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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. Surface rippling by oblique ion incidence during plasma etching of silicon: Experimental demonstration using sheath control plates

    NASA Astrophysics Data System (ADS)

    Nakazaki, Nobuya; Matsumoto, Haruka; Eriguchi, Koji; Ono, Kouichi

    2015-09-01

    In the microfabrication of 3D transistors (e.g. Fin-FET), the sidewall roughness, such as LER and LWR caused by off-normal or oblique ion incidence during plasma etching, is a critical issue to be resolved, which in turn requires a better understanding of the effects of ion incidence angle θi on surface roughening. This paper presents surface roughening and rippling by oblique ion incidence during inductively coupled plasma etching of Si in Cl2, using the experimental setup as in our previous study. The oblique ion incidence was achieved by sheath control plates, which were placed on and electrically connected to the wafer stage. The plates had slits to vary the sheath structure thereon and to extract ions from plasma to samples on the bottom and/or side of the slits. The results indicated that at θi ~ 40° or oblique incidence; ripple structures were formed on surfaces perpendicularly to the direction of ion incidence, on the other hand, at θi ~ 80° or grazing incidence, small ripples or slit like grooves were formed on surfaces parallel to the direction of ion incidence, as predicted in our previous numerical investigations.

  4. 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.

  5. Radio frequency sheaths in an oblique magnetic field

    DOE PAGES

    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

  6. 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.

  7. 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.

  8. Dust particle dynamics in magnetized plasma sheath

    SciTech Connect

    Davoudabadi, M.; Mashayek, F.

    2005-07-15

    In this paper, the structure of a plasma sheath in the presence of an oblique magnetic field is investigated, and dynamics of a dust particle embedded in the sheath is elaborated. To simulate the sheath, a weakly collisional two-fluid model is implemented. For various magnitudes and directions of the magnetic field and chamber pressures, different plasma parameters including the electron and ion densities, ion flow velocity, and electric potential are calculated. A complete set of forces acting on the dust particle originating from the electric field in the sheath, the static magnetic field, gravity, and ion and neutral drags is taken into account. Through the trapping potential energy, the particle stable and unstable equilibria are studied while the particle is stationary inside the sheath. Other features such as the possibility of the dust levitation and trapping in the sheath, and the effect of the Lorentz force on the charged dust particle motion are also examined. An interesting feature is captured for the variation of the particle charge as a function of the magnetic field magnitude.

  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. Generalized sheath criterion for arbitrary degenerate plasmas

    NASA Astrophysics Data System (ADS)

    Akbari-Moghanjoughi, M.

    2017-01-01

    In this research, we study the generalized sheath criterion for plasmas with an arbitrary degree of electron degeneracy and temperature, ranging from the classical dilute regime to the fully degenerate quantum plasmas. The latter may be relevant to warm dense matter and/or laboratory high energy density matter or even astrophysical stellar plasmas. The hydrostatic one dimensional model is used to establish the generalized Bohm's criterion for sheath entrance ion speed limits, and the small amplitude theory of the sheath problem, which accurately describes the sheath parameters for lower ion acoustic Mach numbers, is developed. Our results indicate that the sheath characteristic parameters such as electrostatic potential and density profiles, as well as the wall potential and the sheath length, are significantly affected by plasma parameters such as the ion and electron temperature and number densities in the plasma region. In particular, there are fundamental differences between sheath structures of the dilute classical plasmas and those of dense quantum ones.

  12. Structure of the magnetized sheath of a dusty plasma

    SciTech Connect

    Mehdipour, H.; Denysenko, I.; Ostrikov, K.

    2010-12-15

    A three-component fluid model for a dusty plasma-sheath in an oblique magnetic field is presented. The study is carried out for the conditions when the thermophoretic force associated with the electron temperature gradient is one of the most important forces affecting dust grains in the sheath. It is shown that the sheath properties (the sheath size, the electron, ion and dust particle densities and velocities, the electric field potential, and the forces affecting the dust particles) are functions of the neutral gas pressure and ion temperature, the dust size, the dust material density, and the electron temperature gradient. Effects of plasma-dust collisions on the sheath structure are studied. It is shown that an increase in the forces pushing dust particles to the wall is accompanied by a decrease in the sheath width. The results of this work are particularly relevant to low-temperature plasma-enabled technologies, where effective control of nano- and microsized particles near solid or liquid surfaces is required.

  13. 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.

  14. Sheath formation criterion in magnetized electronegative plasmas with thermal ions

    SciTech Connect

    Hatami, M. M.; Shokri, B.

    2013-03-15

    Taking into account the effect of collisions and positive ion temperatures, the sheath formation criterion is investigated in a weakly magnetized electronegative plasma consisting of electrons, negative and positive ions by using the hydrodynamics equations. It is assumed that the electron and negative ion density distributions are the Boltzmann distribution with two different temperatures. Also, it is assumed that the velocity of positive ions at the sheath edge is not normal to the wall (oblique entrance). Our results show that a sheath region will be formed when the initial velocity of positive ions or the ion Mach number M lies in a specific interval with particular upper and lower limits. Also, it is shown that the presence of the magnetic field affects both of these limits. Moreover, as an practical application, the density distribution of charged particles in the sheath region is studied for an allowable value of M, and it is seen that monotonically reduction of the positive ion density distribution leading to the sheath formation occurs only when M lies between two above mentioned limits.

  15. Sheath Physics and Boundary Conditions for Edge Plasmas

    SciTech Connect

    Cohen, R H; Ryutov, D D

    2003-09-03

    The boundary conditions of mass, momentum, energy, and charge appropriate for fluid formulations of edge plasmas are surveyed. We re-visit the classic problem of 1-dimensional flow, and note that the ''Bohm sheath criterion'' is requirement of connectivity of the interior plasma with the external world, not the result of termination of the plasma by a wall. We show that the nature of the interior plasma solution is intrinsically different for ion sources that inject above and below the electron sound speed. We survey the appropriate conditions to apply, and resultant fluxes, for a magnetic field obliquely incident on a wall, including the presence of drifts and radial transport. We discuss the consequences of toroidal asymmetries in wall properties, as well as experimental tests of such effects. Finally, we discuss boundary-condition modifications in the case of rapidly varying plasma conditions.

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

    NASA Astrophysics Data System (ADS)

    Shneider, Mikhail N.; Kaganovich, Igor D.

    2002-11-01

    Most plasmas have very thin sheath compared with plasma dimension. This necessitates separate calculation of plasma and sheath. Bohm criterion provides 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 Bohm criterion. The value of the boundary electric field and robust procedure to approximately patch plasma and collisionless sheath with a very good accuracy is reported. Additional information on the subject will be posted in http://www.pppl.gov/pub/report/2002/ http://arxiv.org/abs/physics/ Work supported by the Princeton Plasma Physics Laboratory through a University Research Support Program.

  17. 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.

  18. 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.

  19. How to Patch Active Plasma and Collisionless Sheath: Pragmatical Guide

    NASA Astrophysics Data System (ADS)

    Kaganovich, Igor D.

    2002-10-01

    Most plasmas have very thin sheath compared with plasma dimension. This necessitates separate calculation of plasma and sheath. Bohm criterion provides 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 Bohm criterion. The value of the boundary electric field and robust procedure to approximately patch plasma and collisionless sheath with a very good accuracy is reported. Additional information on the subject is posted on the web http://www.pppl.gov/pub/report/2002/ http://arxiv.org/abs/physics/0208041. Work supported by the Department of Energy via the University Research Support Program of Princeton Plasma Physics Laboratory.

  20. Electron Sheaths and Non-ambipolar Diffusion in Laboratory Plasma

    NASA Astrophysics Data System (ADS)

    Baalrud, Scott; Hershkowitz, Noah

    2006-10-01

    Electron sheaths were first predicted by Langmuir in 1929 when he stated that, ``with a large area, A, an anode sheath is a positive ion sheath, but that as A decreases, a point is reached where the positive ion sheath disappears and it is replaced by an electron sheath.''. We show that electron sheath formation near a positive anode depends on the anode area, Aa, as well as the area available for ion loss, Ai. When Aa/Ai< (me/mi)^1/2, the electron sheath potential monotonically decreases from the anode to the bulk plasma. When the anode is larger than this, a potential dip forms in the electron sheath to reduce the electron current lost to the anode. This potential dip is necessary to preserve global current balance and when it is present, total non-ambipolar diffusion can occur where all electrons are lost from the plasma through an electron sheath and all positive ions are lost elsewhere. Additional measurements were carried out to identify the transition from positive (ion) to negative (electron) sheaths. Data were taken in low-pressure argon plasma generated by hot filaments and confined in a multidipole chamber. I. Langmuir, Physical Review. 33, 954 (1929).

  1. Simulation study of the magnetized sheath of a dusty plasma

    SciTech Connect

    Foroutan, G.; Mehdipour, H.; Zahed, H.

    2009-10-15

    Numerical solutions of stationary multifluid equations are used to study the formation and properties of the magnetized sheath near the boundary of a dusty plasma. The impacts of the strength of the magnetic field, the dust and plasma number densities, and the electron temperature on the sheath structure and spatial distributions of various quantities are investigated. It is shown that for a given angle of incidence of the magnetic field, there is a threshold magnetic field intensity above which some kind of large regular inhomogeneities develop on the spatial profile of the dust particles. The sheath thickness, the electron and ion number densities, and the absolute dust charge are strongly affected by the variation in the dust number density. The sheath demonstrates a nonlinear dependence on the electron temperature; as the electron temperature rises, the sheath first is broadened and the absolute wall potential decreases but then at higher temperatures the sheath becomes narrower and the absolute wall potential increases.

  2. Abdominal wall injuries: rectus abdominis strains, oblique strains, rectus sheath hematoma.

    PubMed

    Johnson, Rob

    2006-04-01

    Abdominal wall injuries are reported to be less common than actually perceived by sports medicine practitioners. National Collegiate Athletic Association injury statistics for 2004-2005 cite a high of 0.71 abdominal muscle injuries per 1000 player-hours in wrestling competition to a low of 0.01 injuries per 1000 player-hours in autumn football practices. British professional soccer clubs reported an incidence of "torso" injuries of up to 7% of all injuries over the course of several seasons. Injury definition is most likely the explanation for this discrepancy. The abdominal wall muscles (rectus abdominis, external and internal obliques, and transverse abdominis) are injured by direct blows to the abdomen or by sudden or repetitive trunk movement, either rotation or flexion/extension. With the exception of the rare rectus sheath hematoma that does not self-tamponade, the treatment for these problems is nonoperative with symptoms guiding rehabilitation and return to play decisions.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Laser Diagnostic Method for Plasma Sheath Potential Mapping

    NASA Astrophysics Data System (ADS)

    Walsh, Sean P.

    Electric propulsion systems are gaining popularity in the aerospace field as a viable option for long term positioning and thrusting applications. In particular, Hall thrusters have shown promise as the primary propulsion engine for space probes during interplanetary journeys. However, the interaction between propellant xenon ions and the ceramic channel wall continues to remain a complex issue. The most significant source of power loss in Hall thrusters is due to electron and ion currents through the sheath to the channel wall. A sheath is a region of high electric field that separates a plasma from a wall or surface in contact. Plasma electrons with enough energy to penetrate the sheath may result emission of a secondary electron from the wall. With significant secondary electron emission (SEE), the sheath voltage is reduced and so too is the electron retarding electric field. Therefore, a lower sheath voltage further increases the particle loss to the wall of a Hall thruster and leads to plasma cooling and lower efficiency. To further understand sheath dynamics, laser-induced fluorescence is employed to provide a non-invasive, in situ, and spatially resolved technique for measuring xenon ion velocity. By scanning the laser wavelength over an electronic transition of singly ionized xenon and collecting the resulting fluorescence, one can determine the ion velocity from the Doppler shifted absorption. Knowing the velocity at multiple points in the sheath, it can be converted to a relative electric potential profile which can reveal a lot about the plasma-wall interaction and the severity of SEE. The challenge of adequately measuring sheath potential profiles is optimizing the experiment to maximize the signal-to-noise ratio. A strong signal with low noise, enables high resolution measurements and increases the depth of measurement in the sheath, where the signal strength is lowest. Many improvements were made to reduce the background luminosity, increase the

  9. 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.

  10. 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.

  11. Plasma-sheath effects on the Debye screening problem

    SciTech Connect

    Sarmah, D.; Tessarotto, M.; Salimullah, M.

    2006-03-15

    The classical Debye-Hueckel screening effect of the electrostatic field generated by isolated charged particles immersed in a plasma is reviewed. The validity of the underlying mathematical model, and particularly of the weak-field approximation, is analyzed. It is shown that the presence of the plasma sheath around test particles and the resulting effect of charge screening are essential for the description of plasmas that are strongly coupled.

  12. Role of the ion plasma frequency in RF sheaths

    NASA Astrophysics Data System (ADS)

    Waelbroeck, F. L.; Hazeltine, R. D.; Xiang, N.

    1999-11-01

    Semiconductor etching relies on rf biasing of the substrate to produce a suitable distribution of energetic ions. The properties of the resulting oscillating sheath depend on two parameters: the ratio of the bias amplitude to the electron temperature, and the ratio of the ion plasma frequency to the rf frequency. In industrial applications, V_rf>> T_e, and nonlinear effects are important. For such large bias the dynamics of the oscillating sheath can be divided into three regimes according to the ratio of the rf frequency to the plasma frequency at the entrance of the sheath and that at the surface of the substrate. Liebermann has given an analytic solution in the high frequency regime. With the increase in plasma density, however, the ion plasma frequency often exceeds the standard rf frequency of 13.56 KHz. We present an analytic solution for the sheath dynamics in the opposite, low-frequency regime. We compare the two regimes, giving particular attention to the distribution of ion energy at the substrate.

  13. Sheath overlap during very large scale plasma source ion implantation

    NASA Astrophysics Data System (ADS)

    Cluggish, B. P.; Munson, C. P.

    1998-12-01

    Measurements of plasma source ion implantation have been performed on a large target of complex geometry. The target consists of 1000 aluminum, automotive piston surrogates mounted on four racks; total surface area is over 16 m2. The four racks are positioned parallel to each other, 0.25 m apart, in an 8 m3 vacuum chamber. The racks of pistons are immersed in a capacitive radio frequency plasma, with an argon gas pressure of 20-65 mPa. Langmuir probe measurements indicate that the plasma density profile is highly nonuniform, due to particle losses to the racks of pistons. The plasma ions are implanted into the pistons by pulse biasing the workpiece to negative voltages as low as -18 kV for up to 20 μs. During the voltage pulse, the high-voltage sheaths from adjacent racks of pistons converge towards each other. At plasma densities less than 109 cm-3 the sheaths are observed to overlap. Measurements of the sheath overlap time are compared with standard analytic theory and with simulations run with a two-dimensional particle-in-cell code.

  14. Investigation of plasma-sheath resonances in low pressure discharges

    NASA Astrophysics Data System (ADS)

    Naggary, Schabnam; Kemaneci, Efe; Brinkmann, Ralf Peter; Megahed, Mustafa

    2016-09-01

    Plasma sheath resonances (PSR) arise from a periodic exchange between the kinetic electron energy in the plasma bulk and the electric field energy in the sheath and can easily be excited by the sheath-generated harmonics of the applied RF. In this contribution, we employ a series of models to obtain a well-defined description of these phenomena. In the first part, we use a global model to study the influence of the nonlinear charge-voltage characteristics on the electron dynamics. However, the global model is restricted to the assumption of spatially constant potential at each driven and grounded electrode and thus delivers only the fundamental mode of the current. In order to remedy the deficiency, we introduce a spatially resolved model for arbitrary reactor geometries with no assumptions on the homogeneity of the plasma. An exact evaluation of the analytical solution is realized on the assumption of a cylinderical plasma reactor geometry with uniform conductance. Furthermore, the spatially resolved model is capable of being utilized for a more realistic CCP reactor geometry and non homogeneous plasma provided the conductance distribution is known. For this purpose, we use the CFD-ACE+ tool. The results show that the proposed multi-mode model provides a significant improvement. The authors gratefully acknowledge the financial support by the ESI Group and the SFB- TR 87.

  15. 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.

  16. Structure of the bipolar plasma sheath generated by SPEAR I

    SciTech Connect

    Katz, I.; Jongeward, G.A.; Davis, V.A.; Mandell, M.J.; Kuharski, R.A.; Lilley, J.R. Jr. ); Raitt, W.J. ); Cooke, D.L. ); Torbert, R.B.; Larson, G.; Rau, D. )

    1989-02-01

    The Space Power Experiment Aboard Rockets I (SPEAR I) biased two 10-cm radius spheres as high as 46,000 V positive with respect to an aluminum rocket body. The experiment measured the steady state current to the spheres and the floating potential of the rocket body. Three-dimensional calculations performed using NASCAP/LEO and POLAR 2.0 show that both ion-collecting and electron-collecting sheaths were formed. The rocket body potential with respect to the ionospheric plasma adjusted to achieve a balance between the electron current collected by the spheres and the secondary electron-enhanced ion current to the rocket body. This current balance was obtained with a large ion-collecting sheath that enveloped most of the electron-collecting sheath and reduced the area for collection of ionospheric electrons. The calculated current is in agreement with the flight measurement of a steady state current of less than 1/10 A. The calculations show that the rocket body was driven thousands of volts negative with respect to the ionospheric plasma. The calculated rocket potential is within the uncertainty of that inferred from ion spectrometer data. The current flowed through the space plasma. There was almost no direct charge transport between the spheres and the rocket body.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. A time-dependent model of pulse-driven radio frequency capacitively coupled collisional plasma sheath

    NASA Astrophysics Data System (ADS)

    Rahman, M. T.; Hossain, M. Mofazzal

    2017-01-01

    The time-dependent model of ion motion is used to propose an analytical model for dual frequency (DF) capacitively coupled plasma (CCP) sheath driven by a pulsed source and a radio-frequency source. In this model, the sheath is considered to be collisional. In this model, the time dependent terms of ion fluid equations are ignored, but the electric field, ion motion and ion density remain time dependent. Electron profile is assumed to be step-like. Analytical expressions for electron sheath width and sheath potential have been developed. The calculated sheath width and potential are compared with the dual radio frequency driven time dependent models of capacitively coupled plasma sheath. From the temporal evaluation of sheath motion and potential, it has been found that pulse driven sheath has higher sheath potential and sheath width than that of conventional radio frequency driven DF CCP. Moreover, it is also found that ion energy spread can be reduced using pulsed power. From the temporal investigation of sheath motion and potential, it has been found that the duty cycle of the pulse power significantly affects sheath width and sheath potential.

  3. Oblique ion acoustic shock waves in a magnetized plasma

    SciTech Connect

    Shahmansouri, M.; Mamun, A. A.

    2013-08-15

    Ion acoustic (IA) shock waves are studied in a magnetized plasma consisting of a cold viscous ion fluid and Maxwellian electrons. The Korteweg–de Vries–Burgers equation is derived by using the reductive perturbation method. It is shown that the combined effects of external magnetic field and obliqueness significantly modify the basic properties (viz., amplitude, width, speed, etc.) of the IA shock waves. It is observed that the ion-viscosity is a source of dissipation, and is responsible for the formation of IA shock structures. The implications of our results in some space and laboratory plasma situations are discussed.

  4. 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.

  5. 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.

  6. 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.

  7. Sputtering, Plasma Chemistry, and RF Sheath Effects in Low-Temperature and Fusion Plasma Modeling

    NASA Astrophysics Data System (ADS)

    Jenkins, Thomas G.; Kruger, Scott E.; McGugan, James M.; Pankin, Alexei Y.; Roark, Christine M.; Smithe, David N.; Stoltz, Peter H.

    2016-09-01

    A new sheath boundary condition has been implemented in VSim, a plasma modeling code which makes use of both PIC/MCC and fluid FDTD representations. It enables physics effects associated with DC and RF sheath formation - local sheath potential evolution, heat/particle fluxes, and sputtering effects on complex plasma-facing components - to be included in macroscopic-scale plasma simulations that need not resolve sheath scale lengths. We model these effects in typical ICRF antenna operation scenarios on the Alcator C-Mod fusion device, and present comparisons of our simulation results with experimental data together with detailed 3D animations of antenna operation. Complex low-temperature plasma chemistry modeling in VSim is facilitated by MUNCHKIN, a standalone python/C++/SQL code that identifies possible reaction paths for a given set of input species, solves 1D rate equations for the ensuing system's chemical evolution, and generates VSim input blocks with appropriate cross-sections/reaction rates. These features, as well as principal path analysis (to reduce the number of simulated chemical reactions while retaining accuracy) and reaction rate calculations from user-specified distribution functions, will also be demonstrated. Supported by the U.S. Department of Energy's SBIR program, Award DE-SC0009501.

  8. The 10 sheath-accelerated electrons and ions. [atmospheric models of plasma sheaths and ionospheric electron density

    NASA Technical Reports Server (NTRS)

    Shawhan, S. D.

    1975-01-01

    A model is presented that suggests that plasma sheaths form between the ionospheric plasma moving with Io and the ambient plasma corotating with Jupiter. Potentials across these sheaths could be as high as 580 kV which is the motional emf across Io's ionosphere. Electrons and ions can be accelerated across these sheaths. The sheaths may exist at the top of the Io ionosphere with characteristic thicknesses of 1/4 kilometers. The model is consistent with the Pioneer observations of 0.15 MeV electrons at the inner edge of Io's L-shell and the enhanced number density of low-energy protons at the outer edge. Ion sputtering of the Io surface is discussed and may explain the presence of atomic hydrogen and sodium in the vicinity of Io. Also these accelerated particles may be important to the formation of the Io ionosphere. High electron flux which may lead to decametric radio emissions, Jovian atmospheric heating and optical and X-ray emissions is also discussed.

  9. Up- and downstream sheaths in an ion-beam-plasma system

    SciTech Connect

    Wei, Zi-an; Ma, J. X.

    2016-02-15

    Ion sheaths formed in the up- and downstream sides of a negatively biased metal plate/mesh in an ion-beam-background-plasma system were experimentally investigated in a double plasma device. Measured potential profiles near the plate exhibit asymmetric structure, showing thicker sheath in the downstream side. The presence of the ion beam causes the shrink of the sheaths on both sides. The sheath thickness decreases with the increase of beam energy and density. Furthermore, the sheaths near the mesh are substantially thinner than that near the plate because of the partial transmission of the mesh to the ions. In addition, the increase of neutral gas pressure leads to the reduction of the beam energy and density, resulting in the increase of the sheath thickness.

  10. 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

  11. 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

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. Discontinuous model with semi analytical sheath interface for radio frequency plasma

    NASA Astrophysics Data System (ADS)

    Miyashita, Masaru

    2016-09-01

    Sumitomo Heavy Industries, Ltd. provide many products utilizing plasma. In this study, we focus on the Radio Frequency (RF) plasma source by interior antenna. The plasma source is expected to be high density and low metal contamination. However, the sputtering the antenna cover by high energy ion from sheath voltage still have been problematic. We have developed the new model which can calculate sheath voltage wave form in the RF plasma source for realistic calculation time. This model is discontinuous that electronic fluid equation in plasma connect to usual passion equation in antenna cover and chamber with semi analytical sheath interface. We estimate the sputtering distribution based on calculated sheath voltage waveform by this model, sputtering yield and ion energy distribution function (IEDF) model. The estimated sputtering distribution reproduce the tendency of experimental results.

  17. A Self-Consistent Plasma-Sheath Model for the Inductively Coupled Plasma Reactor

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    Accurate determination of ion flux on a wafer requires a self-consistent, multidimensional modeling of plasma reactor that adequately resolves the sheath region adjoining the wafer. This level of modeling is difficult to achieve since non-collisional sheath lengths are usually 3-4 orders of magnitude smaller than the reactor scale. Also, the drift-diffusion equations used for ion transport becomes invalid in the sheath since the ion frictional force is no longer in equilibrium with drift and diffusion forces. The alternative is to use a full momentum equation for each ionic species. In this work we will present results from a self-consistent reactor scale-sheath scale model for 2D inductively coupled plasmas. The goal of this study is to improve the modeling capabilities and assess the importance of additional physics in determining important reactor performance features, such as the ion flux uniformity, coil frequency and configuration effects, etc. Effect of numerical dissipation on the solution quality will also be discussed.

  18. Dynamics of the plasma current sheath in plasma focus discharges in different gases

    NASA Astrophysics Data System (ADS)

    Vinogradov, V. P.; Krauz, V. I.; Mokeev, A. N.; Myalton, V. V.; Kharrasov, A. M.

    2016-12-01

    The shape of the plasma current sheath (PCS) in the final stage of its radial compression, the dynamics of pinching, and the subsequent pinch decay in plasma focus (PF) discharges in different gases are studied using an improved multichannel system of electron-optical plasma photography and a newly elaborated synchronization system. The PCS structure in discharges in heavy gases (Ne, Ar) is found to differ significantly from that in discharges in hydrogen and deuterium. The influence of a heavy gas (Xe) additive to hydrogen and deuterium on the structure and compression dynamics of the PCS is investigated.

  19. Oblique solitary waves in a five component plasma

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    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.

  20. 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.

  1. 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.

  2. Temporally resolved ion velocity distribution measurements in a radio-frequency plasma sheath

    SciTech Connect

    Jacobs, B.; Gekelman, W.; Pribyl, P.; Barnes, M.

    2011-05-15

    The ion velocity distribution function (IVDF) above and within a radio-frequency (RF) biased plasma sheath is studied experimentally with a pulsed laser-induced fluorescence diagnostic in an industrial plasma etch tool. Temporally resolved measurements taken at eight different phases of the 2.2 MHz bias waveform show that the ion dynamics vary dramatically throughout the RF cycle (the ratio of the average ion transit time through the sheath to the RF period is {tau}{sub ion}/{tau}{sub RF} = 0.3). The position of the presheath/sheath edge is constant throughout the RF cycle and the time-averaged ion flux is conserved within the sheath region. The characteristic bimodal structure of the time-averaged ion distributions found in previous experiments is observed to arise from the time-dependent ion dynamics, in accord with existing theory. The large temporal variation of the IVDF has implications for the plasma chemistry and etching quality.

  3. Current Sheath Dynamics and its Evolution Studies in Sahand Filippov Type Plasma Focus

    NASA Astrophysics Data System (ADS)

    Mohammadi, M. A.; Sobhanian, S.; Ghomeishi, M.; Ghareshabani, E.; Moslehi-fard, M.; Lee, S.; Rawat, R. S.

    2009-12-01

    One of the most important factors for optimizing the plasma focus device operation is the dynamics of the plasma. In this paper, we investigated the profile and dynamics of the current sheath by measuring the velocity and distribution of current sheath in Sahand as a Filippov type plasma focus device. For this purpose, the discharge is produced in pure neon gas with capacitor bank stored energies in the range of 14-50 kJ. The current sheath is monitored using two sets of magnetic probes, one with four and other with three equi-distant probe coils. These probes, installed in both radial and axial directions near the edge of the interior electrode (anode), are used for monitoring the distributions and dynamics of the current sheath. The maximum current sheath velocities at radial and axial phase are 4 ± 0.13 and 3.51 ± 0.22 (cm/μs) respectively for 0.25 Torr. The decreasing of CS velocities in going move away from anode surface is one of the our results in this paper. In this paper we conclude that the current sheath velocity at radial phase in Sahand is greater than axial phase. The effect of the neon working gas pressure and working voltage on the current sheath dynamics and its spatial evolution is investigated and presented.

  4. Effect of q-nonextensive distribution of electrons on the sheath in dusty plasma

    NASA Astrophysics Data System (ADS)

    Driouch, Ismael; Chatei, Hassan

    2017-01-01

    In this paper, a sheath model has been developed to investigate the characteristics of a magnetised dusty plasma sheath in the presence of a q-nonextensive distribution of electrons. For this, we have established a one-dimensional fluid model. The electrons are considered following the q-nonextensive distribution (i.e. the deflection of the electrons for their Maxwell-Boltzmann distribution); however the ions and dust grains are described by fluid equations. According to multi-fluid equations and some dimensionless variables, the dimensionless equations are obtained and solved numerically. The effect of the nonextensivity q-parameter on the plasma sheath parameters is examined. A significant change is observed in the quantities characterising the sheath when the electrons evolve far away from their thermodynamic equilibrium Maxwellian ( q = 1) assumption.

  5. Unified model of the rf plasma sheath: Part 2, Asymptotic connection formulae

    SciTech Connect

    Riley, M.E.

    1996-08-01

    A previously-developed approximation to the first integral of the Poisson equation enables one to obtain solutions for the voltage- current characteristics of a radio-frequency (rf) plasma sheath that are valid over the whole range of inertial response of the ions to an imposed rf voltage or current-specified conditions. The theory reproduced the time-dependent voltage-current characteristics of the two extreme cases corresponding to the Lieberman rf sheath theory and the Metze-Ernie-Oskam theory. In this paper the sheath model is connected to the plasma bulk description, and a prescription is given for the ion relaxation time constant, which determines the time-dependent ion impact energy on the electrode surface. It appears that this connected model should be applicable to those high density, low pressure plasmas in which the Debye length is a small fraction of the ion mean free path, which itself is a small fraction of the plasma dimension.

  6. Numerical study of an electrostatic plasma sheath containing two species of charged dust particles

    SciTech Connect

    Foroutan, G.; Akhoundi, A.

    2012-10-01

    A multi-fluid model is used to study the dynamics of a dusty plasma sheath consists of electrons, ions, and two species of charged dust particles, i.e., nano-size and micron-size particles. It is found that, when the sheath is dominated by the nano-size dust grains, spatially periodic fluctuations are developed in the profiles of the sheath potential, and the number density and velocity of the plasma and dust particles. Due to inertial effects, the fluctuations in the parameters of the micron-size grains are much lower than those of the other parameters. The competition between the electric and ion drag forces plays the primary role in development of the fluctuations. The spatial period of the fluctuations is approximately a few Debye lengths and their amplitude depends on the plasma and dust parameters. The fluctuations are reduced by the increase in the radius, mass density, and Mach number of the nano-size particles, as well as the density and Mach number of the ions. But, they are enhanced by the increase in the plasma number density and the electron temperature. The sheath thickness demonstrates a non-monotonic behavior against variation of the nanoparticle parameters, i.e., it first decreases quickly, shows a minimum, and then increases. However, the sheath width always decreases with the plasma number density and ion Mach number, while grows linearly with the electron temperature.

  7. 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.

  8. 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

  9. 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

  10. 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.

  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. 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.

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

    NASA Astrophysics Data System (ADS)

    Gao, Xiaotian; Jiang, Binhao

    2015-06-01

    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. 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.

  17. Effect of collision parameters in electronegative plasma sheath with two species of positive ions

    SciTech Connect

    Moulick, R.; Goswami, K. S.; Mahanta, M. K.

    2013-09-15

    The effect of ion neutral collision is shown for two species of positive ions in electronegative plasma. The ion neutral collision is modeled using power law of collision cross section. It is a usual case for processing plasma to have two species of positive ions and hence we attempt to study the dynamics of the two species of ions inside the collisional sheath of electronegative plasma.

  18. Effect of sheath gas in atmospheric-pressure plasma jet for potato sprouting suppression

    NASA Astrophysics Data System (ADS)

    Nishiyama, S.; Monma, M.; Sasaki, K.

    2016-09-01

    Recently, low-temperature atmospheric-pressure plasma jets (APPJs) attract much interest for medical and agricultural applications. We try to apply APPJs for the suppression of potato sprouting in the long-term storage. In this study, we investigated the effect of sheath gas in APPJ on the suppression efficiency of the potato sprouting. Our APPJ was composed of an insulated thin wire electrode, a glass tube, a grounded electrode which was wound on the glass tube, and a sheath gas nozzle which was attached at the end of the glass tube. The wire electrode was connected to a rectangular-waveform power supply at a frequency of 3 kHz and a voltage of +/- 7 kV. Helium was fed through the glass tube, while we tested dry nitrogen, humid nitrogen, and oxygen as the sheath gas. Eyes of potatoes were irradiated by APPJ for 60 seconds. The sprouting probability was evaluated at two weeks after the plasma irradiation. The sprouting probability was 28% when we employed no sheath gases, whereas an improved probability of 10% was obtained when we applied dry nitrogen as the sheath gas. Optical emission spectroscopy was carried out to diagnose the plasma jet. It was suggested that reactive species originated from nitrogen worked for the efficient suppression of the potato sprouting.

  19. 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.

  20. 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.

  1. 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.

  2. Study of Current Sheath Velocity and Its Distribution Using Tridimensional Magnetic Probe in Sahand Plasma Focus

    NASA Astrophysics Data System (ADS)

    A. Mohammadi, M.; Hedyeh, S.

    2015-05-01

    The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is measured for argon, oxygen and nitrogen. Additionally, the effect of charging voltage on the current sheath velocity is studied in both axial and radial phases. We found that, the maximum current sheath velocities at both radial and axial phases are respectively 4.33 ± 0.28 (cm/μs) and 3.92 ± 0.75 (cm/μs) with argon as the working gas at 17 kV. Also, the minimum values of current sheath velocity are 1.48 ± 0.15 (cm/μs) at the radial phase and 1.14 ± 0.09 (cm/μs) at the axial phase with oxygen at 12 kV. The current sheath velocity at the radial phase is higher than that at the axial phase for all gases and voltages. In this study, variation of the full width half maximum (FWHM) of magnetic probe signals with voltage is investigated for different gases at radial and axial phases.

  3. 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.

  4. Scaling of the plasma sheath in a magnetic field parallel to the wall

    SciTech Connect

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

    2010-05-15

    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: rho{sub the}, rho{sub thi}, and lambda{sub D}. Furthermore, the study of the sheath width scaling through the analysis of the full width at half max of electric field, x{sub Eh}, elucidates three distinct types of behavior of x{sub Eh}, corresponding to three different regimes: rho{sub thi}sheath width, the scaling of the wall potential phi{sub Wall}, 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.

  5. 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.

  6. 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.

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

    SciTech Connect

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

    2007-02-15

    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.

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

    NASA Astrophysics Data System (ADS)

    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 ˜1 kW and arc plasma temperature of ˜3000 K, schlieren photography and gas pressure measurements indicated that the start point of shock wave shifted upstream of ˜4 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.

  9. 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.

  10. Determination of the levitation limits of dust particles within the sheath in complex plasma experiments

    SciTech Connect

    Douglass, Angela; Land, Victor; Qiao Ke; Matthews, Lorin; Hyde, Truell

    2012-01-15

    Experiments are performed in which dust particles are levitated at varying heights above the powered electrode in a radio frequency plasma discharge by changing the discharge power. The trajectories of particles dropped from the top of the discharge chamber are used to reconstruct the vertical electric force acting on the particles. The resulting data, together with the results from a self-consistent fluid model, are used to determine the lower levitation limit for dust particles in the discharge and the approximate height above the lower electrode where quasineutrality is attained, locating the sheath edge. These results are then compared with current sheath models. It is also shown that particles levitated within a few electron Debye lengths of the sheath edge are located outside the linearly increasing portion of the electric field.

  11. Electromagnetic particle in cell modeling of the plasma focus: Current sheath formation and lift off

    SciTech Connect

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

    2014-02-15

    The shaping and formation of the current sheath takes place in the breakdown phase of a plasma focus device and critically controls the device performance. Electrostatic particle in cell codes, with magnetic effects ignored, have been used to model the breakdown phase. This Letter reports the successful development and implementation of an electromagnetic particle in cell (EMPIC) code, including magnetic effects self-consistently, to simulate the breakdown phase; from the ionization, localization and gliding discharge along the insulator to the time instant of current sheath lift off. The magnetic field was found to be appreciable from the time the current sheath came into contact with the anode with increased local current, initiating the voltage breakdown of the device as a result.

  12. Confinement and structure of electrostatically coupled dust clouds in a direct current plasma-sheath

    NASA Astrophysics Data System (ADS)

    Nunomura, S.; Ohno, N.; Takamura, S.

    1998-10-01

    Mechanisms for the confinement and the internal structure of an electrostatically coupled dust cloud formed in a dc glow discharge have been investigated from a comparative viewpoint between experimental observations and a simple model. Two kinds of dust clouds with different internal structures are clearly observed, depending on the dispersion of the size distribution of dust particles. The dust cloud can be trapped only in the plasma-sheath boundary area, corresponding to the potential minimum region determined by gravitational and electrostatic forces in the cathode sheath. No dust particles were found deep inside of the sheath, which is consistent with the analysis because the dust particles may be charged positively due to an extreme reduction of the electron density. The internal structure of the electrostatically coupled dust cloud was found to be arranged so that the total potential energy, including the repulsive Coulomb interaction among negative dust particles, may become minimal.

  13. 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).

  14. The effect of intermediate frequency on sheath dynamics in collisionless current driven triple frequency capacitive plasmas

    NASA Astrophysics Data System (ADS)

    Sharma, S.; Mishra, S. K.; Kaw, P. K.; Turner, M. M.

    2017-01-01

    The Capacitively Coupled Plasma discharge featuring operation in current driven triple frequency configuration has analytically been investigated, and the outcome is verified by utilising the 1D3V particle-in-cell (PIC) simulation code. In this analysis, the role of middle frequency component of the applied signal has precisely been explored. The discharge parameters are seen to be sensitive to the ratio of the chosen middle frequency to lower and higher frequencies for fixed amplitudes of the three frequency components. On the basis of analysis and PIC simulation results, the middle frequency component is demonstrated to act as additional control over sheath potential, electron sheath heating, and ion energy distribution function (iedf) of the plasma discharge. For the electron sheath heating, effect of the middle frequency is seen to be pronounced as it approaches to the lower frequency component. On the other hand, for the iedf, the control is more sensitive as the middle frequency approaches towards the higher frequency. The PIC estimate for the electron sheath heating is found to be in reasonably good agreement with the analytical prediction based on the Kaganovich formulation.

  15. Collaborative Research: Understanding Ion Losses to Plasma Boundaries Sheaths and Presheaths

    SciTech Connect

    Hershkowitz, Noah

    2015-10-01

    Sheaths are common to all bounded steady-state plasmas. This includes laboratory, industrial, fusion, and in some cases even space plasmas. They form in general to balance particle loss and maintain quasi-neutrality in plasmas. Electrons are lighter than the ions by 2000 times or more (depending on the gas), and in most plasmas ion temperatures are rarely higher than the electron temperature and generally much lower. Thus in most cases, negative potential sheaths occur to confine electrons and allow ions to be freely lost. We have investigated how a plasma locally response to a positive bias on a small electrode, and have established area criteria which plasma reacts differently to the positive bias – first a pure electron sheath, and a global non-ambipolar regime where all electrons are lost to the electrode, and a double layer structure identified as a virtual cathode forms to limiting electron loss and maintain quasi-neutrality, and finally a anode spot regime where a secondary discharge occurs in front of the electrode, turning it into the major loss area of the entire plasma. Electrode area and plasma parameters criteria for these regimes were established, and the effect of the virtual cathode on the electrode’s I-V characteristics was investigated. We have also developed a global non-ambipolar electron source to replace hollow cathodes in a number of plasma applications. This eliminates the lifetime limitation and maintenance cost of hollow cathodes as they easily wear out easily and cannot be replaced in space applications.

  16. Observations on the dynamics of the plasma sheath axial acceleration phase on a Plasma Focus Discharge of hundreds of Joules

    NASA Astrophysics Data System (ADS)

    Avaria, Gonzalo; Clausse, Alejandro; Cuadrado, Osvaldo; Villalba, Nelson; Moreno, Jose; Pavez, Cristian; Soto, Leopoldo

    2016-10-01

    The plasma sheath evolution in the axial acceleration phase of plasma focus discharges is of interest for fundamental studies of the ionization and electron density evolution at the early stages of plasma formation, in order to improve the understanding of its influence in pinch development characteristics. We present spatial and temporal resolved measurements performed with a 0.5 m imaging spectrometer that captures the emission of the interelectrode region in the PF-400J (176-539 J, 880 nF, 20-35 kV, quarter period 300 ns) Plasma Focus Discharge. Spectral images of the plasma sheath at different times of the current pulse evolution were acquired with an ICCD integrating over a 3 ns window. The sheath speed was determined to be approximately 43.6 km/s for discharges in Hydrogen at 9 mbar. Comparison of these measurements with numerical calculations, based on a lumped parameter model, show excellent correspondence. Electron density calculations at different stages of the plasma evolution are also presented. Work supported by FONDECYT Iniciación 11121587 and CONICYT-PIA Anillo ACT 1115.

  17. Investigation of the sheath formation in a dusty plasma containing energetic electrons and nano-size dust grains

    SciTech Connect

    Foroutan, G.; Akhoundi, A.

    2012-10-15

    Numerical simulations of the stationary multi-fluid equations are used to study the structure of a dusty plasma sheath in the presence of a beam of energetic electrons. It is found that even a small number of energetic electrons can strongly modify the sheath parameters, specially the sheath thickness. Depending on the magnitude of the beam flux, two different regimes of sheath thickness can be recognized; At small beam fluxes, the sheath is in the regime of thin sheath and its thickness grows linearly with the beam flux. As the beam flux increases, at a certain beam energy or beam number density, the sheath demonstrates a sharp transition to the regime of thick sheath where the width is almost three times larger. The beam parameters corresponding to the transition between the two regimes depend on the parameters of the background plasma. The beam transition energy increases with the electron temperature and dust number density while decreases with the dust radius. On the other hand, the beam transition number density is a non-monotonic function of the background plasma number density. The localization of dust particles above the substrate is intensified by the increase in the beam number density.

  18. 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.

  19. Generation of dust projectiles passing over an obstacle in the plasma sheath

    SciTech Connect

    Ticos, Catalin M.; Stoica, Daniel S.; Delzanno, Gian Luca

    2012-08-15

    Dust projectiles were produced in a radio-frequency plasma by increasing 6-fold the radio-frequency power put into the discharge. The initial static dust particles were observed to gain speed while moving away from the confining region and escaped from the inter-electrode space on a ballistic-like trajectory. Single-grain dynamics simulations indicated that the dust particles were accelerated by changes induced in the sheath electric field profile.

  20. Plasmas fluxes to surfaces for an oblique magnetic field

    SciTech Connect

    Pitcher, C.S.; Stangeby, P.C.; Elder, J.D.; Bell, M.G.; Kilpatrick, S.J.; Manos, D.M.; Medley, S.S.; Owens, D.K.; Ramsey, A.T.; Ulrickson, M.

    1992-07-01

    The poloidal and toroidal spatial distributions of D{sub {alpha}}, He I and C II emission have been obtained in the vicinity of the TFTR bumper limiter and are compared with models of ion flow to the surface. The distributions are found not to agree with a model (the ``Cosine`` model) which determines the incident flux density using only the parallel fluxes in the scrape-off layer and the projected area of the surface perpendicular to the field lines. In particular, the Cosine model is not able to explain the significant fluxes observed at locations on the surface which are oblique to the magnetic field. It is further shown that these fluxes cannot be explained by the finite Larmor radius of impinging ions. Finally, it is demonstrated, with the use of Monte Carlo codes, that the distributions can be explained by including both parallel and cross-field transport onto the limiter surface.

  1. Plasmas fluxes to surfaces for an oblique magnetic field

    SciTech Connect

    Pitcher, C.S. ); Stangeby, P.C.; Elder, J.D. ); Bell, M.G.; Kilpatrick, S.J.; Manos, D.M.; Medley, S.S.; Owens, D.K.; Ramsey, A.T.; Ulrickson, M. . Plasma Physics Lab.)

    1992-07-01

    The poloidal and toroidal spatial distributions of D{sub {alpha}}, He I and C II emission have been obtained in the vicinity of the TFTR bumper limiter and are compared with models of ion flow to the surface. The distributions are found not to agree with a model (the Cosine'' model) which determines the incident flux density using only the parallel fluxes in the scrape-off layer and the projected area of the surface perpendicular to the field lines. In particular, the Cosine model is not able to explain the significant fluxes observed at locations on the surface which are oblique to the magnetic field. It is further shown that these fluxes cannot be explained by the finite Larmor radius of impinging ions. Finally, it is demonstrated, with the use of Monte Carlo codes, that the distributions can be explained by including both parallel and cross-field transport onto the limiter surface.

  2. Comprehensive Study of Plasma-Wall Sheath Transport Phenomena

    DTIC Science & Technology

    2012-09-10

    microstructure obtained form micrographs provided by UA. Anisotropic thermal expansion coefficient and elastic properties are assigned to each boron nitride ...of the HET plasma discharge in which a kinetic treatment is used to model electron transport along magnetic field lines while a 2D macroscopic model...calculate electron mobility. This mobility is then used in a hybrid 2D axial code for thruster discharge (b). Upon reaching steady state, ions exiting the

  3. Potential application of X-ray communication through a plasma sheath encountered during spacecraft reentry into earth's atmosphere

    NASA Astrophysics Data System (ADS)

    Li, Huan; Tang, Xiaobin; Hang, Shuang; Liu, Yunpeng; Chen, Da

    2017-03-01

    Rapid progress in exploiting X-ray science has fueled its potential application in communication networks as a carrier wave for transmitting information through a plasma sheath during spacecraft reentry into earth's atmosphere. In this study, we addressed the physical transmission process of X-rays in the reentry plasma sheath and near-earth space theoretically. The interactions between the X-rays and reentry plasma sheath were investigated through the theoretical Wentzel-Kramers-Brillouin method, and the Monte Carlo simulation was employed to explore the transmission properties of X-rays in the near-earth space. The simulation results indicated that X-ray transmission was not influenced by the reentry plasma sheath compared with regular RF signals, and adopting various X-ray energies according to different spacecraft reentry altitudes is imperative when using X-ray uplink communication especially in the near-earth space. Additionally, the performance of the X-ray communication system was evaluated by applying the additive white Gaussian noise, Rayleigh fading channel, and plasma sheath channel. The Doppler shift, as a result of spacecraft velocity changes, was also calculated through the Matlab Simulink simulation, and various plasma sheath environments have no significant influence on X-ray communication owing to its exceedingly high carrier frequency.

  4. 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.

  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. Revealing an intermediate region between the collisional radiofrequency plasma bulk and its sheath

    NASA Astrophysics Data System (ADS)

    Beckers, J.; Trienekens, D. J. M.; Kroesen, G. M. W.

    2015-03-01

    Experimental evidence of the existence of an intermediate region between a capacitively coupled plasma and the collisional space-charge region at its borders is presented. This proof is generated by monitoring—in an airplane carrying out parabolic flights—the trajectory of plasma-confined microparticles. Based on only primary data and without the need for a sophisticated model, our analysis concludes a sharply marked transition from the sheath region into another region with a significantly lower—yet nonzero—space-charge density, i.e., a region which is often called the presheath.

  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. High voltage plasma sheath analysis related to TSS-1

    NASA Astrophysics Data System (ADS)

    Sheldon, John W.

    1991-10-01

    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.

  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. 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

  13. On the ion acoustic obliquely propagation in magnetized inhomogeneous plasmas

    NASA Astrophysics Data System (ADS)

    Mowafy, A. E.; El-Shewy, E. K.; Abdelwahed, H. G.

    2017-02-01

    Inhomogeneous multi-component magnetized plasmas containing inertial ions, nonthermal electrons, and Boltzmannian positrons have been investigated theoretically. Variable coefficients Zakharov Kuznetsov (VZK) equation has been derived in a small amplitude limit. It is found that the propagation directions, positron parameters and magnetic field affected the properties of propagation of positive-negative solitary waves.

  14. 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.

  15. Online platform for simulations of ion energy distribution functions behind a plasma boundary sheath

    NASA Astrophysics Data System (ADS)

    Wollny, Alexander; Shihab, Mohammed; Brinkmann, Ralf Peter

    2012-10-01

    Plasma processes, particularly plasma etching and plasma deposition are crucial for a large variety of industrial manufacturing purposes. For these processes the knowledge of the ion energy distribution function plays a key role. Measurements of the ion energy and ion angular distribution functions (IEDF, IADF) are at least challenging and often impossible in industrial processes. An alternative to measurements of the IEDF are simulations. With this contribution we present a self-consistent model available online for everyone. The simulation of ion energy and ion angular distribution functions involves the well known plasma boundary sheath model by Brinkmann [1-4], which is controlled via a web interface (http://sheath.tet.rub.de). After a successful simulation run all results are evaluable within the browser and ready for download for further analysis.[4pt] [1] R.P. Brinkmann, J. Phys. D: Appl. Phys. 44, 042002 (2011)[0pt] [2] R.P. Brinkmann, J. Phys. D: Appl. Phys. 42, 194009 (2009)[0pt] [3] R.P. Brinkmann, J. App. Phys. 102, 093303 (2007)[0pt] [4] M. Kratzer et al., J. Appl. Phys. 90, 2169 (2001)

  16. Computational study of sheath structure in oxygen containing plasmas at medium pressures

    NASA Astrophysics Data System (ADS)

    Hrach, Rudolf; Novak, Stanislav; Ibehej, Tomas; Hrachova, Vera

    2016-09-01

    Plasma mixtures containing active species are used in many plasma-assisted material treatment technologies. The analysis of such systems is rather difficult, as both physical and chemical processes affect plasma properties. A combination of experimental and computational approaches is the best suited, especially at higher pressures and/or in chemically active plasmas. The first part of our study of argon-oxygen mixtures was based on experimental results obtained in the positive column of DC glow discharge. The plasma was analysed by the macroscopic kinetic approach which is based on the set of chemical reactions in the discharge. The result of this model is a time evolution of the number densities of each species. In the second part of contribution the detailed analysis of processes taking place during the interaction of oxygen containing plasma with immersed substrates was performed, the results of the first model being the input parameters. The used method was the particle simulation technique applied to multicomponent plasma. The sheath structure and fluxes of charged particles to substrates were analysed in the dependence on plasma pressure, plasma composition and surface geometry.

  17. 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.

  18. 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.

  19. 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.

  20. Effects of plasma aerodynamic actuation on oblique shock wave in a cold supersonic flow

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Li, Yinghong; Cheng, Bangqin; Su, Changbing; Song, Huimin; Wu, Yun

    2009-08-01

    Wedge oblique shock wave control using an arc discharge plasma aerodynamic actuator was investigated both experimentally and theoretically. Schlieren photography measurements in a small-scale short-duration supersonic wind tunnel indicated that the shock wave angle decreased and its start point shifted upstream with the plasma aerodynamic actuation. Also the shock wave intensity weakened, as shown by the decrease in the gas static pressure ratio of flow downstream and upstream of the shock wave. Moreover, the shock wave control effect was intensified when a static magnetic field was applied. Under test conditions of Mach 2.2, magnetic control and input voltage 3 kV, the start point of the shock wave shifted 4 mm upstream, while its angle and intensity decreased 8.6% and 8.8%, respectively. A thermal choking model was proposed to deduce the change laws of oblique shock wave control by surface arc discharge. The theoretical result was consistent with the experimental result, which demonstrated that the thermal choking model can effectively forecast the effect of plasma actuation on an oblique shock wave in a cold supersonic flow.

  1. Plasma sheath model in the presence of field-induced electron emission

    NASA Astrophysics Data System (ADS)

    Dahal, Jiba; Ayyaswamy, Venkattraman

    2016-10-01

    Microplasmas have become an active area of research during the last two decades with several applications including nanomaterial synthesis, electronics, lighting, biomedicine, and metamaterials for controlling electromagnetic waves. The advances in micro/nanofabrication and the further miniaturization of plasma devices have contributed to the increasing role of new physical mechanisms that were previously neglected. Electric field-induced emission of electrons is one such mechanism that is gaining significance particularly with the discovery of novel electrodes that demonstrate excellent field emission properties. These field emitted electrons and their interaction with microdischarges has shown to affect both pre-breakdown and post-breakdown regimes of operation. The current work focuses on the development of self-consistent sheath model that includes the effects of field-induced electron emission. Sheath models presented earlier accounts for other emission mechanisms such as thermionic and secondary electron emission, the strong influence of electric field on electron emission is shown to lead to unique interplay. The results obtained from the sheath model for various parameters including current-voltage characteristics, and ion/electron number density are validated with PIC-MCC results.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    Auluck, S. K. H.

    2009-12-01

    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.

  4. 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.

  5. 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.

  6. Two-plasmon decay instability in inhomogeneous plasmas at oblique laser incidence

    NASA Astrophysics Data System (ADS)

    Wen, H.; Maximov, A. V.; Short, R. W.; Myatt, J. F.; Yan, R.; Ren, C.

    2016-09-01

    The two-plasmon decay (TPD) instability has been studied in the region near the quarter-critical density in the plasmas of the laser-driven inertial confinement fusion for a wide range of laser angles of incidence. The TPD equations for the oblique laser incidence in the inhomogeneous plasmas have been analyzed theoretically. The range of wave vectors for the instability growth has been identified. The theoretical growth rates and thresholds have been compared with the results of the fluid-type simulations, and a good agreement has been found.

  7. Modeling of and experiments on dust particle levitation in the sheath of a radio frequency plasma reactor

    SciTech Connect

    Setyawan, Heru; Shimada, Manabu; Hayashi, Yutaka; Okuyama, Kikuo; Winardi, Sugeng

    2005-02-15

    The equilibrium and trapping of dust particles in a plasma sheath are investigated, both experimentally and theoretically. A self-consistent sheath model including input power as one of the model parameters is proposed, to predict the equilibrium position of particle trap. The electron temperature and density are estimated from the observed current and power (I-P) characteristics using the sheath model developed. Direct comparisons are made between the measured equilibrium position and the predicted equilibrium position. The equilibrium position moves closer to the electrode with increasing rf power and particle size. The position is apparently related to the sheath thickness, which decreases with increasing rf power. The model can correctly predict the experimentally observed trend in the equilibrium position of particle trap. It is found that the particle charge becomes positive when the particle gets closer to the electrode, due to the dominant influence of ion currents to the particle surface.

  8. Experimental Characterization of the Stagnation Layer between Two Obliquely Merging Supersonic Plasma Jets

    NASA Astrophysics Data System (ADS)

    Merritt, Elizabeth C.

    2013-10-01

    Experiments on the oblique merging of two supersonic argon plasma jets have been conducted at LANL in order to assess the use of such jets to form imploding spherical plasma liners for high energy density physics applications. The plasma jets are formed and launched by pulsed-power-driven railguns and have initial jet parameters of n ~ 2 ×1016 cm-3, Te ~ 1 . 4 eV, ionization fraction ~ 0 . 96 , velocity ~ 30 km/s, diameter = 5 cm, and length ~ 20 cm. We have experimentally identified density increases that are consistent with shock formation, and a few-cm thick stagnation layer structure observed both in CCD camera images and interferometer density profiles. Although the jets are each individually collisional, the mean free path between counter-streaming ions is on the same order as the stagnation layer thickness, placing the jet merging in a semi-collisional regime. It was not known a priori whether the observations corresponded to hydrodynamic oblique shocks and whether two-fluid or kinetic effects played a role. Through careful analysis of the stagnation layer density and emission profiles, and comparisons between the data and both analytic hydrodynamic shock theory and multi-fluid plasma simulations, we demonstrate that our observations are consistent with collisional shocks. Work performed in collaboration with colleagues from LANL, Univ. of New Mexico, HyperV Technologies, Univ. of Alabama in Huntsville, Voss Scientific, Prism Computational Sciences, and Tech-X; supported by DOE-OFES.

  9. Impact of Plasma Sheath on Rocket-based E-region Ion Measurements

    NASA Astrophysics Data System (ADS)

    Imtiaz, N.; Burchill, J. K.; Marchand, R.

    2013-12-01

    We model the particle velocity distribution functions around the entrance window of the Suprathermal Ion Imager (SII) to assess the impact of electrostatic sheath on ion measurements in the E-region ionosphere. 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 sensor SII that was affixed to a 1-m NASA rocket 36.234 as part of the Joule II mission to investigate Joule heating in the E-region ionosphere. The rocket flew into quiet auroral conditions above Northern Alaska on 19 January 2007. The payload was spin-stabilitized with a period of 1.6 s, giving an apparent rotation of the ion flow velocity in the frame of reference of the SII. We numerically investigate the ram velocity effect on the ions velocity distributions in the vicinity of SII aperture at an altitudes of approximately 150km. The electrostatic sheath potential profiles surrounding the sensor and payload are calculated numerically with the PIC code PTetra. It is observed that the direction of the ion flow velocity vector modifies the plasma sheath potential profile. This in turn impacts the velocity distributions of molecular oxygen and Nitric oxideions at the aperture of the particle sensor. The velocity distribution functions are calculated by using test-particle modeling. These particle distribution functions are then used to inject the particles in the particle sensor, and to calculate the fluxes on the sensor microchannel plate (MCP).

  10. Effects of external magnetic field on oblique propagation of ion acoustic cnoidal wave in nonextensive plasma

    NASA Astrophysics Data System (ADS)

    Farhad Kiyaei, Forough; Dorranian, Davoud

    2017-01-01

    Effects of the obliqueness and the strength of external magnetic field on the ion acoustic (IA) cnoidal wave in a nonextensive plasma are investigated. The reductive perturbation method is employed to derive the corresponding KdV equation for the IA wave. Sagdeev potential is extracted, and the condition of generation of IA waves in the form of cnoidal waves or solitons is discussed in detail. In this work, the domain of allowable values of nonextensivity parameter q for generation of the IA cnoidal wave in the plasma medium is considered. The results show that only the compressive IA wave may generate and propagate in the plasma medium. Increasing the strength of external magnetic field will increase the frequency of the wave and decrease its amplitude, while increasing the angle of propagation will decrease the frequency of the wave and increase its amplitude.

  11. 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.

  12. 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)].

  13. 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.

  14. 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.

  15. 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.

  16. Experimental test of Baalrud's model for ion velocity at the sheath edge for a two ion species plasma

    NASA Astrophysics Data System (ADS)

    Hershkowitz, Noah; Yip, Chi-Shung; Severn, Greg

    2009-11-01

    Recent experiments have shown that ions in plasmas containing two ion species reach a common velocity at the sheath-presheath boundary [1]. A new theory [2] suggests that collisional friction between the two ion species enhanced by two stream instability affects the drift velocity of each ion species near the sheath edge and finds that the difference in ion velocities at the sheath-presheath boundary is given by √12α (v^2th1+ αv^2th2), where α= n1M1/(n2M2). We report the first experimental test of this model. We measure ion velocity distribution functions (ivdfs) near sheath edge in Argon/Xenon and Argon/Helium plasmas as a function of the concentration ratios. We show that for sufficiently great relative Xenon concentration, ions do not reach a common speed at the sheath edge. The relative concentration of the two ion species, which determines α, is inferred from Ion Acoustic Wave phase velocity measurements, the ivdfs are determined by Laser Induced Florescence. [1] Lee, D; Hershkowitz, N; Severn, GD. Appl. Phys. Lett. 91, 041505 (2007) [2] S.D. Baalrud, J.D. Callen, and C.C. Hegna, GEC 2009

  17. Development of a formalism for computing transits of Earth-directed CMEs, plasma sheaths, and shocks. Towards a forecasting tool

    NASA Astrophysics Data System (ADS)

    Corona-Romero, P.; Gonzalez-Esparza, J. A.

    2016-11-01

    Interplanetary Coronal mass ejections (ICMEs) (super-magnetosonically) faster than the ambient solar wind are preceded by shock waves. Earth-directed shock waves, plasma sheaths and ICMEs are precursors of the major geomagnetic storms. The plasma sheath between the shock and the ICME leading edge plays a very important role to determine the geoeffectiveness of the events. There are multiple efforts (empirical, analytical and numerical) to forecast ICME-shock transit times and arrival speeds to 1 AU. We present a formalism (combining analytical and empirical solutions) to compute trajectories of fast halo Earth directed ICMEs, plasma sheaths, and shocks. This formalism combines the 'piston-shock' semi-empirical model (Corona-Romero et al., 2013), and the MHD polytropic jump relations (Petrinec and Russell, 1997) to approximate the 1 AU plasma sheath and ICME properties. Nine Earth directed ICME-shock cases, including the ;Bastille; and ;Halloween; events were analyzed. The model obtained compares well with in situ data. Finally, we found a possible empiric relation for the free parameter of our formalism. If this empiric relationship is confirmed, it could turn this formalism into a space weather forecasting tool.

  18. Measurements of railgun generated supersonic plasma jet propagation and two jet oblique merging

    NASA Astrophysics Data System (ADS)

    Merritt, Elizabeth C.

    Imploding spherical plasma liners have been proposed as a possible method for creating high-energy-density (HED) laboratory plasmas and as a standoff driver for magneto-inertial fusion (MIF). The Plasma Liner Experiment (PLX) planned a three-phase experimental program to study the feasibility of using railgun-driven supersonic jets to form imploding spherical plasma liners. The three phases are to investigate single-jet evolution during propagation, to merge 2-5 jets to assess the suitability of merging for liner formation, and to merge 30 jets in spherical symmetry to form a complete liner. We present here details of single-jet propagation and two-jet oblique merging experiments completed on PLX. A key component of this dissertation was the design, implementation, and operation of a novel 8 chord, fiber-coupled interferometer based on a long coherence length (> 100 m) 561 nm diode-pumped solid state laser. This interferometer was a critical diagnostic in both single-jet propagation and two-jet merging studies. The long laser coherence length and fiber-optic design allowed signal and reference path lengths in the interferometer to be mismatched by many meters without signal degradation, greatly simplified interferometer optical layout, and added flexibility in interferometer positioning for both propagation and merging experiments. The interferometer sensitivity to ions, neutral atoms, and electrons required development of a phase shift analysis that incorporated the presence of neutrals, impurities, and multiply ionized species. Interferometry, coupled with spectroscopic ionization fraction estimates, was used to assess time resolved density profile measurements. Survey spectroscopy inferred both Te and ionization fraction f via non-local-thermodynamic-equilibrium (non-LTE) atomic/equation-of-state (EOS) modeling. A fast CCD camera and photo-diode array allowed for assessment of plasma emission for velocity and jet profile measurements. Initial jet parameters were

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

    NASA Astrophysics Data System (ADS)

    Schweigert, I. V.

    2012-08-01

    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.

  4. Oblique Bernstein Mode Generation Near the Upper-hybrid Frequency in Solar Pre-flare Plasmas

    NASA Astrophysics Data System (ADS)

    Kryshtal, A.; Fedun, V.; Gerasimenko, S.; Voitsekhovska, A.

    2015-11-01

    We study analytically the generation process of the first harmonics of the pure electron weakly oblique Bernstein modes. This mode can appear as a result of the rise and development of a corresponding instability in a solar active region. We assume that this wave mode is modified by the influence of pair Coulomb collisions and a weak large-scale sub-Dreicer electric field in the pre-flare chromosphere near the footpoints of a flare loop. To describe the pre-flare plasma we used the model of the solar atmosphere developed by Fontenla, Avrett, and Loeser ( Astrophys. J. 406, 319, 1993). We show that the generated first harmonic is close to the upper-hybrid frequency. This generation process begins at the very low threshold values of the sub-Dreicer electric field and well before the beginning of the preheating phase of a flare. We investigate the necessary conditions for the existence of non-damped first harmonics of oblique Bernstein waves with small amplitudes in the flare area.

  5. The Study Of Low-Frequency Instabilities Of Current Sheaths Of Space Plasma Within The Quasi-Linear Theory

    NASA Astrophysics Data System (ADS)

    Lyahov, Vladimir; Neshchadim, Vladimir

    2015-04-01

    Investigation of the stability nonelectroneutral current sheets in the linear approximation [1-4] gives information only on the initial stage of development of perturbations when their amplitudes are small. Within the framework of the quasi-linear theory one can give an answer to the question of how long the initial perturbations can grow and how change the equilibrium state of the plasma current sheet under the reverse effect of these perturbations. We derive a system of nonlinear kinetic equation with self-consistent electromagnetic field in order to study the evolution of the distribution function of the background plasma current sheet in the approximation of low-frequency eigenmodes of instabilities. Evolution equation was obtained for the perturbation of the electromagnetic field and the instability growth rate in the current sheet. Algorithms were tested for solutions of the equations obtained. 1. Lyahov V.V., Neshchadim V.M. Kinetic theory of the current sheath. I. On polarization of an equilibrium current sheath// Advances in Space Research. -2012. -Vol. 50. -P. 318-326. 2. Lyahov V.V., Neshchadim V.M. Kinetic theory of the current sheath. II. Effect of polarization on the stability of a current sheath.// Advances in Space Research.-2013. -Vol. 51. -P. 730-741. 3. Lyahov V.V., Neshchadim V.M. The Effect of Polarization on the Stability of Current Sheaths in Space Plasma // EGU General Assembly 2013, held 7-12 April, 2013 in Vienna, Austria, id. EGU2013-1379, 04/2013, Bibliographic Code: 2013EGUGA..15.1379L 4. Lyahov V.V., Neshchadim V.M. About the eguilibrium and stability of nonelectroneutral current sheats // Advances in Space Research.-2014. -Vol. 54. -P. 901-907.

  6. 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.

  7. Two-plasmon decay instability in inhomogeneous plasmas at oblique laser incidence

    SciTech Connect

    Wen, H.; Maximov, A. V.; Short, R. W.; Myatt, J. F.; Yan, R.; Ren, C.

    2016-09-30

    The two-plasmon decay (TPD) and stimulated Raman scattering (SRS) instabilities have been studied in the region near the quarter-critical density in the plasmas of the laser-driven inertial confinement fusion for a wide range of laser angles of incidence. The theoretical analysis of the TPD for oblique laser incidence has been carried out. The theoretical growth rates and thresholds have been compared with the results of the fluid-type simulations, and a good agreement has been found. Here, in the modeling including both TPD and SRS, the spectra of the growing perturbations have multiple peaks, and the maximum growth may be influenced by the interplay between TPD and SRS.

  8. Two-plasmon decay instability in inhomogeneous plasmas at oblique laser incidence

    DOE PAGES

    Wen, H.; Maximov, A. V.; Short, R. W.; ...

    2016-09-30

    The two-plasmon decay (TPD) and stimulated Raman scattering (SRS) instabilities have been studied in the region near the quarter-critical density in the plasmas of the laser-driven inertial confinement fusion for a wide range of laser angles of incidence. The theoretical analysis of the TPD for oblique laser incidence has been carried out. The theoretical growth rates and thresholds have been compared with the results of the fluid-type simulations, and a good agreement has been found. Here, in the modeling including both TPD and SRS, the spectra of the growing perturbations have multiple peaks, and the maximum growth may be influencedmore » by the interplay between TPD and SRS.« less

  9. Plasma heating and current drive by an obliquely propagating upper-hybrid cyclotron beat wave

    NASA Astrophysics Data System (ADS)

    Amin, M. R.; Cairns, R. A.

    1991-01-01

    Excitation of an obliquely propagating upper-hybrid cyclotron beat wave is considered for plasma heating and current drive in tokamaks. The beat wave is excited by the interaction of two intense free-electron laser (FEL) pulses at their difference frequency. The three-wave nonlinear interaction equations in a magnetized plasma are solved numerically in a steady-state two-dimensional (2-D) geometry for this purpose. The 2-D toroidal inhomogeneity effect and the effect of finite spatial width of the pump microwave pulses are taken into account for the beat wave excitation. To illustrate the principle, the microwave tokamak experiment (MTX) [Plasma Phys. Controlled Fusion 30, 57 (1988)] is considered. It has been found that the fraction of total input power of the pump microwaves deposited in the cyclotron beat wave is lower than the case of a Langmuir type beat wave considered by Amin and Cairns [Nucl. Fusion 30, 327 (1990)]. However, increasing the input powers of the pump microwaves, a substantial amount of input power can be deposited in the excited beat wave. The beat wave eventually transfers this power to the electrons by cyclotron damping. It has also been found that for the same input parameters, right-hand polarized pumps are more efficient than left-hand polarized pump microwaves for beat wave excitation.

  10. The effect of helium impurity addition on current sheath speed in argon-operated plasma focus using a tridimensional magnetic probe

    NASA Astrophysics Data System (ADS)

    Panahi, N.; Mohammadi, M. A.; Hedyeh, S.; Rawat, R. S.; Rawat

    2013-10-01

    Using the tridimensional magnetic probe, the current sheath velocity at 0.25 Torr is studied in Sahand, a Filippov-type plasma focus facility. The current sheath velocity in argon-filled plasma focus with different percentages of helium impurity at different operating voltages was studied. The highest average current sheath velocity of 12.26 +/- 1.51 cm μs-1 at the top of the anode in the axial phase was achieved at 17 kV. Minimum average current sheath velocity is 5.24 +/- 1.18 cm μs-1 at 12 kV with 80% argon + 20% helium as a working gas. The full width at half-maximum of peaks of the magnetic probe was found to be inversely related to the current sheath velocity, i.e. smaller at higher voltages for different impurity and decreased with increasing of impurity.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

    Toida, Mieko; Kondo, Yuichi

    2011-06-01

    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 θ, 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 θs 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.

  13. 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.

  14. Extension of the Bissell-Johnson plasma-sheath model for application to fusion-relevant and general plasmas

    NASA Astrophysics Data System (ADS)

    Kos, L.; Jelić, N.; Kuhn, S.; Duhovnik, J.

    2009-09-01

    This article presents an approach to solving a special Fredholm-type integral equation of the first kind with a particular kernel containing a modified Bessel function for applications in plasma physics. From the physical point of view, the problem was defined by Bissell and Johnson (B&J) [Phys. Fluids 30, 779 (1987)] as a task to find the potential profile and the ion velocity distribution function in a plane-parallel discharge with a Maxwellian ion source. The B&J model is a generalization of the well-known Tonks-Langmuir (T&L) [Phys. Rev. 34, 876 (1929)] discharge model characterized by a "cold" ion source. Unlike the T&L model, which can be readily solved analytically, attempts to solve the B&J model with a "warm" ion source have been done only numerically. However, the validity of numerical solutions up to date remains constrained to a rather limited range of a crucial independent parameter of the B&J integral equation, which mathematically is the width of a Gaussian distribution and physically represents the ion temperature. It was solved only for moderately warm ion sources. This paper presents the exact numerical solution of the B&J model, which is valid without any restriction regarding the above-mentioned parameter. It is shown that the ion temperature is very different from the temperature of the ion source. The new results with high-temperature ion sources are not only of particular importance for understanding and describing the plasma-sheath boundary in fusion plasmas, but are of considerable interest for discharge problems in general. The eigenvalue of the problem, found analytically by Harrison and Thompson [Proc. Phys. Soc. 74, 145 (1959)] for the particular case of a cold ion source, is here extended to arbitrary ion-source temperatures.

  15. Plasma parameters and existence conditions of monolayer dust structures in the electrode sheath of an RF discharge

    SciTech Connect

    Vaulina, O. S.; Vasilieva, E. V.; Timirkhanov, R. A.

    2011-12-15

    The plasma parameters in the electrode sheath of an RF discharge were studied experimentally under the conditions of dust monolayer levitation. A new method is proposed for determining the plasma parameters, such as the average electric field, ion density, and ion velocity. The screening parameter and the dust grain charge are estimated. The criteria of stable levitation of a dust monolayer are considered. The obtained results are compared with the available theoretical and numerical data, as well as with the results obtained using other diagnostic methods.

  16. 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)].

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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 nse at a poloidal limiter, where blobs are connected, and the upstream density n0 at a location half way to the other end of the blobs. The pre-sheath density drop nse/n0 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)].

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Two-Dimensional Fluid Simulation of Collisional Plasma Sheath over rf Powered Electrode with Cylindrical Hole

    NASA Astrophysics Data System (ADS)

    Hou, Lujing; Wang, Younian; Z, L. Miskvic

    2004-08-01

    The characteristics of collisional radio-frequency (rf) sheath dynamics over an electrode with a cylindrical hole is simulated by means of a self-consistent model which consists of two-dimensional time-dependent fluid equations coupled with Poisson equation. In addition, an equivalent-circuit model is coupled to the fluid equations in order to self-consistently determine relationship between the instantaneous potential at the rf-biased electrode and the sheath thickness. Two-dimensional profiles of the potential, the ion fluid velocity, and the distributions of the ion and electron densities within the sheath are computed under various discharge conditions, such as the discharge powers and the gas pressures. The results show that the existence of the cylindrical hole on the electrode significantly affects the sheath structure and generates a potential trap in the horizontal direction, which is particularly strong when the sheath thickness is comparable to the depth of the hole. Moreover, it is found that the collisional effects have a significant influence on the sheath characteristics.

  3. Stochastic heating of a single Brownian particle by charge fluctuations in a radio-frequency produced plasma sheath.

    PubMed

    Schmidt, Christian; Piel, Alexander

    2015-10-01

    The Brownian motion of a single particle in the plasma sheath is studied to separate the effect of stochastic heating by charge fluctuations from heating by collective effects. By measuring the particle velocities in the ballistic regime and by carefully determining the particle mass from the Epstein drag it is shown that for a pressure of 10 Pa, which is typical of many experiments, the proper kinetic temperature of the Brownian particle remains close to the gas temperature and rises only slightly with particle size. This weak effect is confirmed by a detailed model for charging and charge fluctuations in the sheath. A substantial temperature rise is found for decreasing pressure, which approximately shows the expected scaling with p(-2). The system under study is an example for non-equilibrium Brownian motion under the influence of white noise without corresponding dissipation.

  4. 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.

  5. 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)

  6. Oblique propagation of solitary electrostatic waves in magnetized plasmas with cold ions and nonthermal electrons

    NASA Astrophysics Data System (ADS)

    Verheest, Frank; Hellberg, Manfred A.

    2017-02-01

    Oblique propagation of large amplitude electrostatic waves and solitary structures is investigated in magnetized plasmas, comprising cold fluid ions and Cairns nonthermally distributed electrons, by using a Sagdeev pseudopotential formalism. To perform the analysis, quasineutrality is assumed, so that in normalized variables the electrostatic potential and the occurrence of solitary structures are governed by three parameters: the Mach number M, the typical Cairns parameter β, and the angle ϑ between the directions of propagation and the static magnetic field. Below a critical β, only positive compressive solitons are possible, and their amplitudes increase with increasing β, M, and ϑ. Above the critical β, there is coexistence between negative rarefactive and positive compressive solitons, and the range of negative solitons, at increasing M, ends upon encountering a double layer or a singularity. The double layer amplitudes (in absolute value) increase with β but are independent of ϑ. Roots of the Sagdeev pseudopotential beyond the double layer are not accessible from the undisturbed conditions, because of an intervening singularity where the pseudopotential becomes infinite. Recent claims of finding supersolitons beyond a double layer appear to be based on a misinterpretation of the nature of the singularity.

  7. 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.

  8. 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.

  9. On the stability of obliquely propagating dust ion-acoustic solitary waves in hot adiabatic magnetized dusty plasmas

    NASA Astrophysics Data System (ADS)

    Shalaby, M.; EL-Labany, S. K.; EL-Shamy, E. F.; El-Taibany, W. F.; Khaled, M. A.

    2009-12-01

    Obliquely propagating dust ion acoustic solitary waves (DIASWs) are investigated in hot adiabatic magnetized dusty plasmas consisting of hot adiabatic inertial ions, hot adiabatic inertialess electrons, and negatively/positively charged static dust grains. Using a reductive perturbation method, a nonlinear Zakharov-Kuznetsov equation is derived. The effects of the concentration of negatively/positively charged dust particles and ion-neutral collision on the basic characteristics of DIASWs are studied. The three-dimensional stability of these waves is examined by the use of small-k (long wavelength plane wave) perturbation expansion technique. It is shown that the instability criterion and their growth rate depend on external magnetic field, obliqueness, the concentration of charged dust grains, ion-neutral, and ion-dust collisions.

  10. 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.

  11. Observation of ion-ion counter streaming instability in presheath-sheath region of a mesh grid immersed in low temperature plasma

    NASA Astrophysics Data System (ADS)

    Prasad Kella, Vara; Ghosh, J.; Chattopadhyay, P. K.; Sharma, D.; Saxena, Y. C.

    2017-03-01

    Instabilities in the sheath-presheath region formed in plasma-boundary layers are known to modify the particle flow velocities and their distribution functions, hence influencing the particle transport in this region significantly. In this paper, experimental observations of the ion-ion counter streaming instability excited in the sheath-presheath region of Argon (Ar), Helium (He), and Ar + He plasmas have been reported. These instabilities are excited in the vicinity of a stainless steel mesh grid placed inside the plasma. Floating potential (FP) fluctuations from the grid and from a movable Langmuir probe placed in the sheath-presheath region are measured. The frequency spectra of FP fluctuations in an argon plasma show a dominant broad peak in the range of 10-20 kHz centering around 15 kHz, which is identified as due to the ion-ion counter streaming instability. This frequency peak exists only in the sheath-presheath region and ceases to exist when the mesh grid is covered with a thin metal foil from one side, which restricts the counter streaming of the ions. The measured wave number, k, of the wave matches quite well with the calculated one from the dispersion relation of ion-ion counter streaming instability. The experiments are repeated to study the instability in He and Ar + He (two ion species) plasmas in similar experimental conditions. The neutral pressure threshold for sustenance of this instability has also been observed.

  12. Oblique propagation of low frequency nonlinear waves in an electron depleted magnetized plasma with positive and negative dust

    NASA Astrophysics Data System (ADS)

    Mobarak Hossen, M.; Alam, M. S.; Sultana, S.; Mamun, A. A.

    2016-02-01

    A rigorous theoretical investigation has been carried out to study the properties of obliquely propagating dust-acoustic (DA) waves in an electron depleted magnetized dusty plasma system containing nonextensive q-distributed ions and mobile positively charged, as well as negatively charged dust particles. The reductive perturbation technique is employed to derive the modified Korteweg-de Vries (mK-dV) equation to analyze solitary waves (SWs) and the standard Gardner (SG) equation to analyze SWs and double layers (DLs) solution. The basic features (viz., amplitude, polarity, speed, width, etc.) of the DA mK-dV SWs, SG SWs, and DLs are examined. The comparison between mK-dV SWs and SG SWs is also made. It is seen that the amplitude, polarity, speed, width of such DA SWs, and DLs are significantly modified by the presence of nonextensive ions, external magnetic field, and obliquity angle (the angle between the external magnetic field and wave propagation). The results of our present investigation may be useful for understanding the nonlinear wave propagation in various interstellar space plasma environments where positive and negative dust particles are available.

  13. On the characteristics of obliquely propagating electrostatic structures in non-Maxwellian plasmas in the presence of ion pressure anisotropy

    NASA Astrophysics Data System (ADS)

    Adnan, Muhammad; Qamar, Anisa; Mahmood, Shahzad; Kourakis, Ioannis

    2017-03-01

    The dynamical characteristics of large amplitude ion-acoustic waves are investigated in a magnetized plasma comprising ions presenting space asymmetry in the equation of state and non-Maxwellian electrons. The anisotropic ion pressure is defined using the double adiabatic Chew-Golberger-Low theory. An excess in the superthermal component of the electron population is assumed, in agreement with long-tailed (energetic electron) distribution observations in space plasmas; this is modeled via a kappa-type distribution function. Large electrostatic excitations are assumed to propagate in a direction oblique to the external magnetic field. In the linear (small amplitude) regime, two electrostatic modes are shown to exist. The properties of arbitrary amplitude (nonlinear) obliquely propagating ion-acoustic solitary excitations are thus investigated via a pseudomechanical energy balance analogy, by adopting a Sagdeev potential approach. The combined effect of the ion pressure anisotropy and excess superthermal electrons is shown to alter the parameter region where solitary waves can exist. An excess in the suprathermal particles is thus shown to be associated with solitary waves, which are narrower, faster, and of larger amplitude. Ion pressure anisotropy, on the other hand, affects the amplitude of the solitary waves, which become weaker (in strength), wider (in spatial extension), and thus slower in comparison with the cold ion case.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

    Misra, A. P.; Barman, Arnab

    2014-07-01

    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 mc (≫ 1) which typically depends on T and δ. It is shown that the nonlinear coefficient of the KdV equation vanishes at m = mc, 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.

  16. 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.

  17. Laboratory simulation of laser propagation through plasma sheaths containing ablation particles of ZrB2-SiC-C during hypersonic flight.

    PubMed

    Zang, Qing; Bai, Xiangxing; Ma, Ping; Huang, Jie; Ma, Jing; Yu, Siyuan; Shi, Hongyan; Sun, Xiudong; Liu, Yang; Lu, Yueguang

    2017-02-15

    The optical communication method has potential for solving the blackout problem, which is a big challenge faced in the development of aerospace. Two laser transmission systems were set up to explore the influence of the plasma and the ablation particles on the propagation of the laser. The experimental results indicate that the laser can transmit through the plasma with little attenuation. When there are ablation particles of ZrB2-SiC-C added in the plasma, the intensity of the laser has fluctuations. The work introduced in this Letter can be regarded as basic research of the propagation characters of the laser through plasma sheaths.

  18. Stability of the Halley Cometo-Sheath with Resistivity and Plasma Motion

    NASA Technical Reports Server (NTRS)

    Srivastava, K.

    1993-01-01

    The MHD stability of the cometary inner shealth determined by the balance between the inward Lorentz body force and the outward ion-neutral drag force is investigated by numerically solving the wave equations which include resistivity, plasma motion and plasma pressure with the help of two-point boundary value method.

  19. Modulational instability of dust acoustic waves in dusty plasmas: Modulation obliqueness, background ion nonthermality, and dust charging effects

    SciTech Connect

    El-Taibany, W.F.; Kourakis, I.

    2006-06-15

    The oblique modulational instability of dust acoustic (DA) waves in an unmagnetized warm dusty plasma with nonthermal ions, taking into account dust grain charge variation (charging), is investigated. A nonlinear Schroedinger-type equation governing the slow modulation of the wave amplitude is derived. The effects of dust temperature, dust charge variation, ion deviation from Maxwellian equilibrium (nonthermality) and constituent species' concentration on the modulational instability of DA waves are examined. It is found that these parameters modify significantly the oblique modulational instability domain in the k-{theta} plane. Explicit expressions for the instability rate and threshold have been obtained in terms of the dispersion laws of the system. The possibility and conditions for the existence of different types of localized excitations are also discussed. The findings of this investigation may be useful in understanding the stable electrostatic wave packet acceleration mechanisms close to the Moon, and also enhances our knowledge on the occurrence of instability associated to pickup ions around unmagnetized bodies, such as comets, Mars, and Venus.

  20. Dispersive Nature of High Mach Number Collisionless Plasma Shocks: Poynting Flux of Oblique Whistler Waves

    NASA Astrophysics Data System (ADS)

    Sundkvist, David; Krasnoselskikh, V.; Bale, S. D.; Schwartz, S. J.; Soucek, J.; Mozer, F.

    2012-01-01

    Whistler wave trains are observed in the foot region of high Mach number quasiperpendicular shocks. The waves are oblique with respect to the ambient magnetic field as well as the shock normal. The Poynting flux of the waves is directed upstream in the shock normal frame starting from the ramp of the shock. This suggests that the waves are an integral part of the shock structure with the dispersive shock as the source of the waves. These observations lead to the conclusion that the shock ramp structure of supercritical high Mach number shocks is formed as a balance of dispersion and nonlinearity.

  1. Progress on Quantitative Modeling of rf Sheaths

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    A new quantitative approach for computing the rf sheath potential is described, which incorporates plasma dielectric effects and the relative geometry of the magnetic field and the material boundaries. The new approach uses a modified boundary condition ("rf sheath BC") that couples the rf waves and the sheaths at the boundary. It treats the sheath as a thin vacuum region and matches the fields across the plasma-vacuum boundary. When combined with the Child-Langmuir Law (relating the sheath width and sheath potential), the model permits a self-consistent determination of the sheath parameters and the rf electric field at the sheath-plasma boundary. Semi-analytic models using this BC predict a number of general features, including a sheath voltage threshold, a dimensionless parameter characterizing rf sheath effects, and the existence of sheath plasma waves with an associated resonance. Since the sheath BC is nonlinear and dependent on geometry, computing the sheath potential numerically is a challenging computational problem. Numerical results will be presented from a new parallel-processing finite-element rf wave code for the tokamak scrape-off layer (called "rfSOL"). The code has verified the physics predicted by analytic theory in 1D, and extended the solutions into model 2D geometries. The numerical calculations confirm the existence of multiple roots and hysteresis effects, and parameter studies have been carried out. Areas for future work will be discussed.

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

    PubMed

    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 n(0) ∼ 10(27) cm(-3) and high-magnetic-field B(0)=10(10) 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.

  3. 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.

  4. 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.

  5. Ion Heating in Inhomogeneous Expanding Solar Wind Plasma: The Role of Parallel and Oblique Ion-cyclotron Waves

    NASA Astrophysics Data System (ADS)

    Ozak, N.; Ofman, L.; Viñas, A.-F.

    2015-01-01

    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++ - 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.

  6. 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.

  7. 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)

  8. 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.

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

    NASA Astrophysics Data System (ADS)

    Khaziev, Rinat; Curreli, Davide

    2015-04-01

    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.

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

    SciTech Connect

    Kichigin, G. N.

    2016-01-15

    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.

  11. Oblique discord

    NASA Astrophysics Data System (ADS)

    Xu, Jianwei

    2017-01-01

    Discord and entanglement characterize two kinds of quantum correlations, and discord captures more correlation than entanglement in the sense that even separable states may have nonzero discord. In this paper, we propose a new kind of quantum correlation that we call as oblique discord. A zero-discord state corresponds to an orthonormal basis, while a zero-oblique-discord state corresponds to a basis which is not necessarily orthogonal. Under this definition, the set of zero-discord states is properly contained inside the set of zero-oblique-discord states, and the set of zero-oblique-discord states is properly contained inside the set of separable states. We give a characterization of zero-oblique-discord states via quantum mapping, provide a geometric measure for oblique discord, and raise a conjecture, which if it holds, then we can define an information-theoretic measure for oblique discord. Also, we point out that the definition of oblique discord can be properly extended to some different versions just as the case of quantum discord.

  12. 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.

  13. Linear and nonlinear obliquely propagating ion-acoustic waves in magnetized negative ion plasma with non-thermal electrons

    NASA Astrophysics Data System (ADS)

    Mishra, M. K.; Jain, S. K.; Jain

    2013-10-01

    Ion-acoustic solitons in magnetized low-β plasma consisting of warm adiabatic positive and negative ions and non-thermal electrons have been studied. The reductive perturbation method is used to derive the Korteweg-de Vries (KdV) equation for the system, which admits an obliquely propagating soliton solution. It is found that due to the presence of finite ion temperature there exist two modes of propagation, namely fast and slow ion-acoustic modes. In the case of slow-mode if the ratio of temperature to mass of positive ion species is lower (higher) than the negative ion species, then there exist compressive (rarefactive) ion-acoustic solitons. It is also found that in the case of slow mode, on increasing the non-thermal parameter (γ) the amplitude of the compressive (rarefactive) soliton decreases (increases). In fast ion-acoustic mode the nature and characteristics of solitons depend on negative ion concentration. Numerical investigation in case of fast mode reveals that on increasing γ, the amplitude of compressive (rarefactive) soliton increases (decreases). The width of solitons increases with an increase in non-thermal parameters in both the modes for compressive as well as rarefactive solitons. There exists a value of critical negative ion concentration (α c ), at which both compressive and rarefactive ion-acoustic solitons appear as described by modified KdV soliton. The value of α c decreases with increase in γ.

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. Effect of driving frequency on the electron-sheath interaction and electron energy distribution function in a low pressure capacitively coupled plasmas

    NASA Astrophysics Data System (ADS)

    Sharma, Sarveshwar; Sirse, Nishant; Kaw, Predhiman; Turner, Miles; Ellingboe, Albert R.; InstitutePlasma Research, Gandhinagar, Gujarat Team; School Of Physical Sciences; Ncpst, Dublin City University, Dublin 9, Ireland Collaboration

    2016-09-01

    The effect of driving frequency (27.12-70 MHz) on the electron-sheath interaction and electron energy distribution function (EEDF) is investigated in a low pressure capacitive discharges using a self-consistent particle-in-cell simulation. At a fixed discharge voltage the EEDF evolves from a strongly bi-Maxwellian at low frequency, 27.12 MHz, to a convex type distribution at an intermediate frequency, 50 MHz, and finally becomes a weak biMaxwellian above 50 MHz. The EEDF evolution leads to a two-fold increase in the effective electron temperature up to 50 MHz, whereas the electron density remains constant in this range. After 50MHz, the electron density increases rapidly and the electron temperature decreases. The transition is caused by the transient electric field excited by bursts of high energy electrons interacting strongly with the sheath edge. Above the transition frequency, high energy electrons are confined between two sheaths which increase the ionization probability and thus the plasma density increases.

  19. Numerical and experimental investigations of splat geometric characteristics during oblique impact of plasma spraying

    NASA Astrophysics Data System (ADS)

    Kang, Chang-Wei; Tan, Jiak Kwang; Pan, Lunsheng; Low, Cheng Yee; Jaffar, Ahmed

    2011-10-01

    Splats are obtained on the substrates inclined at different angles (0°, 20°, 40° and 60°) by plasma spraying process and characterized by SEM and WYKO ® optical surface profiler. Numerical model is developed using CFD software FLOW-3D ® to simulate the process of droplet impact, spreading and solidification onto the substrates. Splat characteristics such as spread factor, aspect ratio and fractional factor are defined and compared between simulation and experiment. Fair agreements are obtained. In addition, the impacting behavior including spreading and solidification are analyzed in details from the simulation results. The rates of reduction in droplet kinetic energy during impact, spreading and solidification are also compared between different inclination angles.

  20. Dust in the magnetized sheath

    SciTech Connect

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

    2007-09-15

    In the present work the structure of the magnetized sheath is investigated in the multifluid framework. The ambient magnetic field is assumed parallel to the wall and the effect of the plasma magnetization, plasma ionization, and plasma-neutral collisions on the sheath is examined. It is shown that the width of the non-neutral boundary layer is dependent on the collision frequencies as well as on the plasma magnetization. The size of the sheath layer can decrease with the increase in magnetic field. The increase in the ion-neutral collision can also adversely affect the sheath size. The equilibrium and levitation of the dust particles in a collisional magnetized sheath are shown to depend on the collision frequencies and on the magnetization. Further, the increase in the collision or magnetization invariably leads to the presence of the positively charged grains near the plasma wall suggesting that the grain levitation inside the charged layer is implicitly dependent on the plasma parameters in a nontrivial way.

  1. 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.

  2. 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.

  3. 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

  4. Measurement of the sheath capacitance of a planar probe

    SciTech Connect

    Oh, Se-Jin; Lee, Young-Kwang; Chung, Chin-Wook

    2011-10-15

    The sheath capacitance was measured on a planar probe dc-biased with respect to the plasma potential using the phase sensitive detection method in the region separated from the rf discharge plasmas by an immersed grid. It was observed that the sheath capacitance was negative when the collecting electrode of the probe was positioned downward toward the grid and biased near the plasma potential. This indicates that a double sheath had built up near the probe electrode. This tendency can be explained by the sheath capacitance, which is calculated using Poisson's equation with a non-zero electrical field and an ion velocity condition at the sheath edge.

  5. Collisionless absorption of light waves incident on overdense plasmas with steep density gradients

    SciTech Connect

    Yang, T.Y.B.; Kruer, W.L.; Langdon, A.B.

    1995-07-31

    Collisionless absorption of laser light incident on overdense plasmas with steep density gradients is studied analytically and numerically. For the normal incidence case, it is shown that both sheath inverse bremsstrahlung and the anomalous skin effect are limiting cases of the same collisionless absorption mechanism. Using particle-in-cell (PIC) plasma simulations, the effects of finite sheath-transit time and finite density gradient are investigated. The analyses are extended to oblique incident cases. For p-polarized obliquely incident light, the results are significantly different from those for the normal incidence case. Most noticeable is the absorption enhancement for the p-polarized light due to the interaction of the electrons with the normal (parallel to the density gradient) component of the laser electric field in the sheath region.

  6. 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.

  7. Study of a dual frequency capacitively coupled rf discharge in the background of multi-component plasma and its validation by a simple analytical sheath model

    NASA Astrophysics Data System (ADS)

    Bhuyan, Heman; Saikia, Partha; Favre, Mario; Wyndham, Edmundo; Veloso, Felipe

    2016-10-01

    The behavior of a phase-locked dual frequency capacitively coupled rf discharges (2f-CCRF) in the background of multi-component plasma is experimentally studied by rf current-voltage measurements and optical emission spectroscopy (OES). The multi-component plasma is produced by adding hydrogen to the argon CCRF discharge. Variation of experimental parameters, like working pressure, low frequency (LF) and high frequency (HF) rf power indicate significant changes in the electron density and temperature as well as the DC self-bias developed on the power electrode. It is observed that the electron density decreases as the percentage of hydrogen increases in the argon plasma while the electron temperature follows opposite trend. An analytical sheath model for the 2f-CCRF discharge in the background of multi-component plasma is developed and its prediction on the observed variation of DC self-bias is well agreed with the experimental observations. Authors acknowledge Proyecto Puente No P1611 and FONDECYT 3160179.

  8. 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.

  9. 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.

  10. 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.

  11. Benchmarking sheath subgrid boundary conditions for macroscopic-scale simulations

    NASA Astrophysics Data System (ADS)

    Jenkins, T. G.; Smithe, D. N.

    2015-02-01

    The formation of sheaths near metallic or dielectric-coated wall materials in contact with a plasma is ubiquitous, often giving rise to physical phenomena (sputtering, secondary electron emission, etc) which influence plasma properties and dynamics both near and far from the material interface. In this paper, we use first-principles PIC simulations of such interfaces to formulate a subgrid sheath boundary condition which encapsulates fundamental aspects of the sheath behavior at the interface. Such a boundary condition, based on the capacitive behavior of the sheath, is shown to be useful in fluid simulations wherein sheath scale lengths are substantially smaller than scale lengths for other relevant physical processes (e.g. radiofrequency wavelengths), in that it enables kinetic processes associated with the presence of the sheath to be numerically modeled without explicit resolution of spatial and temporal sheath scales such as electron Debye length or plasma frequency.

  12. Comment on "Droplet shaped anode double layer and electron sheath formation in magnetically constricted anode" [Phys. Plasmas 23, 013502 (2016)

    NASA Astrophysics Data System (ADS)

    Gruenwald, J.

    2016-02-01

    This comment aims at clarifying some points in the very recent work of Chauhan et al. who presented an experimental study of a fireball (FB) configuration in a magnetized plasma, similar to R. L. Stenzel et al., Plasma Sources Sci. Technol. 21, 015012 (2012).

  13. Numerical simulation of sheath structure and current-voltage characteristics of a conductor-dielectric disk in a plasma

    NASA Technical Reports Server (NTRS)

    Chaky, R. C.; Nonnast, J. H.; Enoch, J.

    1981-01-01

    A computer program is being developed to simulate the interaction of a plasma with a conducting disk. Two configurations are examined: (1) the conductor is a 'button' in the center of a larger dielectric disk, and (2) the conducting disk is covered by a dielectric disk to the same size with a circular hole in the center of the dielectric, exposing a region of conductor. Results of the electrostatic plasma simulation are presented both with and without secondary electron emission from the dielectric; characteristic curves and voltage profiles are included.

  14. 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.

  15. Theory of the electron sheath and presheath

    DOE PAGES

    Scheiner, Brett; Baalrud, Scott D.; Yee, Benjamin T.; ...

    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

  16. 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.

  17. 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.

  18. 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

  19. Effect of the reference electrode size on the ionization instability in the plasma sheath of a small positively biased electrode

    SciTech Connect

    Bliokh, Y. P.; Brodsky, Yu. L.; Chashka, Kh. B.; Felsteiner, J.; Slutsker, Ya. Z.

    2011-06-01

    It is well known that additional ionization in the vicinity of a positively biased electrode immersed into a weakly ionized plasma is responsible for a hysteresis in the electrode current-voltage characteristics and the current self-oscillations rise. Here we show both experimentally and theoretically that under certain conditions these phenomena cannot be correctly interpreted once considered separately from the reference electrode current-voltage characteristics. It is shown that small electrodes can be separated into three groups according to the relation between the electrode and the reference electrode areas. Each group is characterized by its own dependence of the collected current on the bias voltage.

  20. 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)

  1. Characteristics of a Sheath with Secondary Electron Emission in the Double Walls of a Hall Thruster

    NASA Astrophysics Data System (ADS)

    Duan, Ping; Li, Xi; Shen, Hongjuan; Chen, Long; E, Peng

    2012-09-01

    In order to investigate the effects of secondary electrons, which are emitted from the wall, on the performance of a thruster, a one-dimensional fluid model of the plasma sheath in double walls is applied to study the characteristics of a magnetized sheath. The effects of secondary electron emission (SEE) coefficients and trapping coefficients, as well as magnetic field, on the structure of the plasma sheath are investigated. The results show that sheath potential and wall potential rise with the increment of SEE coefficient and trapping coefficient which results in a reduced sheath thickness. In addition, magnetic field strength will influence the sheath potential distributions.

  2. 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.

  3. 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.

  4. Experimental Observation of Sheath-presheath Instabilities

    NASA Astrophysics Data System (ADS)

    Kella, Vara Prasad; Ghosh, Joydeep; Sharma, Devendra; Chattopadhyay, Prabal K.

    2016-10-01

    Instabilities in the Sheath-presheath regime are most important phenomena that can affect the plasma-wall interaction. These instabilities can modify the particle flow velocities and distribution functions in that regime. In this present work, instabilities exists in the sheath-presheath in a low temperature plasma are observed. Experiments are carried in single ion species argon plasma and multi ion species Ar-He plasma. Experiments are carried in a stainless steel chamber with filament discharge plasma. Sheath is produced around a stainless steel grid at center of the chamber. Fluctuations from the grid and cylindrical Langmuir probe are recorded. Langmuir probe is used to get the floating potential fluctuations from presheath and bulk plasma as well. In single ion species argon plasma, there are two instabilities observed namely ion-ion counter streaming instability through mesh grid and ion acoustic instability respectively arises in the presheath. In case of multi-ion Ar-He plasma, two stream instability also explored. The neutral pressure threshold for the sustain of these instabilities also observed.

  5. 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.

  6. 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.

  7. Effect of collisions on photoelectron sheath in a gas

    NASA Astrophysics Data System (ADS)

    Sodha, Mahendra Singh; Mishra, S. K.

    2016-02-01

    This paper presents a study of the effect of the collision of electrons with atoms/molecules on the structure of a photoelectron sheath. Considering the half Fermi-Dirac distribution of photo-emitted electrons, an expression for the electron density in the sheath has been derived in terms of the electric potential and the structure of the sheath has been investigated by incorporating Poisson's equation in the analysis. The method of successive approximations has been used to solve Poisson's equation with the solution for the electric potential in the case of vacuum, obtained earlier [Sodha and Mishra, Phys. Plasmas 21, 093704 (2014)], being used as the zeroth order solution for the present analysis. The inclusion of collisions influences the photoelectron sheath structure significantly; a reduction in the sheath width with increasing collisions is obtained.

  8. What is the size of a floating sheath? An answer

    NASA Astrophysics Data System (ADS)

    Voigt, Farina; Naggary, Schabnam; Brinkmann, Ralf Peter

    2016-09-01

    The formation of a non-neutral boundary sheath in front of material surfaces is universal plasma phenomenon. Despite several decades of research, however, not all related issues are fully clarified. In a recent paper, Chabert pointed out that this lack of clarity applies even to the seemingly innocuous question ``What the size of a floating sheath?'' This contribution attempts to provide an answer that is not arbitrary: The size of a floating sheath is defined as the plate separation of an equivalent parallel plate capacitor. The consequences of the definition are explored with the help of a self-consistent sheath model, and a comparison is made with other sheath size definitions. Deutsche Forschungsgemeinschaft within SFB TR 87.

  9. Sheath waves observed on OEDIPUS A

    NASA Astrophysics Data System (ADS)

    James, H. G.; Balmain, K. G.; Bantin, C. C.; Hulbert, G. W.

    1995-01-01

    An important novel feature of the tethered sounding rocket experiment OEDIPUS A (Observations of Electric-field Distributions in the Ionospheric Plasma—A Unique Strategy) was its direct excitation and detection of electromagnetic waves on conductors in space plasmas. We present quantitative evidence about sheath waves excited in the ionosphere by a high-frequency transmitter on one end of the 1-km tether and detected by a synchronized receiver on the other end. An important characteristic of sheath waves is their sequence of sharply defined passbands and stop bands in the frequency range 0.1-5 MHz. The lowest passband is between 0.1 MHz and the plasma frequency near 2 MHz, the bandwidth where existing theory predicts sheath waves. Resonance fringes in this band have been scaled to determine the phase and group refractive indices of sheath waves. These agree reasonably well with the theory, considering the approximations therein. Passbands and stop bands observed in the range between 2 and 5 MHz are not expected on the basis of the current theory. In this range, band limits have clear signatures of the interaction of the tether fields with electrostatic cyclotron waves. Finite wire moment method modeling of the payload shows that in the low-frequency passband, RF coupling along the tether is increased by 20 dB over vacuum conditions. Similarly, isolation is greater than vacuum isolation in the stop bands. Because sheath waves at frequencies up to 2 MHz are guided efficiently along conductors in plasma, they are a significant design issue in the electromagnetic compatibility of avionics at frequencies up to HF on large metal space structures.

  10. Obliquity along plate boundaries

    NASA Astrophysics Data System (ADS)

    Philippon, Mélody; Corti, Giacomo

    2016-12-01

    Most of the plate boundaries are activated obliquely with respect to the direction of far field stresses, as roughly only 8% of the plate boundaries total length shows a very low obliquity (ranging from 0 to 10°, sub-orthogonal to the plate displacement). The obliquity along plate boundaries is controlled by (i) lateral rheological variations within the lithosphere and (ii) consistency with the global plate circuit. Indeed, plate tectonics and magmatism drive rheological changes within the lithosphere and consequently influence strain localization. Geodynamical evolution controls large-scale mantle convection and plate formation, consumption, and re-organization, thus triggering plate kinematics variations, and the adjustment and re-orientation of far field stresses. These geological processes may thus result in plate boundaries that are not perpendicular but oblique to the direction of far field stresses. This paper reviews the global patterns of obliquity along plate boundaries. Using GPlate, we provide a statistical analysis of present-day obliquity along plate boundaries. Within this framework, by comparing natural examples and geological models, we discuss deformation patterns and kinematics recorded along oblique plate boundaries.

  11. Evolution of Mercury's Obliquity

    NASA Astrophysics Data System (ADS)

    Yseboodt, M.; Margot, J. L.

    2005-05-01

    Mercury has a near-zero obliquity, i.e. its spin axis is nearly perpendicular to its orbital plane. In order to constrain the size of the planet's core with the framework suggested by Peale (1976), the obliquity must be known precisely. Rambaux and Bois (2004) have suggested that Mercury's obliquity varies on thousand-year timescales due to planetary perturbations, potentially ruining the feasibility of Peale's experiment. We use a Hamiltonian approach (free of energy dissipation) to study the spin-orbit evolution of Mercury subject to planetary perturbations. We can reproduce an obliquity evolution similar to that of Rambaux and Bois (2004) if we introduce the planetary perturbations abruptly, i.e. by a step function. But if we introduce the planetary effects smoothly starting from an equilibrium position corresponding to the Cassini state (where the spin axis, the normal to the invariable plane and the normal to the orbital plane are aligned), the thousand-year oscillations in the obliquity do not appear. We find an equilibrium value for the obliquity of ˜1.6 arcmin for (B-A)/C = 1.2 10-4 and (C-A)/C = 2.4 10-4, which are combinations of the moments of inertia corresponding to the Mariner 10 gravity data. Our results indicate that planetary perturbations do not force short-period oscillations in Mercury's obliquity, even though such oscillations may appear in numerical integrations involving artificial departures from the Cassini state or the sudden onset of perturbations. Peale (2004) has shown that the periods of damping of the free motions (free precession or free libration) are short compared to the age of the solar system, such that oscillations in obliquity are expected to decay. In the absence of excitation processes, Mercury's obliquity will remain constant, suggesting that one of the important conditions for the success of Peale's experiment is realized.

  12. Boundary conditions for electropositive and electronegative radio-frequency sheaths

    NASA Astrophysics Data System (ADS)

    Sobolewski, Mark

    2016-09-01

    Plasma sheaths play a dominant role in determining ion bombardment energies. To optimize plasma processes, sheaths must be understood and carefully controlled, which requires predictive models. One very efficient approach is to only model the sheath, excluding the bulk plasma. This approach, however, requires boundary conditions at the plasma/sheath boundary. Models that use the step approximation for electron density require initial ion velocities. More exact models with Boltzmann electrons (and, for electronegative discharges, negative ions) require the electron temperature (and the temperature and relative density of negative ions). It is often assumed that these boundary conditions have negligible effects on ion energies, but, for certain conditions in radio-frequency sheaths, this is not true. Analytic models as well as numerical simulations show that, at low frequencies (<= 1 MHz) and high bias voltages, the amplitude of the low-energy peak in ion energy distributions (IEDs) at the electrode is very sensitive to the boundary conditions. By measuring IEDs and sheath voltage waveforms, we obtain the most appropriate values of the boundary conditions for electropositive (Ar) as well as electronegative (CF4) discharges and insight into their presheath dynamics.

  13. 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.

  14. Modeling, Theoretical and Observational Studies of the Lunar Photoelectron Sheath

    NASA Astrophysics Data System (ADS)

    Poppe, Andrew Reinhold

    2011-08-01

    The Moon, lacking an atmosphere and a global magnetic field, is directly exposed to both solar ultraviolet radiation and a variety of ambient plasmas. On the lunar dayside, a photoelectron sheath develops and the surface typically charges positively since the photoemission current is at least an order-of-magnitude greater than any ambient current. This sheath dominates the nearsurface plasma environment and controls the charging, levitation and transport of micron-sized dust grains. In this thesis, we first model the lunar near-surface plasma environment via a one-dimensional particle-in-cell code. The sheath potential, electric field and plasma densities are presented over a wide range of plasma parameters. Additionally, the charging and transport of micron- and submicron sized dust grains is modeled via a test-particle approach in an attempt to explain Apolloera observations of lunar dust dynamics. Secondly, we present a comparison of the particle-in-cell results with theoretical, kinetic derivations of the lunar photoelectron sheath. We extend previous theories to include the presence of a kappa-distribution for the solar wind electrons. Finally, we present a comparison of in-situ measurements of the lunar photoelectron sheet in the terrestrial plasma sheet by the Lunar Prospector Electron Reflectometer with particle-in-cell simulations to confirm the presence of non-monotonic sheath potentials above the Moon. Future work in all three sections, (simulation, theory and observation) is presented as a guide for continuing research.

  15. 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.

  16. 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.

  17. Sheath effects on DEMETER ion drift measurements

    NASA Astrophysics Data System (ADS)

    Marchand, Richard; Knutson, Nelson; Berthelier, Jean-Jacques

    2010-08-01

    The "Instrument d'Analyse du Plasma" on DEMETER includes an ion drift meter used to measure the direction of the incoming ram plasma ( Berthelier et al., 2006a, b ). Given the velocity of the satellite, and expected flow velocities of plasma along DEMETER's orbit, it is estimated that at mid latitudes, the direction of incident plasma as measured by IAP should be within approximately 2° of the ram direction. Yet, significantly larger angular deviations are measured routinely. An important assumption made in the interpretation of onboard instruments, such as IAP, is that neither the spacecraft nor the instrument significantly perturb the plasma that is being measured. In view of the large observed angular deviations, this paper examines the possible effect of the electrostatic sheath surrounding IAP. This is done with the 3D PIC simulation code PTetra. The model uses a full 3D particle in cell code with unstructured tetrahedral mesh capable of accurately representing the satellite geometry. The mesh is also adaptive so as to provide a fine spatial resolution in the vicinity of the particle sensor where it is needed, and a coarse resolution in regions where plasma parameters vary over a longer scale length. Calculation results show that while particle deflection associated with the electrostatic sheath near IAP can account for appreciable angular deflections for representative ionospheric plasmas, they are typically smaller than the ones observed. Additionally, the model is unable to reproduce the latitudinal dependence of the observed large deflection angles. It is concluded that sheath effects may cause appreciable distortions on the IAP type of ion flow meter instruments, and on other particle sensors in general. The larger observed deviations and their latitudinal dependence, however, must be attributable to other physical processes not accounted for in the model.

  18. 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.

  19. 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.

  20. Mars Obliquity Cycle Illustration

    NASA Technical Reports Server (NTRS)

    2008-01-01

    The tilt of Mars' spin axis (obliquity) varies cyclically over hundreds of thousands of years, and affects the sunlight falling on the poles. Because the landing site of NASA's Phoenix Mars Lander is so near the north pole, higher sun and warmer temperatures during high obliquity lead to warmer, more humid surface environments, and perhaps thicker, more liquid-like films of water in soil.

    The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  1. 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.

  2. 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.

  3. The obliquity of Pluto

    NASA Technical Reports Server (NTRS)

    Dobrovolskis, A. R.; Harris, A. W.

    1983-01-01

    Pluto's obliquity (the angle between its spin axis and orbit normal) varies between 102 and 126 deg over a period of about 3 million years. These oscillations are nearly sinusoidal and quite stable, leading to only modest changes in the insolation regime. Thus, Pluto's rotation has been slightly retrograde ever since its current orbit and rotation rate were established.

  4. Modelling Electrostatic Sheath Effects on Swarm Electric Field Instrument Measurements

    NASA Astrophysics Data System (ADS)

    Marchand, R.; Burchill, J. K.; Knudsen, D. J.

    2010-10-01

    The Electric Field Instrument (EFI) was designed to measure ionospheric ion flow velocities, temperatures and distribution functions at the ram face of the European Space Agency’s Swarm spacecraft. These flow velocities, combined with the known orbital velocity of the satellite and local magnetic field, will be used to infer local electric fields from the relation E=- v× B. EFI is among a class of many particle sensors and flow meters mounted on satellites to monitor in situ plasma conditions. The interpretation of the measurements made with EFI and similar sensors relies on a spacecraft sheath model. A common approach, valid in the relatively cold and dense ionospheric plasma, is to assume a potential drop in a thin sheath through which particle deflection and energisation can be calculated analytically. In such models, sheath effects only depend on the spacecraft floating potential, and on the angle of incidence of particles with respect to the normal to the surface. Corrections to measurements are therefore local as they do not depend on the geometry of nearby objects. In an actual plasma, satellites are surrounded by electrostatic sheaths with a finite thickness. As a result, local corrections to particle distribution functions can only be seen as an approximation. A correct interpretation of measured particle fluxes or particle distribution functions must, at least in principle, account for the extent and shape of the sheath in the vicinity of the measuring instrument. This in turn requires a careful analysis of the interaction of the satellite with the surrounding plasma, while accounting for detailed aspects of the geometry, as well as for several physical effects. In this paper, the validity of the thin sheath model is tested by comparing its predictions with detailed PIC (Particle In Cell) calculations of satellite-plasma interaction. Deviations attributed to sheath finite thickness effects are calculated for EFI measurements, with representative plasma

  5. Continuum kinetic and multi-fluid simulations of classical sheaths

    NASA Astrophysics Data System (ADS)

    Cagas, P.; Hakim, A.; Juno, J.; Srinivasan, B.

    2017-02-01

    The kinetic study of plasma sheaths is critical, among other things, to understand the deposition of heat on walls, the effect of sputtering, and contamination of the plasma with detrimental impurities. The plasma sheath also provides a boundary condition and can often have a significant global impact on the bulk plasma. In this paper, kinetic studies of classical sheaths are performed with the continuum kinetic code, Gkeyll, which directly solves the Vlasov-Maxwell equations. The code uses a novel version of the finite-element discontinuous Galerkin scheme that conserves energy in the continuous-time limit. The fields are computed using Maxwell equations. Ionization and scattering collisions are included; however, surface effects are neglected. The aim of this work is to introduce the continuum kinetic method and compare its results with those obtained from an already established finite-volume multi-fluid model also implemented in Gkeyll. Novel boundary conditions on the fluids allow the sheath to form without specifying wall fluxes, so the fluids and fields adjust self-consistently at the wall. The work presented here demonstrates that the kinetic and fluid results are in agreement for the momentum flux, showing that in certain regimes, a multi-fluid model can be a useful approximation for simulating the plasma boundary. There are differences in the electrostatic potential between the fluid and kinetic results. Further, the direct solutions of the distribution function presented here highlight the non-Maxwellian distribution of electrons in the sheath, emphasizing the need for a kinetic model. The densities, velocities, and the potential show a good agreement between the kinetic and fluid results. However, kinetic physics is highlighted through higher moments such as parallel and perpendicular temperatures which provide significant differences from the fluid results in which the temperature is assumed to be isotropic. Besides decompression cooling, the heat flux

  6. 21 CFR 884.5320 - Glans sheath.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 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...

  7. 21 CFR 884.5320 - Glans sheath.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 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...

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. Magnetic Field Generation in Core-sheath Jets via the Kinetic Kelvin-Helmholtz Instability

    NASA Astrophysics Data System (ADS)

    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.

    2014-09-01

    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.

  13. Sheath-accumulating Propagation of Interplanetary Coronal Mass Ejection

    NASA Astrophysics Data System (ADS)

    Takahashi, Takuya; Shibata, Kazunari

    2017-03-01

    Fast interplanetary coronal mass ejections (ICMEs) are the drivers of strong space weather storms such as solar energetic particle events and geomagnetic storms. The connection between the space-weather-impacting solar wind disturbances associated with fast ICMEs at Earth and the characteristics of causative energetic CMEs observed near the Sun is a key question in the study of space weather storms, as well as in the development of practical space weather prediction. Such shock-driving fast ICMEs usually expand at supersonic speeds during the propagation, resulting in the continuous accumulation of shocked sheath plasma ahead. In this paper, we propose a “sheath-accumulating propagation” (SAP) model that describes the coevolution of the interplanetary sheath and decelerating ICME ejecta by taking into account the process of upstream solar wind plasma accumulation within the sheath region. Based on the SAP model, we discuss (1) ICME deceleration characteristics; (2) the fundamental condition for fast ICMEs at Earth; (3) the thickness of interplanetary sheaths; (4) arrival time prediction; and (5) the super-intense geomagnetic storms associated with huge solar flares. We quantitatively show that not only the speed but also the mass of the CME are crucial for discussing the above five points. The similarities and differences between the SAP model, the drag-based model, and the“snow-plow” model proposed by Tappin are also discussed.

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Ion temperature effects on its chaotic behavior in ion-sheath

    NASA Astrophysics Data System (ADS)

    Soleimani-Iraei, M.; Esfandyari-Kalejahi, A.; Sobhanian, S.

    2017-02-01

    Nonlinear dynamical behavior of an ion with finite temperature in a driven plasma ion-sheath has been studied by a numerical solution of fluid equations. Using the concepts of the nonlinear dynamical system theory, the conditions under which the dynamical behavior of the ion becomes chaotic have been investigated. The numerical results have revealed that there is an order-chaos-order transition in the isothermal plasma ion-sheath due to the external oscillating electric field. In the case of an adiabatic ion-sheath, even with a strong external electric field, no chaotic motion has appeared.

  1. Phase-resolved measurements of ion velocity in a radio-frequency sheath.

    PubMed

    Jacobs, Brett; Gekelman, Walter; Pribyl, Pat; Barnes, Michael

    2010-08-13

    The time-dependent argon-ion velocity distribution function above and within the plasma sheath of an rf-biased substrate has been measured using laser-induced fluorescence in a commercial plasma processing tool. Discharge parameters were such that the 2.2 MHz rf-bias period was on the order of the ion transit time through the sheath (τ{ion}/τ{rf}=0.3). This work embodies the first time-resolved measurement of ion velocity distribution functions within an rf-biased sheath over a large area (30 cm diameter) silicon wafer substrate.

  2. 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.

  3. 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.

  4. Optic Nerve Sheath Meningiomas.

    PubMed

    Radhakrishnan, Sunita; Lee, Michael S

    2005-01-01

    Optic nerve sheath meningiomas (ONSMs) grow slowly and, if untreated, patients may have stable visual function for up to several years. Treatment of an ONSM may lead to vision loss (radiation retinopathy or optic neuropathy). Therefore, observation is recommended for a patient with ONSM and relatively preserved visual acuity, color vision, pupils, and visual fields. Follow-up every 4 to 6 months initially is recommended extending to annual examinations if visual function and tumor size remain stable for a few years. Neuroimaging can be repeated every 12 months. An undisputed decline in visual function or any intracranial extension warrants treatment of the ONSM. The treatment of choice for a tumor confined to the orbit is stereotactic fractionated radiation. Stereotactic fractionated radiation uses multiple small doses of radiation using tight margins. A reasonable alternative, three-dimensional conformal fractionated radiation uses computed tomography-guided planning but usually requires wider margins. Conventional radiation uses much wider margins and would not be recommended for treatment of ONSM. The radiation can be administered during 5 to 6 weeks in 28 daily fractions of 1.8 to 2 Gy/fraction to a total of 50.4 to 56 Gy. Many patients have improvement or stabilization of their visual function. Gamma knife radiosurgery does not have a role in ONSM because the required dose is toxic to the optic nerve. A tumor that extends intracranially may be treated with fractionated radiation if any vision remains. Surgical excision can be considered for significant intracranial extension but this often leads to complete vision loss in the ipsilateral eye. A blind, disfigured eye also may be treated with en bloc surgical resection of the meningioma.

  5. 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.

  6. 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.

  7. Assessment Of An Oblique ECE Diagnostic For ITER

    SciTech Connect

    Gary Taylor and Robert W. Harvey

    2009-07-15

    A systematic disagreement between the electron temperature measured by electron cyclotron emission (TECE) and laser Thomson scattering (TTS), that increases with TECE, is observed in JET and TFTR plasmas, such that TECE ~ 1.2 TTS when TECE ~ 10 keV. The disagreement is consistent with a non-Maxwellian distortion in the bulk electron momentum distribution. ITER is projected to operate with Te(0) ~ 20-40 keV so the disagreement between TECE and TTS could be > 50%, with significant physics implications. The GENRAY ray tracing code predicts that a two-view ECE system, with perpendicular and moderately oblique viewing antennas, would be sufficient to reconstruct a two-temperature bulk distribution. If the electron momentum distribution remains Maxwellian the moderately oblique view could still be used to measure Te(R). A viewing dump will not be required for the oblique view and plasma refraction will be minimal. The oblique view has a similar radial resolution to the perpendicular view, but with some reduction in radial coverage. Oblique viewing angles of up to 20o can be implemented without a major revision to the front end of the existing ITER ECE diagnostic design.

  8. Anode Sheath Contributions in Plasma Thrusters

    DTIC Science & Technology

    1994-03-01

    DGEA4220 1 IWITP SDtEW * NC, uaC, "FLAO, JSTART, NSQ , NQUSED, UDOZ423 0 2 ESTEP, N73, N33.3NW, 3331CR, NUVE1 * NSAVE2 , NSQUL * UD4E240 3 NY, IDM, NO...DABS(X-XRD)*10.DO DOZA4720 EPSC - TOL DOZA4 730 JSTART a 0 DGMA4 740 N0O N DG3A4750 NSQ a 3030 DGEA4760 EPSJ aDSQRT (UR3UND) DGRM 770 MaCUT 0...NSTEP, NFE,NJE, NSQ , DGRS0360 1 I,METH,MITER, NQ, L, IDOUB,MFOLD, NOLD, IRET,MEO, DGRS0370 2 MIO,IWEVAL,MAXDER,LMAX,IREDO,J,NSTEPJ,J1,J2, DGRS0380 3 M

  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. Obliquity Tides in Hot Jupiters

    NASA Astrophysics Data System (ADS)

    Peale, S. J.

    Tidal dissipation in HD209458b while it has a very high obliquity has been proposed as a means of inflating the planet to its observed oversize (Winn and Holman, 2005). The high obliquity is maintained by the planet's being trapped into Cassini state 2 at an obliquity near 90° while the planet maintains a rotation rate synchronous with its orbital mean motion. In a Cassini state the spin axis and orbit normal remain coplanar with the normal to the Laplace plane as they precess around the latter, where the orbit has a significant inclination to the Laplace plane. The orbit of HD209458b is inclined to equatorial plane of the star by about 4°. If the stellar equator plane is coincident with the plane of the initially massive nebula, that plane is the Laplace plane on which the orbit is precessing. A planet can evolve to Cassini state 2 by tidal dissipation on a time scale comparable with that of the retardation of the spin rate. The latter time scale can become relatively short as the planet migrates toward the star. While the nebula is there, the orbital precession rate is rapid, Cassini state 2 has a small obliquity, and tidal friction will drive the planet to that state. That evolution may not occur for cases where the obliquity of state 2 is relatively large. As the nebula is dispersed, the orbital precession slows with the result that the Cassini state obliquity increases. The spin follows the Cassini state to high obliquity because the solid angle traced by the spin as it precesses about the Cassini state position is an adiabatic invariant. With no nebula, only the quadrupole moment of the star is left to cause the orbit to precess. At the slow precession rate thus induced, the obliquity of the Cassini state is nearly 90°, which if maintained while the spin remains synchronous with the orbital motion, causes the dissipation inferred by Winn and Holman. Implicit in this scenario is the assumption that the synchronous rotation is somehow maintained. Authors of

  11. Ionospheric heating with oblique HF waves

    NASA Astrophysics Data System (ADS)

    Field, Edward C., Jr.; Bloom, Ron M.

    1990-10-01

    Calculations of ionospheric electron density perturbations and ground-level signal changes produce by intense oblique high frequency (HF) transmitters are presented. This analysis considers radio field focusing at caustics, the consequent joule-heating of the surrounding plasma, heat conduction, diffusion, and recombination processes: these being the effects of a powerful oblique 'modifying' wave. It neglects whatever plasma instabilities might occur. Then effects on a secondary 'test' wave that is propagated along the same path as the first are investigated. Calculations predict ground-level field-strength reductions of several dB in the test wave for modifying waves having ERP in the 85 to 90 dBW range. These field-strength changes are similar in sign, magnitude, and location to ones measured in Soviet experiments. The results are sensitive to the model ionosphere assumed, so future experiments should employ the widest possible range of frequencies and propagation conditions. An effective power of 90 dBW seems to be a sort of threshold that, if exceeded, results in substantial rather than small signal changes. The conclusions are based solely on joule-heating and subsequent defocusing of waves passing through caustic regions.

  12. Resonance Cone Interaction With a Self-Consistent Radio-Frequency Sheath

    SciTech Connect

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

    2008-11-07

    We study the propagation of lower-hybrid-type resonance cones in a tenuous magnetized plasma, and, in particular, their interaction with, and reflection from, the plasma sheath near a conducting wall. The sheath is modeled as a vacuum gap whose width is given by the Child-Langmuir law. The application of interest is when the resonance cones are launched (parasitically) by an ion-cyclotron radio-frequency antenna in a typical rf-heated tokamak fusion experiment. We calculate the fraction of launched voltage in the resonance cones that is transmitted to the sheath, and show that it has a sensitive thresholdlike turn on when a critical parameter reaches order unity. Above threshold, the fractional voltage transmitted to the sheath is order unity, leading to strong and potentially deleterious rf-wall interactions in tokamak rf heating experiments. Below threshold, these interactions can be avoided.

  13. Fully kinetic model of breakdown during sheath expansion after interruption of vacuum arcs

    NASA Astrophysics Data System (ADS)

    Wang, Zhenxing; Wang, Haoran; Zhou, Zhipeng; Tian, Yunbo; Geng, Yingsan; Wang, Jianhua; Liu, Zhiyuan

    2016-08-01

    Research on sheath expansion is critical to the understanding of the dielectric recovery process in a vacuum interrupter after interruption of vacuum arcs. In this paper, we investigated how residual plasma affects breakdown in the sheath expansion period after the current zero. To simulate sheath expansion and breakdown, we developed a fully kinetic particle-in-cell Monte Carlo collision model with one spatial dimension and three velocity dimensions. The model accounted for various collisions, including ionization, excitation, elastic collisions, charge exchange, and momentum exchange, and we added an external circuit to the model to make the calculations self-consistent. The existence of metal vapor slowed the sheath expansion in the gap and caused high electric field formation in front of the cathode surface. The initial residual plasma, which was at sufficiently low density, seemed to have a limited impact on breakdown, and the metal vapor dominated the breakdown in this case. Additionally, the breakdown probability was sensitive to the initial plasma density if the value exceeded a specific threshold, and plasma at sufficiently high density could mean that breakdown would occur more easily. We found that if the simulation does not take the residual plasma into account, it could overestimate the critical value of the metal vapor density, which is always used to describe the boundary of breakdown after interruption of vacuum arcs. We discussed the breakdown mechanism in sheath expansion, and the breakdown is determined by a combination of metal vapor, residual plasma, and the electric field in front of the cathode surface.

  14. 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.

  15. 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.

  16. Habitable planets with high obliquities.

    PubMed

    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.

  17. 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.

  18. Plasma and MHD Control of Oblique Shocks

    DTIC Science & Technology

    2007-11-02

    series of energy addition pulses is shown in Fig. 1. These are five frames from a ‘movie’ that show the dynamics of the interaction. Fig. 2 shows the...operating in the self-powered mode. 4.1. The model As in Refs. 15, 36, and 37, we consider hypersonic gas flow along a series of compression ramps...opposite to the Faraday electromotive force. This effect was indeed observed in all computed cases. As an example, Fig. 9 shows the current profile

  19. On radiative acceleration in spine-sheath structured blazar jets

    NASA Astrophysics Data System (ADS)

    Chhotray, A.; Nappo, F.; Ghisellini, G.; Salafia, O. S.; Tavecchio, F.; Lazzati, D.

    2017-04-01

    It has been proposed that blazar jets are structured, with a fast spine surrounded by a slower sheath or layer. This structured jet model explains some properties of their emission and morphology. Because of their relative motion, the radiation produced by one component is seen amplified by the other, thus enhancing the inverse Compton emission of both. Radiation is emitted anisotropically in the comoving frames and causes the emitting plasma to recoil. As seen in the observer frame, this corresponds to a deceleration of the fastest component (the spine) and an acceleration of the slower one (the layer). While the deceleration of the spine has already been investigated, here we study for the first time the acceleration of the sheath and find self-consistent velocity profile solutions for both the spine and the sheath while accounting for radiative cooling. We find that the sheath can be accelerated to the velocities required by the observations if its leptons remain energetic in the acceleration region, assumed to be of the order of ∼100 Schwarzschild radii, demanding continuous injection of energetic particles in that region.

  20. Oblique ionospheric reflections in the MARSIS data set

    NASA Astrophysics Data System (ADS)

    Andrews, D. J.; Duru, F.; Morgan, D. D.; Opgenoorth, H. J.; Witasse, O. G.; Withers, P.

    2012-12-01

    In addition to reflections from the Martian ionosphere along the nadir direction, the Mars Advanced Radar for Sub-surface and Ionospheric Sounding (MARSIS) on board ESA's Mars Express (MEX) orbiter frequently detects 'oblique reflections' from additional targets away from the nadir direction. Such oblique reflections have been attributed to the presence of anomalous horizontal structure within the ionosphere, in which the ionospheric scale height is thought to have increased in regions where Mars' remnant crustal magnetic field has a 'open' or cusp-like configuration, possibly allowing for the heating of the ionosphere by precipitating solar wind plasma. This spatial structuring gives constant-density surfaces which are not parallel to the planet's surface, from which the sounding pulse from the MARSIS instrument can be reflected back towards the spacecraft at what would otherwise be oblique incidence. These oblique reflections form distinctive hyperbolas in time and apparent range, the apices of which are generally above the surrounding ionosphere, strongly suggesting that they have an extended horizontal structure. Here, employing the substantial MARSIS data set, we examine both the spatial distribution and repeatability of detection of these oblique reflections. These results are then related to the highly structured Martian crustal magnetic field, utilising a simplified ray-tracing code.

  1. Oblique ionospheric reflections in the MARSIS data set

    NASA Astrophysics Data System (ADS)

    Andrews, David; Duru, Firdevs; Morgan, David; Opgenoorth, Hermann; Witasse, Olivier; Withers, Paul

    2013-04-01

    In addition to reflections from the Martian ionosphere along the nadir direction, the Mars Advanced Radar for Sub-surface and Ionospheric Sounding (MARSIS) on board ESA's Mars Express (MEX) orbiter frequently detects 'oblique reflections' from additional targets away from the nadir direction. Such oblique reflections have been attributed to the presence of anomalous horizontal structure within the ionosphere, in which the ionospheric scale height is thought to have increased in regions where Mars' remnant crustal magnetic field has a 'open' or cusp-like configuration, possibly allowing for the heating of the ionosphere by precipitating solar wind plasma. This spatial structuring gives constant-density surfaces which are not parallel to the planet's surface, from which the sounding pulse from the MARSIS instrument can be reflected back towards the spacecraft at what would otherwise be oblique incidence. These oblique reflections form distinctive hyperbolas in time and apparent range, the apices of which are generally above the surrounding ionosphere, strongly suggesting that they have an extended horizontal structure. Here, employing the substantial MARSIS data set, we examine both the spatial distribution and repeatability of detection of these oblique reflections. These results are then related to the highly structured Martian crustal magnetic field, utilising a simplified ray-tracing code.

  2. Secular obliquity variations for Ceres

    NASA Astrophysics Data System (ADS)

    Bills, Bruce; Scott, Bryan R.; Nimmo, Francis

    2016-10-01

    We have constructed secular variation models for the orbit and spin poles of the asteroid (1) Ceres, and used them to examine how the obliquity, or angular separation between spin and orbit poles, varies over a time span of several million years. The current obliquity is 4.3 degrees, which means that there are some regions near the poles which do not receive any direct Sunlight. The Dawn mission has provided an improved estimate of the spin pole orientation, and of the low degree gravity field. That allows us to estimate the rate at which the spin pole precesses about the instantaneous orbit pole.The orbit of Ceres is secularly perturbed by the planets, with Jupiter's influence dominating. The current inclination of the orbit plane, relative to the ecliptic, is 10.6 degrees. However, it varies between 7.27 and 11.78 degrees, with dominant periods of 22.1 and 39.6 kyr. The spin pole precession rate parameter has a period of 205 kyr, with current uncertainty of 3%, dominated by uncertainty in the mean moment of inertia of Ceres.The obliquity varies, with a dominant period of 24.5 kyr, with maximum values near 26 degrees, and minimum values somewhat less than the present value. Ceres is currently near to a minimum of its secular obliquity variations.The near-surface thermal environment thus has at least 3 important time scales: diurnal (9.07 hours), annual (4.60 years), and obliquity cycle (24.5 kyr). The annual thermal wave likely only penetrates a few meters, but the much long thermal wave associated with the obliquity cycle has a skin depth larger by a factor of 70 or so, depending upon thermal properties in the subsurface.

  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. Analysis of Plasma Communication Schemes for Hypersonic Vehicles: Final Report

    DTIC Science & Technology

    2009-02-01

    the ReComm scheme for communications through the plasma sheath surrounding a hypersonic vehicle during re-entry. We demonstrate that the time...physical processes of the ReComm scheme for communications through the plasma sheath surrounding a hypersonic vehicle during re-entry. The ReComm scheme...relation is derived to estimate the plasma heating in the sheath due to plasma waves excited by the antenna. Contents I. Introduction 4 II. Electron

  5. 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.

  6. Studies of anode sheath phenomena in a Hall-effect thruster discharge

    NASA Astrophysics Data System (ADS)

    Dorf, Leonid

    2005-10-01

    Crossed electric and magnetic fields devices (plasma thrusters, magnetrons, coaxial plasma guns, plasma opening switches, etc.) are routinely used for plasma production and in other applications. Despite these numerous applications, the fundamental anode sheath phenomena in many of these devices have received surprisingly little experimental scrutiny. We chose a Hall-effect thruster (HT) discharge for our study of the anode sheath. It has been typically assumed in most fluid models of an HT that its steady-state operation requires the presence of a negative anode fall (electron-repelling anode sheath). Such anode fall behavior, opposite to that in typical glow discharges or hollow-anode plasma sources, is the result of a relatively high degree of ionization in HTs, achieved by applying a radial magnetic field transverse to the direction of the discharge current. Our data from non-perturbing probe measurements showed for the first time that the anode fall in HTs can be either negative or positive (electron-attracting anode sheath), depending on conditions at the anode surface. The path for current closure to the anode turns out to be quite subtle in HTs. This path determines the mechanism of the anode fall formation. In varying the magnetic field topology in the channel from a more uniform to a cusp-like one, we uncover intriguing results. For cusp configurations, in which the radial magnetic field changes polarity somewhere along the channel, the anode fall is positive, whereas it is negative for a more uniform field. This polarity difference could be attributed to the decreased electron mobility across the magnetic field in the cusp-like configuration. Our theoretical modeling of the anode sheath correlates well with the experimental results in describing how the magnitude of the sheath varies with the discharge voltage and mass flow rate.

  7. 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

  8. 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.

  9. Ion flow and sheath structure near positively biased electrodes

    NASA Astrophysics Data System (ADS)

    Hood, R.; Scheiner, B.; Baalrud, S. D.; Hopkins, M. M.; Barnat, E. V.; Yee, B. T.; Merlino, R. L.; Skiff, F.

    2016-11-01

    What effect does a dielectric material surrounding a small positively biased electrode have on the ion flow and sheath structure near the electrode? Measurements of the ion velocity distribution function and plasma potential near positively biased electrodes were made using laser-induced fluorescence and an emissive probe. The results were compared with 2D particle-in-cell simulations. Both measurements and simulations showed that when the positive electrode was surrounded by the dielectric material, ions were accelerated toward the electrode to approximately 0.5 times the ion sound speed before being deflected radially by the electron sheath potential barrier of the electrode. The axial potential profile in this case contained a virtual cathode. In comparison, when the dielectric material was removed from around the electrode, both the ion flow and virtual cathode depth near the electrode were dramatically reduced. These measurements suggest that the ion presheath from the dielectric material surrounding the electrode may enclose the electron sheath of the electrode, resulting in a virtual cathode that substantially influences the ion flow profile in the region.

  10. Effects of neutral gas collisions on the power transmission factor at the divertor sheath

    NASA Astrophysics Data System (ADS)

    Futch, A. H.; Hill, D. N.; Jong, R. A.; Porter, G. D.; Matthews, G. F.; Buchenauer, D.

    1992-03-01

    We show that charge-exchange and other ion-neutral collisions can reduce the power transmission factor of the plasma sheath, thereby lowering the ion impact energy and target plate sputtering. The power transmission factor relates the heat flux reaching the divertor target to the surface: Delta= Q(sub surf)/n(sub e)T(sub e)C(sub s). Experimental data from the D3-D tokamak suggest that Delta could be as low as 2-3 near the region of peak divertor particle flux, instead of the 7-8 expected from usual sheath theory. Several effects combine to allow ion-neutral interactions to be important in the divertor plasma sheath. The shallow angle of incidence of the magnetic field (1-3 degrees in D3-D) leads to the spatial extension of the sheath from approximately (pi)i approximately = 1 mm normal to the plate to several centimeters along the field lines. Ionization reduces the sheath potential, and collisions reduce the ion impact energy.

  11. Non-Linear Effects of Self Generated Alfven Waves in Oblique Shocks and Cosmic Ray Acceleration Efficiency

    NASA Astrophysics Data System (ADS)

    Medina-Tanco, G. A.; Opher, R.

    1990-11-01

    RESUMEN. Se presentan resultados numericos para un modelo hidrodinamico de cuatro componentes (plasma de fondo, particulas energeticas, ondas de Alfven autogeneradas y campo magnetico) para choques oblicuos. ABSTRACT. Numerical results of a four component hydrodynamic model (background plasma, energetic particles, self-generated Alfven waves and magnetic field) for oblique shocks are presented. Keq wo't : COSMIC RAY-GENERAL - PLASMAS - SHOCK WAVES

  12. 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

  13. 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.

  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. 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.

  16. 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.

  17. Rectus sheath abscess after laparoscopic appendicectomy

    PubMed Central

    Golash, Vishwanath

    2007-01-01

    Port site wound infection, abdominal wall hematoma and intraabdominal abscess formation has been reported after laparoscopic appendicectomy. We describe here a rectus sheath abscess which occurred three weeks after the laparoscopic appendicectomy. It was most likely the result of secondary infection of the rectus sheath hematoma due to bleeding into the rectus sheath from damage to the inferior epigastric arteries or a direct tear of the rectus muscle. As far as we are aware this complication has not been reported after laparoscopic appendicectomy. PMID:21124654

  18. 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.

  19. Electron Emission from Nano and Microstructured Materials for Fusion and Plasma Discharge Applications

    NASA Astrophysics Data System (ADS)

    Patino, Marlene; Raitses, Yevgeny; Wirz, Richard

    2016-10-01

    Secondary electron emission (SEE) from plasma-facing walls can lead to adverse effects (e.g. increased plasma heat flux to the wall) in plasma devices, including plasma processing, confinement fusion, and plasma thrusters. Experimental and computational efforts of engineered materials with nm to mm-sized structures (grooves, pores, fibers) have previously shown a decrease in SEE for primary electrons incident normal and oblique to the material. Here we present SEE measurements from one such engineered material, carbon velvet with μm fibers, and from a plasma-structured material, tungsten fuzz with nm fibers. Results show two trends: (a) significant reduction in SEE at normal incidence for carbon velvet (75% reduction) and tungsten fuzz (40-50% reduction) over smooth graphite and tungsten, respectively, and (b) SEE from tungsten fuzz is nearly independent of incident angle (i.e. not a cosine dependence on incident angle observed for smooth materials). Hence, the reduction in SEE from tungsten fuzz over smooth tungsten is more pronounced (up to 63%) at grazing angles. This is important for many plasma devices since in a negative-going sheath the potential structure leads to relatively high incident angles. This work was supported by DOE contract DE-AC02-09CH11466; AFOSR Grants FA9550-14-1-0053, FA9550-11-1-0282, AF9550-09-1-0695, and FA9550-14-10317; and DOE Office of Science Graduate Student Research Program.

  20. 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.

  1. The chaotic obliquity of Mars

    NASA Technical Reports Server (NTRS)

    Touma, Jihad; Wisdom, Jack

    1993-01-01

    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.

  2. 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.

  3. 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

  4. Intrasellar malignant peripheral nerve sheath tumor (MPNST).

    PubMed

    Krayenbühl, N; Heppner, F; Yonekawa, Y; Bernays, R L

    2007-02-01

    Intracranial malignant peripheral nerve sheath tumors (MPNST) and intrasellar schwannomas are rare tumors. We describe a case of an intrasellar schwannoma with progression to a MPNST, a finding that, although very rare, extends the differential diagnosis of intrasellar lesions.

  5. On the Non-Intrusive Determination of Electron Density in the Sheath of a Spherical Probe

    DTIC Science & Technology

    2007-04-20

    PAGE 18. NUMBER OF PAGES 17. LIMITATION OF ABSTRACT On the Non-intrusive Determination of Electron Density in the Sheath of a Spherical Probe David N...07-9033 Approved for public release; distribution is unlimited. Unclassified Unclassified Unclassified UL 15 David Walker (202) 767-2248 Plasma...approximations where the ion flow velocity is well known from the Bohm condition. When plasmas become highly collisional, the analysis is further

  6. Carotid sheath haematoma: a case report.

    PubMed

    Yadav, Jayanthi; Badkur, D S; Arora, Arneet

    2009-10-01

    Carotid sheath haematoma is a rare finding, sometimes the only injury found in cases of manual strangulation without any associated external or internal injury to the neck. One such rare case is reported in an 8 year old female victim where presence of carotid sheath haematoma not only helped to ascertain the cause of death but also helped in the reconstruction of mechanism of infliction of force on the neck.

  7. Lipoma arborescens of the biceps tendon sheath.

    PubMed

    White, Eric A; Omid, Reza; Matcuk, George R; Domzalski, Jerome T; Fedenko, Alexander N; Gottsegen, Christopher J; Forrester, Deborah M; Patel, Dakshesh B

    2013-10-01

    Lipoma arborescens, described as lipomatous infiltration and distention of synovial villi resulting in a frond-like appearance, most frequently affects the suprapatellar recess of the knee. While there have been reports of this entity involving the upper extremity joints, bursa, and tendon sheaths, we present the first reported case of lipoma arborescens isolated to the biceps tendon sheath. We describe imaging and histologic findings with clinical correlation.

  8. Space-charge saturation and current limits in cylindrical drift tubes and planar sheaths

    NASA Astrophysics Data System (ADS)

    Stephens, Kenneth Frank, II

    2000-12-01

    Space-charge effects play a dominant role in many areas of physics. In high-power microwave devices using high-current, relativistic electron beams, it places a limit on the amount of radiation a device can produce. Because the beam's space-charge can actually reflect a portion of the beam, the ability to accurately predict the amount of current a device can carry is needed. This current value is known as the space-charge limited current. Because of the mathematical difficulties, this limit is typically estimated from a one-dimensional theory. This work presents a two-dimensional theory for calculating an upper-bound for the space-charge limited current of relativistic electron beams propagating in grounded coaxial drift tubes. Applicable to annular beams of arbitrary radius and thickness, the theory includes the effect introduced by a finite-length drift tube of circular cross-section. Using Green's second identity, the need to solve Poisson's equation is transferred to solving a Sturm-Liouville eigenvalue problem, which is easily solved by elementary methods. In general, the resulting eigenvalue, which is required to estimate the limiting current, must be numerically determined. However, analytic expressions can be found for frequently encountered limiting cases. Space-charge effects also produce the fundamental collective behavior found in plasmas, especially in plasma sheaths. A plasma sheath is the transition region between a bulk plasma and an adjacent plasma-facing surface. The sheath controls the loss of particles from the plasma in order to maintain neutrality. Using a fully kinetic theory, the problem of a planar sheath with a single-minimum electric potential profile is investigated. Appropriate for single charge-state ions of arbitrary temperature, the theory includes the emission of warm electrons from the surface as well as a net current through the sheath and is compared to particle-in-cell simulations. Approximate expressions are developed for

  9. 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)

  10. 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.

  11. Protective sheath for a continuous measurement thermocouple

    SciTech Connect

    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.

  12. Protective sheath for a continuous measurement thermocouple

    SciTech Connect

    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.

  13. 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.

  14. 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.

  15. A perturbative correction for electron-inertia in magnetized sheath structures

    NASA Astrophysics Data System (ADS)

    Gohain, Munmi; Karmakar, Pralay K.

    2016-10-01

    We propose a hydrodynamic model to study the equilibrium properties of planar plasma sheaths in two-component quasi-neutral magnetized plasmas. It includes weak but finite electron-inertia incorporated via a regular perturbation of the electronic fluid dynamics only relative to a new smallness parameter, δ, assessing the weak inertial-to-electromagnetic strengths. The zeroth-order perturbation around δ leads to the usual Boltzmann distribution law, which describes inertialess thermalized electrons. The forthwith next higher-order yields the modified Boltzmann law describing the putative lowest-order electron-inertial correction, which is applied meticulously to derive the local Bohm criterion for sheath formation. It is found to be influenced jointly by electron-inertial corrective effects, magnetic field and field orientation relative to the bulk plasma flow. We establish that the mutualistic action of electron-inertia amid gyro-kinetic effects slightly enhances the ion-flow Mach threshold value (typically, M i0 ⩾ 1.140), against the normal value of unity, confrontationally towards the sheath entrance. A numerical illustrative scheme is methodically constructed to see the parametric dependence of the new sheath properties on diverse problem arguments. The merits and demerits are highlighted in the light of the existing results conjointly with clear indication to future ameliorations.

  16. Cathode Sheath Charge Transfer Effects

    DTIC Science & Technology

    1993-03-01

    Plasma Chemistry Plasma Processing,2, p. 61. 1982. 8. Hess, G. G. and F. W. Lampe: Ionic Reactions in Gaseous Monosilane . Journal of Chemical Physics...Dissociation of Monosilane and Disilane. Journal of Physical Chemistry, 2l, p. 3912, 1969. 118. Ebinghaus, Von H., K. Kraus, W. Mtiller-Duysing and H...Doncaster, A. M. and R. Walsh: Kinetics of the Gas-Phase Reaction Between Iodine and Monosilane and the Bond Dissociation Energy D(H3Si-H). International

  17. 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.

  18. 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.

  19. The obliquity of Mars and 'climate friction'

    NASA Technical Reports Server (NTRS)

    Rubincam, David P.

    1993-01-01

    A mathematical theory is presented which explains the increase of the mean obliquity of Mars over geologic time due to the so called 'climate friction' (i.e., the climatic changes associated with obliquity oscillations of Mars). The theory is compared with a 10 m.y. numerical integration of the equations performed for a hypothetically large amount of climate friction for two cases of the obliquity oscillations: (1) a single sinusoid and (2) a sum of three sinusoids. The theory and numerics agree for both cases within about 12 percent on the size of the secular increase in obliquity. One possible mechanism of climate friction investigated is 'postglacial rebound' on Mars. According to this theory, giant polar caps form when the obliquity is low, and slowly squeeze out an equatorial bulge. When the obliquity is high, the caps disappear, but the bulge takes some time to collapse, due to mantle viscosity, causing it to oscillate out of phase with the obliquity oscillations. This causes a secular increase in the average obliquity.

  20. Melt Production in Oblique Impacts

    NASA Astrophysics Data System (ADS)

    Pierazzo, E.; Melosh, H. J.

    2000-05-01

    Hydrocode modeling is a fundamental tool for the study of melt production in planetary impact events. Until recently, however, numerical modeling of impacts for melt production studies has been limited to vertical impacts. We present the first results of the investigation of melt production in oblique impacts. Simulations were carried out using Sandia's three-dimensional hydrocode CTH, coupled to the SESAME equation of state. While keeping other impact parameters constant, the calculations span impact angles (measured from the surface) from 90° (vertical impact) to 15°. The results show that impact angle affects the strength and distribution of the shock wave generated in the impact. As a result, both the isobaric core and the regions of melting in the target appear asymmetric and concentrated in the downrange, shallower portion of the target. The use of a pressure-decay power law (which describes pressure as function of linear distance from the impact point) to reconstruct the region of melting and vaporization is therefore complicated by the asymmetry of the shock wave. As an analog to the pressure decay versus distance from the impact point, we used a "volumetric pressure decay," where the pressure decay is modeled as a function of volume of target material shocked at or above the given shock pressure. We find that the volumetric pressure decay exponent is almost constant for impact angles from 90° to 30°, dropping by about a factor of two for a 15° impact. In the range of shock pressures at which most materials of geologic interest melt or begin to vaporize, we find that the volume of impact melt decreases by at most 20% for impacts from 90° down to 45°. Below 45°, however, the amount of melt in the target decreases rapidly with impact angle. Compared to the vertical case, the reduction in volume of melt is about 50% for impacts at 30° and more than 90% for a 15° impact. These estimates do not include possible melting due to shear heating, which can

  1. Magnetised bow shocks and oblique shock interactions: HEDLA experiments on the Magpie pulsed-power facility

    NASA Astrophysics Data System (ADS)

    Burdiak, G. C.; Lebedev, S. V.; Chittenden, J. P.; Clayson, T.; Garcia, C.; Hare, J. D.; Niasse, N.; Suttle, L. G.; Suzuki-Vidal, F.; Frank, A.; Ciardi, A.

    2016-10-01

    We present results from magnetised shock experiments performed on the Magpie ( 1 MA, 250 ns) pulsed-power facility. Shocks are formed around cylindrical and oblique planar obstacles positioned in a supersonic, super-Alfvenic plasma flow (MS = 5 , MA = 2.5 , vf = 70 km/s). The plasma flow is produced by an inverse, exploding wire array z-pinch and carries an embedded magnetic field that is well frozen in (ReM = 20). We show how the structure of bow and oblique shocks is dramatically affected by the orientation of the advected magnetic field with respect to the obstacles. More complex obstacle geometries allow us to study the interaction of multiple magnetised oblique shocks. These systems can cause the annihilation of magnetic flux and the generation of shear flow along a slip layer. Work supported by DOE cooperative agreements No. DE-F03- 02NA00057 and No. DE-SC-0001063.

  2. 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.

  3. A Coupled MHD and Thermal Model Including Electrostatic Sheath for Magnetoplasmadynamic Thruster Simulation

    NASA Astrophysics Data System (ADS)

    Kawasaki, Akira; Kubota, Kenichi; Funaki, Ikkoh; Okuno, Yoshihiro

    2016-09-01

    Steady-state and self-field magnetoplasmadynamic (MPD) thruster, which utilizes high-intensity direct-current (DC) discharge, is one of the prospective candidates of future high-power electric propulsion devices. In order to accurately assess the thrust performance and the electrode temperature, input electric power and wall heat flux must correctly be evaluated where electrostatic sheaths formed in close proximity of the electrodes affect these quantities. Conventional model simulates only plasma flows occurring in MPD thrusters with the absence of electrostatic sheath consideration. Therefore, this study extends the conventional model to a coupled magnetohydrodynamic (MHD) and thermal model by incorporating the phenomena relevant to the electrostatic sheaths. The sheaths are implemented as boundary condition of the MHD model on the walls. This model simulated the operation of the 100-kW-class thruster at discharge current ranging from 6 to 10 kA with argon propellant. The extended model reproduced the discharge voltages and wall heat load which are consistent with past experimental results. In addition, the simulation results indicated that cathode sheath voltages account for approximately 5-7 V subject to approximately 20 V of discharge voltages applied between the electrodes. This work was supported by JSPS KAKENHI Grant Numbers 26289328 and 15J10821.

  4. 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.

  5. 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

  6. Computer modeling of test particle acceleration at oblique shocks

    NASA Technical Reports Server (NTRS)

    Decker, Robert B.

    1988-01-01

    The present evaluation of the basic techniques and illustrative results of charged particle-modeling numerical codes suitable for particle acceleration at oblique, fast-mode collisionless shocks emphasizes the treatment of ions as test particles, calculating particle dynamics through numerical integration along exact phase-space orbits. Attention is given to the acceleration of particles at planar, infinitessimally thin shocks, as well as to plasma simulations in which low-energy ions are injected and accelerated at quasi-perpendicular shocks with internal structure.

  7. 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)

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

    SciTech Connect

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

    2016-08-09

    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/2e 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. In conclusion, the flow moment has significant contributions from both the flow shift of the EVDF maximum, and the loss-cone truncation.

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

    DOE PAGES

    Scheiner, Brett; Baalrud, Scott D.; Hopkins, Matthew M.; ...

    2016-08-09

    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/2e 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 ismore » 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. In conclusion, the flow moment has significant contributions from both the flow shift of the EVDF maximum, and the loss-cone truncation.« less

  10. Deterministic shape control in plasma-aided nanotip assembly

    NASA Astrophysics Data System (ADS)

    Tam, E.; Levchenko, I.; Ostrikov, K.

    2006-08-01

    The possibility of deterministic plasma-assisted reshaping of capped cylindrical seed nanotips by manipulating the plasma parameter-dependent sheath width is shown. Multiscale hybrid gas phase/solid surface numerical experiments reveal that under the wide-sheath conditions the nanotips widen at the base and when the sheath is narrow, they sharpen up. By combining the wide- and narrow-sheath stages in a single process, it turns out possible to synthesize wide-base nanotips with long- and narrow-apex spikes, ideal for electron microemitter applications. This plasma-based approach is generic and can be applied to a larger number of multipurpose nanoassemblies.

  11. 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.

  12. Attic construction with sheathing-applied insulation

    SciTech Connect

    Rose, W.B.

    1995-12-31

    Two years of study at a building research laboratory have been applied to cathedralized residential attic construction. Cathedralized attics are rafter-framed or truss-framed attics with flat ceilings in which the insulation is placed against the underside of the roof sheathing rather than on top of the ceiling drywall. The potential benefits of sheathing-applied insulation are considerable and are due to the fact that the attic space becomes part of the conditioned volume. Concern is often expressed that moisture damage may occur in the sheathing. The intent of the current study was to address those concerns. This study allowed an assessment of the performance of cathedralized ceilings, given the following construction variables: (1) ventilation vs. no ventilation, (2) continuous air chute construction vs. stuffed insulation construction, and (3) opens joints in exposed kraft facing vs. taped joints. The results were compared to a concurrent study of the performance of cathedral ceilings with sloped ceiling drywall. The results show that having an air chute that ensures an air gap between the sheathing and the top of the insulation is the critical factor. Ventilation and the taping of joints were minor determinants of the moisture performance of the sheathing. These results are consistent with the results of normal cathedral ceiling construction performance.

  13. The sheath structure around a negatively charged rocket payload

    SciTech Connect

    Neubert, T.; Gilchrist, B.E.; Banks, P.M.; Williamson, P.R. ); Mandell, M.J.; Katz, I. ); Sasaki, S.; Oyama, K.I. ); Raitt, W.J.; Meyers, N.B. )

    1990-05-01

    The sheath structure around a rocket payload charged up to 460 V negative relative to the ambient ionospheric plasma is investigated experimentally and by computer simulations. In one of the experimental modes, the voltage between the payloads was increased linearly from 0 to 460 V in 2.5 s. In this case the tethered mother/daughter functioned as a double probe, the negative probe (mother) reaching large negative potentials, while the positive probe (daughter) stayed close to the ambient plasma potential. A floating probe array was mounted on the mother with probes located, 25, 50, 75, and 100 cm from the rocket surface. The internal impedance of the array was smaller than the probe/plasma impedance, which influenced the potential measurements. However, the measurements contain signatures, which the authors interpret as resulting from the outward expansion of the ion sheath with increasing negative mother potential. This conclusion is substantiated by NASCAP/LEO computer simulations of space charge limited flow. At high potentials, the observed ion current flowing to the mother increased more strongly with bias potential than found from the simulations. It is suggested that the enhancement of the current is generated by secondary electrons emitted by the ions bombarding the payload skin. The effects of the motion of the mother (540-580 m/s) and of the ambient magnetic field have been assessed by the code. It was estimated that the ion current to the mother was increased by 20% relative to a stationary payload, while the incorporation of a magnetic field had no practical influence on the simulation results.

  14. Observation of Ion-neutral Collision Effect on Two-Ion-Stream Instability near Sheath-Presheath Boundary

    NASA Astrophysics Data System (ADS)

    Kim, Nam-Kyun; Song, J.; Roh, H.-J.; Jang, Y.; Ryu, S.; Kim, G.-H.

    2016-09-01

    The ion velocity normal to the sheath-presheath boundary in weakly-collisional Ar/Xe mixture plasmas was measured by using LIF measurement. This investigation would give an answer to the old debate topic in the sheath community, whether each ion enters the sheath with their own Bohm velocity, CB = (Te /Mi) 1 / 2 . In collisionless two-ion-species plasmas, Barrud and Hershkowitz concluded that the two-stream instability limits their velocities to become the common system sound speed, Cs = (n1Te /neM1 +n2Te /neM2) 1 / 2 . This instability is activated when the relative velocity becomes a critical velocity. In practices, the collisionless condition is not achievable. In this study, the ion-neutral collision effect on the instability was investigated with increasing the pressure of the Ar/Xe mixture gas in the range of 0.5 - 2 mTorr. Plasma is generated in a DC multi-dipole source in which n(Ar+) / n(Xe+) is controlled to be 1. Results show that the instability is grown at p <2 mTorr and the ion drift velocities at the sheath edge are close to Cs. At 2 mTorr, the ions reach their individual CB at the sheath edge because the instability is not grown, observing that the characteristic length of the instability is a function of the ion-neutral collisions. The details will be discussed in the conference.

  15. Attenuation of low-frequency electromagnetic wave in the thin sheath enveloping a high-speed vehicle upon re-entry

    NASA Astrophysics Data System (ADS)

    Liu, DongLin; Li, XiaoPing; Liu, YanMing; Xie, Kai; Bai, BoWen

    2017-02-01

    Low-frequency (LF) electromagnetic (EM) waves are suggested as potentially solving "radio blackout" caused by a plasma sheath enveloping a high-speed vehicle on re-entry. However, the traditional plasma absorption theory neglects the fact that the plasma sheath is electrically small compared to LF EM wavelengths. To understand clearly the attenuation of such waves through the plasma sheath, different attenuation mechanisms for the electric field (SE) and magnetic field (SH) were studied using the equivalent circuit approach. Analytical expressions were derived by modeling the plasma sheath as a spherical shell, and numerical simulations were performed to validate the effectiveness of the expressions. SE and SH are calculated for various plasma parameter settings; the EM wave attenuations obtained from plasma absorption theory are used for comparison. Results show that, instead of SE and SH being equal in the plasma absorption theory, SE and SH are no longer the same for electrically small sizes. Whereas |SH| is close to that from plasma absorption theory, |SE| is much higher. Further analysis shows that |SH| is a function of the ratio of electron density (ne) and collision frequency (ve) and increases with increasing ne/ve. Numerical simulations with radio-attenuation-measurement-C-like vehicle's plasma sheath parameters are performed and the results show that the magnetic field attenuation in the front part of the vehicle is much lower than in the rear. So it is suggested to place the magnetic loop antenna in the very front part of the vehicle. Finally, SH at different frequencies are calculated using plasma sheath parameter values simulating the re-entry phase of a radio-attenuation measurement-C vehicle and results show that such a vehicle might overcome radio blackout during the entire re-entry phase if systems operating below 3 MHz and above the L-band are combined with a lower-frequency system working below Earth's ionosphere and a higher-frequency system

  16. Ion flow and sheath structure near positively biased electrodes

    NASA Astrophysics Data System (ADS)

    Hood, Ryan; Scheiner, Brett; Baalrud, Scott; Hopkins, Matthew; Barnat, Ed; Yee, Benjamin; Merlino, Robert; Skiff, Fred

    2016-10-01

    Measurements of the ion velocity distribution function (IVDF) and plasma potential were made near small positively biased electrodes using laser-induced fluorescence (LIF) and an emissive probe. The effect of dielectric around the electrode was tested and compared with a 2D particle-in-cell (PIC) simulation. Both measurements and simulation reveal that if the electrode is embedded within a surrounding dielectric, ions are accelerated toward the electrode to approximately 0.5 times the ion sound speed before being deflected radially by the electron sheath potential barrier. The axial potential profile in this case contains a virtual cathode. In comparison, when the surrounding dielectric is removed, both the ion flow and virtual cathode depth are dramatically reduced. These measurements suggest that the ion presheath from the dielectric may enclose the electron sheath of the electrode resulting in a virtual cathode that substantially influences the local ion flow profile. This research was supported by the Office of Fusion Energy Sciences at the U.S. Department of Energy under contract DE-AC04-94SL85000.

  17. Negative plasma potential relative to electron-emitting surfaces.

    PubMed

    Campanell, M D

    2013-09-01

    Most works on plasma-wall interaction predict that with strong electron emission, a nonmonotonic "space-charge-limited" (SCL) sheath forms where the plasma potential is positive relative to the wall. We show that a fundamentally different sheath structure is possible where the potential monotonically increases toward a positively charged wall that is shielded by a single layer of negative charge. No ion-accelerating presheath exists in the plasma and the ion wall flux is zero. An analytical solution of the "inverse sheath" regime is demonstrated for a general plasma-wall system where the plasma electrons and emitted electrons are Maxwellian with different temperatures. Implications of the inverse sheath effect are that (a) the plasma potential is negative, (b) ion sputtering vanishes, (c) no charge is lost at the wall, and (d) the electron energy flux is thermal. To test empirically what type of sheath structure forms under strong emission, a full plasma bounded by strongly emitting walls is simulated. It is found that inverse sheaths form at the walls and ions are confined in the plasma. This result differs from past particle-in-cell simulation studies of emission which contain an artificial "source sheath" that accelerates ions to the wall, leading to a SCL sheath at high emission intensity.

  18. Ionospheric profile inversion using oblique-incidence ionograms

    NASA Technical Reports Server (NTRS)

    Nielson, D. L.; Watt, T. M.

    1972-01-01

    Some of the elementary methods used in deriving true-height profiles from oblique-incidence ionograms are reviewed. The two principal methods presented are oblique-to-vertical transformation and direct inversion of the oblique-incidence ionogram. Limitations in oblique-incidence inversion due to magnetic-field effects, horizontal gradients, and absolute time delay are discussed.

  19. 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

  20. Oblique shear fractures of the lunate.

    PubMed

    Freeland, Alan E; Ahmad, Nawaiz

    2003-08-01

    Traumatic fractures of the lunate are rare. This article presents two patients who had displaced oblique lunate fractures and distal radius fractures. Both fractures achieved union; however, transient avascular necrosis occurred in the proximal healing of one patient.

  1. Oblique Wing Research Aircraft on ramp

    NASA Technical Reports Server (NTRS)

    1976-01-01

    This 1976 photograph of the Oblique Wing Research Aircraft was taken in front of the NASA Flight Research Center hangar, located at Edwards Air Force Base, California. In the photograph the noseboom, pitot-static probe, and angles-of-attack and sideslip flow vanes(covered-up) are attached to the front of the vehicle. The clear nose dome for the television camera, and the shrouded propellor for the 90 horsepower engine are clearly seen. The Oblique Wing Research Aircraft was a small, remotely piloted, research craft designed and flight tested to look at the aerodynamic characteristics of an oblique wing and the control laws necessary to achieve acceptable handling qualities. NASA Dryden Flight Research Center and the NASA Ames Research Center conducted research with this aircraft in the mid-1970s to investigate the feasibility of flying an oblique wing aircraft.

  2. 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.

  3. 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.

  4. 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)

  5. 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

  6. Ionospheric heating with oblique high-frequency waves

    SciTech Connect

    Field, E.C. Jr.; Bloom, R.M. ); Kossey, P.A. )

    1990-12-01

    This paper presents calculations of ionospheric electron temperature and density perturbations and ground-level signal changes produced by intense oblique high-frequency (HF) radio waves. The analysis takes into account focusing at caustics, the consequent Joule heating of the surrounding plasma, heat conduction, diffusion, and recombination processes, these being the effects of a powerful oblique modifying wave. It neglects whatever plasma instabilities might occur. The authors then seek effects on a secondary test wave that is propagated along the same path as the first. The calculations predict ground-level field strength reductions of several decibels in the test wave for modifying waves having effective radiated power (ERP) in the 85- to 90-dBW range. These field strength changes are similar in sign, magnitude, and location to ones measured in Soviet experiments. The location of the signal change is sensitive to the frequency and the model ionosphere assumed; so future experiments should employ the widest possible range of frequencies and propagation conditions. An ERP of 90 dBW seems to be a sort of threshold that, if exceeded, might result in substantial rather than small signal changes. The conclusions are based solely on Joule heating and subsequent refraction of waves passing through caustic regions.

  7. 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.

  8. Studies on LH-generated Fast Electron Tail Using the Oblique ECE Diagnostic at JET

    SciTech Connect

    Sozzi, C.; Grossetti, G.; Farina, D.; Figini, L.; Garavaglia, S.; Nowak, S.; Baranov, Y.; Kirov, K.; Luna, E. de la

    2009-11-26

    The new Oblique ECE diagnostics of JET allows simultaneous measurement along three lines of sight at different toroidal angles. JET pulses, in which modulated LHCD power was applied, were analyzed by means of the SPECE emission code, which takes into account the fast electron tail generated by LH. The code results were compared to the ECE spectra from the oblique ECE diagnostic. The match between the computed and the experimental data from the three lines of sight provides an estimate of the density of superthermal electrons and of their maximum energy from which the fraction of the plasma current driven by LHCD is derived.

  9. 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.

  10. Spatial proximity effects on the excitation of sheath RF voltages by evanescent slow waves in the ion cyclotron range of frequencies

    NASA Astrophysics Data System (ADS)

    Colas, Laurent; Lu, Ling-Feng; Křivská, Alena; Jacquot, Jonathan; Hillairet, Julien; Helou, Walid; Goniche, Marc; Heuraux, Stéphane; Faudot, Eric

    2017-02-01

    We investigate theoretically how sheath radio-frequency (RF) oscillations relate to the spatial structure of the near RF parallel electric field E ∥ emitted by ion cyclotron (IC) wave launchers. We use a simple model of slow wave (SW) evanescence coupled with direct current (DC) plasma biasing via sheath boundary conditions in a 3D parallelepiped filled with homogeneous cold magnetized plasma. Within a ‘wide-sheath’ asymptotic regime, valid for large-amplitude near RF fields, the RF part of this simple RF  +  DC model becomes linear: the sheath oscillating voltage V RF at open field line boundaries can be re-expressed as a linear combination of individual contributions by every emitting point in the input field map. SW evanescence makes individual contributions all the larger as the wave emission point is located closer to the sheath walls. The decay of |V RF| with the emission point/sheath poloidal distance involves the transverse SW evanescence length and the radial protrusion depth of lateral boundaries. The decay of |V RF| with the emitter/sheath parallel distance is quantified as a function of the parallel SW evanescence length and the parallel connection length of open magnetic field lines. For realistic geometries and target SOL plasmas, poloidal decay occurs over a few centimeters. Typical parallel decay lengths for |V RF| are found to be smaller than IC antenna parallel extension. Oscillating sheath voltages at IC antenna side limiters are therefore mainly sensitive to E ∥ emission by active or passive conducting elements near these limiters, as suggested by recent experimental observations. Parallel proximity effects could also explain why sheath oscillations persist with antisymmetric strap toroidal phasing, despite the parallel antisymmetry of the radiated field map. They could finally justify current attempts at reducing the RF fields induced near antenna boxes to attenuate sheath oscillations in their vicinity.

  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. Tectonics of oblique plate boundary systems

    NASA Astrophysics Data System (ADS)

    Díaz-Azpiroz, Manuel; Brune, Sascha; Leever, Karen A.; Fernández, Carlos; Czeck, Dyanna M.

    2016-12-01

    The relative displacement between lithospheric plates normally results in obliquely deforming plate boundaries. This is simply caused by the fact that, on plate tectonics basis, irregularly shaped plate boundaries are rarely perpendicular or parallel to small-circle rotation paths, which describe plate motion on a sphere (Fig. 1a). Global current relative plate motions estimated from geological data (DeMets et al., 2010; Argus et al., 2011) and GPS measurements (e.g., Kreemer et al., 2003; Argus et al., 2010) provide insight to the prevalent degrees of obliquity on Earth's surface. Based on these global data sets, Philippon and Corti (2016), statistically show that current orthogonal boundaries (obliquity angle smaller than 10°) represent around 8% of the total boundary length whereas strike-slip boundaries (obliquity angle larger than 80°) are encountered in < 10% of the total boundary length. Therefore, around 80% of active plate boundaries present oblique relative motions. Furthermore, changes in plate kinematics leading to migration or jumps in the rotation poles necessarily cause obliquity along former pure strike-slip or convergent/divergent boundaries (Fig. 1b).

  14. 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.

  15. 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...

  16. 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...

  17. 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...

  18. 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...

  19. 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...

  20. ULTRASTRUCTURE OF THE PRAWN NERVE SHEATHS

    PubMed Central

    Doggenweiler, C. F.; Heuser, John E.

    1967-01-01

    The sheaths from freshly teased nerve fibers of the prawn exhibit a positive radial birefringence, consistent with their EM appearance as highly organized laminated structures composed of numerous thin cytoplasmic sheets or laminae bordered by unit membranes and arranged concentrically around the axon. The closely apposed membranes in these sheaths are fragile and often break down into rows of vesicles during fixation. Desmosome-like attachment zones occur in many regions of the sheath. The membranes within these zones resist vesiculation and thereby provide a "control" region for relating the type of vesicles formed in the fragile portions of the sheaths to the specific fixation conditions. It is proposed that during fixation the production of artifactual vesicles is governed by an interplay of three factors: (a) direct chemical action of the fixative on the polar strata of adjacent unit membranes, (b) osmotic forces applied to membranes during fixation, and (c) the pre-existing natural relations between adjacent membranes. It is found that permanganate best preserves the continuity of the membranes but will still produce vesicles if the fixative exerts severe osmotic forces. These results support other reports (19) of the importance of comparing tissues fixed by complementary procedures so that systematic artifacts will not be described as characteristic of the natural state. PMID:4166578

  1. Space charge saturated sheath regime and electron temperature saturation in Hall thrusters

    NASA Astrophysics Data System (ADS)

    Raitses, Y.; Staack, D.; Smirnov, A.; Fisch, N. J.

    2005-07-01

    Existing electron-wall interaction models predict that secondary electron emission in Hall thrusters is significant and that the near-wall sheaths are space charge saturated. The experimental electron-wall collision frequency is computed using plasma parameters measured in a laboratory Hall thruster. In spite of qualitative similarities between the measured and predicted dependencies of the maximum electron temperature on the discharge voltage, the deduced electron-wall collision frequency for high discharge voltages is much lower than the theoretical value obtained for space charge saturated sheath regime, but larger than the wall recombination frequency. The observed electron temperature saturation appears to be directly associated with a decrease of the Joule heating rather than with the enhancement of the electron energy loss at the walls due to a strong secondary electron emission. Another interesting experimental result is related to the near-field plasma plume, where electron energy balance appears to be independent on the magnetic field.

  2. 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.

  3. 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.

  4. 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.

  5. SF6 and C4F8 global kinetic models coupled to sheath models

    NASA Astrophysics Data System (ADS)

    Haidar, Yehya; Pateau, Amand; Rhallabi, Ahmed; Fernandez, Marie Claude; Mokrani, Arezki; Taher, Fadia; Roqueta, Fabrice; Boufnichel, Mohamed

    2014-12-01

    Global kinetic models combined with Monte Carlo sheath models are developed for SF6 and C4F8 plasma discharges for silicon etching under the Bosch process. In SF6 plasma, the dominant positive ions are SF_5+ , SF_4+ , SF_3+ and F+ while in C4F8 the dominant positive ions are CF_3+ and C_2F_3+ . The simulation results show that the electrical parameters, such as the electron density and electron temperature, clearly affect the sheath dynamics and consequently the ion energy distribution function evolutions. In this context, we showed the effects of the operating conditions, such as the pressure and the radiofrequency power, on the electron density and electron temperature evolutions as well as the reactive particle fluxes (neutral and positive ions) involved in the plasma surface interactions for etching/deposition under the Bosch process. Ion energy distribution functions obtained from SF6 and C4F8 plasmas are compared with each other as regards the electrical properties of their associated plasmas. The simulation results show that the bimodal peaks of ion energy distribution functions are wider for SF6 plasma than for C4F8 plasma due to the high sheath thickness of SF6 compared to that of C4F8. This is explained by the low electron density due to the high electronegativity of SF6 in comparison to that of C4F8. The simulations also reveal that the bimodal peak of the ion energy distribution function is wider when the ion mass is low.

  6. 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.

  7. Dynamics of current sheath in a hollow electrode Z-pinch discharge using slug model

    NASA Astrophysics Data System (ADS)

    Abd Al-Halim, Mohamed A.; Afify, M. S.

    2017-03-01

    The hollow electrode Z-pinch (HEZP) experiment is a new construction for the electromagnetic propulsion application in which the plasma is formed by the discharge between a plate and ring electrodes through which the plasma is propelled. The experimental results for 8 kV charging voltage shows that the peak discharge current is about 109 kA, which is in good agreement with the value obtained from the simulation in the slug model that simulates the sheath dynamics in the HEZP. The fitting of the discharge current from the slug model indicates that the total system inductance is 238 nH which is relatively a high static inductance accompanied with a deeper pinch depth indicating that the fitted anomalous resistance would be about 95 mΩ. The current and mass factors vary with the changing the gas pressure and the charging voltage. The current factor is between 0.4 and 0.5 on average which is relatively low value. The mass factor decreases by increasing the gas pressure indicating that the sheath is heavy to be driven by the magnetic pressure, which is also indicated from the decreases of the drive factor, hence the radial sheath velocity decreases. The plasma inductance and temperature increase with the increase of the drive factor while the minimum pinch radius decreases.

  8. 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.

  9. 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.

  10. 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

  11. Structural characterization of highly branched glucan sheath from Ceriporiopsis subvermispora.

    PubMed

    Suzuki, Daisuke; Nishimura, Hiroshi; Yoshioka, Koichi; Kaida, Rumi; Hayashi, Takahisa; Takabe, Keiji; Watanabe, Takashi

    2017-02-01

    Wood rotting basidiomycetes produce extracellular mucilaginous sheaths interfacing fungal hyphae and plant biomass. While the versatility of these fungal sheaths has been addressed, sheaths generated by selective white-rot fungi remain poorly understood. To fill this gap, the sheath produced by the basidiomycete Ceriporiopsis subvermispora, which degrades lignin while inflicting limited cellulose damage, was analyzed in this study. Fluorescence and transmission electron microscopy revealed that the sheath formed three days after inoculation into a beech wood slice on an agar plate and was embedded at the interface between fungal hyphae and wood cell walls. The sheath's chemical structure was evaluated from fungus cultures in a liquid medium containing [U-(13)C6]-d-glucose and beech wood slices. Compositional analysis, methylation analysis, and (13)C NMR demonstrated that the sheath mainly consisted of a comb-like β-1,6-glucopyranose residue-branched β-1,3-glucan, which is advantageous to retain water and extracellular secondary metabolites.

  12. Oblique reflections in the Mars Express MARSIS data set: Stable density structures in the Martian ionosphere

    NASA Astrophysics Data System (ADS)

    Andrews, D. J.; André, M.; Opgenoorth, H. J.; Edberg, N. J. T.; Diéval, C.; Duru, F.; Gurnett, D. A.; Morgan, D.; Witasse, O.

    2014-05-01

    The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) onboard the European Space Agency's Mars Express (MEX) spacecraft routinely detects evidence of localized plasma density structures in the Martian dayside ionosphere. Such structures, likely taking the form of spatially extended elevations in the plasma density at a given altitude, give rise to oblique reflections in the Active Ionospheric Sounder data. These structures are likely related to the highly varied Martian crustal magnetic field. In this study we use the polar orbit of MEX to investigate the repeatability of the ionospheric structures producing these anomalous reflections, examining data taken in sequences of multiple orbits which pass over the same regions of the Martian surface under similar solar illuminations, within intervals lasting tens of days. Presenting three such examples, or case studies, we show for the first time that these oblique reflections are often incredibly stable, indicating that the underlying ionospheric structures are reliably reformed in the same locations and with qualitatively similar parameters. The visibility, or lack thereof, of a given oblique reflection on a single orbit can generally be attributed to variations in the crustal field within the ionosphere along the spacecraft trajectory. We show that, within these examples, oblique reflections are generally detected whenever the spacecraft passes over regions of intense near-radial crustal magnetic fields (i.e., with a "cusp-like" configuration). The apparent stability of these structures is an important feature that must be accounted for in models of their origin.

  13. Solar Obliquity Induced by Planet Nine

    NASA Astrophysics Data System (ADS)

    Bailey, Elizabeth; Batygin, Konstantin; Brown, Michael E.

    2016-10-01

    The six-degree obliquity of the sun suggests that either an asymmetry was present in the solar system's formation environment, or an external torque has misaligned the angular momentum vectors of the sun and the planets. However, the exact origin of this obliquity remains an open question. Batygin and Brown (2016) have recently shown that the physical alignment of distant Kuiper Belt orbits can be explained by a m9 = 10-20 mEarth planet on a distant, eccentric, and inclined orbit, with an approximate perihelion distance of q9 ˜ 250 AU. Using an analytic model for secular interactions between Planet Nine and the remaining giant planets, here we show that a planet with similar parameters can naturally generate the observed obliquity as well as the specific pole position of the sun's spin axis. Thus, Planet Nine offers a testable explanation for the otherwise mysterious spin-orbit misalignment of the solar system.

  14. Solar Obliquity Induced by Planet Nine

    NASA Astrophysics Data System (ADS)

    Bailey, Elizabeth; Batygin, Konstantin; Brown, Michael E.

    2016-11-01

    The six-degree obliquity of the Sun suggests that either an asymmetry was present in the solar system’s formation environment, or an external torque has misaligned the angular momentum vectors of the Sun and the planets. However, the exact origin of this obliquity remains an open question. Batygin & Brown have recently shown that the physical alignment of distant Kuiper Belt orbits can be explained by a 5{--}20 {m}\\oplus planet on a distant, eccentric, and inclined orbit, with an approximate perihelion distance of ˜250 au. Using an analytic model for secular interactions between Planet Nine and the remaining giant planets, here, we show that a planet with similar parameters can naturally generate the observed obliquity as well as the specific pole position of the Sun’s spin axis, from a nearly aligned initial state. Thus, Planet Nine offers a testable explanation for the otherwise mysterious spin-orbit misalignment of the solar system.

  15. Obliquity Evolution of an Early Venus

    NASA Astrophysics Data System (ADS)

    Quarles, Billy L.; Barnes, Jason; Lissauer, Jack J.; Chambers, John

    2014-11-01

    Stark differences in both atmospheric mass and rotation are apparent between the present-day Earth and neighboring Venus. These planets may have been more similar 4 Gyr ago when most of the carbon within Venus may have been in solid form, implying a low-mass atmosphere. As a result, Venus's rotation rate could have been much faster than at present due to the smaller cumulative effects of solid-body and atmospheric tides. We investigate how the obliquity of a hypothetical rapidly-rotating Early Venus would have evolved as compared to a Moonless Earth. As with our previous investigation [Lissauer, Barnes, & Chambers 2012], slow prograde rotation of our hypothesized Early Venus generally leads to larger variations in obliquity than does retrograde rotation. However, the variability of obliquity for retrograde rotations differs from the Moonless Earth and can change with the initial spin period. The implications for early habitability of extrasolar Venus analogs will also be discussed.

  16. 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.

  17. Continuum-kinetic approach to sheath simulations

    NASA Astrophysics Data System (ADS)

    Cagas, Petr; Hakim, Ammar; Srinivasan, Bhuvana

    2016-10-01

    Simulations of sheaths are performed using a novel continuum-kinetic model with collisions including ionization/recombination. A discontinuous Galerkin method is used to directly solve the Boltzmann-Poisson system to obtain a particle distribution function. Direct discretization of the distribution function has advantages of being noise-free compared to particle-in-cell methods. The distribution function, which is available at each node of the configuration space, can be readily used to calculate the collision integrals in order to get ionization and recombination operators. Analytical models are used to obtain the cross-sections as a function of energy. Results will be presented incorporating surface physics with a classical sheath in Hall thruster-relevant geometry. This work was sponsored by the Air Force Office of Scientific Research under Grant Number FA9550-15-1-0193.

  18. 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.

  19. TOPICAL REVIEW: Complex plasma: dusts in plasma

    NASA Astrophysics Data System (ADS)

    Ishihara, Osamu

    2007-04-01

    Dust particles in a plasma are charged negatively and are subject to various types of forces, including a drag force by plasma particles and a force due to the collective nature of a plasma. Dust particles are found in a sheath in laboratories balanced by the gravitational force and the electric force, while dust particles in space are ubiquitous, including planetary magnetospheres and interstellar space. Because of the novel nature of a complex system involving plasma particles and dust particles in a collective way, the dusty plasma is often called a complex plasma. The complex plasma is characterized by two distinctly different scales in time and in space. The plasma with electrons, ions and neutrals is characterized by the collective motion with a fast time scale and a short wavelength, while the dust particles move in a slow time scale and a long spatial scale. Some fundamental aspects of a complex plasma are reviewed and possible applications are discussed.

  20. 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.

  1. Aeroelastic tailoring for oblique wing lateral trim

    NASA Technical Reports Server (NTRS)

    Bohlmann, Jonathan D.; Weisshaar, Terrence A.; Eckstrom, Clinton V.

    1988-01-01

    Composite material aeroelastic tailoring is presently explored as a means for the correction of the roll trim imbalance of oblique-wing aircraft configurations. The concept is demonstrated through the analysis of a realistic oblique wing by a static aeroelastic computational procedure encompassing the full potential transonic aerodynamic code FLO22 and a Ritz structural plate program that models the stiffness due to symmetrical-but-unbalanced composite wing skins. Results indicate that asymetric composite tailoring reduces the aileron deflection needed for roll equilibrium, and reduces control surface hinge moment and drag. Wing skin stresses are, however, very high.

  2. Experimental investigation of virtual cathode sheath in the presence of secondary electrons produced by streaming ions

    NASA Astrophysics Data System (ADS)

    Li, Wei; Ma, J. X.; Li, Jing-ju; Wei, Zi-an

    2012-11-01

    The potential profiles near a negatively biased stainless steel plate or mesh immersed in an unmagnetized weakly collisional plasma were investigated experimentally. The results show that deep virtual cathode structures arise inside the sheath region in front of the plate caused by secondary electrons produced by streaming ions hitting the surface of the plate. The characteristics of the virtual cathode depend on the incoming ion energy, neutral gas pressure, and bulk plasma density. In addition, the replacement of the plate with the mesh results in the suppression of the virtual cathode because of the equivalent reduction in the secondary electron yield.

  3. Optic Nerve Sheath Mechanics in VIIP Syndrome

    NASA Technical Reports Server (NTRS)

    Raykin, Julia; Forte, Taylor E.; Wang, Roy; Feola, Andrew; Samuels, Brian; Myers, Jerry; Nelson, Emily; Gleason, Rudy; Ethier, C. Ross

    2016-01-01

    Visual Impairment Intracranial Pressure (VIIP) syndrome is a major concern in current space medicine research. While the exact pathology of VIIP is not yet known, it is hypothesized that the microgravity-induced cephalad fluid shift increases intracranial pressure (ICP) and drives remodeling of the optic nerve sheath. To investigate this possibility, we are culturing optic nerve sheath dura mater samples under different pressures and investigating changes in tissue composition. To interpret results from this work, it is essential to first understand the biomechanical response of the optic nerve sheath dura mater to loading. Here, we investigated the effects of mechanical loading on the porcine optic nerve sheath.Porcine optic nerves (number: 6) were obtained immediately after death from a local abattoir. The optic nerve sheath (dura mater) was isolated from the optic nerve proper, leaving a hollow cylinder of connective tissue that was used for biomechanical characterization. We developed a custom mechanical testing system that allowed for unconfined lengthening, twisting, and circumferential distension of the dura mater during inflation and under fixed axial loading. To determine the effects of variations in ICP, the sample was inflated (0-60 millimeters Hg) and circumferential distension was simultaneously recorded. These tests were performed under variable axial loads (0.6 grams - 5.6 grams at increments of 1 gram) by attaching different weights to one end of the dura mater. Results and Conclusions: The samples demonstrated nonlinear behavior, similar to other soft connective tissue (Figure 1). Large increases in diameter were observed at lower transmural pressures (approximately 0 to 5 millimeters Hg), whereas only small diameter changes were observed at higher pressures. Particularly interesting was the existence of a cross-over point at a pressure of approximately 11 millimeters Hg. At this pressure, the same diameter is obtained for all axial loads applied

  4. 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.

  5. 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.

  6. 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).

  7. Oblique patterned etching of vertical silicon sidewalls

    SciTech Connect

    Burckel, D. Bruce; Finnegan, Patrick S.; Henry, M. David; Resnick, Paul J.; Jarecki, Jr., Robert L.

    2016-04-05

    A method for patterning on vertical silicon surfaces in high aspect ratio silicontopography is presented. A Faraday cage is used to direct energetic reactive ions obliquely through a patterned suspended membrane positioned over the topography. The technique is capable of forming high-fidelity pattern (100 nm) features, adding an additional fabrication capability to standard top-down fabrication approaches.

  8. 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.

  9. Orientation Strategies for Aerial Oblique Images

    NASA Astrophysics Data System (ADS)

    Wiedemann, A.; Moré, J.

    2012-07-01

    Oblique aerial images become more and more distributed to fill the gap between vertical aerial images and mobile mapping systems. Different systems are on the market. For some applications, like texture mapping, precise orientation data are required. One point is the stable interior orientation, which can be achieved by stable camera systems, the other a precise exterior orientation. A sufficient exterior orientation can be achieved by a large effort in direct sensor orientation, whereas minor errors in the angles have a larger effect than in vertical imagery. The more appropriate approach is by determine the precise orientation parameters by photogrammetric methods using an adapted aerial triangulation. Due to the different points of view towards the object the traditional aerotriangulation matching tools fail, as they produce a bunch of blunders and require a lot of manual work to achieve a sufficient solution. In this paper some approaches are discussed and results are presented for the most promising approaches. We describe a single step approach with an aerotriangulation using all available images; a two step approach with an aerotriangulation only of the vertical images plus a mathematical transformation of the oblique images using the oblique cameras excentricity; and finally the extended functional model for a bundle block adjustment considering the mechanical connection between vertical and oblique images. Beside accuracy also other aspects like efficiency and required manual work have to be considered.

  10. 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…

  11. Oblique patterned etching of vertical silicon sidewalls

    NASA Astrophysics Data System (ADS)

    Bruce Burckel, D.; Finnegan, Patrick S.; David Henry, M.; Resnick, Paul J.; Jarecki, Robert L.

    2016-04-01

    A method for patterning on vertical silicon surfaces in high aspect ratio silicon topography is presented. A Faraday cage is used to direct energetic reactive ions obliquely through a patterned suspended membrane positioned over the topography. The technique is capable of forming high-fidelity pattern (100 nm) features, adding an additional fabrication capability to standard top-down fabrication approaches.

  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. Effect of surface produced secondary electrons on the sheath structure induced by high-power microwave window breakdown

    SciTech Connect

    Cheng Guoxin; Liu Lie

    2011-03-15

    Dielectric window breakdown, whose mechanism is not thoroughly understood, is a major factor of limiting the transmission and radiation of high-power microwave on the order of 1 GW. In this paper, a one-dimensional fluid-like sheath model is developed to investigate the sheath structures formed at different gas pressures. The dominant processes during the surface flashover are isolated by this model. In vacuum, electron multipactor is self-sustained by secondary electron emission, a positive space-charge potential is formed on the dielectric surface. With increasing gas pressure, electron-neutral ionization prevails against secondary electron emission. The multipactor effect is suppressed by the shielding of plasma electrons. This leads to the sheath potential changing gradually from a positive space-charge potential to a negative space-charge potential. For argon gas pressure lower than 14 Torr, the sheath is space charge limited. A potential minimum could be formed in front of the dielectric which traps secondary electrons emitted from the wall. With the higher argon gas pressure, the number density of ions becomes comparable to that of electrons, all surface produced electrons are accelerated toward the presheath region. Therefore, the normal sheath is formed and the resulting surface flashover on the dielectric surface becomes rf-driven volumetric breakdown.

  14. 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

  15. Nondestructive testing of metallic sheath for internally cooled superconductor

    SciTech Connect

    McClung, R.W.; Cook, K.V.; Dodd, C.V.; Smith, J.H.

    1983-01-01

    For quality assurance in the Oak Ridge National Laboratory Large Coil Program, we developed ultrasonic and eddy-current techniques to examine the JBK-75 alloy sheath for superconducting cable for a large magnet. Ultrasound was used to examine the strip before forming into the sheath, and eddy currents were used to examine the seam weld after the sheath had been formed around the cable.

  16. Steerable sheath technology in the ablation of atrial fibrillation.

    PubMed

    Joseph, Jubin; Wong, Kelvin C K; Ginks, Matthew R; Bashir, Yaver; Betts, Timothy R; Rajappan, Kim

    2013-12-01

    Steerable sheaths have been shown to reduce procedure time in the catheter ablation of atrial fibrillation (AF), where catheter positioning and stability is typically challenging. This review critically addresses and highlights the recent developments in design of sheaths used to manipulate the ablation catheter and how these developments may impact on the ablation procedure itself, in particular the likelihood of first-time success. Patents relating to steerable sheaths are reviewed and discussed to gauge potential future developments in this area.

  17. The Chicxulub Impact Crater and Oblique Impact

    NASA Astrophysics Data System (ADS)

    McDonald, M.; Gulick, S.; Melosh, H.; Christeson, G.

    2007-05-01

    Determining whether or not the Chicxulub impact was oblique (<45 degrees) will aid in our understanding of the environmental consequences 65 Ma. Planetary impact events, and impact simulations in the laboratory, show that oblique impacts have clear asymmetric ejecta distributions. However, the subsurface structures of the resultant craters are not well understood. In 2005, we acquired 1822 km of seismic reflection data onboard the R/V Maurice Ewing imaging the massive (200+ km) Chicxulub impact crater. The seismic profiles show that pre- crater stratigraphy outside the central basin of the Chicxulub impact crater is offset downward into the crater marking the post-impact slumping and formation of the terrace zone. The inward collapse of the Chicxulub terrace zone coincides with the outward collapse of the central uplift to form the peak ring. Chicxulub's peak ring is offset to the southeast, away from the deepest terrace zone mapped in the seismic data, suggesting that its peak ring was offset toward a more gradual wall of the transient cavity. Peak ring offsets, relative to crater center, of Venusian craters from radar images in the Magellan data set allow us to determine whether there are systematic variations in peak ring offset due to oblique impact. Ten pristine Venusian peak ring craters formed by oblique impact show that peak rings are offset both uprange and downrange, suggesting that peak ring position, and related subsurface asymmetries in the terrace zone, do not provide information about impact obliquity. This analysis supports the idea that Chicxulub's peak ring offset is a consequence of target properties and pre-impact structure and independent of impact trajectory.

  18. 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.

  19. 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.

  20. Lunar photoelectron sheath and levitation of dust

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    The decision to launch Luna Glob and Luna Resus satellites, carrying instrumentation to investigate the structure of photoelectron sheath and levitation of dust particles in the sheath, adjacent to the surface of the moon has intensified interest in this exciting area. The present analysis incorporates the following novel features: (i) In contrast to intuitive half Maxwellian (M) distribution of velocities of the photoelectrons, emitted from the surface of the moon, which corresponds to an arbitrary temperature, a well-established half Fermi Dirac (F-D) distribution [R. H. Fowler, Phys. Rev. 38, 45 (1931)] has been used, (ii) the profiles for electric potential, electric field, and electron density have been derived (not a priori assumed), (iii) an expression for the rate of electron accretion on a positively charged dust particle, which takes account of the anisotropic flux of electrons has been derived and used in the analysis, and (iv) a derived (rather than intuitive) expression for the rate of photoelectron emission from a positively charged dust particle has been used for the first time in such analyses. The profiles of the electric potential, electric field, and electron density in the photoelectric sheath have been evaluated for typical lunar environment and used to obtain the profile of the radius of a dust particle for levitation. The dependence of the electric potential on the surface of the moon on the parameters of the solar wind and photo-efficiency of the material of moon's surface has also been discussed. It is seen that the results based on half F-D distribution are significantly different from those obtained on the basis of M-distribution.

  1. Prediction of etching-shape anomaly due to distortion of ion sheath around a large-scale three-dimensional structure by means of on-wafer monitoring technique and computer simulation

    NASA Astrophysics Data System (ADS)

    Kubota, Tomohiro; Ohtake, Hiroto; Araki, Ryosuke; Yanagisawa, Yuuki; Iwasaki, Takuya; Ono, Kohei; Miwa, Kazuhiro; Samukawa, Seiji

    2013-10-01

    A system for predicting distortion of a profile during plasma etching was developed. The system consists of a combination of measurement and simulation. An ‘on-wafer sheath-shape sensor’ for measuring the plasma-sheath parameters (sheath potential and thickness) on the stage of the plasma etcher was developed. The sensor has numerous small electrodes for measuring sheath potential and saturation ion-current density, from which sheath thickness can be calculated. The results of the measurement show reasonable dependence on source power, bias power and pressure. Based on self-consistent calculation of potential distribution and ion- and electron-density distributions, simulation of the sheath potential distribution around an arbitrary 3D structure and the trajectory of incident ions from the plasma to the structure was developed. To confirm the validity of the distortion prediction by comparing it with experimentally measured distortion, silicon trench etching under chlorine inductively coupled plasma (ICP) was performed using a sample with a vertical step. It was found that the etched trench was distorted when the distance from the step was several millimetres or less. The distortion angle was about 20° at maximum. Measurement was performed using the on-wafer sheath-shape sensor in the same plasma condition as the etching. The ion incident angle, calculated as a function of distance from the step, successfully reproduced the experimentally measured angle, indicating that the combination of measurement by the on-wafer sheath-shape sensor and simulation can predict distortion of an etched structure. This prediction system will be useful for designing devices with large-scale 3D structures (such as those in MEMS) and determining the optimum etching conditions to obtain the desired profiles.

  2. 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.

  3. 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

  4. Boundary conditions for plasma fluid models at the magnetic presheath entrance

    SciTech Connect

    Loizu, J.; Ricci, P.; Halpern, F. D.; Jolliet, S.

    2012-12-15

    The proper boundary conditions at the magnetic presheath entrance for plasma fluid turbulence models based on the drift approximation are derived, focusing on a weakly collisional plasma sheath with T{sub i} Much-Less-Than T{sub e} and a magnetic field oblique to a totally absorbing wall. First, the location of the magnetic presheath entrance is rigorously derived. Then boundary conditions at the magnetic presheath entrance are analytically deduced for v{sub ||i}, v{sub ||e}, n, {phi}, T{sub e}, and for the vorticity {omega}={nabla}{sub Up-Tack }{sup 2}{phi}. The effects of E Multiplication-Sign B and diamagnetic drifts on the boundary conditions are also investigated. Kinetic simulations are performed that confirm the analytical results. Finally, the new set of boundary conditions is implemented in a three-dimensional global fluid code for the simulation of plasma turbulence and, as an example, the results of a tokamak scrape-off layer simulation are discussed. The framework presented can be generalized to obtain boundary conditions at the magnetic presheath entrance in more complex scenarios.

  5. The Obliquities of the Giant Planets

    NASA Astrophysics Data System (ADS)

    Hamilton, D. P.; Ward, Wm. R.

    2002-09-01

    Jupiter has by far the smallest obliquity ( ~ 3o) of the planets (not counting tidally de-spun Mercury and Venus) which may be reflective of its formation by hydrodynamic gas flow rather than stochastic impacts. Saturn's obliquity ( ~ 26o), however, seems to belie this simple formation picture. But since the spin angular momentum of any planet is much smaller than its orbital angular momentum, post-formation obliquity can be strongly modified by passing through secular spin-orbit resonances, i.e., when the spin axis precession rate of the planet matches one of the frequencies describing the precession of the orbit plane. Spin axis precession is due to the solar torque on both the oblate figure of the planet and any orbiting satellites. In the case of Jupiter, the torque on the Galilean satellites is the principal cause of its 4.5*105 year precession; Saturn's precession of 1.8*106 years is dominated by Titan. In the past, the planetary spin axis precession rates should have been much faster due to the massive circumplanetary disks from which the current satellites condensed. The regression of the orbital node of a planet is due to the gravitational perturbations of the other planets. Nodal regression is not uniform, but is instead a composite of the planetary system's normal modes. For Jupiter and Saturn, the principal frequency is the nu16, with a period of ~ 49,000 years; the amplitude of this term is I ~ 0o.36 for Jupiter and I ~ 0o.90 for Saturn. In spite of the small amplitudes, slow adiabatic passages through this resonance (due to circumplanetary disk dispersal) could increase planetary obliquities from near zero to ~ [tan1/3 I] ~ 10o. We will discuss scenarios in which giant planet obliquities are affected by this and other resonances, and will use Jupiter's low obliquity to constrain the mass and duration of a satellite precursor disk. DPH acknowledges support from NSF Career Grant AST 9733789 and WRW is grateful to the NASA OSS and PGG programs.

  6. An experiment to study and control the Langmuir sheath around INTERBALL-2

    NASA Astrophysics Data System (ADS)

    Torkar, K.; Veselov, M. V.; Afonin, V. V.; Arends, H.; Fehringer, M.; Fremuth, G.; Fritzenwallner, K.; Galperin, Y. I.; Kozlov, A. I.; Pedersen, A.; Perraut, S.; Riedler, W.; Rüdenauer, F.; Schmidt, R.; Smit, A.; Valavanoglou, N.; Zinin, L. V.

    1998-09-01

    The satellite INTERBALL-2 has an orbit with high inclination (62.8°), covering the altitude range between a few hundred and about 20000 km. The ambient plasma conditions along this orbit are highly variable, and the interactions of this plasma with the spacecraft body as well as the photo-electron sheath around it are considered to be interesting topics for detailed studies. The electric potential of the spacecraft with respect to the ambient plasma that develops as a result of the current equilibrium reacts sensitively to variations of the boundary conditions. The measurement and eventual control of this potential is a prerequisite for accurate measurements of the thermal plasma. We describe the purpose and technical implementation of an ion emitter instrument on-board INTERBALL-2 utilising ion beams at energies of several thousand electron volts in order to reduce and stabilise the positive spacecraft potential. First results of the active ion beam experiments, and other measures taken on INTERBALL-2 to reduce charging are presented. Furthermore, the approach and initial steps of modelling efforts of the sheath in the vicinity of the INTERBALL-2 spacecraft are described together with some estimates on the resulting spacecraft potential, and effects on thermal ion measurements. It is concluded that even moderate spacecraft potentials as are commonly observed on-board INTERBALL-2 can significantly distort the measurements of ion distribution functions, especially in the presence of strongly anisotropic distributions.

  7. Sorghum [Sorghum bicolor (L.) Moench] leaf sheath dye protects against cisplatin-induced hepatotoxicity and oxidative stress in rats.

    PubMed

    Ademiluyi, Adedayo O; Oboh, Ganiyu; Agbebi, Oluwaseun J; Boligon, Aline A; Athayde, Margareth L

    2014-12-01

    This study sought to determine the protective effect of dietary inclusion of sorghum leaf sheath dye on cisplatin-induced hepatotoxicity and oxidative stress in rats. Adult male rats were randomly divided into four groups with six animals in each group. Groups I and II were fed a basal diet, while groups III and IV were fed diets containing 0.5% and 1% sorghum leaf sheath dye, respectively, for 20 days before cisplatin administration. Hepatotoxicity was induced by a single dose of cisplatin (7 mg/kg body weight, i.p.), and the experiment was terminated at 3 days after cisplatin injection. The liver and plasma were studied for hepatotoxicity and antioxidant capacity. Cisplatin caused a significant (P<.05) alteration in plasma and liver enzymatic (catalase, glutathione-S-transferase [GST], and superoxide dismutase [SOD]) and nonenzymatic (glutathione [GSH] and vitamin C) antioxidant indices with a concomitant increase in the malondialdehyde (MDA) content; however, there was a significant (P<.05) restoration of the antioxidant status coupled with a significant (P<.05) decrease in the tissue MDA content, after consumption of diets containing sorghum leaf sheath dye. Furthermore, dietary inclusion of sorghum leaf sheath dye caused a marked reduction in the activities of alanine aminotransferase and aspartate aminotransferase after cisplatin administration. However, the ability of the dye to prevent significant cisplatin-induced alteration of both plasma and liver antioxidant indices suggests an antioxidant mechanism of action. Hence, this protective effect of Sorghum bicolor leaf sheath dye against cisplatin-induced hepatotoxicity in rats reflects its potential and beneficial role in the prevention of liver damage associated with cisplatin administration.

  8. 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.

  9. 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).

  10. 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.

  11. Ionospheric true height profiles from oblique ionograms

    SciTech Connect

    Reilly, M.H.

    1985-06-01

    An improved direct technique in which HF oblique ionograms are reduced to ionospheric true height profiles is introduced. The benefits of this method result principally from the use of a more accurate Breit-Tuve relation to curved earth and ionosphere geometries. By comparing the results of calculations on known cases, the extent of improvement with this technique relative to the techniques by Gething and Maliphant (1967), George (1970), and Smith (1970), is demonstrated. 14 references.

  12. Resolution of superior oblique myokymia with memantine.

    PubMed

    Jain, Saurabh; Farooq, Shegufta J; Gottlob, Irene

    2008-02-01

    We describe a novel treatment of superior oblique myokymia. A 40-year-old woman was treated with gabapentin for this disorder with partial success and reported significant side effects including loss of libido and weight gain. After a drug holiday, memantine therapy was initiated resulting in a substantial improvement in her symptoms with far fewer side effects and stability on long-term maintenance therapy.

  13. Electrospinning jet behaviors under the constraints of a sheath gas

    NASA Astrophysics Data System (ADS)

    Zhao, Yang; Jiang, Jiaxin; Li, Wenwang; Wang, Xiang; Zhang, Kai; Zhu, Ping; Zheng, Gaofeng

    2016-11-01

    Increasing the ejection efficiency and uniformity of nanofibers is the key to applications of electrospinning technology. In this work, a novel electrospinning spinneret with a sheath gas passageway is designed. The frictional resistance that stems from the sheath gas provides additional stretching and restriction forces on the jet. The sheath gas also reduces interference and enhances the stability of the charged jet. A bead-on-strain simulation model is built up to determine the constraint effects of the sheath gas. Simulation results show that the sheath gas decreases the motion area and increases the stretching ratio of the liquid jet. The stretching force from the sheath gas decreases the diameter and increases the uniformity of the nanofiber. As the gas pressure increases from 0 kPa to 50 kPa, the critical voltage of the jet ejection decreases from 8.4 kV to 2.5 kV, the diameter of the nanofiber deposition zone decreases from 40 cm to 10 cm, and the diameter of the nanofibers decreases from 557.97 nm to 277.73 nm. The uniformity of nanofibers can be improved significantly using a sheath gas. The sheath gas contributes to the rapid deposition of a uniform nanofibrous membrane and the industrial applications of electrospinning.

  14. Electrohydrodynamic direct-writing orderly pattern with sheath gas focusing

    NASA Astrophysics Data System (ADS)

    Zheng, Jianyi; Zhang, Kai; Jiang, Jiaxin; He, Guangqi; Xu, Lei; Liu, Yifang; Liu, Juan; Wu, Dezhi; Zheng, Gaofeng

    2016-11-01

    Laminar sheath gas is introduced to increase the stability of Electrohydrodynamic Direct-Writing (EDW). The external stretching force from sheath gas promotes the ejection threshold, the diameter of jet and printed fibers as well. The critical voltage decreases with the increase of sheath gas pressure. The stretching force from sheath gas decreases the diameter of printed fiber as well as that of charged jet. As sheath gas pressure increases from 0 to 25 kPa, the average diameter of micro/nano structure reduces from 4.46 μ m to 845.25 nm. The laminar field flow of sheath gas shelters the charged jet free from the surrounding interferences, and helps charged jet to move in a straight line. With the help of sheath gas, the stability of charged jet can be improved to direct-write precise complex micro-pattern. The position precision of direct-written pattern is less than 5 μ m . As a novel method, EDW with laminar sheath gas would promote the deposition precision of printed micro/nano structure and its application.

  15. Dynamic reversibility of hydrodynamic focusing for recycling sheath fluid.

    PubMed

    Hashemi, Nastaran; Howell, Peter B; Erickson, Jeffrey S; Golden, Joel P; Ligler, Frances S

    2010-08-07

    The phenomenon of "unmixing" has been demonstrated in microfluidic mixers, but here we manipulate laminar flow streams back to their original positions in order to extend the operational utility of an analytical device where no mixing is desired. Using grooves in the channel wall, we passively focus a sample stream with two sheath streams to center it in a microchannel for optical analysis. Even though the sample stream is completely surrounded by sheath fluid, reversing the orientation of the grooves in the channel walls returns the sample stream to its original position with respect to the sheath streams. We demonstrate the separation of the sample stream from the contiguous sheath streams and the recycling of the sheath fluid using the reversibility of laminar flow. Polystyrene microspheres and fluorescent dye were used to quantify the performance of the unsheathing process. We found that the maximum numbers of microspheres and all of the fluorescent dye were recaptured at sheath recycling levels <92%. The use of this sheathing technique has previously been demonstrated in a sensitive microflow cytometer; the unsheathing capability now provides the opportunity to recover particles from the sensor with minimal dilution or to recycle the sheath fluid for long-term unattended operation.

  16. Two simple and rugged designs for creating microfluidic sheath flow

    PubMed Central

    Howell, Peter B.; Golden, Joel P.; Hilliard, Lisa R.; Erickson, Jeffrey S.; Mott, David R.; Ligler, Frances S.

    2009-01-01

    A simple design capable of 2-dimensional hydrodynamic focusing is proposed and successfully demonstrated. In the past, most microfluidic sheath flow systems have often only confined the sample solution on the sides, leaving the top and bottom of the sample stream in contact with the floor and ceiling of the channel. While relatively simple to build, these designs increase the risk of adsorption of sample components to the top and bottom of the channel. A few designs have been successful in completely sheathing the sample stream, but these typically require multiple sheath inputs and several alignment steps. In the designs presented here, full sheathing is accomplished using as few as one sheath input, which eliminates the need to carefully balance the flow of two or more sheath inlets. The design is easily manufactured using current microfabrication techniques. Furthermore, the sample and sheath fluid can be subsequently separated for recapture of the sample fluid or re-use of the sheath fluid. Designs were demonstrated in poly(dimethylsiloxane) (PDMS) using soft lithography and poly(methyl methacrylate) (PMMA) using micromilling and laser ablation. PMID:18584084

  17. Truncation correction for oblique filtering lines

    SciTech Connect

    Hoppe, Stefan; Hornegger, Joachim; Lauritsch, Guenter; Dennerlein, Frank; Noo, Frederic

    2008-12-15

    State-of-the-art filtered backprojection (FBP) algorithms often define the filtering operation to be performed along oblique filtering lines in the detector. A limited scan field of view leads to the truncation of those filtering lines, which causes artifacts in the final reconstructed volume. In contrast to the case where filtering is performed solely along the detector rows, no methods are available for the case of oblique filtering lines. In this work, the authors present two novel truncation correction methods which effectively handle data truncation in this case. Method 1 (basic approach) handles data truncation in two successive preprocessing steps by applying a hybrid data extrapolation method, which is a combination of a water cylinder extrapolation and a Gaussian extrapolation. It is independent of any specific reconstruction algorithm. Method 2 (kink approach) uses similar concepts for data extrapolation as the basic approach but needs to be integrated into the reconstruction algorithm. Experiments are presented from simulated data of the FORBILD head phantom, acquired along a partial-circle-plus-arc trajectory. The theoretically exact M-line algorithm is used for reconstruction. Although the discussion is focused on theoretically exact algorithms, the proposed truncation correction methods can be applied to any FBP algorithm that exposes oblique filtering lines.

  18. Truncation correction for oblique filtering lines.

    PubMed

    Hoppe, Stefan; Hornegger, Joachim; Lauritsch, Günter; Dennerlein, Frank; Noo, Frédéric

    2008-12-01

    State-of-the-art filtered backprojection (FBP) algorithms often define the filtering operation to be performed along oblique filtering lines in the detector. A limited scan field of view leads to the truncation of those filtering lines, which causes artifacts in the final reconstructed volume. In contrast to the case where filtering is performed solely along the detector rows, no methods are available for the case of oblique filtering lines. In this work, the authors present two novel truncation correction methods which effectively handle data truncation in this case. Method 1 (basic approach) handles data truncation in two successive preprocessing steps by applying a hybrid data extrapolation method, which is a combination of a water cylinder extrapolation and a Gaussian extrapolation. It is independent of any specific reconstruction algorithm. Method 2 (kink approach) uses similar concepts for data extrapolation as the basic approach but needs to be integrated into the reconstruction algorithm. Experiments are presented from simulated data of the FORBILD head phantom, acquired along a partial-circle-plus-arc trajectory. The theoretically exact M-line algorithm is used for reconstruction. Although the discussion is focused on theoretically exact algorithms, the proposed truncation correction methods can be applied to any FBP algorithm that exposes oblique filtering lines.

  19. 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.

  20. Oblique Impact and Its Ejecta: Numerical Modeling

    NASA Astrophysics Data System (ADS)

    Artemieva, N.; Pierazzo, E.

    2003-01-01

    It is well known that impact events strike planetary surfaces at an angle from the surface. Assuming an isotropic flux of projectiles, probability theory indicates that the most likely angle of impact is 45 regardless of the body's gravitational field. While crater rims appear circular down to low impact angles, the distribution of ejecta around the crater is sensitive to the angle of impact and currently serves as the best guide to obliquity of impacts. A fair amount of numerical modeling of vertical impacts has been carried out from the early 60-s to the present time and references herein]. In vertical impacts, the axial symmetry of the process allows the simplification of the model to two dimensions (2D). Oblique impact modeling requires 3D hydro-codes and, hence, much more powerful computers. The first documented detailed oblique impact studies were carried out at Sandia National Labs' supercomputers less than 10 years ago to describe the 1994 collision of comet SL9 with Jupiter. Since then, substantial progress in computer science has made 3D modeling a reachable objective for the scientific community.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Linear electromagnetic excitation of an asymmetric low pressure capacitive discharge with unequal sheath widths

    SciTech Connect

    Lieberman, M. A. Lichtenberg, A. J.; Kawamura, E.; Chabert, P.

    2016-01-15

    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.

  9. Are two plasma equilibrium states possible when the emission coefficient exceeds unity?

    DOE PAGES

    Campanell, Michael D.; Umansky, M. V.

    2017-02-28

    Two floating sheath solutions with strong electron emission in planar geometry have been proposed, a “space-charge limited” (SCL) sheath and an “inverse” sheath. SCL and inverse models contain different assumptions about conditions outside the sheath (e.g., the velocity of ions entering the sheath). So it is not yet clear whether both sheaths are possible in practice, or only one. Here we treat the global presheath-sheath problem for a plasma produced volumetrically between two planar walls. We show that all equilibrium requirements (a) floating condition, (b) plasma shielding, and (c) presheath force balance, can indeed be satisfied in two different waysmore » when the emission coefficient γ > 1. There is one solution with SCL sheaths and one with inverse sheaths, each with sharply different presheath distributions. As we show for the first time in 1D-1V simulations, a SCL and inverse equilibrium are both possible in plasmas with the same upstream properties (e.g., same N and Te). However, maintaining a true SCL equilibrium requires no ionization or charge exchange collisions in the sheath, or else cold ion accumulation in the SCL's “dip” forces a transition to the inverse. This suggests that only a monotonic inverse type sheath potential should exist at any plasma-facing surface with strong emission, whether be a divertor plate, emissive probe, dust grain, Hall thruster channel wall, sunlit object in space, etc. Nevertheless, SCL sheaths might still be possible if the ions in the dip can escape. Finally, our simulations demonstrate ways in which SCL and inverse regimes might be distinguished experimentally based on large-scale presheath effects, without having to probe inside the sheath.« less

  10. Nonlinear effects associated with oblique whistler waves in space plasmas

    NASA Astrophysics Data System (ADS)

    Sharma, R. P.; Nandal, P.; Yadav, N.; Uma, R.

    2016-10-01

    In the present work, we have examined the nonlinear interaction of pump whistler wave and low frequency kinetic Alfvén wave (KAW) in three regions viz., solar wind, earth's radiation belt, and magnetopause. The modification in the background density leads to the introduction of nonlinearity. The nonlinear ponderomotive force is responsible for this change in density. Low frequency kinetic Alfvén wave is excited by the nonlinear ponderomotive force of pump whistler wave. A set of dimensionless equations characterizing the dynamics of whistler wave and low frequency KAW perturbed by whistler wave were developed. The coupled equations were then simulated numerically. The nonlinear effects related with the whistler wave were studied. The resulting localized structures and the magnetic turbulent spectra in various regions have been investigated.

  11. Malignant peripheral nerve sheath tumour of penis.

    PubMed

    Kaur, J; Madan, R; Singh, L; Sharma, D N; Julka, P K; Rath, G K; Roy, S

    2015-04-01

    Malignant peripheral nerve sheath tumour (MPNST) is a rare variety of soft tissue sarcoma that originates from Schwann cells or pluripotent cells of neural crest origin. They have historically been difficult tumours to diagnose and treat. Surgery is the mainstay of treatment with a goal to achieve negative margins. Despite aggressive surgery and adjuvant therapy, the prognosis of patients with MPNST remains poor. MPNST arising from penis is a very rare entity; thus, it presents a diagnostic and therapeutic challenge. We present a case of penile MPNST in a 38-year-old man in the absence of neurofibromatosis treated with surgery followed by post-operative radiotherapy to a dose of 60 Gray in 30 fractions and adjuvant chemotherapy with ifosfamide and adriamycin.

  12. 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.

  13. Measurements of Sheath Currents and Equilibrium Potential on the Explorer VIII Satellite (1960 xi)

    NASA Technical Reports Server (NTRS)

    Bourdeau, R. E.; Donley, J. L.; Serbu, G. P.; Whipple, E. C., Jr.

    1961-01-01

    Experimental data were obtained from the Explorer VIII satellite on five parameters pertinent to the problem of the interaction of space vehicles with an ionized atmosphere. The five parameters are: photoemission current due to electrons emitted from the satellite surfaces as a result of solar radiation; electron and positive ion currents due to the diffusion of charged particles from the medium to the spacecraft; the vehicle potential relative to the medium, and the ambient electron temperature. Included in the experimental data is the aspect dependence of the photoemission and diffusion currents. On the basis of the observations, certain characteristics of the satellite's plasma sheath are postulated.

  14. Enhanced sheath heating in capacitively coupled discharges due to non-sinusoidal voltage waveforms

    SciTech Connect

    Lafleur, T.; Boswell, R. W.; Booth, J. P.

    2012-05-07

    Through the use of particle-in-cell simulations, we demonstrate that the power deposition in capacitively coupled discharges (in argon) can be increased by replacing sinusoidal waveforms with Gaussian-shaped voltage pulses (with a repetition frequency of 13.56 MHz). By changing the Gaussian pulse width, electron heating can be directly controlled, allowing for an increased plasma density and ion flux for the same gas pressure and geometrical operating conditions. Analysis of the power deposition profiles and electron distribution functions shows that enhanced electron-sheath heating is responsible for the increased power absorption.

  15. RF-sheath heat flux estimates on Tore Supra and JET ICRF antennae. Extrapolation to ITER

    SciTech Connect

    Colas, L.; Portafaix, C.; Goniche, M.; Jacquet, Ph.

    2009-11-26

    RF-sheath induced heat loads are identified from infrared thermography measurements on Tore Supra ITER-like prototype and JET A2 antennae, and are quantified by fitting thermal calculations. Using a simple scaling law assessed experimentally, the estimated heat fluxes are then extrapolated to the ITER ICRF launcher delivering 20 MW RF power for several plasma scenarios. Parallel heat fluxes up to 6.7 MW/m{sup 2} are expected very locally on ITER antenna front face. The role of edge density on operation is stressed as a trade-off between easy RF coupling and reasonable heat loads. Sources of uncertainty on the results are identified.

  16. 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.

  17. Controllable fabrication of ultrafine oblique organic nanowire arrays and their application in energy harvesting

    NASA Astrophysics Data System (ADS)

    Zhang, Lu; Cheng, Li; Bai, Suo; Su, Chen; Chen, Xiaobo; Qin, Yong

    2015-01-01

    Ultrafine organic nanowire arrays (ONWAs) with a controlled direction were successfully fabricated by a novel one-step Faraday cage assisted plasma etching method. The mechanism of formation of nanowire arrays is proposed; the obliquity and aspect ratio can be accurately controlled from approximately 0° to 90° via adjusting the angle of the sample and the etching time, respectively. In addition, the ONWAs were further utilized to improve the output of the triboelectric nanogenerator (TENG). Compared with the output of TENG composed of vertical ONWAs, the open-circuit voltage, short-circuit current and inductive charges were improved by 73%, 150% and 98%, respectively. This research provides a convenient and practical method to fabricate ONWAs with various obliquities on different materials, which can be used for energy harvesting.

  18. Controllable fabrication of ultrafine oblique organic nanowire arrays and their application in energy harvesting.

    PubMed

    Zhang, Lu; Cheng, Li; Bai, Suo; Su, Chen; Chen, Xiaobo; Qin, Yong

    2015-01-28

    Ultrafine organic nanowire arrays (ONWAs) with a controlled direction were successfully fabricated by a novel one-step Faraday cage assisted plasma etching method. The mechanism of formation of nanowire arrays is proposed; the obliquity and aspect ratio can be accurately controlled from approximately 0° to 90° via adjusting the angle of the sample and the etching time, respectively. In addition, the ONWAs were further utilized to improve the output of the triboelectric nanogenerator (TENG). Compared with the output of TENG composed of vertical ONWAs, the open-circuit voltage, short-circuit current and inductive charges were improved by 73%, 150% and 98%, respectively. This research provides a convenient and practical method to fabricate ONWAs with various obliquities on different materials, which can be used for energy harvesting.

  19. Mixing the Solar Wind Proton and Electron Scales: Effects of Electron Temperature Anisotropy on the Oblique Proton Firehose Instability

    NASA Technical Reports Server (NTRS)

    Maneva, Y.; Lazar, M.; Vinas, A.; Poedts, S.

    2016-01-01

    The double adiabatic expansion of the nearly collisionless solar wind plasma creates conditions for the firehose instability to develop and efficiently prevent the further increase of the plasma temperature in the direction parallel to the interplanetary magnetic field. The conditions imposed by the firehose instability have been extensively studied using idealized approaches that ignore the mutual effects of electrons and protons. Recently, more realistic approaches have been proposed that take into account the interplay between electrons and protons,? unveiling new regimes of the parallel oscillatory modes. However, for oblique wave propagation the instability develops distinct branches that grow much faster and may therefore be more efficient than the parallel firehose instability in constraining the temperature anisotropy of the plasma particles. This paper reports for the first time on the effects of electron plasma properties on the oblique proton firehose (PFH) instability and provides a comprehensive vision of the entire unstable wave-vector spectrum, unifying the proton and the smaller electron scales. The plasma ß and temperature anisotropy regimes considered here are specific for the solar wind and magnetospheric conditions, and enable the electrons and protons to interact via the excited electromagnetic fluctuations. For the selected parameters, simultaneous electron and PFH instabilities can be observed with a dispersion spectrum of the electron firehose (EFH) extending toward the proton scales. Growth rates of the PFH instability are markedly boosted by the anisotropic electrons, especially in the oblique direction where the EFH growth rates are orders of magnitude higher.

  20. Abiotic Deposition of Fe Complexes onto Leptothrix Sheaths.

    PubMed

    Kunoh, Tatsuki; Hashimoto, Hideki; McFarlane, Ian R; Hayashi, Naoaki; Suzuki, Tomoko; Taketa, Eisuke; Tamura, Katsunori; Takano, Mikio; El-Naggar, Mohamed Y; Kunoh, Hitoshi; Takada, Jun

    2016-06-03

    Bacteria classified in species of the genus Leptothrix produce extracellular, microtubular, Fe-encrusted sheaths. The encrustation has been previously linked to bacterial Fe oxidases, which oxidize Fe(II) to Fe(III) and/or active groups of bacterial exopolymers within sheaths to attract and bind aqueous-phase inorganics. When L. cholodnii SP-6 cells were cultured in media amended with high Fe(II) concentrations, Fe(III) precipitates visibly formed immediately after addition of Fe(II) to the medium, suggesting prompt abiotic oxidation of Fe(II) to Fe(III). Intriguingly, these precipitates were deposited onto the sheath surface of bacterial cells as the population was actively growing. When Fe(III) was added to the medium, similar precipitates formed in the medium first and were abiotically deposited onto the sheath surfaces. The precipitates in the Fe(II) medium were composed of assemblies of globular, amorphous particles (ca. 50 nm diameter), while those in the Fe(III) medium were composed of large, aggregated particles (≥3 µm diameter) with a similar amorphous structure. These precipitates also adhered to cell-free sheaths. We thus concluded that direct abiotic deposition of Fe complexes onto the sheath surface occurs independently of cellular activity in liquid media containing Fe salts, although it remains unclear how this deposition is associated with the previously proposed mechanisms (oxidation enzyme- and/or active group of organic components-involved) of Fe encrustation of the Leptothrix sheaths.

  1. Morphogenesis of the fibrous sheath in the marsupial spermatozoon.

    PubMed

    Ricci, M; Breed, W G

    2005-08-01

    The spermatozoon fibrous sheath contains longitudinal columns and circumferential ribs. It surrounds the axoneme of the principal piece of the mammalian sperm tail, and may be important in sperm stability and motility. Here we describe its assembly during spermiogenesis in a marsupial, the brush-tail possum, and compare its structural organization with that of eutherian mammals, birds and reptiles. Transmission electron microscopy showed that possum fibrous sheath assembly is a multistep process extending in a distal-to-proximal direction along the axoneme from steps 4 to 14 of spermiogenesis. For the most part, assembly of the longitudinal columns occurs before that of the circumferential ribs. Immunohistochemical and immunogold labelling showed that fibrous sheath proteins are first present in the spermatid cytoplasm; at least some of the proteins of the sheath precursors differ from those in the mature fibrous sheath. That immunoreactivity develops after initiation of chromatin condensation suggests that fibrous sheath proteins, or their mRNAs, are stored within the spermatid cytoplasmic lobule prior to their assembly along the axoneme. These findings are similar to those in laboratory rats, and thus suggests that the mode of fibrous sheath assembly evolved in a common ancestor over 125 million years ago, prior to the divergence of marsupial and eutherian lineages.

  2. Abiotic Deposition of Fe Complexes onto Leptothrix Sheaths

    PubMed Central

    Kunoh, Tatsuki; Hashimoto, Hideki; McFarlane, Ian R.; Hayashi, Naoaki; Suzuki, Tomoko; Taketa, Eisuke; Tamura, Katsunori; Takano, Mikio; El-Naggar, Mohamed Y.; Kunoh, Hitoshi; Takada, Jun

    2016-01-01

    Bacteria classified in species of the genus Leptothrix produce extracellular, microtubular, Fe-encrusted sheaths. The encrustation has been previously linked to bacterial Fe oxidases, which oxidize Fe(II) to Fe(III) and/or active groups of bacterial exopolymers within sheaths to attract and bind aqueous-phase inorganics. When L. cholodnii SP-6 cells were cultured in media amended with high Fe(II) concentrations, Fe(III) precipitates visibly formed immediately after addition of Fe(II) to the medium, suggesting prompt abiotic oxidation of Fe(II) to Fe(III). Intriguingly, these precipitates were deposited onto the sheath surface of bacterial cells as the population was actively growing. When Fe(III) was added to the medium, similar precipitates formed in the medium first and were abiotically deposited onto the sheath surfaces. The precipitates in the Fe(II) medium were composed of assemblies of globular, amorphous particles (ca. 50 nm diameter), while those in the Fe(III) medium were composed of large, aggregated particles (≥3 µm diameter) with a similar amorphous structure. These precipitates also adhered to cell-free sheaths. We thus concluded that direct abiotic deposition of Fe complexes onto the sheath surface occurs independently of cellular activity in liquid media containing Fe salts, although it remains unclear how this deposition is associated with the previously proposed mechanisms (oxidation enzyme- and/or active group of organic components-involved) of Fe encrustation of the Leptothrix sheaths. PMID:27271677

  3. Morphogenesis of the fibrous sheath in the marsupial spermatozoon

    PubMed Central

    Ricci, M; Breed, WG

    2005-01-01

    The spermatozoon fibrous sheath contains longitudinal columns and circumferential ribs. It surrounds the axoneme of the principal piece of the mammalian sperm tail, and may be important in sperm stability and motility. Here we describe its assembly during spermiogenesis in a marsupial, the brush-tail possum, and compare its structural organization with that of eutherian mammals, birds and reptiles. Transmission electron microscopy showed that possum fibrous sheath assembly is a multistep process extending in a distal-to-proximal direction along the axoneme from steps 4 to 14 of spermiogenesis. For the most part, assembly of the longitudinal columns occurs before that of the circumferential ribs. Immunohistochemical and immunogold labelling showed that fibrous sheath proteins are first present in the spermatid cytoplasm; at least some of the proteins of the sheath precursors differ from those in the mature fibrous sheath. That immunoreactivity develops after initiation of chromatin condensation suggests that fibrous sheath proteins, or their mRNAs, are stored within the spermatid cytoplasmic lobule prior to their assembly along the axoneme. These findings are similar to those in laboratory rats, and thus suggests that the mode of fibrous sheath assembly evolved in a common ancestor over 125 million years ago, prior to the divergence of marsupial and eutherian lineages. PMID:16050902

  4. Influence of geophysical factors on oblique-sounder ionospheric characteristics

    SciTech Connect

    Baranets, A.N.; Blagoveshchenskaya, N.F.; Borisova, T.D.; Bubnov, V.A.

    1988-10-01

    The purpose of this paper is to study the influence of geophysical factors, including magnetoionospheric disturbances, on decameter wave propagation over extended paths using oblique sounding (OS) data, and also to compare experimental and calculated OS ionograms for various conditions of radio waver propagation (season, time of day). Variations of oblique-sounder ionospheric characteristics along a 9000 km long subauroral path for various geophysical conditions are considered. A comparison is made of experimental and calculated ionograms of oblique sounding.

  5. On the interpretation of Langmuir probe data inside a spacecraft sheath.

    PubMed

    Olson, J; Brenning, N; Wahlund, J-E; Gunell, H

    2010-10-01

    If a Langmuir probe is located inside the sheath of a negatively charged spacecraft, there is a risk that the probe characteristic is modified compared to that of a free probe in the ambient plasma. We have studied this probe-in-spacecraft-sheath problem in the parameter range of a small Langmuir probe (with radius r(LP)≪λ(D)) using a modified version of the orbit motion limited (OML) probe theory. We find that the ambient electron contribution I(e)(U(LP)) to the probe characteristic is suitably analyzed in terms of three regions of applied probe potential U(LP). In region I, where the probe is negatively charged (i.e., U(LP)sheath at the probe position), the probe characteristic I(e)(U(LP)) is close to that of OML theory for a free probe in the ambient plasma. In the probe potential range U(LP)>U(1), there is first a transition region II in applied potential, U(1)plasma. This minimum gives the depth U(pl)-U(M) of a potential barrier that prevents the lowest energy ambient electrons from reaching the probe. For a high enough positive probe potential, in region III, the barrier becomes small. Here, I(e)(U(LP)) again approaches OML theory for a free probe. The boundary U(2) between regions II and III is somewhat arbitrary; we propose a condition on the barrier, U(pl)-U(M)≪k(B)T(e)/e, as the definition of region III. The main findings in this work are qualitative rather than quantitative. The existence of the transition region points to that special care must be taken to extract plasma parameters from measured I(U(LP)) as the probe characteristic is likely to depart from usual OML in crucial respects: (1) the ambient plasma potential U(pl) falls into the transition region, but there is no obvious knee or other feature to identify it, (2) there is in this region no exponential part of I

  6. On the interpretation of Langmuir probe data inside a spacecraft sheath

    SciTech Connect

    Olson, J.; Brenning, N.; Wahlund, J.-E.; Gunell, H.

    2010-10-15

    If a Langmuir probe is located inside the sheath of a negatively charged spacecraft, there is a risk that the probe characteristic is modified compared to that of a free probe in the ambient plasma. We have studied this probe-in-spacecraft-sheath problem in the parameter range of a small Langmuir probe (with radius r{sub LP}<<{lambda}{sub D}) using a modified version of the orbit motion limited (OML) probe theory. We find that the ambient electron contribution I{sub e}(U{sub LP}) to the probe characteristic is suitably analyzed in terms of three regions of applied probe potential U{sub LP}. In region I, where the probe is negatively charged (i.e., U{sub LP}sheath at the probe position), the probe characteristic I{sub e}(U{sub LP}) is close to that of OML theory for a free probe in the ambient plasma. In the probe potential range U{sub LP}>U{sub 1}, there is first a transition region II in applied potential, U{sub 1}plasma. This minimum gives the depth U{sub pl}-U{sub M} of a potential barrier that prevents the lowest energy ambient electrons from reaching the probe. For a high enough positive probe potential, in region III, the barrier becomes small. Here, I{sub e}(U{sub LP}) again approaches OML theory for a free probe. The boundary U{sub 2} between regions II and III is somewhat arbitrary; we propose a condition on the barrier, U{sub pl}-U{sub M}<plasma parameters from measured I(U{sub LP}) as the probe characteristic is likely to depart from usual OML in crucial respects: (1) the ambient plasma potential U{sub pl} falls into the transition

  7. 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.

  8. 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

  9. Rectus sheath haematoma: a rare masquerader for abdominal pain.

    PubMed

    Changal, Khalid Hamid; Saleem, Saad; Ghous, Ghulam

    2017-04-13

    Rectus sheath haematoma is a rare cause of abdominal pain. It can be easily confused for other causes of acute abdomen and may even lead to unnecessary laparotomies. Our patient has the rectus sheath haematoma because of violent coughing and on presentation had no obvious clinical sign pointing to the same. Diagnosis was made by a CT scan of the abdomen, and patient was treated conservatively. Rectus sheath haematomas are usually present on the posterior aspect of the rectus muscles and thus may not be clinically appreciable.

  10. Analytical model for the radio-frequency sheath.

    PubMed

    Czarnetzki, Uwe

    2013-12-01

    A simple analytical model for the planar radio-frequency (rf) sheath in capacitive discharges is developed that is based on the assumptions of a step profile for the electron front, charge exchange collisions with constant cross sections, negligible ionization within the sheath, and negligible ion dynamics. The continuity, momentum conservation, and Poisson equations are combined in a single integro-differential equation for the square of the ion drift velocity, the so called sheath equation. Starting from the kinetic Boltzmann equation, special attention is paid to the derivation and the validity of the approximate fluid equation for momentum balance. The integrals in the sheath equation appear in the screening function which considers the relative contribution of the temporal mean of the electron density to the space charge in the sheath. It is shown that the screening function is quite insensitive to variations of the effective sheath parameters. The two parameters defining the solution are the ratios of the maximum sheath extension to the ion mean free path and the Debye length, respectively. A simple general analytic expression for the screening function is introduced. By means of this expression approximate analytical solutions are obtained for the collisionless as well as the highly collisional case that compare well with the exact numerical solution. A simple transition formula allows application to all degrees of collisionality. In addition, the solutions are used to calculate all static and dynamic quantities of the sheath, e.g., the ion density, fields, and currents. Further, the rf Child-Langmuir laws for the collisionless as well as the collisional case are derived. An essential part of the model is the a priori knowledge of the wave form of the sheath voltage. This wave form is derived on the basis of a cubic charge-voltage relation for individual sheaths, considering both sheaths and the self-consistent self-bias in a discharge with arbitrary

  11. Analytical model for the radio-frequency sheath

    NASA Astrophysics Data System (ADS)

    Czarnetzki, Uwe

    2013-12-01

    A simple analytical model for the planar radio-frequency (rf) sheath in capacitive discharges is developed that is based on the assumptions of a step profile for the electron front, charge exchange collisions with constant cross sections, negligible ionization within the sheath, and negligible ion dynamics. The continuity, momentum conservation, and Poisson equations are combined in a single integro-differential equation for the square of the ion drift velocity, the so called sheath equation. Starting from the kinetic Boltzmann equation, special attention is paid to the derivation and the validity of the approximate fluid equation for momentum balance. The integrals in the sheath equation appear in the screening function which considers the relative contribution of the temporal mean of the electron density to the space charge in the sheath. It is shown that the screening function is quite insensitive to variations of the effective sheath parameters. The two parameters defining the solution are the ratios of the maximum sheath extension to the ion mean free path and the Debye length, respectively. A simple general analytic expression for the screening function is introduced. By means of this expression approximate analytical solutions are obtained for the collisionless as well as the highly collisional case that compare well with the exact numerical solution. A simple transition formula allows application to all degrees of collisionality. In addition, the solutions are used to calculate all static and dynamic quantities of the sheath, e.g., the ion density, fields, and currents. Further, the rf Child-Langmuir laws for the collisionless as well as the collisional case are derived. An essential part of the model is the a priori knowledge of the wave form of the sheath voltage. This wave form is derived on the basis of a cubic charge-voltage relation for individual sheaths, considering both sheaths and the self-consistent self-bias in a discharge with arbitrary

  12. Insolation on exoplanets with eccentricity and obliquity

    NASA Astrophysics Data System (ADS)

    Dobrovolskis, Anthony R.

    2013-09-01

    The pattern of insolation on an extrasolar planet has profound implications for its climate and habitability. A planet’s insolation regime depends on its orbital eccentricity, the obliquity of its spin axis, its rotation rate, and its longitude of vernal equinox. For example, although a planet receives the same time-averaged insolation at both poles, the peak insolation at its poles can differ by a factor up to 27, depending on its eccentricity and equinox. This is of particular interest for planets with polar icecaps (or lakes and seas), like Mercury, Earth, and Mars (or Titan). The nearly 600 exoplanets now with known eccentricities span a wide range of eccentricity from essentially zero up to near unity; but their obliquities are still unknown, and also may range widely. Including both non-zero eccentricity and obliquity together vastly broadens the variety of global insolation patterns on extrasolar planets. This applies especially to planets in synchronous rotation, or in other spin-orbit resonances (like Mercury), which can exhibit quite complicated and unusual insolation patterns. For example, regions of eternal daylight and endless night occur only on synchronous exoplanets, whose rotation periods equal their orbital periods; but the peak and time-averaged insolation can vary by factors of at least 32 and 88, respectively, over a planet with a rotation period of half its orbital period, an eccentricity of 0.20, and an obliquity of 60°. Patterns of both mean and peak insolation display various symmetries with respect to latitude and longitude on the planet’s surface. Most of these are relatively simple and easily understood; for example, a resonant planet whose orbital period is half of an odd multiple of its rotation period (as in Mercury’s 3/2 resonance) experiences identical insolation patterns at longitudes 180° apart. However, such half-odd resonances also exhibit a totally unexpected symmetry of the time-averaged insolation with respect to the

  13. Distal oblique osteotomy for tailor's bunion.

    PubMed

    Zvijac, J E; Janecki, C J; Freeling, R M

    1991-12-01

    Thirty-six patients with a total of 50 symptomatic tailor's bunions were evaluated clinically, radiographically, and subjectively, both before and after a distal oblique osteotomy procedure was performed. Thirty-four of 36 patients were satisfied with pain relief. Radiographic measurements derived from this study were consistent with those of other studies. Avascular necrosis, nonunions, or neuroma formation were not encountered in this study. The significant advantages of this procedure are its simplicity, safety, and predictability. The procedure does not require internal fixation or postoperative immobilization.

  14. Polarization and Compressibility of Oblique Kinetic Alfven Waves

    NASA Technical Reports Server (NTRS)

    Hunana, Peter; Goldstein, M. L.; Passot, T.; Sulem, P. L.; Laveder, D.; Zank, G. P.

    2012-01-01

    Even though solar wind, as a collisionless plasma, is properly described by the kineticMaxwell-Vlasov description, it can be argued that much of our understanding of solar wind observational data comes from an interpretation and numerical modeling which is based on a fluid description of magnetohydrodynamics. In recent years, there has been a significant interest in better understanding the importance of kinetic effects, i.e. the differences between the kinetic and usual fluid descriptions. Here we concentrate on physical properties of oblique kinetic Alfvn waves (KAWs), which are often recognized as one of the key ingredients in the solar wind turbulence cascade. We use three different fluid models with various degrees of complexity and calculate polarization and magnetic compressibility of oblique KAWs (propagation angle q = 88), which we compare to solutions derived from linear kinetic theory. We explore a wide range of possible proton plasma b = [0.1,10.0] and a wide range of length scales krL = [0.001,10.0]. It is shown that the classical isotropic two-fluid model is very compressible in comparison with kinetic theory and that the largest discrepancy occurs at scales larger than the proton gyroscale. We also show that the two-fluid model contains a large error in the polarization of electric field, even at scales krL 1. Furthermore, to understand these discrepancies between the two-fluid model and the kinetic theory, we employ two versions of the Landau fluid model that incorporate linear low-frequency kinetic effects such as Landau damping and finite Larmor radius (FLR) corrections into the fluid description. It is shown that Landau damping significantly reduces the magnetic compressibility and that FLR corrections (i.e. nongyrotropic contributions) are required to correctly capture the polarization.We also show that, in addition to Landau damping, FLR corrections are necessary to accurately describe the damping rate of KAWs. We conclude that kinetic effects

  15. Reproducing continuous radio blackout using glow discharge plasma

    SciTech Connect

    Xie, Kai; Li, Xiaoping; Liu, Donglin; Shao, Mingxu; Zhang, Hanlu

    2013-10-15

    A novel plasma generator is described that offers large-scale, continuous, non-magnetized plasma with a 30-cm-diameter hollow structure, which provides a path for an electromagnetic wave. The plasma is excited by a low-pressure glow discharge, with varying electron densities ranging from 10{sup 9} to 2.5 × 10{sup 11} cm{sup −3}. An electromagnetic wave propagation experiment reproduced a continuous radio blackout in UHF-, L-, and S-bands. The results are consistent with theoretical expectations. The proposed method is suitable in simulating a plasma sheath, and in researching communications, navigation, electromagnetic mitigations, and antenna compensation in plasma sheaths.

  16. One-dimensional particle-in-cell simulation on the influence of electron and ion temperature on the sheath expansion process in the post-arc stage of vacuum circuit breaker

    SciTech Connect

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

    2015-02-15

    The inter-contact region of vacuum circuit breakers is filled with residual plasma at the moment when the current is zero after the burning of metal vapor arc. The residual plasma forms an ion sheath in front of the post-arc cathode. The sheath then expands towards the post-arc anode under the influence of a transient recovery voltage. In this study, a one-dimensional particle-in-cell model is developed to investigate the post-arc sheath expansion. The influence of ion and electron temperatures on the decrease in local plasma density at the post-arc cathode side and post-arc anode side is discussed. When the decay in the local plasma density develops from the cathode and anode sides into the high-density region and merges, the overall plasma density in the inter-contact region begins to decrease. Meanwhile, the ion sheath begins to expand faster. Furthermore, the theory of ion rarefaction wave only explains quantitatively the decrease in the overall plasma density at relatively low ion temperatures. With the increase of ion temperature to certain extent, another possible reason for the decrease in the overall plasma density is proposed and results from the more active thermal diffusion of plasma.

  17. Experimental Study of Convective Cells and RF Sheaths Excited by a Fast Wave Antenna in the LAPD

    NASA Astrophysics Data System (ADS)

    Martin, Michael; Gekelman, Walter; Pribyl, Patrick; van Compernolle, Bart; Carter, Troy; van Eester, Dirk; Crombé, Kristel

    2016-10-01

    Ion cyclotron resonance heating (ICRH) will be essential for ITER where it is planned to couple 20 MW to the plasma. During ICRH, radio frequency (RF) sheaths may form on the antenna or farther away, and convective cells are suspected to form adjacent to ICRH antennas, negatively affecting both machine and plasma performance. The LAPD (ne 10 12 - 13cm-3 , Te 1-10 eV, B0 0.4 to 2 kG, diameter 60 cm, length 17m) is an ideal device for performing detailed experiments to fully diagnose these phenomena. A 200 kW RF system capable of pulsing at the 1 Hz. rep. rate of the LAPD and operating from 2 to 2.5 MHz has been constructed to perform such studies. B0 can be adjusted so that this encompasses the 1st to 7th harmonic of fci in H plasmas. Emissive, Mach, Langmuir, and B-field probes measured plasma potential, bulk plasma flows, wave patterns, ne, and Te in 2D planes at various axial locations from the antenna. Plasma potential enhancements of up to 90 V along magnetic field lines connected to the antenna and induced ExB flows consistent in structure with convective cells were observed. Details of these observations along with power scaling of RF sheath voltage and convective cell flows will be presented.

  18. Oblique slip in Laramide foreland arches

    SciTech Connect

    Erslev, E.A.; Selvig, B.; Molzer, P. . Dept. of Earth Resources)

    1993-03-01

    Don Wise was one of the first structural geologists to recognize the complex, four-dimensional (space and time) nature of basement-involved faulting in the Rocky Mountain foreland. His focus on both small scale kinematic indicators and regional tectonic hypotheses has provided a launching point for many Rocky Mountain geologists. The implications of the anastomosing patterns of Laramide foreland arches on models of regional stress and strain have provoked considerable debate. Hypotheses range from those invoking multiple stages of lateral compression from different directions to single-stage models necessitating a component of strike-slip motion in east-west and north-south arches. These hypotheses were tested using slickenline analysis of minor faulting in structures with different orientations. In Wyoming, structures paralleling the dominant northwest structural trend have slickenlines in the NE-SW vertical plane, consistent with shortening and compression in this direction. The east-west Owl Creek and Casper Mountain structures also have NE-SW trending slickenlines, indicating slip oblique to these arches. In Colorado, minor faults in the north-south margin of the northeastern Front Range also indicate oblique slip, with shortening in the NE-SW quadrant. The actual trend of the slickenlines is more easterly, however, suggesting a change of slip trajectory with latitude, not time, possibly in response to identation by the Colorado Plateau.

  19. Venus - Oblique View of Crater Riley

    NASA Technical Reports Server (NTRS)

    1992-01-01

    This Magellan full resolution radar mosaic centered at 14 degrees north latitude, 72 degrees east longitude, shows an oblique view of the impact crater Riley, named for Margaretta Riley, a 19th Century botanist. This view was prepared from two left-looking Magellan radar images acquired with different incidence angles. Because the relief displacements of the two images are different, depths from the crater rim to the crater floor and heights of the crater rim and flanks above the surrounding plains can be measured. The crater is 25 kilometers (15.5 miles) in diameter. The floor of the crater is 580 meters (1,914 feet) below the plains surrounding the crater. The crater's rim rises 620 meters (2,046 feet) above the plains and 1,200 meters (3,960 feet) above the crater floor. The crater's central peak is 536 meters (1,769 feet) high. The crater's diameter is 40 times the depth resulting in a relatively shallow appearance. The topography is exaggerated by 22 times to emphasize the crater's features. This oblique view was produced from two left-looking radar stereo image mosaics utilizing photogrammetric software developed by the Solar System Visualization Project and the Digital Image Animation Laboratory at JPL's Multimission Image Processing Laboratory.

  20. Use of a straight, side-hole delivery sheath for improved delivery of Amplatzer ASD occluder.

    PubMed

    Kutty, Shelby; Asnes, Jeremy D; Srinath, Gowdagere; Preminger, Tamar J; Prieto, Lourdes R; Latson, Larry A

    2007-01-01

    The Amplatzer ASD occluder may be difficult to position in some patients with a large atrial septal defect (ASD) or deficiency of one or more atrial septal rims. We developed a method to modify a Mullins transseptal sheath to enhance delivery. The resulting sheath is straight and has an exit orifice essential in the side of the distal portion of the sheath-a straight, side-hole (SSH) delivery sheath. We have used this modified delivery sheath in 140 successive patients with excellent results. The techniques of sheath modification and delivery of the device using the modified sheath are described.

  1. Oblique and lateral impact response of the PMHS thorax.

    PubMed

    Shaw, Joshua M; Herriott, Rodney G; McFadden, Joseph D; Donnelly, Bruce R; Bolte, John H

    2006-11-01

    This study characterizes the PMHS thoracic response to blunt impact in oblique and lateral directions. A significant amount of data has been collected from lateral impacts conducted on human cadavers. Substantially less data has been collected from impacts that are anterior of lateral in an oblique direction. In the past, data collected from the handful of oblique impact studies were considered to be similar enough to the data from purely lateral impacts such that the oblique data were combined with data from lateral impacts. Defining the biomechanical response of the PMHS thorax to oblique impact is of great importance in side impact vehicle crashes where the loading is often anterior-oblique in direction. Data in this study was obtained from a chestband placed on the thorax at the level of impact to measure thoracic deflection. Two low energy impacts were conducted on each of seven subjects at 2.5 m/s, with one lateral impact and one oblique impact to opposite sides of each PMHS. Data was normalized using the Mertz-Viano method for a two mass system to allow for inter-subject comparisons. Force versus deflection response corridors were generated for the two impact types using an objective mathematical approach and compared to one another. Results were also compared to existing data for oblique and lateral thoracic impacts. The oblique thoracic response in low speed pendulum impacts was found to be different than the lateral thoracic response, in terms of force and deflection. Specifically, the lateral force was greater than the oblique force, and oblique deflection greater than lateral deflection for equal energy impacts.

  2. Measure Guideline: Guidance on Taped Insulating Sheathing Drainage Planes

    SciTech Connect

    Grin, A.; Lstiburek, J.

    2014-09-01

    The goal of this research is to provide durable and long-term water management solutions using exterior insulating sheathing as part of the water management system. It is possible to tape or seal the joints in insulating sheathing to create a drainage plane and even an air control layer. There exists the material durability component of the tape as well as the system durability component being the taped insulating sheathing as the drainage plane. This measure guideline provides best practice and product recommendations from the interviewed contractors and homebuilders who collectively have a vast amount of experience. Three significant issues were discussed with the group, which are required to make taped insulating sheathing a simple, long-term, and durable drainage plane: horizontal joints should be limited or eliminated wherever possible; where a horizontal joint exists use superior materials; and frequent installation inspection and regular trade training are required to maintain proper installation.

  3. Detail of trusses and wood sheathing in the leanto bay ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Detail of trusses and wood sheathing in the lean-to bay of the roundhouse and car repair shop looking north. - U.S. Steel National Tube Works, Auxiliary Buildings, Along Monongahela River, McKeesport, Allegheny County, PA

  4. Porous protective solid phase micro-extractor sheath

    DOEpatents

    Andresen, Brian D.; Randich, Erik

    2005-03-29

    A porous protective sheath for active extraction media used in solid phase microextraction (SPME). The sheath permits exposure of the media to the environment without the necessity of extending a fragile coated fiber from a protective tube or needle. Subsequently, the sheath can pierce and seal with GC-MS septums, allowing direct injection of samples into inlet ports of analytical equipment. Use of the porous protective sheath, within which the active extraction media is contained, mitigates the problems of: 1) fiber breakage while the fiber is extended during sampling, 2) active media coating loss caused by physical contact of the bare fiber with the sampling environment; and 3) coating slough-off during fiber extension and retraction operations caused by rubbing action between the fiber and protective needle or tube.

  5. 32. DETAIL OF GEARS LOOKING NORTH WITH SHEATHING REMOVED AND ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    32. DETAIL OF GEARS LOOKING NORTH WITH SHEATHING REMOVED AND SHAFT OF KING GEAR BEYOND - Caleb Crosby Threshing Barn, Noeton (moved to Norris Dam State Park, Lake City), Morristown, Hamblen County, TN

  6. Smoky Plasma

    NASA Astrophysics Data System (ADS)

    Robertson, Scott; Sternovsky, Zoltan

    2006-10-01

    The mesosphere contains nanometer-sized smoke particles that have formed in the vapor trails of meteors and that are thought to be the condensation nuclei for noctilucent clouds. Laboratory dusty plasmas often have the dust particles in a layer at the lower sheath boundary. We examine the possibility of creating in a double-plasma device a smoky plasma in which the particles would be sufficiently small to fill the plasma nearly uniformly while being sufficiently large to exhibit multiple charge states that would distinguish the smoky plasma from one containing heavy negative ions. For example, nanometer sized atomic clusters of Ag (4 nm radius, 10,000 atoms) can be generated in an oven with an inert gas that carries the particles into the plasma chamber. These particles will become charged negatively with about 8 electrons and will then be electrostatically contained by the presheath electric field The confining electric force will also be greater than the ion drag force that could otherwise create a void in the smoke particle density distribution. This plasma would make possible, for example, experiments on the coupling of electrostatic waves to fluid turbulence by the neutral drag force. An acoustic wave propagating in smoky plasma will exert different drag forces on electrons, ions, and smoke particles thus creating a charge-separation electric field that can be measured by potential probes. This coupling may be the origin of electrostatic fluctuations seen by rocket-borne electric field probes in the mesosphere. Supported by the NSF/DOE Plasma Science Initiative.

  7. Sheath ionization model of beam emissions from large spacecraft

    NASA Technical Reports Server (NTRS)

    Lai, S. T.; Cohen, H. A.; Bhavnani, K. H.; Tautz, M. E.

    1985-01-01

    An analytical model of the charging of a spacecraft emitting electron and ion beams has been applied to the case of large spacecraft. In this model, ionization occurs in the sheath due to the return current. Charge neutralization of spherical space charge flow is examined by solving analytical equations numerically. Parametric studies of potential large spacecraft are performed. As in the case of small spacecraft, the ions created in the sheath by the returning current play a large role in determining spacecraft potential.

  8. Oblique echoes at unusually high frequencies in MARSIS-AIS measurements of the topside ionosphere of Mars

    NASA Astrophysics Data System (ADS)

    Fallows, Kathryn J.; Withers, Paul; Morgan, David

    2016-10-01

    The topside plasma density measurements from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on the Mars Express orbiter have been invaluable for studying the influence of the crustal magnetic fields on the distribution of plasma in the Mars ionosphere. A common feature, especially in the southern crustal field region, is an "oblique echo," or an off-nadir reflection consistent with the spacecraft passing by, or directly above, a localized region with a sharp gradient in electron density. These are often interpreted as regions where the ionosphere is heated by the solar wind fields and plasma which penetrate the ionosphere along vertical field lines.We present a subset of these oblique echoes which are characterized by reflections at frequencies much higher than those from the nadir ionosphere. If these are interpreted in the same way as typical return signals, where the frequency of the reflected signal is assumed to be the plasma frequency at the point of reflection, then these may be the highest plasma densities reported to date at Mars. In two cases, reflections are detected at the maximum sounding frequency of the instrument, 5.5 MHz, which corresponds to electron densities of 3.75x105 cm-3.These features are associated with strong, vertical magnetic fields, as expected for typical oblique echoes. However, they are only observed in regions where there is also an above-average likelihood of the field lines being open to the solar wind. This is consistent with the interpretation that these cusp-like regions can allow for interaction with the solar wind, but it is not yet clear whether these are an extreme case of "typical" oblique echoes, or whether these high-frequency echoes are caused by a unique physical process or observation geometry.

  9. Magnetic probe measurements of the current sheath on the PF-3 facility

    SciTech Connect

    Krauz, V. I.; Mitrofanov, K. N.; Myalton, V. V.; Vinogradov, V. P.; Vinogradova, Yu. V.; Grabovski, E. V.; Zukakishvili, G. G.; Koidan, V. S.; Mokeev, A. N.

    2010-11-15

    Results are presented from experimental studies of the dynamics of the current sheath (CS) on the PF-3 plasma focus facility. The parameters of the sheath, including the current distribution in it, were measured using absolutely calibrated magnetic probes installed at different positions with respect to the facility axis and the anode surface. The CS dynamics in discharges operating in argon and neon was investigated, and the skin depth in different stages of the discharge was determined. One of the probes was installed at a distance of {approx}2 cm from the facility axis, which made it possible to estimate the efficiency of current transfer to the region of pinch formation. Operating modes were obtained in which the current dynamics detected by magnetic probes at different distances from the axis agreed well with the dynamics of the total discharge current until the instant of singularity in the current time derivative. It is shown that shunting breakdowns can lead to the formation of closed current loops. The shunting of the discharge current by the residual plasma is directly related to the efficiency of snowplowing of the working gas by the CS as it propagates from the insulator toward the facility axis.

  10. On Plasma Theory and Simulation.

    DTIC Science & Technology

    2014-09-26

    SHEATH REGION INCLUDING ION REFLECTION Lou Ann Schwager (Prof. C. K. Birdsall, Dr. I. Roth ) A low temperature plasma interacts with a collector plate...Hitchcock. Katz. Lankford. Nelson. Barnes. Borovsky. Forslund. Kwan. Sadowski Lindemuth. Mason . Mostrom. Nielson, Oliphant. Sgro. Thode Department of

  11. Rectus sheath tunnels for continent stomas.

    PubMed

    Dickson, Alan P; Khalil, Basem A; Cervellione, Raimondo M

    2008-03-01

    Continent stoma rectus sheath tunnel (CSRST) has been used in antegrade colonic enema (ACE) and urinary continent cutaneous diversion (UCCD) stomas to reduce leakage and to support a straight track for the continent conduit. All patients that underwent CSRST between 1995 and 2005 were identified and their case notes retrospectively reviewed. Patients were divided into two groups: the ACE group and the UCCD group. Demographic data, age at surgery and complications including stenosis and leakage were recorded. Forty patients underwent CSRST between 1995 and 2005. The mean age and standard deviation (SD) at surgery was 6.8 (2.1) years. Eighteen patients underwent ACE with a mean (SD) follow-up of 7.6 (3.1) years. No patient has faecal leakage. No patient had stomal revision, but one patient (5.5%) required an indwelling gastrostomy button to maintain patency. Twenty-two patients underwent UCCD with a mean (SD) follow-up of 8.1 (2.8) years. No patient developed urinary leakage. Two patients (9%) required revision of the stoma and one (4.5%) required an indwelling catheter because of recurring stomal stenosis. CSRST prevents stoma leakage. Revision surgery rate after CSRST is low, particularly after ACE reconstruction.

  12. Solitary fibrous tumor surrounding the carotid sheath.

    PubMed

    Gómez-Oliveira, Guillermo; Alvarez-Flores, Modesto; Arribas-García, Ignacio; Martínez-Gimeno, Carlos

    2010-03-01

    Solitary fibrous tumors (SFTs) are rare spindle cell neoplasms that are mostly found arising from the pleura. Although SFTs recently have been reported in other regions, they are rare in the head and neck and have often been misdiagnosed due to their rarity. SFTs are benign in most cases. Clinically, SFTs usually manifest as well-circumscribed, slow-growing, smooth and painless masses. Symptoms are often minimal, although they may include sore throat, difficulty in swallowing, change of voice or trismus. CT-Scan and MRI are the most sensitive imaging procedures used. The treatment of choice is complete surgical excision of the lesion. Because recurrences have been noted up to 30 years after surgery, long-term follow up is mandatory. In this article, we present a case of a Solitary Fibrous Tumor arising in the parapharyngeal space in a 20-year-old man, involving the carotid sheath, treated by surgical excision with no recurrence after 1 year. The clinical presentation, surgical management and pathological findings are described.

  13. Comment on 'Sheath model for dual-frequency capacitive discharges'

    NASA Astrophysics Data System (ADS)

    Chen, Wen-Cong; Pu, Yi-Kang

    2015-07-01

    Boyle et al (2004 J. Phys. D: Appl. Phys. 37 1451) introduced a sheath model for dual-frequency capacitive discharges. The electron sheath edge position s and the dc potential Φdc in the sheath are obtained with the assumption α/β  >> 1 (where α/β is the ratio of the low-frequency electric field to the high-frequency electric field). However, α/β  ≤  4 is usually found in processing applications. Under this condition, we show that the Boyle et al model gives multiple values for the dc potential Φdc(x) at any given position x in the sheath. For this reason, we introduce a model without the assumption α/β  >> 1. By comparing the results from the two models, it is found that, as the ratio α/β approaches 1, the sheath thickness sm and the sheath dc voltage Vdc obtained with the Boyle et al model are significantly underestimated.

  14. 33 CFR 118.90 - Bridges crossing channel obliquely.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 33 Navigation and Navigable Waters 1 2012-07-01 2012-07-01 false Bridges crossing channel obliquely. 118.90 Section 118.90 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY BRIDGES BRIDGE LIGHTING AND OTHER SIGNALS § 118.90 Bridges crossing channel obliquely....

  15. 33 CFR 118.90 - Bridges crossing channel obliquely.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 33 Navigation and Navigable Waters 1 2013-07-01 2013-07-01 false Bridges crossing channel obliquely. 118.90 Section 118.90 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY BRIDGES BRIDGE LIGHTING AND OTHER SIGNALS § 118.90 Bridges crossing channel obliquely....

  16. 33 CFR 118.90 - Bridges crossing channel obliquely.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 33 Navigation and Navigable Waters 1 2014-07-01 2014-07-01 false Bridges crossing channel obliquely. 118.90 Section 118.90 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY BRIDGES BRIDGE LIGHTING AND OTHER SIGNALS § 118.90 Bridges crossing channel obliquely....

  17. Uses of the Inferior Oblique Muscle in Strabismus Surgery

    PubMed Central

    Stager, David; Dao, Lori M.; Felius, Joost

    2015-01-01

    Inferior oblique muscle weakening is typically performed for overaction of the muscle. In this article, we review inferior oblique muscle anatomy, different weakening procedures, and recent surgical techniques that take advantage of the muscle's unique anatomy for the treatment of additional indications such as excyclotorsion and hypertropia in primary gaze. PMID:26180466

  18. Measurement of Oblique Impact-generated Shear Waves

    NASA Technical Reports Server (NTRS)

    Dahl, J. M.; Schultz, P. H.

    2001-01-01

    Experimental strain measurements reveal that oblique impacts can generate shear waves with displacements as large as those in the P-wave. Large oblique impacts may thus be more efficient sources of surface disruption than vertical impacts. Additional information is contained in the original extended abstract.

  19. Reduced Oblique Effect in Children with Autism Spectrum Disorders (ASD)

    PubMed Central

    Sysoeva, Olga V.; Davletshina, Maria A.; Orekhova, Elena V.; Galuta, Ilia A.; Stroganova, Tatiana A.

    2016-01-01

    People are very precise in the discrimination of a line orientation relative to the cardinal (vertical and horizontal) axes, while their orientation discrimination sensitivity along the oblique axes is less refined. This difference in discrimination sensitivity along cardinal and oblique axes is called the “oblique effect.” Given that the oblique effect is a basic feature of visual processing with an early developmental origin, its investigation in children with Autism Spectrum Disorder (ASD) may shed light on the nature of visual sensory abnormalities frequently reported in this population. We examined line orientation sensitivity along oblique and vertical axes in a sample of 26 boys with ASD (IQ > 68) and 38 typically developing (TD) boys aged 7–15 years, as well as in a subsample of carefully IQ-matched ASD and TD participants. Children were asked to detect the direction of tilt of a high-contrast black-and-white grating relative to vertical (90°) or oblique (45°) templates. The oblique effect was reduced in children with ASD as compared to TD participants, irrespective of their IQ. This reduction was due to poor orientation sensitivity along the vertical axis in ASD children, while their ability to discriminate line orientation along the oblique axis was unaffected. We speculate that this deficit in sensitivity to vertical orientation may reflect disrupted mechanisms of early experience-dependent learning that takes place during the critical period for orientation selectivity. PMID:26834540

  20. Plasma diagnostics and plasma-surface interactions in inductively coupled plasmas

    NASA Astrophysics Data System (ADS)

    Titus, Monica Joy

    The semiconductor industry's continued trend of manufacturing device features on the nanometer scale requires increased plasma processing control and improved understanding of plasma characteristics and plasma-surface interactions. This dissertation presents a series of experimental results for focus studies conducted in an inductively coupled plasma (ICP) system. First novel "on-wafer" diagnostic tools are characterized and related to plasma characteristics. Second, plasma-polymer interactions are characterized as a function of plasma species and processing parameters. Complementary simulations accompany each focus study to supplement experimental findings. Wafer heating mechanisms in inductively coupled molecular gas plasmas are explored with PlasmaTemp(TM), a novel "on-wafer" diagnostic tool. Experimental wafer measurements are obtained with the PlasmaTemp(TM) wafer processed in argon (Ar) and argon-oxygen (Ar/O2) mixed plasmas. Wafer heating mechanisms were determined by combining the experimental measurements with a 3-dimensional heat transfer model of the wafer. Comparisons between pure Ar and Ar/O2 plasmas demonstrate that two additional wafer heating mechanisms can be important in molecular gas plasmas compared to atomic gas discharges. Thermal heat conduction from the neutral gas and O-atom recombination on wafer surface can contribute as much as 60% to wafer heating under conditions of low-energy ion bombardment in molecular plasmas. Measurements of a second novel "on-wafer" diagnostic sensor, the PlasmaVolt(TM), were tested and validated in the ICP system for Ar plasmas varying in power and pressure. Sensor measurements were interpreted with a numerical sheath simulation and comparison to scaling laws derived from the inhomogeneous sheath model. The study demonstrates sensor measurements are proportional to the RF-current through the sheath and the scaling is a function of sheath impedance. PlasmaVolt(TM) sensor measurements are proportional to the

  1. Mars Secular Obliquity Decrease and the Layered Terrain

    NASA Technical Reports Server (NTRS)

    Rubincam, D. P.

    2000-01-01

    Mars may have substantially decreased its average axial tilt over geologic time due to the waxing and waning of water ice caps through the phenomenon of climate friction (also called obliquity-oblateness feedback). Depending upon Mars' climate and internal structure, water caps of the order of 10(exp 17) - 10(exp 18) kg cycling with the obliquity oscillations could have either increased or decreased the average obliquity by possibly tens of degrees over the age of the solar system. Gravity and topography observations by the Mars Global Surveyor indicate that the south polar cap is mostly uncompensated, so that Mars may be largely rigid on the obliquity timescale. Further, Mars may be a water-rich planet, so that there is a large phase angle between insolation forcing and the size of the obliquity-driven water caps. A stiff, water-rich planet implies an obliquity decrease over the eons. Such a decrease might account for the apparent youthfulness of the polar layered terrain. The idea is that fewer volatiles were available to be cycled into and out of the terrain at high mean obliquity, because of the eveness of insolation between equator and pole, and because of small insolation variations as the obliquity oscillated; so that the movement of volatiles and dust produced thin layers or perhaps no layers at all. As the average obliquity decreased, the insolation contrast between high and low latitudes increased, plus the insolation variations over the obliquity cycle grew somewhat bigger, so that more volatiles and dust might have shuttled into and out of the polar regions, forming the observed thick layers late in Mars' history. It may also be that the average tilt has decreased to the point where the climate friction mechanism is starving itself: more and more water has gotten locked up in the polar regions, making less available for cycling with the oscillations. And the layer-forming mechanism may be starving too: not only less water, but also at low average

  2. Particle-in-cell and Monte Carlo collision simulations of the cathode sheath in an atmospheric direct-current arc discharge

    NASA Astrophysics Data System (ADS)

    Zhou, Wen; Guo, Heng; Jiang, Wei; Li, He-Ping; Li, Zeng-Yao; Lapenta, Giovanni

    2016-10-01

    A sheath is the transition region from plasma to a solid surface, which also plays a critical role in determining the behaviors of many lab and industrial plasmas. However, the cathode sheath properties in arc discharges are not well understood yet due to its multi-scale and kinetic features. In this letter, we have adopted an implicit particle-in-cell Monte Carlo collision (PIC-MCC) method to study the cathode sheath in an atmospheric arc discharge plasma. The cathode sheath thickness, number densities and averaged energies of electrons and ions, the electric field distribution, as well as the spatially averaged electron energy probability function (EEPF), are predicted self-consistently by using this newly developed kinetic model. It is also shown that the thermionic emission at the hot cathode surface is the dominant electron emission process to sustain the arc discharges, while the effects from secondary and field electron emissions are negligible. The present results verify the previous conjectures and experimental observations.

  3. Obliquity Variability of a Potentially Habitable Early Venus

    NASA Astrophysics Data System (ADS)

    Barnes, Jason W.; Quarles, Billy; Lissauer, Jack J.; Chambers, John; Hedman, Matthew M.

    2016-07-01

    Venus currently rotates slowly, with its spin controlled by solid-body and atmospheric thermal tides. However, conditions may have been far different 4 billion years ago, when the Sun was fainter and most of the carbon within Venus could have been in solid form, implying a low-mass atmosphere. We investigate how the obliquity would have varied for a hypothetical rapidly rotating Early Venus. The obliquity variation structure of an ensemble of hypothetical Early Venuses is simpler than that Earth would have if it lacked its large moon (Lissauer et al., 2012), having just one primary chaotic regime at high prograde obliquities. We note an unexpected long-term variability of up to ±7° for retrograde Venuses. Low-obliquity Venuses show very low total obliquity variability over billion-year timescales, comparable to that of the real Moon-influenced Earth.

  4. Bow and Oblique Shock Formation in Soap Film

    NASA Astrophysics Data System (ADS)

    Kim, Ildoo; Mandre, Shreyas; Sane, Aakash

    2015-11-01

    In recent years, soap films have been exploited primarily to approximate two-dimensional flows while their three-dimensional character is relatively unattended. An example of the three-dimensional character of the flow in a soap film is the observed Marangoni shock wave when the flow speed exceeds the wave speed. In this study, we investigated the formation of bow and oblique shocks in soap films generated by wedges with different deflection angles. When the wedge deflection angle is small and the film flows fast, oblique shocks are observed. When the oblique shock cannot exists, bow shock is formed upstream the wedge. We characterized the oblique shock angle as a function of the wedge deflection angle and the flow speed, and we also present the criteria for transition between bow and oblique Marangoni shocks in soap films.

  5. PREDICTING CME EJECTA AND SHEATH FRONT ARRIVAL AT L1 WITH A DATA-CONSTRAINED PHYSICAL MODEL

    SciTech Connect

    Hess, Phillip; Zhang, Jie

    2015-10-20

    We present a method for predicting the arrival of a coronal mass ejection (CME) flux rope in situ, as well as the sheath of solar wind plasma accumulated ahead of the driver. For faster CMEs, the front of this sheath will be a shock. The method is based upon geometrical separate measurement of the CME ejecta and sheath. These measurements are used to constrain a drag-based model, improved by including both a height dependence and accurate de-projected velocities. We also constrain the geometry of the model to determine the error introduced as a function of the deviation of the CME nose from the Sun–Earth line. The CME standoff-distance in the heliosphere fit is also calculated, fit, and combined with the ejecta model to determine sheath arrival. Combining these factors allows us to create predictions for both fronts at the L1 point and compare them against observations. We demonstrate an ability to predict the sheath arrival with an average error of under 3.5 hr, with an rms error of about 1.58 hr. For the ejecta the error is less than 1.5 hr, with an rms error within 0.76 hr. We also discuss the physical implications of our model for CME expansion and density evolution. We show the power of our method with ideal data and demonstrate the practical implications of having a permanent L5 observer with space weather forecasting capabilities, while also discussing the limitations of the method that will have to be addressed in order to create a real-time forecasting tool.

  6. Ion energy distributions in silane-hydrogen plasmas

    SciTech Connect

    Hamers, E.A.G.; Sark, W.G.J.H.M. van; Bezemer, J.; Weg, W.F. van der; Goedheer, W.J.

    1996-12-31

    For the first time ion energy distributions (IED) of different ions from silane-hydrogen (SiH{sub 4}-H{sub 2}) RF plasmas are presented, i.e., the distributions of SiH{sub 3}{sup +}, SiH{sub 2}{sup +} and Si{sub 2}H{sub 4}{sup +}. The energy distributions of SiH{sub 3}{sup +} and SiH{sub 2}{sup +} ions show peaks, which are caused by a charge exchange process in the sheath. A method is presented by which the net charge density in the sheath is determined from the plasma potential and the energy positions of the charge exchange peaks. Knowing the net charge density in the sheath and the plasma potential, the sheath thickness can be determined and an estimation of the absolute ion fluxes can be made. The flux of ions can, at maximum, account for 10% of the observed deposition rate.

  7. The Role of Rift Obliquity During Pangea Fragmentation

    NASA Astrophysics Data System (ADS)

    Brune, S.; Butterworth, N. P.; Williams, S.; Müller, D.

    2014-12-01

    Does supercontinent break-up follow specific laws? What parameters control the success and the failure of rift systems? Recent analytical and geodynamic modeling suggests that oblique rifting is energetically preferred over orthogonal rifting. This implies that during rift competition, highly oblique branches proceed to break-up while less oblique ones become inactive. These models predict that the relative motion of Earth's continents during supercontinent break-up is affected by the orientation and shape of individual rift systems. Here, we test this hypothesis based on latest plate tectonic reconstructions. Using PyGPlates, a recently developed Python library that allows script-based access to the plate reconstruction software GPlates, we quantify rift obliquity, extension velocity and their temporal evolution for continent-scale rift systems of the past 200 Myr. Indeed we find that many rift systems contributing to Pangea fragmentation involved strong rift obliquity. East and West Gondwana for instance split along the East African coast with a mean obliquity of 55° (measured as the angle between local rift trend normal and extension direction). While formation of the central and southern South Atlantic segment involved a low obliquity of 10°, the Equatorial Atlantic opened under a high angle of 60°. Rifting between Australia and Antarctica involved two stages with 25° prior to 100 Ma followed by 50° obliquity and distinct increase of extension velocity. Analyzing the entire passive margin system that formed during Pangea breakup, we find a mean obliquity of 40°, with a standard deviation of 20°. Hence 50% of these margins formed with an angle of 40° or more. Considering that many conceptual models of rifting and passive margin formation assume 2D deformation, our study quantifies the degree to which such 2D models are globally applicable, and highlights the importance of 3D models where oblique rifting is the dominant mode of deformation.

  8. A theoretical model of sheath fold morphology in simple shear

    NASA Astrophysics Data System (ADS)

    Reber, Jacqueline E.; Dabrowski, Marcin; Galland, Olivier; Schmid, Daniel W.

    2013-04-01

    Sheath folds are highly non-cylindrical structures often associated with shear zones. The geometry of sheath folds, especially cross-sections perpendicular to the stretching direction that display eye-patterns, have been used in the field to deduce kinematic information such as shear sense and bulk strain type. However, how sheath folds form and how they evolve with increasing strain is still a matter of debate. 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 systematically vary the slip surface orientation and shape and evaluate the impact on the evolving eye-pattern. In addition we compare our results to existing classifications. Based on field observations it has been suggested that the shear sense of a shear zone can be determined by knowing the position of the center of an eye-pattern and the closing direction of the corresponding sheath fold. In our modeled sheath folds we can observe for a given strain that 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, questioning the usefulness of sheath folds as shear sense indicators. The location of the center of the eye structure, however, is largely invariant to the initial configurations of the slip surface as well as to strain. It has been suggested that the ratio of the aspect ratio of the innermost and outermost closed contour in eye-patterns could be linked to the bulk strain type based on filed observations. We apply this classification to our modeled sheath folds and we observe that 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

  9. Oscillating plasma bubbles. IV. Grids, geometry, and gradients

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.

    2012-08-15

    Plasma bubbles are created in an ambient plasma. The bubble is formed inside a cavity bounded by a negatively biased grid. Ions are injected through the grid and neutralized by electrons from either the background plasma or an internal electron emitter. The external electron supply is controlled by the grid bias relative to the external plasma potential. When the electron flux is restricted to the ion flux, the sheath of the bubble becomes unstable and causes the plasma potential to oscillate near the ion plasma frequency. The exact frequency depends on the net space charge density in the bubble sheath. The frequency increases with density and grid voltage, provided the grid forms a parallel equipotential surface. The present investigation shows that when the Debye length becomes smaller than the grid openings the electron flux cannot be controlled by the grid voltage. The frequency dependence on grid voltage and density is modified creating frequency and amplitude jumps. Low frequency sheath oscillations modulate the high frequency normal oscillations. Harmonics and subharmonics are excited by electrons in an ion-rich sheath. When the plasma parameters vary over the bubble surface, the sheath may oscillate at different frequencies. A cavity with two isolated grids has been used to investigate anisotropies of the energetic electron flux in a discharge plasma. The frequency dependence on grid voltage is entirely different when the grid controls the energetic electrons or the bulk electrons. These observations are important to several fields of basic plasma physics, such as sheaths, sheath instabilities, diagnostic probes, current, and space charge neutralization of ion beams.

  10. Scattering of relativistic and ultra-relativistic electrons by obliquely propagating Electromagnetic Ion Cyclotron waves

    NASA Astrophysics Data System (ADS)

    Uzbekov, Bogdan; Shprits, Yuri Y.; Orlova, Ksenia

    2016-10-01

    Electromagnetic Ion Cyclotron (EMIC) waves are transverse plasma waves that are generated in the Earth magnetosphere by ring current protons with temperature anisotropy in three different bands: below the H+, He+ and O+ ion gyrofrequencies. EMIC events are enhanced during the main phase of a geomagnetic storm when intensifications in the electric field result in enhanced injections of ions and are usually confined to high-density regions just inside the plasmapause or within drainage plumes. EMIC waves are capable of scattering radiation belt electrons and thus provide an important link between the intensification of the electric field, ion populations, and radiation belt electrons. Bounce-averaged diffusion coefficients computed with the assumption of parallel wave propagation are compared to the results of the code that uses the full cold plasma dispersion relation taking into account oblique propagation of waves and higher-order resonances. We study the sensitivity of the scattering rates to a number of included higher-order resonances, wave spectral distribution parameters, wave normal angle distribution parameters, ambient plasma density, and ion composition. Inaccuracies associated with the neglect of higher-order resonances and oblique propagation of waves are compared to potential errors introduced by uncertainties in the model input parameters.

  11. Hellas basin, Mars: Formation by oblique impact

    NASA Technical Reports Server (NTRS)

    Leonard, Gregory J.; Tanaka, Kenneth L.

    1993-01-01

    Hellas, a 2,000-km-diameter, roughly circular multiring impact basin in the southern highlands of Mars, has a pronounced southeastern lobe of rim material that extends for some 1,500 km. This lobe and a system of ridges concentric to the southern part of the basin (including part of the lobe) were interpreted to be formed by an oblique impact that was inclined in the direction of the lobe. Our preliminary geologic mapping of the Hellas region (lat -20 to -65 deg, long 250 to 320 deg) at 1:5,000,000 scale gives this hypothesis additional supporting evidence, including a symmetric distribution of basin ejecta and volcanic centers across the inferred trend of the impact. Furthermore, measurements of relief indicate that the downrange ejecta may be about twice as thick as they are elsewhere around the rim.

  12. Calibration Procedures on Oblique Camera Setups

    NASA Astrophysics Data System (ADS)

    Kemper, G.; Melykuti, B.; Yu, C.

    2016-06-01

    Beside the creation of virtual animated 3D City models, analysis for homeland security and city planning, the accurately determination of geometric features out of oblique imagery is an important task today. Due to the huge number of single images the reduction of control points force to make use of direct referencing devices. This causes a precise camera-calibration and additional adjustment procedures. This paper aims to show the workflow of the various calibration steps and will present examples of the calibration flight with the final 3D City model. In difference to most other software, the oblique cameras are used not as co-registered sensors in relation to the nadir one, all camera images enter the AT process as single pre-oriented data. This enables a better post calibration in order to detect variations in the single camera calibration and other mechanical effects. The shown sensor (Oblique Imager) is based o 5 Phase One cameras were the nadir one has 80 MPIX equipped with a 50 mm lens while the oblique ones capture images with 50 MPix using 80 mm lenses. The cameras are mounted robust inside a housing to protect this against physical and thermal deformations. The sensor head hosts also an IMU which is connected to a POS AV GNSS Receiver. The sensor is stabilized by a gyro-mount which creates floating Antenna -IMU lever arms. They had to be registered together with the Raw GNSS-IMU Data. The camera calibration procedure was performed based on a special calibration flight with 351 shoots of all 5 cameras and registered the GPS/IMU data. This specific mission was designed in two different altitudes with additional cross lines on each flying heights. The five images from each exposure positions have no overlaps but in the block there are many overlaps resulting in up to 200 measurements per points. On each photo there were in average 110 well distributed measured points which is a satisfying number for the camera calibration. In a first step with the help of

  13. MIX and Instability Growth from Oblique Shock

    SciTech Connect

    Molitoris, J D; Batteux, J D; Garza, R G; Tringe, J W; Souers, P C; Forbes, J W

    2011-07-22

    We have studied the formation and evolution of shock-induced mix resulting from interface features in a divergent cylindrical geometry. In this research a cylindrical core of high-explosive was detonated to create an oblique shock wave and accelerate the interface. The interfaces studied were between the high-explosive/aluminum, aluminum/plastic, and finally plastic/air. Pre-emplaced surface features added to the aluminum were used to modify this interface. Time sequence radiographic imaging quantified the resulting instability formation from the growth phase to over 60 {micro}s post-detonation. Thus allowing the study of the onset of mix and evolution to turbulence. The plastic used here was porous polyethylene. Radiographic image data are compared with numerical simulations of the experiments.

  14. Thin oblique airfoils at supersonic speed

    NASA Technical Reports Server (NTRS)

    Jone, Robert T

    1946-01-01

    The well-known methods of thin-airfoil theory have been extended to oblique or sweptback airfoils of finite aspect ratio moving at supersonic speeds. The cases considered thus far are symmetrical airfoils at zero lift having plan forms bounded by straight lines. Because of the conical form of the elementary flow fields, the results are comparable in simplicity to the results of the two-dimensional thin-airfoil theory for subsonic speeds. In the case of untapered airfoils swept back behind the Mach cone the pressure distribution at the center section is similar to that given by the Ackeret theory for a straight airfoil. With increasing distance from the center section the distribution approaches the form given by the subsonic-flow theory. The pressure drag is concentrated chiefly at the center section and for long wings a slight negative drag may appear on outboard sections. (author)

  15. Extraocular Muscle Compartments in Superior Oblique Palsy

    PubMed Central

    Suh, Soh Youn; Clark, Robert A.; Le, Alan; Demer, Joseph L.

    2016-01-01

    Purpose To investigate changes in volumes of extraocular muscle (EOM) compartments in unilateral superior oblique (SO) palsy using magnetic resonance imaging (MRI). Methods High-resolution, surface-coil MRI was obtained in 19 patients with unilateral SO palsy and 19 age-matched orthotropic control subjects. Rectus EOMs and the SO were divided into two anatomic compartments for volume analysis in patients with unilateral SO palsy, allowing comparison of total compartmental volumes versus controls. Medial and lateral compartmental volumes of the SO muscle were compared in patients with isotropic (round shape) versus anisotropic (elongated shape) SO atrophy. Results The medial and lateral compartments of the ipsilesional SO muscles were equally atrophic in isotropic SO palsy, whereas the lateral compartment was significantly smaller than the medial in anisotropic SO palsy (P = 0.01). In contrast to the SO, there were no differential compartmental volume changes in rectus EOMs; however, there was significant total muscle hypertrophy in the ipsilesional inferior rectus (IR) and lateral rectus (LR) muscles and contralesional superior rectus (SR) muscles. Medial rectus (MR) volume was normal both ipsi- and contralesionally. Conclusions A subset of patients with SO palsy exhibit selective atrophy of the lateral, predominantly vertically acting SO compartment. Superior oblique atrophy is associated with whole-muscle volume changes in the ipsilesional IR, ipsilesional LR, and contralesional SR; however, SO muscle atrophy is not associated with compartmentally selective volume changes in the rectus EOMs. Selective compartmental SO pathology may provide an anatomic mechanism that explains some of the variability in clinical presentations of SO palsy. PMID:27768791

  16. Oblique impacts: Catastrophic vs. protracted effects

    NASA Technical Reports Server (NTRS)

    Schultz, P. H.

    1988-01-01

    Proposed impacts as the cause of biologic catastrophes at the end of the Cretaceous and Eocene face several enigmas: protracted extinctions, even prior to the stratigraphic cosmogenic signature; widespread but non-uniform dispersal of the meteoritic component; absence of a crater of sufficient size; and evidence for massive intensive fires. Various hypotheses provide reasonable mechanisms for mass mortalities: global cooling by continental impact sites; global warming by oceanic impact sites; contrasting effects of asteroidal, cometary, and even multiple impacts; and stress on an already fragile global environment. Yet not every known large impact is associated with a major biologic catastrophe. An alternative is expanded: the consequences of an oblique impact. The most probable angle of impact is 45 deg with the probability for an impact at smaller angles decreasing: A vertical impact is as rare as a tangential impact with a 5 deg impact angle or less occurring only 8 percent of the time. Consequently a low-angle impact is a rare but probable event. Laboratory experiments at the NASA-Ames Vertical Gun Range reveal important information about cratering efficiency, impact vaporization, projectile dispersal, and phenomenology, thereby providing perspective for possible consequences of such an impact on both the Earth and Moon. Oblique impacts are rare but certain events through geologic time: A 5 deg impact by a 2 km-diameter impactor on the Earth would occur only once in about 18 my with a 10 km-diameter once in about 450 my. Major life extinctions beginning prior to the stratigraphic cosmogenic signature or protracted extinctions seemingly too long after the proposed event may not be evidence against an impact as a cause but evidence for a more complex but probable sequence of events.

  17. Numerical studies of electron dynamics in oblique quasi-perpendicular collisionless shock waves

    NASA Technical Reports Server (NTRS)

    Liewer, P. C.; Decyk, V. K.; Dawson, J. M.; Lembege, B.

    1991-01-01

    Linear and nonlinear electron damping of the whistler precursor wave train to low Mach number quasi-perpendicular oblique shocks is studied using a one-dimensional electromagnetic plasma simulation code with particle electrons and ions. In some parameter regimes, electrons are observed to trap along the magnetic field lines in the potential of the whistler precursor wave train. This trapping can lead to significant electron heating in front of the shock for low beta(e). Use of a 64-processor hypercube concurrent computer has enabled long runs using realistic mass ratios in the full particle in-cell code and thus simulate shock parameter regimes and phenomena not previously studied numerically.

  18. A computational study of laser-supported detonation waves propagating up an oblique incident beam

    NASA Astrophysics Data System (ADS)

    Bohn, C. L.; Crawford, M. L.

    1987-01-01

    A series of numerical experiments was conducted to study the propagation of laser-supported detonation waves (LSDWs) in the case that a CO2 laser beam strikes an aluminum surface obliquely in air. A reflected shock formed at the aluminum surface was more prominent at higher angles of incidence theta of the beam, but otherwise the hydrodynamics of the plasma and the LSDW were insensitive to theta. Furthermore, the total impulse delivered to the aluminum varied approximately as 1/cos theta, a result that can be modeled with elementary blast-wave theory.

  19. Transmission of waves near the lower oblique resonance using dipoles in the ionosphere

    NASA Astrophysics Data System (ADS)

    Chugunov, Y. V.; Mareev, E. A.; Fiala, V.; James, H. G.

    2003-04-01

    The observations in the OEDIPUS-C experiment of bistatic propagation along the lower oblique resonance cone between a separated transmitter and receiver in the ionosphere are explained through detailed calculations of the radiated field of the V-dipole antenna used in the experiment and by a novel theory of the receiving antenna under resonance conditions. Unexpectedly high values of 25 kHz signal observed at the resonance and its structure agree well with calculations of the transmission between the exciter and receiver, when antenna layout and dispersive properties of the plasma at resonance are taken into account.

  20. Spherical carbon liquids generated in a low pressure CH{sub 4}/Ar plasma

    SciTech Connect

    Feng Zongbao; Kono, Akihiko; Nagai, Tatsuzo; Shoji, Fumiya

    2007-05-28

    The authors present a study on spherical carbon particles of micron sizes grown in the plasma sheath as spherical liquids that can be agglomerated by capillary force based on the Laplace pressure. In addition, it is suggested that those spherical carbon liquids with negative charges that are levitating in the sheath region begin to display a collective behavior of Coulomb crystals.