-ion plasma, immersed in a uniform external magnetic field. Quantum magneto-hydrodynamic model has been used to find the linear and non-linear response of a high density quantum magneto-plasma. Going to the classical limit (ℏ→0) retrieves the results for low density classical plasma. Nonlinear dispersion relations and growth rates are derived with analytically and numerically. It is observed that growth rate in the high density degenerate magneto-plasma increases exponentially, while in the low density classical case it increases logarithmically.

  1. Characteristics of sheath-driven tangential flow produced by a low-current DC surface glow discharge plasma actuator

    NASA Astrophysics Data System (ADS)

    Shin, Jichul; Shajid Rahman, Mohammad

    2014-08-01

    An experimental investigation of low-speed flow actuation at near-atmospheric pressure is presented. The flow actuation is achieved via low-current ( \\lesssim 1.0 mA) continuous or pulsed DC surface glow discharge plasma. The plasma actuator, consisting of two sharp-edged nickel electrodes, produces a tangential flow in a direction from anode to cathode, and is visualized using high-speed schlieren photography. The induced flow velocity estimated via the schlieren images reaches up to 5 m/s in test cases. The actuation capability increases with pressure and electrode gap distances, and the induced flow velocity increases logarithmically with the discharge power. Pulsed DC exhibits slightly improved actuation capability with better directionality. An analytic estimation of induced flow velocity obtained based on ion momentum in the cathode sheath and gas dynamics in one-dimensional flow yields values similar to those measured.

  2. Study of Sheath Potential and Plasma Density Profiles in the Presence of Strong Secondary Electron Emission from Walls

    NASA Astrophysics Data System (ADS)

    Trung, Huy-Sinh; Kaganovich, Igor; Khrabrov, Alexander

    2011-10-01

    We study the behavior of plasmas confined within walls, which emit secondary electrons. A set of fluid equations for ions, the Vlasov equation for electrons, and Poisson's equation are solved together numerically to obtain potential and density distributions. We explore the transition to the space charge limited regime in the sheath. The potential and density profiles are monotonic if the emission coefficient is set below the critical emission coefficient. Above the critical emission coefficient, the profiles become non monotonic. We recover the results obtained by Hobbs & Wesson and compare them to the full-scale simulation results of a particle-in-cell code, EDIPIC. Research supported by the Department of Energy National Undergraduate Fellowship Program in Plasma Physics and Fusion Energy Sciences.

  3. Plasma wall sheath contributions to flux retention during the formation of field-reversed configurations

    NASA Astrophysics Data System (ADS)

    Milroy, R. D.; Slough, J. T.; Hoffman, A. L.

    1984-06-01

    Flux loss during field reversal on the TRX-1 field-reversed θ pinch is found to be much less than predicted by the inertial model of Green and Newton. This can be explained by a pressure bearing, conducting sheath which naturally forms at the wall and limits the flux loss. A one-dimensional (r-t) magnetohydrodynamic (MHD) numerical model has been used to study the formation and effectiveness of the sheath. The calculations are in excellent agreement with experimental measurements over a wide range of operating parameters. The results indicate that good flux trapping can be achieved through the field reversal phase of FRC formation with much slower external field reversal rates than in current experiments.

  4. Analytic Model of Antenna Sheaths

    NASA Astrophysics Data System (ADS)

    D'Ippolito, D. A.; Myra, J. R.

    2008-11-01

    RF sheaths are generated on ICRF antennas whenever the launched fast wave also drives a slow wave, e.g. when the magnetic field is tilted (not perpendicular to the current straps). A new approach to sheath modeling was recently proposed in which the RF waves are computed using a modified boundary condition at the sheath surface to describe the plasma-sheath coupling. Here, we illustrate the use of the sheath BC for antenna sheaths by a model electromagnetic perturbation calculation, treating the B field tilt as a small parameter. Analytic expressions are obtained for the sheath voltage and the rf electric field parallel to B in both sheath and plasma regions, including the Child-Langmuir (self-consistency) constraint. It is shown that the plasma corrections to the sheath voltage (which screen the rf field) can be important. The simple vacuum-field sheath-voltage estimate is obtained as a limiting case. Implications for antenna codes such as TOPICA will be discussed. D.A. D'Ippolito and J.R. Myra, Phys. Plasmas 13, 102508 (2006). V. Lancellotti et al., Nucl. Fusion 46, S476 (2006).

  5. Modeling of the sheath and the energy distribution of ions bombarding rf-biased substrates in high density plasma reactors and comparison to experimental measurements

    NASA Astrophysics Data System (ADS)

    Edelberg, Erik A.; Aydil, Eray S.

    1999-11-01

    In plasma etching and deposition processes, the energy distribution of ions incident onto the substrate strongly affects the surface reactions and the film deposition and etching rates. The magnitude and frequency of the rf-bias power applied to the substrate electrode determines the spatiotemporal variations of the sheath potentials and hence the energy distribution of the ions impinging upon the substrate. A self-consistent dynamic model of the sheath, capable of predicting ion energy distributions impinging on a rf-biased electrode, was developed. The model consists of equations describing the charge transport in the sheath coupled to an equivalent circuit model of the sheath to predict the spatiotemporal charge and potential distributions near the surface. Experimental measurements of the energy distributions of ions impinging on a rf-biased electrostatic chuck have also been made in a high density transformer coupled plasma reactor through Ar and Ne plasmas. The predicted ion energy distributions and sheath profiles are in very good agreement with the experimental measurements.

  6. Filamentary structure of plasma produced by compression of puffing deuterium by deuterium or neon plasma sheath on plasma-focus discharge

    SciTech Connect

    Kubes, P.; Cikhardt, J.; Kortanek, J.; Cikhardtova, B.; Rezac, K.; Klir, D.; Kravarik, J.; Paduch, M.; Zielinska, E.

    2014-12-15

    The present experiments were performed on the PF-1000 plasma focus device at a current of 2 MA with the deuterium injected from the gas-puff placed in the axis of the anode face. The XUV frames showed, in contrast with the interferograms, the fine structure: filaments and spots up to 1 mm diameter. In the deuterium filling, the short filaments are registered mainly in the region of the internal plasmoidal structures and their number correlates with the intensity of neutron production. The longer filamentary structure was recorded close to the anode after the constriction decay. The long curve-like filaments with spots were registered in the big bubble formed after the pinch phase in the head of the umbrella shape of the plasma sheath. Filaments can indicate the filamentary structure of the current in the pinch. Together with the filaments, small compact balls a few mm in diameter were registered by both interferometry and XUV frame pictures. They emerge out of the dense column and their life-time can be greater than hundreds of ns.

  7. Difference in chemical reactions in bulk plasma and sheath regions during surface modification of graphene oxide film using capacitively coupled NH3 plasma

    NASA Astrophysics Data System (ADS)

    Lee, Sung-Youp; Kim, Chan; Kim, Hong Tak

    2015-09-01

    Reduced graphene oxide (r-GO) films were obtained from capacitively coupled NH3 plasma treatment of spin-coated graphene oxide (GO) films at room temperature. Variations were evaluated according to the two plasma treatment regions: the bulk plasma region (Rbulk) and the sheath region (Rsheath). Reduction and nitridation of the GO films began as soon as the NH3 plasma was exposed to both regions. However, with the increase in treatment time, the reduction and nitridation reactions differed in each region. In the Rbulk, NH3 plasma ions reacted chemically with oxygen functional groups on the GO films, which was highly effective for reduction and nitridation. While in the Rsheath, physical reactions by ion bombardment were dominant because plasma ions were accelerated by the strong electrical field. The accelerated plasma ions reacted not only with the oxygen functional groups but also with the broken carbon chains, which caused the removal of the GO films by the formation of hydrocarbon gas species. These results showed that reduction and nitridation in the Rbulk using capacitively coupled NH3 plasma were very effective for modifying the properties of r-GO films for application as transparent conductive films.

  8. Oblique propagation of dust ion-acoustic solitary waves in a magnetized dusty pair-ion plasma

    SciTech Connect

    Misra, A. P. E-mail: apmisra@gmail.com; Barman, Arnab

    2014-07-15

    We investigate the propagation characteristics of electrostatic waves in a magnetized pair-ion plasma with immobile charged dusts. It is shown that obliquely propagating (OP) low-frequency (in comparison with the negative-ion cyclotron frequency) long-wavelength “slow” and “fast” modes can propagate, respectively, as dust ion-acoustic (DIA) and dust ion-cyclotron (DIC)-like waves. The properties of these modes are studied with the effects of obliqueness of propagation (θ), the static magnetic field, the ratios of the negative to positive ion masses (m), and temperatures (T) as well as the dust to negative-ion number density ratio (δ). Using the standard reductive perturbation technique, we derive a Korteweg-de Vries (KdV) equation which governs the evolution of small-amplitude OP DIA waves. It is found that the KdV equation admits only rarefactive solitons in plasmas with m well below its critical value m{sub c} (≫ 1) which typically depends on T and δ. It is shown that the nonlinear coefficient of the KdV equation vanishes at m = m{sub c}, i.e., for plasmas with much heavier negative ions, and the evolution of the DIA waves is then described by a modified KdV (mKdV) equation. The latter is shown to have only compressive soliton solution. The properties of both the KdV and mKdV solitons are studied with the system parameters as above, and possible applications of our results to laboratory and space plasmas are briefly discussed.

  9. Simulation study of wave phenomena from the sheath region in single frequency capacitively coupled plasma discharges; field reversals and ion reflection

    SciTech Connect

    Sharma, S.; Turner, M. M.

    2013-07-15

    Capacitively coupled radio-frequency (RF) discharges have great significance for industrial applications. Collisionless electron heating in such discharges is important, and sometimes is the dominant mechanism. This heating is usually understood to originate in a stochastic interaction between electrons and the electric fields. However, other mechanisms may also be important. There is evidence of wave emission with a frequency near the electron plasma frequency, i.e., ω{sub pe}, from the sheath region in collisionless capacitive RF discharges. This is the result of a progressive breakdown of quasi-neutrality close to the electron sheath edge. These waves are damped in a few centimeters during their propagation from the sheath towards the bulk plasma. The damping occurs because of the Landau damping or some related mechanism. This research work reports that the emission of waves is associated with a field reversal during the expanding phase of the sheath. Trapping of electrons near to this field reversal region is observed. The amplitude of the wave increases with increasing RF current density amplitude J(tilde sign){sub 0} until some maximum is reached, beyond which the wave diminishes and a new regime appears. In this new regime, the density of the bulk plasma suddenly increases because of ion reflection, which occurs due to the presence of strong field reversal near sheath region. Our calculation shows that these waves are electron plasma waves. These phenomena occur under extreme conditions (i.e., higher J(tilde sign){sub 0} than in typical experiments) for sinusoidal current waveforms, but similar effects may occur with non-sinusoidal pulsed waveforms for conditions of experimental interest, because the rate of change of current is a relevant parameter. The effect of electron elastic collisions on plasma waves is also investigated.

  10. Microparticles in a Collisional Rf Plasma Sheath under Hypergravity Conditions as Probes for the Electric Field Strength and the Particle Charge

    SciTech Connect

    Beckers, J.; Stoffels, W. W.; Dijk, J. van; Kroesen, G. M. W.; Ockenga, T.; Wolter, M.; Kersten, H.

    2011-03-18

    We used microparticles under hypergravity conditions, induced by a centrifuge, in order to measure nonintrusively and spatially resolved the electric field strength as well as the particle charge in the collisional rf plasma sheath. The measured electric field strengths demonstrate good agreement with the literature, while the particle charge shows decreasing values towards the electrode. We demonstrate that it is indeed possible to measure these important quantities without changing or disturbing the plasma.

  11. Propagation of a narrow plasma beam in an oblique magnetic field

    NASA Technical Reports Server (NTRS)

    Heidbrink, W. W.; Adams, D.; Drum, S.; Evans, K.; Manson, J.; Price, T.; Urayama, P.; Wessel, F. J.

    1992-01-01

    The propagation of an intense neutralized ion beam (v is about 5 x 10 exp 8 cm/sec, n is about 10 exp 10/cu cm) through a large insulated vacuum chamber is measured as a function of magnetic field strength and direction. When the beam propagates parallel to the applied field, beam divergence is reduced. When the beam propagates perpendicular to the applied fields, the downstream beam density decreases with increasing field strength. When the beam velocity vector intersects the magnetic field at an oblique angle, beam propagation is determined primarily by the perpendicular component of the field.

  12. Nonthermal atmospheric rf plasma in one-dimensional spherical coordinates: Asymmetric sheath structure and the discharge mechanism

    SciTech Connect

    Sakiyama, Yukinori; Graves, David B.

    2007-04-01

    We present one-dimensional simulations of atmospheric pressure rf-excited plasma with two concentric spherical electrodes and the inner electrode powered. The gas used is helium with 0.1% nitrogen addition. The gap distance between the inner and outer electrodes is 1 mm. The coupled continuity equations and electron energy equation are solved with Poisson's equation using the finite element method. A mode transition is observed in the discharge power-voltage curve between 1 and 1000 mW. In the low power mode, ionization rate peaks only near the inner electrode. The electron-impact excitation and ionization rates peak in the local cathodic phase. In the high power mode, the rate of ionization peaks near the outer electrode as well as the inner electrode. The inner sheath significantly shrinks and the direct electron-impact ionization is the primary ionization reaction near the inner electrode. The ionization rate near the outer electrode is due to Ohmic sheath oscillation heating of electrons, resulting in a peak in metastable helium creation. Penning ionization is the major ionization reaction near the outer electrode. Thus, two different ionization mechanisms coexist near the inner and outer electrodes. Electron heating near the outer electrode may have implications for surface processing in atmospheric pressure microdischarges. The local field approximation (LFA) in high power mode fails to predict the ionization rate peak near the outer electrode due to its inability to properly account for electron diffusion in the presence of both a strong electric field and electron density gradient. However, use of the LFA is adequate to model the low power mode and it correctly predicts the existence of the mode transition.

  13. Rich eight-branch spectrum of the oblique propagating longitudinal waves in partially spin-polarized electron-positron-ion plasmas

    NASA Astrophysics Data System (ADS)

    Andreev, Pavel A.; Iqbal, Z.

    2016-03-01

    We consider the separate spin evolution of electrons and positrons in electron-positron and electron-positron-ion plasmas. We consider the oblique propagating longitudinal waves in these systems. Working in a regime of high-density n0˜1027cm-3 and high-magnetic-field B0=1010 G, we report the presence of the spin-electron acoustic waves and their dispersion dependencies. In electron-positron plasmas, similarly to the electron-ion plasmas, we find one spin-electron acoustic wave (SEAW) at the propagation parallel or perpendicular to the external field and two spin-electron acoustic waves at the oblique propagation. At the parallel or perpendicular propagation of the longitudinal waves in electron-positron-ion plasmas, we find four branches: the Langmuir wave, the positron-acoustic wave, and a pair of waves having spin nature, they are the SEAW and the wave discovered in this paper, called the spin-electron-positron acoustic wave (SEPAW). At the oblique propagation we find eight longitudinal waves: the Langmuir wave, the Trivelpiece--Gould wave, a pair of positron-acoustic waves, a pair of SEAWs, and a pair of SEPAWs. Thus, for the first time, we report the existence of the second positron-acoustic wave existing at the oblique propagation and the existence of SEPAWs.

  14. The effect of non-thermal electrons on obliquely propagating electron acoustic waves in a magnetized plasma

    NASA Astrophysics Data System (ADS)

    Singh, Satyavir; Bharuthram, Ramashwar

    2016-07-01

    Small amplitude electron acoustic solitary waves are studied in a magnetized plasma consisting of hot electrons following Cairn's type non-thermal distribution function and fluid cool electrons, cool ions and an electron beam. Using reductive perturbation technique, the Korteweg-de-Vries-Zakharov-Kuznetsov (KdV-ZK) equation is derived to describe the nonlinear evolution of electron acoustic waves. It is observed that the presence of non-thermal electrons plays an important role in determining the existence region of solitary wave structures. Theoretical results of this work is used to model the electrostatic solitary structures observed by Viking satellite. Detailed investigation of physical parameters such as non-thermality of hot electrons, beam electron velocity and temperature, obliquity on the existence regime of solitons will be discussed.

  15. Nonlinear Zakharov-Kuznetsov equation for obliquely propagating two-dimensional ion-acoustic solitary waves in a relativistic, rotating magnetized electron-positron-ion plasma

    SciTech Connect

    Mushtaq, A.; Shah, H.A.

    2005-07-15

    The purpose of this work is to investigate the linear and nonlinear properties of the ion-acoustic waves (IAW), propagating obliquely to an external magnetic field in a weakly relativistic, rotating, and magnetized electron-positron-ion plasma. The Zakharov-Kuznetsov equation is derived by employing the reductive perturbation technique for this wave in the nonlinear regime. This equation admits the solitary wave solution. The amplitude and width of this solitary wave have been discussed with the effects of obliqueness, relativity, ion temperature, positron concentration, magnetic field, and rotation of the plasma and it is observed that for IAW these parameters affect the propagation properties of solitary waves and these plasmas behave differently from the simple electron-ion plasmas. Likewise, the current density and electric field of these waves are investigated for their dependence on the above-mentioned parameters.

  16. Interference patterns in the Spacelab 2 plasma wave data - oblique electrostatic waves generated by the electron beam

    SciTech Connect

    Feng, Wei; Gurnett, D.A.; Cairns, I.H. )

    1992-11-01

    During the Spacelab 2 mission the University of Iowa's Plasma Diagnostics Package (PDP) explored the plasma environment around the shuttle. Wideband spectrograms of plasma waves were obtained from the PDP at frequencies of 0-30 kHz and at distances up to 400 m from the shuttle. Strong low-frequency (below 10 kHz) electric field noise was observed in the wideband data during two periods in which an electron beam was ejected from the shuttle. This noise shows clear evidence of interference patterns caused by the finite (3.89 m) antenna length. The low-frequency noise was the most dominant type of noise produced by the ejected electron beam. Analysis of antenna interference patterns generated by these waves permits a determination of the wavelength, the direction of propagation, and the location of the source region. The observed waves have a linear dispersion relation very similar to that of ion acoustic waves. The waves are believed to be oblique ion acoustic or high-order ion cyclotron waves generated by a current of ambient electrons returning to the shuttle in response to the ejected electron beam. 31 refs.

  17. Scattering of electromagnetic waves from a magnetized plasma column at oblique incidence

    SciTech Connect

    Ghaffari-Oskooei, Sara S.; Aghamir, Farzin M.

    2015-07-14

    Scattering of electromagnetic waves from a magnetized plasma column is investigated using Maxwell's equations and applying boundary conditions. Backscattering cross section is evaluated by analytic solution of electric fields inside and outside of plasma column. Plots of backscattering cross section versus frequency, for the range up to J band, reveal two main peaks and two sidebands. Effects of plasma density and radius, as main parameters determining the characteristics of plasma column, on backscattering are discussed. Furthermore, the effect of electromagnetic wave incidence angle on backscattering of plasma column is included in the analysis. The influence of wave incidence angle and frequency, as well as, plasma density and radius on scattering pattern, which is an indicator of the distribution of scattered power in different azimuthal angles, is discussed.

  18. ION HEATING IN INHOMOGENEOUS EXPANDING SOLAR WIND PLASMA: THE ROLE OF PARALLEL AND OBLIQUE ION-CYCLOTRON WAVES

    SciTech Connect

    Ozak, N.; Ofman, L.; Viñas, A.-F.

    2015-01-20

    Remote sensing observations of coronal holes show that heavy ions are hotter than protons and their temperature is anisotropic. In-situ observations of fast solar wind streams provide direct evidence for turbulent Alfvén wave spectrum, left-hand polarized ion-cyclotron waves, and He{sup ++} - proton drift in the solar wind plasma, which can produce temperature anisotropies by resonant absorption and perpendicular heating of the ions. Furthermore, the solar wind is expected to be inhomogeneous on decreasing scales approaching the Sun. We study the heating of solar wind ions in inhomogeneous plasma with a 2.5D hybrid code. We include the expansion of the solar wind in an inhomogeneous plasma background, combined with the effects of a turbulent wave spectrum of Alfvénic fluctuations and initial ion-proton drifts. We study the influence of these effects on the perpendicular ion heating and cooling and on the spectrum of the magnetic fluctuations in the inhomogeneous background wind. We find that inhomogeneities in the plasma lead to enhanced heating compared to the homogenous solar wind, and the generation of significant power of oblique waves in the solar wind plasma. The cooling effect due to the expansion is not significant for super-Alfvénic drifts, and is diminished further when we include an inhomogeneous background density. We reproduce the ion temperature anisotropy seen in observations and previous models, which is present regardless of the perpendicular cooling due to solar wind expansion. We conclude that small scale inhomogeneities in the inner heliosphere can significantly affect resonant wave ion heating.

  19. Generation of obliquely incident ions using phase-shifted RF voltages applied on rod electrodes

    NASA Astrophysics Data System (ADS)

    Ui, Akio; Sato, Yosuke; Sasaki, Toshiyuki; Sakai, Itsuko; Hayashi, Hisataka

    2016-06-01

    A new method of generating obliquely incident ions has been investigated. A plasma system with a cathode consisting of a repetition of a group of four electrode rods connected to their respective RF power supplies is proposed. The ion angular distribution (IAD) is controlled by modulating the phase shift of the four RF powers. The IAD of an argon high-density plasma was analyzed on the basis of transient plasma simulation. When the RF voltages are controlled so that the phase shift is π/2, a convex-shaped plasma sheath corresponding to each group of four rods appears and propagates parallel to the wafer with time. By propagating this “wavy” sheath, a bimodal IAD consisting of ions obliquely incident mainly from two directions are obtained nearly uniformly across the wafer. This method is capable of generating obliquely incident ions, which is expected to be effective as an additional knob for precise profile control in fine-pattern reactive-ion etching (RIE).

  20. Hysteresis and mode transitions in plasma sheath collapse due to secondary electron emission

    NASA Astrophysics Data System (ADS)

    Langendorf, Samuel; Walker, Mitchell

    2016-03-01

    In this experiment, hysteresis is observed in the floating potential of wall material samples immersed in a low-temperature plasma as the energy of a prevalent non-thermal electron population is varied from 30-180 eV. It is indicated that the hysteresis is due to secondary electron emission from the wall material surface. Measurements are performed in a filament discharge in argon gas pressure 10 - 4 Torr of order 10 7 cm - 3 plasma number density. The primary ionizing electrons from the discharge filament make up 1%-10% of the overall plasma number density, depending on discharge voltage. Immersed LaB6-coated steel and roughened boron nitride (BN) wall material samples are mounted on the face of a radiative heater, and the wall temperature is controlled from 50-400 °C such that thermionic emission from the LaB6-coated sample is not significant. The energy of the primary plasma electrons from the discharge filament is varied and the floating potentials of the material samples are monitored. The floating potentials are observed to transition to a "collapsed" state as the primary electron energy is increased above 110 and 130 eV for the LaB6 and rough BN, respectively. As primary electron energy is subsequently decreased, the floating potentials do not "un-collapse" until lower energies of 80 and 100 eV, respectively. The hysteresis behavior agrees with a kinetic model. The results may help explain observations of global hysteresis and mode transitions in bounded plasma devices with dielectric walls, significant secondary electron emission, and departures of electron energy distribution function from a thermal Maxwellian.

  1. Self consistent radio-frequency wave propagation and peripheral direct current plasma biasing: Simplified three dimensional non-linear treatment in the 'wide sheath' asymptotic regime

    SciTech Connect

    Colas, L.; Jacquot, J.; Hillairet, J.; Goniche, M.; Heuraux, S.; Faudot, E.; Crombe, K.; Kyrytsya, V.

    2012-09-15

    A minimal two-field fluid approach is followed to describe the radio-frequency (RF) wave propagation in the bounded scrape-off layer plasma of magnetic fusion devices self-consistently with direct current (DC) biasing of this plasma. The RF and DC parts are coupled by non-linear RF and DC sheath boundary conditions at both ends of open magnetic field lines. The physical model is studied within a simplified framework featuring slow wave (SW) only and lateral walls normal to the straight confinement magnetic field. The possibility is however kept to excite the system by any realistic 2D RF field map imposed at the outer boundary of the simulation domain. The self-consistent RF + DC system is solved explicitly in the asymptotic limit when the width of the sheaths gets very large, for several configurations of the RF excitation and of the target plasma. In the case of 3D parallelepipedic geometry, semi-analytical results are proposed in terms of asymptotic waveguide eigenmodes that can easily be implemented numerically. The validity of the asymptotic treatment is discussed and is illustrated by numerical tests against a quantitative criterion expressed from the simulation parameters. Iterative improvement of the solution from the asymptotic result is also outlined. Throughout the resolution, key physical properties of the solution are presented. The radial penetration of the RF sheath voltages along lateral walls at both ends of the open magnetic field lines can be far deeper than the skin depth characteristic of the SW evanescence. This is interpreted in terms of sheath-plasma wave excitation. Therefore, the proper choice of the inner boundary location is discussed as well as the appropriate boundary conditions to apply there. The asymptotic scaling of various quantities with the amplitude of the input RF excitation is established.

  2. Extremely Nonsinusoidal Emissions and Fast Electron Phenomena from Strong Laser Pulses Obliquely P-Incident on Sharp-Edged Plasmas

    NASA Astrophysics Data System (ADS)

    Johnston, T. W.; Nikolic, L.; Tyshetskiy, Y.; Vidal, F.

    2007-11-01

    High laser harmonic light [1] emerges when the Vulcan petawatt laser's sub-ps laser pulses are obliquely incident on slab targets with extremely low pre-pulse energy. Similar work is in progress with the ALLS 200 TW Ti-Saph laser at INRS EMT. (Pulses are 24 fs at 10 Hz with 10-10 contrast, even without plasma mirrors). 2-D PIC (OSIRIS code at INRS) results on basic mechanism(s) resemble those of Gibbon [2], Naumova et al. [3] and Thaury et al. [4]. The very large and asymmetric electromagnetic ``spikes'' which account for the high harmonic content are produced by extremely concentrated 2D plasma surface currents. The connection between our 2D PIC results (also those in [3] and 1D PIC results [2,4] using the Gibbon-Bourdier moving 1D formalism[2] is also discussed, as are the fast electrons, including some related quasi-steady magnetic fields. [1] B. Dromey et al Nature Phys. Lett., 2, 456-459 (2006) [2] Paul Gibbon, Phys. Rev. Lett. 76, 50 (1996) [3] N. Naumova, et al., Phys. Rev. Lett. 93, 195003 (2004). [4] C. Thaury, et al., Nature Phys. 3, 424 (2007)

  3. Ion energy-angle distribution functions at the plasma-material interface in oblique magnetic fields

    SciTech Connect

    Khaziev, Rinat; Curreli, Davide

    2015-04-15

    The ion energy-angle distribution (IEAD) at the wall of a magnetized plasma is of fundamental importance for the determination of the material processes occurring at the plasma-material interface, comprising secondary emissions and material sputtering. Here, we present a numerical characterization of the IEAD at the wall of a weakly collisional magnetized plasma with the magnetic field inclined at an arbitrary angle with respect to the wall. The analysis has been done using two different techniques: (1) a fluid-Monte Carlo method, and (2) particle-in-cell simulations, the former offering a fast but approximate method for the determination of the IEADs, the latter giving a computationally intensive but self-consistent treatment of the plasma behavior from the quasi-neutral region to the material boundary. The two models predict similar IEADs, whose similarities and differences are discussed. Data are presented for magnetic fields inclined at angles from normal to grazing incidence (0°–85°). We show the scaling factors of the average and peak ion energy and trends of the pitch angle at the wall as a function of the magnetic angle, for use in the correlation of fluid plasma models to material models.

  4. Solitary fast magnetosonic waves propagating obliquely to the magnetic field in cold collisionless plasma

    NASA Astrophysics Data System (ADS)

    Kichigin, G. N.

    2016-01-01

    Solutions describing solitary fast magnetosonic (FMS) waves (FMS solitons) in cold magnetized plasma are obtained by numerically solving two-fluid hydrodynamic equations. The parameter domain within which steady-state solitary waves can propagate is determined. It is established that the Mach number for rarefaction FMS solitons is always less than unity. The restriction on the propagation velocity leads to the limitation on the amplitudes of the magnetic field components of rarefaction solitons. It is shown that, as the soliton propagates in plasma, the transverse component of its magnetic field rotates and makes a complete turn around the axis along which the soliton propagates.

  5. End-boundary sheath potential, Langmuir waves, electron and ion energy distribution in the low pressure DC powered Non-ambipolar Electron Plasma

    NASA Astrophysics Data System (ADS)

    Chen, Lee; Chen, Zhiying; Funk, Merritt

    2013-09-01

    The non-ambipolar electron plasma (NEP) is heated by electron beam extracted from the electron-source Ar plasma through a dielectric injector by an accelerator located inside NEP. NEP pressure is in the 1-3mTorr range of N2 and its accelerator voltage varied from VA = + 80 to VA = + 600V. The non-ambipolar beam-current injected into NEP is in the range of 10s Acm-2 and it heats NEP through beam-plasma instabilities. Its EED f has a Maxwellian bulk followed by a broad energy-continuum connecting to the most energetic group with energies above the beam-energy. The remnant of the injected electron-beam power terminates at the NEP end-boundary floating-surface setting up sheath potentials from VS = 80 to VS = 580V in response to the applied values of VA. The floating-surface is bombarded by a space-charge neutral plasma-beam whose IED f is near mono-energetic. When the injected electron-beam power is adequately damped by NEP, its end-boundary floating-surface VS can be linearly controlled at almost 1:1 ratio by VA. NEP does not have an electron-free sheath; its ``sheath'' is a widen presheath that consists of a thermal presheath followed by an ``anisotropic'' presheath, leading up to the end-boundary floating-surface. Its ion-current of the plasma-beam is much higher than what a conventional thermal presheath can supply. If the NEP parameters cannot damp the electron beam power sufficiently, VS will collapse and becomes irresponsive to VA.

  6. Obliquely propagating waves in the magnetized strongly coupled one-component plasma

    SciTech Connect

    Kählert, Hanno; Kalman, Gabor J.; Ott, Torben; Bonitz, Michael; Reynolds, Alexi

    2013-05-15

    The quasi-localized charge approximation is used to calculate the wave spectrum of the magnetized three-dimensional strongly coupled one-component plasma at arbitrary angles θ between the wave vector and the magnetic field axis. Three frequency branches are identified whose interplay is strongly determined by β=ω{sub c}/ω{sub p}, the ratio of the cyclotron frequency ω{sub c}, and the plasma frequency ω{sub p}. The frequency dispersion relations for the three principal modes along the magnetic field cross in the case β<1, which strongly affects the transition from parallel to perpendicular wave propagation. For β>1, the frequencies of the different branches are well separated, and the long-wavelength dispersion in the intermediate and upper branch changes sign as θ is varied from 0 to π/2. In addition to the frequencies, we also investigate the waves' polarization properties.

  7. Oblique Stimulated Raman Scattering of a Short Laser Pulse in a Plasma Channel

    NASA Astrophysics Data System (ADS)

    Turano, E. J.; McKinstrie, C. J.; Kanaev, A. V.

    1997-11-01

    The stimulated Raman scattering (SRS) of a primary laser pulse can occur in a plasma channel that is dug by the primary laser pulse(P. Monot et al.),* Phys. Rev. Lett. 74,* 2953 (1995).* or preformed by a secondary pulse.(H.M. Milchberg et al.),* Phys. Plasmas 3,* 2149 (1996).* For most scattering angles the partial reflection of Stokes radiation by the channel walls significantly alters the two-dimensional evolution of SRS.(C.J. McKinstrie et al.),* Phys. Rev. E 51,* 3752 (1995).*^,*(C.J. McKinstrie and E.J. Turano, to be published in Physics of Plasmas.)* We extend a previous analysis of sideward SRS(C.J. McKinstrie, A.V. Kanaev, and E.J. Turano, to be published in Physical Review E.)* to include all scattering angles. The enhancement of SRS growth is greatest for near-backward and near-forward scattering because the Stokes rays strike the channel walls at grazing incidence and are reflected completely. In this presentation we summarize our complicated exact results and describe a simple eigenmode model which asymptotically reproduces the exact results. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460.

  8. Sheaths: A Comparison of Magnetospheric, ICME, and Heliospheric Sheaths

    NASA Technical Reports Server (NTRS)

    Sibeck, D. G.; Richardson, J. D.; Liu, W.

    2007-01-01

    When a supersonic flow encounters an obstacles, shocks form to divert the flow around the obstacle. The region between the shock and the obstacle is the sheath, where the supersonic flow is compressed, heated, decelerated, and deflected. Supersonic flows, obstacles, and thus sheaths are observed on many scales throughout the Universe. We compare three examples seen in the heliosphere, illustrating the interaction of the solar wind with obstacles of three very different scales lengths. Magnetosheaths form behind planetary bow shocks on scales ranging from tens to 100 planetary radii. ICME sheath form behind shocks driven by solar disturbances on scale lengths of a few to tens of AU. The heliosheath forms behind the termination shock due to the obstacle presented by the interstellar medium on scale lengths of tens to a hundred AU. Despite this range in scales some common features have been observed. Magnetic holes, possibly due to mirror mode waves, have been observed in all three of these sheaths. Plasma depletion layers are observed in planetary and ICME sheaths. Other features observed in some sheaths are wave activity (ion cyclotron, plasma), energetic particles, transmission of Alfven waves/shocks, tangential discontinuities turbulence behind quasi-parallel shocks, standing slow mode waves, and reconnection on the obstacle boundary. We compare these sheath regions, discussing similarities and differences and how these may relate to the scale lengths of these regions.

  9. Role of Parallel and Oblique Ion-Cyclotron Waves in Heating Ions in an Inhomogeneous Expanding Solar Wind Plasma

    NASA Astrophysics Data System (ADS)

    Ofman, L.; Ozak, N. O.; Vinas, A. F.

    2014-12-01

    In-situ observations of fast solar wind streams at distances of 0.29 AU and beyond by Helios and recently by MESSENGER, and at ~1 AU by STEREO, ACE, and Wind spacecraft provide direct evidence for the presence of turbulent Alfvén wave spectrum and of left-hand polarized ion-cyclotron waves as well as He++ - proton drift in the solar wind plasma. The waves and the super-Alfvénic drift can produce temperature anisotropies by resonant absorption and perpendicular heating of the ions. Measurements indicate that proton velocity distributions are generally non-Maxwellian with evidence for beams, while remote sensing observations of coronal holes have shown that heavy ions are hotter than protons with a temperature anisotropy greater than one (Ti,perp> Ti,||). In addition to the anisotropy, it is expected that the solar wind will be inhomogeneous on decreasing scales approaching the Sun. Here we use a 2.5 D hybrid code and extend previous work to study the heating of solar wind ions (H+, He+) in an inhomogeneous plasma background. We explore the effects of an initial ion drift and of a turbulent wave spectrum on the perpendicular ion heating and cooling and on the spectrum of the magnetic fluctuations in the inhomogeneous background solar wind. Using the 2D hybrid model we find that inhomogeneities in the plasma generate significant power of oblique waves in the solar wind plasma, in addition to enhanced heating compared to the homogenous solar wind case. We find that the cooling effect due to the solar wind expansion is only significant when sub-Alfvénic drifts are explored. On the other hand, the cooling is not significant in the presence of a super-Alfvénic drift, and it is even less significant when we include an inhomogeneous background density. We are able to reproduce the ion temperature anisotropy seen in observations and previous models and find that small-scale inhomogeneities in the inner heliosphere can have a significant impact on resonant wave ion

  10. Oblique Stimulated Raman Scattering of a Short Laser Pulse in a Plasma Channel

    SciTech Connect

    Turano, E.J.; McKinstrie, C.J.

    2000-02-22

    The spatiotemporal evolution of parametric instabilities such as stimulated Raman scattering is studied analytically in time and two spatial dimensions. Initial and boundary conditions are chosen to represent the entrance, propagation, and exit of a laser pulse of finite extent as it progresses through a homogeneous collisional plasma channel. For most scattering angles daughter wave growth is enhanced by lateral reflections within the channel. At late times the two-dimensional interaction approaches a one-dimensional damped mode in which the dissipative loss from lateral transmission of the Stokes wave through the channel boundaries is equivalent to an overall damping of the Stokes amplitudes within the channel.

  11. Using the cold plasma dispersion relation and whistler mode waves to quantify the antenna sheath impedance of the Van Allen Probes EFW instrument

    NASA Astrophysics Data System (ADS)

    Hartley, D. P.; Kletzing, C. A.; Kurth, W. S.; Bounds, S. R.; Averkamp, T. F.; Hospodarsky, G. B.; Wygant, J. R.; Bonnell, J. W.; Santolík, O.; Watt, C. E. J.

    2016-05-01

    Cold plasma theory and parallel wave propagation are often assumed when approximating the whistler mode magnetic field wave power from electric field observations. The current study is the first to include the wave normal angle from the Electric and Magnetic Field Instrument Suite and Integrated Science package on board the Van Allen Probes in the conversion factor, thus allowing for the accuracy of these assumptions to be quantified. Results indicate that removing the assumption of parallel propagation does not significantly affect calculated plasmaspheric hiss wave powers. Hence, the assumption of parallel propagation is valid. For chorus waves, inclusion of the wave normal angle in the conversion factor leads to significant alterations in the distribution of wave power ratios (observed/ calculated); the percentage of overestimates decreases, the percentage of underestimates increases, and the spread of values is significantly reduced. Calculated plasmaspheric hiss wave powers are, on average, a good estimate of those observed, whereas calculated chorus wave powers are persistently and systematically underestimated. Investigation of wave power ratios (observed/calculated), as a function of frequency and plasma density, reveals a structure consistent with signal attenuation via the formation of a plasma sheath around the Electric Field and Waves spherical double probes instrument. A simple, density-dependent model is developed in order to quantify this effect of variable impedance between the electric field antenna and the plasma interface. This sheath impedance model is then demonstrated to be successful in significantly improving agreement between calculated and observed power spectra and wave powers.

  12. Polarization force-induced changes in the dust sheath formation

    SciTech Connect

    Mayout, Saliha; Bentabet, Karima; Tribeche, Mouloud

    2015-09-15

    The modifications arising in the dusty plasma sheath structure due to the presence of polarization forces acting on the dust grains are investigated. The corresponding appropriate Bohm criterion for sheath formation is obtained. It is found that the critical Mach number, beyond which the dusty plasma electrostatic sheath sets in, decreases whenever the polarization effects become important. In addition, when the polarization force dominates over the electrical one, the dust plasma sheath cannot set in. This happens whenever the dust grain size exceeds a critical threshold. Moreover, the sheath electrostatic potential-gradient becomes abruptly steep, and the sheath thickness becomes broader as the polarization force effects strengthen.

  13. Maternal filarial infection: association of anti-sheath antibody responses with plasma levels of IFN-γ and IL-10.

    PubMed

    Achary, K G; Mandal, N N; Mishra, S; Sarangi, S S; Kar, S K; Satapathy, A K; Bal, M S

    2013-04-01

    Maternal filarial infection influences the risk of acquiring infection and development of immunity in children. Here we have analysed the blood samples of 60 mothers (24 infected and 36 uninfected) and their corresponding cord bloods to assess the impact of maternal infection on the anti-sheath antibodies and cytokine production in neonates born from them. About 69·4% of non-infected mothers and their cord bloods showed the presence of anti-sheath antibodies, while only 16·6% of the cord bloods from infected mothers were positive for it. The IL-10 level was significantly high in cord bloods of infected mothers compared with non-infected mothers. At the same time the IL-10 level was also observed to be remarkably high in cord bloods of both infected and non-infected mothers negative for anti-sheath antibody. In contrast, IFN-γ levels were significantly high in cord bloods of non-infected mothers compared with infected mothers and the increment was prominent in cord bloods of both infected and non-infected mothers positive for anti-sheath antibody. The study reveals that the presence or absence of anti-sheath antibodies in association with cytokines skews the filarial specific immunity to either Th1 or Th2 responses in neonates. This may affect the natural history of filarial infection in early childhood. PMID:23343479

  14. Oblique propagation of longitudinal waves in magnetized spin-1/2 plasmas: Independent evolution of spin-up and spin-down electrons

    SciTech Connect

    Andreev, Pavel A. Kuz’menkov, L.S.

    2015-10-15

    We consider quantum plasmas of electrons and motionless ions. We describe separate evolution of spin-up and spin-down electrons. We present corresponding set of quantum hydrodynamic equations. We assume that plasmas are placed in an uniform external magnetic field. We account different occupation of spin-up and spin-down quantum states in equilibrium degenerate plasmas. This effect is included via equations of state for pressure of each species of electrons. We study oblique propagation of longitudinal waves. We show that instead of two well-known waves (the Langmuir wave and the Trivelpiece–Gould wave), plasmas reveal four wave solutions. New solutions exist due to both the separate consideration of spin-up and spin-down electrons and different occupation of spin-up and spin-down quantum states in equilibrium state of degenerate plasmas.

  15. Large-amplitude, circularly polarized, compressive, obliquely propagating electromagnetic proton cyclotron waves throughout the Earth's magnetosheath: low plasma β conditions

    SciTech Connect

    Remya, B.; Reddy, R. V.; Lakhina, G. S.; Tsurutani, B. T.; Falkowski, B. J.; Echer, E.; Glassmeier, K.-H.

    2014-09-20

    During 1999 August 18, both Cassini and WIND were in the Earth's magnetosheath and detected transverse electromagnetic waves instead of the more typical mirror-mode emissions. The Cassini wave amplitudes were as large as ∼14 nT (peak to peak) in a ∼55 nT ambient magnetic field B {sub 0}. A new method of analysis is applied to study these waves. The general wave characteristics found were as follows. They were left-hand polarized and had frequencies in the spacecraft frame (f {sub scf}) below the proton cyclotron frequency (f{sub p} ). Waves that were either right-hand polarized or had f {sub scf} > f{sub p} are shown to be consistent with Doppler-shifted left-hand waves with frequencies in the plasma frame f{sub pf} < f{sub p} . Thus, almost all waves studied are consistent with their being electromagnetic proton cyclotron waves. Most of the waves (∼55%) were found to be propagating along B {sub 0} (θ{sub kB{sub 0}}<30{sup ∘}), as expected from theory. However, a significant fraction of the waves were found to be propagating oblique to B {sub 0}. These waves were also circularly polarized. This feature and the compressive ([B {sub max} – B {sub min}]/B {sub max}, where B {sub max} and B {sub min} are the maximum and minimum field magnitudes) nature (ranging from 0.27 to 1.0) of the waves are noted but not well understood at this time. The proton cyclotron waves were shown to be quasi-coherent, theoretically allowing for rapid pitch-angle transport of resonant protons. Because Cassini traversed the entire subsolar magnetosheath and WIND was in the dusk-side flank of the magnetosheath, it is surmised that the entire region was filled with these waves. In agreement with past theory, it was the exceptionally low plasma β (0.35) that led to the dominance of the proton cyclotron wave generation during this interval. A high-speed solar wind stream ((V{sub sw} ) = 598 km s{sup –1}) was the source of this low-β plasma.

  16. Effects of obliqueness and strong electrostatic interaction on linear and nonlinear propagation of dust-acoustic waves in a magnetized strongly coupled dusty plasma

    SciTech Connect

    Shahmansouri, M.; Mamun, A. A.

    2014-03-15

    Linear and nonlinear propagation of dust-acoustic waves in a magnetized strongly coupled dusty plasma is theoretically investigated. The normal mode analysis (reductive perturbation method) is employed to investigate the role of ambient/external magnetic field, obliqueness, and effective electrostatic dust-temperature in modifying the properties of linear (nonlinear) dust-acoustic waves propagating in such a strongly coupled dusty plasma. The effective electrostatic dust-temperature, which arises from strong electrostatic interactions among highly charged dust, is considered as a dynamical variable. The linear dispersion relation (describing the linear propagation characteristics) for the obliquely propagating dust-acoustic waves is derived and analyzed. On the other hand, the Korteweg-de Vries equation describing the nonlinear propagation of the dust-acoustic waves (particularly, propagation of dust-acoustic solitary waves) is derived and solved. It is shown that the combined effects of obliqueness, magnitude of the ambient/external magnetic field, and effective electrostatic dust-temperature significantly modify the basic properties of linear and nonlinear dust-acoustic waves. The results of this work are compared with those observed by some laboratory experiments.

  17. Enhancing Micro-Cathode Arc Thruster (muCAT) Plasma Generation to Analyze Magnetic Field Angle Effects on Sheath Formation in Hall Thrusters

    NASA Astrophysics Data System (ADS)

    Lukas, Joseph Nicholas

    Using a Delta IV or Atlas V launch vehicle to send a payload into Low Earth Orbit can cost between 13,000 and 14,000 per kilogram. With payloads that utilize a propulsion system, maximizing the efficiency of that propulsion system would not only be financially beneficial, but could also increase the range of possible missions and allow for a longer mission lifetime. This dissertation looks into efficiency increases in the Micro-Cathode Arc Thruster (muCAT) and Hall Thruster. The muCAT is an electric propulsion device that ablates solid cathode material, through an electrical arc discharge, to create plasma and ultimately produce thrust. About 90% of the arc discharge current is conducted by electrons, which go toward heating the anode and contribute very little to thrust, with only the remaining 10% going toward thrust in the form of ion current. I will discuss the results of an experiment in which electron heating on a low melting point anode was shown to increase ion current, which theoretically should increase thrust levels at low frequencies. Another feature of the muCAT is the use of an external magnetic solenoid which increases thrust, ion current, and causes uniform cathode erosion. An experiment has shown that efficiency can also be increased by removing the external magnetic field power supply and, instead, utilizing the residual arc current to power the magnetic solenoid. A Hall Thruster is a type of electric propulsion device that accelerates ions across an electric potential between an anode and magnetically trapped electrons. The limiting factor in Hall Thruster operation is the lifetime of the wall material. During operation, a positively charged layer forms over the surface of the walls, known as a plasma sheath, which contributes to wall erosion. Therefore, by reducing or eliminating the sheath layer, Hall Thruster operational lifetime can increase. Computational modeling has shown that large magnetic field angles and large perpendicular electric

  18. Electron acceleration based on a laser pulse propagating through a plasma in the simultaneous presence of a helical wiggler and an obliquely applied external magnetic field

    NASA Astrophysics Data System (ADS)

    Gashti, M. A.; Jafari, S.

    2016-06-01

    Electron acceleration based on a laser pulse propagating through plasma channel has been studied in the simultaneous presence of a helical magnetic wiggler and an obliquely applied external magnetic field. A numerical study of electron energy and electron trajectory has been made using the fourth-order Runge-kutta method. Numerical results indicate that electron energy increases with decreasing θ -angle of the obliquely external magnetic field. Besides, it increases with increasing the amplitude of the obliquely magnetic field. It is also found that the electron attains a higher energy at shorter distances for higher amplitude of the wiggler field Ωw . Therefore, employing a magnetic wiggler field is very beneficial for electron acceleration in short distances. Further new results reveal that in the absence of the wiggler field (Ωw=0) , the electron energy increases with increasing the laser intensity, whereas in the presence of the wiggler field (Ωwneq0) , the electron energy increases with decreasing the laser intensity. As a result, employing a wiggler magnetic field in the laser-based electron accelerators can be worthwhile in the design of table top accelerators and it can enhance the electron energy at lower laser intensities.

  19. Modeling Sheaths in DC Discharges

    NASA Astrophysics Data System (ADS)

    Robertson, Scott

    2014-10-01

    Textbook presentations on sheaths are often limited to a discussion of Bohm's criterion because more detailed analysis results in equations that can be solved only by numerical methods. There are both fluid and kinetic models for sheaths that can be solved by packaged numerical integration routines in a mathematical spreadsheet such as Mathematica, Matlab, or Mathcad. The potential profiles and the currents for sheaths at boundaries usually have monotonic profiles that are easily modeled using a Boltzmann distribution for electrons and for ions using the fluid momentum equation and the continuity equation with a source term describing plasma production. Additional ion species and bi-Maxwellian electron distributions are easily included. Virtual cathodes may form above emissive surfaces which divide the distribution function of emitted electrons into a passing population and a reflected population that can be modeled only by a kinetic approach. For sheaths at inserted objects such as probes and dust particles, it is customary to prescribe the plasma characteristics at infinity, to ignore creation of new plasma by ionization, and to solve for the radial variation of the density near the object and for the current collected by the object. A kinetic model is required for sheaths at inserted objects because the distribution function must be divided into passing particles and collected particles.

  20. Effects of electron emission on sheath potential

    NASA Astrophysics Data System (ADS)

    Dow, Ansel; Khrabrov, Alexander; Kaganovich, Igor; Schamis, Hanna

    2015-11-01

    We investigate the potential profile of a sheath under the influence of surface electron emission. The plasma and sheath profiles are simulated using the Large Scale Plasma (LSP) particle-in-cell code. Using one dimensional models we corroborate the analytical relationship between sheath potential and plasma electron and emitted electron temperatures derived earlier. This work was made possible by funding from the Department of Energy for the Summer Undergraduate Laboratory Internship (SULI) program. This work is supported by the US DOE Contract No. DE-AC02-09CH11466.

  1. True asymptotic plasma-sheath matching with an asymptotically correct collisional presheath. Final report, 1 September 1985-31 October 1988

    SciTech Connect

    Main, G.L.

    1989-06-30

    The work on plasma presheaths, which form a transition region between the collisionless electrode sheaths and the plasma, is directed toward the problems of the Thermionic Energy Converter (TEC). A schematic of a TEC is shown in a reactor core for space power applications. Cesium is put into the gap between the emitter and collector for two purposes: First, to ionize and neutralize the space charge so that a useful electron current density can pass (10 - 100 amps/square cm), and second to reduce the electrode work functions by adsorption of cesium. Of the plasma physics of the cesium filled gap of the TEC, the plasma-electrode interactions are the most significant part because these regions form boundary conditions which control the plasma density and temperatures of the entire gap. Thus the research under this grant has been directed toward the study of collisional presheaths which form the layer adjacent to an electrode on the order of one ion mean free path thick. However, the research pursued under this grant is not limited in applicability to TECs but is on interest to plasma-surface interactions in general. Other applications include electric propulsion where electrode erosion is a problem and not fully understood and more generally any plasma-surface interaction. This report included the asymptotic presheath theory developed, and is preceded by the basic theory of the Thermionic Energy Converter (TEC) and is followed by the application of the theory to a time dependent model of the TEC in the program called TEC. As shown in the TEC results, the agreement with experiment is good except in the low current regime of the TEC where an unexplained disagreement remains. This is still a puzzle.

  2. Characteristics of plasma plume expansion from Al target induced by oblique incidence of 1064 and 355 nm nanosecond Nd : YAG laser

    NASA Astrophysics Data System (ADS)

    Liu, Tianhang; Gao, Xun; Hao, Zuoqiang; Liu, Zehao; Lin, Jingquan

    2013-12-01

    Evolution of a plasma plume from an Al target ablated with a nanosecond 1064 and 355 nm laser respectively under oblique incidence in air is studied using the time-resolved shadowgraph imaging technique. The characteristics of plasma plume expansion with different focusing conditions (focal point on, ahead of and after the target surface) are experimentally investigated. Experimental results show that the evolution of the plasma plume is strongly influenced by air breakdown which occurs prior to the laser beam reaching the target. Without the occurrence of air breakdown, the temporal evolution of the Al plasma plume with both UV and IR ablation laser wavelengths shows the plume expansion with an ellipsoid-shaped plume front travelling mainly against the incoming laser beam due to the formation of a laser-supported detonation wave at the initial stage of laser ablation, and then the shape of the plume front turns into a sphere. Experimental results also show that a higher portion of the laser pulse energy reaches the target surface at UV laser wavelength than that of an IR laser due to the higher penetrating ability of the UV laser wavelength to the plasma.

  3. Effects of oblique wave propagation on the nonlinear plasma resonance in the two-dimensional channel of the Dyakonov-Shur detector

    NASA Astrophysics Data System (ADS)

    Rupper, Greg; Rudin, Sergey; Crowne, Frank J.

    2012-12-01

    In the Dyakonov-Shur terahertz detector the conduction channel of a heterostructure High Electron Mobility Transistor (HEMT) is used as a plasma wave resonator for density oscillations in electron gas. Nonlinearities in the plasma wave propagation lead to a constant source-to-drain voltage, providing the detector output. In this paper, we start with the quasi-classical Boltzmann equation and derive the hydrodynamic model with temperature dependent transport coefficients for a two-dimensional viscous flow. This derivation allows us to obtain the parameters for the hydrodynamic model from the band-structure of the HEMT channel. The treatment here also includes the energy balance equation into the analysis. By numerical solution of the hydrodynamic equations with a non-zero boundary current we evaluate the detector response function and obtain the temperature dependence of the plasma resonance. The present treatment extends the theory of Dyakonov-Shur plasma resonator and detector to account for the temperature dependence of viscosity, the effects of oblique wave propagation on detector response, and effects of boundary current in two-dimensional flow on quality of the plasma resonance. The numerical results are given for a GaN channel. We also investigated a stability of source to drain flow and formation of shock waves.

  4. Effect of obliqueness and external magnetic field on the characteristics of dust acoustic solitary waves in dusty plasma with two-temperature nonthermal ions

    NASA Astrophysics Data System (ADS)

    Sabetkar, Akbar; Dorranian, Davoud

    2015-03-01

    In this paper, a theoretical investigation has been made of obliquely propagating dust acoustic solitary wave (DASW) structures in a cold magnetized dusty plasma consisting of a negatively charged dust fluid, electrons, and two different types of nonthermal ions. The Zakharov-Kuznetsov (ZK) and modified Zakharov-Kuznetsov (MZK) equations, describing the small but finite amplitude DASWs, are derived using a reductive perturbation method. The combined effects of the external magnetic field, obliqueness (i.e. the propagation angle), and the presence of second component of nonthermal ions, which are found to significantly modify the basic features (viz. amplitude, width, polarity) of DASWs, are explicitly examined. The results show that the external magnetic field, the propagation angle, and the second component of nonthermal ions have strong effects on the properties of dust acoustic solitary structures. The solitary waves may become associated with either positive potential or negative potential in this model. As the angle between the direction of external magnetic field and the propagation direction of solitary wave increases, the amplitude of the solitary wave (for both positive potential and negative potential) increases. With changing this angle, the width of solitary wave shows a maximum. The magnitude of the external magnetic field has no direct effect on the solitary wave amplitude. However, with decreasing the strength of magnetic field, the width of DASW increases.

  5. Analysis of Electromagnetic Wave Propagation in a Magnetized Re-Entry Plasma Sheath Via the Kinetic Equation

    NASA Technical Reports Server (NTRS)

    Manning, Robert M.

    2009-01-01

    Based on a theoretical model of the propagation of electromagnetic waves through a hypersonically induced plasma, it has been demonstrated that the classical radiofrequency communications blackout that is experienced during atmospheric reentry can be mitigated through the appropriate control of an external magnetic field of nominal magnitude. The model is based on the kinetic equation treatment of Vlasov and involves an analytical solution for the electric and magnetic fields within the plasma allowing for a description of the attendant transmission, reflection and absorption coefficients. The ability to transmit through the magnetized plasma is due to the magnetic windows that are created within the plasma via the well-known whistler modes of propagation. The case of 2 GHz transmission through a re-entry plasma is considered. The coefficients are found to be highly sensitive to the prevailing electron density and will thus require a dynamic control mechanism to vary the magnetic field as the plasma evolves through the re-entry phase.

  6. A micro-machined sensor for in situ characterization of plasma sheath potentials and ion energy distributions

    SciTech Connect

    Jewett, R.; Blain, M.; Anderson, H.M. |

    1992-12-01

    A micromachined array of ion lenses was fabricated and used to characterize several plasma chemistries. Although present measurement tools, such as Langmuir Probes, can provide insight into potentials present in laboratory plasmas, as well as useful density measurements, they also significantly change the characteristics of plasma around the probe. This unfortunate quality renders them unsuitable as a production diagnostics tool, and hinders their effectiveness as a laboratory instrument. The micromachined array of 2.5 million ion lenses provides a non-intrusive view of ion energy, current, and potential on plasma boundaries. Preliminary tests in argon and CF{sub 4} plasmas using the GEC Reference Cell are discussed. Comparisons are made to a simple computer model and future changes to the measurement tool are suggested.

  7. Complete parametrization of the plasma-sheath transition and I-V curves for a cylindrical or spherical Langmuir probe according to the features of the probe, simultaneously including geometry, ionization and collisions

    NASA Astrophysics Data System (ADS)

    Morales Crespo, R.

    2015-08-01

    This paper solves and analyses the complete characterization of the plasma-sheath transition and the characteristic I-V curves of an active and collisional plasma close to a cylindrical or spherical wall considering a wide range of the parameter which describe the model to be useful for experimental measures. Despite the difficulty of including the three possible pre-sheath mechanisms, this characterization is obtained from a self-consistent model using three easily measurable parameters, namely the electric potential of the wall, the positive ion current collected by the wall, and the radius of the wall. These parameters are easy to measure and facilitate the diagnosis of plasmas from an experimental point of view.

  8. Bohm's criterion in a collisional magnetized plasma with thermal ions

    SciTech Connect

    Hatami, M. M.; Shokri, B.

    2012-08-15

    Using the hydrodynamic model and considering a planar geometry, the modified Bohm's sheath criterion is investigated in a magnetized, collisional plasma consisting of electron and positive ions with finite temperature. It is assumed that the singly charged positive ions enter into the sheath region obliquely, i.e., their velocity at the sheath edge is not normal to the wall, and the electron densities obey Boltzmann relations. It is shown that there are both upper and lower limit for the Bohm entrance velocity of ions in this case and both of these limits depend on the magnitude and direction of the applied magnetic field. To determine the accuracy of our derived generalized Bohm's criterion, it reduced to some familiar physical condition. Also, using this generalized Bohm's criterion, the behavior of the electron and positive ion density distributions are studied in the sheath region.

  9. APPARATUS FOR SHEATHING RODS

    DOEpatents

    Ford, W.K.; Wyatt, M.; Plail, S.

    1961-08-01

    An arrangement is described for sealing a solid body of nuclear fuel, such as a uranium metal rod, into a closelyfitting thin metallic sheath with an internal atmosphere of inert gas. The sheathing process consists of subjecting the sheath, loaded with the nuclear fuel body, to the sequential operations of evacuation, gas-filling, drawing (to entrap inert gas and secure close contact between sheath and body), and sealing. (AEC)

  10. Two dimensional investigation of ion acoustic waves reflection from the sheath

    SciTech Connect

    Cartwright, K.L.; Birdsall, C.K.

    1995-12-31

    Preliminary results show that oblique ion waves propagate from the bulk plasma into and all the way through the sheath in both 1D and 2D simulation. These waves are launched from one side of the system with a AC voltage or a current source with a frequency less than the ion plasma frequency. The one and initial two dimensional PIC simulations show the details of densities, potentials, fields, particle moments and time-distance plots of the average density minus the instantaneous density. From the time-distance plot the direction and magnitude of the ion acoustic wave is measured. From this the coefficients of reflection and transmission as a function of the incident angle is calculated. The observations are compared with laboratory experiments and theory.

  11. Theory of the electron sheath and presheath

    SciTech Connect

    Scheiner, Brett; Baalrud, Scott D.; Yee, Benjamin T.; Hopkins, Matthew M.; Barnat, Edward V.

    2015-12-30

    Here, electron sheaths are commonly found near Langmuir probes collecting the electron saturation current. The common assumption is that the probe collects the random flux of electrons incident on the sheath, which tacitly implies that there is no electron presheath and that the flux collected is due to a velocity space truncation of the electron velocity distribution function (EVDF). This work provides a dedicated theory of electron sheaths, which suggests that they are not so simple. Motivated by EVDFs observed in particle-in-cell(PIC) simulations, a 1D model for the electron sheath and presheath is developed. In the model, under low temperature plasma conditions (Te >> Ti), an electron pressure gradient accelerates electrons in the presheath to a flow velocity that exceeds the electron thermal speed at the sheath edge. This pressure gradient generates large flow velocities compared to what would be generated by ballistic motion in response to the electric field. It is found that in many situations, under common plasma conditions, the electron presheath extends much further into the plasma than an analogous ion presheath. PIC simulations reveal that the ion density in the electron presheath is determined by a flow around the electron sheath and that this flow is due to 2D aspects of the sheath geometry. Simulations also indicate the presence of ion acoustic instabilities excited by the differential flow between electrons and ions in the presheath, which result in sheath edge fluctuations. The 1D model and time averaged PIC simulations are compared and it is shown that the model provides a good description of the electron sheath and presheath.

  12. Theory of the electron sheath and presheath

    DOE PAGESBeta

    Scheiner, Brett; Baalrud, Scott D.; Yee, Benjamin T.; Hopkins, Matthew M.; Barnat, Edward V.

    2015-12-30

    Here, electron sheaths are commonly found near Langmuir probes collecting the electron saturation current. The common assumption is that the probe collects the random flux of electrons incident on the sheath, which tacitly implies that there is no electron presheath and that the flux collected is due to a velocity space truncation of the electron velocity distribution function (EVDF). This work provides a dedicated theory of electron sheaths, which suggests that they are not so simple. Motivated by EVDFs observed in particle-in-cell(PIC) simulations, a 1D model for the electron sheath and presheath is developed. In the model, under low temperaturemore » plasma conditions (Te >> Ti), an electron pressure gradient accelerates electrons in the presheath to a flow velocity that exceeds the electron thermal speed at the sheath edge. This pressure gradient generates large flow velocities compared to what would be generated by ballistic motion in response to the electric field. It is found that in many situations, under common plasma conditions, the electron presheath extends much further into the plasma than an analogous ion presheath. PIC simulations reveal that the ion density in the electron presheath is determined by a flow around the electron sheath and that this flow is due to 2D aspects of the sheath geometry. Simulations also indicate the presence of ion acoustic instabilities excited by the differential flow between electrons and ions in the presheath, which result in sheath edge fluctuations. The 1D model and time averaged PIC simulations are compared and it is shown that the model provides a good description of the electron sheath and presheath.« less

  13. Theory of the electron sheath and presheath

    NASA Astrophysics Data System (ADS)

    Scheiner, Brett; Baalrud, Scott D.; Yee, Benjamin T.; Hopkins, Matthew M.; Barnat, Edward V.

    2015-12-01

    Electron sheaths are commonly found near Langmuir probes collecting the electron saturation current. The common assumption is that the probe collects the random flux of electrons incident on the sheath, which tacitly implies that there is no electron presheath and that the flux collected is due to a velocity space truncation of the electron velocity distribution function (EVDF). This work provides a dedicated theory of electron sheaths, which suggests that they are not so simple. Motivated by EVDFs observed in particle-in-cell (PIC) simulations, a 1D model for the electron sheath and presheath is developed. In the model, under low temperature plasma conditions ( Te≫Ti ), an electron pressure gradient accelerates electrons in the presheath to a flow velocity that exceeds the electron thermal speed at the sheath edge. This pressure gradient generates large flow velocities compared to what would be generated by ballistic motion in response to the electric field. It is found that in many situations, under common plasma conditions, the electron presheath extends much further into the plasma than an analogous ion presheath. PIC simulations reveal that the ion density in the electron presheath is determined by a flow around the electron sheath and that this flow is due to 2D aspects of the sheath geometry. Simulations also indicate the presence of ion acoustic instabilities excited by the differential flow between electrons and ions in the presheath, which result in sheath edge fluctuations. The 1D model and time averaged PIC simulations are compared and it is shown that the model provides a good description of the electron sheath and presheath.

  14. Axial magnetic field and toroidally streaming fast ions in the dense plasma focus are natural consequences of conservation laws in the curved axisymmetric geometry of the current sheath

    NASA Astrophysics Data System (ADS)

    Auluck, S. K. H.

    2014-10-01

    Direct measurement of axial magnetic field in the PF-1000 dense plasma focus (DPF), and its reported correlation with neutron emission, call for a fresh look at previous reports of existence of axial magnetic field component in the DPF from other laboratories, and associated data suggesting toroidal directionality of fast ions participating in fusion reactions, with a view to understand the underlying physics. In this context, recent work dealing with application of the hyperbolic conservation law formalism to the DPF is extended in this paper to a curvilinear coordinate system, which reflects the shape of the DPF current sheath. Locally unidirectional shock propagation in this coordinate system enables construction of a system of 7 one-dimensional hyperbolic conservation law equations with geometric source terms, taking into account all the components of magnetic field and flow velocity. Rankine-Hugoniot jump conditions for this system lead to expressions for the axial magnetic field and three components of fluid velocity having high ion kinetic energy.

  15. Axial magnetic field and toroidally streaming fast ions in the dense plasma focus are natural consequences of conservation laws in the curved axisymmetric geometry of the current sheath

    SciTech Connect

    Auluck, S. K. H.

    2014-10-15

    Direct measurement of axial magnetic field in the PF-1000 dense plasma focus (DPF), and its reported correlation with neutron emission, call for a fresh look at previous reports of existence of axial magnetic field component in the DPF from other laboratories, and associated data suggesting toroidal directionality of fast ions participating in fusion reactions, with a view to understand the underlying physics. In this context, recent work dealing with application of the hyperbolic conservation law formalism to the DPF is extended in this paper to a curvilinear coordinate system, which reflects the shape of the DPF current sheath. Locally unidirectional shock propagation in this coordinate system enables construction of a system of 7 one-dimensional hyperbolic conservation law equations with geometric source terms, taking into account all the components of magnetic field and flow velocity. Rankine-Hugoniot jump conditions for this system lead to expressions for the axial magnetic field and three components of fluid velocity having high ion kinetic energy.

  16. The Role of Plasma Membrane Aquaporins in Regulating the Bundle Sheath-Mesophyll Continuum and Leaf Hydraulics1[C][W][OPEN

    PubMed Central

    Sade, Nir; Shatil-Cohen, Arava; Attia, Ziv; Maurel, Christophe; Boursiac, Yann; Kelly, Gilor; Granot, David; Yaaran, Adi; Lerner, Stephen; Moshelion, Menachem

    2014-01-01

    Our understanding of the cellular role of aquaporins (AQPs) in the regulation of whole-plant hydraulics, in general, and extravascular, radial hydraulic conductance in leaves (Kleaf), in particular, is still fairly limited. We hypothesized that the AQPs of the vascular bundle sheath (BS) cells regulate Kleaf. To examine this hypothesis, AQP genes were silenced using artificial microRNAs that were expressed constitutively or specifically targeted to the BS. MicroRNA sequences were designed to target all five AQP genes from the PLASMA MEMBRANE-INTRINSIC PROTEIN1 (PIP1) subfamily. Our results show that the constitutively silenced PIP1 (35S promoter) plants had decreased PIP1 transcript and protein levels and decreased mesophyll and BS osmotic water permeability (Pf), mesophyll conductance of CO2, photosynthesis, Kleaf, transpiration, and shoot biomass. Plants in which the PIP1 subfamily was silenced only in the BS (SCARECROW:microRNA plants) exhibited decreased mesophyll and BS Pf and decreased Kleaf but no decreases in the rest of the parameters listed above, with the net result of increased shoot biomass. We excluded the possibility of SCARECROW promoter activity in the mesophyll. Hence, the fact that SCARECROW:microRNA mesophyll exhibited reduced Pf, but not reduced mesophyll conductance of CO2, suggests that the BS-mesophyll hydraulic continuum acts as a feed-forward control signal. The role of AQPs in the hierarchy of the hydraulic signal pathway controlling leaf water status under normal and limited-water conditions is discussed. PMID:25266632

  17. Oblique dust density waves

    NASA Astrophysics Data System (ADS)

    Piel, Alexander; Arp, Oliver; Menzel, Kristoffer; Klindworth, Markus

    2007-11-01

    We report on experimental observations of dust density waves in a complex (dusty) plasma under microgravity. The plasma is produced in a radio-frequency parallel-plate discharge (argon, p=15Pa, U=65Vpp). Different sizes of dust particles were used (3.4 μm and 6.4μm diameter). The low-frequency (f 11Hz) dust density waves are naturally unstable modes, which are driven by the ion flow in the plasma. Surprisingly, the wave propagation direction is aligned with the ion flow direction in the bulk plasma but becomes oblique at the boundary of the dust cloud with an inclination of 60^o with respect to the plasma boundary. The experimental results are compared with a kinetic model in the electrostatic approximation [1] and a fluid model [2]. Moreover, the role of dust surface waves is discussed. [1] M. Rosenberg, J. Vac. Sci. Technol. A 14, 631 (1996) [2] A. Piel et al, Phys. Rev. Lett. 97, 205009 (2006)

  18. Particle-in-cell simulations of sheath formation around biased interconnectors in a low-earth-orbit plasma

    NASA Technical Reports Server (NTRS)

    Thiemann, H.; Schunk, R. W.

    1990-01-01

    The interaction between satellite solar arrays and the LEO plasma is presently studied with particle-in-cell simulations in which an electrical potential was suddenly applied to the solar cell interconnector. The consequent temporal response was followed for the real O(+)-electron mass ratio in the cases of 100- and 250-V solar cells, various solar cell thicknesses, and solar cells with secondary electron emission. Larger applied potentials and thinner solar cells lead to greater initial polarization surface charges, and therefore longer discharging and shielding times. When secondary electron emission from the cover glass is brought to bear, however, the potential structure is nearly planar, allowing constant interaction between plasma electrons and cover glass; a large fraction of the resulting secondary electrons is collected by the interconnector, constituting an order-of-magnitude increase in collected current.

  19. Modeling and Simulation of Plasma Edge Behavior

    SciTech Connect

    Charles K. Birdsall, Professor

    2002-02-14

    A typical steady state plasma edge consists of a strongly nonneutral sheath region, starting from the wall, joined to a quasineutral pre-sheath region, & then becoming the plasma bulk, which is essentially neutral. In particular, we find that the sheath/pre-sheath boundary not static, but dynamic, both in a stable thermal plasma, with considerable sheath boundary motion and heating.

  20. Quantitative modelling of the electrostatic sheath around a photo-electron emitting spacecraft and of the possible influence on magnetospheric plasma instruments

    NASA Astrophysics Data System (ADS)

    Hilgers, A.; Thiebault, B.; Forest, J.; Escoubet, P.; Fehringer, M.; Laakso, H.

    2003-04-01

    It is well known that photo-electrons emitted from sunlit surfaces in space may affect plasma measurements by several processes, e.g., via the resulting (i) surface potential, (ii) space charge effects, or/and (iii) direct propagation to detectors [e.g. Szita et al., 2001; Pedersen et al., 1984]. We have used a fully kinetic particle-in-cell code, PicUp3D [Forest et al., 2001] which is now made available in public domain, for modelling in three dimensions the electrostatic sheath and photo-electron cloud around a conductive volume representative of a spacecraft like Cluster in a typical magnetospheric plasma environment. The model shows several features of key interest for the interpretation of the measurements and for optimizing the design of future instruments. It is found that photo-electrons fill a large volume around the spacecraft where they can dominate over the ambient environment and a significant part of photo-electrons propagates to the antisunward sector. The resulting space charge has been found to generate negative potential barriers under certain conditions. Also long wire booms which are generally used for mounting electrostatic sensors away from the influence of the spacecraft are found to induce significant transport of the spacecraft generated photo-electrons toward the boom mounted detectors. In this presentation the feature of the computer code and the results of the numerical model are reviewed and the implications for plasma instruments are discussed. Forest J., L. Eliasson, A. Hilgers, A New Spacecraft Plasma Simulation Software, PicUp3D/SPIS, ESA Special Publication, SP-476, ISBN No 92-9092-745-3, pp.515-520, ESA-ESTEC, Noordwijk, The Netherlands, 2001. Pedersen, A., C. A. Cattel, C.-G. Faelthammar, V. Formisano, P.-A. Lindqvist, F. Mozer, and R. Torbert, Quasistatic electric field measurements with spherical double probes on the GEOS and ISEE satellites, Space Sci. Rev., 37, pp 269-312, 1984. Szita, S., A. N. Fazakerley, P. J. Carter, A. M

  1. Sheaths: More complicated than you think

    SciTech Connect

    Hershkowitz, Noah

    2005-05-15

    Sheaths in low temperature collisionless and weakly collisional plasmas are often viewed as simple examples of nonlinear physics. How well do we understand them? Closer examination indicates that they are far from simple. Moreover, many predicted sheath properties have not been experimentally verified and even the appropriate 'Bohm velocity' for often encountered two-ion species plasma is unknown. In addition, a variety of sheathlike structures, e.g., double layers, can exist, and many two- and three-dimensional sheath effects have not been considered. Experimental studies of sheaths and presheaths in weakly collisional plasmas are described. A key diagnostic is emissive probes operated in the 'limit of zero emission'. Emissive probes provide a sensitive diagnostic of plasma potential with a resolution approaching 0.1 V and a spatial resolution of 0.1 cm. Combined with planar Langmuir probes and laser-induced fluorescence, they have been used to investigate a wide variety of sheath, presheath, and sheathlike structures. Our experiments have provided some answers but have also raised more questions.

  2. Accuracy of the Unified Sheath Model

    NASA Astrophysics Data System (ADS)

    Riley, Merle E.

    1997-10-01

    The Unified Sheath Model ( M. E. Riley, Sandia Labs Tech Reports SAND95-0775 UC-401 (May, 1995) and SAND96-1948 UC-401 (August, 1996)) is designed to bridge the intermediate region of ion response between the high frequency Lieberman model and the low frequency Metze, Ernie, and Oskam model. In order to make a quantitative check of the effective ion response time (inverse ion plasma radian frequency at the presheath boundary), I have compared the semi-analytic Unified Model predictions to time- and space-dependent numerical solutions of the ion fluid equations in an rf-biased plasma sheath. In so doing, one is testing the most crucial of the physical approximations made in the model. The comparisons are good and lend confidence to use of the sheath model in the simulation of rf-biased plasmas in processing applications.

  3. Theory of the Electron Sheath and Presheath

    NASA Astrophysics Data System (ADS)

    Scheiner, Brett; Baalrud, Scott; Yee, Benjamin; Hopkins, Matthew; Barnat, Edward

    2015-09-01

    Electron sheaths are commonly found near Langmuir probes collecting the electron saturation current. The common assumption is that the probe collects the random flux of electrons incident on the sheath, which tacitly implies that there is no electron presheath and that the flux collected is due to a velocity space truncation of the velocity distribution function (VDF). This work provides a dedicated theory of electron sheaths, which suggests that electron sheaths are not so simple. Motivated by VDFs observed in recent Particle-In-Cell (PIC) simulations, we develop a 1D model for the electron sheath and presheath. In the model, under low temperature plasma conditions, an electron pressure gradient accelerates electrons in the presheath to a flow velocity that exceeds the electron thermal speed at the sheath edge. This pressure gradient allows the generation of large flows compared to those that would be generated by the electric field alone. It is due to this pressure gradient that the electron presheath extends much further into the plasma (nominally by a factor of √{mi /me }) than an analogous ion presheath. Results of the model are compared with PIC simulations. This work was supported by the Office of Fusion Energy Science at the U.S. Department of Energy under contract DE-AC04-94SL85000 and by the Office of Science Graduate Student Research (SCGSR) program under Contract Number DE-AC05-06OR23100.

  4. Stability of three-dimensional obliquely propagating dust acoustic waves in dusty plasma including the polarization force effect

    NASA Astrophysics Data System (ADS)

    El-Labany, S. K.; El-Taibany, W. F.; Behery, E. E.; Zedan, N. A.

    2015-12-01

    Propagation of dust acoustic solitary waves (DASWs) in a magnetized dusty plasma consisting of extremely massive, negatively/positively charged dust fluid and Boltzmann distributed electrons and ions is studied. A nonlinear Zakharov-Kuznetsov (ZK) equation adequate for describing the solitary waves is derived by applying a reductive perturbation technique. Moreover, an extended Zakharov Kuznetsov (EZK) equation is derived at the vicinity of the critical phase velocity. The effects of the polarization force are explicitly discussed and the growth rate of the produced waves is calculated. It is found that the physical parameters have strong effects on the instability criterion as well as on the growth rate. It is noted that the phase velocity decreases as the polarization force, the effective-to-ion temperature ratio, and the ion-to-electron temperature ratio increase. Moreover, the nonlinearity coefficient and the critical phase velocity increase by increasing the polarization force. The relevance of these findings to a recent plasma experiment and astrophysical plasma observations is briefly discussed.

  5. Oblique interactions of dust density waves

    SciTech Connect

    Li Yangfang; Wang Zhehui; Hou Lujing; Jiang Ke; Thomas, Hubertus M.; Morfill, Gregor E.; Wu Dejin

    2010-06-16

    Self-excited dust density waves (DDWs) are studied in a striped electrode device. In addition to the usual perpendicularly (with respect to the electrode) propagating DDWs, which have been frequently observed in dusty plasma experiments on the ground, a low-frequency oblique mode is also observed. This low-frequency oblique DDW has a frequency much lower than the dust plasma frequency and its spontaneous excitation is observed even with a very low dust density. It is found that the low-frequency oblique mode can exist either separately or together with the usual perpendicular mode. In the latter case, a new mode arises as a result of the interactions between the perpendicular and the oblique modes. The experiments show that these three modes satisfy the wave coupling conditions in both the frequencies and the wave-vectors.

  6. Oblique interactions of dust density waves

    SciTech Connect

    Wang, Zhelchui; Li, Yang - Fang; Hou, Lujing; Jiang, Ke; Wu, De - Jin; Thomas, Hubertus M; Morfill, Gregor E

    2010-01-01

    Self-excited dust density waves (DDWs) are studied in a striped electrode device. In addition to the usual perpendicularly (with respect to the electrode) propagating DDWs, which have been frequently observed in dusty plasma experiments on the ground, a low-frequency oblique mode is also observed. This low-frequency oblique DDW has a frequency much lower than the dust plasma frequency and its spontaneous excitation is observed even with a very low dust density. It is found that the low-frequency oblique mode can exist either separately or together with the usual perpendicular mode. In the latter case, a new mode arises as a result of the interactions between the perpendicular and the oblique modes. The experiments show that these three modes satisfy the wave coupling conditions in both the frequencies and the wave-vectors.

  7. Plasma theory and simulation. Third and fourth quarter progress report, July 1-December 31, 1984

    SciTech Connect

    Birdsall, C.K.

    1984-01-01

    Several theoretical investigations are reported. These topics include: (1) oblique electron Bernstein waves; (2) the effect of large amplitude rf waves on the interchange instability; (3) one-beam Alfven ion-cyclotron instabilities of multibeam ion distribution; (4) linear mode coupling in simulations of the Alfven ion-cyclotron instability; (5) plasma-sheath region; (6) planar magnetron discharges; (7) low-alpha Pierce diode; and (8) ion-acoustic double layers. 8 refs., 37 figs.

  8. Sheath structure transition controlled by secondary electron emission

    NASA Astrophysics Data System (ADS)

    Schweigert, I. V.; Langendorf, S. J.; Walker, M. L. R.; Keidar, M.

    2015-04-01

    In particle-in-cell Monte Carlo collision (PIC MCC) simulations and in an experiment we study sheath formation over an emissive floating Al2O3 plate in a direct current discharge plasma at argon gas pressure 10-4 Torr. The discharge glow is maintained by the beam electrons emitted from a negatively biased hot cathode. We observe three types of sheaths near the floating emissive plate and the transition between them is driven by changing the negative bias. The Debye sheath appears at lower voltages, when secondary electron emission is negligible. With increasing applied voltage, secondary electron emission switches on and a first transition to a new sheath type, beam electron emission (BEE), takes place. For the first time we find this specific regime of sheath operation near the floating emissive surface. In this regime, the potential drop over the plate sheath is about four times larger than the temperature of plasma electrons. The virtual cathode appears near the emissive plate and its modification helps to maintain the BEE regime within some voltage range. Further increase of the applied voltage U initiates the second smooth transition to the plasma electron emission sheath regime and the ratio Δφs/Te tends to unity with increasing U. The oscillatory behavior of the emissive sheath is analyzed in PIC MCC simulations. A plasmoid of slow electrons is formed near the plate and transported to the bulk plasma periodically with a frequency of about 25 kHz.

  9. Oblique rotation of factors: a novel pattern recognition strategy to classify fluorescence excitation-emission matrices of human blood plasma for early diagnosis of colorectal cancer.

    PubMed

    Shahbazy, Mohammad; Vasighi, Mahdi; Kompany-Zareh, Mohsen; Ballabio, Davide

    2016-05-24

    Colorectal cancer (CRC) ranks high in both men and women, accounting for about 13% of all cancers. In this study, a novel pattern recognition strategy is proposed to improve early diagnosis of CRC through visualizing the relationship between different spectral patterns in a case-control research. Partial least squares-discriminant analysis (PLS-DA) and supervised Kohonen network (SKN) were used to classify the fluorescence excitation-emission matrices (EEMs) from 289 human blood plasma samples containing CRC patients, adenomas tumor, other non-malignant findings and healthy individuals. To obtain optimal factors, oblique rotation (OR) and genetic algorithm (GA) were used to rotate the factors by optimizing transformation matrix elements. Transformed factors were introduced to SKN to build a classification model and the model performance was examined via comparison with a common classifier; PLS-DA. Classification models were built for CRC-healthy and adenomas-healthy samples and the best results were obtained through applying GA-OR on PLS factors and introducing them to the classifiers. Non-error rates for SKN and PLS-DA models assisted with GA (for selecting more informative PLS factors) and OR were equal to 0.97 and 0.95 in cross validation and 0.93 and 0.90 for prediction of the external test set, respectively. Moreover, according to the acceptable results for adenomas-healthy cases using optimal factors, CRC can be diagnosed in early stages. Combining classifiers and optimal factors proved to be efficient for distinguishing healthy and malignant samples, and OR can significantly improve performance of the classification model. PMID:27076033

  10. Report of the Plasma Physics and Environmental Perturbation Laboratory (PPEPL) working groups. Volume 1: Plasma probes, wakes, and sheaths working group

    NASA Technical Reports Server (NTRS)

    1974-01-01

    It is shown in this report that comprehensive in-situ study of all aspects of the entire zone disturbance caused by a body in a flowing plasma resulted in a large number if requirements on the shuttle-PPEPL facility. A large amount of necessary in-situ observation can be obtained by adopting appropriate modes of performing the experiments. Requirements are indicated for worthwhile studies, of some aspects of the problems, which can be carried out effectively while imposing relatively few constraints on the early missions. Considerations for the desired growth and improvement of the PPEPL to facilitate more complete studies in later missions are also discussed. For Vol. 2, see N74-28170; for Vol# 3, see N74-28171.

  11. Vergence and facing patterns in large-scale sheath folds

    NASA Astrophysics Data System (ADS)

    Alsop, G. I.; Holdsworth, R. E.

    1999-10-01

    The careful geometric analysis of minor structural detail elucidates the relationships and evolution of associated large-scale curvilinear hinge geometries, developed during WNW-directed Caledonian thrusting exposed in Neoproterozoic Moine psammites of the Moine Nappe. Reversals in the polarity of structural facing associated with minor folding, mark the position of major sheath folds which parallel transport. Upwardly convex sheaths (closing in the direction of thrust transport) cored by older gneissose basement inliers are termed culminations, whilst those opening in the transport direction (and cored by Moine psammites) are termed depressions. Sheath folds are bisected by transport parallel and foliation normal (culmination/depression) surfaces which separate not only the reversals in facing, but also delineate zones of minor fold hinge obliquity into clockwise and anticlockwise domains relative to the transport direction. The sense of obliquity of minor Z and S folds is thus dependent on position with respect to the surfaces of culmination and depression and not the fold axial surfaces. Surfaces of culmination and depression may be superimposed on original overturned antiformal and synformal folds to produce a variety of dome (culmination on antiform), saddle (depression on antiform), inverted saddle (culmination on synform) and basin (depression on synform) configurations. The curvilinear hinges of minor folds may also be asymmetrical about the transport direction and within the plane of the regional foliation to define patterns of fold hinge-line vergence. Classical concepts of fold limb vergence may thus relate to larger antiformal and synformal hinges, whilst the fold hinge-line vergence defines major curvilinear hinges associated with culminations and depressions. Major sheath folds may therefore be interpreted in terms of both minor fold hinge-line and limb vergence, coupled with fold axis obliquity and reversals in the polarity of structural facing. The

  12. Oblique effect in stereopsis?

    NASA Astrophysics Data System (ADS)

    Davis, Elizabeth T.; King, Robert A.; Anoskey, Alana M.

    1992-08-01

    Contrast thresholds are lower for detection of a vertical pattern than for an obliquely-oriented pattern. Is there an analogous oblique effect for the depth threshold of a stereoscopic luminance pattern? If so, why? Are the causes different from those for an oblique effect with monocular vision? To explore these issues, we used stereoscopic blurry bar (D6) luminance patterns with a peak spatial frequency of 2 or 4 cycles/degree (cpd) and either a vertical or an oblique orientation. We obtained psychometric functions for data obtained from a method of constant stimuli procedure, using 100 forced-choice trials for each datum. For each of three observers we estimated stereoacuity with a maximum-likelihood curve-fitting procedure. Subjects showed better stereoacuity for the vertical spatial patterns than for the oblique patterns. Some possible causes are that for oblique patterns (unlike vertical patterns) (1) the total vertical extent of the pattern is shrunk by a factor of sin((theta) ), where (theta) equals 90 degree(s) for vertical; (2) the pattern is 'stretched out' in the horizontal direction by a factor of csc((theta) ); (3) there are vertical as well as horizontal retinal disparities. Perhaps the resulting sparseness of horizontal disparity information or the potential vertical disparities in the oblique patterns reduce stereoacuity. To disentangle these causes, we used several different experimental conditions (e.g., elongation of oblique patterns) run in randomized blocks of trials. We will discuss these results and implications for stereopsis.

  13. Absence of Debye Sheaths Due to Secondary Electron Emission

    SciTech Connect

    M.D. Campanell, A. Khrabrov and I. D. Kaganovich

    2012-05-11

    A bounded plasma where the hot electrons impacting the walls produce more than one secondary on average is studied via particle-in-cell simulation. It is found that no classical Debye sheath or space-charge limited sheath exists. Ions are not drawn to the walls and electrons are not repelled. Hence the unconfined plasma electrons travel unobstructed to the walls, causing extreme particle and energy fluxes. Each wall has a positive charge, forming a small potential barrier or "inverse sheath" that pulls some secondaries back to the wall to maintain the zero current condition.

  14. Why ions enter the sheath entrance at supersonic speed?

    NASA Astrophysics Data System (ADS)

    Tang, Xianzhu; Guo, Zehua

    2015-11-01

    In a boundary plasma of a fusion device, the sheath Knudsen number, which is defined as the ratio of the plasma mean-free-path and the plasma Debye length, is much greater than unity, so one anticipates a collisionless sheath, even though the overall boundary plasma in the scrape-off layer is collisional. This is supposed to be the regime for which the Bohm criteria for the ion entry flow at the sheath entrance, v >=cs with cs the sound speed, is usually satisfied at the equal sign. But numerical simulations using first-principles particle-in-cell codes tend to report a supersonic flow. Here we revisit the two-scale and transition layer analysis of the sheath-presheath transition, in tandem with the conventional Bohm criteria analysis, to understand why and how the supersonic sheath entry flow is established at the sheath entrance, which is a few Debye length away from the wall, and its impact on plasma particle and power load at the wall. Works upported by DOE OFES. Work supported by DOE OFES.

  15. Measurement of effective sheath width around the cutoff probe based on electromagnetic simulation

    NASA Astrophysics Data System (ADS)

    Kim, D. W.; You, S. J.; Kim, J. H.; Chang, H. Y.; Yoon, J.-S.; Oh, W. Y.

    2016-05-01

    We inferred the effective sheath width using the cutoff probe and incorporating a full-wave three-dimensional electromagnetic (EM) simulation. The EM simulation reproduced the experimentally obtained plasma-sheath resonance (PSR) on the microwave transmission (S21) spectrum well. The PSR frequency has a one-to-one correspondence with the width of the vacuum layer assumed to be the effective sheath in the EM simulation model. The sheath width was estimated by matching the S21 spectra of the experiment and the EM simulation for different widths of the sheath. We found that the inferred sheath widths quantitatively and qualitatively agree with the sheath width measured by incorporating an equivalent circuit model. These results demonstrate the excellent potential of the cutoff probe for inferring the effective sheath width from its experimental spectrum data.

  16. The obliquity of Enceladus

    NASA Astrophysics Data System (ADS)

    Baland, Rose-Marie; Yseboodt, Marie; Van Hoolst, Tim

    2016-04-01

    The extraordinary activity at Enceladus' warm south pole indicates the presence of an internal global or local reservoir of liquid water beneath the surface. While Tyler (Tyler, R.H. [2009]. Geophys. Res. Lett. 36(15), L15205; Tyler, R.H. [2011]. Icarus 211(1), 770-779) has suggested that the geological activity and the large heat flow of Enceladus could result from tidal heating triggered by a large obliquity of at least 0.05-0.1°, theoretical models of the Cassini state predict the obliquity to be two to three orders of magnitude smaller for an entirely solid and rigid Enceladus. We investigate the influence of an internal subsurface ocean and of tidal deformations of the solid layers on the obliquity of Enceladus. Our Cassini state model takes into account the external torque exerted by Saturn on each layer of the satellite and the internal gravitational and pressure torques induced by the presence of the liquid layer. As a new feature, our model also includes additional torques that arise because of the periodic tides experienced by the satellite. We find that the upper limit for the obliquity of a solid Enceladus is 4.5 ×10-4 degrees and is negligibly affected by elastic deformations. The presence of an internal ocean decreases this upper limit by 13.1%, elasticity attenuating this decrease by only 0.5%. For larger satellites, such as Titan, elastic effects could be more significant because of their larger tidal deformations. As a consequence, it appears that it is easier to reconcile the theoretical estimates of Titan's obliquity with the measured obliquity than reported in previous studies wherein the solid layers or the entire satellite were assumed to be rigid. Since the obliquity of Enceladus cannot reach Tyler's requirement, obliquity tides are unlikely to be the source of the large heat flow of Enceladus. More likely, the geological activity at Enceladus' south pole results from eccentricity tides. Even in the most favorable case, the upper limit for

  17. Sheath formation under collisional conditions in presence of dust

    SciTech Connect

    Moulick, R. Goswami, K. S.

    2014-08-15

    Sheath formation is studied for collisional plasma in presence of dust. In common laboratory plasma, the dust acquires negative charges because of high thermal velocity of the electrons. The usual dust charging theory dealing with the issue is that of the Orbit Motion Limited theory. However, the theory does not find its application when the ion neutral collisions are significantly present. An alternate theory exists in literature for collisional dust charging. Collision is modeled by constant mean free path model. The sheath is considered jointly with the bulk of the plasma and a smooth transition of the plasma profiles from the bulk to the sheath is obtained. The various plasma profiles such as the electrostatic force on the grain, the ion drag force along with the dust density, and velocity are shown to vary spatially with increasing ion neutral collision.

  18. Generalized Analytical Model for the Radio-Frequency Sheath

    NASA Astrophysics Data System (ADS)

    Czarnetzki, Uwe

    2014-10-01

    An analytical model for the planar radio frequency (RF) sheath in capacitive discharges is developed based on the applied RF voltage as the boundary condition. The model applies to all kind of waveforms for the applied RF voltage, includes both sheaths in a discharge of arbitrary symmetry, and allows for an arbitrary degree of ion collisionallity in the sheaths (charge-exchange collisions). Further, effects of the finite floating potential during sheath collapse are included. The model can even be extended to electronegative plasmas with low bulk conductivity. The individual sheath voltages, the self-bias, and the RF floating potentials are explicitly calculated by a voltage balance equation using a cubic-charge voltage relation for the sheaths. In particular, the RF-phase as a function of the sheath voltage is determined. This is an input for a single second order non-linear integro-differential equation which is governing the ion flow velocity in the sheath. Fast numerical integration is straight forward and in many cases approximate analytical solutions can be obtained. Based on the solution for the ion flow velocity, densities, electric fields, currents, and charge-voltage relations are calculated. Further, the Child-Langmuir laws for the collisionless as well as the highly collisional case are derived. Very good agreement between model and experiments is obtained.

  19. A radio-frequency sheath model for complex waveforms

    SciTech Connect

    Turner, M. M.; Chabert, P.

    2014-04-21

    Plasma sheaths driven by radio-frequency voltages occur in contexts ranging from plasma processing to magnetically confined fusion experiments. An analytical understanding of such sheaths is therefore important, both intrinsically and as an element in more elaborate theoretical structures. Radio-frequency sheaths are commonly excited by highly anharmonic waveforms, but no analytical model exists for this general case. We present a mathematically simple sheath model that is in good agreement with earlier models for single frequency excitation, yet can be solved for arbitrary excitation waveforms. As examples, we discuss dual-frequency and pulse-like waveforms. The model employs the ansatz that the time-averaged electron density is a constant fraction of the ion density. In the cases we discuss, the error introduced by this approximation is small, and in general it can be quantified through an internal consistency condition of the model. This simple and accurate model is likely to have wide application.

  20. Measurement of sheath thickness at a floating potential

    SciTech Connect

    Han, Hyung-Sik; Lee, Hyo-Chang; Oh, Se-Jin; Chung, Chin-Wook

    2014-02-15

    In a cylindrical Langmuir probe measurement, ion current is collected from the surface of the sheath surrounded at probe tip, not at the surface of the probe tip. By using this, the sheath thickness can be obtained, if we know some unknown parameters, such as ion current, plasma density, and electron temperature. In this paper, we present a method to measure sheath thickness by using a wave cutoff method and a floating harmonic method. The measured result is in a good agreement with Allen-Boyd-Reynolds theory.

  1. Studies of RF sheaths and diagnostics on IShTAR

    NASA Astrophysics Data System (ADS)

    Crombé, K.; Devaux, S.; D'Inca, R.; Faudot, E.; Faugel, H.; Fünfgelder, H.; Heuraux, S.; Jacquot, J.; Louche, F.; Moritz, J.; Ochoukov, R.; Tripsky, M.; Van Eester, D.; Wauters, T.; Noterdaeme, J.-M.

    2015-12-01

    IShTAR (Ion cyclotron Sheath Test ARrangement) is a linear magnetised plasma test facility for RF sheaths studies at the Max-Planck-Institut für Plasmaphysik in Garching. In contrast to a tokamak, a test stand provides more liberty to impose the parameters and gives better access for the instrumentation and antennas. The project will support the development of diagnostic methods for characterising RF sheaths and validate and improve theoretical predictions. The cylindrical vacuum vessel has a diameter of 1 m and is 1.1 m long. The plasma is created by an external cylindrical plasma source equipped with a helical antenna that has been designed to excite the m=1 helicon mode. In inductive mode, plasma densities and electron temperatures have been characterised with a planar Langmuir probe as a function of gas pressure and input RF power. A 2D array of RF compensated Langmuir probes and a spectrometer are planned. A single strap RF antenna has been designed; the plasma-facing surface is aligned to the cylindrical plasma to ease the modelling. The probes will allow direct measurements of plasma density profiles in front of the RF antenna, and thus a detailed study of the density modifications induced by RF sheaths, which influences the coupling. The RF antenna frequency has been chosen to study different plasma wave interactions: the accessible plasma density range includes an evanescent and propagative behaviour of slow or fast waves, and allows the study of the effect of the lower hybrid resonance layer.

  2. A Sheath Model for Negative Ion Sources Including the Formation of a Virtual Cathode

    SciTech Connect

    McAdams, R.; King, D. B.; Surrey, E.

    2011-09-26

    A one dimensional model of the sheath between the plasma and the wall in a negative ion source has been developed. The plasma consists of positive ions, electrons and negative ions. The model takes into account the emission of negative ions from the wall into the sheath and thus represents the conditions in a caesiated ion source with surface production of negative ions. At high current densities of the emitted negative ions, the sheath is unable to support the transport of all the negative ions to the plasma and a virtual cathode is formed. This model takes this into account and allows the calculation of the transported negative ions across the sheath with the virtual cathode. The model has been extended to allow the linkage between plasma conditions at the sheath edge and the plasma to be made. Comparisons are made between the results of the model and experimental measurements.

  3. The oblique electron lens.

    NASA Technical Reports Server (NTRS)

    Johnson, C. B.; Hallam, K. L.

    1973-01-01

    An oblique electron lens is described that is especially applicable to image converters and camera tubes employing flat opaque photocathodes. The use of optical lenses, corrector plates, and/or mirrors (often employed in other electron lenses designed for use with opaque photocathodes) are eliminated. The oblique electron lens is well suited to ultraviolet and vacuum ultraviolet image converters, and to image converters employing opaque negative electron affinity photocathodes. It is also possible to use this oblique electron lens for electronography. Measurements on an experimental tube show that a limiting resolution of 50 line pairs/mm is possible, but the intrinsic lens quality is believed to approach that of a conventional electromagnetic lens having uniform and colinear electric and magnetic fields.

  4. The three dimensional shape and localisation of deformation within multilayer sheath folds

    NASA Astrophysics Data System (ADS)

    Alsop, G. I.; Holdsworth, R. E.

    2012-11-01

    Sheath folds are widely believed to develop by the passive geometric amplification of folds in which layering has no mechanical influence during non-coaxial deformation. Where layering becomes rheologically significant, then active sheath folds may form in which the inner nose of the sheath decouples along detachments, and undergoes a translation relative to the outer folded layers that surround and envelope the nose. We present a systematic 3-D analysis of multiple folded layer geometries in a serially-sectioned natural sheath fold. Weak layers, which are reactivated as detachments, define different-shaped sheath folds relative to other layers, with the sense of cut-off along detachments reversing across the axial surface as the inner fold nose has “protruded” into the surrounding sheath envelope. Detachment layers are more tightly folded meaning that such active sheath folds are non-similar shapes. The obliquely oriented, bifurcating, en-echelon nature of the fold hinges developed in adjacent layers suggest that pre-cursor folds formed with pronounced 3-D obliquity relative to the subsequent shear plane. Mineral lineations folded around sheath closures display asymmetric “star-burst” patterns consistent with recrystallisation during active folding and hinge rotation. We show that the eye-fold shapes exposed in any 2-D y-z slice can be used to predict the geometry of marker horizons back along the x-axis in the third dimension. This self-similarity may be of value when tracing stratiform mineralised horizons in large-scale sheath folds.

  5. Ion Dynamics Model for Collisionless Radio Frequency Sheaths

    NASA Technical Reports Server (NTRS)

    Bose, Deepak; Govindan, T.R.; Meyyappan, M.

    2000-01-01

    Full scale reactor model based on fluid equations is widely used to analyze high density plasma reactors. It is well known that the submillimeter scale sheath in front of a biased electrode supporting the wafer is difficult to resolve in numerical simulations, and the common practice is to use results for electric field from some form of analytical sheath model as boundary conditions for full scale reactor simulation. There are several sheath models in the literature ranging from Child's law to a recent unified sheath model [P. A. Miller and M. E. Riley, J. Appl. Phys. 82, 3689 (1997)l. In the present work, the cold ion fluid equations in the radio frequency sheath are solved numerically to show that the spatiotemporal variation of ion flux inside the sheath, commonly ignored in analytical models, is important in determining the electric field and ion energy at the electrode. Consequently, a semianalytical model that includes the spatiotemporal variation of ion flux is developed for use as boundary condition in reactor simulations. This semianalytical model is shown to yield results for sheath properties in close agreement with numerical solutions.

  6. Investigation on measurement of effective sheath width using a cutoff probe

    NASA Astrophysics Data System (ADS)

    Kim, Jung-Hyung; Kim, Dae-Woong; You, Shin-Jae

    2015-09-01

    The plasma density is the key parameter showing electric plasma property as well as processing rate. Therefore, various diagnostic methods have been developed and researched for measuring the absolute plasma density. One of them, cutoff probe, has been developed for more accurate measurement of the plasma density. The cutoff probe is the promising diagnostics method having diagnostic advantages: high accuracy in measured plasma density, simple assumption in measurement process, and readily use and interpretation of results for diagnostics. The sheath is also an important parameter in plasma researches and applications. In this presentation, we introduce measurement method of the effective sheath width using equivalent circuit model of S21 phase spectrum of the cutoff probe. The reliability of this method was verified by investigation of the FDTD simulation and comparative experiment with calculated Child-Langmuir law sheath width from Langmuir probe data. The results show that measured sheath width has an acceptable error when it was compared with input sheath width in the FDTD simulation. Furthermore, the measured sheath width was found to be in good agreement with the floated sheath width calculated from the Child-Langmuir sheath law.

  7. Model and particle-in-cell simulation of ion energy distribution in collisionless sheath

    SciTech Connect

    Zhou, Zhuwen; Kong, Bo; Luo, Yuee; Chen, Deliang; Wang, Yuansheng

    2015-06-15

    In this paper, we propose a self-consistent theoretical model, which is described by the ion energy distributions (IEDs) in collisionless sheaths, and the analytical results for different combined dc/radio frequency (rf) capacitive coupled plasma discharge cases, including sheath voltage errors analysis, are compared with the results of numerical simulations using a one-dimensional plane-parallel particle-in-cell (PIC) simulation. The IEDs in collisionless sheaths are performed on combination of dc/rf voltage sources electrodes discharge using argon as the process gas. The incident ions on the grounded electrode are separated, according to their different radio frequencies, and dc voltages on a separated electrode, the IEDs, and widths of energy in sheath and the plasma sheath thickness are discussed. The IEDs, the IED widths, and sheath voltages by the theoretical model are investigated and show good agreement with PIC simulations.

  8. Photoelectric sheath formation around small spherical objects in space

    NASA Astrophysics Data System (ADS)

    Misra, Shikha; Mishra, S. K.; Sodha, M. S.

    2015-04-01

    The formation of a photoelectron sheath around positively charged small (˜cm) spherical objects roaming in near earth space due to the solar radiation (with continuous spectrum) and the solar wind plasma has been investigated. The sheath structure has been derived, taking into account anisotropic photoelectron flux with the Poisson equation, spherical geometry of the object, and half Fermi Dirac distribution of photoelectron velocities. Two cases, viz., when the object is illuminated by (i) isotropic or (ii) unidirectional (parallel beam) radiation, have been analyzed. The analysis predicts a spherically symmetric sheath in case of isotropic illumination, while a symmetry in sheath about a θ = π / 4 is seen in case of parallel beam illumination; θ is the angle of incidence which is the angle made by the normal to a surface element with the direction of incidence of solar radiation. The radial and angular profiles of the electric potential and electron density in the photoelectron sheath have been evaluated and illustrated graphically; the dependence of the sheath structure on the solar wind plasma parameters, material properties of the spherical object, and its size have been discussed.

  9. Photoelectric sheath formation around small spherical objects in space

    SciTech Connect

    Misra, Shikha Sodha, M. S.; Mishra, S. K.

    2015-04-15

    The formation of a photoelectron sheath around positively charged small (∼cm) spherical objects roaming in near earth space due to the solar radiation (with continuous spectrum) and the solar wind plasma has been investigated. The sheath structure has been derived, taking into account anisotropic photoelectron flux with the Poisson equation, spherical geometry of the object, and half Fermi Dirac distribution of photoelectron velocities. Two cases, viz., when the object is illuminated by (i) isotropic or (ii) unidirectional (parallel beam) radiation, have been analyzed. The analysis predicts a spherically symmetric sheath in case of isotropic illumination, while a symmetry in sheath about a θ=π/4 is seen in case of parallel beam illumination; θ is the angle of incidence which is the angle made by the normal to a surface element with the direction of incidence of solar radiation. The radial and angular profiles of the electric potential and electron density in the photoelectron sheath have been evaluated and illustrated graphically; the dependence of the sheath structure on the solar wind plasma parameters, material properties of the spherical object, and its size have been discussed.

  10. Radio-frequency sheath voltages and slow wave electric field spatial structure

    SciTech Connect

    Colas, Laurent Lu, Ling-Feng; Křivská, Alena; Jacquot, Jonathan

    2015-12-10

    We investigate theoretically how sheath radio-frequency (RF) oscillations relate to the spatial structure of the RF parallel electric field emitted by Ion Cyclotron (IC) wave launchers, using a simple model of Slow Wave (SW) evanescence coupled with Direct Current (DC) plasma biasing via sheath boundary conditions in a plasma-filled 2-dimensional (parallel, radial) rectangle. Within a “wide sheaths” asymptotic regime, valid for large-amplitude near RF fields, our model becomes partly linear: the sheath oscillating voltage at open field line boundaries is a linear combination of elementary contributions by every source point of the radiated RF field map. These individual contributions are all the more intense as the SW emission point is toroidally nearer to the sheath walls. A limit formula is given for a source infinitely close to the sheaths. The decay of sheath RF voltages with the sheath/source parallel distance is quantified as a function of two characteristic SW evanescence lengths. Decay lengths are smaller than antenna parallel extensions. The sheath RF voltages at an IC antenna side limiter are therefore mainly sensitive to SW emission near this limiter, as recent observations suggest. Toroidal proximity effects could also explain why sheath oscillations persist with antisymmetric strap toroidal phasing, despite the parallel anti-symmetry of the radiated field map. They could also justify current attempts at reducing the RF fields induced near antenna boxes to attenuate sheath oscillations in their vicinity.

  11. Climates of Oblique Exoplanets

    NASA Astrophysics Data System (ADS)

    Dobrovolskis, A. R.

    2008-12-01

    A previous paper (Dobrovolskis 2007; Icarus 192, 1-23) showed that eccentricity can have profound effects on the climate, habitability, and detectability of extrasolar planets. This complementary study shows that obliquity can have comparable effects. The known exoplanets exhibit a wide range of orbital eccentricities, but those within several million km of their suns are generally in near-circular orbits. This fact is widely attributed to the dissipation of tides in the planets, which is particularly effective for solid/liquid bodies like "Super-Earths". Along with friction between a solid mantle and a liquid core, tides also are expected to despin a planet until it is captured in the synchronous resonance, so that its rotation period is identical to its orbital period. The canonical example of synchronous spin is the way that our Moon always keeps nearly the same hemisphere facing the Earth. Tides also tend to reduce the planet's obliquity (the angle between its spin and orbital angular velocities). However, orbit precession can cause the rotation to become locked in a "Cassini state", where it retains a nearly constant non-zero obliquity. For example, our Moon maintains an obliquity of about 6.7° with respect to its orbit about the Earth. For comparison, stable Cassini states can exist for practically any obliquity up to 180° for planets of binary stars, or in multi-planet systems with high mutual inclinations, such as are produced by scattering or by the Kozai mechanism. This work considers planets in synchronous rotation with circular orbits. For obliquities greater than 90°, the ground track of the sub-solar point wraps around all longitudes on the surface of such a planet. For smaller obliquities, the sub-solar track takes the figure-8 shape of an analemma. This can be visualized as the intersection of the planet's spherical surface with a right circular cylinder, parallel to the spin axis and tangent to the equator from the inside. The excursion of the

  12. The dust motion inside the magnetized sheath - The effect of drag forces

    SciTech Connect

    Pandey, B. P.; Samarian, A.; Vladimirov, S. V.

    2010-08-15

    The isolated charged dust inside the magnetized plasma sheath moves under the influence of the electron and ion drag force and the sheath electrostatic field. The charge on the dust is a function of its radius as well as the value of the ambient sheath potential. It is shown that the charge on the dust determines its trajectory and dust performs the spiraling motion inside the sheath. The location of the turning spiral is determined by the number of negative charge on the dust, which in turn is a function of the dust radius. The back and forth spiraling motion finally causes the dust to move in a small, narrow region of the sheath. For a bigger dust particle, the dust moves closer to the sheath presheath boundary suggesting that the bigger grains, owing to the strong repulsion between the wall and dust, will be unable to travel inside the sheath. Only small, micron-sized grains can travel closer to the wall before repulsion pushes it back toward the plasma-sheath boundary. The temporal behavior of the spiraling dust motion appears like a damped harmonic oscillation, suggesting that the plasma drag force causes dissipation of the electrostatic energy. However, after initial damping, the grain keeps oscillating although with much smaller amplitude. The possible application of the present results to the ongoing sheath experiments is discussed.

  13. 21 CFR 884.5320 - Glans sheath.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... sheath. (a) Identification. A glans sheath device is a sheath which covers only the glans penis or part... the entire shaft of the penis. It is indicated only for the prevention of pregnancy and not for...

  14. 21 CFR 884.5320 - Glans sheath.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... sheath. (a) Identification. A glans sheath device is a sheath which covers only the glans penis or part... the entire shaft of the penis. It is indicated only for the prevention of pregnancy and not for...

  15. 21 CFR 884.5320 - Glans sheath.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... sheath. (a) Identification. A glans sheath device is a sheath which covers only the glans penis or part... the entire shaft of the penis. It is indicated only for the prevention of pregnancy and not for...

  16. Challenging diagnosis of peripillous sheaths.

    PubMed

    Gnarra, Maria; Saraceni, Pierluigi; Rossi, Alfredo; Murabit, Amera; Caradonna, Emanuela; Fania, Luca; Feliciani, Claudio

    2014-01-01

    Peripillous sheaths, or hair casts, are asymptomatic, white, cylindrical concretions that encircle the hair without adhering to it. They are infrequently documented in the literature, are often misdiagnosed, and generate avoidable apprehension and expense for parents and caregivers. Dermoscopy is the standard for a rapid, noninvasive, cost-effective diagnosis. We describe a case of peripillous sheaths presenting in a boy. PMID:24846654

  17. Analytical expression for the sheath edge around wedge-shaped cathodes

    NASA Astrophysics Data System (ADS)

    Sheridan, T. E.

    2008-03-01

    The sheath is the boundary layer separating a quasi-neutral plasma from a material electrode. Understanding the sheath is important for numerous applications, including plasma-based ion implantation, plasma etching of semiconductors, plasma assisted electrostatic cleaning, and Langmuir probes. In a 1D planar geometry, the Child-Langmuir (CL) law describes the sheath when the bias on a negative electrode, i.e., a cathode, is much greater than the electron temperature. In this case, the sheath width s is an eigenvalue of the problem. In 2D, the sheath edge is an unknown line (an ``eigen-boundary") which is determined by a set of coupled, nonlinear, partial differential equations. I have found an expression for the sheath edge around a 2D wedge-shaped cathode with included angle θw. In polar coordinates (r,θ), the sheath edge is a solution of r(aθ)=as where s is the planar sheath width far from the corner and θw=2π- π/a, so that a=1/2 gives a knife edge, while a=2/3 gives a square corner. This result is verified by comparison with the numerical solutions of Watterson [P. A. Watterson, J. Phys. D 22, 1300 (1989)].

  18. Anomalous Capacitive Sheath with Deep Radio Frequency Electric Field Penetration

    SciTech Connect

    Igor D. Kaganovich

    2002-01-18

    A novel nonlinear effect of anomalously deep penetration of an external radio-frequency electric field into a plasma is described. A self-consistent kinetic treatment reveals a transition region between the sheath and the plasma. Because of the electron velocity modulation in the sheath, bunches in the energetic electron density are formed in the transition region adjusted to the sheath. The width of the region is of order V(subscript T)/omega, where V(subscript T) is the electron thermal velocity, and w is frequency of the electric field. The presence of the electric field in the transition region results in a cooling of the energetic electrons and an additional heating of the cold electrons in comparison with the case when the transition region is neglected.

  19. Formation and stability of polarization sheaths of a cross-field beam

    NASA Technical Reports Server (NTRS)

    Cai, Dong S.; Buneman, Oscar

    1992-01-01

    A simple description is presented for a pure ion sheath formed on one side and a pure electron sheath formed on the other side of a neutral plasma beam. Both the ion and the electron sheath are found to be one-dimensionally stable and two-dimensionally unstable in a mode known as magnetron, slipping stream, and diocotron. This mode connects with the Kelvin-Helmholtz instability in neutral matter. The analytical results are confirmed both qualitatively and quantitatively by numerical simulations. The simulations help define the linear behavior of the long-wave instability generated in the electron (or ion) sheath, including a strong shear.

  20. The sheath effect on the floating harmonic method

    SciTech Connect

    Lee, Jaewon; Kim, Kyung-Hyun; Chung, Chin-Wook

    2015-12-15

    The floating harmonic method biases sinusoidal voltage to a probe sheath, and as its response, harmonic currents can be obtained. These currents can be used to determine the plasma parameters. However, different shapes of probes have different shapes of sheaths that can affect the diagnostic results. However, no research has been done on the sheath effect on the floating harmonic method. Therefore, we investigate the effect of the sheath during floating harmonic diagnostics by comparing cylindrical and planar probes. While the sinusoidal voltages were applied to a probe, because the sheath oscillated, the time variant ion current and their harmonic currents were added to the electron harmonic currents. In the floating harmonic method, the harmonic currents are composed of only the electron harmonic currents. Therefore, the ion harmonic currents affect the diagnostic results. In particular, the electron temperature obtained by the small probe tip was higher than that of the large probe tip. This effect was exacerbated when the ratio of the probe tip radius to the sheath length was smaller.

  1. Rarefaction solitons initiated by sheath instability

    SciTech Connect

    Levko, Dmitry

    2015-09-15

    The instability of the cathode sheath initiated by the cold energetic electron beam is studied by the one-dimensional fluid model. Numerical simulations show the generation of travelling rarefaction solitons at the cathode. It is obtained that the parameters of these solitons strongly depend on the parameters of electron beam. The “stretched” variables are derived using the small-amplitude analysis. These variables are used in order to obtain the Korteweg-de Vries equation describing the propagation of the rarefaction solitons through the plasma with cold energetic electron beam.

  2. Self-consistently simulation of RF sheath boundary condition in BOUT + + framework

    NASA Astrophysics Data System (ADS)

    Gui, Bin; Xu, Xueqiao; Xia, Tianyang

    2015-11-01

    The effect of the RF sheath boundary condition on the edge-localized modes and the turbulent transport is simulated in this work. The work includes two parts. The first part is to calculate the equilibrium radial electric field with RF sheath boundary condition. It is known the thermal sheath or the rectified RF sheath will modify the potential in the SOL region. The modified potential induces addition shear flow in SOL. In this part, the equilibrium radial electric field across the separatrix is calculated by solving the 2D current continuity equation with sheath boundary condition, drifts and viscosity. The second part is applying the sheath boundary condition on the perturbed variables of the six-field two fluid model in BOUT + + framework. The six-field two-fluid model simulates the ELMs and turbulent transport. The sheath boundary condition is applied in this model and it aims to simulate effect of sheath boundary condition on the turbulent transport. It is found the sheath boundary plays as a sink in the plasma and suppresses the local perturbation. Based on this two work, the effect of RF sheath boundary condition on the ELMs and turbulent transport could be self-consistently simulated. Prepared by LLNL under Contract DE-AC52-07NA27344.

  3. Laminated magnet field coil sheath

    DOEpatents

    Skaritka, John R.

    1987-12-01

    a method for manufacturing a magnet cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible sheath, with the trim coil pattern precisely positioned thereon, is accurately positioned at a precise location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator.

  4. Laminated magnet field coil sheath

    DOEpatents

    Skaritka, J.R.

    1987-05-15

    A method for manufacturing a magnetic cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible substrate sheath, with the trim coil pattern precisely location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator. 1 fig.

  5. Magnetic field generation in core-sheath jets via the kinetic Kelvin-Helmholtz instability

    SciTech Connect

    Nishikawa, K.-I.; Hardee, P. E.; Duţan, I.; Niemiec, J.; Medvedev, M.; Mizuno, Y.; Meli, A.; Sol, H.; Zhang, B.; Pohl, M.; Hartmann, D. H.

    2014-09-20

    We have investigated magnetic field generation in velocity shears via the kinetic Kelvin-Helmholtz instability (kKHI) using a relativistic plasma jet core and stationary plasma sheath. Our three-dimensional particle-in-cell simulations consider plasma jet cores with Lorentz factors of 1.5, 5, and 15 for both electron-proton and electron-positron plasmas. For electron-proton plasmas, we find generation of strong large-scale DC currents and magnetic fields that extend over the entire shear surface and reach thicknesses of a few tens of electron skin depths. For electron-positron plasmas, we find generation of alternating currents and magnetic fields. Jet and sheath plasmas are accelerated across the shear surface in the strong magnetic fields generated by the kKHI. The mixing of jet and sheath plasmas generates a transverse structure similar to that produced by the Weibel instability.

  6. Plasma theory and simulation. Quarterly progress report Nos. 3 and 4, 1 July-30 December 1984

    SciTech Connect

    Birdsall, C.K.

    1984-12-31

    Contents include: oblique-electron Bernstein-wave investigations; simulation of the effect of large-amplitude rf waves on the interchange instability-supporting theory; one-beam Alfven ion-cyclotron instabilities of multiple-ion distribution functions; linear-mode coupling in simulations of the Alfven ion-cyclotron instability; simulation of the plasma-sheath region including ion reflection; planar magnetron discharges; partial simulations of the low-alpha Pierce diode; theory and simulation of ion-acoustic double layers; and uniform-number generation for quiet starts.

  7. On the upper bound in the Bohm sheath criterion

    NASA Astrophysics Data System (ADS)

    Kotelnikov, I. A.; Skovorodin, D. I.

    2016-02-01

    The question is discussed about the existence of an upper bound in the Bohm sheath criterion, according to which the Debye sheath at the interface between plasma and a negatively charged electrode is stable only if the ion flow velocity in plasma exceeds the ion sound velocity. It is stated that, with an exception of some artificial ionization models, the Bohm sheath criterion is satisfied as an equality at the lower bound and the ion flow velocity is equal to the speed of sound. In the one-dimensional theory, a supersonic flow appears in an unrealistic model of a localized ion source the size of which is less than the Debye length; however, supersonic flows seem to be possible in the two- and three-dimensional cases. In the available numerical codes used to simulate charged particle sources with a plasma emitter, the presence of the upper bound in the Bohm sheath criterion is not supposed; however, the correspondence with experimental data is usually achieved if the ion flow velocity in plasma is close to the ion sound velocity.

  8. Verification of high voltage rf capacitive sheath models with particle-in-cell simulations

    NASA Astrophysics Data System (ADS)

    Wang, Ying; Lieberman, Michael; Verboncoeur, John

    2009-10-01

    Collisionless and collisional high voltage rf capacitive sheath models were developed in the late 1980's [1]. Given the external parameters of a single-frequency capacitively coupled discharge, plasma parameters including sheath width, electron and ion temperature, plasma density, power, and ion bombarding energy can be estimated. One-dimensional electrostatic PIC codes XPDP1 [2] and OOPD1 [3] are used to investigate plasma behaviors within rf sheaths and bulk plasma. Electron-neutral collisions only are considered for collisionless sheaths, while ion-neutral collisions are taken into account for collisional sheaths. The collisionless sheath model is verified very well by PIC simulations for the rf current-driven and voltage-driven cases. Results will be reported for collisional sheaths also. [1] M. A. Lieberman, IEEE Trans. Plasma Sci. 16 (1988) 638; 17 (1989) 338 [2] J. P. Verboncoeur, M. V. Alves, V. Vahedi, and C. K. Birdsall, J. Comp. Phys. 104 (1993) 321 [3] J. P. Verboncoeur, A. B. Langdon and N. T. Gladd, Comp. Phys. Comm. 87 (1995) 199

  9. Cosmic-ray shock acceleration in oblique MHD shocks

    NASA Technical Reports Server (NTRS)

    Webb, G. M.; Drury, L. OC.; Volk, H. J.

    1986-01-01

    A one-dimensional, steady-state hydrodynamical model of cosmic-ray acceleration at oblique MHD shocks is presented. Upstream of the shock the incoming thermal plasma is subject to the adverse pressure gradient of the accelerated particles, the J x B force, as well as the thermal gas pressure gradient. The efficiency of the acceleration of cosmic-rays at the shock as a function of the upstream magnetic field obliquity and upstream plasma beta is investigated. Astrophysical applications of the results are briefly discussed.

  10. Comparison of sheath thickness obtained from the theories of ion correction in the floating potential

    NASA Astrophysics Data System (ADS)

    Han, Hyeong Sik; Hwang, Kwang Tae; Choe, Ik Jin; Chung, Chin Wook

    2009-10-01

    In the cold plasmas, when the cylindrical probe is used to measure the ion density, an expansion of the sheath thickness related to the sheath voltage increases the ion current. The expansion of the sheath thickness results in an incorrect measurement of ion current. To measure ion density correctly, the sheath thickness should be considered. In the collisionless sheath, the sheath thickness can be calculated by the Child- Langmuir (CL) theory or the Allen-Boyd-Reynolds(ABR) theory. We measured the sheath thicknesses using the floating harmonics method [1] and the cut-off method by the microwave [2], and the results compared with the CL theory [3] and ABR theory [4] in the floating potential. The sheath thicknesses obtained from the ABR theory were in good agreement with the experimental results. [4pt] [1] M. H. Lee, S. H. Jang and C. W. Chung, J. Appl. Phys., 101, 033305 (2007)[0pt] [2] J.H. Kim, S.C. Choi, Y.H. Shin, and K. H. Chung, Rev. Sci. Instrum. 75, 2706 (2004)[0pt] [3] FF Chen, JD Evans, D Arnush, Phys. Plasmas 9, 1449 (2002)[0pt] [4] F. F. Chen and D. Arnush, Phys. Plasmas 8, 5051 (2001)

  11. Studies of RF sheaths and diagnostics on IShTAR

    SciTech Connect

    Crombé, K.; D’Inca, R.; Faugel, H.; Fünfgelder, H.; Jacquot, J.; Ochoukov, R.; Louche, F.; Tripsky, M.; Van Eester, D.; Wauters, T.

    2015-12-10

    IShTAR (Ion cyclotron Sheath Test ARrangement) is a linear magnetised plasma test facility for RF sheaths studies at the Max-Planck-Institut für Plasmaphysik in Garching. In contrast to a tokamak, a test stand provides more liberty to impose the parameters and gives better access for the instrumentation and antennas. The project will support the development of diagnostic methods for characterising RF sheaths and validate and improve theoretical predictions. The cylindrical vacuum vessel has a diameter of 1 m and is 1.1 m long. The plasma is created by an external cylindrical plasma source equipped with a helical antenna that has been designed to excite the m=1 helicon mode. In inductive mode, plasma densities and electron temperatures have been characterised with a planar Langmuir probe as a function of gas pressure and input RF power. A 2D array of RF compensated Langmuir probes and a spectrometer are planned. A single strap RF antenna has been designed; the plasma-facing surface is aligned to the cylindrical plasma to ease the modelling. The probes will allow direct measurements of plasma density profiles in front of the RF antenna, and thus a detailed study of the density modifications induced by RF sheaths, which influences the coupling. The RF antenna frequency has been chosen to study different plasma wave interactions: the accessible plasma density range includes an evanescent and propagative behaviour of slow or fast waves, and allows the study of the effect of the lower hybrid resonance layer.

  12. Sheath dynamics and energetic particle distributions on substrates

    NASA Astrophysics Data System (ADS)

    Lieberman, Michael A.

    2009-10-01

    The energy and angular distributions (EAD's) of energetic particles arriving at a substrate determine crucial plasma processing characteristics; thus knowledge and control of the EAD's are vital for nanoelectronics design and fabrication during scale-down to the ultimate 4--6 nm transistor gate lengths over the next 15 years. We review the history and state-of-the-art of measurements, simulations, and analyses of ion, fast neutral, and ballistic electron EAD's. Ion measurements have been made using electrostatic energy analyzers, cylindrical mirror analyzers, and retarding grid analyzers, often now coupled with quadrupole mass spectrometers to compare different ions in the same discharge. The state-of-the-art for capacitive rf sheaths has advanced greatly since the first observation of a bi-modal ion energy distribution (IED) over 50 years ago. More recently, measurement techniques and models have been developed to determine fast neutral distributions. Monte Carlo, and particle-in-cell simulations with Monte Carlo collisions (PIC-MCC) have been used to study IED's since the late 1980's. Recently, PIC-MCC simulations were used to obtain ballistic electron EAD's. Analytical models of the IED for collisionless rf sheaths have emphasized the role of τi/τrf, the ratio of ion transit time across the sheath to rf period, with separate models for the low and high frequency regimes. Various simplifications and bridging models now exist. For collisional rf sheaths, the important role of λi/s, the ratio of ion-neutral mean free path to sheath width, in modifying the collisionless bi-modal IED was demonstrated in the early 1990's. Surface charging effects on insulating substrates are important for low frequency rf discharges or for pulsed transient sheaths; the latter are found during plasma ion implantation processes. Analytical models of the IED for plasma ion implantation have been extended to insulating surfaces and compared with experimental results.

  13. Magnetized sheath near positively biased wall between two permanent magnetic plates

    SciTech Connect

    Sun, Yan; Wei, Zi-an; Ma, J. X. Jiang, Zheng-qi; Wu, Fei

    2015-06-15

    The characteristics of magnetized electron sheath near a positively biased conducting wall parallel to magnetic field formed between two permanent magnetic plates were experimentally investigated in a double plasma device. The magnetic field strength between the magnetic plates is about 1200 G which is sufficient to magnetize the plasma such that the ion gyroradius is comparable to the electron Debye length. A virtual cathode (or potential dip) structure was found between the electron-rich sheath and bulk plasma. For a given neutral gas pressure, the potential minimum (dip position) remains almost the same for different positive biases on the wall. For a given bias on the wall, however, the electron sheath thickness and the potential drop from the bulk plasma to the dip decrease with the increase of the neutral gas pressure. In addition, the electron sheath and potential dip appear to be wider and deeper in the downstream side of the wall.

  14. MOLYBDENUM DISILICIDE MATERIALS FOR GLASS MELTING SENSOR SHEATHS

    SciTech Connect

    J. PETROVIC; R. CASTRO; ET AL

    2001-01-01

    Sensors for measuring the properties of molten glass require protective sensor sheaths in order to shield them from the extremely corrosive molten glass environment. MoSi{sub 2} has been shown to possess excellent corrosion resistance in molten glass, making it a candidate material for advanced sensor sheath applications. MoSi{sub 2}-coated Al{sub 2}O{sub 3} tubes, MoSi{sub 2}-Al{sub 2}O{sub 3} laminate composite tubes, and MoSi{sub 2}-Al{sub 2}O{sub 3} functionally graded composite tubes have been produced by plasma spray-forming techniques for such applications.

  15. Proton Acceleration at Oblique Shocks

    NASA Astrophysics Data System (ADS)

    Galinsky, V. L.; Shevchenko, V. I.

    2011-06-01

    Acceleration at the shock waves propagating oblique to the magnetic field is studied using a recently developed theoretical/numerical model. The model assumes that resonant hydromagnetic wave-particle interaction is the most important physical mechanism relevant to motion and acceleration of particles as well as to excitation and damping of waves. The treatment of plasma and waves is self-consistent and time dependent. The model uses conservation laws and resonance conditions to find where waves will be generated or damped, and hence particles will be pitch-angle-scattered. The total distribution is included in the model and neither introduction of separate population of seed particles nor some ad hoc escape rate of accelerated particles is needed. Results of the study show agreement with diffusive shock acceleration models in the prediction of power spectra for accelerated particles in the upstream region. However, they also reveal the presence of spectral break in the high-energy part of the spectra. The role of the second-order Fermi-like acceleration at the initial stage of the acceleration is discussed. The test case used in the paper is based on ISEE-3 data collected for the shock of 1978 November 12.

  16. PROTON ACCELERATION AT OBLIQUE SHOCKS

    SciTech Connect

    Galinsky, V. L.; Shevchenko, V. I.

    2011-06-20

    Acceleration at the shock waves propagating oblique to the magnetic field is studied using a recently developed theoretical/numerical model. The model assumes that resonant hydromagnetic wave-particle interaction is the most important physical mechanism relevant to motion and acceleration of particles as well as to excitation and damping of waves. The treatment of plasma and waves is self-consistent and time dependent. The model uses conservation laws and resonance conditions to find where waves will be generated or damped, and hence particles will be pitch-angle-scattered. The total distribution is included in the model and neither introduction of separate population of seed particles nor some ad hoc escape rate of accelerated particles is needed. Results of the study show agreement with diffusive shock acceleration models in the prediction of power spectra for accelerated particles in the upstream region. However, they also reveal the presence of spectral break in the high-energy part of the spectra. The role of the second-order Fermi-like acceleration at the initial stage of the acceleration is discussed. The test case used in the paper is based on ISEE-3 data collected for the shock of 1978 November 12.

  17. Role of magnetic field tangency points in ICRF sheath interactions

    NASA Astrophysics Data System (ADS)

    Myra, J. R.; D'Ippolito, D. A.; Kohno, H.

    2014-02-01

    ICRF waves can sometimes interact with plasma-facing surfaces in tokamak fusion experiments causing degradation of core heating efficiency, impurity injection and even component damage. While presently available low dimensionality rf sheath models are useful in understanding many features of these interactions, more quantitative modeling will require attention to realistic geometrical details of the boundary plasma and surfaces. In this paper, we explore the situation in which there exists a tangency point of the background magnetic field with a surface. We find that the rf interactions are strongly influenced by the generation and propagation of sheath-plasma waves (SPW) along the surface. It is found that these waves preferentially propagate towards, and accumulate at, a convex tangency point. An analytical theory of SPW propagation is developed to understand these features.

  18. Collisionless "thermalization" in the sheath of an argon discharge

    NASA Astrophysics Data System (ADS)

    Coulette, David; Manfredi, Giovanni

    2015-04-01

    We performed kinetic Vlasov simulations of the plasma-wall transition for a low-pressure argon discharge without external magnetic fields, using the same plasma parameters as in the experiments of Claire et al. [Phys. Plasmas 13, 062103 (2006)]. Experimentally, it was found that the ion velocity distribution function is highly asymmetric in the presheath, but, surprisingly, becomes again close to Maxwellian inside the sheath. Here, we show that this "thermalization" can be explained by purely collisionless effects that are akin to the velocity bunching phenomenon observed in charged particles beams. Such collisionless thermalization is also observed in the presheath region close to the sheath entrance, although it is much weaker there and in practice probably swamped by collisional processes (standard or enhanced by instabilities).

  19. Role of magnetic field tangency points in ICRF sheath interactions

    SciTech Connect

    Myra, J. R.; D'Ippolito, D. A.; Kohno, H.

    2014-02-12

    ICRF waves can sometimes interact with plasma-facing surfaces in tokamak fusion experiments causing degradation of core heating efficiency, impurity injection and even component damage. While presently available low dimensionality rf sheath models are useful in understanding many features of these interactions, more quantitative modeling will require attention to realistic geometrical details of the boundary plasma and surfaces. In this paper, we explore the situation in which there exists a tangency point of the background magnetic field with a surface. We find that the rf interactions are strongly influenced by the generation and propagation of sheath-plasma waves (SPW) along the surface. It is found that these waves preferentially propagate towards, and accumulate at, a convex tangency point. An analytical theory of SPW propagation is developed to understand these features.

  20. Experimental studies of anode sheath phenomena in a Hall thruster discharge

    NASA Astrophysics Data System (ADS)

    Dorf, L.; Raitses, Y.; Fisch, N. J.

    2005-05-01

    Both electron-repelling and electron-attracting anode sheaths in a Hall thruster were characterized by measuring the plasma potential with biased and emissive probes [L. Dorf, Y. Raitses, V. Semenov, and N. J. Fisch, Appl. Phys. Lett. 84, 1070 (2004)]. In the present work, two-dimensional structures of the plasma potential, electron temperature, and plasma density in the near-anode region of a Hall thruster with clean and dielectrically coated anodes are identified. Possible mechanisms of anode sheath formation in a Hall thruster are analyzed. The path for current closure to the anode appears to be the determining factor in the anode sheath formation process. The main conclusion of this work is that the anode sheath formation in Hall thrusters differs essentially from that in the other gas discharge devices, such as a glow discharge or a hollow anode, because the Hall thruster utilizes long electron residence times to ionize rather than high neutral pressures.

  1. Experimental studies of anode sheath phenomena in a Hall thruster discharge

    SciTech Connect

    Dorf, L.; Raitses, Y.; Fisch, N.J.

    2005-05-15

    Both electron-repelling and electron-attracting anode sheaths in a Hall thruster were characterized by measuring the plasma potential with biased and emissive probes [L. Dorf, Y. Raitses, V. Semenov, and N. J. Fisch, Appl. Phys. Lett. 84, 1070 (2004)]. In the present work, two-dimensional structures of the plasma potential, electron temperature, and plasma density in the near-anode region of a Hall thruster with clean and dielectrically coated anodes are identified. Possible mechanisms of anode sheath formation in a Hall thruster are analyzed. The path for current closure to the anode appears to be the determining factor in the anode sheath formation process. The main conclusion of this work is that the anode sheath formation in Hall thrusters differs essentially from that in the other gas discharge devices, such as a glow discharge or a hollow anode, because the Hall thruster utilizes long electron residence times to ionize rather than high neutral pressures.

  2. Experimental Studies of Anode Sheath Phenomena in a Hall Thruster Discharge

    SciTech Connect

    L. Dorf; Y. Raitses; N.J. Fisch

    2004-12-17

    Both electron-repelling and electron-attracting anode sheaths in a Hall thruster were characterized by measuring the plasma potential with biased and emissive probes [L. Dorf, Y. Raitses, V. Semenov, and N.J. Fisch, Appl. Phys. Let. 84 (2004) 1070]. In the present work, two-dimensional structures of the plasma potential, electron temperature, and plasma density in the near-anode region of a Hall thruster with clean and dielectrically coated anodes are identified. Possible mechanisms of anode sheath formation in a Hall thruster are analyzed. The path for current closure to the anode appears to be the determining factor in the anode sheath formation process. The main conclusion of this work is that the anode sheath formation in Hall thrusters differs essentially from that in the other gas discharge devices, like a glow discharge or a hollow anode, because the Hall thruster utilizes long electron residence times to ionize rather than high neutral pressures.

  3. Instability, collapse, and oscillation of sheaths caused by secondary electron emission

    NASA Astrophysics Data System (ADS)

    Campanell, M. D.; Khrabrov, A. V.; Kaganovich, I. D.

    2012-12-01

    The Debye sheath is shown to be unstable under general conditions. For surface materials with sufficient secondary electron emission (SEE) yields, the surface's current-voltage characteristic has an unstable branch when the bulk plasma temperature (Te) exceeds a critical value, or when there are fast electron populations present. The plasma-surface interaction becomes dynamic where the sheath may undergo spontaneous transitions or oscillations. Using particle-in-cell simulations, we analyze sheath instabilities occurring in a high Te plasma slab bounded by walls with SEE. As the plasma evolves, whenever the sheath enters an unstable state, its amplitude rapidly collapses, allowing a large flux of previously trapped electrons to hit the wall. These hot electrons induce more than one secondary on average, causing a net loss of electrons from the wall. The sheath collapse quenches when the surface charge becomes positive because the attractive field inhibits further electrons from escaping. Sheath instabilities influence the current balance, energy loss, cross-B-field transport and even the bulk plasma properties. Implications for discharges including Hall thrusters are discussed. More generally, the results show that common theories that treat emission as a fixed (time-independent) "coefficient" do not capture the full extent of SEE effects.

  4. Instability, Collapse and Oscillation of Sheaths Caused by Secondary Electron Emission

    SciTech Connect

    M.D. Campanell, A.V. Khrabrov and I.D. Kaganovich

    2013-01-03

    The Debye sheath is shown to be unstable under general conditions. For surface materials with sufficient secondary electron emission (SEE) yields, the surface's current-voltage characteristic has an unstable branch when the bulk plasma temperature (Te ) exceeds a critical value, or when there are fast electron populations present. The plasma-surface interaction becomes dynamic where the sheath may undergo spontaneous transitions or oscillations. Using particle-in-cell simulations, we analyze sheath instabilities occurring in a high Te plasma slab bounded by walls with SEE. As the plasma evolves, whenever the sheath enters an unstable state, its amplitude rapidly collapses, allowing a large flux of previously trapped electrons to hit the wall. These hot electrons induce more than one secondary on average, causing a net loss of electrons from the wall. The sheath collapse quenches when the surface charge becomes positive because the attractive field inhibits further electrons from escaping. Sheath instabilities influence the current balance, energy loss, cross-B-field transport and even the bulk plasma properties. Implications for discharges including Hall thrusters are discussed. More generally, the results show that common theories that treat emission as a fixed (time-independent) "coefficient" do not capture the full extent of SEE effects.

  5. The Confinement and Sheath Within a Glass Box

    NASA Astrophysics Data System (ADS)

    Chen, Mudi; Dropmann, Michael; Kong, Jie; Qiao, Ke; Carmona-Reyes, Jorge; Matthews, Lorin; Hyde, Truell

    2015-11-01

    The confinement structure provided by a glass box placed on the lower powered electrode of a GEC rf Reference Cell is proving to be ideal for the formation of vertically aligned structures which are often difficult to obtain under other types of confinement. A glass box also provides a mechanism for controlling the number of dust particles comprising a particular dust structure as well as their size and symmetry. However, given the small volume of the glass box and the fact that each of the glass panes comprising the box develop a new sheath within the plasma environment, the structure of the overall sheath inside is quite different from that produced by the lower electrode alone. Since both the confinement and sheath structure are vital for producing ordered dust particle structures, a better understanding of the underlying physics is sorely needed. In this experiment, the trajectories of dust particles acting as probes while falling through the glass box under various plasma environments are tracked and analyzed. It will be shown that the resulting data provides a map of both the confining force and the structure of the sheath inside the glass box. Support from the NSF and the DOE (award numbers PHY-1262031 and PHY-1414523) is gratefully acknowledged.

  6. Malignant Peripheral Nerve Sheath Tumor.

    PubMed

    James, Aaron W; Shurell, Elizabeth; Singh, Arun; Dry, Sarah M; Eilber, Fritz C

    2016-10-01

    Malignant peripheral nerve sheath tumor (MPNST) is the sixth most common type of soft tissue sarcoma. Most MPNSTs arise in association with a peripheral nerve or preexisting neurofibroma. Neurofibromatosis type is the most important risk factor for MPNST. Tumor size and fludeoxyglucose F 18 avidity are among the most helpful parameters to distinguish MPNST from a benign peripheral nerve sheath tumor. The histopathologic diagnosis is predominantly a diagnosis of light microscopy. Immunohistochemical stains are most helpful to distinguish high-grade MPNST from its histologic mimics. Current surgical management of high-grade MPNST is similar to that of other high-grade soft tissue sarcomas. PMID:27591499

  7. Cascaded target normal sheath acceleration

    SciTech Connect

    Wang, W. P.; Shen, B. F.; Zhang, X. M.; Wang, X. F.; Xu, J. C.; Zhao, X. Y.; Yu, Y. H.; Yi, L. Q.; Shi, Y.; Zhang, L. G.; Xu, T. J.; Xu, Z. Z.

    2013-11-15

    A cascaded target normal sheath acceleration (TNSA) scheme is proposed to simultaneously increase energy and improve energy spread of a laser-produced mono-energetic proton beam. An optimum condition that uses the maximum sheath field to accelerate the center of the proton beam is theoretically found and verified by two-dimensional particle-in-cell simulations. An initial 10 MeV proton beam is accelerated to 21 MeV with energy spread decreased from 5% to 2% under the optimum condition during the process of the cascaded TNSA. The scheme opens a way to scale proton energy lineally with laser energy.

  8. Particle-in-cell study of the ion-to-electron sheath transition

    NASA Astrophysics Data System (ADS)

    Scheiner, Brett; Baalrud, Scott D.; Hopkins, Matthew M.; Yee, Benjamin T.; Barnat, Edward V.

    2016-08-01

    The form of a sheath near a small electrode, with bias changing from below to above the plasma potential, is studied using 2D particle-in-cell simulations. When the electrode is biased within Te/2 e below the plasma potential, the electron velocity distribution functions (EVDFs) exhibit a loss-cone type truncation due to fast electrons overcoming the small potential difference between the electrode and plasma. No sheath is present in this regime, and the plasma remains quasineutral up to the electrode. The EVDF truncation leads to a presheath-like density and flow velocity gradients. Once the bias exceeds the plasma potential, an electron sheath is present. In this case, the truncation driven behavior persists, but is accompanied by a shift in the maximum value of the EVDF that is not present in the negative bias cases. The flow moment has significant contributions from both the flow shift of the EVDF maximum, and the loss-cone truncation.

  9. Numerical investigation of fast-wave propagation and radio-frequency sheath interaction with a shaped tokamak wall

    SciTech Connect

    Kohno, H.; Myra, J. R.; D'Ippolito, D. A.

    2015-07-15

    Interactions between propagating fast waves and radio-frequency (RF) sheaths in the ion cyclotron range of frequencies are numerically investigated based on a cold fluid plasma model coupled with a sheath boundary condition. In this two-dimensional study, the capability of the finite element code rfSOL, which was developed in previous numerical work, is extended to analyze self-consistent RF sheath-plasma interaction problems in a tokamak with a non-circular cross-section. It is found that a large sheath voltage is generated near the edges of the limiter-shaped deformation as a result of the conversion from fast to slow waves on the sheaths. The sheath voltage associated with this conversion is particularly significant in the localized region where the contact angle between the magnetic field line and the conducting wall varies rapidly along the curved sheath surface, which is consistent with the results in previous one-dimensional theoretical work. The dependences of the RF sheaths on various parameters in plasma such as the toroidal wavenumber, edge plasma density, and the degree of the RF wave absorption in the core region are also examined in detail.

  10. Habitable planets with high obliquities

    NASA Technical Reports Server (NTRS)

    Williams, D. M.; Kasting, J. F.

    1997-01-01

    Earth's obliquity would vary chaotically from 0 degrees to 85 degrees were it not for the presence of the Moon (J. Laskar, F. Joutel, and P. Robutel, 1993, Nature 361, 615-617). The Moon itself is thought to be an accident of accretion, formed by a glancing blow from a Mars-sized planetesimal. Hence, planets with similar moons and stable obliquities may be extremely rare. This has lead Laskar and colleagues to suggest that the number of Earth-like planets with high obliquities and temperate, life-supporting climates may be small. To test this proposition, we have used an energy-balance climate model to simulate Earth's climate at obliquities up to 90 degrees. We show that Earth's climate would become regionally severe in such circumstances, with large seasonal cycles and accompanying temperature extremes on middle- and high-latitude continents which might be damaging to many forms of life. The response of other, hypothetical, Earth-like planets to large obliquity fluctuations depends on their land-sea distribution and on their position within the habitable zone (HZ) around their star. Planets with several modest-sized continents or equatorial supercontinents are more climatically stable than those with polar supercontinents. Planets farther out in the HZ are less affected by high obliquities because their atmospheres should accumulate CO2 in response to the carbonate-silicate cycle. Dense, CO2-rich atmospheres transport heat very effectively and therefore limit the magnitude of both seasonal cycles and latitudinal temperature gradients. We conclude that a significant fraction of extrasolar Earth-like planets may still be habitable, even if they are subject to large obliquity fluctuations.

  11. A Semianalytical Ion Current Model for Radio Frequency Driven Collisionless Sheaths

    NASA Technical Reports Server (NTRS)

    Bose, Deepak; Govindan, T. R.; Meyyappan, M.; Arnold, Jim (Technical Monitor)

    2001-01-01

    We propose a semianalytical ion dynamics model for a collisionless radio frequency biased sheath. The model uses bulk plasma conditions and electrode boundary condition to predict ion impact energy distribution and electrical properties of the sheath. The proposed model accounts for ion inertia and ion current modulation at bias frequencies that are of the same order of magnitude as the ion plasma frequency. A relaxation equation for ion current oscillations is derived which is coupled with a damped potential equation in order to model ion inertia effects. We find that inclusion of ion current modulation in the sheath model shows marked improvements in the predictions of sheath electrical properties and ion energy distribution function.

  12. Dust charging and charge fluctuations in a weakly collisional radio-frequency sheath at low pressure

    SciTech Connect

    Piel, Alexander Schmidt, Christian

    2015-05-15

    Models for the charging of dust particles in the bulk plasma and in the sheath region are discussed. A new model is proposed that describes collision-enhanced ion currents in the sheath. The collisions result in a substantial reduction of the negative charge of the dust. Experimental data for the dust charge in the sheath can be described by this model when a Bi-Maxwellian electron distribution is taken into account. Expressions for the dust charging rate for all considered models are presented and their influence on the rise of the kinetic dust temperature is discussed.

  13. Sheath broadening in imploding z-pinches due to large-bandwidth Rayleigh-Taylor instability

    SciTech Connect

    Hammer, J.H.; Eddleman, J.L.; Tabak, M.; Toor, A.; Zimmerman, G.B.; De Groot, J.S.

    1996-06-04

    The magnetic Rayleigh-Taylor (RT) instability has been predicted and observed to cause breakup of the plasma sheath in imploding Z-pinches. In this work we show that for the type of density profile encountered in strongly radiating pinches, instability at very short wavelengths grows to the non-linear stage and seeds progressively longer wavelengths. The result is a self-similar broadening of the sheath as found for mix layers in fluid RT unstable systems.

  14. Sheath Effects on Electron Density Measurements in Frequency Shift Probe and their Application to Electron Temperature Measurements

    NASA Astrophysics Data System (ADS)

    Nakamura, Keiji; Zhang, Qi; Sugai, Hideo

    2009-10-01

    Technologies of plasma monitoring are important for accurate plasma control. We have developed a frequency shift probe, and the probe enables us to measure an electron density from variation of resonance frequency of the probe head similarly to the hairpin probe. A plane structure of the probe head make it possible to minimizes disturbance to the processing plasma, and the probe is applicable to a reactive polymer-deposition plasmas since the polymer has no significant effects on the resonance frequency. The electron density is usually obtained from a plasma-induced shift of the probe resonance frequency, however influences of a sheath around the probe should been considered for more precise density measurements. In this work, sheath effects on the frequency shift probe were investigated, and the frequency shift probe was applied to measure a electron temperature using the sheath effects. As the sheath thickness increased, the resonance frequency decreased, and the sheath effect is enhanced depending on probe structure. Since the sheath width is proportional to Debye length, the probe resonance frequency depends on electron density and electron temperature, suggesting that resonance frequencies obtained in two probes having different sheath dependence gives an unique solution of the density and temperature of electrons.

  15. Obliquely incident ion beam figuring

    NASA Astrophysics Data System (ADS)

    Zhou, Lin; Dai, Yifan; Xie, Xuhui; Li, Shengyi

    2015-10-01

    A new ion beam figuring (IBF) technique, obliquely incident IBF (OI-IBF), is proposed. In OI-IBF, the ion beam bombards the optical surface obliquely with an invariable incident angle instead of perpendicularly as in the normal IBF. Due to the higher removal rate in oblique incidence, the process time in OI-IBF can be significantly shortened. The removal rates at different incident angles were first tested, and then a test mirror was processed by OI-IBF. Comparison shows that in the OI-IBF technique with a 30 deg incident angle, the process time was reduced by 56.8%, while keeping the same figure correcting ability. The experimental results indicate that the OI-IBF technique is feasible and effective to improve the surface correction process efficiency.

  16. Anisotropic emission of neutral atoms: evidence of an anisotropic Rydberg sheath in nanoplasma

    NASA Astrophysics Data System (ADS)

    Rajeev, R.; Madhu Trivikram, T.; Rishad, K. P. M.; Krishnamurthy, M.

    2015-02-01

    Intense laser-produced plasma is a complex amalgam of ions, electrons and atoms both in ground and excited states. Little is known about the spatial composition of the excited states that are an integral part of most gaseous or cluster plasma. In cluster-plasma, Rydberg excitations change the charge composition of the ions through charge transfer reactions and shape the angular distributions. Here, we demonstrate a non-invasive technique that reveals the anisotropic Rydberg excited cluster sheath by measuring anisotropy in fast neutral atoms. The sheath is stronger in the direction of light polarization and the enhanced charge transfer by the excited clusters results in larger neutralization.

  17. Silver-sheathed multifilament wires

    NASA Astrophysics Data System (ADS)

    Wu, C. T.; Goretta, K. C.; Shi, D.; Lanagan, M. T.; Poeppel, R. B.

    1991-01-01

    The process for manufacturing Ag-sheathed multifilament superconducting wires was investigated. Bi2Sr(1.7)CaCu2O(x), Pb-doped Bi2Sr2Ca2Cu3O(x), or YBa2Cu3O(x) powders were packed into Ag tubes and swaged into long wires. Pieces were cut from each wire, packed into a second Ag tube and swaged or rolled into multifilament wires. Each wire was then sintered to produce a superconductor. Processing considerations included the sheath workability, effects of compacting and residual stresses, and heat treatment schedules. The superconducting properties of the Bi-based wires were superior to those of the YBa2Cu3O(x) wires at 4.2 K, but not at 77 K.

  18. Oscillation, Collapse and Disappearance of Debye Sheaths Due to Secondary Electron Emission

    NASA Astrophysics Data System (ADS)

    Campanell, Michael; Khrabrov, Alexander; Kaganovich, Igor

    2012-10-01

    Most theories of PSI with secondary electron emission (SEE) implicitly assume a stable sheath exists. Ions are assumed to be drawn to the wall and the SEE is characterized by a fixed ``coefficient'' (e.g. G.D. Hobbs and J.A. Wesson, Plasma Phys. 9, 85 (1967)). We present simulations and basic theory showing a class of sheath instabilities that can arise under general conditions. Instabilities cause abrupt changes in the plasma, drive spontaneous oscillations, and dramatically increase cross-B-field transport, wall flux and energy loss. (M.D. Campanell et. al. PRL 108, 235001 (2012)). Also, if the SEE yield of hot plasma electrons impacting the walls exceeds unity, the sheath and presheath may disappear completely because there is no need for ions to be drawn to the wall in order to maintain current balance (M.D. Campanell et. al. PRL 108, 255001 (2012)). Instead, the walls acquire a positive charge. The plasma potential is negative, the ion flux is zero and plasma electrons are unconfined. These three properties all differ from the ``space charge limited'' sheath often assumed to form when SEE yield exceeds 1. In the new ``inverse sheath'' regime, zero current is maintained only by pulling the ``extra'' secondaries back to the wall.

  19. Testing obliquity-tuned timescales

    NASA Astrophysics Data System (ADS)

    Zeeden, Christian; Meyers, Stephen R.; Lourens, Lucas J.; Hilgen, Frederik J.

    2016-04-01

    Astrochronology seeks to use rhythmic sedimentary alterations to provide high-resolution age models, and this method now provides a backbone for much of the Cenozoic and Mesozoic time scale. While a range of methods for orbital tuning are available, a common approach is to directly match observed sedimentary alternations to target curves from astronomical computations, followed by evaluation of amplitude modulations (AM) as a means of verification. A quantitative test for precession-eccentricity modulations in astronomically-tuned data has been recently developed, however, a similar test for obliquity is lacking. Here, we introduce an algorithm for obliquity AM assessment, which avoids effects of obliquity frequency modulation that can artificially mimic the expected AM. The approach can be used to test for correlation with the theoretical astronomical solution in a way similar to the precession AM method. Obliquity is an especially dominant component of orbitally-driven climate variability in the early Quaternary; here Quaternary models and climate proxy records are used to evaluate the reliability of the proposed method.

  20. Characteristics of wall sheath and secondary electron emission under different electron temperature in Hall thruster

    NASA Astrophysics Data System (ADS)

    Duan, Ping; Qin, Haijuan; Cao, Anning; Zhou, Xinwei; Chen, Long; Gao, Hong

    2013-09-01

    Characteristics of discharge channel wall plasma sheath in Hall thruster have great effects on its performance. In this paper, we establish a two-dimensional physical model in Hall thruster sheath area to investigate the influences of the different electron temperature, propellant and particle weight on sheath potential and secondary electron emission in Hall thruster, by the method of Particle In Cell (PIC) simulation. And the electric field at the particle position is obtained by solving the Poisson's equation. The numerical results show that when the electron temperature is low, the change of sheath potential drop is bigger than that with electrons at high temperature, the surface potential maintains a stable value and the stability of the sheath is good. When the electron temperature is high, the surface potential maintains persistent oscillation, and the stability of the sheath is reduced. Along with the increase of electron temperature, the coefficient of secondary electron emission in wall reduce after the first increasing. For three kinds of propellant (Ar, Kr, Xe), with the increase of ion mass, sheath potential and the secondary electron emission coefficient in turn reduce.

  1. Plasma-wall transition in weakly collisional plasmas

    SciTech Connect

    Manfredi, G.; Devaux, S.

    2008-10-15

    This paper reviews some theoretical and computational aspects of plasma-wall interactions, in particular the formation of sheaths. Some fundamental results are derived analytically using a simple fluid model, and are subsequently tested with kinetic simulations. The various regions composing the plasma-wall transition (Debye sheath, collisional and magnetic presheaths) are discussed in details.

  2. Gold ink coating of thermocouple sheaths

    DOEpatents

    Ruhl, H. Kenneth

    1992-01-01

    A method is provided for applying a gold ink coating to a thermocouple sheath which includes the steps of electropolishing and oxidizing the surface of the thermocouple sheath, then dipping the sheath into liquid gold ink, and finally heat curing the coating. The gold coating applied in this manner is highly reflective and does not degrade when used for an extended period of time in an environment having a temperature over 1000.degree. F. Depending on the application, a portion of the gold coating covering the tip of the thermocouple sheath is removed by abrasion.

  3. Effect of anisotropy of electron velocity distribution function on dynamic characteristics of sheath in Hall thrusters

    SciTech Connect

    Zhang Fengkui; Wu Xiande; Ding Yongjie; Li Hong; Yu Daren

    2011-10-15

    In Hall thrusters, the electron velocity distribution function is not only depleted at high energies, but also strongly anisotropic. With these electrons interacting with the channel wall, the sheath will be changed in its dynamic characteristics. In the present letter, a two dimensional particle-in-cell code is used to simulate these effects in a collisionless plasma slab. The simulated results indicate that the sheath changes from steady regime to temporal oscillation regime when the electron velocity distribution function alters from isotropy to anisotropy. Moreover, the temporal oscillation sheath formed by the anisotropic electrons has a much greater oscillating amplitude and a much smaller average potential drop than that formed by the isotropic electrons has. The anisotropic electrons are also found to lower the critical value of electron temperature needed for the appearance of the spatial oscillation sheath.

  4. Sheath structure transition controlled by secondary electron emission at low gas pressure

    NASA Astrophysics Data System (ADS)

    Schweigert, Irina; Langendorf, Samuel J.; Keidar, Michael; Walker, Mitchell L. R.

    2014-10-01

    Previously the experiments demonstrated that the growth of the electron temperature with power in the Hall thruster is restricted by plasma-wall interaction if the wall has an enhanced secondary electron emission (SEE) yield. It is known that the plasma and wall is separated by the sheath potential drop to provide the condition of zero-current on the surface with floating potential. The rearrangement of the sheath structure near the plate with enhanced SEE is the subject of our experimental and theoretical study. The experiment was carried out in multidipole plasma device, where plasma is maintained by the negatively-biased emissive filament. The plate with sapphire surface is placed 50 cm apart from the filament. The plasma parameters were measured for different negative biases Ub and discharge currents J at P = 10-4 Torr. In our PIC simulations the plasma was calculated for the experimental conditions. We solved self-consistently the Boltzmann equations for the electron and ion distribution functions and Poisson equation for electrical field. Both in the experiment and simulation we found non-monotonic change in sheath structure near the plate depending on Ub and J. The kinetic simulations allowed us to describe the sheath rearrangement in terms of the electron energy distribution function.

  5. Propagation characteristics of dust-acoustic waves in presence of a floating cylindrical object in the DC discharge plasma

    NASA Astrophysics Data System (ADS)

    Choudhary, Mangilal; Mukherjee, S.; Bandyopadhyay, P.

    2016-08-01

    The experimental observation of the self-excited dust acoustic waves (DAWs) and its propagation characteristics in the absence and presence of a floating cylindrical object is investigated. The experiments are carried out in a direct current (DC) glow discharge dusty plasma in a background of argon gas. Dust particles are found levitated at the interface of plasma and cathode sheath region. The DAWs are spontaneously excited in the dust medium and found to propagate in the direction of ion drift (along the gravity) above a threshold discharge current at low pressure. Excitation of such a low frequency wave is a result of the ion-dust streaming instability in the dust cloud. Characteristics of the propagating dust acoustic wave get modified in the presence of a floating cylindrical object of radius larger than that of the dust Debye length. Instead of propagation in the vertical direction, the DAWs are found to propagate obliquely in the presence of the floating object (kept either vertically or horizontally). In addition, a horizontally aligned floating object forms a wave structure in the cone shaped dust cloud in the sheath region. Such changes in the propagation characteristics of DAWs are explained on the basis of modified potential (or electric field) distribution, which is a consequence of coupling of sheaths formed around the cylindrical object and the cathode.

  6. Anaglyph videoanimations from oblique stereoimages

    NASA Astrophysics Data System (ADS)

    Vozenilek, Vit; Kralik, Tomas

    2015-03-01

    The paper deals with the approach of compiling of animations from a pair of oblique stereoimages. The authors investigated as simple and cheap way as possible to develop such approach which will be available for wide scope of ordinary users with common equipment. They concentrated on three procedures of oblique stereoimage handling to compile sets of images, animations and analogue documents. After capturing construction site by a pair of web cameras the data were corrected, photogrammetrically adjusted (due to radial distortion) and exported. Firstly, a set of anaglyphic images were compiled, then they were trimmed and timeline was inserted. The final anaglyph animations are compiled in various versions. In addition, an anaglyphic book containing 150 images was created in a special way that the user can easily browse through its content. The main outputs are several unique anaglyph products, but more beneficial outputs are developed procedures of anaglyph visualization that can be applied with minor modifications to photographing of any objects.

  7. Oblique focus ICCD laboratory evaluation

    NASA Technical Reports Server (NTRS)

    York, D. G.

    1982-01-01

    An oblique focus intensified charge coupled device (ICCD) was constructed and operated in a vacuum system. Special gratings were obtained and an optical system set up to try to model a candidate UV spectrometer (Milieu Interstellaire et Intergalactique-MISIG), and to produce small enough images to test the theoretical subpixel resolution capability of the ICCD system. The efforts were only partly successful. Based on the results, a similar detector was built and flown successfully on a Princeton rocket program.

  8. DEM simulation of oblique boudinage

    NASA Astrophysics Data System (ADS)

    Komoroczi, Andrea; Abe, Steffen; Urai, Janos L.

    2013-04-01

    Boudinage occurs in mechanically layered rocks if there is a component of lengthening parallel to a brittle layer in a ductile matrix. Asymmetric boudin structures develop if the extension is not layer-parallel, and the boudin blocks rotate. The amount of block rotation is commonly used as shear indicators; therefore, it has been well studied. However, full oblique boudinage has not been modeled yet. We simulated full boudinage processes during layer oblique extension using DEM simulation software. In our boudinage model, the initial setup consists of three layers: there is a brittle center oblique layer in a ductile matrix. We simulated horizontal extension by applying vertical displacement: the top and bottom boundaries of the model are moved at a constant velocity, while the side boundaries were force controlled by applying a constant confining force. By varying the cohesion of the competent layer, various type and shape of boudin blocks were developed. By varying the angle of the competent layer, the rotation of the boudin blocks changed. With higher dip of the competent layer, the rotation of the boudin blocks is more consistent. We also studied the stress field during the simulation. The results show, that in case of ductile material, the disruptions of the layer are driven by the angle of the layer and not the orientation of the external stress field.

  9. History of the earth's obliquity

    NASA Astrophysics Data System (ADS)

    Williams, George E.

    1993-03-01

    The evolution of the obliquity of the ecliptic (ɛ), the Earth's axial tilt of 23.5°, may have greatly influenced the Earth's dynamical, climatic and biotic development. For ɛ > 54°, climatic zonation and zonal surface winds would be reversed, low to equatorial latitudes would be glaciated in preference to high latitudes, and the global seasonal cycle would be greatly amplified. Phanerozoic palaeoclimates were essentially uniformitarian in regard to obliquity, with normal climatic zonation and zonal surface winds, circum-polar glaciation and little seasonal change in low latitudes. Milankovitch-band periodicity in early Palaeozoic evaporites implies ɛ¯≈ 26.4 ± 2.1°at ˜ 430 Ma, suggesting that the obliquity during most of Phanerozoic time was comparable to the present value. By contrast, the paradoxical Late Proterozoic (˜ 800-600Ma) glacial environment— frigid, strongly seasonal climates, with permafrost and grounded ice-sheets near sea level preferentially in low to equatorial palaeolatitudes—implies glaciation with ɛ > 54° (assuming a geocentric axial dipolar magnetic field). Palaeotidal data accord with a large obliquity in Late Proterozoic time. Indeed, Proterozoic palaeoclimates in general appear non-uniformitarian with respect to climatic zonation, consistent with ɛ > 54°. The primordial Earth's obliquity is unconstrained by the widely-accepted single-giant-impact hypothesis for the origin of the Moon; an impact-induced obliquity ≳ 70° is possible, depending on the impact parameters. Subsequent evolution of ɛ depends on the relative magnitudes of the rate of obliquity-increase ɛ caused by tidal friction, and the rate of decrease ɛ due to dissipative core-mantle torques during precession (ɛ < 90° is required for precessional torques to move ɛ toward 0°). Proterozoic palaeotidal data indicate ɛ ≈ 0.0003-0.0006″/cy (seconds of arc per century) during most of Earth history, only half the rate estimated using the modern, large

  10. SHEATH BLIGHT RESISTANCE IN SOUTHERN RICE

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sheath blight is a serious fungal disease problem in southern US rice production, making it necessary for rice farmers to diligently use fungicides for its control. There are no long grain rice varieties adapted to commercial production in the southern US that have adequate resistance to sheath bli...

  11. Observation of self-sustaining relativistic ionization wave launched by a sheath field.

    PubMed

    McCormick, M; Arefiev, A V; Quevedo, H J; Bengtson, R D; Ditmire, T

    2014-01-31

    We present experimental evidence supported by simulations of a relativistic ionization wave launched into a surrounding gas by the sheath field of a plasma filament with high energy electrons. Such a filament is created by irradiating a clustering gas jet with a short pulse laser (115  fs) at a peak intensity of 5×10(17)  W/cm2. We observe an ionization wave propagating radially through the gas for about 2 ps at 0.2-0.5 c after the laser has passed, doubling the initial radius of the filament. The gas is ionized by the sheath field, while the longevity of the wave is explained by a moving field structure that traps the high energy electrons near the boundary, maintaining a strong sheath field despite the significant expansion of the plasma. PMID:24580461

  12. Sheath oscillation characteristics and effect on near-wall conduction in a krypton Hall thruster

    SciTech Connect

    Zhang, Fengkui Kong, Lingyi; Li, Chenliang; Yang, Haiwei; Li, Wei

    2014-11-15

    Despite its affordability, the krypton Hall-effect thruster in applications always had problems in regard to performance. The reason for this degradation is studied from the perspective of the near-wall conductivity of electrons. Using the particle-in-cell method, the sheath oscillation characteristics and its effect on near-wall conduction are compared in the krypton and xenon Hall-effect thrusters both with wall material composed of BNSiO{sub 2}. Comparing these two thrusters, the sheath in the krypton-plasma thruster will oscillate at low electron temperatures. The near-wall conduction current is only produced by collisions between electrons and wall, thereby causing a deficiency in the channel current. The sheath displays spatial oscillations only at high electron temperature; electrons are then reflected to produce the non-oscillation conduction current needed for the krypton-plasma thruster. However, it is accompanied with intensified oscillations.

  13. Sheath oscillation characteristics and effect on near-wall conduction in a krypton Hall thruster

    NASA Astrophysics Data System (ADS)

    Zhang, Fengkui; Kong, Lingyi; Li, Chenliang; Yang, Haiwei; Li, Wei

    2014-11-01

    Despite its affordability, the krypton Hall-effect thruster in applications always had problems in regard to performance. The reason for this degradation is studied from the perspective of the near-wall conductivity of electrons. Using the particle-in-cell method, the sheath oscillation characteristics and its effect on near-wall conduction are compared in the krypton and xenon Hall-effect thrusters both with wall material composed of BNSiO 2 . Comparing these two thrusters, the sheath in the krypton-plasma thruster will oscillate at low electron temperatures. The near-wall conduction current is only produced by collisions between electrons and wall, thereby causing a deficiency in the channel current. The sheath displays spatial oscillations only at high electron temperature; electrons are then reflected to produce the non-oscillation conduction current needed for the krypton-plasma thruster. However, it is accompanied with intensified oscillations.

  14. Analysis of oblique hypervelocity impact phenomena

    NASA Technical Reports Server (NTRS)

    Schonberg, William P.; Taylor, Roy A.

    1988-01-01

    This paper describes the results of an experimental investigation of phenomena associated with the oblique hypervelocity impact of spherical projectiles on multisheet aluminum structures. A model that can be employed in the design of meteoroid and space debris protection systems for space structures is developed. The model consists of equations that relate crater and perforation damage of a multisheet structure to parameters such as projectile size, impact velocity, and trajectory obliquity. The equations are obtained through a regression analysis of oblique hypervelocity impact test data. This data shows that the response of a multisheet structure to oblique impact is significantly different from its response to normal hypervelocity impact. It was found that obliquely incident projectiles produce ricochet debris that can severely damage panels or instrumentation located on the exterior of a space structure. Obliquity effects of high-speed impact must, therefore, be considered in the design of any structure exposed to a meteoroid or space debris environement.

  15. An investigation of oblique hypervelocity impact

    NASA Technical Reports Server (NTRS)

    Schonberg, William P.

    1987-01-01

    This report describes the results of an investigation of phenomena associated with the oblique hypervelocity impact of spherical projectiles on multi-sheet aluminum structures. A model to be employed in the design of meteoroid and space debris protection systems for space structures is developed. The model consists of equations relating crater and perforation damage of a multi-sheet structure to parameters such as projectile size, impact velocity, and trajectory obliquity. The equations are obtained through a regression analysis of oblique hypervelocity impact test data. This data shows that the response of a multi-sheet structure to oblique impact is significantly different from its response to normal hypervelocity impact. It was found that obliquely incident projectiles produce ricochet debris that can severely damage panels or instrumentation located on the exterior of a space structure. Obliquity effects of high-speed impact must, therefore, be considered in the design of any structure exposed to the hazardous meteoroid and space debris environment.

  16. First and second quarter progress report 1987 on plasma theory and simulation, January 1-June 30, 1987

    SciTech Connect

    Birdsall, C.K.

    1987-01-01

    This paper contains papers on general plasma theory and plasma-wall physics. Specific titles enclosed are as follows: ion acceleration in a source sheath with an initial velocity; collector and source sheaths of a finite ion temperature plasma; effects of secondary electron emission on the collector and source sheaths of a finite ion temperature plasma; effects of ion reflection on the collector and source sheaths of a finite ion temperature plasma; and vortex dynamics and transport to the wall in a crossed field plasma sheath.

  17. Oblique Alfvén instabilities driven by compensated currents

    SciTech Connect

    Malovichko, P.; Voitenko, Y.; De Keyser, J.

    2014-01-10

    Compensated-current systems created by energetic ion beams are widespread in space and astrophysical plasmas. The well-known examples are foreshock regions in the solar wind and around supernova remnants. We found a new oblique Alfvénic instability driven by compensated currents flowing along the background magnetic field. Because of the vastly different electron and ion gyroradii, oblique Alfvénic perturbations react differently on the currents carried by the hot ion beams and the return electron currents. Ultimately, this difference leads to a non-resonant aperiodic instability at perpendicular wavelengths close to the beam ion gyroradius. The instability growth rate increases with increasing beam current and temperature. In the solar wind upstream of Earth's bow shock, the instability growth time can drop below 10 proton cyclotron periods. Our results suggest that this instability can contribute to the turbulence and ion acceleration in space and astrophysical foreshocks.

  18. The oblique behavior of low-frequency electromagnetic waves excited by newborn cometary ions

    NASA Technical Reports Server (NTRS)

    Brinca, Armando L.; Tsurutani, Bruce T.

    1989-01-01

    The free energy in oxygen or hydrogen ions freshly created in the solar wind stimulates low-frequency electromagnetic waves whose growth does not always maximize at parallel propagation. Exploration of the wave vector plane discloses the frequent occurrence of islets of oblique growth unconnected to the unstable parallel modes. Contour plots of the growth rate, real frequency, polarization, and magnetic compression characterize the oblique wave behavior for large values of the initial pitch angle of the cometary particles. Although wave-particle (Landau and cyclotron) resonances feed most of the surveyed oblique instabilities, some are seemingly fluidlike. The results, obtained from the numerical solution of the kinetic dispersion and wave equations, imply that newborn ions can easily excite significant oblique hydromagnetic wave activity. Cometary environments provide the adopted plasma model, but the study is helpful in the interpretation of other low-frequency wave observations in space.

  19. Planar magnetic structures in coronal mass ejection-driven sheath regions

    NASA Astrophysics Data System (ADS)

    Palmerio, Erika; Kilpua, Emilia; Savani, Neel

    2016-04-01

    Coronal Mass Ejections (CMEs) often travel in the interplanetary space faster than the ambient solar wind. When their relative velocities exceed the local magnetosonic speed, a shock wave forms. The region between the shock front and the leading edge is known as sheath region. Sheaths are compressed regions characterized by turbulent magnetic field and plasma properties and they can cause significant space weather disturbances. Moreover, sheaths often exhibit a complex internal structure, which makes understanding their formation and predicting their geoeffectivity particularly difficult. Planar magnetic structures (PMSs) are frequently reported in CME-driven sheath regions. The magnetic field vectors in a PMS are characterized by abrupt changes in direction and magnitude, but they all remain for a time interval of several hours nearly parallel to a single plane that includes the interplanetary magnetic field (IMF) spiral direction but is inclined to the ecliptic plane. We present the study of PMSs in the sheath region of CMEs for a sample of 95 events observed in situ by the ACE and Wind spacecraft in the period 1997-2015. The presence of planar structures is detected with an automated method and evaluated through the minimum variance analysis (MVA), needed for determining the normal vector to the PMS-plane. We relate the occurrence and location of the PMSs to various shock, sheath and CME properties. We show in addition the dependence of the angle between the IP shock and PMS plane normals with respect to the PMS location within the sheath. Finally, we study the amount of strongly southward magnetic fields in planar and non-planar parts of the sheath, aiming at determining whether either feature is more likely to drive magnetospheric activity.

  20. Obliquity Variations of Extrasolar Terrestrial Planets

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Chambers, John E.

    2004-01-01

    A planet's obliquity, which is the angle between its orbital angular momentum and its rotational angular momentum, is an important factor in determining its climate and habitability. For small obliquities, as well as obliquities close to 180 degrees, the planet receives more radiant energy from its star at equatorial latitudes than near its poles, whereas the poles are heated the most for obliquities near 90 degrees. Jacques Laskar has analyzed possible obliquity variations of the planets in our Solar System. His study also considers the same planets with different rotational periods, and the Earth without the Moon. He finds, using frequency map analysis, that the obliquity of the Earth is stabilized by the Moon, and can vary by at most a few degrees. In contrast, the obliquity of Mars can range from 0 to 60 degrees, and a hypothetical moonless Earth's axial tilt could be close to 0 degrees or as large as 85 degrees. Numerical integrations by Laskar and others have shown that Mars' obliquity indeed varies over most of its permitted range on time scales of tens of millions of years. In contrast, our analysis shows that the obliquity of a moonless Earth appears to be confined to the range of approximately 12 - 38 degrees over time scales of 100 million years. Results of ongoing longer integrations will be presented, and their implications discussed.

  1. Double Layers: Potential Formation and Related Nonlinear Phenomena in Plasmas: Proceedings of the 5th Symposium

    NASA Astrophysics Data System (ADS)

    Iizuka, S.

    1998-02-01

    The Table of Contents for the book is as follows: * PREFACE * INTERNATIONAL SCIENTIFIC COMMITTEE * LOCAL ORGANIZING COMMITTEE AT TOHOKU UNIVERSITY * CHAPTER 1: DOUBLE LAYERS, SHEATHS, AND POTENTIAL STRUCTURES * 1.1 Double Layers * On Fluid Models of Stationary, Acoustic Double Layers (Invited) * Particle Simulation of Double Layer (Invited) * Space-Time Dependence of Non-Steady Double Layers * The Role of Low Energy Electrons for the Generation of Anode Double Layers in Glow Discharges * Arbitrary Amplitude Ion-Acoustic Double Layers in a Dusty Plasma * 1.2 Sheaths * Bounded Plasma Edge Physics as Observed from Simulations in 1D and 2D (Invited) * Control of RF Sheath Structure in RF Diode Discharge * Observation of Density Gradients with Fine Structures and Low Frequency Wave Excitation at the Plasma-Sheath Boundary * Double Sheath Associated with an Electron Emission to a Plasma Containing Negative Ions * Sheath Edge and Floating Potential for Multi-Species Plasmas Including Dust Particles * 1.3 Potential Structures and Oscillations * Potential Structure Formed at a Constriction of a DC He Positive Column and its Coupling with Ionization Wave * Potential Structure in a New RF Magnetron Device with a Hollow Electrode * Potential Disruption in a RF Afterglow Electronegative Plasma * Potential Oscillation in a Strongly Asymmetry RF Discharge Containing Negative Ions * Effects of External Potential Control on Coulomb Dust Behavior * Potential Structure of Carbon Arc Discharge for High-Yield Fullerenes Formation * Control of Axial and Radial Potential Profiles in Tandem Mirrors (Invited) * CHAPTER 2: FIELD-ALIGNED ELECTRIC FIELDS AND RELATED PARTICLE ACCELERATIONS * 2.1 Field-Aligned Potential Formation * Formation of Large Potential Difference in a Plasma Flow along Converging Magnetic Field Lines (Invited) * Presheath Formation in front of an Oblique End-Plate in a Magnetized Sheet Plasma * Plasma Potential Formation Due to ECRH in a Magnetic Well * Electrostatic

  2. Unusual stability of the Methanospirillum hungatei sheath.

    PubMed Central

    Beveridge, T J; Stewart, M; Doyle, R J; Sprott, G D

    1985-01-01

    The proteinaceous sheath of Methanospirillum hungatei was isolated by lysing cells in 50 mM dithiothreitol, separating the sheath from other cellular material by discontinuous sucrose density centrifugation, and removing the "cell spacers" with dilute NaOH. The isolated sheath material consisted of hollow tubes which had a highly ordered surface array. The stability of the sheath to treatment with denaturants and to enzymatic digestion was examined by a turbidimetric assay in conjunction with electron microscopy and optical or electron diffraction. The sheath was resistant to a range of proteases and also was not digested by peptidoglycan-degrading enzymes, a lipase, a cellulase, a glucosidase, or Rhozyme (a mixture of galactosidases, acetylglucosaminidase, acetylgalactosaminidase, fucosidase, and mannosidases). In addition to being unaffected by common salts, thiol-reducing agents, and EDTA, the layer was resistant to powerful denaturants such as 6 M urea, 6 M guanidinium hydrochloride, 10 M LiSCN, cyanogen bromide, sodium periodate, and 1% sodium dodecyl sulfate. Strong bases, boiling 3 N HCl, and performic acid did attack the sheath; in these cases, the array was systematically disassembled in a progressive manner, which was followed by electron microscopy. The layer was slightly modified by N-bromosuccinimide in urea, but the array remained intact. The stability of the sheath was remarkable, not only as compared to other bacterial surface arrays, but also as compared to proteins generally, and possibly indicated the presence of covalent cross-links between protein subunits. Images PMID:3988711

  3. Disposable sheath that facilitates endoscopic Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Wenbo; Short, Michael; Tai, Isabella T.; Zeng, Haishan

    2016-02-01

    In vivo endoscopic Raman spectroscopy of human tissue using a fiber optic probe has been previously demonstrated. However, there remain several technical challenges, such as a robust control over the laser radiation dose and measurement repeatability during endoscopy. A decrease in the signal to noise was also observed due to aging of Raman probe after repeated cycles of harsh reprocessing procedures. To address these issues, we designed and tested a disposable, biocompatible, and sterile sheath for use with a fiber optic endoscopic Raman probe. The sheath effectively controls contamination of Raman probes between procedures, greatly reduces turnaround time, and slows down the aging of the Raman probes. A small optical window fitted at the sheath cap maintained the measurement distance between Raman probe end and tissue surface. To ensure that the sheath caused a minimal amount of fluorescence and Raman interference, the optical properties of materials for the sheath, optical window, and bonding agent were studied. The easy-to-use sheath can be manufactured at a moderate cost. The sheath strictly enforced a maximum permissible exposure standard of the tissue by the laser and reduced the spectral variability by 1.5 to 8.5 times within the spectral measurement range.

  4. Document segmentation via oblique cuts

    NASA Astrophysics Data System (ADS)

    Svendsen, Jeremy; Branzan-Albu, Alexandra

    2013-01-01

    This paper presents a novel solution for the layout segmentation of graphical elements in Business Intelligence documents. We propose a generalization of the recursive X-Y cut algorithm, which allows for cutting along arbitrary oblique directions. An intermediate processing step consisting of line and solid region removal is also necessary due to presence of decorative elements. The output of the proposed segmentation is a hierarchical structure which allows for the identification of primitives in pie and bar charts. The algorithm was tested on a database composed of charts from business documents. Results are very promising.

  5. History of the earth's obliquity

    NASA Astrophysics Data System (ADS)

    Williams, George E.

    1993-03-01

    The evolution of the obliquity of the ecliptic (ɛ), the Earth's axial tilt of 23.5°, may have greatly influenced the Earth's dynamical, climatic and biotic development. For ɛ > 54°, climatic zonation and zonal surface winds would be reversed, low to equatorial latitudes would be glaciated in preference to high latitudes, and the global seasonal cycle would be greatly amplified. Phanerozoic palaeoclimates were essentially uniformitarian in regard to obliquity, with normal climatic zonation and zonal surface winds, circum-polar glaciation and little seasonal change in low latitudes. Milankovitch-band periodicity in early Palaeozoic evaporites implies ɛ¯≈ 26.4 ± 2.1°at ˜ 430 Ma, suggesting that the obliquity during most of Phanerozoic time was comparable to the present value. By contrast, the paradoxical Late Proterozoic (˜ 800-600Ma) glacial environment— frigid, strongly seasonal climates, with permafrost and grounded ice-sheets near sea level preferentially in low to equatorial palaeolatitudes—implies glaciation with ɛ > 54° (assuming a geocentric axial dipolar magnetic field). Palaeotidal data accord with a large obliquity in Late Proterozoic time. Indeed, Proterozoic palaeoclimates in general appear non-uniformitarian with respect to climatic zonation, consistent with ɛ > 54°. The primordial Earth's obliquity is unconstrained by the widely-accepted single-giant-impact hypothesis for the origin of the Moon; an impact-induced obliquity ≳ 70° is possible, depending on the impact parameters. Subsequent evolution of ɛ depends on the relative magnitudes of the rate of obliquity-increase ɛ caused by tidal friction, and the rate of decrease ɛ due to dissipative core-mantle torques during precession (ɛ < 90° is required for precessional torques to move ɛ toward 0°). Proterozoic palaeotidal data indicate ɛ ≈ 0.0003-0.0006″/cy (seconds of arc per century) during most of Earth history, only half the rate estimated using the modern, large

  6. The chaotic obliquity of Mars

    NASA Astrophysics Data System (ADS)

    Touma, J.; Wisdom, J.

    1993-02-01

    The discovery (by Laskar, 1989, 1990) that the evolution of the solar system is chaotic, made in a numerical integration of the averaged secular approximation of the equations of motions for the planets, was confirmed by Sussman and Wisdom (1992) by direct numerical integration of the whole solar system. This paper presents results of direct integrations of the rotation of Mars in the chaotically evolved planetary system, made using the same model as that used by Sussman and Wisdom. The numerical integration shows that the obliquity of Mars undergoes large chaotic variations, which occur as the system evolves in the chaotic zone associated with a secular spin-orbit resonance.

  7. Side-welded fast response sheathed thermocouple

    DOEpatents

    Carr, Kenneth R.

    1981-01-01

    A method of fabricating the measuring junction of a grounded-junction sheathed thermocouple to obtain fast time response and good thermal cycling performance is provided. Slots are tooled or machined into the sheath wall at the measuring junction, the thermocouple wires are laser-welded into the slots. A thin metal closure cap is then laser-welded over the end of the sheath. Compared to a conventional grounded-junction thermocouple, the response time is 4-5 times faster and the thermal shock and cycling capabilities are substantially improved.

  8. Side-welded fast response sheathed thermocouple

    DOEpatents

    Carr, K.R.

    A method of fabricating the measuring junction of a grounded-junction sheathed thermocouple to obtain fast time response and good thermal cycling performance is provided. Slots are tooled or machined into the sheath wall at the measuring junction, the thermocouple wires are laser-welded into the slots. A thin metal closure cap is then laser-welded over the end of the sheath. Compared to a conventional grounded-junction thermocouple, the response time is 4 to 5 times faster and the thermal shock and cycling capabilities are substantially improved.

  9. Erosion due to ion sputtering in absence of Debye Sheath at Divertor plates: PIC simulation

    NASA Astrophysics Data System (ADS)

    Goswami, K. S.; Adhikari, S.

    2014-10-01

    A 2D-3V Particle-in-Cell code with Monte Carlo Collision and a Plasma Surface Interaction Code written in Matlab is used to study the effect of grazing angle (α) on solid surface (divertor) erosion due to ion sputtering in magnetic fusion devices, where α is the angle between the magnetic field and the surface tangent. The ion distribution in front of an absorbing wall is computed using a kinetic model. Important factors like ion energy and impact angle for wall erosion and sputtering are highlighted. The dependence of these two parameters on grazing angle is investigated in detail. Physical Sputtering for ion bombardment is strongly dependent on incident ion energy and this energy is mainly gained by the ions when they travel through the potential drop across the combined Chodura Sheath and Debye Sheath. The present work contains the study of two scenario. In the first one we have studied the usual case to compare our result to the other similar work i.e. in presence of both Chodura Sheath and Debye Sheath. In the second one with the idea of previous work we have created the scenario where Debye Sheath cease to appear. The second scenario provides us the result that was never expected that the incident energy profile got reversed. The study is focused on the effect of grazing angle and its relation with the material erosion. Our study covers different materials (e.g. Be, Fe, W etc.) which are used as plasma facing components.

  10. Laser-induced fluorescence measurement of the dynamics of a pulsed planar sheath

    SciTech Connect

    Goeckner, M.J.; Malik, S.M. ); Conrad, J.R. ); Breun, R.A. )

    1994-04-01

    Using laser-induced fluorescence (LIF) the ion density near the edge of an expanding plasma sheath has been measured. These measurements utilized a transition of N[sup +][sub 2] [the P12 component of the [ital X] [sup 2][Sigma][sup +][sub [ital g

  11. Self-sustaining relativistic ionization wave launched by a sheath field

    NASA Astrophysics Data System (ADS)

    Arefiev, Alexey; McCormick, Matt; Quevedo, Hernan; Bengtson, Roger; Ditmire, Todd

    2013-10-01

    We present experimental evidence supported by particle-in-cell (PIC) simulations of a self-sustaining relativistic ionization wave launched into a surrounding gas by the sheath field of a high energy density plasma. We create a plasma filament with hot electrons by irradiating a supersonic clustering gas jet with a short pulse laser (115 fs) at an intensity of 5 ×1017 W/cm2. In contrast with a single atom, a cluster of atoms produces super-ponderomotive electrons in the field of the laser. These electrons generate a sheath field at the edge of the plasma filament strong enough to ionize the gas atoms in the sheath. We observe that a collisionless ionization wave is launched in this regime, propagating radially through the gas at up to 0.5 c after the laser has passed. The expansion of the resulting plasma filament due to the ionization wave occurs in about 2 ps, more than doubling the initial radius of the filament. The remarkable longevity of the wave without continuous energy deposition into the electron population is explained by a moving field structure that traps the hot electrons near the boundary. 2D PIC simulations confirm that the trapped hot electrons maintain a sheath field required for the ionization despite the significant expansion of the filament.

  12. Rectus sheath hematoma: three case reports

    PubMed Central

    Kapan, Selin; Turhan, Ahmet N; Alis, Halil; Kalayci, Mustafa U; Hatipoglu, Sinan; Yigitbas, Hakan; Aygun, Ersan

    2008-01-01

    Introduction Rectus sheath hematoma is an uncommon cause of acute abdominal pain. It is an accumulation of blood in the sheath of the rectus abdominis, secondary to rupture of an epigastric vessel or muscle tear. It could occur spontaneously or after trauma. They are usually located infraumblically and often misdiagnosed as acute abdomen, inflammatory diseases or tumours of the abdomen. Case presentation We reported three cases of rectus sheath hematoma presenting with a mass in the abdomen and diagnosed by computerized tomography. The patients recovered uneventfully after bed rest, intravenous fluid replacement, blood transfusion and analgesic treatment. Conclusion Rectus sheath hematoma is a rarely seen pathology often misdiagnosed as acute abdomen that may lead to unnecessary laparotomies. Computerized tomography must be chosen for definitive diagnosis since ultrasonography is subject to error due to misinterpretation of the images. Main therapy is conservative management. PMID:18221529

  13. Evaluation of the oblique detonation wave ramjet

    NASA Technical Reports Server (NTRS)

    Morrison, R. B.

    1978-01-01

    The potential performance of oblique detonation wave ramjets is analyzed in terms of multishock diffusion, oblique detonation waves, and heat release. Results are presented in terms of thrust coefficients and specific impulses for a range of flight Mach numbers of 6 to 16.

  14. Malignant Peripheral Nerve Sheath Tumors.

    PubMed

    Durbin, Adam D; Ki, Dong Hyuk; He, Shuning; Look, A Thomas

    2016-01-01

    Malignant peripheral nerve sheath tumors (MPNST) are tumors derived from Schwann cells or Schwann cell precursors. Although rare overall, the incidence of MPNST has increased with improved clinical management of patients with the neurofibromatosis type 1 (NF1) tumor predisposition syndrome. Unfortunately, current treatment modalities for MPNST are limited, with no targeted therapies available and poor efficacy of conventional radiation and chemotherapeutic regimens. Many murine and zebrafish models of MPNST have been developed, which have helped to elucidate the genes and pathways that are dysregulated in MPNST tumorigenesis, including the p53, and the RB1, PI3K-Akt-mTOR, RAS-ERK and Wnt signaling pathways. Preclinical results have suggested that new therapies, including mTOR and ERK inhibitors, may synergize with conventional chemotherapy in human tumors. The discovery of new genome editing technologies, like CRISPR-cas9, and their successful application to the zebrafish model will enable rapid progress in the faithful modeling of MPNST molecular pathogenesis. The zebrafish model is especially suited for high throughput screening of new targeted therapeutics as well as drugs approved for other purposes, which may help to bring enhanced treatment modalities into human clinical trials for this devastating disease. PMID:27165368

  15. Sheath rot of rice in Iran.

    PubMed

    Naeimi, S; Okhovvat, S M; Hedjaroude, G A; Khosravi, V

    2003-01-01

    Sheath rot of rice occurs in most rice-growing regions of the world. It usually causes yield losses from 20 to 85%. Sheath rot was reported from Iran in 1993. Year after year, the number of diseased plants increased in the Northern Iran. In summer of 2001, these symptoms were observed in most fields: lesions occur on the upper leaf sheaths, especially the flag leaf sheath. As the disease progresses, lesions enlarge and coalesce and may cover most of the leaf sheath. Panicle may fail to completely or at all. Brown or partially brown not filled or partially filled grain is also associated with infection of the panicle. A whitish powdery growth may be found inside affected sheaths. Infected plants were collected and trasferred to laboratory. Small pieces of diseased tissues were washed under tap water for one hour. Then tissues were placed on WA and incubated at 25 degrees C. These isolates were purified and identified as: Sarocladium oryzae, Fusarium udum, F. semitectum, F. avenaceum, F. flocciferum, F. graminearum, Bipolaris oryzae, Alternaria padwickii, Rhizoctonia solani, Paecilomyces sp., Nigrospora sp. and Trichoderma sp. This is the first report of F. udum in Iran. Also this is the first report that rice is the host for F. semitectum, F. avenaceum and F. flocciferum in Iran. Pathogenicity tests were conducted in glass house. Following species were found to be associated with sheath rot of rice: S. oryzae, F. graminearum, F. udum, F. avenaceum, B. oryzae, A. padwickii. This is the first report in the world that F. udum and A. padwickii are the causal agents of the sheath rot on rice plants. PMID:15151303

  16. Obliquity Variations of a Moonless Earth

    NASA Astrophysics Data System (ADS)

    Lissauer, Jack J.; Barnes, J. W.; Chambers, J. E.

    2011-05-01

    We numerically explore the obliquity (axial tilt) variations of a hypothetical moonless Earth. Previous work has shown that the Earth's Moon stabilizes Earth's obliquity such that it remains within a narrow range, between 22.1° and 24.5°. Without lunar influence, a frequency map analysis by Laskar et al. (1993 Nature 361, 615) showed that the obliquity could vary between 0° and 85°. Using a modified version of the orbital integrator mercury, we calculate the obliquity evolution for moonless Earths with various initial conditions for up to 4 billion years. We find many configurations in which obliquity variations are small. This implies that moonless extrasolar planets may well have the climate stability thought to be required for the development of advanced life.

  17. Protective sheath for a continuous measurement thermocouple

    DOEpatents

    Phillippi, R.M.

    1991-12-03

    Disclosed is a protective thermocouple sheath of a magnesia graphite refractory material for use in continuous temperature measurements of molten metal in a metallurgical ladle and having a basic slag layer thereon. The sheath includes an elongated torpedo-shaped sheath body formed of a refractory composition and having an interior borehole extending axially therethrough and adapted to receive a thermocouple. The sheath body includes a lower end which is closed about the borehole and forms a narrow, tapered tip. The sheath body also includes a first body portion integral with the tapered tip and having a relatively constant cross section and providing a thin wall around the borehole. The sheath body also includes a second body portion having a relatively constant cross section larger than the cross section of the first body portion and providing a thicker wall around the borehole. The borehole terminates in an open end at the second body portion. The tapered tip is adapted to penetrate the slag layer and the thicker second body portion and its magnesia constituent material are adapted to withstand chemical attack thereon from the slag layer. The graphite constituent improves thermal conductivity of the refractory material and, thus, enhances the thermal responsiveness of the device. 4 figures.

  18. Protective sheath for a continuous measurement thermocouple

    DOEpatents

    Phillippi, R. Michael

    1991-01-01

    Disclosed is a protective thermocouple sheath of a magnesia graphite refractory material for use in continuous temperature measurements of molten metal in a metallurgical ladle and having a basic slag layer thereon. The sheath includes an elongated torpedo-shaped sheath body formed of a refractory composition and having an interior borehole extending axially therethrough and adapted to receive a thermocouple. The sheath body includes a lower end which is closed about the borehole and forms a narrow, tapered tip. The sheath body also includes a first body portion integral with the tapered tip and having a relatively constant cross section and providing a thin wall around the borehole. The sheath body also includes a second body portion having a relatively constant cross section larger than the cross section of the first body portion and providing a thicker wall around the borehole. The borehole terminates in an open end at the second body portion. The tapered tip is adapted to penetrate the slag layer and the thicker second body portion and its magnesia constituent material are adapted to withstand chemical attack thereon from the slag layer. The graphite constituent improves thermal conductivity of the refractory material and, thus, enhances the thermal responsiveness of the device.

  19. Hydrodynamic Instabilities at an Oblique Interface

    NASA Astrophysics Data System (ADS)

    Kuranz, Carolyn; di Stefano, Carlos; Wan, W. C.; Drake, R. P.; Malamud, G.; Shimony, A.; Shvarts, D.

    2015-11-01

    Hydrodynamic instabilities are an important phenomenon that have consequences in many high-energy-density systems, including astrophysical systems and inertial confinement fusion experiments. Using the Omega EP laser we have created a sustained shock platform to drive a steady shock wave using a ~ 30 ns laser pulse. Coupled with a Spherical Crystal Imager we have created high-resolution x-ray radiographs to diagnose the evolution of complex hydrodynamic structures. This experiment involves a hydrodynamically unstable interface at an oblique angle so that the Richtmyer-Meshkov and Kelvin-Helmholtz processes are present. A dual-mode perturbation is machined onto the interface and we seek to observe the merging of vertical structures. Preliminary data from recent experiments and simulations results will be shown. This work is funded by the U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0001840, and the National Laser User Facility Program, grant number DE-NA0002032 and through the Laboratory for Laser Energetics, University of Rochester by the NNSA/OICF under Cooperative Agreement No. DE-NA0001944.

  20. Sheath effects on current collection by particle detectors with narrow acceptance angles

    NASA Technical Reports Server (NTRS)

    Singh, N.; Baugher, C. R.

    1981-01-01

    Restriction of the aperture acceptance angle of an ion or electron trap on an attracting spacecraft significantly alters the volt-ampere characteristics of the instrument in a low Mach number plasma. It is shown when the angular acceptance of the aperture is restricted the current to the collector tends to be independent of the Debye length. Expressions for the RPA characteristics for both a thin sheath and a thick sheath are derived; and it is shown that as the aperture is narrowed the curves tend toward equivalence.

  1. Spatial dependence of the sheath power transmission factor in DIII-D

    SciTech Connect

    Futch, A.H.; Hill, D.N.; Porter, G.D. ); Matthews, G.F. ); Buchenauer, D. )

    1991-02-01

    The spatial dependence of the power transmission factor, d, associated with an ion-electron pair passing through the sheath at the DIII-D divertor plate has been determined by sweeping the edge plasma across Langmuir probe detectors. Our results show that d decreases from the classically expected value of eight near the low density edge of the scrape-off-layer plasma to values less than unity at the peak of the profile. 13 refs., 16 figs.

  2. Obliquity variations of a moonless Earth

    NASA Astrophysics Data System (ADS)

    Lissauer, Jack J.; Barnes, Jason W.; Chambers, John E.

    2012-01-01

    We numerically explore the obliquity (axial tilt) variations of a hypothetical moonless Earth. Previous work has shown that the Earth's Moon stabilizes Earth's obliquity such that it remains within a narrow range, between 22.1° and 24.5°. Without lunar influence, a frequency map analysis by Laskar et al. (Laskar, J., Joutel, F., Robutel, P. [1993]. Nature 361, 615-617) showed that the obliquity could vary between 0° and 85°. This has left an impression in the astrobiology community that a big moon is necessary to maintain a habitable climate on an Earth-like planet. Using a modified version of the orbital integrator mercury, we calculate the obliquity evolution for moonless Earths with various initial conditions for up to 4 Gyr. We find that while obliquity varies significantly more than that of the actual Earth over 100,000 year timescales, the obliquity remains within a constrained range, typically 20-25° in extent, for timescales of hundreds of millions of years. None of our Solar System integrations in which planetary orbits behave in a typical manner show obliquity accessing more than 65% of the full range allowed by frequency-map analysis. The obliquities of moonless Earths that rotate in the retrograde direction are more stable than those of prograde rotators. The total obliquity range explored for moonless Earths with rotation periods less than 12 h is much less than that for slower-rotating moonless Earths. A large moon thus does not seem to be needed to stabilize the obliquity of an Earth-like planet on timescales relevant to the development of advanced life.

  3. Ion Velocimetry In Magnetized DC Sheaths

    NASA Astrophysics Data System (ADS)

    Young, Christopher; Lucca Fabris, Andrea; Cappelli, Mark

    2013-09-01

    Particle dynamics near the magnetic cusps in cusped field plasma thrusters are still not well understood; characterizing the ion velocity distribution functions in these regions can help thruster designs maximize electron trapping and minimize erosion of the channel wall. To that end, a robust argon ion velocity sensor is developed using a three-level laser-induced fluorescence (LIF) technique. The 3d4F7 / 2 --> 4p4D5/ 2 0 ArII transition at 668.61 nm is pumped with a 25 mW tunable external cavity diode laser, and fluorescence down to the 4s4P3 / 2 state at 442.72 nm is collected with phase-sensitive detection. The Doppler shift in the acquired signal peak, compared to a stationary reference, gives the ion velocity component parallel to the exciting laser. We demonstrate this LIF scheme by obtaining the argon ion velocity profile through a magnetized DC sheath. The LIF measurement is used to validate a new optogalvanic velocimetry technique in which two lasers (chopped at different frequencies) intersect one another at 90° in the measurement volume. Using a lock-in amplifier, changes observed in the DC discharge current at the sum and difference of the two chopping frequencies may be related back to the mean ion velocity at that point. The authors acknowledge support from the Air Force Office of Scientific Research (AFOSR). CY acknowledges support from the DOE NNSA Stewardship Science Graduate Fellowship under contract DE-FC52-08NA28752.

  4. Oblique View of Eros' Crater

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This image, showing an oblique view of Eros' large central crater, was taken at a resolution of about 20 meters (65 feet) per pixel. The brightness or albedo patterns on the walls of this crater are clearly visible, with the brighter materials near the tops of the walls and darker materials on the lower walls. Boulders are seen inside this crater and the smaller nearby craters. The higher density of craters to the left of the large crater implies that this region is older than the smoother area seen associated with the saddle region on the opposite side of the asteroid.

    Built and managed by The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, NEAR was the first spacecraft launched in NASA's Discovery Program of low-cost, small-scale planetary missions. See the NEAR web page at http://near.jhuapl.edu for more details.

  5. Microwave Imaging under Oblique Illumination.

    PubMed

    Meng, Qingyang; Xu, Kuiwen; Shen, Fazhong; Zhang, Bin; Ye, Dexin; Huangfu, Jiangtao; Li, Changzhi; Ran, Lixin

    2016-01-01

    Microwave imaging based on inverse scattering problem has been attracting many interests in the microwave society. Among some major technical challenges, the ill-posed, multi-dimensional inversion algorithm and the complicated measurement setup are critical ones that prevent it from practical applications. In this paper, we experimentally investigate the performance of the subspace-based optimization method (SOM) for two-dimensional objects when it was applied to a setup designed for oblique incidence. Analytical, simulation, and experimental results show that, for 2D objects, neglecting the cross-polarization scattering will not cause a notable loss of information. Our method can be potentially used in practical imaging applications for 2D-like objects, such as human limbs. PMID:27399706

  6. Microwave Imaging under Oblique Illumination

    PubMed Central

    Meng, Qingyang; Xu, Kuiwen; Shen, Fazhong; Zhang, Bin; Ye, Dexin; Huangfu, Jiangtao; Li, Changzhi; Ran, Lixin

    2016-01-01

    Microwave imaging based on inverse scattering problem has been attracting many interests in the microwave society. Among some major technical challenges, the ill-posed, multi-dimensional inversion algorithm and the complicated measurement setup are critical ones that prevent it from practical applications. In this paper, we experimentally investigate the performance of the subspace-based optimization method (SOM) for two-dimensional objects when it was applied to a setup designed for oblique incidence. Analytical, simulation, and experimental results show that, for 2D objects, neglecting the cross-polarization scattering will not cause a notable loss of information. Our method can be potentially used in practical imaging applications for 2D-like objects, such as human limbs. PMID:27399706

  7. Equilibrium in the oblique rotating outer pulsar magnetosphere

    NASA Astrophysics Data System (ADS)

    Endean, Geoffrey

    1995-06-01

    A simple solution to the problem of plasma equilibrium outside the velocity-of-light cylinder of the oblique rotating pulsar magnetosphere is presented. The magnetic field has a swept-back, open spiral structure with zero axial component. The corotational motion of the plasma just inside the velocity-of-light cylinder transits to radial motion at large radius while maintaining highly relativistic speed throughout. There are no streaming currents along the magnetic field lines, but, in addition to a net charge density and associated convection current density, there is a non-force-free axial current density which is arbitraily large at the velocity-of-light cylinder but gives a finite current when integrated over radius. This axial current density is directly responsible for pulses of coherent radiation. The solution presented applies independently of the inclination angle and nondipolar content of the source magnetic field of the pulsar and includes both the axisymmetric field and the fully oblique or orthogonal field as special cases. It is a plasma equilibrium solution, with any similarities to vacuum fields, particularly outside the velocity-of-light cylinder, being purely coincidental.

  8. Comprehensive kinetic analysis of the plasma-wall transition layer in a strongly tilted magnetic field

    SciTech Connect

    Tskhakaya, D. D.; Kos, L.

    2014-10-15

    The magnetized plasma-wall transition (MPWT) layer at the presence of the obliquity of the magnetic field to the wall consists of three sub-layers: the Debye sheath (DS), the magnetic pre-sheath (MPS), and the collisional pre-sheath (CPS) with characteristic lengths λ{sub D} (electron Debye length), ρ{sub i} (ion gyro-radius), and ℓ (the smallest relevant collision length), respectively. Tokamak plasmas are usually assumed to have the ordering λ{sub D}≪ρ{sub i}≪ℓ, when the above-mentioned sub-layers can be distinctly distinguished. In the limits of ε{sub Dm}(λ{sub D}/ρ{sub i})→0 and ε{sub mc}(ρ{sub i}/ℓ)→0 (“asymptotic three-scale (A3S) limits”), these sub-layers are precisely defined. Using the smallness of the tilting angle of the magnetic field to the wall, the ion distribution functions are found for three sub-regions in the analytic form. The equations and characteristic length-scales governing the transition (intermediate) regions between the neighboring sub-layers (CPS – MPS and MPS – DS) are derived, allowing to avoid the singularities arising from the ε{sub Dm}→0 and ε{sub mc}→0 approximations. The MPS entrance and the related kinetic form of the Bohm–Chodura condition are successfully defined for the first time. At the DS entrance, the Bohm condition maintains its usual form. The results encourage further study and understanding of physics of the MPWT layers in the modern plasma facilities.

  9. Self-consistent one dimension in space and three dimension in velocity kinetic trajectory simulation model of magnetized plasma-wall transition

    SciTech Connect

    Chalise, Roshan Khanal, Raju

    2015-11-15

    We have developed a self-consistent 1d3v (one dimension in space and three dimension in velocity) Kinetic Trajectory Simulation (KTS) model, which can be used for modeling various situations of interest and yields results of high accuracy. Exact ion trajectories are followed, to calculate along them the ion distribution function, assuming an arbitrary injection ion distribution. The electrons, on the other hand, are assumed to have a cut-off Maxwellian velocity distribution at injection and their density distribution is obtained analytically. Starting from an initial guess, the potential profile is iterated towards the final time-independent self-consistent state. We have used it to study plasma sheath region formed in presence of an oblique magnetic field. Our results agree well with previous works from other models, and hence, we expect our 1d3v KTS model to provide a basis for the studying of all types of magnetized plasmas, yielding more accurate results.

  10. Space plasma contactor research, 1987

    NASA Technical Reports Server (NTRS)

    Wilbur, Paul J.

    1988-01-01

    A simple model describing the process of electron collection from a low pressure ambient plasma in the absence of magnetic field and contactor velocity effects is presented. Experimental measurments of the plasma surrounding the contactor are used to demonstrate that a double-sheath generally develops and separates the ambient plasma from a higher density, anode plasma located adjacent to the contactor. Agreement between the predictions of the model and experimental measurements obtained at the electron collection current levels ranging to 1 A suggests the surface area at the ambient plasma boundary of the double-sheath is equal to the electron current being collected divided by the ambient plasma random electron current density; the surface area of the higher density anode plasma boundary of the double-sheath is equal to the ion current being emitted across this boundary divided by the ion current density required to sustain a stable sheath; and the voltage drop across the sheath is determined by the requirement that the ion and electron currents counterflowing across the boundaries be at space-charge limited levels. The efficiency of contactor operation is shown to improve when significant ionization and excitation is induced by electrons that stream from the ambient plasma through the double-sheath and collide with neutral atoms being supplied through the hollow cathode.

  11. Estimation of sheath potentials in front of ASDEX upgrade ICRF antenna with SSWICH asymptotic code

    NASA Astrophysics Data System (ADS)

    Křivská, A.; Bobkov, V.; Colas, L.; Jacquot, J.; Milanesio, D.; Ochoukov, R.

    2015-12-01

    Multi-megawatt Ion Cyclotron Range of Frequencies (ICRF) heating became problematic in ASDEX Upgrade (AUG) tokamak after coating of ICRF antenna limiters and other plasma facing components by tungsten. Strong impurity influx was indeed produced at levels of injected power markedly lower than in the previous experiments. It is assumed that the impurity production is mainly driven by parallel component of Radio-Frequency (RF) antenna electric near-field E// that is rectified in sheaths. In this contribution we estimate poloidal distribution of sheath Direct Current (DC) potential in front of the ICRF antenna and simulate its relative variations over the parametric scans performed during experiments, trying to reproduce some of the experimental observations. In addition, relative comparison between two types of AUG ICRF antenna configurations, used for experiments in 2014, has been performed. For this purpose we use the Torino Polytechnic Ion Cyclotron Antenna (TOPICA) code and asymptotic version of the Self-consistent Sheaths and Waves for Ion Cyclotron Heating (SSWICH) code. Further, we investigate correlation between amplitudes of the calculated oscillating sheath voltages and the E// fields computed at the lateral side of the antenna box, in relation with a heuristic antenna design strategy at IPP Garching to mitigate RF sheaths.

  12. The structural sheath protein of aphids is required for phloem feeding.

    PubMed

    Will, Torsten; Vilcinskas, Andreas

    2015-02-01

    Aphids produce two types of saliva that mediate their interactions with plants. Watery saliva is secreted during cell penetration and ingestion, whereas gel saliva is secreted during stylet movement through the apoplast where it forms a sheath around the stylet to facilitate penetration and seal puncture sites on cell membranes. In order to study the function of the sheath when aphids interact with plants, we used RNA interference (RNAi) to silence the aphid structural sheath protein (SHP) in the pea aphid Acyrthosiphon pisum. The injection of 50 ng of double stranded RNA completely disrupted sheath formation, as confirmed by scanning electron microscopy. Aphid behavior was monitored using the electrical penetration graph technique, revealing that disrupted sheath formation prevented efficient long-term feeding from sieve tubes, with a silencing effect on reproduction but not survival. We propose that sealing the stylet penetration site in the sieve tube plasma membrane is part of a two-step mechanism to suppress sieve-tube occlusion by preventing calcium influx into the sieve tube lumen. The SHP is present in several aphid species and silencing has a similar impact to aphid-resistant plants, suggesting that SHP is an excellent target for RNAi-mediated pest control. PMID:25527379

  13. Estimation of sheath potentials in front of ASDEX upgrade ICRF antenna with SSWICH asymptotic code

    SciTech Connect

    Křivská, A.; Colas, L.; Milanesio, D.

    2015-12-10

    Multi-megawatt Ion Cyclotron Range of Frequencies (ICRF) heating became problematic in ASDEX Upgrade (AUG) tokamak after coating of ICRF antenna limiters and other plasma facing components by tungsten. Strong impurity influx was indeed produced at levels of injected power markedly lower than in the previous experiments. It is assumed that the impurity production is mainly driven by parallel component of Radio-Frequency (RF) antenna electric near-field E// that is rectified in sheaths. In this contribution we estimate poloidal distribution of sheath Direct Current (DC) potential in front of the ICRF antenna and simulate its relative variations over the parametric scans performed during experiments, trying to reproduce some of the experimental observations. In addition, relative comparison between two types of AUG ICRF antenna configurations, used for experiments in 2014, has been performed. For this purpose we use the Torino Polytechnic Ion Cyclotron Antenna (TOPICA) code and asymptotic version of the Self-consistent Sheaths and Waves for Ion Cyclotron Heating (SSWICH) code. Further, we investigate correlation between amplitudes of the calculated oscillating sheath voltages and the E// fields computed at the lateral side of the antenna box, in relation with a heuristic antenna design strategy at IPP Garching to mitigate RF sheaths.

  14. Anode sheath transition in an anodic arc for synthesis of nanomaterials

    NASA Astrophysics Data System (ADS)

    Nemchinsky, V. A.; Raitses, Y.

    2016-06-01

    The arc discharge with ablating anode or so-called anodic arc is widely used for synthesis of nanomaterials, including carbon nanotubes and fullerens, metal nanoparticles etc. We present the model of this arc, which confirms the existence of the two different modes of the arc operation with two different anode sheath regimes, namely, with negative anode sheath and with positive anode sheath. It was previously suggested that these regimes are associated with two different anode ablating modes—low ablation mode with constant ablation rate and the enhanced ablation mode (Fetterman et al 2008 Carbon 46 1322). The transition of the arc operation from low ablation mode to high ablation mode is determined by the current density at the anode. The model can be used to self-consistently determine the distribution of the electric field, electron density and electron temperature in the near-anode region of the arc discharge. Simulations of the carbon arc predict that for low arc ablating modes, the current is driven mainly by the electron diffusion to the anode. For positive anode sheath, the anode voltage is close to the ionization potential of anode material, while for negative anode sheath, the anode voltage is an order of magnitude smaller. It is also shown that the near-anode plasma, is far from the ionization equilibrium.

  15. Enhanced target normal sheath acceleration based on the laser relativistic self-focusing

    SciTech Connect

    Zou, D. B.; Zhuo, H. B. Yang, X. H.; Shao, F. Q.; Ma, Y. Y.; Yu, T. P.; Yin, Y.; Ge, Z. Y.; Li, X. H.; Wu, H. C.

    2014-06-15

    The enhanced target normal sheath acceleration of ions in laser target interaction via the laser relativistic self-focusing effect is investigated by theoretical analysis and particle-in-cell simulations. The temperature of the hot electrons in the underdense plasma is greatly increased due to the occurrence of resonant absorption, while the electron-betatron-oscillation frequency is close to its witnessed laser frequency [Pukhov et al., Phys. Plasma 6, 2847 (1999)]. While these hot electrons penetrate through the backside solid target, a stronger sheath electric field at the rear surface of the target is induced, which can accelerate the protons to a higher energy. It is also shown that the optimum length of the underdense plasma is approximately equal to the self-focusing distance.

  16. Collisionless “thermalization” in the sheath of an argon discharge

    SciTech Connect

    Coulette, David Manfredi, Giovanni

    2015-04-15

    We performed kinetic Vlasov simulations of the plasma-wall transition for a low-pressure argon discharge without external magnetic fields, using the same plasma parameters as in the experiments of Claire et al. [Phys. Plasmas 13, 062103 (2006)]. Experimentally, it was found that the ion velocity distribution function is highly asymmetric in the presheath, but, surprisingly, becomes again close to Maxwellian inside the sheath. Here, we show that this “thermalization” can be explained by purely collisionless effects that are akin to the velocity bunching phenomenon observed in charged particles beams. Such collisionless thermalization is also observed in the presheath region close to the sheath entrance, although it is much weaker there and in practice probably swamped by collisional processes (standard or enhanced by instabilities)

  17. Compressibility and cyclotron damping in the oblique Alfven wave

    SciTech Connect

    Harmon, J.K. )

    1989-11-01

    Compressibility, magnetic compressibility, and damping rate are calculated for the obliquely propagating Alfven shear wave in high- and low-beta Vlasov plasmas. There is an overall increase in compressibility as beta is reduced from {beta} = 1 to {beta}{much lt}1. For high obliquity {theta} and low frequency ({omega} {much lt} {Omega}{sub p}) the compressibility C follows a k{sup 2} wave number dependence; for high {theta} and low {beta} the approximation C(k) {approx} k{sub n}{sup 2} {identical to} (kV{sub A}/{Omega}{sub p}){sup 2} holds for wave numbers up to the proton cyclotron resonance, where {Omega}{sub p} is the proton cyclotron frequency and V{sub A} is the Alfven velocity. Strong proton cyclotron damping sets in at k{sub n} of the order of unity; the precise k{sub n} position of the damping cutoff increases with decreasing {beta} and increasing {theta}. Hence compressibility can exceed unity near the damping cutoff for high-{theta} waves in a low-{beta} plasma. The magnetic compressibility of the oblique Alfven wave also has a k{sup 2} dependence and can reach a maximum value of the order of 10% at high wave number. It is shown that Alfven compressibility could be the dominant contributor to the near-Sun solar wind density fluctuation spectrum for k>10{sup {minus}2} km{sup {minus}1} and hence might cause some of the flattening at high wave number seen in radio scintillation measurements. This would also be consistent with the notion that the observed density spectrum inner scale is a signature of cyclotron damping.

  18. Full wave propagation modelling in view to integrated ICRH wave coupling/RF sheaths modelling

    NASA Astrophysics Data System (ADS)

    Jacquot, Jonathan; Bobkov, Volodymyr; Colas, Laurent; Heuraux, Stéphane; Křivská, Alena; Lu, Lingfeng; Noterdaeme, Jean-Marie

    2015-12-01

    RF sheaths rectification can be the reason for operational limits for Ion Cyclotron Range of Frequencies (ICRF) heating systems via impurity production or excessive heat loads. To simulate this process in realistic geometry, the Self-consistent Sheaths and Waves for Ion Cyclotron Heating (SSWICH) code is a minimal set of coupled equations that computes self-consistently wave propagation and DC plasma biasing. The present version of its wave propagation module only deals with the Slow Wave assumed to be the source of RF sheath oscillations. However the ICRF power coupling to the plasma is due to the fast wave (FW). This paper proposes to replace this one wave equation module by a full wave module in either 2D or 3D as a first step towards integrated modelling of RF sheaths and wave coupling. Since the FW is propagative in the main plasma, Perfectly Matched Layers (PMLs) adapted for plasmas were implemented at the inner side of the simulation domain to absorb outgoing waves and tested numerically with tilted B0 in Cartesian geometry, by either rotating the cold magnetized plasma dielectric tensors in 2D or rotating the coordinate vector basis in 3D. The PML was further formulated in cylindrical coordinates to account for for the toroidal curvature of the plasma. Toroidal curvature itself does not seem to change much the coupling. A detailed 3D geometrical description of Tore Supra and ASDEX Upgrade (AUG) antennas was included in the coupling code. The full antenna structure was introduced, since its toroidal symmetry with respect to the septum plane is broken (FS bars, toroidal phasing, non-symmetrical structure). Reliable convergence has been obtained with the density profile up to the leading edge of antenna limiters. Parallel electric field maps have been obtained as an input for the present version of SSWICH.

  19. PLASMA DEVICE

    DOEpatents

    Gow, J.D.; Wilcox, J.M.

    1961-12-26

    A device is designed for producing and confining highenergy plasma from which neutrons are generated in copious quantities. A rotating sheath of electrons is established in a radial electric field and axial magnetic field produced within the device. The electron sheath serves as a strong ionizing medium to gas introdueed thereto and also functions as an extremely effective heating mechanism to the resulting plasma. In addition, improved confinement of the plasma is obtained by ring magnetic mirror fields produced at the ends of the device. Such ring mirror fields are defined by the magnetic field lines at the ends of the device diverging radially outward from the axis of the device and thereafter converging at spatial annular surfaces disposed concentrically thereabout. (AFC)

  20. Graduated recession of the superior oblique muscle.

    PubMed Central

    Caldeira, J A

    1975-01-01

    Recession of the superior oblique was performed bilaterally in 12 patients with the A phenomenon and unilaterally in four patients with vertical imbalance. The results are discussed. Images PMID:1191613

  1. Obliquity dependence of the tangential YORP

    NASA Astrophysics Data System (ADS)

    Ševeček, P.; Golubov, O.; Scheeres, D. J.; Krugly, Yu. N.

    2016-08-01

    Context. The tangential Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect is a thermophysical effect that can alter the rotation rate of asteroids and is distinct from the so-called normal YORP effect, but to date has only been studied for asteroids with zero obliquity. Aims: We aim to study the tangential YORP force produced by spherical boulders on the surface of an asteroid with an arbitrary obliquity. Methods: A finite element method is used to simulate heat conductivity inside a boulder, to find the recoil force experienced by it. Then an ellipsoidal asteroid uniformly covered by these types of boulders is considered and the torque is numerically integrated over its surface. Results: Tangential YORP is found to operate on non-zero obliquities and decreases by a factor of two for increasing obliquity.

  2. Obliquity-oblateness feedback on Mars

    NASA Astrophysics Data System (ADS)

    Bills, Bruce G.

    A simple model is presented for the coupled dynamics of the orbit-rotation-climate system of Mars. Changes in the orientation of the spin pole, relative to the orbit pole, influence the spatiotemporal pattern of incident radiation and thus drive climatic mass transport into and out of the polar regions on a variety of timescales. Changes in the mass distribution occur from direct climatic forcing and compensating viscous flow in the interior. The net change in mass distribution influences the rate of spin axis precession and thereby influences obliquity. The rate of secular obliquity drift depends on several poorly known parameters, including the magnitudes and response times of volatile inventories and viscosity structure within Mars. Even relatively modest secular obliquity drift can lead to trapping in nearby resonances. The dissipative nature of the coupled dynamical system makes reconstruction of past evolution much more difficult than for a purely inertial system. The long-term obliquity history of Mars is dominated by climate.

  3. Oblique orthographic projections and contour plots

    NASA Technical Reports Server (NTRS)

    Giles, G. L.

    1977-01-01

    Oblique orthographic projections allow model to be viewed in any selected orientation specified by Euler-angle transformation. This transformation resolves coordinate system of model to principal plane on which display is to be plotted.

  4. Obliquity Variations of a Rapidly Rotating Venus

    NASA Astrophysics Data System (ADS)

    Quarles, Billy L.; Barnes, Jason W.; Lissauer, Jack J.; Chambers, John E.; Hedman, Matthew M.

    2016-05-01

    Venus clearly differs from Earth in terms of its spin and atmospheric composition, where the former is controlled by solid-body and atmospheric thermal tides. However, this may have been different during earlier stages of planetary evolution, when the Sun was fainter and the Venusian atmosphere was less massive. We investigate how the axial tilt, or obliquity, would have varied during this epoch considering a rapidly rotating Venus. Through numerical simulation of an ensemble of hypothetical Early Venuses, we find the obliquity variation to be simpler than a Moonless Earth (Lissauer et al., 2012). Most low-obliquity Venuses show very low total obliquity variability comparable to that of the real Moon-influenced Earth.

  5. Red Shifts with Obliquely Approaching Light Sources.

    ERIC Educational Resources Information Center

    Head, C. E.; Moore-Head, M. E.

    1988-01-01

    Refutes the Doppler effect as the explanation of large red shifts in the spectra of distant galaxies and explains the relativistic effects in which the light sources approach the observer obliquely. Provides several diagrams and graphs. (YP)

  6. Modal control of an oblique wing aircraft

    NASA Technical Reports Server (NTRS)

    Phillips, James D.

    1989-01-01

    A linear modal control algorithm is applied to the NASA Oblique Wing Research Aircraft (OWRA). The control law is evaluated using a detailed nonlinear flight simulation. It is shown that the modal control law attenuates the coupling and nonlinear aerodynamics of the oblique wing and remains stable during control saturation caused by large command inputs or large external disturbances. The technique controls each natural mode independently allowing single-input/single-output techniques to be applied to multiple-input/multiple-output systems.

  7. Useful angular selectivity in oblique columnar aluminum

    NASA Astrophysics Data System (ADS)

    Ditchburn, R. J.; Smith, G. B.

    1991-03-01

    A useful magnitude of angular selective transmittance of incident unpolarized light is demonstrated in obliquely deposited aluminum. Required deposition procedures and anisotropic optical properties are discussed. Angular selectivity is very strong at visible wavelengths but both experiment and theory indicate that a single oblique layer with well defined columns gives high transmittance at near-infrared wavelengths compared with normal films. There are ways of reducing this to enhance the energy control capability. Both solar and luminous angular selectivity are reported.

  8. Studies of a sheath structure in an RF discharge using experimental, analytical and simulation approaches

    NASA Astrophysics Data System (ADS)

    Kim, J. B.; Kawamura, K.; Bowden, M. D.; Muraoka, K.; Choi, Y. W.

    1999-10-01

    The electric field distributions in the sheath region were measured using laser-induced fluorescence (LIF) method in capacitively coupled RF glow discharges operated at different pressures in helium. The measured distributions and sheath thicknesses obtained from the electric field distributions were compared with those obtained from an existing analytical theory1 and with a numerical simulation2. The comparison yielded reasonable agreement, both in general tendency with regard to the pressure dependence and in the absolute magnitude. These results provided evidence of the validity of the analytical sheath theory and the numerical simulation for predicting the sheath properties of an RF glow discharge. 1. M. A. Lieberman and A. J. Lichtenberg, Principles of Plasma Discharges and Materials Processing, New York: Wiley, 1994 2. J. P. Verboncoeur, V. Vahedi, M. V. Alves, and C. K. Birdsall, \\x81gPDP1, PDC1, PDS1 plasma device 1 dimensional bounded electrostatic codes,\\x81h Reference manual PDx1 PC version 2.1, 1993

  9. Magnetic sheath effect on the gross and net erosion rates due to impurities

    NASA Astrophysics Data System (ADS)

    Mellet, N.; Pégourié, B.; Martin, C.; Gunn, J. P.; Bufferand, H.; Roubin, P.

    2016-02-01

    Simulations of impurity trajectories in deuterium plasmas in the vicinity of the surface are performed by taking into account the magnetic sheath in conditions relevant for ITER and WEST. We show that the magnetic sheath has a strong effect on the average impact angle of impurities in divertor conditions and that it can lead to an increase of ≈ 60% at the gross erosion maximum for neon (Ne+4) compared to the case when only the cyclotron motion is considered. The evaluation of the net erosion has been undertaken by retaining local redeposition of tungsten (W). We investigate how it is affected by the sheath magnetic potential profile. The largest effect is however observed when an energy distribution is considered. In this case the number of particles that manage to exit the sheath is larger as it is dominated by the more energetic particles. The comparison with other work is also discussed. The application to a scenario of the WEST project is finally performed, which exhibits a moderate, however non negligible, erosion of the plasma facing components.

  10. The ion polytropic coefficient in a collisionless sheath containing hot ions

    NASA Astrophysics Data System (ADS)

    Lin, Binbin; Xiang, Nong; Ou, Jing

    2016-08-01

    The fluid approach has been widely used to study plasma sheath dynamics. For a sheath containing hot ions whose temperature is greater than the electron's, how to truncate the fluid hierarchy chain equations while retaining to the fullest extent of the kinetic effects is always a difficult problem. In this paper, a one-dimensional, collisionless sheath containing hot ions is studied via particle-in-cell simulations. By analyzing the ion energy equation and taking the kinetic effects into account, we have shown that the ion polytropic coefficient in the vicinity of the sheath edge is approximately constant so that the state equation with the modified polytropic coefficient can be used to close the hierarchy chain of the ion fluid equations. The value of the polytropic coefficient strongly depends on the hot ion temperature and its concentration in the plasma. The semi-analytical model is given to interpret the simulation results. As an application, the kinetic effects on the ion saturation current density in the probe theory are discussed.

  11. The effect of polar caps on obliquity

    NASA Technical Reports Server (NTRS)

    Lindner, B. L.

    1993-01-01

    Rubincam has shown that the Martian obliquity is dependent on the seasonal polar caps. In particular, Rubincam analytically derived this dependence and showed that the change in obliquity is directly proportional to the seasonal polar cap mass. Rubincam concludes that seasonal friction does not appear to have changed Mars' climate significantly. Using a computer model for the evolution of the Martian atmosphere, Haberle et al. have made a convincing case for the possibility of huge polar caps, about 10 times the mass of the current polar caps, that exist for a significant fraction of the planet's history. Since Rubincam showed that the effect of seasonal friction on obliquity is directly proportional to polar cap mass, a scenario with a ten-fold increase in polar cap mass over a significant fraction of the planet's history would result in a secular increase in Mars' obliquity of perhaps 10 degrees. Hence, the Rubincam conclusion of an insignificant contribution to Mars' climate by seasonal friction may be incorrect. Furthermore, if seasonal friction is an important consideration in the obliquity of Mars, this would significantly alter the predictions of past obliquity.

  12. Towards Efficiency of Oblique Images Orientation

    NASA Astrophysics Data System (ADS)

    Ostrowski, W.; Bakuła, K.

    2016-03-01

    Many papers on both theoretical aspects of bundle adjustment of oblique images and new operators for detecting tie points on oblique images have been written. However, only a few achievements presented in the literature were practically implemented in commercial software. In consequence often aerial triangulation is performed either for nadir images obtained simultaneously with oblique photos or bundle adjustment for separate images captured in different directions. The aim of this study was to investigate how the orientation of oblique images can be carried out effectively in commercial software based on the structure from motion technology. The main objective of the research was to evaluate the impact of the orientation strategy on both duration of the process and accuracy of photogrammetric 3D products. Two, very popular software: Pix4D and Agisoft Photoscan were tested and two approaches for image blocks were considered. The first approach based only on oblique images collected in four directions and the second approach included nadir images. In this study, blocks for three test areas were analysed. Oblique images were collected with medium-format cameras in maltan cross configuration with registration of GNSS and INS data. As a reference both check points and digital surface models from airborne laser scanning were used.

  13. Oscillating plasma bubbles. II. Pulsed experiments

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.

    2012-08-15

    Time-dependent phenomena have been investigated in plasma bubbles which are created by inserting spherical grids into an ambient plasma and letting electrons and ions form a plasma of different parameters than the ambient one. There are no plasma sources inside the bubble. The grid bias controls the particle flux. There are sheaths on both sides of the grid, each of which passes particle flows in both directions. The inner sheath or plasma potential develops self consistently to establish charge neutrality and divergence free charge and mass flows. When the electron supply is restricted, the inner sheath exhibits oscillations near the ion plasma frequency. When all electrons are excluded, a virtual anode forms on the inside sheath, reflects all ions such that the bubble is empty. By pulsing the ambient plasma, the lifetime of the bubble plasma has been measured. In an afterglow, plasma electrons are trapped inside the bubble and the bubble decays as slow as the ambient plasma. Pulsing the grid voltage yields the time scale for filling and emptying the bubble. Probes have been shown to modify the plasma potential. Using pulsed probes, transient ringing on the time scale of ion transit times through the bubble has been observed. The start of sheath oscillations has been investigated. The instability mechanism has been qualitatively explained. The dependence of the oscillation frequency on electrons in the sheath has been clarified.

  14. 56. POWDER MAGAZINE, VIEW OF INTACT WOOD SHEATHING ON THE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    56. POWDER MAGAZINE, VIEW OF INTACT WOOD SHEATHING ON THE SOUTHWEST REAR VENTILATION PASSAGE. (SHEATHING HELP CONTROL HUMIDITY AND DECREASE DANGER OF MAETAL STRIKING STONE AND SPARKING.) - Fort Monroe, Fortress, Hampton, Hampton, VA

  15. Proton fire hose instabilities in the expanding solar wind: Role of oblique magnetic field

    NASA Astrophysics Data System (ADS)

    Hellinger, Petr

    2016-04-01

    The double adiabatic (CGL) approximation for the ideal (Parker) interplanetary magnetic field (IMF) predicts generation of the parallel particle temperature anisotropy (T∥ > T⊥) for a nearly radial magnetic field whereas for a strongly oblique IMF generation of the opposite temperature anisotropy is expected. The transition between the two behaviours is expected at around 45o, i.e. around 1 AU in the solar wind in the ecliptic plane. We investigate properties of a proton-electron plasma system in the solar wind using hybrid expanding box simulations starting with an oblique IMF. The simulated system becomes unstable with respect to the parallel and oblique fire hose instabilities and is forced to stay around the corresponding marginal stability. Rotation of the IMF reduces the time system stays near the marginal stability regions and for a strongly transverse IMF the system moves away from the regions unstable with respect to the fire hose instabilities.

  16. Massive exophytic malignant peripheral nerve sheath tumor.

    PubMed

    Khorsand, Derek; Porrino, Jack; Flaherty, Erin; Bandhlish, Anshu; Davidson, Darin

    2016-06-01

    We present a case of a solitary neurofibroma involving the right posterior shoulder of a 69-year-old man with degeneration into a massive, malignant peripheral nerve sheath tumor measuring more than 3 times the average reported size. The radiographic, magnetic resonance imaging, and computed tomographic features are compared with the gross appearance and pathology. PMID:27257459

  17. Sheath fold morphology in simple shear

    NASA Astrophysics Data System (ADS)

    Reber, Jacqueline E.; Dabrowski, Marcin; Galland, Olivier; Schmid, Daniel W.

    2013-08-01

    Sheath folds are highly non-cylindrical structures often associated with shear zones. We investigate the formation of sheath folds around a weak inclusion acting as a slip surface in simple shear by means of an analytical model. We present results for different slip surface orientations and shapes. Cross-sections perpendicular to the shear direction through the sheath fold display closed contours, so called eye-structures. The aspect ratio of the outermost closed contour is strongly dependent on the initial slip surface configuration. The center of the eye-structure is subject to change in height with respect to the upper edge of the outermost closed contour for different cross-sections perpendicular to the shear direction. This results in a large variability in layer thickness across the sheath fold length, questioning the usefulness of eye-structures as shear sense indicators. The location of the center of the eye structure is largely invariant to the initial configurations of the slip surface as well as to strain. The values of the aspect ratios of the closed contours within the eye-pattern are dependent on the strain and the cross-section location. The ratio (R') of the aspect ratios of the outermost closed contour (Ryz) and the innermost closed contour (Ry'z') shows values above and below 1. R' shows dependence on the slip surface shape and orientation but not on the number of involved contours. Using R' measurements to deduce the bulk strain type may be erroneous.

  18. Accurate method for measuring oblique astigmatism and oblique power of ophthalmic lenses

    NASA Astrophysics Data System (ADS)

    Wihardjo, Erning; Silva, Donald E.

    1991-12-01

    The measurement of oblique astigmatism error and its oblique power of ophthalmic lens under identical conditions of the human visual system--such as the distance from the center rotation of the eye to the back vertex surface of the lens--viewing distance, and lens aperture using a Mach Zehnder interferometer is describe.

  19. Identification of when a Langmuir probe is in the sheath of a spacecraft: The effects of secondary electron emission from the probe

    NASA Astrophysics Data System (ADS)

    Wang, X.; Hsu, H.-W.; Horányi, M.

    2015-04-01

    Langmuir probes on spacecraft have been used for characterizing the ambient plasma parameters in space. When their boom is short compared to the Debye length, the probes remain immersed in the spacecraft sheath, causing the current-voltage (I-V) characteristics to deviate from that of a probe far away from the spacecraft. We present identification of when a Langmuir probe is in a sheath, based on the secondary electron (SE) emission from the probe itself. The I-V characteristics of a spherical probe are investigated in a plasma sheath above a conducting plate. Plasmas with cold and hot electrons (1 eV and 10 eV), as well as monoenergetic electrons (50-100 eV), are created. The derivative (dI/dV) of the probe I-V curves shows that in addition to a "knee" at a potential more positive than the plasma potential, an additional knee appears at a sheath potential at the probe location. This additional knee is created due to the SE emission from the probe and is identified as an indication of the probe being immersed in the sheath. Our experimental results reproduced the aspects of the Cassini Langmuir probe I-V characteristics, suggesting that at times, the probe may have been immersed in the sheath of the spacecraft in Saturn's magnetosphere, and SE emission from the probe itself may have significantly altered its I-V characteristics.

  20. 30 CFR 75.1314 - Sheathed explosive units.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Sheathed explosive units. 75.1314 Section 75... HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Explosives and Blasting § 75.1314 Sheathed explosive units. (a) A separate instantaneous detonator shall be used to fire each sheathed explosive...

  1. 30 CFR 75.1314 - Sheathed explosive units.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Sheathed explosive units. 75.1314 Section 75... HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Explosives and Blasting § 75.1314 Sheathed explosive units. (a) A separate instantaneous detonator shall be used to fire each sheathed explosive...

  2. 30 CFR 75.1314 - Sheathed explosive units.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Sheathed explosive units. 75.1314 Section 75... HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Explosives and Blasting § 75.1314 Sheathed explosive units. (a) A separate instantaneous detonator shall be used to fire each sheathed explosive...

  3. 30 CFR 75.1314 - Sheathed explosive units.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Sheathed explosive units. 75.1314 Section 75... HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Explosives and Blasting § 75.1314 Sheathed explosive units. (a) A separate instantaneous detonator shall be used to fire each sheathed explosive...

  4. 30 CFR 75.1314 - Sheathed explosive units.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Sheathed explosive units. 75.1314 Section 75... HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Explosives and Blasting § 75.1314 Sheathed explosive units. (a) A separate instantaneous detonator shall be used to fire each sheathed explosive...

  5. Linear and nonlinear interactions of an electron beam with oblique whistler and electrostatic waves in the magnetosphere

    NASA Astrophysics Data System (ADS)

    Zhang, Y. L.; Matsumoto, H.; Omura, Y.

    1993-12-01

    Both linear and nonlinear interactions between oblique whistler, electrostatic, quasi-upper hybrid mode waves and an electron beam are studied by linear analyses and electromagnetic particle simulations. In addition to a background cold plasma, we assumed a hot electron beam drifting along a static magnetic field. Growth rates of the oblique whistler, oblique electrostatic, and quasi-upper hybrid instabilities were first calculated. We found that there are four kinds of unstable mode waves for parallel and oblique propagations. They are the electromagnetic whistler mode wave (WW1), the electrostatic whistler mode wave (WW2), the electrostatic mode wave (ESW), and the quasi-upper hybrid mode wave (UHW). A possible mechanism is proposed to explain the satellite observations of whistler mode chorus and accompanied electrostatic waves, whose amplitudes are sometimes modulated at the chorus frequency.

  6. SHARP OBLIQUE PERSPECTIVE OF DECK AND APPROACH SPANS ALONG WITH ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    SHARP OBLIQUE PERSPECTIVE OF DECK AND APPROACH SPANS ALONG WITH PRINCIPLE CANTILEVER SPAN SHARP OBLIQUE PERSPECTIVE OF DECK AND APPROACH SPANS ALONG WITH PRINCIPLE CANTILEVER SPAN SHARP OBLIQUE PERSPECTIVE OF DECK AND APPROACH SPANS ALONG WITH PRINCIPLE CANTILEVER SPAN SHARP OBLIQUE PERSPECTIVE OF DECK AND APPROACH SPANS ALONG WITH PRINCIPLE CANTILEVER SPAN SHARP OBLIQUE PERSPECTIVE OF DECK AND APPROACH SPANS ALONG WITH PRINCIPLE CANTILEVER SPAN SHARP OBLIQUE PERSPECTIVE OF DECK AND APPROACH SPANS ALONG WITH PRINCIPLE CANTILEVER SPAN vSHARP OBLIQUE PERSPECTIVE OF DECK AND APPROACH SPANS ALONG WITH PRINCIPLE CANTILEVER SPAN SHARP OBLIQUE PERSPECTIVE OF DECK AND APPROACH SPANS ALONG WITH PRINCIPLE CANTILEVER SPAN SHARP OBLIQUE PERSPECTIVE OF DECK AND APPROACH SPANS ALONG WITH PRINCIPLE CANTILEVER SPAN - Snake River Bridge at Lyons' Ferry, State Route 261 spanning Snake River, Starbuck, Columbia County, WA

  7. Including sheath effects in the interpretation of planar retarding potential analyzer's low-energy ion data

    NASA Astrophysics Data System (ADS)

    Fisher, L. E.; Lynch, K. A.; Fernandes, P. A.; Bekkeng, T. A.; Moen, J.; Zettergren, M.; Miceli, R. J.; Powell, S.; Lessard, M. R.; Horak, P.

    2016-04-01

    The interpretation of planar retarding potential analyzers (RPA) during ionospheric sounding rocket missions requires modeling the thick 3D plasma sheath. This paper overviews the theory of RPAs with an emphasis placed on the impact of the sheath on current-voltage (I-V) curves. It then describes the Petite Ion Probe (PIP) which has been designed to function in this difficult regime. The data analysis procedure for this instrument is discussed in detail. Data analysis begins by modeling the sheath with the Spacecraft Plasma Interaction System (SPIS), a particle-in-cell code. Test particles are traced through the sheath and detector to determine the detector's response. A training set is constructed from these simulated curves for a support vector regression analysis which relates the properties of the I-V curve to the properties of the plasma. The first in situ use of the PIPs occurred during the MICA sounding rocket mission which launched from Poker Flat, Alaska in February of 2012. These data are presented as a case study, providing valuable cross-instrument comparisons. A heritage top-hat thermal ion electrostatic analyzer, called the HT, and a multi-needle Langmuir probe have been used to validate both the PIPs and the data analysis method. Compared to the HT, the PIP ion temperature measurements agree with a root-mean-square error of 0.023 eV. These two instruments agree on the parallel-to-B plasma flow velocity with a root-mean-square error of 130 m/s. The PIP with its field of view aligned perpendicular-to-B provided a density measurement with an 11% error compared to the multi-needle Langmuir Probe. Higher error in the other PIP's density measurement is likely due to simplifications in the SPIS model geometry.

  8. Including sheath effects in the interpretation of planar retarding potential analyzer's low-energy ion data.

    PubMed

    Fisher, L E; Lynch, K A; Fernandes, P A; Bekkeng, T A; Moen, J; Zettergren, M; Miceli, R J; Powell, S; Lessard, M R; Horak, P

    2016-04-01

    The interpretation of planar retarding potential analyzers (RPA) during ionospheric sounding rocket missions requires modeling the thick 3D plasma sheath. This paper overviews the theory of RPAs with an emphasis placed on the impact of the sheath on current-voltage (I-V) curves. It then describes the Petite Ion Probe (PIP) which has been designed to function in this difficult regime. The data analysis procedure for this instrument is discussed in detail. Data analysis begins by modeling the sheath with the Spacecraft Plasma Interaction System (SPIS), a particle-in-cell code. Test particles are traced through the sheath and detector to determine the detector's response. A training set is constructed from these simulated curves for a support vector regression analysis which relates the properties of the I-V curve to the properties of the plasma. The first in situ use of the PIPs occurred during the MICA sounding rocket mission which launched from Poker Flat, Alaska in February of 2012. These data are presented as a case study, providing valuable cross-instrument comparisons. A heritage top-hat thermal ion electrostatic analyzer, called the HT, and a multi-needle Langmuir probe have been used to validate both the PIPs and the data analysis method. Compared to the HT, the PIP ion temperature measurements agree with a root-mean-square error of 0.023 eV. These two instruments agree on the parallel-to-B plasma flow velocity with a root-mean-square error of 130 m/s. The PIP with its field of view aligned perpendicular-to-B provided a density measurement with an 11% error compared to the multi-needle Langmuir Probe. Higher error in the other PIP's density measurement is likely due to simplifications in the SPIS model geometry. PMID:27131671

  9. Relativistic electron acceleration by oblique whistler waves

    SciTech Connect

    Yoon, Peter H.; Pandey, Vinay S.; Lee, Dong-Hun

    2013-11-15

    Test-particle simulations of electrons interacting with finite-amplitude, obliquely propagating whistler waves are carried out in order to investigate the acceleration of relativistic electrons by these waves. According to the present findings, an efficient acceleration of relativistic electrons requires a narrow range of oblique propagation angles, close to the whistler resonance cone angle, when the wave amplitude is held constant at relatively low value. For a constant wave propagation angle, it is found that a range of oblique whistler wave amplitudes permits the acceleration of relativistic electrons to O(MeV) energies. An initial distribution of test electrons is shown to form a power-law distribution when plotted in energy space. It is also found that the acceleration is largely uniform in electron pitch-angle space.

  10. Ion stochastic heating by obliquely propagating magnetosonic waves

    SciTech Connect

    Gao Xinliang; Lu Quanming; Wu Mingyu; Wang Shui

    2012-06-15

    The ion motions in obliquely propagating Alfven waves with sufficiently large amplitudes have already been studied by Chen et al.[Phys. Plasmas 8, 4713 (2001)], and it was found that the ion motions are stochastic when the wave frequency is at a fraction of the ion gyro-frequency. In this paper, with test particle simulations, we investigate the ion motions in obliquely propagating magnetosonic waves and find that the ion motions also become stochastic when the amplitude of the magnetosonic waves is sufficiently large due to the resonance at sub-cyclotron frequencies. Similar to the Alfven wave, the increase of the propagating angle, wave frequency, and the number of the wave modes can lower the stochastic threshold of the ion motions. However, because the magnetosonic waves become more and more compressive with the increase of the propagating angle, the decrease of the stochastic threshold with the increase of the propagating angle is more obvious in the magnetosonic waves than that in the Alfven waves.

  11. Magnetic and Electric Field Polarizations of Oblique Magnetospheric Chorus Waves

    NASA Technical Reports Server (NTRS)

    Verkhoglyadova, Olga; Tsurutani, Bruce T.; Lakhina, Gurbax S.

    2012-01-01

    A theory was developed to explain the properties of the chorus magnetic and electric field components in the case of an arbitrary propagation angle. The new theory shows that a whistler wave has circularly polarized magnetic fields for oblique propagation. This theoretical result is verified by GEOTAIL observations. The wave electric field polarization plane is not orthogonal to the wave vector, and in general is highly elliptically polarized. A special case of the whistler wave called the Gendrin mode is also discussed. This will help to construct a detailed and realistic picture of wave interaction with magnetosphere electrons. It is the purpose of this innovation to study the magnetic and electric polarization properties of chorus at all frequencies, and at all angles of propagation. Even though general expressions for electromagnetic wave polarization in anisotropic plasma are derived in many textbooks, to the knowledge of the innovators, a detailed analysis for oblique whistler wave mode is lacking. Knowledge of the polarization properties is critical for theoretical calculations of resonant wave-particle interactions.

  12. Wave properties near the subsolar magnetopause - Pc 1 waves in the sheath transition layer

    NASA Technical Reports Server (NTRS)

    Song, P.; Russell, C. T.; Huang, C. Y.

    1993-01-01

    We study the waves in the frequency range of Pc 1 in the sheath transition layer of the magnetopause from the ISEE 1 and 2 observations. The waves are enhanced in the sheath transition layer, although they are scattered into the magnetosheath when the outer edge of the sheath transition layer is not sharp. The wave frequency is proportional to, and equal to, about 44 percent of the ion gyrofrequency. The waves are left-handed polarized for southward IMF, but linearly polarized for northward IMF. The direction of maximum variation is perpendicular to both the background field and the gradients of the field and density for northward IMF; for southward IMF, the waves are more turbulent. Wave generation mechanisms may depend on IMF orientations rather than the shock geometry. To investigate the free energy generating the waves for northward IMF, a method is developed combining the measurements from the fast plasma experiment and Lepedea to obtain a high time resolution estimate of the temperature anisotropy for strongly northward IMF. The estimated ion temperature anisotropy is enhanced, up to a factor of 2, within the sheath transition layer for northward IMF.

  13. Screening and sheath formation in a nonequilibrium mixed Cairns-Tsallis electron distribution

    NASA Astrophysics Data System (ADS)

    Bouzit, Omar; Gougam, Leila Ait; Tribeche, Mouloud

    2015-05-01

    The effects of electron nonextensivity for a given nonthermality state, on Debye shielding and electrostatic sheath formation are examined. A physically meaningful Cairns-Tsallis distribution is outlined and a generalized expression for the Debye screening length λD q , α is obtained. It is shown that an increase of the entropic index q causes λD q , α to decrease whatever the amount of plasma nonthermality α. In addition, smaller pertinent values of q along with relatively higher values of α provide larger values of λD q , α . The shielded electrostatic potential falls off as a function of distance more slowly as α increases, a result somewhat analogous to the dynamical shielding decrease (albeit in a different context) of a free charge as it begins to move. Moreover, smaller pertinent values of q along with relatively higher values of α are found to involve higher ion drift speed v i 0 for proper sheath formation. As α increases, the sheath electrostatic potential-gradient d Ψ s / d ξ becomes abruptly steep slowing down the energetic electrons leakage to the wall. Moreover, the sheath thickness broadens as the electron nonthermality strengthens.

  14. Screening and sheath formation in a nonequilibrium mixed Cairns-Tsallis electron distribution

    SciTech Connect

    Bouzit, Omar; Gougam, Leila Ait; Tribeche, Mouloud

    2015-05-15

    The effects of electron nonextensivity for a given nonthermality state, on Debye shielding and electrostatic sheath formation are examined. A physically meaningful Cairns-Tsallis distribution is outlined and a generalized expression for the Debye screening length λ{sub D}{sup q,α} is obtained. It is shown that an increase of the entropic index q causes λ{sub D}{sup q,α} to decrease whatever the amount of plasma nonthermality α. In addition, smaller pertinent values of q along with relatively higher values of α provide larger values of λ{sub D}{sup q,α}. The shielded electrostatic potential falls off as a function of distance more slowly as α increases, a result somewhat analogous to the dynamical shielding decrease (albeit in a different context) of a free charge as it begins to move. Moreover, smaller pertinent values of q along with relatively higher values of α are found to involve higher ion drift speed v{sub i0} for proper sheath formation. As α increases, the sheath electrostatic potential-gradient dΨ{sub s}/dξ becomes abruptly steep slowing down the energetic electrons leakage to the wall. Moreover, the sheath thickness broadens as the electron nonthermality strengthens.

  15. The Geo-Effectiveness of CME-Driven Shocks and Sheaths

    NASA Astrophysics Data System (ADS)

    Lugaz, Noé; Al-haddad, Nada; Schwadron, Nathan; Riley, Pete; Farrugia, Charles; Winslow, Reka

    2016-07-01

    Past studies have found that ˜30% of intense geomagnetic storms and ˜20% of moderate geomagnetic storms are caused by forward fast magnetosonic shocks and the sheath plasma and magnetic field behind these shocks, making shocks the second most important cause of geomagnetic storms after magnetic ejecta. Since only about 20% of fast-mode shocks are followed by a moderate geomagnetic storm, it is important to understand which shock and upstream properties are most effective in creating optimal conditions for the development of geomagnetic storms. To do so, we identify all fast-mode forwards shocks (˜100), for which the sheath region resulted in a moderate or intense geomagnetic storm during solar cycles 23 and 24 (1997 - 2015). We find that about half such shocks are shocks propagating into a preceding CME or shocks propagating into the sheath region of a preceding shock. Overall, only a small fraction of shocks propagating through normal solar wind are geo-effective (less than 15%), whereas the majority of shocks propagating through a previous CME are geo-effective. We further discuss the conditions which can result in the formation of southward Bz in the sheath region behind a shock.

  16. F-8 oblique wing structural feasibility study

    NASA Technical Reports Server (NTRS)

    Koltko, E.; Katz, A.; Bell, M. A.; Smith, W. D.; Lauridia, R.; Overstreet, C. T.; Klapprott, C.; Orr, T. F.; Jobe, C. L.; Wyatt, F. G.

    1975-01-01

    The feasibility of fitting a rotating oblique wing on an F-8 aircraft to produce a full scale manned prototype capable of operating in the transonic and supersonic speed range was investigated. The strength, aeroelasticity, and fatigue life of such a prototype are analyzed. Concepts are developed for a new wing, a pivot, a skewing mechanism, control systems that operate through the pivot, and a wing support assembly that attaches in the F-8 wing cavity. The modification of the two-place NTF-8A aircraft to the oblique wing configuration is discussed.

  17. Ground-based plasma contractor characterization

    NASA Technical Reports Server (NTRS)

    Patterson, Michael J.; Aadland, Randall S.

    1987-01-01

    Presented are recent NASA Lewis Research Center (LeRC) plasma contractor experimental results, as well as a description of the plasma contractor test facility. The operation of a 24 cm diameter plasma source with hollow cathode was investigated in the lighted-mode regime of electron current collection from 0.1 to 7.0 A. These results are compared to those obtained with a 12 cm plasma source. Full two-dimensional plasma potential profiles were constructed from emissive probe traces of the contractor plume. The experimentally measured dimensions of the plume sheaths were then compared to those theoretically predicted using a model of a spherical double sheath. Results are consistent for currents up to approximately 1.0 A. For currents above 1.0 A, substantial deviations from theory occur. These deviations are due to sheath asphericity, and possibly volume ionization in the double-sheath region.

  18. Male urinary incontinence and the urinary sheath.

    PubMed

    Smart, Clare

    This article addresses the assessment and management of male incontinence with a specific focus on the use of the male external catheter (MEC) or urinary sheath. Education and expertise when dealing with a man with urinary incontinence, as well as a tactful and sensitive attitude towards this embarrassing problem, are essential for a successful outcome. The urinary sheath is often perceived by nurses and patients as a difficult product to master and is prone to failure owing to incorrect fitting and management. With correct usage it can make a great difference to a patient's quality of life and avoid problems often associated with urinary catheters and pads such as urinary infection and skin excoriation. Detailed assessment of the patient as well as his suitability for the MEC is essential for a successful outcome. PMID:24820510

  19. Optic Nerve Sheath Mechanics in VIIP Syndrome

    NASA Technical Reports Server (NTRS)

    Raykin, Julia; Feola, Andrew; Gleason, Rudy; Mulugeta, Lealem; Myers, Jerry; Nelson, Emily; Samuels, Brian; Ethier, C. Ross

    2015-01-01

    Visual Impairment and Intracranial Pressure (VIIP) syndrome results in a loss of visual function and occurs in astronauts following long-duration spaceflight. Understanding the mechanisms that lead to the ocular changes involved in VIIP is of critical importance for space medicine research. Although the exact mechanisms of VIIP are not yet known, it is hypothesized that microgravity-induced increases in intracranial pressures (ICP) drive the remodeling of the optic nerve sheath, leading to compression of the optic nerve which in turn may reduce visual acuity. Some astronauts present with a kink in the optic nerve after return to earth, suggesting that tissue remodeling in response to ICP increases may be taking place. The goal of this work is to characterize the mechanical properties of the optic nerve sheath (dura mater) to better understand its biomechanical response to increased ICP.

  20. Dispersion relations for a plasma-filled helix-loaded-waveguide

    SciTech Connect

    Makowski, M.A.; Hooper, E.B.; Stallard, B.W.

    1994-01-01

    The propagation of waves on bounded, magnetized plasma columns arises in connection with a variety of applications. To this end dispersion relations axe developed for a variety of multi-region circularly symmetric configurations. These include, a sheath helix in free space, a plasma column in free space, a plasma filled conducting tube, a plasma filled sheath-helix in free space, a sheath helix within a conducting cylinder, a plasma filled sheath-helix within a conducting cylinder, and a plasma column within a sheath-helix contained within a conducting cylinder. The latter configuration is of the most interest for whistler wave excitation for plasma thruster applications, since it includes the effect of a vacuum region separating the plasma column from the helical excitation structure.

  1. Formation of double sheaths and the J-V characteristics of the obstructed region

    SciTech Connect

    Wang, C.C.

    1980-06-01

    The arc drop of the vapor thermionic converter is determined by the difference of sheath heights and the potential difference across the plasma. The J-V characteristics of cesium vapor diodes operating in the ignited mode show a knee corresponding to near optimum power. When the diode is operating in the region above the knee, the dominant contributor to the arc drop is the difference of the sheath heights (i.e., the potential difference across the plasma produces either a very small loss or may, in fact, reverse sign and reduce the arc drop). In this region the power decreases because the increase in output current is usually not able to compensate for the loss of output voltage. When the diode is operating in the region below the knee, the potential difference in the plasma becomes the dominant contributor to the arc drop. For these reasons, the shape of the J-V characteristics below the knee is different from that above the knee. The location of the knee is a good indicator of the maximum power and the maximum efficiency points. Under the fully optimized conditions, the knee also indicates the barrier index of the diode. Therefore, how and where the knee will appear is of great theoretical and practical interest. Some workers in the thermionic field have speculated that the appearance of the knee is due to the formation of the double sheath. However, this study indicates that the formation of the double sheath takes place significantly below the knee. In addition, this study evaluates J-V characteristics in the obstructed region.

  2. Oblique and Head-On Elastic Collisions

    ERIC Educational Resources Information Center

    Ng, Chiu-king

    2008-01-01

    When a moving ball collides elastically with an identical, initially stationary ball, the incident ball will either come to rest (head-on collision; see Fig. 1) or will acquire a velocity that is perpendicular to that acquired by the target ball (oblique collision; see Fig. 2). These two possible outcomes are related in an interesting way, which…

  3. Obliquity Modulation of the Incoming Solar Radiation

    NASA Technical Reports Server (NTRS)

    Liu, Han-Shou; Smith, David E. (Technical Monitor)

    2001-01-01

    Based on a basic principle of orbital resonance, we have identified a huge deficit of solar radiation induced by the combined amplitude and frequency modulation of the Earth's obliquity as possibly the causal mechanism for ice age glaciation. Including this modulation effect on solar radiation, we have performed model simulations of climate change for the past 2 million years. Simulation results show that: (1) For the past 1 million years, temperature fluctuation cycles were dominated by a 100-Kyr period due to amplitude-frequency resonance effect of the obliquity; (2) From 2 to 1 million years ago, the amplitude-frequency interactions. of the obliquity were so weak that they were not able to stimulate a resonance effect on solar radiation; (3) Amplitude and frequency modulation analysis on solar radiation provides a series of resonance in the incoming solar radiation which may shift the glaciation cycles from 41-Kyr to 100-Kyr about 0.9 million years ago. These results are in good agreement with the marine and continental paleoclimate records. Thus, the proposed climate response to the combined amplitude and frequency modulation of the Earth's obliquity may be the key to understanding the glaciation puzzles in paleoclimatology.

  4. Insolation patterns on synchronous exoplanets with obliquity

    NASA Astrophysics Data System (ADS)

    Dobrovolskis, Anthony R.

    2009-11-01

    A previous paper [Dobrovolskis, A.R., 2007. Icarus 192, 1-23] showed that eccentricity can have profound effects on the climate, habitability, and detectability of extrasolar planets. This complementary study shows that obliquity can have comparable effects. The known exoplanets exhibit a wide range of orbital eccentricities, but those within several million kilometers of their suns are generally in near-circular orbits. This fact is widely attributed to the dissipation of tides in the planets. Tides in a planet affect its spin even more than its orbit, and such tidally evolved planets often are assumed to be in synchronous rotation, so that their rotation periods are identical to their orbital periods. The canonical example of synchronous spin is the way that our Moon always keeps nearly the same hemisphere facing the Earth. Tides also tend to reduce the planet's obliquity (the angle between its spin and orbital angular velocities). However, orbit precession can cause the rotation to become locked in a "Cassini state", where it retains a nearly constant non-zero obliquity. For example, our Moon maintains an obliquity of about 6.7° with respect to its orbit about the Earth. In comparison, stable Cassini states can exist for practically any obliquity up to ˜90° or more for planets of binary stars, or in multi-planet systems with high mutual inclinations, such as are produced by scattering or by the Kozai mechanism. This work considers planets in synchronous rotation with circular orbits, but arbitrary obliquity β; this affects the distribution of insolation over the planet's surface, particularly near its poles. For β=0, one hemisphere bakes in perpetual sunshine, while the opposite hemisphere experiences eternal darkness. As β increases, the region of permanent daylight and the antipodal realm of endless night both shrink, while a more temperate area of alternating day and night spreads in longitude, and especially in latitude. The regions of permanent day or

  5. Rotation Driven by Rectified RF-sheath Potentials and Spatial Dispersion

    SciTech Connect

    Hellsten, T.

    2009-11-26

    Plasma rotation is of interest for improving confinement and stabilising plasma. Effects from fast particles with broad orbits can only partly explain the changes in the rotation profiles during ICRH. The effect on wave-particle interaction of a finite poloidal mode number is discussed and two new RF-mechanisms are proposed: Co-current torque caused by sputtering by rectified RF-sheath potentials and transport of momentum due to spatial dispersion. The latter effect affects the RF-current drive, in particular, in conjunction with mode conversion.

  6. Mechanism of cathode spot splitting in vacuum arcs in an oblique magnetic field

    SciTech Connect

    Beilis, I. I.

    2015-10-15

    Experiments in the last decade showed that for cathode spots in a magnetic field that obliquely intercepts the cathode surface, the current per spot increased with the transverse component of the magnetic field and decreased with the normal component. The present work analyzes the nature of cathode spot splitting in an oblique magnetic field. A physical model for cathode spot current splitting was developed, which considered the relation between the plasma kinetic pressure, self-magnetic pressure, and applied magnetic pressure in a current carrying cathode plasma jet. The current per spot was calculated, and it was found to increase with the tangential component of the magnetic field and to decrease with the normal component, which agrees well with the experimental dependence.

  7. LOW STELLAR OBLIQUITIES IN COMPACT MULTIPLANET SYSTEMS

    SciTech Connect

    Albrecht, Simon; Winn, Joshua N.; Marcy, Geoffrey W.; Isaacson, Howard; Howard, Andrew W.; Johnson, John A.

    2013-07-01

    We measure the sky-projected stellar obliquities ({lambda}) in the multiple-transiting planetary systems KOI-94 and Kepler-25, using the Rossiter-McLaughlin effect. In both cases, the host stars are well aligned with the orbital planes of the planets. For KOI-94 we find {lambda} = -11 Degree-Sign {+-} 11 Degree-Sign , confirming a recent result by Hirano and coworkers. Kepler-25 was a more challenging case, because the transit depth is unusually small (0.13%). To obtain the obliquity, it was necessary to use prior knowledge of the star's projected rotation rate and apply two different analysis methods to independent wavelength regions of the spectra. The two methods gave consistent results, {lambda} = 7 Degree-Sign {+-} 8 Degree-Sign and -0. Degree-Sign 5 {+-} 5. Degree-Sign 7. There are now a total of five obliquity measurements for host stars of systems of multiple-transiting planets, all of which are consistent with spin-orbit alignment. This alignment is unlikely to be the result of tidal interactions because of the relatively large orbital distances and low planetary masses in the systems. In this respect, the multiplanet host stars differ from hot-Jupiter host stars, which commonly have large spin-orbit misalignments whenever tidal interactions are weak. In particular, the weak-tide subset of hot-Jupiter hosts has obliquities consistent with an isotropic distribution (p = 0.6), but the multiplanet hosts are incompatible with such a distribution (p {approx} 10{sup -6}). This suggests that high obliquities are confined to hot-Jupiter systems, and provides further evidence that hot-Jupiter formation involves processes that tilt the planetary orbit.

  8. Examination of ionic wind and cathode sheath effects in a E-field premixed flame with ion density measurements

    NASA Astrophysics Data System (ADS)

    Jacobs, Stewart V.; Xu, Kunning G.

    2016-04-01

    The effect of the ionic wind on a premixed methane-air flame under a DC electric field is studied via mapping of the ion density with Langmuir probes. Ion densities were observed to increase near the burner with increasing electrode voltage up to 6 kV. Past this electrode supply voltage, ion densities ceased increasing and began to decline in some locations within the premixed flame. The increased ion density is caused by an increase in ionic wind force and cathode sheath thickness. The plateau in density is due to the cathode sheath fully encompassing the flame front which is the ion source, thereby collecting all ions in the flame. The spatial density data support the ionic wind hypothesis and provide further explanation of its limits based on the plasma sheath.

  9. Magnetoplasma sheath waves on a conducting tether in the ionosphere with applications to EMI propagation on large space structures

    NASA Technical Reports Server (NTRS)

    Balmain, K. G.; James, H. G.; Bantin, C. C.

    1991-01-01

    A recent space experiment confirmed sheath-wave propagation of a kilometer-long insulated wire in the ionosphere, oriented parallel to the Earth's magnetic field. This space tether experiment, Oedipus-A, showed a sheath-wave passband up to about 2 MHz and a phase velocity somewhat slower than the velocity of light in a vacuum, and also demonstrated both ease of wave excitation and low attenuation. The evidence suggests that, on any large structure in low Earth orbit, transient or continuous wave electromagnetic interference, once generated, could propagate over the structure via sheath waves, producing unwanted signal levels much higher than in the absence of the ambient plasma medium. Consequently, there is a need for a review of both electromagnetic interference/electromagnetic compatibility standards and ground test procedures as they apply to large structures in low Earth orbit.

  10. Note: Refined possibilities for plasma probe diagnostics

    NASA Astrophysics Data System (ADS)

    Masherov, P. E.; Riaby, V. A.; Abgaryan, V. K.

    2016-08-01

    In an earlier publication, the ion mass determination technique was proposed using the Langmuir probe measurement results for low-pressure Maxwellian plasmas and their analysis, based on the Bohm effect and the Child-Boguslavsky-Langmuir (CBL) probe sheath model, allowing for probe sheath thickness and ion mass evaluations after the Bohm coefficient CBCyl ≈ 1.13 for cylindrical probes had been determined. In the present study, the step-front sheath model, being physically closer to the reality of gas discharge plasmas, was considered in order to correct the CBL sheath model results. At this stage, more real Bohm coefficient (CBCyl ≈ 1.23) for cylindrical probes was found to provide a more reliable method of probe sheath thickness and ion mass determination.

  11. Note: Refined possibilities for plasma probe diagnostics.

    PubMed

    Masherov, P E; Riaby, V A; Abgaryan, V K

    2016-08-01

    In an earlier publication, the ion mass determination technique was proposed using the Langmuir probe measurement results for low-pressure Maxwellian plasmas and their analysis, based on the Bohm effect and the Child-Boguslavsky-Langmuir (CBL) probe sheath model, allowing for probe sheath thickness and ion mass evaluations after the Bohm coefficient CBCyl ≈ 1.13 for cylindrical probes had been determined. In the present study, the step-front sheath model, being physically closer to the reality of gas discharge plasmas, was considered in order to correct the CBL sheath model results. At this stage, more real Bohm coefficient (CBCyl ≈ 1.23) for cylindrical probes was found to provide a more reliable method of probe sheath thickness and ion mass determination. PMID:27587177

  12. Sheath insulator final test report, TFE Verification Program

    SciTech Connect

    Not Available

    1994-07-01

    The sheath insulator in a thermionic cell has two functions. First, the sheath insulator must electrically isolate the collector form the outer containment sheath tube that is in contact with the reactor liquid metal coolant. Second, The sheath insulator must provide for high uniform thermal conductance between the collector and the reactor coolant to remove away waste heat. The goals of the sheath insulator test program were to demonstrate that suitable ceramic materials and fabrication processes were available, and to validate the performance of the sheath insulator for TFE-VP requirements. This report discusses the objectives of the test program, fabrication development, ex-reactor test program, in-reactor test program, and the insulator seal specifications.

  13. Nerve sheath myxoma: report of a rare case.

    PubMed

    Bhat, Amoolya; Narasimha, Apaparna; C, Vijaya; Vk, Sundeep

    2015-04-01

    Nerve sheath myxoma defined by Harkin and Reed is an uncommon benign neoplasm with nerve sheath like features. It has several cytological and histological differential diagnoses. One such lesion is neurothekeoma, which can be differentiated using immunohistochemistry. In most of the previous reports nerve sheath myxoma and neurothekeoma were considered synonymous and were often confused for one another. This case report separates the two using immunohistochemistry. Also, the cytological features of nerve sheath myxoma are not well documented in the past. This case report attempts to display the cyto-morphology of nerve sheath myxoma. We report a rare case of nerve sheath myxoma diagnosed on cytological features confirmed by histopathology and immunohistochemistry in a 32-year-old lady who presented with an asymptomatic nodule over the left cervical area and discuss its cyto-histological mimics. PMID:26023558

  14. [When and how to perform the superior oblique tucking surgery].

    PubMed

    Zhang, W

    2016-08-01

    Either superior oblique weakening or strengthening surgery is the most complicated and most difficult to perform in the field of strabismus surgery. The effect of superior oblique surgery is also unpredictable. In addition, improper superior oblique strengthening surgery may produce limited elevation in adduction (iatrogenic Brown syndrome). In this article, we reviewed the history of superior oblique surgery, especially on when and how to perform the superior oblique strengthening surgery for providing reference to the clinicians in the field of strabismus and pediatric ophthalmology. (Chin J Ophthalmol, 2016, 52: 565-567). PMID:27562275

  15. Normalized ion distribution function in expanding sheaths of 2D grid electrodes

    NASA Astrophysics Data System (ADS)

    Yi, Changho; Namkung, Won; Cho, Moohyun

    2016-04-01

    Ion distributions in expanding collisionless sheaths of two-dimensional (2D) grid electrodes were studied by using XOOPIC (particle-in-cell) simulations when short pulses of negative high-voltage were applied to electrodes immersed in plasmas. 2D grid electrodes consist of a periodic array of cylindrical electrodes, and the opening ratio of the grid electrodes is defined by the ratio of the spacing between cylindrical electrodes to the periodic length of the grid electrodes. In this paper, we introduce a normalized ion distribution function in normalized coordinates, and it is shown by simulation that the normalized ion distribution function depends only on the opening ratio of the grid electrodes. When the opening ratio of the grid electrodes is fixed, the ion distribution in expanding sheaths can be easily found in various conditions using only a single run of a PIC simulation, and the computation time can be significantly reduced.

  16. Numerical solution of wave equations for the stability of the inner cometo-sheath

    NASA Technical Reports Server (NTRS)

    Srivastava, Krishna M.; Tsurutani, Bruce T.; Goldstein, Bruce E.

    1993-01-01

    Numerical solution of the MHD wave equations for stability of the cometary sheath determined by the balance between the inward Lorentz body force and the outward ion-neutral drag force is obtained by using a two-point boundary value method. The eigenvalues and the eigenfunctions are obtained numerically by treating the cometary inner sheath as a layer of finite thickness, bounded by the contact surface, i.e., the diamagnetic cavity boundary. The magnetic field structure discovered in the ionosphere of Comets Halley and Giacobini-Zinner is found to be unstable. The effects of finite plasma pressure, dissociative recombination, and mass loading due to photoionization are found to be stabilizing but are unable to quench the instability completely. It is also found that the higher the neutral production rate the lesser is the growth rate for the instability.

  17. Detached tip of a transseptal sheath during left atrial ablation.

    PubMed

    El-Damaty, Ahmed; Love, Michael; Parkash, Ratika

    2012-02-15

    Left atrial ablation has become more commonplace with the advent of catheter ablation for atrial fibrillation. A number of transseptal sheaths have been produced to enhance safe and efficient catheter manipulation in the left atrium (LA) for these procedures. Some of the sheaths have been subject to recall due to partial or complete detachment of its radiopaque tip. We report a case of a 46 year-old female diagnosed with idiopathic dilated cardiomyopathy that presented with atypical left atrial flutter. During electrophysiologic study, a Swartz braided SL1 (SL-1) transseptal sheath was used to introduce the ablation catheter to the left atrium. During left atrial mapping, the radiopaque tip of the sheath detached from the rest of the sheath and was seen floating in the LA. After exchanging the SL-1 sheath with a deflectable sheath, the detached segment was retrieved out of the LA and eventually out of the vascular system using an angioplasty balloon advanced over a wire and inflated distal to the lumen of the detached tip. The root cause of this malfunction was found to be lack of a secondary bonding process that these sheaths generally undergo during the manufacturing process. We describe the case of a left atrial ablation procedure where a novel percutaneous method was able to successfully retrieve the detached tip of a transseptal sheath from the vascular system, thereby avoiding a potential catastrophic complication or thoracotomy. This method may be useful in other cases where similar circumstances may present. PMID:22162088

  18. Controversies in ureteroscopy: Wire, basket, and sheath

    PubMed Central

    Rizkala, Emad R; Monga, Manoj

    2013-01-01

    In the last one to two decades, flexible ureteroscopy has rapidly expanded its role in the treatment of urologic stone disease. With the frequent and expanded use of flexible ureteroscopy, other ancillary instruments were developed in order to ease and facilitate this technique, such as ureteral access sheaths (UAS) and a variety of wires and baskets. These developments, along with improved surgeon ureteroscopic competence, have often brought into question the need to implement the “traditional technique” of flexible ureteroscopy. In this review, we discuss a brief history of flexible ureteroscopy, its expanded indications, and the controversy surrounding the use of UAS, wires, and baskets. PMID:24082447

  19. Target normal sheath acceleration sheath fields for arbitrary electron energy distribution

    SciTech Connect

    Schmitz, Holger

    2012-08-15

    Relativistic electrons, generated by ultraintense laser pulses, travel through the target and form a space charge sheath at the rear surface which can be used to accelerate ions to high energies. If the laser pulse duration is comparable or shorter than the time needed for the electrons to travel through the target, the electrons will not have the chance to form an equilibrium distribution but must be described by a non-equilibrium distribution. We present a kinetic theory of the rear sheath for arbitrary electron distribution function f(E), where E is the electron energy, and evaluate it for different shapes of f(E). We find that the far field is mainly determined by the high energy tail of the distribution, a steep decay of f(E) for high energies results in a small electric field and vice versa. The model is extended to account for electrons escaping the sheath region thereby allowing a finite potential drop over the sheath. The consequences of the model for the acceleration of ions are discussed.

  20. Potential contour shaping and sheath behavior with wall electrodes and near-wall magnetic fields in Hall thrusters

    SciTech Connect

    Xu, K. G.; Dao, H.; Walker, M. L. R.

    2012-10-15

    Graphite electrodes are embedded within the discharge channel of a Hall effect thruster to focus ions for improved performance. Cusp-shaped magnetic fields are added around the electrodes to shield the electrodes from high electron current. Internal plasma potential measurements inside the discharge channel show that the presence of floating graphite does not significantly affect the potential contours at 150 V anode potential. Creation of closed contour pockets are observed with the electrodes biased 10 and 30 V above the anode potential. The electrodes also cause a compression of the acceleration region in the thruster. The cause of the changes in the potential contours is attributed to a shifting of discharge electrode from the anode to the electrodes and an expansion of the near-wall plasma sheath. The presence of the cusp magnetic fields is shown to affect the current collected by the electrodes, a behavior associated with modification of the plasma sheath properties due to magnetization of electrons.

  1. Oblique wing transonic transport configuration development

    NASA Technical Reports Server (NTRS)

    1977-01-01

    Studies of transport aircraft designed for boom-free supersonic flight show the variable sweep oblique wing to be the most efficient configuration for flight at low supersonic speeds. Use of this concept leads to a configuration that is lighter, quieter, and more fuel efficient than symmetric aircraft designed for the same mission. Aerodynamic structural, weight, aeroelastic and flight control studies show the oblique wing concept to be technically feasible. Investigations are reported for wing planform and thickness, pivot design and weight estimation, engine cycle (bypass ratio), and climb, descent and reserve fuel. Results are incorporated into a final configuration. Performance, weight, and balance characteristics are evaluated. Flight control requirements are reviewed, and areas in which further research is needed are identified.

  2. Proton beam generation of oblique whistler waves

    NASA Technical Reports Server (NTRS)

    Wong, H. K.; Goldstein, M. L.

    1988-01-01

    It is known that ion beams are capable of generating whistler waves that propagate parallel to the mean magnetic field. Such waves may have been observed both upstream of the earth's bow shock and in the vicinity of comets. Previous analyses are extended to include propagation oblique to the mean magnetic field. The instability is generated by the perpendicular component of free energy in the ions, which can arise either via a temperature anisotropy or via a gyrating distribution. In the former case, the generation of whistler waves is confined to a fairly narrow cone of propagation directions centered about parallel propagation; in the latter case, the maximum growth of the instability can occur at fairly large obliquities (theta equal to about 50 deg).

  3. Do oblique impacts produce Martian meteorites?

    NASA Astrophysics Data System (ADS)

    Nyquist, L. E.

    Geochronological and geochemical characteristics of several achondritic meteorites match those expected of Martian rocks. Several authors have suggested that these meteorites might have originated on Mars, but no satisfactory explanation has been given of how they may have been ejected from the Martian surface. It is suggested that the oblique impact of large meteoroids may produce ejecta which is entrained with the ricocheting projectile and accelerated to velocities in excess of Martian escape velocity. This suggestion is based on earlier experimental studies of oblique impacts and on the observation of several large Martian craters with the characteristic 'butterfly' ejecta pattern produced by low angle impacts. Several acceleration mechanisms may act on the Martian ejecta. The considerations suggest that a Martian origin of the shergottite meteorites is dynamically possible.

  4. Oblique waves lift the flapping flag.

    PubMed

    Hœpffner, Jérôme; Naka, Yoshitsugu

    2011-11-01

    The flapping of the flag is a classical model problem for the understanding of fluid-structure interaction: How does the flat state lose stability? Why do the nonlinear effects induce hysteretic behavior? We show in this Letter that, in contrast with the commonly studied model, the full three-dimensional flag with gravity has no stationary state whose stability can be formally studied: The waves are oblique and must immediately be of large amplitude. The remarkable structure of these waves results from the interplay of weight, geometry, and aerodynamic forces. This pattern is a key element in the force balance which allows the flag to hold and fly in the wind: Large amplitude oblique waves are responsible for lift. PMID:22181612

  5. Fabricational morphology of oblique ribs in bivalves.

    PubMed

    Checa, Antonio G

    2002-11-01

    The formation of oblique ribs of bivalve shells usually has been attributed to processes of reaction-diffusion of morphogens from cell to cell at the mantle margin or neural activation and lateral inhibition in the mantle. In particular, such ribs appear with high rates of lateral diffusion. Nevertheless, theoretical models fail to explain either partially or wholly some varieties of oblique ribs. After surveying the modes of formation of the shell and oblique ribs by the bivalve mantle and associated fabricational defects, I have determined that the mantle is able to develop an elaborate behavior in order to displace the rib in a particular direction during growth. The mantle margin is, therefore, not only the shell-secreting organ, but also the main morphogenetic unit. In particular, there are two main fabricational strategies. In forms with strict contact guidance (SCG) the mantle is able to project far enough beyond the shell margins so as to feel the already formed reliefs and to align new growth increments of the ribs in the appropriate directions. The shell margin is always strongly reflected. In bivalves with reduced contact guidance plus constant lateral shift (RCG), the margin is usually acute and the information about ribs available to the mantle is reduced. During rib construction the mantle extrudes slightly from the shell edge and then pushes laterally by muscular action; in this way, the new growth increment of the rib is displaced laterally on a small scale. The contact-guidance model is supported also by the homogeneous structure of the shell-secreting mantle. From the morphogenetic standpoint, oblique ribs are related to commarginal ones and both differ completely from other ribbing patterns of bivalves. PMID:12353301

  6. Oblique interaction of waves with shocks

    NASA Astrophysics Data System (ADS)

    Morro, A.

    The oblique interaction between plane waves and shocks in materials described by a system of conservation equations is investigated. Two results are found. First, a straightforward geometric-kinematic analysis of the interaction yields a relation for each emergent mode (i.e., the outgoing wave) which determines the relation of propagation once the incident wave is given. Second, the shock may undergo an angular velocity which is ultimately related to the shock acceleration

  7. The oblique mastectomy incision: advantages and outcomes.

    PubMed

    Gronet, Edward M; Halvorson, Eric G

    2014-01-01

    Mastectomy has traditionally been performed using a transverse elliptical incision. The disadvantages of this approach are a potentially visible scar medially and poor subincisional soft-tissue coverage of implants laterally. A more natural and aesthetic result is obtained with an oblique incision running parallel to the pectoralis major muscle fibers. This approach offers women more freedom of choice in clothing as well as the potential for complete subincisional muscle coverage in alloplastic breast reconstruction, in addition to other functional advantages. PMID:24835870

  8. CNS Myelin Sheath Lengths Are an Intrinsic Property of Oligodendrocytes

    PubMed Central

    Bechler, Marie E.; Byrne, Lauren; ffrench-Constant, Charles

    2015-01-01

    Summary Since Río-Hortega’s description of oligodendrocyte morphologies nearly a century ago, many studies have observed myelin sheath-length diversity between CNS regions [1–3]. Myelin sheath length directly impacts axonal conduction velocity by influencing the spacing between nodes of Ranvier. Such differences likely affect neural signal coordination and synchronization [4]. What accounts for regional differences in myelin sheath lengths is unknown; are myelin sheath lengths determined solely by axons or do intrinsic properties of different oligodendrocyte precursor cell populations affect length? The prevailing view is that axons provide molecular cues necessary for oligodendrocyte myelination and appropriate sheath lengths. This view is based upon the observation that axon diameters correlate with myelin sheath length [1, 5, 6], as well as reports that PNS axonal neuregulin-1 type III regulates the initiation and properties of Schwann cell myelin sheaths [7, 8]. However, in the CNS, no such instructive molecules have been shown to be required, and increasing in vitro evidence supports an oligodendrocyte-driven, neuron-independent ability to differentiate and form initial sheaths [9–12]. We test this alternative signal-independent hypothesis—that variation in internode lengths reflects regional oligodendrocyte-intrinsic properties. Using microfibers, we find that oligodendrocytes have a remarkable ability to self-regulate the formation of compact, multilamellar myelin and generate sheaths of physiological length. Our results show that oligodendrocytes respond to fiber diameters and that spinal cord oligodendrocytes generate longer sheaths than cortical oligodendrocytes on fibers, co-cultures, and explants, revealing that oligodendrocytes have regional identity and generate different sheath lengths that mirror internodes in vivo. PMID:26320951

  9. Sensitivity of Martian circulation to obliquity changes

    NASA Astrophysics Data System (ADS)

    Segschneider, J.; Grieger, B.; Lunkeit, F.; Kirk, E.

    2003-04-01

    The obliquity of the Martian rotation axis varies between 15 and 35 degrees with main periods of 125 kyr and 1.3 My. This is thought to have similar impact on the Martian climate as the Milancovic cycles on Earth. The northern layered terrains indicate that climate cycles of yet unknown nature have led to varying accumulation and ablation rates. This study aims at investigating the impact of orbital changes on the Martian atmospheric circulation, while an accompanying study (CR5.05) aims at exploring the internal dynamics of the ice sheet. Here, PUMA, the Portable University Model of the Atmosphere, is used in the Martian set-up to perform sensitivity studies for minimum and maximum obliquity. PUMA is a spectral model with sigma co-ordinates that solves the dynamical equations for vorticity and divergence. Additional modules compute radiative transfers, the soil temperature and heat fluxes between the surface and the atmosphere. So far PUMA has been sucesfully used for modelling of the terrestial climate. As a first step towards a more complete simulation of the evolution of the Martian climate, simulations over one Martian year for minimum and maximum obliquity will be shown.

  10. Vortex-induced vibrations under oblique shedding

    NASA Astrophysics Data System (ADS)

    Bourguet, Remi; Karniadakis, George; Triantafyllou, Michael

    2014-11-01

    A slender flexible body with bluff cross-section placed at normal incidence within a current may be subjected to vortex-induced vibrations (VIV). In practical applications, the structures (e.g. marine risers, towing cables) are often inclined with respect to the direction of the oncoming flow, sometimes at large angles. The vibrations that may appear in such configurations are investigated in the present work on the basis of direct numerical simulation results. We find that a flexible cylinder inclined at 80 degrees exhibits regular large-amplitude vibrations and that the structural responses are excited under the lock-in condition, i.e. synchronization between body oscillation and vortex formation, which is the central mechanism of VIV. We show that the lock-in condition may involve parallel vortex shedding, where the vortex rows are aligned with the body axis, but also oblique vortex shedding patterns. The excited structural wavenumber and the spanwise wavenumber of the obliquely shed vortices coincide; therefore, the flexible structure and the wake are locked both temporally and spatially. In addition, we find that the VIV occurring under oblique shedding may reach very high frequencies compared to the vibrations observed under parallel shedding.

  11. Jet ejecta mass upon oblique impact

    NASA Technical Reports Server (NTRS)

    Yang, W.; Ahrens, T. J.; Miller, G. H.; Petach, M. B.

    1991-01-01

    Theoretical models in the jetting regime for symmetric and asymmetric impact of thin plates predict the mass and velocity of jetted material upon oblique impact. However, experimental constraints on the amount of material which form jets upon oblique impact are not known. A series of preliminary experiments were conducted in which tungsten (W) flyer plates at speeds of 1.5 to 2.0 km/s were obliquely impacted into carbon targets at 30 deg in the regime of jetting, yielding radiation temperatures in the about 3200 K range. Both framing-camera and flash X-ray imaging were conducted. Broad cm-sized craters induced by jet ejecta on 2024 Al witness plates were used to infer jet mass. We infer, from measured witness plate crater volumes, that jet masses in the range of 0.01 to 0.06 g are produced by a 32 mm diameter, 6 mm thick W impactor. This is about one to two orders of magnitude less than those calculated from present theoretical models. In contrast, in refractory material experiments, the mass of gabbro ejecta trapped in styrofoam is 0.52 g, which is similar to that calculated.

  12. DYNAMICAL INSTABILITIES IN HIGH-OBLIQUITY SYSTEMS

    SciTech Connect

    Tamayo, D.; Nicholson, P. D.; Burns, J. A.; Hamilton, D. P.

    2013-03-01

    High-inclination circumplanetary orbits that are gravitationally perturbed by the central star can undergo Kozai oscillations-large-amplitude, coupled variations in the orbital eccentricity and inclination. We first study how this effect is modified by incorporating perturbations from the planetary oblateness. Tremaine et al. found that, for planets with obliquities >68. Degree-Sign 875, orbits in the equilibrium local Laplace plane are unstable to eccentricity perturbations over a finite radial range and execute large-amplitude chaotic oscillations in eccentricity and inclination. In the hope of making that treatment more easily understandable, we analyze the problem using orbital elements, confirming this threshold obliquity. Furthermore, we find that orbits inclined to the Laplace plane will be unstable over a broader radial range, and that such orbits can go unstable for obliquities less than 68. Degree-Sign 875. Finally, we analyze the added effects of radiation pressure, which are important for dust grains and provide a natural mechanism for particle semimajor axes to sweep via Poynting-Robertson drag through any unstable range. For low-eccentricity orbits in the equilibrium Laplace plane, we find that generally the effect persists; however, the unstable radial range is shifted and small retrograde particles can avoid the instability altogether. We argue that this occurs because radiation pressure modifies the equilibrium Laplace plane.

  13. Further investigations of oblique hypervelocity impact phenomena

    NASA Technical Reports Server (NTRS)

    Schonberg, William P.

    1988-01-01

    The results of a continuing investigation of the phenomena associated with the oblique hypervelocity impact of spherical projectiles onto multi-sheet aluminum structures are described. A series of equations that quantitatively describes these phenomena is obtained through a regression of experimental data. These equations characterize observed ricoshet and penetration damage phenomena in a multi-sheet structure as functions of the geometric parameters of the structure and the diameter, obliquity, and velocity of the impacting projectile. Crater damage observed on the ricochet witness plates is used to determine the sizes and speeds of the ricochet debris particles that caused the damage. It is shown that, in general, the most damaging ricochet debris particle is approximately 0.25 cm (0.10 in) in diameter and travels at the speed of approximately 2.1 km/sec (6,890 ft/sec). The equations necessary for the design of shielding panels that will protect external systems from such ricochet debris damage are also developed. The dimensions of these shielding panels are shown to be strongly dependent on their inclination and on their circumferential distribution around the spacecraft. It is concluded that obliquity effects of high-speed impacts must be considered in the design of any structure exposed to the meteoroid and space debris environment.

  14. ''SensArray'' voltage sensor analysis in an inductively coupled plasma

    SciTech Connect

    Titus, M. J.; Hsu, C. C.; Graves, D. B.

    2010-01-15

    A commercially manufactured PlasmaVolt sensor wafer was studied in an inductively coupled plasma reactor in an effort to validate sensor measurements. A pure Ar plasma at various powers (25-420 W), for a range of pressures (10-80 mT), and bias voltages (0-250 V) was utilized. A numerical sheath simulation was simultaneously developed in order to interpret experimental results. It was found that PlasmaVolt sensor measurements are proportional to the rf-current through the sheath. Under conditions such that the sheath impedance is dominantly capacitive, sensor measurements follow a scaling law derived from the inhomogeneous sheath model of Lieberman and Lichtenberg, [Principles of Plasma Discharges and Materials Processing (Wiley, New York, 2005)]. Under these conditions, sensor measurements are proportional to the square root of the plasma density at the plasma-sheath interface, the one-fourth root of the electron temperature, and the one-fourth root of the rf bias voltage. When the sheath impedance becomes increasingly resistive, the sensor measurements deviate from the scaling law and tend to be directly proportional to the plasma density. The measurements and numerical sheath simulation demonstrate the scaling behavior as a function of changing sheath impedance for various plasma conditions.

  15. Effect of Oblique Electromagnetic Ion Cyclotron Waves on Relativistic Electron Scattering: CRRES Based Calculation

    NASA Technical Reports Server (NTRS)

    Gamayunov, K. V.; Khazanov, G. V.

    2007-01-01

    We consider the effect of oblique EMIC waves on relativistic electron scattering in the outer radiation belt using simultaneous observations of plasma and wave parameters from CRRES. The main findings can be s ummarized as follows: 1. In 1comparison with field-aligned waves, int ermediate and highly oblique distributions decrease the range of pitc h-angles subject to diffusion, and reduce the local scattering rate b y an order of magnitude at pitch-angles where the principle absolute value of n = 1 resonances operate. Oblique waves allow the absolute va lue of n > 1 resonances to operate, extending the range of local pitc h-angle diffusion down to the loss cone, and increasing the diffusion at lower pitch angles by orders of magnitude; 2. The local diffusion coefficients derived from CRRES data are qualitatively similar to the local results obtained for prescribed plasma/wave parameters. Conseq uently, it is likely that the bounce-averaged diffusion coefficients, if estimated from concurrent data, will exhibit the dependencies similar to those we found for model calculations; 3. In comparison with f ield-aligned waves, intermediate and highly oblique waves decrease th e bounce-averaged scattering rate near the edge of the equatorial lo ss cone by orders of magnitude if the electron energy does not excee d a threshold (approximately equal to 2 - 5 MeV) depending on specified plasma and/or wave parameters; 4. For greater electron energies_ ob lique waves operating the absolute value of n > 1 resonances are more effective and provide the same bounce_averaged diffusion rate near the loss cone as fiel_aligned waves do.

  16. Model for resonant plasma probe.

    SciTech Connect

    Warne, Larry Kevin; Johnson, William Arthur; Hebner, Gregory Albert; Jorgenson, Roy E.; Coats, Rebecca Sue

    2007-04-01

    This report constructs simple circuit models for a hairpin shaped resonant plasma probe. Effects of the plasma sheath region surrounding the wires making up the probe are determined. Electromagnetic simulations of the probe are compared to the circuit model results. The perturbing effects of the disc cavity in which the probe operates are also found.

  17. Plasma theory and simulation research

    SciTech Connect

    Birdsall, C.K.

    1989-01-01

    Our research group uses both theory and simulation as tools in order to increase the understanding of instabilities, heating, diffusion, transport and other phenomena in plasmas. We also work on the improvement of simulation, both theoretically and practically. Our focus has been more and more on the plasma edge (the sheath''), interactions with boundaries, leading to simulations of whole devices (someday a numerical tokamak).

  18. Self-consistent treatment of the sheath boundary conditions by introducing anisotropic ion temperatures and virtual divertor model

    NASA Astrophysics Data System (ADS)

    Togo, Satoshi; Takizuka, Tomonori; Nakamura, Makoto; Hoshino, Kazuo; Ibano, Kenzo; Lang, Tee Long; Ogawa, Yuichi

    2016-04-01

    One-dimensional SOL-divertor plasma fluid simulation code which considers anisotropy of ion temperature has been developed so as to deal with sheath theory self-consistently. In our fluid modeling, explicit use of boundary condition for Mach number M at divertor plate, e.g., M = 1, becomes unnecessary. In order to deal with the Bohm condition and the sheath heat transmission factors at divertor plate self-consistently, we introduced a virtual divertor (VD) model which sets an artificial region beyond divertor plates and artificial sinks for particle, momentum and energy there to model the effects of the sheath region in front of the divertor plate. Validity of our fluid model with VD model is confirmed by showing that simulation results agree well with those from a kinetic code regarding the Bohm condition, ion temperature anisotropy and supersonic flow. We also show that the strength of artificial sinks in VD region does not affect profiles in plasma region at least in the steady state and that sheath heat transmission factors can be adjusted to theoretical values by VD model. Validity of viscous flux is also investigated.

  19. The local dayside reconnection rate for oblique interplanetary magnetic fields

    NASA Astrophysics Data System (ADS)

    Komar, C. M.; Cassak, P. A.

    2016-06-01

    We present an analysis of local properties of magnetic reconnection at the dayside magnetopause for various interplanetary magnetic field (IMF) orientations in global magnetospheric simulations. This has heretofore not been practical because it is difficult to locate where reconnection occurs for oblique IMF, but new techniques make this possible. The approach is to identify magnetic separators, the curves separating four regions of differing magnetic topology, which map the reconnection X line. The electric field parallel to the X line is the local reconnection rate. We compare results to a simple model of local two-dimensional asymmetric reconnection. To do so, we find the plasma parameters that locally drive reconnection in the magnetosheath and magnetosphere in planes perpendicular to the X line at a large number of points along the X line. The global magnetohydrodynamic simulations are from the three-dimensional Block-Adaptive, Tree Solarwind Roe-type Upwind Scheme (BATS-R-US) code with a uniform resistivity, although the techniques described here are extensible to any global magnetospheric simulation model. We find that the predicted local reconnection rates scale well with the measured values for all simulations, being nearly exact for due southward IMF. However, the absolute predictions differ by an undetermined constant of proportionality, whose magnitude increases as the IMF clock angle changes from southward to northward. We also show similar scaling agreement in a simulation with oblique southward IMF and a dipole tilt. The present results will be an important component of a full understanding of the local and global properties of dayside reconnection.

  20. INCORPORATING FOREIGN SHEATH BLIGHT RESISTANCE GENES INTO US RICE GEMPLASM

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sheath blight disease, caused by the Rhizoctonia solani fungus, has been the most economically significant rice disease throughout Texas, Louisiana, and Arkansas since the early 1970s. While diseases such as blast and straighthead can also devastate yield, sheath blight disease occurs more consiste...

  1. Quality of paper boards from arecanut leaf sheath.

    PubMed

    Raghupathy, R; Viswanathan, R; Devadas, C T

    2002-03-01

    A study was carried on utilizing arecanut leaf sheath for making paper boards. Paper boards were made with various combinations of arecanut leaf sheath with waste paper, 1:1, 1:2, 1:3, 3:1, 2:1, control (100% areca leaf sheath) and the qualities of these paper boards were tested as per the Bureau of Indian Standards (IS: 1060 (part-I)-1966). The paper boards made with more arecanut sheath materials had more resistance to water absorption. The addition of paper increased the substance weight of the paper boards. The 2:1 and 3:1 combinations of arecanut leaf sheath and waste paper had best tear strength, tensile strength, bursting strength and water resistance with minimum substance weight. PMID:11848383

  2. An Everting Ureteral Access Sheath: Concepts and In Vitro Testing

    NASA Astrophysics Data System (ADS)

    Lee, Keith L.; Stoller, Marshall L.

    2007-04-01

    Ureteral access sheaths have been a recent innovation in facilitating ureteral stone surgery. Once properly placed, access sheaths allow the movement of ureteroscopes and other instruments through the ureter with minimal injury to the urothelium. However, there are shortcomings of the current device designs. Initial sheath placement requires significant force, and shear stress can injure the ureter. In addition, inadvertent advancement of the outer sheath without the inner introducer stylet can tear and avulse the ureter. A novel eversion design incorporating a lubricous film provides marked improvement over current access sheaths. In bench top and animal models, the eversion shealths require less force during advancement, cause less injury to the urothelial tissue, and have a lower potential of introducing extraneous materials (e.g., microbes) into a simulated urinary tract. While, the everting design provides important advantages over traditional non-everting designs, further preclinical and clinical trials are required.

  3. Gas insulated transmission line having low inductance intercalated sheath

    DOEpatents

    Cookson, Alan H.

    1978-01-01

    A gas insulated transmission line including an outer sheath, an inner conductor disposed within the outer sheath, and an insulating gas between the inner conductor and the outer sheath. The outer sheath comprises an insulating tube having first and second ends, and having interior and exterior surfaces. A first electrically conducting foil is secured to the interior surface of the insulating tube, is spirally wound from one tube end to the second tube end, and has a plurality of overlapping turns. A second electrically conducting foil is secured to the exterior surface of the insulating tube, and is spirally wound in the opposite direction from the first electrically conducting foil. By winding the foils in opposite directions, the inductances within the intercalated sheath will cancel each other out.

  4. Similarities and distinctions of CIR and Sheath

    NASA Astrophysics Data System (ADS)

    Yermolaev, Yuri; Lodkina, Irina; Nikolaeva, Nadezhda; Yermolaev, Michael

    2016-04-01

    On the basis of OMNI data and our catalog of large scale solar wind (SW) streams during 1976-2000 [Yermolaev et al., 2009] we study the average temporal profiles for two types of compressed regions: CIR (corotating interaction region - compressed region before High Speed Stream (HSS)) and Sheath (compressed region before fast Interplanetary CMEs (ICMEs), including Magnetic Cloud (MC) and Ejecta). As have been shown by Nikolaeva et al, [2015], the efficiency of magnetic storm generation is ~50% higher for Sheath and CIR than for ICME (MC and Ejecta), i.e. reaction magnetosphere depends on type of driver. To take into account the different durations of SW types, we use the double superposed epoch analysis (DSEA) method: rescaling the duration of the interval for all types in such a manner that, respectively, beginning and end for all intervals of selected type coincide [Yermolaev et al., 2010; 2015]. Obtained data allows us to suggest that the formation of all types of compression regions has the same physical mechanism irrespective of piston (HSS or ICME) type and differences are connected with geometry and full jumps of speed in edges of compression regions. If making the natural assumption that the gradient of speed is directed approximately on normal to the piston, CIR has the largest angle between the gradient of speed and the direction of average SW speed, and ICME - the smallest angle. The work was supported by the Russian Foundation for Basic Research, projects 13-02-00158, 16-02-00125 and by Program of Presidium of the Russian Academy of Sciences. References: Nikolaeva, N. S. , Yu. I. Yermolaev, and I. G. Lodkina (2015), Modeling of the Corrected Dst* Index Temporal Profile on the Main Phase of the Magnetic Storms Generated by Different Types of Solar Wind, Cosmic Research, Vol. 53, No. 2, pp. 119-127. Yermolaev, Yu. I., N. S. Nikolaeva, I. G. Lodkina, and M. Yu. Yermolaev (2009), Catalog of Large-Scale Solar Wind Phenomena during 1976-2000, Cosmic Research

  5. Bladder outlet reconstruction: fate of the silicone sheath.

    PubMed

    Kropp, B P; Rink, R C; Adams, M C; Keating, M A; Mitchell, M E

    1993-08-01

    The placement of a 1.5 cm. wide silicone sheath around a newly constructed urethra/bladder neck to ensure maintenance of repair length and to facilitate future placement of a sphincter cuff was reported by our institution in 1985. We present our long-term followup and new recommendations for use of the silicone sheath. A total of 15 silicone sheaths was placed between March 1981 and July 1984. Of the sheaths 14 were placed at the time of urinary reconstruction around the Young-Dees-Leadbetter bladder neck repair and 1 was placed after erosion of an artificial urinary sphincter cuff. Of the 15 sheaths 10 have eroded into the urethra and 4 sheaths remain in situ. Another sheath was replaced 2 years after its original insertion with an artificial urinary sphincter cuff. Mean time to erosion was 48.2 months, with a range of 2 to 108 months. Long-term followup of 10 patients revealed that 4 ultimately required ligation of the bladder neck and construction of continent stoma after erosion, 1 is dry after placement of a bulbar artificial urinary sphincter, 2 remain dry after removal of the eroded sheath alone, 2 required bladder neck revision to achieve continence after erosion and the most recent patient remains diverted with a suprapubic tube. All 4 patients with sheaths still remaining are dry without evidence of erosion (mean duration 116 months). These long-term results using a silicone wrap around a newly constructed bladder neck reveal an unacceptably high rate of erosion. Therefore, we no longer recommend or support the use of the silicone sheath in the manner we have described for bladder neck reconstruction. PMID:8326628

  6. Space plasma contractor research, 1988

    NASA Technical Reports Server (NTRS)

    Williams, John D.; Wilbur, Paul J.

    1989-01-01

    Results of experiments conducted on hollow cathode-based plasma contractors are reported. Specific tests in which attempts were made to vary plasma conditions in the simulated ionospheric plasma are described. Experimental results showing the effects of contractor flowrate and ion collecting surface size on contactor performance and contactor plasma plume geometry are presented. In addition to this work, one-dimensional solutions to spherical and cylindircal space-charge limited double-sheath problems are developed. A technique is proposed that can be used to apply these solutions to the problem of current flow through elongated double-sheaths that separate two cold plasmas. Two conference papers which describe the essential features of the plasma contacting process and present data that should facilitate calibration of comprehensive numerical models of the plasma contacting process are also included.

  7. Penetration and ricochet phenomena in oblique hypervelocity impact

    NASA Technical Reports Server (NTRS)

    Schonberg, William P.; Taylor, Roy A.

    1989-01-01

    An experimental investigation of phenomena associated with the oblique hypervelocity impact of spherical projectile on multisheet aluminum structures is described. A model that can be employed in the design of meteoroid and space debris protection systems for space structures is developed. The model consists of equations that relate crater and perforation damage of a multisheet structure to parameters such as projectile size, impact velocity, and trajectory obliquity. The equations are obtained through a regression analysis of oblique hypervelocity impact test data. This data shows that the response of a multisheet structure to oblique impact is significantly different from its response to normal hypervelocity impact. It was found that obliquely incident projectiles produce ricochet debris that can severely damage panels or instrumentation located on the exterior of a space structure. Obliquity effects of high-speed impact must, therefore, be considered in the design of any structure exposed to the meteoroid and space debris environment.

  8. Radio-frequency sheaths physics: Experimental characterization on Tore Supra and related self-consistent modeling

    NASA Astrophysics Data System (ADS)

    Jacquot, Jonathan; Milanesio, Daniele; Colas, Laurent; Corre, Yann; Goniche, Marc; Gunn, Jamie; Heuraux, Stéphane; Kubič, Martin

    2014-06-01

    During the 2011 experimental campaign, one of the three ion cyclotron resonance heating (ICRH) antennas in the Tore Supra tokamak was equipped with a new type of Faraday screen (FS). The new design aimed at minimizing the integrated parallel electric field over long field lines as well as increasing the heat exhaust capability of the actively cooled screen. It proved to be inefficient for attenuating the radio-frequency (RF)-sheaths on the screen itself on the contrary to the heat exhaust concept that allowed operation despite higher heat fluxes on the antenna. In parallel, a new approach has been proposed to model self-consistently RF sheaths: the SSWICH (Self-consistent Sheaths and Waves for IC Heating) code. Simulations results from SSWICH coupled with the TOPICA antenna code were able to reproduce the difference between the two FS designs and part of the spatial pattern of heat loads and Langmuir probe floating potential. The poloidal pattern is a reliable result that mainly depends on the electrical design of the antenna while the radial pattern is on the contrary highly sensitive to loosely constrained parameters such as perpendicular conductivity that generates a DC current circulation from the private region inside the antenna limiters to the free scrape off layer outside these limiters. Moreover, the cantilevered bars seem to be the element in the screen design that enhanced the plasma potential.

  9. Radio-frequency sheaths physics: Experimental characterization on Tore Supra and related self-consistent modeling

    SciTech Connect

    Jacquot, Jonathan; Colas, Laurent Corre, Yann; Goniche, Marc; Gunn, Jamie; Kubič, Martin; Milanesio, Daniele; Heuraux, Stéphane

    2014-06-15

    During the 2011 experimental campaign, one of the three ion cyclotron resonance heating (ICRH) antennas in the Tore Supra tokamak was equipped with a new type of Faraday screen (FS). The new design aimed at minimizing the integrated parallel electric field over long field lines as well as increasing the heat exhaust capability of the actively cooled screen. It proved to be inefficient for attenuating the radio-frequency (RF)-sheaths on the screen itself on the contrary to the heat exhaust concept that allowed operation despite higher heat fluxes on the antenna. In parallel, a new approach has been proposed to model self-consistently RF sheaths: the SSWICH (Self-consistent Sheaths and Waves for IC Heating) code. Simulations results from SSWICH coupled with the TOPICA antenna code were able to reproduce the difference between the two FS designs and part of the spatial pattern of heat loads and Langmuir probe floating potential. The poloidal pattern is a reliable result that mainly depends on the electrical design of the antenna while the radial pattern is on the contrary highly sensitive to loosely constrained parameters such as perpendicular conductivity that generates a DC current circulation from the private region inside the antenna limiters to the free scrape off layer outside these limiters. Moreover, the cantilevered bars seem to be the element in the screen design that enhanced the plasma potential.

  10. Linear electromagnetic excitation of an asymmetric low pressure capacitive discharge with unequal sheath widths

    NASA Astrophysics Data System (ADS)

    Lieberman, M. A.; Lichtenberg, A. J.; Kawamura, E.; Chabert, P.

    2016-01-01

    It is well-known that standing waves having radially center-high radio frequency (rf) voltage profiles exist in high frequency capacitive discharges. In this work, we determine the symmetric and antisymmetric radially propagating waves in a cylindrical capacitive discharge that is asymmetrically driven at the lower electrode by an rf voltage source. The discharge is modeled as a uniform bulk plasma which at lower frequencies has a thicker sheath at the smaller area powered electrode and a thinner sheath at the larger area grounded electrode. These are self-consistently determined at a specified density using the Child law to calculate sheath widths and the electron power balance to calculate the rf voltage. The fields and the system resonant frequencies are determined. The center-to-edge voltage ratio on the powered electrode is calculated versus frequency, and central highs are found near the resonances. The results are compared with simulations in a similar geometry using a two-dimensional hybrid fluid-analytical code, giving mainly a reasonable agreement. The analytic model may be useful for finding good operating frequencies for a given discharge geometry and power.

  11. Identification of a Gene Essential for Sheathed Structure Formation in Sphaerotilus natans, a Filamentous Sheathed Bacterium

    PubMed Central

    Suzuki, Toshihiko; Kanagawa, Takahiro; Kamagata, Yoichi

    2002-01-01

    Sphaerotilus natans, a filamentous bacterium that causes bulking in activated sludge processes, can assume two distinct morphologies, depending on the substrate concentration for growth; in substrate-rich media it grows as single rod-shaped cells, whereas in substrate-limited media it grows as filaments. To identify genes responsible for sheath formation, we carried out transposon Tn5 mutagenesis. Of the approximately 20,000 mutants obtained, 7 did not form sheathed structures. Sequencing of the Tn5-flanking regions showed that five of the seven Tn5 insertions converged at the same open reading frame, designated sthA. The deduced amino acids encoded by sthA were found to be homologous to glycosyltransferase, which is known to be involved in linking sugars to lipid carriers during bacterial exopolysaccharide biosynthesis. Disruption of the gene of the wild-type strain by inserting a kanamycin resistance gene cassette also resulted in sheathless growth under either type of nutrient condition. These findings indicate that sthA is a crucial component responsible for sheath formation. PMID:11772646

  12. Modeling RF-induced Plasma-Surface Interactions with VSim

    NASA Astrophysics Data System (ADS)

    Jenkins, Thomas G.; Smithe, David N.; Pankin, Alexei Y.; Roark, Christine M.; Stoltz, Peter H.; Zhou, Sean C.-D.; Kruger, Scott E.

    2014-10-01

    An overview of ongoing enhancements to the Plasma Discharge (PD) module of Tech-X's VSim software tool is presented. A sub-grid kinetic sheath model, developed for the accurate computation of sheath potentials near metal and dielectric-coated walls, enables the physical effects of DC and RF sheath dynamics to be included in macroscopic-scale plasma simulations that need not explicitly resolve sheath scale lengths. Sheath potential evolution, together with particle behavior near the sheath (e.g. sputtering), can thus be simulated in complex, experimentally relevant geometries. Simulations of RF sheath-enhanced impurity production near surfaces of the C-Mod field-aligned ICRF antenna are presented to illustrate the model; impurity mitigation techniques are also explored. Model extensions to capture the physics of secondary electron emission and of multispecies plasmas are summarized, together with a discussion of improved tools for plasma chemistry and IEDF/EEDF visualization and modeling. The latter tools are also highly relevant for commercial plasma processing applications. Ultimately, we aim to establish VSimPD as a robust, efficient computational tool for modeling fusion and industrial plasma processes. Supported by U.S. DoE SBIR Phase I/II Award DE-SC0009501.

  13. Oblique view of southeast corner; camera facing northwest. Mare ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Oblique view of southeast corner; camera facing northwest. - Mare Island Naval Shipyard, Defense Electronics Equipment Operating Center, I Street, terminus west of Cedar Avenue, Vallejo, Solano County, CA

  14. Oblique Raman and polariton scattering in lithium iodate

    SciTech Connect

    Falk, J.; Moshrefzadeh, R.

    1985-02-01

    The authors have predicted and measured tuning of the LO and TO oblique Raman and the oblique polariton frequencies in the 769-848 cm/sup -1/ spectral region in lithium iodate. Oblique scattering in LilO/sub 3/ is produced by coupling of A and E symmetry crystal modes. The resulting LO and TO frequencies lie between the frequencies of the contributing modes. The intensity of the scattered light observed indicates that construction of CW or quasi-CW stimulated oblique Raman and polariton oscillators are possible.

  15. OBLIQUE VIEW, REAR ELEVATION, LOOKING NORTHEAST Mountain Home Air ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    OBLIQUE VIEW, REAR ELEVATION, LOOKING NORTHEAST - Mountain Home Air Force Base 1958 Senior Officers' Housing, General's Residence, Rabeni Street (originally Ivy Street), Mountain Home, Elmore County, ID

  16. Oblique Photogrammetry and Usage on Land Administration

    NASA Astrophysics Data System (ADS)

    Kisa, A.; Ozmus, L.; Erkek, B.; Ates, H. B.; Bakici, S.

    2013-08-01

    Projects based on Geographic Information Systems (GIS) have started within the body of the General Directorate of Land Registry and Cadastre (GDLRC) by the Land Registry and Cadastre Information System (LRCIS) in the beginning of 2000s. LRCIS was followed by other projects which are Turkish National Geographic Information System (TNGIS), Continuously Operating GPS Reference Stations (CORS-TR), Geo Metadata Portal (GMP), Orthophoto Web Services, Completion of Initial Cadastre, Cadastre Renovation Project (CRP), 2B and Land Registry Achieve Information System (LRAIS). When examining the projects generated by GDLRC, it is realized that they include basic functions of land administration required for sustainable development. Sustainable development is obtained through effective land administration as is known. Nowadays, land use becomes more intense as a result of rapid population increase. The importance of land ownership has increased accordingly. At this point, the necessity of cadastre appears. In Turkey, cadastral registration is carried out by the detection of parcels. In other words, it is obtained through the division of land surface into 2D boundaries and mapping of them. However, existing land administration systems have begun to lose their efficiency while coping with rights, restrictions and responsibilities (RRRs) belonging to land which become more complicated day by day. Overlapping and interlocking constructions appear particularly in urban areas with dense housing and consequently, the problem of how to project these structures onto the surface in 2D cadastral systems has arisen. Herein, the necessity of 3D cadastre concept and 3D property data is confronted. In recent years, oblique photogrammetry, whose applications are gradually spreading, is used as an effective method for producing 3D data. In this study, applications of oblique photogrammetry and usability of oblique images as base for 3D Cadastre and Land Administration projects are examined.

  17. Spin Precession in Oblique Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Li, Jing; Huang, Biqin; Appelbaum, Ian

    2009-03-01

    Spin precession and dephasing (``Hanle effect'') provide an unambiguous means to establish the presence of spin transport in semiconductors. We compare theoretical modeling with experimental data from drift-dominated silicon spin-transport devices, illustrating the non-trivial consequences of employing oblique magnetic fields (due to misalignment or intentional, fixed in-plane field components) to measure the effects of spin precession. Model results are also calculated for Hanle measurements under conditions of diffusion-dominated transport, revealing an expected Hanle peak-widening effect induced by the presence of fixed in-plane magnetic bias fields.

  18. Resistivity in the dynamic current sheath of a field reversed configuration

    NASA Astrophysics Data System (ADS)

    Kayama, M. E.

    2012-03-01

    The resistivity of a field reversed configuration in a theta-pinch with slow rising current was investigated during the turbulent phase from the moment of field reversal until end of plasma radial implosion. This transport coefficient was obtained in a hydrogen plasma by local measurements with magnetic probe and compared to numerical calculations with Chodura resistivity and evolution of lower hybrid drift instability. The values of resistivity are higher than those predicted by classical binary collision. During early phase of confinement, the doubly layer structure of current sheath in the low electric field machine was theoretically well reproduced with anomalous collision frequency calculated with Chodura resistivity that provides appropriate conditions for onset of lower hybrid drift instability and the regular evolution of pinch. The plasma dynamic, radial profiles of magnetic field during the radial compression and resistivity values were equally close to those observed by the measurements.

  19. Experimental Study of RF Sheath Formation on a Fast Wave Antenna and Limiter in the LAPD

    NASA Astrophysics Data System (ADS)

    Martin, Michael; Gekelman, Walter; Pribyl, Patrick; van Compernolle, Bart; Carter, Troy

    2015-11-01

    Ion cyclotron resonance heating (ICRH) will be an essential component of heating power in ITER. During ICRH, radio frequency (RF) sheaths may form both at the exciting antenna and further away, e.g. in the divertor region, and may cause wall material sputtering and decreased RF power coupling to the plasma. It is important to do detailed laboratory experiments that fully diagnose the sheaths and wave fields. This is not possible in fusion devices. A new RF system has recently been constructed for performing such studies in the LAPD plasma column (ne ~1012 -1013cm-3 , Te ~ 1 - 10 eV ,B0 ~ 400 - 2000 G , diameter ~ 60cm , length ~ 18 m) . The RF system is capable of pulsing at the 1 Hz rep. rate of the LAPD plasma and operating between 2-6 MHz (1st - 9th harmonic of fci in H) with a power output of 200 kW. First results of this system driving a single-strap fast wave antenna will be presented. Emissive and Langmuir probe measurements in the vicinity of both the antenna and a remote limiter and wave coupling measured by magnetic pickup loops will be presented.

  20. Oscillating plasma bubbles. I. Basic properties and instabilities

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.

    2012-08-15

    Plasma bubbles are created in an ambient discharge plasma. A bubble is a plasma volume of typically spherical shape, which is separated from the ambient plasma by a negatively biased grid of high transparency. Ions and electrons from the ambient plasma flow into the bubble volume. In steady state the flow of particles and currents is divergence-free, which is established by the plasma potential inside the bubble. The grid has two sheaths, one facing the ambient plasma, the other the bubble plasma. The inner sheath is observed to become unstable, causing the plasma potential in the bubble to oscillate. The instability arises from an excess of ions and a deficiency of electrons. Its frequency is in the range of the ion plasma frequency but depends on all parameters which influence the charge density in the sheath. When the grid voltage is very negative, electrons cannot enter the outer sheath, and the inner sheath becomes a virtual anode which reflects ions such that the bubble interior is empty. When an electron source is placed into the bubble it can neutralize the ions and the bubble refills. Without plasma sources or sinks the bubble plasma is extremely sensitive to perturbations by probes. Modified current-voltage characteristics of Langmuir and emissive probes are demonstrated. A sequence of papers first describes the basic steady-state properties, then the time evolution of bubbles, the effects of electron sources in bubbles, and the role of the grid and bubble geometry. The physics of plasma bubbles is important to several fields of basic plasma physics such as sheaths, sheath instabilities, diagnostic probes, electrostatic confinement, and current and space charge neutralization of beams.