Kinetic instability of electrostatic ion cyclotron waves in inter-penetrating plasmas

NASA Astrophysics Data System (ADS)

Bashir, M. F.; Ilie, R.; Murtaza, G.

2018-05-01

The Electrostatic Ion Cyclotron (EIC) instability that includes the effect of wave-particle interaction is studied owing to the free energy source through the flowing velocity of the inter-penetrating plasmas. It is shown that the origin of this current-less instability is different from the classical current driven EIC instability. The threshold conditions applicable to a wide range of plasma parameters and the estimate of the growth rate are determined as a function of the normalized flowing velocity ( u0/vt f e ), the temperature ( Tf/Ts ) and the density ratios ( nf 0/ns 0 ) of flowing component to static one. The EIC instability is driven by either flowing electrons or flowing ions, depending upon the different Doppler shifted frequency domains. It is found that the growth rate for electron-driven instability is higher than the ion-driven one. However, in both cases, the denser (hotter) is the flowing plasma, the lesser (greater) is the growth rate. The possible applications related to the terrestrial solar plasma environment are also discussed.

Calculations of Alfven Wave Driving Forces, Plasma Flow and Current Drive in Tokamak Plasmas

NASA Astrophysics Data System (ADS)

Elfimov, Artur; Galvao, Ricardo; Amarante-Segundo, Gesil; Nascimento, Ivan

2000-10-01

A general form of time-averaged poloidal ponderomotive forces induced by fast and kinetic Alfvin waves by direct numerical calculations and in geometric optics approximation are analyzed on the basis of the collisionless two fluid (ions and electrons) magneto-hydrodynamics equation. Analytical approximations are used to clarify the effect of Larmour radius on radio-frequency (RF) ponderomotive forces and on poloidal flows induced by them in tokamak plasmas.The RF ponderomotive force is expressed as a sum of a gradient part and of a wave momentum transfer force, which is proportional to wave dissipation. The gradient electromagnetic stress force is combined with fluid dynamic (Reynolds) stress force. It is shown that accounting only Reynolds stress term can overestimate the plasma flow and it is found that the finite ion Larmor radius effect play fundamental role in ponderomotive forces that can drive a poloidal flow, which is larger than a flow driven by a wave momentum transfer force. Finally, balancing the RF forces by the electron-ion friction and viscous force the current and plasma flows driven by ponderomotive forces are calculated for tokamak plasmas, using a kinetic code [Phys. Plasmas, v.6 (1999) p.2437]. Strongly sheared current and plasma flow waves is found.

Gas flow dependence for plasma-needle disinfection of S. mutans bacteria

NASA Astrophysics Data System (ADS)

Goree, J.; Liu, Bin; Drake, David

2006-08-01

The role of gas flow and transport mechanisms are studied for a small low-power impinging jet of weakly-ionized helium at atmospheric pressure. This plasma needle produces a non-thermal glow discharge plasma that kills bacteria. A culture of Streptococcus mutans (S. mutans) was plated onto the surface of agar, and spots on this surface were then treated with plasma. Afterwards, the sample was incubated and then imaged. These images, which serve as a biological diagnostic for characterizing the plasma, show a distinctive spatial pattern for killing that depends on the gas flow rate. As the flow is increased, the killing pattern varies from a solid circle to a ring. Images of the glow reveal that the spatial distribution of energetic electrons corresponds to the observed killing pattern. This suggests that a bactericidal species is generated in the gas phase by energetic electrons less than a millimetre from the sample surface. Mixing of air into the helium plasma is required to generate the observed O and OH radicals in the flowing plasma. Hydrodynamic processes involved in this mixing are buoyancy, diffusion and turbulence.

Non-thermal atmospheric pressure HF plasma source: generation of nitric oxide and ozone for bio-medical applications

NASA Astrophysics Data System (ADS)

Kühn, S.; Bibinov, N.; Gesche, R.; Awakowicz, P.

2010-01-01

A new miniature high-frequency (HF) plasma source intended for bio-medical applications is studied using nitrogen/oxygen mixture at atmospheric pressure. This plasma source can be used as an element of a plasma source array for applications in dermatology and surgery. Nitric oxide and ozone which are produced in this plasma source are well-known agents for proliferation of the cells, inhalation therapy for newborn infants, disinfection of wounds and blood ozonation. Using optical emission spectroscopy, microphotography and numerical simulation, the gas temperature in the active plasma region and plasma parameters (electron density and electron distribution function) are determined for varied nitrogen/oxygen flows. The influence of the gas flows on the plasma conditions is studied. Ozone and nitric oxide concentrations in the effluent of the plasma source are measured using absorption spectroscopy and electro-chemical NO-detector at variable gas flows. Correlations between plasma parameters and concentrations of the particles in the effluent of the plasma source are discussed. By varying the gas flows, the HF plasma source can be optimized for nitric oxide or ozone production. Maximum concentrations of 2750 ppm and 400 ppm of NO and O3, correspondingly, are generated.

Influence of the shear flow on electron cyclotron resonance plasma confinement in an axisymmetric magnetic mirror trap of the electron cyclotron resonance ion source.

PubMed

Izotov, I V; Razin, S V; Sidorov, A V; Skalyga, V A; Zorin, V G; Bagryansky, P A; Beklemishev, A D; Prikhodko, V V

2012-02-01

Influence of shear flows of the dense plasma created under conditions of the electron cyclotron resonance (ECR) gas breakdown on the plasma confinement in the axisymmetric mirror trap ("vortex" confinement) was studied experimentally and theoretically. A limiter with bias potential was set inside the mirror trap for plasma rotation. The limiter construction and the optimal value of the potential were chosen according to the results of the preliminary theoretical analysis. This method of "vortex" confinement realization in an axisymmetric mirror trap for non-equilibrium heavy-ion plasmas seems to be promising for creation of ECR multicharged ion sources with high magnetic fields, more than 1 T.

Theory and Simulation of Electron Sheaths and Anode Spots in Low Pressure Laboratory Plasmas

NASA Astrophysics Data System (ADS)

Scheiner, Brett Stanford

Electrodes in low pressure laboratory plasmas have a multitude of possible sheath structures when biased at a large positive potential. When the size of the electrode is small enough the electrode bias can be above the plasma potential. When this occurs an electron-rich sheath called an electron sheath is present at the electrode. Electron sheaths are most commonly found near Langmuir probes and other electrodes collecting the electron saturation current. Such electrodes have applications in the control of plasma parameters, dust confinement and circulation, control of scrape off layer plasmas, RF plasmas, and in plasma contactors and tethered space probes. The electron sheaths in these various systems most directly influence the plasma by determining how electron current is lost from the system. An understanding of how the electron sheath interfaces with the bulk plasma is necessary for understanding the behavior induced by positively biased electrodes in these plasmas. This thesis provides a dedicated theory of electron sheaths. Motivated by electron velocity distribution functions (EVDFs) observed in particle-in-cell (PIC) simulations, a 1D model for the electron sheath and presheath is developed. In the presheath model, an electron pressure gradient accelerates electrons to near the electron thermal speed by 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. Using PIC simulations, the form of a sheath near a small electrode with bias near the plasma potential is also studied. When the electrode is biased near the plasma potential, the 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, instead the plasma remains quasineutral up to the electrode. Once the bias exceeds the plasma potential an electron sheath is present. In this case, 2D EVDFs indicate that the flow moment has comparable contributions from the flow shift and loss-cone truncation. The case of an electrode at large positive bias relative to the plasma potential is also studied. Here, the rate of electron impact ionization of neutrals increases near the electrode. If this ionization rate is great enough a double layer forms. This double layer can move outward separating a high potential plasma at the electrode surface from the bulk plasma. This phenomenon is known as an anode spot. Informed by observations from the first PIC simulations of an anode spot, a model has been developed describing the onset in which ionization leads to the buildup of positive space charge and the formation of a potential well that traps electrons near the electrode surface. A model for steady-state properties based on current loss, power, and particle balance of the anode spot plasma is also presented.

ION-STABILIZED ELECTRON INDUCTION ACCELERATOR

DOEpatents

Finkelstein, D.

1960-03-22

A method and apparatus for establishing an ion-stabilized self-focusing relativistic electron beam from a plasma are reported. A plasma is introduced into a specially designed cavity by plasma guns, and a magnetic field satisfying betatron conditions is produced in the cavity by currents flowing in the highly conductive, non-magnetic surface of the cavity. This field forms the electron beam by induction from the plasma.

Simulation of rarefied low pressure RF plasma flow around the sample

NASA Astrophysics Data System (ADS)

Zheltukhin, V. S.; Shemakhin, A. Yu

2017-01-01

The paper describes a mathematical model of the flow of radio frequency plasma at low pressure. The hybrid mathematical model includes the Boltzmann equation for the neutral component of the RF plasma, the continuity and the thermal equations for the charged component. Initial and boundary conditions for the corresponding equations are described. The electron temperature in the calculations is 1-4 eV, atoms temperature in the plasma clot is (3-4) • 103 K, in the plasma jet is (3.2-10) • 102 K, the degree of ionization is 10-7-10-5, electron density is 1015-1019 m-3. For calculations plasma parameters is developed soft package on C++ program language, that uses the OpenFOAM library package. Simulations for the vacuum chamber in the presence of a sample and the free jet flow were carried out.

Cassini Observations of Saturn's Magnetotail Region: Preliminary Results

NASA Technical Reports Server (NTRS)

Sittler, E. C.; Arridge, C.; Rymer, A.; Coates, A.; Krupp, N.; Blanc, M.; Richardson, J.; Andre, N.; Thomsen, M.; Tokar, R. L.;

Experimental investigation of gas flow rate and electric field effect on refractive index and electron density distribution of cold atmospheric pressure-plasma by optical method, Moiré deflectometry

NASA Astrophysics Data System (ADS)

Khanzadeh, Mohammad; Jamal, Fatemeh; Shariat, Mahdi

2018-04-01

Nowadays, cold atmospheric-pressure (CAP) helium plasma jets are widely used in material processing devices in various industries. Researchers often use indirect and spectrometric methods for measuring the plasma parameters which are very expensive. In this paper, for the first time, characterization of CAP, i.e., finding its parameters such as refractive index and electron density distribution, was carried out using an optical method, Moiré deflectometry. This method is a wave front analysis technique based on geometric optics. The advantages of this method are simplicity, high accuracy, and low cost along with the non-contact, non-destructive, and direct measurement of CAP parameters. This method demonstrates that as the helium gas flow rate decreases, the refractive index increases. Also, we must note that the refractive index is larger in the gas flow consisting of different flow rates of plasma comparing with the gas flow without the plasma.

High-order Two-Fluid Plasma Solver for Direct Numerical Simulations of Magnetic Flows with Realistic Transport Phenomena

NASA Astrophysics Data System (ADS)

Li, Zhaorui; Livescu, Daniel

2017-11-01

The two-fluid plasma equations with full transport terms, including temperature and magnetic field dependent ion and electron viscous stresses and heat fluxes, frictional drag force, and ohmic heating term have been solved by using the sixth-order non-dissipative compact scheme for plasma flows in several different regimes. In order to be able to fully resolve all the dynamically relevant time and length scales while maintaining computational feasibility, the assumptions of infinite speed of light and negligible electron inertia have been made. The accuracy and robustness of this two-fluid plasma solver in handling plasma flows have been tested against a series of canonical problems, such as Alfven-Whistler dispersion relation, electromagnetic plasma shock, magnetic reconnection, etc. For all test cases, grid convergence tests have been conducted to achieve fully resolved results. The roles of heat flux, viscosity, resistivity, Hall and Biermann battery effects, are investigated for the canonical flows studied.

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 T e/2 e below the plasma potential, the electron velocity distribution functions (EVDFs) exhibit a loss-cone type truncation due to fast electrons overcoming the small potential difference between the electrode and plasma. No sheath is present in this regime, and the plasma remains quasineutral up to the electrode. The EVDF truncation leads to a presheath-like density and flow velocity gradients. Once the bias exceeds the plasma potential, an electronmore » 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.« less

Linear and nonlinear dynamics of current-driven waves in dusty plasmas

NASA Astrophysics Data System (ADS)

Ahmad, Ali; Ali Shan, S.; Haque, Q.; Saleem, H.

2012-09-01

The linear and nonlinear dynamics of a recently proposed plasma mode of dusty plasma is studied using kappa distribution for electrons. This electrostatic wave can propagate in the plasma due to the sheared flow of electrons and ions parallel to the external magnetic field in the presence of stationary dust. The coupling of this wave with the usual drift wave and ion acoustic wave is investigated. D'Angelo's mode is also modified in the presence of superthermal electrons. In the nonlinear regime, the wave can give rise to dipolar vortex structures if the shear in flow is weaker and tripolar vortices if the flow has steeper gradient. The results have been applied to Saturn's magnetosphere corresponding to negatively charged dust grains. But the theoretical model is applicable for positively charged dust as well. This work will be useful for future observations and studies of dusty environments of planets and comets.

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 (T e >> T i), 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

Boundary conditions on the plasma emitter surface in the presence of a particle counter flow: I. Ion emitter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Astrelin, V. T., E-mail: V.T.Astrelin@inp.nsk.su; Kotelnikov, I. A.

Emission of positively charged ions from a plasma emitter irradiated by a counterpropagating electron beam is studied theoretically. A bipolar diode with a plasma emitter in which the ion temperature is lower than the electron temperature and the counter electron flow is extracted from the ion collector is calculated in the one-dimensional model. An analog of Bohm’s criterion for ion emission in the presence of a counterpropagating electron beam is derived. The limiting density of the counterpropagating beam in a bipolar diode operating in the space-charge-limited-emission regime is calculated. The full set of boundary conditions on the plasma emitter surfacemore » that are required for operation of the high-current optics module in numerical codes used to simulate charged particle sources is formulated.« less

Development and Evaluation of an Externally Air-Cooled Low-Flow torch and the Attenuation of Space Charge and Matrix Effects in Inductively Coupled Plasma Mass Spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Praphairaksit, Narong

2000-09-12

An externally air-cooled low-flow torch has been constructed and successfully demonstrated for applications in inductively coupled plasma mass spectrometry (ICP-MS). The torch is cooled by pressurized air flowing at ~70 L/min through a quartz air jacket onto the exterior of the outer tube. The outer gas flow rate and operating RF forward power are reduced considerably. Although plasmas can be sustained at the operating power as low as 400 W with a 2 L/min of outer gas flow, somewhat higher power and outer gas flows are advisable. A stable and analytical useful plasma can be obtained at 850 W withmore » an outer gas flow rate of ~4 L/min. Under these conditions, the air-cooled plasma produces comparable sensitivities, doubly charged ion ratios, matrix effects and other analytical merits as those produced by a conventional torch while using significantly less argon and power requirements. Metal oxide ion ratios are slightly higher with the air-cooled plasma but can be mitigated by reducing the aerosol gas flow rate slightly with only minor sacrifice in analyte sensitivity. A methodology to alleviate the space charge and matrix effects in ICP-MS has been developed. A supplemental electron source adapted from a conventional electron impact ionizer is added to the base of the skimmer. Electrons supplied from this source downstream of the skimmer with suitable amount and energy can neutralize the positive ions in the beam extracted from the plasma and diminish the space charge repulsion between them. As a result, the overall ion transmission efficiency and consequent analyte ion sensitivities are significantly improved while other important analytical aspects, such as metal oxide ion ratio, doubly charged ion ratio and background ions remain relatively unchanged with the operation of this electron source. This technique not only improves the ion transmission efficiency but also minimizes the matrix effects drastically. The matrix-induced suppression of signal for even the most troublesome combination of light analyte and heavy matrix elements can be attenuated from 90-99% to only 2-10% for 2 mM matrix solutions with an ultrasonic nebulizer. The supplemental electron current can be adjusted to ''titrate'' out the matrix effects as desired.« less

Influence of Magnetic Topology on Mars' Ionospheric Structure

NASA Astrophysics Data System (ADS)

Adams, D.; Xu, S.; Mitchell, D. L.; Fillingim, M. O.; Lillis, R. J.; Andersson, L.; Fowler, C. M.; Benna, M.; Connerney, J. E. P.; Elrod, M. K.; Girazian, Z.; Vogt, M.

2017-12-01

The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has been in Mars' orbit since September 2014 (>1 Mars year), and has collected particle and field data within the ionosphere over wide ranges of altitudes, latitudes, and local times. This study uses MAVEN data to (1) analyze the influence of magnetic topology on the day-side ionosphere and (2) identify the sources of the night-side ionosphere. On the day side, magnetic strength and elevation angle are commonly used as proxies for magnetic topology. In this study, we use pitch-angle-resolved suprathermal electron measurements by the Solar Wind Electron Analyzer (SWEA) to directly deduce the magnetic topology instead of using a proxy. On the night side, the main sources of ionospheric plasma are bulk transport and plasma pressure gradient flow from the day side, as well as in situ production by electron impact ionization (EII). Plasma transport at Mars is complicated by the presence of intense crustal magnetic fields. Closed crustal magnetic fields form isolated plasma environments ("miniature magnetospheres") that inhibit external sources of cold ionospheric plasma as well as suprathermal (ionizing) electrons. Inside these closed magnetic loops, we study how the plasma evolves with bulk flow transport as the only source. By comparing closed and non-closed magnetic configurations, the effects of pressure gradient flow and EII can be distinguished. Finally, the densities of O2+, O+, and NO+, as measured by the Neutral Gas and Ion Mass Spectrometer (NGIMS), are examined. Inside miniature magnetospheres on the night side, the abundances of these species are found to be primarily controlled by the different recombination rates, as there is little plasma created within these regions by EII or transported from the neighboring regions by plasma pressure gradient flow.

Survey of Magnetosheath Plasma Properties at Saturn and Inference of Upstream Flow Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomsen, M. F.; Coates, A. J.; Jackman, C. M.

A new Cassini magnetosheath data set is introduced that is based on a comprehensive survey of intervals in which the observed magnetosheath flow was encompassed within the plasma analyzer field of view and for which the computed numerical moments are therefore expected to be accurate. The data extend from 2004 day 299 to 2012 day 151 and comprise 19,155 416-s measurements. In addition to the plasma ion moments (density, temperature, and flow velocity), merged values of the plasma electron density and temperature, the energetic particle pressure, and the magnetic field vector are included in the data set. Statistical properties ofmore » various magnetosheath parameters, including dependence on local time, are presented. The magnetosheath field and flow are found to be only weakly aligned, primarily because of a relatively large z-component of the magnetic field, attributable to the field being pulled out of the equatorial orientation by flows at higher latitudes. A new procedure for using magnetosheath properties to estimate the upstream solar wind speed is proposed and used to determine that the amount of electron heating at Saturn's high Mach-number bow shock is ~4% of the dissipated flow energy. The data set is available as an electronic supplement to this paper.« less

Survey of Magnetosheath Plasma Properties at Saturn and Inference of Upstream Flow Conditions

DOE PAGES

Thomsen, M. F.; Coates, A. J.; Jackman, C. M.; ...

2018-03-01

A new Cassini magnetosheath data set is introduced that is based on a comprehensive survey of intervals in which the observed magnetosheath flow was encompassed within the plasma analyzer field of view and for which the computed numerical moments are therefore expected to be accurate. The data extend from 2004 day 299 to 2012 day 151 and comprise 19,155 416-s measurements. In addition to the plasma ion moments (density, temperature, and flow velocity), merged values of the plasma electron density and temperature, the energetic particle pressure, and the magnetic field vector are included in the data set. Statistical properties ofmore » various magnetosheath parameters, including dependence on local time, are presented. The magnetosheath field and flow are found to be only weakly aligned, primarily because of a relatively large z-component of the magnetic field, attributable to the field being pulled out of the equatorial orientation by flows at higher latitudes. A new procedure for using magnetosheath properties to estimate the upstream solar wind speed is proposed and used to determine that the amount of electron heating at Saturn's high Mach-number bow shock is ~4% of the dissipated flow energy. The data set is available as an electronic supplement to this paper.« less

Electron cyclotron thruster new modeling results preparation for initial experiments

NASA Technical Reports Server (NTRS)

Hooper, E. Bickford

1993-01-01

The following topics are discussed: a whistler-based electron cyclotron resonance heating (ECRH) thruster; cross-field coupling in the helicon approximation; wave propagation; wave structure; plasma density; wave absorption; the electron distribution function; isothermal and adiabatic plasma flow; ECRH thruster modeling; a PIC code model; electron temperature; electron energy; and initial experimental tests. The discussion is presented in vugraph form.

Recombination of H3(+) and D3(+) Ions in a Flowing Afterglow Plasma

NASA Technical Reports Server (NTRS)

Gougousi, T.; Johnsen, R.; Golde, M. F.

1995-01-01

The analysis of flowing afterglow plasmas containing H3(+) or D3(+) ions indicates that the de-ionization of such plasmas does not occur by simple dissociative recombination of ions with electrons. An alternative model of de-ionization is proposed in which electrons are captured into H3(**) auto-ionization Rydberg states that are stabilized by collisional mixing of the Rydberg molecules' angular momenta. The proposed mechanism would enable de-ionization to occur without the need for dissociative recombination by the mechanisms of potential-surface crossings.

Self-sustained focusing of high-density streaming plasma

NASA Astrophysics Data System (ADS)

Bugaev, A.; Dobrovolskiy, A.; Goncharov, A.; Gushenets, V.; Litovko, I.; Naiko, I.; Oks, E.

2017-01-01

We describe our observations of the transport through an electrostatic plasma lens of a wide-aperture, high-current, low energy, metal-ion plasma flow produced by a cathodic arc discharge. The lens input aperture was 80 mm, the length of the lens was 140 mm, and there were three electrostatic ring electrodes located in a magnetic field formed by permanent magnets. The lens outer electrodes were grounded and the central electrode was biased up to -3 kV. The plasma was a copper plasma with directed (streaming) ion energy 20-40 eV, and the equivalent ion current was up to several amperes depending on the potential applied to the central lens electrode. We find that when the central lens electrode is electrically floating, the current density of the plasma flow at the lens focus increases by up to 40%-50%, a result that is in good agreement with a theoretical treatment based on plasma-optical principles of magnetic insulation of electrons and equipotentialization along magnetic field lines. When the central lens electrode is biased negatively, an on-axis stream of energetic electrons is formed, which can also provide a mechanism for focusing of the plasma flow. Optical emission spectra under these conditions show an increase in intensity of lines corresponding to both copper atoms and singly charged copper ions, indicating the presence of fast electrons within the lens volume. These energetic electrons, as well as accumulating on-axis and providing ion focusing, can also assist in reducing the microdroplet component in the dense, low-temperature, metal plasma.

Investigation of Ion Acoustic Wave Instabilities Near Positive Electrodes

NASA Astrophysics Data System (ADS)

Hood, Ryan; Chu, Feng; Baalrud, Scott; Merlino, Robert; Skiff, Fred

2017-10-01

Electron sheaths occur when an electrode is biased above the plasma potential, most often during the electron saturation portion of a Langmuir probe trace. Through the presheath, electrons are accelerated to velocities exceeding the electron thermal speed at the sheath edge, while ions do not develop any appreciable flow. PIC simulations have shown that ion acoustic instabilities are excited by the differential flow between ions and electrons in the presheath region of a low temperature plasma. We present the first experimental measurements investigating these instabilities using Laser-Induced Fluorescence diagnostics in a multidipole argon plasma. The plasma dispersion relation is measured from the power spectra of the imaged LIF signal and compared to the simulation results. In addition, optical pumping is measured using time-resolved LIF measurements and fit to a model in order to determine the diffusion rate, which may be enhanced due to the instability. This research was supported by the Office of Fusion Energy Sciences at the U.S. Department of Energy under contract DE-AC04-94SL85000.

Effects of Mass Flow Rate on the Thermal-Flow Characteristics of Microwave CO2 Plasma.

PubMed

Hong, Chang-Ki; Na, Young-Ho; Uhm, Han-Sup; Kim, Youn-Jea

2015-03-01

In this study, the thermal-flow characteristics of atmospheric pressure microwave CO2 plasma were numerically investigated by simulation. The electric and gas flow fields in the reaction chamber with a microwave axial injection torch operated at 2.45 GHz were simulated. The microwave launcher had the standard rectangular waveguide WR340 geometry. The simulation was performed by using the COMSOL Multiphysics plasma model with various mass flow rates of CO2. The electric fields, temperature profiles and the density of electrons were graphically depicted for different CO2 inlet mass flow rates.

Solar wind interaction with dusty plasmas produces instabilities and solitary structures

NASA Astrophysics Data System (ADS)

Saleem, H.; Ali, S.

2017-12-01

It is pointed out that the solar wind interaction with dusty magnetospheres of the planets can give rise to purely growing instabilities as well as nonlinear electric field structures. Linear dispersion relation of the low frequency electrostatic ion-acoustic wave (IAW) is modified in the presence of stationary dust and its frequency becomes larger than its frequency in usual electron ion plasma even if ion temperature is equal to the electron temperature. This dust-ion-acoustic wave (DIAW) either becomes a purely growing electrostatic instability or turns out to be the modified dust-ion-acoustic wave (mDIAW) depending upon the magnitude of shear flow scale length and its direction. Growth rate of shear flow-driven electrostatic instability in a plasma having negatively charged stationary dust is larger than the usual D'Angelo instability of electron-ion plasma. It is shown that shear modified dust ion acoustic wave (mDIAW) produces electrostatic solitons in the nonlinear regime. The fluid theory predicts the existence of electrostatic solitons in the dusty plasmas in those regions where the inhomogeneous solar wind flow is parallel to the planetary or cometary magnetic field lines. The amplitude and width of the solitary structure depends upon dust density and magnitude of shear in the flow. This is a general theoretical model which is applied to dusty plasma of Saturn's F-ring for illustration.

Numerical simulation of current-free double layers created in a helicon plasma device

NASA Astrophysics Data System (ADS)

Rao, Sathyanarayan; Singh, Nagendra

2012-09-01

Two-dimensional simulations reveal that when radially confined source plasma with magnetized electrons and unmagnetized ions expands into diverging magnetic field B, a current-free double layer (CFDL) embedded in a conical density structure forms, as experimentally measured in the Australian helicon plasma device (HPD). The magnetized electrons follow the diverging B while the unmagnetized ions tend to flow directly downstream of the source, resulting in a radial electric field (E⊥) structure, which couples the ion and electron flows. Ions are transversely (radially) accelerated by E⊥ on the high potential side of the double layer in the CFDL. The accelerated ions are trapped near the conical surface, where E⊥ reverses direction. The potential structure of the CFDL is U-shaped and the plasma density is enhanced on the conical surface. The plasma density is severely depleted downstream of the parallel potential drop (φ||o) in the CFDL; the density depletion and the potential drop are related by quasi-neutrality condition, including the divergence in the magnetic field and in the plasma flow in the conical structure. The potential and density structures, the CFDL spatial size, its electric field strengths and the electron and ion velocities and energy distributions in the CFDL are found to be in good agreements with those measured in the Australian experiment. The applicability of our results to measured axial potential profiles in magnetic nozzle experiments in HPDs is discussed.

Azimuthal ExB drift of electrons induced by the radial electric field flowing through a longitudinal magnetic channel with non-magnetized ions

NASA Astrophysics Data System (ADS)

Akatsuka, Hiroshi; Takeda, Jun; Nezu, Atsushi

2016-09-01

To examine of the effect of the radial electric field on the azimuthal electron motion under E × B field for plasmas with magnetized electrons and non-magnetized ions, an experimental study is conducted by a stationary plasma flow. The argon plasma flow is generated by a DC arc generator under atmospheric pressure, followed by a cw expansion into a rarefied gas-wind tunnel with a uniform magnetic field 0 . 16 T. Inside one of the magnets, we set a ring electrode to apply the radial electric field. We applied an up-down probe for the analysis of the electron motion, where one of the tips is also used as a Langmuir probe to measure electron temperature, density and the space potential. We found that the order of the radial electric field is about several hundred V/m, which should be caused by the difference in the magnetization between electrons and ions. Electron saturation current indicates the existence of the E × B rotation of electrons, whose order is about 2000 - 4000 m/s. The order of the observed electron drift velocity is consistent with the theoretical value calculated from the applied magnetic field and the measured electric field deduced from the space potential.

Model for a transformer-coupled toroidal plasma source

NASA Astrophysics Data System (ADS)

Rauf, Shahid; Balakrishna, Ajit; Chen, Zhigang; Collins, Ken

2012-01-01

A two-dimensional fluid plasma model for a transformer-coupled toroidal plasma source is described. Ferrites are used in this device to improve the electromagnetic coupling between the primary coils carrying radio frequency (rf) current and a secondary plasma loop. Appropriate components of the Maxwell equations are solved to determine the electromagnetic fields and electron power deposition in the model. The effect of gas flow on species transport is also considered. The model is applied to 1 Torr Ar/NH3 plasma in this article. Rf electric field lines form a loop in the vacuum chamber and generate a plasma ring. Due to rapid dissociation of NH3, NHx+ ions are more prevalent near the gas inlet and Ar+ ions are the dominant ions farther downstream. NH3 and its by-products rapidly dissociate into small fragments as the gas flows through the plasma. With increasing source power, NH3 dissociates more readily and NHx+ ions are more tightly confined near the gas inlet. Gas flow rate significantly influences the plasma characteristics. With increasing gas flow rate, NH3 dissociation occurs farther from the gas inlet in regions with higher electron density. Consequently, more NH4+ ions are produced and dissociation by-products have higher concentrations near the outlet.

Response to 'Comment on 'Three-dimensional numerical investigation of electron transport with rotating spoke in a cylindrical anode layer Hall plasma accelerator''[Phys. Plasmas 20, 014701 (2013)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, D. L.; Qiu, X. M.; Geng, S. F.

The numerical simulation described in our paper [D. L. Tang et al., Phys. Plasmas 19, 073519 (2012)] shows a rotating dense plasma structure, which is the critical characteristic of the rotating spoke. The simulated rotating spoke has a frequency of 12.5 MHz with a rotational speed of {approx}1.0 Multiplication-Sign 10{sup 6} m/s on the surface of the anode. Accompanied by the almost uniform azimuthal ion distribution, the non-axisymmetric electron distribution introduces two azimuthal electric fields with opposite directions. The azimuthal electric fields have the same rotational frequency and speed together with the rotating spoke. The azimuthal electric fields excite themore » axial electron drift upstream and downstream due to the additional E{sub {theta}} x B field and then the axial shear flow is generated. The axial local charge separation induced by the axial shear electron flow may be compensated by the azimuthal electron transport, finally resulting in the azimuthal electric field rotation and electron transport with the rotating spoke.« less

The effect of high-power plasma flows on tungsten plates with multilayer films of tungsten nanoparticles

NASA Astrophysics Data System (ADS)

Gorokhov, M. V.; Kozhevin, V. M.; Yavsin, D. A.; Voronin, A. V.; Gurevich, S. A.

2017-04-01

We have experimentally studied the action of high-power plasma flows on pure tungsten plates covered with multilayer films of tungsten nanoparticles formed by the method of laser electrodeposition. The samples were irradiated using a plasma gun producing hydrogen (helium) plasma flows with power density up to 35 GW/cm2. The resulting surface morphology was studied by scanning electron microscopy (SEM). SEM data showed that tungsten plates coated by nanoparticles are more resistant to the formation of microcracks than are pure tungsten plates.

Temporal characteristics of electrostatic surface waves in a cold complex plasma containing collision-dominated ion flow

NASA Astrophysics Data System (ADS)

Lee, Myoung-Jae; Jung, Young-Dae

2017-03-01

The influence of electron-ion collision frequency and dust charge on the growth rate of two-stream instability of the electrostatic surface wave propagating at the interface of semi-infinite complex plasma whose constituents are electrons, negatively charged dust, and streaming ions. It is found that the surface wave can be unstable if the multiplication of wave number and ion flow velocity is greater than the total plasma frequency of electrons and dusts. The analytical solution of the growth rate is derived as a function of collision frequency, dust charge, and ion-to-electron density ratio. It is found that the growth rate is inversely proportional to the collision rate, but it is enhanced as the number of electrons residing on the dust grain surface is increased. The growth rate of surface wave is compared to that of the bulk wave.

Multidimensional Visualization of MHD and Turbulence in Fusion Plasmas [Multi-dimensional Visualization of Turbulence in Fusion Plasmas

DOE PAGES

Muscatello, Christopher M.; Domier, Calvin W.; Hu, Xing; ...

2014-08-13

Here, quasi-optical imaging at sub-THz frequencies has had a major impact on fusion plasma diagnostics. Mm-wave imaging reflectometry utilizes microwaves to actively probe fusion plasmas, inferring the local properties of electron density fluctuations. Electron cyclotron emission imaging is a multichannel radiometer that passively measures the spontaneous emission of microwaves from the plasma to infer local properties of electron temperature fluctuations. These imaging diagnostics work together to diagnose the characteristics of turbulence. Important quantities such as amplitude and wavenumber of coherent fluctuations, correlation lengths and decor relation times of turbulence, and poloidal flow velocity of the plasma are readily inferred.

X-ray diagnostics of hohlraum plasma flow

NASA Astrophysics Data System (ADS)

Back, C. A.; Glenzer, S. H.; Landen, O. L.; MacGowan, B. J.; Shepard, T. D.

1997-01-01

In this study we use spectroscopy and x-ray imaging to investigate the macroscopic plasma flow in mm-sized laser-produced hohlraum plasmas. By using multiple diagnostics to triangulate the emission on a single experiment, we can pinpoint the position of dopants placed inside the hohlraum. X-ray emission from the foil has been used in the past to measure electron temperature. Here we analyze the spatial movement of dopant plasmas for comparison to hydrodynamic calculations.

Spectroscopic investigations of microwave generated plasmas

NASA Technical Reports Server (NTRS)

Hawley, Martin C.; Haraburda, Scott S.; Dinkel, Duane W.

1991-01-01

The study deals with the plasma behavior as applied to spacecraft propulsion from the perspective of obtaining better design and modeling capabilities. The general theory of spectroscopy is reviewed, and existing methods for converting emission-line intensities into such quantities as temperatures and densities are outlined. Attention is focused on the single-atomic-line and two-line radiance ratio methods, atomic Boltzmann plot, and species concentration. Electronic temperatures for a helium plasma are determined as a function of pressure and a gas-flow rate using these methods, and the concentrations of ions and electrons are predicted from the Saha-Eggert equations using the sets of temperatures obtained as a function of the gas-flow rate. It is observed that the atomic Boltzmann method produces more reliable results for the electronic temperature, while the results obtained from the single-line method reflect the electron temperatures accurately.

Weakly Ionized Plasmas in Hypersonics: Fundamental Kinetics and Flight Applications

NASA Astrophysics Data System (ADS)

Macheret, Sergey

2005-05-01

The paper reviews some of the recent studies of applications of weakly ionized plasmas to supersonic/hypersonic flight. Plasmas can be used simply as means of delivering energy (heating) to the flow, and also for electromagnetic flow control and magnetohydrodynamic (MHD) power generation. Plasma and MHD control can be especially effective in transient off-design flight regimes. In cold air flow, nonequilibrium plasmas must be created, and the ionization power budget determines design, performance envelope, and the very practicality of plasma/MHD devices. The minimum power budget is provided by electron beams and repetitive high-voltage nanosecond pulses, and the paper describes theoretical and computational modeling of plasmas created by the beams and repetitive pulses. The models include coupled equations for non-local and unsteady electron energy distribution function (modeled in forward-back approximation), plasma kinetics, and electric field. Recent experimental studies at Princeton University have successfully demonstrated stable diffuse plasmas sustained by repetitive nanosecond pulses in supersonic air flow, and for the first time have demonstrated the existence of MHD effects in such plasmas. Cold-air hypersonic MHD devices are shown to permit optimization of scramjet inlets at Mach numbers higher than the design value, while operating in self-powered regime. Plasma energy addition upstream of the inlet throat can increase the thrust by capturing more air (Virtual Cowl), or it can reduce the flow Mach number and thus eliminate the need for an isolator duct. In the latter two cases, the power that needs to be supplied to the plasma would be generated by an MHD generator downstream of the combustor, thus forming the "reverse energy bypass" scheme. MHD power generation on board reentry vehicles is also discussed.

Simulative research on the anode plasma dynamics in the high-power electron beam diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Dan; Liu, Lie; Ju, Jin-Chuan

2015-07-15

Anode plasma generated by electron beams could limit the electrical pulse-length, modify the impedance and stability of diode, and affect the generator to diode power coupling. In this paper, a particle-in-cell code is used to study the dynamics of anode plasma in the high-power electron beam diode. The effect of gas type, dynamic characteristic of ions on the diode operation with bipolar flow model are presented. With anode plasma appearing, the amplitude of diode current is increased due to charge neutralizations of electron flow. The lever of neutralization can be expressed using saturation factor. At same pressure of the anodemore » gas layer, the saturation factor of CO{sub 2} is bigger than the H{sub 2}O vapor, namely, the generation rate of C{sup +} ions is larger than the H{sup +} ions at the same pressure. The transition time of ions in the anode-cathode gap could be used to estimate the time of diode current maximum.« less

Current flow instability and nonlinear structures in dissipative two-fluid plasmas

NASA Astrophysics Data System (ADS)

Koshkarov, O.; Smolyakov, A. I.; Romadanov, I. V.; Chapurin, O.; Umansky, M. V.; Raitses, Y.; Kaganovich, I. D.

2018-01-01

The current flow in two-fluid plasma is inherently unstable if plasma components (e.g., electrons and ions) are in different collisionality regimes. A typical example is a partially magnetized E ×B plasma discharge supported by the energy released from the dissipation of the current in the direction of the applied electric field (perpendicular to the magnetic field). Ions are not magnetized so they respond to the fluctuations of the electric field ballistically on the inertial time scale. In contrast, the electron current in the direction of the applied electric field is dissipatively supported either by classical collisions or anomalous processes. The instability occurs due to a positive feedback between the electron and ion current coupled by the quasi-neutrality condition. The theory of this instability is further developed taking into account the electron inertia, finite Larmor radius and nonlinear effects. It is shown that this instability results in highly nonlinear quasi-coherent structures resembling breathing mode oscillations in Hall thrusters.

Flow impedance in a uniform magnetically insulated transmission line

NASA Astrophysics Data System (ADS)

Mendel, C. W.; Seidel, D. B.

1999-12-01

In two recent publications [C. W. Mendel, Jr. and S. E. Rosenthal, Phys. of Plasmas 2, 1332 (1995), C. W. Mendel, Jr. and S. E. Rosenthal, Phys. of Plasmas 3, 4207 (1996)] relativistic electron flow in cylindrical magnetically insulated transmission lines was analyzed and modeled under the assumption of negligible electron pressure. The model allows power flow in these lines to be accurately calculated under most conditions. The model was developed for coaxial right circular cylindrical electrodes. It is shown here that the model applies equally well to arbitrary cylindrical systems, i.e., systems consisting of electrodes of arbitrary cross section.

Heat flux and plasma flow in the far scrape-off layer of the inboard poloidal field null configuration in QUEST

DOE Office of Scientific and Technical Information (OSTI.GOV)

Onchi, T.; Zushi, H.; Hanada, K.

2015-08-15

Heat flux and plasma flow in the scrape-off layer (SOL) are examined for the inboard poloidal field null (IPN) configuration of the spherical tokamak QUEST. In the plasma current (I{sub p}) ramp-up phase, high heat flux (>1 MW/m{sup 2}) and supersonic flow (Mach number M > 1) are found to be present simultaneously in the far-SOL. The heat flux is generated by energetic electrons excursed from the last closed flux surface. Supersonic flows in the poloidal and toroidal directions are correlated with each other. In the quasi-steady state, sawtooth-like oscillation of I{sub p} at 20 Hz is observed. Heat flux and subsonic plasma flowmore » in the far-SOL are modified corresponding to the I{sub p}-oscillation. The heat flow caused by motion of energetic electrons and the bulk-particle transport to the far-SOL is enhanced during the low-I{sub p} phase. Modification of plasma flow in the far SOL occurs earlier than the I{sub p} crash. The M–I{sub p} curve has a limit-cycle characteristic with sawtooth-like oscillation. Such a core–SOL relationship indicates that the far-SOL flow plays an important role in sustaining the oscillation of I{sub p} in the IPN configuration.« less

Helicon thruster plasma modeling: Two-dimensional fluid-dynamics and propulsive performances

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahedo, Eduardo; Navarro-Cavalle, Jaume

2013-04-15

An axisymmetric macroscopic model of the magnetized plasma flow inside the helicon thruster chamber is derived, assuming that the power absorbed from the helicon antenna emission is known. Ionization, confinement, subsonic flows, and production efficiency are discussed in terms of design and operation parameters. Analytical solutions and simple scaling laws for ideal plasma conditions are obtained. The chamber model is then matched with a model of the external magnetic nozzle in order to characterize the whole plasma flow and assess thruster performances. Thermal, electric, and magnetic contributions to thrust are evaluated. The energy balance provides the power conversion between ionsmore » and electrons in chamber and nozzle, and the power distribution among beam power, ionization losses, and wall losses. Thruster efficiency is assessed, and the main causes of inefficiency are identified. The thermodynamic behavior of the collisionless electron population in the nozzle is acknowledged to be poorly known and crucial for a complete plasma expansion and good thrust efficiency.« less

Radial Profiles of the Plasma Electron Characteristics in a 30 kW Arc Jet

NASA Technical Reports Server (NTRS)

Codron, Douglas A.; Nawaz, Anuscheh

2013-01-01

The present effort aims to strengthen modeling work conducted at the NASA Ames Research Center by measuring the critical plasma electron characteristics within and slightly outside of an arc jet plasma column. These characteristics are intended to give physical insights while assisting in the formulation of boundary conditions to validate full scale simulations. Single and triple Langmuir probes have been used to achieve estimates of the electron temperature (T(sub e)), electron number density (n(sub e)) and plasma potential (outside of the plasma column) as probing location is varied radially from the flow centerline. Both the electron temperature and electron number density measurements show a large dependence on radial distance from the plasma column centerline with T(sub e) approx. = (3 - 12 eV and n(sub e) approx. = 10(exp 12) - 10(exp 14)/cu cm.

Diagnosing pure-electron plasmas with internal particle flux probes.

PubMed

Kremer, J P; Pedersen, T Sunn; Marksteiner, Q; Lefrancois, R G; Hahn, M

2007-01-01

Techniques for measuring local plasma potential, density, and temperature of pure-electron plasmas using emissive and Langmuir probes are described. The plasma potential is measured as the least negative potential at which a hot tungsten filament emits electrons. Temperature is measured, as is commonly done in quasineutral plasmas, through the interpretation of a Langmuir probe current-voltage characteristic. Due to the lack of ion-saturation current, the density must also be measured through the interpretation of this characteristic thereby greatly complicating the measurement. Measurements are further complicated by low densities, low cross field transport rates, and large flows typical of pure-electron plasmas. This article describes the use of these techniques on pure-electron plasmas in the Columbia Non-neutral Torus (CNT) stellarator. Measured values for present baseline experimental parameters in CNT are phi(p)=-200+/-2 V, T(e)=4+/-1 eV, and n(e) on the order of 10(12) m(-3) in the interior.

Transient fields produced by a cylindrical electron beam flowing through a plasma

NASA Astrophysics Data System (ADS)

Firpo, Marie-Christine

2012-10-01

Fast ignition schemes (FIS) for inertial confinement fusion should involve in their final stage the interaction of an ignition beam composed of MeV electrons laser generated at the critical density surface with a dense plasma target. In this study, the out-of-equilibrium situation in which an initially sharp-edged cylindrical electron beam, that could e.g. model electrons flowing within a wire [1], is injected into a plasma is considered. A detailed computation of the subsequently produced magnetic field is presented [2]. The control parameter of the problem is shown to be the ratio of the beam radius to the electron skin depth. Two alternative ways to address analytically the problem are considered: one uses the usual Laplace transform approach, the other one involves Riemann's method in which causality conditions manifest through some integrals of triple products of Bessel functions.[4pt] [1] J.S. Green et al., Surface heating of wire plasmas using laser-irradiated cone geometries, Nature Physics 3, 853--856 (2007).[0pt] [2] M.-C. Firpo, http://hal.archives-ouvertes.fr/hal-00695629, to be published (2012).

Equilibrium structure of the plasma sheet boundary layer-lobe interface

NASA Technical Reports Server (NTRS)

Romero, H.; Ganguli, G.; Palmadesso, P.; Dusenbery, P. B.

1990-01-01

Observations are presented which show that plasma parameters vary on a scale length smaller than the ion gyroradius at the interface between the plasma sheet boundary layer and the lobe. The Vlasov equation is used to investigate the properties of such a boundary layer. The existence, at the interface, of a density gradient whose scale length is smaller than the ion gyroradius implies that an electrostatic potential is established in order to maintain quasi-neutrality. Strongly sheared (scale lengths smaller than the ion gyroradius) perpendicular and parallel (to the ambient magnetic field) electron flows develop whose peak velocities are on the order of the electron thermal speed and which carry a net current. The free energy of the sheared flows can give rise to a broadband spectrum of electrostatic instabilities starting near the electron plasma frequency and extending below the lower hybrid frequency.

Three-dimensional modeling of a negative ion source with a magnetic filter: impact of biasing the plasma electrode on the plasma asymmetry

NASA Astrophysics Data System (ADS)

Fubiani, G.; Boeuf, J. P.

2015-10-01

The effect on the plasma characteristics of biasing positively the plasma electrode (PE) in negative ion sources with a magnetic filter is analysed using a 3D particle-in-cell model with Monte-Carlo collisions (PIC-MCC). We specialize to the one driver (i.e. one inductively coupled radio-frequency discharge) BATMAN negative ion source and the 4-drivers (large volume) ELISE device. Both are ITER prototype high power tandem-type negative ion sources developed for the neutral beam injector (NBI) system. The plasma is generated in the driver and diffuses inside the second chamber which is magnetized. Asymmetric plasma profiles originate from the formation of an electric field transverse to the electron current flowing through the magnetic filter (Hall effect). The model shows that the importance of the asymmetry increases with the PE bias potential, i.e. with the electron flow from the driver to the extraction region and depends on the shape of the magnetic filter field. We find that although the plasma density and potential profiles may be more or less asymmetric depending on the filter field configuration, the electron current to the plasma grid is always strongly asymmetric.

Model for a transformer-coupled toroidal plasma source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rauf, Shahid; Balakrishna, Ajit; Chen Zhigang

2012-01-15

A two-dimensional fluid plasma model for a transformer-coupled toroidal plasma source is described. Ferrites are used in this device to improve the electromagnetic coupling between the primary coils carrying radio frequency (rf) current and a secondary plasma loop. Appropriate components of the Maxwell equations are solved to determine the electromagnetic fields and electron power deposition in the model. The effect of gas flow on species transport is also considered. The model is applied to 1 Torr Ar/NH{sub 3} plasma in this article. Rf electric field lines form a loop in the vacuum chamber and generate a plasma ring. Due tomore » rapid dissociation of NH{sub 3}, NH{sub x}{sup +} ions are more prevalent near the gas inlet and Ar{sup +} ions are the dominant ions farther downstream. NH{sub 3} and its by-products rapidly dissociate into small fragments as the gas flows through the plasma. With increasing source power, NH{sub 3} dissociates more readily and NH{sub x}{sup +} ions are more tightly confined near the gas inlet. Gas flow rate significantly influences the plasma characteristics. With increasing gas flow rate, NH{sub 3} dissociation occurs farther from the gas inlet in regions with higher electron density. Consequently, more NH{sub 4}{sup +} ions are produced and dissociation by-products have higher concentrations near the outlet.« less

Plasma Relaxation and Topological Aspects in Electron Magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Shivamoggi, Bhimsen

2016-10-01

Parker's formulation of isotopological plasma relaxation process toward minimum magnetics energy states in magnetohydrodynamics (MHD) is extended to electron MHD (EMHD). The lower bound on magnetic energy in EMHD is determined by both the magnetic field and the electron vorticity field topologies, and is shown to be reduced further in EMHD by an amount proportional to the sum of total electron-flow kinetic energy and total electron-flow enstrophy. The EMHD Beltrami condition becomes equivalent to the potential vorticity conservation equation in two-dimensional (2D) hydrodynamics, and the torsion coefficient and turns out to be proportional to potential vorticity. The winding pattern of the magnetic field lines appears to evolve therefore in the same way as potential vorticity lines in 2D hydrodynamics.

Plasma relaxation and topological aspects in electron magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Shivamoggi, B. K.

2016-07-01

Parker's formulation of isotopological plasma relaxation process toward minimum magnetics energy states in magnetohydrodynamics (MHD) is extended to electron MHD (EMHD). The lower bound on magnetic energy in EMHD is determined by both the magnetic field and the electron vorticity field topologies, and is shown to be reduced further in EMHD by an amount proportional to the sum of total electron-flow kinetic energy and total electron-flow enstrophy. The EMHD Beltrami condition becomes equivalent to the potential vorticity conservation equation in two-dimensional (2D) hydrodynamics, and the torsion coefficient α turns out to be proportional to potential vorticity. The winding pattern of the magnetic field lines appears to evolve, therefore, in the same way as potential vorticity lines in 2D hydrodynamics.

Observation of an edge coherent mode and poloidal flow in the electron cyclotron wave induced high β{sub p} plasma in QUEST

DOE Office of Scientific and Technical Information (OSTI.GOV)

Banerjee, Santanu, E-mail: sbanerje@ipr.res.in; Mishra, K.; Zushi, H.

Fluctuations are measured in the edge and scrape-off layer (SOL) of QUEST using fast visible imaging diagnostic. Electron cyclotron wave injection in the Ohmic plasma features excitation of low frequency coherent fluctuations near the separatrix and enhanced cross-field transport. Plasma shifts from initial high field side limiter bound (inboard limited, IL) towards inboard poloidal null (IPN) configuration with steepening of the density profile at the edge. This may have facilitated the increased edge and SOL fluctuation activities. Observation of the coherent mode, associated plasma flow, and particle out-flux, for the first time in the IPN plasma configuration in a sphericalmore » tokamak may provide further impetus to the edge and SOL turbulence studies in tokamaks.« less

Thrust and efficiency model for electron-driven magnetic nozzles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Little, Justin M.; Choueiri, Edgar Y.

2013-10-15

A performance model is presented for magnetic nozzle plasmas driven by electron thermal expansion to investigate how the thrust coefficient and beam divergence efficiency scale with the incoming plasma flow and magnetic field geometry. Using a transformation from cylindrical to magnetic coordinates, an approximate analytical solution is derived to the axisymmetric two-fluid equations for a collisionless plasma flow along an applied magnetic field. This solution yields an expression for the half-width at half-maximum of the plasma density profile in the far-downstream region, from which simple scaling relations for the thrust coefficient and beam divergence efficiency are derived. It is foundmore » that the beam divergence efficiency is most sensitive to the density profile of the flow into the nozzle throat, with the highest efficiencies occurring for plasmas concentrated along the nozzle axis. Increasing the expansion ratio of the magnetic field leads to efficiency improvements that are more pronounced for incoming plasmas that are not concentrated along the axis. This implies that the additional magnet required to increase the expansion ratio may be worth the added complexity for plasma sources that exhibit poor confinement.« less

A Multi-ring Ionospheric Plasma Probe

NASA Technical Reports Server (NTRS)

Sheldon, J. W.

1972-01-01

An ionospheric plasma probe was constructed which consists of a long cylinder with the end facing the flow closed by an end plate made up of multiple annular rings and a center disk. A theoretical argument is given which yields the plasma potential and electron temperature in terms of known plasma parameters and the currents to the various rings of the end plate. This probe was successfully operated in an ionospheric flow simulation facility and the resulting plasma potential is in excellent agreement with the traditional Langmuir analysis (1.22 volts).

Flow stagnation at Enceladus: The effects of neutral gas and charged dust

NASA Astrophysics Data System (ADS)

Omidi, N.; Tokar, R. L.; Averkamp, T.; Gurnett, D. A.; Kurth, W. S.; Wang, Z.

2012-06-01

Enceladus is one of Saturn's most active moons. It ejects neutral gas and dust particles from its southern plumes with velocities of hundreds of meters per second. The interaction between the ejected material and the corotating plasma in Saturn's magnetosphere leads to flow deceleration in ways that remain to be understood. The most effective mechanism for the interaction between the corotating plasma and the neutral gas is charge exchange which replaces the hotter corotating ions with nearly stationary cold ions that are subsequently accelerated by the motional electric field. Dust particles in the plume can become electrically charged through electron absorption and couple to the plasma through the motional electric field. The objective of this study is to determine the level of flow deceleration associated with each of these processes using Cassini RPWS dust impact rates, Cassini Plasma Spectrometer (CAPS) plasma data, and 3-D electromagnetic hybrid (kinetic ions, fluid electrons) simulations. Hybrid simulations show that the degree of flow deceleration by charged dust varies considerably with the spatial distribution of dust particles. Based on the RPWS observations of dust impacts during the E7 Cassini flyby of Enceladus, we have constructed a dust model consisting of multiple plumes. Using this model in the hybrid simulation shows that when the dust density is high enough for complete absorption of electrons at the point of maximum dust density, the corotating flow is decelerated by only a few km/s. This is not sufficient to account for the CAPS observation of flow stagnation in the interaction region. On the other hand, charge exchange with neutral gas plumes similar to the modeled dust plumes but with base (plume opening) densities of ˜109 cm-3 result in flow deceleration similar to that observed by CAPS. The results indicate that charge exchange with neutral gas is the dominant mechanism for flow deceleration at Enceladus.

Formation of high-β plasma and stable confinement of toroidal electron plasma in Ring Trap 1a)

NASA Astrophysics Data System (ADS)

Saitoh, H.; Yoshida, Z.; Morikawa, J.; Furukawa, M.; Yano, Y.; Kawai, Y.; Kobayashi, M.; Vogel, G.; Mikami, H.

2011-05-01

Formation of high-β electron cyclotron resonance heating plasma and stable confinement of pure electron plasma have been realized in the Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet. The effects of coil levitation resulted in drastic improvements of the confinement properties, and the maximum local β value has exceeded 70%. Hot electrons are major component of electron populations, and its particle confinement time is 0.5 s. Plasma has a peaked density profile in strong field region [H. Saitoh et al., 23rd IAEA Fusion Energy Conference EXC/9-4Rb (2010)]. In pure electron plasma experiment, inward particle diffusion is realized, and electrons are stably trapped for more than 300 s. When the plasma is in turbulent state during beam injection, plasma flow has a shear, which activates the diocotron (Kelvin-Helmholtz) instability. The canonical angular momentum of the particle is not conserved in this phase, realizing the radial diffusion of charged particles across closed magnetic surfaces. [Z. Yoshida et al., Phys Rev. Lett. 104, 235004 (2010); H. Saitoh et al., Phys. Plasmas 17, 112111 (2010).].

Numerical simulation of current-free double layers created in a helicon plasma device

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rao, Sathyanarayan; Singh, Nagendra

2012-09-15

Two-dimensional simulations reveal that when radially confined source plasma with magnetized electrons and unmagnetized ions expands into diverging magnetic field B, a current-free double layer (CFDL) embedded in a conical density structure forms, as experimentally measured in the Australian helicon plasma device (HPD). The magnetized electrons follow the diverging B while the unmagnetized ions tend to flow directly downstream of the source, resulting in a radial electric field (E{sub Up-Tack }) structure, which couples the ion and electron flows. Ions are transversely (radially) accelerated by E{sub Up-Tack} on the high potential side of the double layer in the CFDL. Themore » accelerated ions are trapped near the conical surface, where E{sub Up-Tack} reverses direction. The potential structure of the CFDL is U-shaped and the plasma density is enhanced on the conical surface. The plasma density is severely depleted downstream of the parallel potential drop ({phi}{sub Double-Vertical-Line Double-Vertical-Line o}) in the CFDL; the density depletion and the potential drop are related by quasi-neutrality condition, including the divergence in the magnetic field and in the plasma flow in the conical structure. The potential and density structures, the CFDL spatial size, its electric field strengths and the electron and ion velocities and energy distributions in the CFDL are found to be in good agreements with those measured in the Australian experiment. The applicability of our results to measured axial potential profiles in magnetic nozzle experiments in HPDs is discussed.« less

Confinement of nonneutral plasmas in the Prototype Ring Trap device

NASA Astrophysics Data System (ADS)

Himura, Haruhiko; Yoshida, Zensho; Nakashima, Chihiro; Morikawa, Junji; Kakuno, Hidekazu; Tahara, Shigeru; Shibayama, Norihisa

1999-12-01

Recently, an internal-ring device named Proto-RT (Prototype Ring Trap) was constructed at University of Tokyo, and experiments on the device have been intensively conducted. The main goal of Proto-RT is to explore an innovative method to attain a plasma equilibrium with extremely high-β (β>1) in a toroidal geometry using non-neutral condition. At the first series of the experiments, pure electron plasmas (ne˜1013m-3) have been successfully confined inside a separatrix. No disruption is so far observed. The confinement time of the electron plasmas is of order 0.1 ms for an X point configuration. The non-neutrality of Δne˜1013m-3 is already beyond the critical value which is required to produce an enough self-electric field E in non-neutral plasmas with n0˜1019m-3, causing a strong E×B flow thoroughly over the plasmas where the hydrodynamic pressure of the flow is predicted to balance with the thermal pressure of the plasmas.

Impact of the Hall effect on high-energy-density plasma jets.

PubMed

Gourdain, P-A; Seyler, C E

2013-01-04

Using a 1-MA, 100 ns-rise-time pulsed power generator, radial foil configurations can produce strongly collimated plasma jets. The resulting jets have electron densities on the order of 10(20) cm(-3), temperatures above 50 eV and plasma velocities on the order of 100 km/s, giving Reynolds numbers of the order of 10(3), magnetic Reynolds and Péclet numbers on the order of 1. While Hall physics does not dominate jet dynamics due to the large particle density and flow inside, it strongly impacts flows in the jet periphery where plasma density is low. As a result, Hall physics affects indirectly the geometrical shape of the jet and its density profile. The comparison between experiments and numerical simulations demonstrates that the Hall term enhances the jet density when the plasma current flows away from the jet compared to the case where the plasma current flows towards it.

Plasma flow around and charge distribution of a dust cluster in a rf discharge

NASA Astrophysics Data System (ADS)

Schleede, J.; Lewerentz, L.; Bronold, F. X.; Schneider, R.; Fehske, H.

2018-04-01

We employ a particle-in-cell Monte Carlo collision/particle-particle particle-mesh simulation to study the plasma flow around and the charge distribution of a three-dimensional dust cluster in the sheath of a low-pressure rf argon discharge. The geometry of the cluster and its position in the sheath are fixed to the experimental values, prohibiting a mechanical response of the cluster. Electrically, however, the cluster and the plasma environment, mimicking also the experimental situation, are coupled self-consistently. We find a broad distribution of the charges collected by the grains. The ion flux shows on the scale of the Debye length strong focusing and shadowing inside and outside the cluster due to the attraction of the ions to the negatively charged grains, whereas the electron flux is characterized on this scale only by a weak spatial modulation of its magnitude depending on the rf phase. On the scale of the individual dust potentials, however, the electron flux deviates in the vicinity of the cluster strongly from the laminar flow associated with the plasma sheath. It develops convection patterns to compensate for the depletion of electrons inside the dust cluster.

Electron concentration distribution in a glow discharge in air flow

NASA Astrophysics Data System (ADS)

Mukhamedzianov, R. B.; Gaisin, F. M.; Sabitov, R. A.

1989-04-01

Electron concentration distributions in a glow discharge in longitudinal and vortex air flows are determined from the attenuation of the electromagnetic wave passing through the plasma using microwave probes. An analysis of the distribution curves obtained indicates that electron concentration decreases in the direction of the anode. This can be explained by charge diffusion toward the chamber walls and electron recombination and sticking within the discharge.

Ion extraction from a plasma

NASA Technical Reports Server (NTRS)

Aston, G.; Wilbur, P. J.

1981-01-01

The physical processes governing ion extraction from a plasma have been examined experimentally. The screen hole plasma sheath (the transition region wherein significant ion acceleration and complete electron retardation occurs) has been defined by equipotential plots for a variety of ion accelerator system geometries and operating conditions. It was found that the screen hole plasma sheath extends over a large distance, and influences ion and electron trajectories at least 15 Debye lengths within the discharge chamber. The electron density variation within the screen hole plasma sheath satisfied a Maxwell-Boltzmann density distribution at an effective electron temperature dependent on the discharge plasma primary-to-Maxwellian electron density ratio. Plasma ion flow up to and through the sheath was predominantly one-dimensional, and the ions entered the sheath region with a modified Bohm velocity. Low values of the screen grid thickness to screen hole diameter ratio were found to give good ion focusing and high extracted ion currents because of the effect of screen webbing on ion focusing.

Structure and Dynamics of Colliding Plasma Jets

DOE PAGES

Li, C.; Ryutov, D.; Hu, S.; ...

2013-12-01

Monoenergetic-proton radiographs of laser-generated, high-Mach-number plasma jets colliding at various angles shed light on the structures and dynamics of these collisions. The observations compare favorably with results from 2D hydrodynamic simulations of multistream plasma jets, and also with results from an analytic treatment of electron flow and magnetic field advection. In collisions of two noncollinear jets, the observed flow structure is similar to the analytic model’s prediction of a characteristic feature with a narrow structure pointing in one direction and a much thicker one pointing in the opposite direction. Spontaneous magnetic fields, largely azimuthal around the colliding jets and generatedmore » by the well-known ∇T e ×∇n e Biermann battery effect near the periphery of the laser spots, are demonstrated to be “frozen in” the plasma (due to high magnetic Reynolds number R M ~5×10⁴) and advected along the jet streamlines of the electron flow. These studies provide novel insight into the interactions and dynamics of colliding plasma jets.« less

Electromagnetic radiation and nonlinear energy flow in an electron beam-plasma system

NASA Technical Reports Server (NTRS)

Whelan, D. A.; Stenzel, R. L.

1985-01-01

It is shown that the unstable electron-plasma waves of a beam-plasma system can generate electromagnetic radiation in a uniform plasma. The generation mechanism is a scattering of the unstable electron plasma waves off ion-acoustic waves, producing electromagnetic waves whose frequency is near the local plasma frequency. The wave vector and frequency matching conditions of the three-wave mode coupling are experimentally verified. The electromagnetic radiation is observed to be polarized with the electric field parallel to the beam direction, and its source region is shown to be localized to the unstable plasma wave region. The frequency spectrum shows negligible intensity near the second harmonic of the plasma frequency. These results suggest that the observed electromagnetic radiation of type III solar bursts may be generated near the local plasma frequency and observed downstream where the wave frequency is near the harmonic of the plasma frequency.

Investigation of operating parameters on CO2 splitting by dielectric barrier discharge plasma

NASA Astrophysics Data System (ADS)

Pan, CHEN; Jun, SHEN; Tangchun, RAN; Tao, YANG; Yongxiang, YIN

2017-12-01

Experiments of CO2 splitting by dielectric barrier discharge (DBD) plasma were carried out, and the influence of CO2 flow rate, plasma power, discharge voltage, discharge frequency on CO2 conversion and process energy efficiency were investigated. It was shown that the absolute quantity of CO2 decomposed was only proportional to the amount of conductive electrons across the discharge gap, and the electron amount was proportional to the discharge power; the energy efficiency of CO2 conversion was almost a constant at a lower level, which was limited by CO2 inherent discharge character that determined a constant gap electric field strength. This was the main reason why CO2 conversion rate decreased as the CO2 flow rate increase and process energy efficiency was decreased a little as applied frequency increased. Therefore, one can improve the CO2 conversion by less feed flow rate or larger discharge power in DBD plasma, but the energy efficiency is difficult to improve.

Thermospheric neutral density estimates from heater-induced ion up-flow at EISCAT

NASA Astrophysics Data System (ADS)

Kosch, Michael; Ogawa, Yasunobu; Yamazaki, Yosuke; Vickers, Hannah; Blagoveshchenskaya, Nataly

We exploit a recently-developed technique to estimate the upper thermospheric neutral density using measurements of ionospheric plasma parameters made by the EISCAT UHF radar during ionospheric modification experiments. Heating the electrons changes the balance between upward plasma pressure gradient and downward gravity, resulting in ion up-flow up to ~200 m/s. This field-aligned flow is retarded by collisions, which is directly related to the neutral density. Whilst the ion up-flow is consistent with the plasma pressure gradient, the estimated thermospheric neutral density depends on the assumed composition, which varies with altitude. Results in the topside ionosphere are presented.

Ion Thruster Discharge Performance Per Magnetic Field Topography

NASA Technical Reports Server (NTRS)

Wirz, Richard E.; Goebel, Dan

2006-01-01

DC-ION is a detailed computational model for predicting the plasma characteristics of rain-cusp ion thrusters. The advanced magnetic field meshing algorithm used by DC-ION allows precise treatment of the secondary electron flow. This capability allows self-consistent estimates of plasma potential that improves the overall consistency of the results of the discharge model described in Reference [refJPC05mod1]. Plasma potential estimates allow the model to predict the onset of plasma instabilities, and important shortcoming of the previous model for optimizing the design of discharge chambers. A magnetic field mesh simplifies the plasma flow calculations, for both the ions and the secondary electrons, and significantly reduces numerical diffusion that can occur with meshes not aligned with the magnetic field. Comparing the results of this model to experimental data shows that the behavior of the primary electrons, and the precise manner of their confinement, dictates the fundamental efficiency of ring-cusp. This correlation is evident in simulations of the conventionally sized NSTAR thruster (30 cm diameter) and the miniature MiXI thruster (3 cm diameter).

Non-thermal plasma instabilities induced by deformation of the electron energy distribution function

NASA Astrophysics Data System (ADS)

Dyatko, N. A.; Kochetov, I. V.; Napartovich, A. P.

2014-08-01

Non-thermal plasma is a key component in gas lasers, microelectronics, medical applications, waste gas cleaners, ozone generators, plasma igniters, flame holders, flow control in high-speed aerodynamics and others. A specific feature of non-thermal plasma is its high sensitivity to variations in governing parameters (gas composition, pressure, pulse duration, E/N parameter). This sensitivity is due to complex deformations of the electron energy distribution function (EEDF) shape induced by variations in electric field strength, electron and ion number densities and gas excitation degree. Particular attention in this article is paid to mechanisms of instabilities based on non-linearity of plasma properties for specific conditions: gas composition, steady-state and decaying plasma produced by the electron beam, or by an electric current pulse. The following effects are analyzed: the negative differential electron conductivity; the absolute negative electron mobility; the stepwise changes of plasma properties induced by the EEDF bi-stability; thermo-current instability and the constriction of the glow discharge column in rare gases. Some of these effects were observed experimentally and some of them were theoretically predicted and still wait for experimental confirmation.

Decontamination of chemical and biological warfare (CBW) agents using an atmospheric pressure plasma jet (APPJ)

NASA Astrophysics Data System (ADS)

Herrmann, H. W.; Henins, I.; Park, J.; Selwyn, G. S.

1999-05-01

The atmospheric pressure plasma jet (APPJ) [A. Schütze et al., IEEE Trans. Plasma Sci. 26, 1685 (1998)] is a nonthermal, high pressure, uniform glow plasma discharge that produces a high velocity effluent stream of highly reactive chemical species. The discharge operates on a feedstock gas (e.g., He/O2/H2O), which flows between an outer, grounded, cylindrical electrode and an inner, coaxial electrode powered at 13.56 MHz rf. While passing through the plasma, the feedgas becomes excited, dissociated or ionized by electron impact. Once the gas exits the discharge volume, ions and electrons are rapidly lost by recombination, but the fast-flowing effluent still contains neutral metastable species (e.g., O2*, He*) and radicals (e.g., O, OH). This reactive effluent has been shown to be an effective neutralizer of surrogates for anthrax spores and mustard blister agent. Unlike conventional wet decontamination methods, the plasma effluent does not cause corrosion and it does not destroy wiring, electronics, or most plastics, making it highly suitable for decontamination of sensitive equipment and interior spaces. Furthermore, the reactive species in the effluent rapidly degrade into harmless products leaving no lingering residue or harmful by-products.

An Experimental Study of Continuous Plasma Flows Driven by a Confined Arc in a Transverse Magnetic Field

NASA Technical Reports Server (NTRS)

Barger, R. L.; Brooks, J. D.; Beasley, W. D.

1961-01-01

A crossed-field, continuous-flow plasma accelerator has been built and operated. The highest measured velocity of the flow, which was driven by the interaction of the electric and magnetic fields, was about 500 meters per second. Some of the problems discussed are ion slip, stability and uniformity of the discharge, effect of the magnetic field on electron emission, use of preionization, and electrode contamination.

Rydberg gas theory of a glow discharge plasma: I. Application to the electrical behaviour of a fast flowing glow discharge plasma.

PubMed

Mason, Rod S; Mitchell, David J; Dickinson, Paul M

2010-04-21

Current-voltage (I-V) curves have been measured, independent of the main discharge, for electricity passing through the steady state fast flowing 'afterglow' plasma of a low power dc glow discharge in Ar. Voltage profiles along the axial line of conduction have been mapped using fixed probes and potentiometry, and the mass spectra of cations emerging from the downstream sampling Cone, also acting as a probe anode, were recorded simultaneously. Floating double probe experiments were also carried out. The electrical behavior is consistent with the well established I-V characteristics of such discharges, but does not comply with classical plasma theory predictions. The plasma decays along the line of conduction, with a lifetime of approximately 1 ms, despite carrying a steady state current, and its potential is below that of the large surface area anode voltage; a situation which cannot exist in the presence of a conventional free ion-electron plasma, unless the electron temperature is super cold. Currents, large by comparison with the main discharge current, and independent of it, are induced to flow through the downstream plasma, from the Anode (acting as a cathode) to the anodic ion exit Cone, induced by electron impact ionisation at the anode, but without necessarily increasing the plasma density. It appears to be conducted by direct charge transfer between a part of the anode surface (acting as cathode to the auxiliary circuit) and the plasma, without secondary electron emission or heating, which suggests the direct involvement of Rydberg atom intermediates. The reaction energy defect (= the work function of the electrode surface) fits with the plasma potential threshold observed for the cathodic reaction to occur. A true free ion-electron plasma is readily detected by the observation of cations at the anode surface, when induced at the downstream anode, at high bias voltages, by the electron impact ionisation in the boundary region. In contrast to the classical model, the complex electrical (and mass spectrometric) behaviour fits qualitatively, but can be understood well, with the Rydberg gas model described in papers II and III (R. S. Mason, and R. S. Mason and P. Douglas, PCCP, 2010, DOI: 10.1039/b918081h and b918083d) over a wide range of probe bias voltages. The full cycle of behavior is then described for the development of a true secondary discharge within the downstream plasma.

Rarefaction waves, solitons, and holes in a pure electron plasma

NASA Astrophysics Data System (ADS)

Moody, J. D.; Driscoll, C. F.

1995-12-01

The propagation of holes, solitons, and rarefaction waves along the axis of a magnetized pure electron plasma column is described. The time dependence of the radially averaged density perturbation produced by the nonlinear waves is measured at several locations along the plasma column for a wide range of plasma parameters. The rarefaction waves are studied by measuring the free expansion of the plasma into a vacuum. A new hydrodynamic theory is described that quantitatively predicts the free expansion measurements. The rarefaction is initially characterized by a self-similar plasma flow, resulting in a perturbed density and velocity without a characteristic length scale. The electron solitons show a small increase in propagation speed with increasing amplitude and exhibit electron bursts. The holes show a decrease in propagation speed with increasing amplitude. Collisions between holes and solitons show that these objects pass through each other undisturbed, except for a small offset.

Non-thermal particle acceleration in collisionless relativistic electron-proton reconnection

NASA Astrophysics Data System (ADS)

Werner, G. R.; Uzdensky, D. A.; Begelman, M. C.; Cerutti, B.; Nalewajko, K.

2018-02-01

Magnetic reconnection in relativistic collisionless plasmas can accelerate particles and power high-energy emission in various astrophysical systems. Whereas most previous studies focused on relativistic reconnection in pair plasmas, less attention has been paid to electron-ion plasma reconnection, expected in black hole accretion flows and relativistic jets. We report a comprehensive particle-in-cell numerical investigation of reconnection in an electron-ion plasma, spanning a wide range of ambient ion magnetizations σi, from the semirelativistic regime (ultrarelativistic electrons but non-relativistic ions, 10-3 ≪ σi ≪ 1) to the fully relativistic regime (both species are ultrarelativistic, σi ≫ 1). We investigate how the reconnection rate, electron and ion plasma flows, electric and magnetic field structures, electron/ion energy partitioning, and non-thermal particle acceleration depend on σi. Our key findings are: (1) the reconnection rate is about 0.1 of the Alfvénic rate across all regimes; (2) electrons can form concentrated moderately relativistic outflows even in the semirelativistic, small-σi regime; (3) while the released magnetic energy is partitioned equally between electrons and ions in the ultrarelativistic limit, the electron energy fraction declines gradually with decreased σi and asymptotes to about 0.25 in the semirelativistic regime; and (4) reconnection leads to efficient non-thermal electron acceleration with a σi-dependent power-law index, p(σ _i)˜eq const+0.7σ _i^{-1/2}. These findings are important for understanding black hole systems and lend support to semirelativistic reconnection models for powering non-thermal emission in blazar jets, offering a natural explanation for the spectral indices observed in these systems.

Physics-based investigation of negative ion behavior in a negative-ion-rich plasma using integrated diagnostics

NASA Astrophysics Data System (ADS)

Tsumori, K.; Takeiri, Y.; Ikeda, K.; Nakano, H.; Geng, S.; Kisaki, M.; Nagaoka, K.; Tokuzawa, T.; Wada, M.; Sasaki, K.; Nishiyama, S.; Goto, M.; Osakabe, M.

2017-08-01

Total power of 16 MW has been successfully delivered to the plasma confined in the Large Helical Device (LHD) from three Neutral Beam Injectors (NBIs) equipped with negative hydrogen (H-) ion sources. However, the detailed mechanisms from production through extraction of H- ions are still yet to be clarified and a similar size ion source on an independent acceleration test bench called Research and development Negative Ion Source (RNIS) serves as the facility to study physics related to H- production and transport for further improvement of NBI. The production of negative-ion-rich plasma and the H- ions behavior in the beam extraction region in RNIS is being investigated by employing an integrated diagnostic system. Flow patterns of electrons, positive ions and H- ions in the extraction region are described in a two-dimensional map. The measured flow patterns indicate the existence a stagnation region, where the H- flow changes the direction at a distance about 20 mm from the plasma grid. The pattern also suggested the H- flow originated from plasma grid (PG) surface that turned back toward extraction apertures. The turning region seems formed by a layer of combined magnetic field produced by the magnetic filter field and the Electron-Deflection Magnetic (EDM) field created by magnets installed in the extraction electrode.

An experimental investigation of hollow cathode-based plasma contactors. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Williams, John D.

1991-01-01

Experimental results are presented which describe operation of the plasma environment associated with a hollow cathod-based plasma contactor collecting electrons from or emitting them to an ambient, low density Maxwellian plasma. A one-dimensional, phenomenological model of the near-field electron collection process, which was formulated from experimental observations, is presented. It considers three regions, namely, a plasma cloud adjacent to the contactor, an ambient plasma from which electrons are collected, and a double layer region that develops between the contactor plasma cloud and the ambient plasma regions. Results of the electron emission experiments are also presented. An important observation is made using a retarding potential analyzer (RPA) which shows that high energy ions generally stream from a contactor along with the electrons being emitted. A mechanism for this phenomenon is presented and it involves a high rate of ionization induced between electrons and atoms flowing together from the hollow cathode orifice. This can result in the development of a region of high positive potential. Langmuir and RPA probe data suggest that both electrons and ions expand spherically from this hill region. In addition to experimental observations, a one-dimensional model which describes the electron emission process and predicts the phenomena just mentioned is presented and shown to agree qualitatively with these observations.

Drift wave stabilized by an additional streaming ion or plasma population

NASA Astrophysics Data System (ADS)

Bashir, M. F.; Vranjes, J.

2015-03-01

It is shown that the universally unstable kinetic drift wave in an electron-ion plasma can very effectively be suppressed by adding an extra flowing ion (or plasma) population. The effect of the flow of the added ions is essential, their response is of the type (vp h-vf 0) exp[-(vph-vf 0) 2] , where vf 0 is the flow speed and vp h is the phase speed parallel to the magnetic field vector. The damping is strong and it is mainly due to this ion exponential term, and this remains so for vf 0

Drift wave stabilized by an additional streaming ion or plasma population.

PubMed

Bashir, M F; Vranjes, J

2015-03-01

It is shown that the universally unstable kinetic drift wave in an electron-ion plasma can very effectively be suppressed by adding an extra flowing ion (or plasma) population. The effect of the flow of the added ions is essential, their response is of the type (vph-vf0)exp[-(vph-vf0)2], where vf0 is the flow speed and vph is the phase speed parallel to the magnetic field vector. The damping is strong and it is mainly due to this ion exponential term, and this remains so for vf0

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.

Device and method for relativistic electron beam heating of a high-density plasma to drive fast liners

DOEpatents

Thode, Lester E.

1981-01-01

A device and method for relativistic electron beam heating of a high-density plasma in a small localized region. A relativistic electron beam generator or accelerator produces a high-voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low-density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high-density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target gas is ionized prior to application of the electron beam by means of a laser or other preionization source to form a plasma. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high-density target plasma causing the relativistic electron beam to efficiently deposit its energy and momentum into a small localized region of the high-density plasma target. Fast liners disposed in the high-density target plasma are explosively or ablatively driven to implosion by a heated annular plasma surrounding the fast liner which is generated by an annular relativistic electron beam. An azimuthal magnetic field produced by axial current flow in the annular plasma, causes the energy in the heated annular plasma to converge on the fast liner.

Relativistic Laser Absorption and Magnetic Field Channel Formation in 3D PIC Simulation

NASA Astrophysics Data System (ADS)

Sentoku, Yasuhiko; Mima, Kunioki; Sheng, Zheng-Ming; Kaw, Predhiman; Nishihara, Katsunobu; Nishikawa, Kyoji

2000-10-01

We carried out 3D PIC simulations on overdense plasmas. On the surface of the plasmas, relativistic electrons are generated and transported into overdense plasmas. In the transport, it is found that energy is transferred to dense plasmas by convective cells. Namely, hot electron and cold electron return flows form convective cells through the magnetic instabilities (e.g. Weibel Instability). The heat flux associating with the convective cells and the anomalous stoppings in 3D simulations are compared with these in 2D simulations by Meyer-ter-Vehn etal. and Taguchi etal. [1] M. Honda, J. Meyer-ter-Vehn, and A. Pukhov, Phys. Plasmas 7, 1302, (2000). [2] ``Relativistic Electron Transport Simulation by 2D hybrid Simulation with Darwin Approximation." by T. Taguchi etal. (to be present in the poster of this conference)

Pulsed electromagnetic gas acceleration. [magnetohydrodynamics, plasma power sources and plasma propulsion

NASA Technical Reports Server (NTRS)

Jahn, R. G.; Vonjaskowsky, W. F.; Clark, K. E.

1975-01-01

Terminal voltage measurements with various cathodes and anodes in a high power, quasi-steady magnetoplasmadynamic (MPD) are discussed. The magnitude of the current at the onset of voltage fluctuations is shown to be an increasing function of cathode area and a weaker decreasing function of anode area. Tests with a fluted cathode indicated that the fluctuations originate in the plasma adjacent to the cathode rather than at the cathode surface. Measurements of radiative output from an optical cavity aligned to examine the current-carrying portion of a two-dimensional, 56 kA magnetoplasmadynamic discharge reveal no lasing in that region, consistent with calculations of electron excitation and resonance radiation trapping. A voltage-swept double probe technique allows single-shot determination of electron temperature and electron number density in the recombining MPD exhaust flow. Current distributions within the cavity of MPD hollow cathodes for various static prefills with no injected mass flow are examined.

Retarding field energy analyzer for the Saskatchewan Torus-Modified plasma boundary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dreval, M.; Rohraff, D.; Xiao, C.

2009-10-15

The retarding field energy analyzer (RFA) is a simple and reliable diagnostic technique to measure the ion temperature in the scrape-off layer and edge of magnetic fusion devices. Design and operation features of a single-sided (facing the ion flow) RFA for ion temperature measurements in the Saskatchewan Torus-Modified (STOR-M) tokamak are described. Its compact size (21x15x20 mm{sup 3}) allows RFA measurements without perturbing plasma significantly. Both ion and electron temperature have been measured by RFA in the STOR-M tokamak. A method is proposed to correct the effects of ion flow on the ion temperature using the simultaneously measured Mach number.more » The measured electron temperature is consistent with the previously reported Langmuir probe data. Abnormal behavior of the RFA has been observed in both ion and electron modes when RFA is inserted deep into the plasma.« less

Three-dimensional simulation of microwave-induced helium plasma under atmospheric pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, G. L.; Hua, W., E-mail: huaw@scu.edu.cn; Guo, S. Y.

2016-07-15

A three-dimensional model is presented to investigate helium plasma generated by microwave under atmospheric pressure in this paper, which includes the physical processes of electromagnetic wave propagation, electron and heavy species transport, gas flow, and heat transfer. The model is based on the fluid approximation calculation and local thermodynamic equilibrium assumption. The simulation results demonstrate that the maxima of the electron density and gas temperature are 4.79 × 10{sup 17 }m{sup −3} and 1667 K, respectively, for the operating conditions with microwave power of 500 W, gas flow rate of 20 l/min, and initial gas temperature of 500 K. The electromagnetic field distribution in the plasma sourcemore » is obtained by solving Helmholtz equation. Electric field strength of 2.97 × 10{sup 4 }V/m is obtained. There is a broad variation on microwave power, gas flow rate, and initial gas temperature to obtain deeper information about the changes of the electron density and gas temperature.« less

Self-generated zonal flows in the plasma turbulence driven by trapped-ion and trapped-electron instabilities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drouot, T.; Gravier, E.; Reveille, T.

This paper presents a study of zonal flows generated by trapped-electron mode and trapped-ion mode micro turbulence as a function of two plasma parameters—banana width and electron temperature. For this purpose, a gyrokinetic code considering only trapped particles is used. First, an analytical equation giving the predicted level of zonal flows is derived from the quasi-neutrality equation of our model, as a function of the density fluctuation levels and the banana widths. Then, the influence of the banana width on the number of zonal flows occurring in the system is studied using the gyrokinetic code. Finally, the impact of themore » temperature ratio T{sub e}/T{sub i} on the reduction of zonal flows is shown and a close link is highlighted between reduction and different gyro-and-bounce-average ion and electron density fluctuation levels. This reduction is found to be due to the amplitudes of gyro-and-bounce-average density perturbations n{sub e} and n{sub i} gradually becoming closer, which is in agreement with the analytical results given by the quasi-neutrality equation.« less

Flow-field differences and electromagnetic-field properties of air and N2 inductively coupled plasmas

NASA Astrophysics Data System (ADS)

Yu, Minghao; Yamada, Kazuhiko; Takahashi, Yusuke; Liu, Kai; Zhao, Tong

2016-12-01

A numerical model for simulating air and nitrogen inductively coupled plasmas (ICPs) was developed considering thermochemical nonequilibrium and the third-order electron transport properties. A modified far-field electromagnetic model was introduced and tightly coupled with the flow field equations to describe the Joule heating and inductive discharge phenomena. In total, 11 species and 49 chemical reactions of air, which include 5 species and 8 chemical reactions of nitrogen, were employed to model the chemical reaction process. The internal energy transfers among translational, vibrational, rotational, and electronic energy modes of chemical species were taken into account to study thermal nonequilibrium effects. The low-Reynolds number Abe-Kondoh-Nagano k-ɛ turbulence model was employed to consider the turbulent heat transfer. In this study, the fundamental characteristics of an ICP flow, such as the weak ionization, high temperature but low velocity in the torch, and wide area of the plasma plume, were reproduced by the developed numerical model. The flow field differences between the air and nitrogen ICP flows inside the 10-kW ICP wind tunnel were made clear. The interactions between the electromagnetic and flow fields were also revealed for an inductive discharge.

Parameters of the plasma of a dc pulsating discharge in a supersonic air flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shibkov, V. M., E-mail: shibkov@phys.msu.ru; Shibkova, L. V.; Logunov, A. A.

A dc discharge in a cold (T = 200 K) supersonic air flow at a static pressure of 200–400 Torr was studied experimentally. The excited unsteady pulsating discharge has the form of a thin plasma channel with a diameter of ≤1 mm, stretched downstream the flow. Depending on the discharge current, the pulsation frequency varies from 800 to 1600 Hz and the electron temperature varies from 8000 to 15000 K.

Flute Instability of Expanding Plasma Cloud

NASA Astrophysics Data System (ADS)

Dudnikova, Galina; Vshivkov, Vitali

2000-10-01

The expansion of plasma against a magnetized background where collisions play no role is a situation common to many plasma phenomena. The character of interaction between expanding plasma and background plasma is depending of the ratio of the expansion velocity to the ambient Alfven velocity. If the expansion speed is greater than the background Alfven speed (super-Alfvenic flows) a collisionless shock waves are formed in background plasma. It is originally think that if the expansion speed is less than Alfvenic speed (sub-Alfvenic flows) the interaction of plasma flows will be laminar in nature. However, the results of laboratory experiments and chemical releases in magnetosphere have shown the development of flute instability on the boundary of expanding plasma (Rayleigh-Taylor instability). A lot of theoretical and experimental papers have been devoted to study the Large Larmor Flute Instability (LLFI) of plasma expanding into a vacuum magnetic field. In the present paper on the base of computer simulation of plasma cloud expansion in magnetizied background plasma the regimes of development and stabilization LLFI for super- and sub-Alfvenic plasma flows are investigated. 2D hybrid numerical model is based on kinetic Vlasov equation for ions and hydrodynamic approximation for electrons. The similarity parameters characterizing the regimes of laminar flows are founded. The stabilization of LLFI takes place with the transition from sub- to super-Alfvenic plasma cloud expansion. The results of the comparision between computer simulation and laboratory simulation are described.

A theoretical and experimental investigation of cylindrical electrostatic probes at arbitrary incidence in flowing plasma

NASA Technical Reports Server (NTRS)

Jenkins, R. V.; Jones, W. L., Jr.

1974-01-01

The theory for calculating the current collected by a negatively biased cylindrical electrostatic probe at an arbitrary angle of attack in a weakley ionized flowing plasma is presented. The theory was constructed by considering both random and directed motion simultaneous with dynamic coupling of the flow properties and of the electric field of the probe. This direct approach yielded a theory that is more general than static plasma theories modified to account for flow. Theoretical calculations are compared with experimental electrostatic probe data obtained in the free stream of an arc-heated hypersonic wind tunnel. The theoretical calculations are based on flow conditions and plasma electron densities measured by an independent microwave interferometer technique. In addition, the theory is compared with laboratory and satellite data previously published by other investigators. In each case the comparison gives good agreement.

Kinetic model for the collisionless sheath of a collisional plasma

DOE PAGES

Tang, Xian-Zhu; Guo, Zehua

2016-08-04

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

Numerical simulations of the Cosmic Battery in accretion flows around astrophysical black holes

NASA Astrophysics Data System (ADS)

Contopoulos, I.; Nathanail, A.; Sądowski, A.; Kazanas, D.; Narayan, R.

2018-01-01

We implement the KORAL code to perform two sets of very long general relativistic radiation magnetohydrodynamic simulations of an axisymmetric optically thin magnetized flow around a non-rotating black hole: one with a new term in the electromagnetic field tensor due to the radiation pressure felt by the plasma electrons on the comoving frame of the electron-proton plasma, and one without. The source of the radiation is the accretion flow itself. Without the new term, the system evolves to a standard accretion flow due to the development of the magneto-rotational instability. With the new term, however, the system eventually evolves to a magnetically arrested disc state in which a large-scale jet-like magnetic field threads the black hole horizon. Our results confirm the secular action of the Cosmic Battery in accretion flows around astrophysical black holes.

Theory of Fine-scale Zonal Flow Generation From Trapped Electron Mode Turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu Wang and T.S. Hahm

Most existing zonal flow generation theory has been developed with a usual assumption of qrρθ¡ << 1 (qr is the radial wave number of zonal flow, and ρθ¡ is the ion poloidal gyrora- dius). However, recent nonlinear gyrokinetic simulations of trapped electron mode (TEM) turbulence exhibit a relatively short radial scale of the zonal flows with qrρθ¡ ~ 1 [Z. Lin et al., IAEA-CN/TH/P2-8 (2006); D. Ernst et al., Phys. Plasmas 16, 055906 (2009)]. This work reports an extension of zonal flow growth calculation to this short wavelength regime via the wave kinetics approach. A generalized expression for the polarizationmore » shielding for arbitrary radial wavelength [Lu Wang and T.S. Hahm, to appear in Phys. Plasmas (2009)] which extends the Rosenbluth-Hinton formula in the long wavelength limit is applied.« less

Ground Simulations of Near-Surface Plasma Field and Charging at the Lunar Terminator

NASA Astrophysics Data System (ADS)

Polansky, J.; Ding, N.; Wang, J.; Craven, P.; Schneider, T.; Vaughn, J.

2012-12-01

Charging in the lunar terminator region is the most complex and is still not well understood. In this region, the surface potential is sensitively influenced by both solar illumination and plasma flow. The combined effects from localized shadow generated by low sun elevation angles and localized wake generated by plasma flow over the rugged terrain can generate strongly differentially charged surfaces. Few models currently exist that can accurately resolve the combined effects of plasma flow and solar illumination over realistic lunar terminator topographies. This paper presents an experimental investigation of lunar surface charging at the terminator region in simulated plasma environments in a vacuum chamber. The solar wind plasma flow is simulated using an electron bombardment gridded Argon ion source. An electrostatic Langmuir probe, nude Faraday probes, a floating emissive probe, and retarding potential analyzer are used to quantify the plasma flow field. Surface potentials of both conducting and dielectric materials immersed in the plasma flow are measured with a Trek surface potential probe. The conducting material surface potential will simultaneously be measured with a high impedance voltmeter to calibrate the Trek probe. Measurement results will be presented for flat surfaces and objects-on-surface for various angles of attack of the plasma flow. The implications on the generation of localized plasma wake and surface charging at the lunar terminator will be discussed. (This research is supported by the NASA Lunar Advanced Science and Exploration Research program.)

Insights into neutrino decoupling gleaned from considerations of the role of electron mass

NASA Astrophysics Data System (ADS)

Grohs, E.; Fuller, George M.

2017-10-01

We present calculations showing how electron rest mass influences entropy flow, neutrino decoupling, and Big Bang Nucleosynthesis (BBN) in the early universe. To elucidate this physics and especially the sensitivity of BBN and related epochs to electron mass, we consider a parameter space of rest mass values larger and smaller than the accepted vacuum value. Electromagnetic equilibrium, coupled with the high entropy of the early universe, guarantees that significant numbers of electron-positron pairs are present, and dominate over the number of ionization electrons to temperatures much lower than the vacuum electron rest mass. Scattering between the electrons-positrons and the neutrinos largely controls the flow of entropy from the plasma into the neutrino seas. Moreover, the number density of electron-positron-pair targets can be exponentially sensitive to the effective in-medium electron mass. This entropy flow influences the phasing of scale factor and temperature, the charged current weak-interaction-determined neutron-to-proton ratio, and the spectral distortions in the relic neutrino energy spectra. Our calculations show the sensitivity of the physics of this epoch to three separate effects: finite electron mass, finite-temperature quantum electrodynamic (QED) effects on the plasma equation of state, and Boltzmann neutrino energy transport. The ratio of neutrino to plasma-component energy scales manifests in Cosmic Microwave Background (CMB) observables, namely the baryon density and the radiation energy density, along with the primordial helium and deuterium abundances. Our results demonstrate how the treatment of in-medium electron mass (i.e., QED effects) could translate into an important source of uncertainty in extracting neutrino and beyond-standard-model physics limits from future high-precision CMB data.

Temperature gradients due to adiabatic plasma expansion in a magnetic nozzle

NASA Astrophysics Data System (ADS)

Sheehan, J. P.; Longmier, B. W.; Bering, E. A.; Olsen, C. S.; Squire, J. P.; Ballenger, M. G.; Carter, M. D.; Cassady, L. D.; Díaz, F. R. Chang; Glover, T. W.; Ilin, A. V.

2014-08-01

A mechanism for ambipolar ion acceleration in a magnetic nozzle is proposed. The plasma is adiabatic (i.e., does not exchange energy with its surroundings) in the diverging section of a magnetic nozzle so any energy lost by the electrons must be transferred to the ions via the electric field. Fluid theory indicates that the change in plasma potential is proportional to the change in average electron energy. These predictions were compared to measurements in the VX-200 experiment which has conditions conducive to ambipolar ion acceleration. A planar Langmuir probe was used to measure the plasma potential, electron density, and electron temperature for a range of mass flow rates and power levels. Axial profiles of those parameters were also measured, showing consistency with the adiabatic ambipolar fluid theory.

THE TOPOLOGY OF CANONICAL FLUX TUBES IN FLARED JET GEOMETRY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lavine, Eric Sander; You, Setthivoine, E-mail: Slavine2@uw.edu, E-mail: syou@aa.washington.edu

2017-01-20

Magnetized plasma jets are generally modeled as magnetic flux tubes filled with flowing plasma governed by magnetohydrodynamics (MHD). We outline here a more fundamental approach based on flux tubes of canonical vorticity, where canonical vorticity is defined as the circulation of the species’ canonical momentum. This approach extends the concept of magnetic flux tube evolution to include the effects of finite particle momentum and enables visualization of the topology of plasma jets in regimes beyond MHD. A flared, current-carrying magnetic flux tube in an ion-electron plasma with finite ion momentum is thus equivalent to either a pair of electron andmore » ion flow flux tubes, a pair of electron and ion canonical momentum flux tubes, or a pair of electron and ion canonical vorticity flux tubes. We examine the morphology of all these flux tubes for increasing electrical currents, different radial current profiles, different electron Mach numbers, and a fixed, flared, axisymmetric magnetic geometry. Calculations of gauge-invariant relative canonical helicities track the evolution of magnetic, cross, and kinetic helicities in the system, and show that ion flow fields can unwind to compensate for an increasing magnetic twist. The results demonstrate that including a species’ finite momentum can result in a very long collimated canonical vorticity flux tube even if the magnetic flux tube is flared. With finite momentum, particle density gradients must be normal to canonical vorticities, not to magnetic fields, so observations of collimated astrophysical jets could be images of canonical vorticity flux tubes instead of magnetic flux tubes.« less

The effect of dust charge variation, due to ion flow and electron depletion, on dust levitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Land, Victor; Douglass, Angela; Qiao Ke

2011-11-29

Using a fluid model, the plasma densities, electron temperature and ion Mach number in front of a powered electrode in different plasma discharges is computed. The dust charge is computed using OML theory for Maxwellian electrons and ions distributed according to a shifted-Maxwellian. By assuming force balance between gravity and the electrostatic force, the dust levitation height is obtained. The importance of the dust charge variation is investigated.

Trapped electron mode turbulence driven intrinsic rotation in Tokamak plasmas.

PubMed

Wang, W X; Hahm, T S; Ethier, S; Zakharov, L E; Diamond, P H

2011-02-25

Progress from global gyrokinetic simulations in understanding the origin of intrinsic rotation in toroidal plasmas is reported. The turbulence-driven intrinsic torque associated with nonlinear residual stress generation due to zonal flow shear induced asymmetry in the parallel wave number spectrum is shown to scale close to linearly with plasma gradients and the inverse of the plasma current, qualitatively reproducing experimental empirical scalings of intrinsic rotation. The origin of current scaling is found to be enhanced k(∥) symmetry breaking induced by the increased radial variation of the safety factor as the current decreases. The intrinsic torque is proportional to the pressure gradient because both turbulence intensity and zonal flow shear, which are two key ingredients for driving residual stress, increase with turbulence drive, which is R/L(T(e)) and R/L(n(e)) for the trapped electron mode. © 2011 American Physical Society

Direct thrust measurements and modelling of a radio-frequency expanding plasma thruster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lafleur, T.; Charles, C.; Boswell, R. W.

2011-08-15

It is shown analytically that the thrust from a simple plasma thruster (in the absence of a magnetic field) is given by the maximum upstream electron pressure, even if the plasma diverges downstream. Direct thrust measurements of a thruster are then performed using a pendulum thrust balance and a laser displacement sensor. A maximum thrust of about 2 mN is obtained at 700 W for a thruster length of 17.5 cm and a flow rate of 0.9 mg s{sup -1}, while a larger thrust of 4 mN is obtained at a similar power for a length of 9.5 cm andmore » a flow rate of 1.65 mg s{sup -1}. The measured thrusts are in good agreement with the maximum upstream electron pressure found from measurements of the plasma parameters and in fair agreement with a simple global approach used to model the thruster.« less

Theory of ion Bernstein wave induced shear suppression of turbulence

NASA Astrophysics Data System (ADS)

Craddock, G. G.; Diamond, P. H.; Ono, M.; Biglari, H.

1994-06-01

The theory of radio frequency induced ion Bernstein wave- (IBW) driven shear flow in the edge is examined, with the goal of application of shear suppression of fluctuations. This work is motivated by the observed confinement improvement on IBW heated tokamaks [Phys. Fluids B 5, 241 (1993)], and by previous low-frequency work on RF-driven shear flows [Phys. Rev. Lett. 67, 1535 (1991)]. It is found that the poloidal shear flow is driven electrostatically by both Reynolds stress and a direct ion momentum source, analogous to the concepts of helicity injection and electron momentum input in current drive, respectively. Flow drive by the former does not necessarily require momentum input to the plasma to induce a shear flow. For IBW, the direct ion momentum can be represented by direct electron momentum input, and a charge separation induced stress that imparts little momentum to the plasma. The derived Er profile due to IBW predominantly points inward, with little possibility of direction change, unlike low-frequency Alfvénic RF drive. The profile scale is set by the edge density gradient and electron dissipation. Due to the electrostatic nature of ion Bernstein waves, the poloidal flow contribution dominates in Er. Finally, the necessary edge power absorbed for shear suppression on Princeton Beta Experiment-Modified (PBX-M) [9th Topical Conference on Radio Frequency Power in Plasmas, Charleston, SC, 1991 (American Institute of Physics, New York, 1991), p. 129] is estimated to be 100 kW distributed over 5 cm.

Using the Multipole Resonance Probe to Stabilize the Electron Density During a Reactive Sputter Process

NASA Astrophysics Data System (ADS)

Oberberg, Moritz; Styrnoll, Tim; Ries, Stefan; Bienholz, Stefan; Awakowicz, Peter

2015-09-01

Reactive sputter processes are used for the deposition of hard, wear-resistant and non-corrosive ceramic layers such as aluminum oxide (Al2O3) . A well known problem is target poisoning at high reactive gas flows, which results from the reaction of the reactive gas with the metal target. Consequently, the sputter rate decreases and secondary electron emission increases. Both parameters show a non-linear hysteresis behavior as a function of the reactive gas flow and this leads to process instabilities. This work presents a new control method of Al2O3 deposition in a multiple frequency CCP (MFCCP) based on plasma parameters. Until today, process controls use parameters such as spectral line intensities of sputtered metal as an indicator for the sputter rate. A coupling between plasma and substrate is not considered. The control system in this work uses a new plasma diagnostic method: The multipole resonance probe (MRP) measures plasma parameters such as electron density by analyzing a typical resonance frequency of the system response. This concept combines target processes and plasma effects and directly controls the sputter source instead of the resulting target parameters.

Energy behaviour of extraordinary waves in magnetized quantum plasmas

NASA Astrophysics Data System (ADS)

Moradi, Afshin

2018-05-01

We study the storage and flow of energy in a homogeneous magnetized quantum electron plasma that occurs when an elliptically polarized extraordinary electromagnetic wave propagates in the system. Expressions for the stored energy, energy flow, and energy velocity of extraordinary electromagnetic waves are derived by means of the quantum magnetohydrodynamics theory in conjunction with the Maxwell equations. Numerical results show that the energy flow of the high-frequency mode of extraordinary wave is modified only due to the Bohm potential in the short wavelength limit.

An unstructured shock-fitting solver for hypersonic plasma flows in chemical non-equilibrium

NASA Astrophysics Data System (ADS)

Pepe, R.; Bonfiglioli, A.; D'Angola, A.; Colonna, G.; Paciorri, R.

2015-11-01

A CFD solver, using Residual Distribution Schemes on unstructured grids, has been extended to deal with inviscid chemical non-equilibrium flows. The conservative equations have been coupled with a kinetic model for argon plasma which includes the argon metastable state as independent species, taking into account electron-atom and atom-atom processes. Results in the case of an hypersonic flow around an infinite cylinder, obtained by using both shock-capturing and shock-fitting approaches, show higher accuracy of the shock-fitting approach.

Device and method for imploding a microsphere with a fast liner

DOEpatents

Thode, Lester E.

1981-01-01

A device and method for relativistic electron beam heating of a high-density plasma in a small localized region. A relativistic electron beam generator or accelerator produces a high-voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low-density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high-density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target gas is ionized prior to application of the electron beam by means of a laser or other preionization source to form a plasma. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high-density target plasma causing the relativistic electron beam to efficiently deposit its energy and momentum into a small localized region of the high-density plasma target. Fast liners disposed in the high-density target plasma are explosively or ablatively driven to implosion by a heated annular plasma surrounding the fast liner generated by an annular relativistic electron beam. An azimuthal magnetic field produced by axial current flow in the annular plasma, causes the energy in the heated annular plasma to converge on the fast liner to drive the fast liner to implode a microsphere.

Microwave processes in the SPD-ATON stationary plasma thruster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirdyashev, K. P., E-mail: kpk@ms.ire.rssi.ru

2016-09-15

Results of experimental studies of microwave processes accompanying plasma acceleration in the SPD-ATON stationary plasma thruster are presented. Specific features of the generation of microwave oscillations in both the acceleration channel and the plasma flow outgoing from the thruster are analyzed on the basis of local measurements of the spectra of the plasma wave fields. Mechanisms for generation of microwave oscillations are considered with allowance for the inhomogeneity of the electron density and magnetic field behind the edge of the acceleration channel. The effect of microwave oscillations on the electron transport and the formation of the discharge current in themore » acceleration channel is discussed.« less

Momentum and Heat Flux Measurements in the Exhaust of VASIMR Using Helium Propellant

NASA Technical Reports Server (NTRS)

Chavers, D. Gregory

2002-01-01

Electromagnetic thrusters typically use electric and magnetic fields to accelerate and exhaust plasma through interactions with the charged particles in the plasma. The energy required to create the plasma, i.e. ionization energy, is potential energy between the electron and ion. This potential energy is typically lost since it is not recovered as the plasma is exhausted and is known as frozen flow loss. If the frozen flow energy is a small fraction of the total plasma energy, this frozen flow loss may be negligible. However, if the frozen flow energy is a major fraction of the total plasma energy, this loss can severely reduce the energy efficiency of the thruster. Recovery and utilization of this frozen flow energy can improve the energy efficiency of a thruster during low specific impulse operating regimes when the ionization energy is a large fraction of the total plasma energy. This paper quantifies the recovery of the frozen flow energy, i.e. recombination energy, via the process of surface recombination for helium. To accomplish this task the momentum flux and heat flux of the plasma flow were measured and compared to calculated values from electrostatic probe data. This information was used to deduce the contribution of recombination energy to the total heat flux on a flat plate as well as to characterize the plasma conditions. Helium propellant was investigated initially due to its high ionization potential and hence available recombination energy.

Modification of anisotropic plasma diffusion via auxiliary electrons emitted by a carbon nanotubes-based electron gun in an electron cyclotron resonance ion source.

PubMed

Malferrari, L; Odorici, F; Veronese, G P; Rizzoli, R; Mascali, D; Celona, L; Gammino, S; Castro, G; Miracoli, R; Serafino, T

2012-02-01

The diffusion mechanism in magnetized plasmas is a largely debated issue. A short circuit model was proposed by Simon, assuming fluxes of lost particles along the axial (electrons) and radial (ions) directions which can be compensated, to preserve the quasi-neutrality, by currents flowing throughout the conducting plasma chamber walls. We hereby propose a new method to modify Simon's currents via electrons injected by a carbon nanotubes-based electron gun. We found this improves the source performances, increasing the output current for several charge states. The method is especially sensitive to the pumping frequency. Output currents for given charge states, at different auxiliary electron currents, will be reported in the paper and the influence of the frequency tuning on the compensation mechanism will be discussed.

Effect of additive oxygen gas on cellular response of lung cancer cells induced by atmospheric pressure helium plasma jet

PubMed Central

Joh, Hea Min; Choi, Ji Ye; Kim, Sun Ja; Chung, T. H.; Kang, Tae-Hong

2014-01-01

The atmospheric pressure helium plasma jet driven by pulsed dc voltage was utilized to treat human lung cancer cells in vitro. The properties of plasma plume were adjusted by the injection type and flow rate of additive oxygen gas in atmospheric pressure helium plasma jet. The plasma characteristics such as plume length, electric current and optical emission spectra (OES) were measured at different flow rates of additive oxygen to helium. The plasma plume length and total current decreased with an increase in the additive oxygen flow rate. The electron excitation temperature estimated by the Boltzmann plot from several excited helium emission lines increased slightly with the additive oxygen flow. The oxygen atom density in the gas phase estimated by actinometry utilizing argon was observed to increase with the additive oxygen flow. The concentration of intracellular reactive oxygen species (ROS) measured by fluorescence assay was found to be not exactly proportional to that of extracellular ROS (measured by OES), but both correlated considerably. It was also observed that the expression levels of p53 and the phospho-p53 were enhanced in the presence of additive oxygen flow compared with those from the pure helium plasma treatment. PMID:25319447

Diagnosing collisions of magnetized, high energy density plasma flows using a combination of collective Thomson scattering, Faraday rotation, and interferometry (invited).

PubMed

Swadling, G F; Lebedev, S V; Hall, G N; Patankar, S; Stewart, N H; Smith, R A; Harvey-Thompson, A J; Burdiak, G C; de Grouchy, P; Skidmore, J; Suttle, L; Suzuki-Vidal, F; Bland, S N; Kwek, K H; Pickworth, L; Bennett, M; Hare, J D; Rozmus, W; Yuan, J

2014-11-01

A suite of laser based diagnostics is used to study interactions of magnetised, supersonic, radiatively cooled plasma flows produced using the Magpie pulse power generator (1.4 MA, 240 ns rise time). Collective optical Thomson scattering measures the time-resolved local flow velocity and temperature across 7-14 spatial positions. The scattering spectrum is recorded from multiple directions, allowing more accurate reconstruction of the flow velocity vectors. The areal electron density is measured using 2D interferometry; optimisation and analysis are discussed. The Faraday rotation diagnostic, operating at 1053 nm, measures the magnetic field distribution in the plasma. Measurements obtained simultaneously by these diagnostics are used to constrain analysis, increasing the accuracy of interpretation.

Electron heating by intense short-pulse lasers propagating through near-critical plasmas

NASA Astrophysics Data System (ADS)

Debayle, A.; Mollica, F.; Vauzour, B.; Wan, Y.; Flacco, A.; Malka, V.; Davoine, X.; Gremillet, L.

2017-12-01

We investigate the electron heating induced by a relativistic-intensity laser pulse propagating through a near-critical plasma. Using particle-in-cell simulations, we show that a specific interaction regime sets in when, due to the energy depletion caused by the plasma wakefield, the laser front profile has steepened to the point of having a length scale close to the laser wavelength. Wave breaking and phase mixing have then occurred, giving rise to a relativistically hot electron population following the laser pulse. This hot electron flow is dense enough to neutralize the cold bulk electrons during their backward acceleration by the wakefield. This neutralization mechanism delays, but does not prevent the breaking of the wakefield: the resulting phase mixing converts the large kinetic energy of the backward-flowing electrons into thermal energy greatly exceeding the conventional ponderomotive scaling at laser intensities > {10}21 {{{W}}{cm}}-2 and gas densities around 10% of the critical density. We develop a semi-numerical model, based on the Akhiezer-Polovin equations, which correctly reproduces the particle-in-cell-predicted electron thermal energies over a broad parameter range. Given this good agreement, we propose a criterion for full laser absorption that includes field-induced ionization. Finally, we show that our predictions still hold in a two-dimensional geometry using a realistic gas profile.

Multiscale Processes in Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Surjalal Sharma, A.; Jain, Neeraj

The characteristic scales of the plasma processes in magnetic reconnection range from the elec-tron skin-depth to the magnetohydrodynamic (MHD) scale, and cross-scale coupling among them play a key role. Modeling these processes requires different physical models, viz. kinetic, electron-magnetohydrodynamics (EMHD), Hall-MHD, and MHD. The shortest scale processes are at the electron scale and these are modeled using an EMHD code, which provides many features of the multiscale behavior. In simulations using initial conditions consisting of pertur-bations with many scale sizes the reconnection takes place at many sites and the plasma flows from these interact with each other. This leads to thin current sheets with length less than 10 electron skin depths. The plasma flows also generate current sheets with multiple peaks, as observed by Cluster. The quadrupole structure of the magnetic field during reconnection starts on the electron scale and the interaction of inflow to the secondary sites and outflow from the dominant site generates a nested structure. In the outflow regions, the interaction of the electron outflows generated at the neighboring sites lead to the development of electron vortices. A signature of the nested structure of the Hall field is seen in Cluster observations, and more details of these features are expected from MMS.

Flowing Plasma Interaction with an Electric Sail Tether Element

NASA Technical Reports Server (NTRS)

Schneider, Todd; Vaughn, Jason; Wright, Kenneth; Andersen, Allen; Stone, Nobie

2017-01-01

Electric sails are a relatively new concept for providing high speed propellant-less propulsion. Employing multiple tethers biased to high positive voltage levels (kV), electric sails are designed to gain momentum from the solar wind by repelling solar wind protons. To maximize the area of the sail that interacts with the solar wind, electric sails rely on the formation of a large plasma sheath around each small diameter tether. Motivated by interest in advancing the development of electric sails, a set of laboratory tests has been conducted to study the interaction of a drifting plasma with a sheath formed around a small diameter tether element biased at positive voltages. The laboratory test setup was created with Debye length scaling in mind to offer a path to extrapolate (via modeling) to full scale electric sail missions. Using an instrument known as a Differential Ion Flux Probe (DIFP) the interaction between a positively biased tether element and a drifting plasma has been measured for several scenarios. Clear evidence of the tether element sheath deflecting ions has been obtained. Maps of the flow angle downstream from the tether element have been made and they show the influence of the plasma sheath. Finally, electron current collection measurements have been made for a wide range of plasma conditions and tether element bias voltages. The electron collection data will have an impact on electric sail power requirements, as high voltage power supplies and electron guns will have to be sized to accommodate the electron currents collected by each tether.

Evolution of an electron plasma vortex in a strain flow

NASA Astrophysics Data System (ADS)

Danielson, J. R.

2016-10-01

Coherent vortex structures are ubiquitous in fluids and plasmas and are examples of self-organized structures in nonlinear dynamical systems. The fate of these structures in strain and shear flows is an important issue in many physical systems, including geophysical fluids and shear suppression of turbulence in plasmas. In two-dimensions, an inviscid, incompressible, ideal fluid can be modeled with the Euler equations, which is perhaps the simplest system that supports vortices. The Drift-Poisson equations for pure electron plasmas in a strong, uniform magnetic field are isomorphic to the Euler equations, and so electron plasmas are an excellent test bed for the study of 2D vortex dynamics. This talk will describe results from a new experiment using pure electron plasmas in a specially designed Penning-Malmberg (PM) trap to study the evolution of an initially axisymmetric 2D vortex subject to externally imposed strains. Complementary vortex-in-cell simulations are conducted to validate the 2D nature of the experimental results and to extend the parameter range of these studies. Data for vortex destruction using both instantaneously applied and time dependent strains with flat (constant vorticity) and extended radial profiles will be presented. The role of vortex self-organization will be discussed. A simple 2D model works well for flat vorticity profiles. However, extended profiles exhibit more complicated behavior, such as filamentation and stripping; and these effects and their consequences will be discussed. Work done in collaboration with N. C. Hurst, D. H. E. Dubin, and C. M. Surko.

Development of a miniature microwave electron cyclotron resonance plasma ion thruster for exospheric micro-propulsion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dey, Indranuj, E-mail: indranuj@aees.kyushu-u.ac.jp; Toyoda, Yuji; Yamamoto, Naoji

A miniature microwave electron cyclotron resonance plasma source [(discharge diameter)/(microwave cutoff diameter) < 0.3] has been developed at Kyushu University to be used as an ion thruster in micro-propulsion applications in the exosphere. The discharge source uses both radial and axial magnetostatic field confinement to facilitate electron cyclotron resonance and increase the electron dwell time in the volume, thereby enhancing plasma production efficiency. Performance of the ion thruster is studied at 3 microwave frequencies (1.2 GHz, 1.6 GHz, and 2.45 GHz), for low input powers (<15 W) and small xenon mass flow rates (<40 μg/s), by experimentally measuring the extractedmore » ion beam current through a potential difference of ≅1200 V. The discharge geometry is found to operate most efficiently at an input microwave frequency of 1.6 GHz. At this frequency, for an input power of 8 W, and propellant (xenon) mass flow rate of 21 μg/s, 13.7 mA of ion beam current is obtained, equivalent to an calculated thrust of 0.74 mN.« less

Three dimensional fluid-kinetic model of a magnetically guided plasma jet

NASA Astrophysics Data System (ADS)

Ramos, Jesús J.; Merino, Mario; Ahedo, Eduardo

2018-06-01

A fluid-kinetic model of the collisionless plasma flow in a convergent-divergent magnetic nozzle is presented. The model combines the leading-order Vlasov equation and the fluid continuity and perpendicular momentum equation for magnetized electrons, and the fluid equations for cold ions, which must be solved iteratively to determine the self-consistent plasma response in a three-dimensional magnetic field. The kinetic electron solution identifies three electron populations and provides the plasma density and pressure tensor. The far downstream asymptotic behavior shows the anisotropic cooling of the electron populations. The fluid equations determine the electric potential and the fluid velocities. In the small ion-sound gyroradius case, the solution is constructed one magnetic line at a time. In the large ion-sound gyroradius case, ion detachment from magnetic lines makes the problem fully three-dimensional.

Method for producing carbon nanotubes

DOEpatents

Phillips, Jonathan [Santa Fe, NM; Perry, William L [Jemez Springs, NM; Chen, Chun-Ku [Albuquerque, NM

2006-02-14

Method for producing carbon nanotubes. Carbon nanotubes were prepared using a low power, atmospheric pressure, microwave-generated plasma torch system. After generating carbon monoxide microwave plasma, a flow of carbon monoxide was directed first through a bed of metal particles/glass beads and then along the outer surface of a ceramic tube located in the plasma. As a flow of argon was introduced into the plasma through the ceramic tube, ropes of entangled carbon nanotubes, attached to the surface of the tube, were produced. Of these, longer ropes formed on the surface portion of the tube located in the center of the plasma. Transmission electron micrographs of individual nanotubes revealed that many were single-walled.

Laboratory simulation of rocket-borne D-region blunt probe flows

NASA Technical Reports Server (NTRS)

Kaplan, L. B.

1977-01-01

The flow of weakly ionized plasmas that is similar to the flow that occurs over rocket-borne blunt probes as they pass through the lower ionosphere has been simulated in a scaled laboratory environment, and electron collection D region blunt probe theories have been evaluated.

Electron Temperature and Plasma Flow Measurements of NIF Hohlraum Plasmas

NASA Astrophysics Data System (ADS)

Barrios, M. A.; Liedahl, D. A.; Schneider, M. B.; Jones, O.; Brow, G. V.; Regan, S. P.; Fournier, K. B.; Moore, A. S.; Ross, J. S.; Eder, D.; Landen, O.; Kauffman, R. L.; Nikroo, A.; Kroll, J.; Jaquez, J.; Huang, H.; Hansen, S. B.; Callahan, D. A.; Hinkel, D. E.; Bradley, D.; Moody, J. D.; LLNL Collaboration; LLE Collaboration; GA Collaboration; SNL Collaboration

2016-10-01

Characterizing the plasma conditions inside NIF hohlraums, in particular mapping the plasma Te, is critical to gaining insight into mechanisms that affect energy coupling and transport in the hohlraum. The dot spectroscopy platform provides a temporal history of the localized Te and plasma flow inside a NIF hohlraum, by introducing a Mn-Co tracer dot, at strategic locations inside the hohlraum, that comes to equilibrium with the local plasma. K-shell X-ray spectroscopy of the tracer dot is recorded onto an absolutely calibrated X-ray streak spectrometer. Isoelectronic and interstage line ratios are used to infer localized Te through comparison with atomic physics calculations using SCRAM. Time resolved X-ray images are simultaneously taken of the expanding dot, providing plasma (ion) flow information. We present recent results provided by this platform and compare with simulations using HYDRA. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344.

High energy density Z-pinch plasmas using flow stabilization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shumlak, U., E-mail: shumlak@uw.edu; Golingo, R. P., E-mail: shumlak@uw.edu; Nelson, B. A., E-mail: shumlak@uw.edu

The ZaP Flow Z-Pinch research project[1] at the University of Washington investigates the effect of sheared flows on MHD instabilities. Axially flowing Z-pinch plasmas are produced that are 100 cm long with a 1 cm radius. The plasma remains quiescent for many radial Alfvén times and axial flow times. The quiescent periods are characterized by low magnetic mode activity measured at several locations along the plasma column and by stationary visible plasma emission. Plasma evolution is modeled with high-resolution simulation codes – Mach2, WARPX, NIMROD, and HiFi. Plasma flow profiles are experimentally measured with a multi-chord ion Doppler spectrometer. Amore » sheared flow profile is observed to be coincident with the quiescent period, and is consistent with classical plasma viscosity. Equilibrium is determined by diagnostic measurements: interferometry for density; spectroscopy for ion temperature, plasma flow, and density[2]; Thomson scattering for electron temperature; Zeeman splitting for internal magnetic field measurements[3]; and fast framing photography for global structure. Wall stabilization has been investigated computationally and experimentally by removing 70% of the surrounding conducting wall to demonstrate no change in stability behavior.[4] Experimental evidence suggests that the plasma lifetime is only limited by plasma supply and current waveform. The flow Z-pinch concept provides an approach to achieve high energy density plasmas,[5] which are large, easy to diagnose, and persist for extended durations. A new experiment, ZaP-HD, has been built to investigate this approach by separating the flow Z-pinch formation from the radial compression using a triaxial-electrode configuration. This innovation allows more detailed investigations of the sheared flow stabilizing effect, and it allows compression to much higher densities than previously achieved on ZaP by reducing the linear density and increasing the pinch current. Experimental results and scaling analyses will be presented. In addition to studying fundamental plasma science and high energy density physics, the ZaP and ZaP-HD experiments can be applied to laboratory astrophysics.« less

UCB current detector experiment on Swedish auroral payloads. [ionospheric current and plasma flow measurements

NASA Technical Reports Server (NTRS)

Mozer, F.

1974-01-01

A split Langmuir probe has been developed to make in situ measurements of ionospheric current density and plasma bulk flow. The probe consists of two conducting elements that are separated by a thin insulator that shield each other over a 2 pi solid angle, and that are simultaneously swept from negative to positive with respect to the plasma. By measuring the current to each plate and the difference current between plates, information is obtained on the plasma's current density, bulk flow, electron temperature, and density. The instrument was successfully flown twice on sounding rockets into auroral events. Measurement data indicate that the total auroral current configuration is composed of several alternating east and west electrojets associated with several alternating up and down Birkeland currents.

Quasi-exospheric heat flux of solar-wind electrons

NASA Technical Reports Server (NTRS)

Eviatar, A.; Schultz, M.

1975-01-01

Density, bulk-velocity, and heat-flow moments are calculated for truncated Maxwellian distributions representing the cool and hot populations of solar-wind electrons, as realized at the base of a hypothetical exosphere. The electrostatic potential is thus calculated by requiring charge quasi-neutrality and the absence of electrical current. Plasma-kinetic coupling of the cool-electron and proton bulk velocities leads to an increase in the electrostatic potential and a decrease in the heat-flow moment.

Effect of Energetic Plasma Flux on Flowing Liquid Lithium Surfaces

NASA Astrophysics Data System (ADS)

Kalathiparambil, Kishor; Jung, Soonwook; Christenson, Michael; Fiflis, Peter; Xu, Wenyu; Szott, Mathew; Ruzic, David

2014-10-01

An operational liquid lithium system with steady state flow driven by thermo-electric magneto-hydrodynamic force and capable of constantly refreshing the plasma exposed surface have been demonstrated at U of I. To evaluate the system performance in reactor relevant conditions, specifically to understand the effect of disruptive plasma events on the performance of the liquid metal PFCs, the setup was integrated to a pulsed plasma generator. A coaxial plasma generator drives the plasma towards a theta pinch which preferentially heats the ions, simulating ELM like flux, and the plasma is further guided towards the target chamber which houses the flowing lithium system. The effect of the incident flux is examined using diagnostic tools including triple Langmuir probe, calorimeter, rogowski coils, Ion energy analyzers, and fast frame spectral image acquisition with specific optical filters. The plasma have been well characterized and a density of ~1021 m-3, with electron temperature ~10 - 20 eV is measured, and final plasma velocities of 34 - 74 kms-1 have been observed. Calorimetric measurements using planar molybdenum targets indicate a maximum plasma energy (with 6 kV plasma gun and 20 kV theta pinch) of 0.08 MJm-2 with plasma divergence effects resulting in marginal reduction of 40 +/- 23 J in plasma energy. Further results from the other diagnostic tools, using the flowing lithium targets and the planar targets coated with lithium will be presented. DOE DE-SC0008587.

Excitation of higher radial modes of azimuthal surface waves in the electron cyclotron frequency range by rotating relativistic flow of electrons in cylindrical waveguides partially filled by plasmas

NASA Astrophysics Data System (ADS)

Girka, Igor O.; Pavlenko, Ivan V.; Thumm, Manfred

2018-05-01

Azimuthal surface waves are electromagnetic eigenwaves of cylindrical plasma-dielectric waveguides which propagate azimuthally nearby the plasma-dielectric interface across an axial external stationary magnetic field. Their eigenfrequency in particular can belong to the electron cyclotron frequency range. Excitation of azimuthal surface waves by rotating relativistic electron flows was studied in detail recently in the case of the zeroth radial mode for which the waves' radial phase change within the layer where the electrons gyrate is small. In this case, just the plasma parameters cause the main influence on the waves' dispersion properties. In the case of the first and higher radial modes, the wave eigenfrequency is higher and the wavelength is shorter than in the case of the zeroth radial mode. This gain being of interest for practical applications can be achieved without any change in the device design. The possibility of effective excitation of the higher order radial modes of azimuthal surface waves is demonstrated here. Getting shorter wavelengths of the excited waves in the case of higher radial modes is shown to be accompanied by decreasing growth rates of the waves. The results obtained here are of interest for developing new sources of electromagnetic radiation, in nano-physics and in medical physics.

A determination of relativistic shock jump conditions using Monte Carlo techniques

NASA Technical Reports Server (NTRS)

Ellison, Donald C.; Reynolds, Stephen P.

1991-01-01

Monte Carlo techniques are used, assuming isotropic elastic scattering of all particles, to calculate jump conditions in parallel relativistic collisionless shocks in the absence of Fermi acceleration. The shock velocity and compression ratios are shown for arbitrary flow velocities and for any upstream temperature. Both single-component electron-positron plasma and two-component proton-electron plasmas are considered. It is shown that protons and electrons must share energy, directly or through the mediation of plasma waves, in order to satisfy the basic conservation conditions, and the electron and proton temperatures are determined for a particular microscopic, kinetic-theory model, namely, that protons always scatter elastically. The results are directly applicable to shocks in which waves of scattering superthermal particles are absent.

The low energy plasma in the Uranian magnetosphere

NASA Technical Reports Server (NTRS)

Mcnutt, R. L., Jr.; Belcher, J.; Bridge, H.; Lazarus, A. J.; Richardson, J.; Sands, M.; Bagenal, F.; Eviatar, A.; Goertz, C.; Ogilvie, K.

1987-01-01

The Plasma Science experiment on Voyager 2 detected a magnetosphere filled with a tenuous plasma, rotating with the planet. Temperatures of the plasma, composed of protons and electrons, ranged from 10 eV to about 1 keV. The sources of these protons and electrons are probably the ionosphere of Uranus or the extended neutral hydrogen cloud surrounding the planet. As at earth, Jupiter, and Saturn, there is an extended magnetotail with a central plasma sheet. Although similar in global structure to the magnetospheres of these planets, the large angle between the rotation and magnetic axes of the planet and the orientation of the rotation axis with respect to the solar wind flow make the Uranian magnetosphere unique.

Active shield technology for space craft protection revisited in new laboratory results and analysis

NASA Astrophysics Data System (ADS)

Bamford, R.; Gibson, K. J.; Thornton, A. T.; Bradford, J.; Bingham, R.; Gargate, L.; Silva, L. O.; Fonseca, R. A.; Hapgood, M.; Norberg, C.; Todd, T.; Stamper, R.

2009-04-01

Energetic ions in the solar wind plasma are a known hazard to both spacecraft electronics and to astronaut's health. Of primary concern is the exposure to keV--MeV protons on manned space flights to the Moon and Mars that extend over long periods of time. Attempts to protect the spacecraft include active shields that are reminiscent of Star Trek "deflector" shields. Here we describe a new experiment to test the shielding concept of a dipole-like magnetic field and plasma, surrounding the spacecraft forming a "mini magnetosphere". Initial laboratory experiments have been conducted to determine the effectiveness of a magnetized plasma barrier to be able to expel an impacting, low beta, supersonic flowing energetic plasma representing the Solar Wind. Optical and Langmuir probe data of the plasma density, the plasma flow velocity, and the intensity of the dipole field clearly show the creation of a narrow transport barrier region and diamagnetic cavity virtually devoid of energetic plasma particles. This demonstrates the potential viability of being able to create a small "hole" in a Solar Wind plasma, of the order of the ion Larmor orbit width, in which an inhabited spacecraft could reside in relative safety. The experimental results have been quantitatively compared to a 3D particle-in-cell ‘hybrid' code simulation that uses kinetic ions and fluid electrons, showing good qualitative agreement and excellent quantitative agreement. Together the results demonstrate the pivotal role of particle kinetics in determining generic plasma transport barriers. [1] [1] R Bamford et al., "The interaction of a flowing plasma with a dipole magnetic field: measurements and modelling of a diamagnetic cavity relevant to spacecraft protection." 2008 Plasma Phys. Control. Fusion 50 124025 (11pp) doi: 10.1088/0741-3335/50/12/124025

Atmospheric pulsed laser deposition of plasmonic nanoparticle films of silver with flowing gas and flowing atmospheric plasma

NASA Astrophysics Data System (ADS)

Khan, T. M.; Pokle, A.; Lunney, J. G.

2018-04-01

Two methods of atmospheric pulsed laser deposition of plasmonic nanoparticle films of silver are described. In both methods the ablation plume, produced by a 248 nm, 20 ns excimer laser in gas, is strongly confined near the target and forms a nanoparticle aerosol. For both the flowing gas, and the atmospheric plasma from a dielectric barrier discharge plasma source, the aerosol is entrained in the flow and carried to a substrate for deposition. The nanoparticle films produced by both methods were examined by electron microscopy and optical absorption spectroscopy. With plasma assistance, the deposition rate was significantly enhanced and the film morphology altered. With argon gas, isolated nanoparticles of 20 nm size were obtained, whereas in argon plasma, the nanoparticles are aggregated in clusters of 90 nm size. Helium gas also leads to the deposition of isolated nanoparticles, but with helium plasma, two populations of nanoparticles are observed: one of rounded particles with a mean size of 26 nm and the other of faceted particles with a mean size 165 nm.

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

NASA Technical Reports Server (NTRS)

Parker, L. W.

1977-01-01

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

Ion heating and characteristics of ST plasma used by double-pulsing CHI on HIST

NASA Astrophysics Data System (ADS)

Hanao, Takafumi; Hirono, Hidetoshi; Hyobu, Takahiro; Ito, Kengo; Matsumoto, Keisuke; Nakayama, Takashi; Oki, Nobuharu; Kikuchi, Yusuke; Fukumoto, Naoyuki; Nagata, Masayoshi

2013-10-01

Multi-pulsing Coaxial Helicity Injection (M-CHI) is an efficient current drive and sustainment method used in spheromak and spherical torus (ST). We have observed plasma current/flux amplification by double pulsing CHI. Poloidal ion temperature measured by Ion Doppler Spectrometer (IDS) has a peak at plasma core region. In this region, radial electric field has a negative peak. At more inboard side that is called separatrix between closed flux region and inner open flux region, poloidal flow has a large shear and radial electric field changes the polarity. After the second CHI pulse, we observed sharp and rapid ion heating at plasma core region and separatrix. In this region, the poloidal ion temperature is selective heating because electron temperature is almost uniform. At this time, flow shear become larger and radial electric field is amplified at separatorix. These effects produce direct heating of ion through the viscous flow damping. Furthermore, we observed decrease of electron density at separatrix. Decreased density makes Hall dynamo electric field as two-fluid effect. When the ion temperature is increasing, dynamo electric field is observed at separatrix. It may have influence with the ion heating. We will discuss characteristic of double pulsing CHI driven ST plasmas and correlation of direct heating of ion with dynamo electric field and any other parameters.

OH and O radicals production in atmospheric pressure air/Ar/H2O gliding arc discharge plasma jet

NASA Astrophysics Data System (ADS)

N, C. ROY; M, R. TALUKDER; A, N. CHOWDHURY

2017-12-01

Atmospheric pressure air/Ar/H2O gliding arc discharge plasma is produced by a pulsed dc power supply. An optical emission spectroscopic (OES) diagnostic technique is used for the characterization of plasmas and for identifications of {{OH}} and {{O}} radicals along with other species in the plasmas. The OES diagnostic technique reveals the excitation T x ≈ 5550-9000 K, rotational T r ≈ 1350-2700 K and gas T g ≈ 850-1600 K temperatures, and electron density {n}{{e}}≈ ({1.1-1.9})× {10}14 {{{cm}}}-3 under different experimental conditions. The production and destruction of {{OH}} and {{O}} radicals are investigated as functions of applied voltage and air flow rate. Relative intensities of {{OH}} and {{O}} radicals indicate that their production rates are increased with increasing {{Ar}} content in the gas mixture and applied voltage. {n}{{e}} reveals that the higher densities of {{OH}} and {{O}} radicals are produced in the discharge due to more effective electron impact dissociation of {{{H}}}2{{O}} and {{{O}}}2 molecules caused by higher kinetic energies as gained by electrons from the enhanced electric field as well as by enhanced {n}{{e}}. The productions of {{OH}} and {{O}} are decreasing with increasing air flow rate due to removal of Joule heat from the discharge region but enhanced air flow rate significantly modifies discharge maintenance properties. Besides, {T}{{g}} significantly reduces with the enhanced air flow rate. This investigation reveals that {{Ar}} plays a significant role in the production of {{OH}} and {{O}} radicals.

The electron distribution function downstream of the solar-wind termination shock: Where are the hot electrons?

NASA Astrophysics Data System (ADS)

Fahr, Hans J.; Richardson, John D.; Verscharen, Daniel

2015-07-01

In the majority of the literature on plasma shock waves, electrons play the role of "ghost particles", since their contribution to mass and momentum flows is negligible, and they have been treated as only taking care of the electric plasma neutrality. In some more recent papers, however, electrons play a new important role in the shock dynamics and thermodynamics, especially at the solar-wind termination shock. They react on the shock electric field in a very specific way, leading to suprathermal nonequilibrium distributions of the downstream electrons, which can be represented by a kappa distribution function. In this paper, we discuss why this anticipated hot electron population has not been seen by the plasma detectors of the Voyager spacecraft downstream of the solar-wind termination shock. We show that hot nonequilibrium electrons induce a strong negative electric charge-up of any spacecraft cruising through this downstream plasma environment. This charge reduces electron fluxes at the spacecraft detectors to nondetectable intensities. Furthermore, we show that the Debye length λDκ grows to values of about λDκ/λD ≃ 106 compared to the classical value λD in this hot-electron environment. This unusual condition allows for the propagation of a certain type of electrostatic plasma waves that, at very large wavelengths, allow us to determine the effective temperature of the suprathermal electrons directly by means of the phase velocity of these waves. At moderate wavelengths, the electron-acoustic dispersion relation leads to nonpropagating oscillations with the ion-plasma frequency ωp, instead of the traditional electron plasma frequency.

3D measurements and simulations of ion and neutral velocity distribution functions in a magnetized plasma boundary

NASA Astrophysics Data System (ADS)

Thompson, Derek S.; Keniley, Shane; Curreli, Davide; Henriquez, Miguel F.; Caron, David D.; Jemiolo, Andrew J.; McLaughlin, Jacob W.; Dufor, Mikal T.; Neal, Luke A.; Scime, Earl E.; Siddiqui, M. Umair

2017-10-01

We present progress toward the first paired 3D laser induced fluorescence measurements of ion and neutral velocity distribution functions (I/NVDFs) in a magnetized plasma boundary. These measurements are performed in the presheath region of an absorbing boundary immersed in a background magnetic field that is obliquely incident to the boundary surface (ψ =74°). Parallel and perpendicular flow measurements demonstrate that cross-field ion flows occur and that ions within several gyro-radii of the surface are accelerated in the E-> × B-> direction. We present electrostatic probe measurements of electron temperature, plasma density, and electric potential in the same region. Ion, neutral and electron measurements are compared to Boltzmann simulations, allowing direct comparison between measured and theoretical distribution functions in the boundary region. NSF PHYS 1360278.

Diagnosing collisions of magnetized, high energy density plasma flows using a combination of collective Thomson scattering, Faraday rotation, and interferometry (invited)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swadling, G. F., E-mail: swadling@imperial.ac.uk; Lebedev, S. V.; Hall, G. N.

2014-11-15

A suite of laser based diagnostics is used to study interactions of magnetised, supersonic, radiatively cooled plasma flows produced using the Magpie pulse power generator (1.4 MA, 240 ns rise time). Collective optical Thomson scattering measures the time-resolved local flow velocity and temperature across 7–14 spatial positions. The scattering spectrum is recorded from multiple directions, allowing more accurate reconstruction of the flow velocity vectors. The areal electron density is measured using 2D interferometry; optimisation and analysis are discussed. The Faraday rotation diagnostic, operating at 1053 nm, measures the magnetic field distribution in the plasma. Measurements obtained simultaneously by these diagnosticsmore » are used to constrain analysis, increasing the accuracy of interpretation.« less

Oblique shock structures formed during the ablation phase of aluminium wire array z-pinches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swadling, G. F.; Lebedev, S. V.; Niasse, N.

A series of experiments has been conducted in order to investigate the azimuthal structures formed by the interactions of cylindrically converging plasma flows during the ablation phase of aluminium wire array Z pinch implosions. These experiments were carried out using the 1.4 MA, 240 ns MAGPIE generator at Imperial College London. The main diagnostic used in this study was a two-colour, end-on, Mach-Zehnder imaging interferometer, sensitive to the axially integrated electron density of the plasma. The data collected in these experiments reveal the strongly collisional dynamics of the aluminium ablation streams. The structure of the flows is dominated by amore » dense network of oblique shock fronts, formed by supersonic collisions between adjacent ablation streams. An estimate for the range of the flow Mach number (M = 6.2-9.2) has been made based on an analysis of the observed shock geometry. Combining this measurement with previously published Thomson Scattering measurements of the plasma flow velocity by Harvey-Thompson et al.[Physics of Plasmas 19, 056303 (2012)] allowed us to place limits on the range of the ZT{sub e} of the plasma. The detailed and quantitative nature of the dataset lends itself well as a source for model validation and code verification exercises, as the exact shock geometry is sensitive to many of the plasma parameters. Comparison of electron density data produced through numerical modelling with the Gorgon 3D MHD code demonstrates that the code is able to reproduce the collisional dynamics observed in aluminium arrays reasonably well.« less

Electron-ion hybrid instability experiment upgrades to the Auburn Linear Experiment for Instability Studies.

PubMed

DuBois, A M; Arnold, I; Thomas, E; Tejero, E; Amatucci, W E

2013-04-01

The Auburn Linear EXperiment for Instability Studies (ALEXIS) is a laboratory plasma physics experiment used to study spatially inhomogeneous flows in a magnetized cylindrical plasma column that are driven by crossed electric (E) and magnetic (B) fields. ALEXIS was recently upgraded to include a small, secondary plasma source for a new dual source, interpenetrating plasma experiment. Using two plasma sources allows for highly localized electric fields to be made at the boundary of the two plasmas, inducing strong E × B velocity shear in the plasma, which can give rise to a regime of instabilities that have not previously been studied in ALEXIS. The dual plasma configuration makes it possible to have independent control over the velocity shear and the density gradient. This paper discusses the recent addition of the secondary plasma source to ALEXIS, as well as the plasma diagnostics used to measure electric fields and electron densities.

Interaction of a neutral cloud moving through a magnetized plasma

NASA Technical Reports Server (NTRS)

Goertz, C. K.; Lu, G.

1990-01-01

Current collection by outgassing probes in motion relative to a magnetized plasma may be significantly affected by plasma processes that cause electron heating and cross field transport. Simulations of a neutral gas cloud moving across a static magnetic field are discussed. The authors treat a low-Beta plasma and use a 2-1/2 D electrostatic code linked with the authors' Plasma and Neutral Interaction Code (PANIC). This study emphasizes the understanding of the interface between the neutral gas cloud and the surrounding plasma where electrons are heated and can diffuse across field lines. When ionization or charge exchange collisions occur a sheath-like structure is formed at the surface of the neutral gas. In that region the crossfield component of the electric field causes the electron to E times B drift with a velocity of the order of the neutral gas velocity times the square root of the ion to electron mass ratio. In addition a diamagnetic drift of the electron occurs due to the number density and temperature inhomogeneity in the front. These drift currents excite the lower-hybrid waves with the wave k-vectors almost perpendicular to the neutral flow and magnetic field again resulting in electron heating. The thermal electron current is significantly enhanced due to this heating.

Plasma in Saturn's Nightside Magnetosphere and the Implications for Global Circulation

NASA Technical Reports Server (NTRS)

McAndrews, H.J.; Thomsen, M.F.; Arridge, C.S.; Jackman, C.M.; Wilson, R.J.; Henderson, M.G.; Tokar, R.L.; Khurana, K.K.; Sittler, E. C.; Coates, A.J.;

Recent progress in understanding electron thermal transport in NSTX

DOE PAGES

Ren, Y.; Belova, E.; Gorelenkov, N.; ...

2017-03-10

The anomalous level of electron thermal transport inferred in magnetically confined configurations is one of the most challenging problems for the ultimate realization of fusion power using toroidal devices: tokamaks, spherical tori and stellarators. It is generally believed that plasma instabilities driven by the abundant free energy in fusion plasmas are responsible for the electron thermal transport. The National Spherical Torus eXperiment (NSTX) (Ono et al 2000 Nucl. Fusion 40 557) provides a unique laboratory for studying plasma instabilities and their relation to electron thermal transport due to its low toroidal field, high plasma beta, low aspect ratio and largemore » ExB flow shear. Recent findings on NSTX have shown that multiple instabilities are required to explain observed electron thermal transport, given the wide range of equilibrium parameters due to different operational scenarios and radial regions in fusion plasmas. Here we review the recent progresses in understanding anomalous electron thermal transport in NSTX and focus on mechanisms that could drive electron thermal transport in the core region. The synergy between experiment and theoretical/ numerical modeling is essential to achieving these progresses. The plans for newly commissioned NSTX-Upgrade will also be discussed.« less

Energy principle for excitations in plasmas with counterstreaming electron flows

NASA Astrophysics Data System (ADS)

Kumar, Atul; Shukla, Chandrasekhar; Das, Amita; Kaw, Predhiman

2018-05-01

A relativistic electron beam propagating through plasma induces a return electron current in the system. Such a system of interpenetrating forward and return electron current is susceptible to a host of instabilities. The physics of such instabilities underlies the conversion of the flow kinetic energy to the electromagnetic field energy. Keeping this in view, an energy principle analysis has been enunciated in this paper. Such analyses have been widely utilized earlier in the context of conducting fluids described by MHD model [I. B. Bernstein et al., Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 244(1236), 17-40 (1958)]. Lately, such an approach has been employed for the electrostatic two stream instability for the electron beam plasma system [C. N. Lashmore-Davies, Physics of Plasmas 14(9), 092101 (2007)]. In contrast, it has been shown here that even purely growing mode like Weibel/current filamentation instability for the electron beam plasma system is amenable to such a treatment. The treatment provides an understanding of the energetics associated with the growing mode. The growth rate expression has also been obtained from it. Furthermore, it has been conclusively demonstrated in this paper that for identical values of S4=∑αn0 αv0α 2/n0γ0 α, the growth rate is higher when the counterstreaming beams are symmetric (i.e. S3 = ∑αn0αv 0α/n0γ0α = 0) compared to the case when the two beams are asymmetric (i.e. when S3 is finite). Here, v 0α, n0α and γ0α are the equilibrium velocity, electron density and the relativistic factor for the electron species `α' respectively and n0 = ∑αn0α is the total electron density. Particle - In - Cell simulations have been employed to show that the saturated amplitude of the field energy is also higher in the symmetric case.

Effect of external plasma flows on the interaction between turbulence and convective cells

NASA Astrophysics Data System (ADS)

Uzawa, Ken; Li, Jiquan

2005-10-01

It is widely recognized that large scale structures, such as zonal flows, streamers and also long wavelength Kelvin-Helmholtz modes are nonlinearly generated from maternal turbulence through modulational instability process and play a crucial role in regulating the transport in tokamaks. In order to control the transport, it is desirable to control such structures and/or modulational process. One of control parameters may be mean flow which intrinsically exists in tokamak plasmas. Besides the direct influence on the transport through vortex decorrelation, the mean flow may indirectly change the zonal flow generation by acting on the modulational process itself. In this work, we theoretically investigate the characteristics of zonal flow generation due to the electron temperature gradient (ETG) turbulence in the presence of long wavelength ITG driven zonal flow. This was done by extending our previous modulational analyses[1]. We have numerically analyzed the influence of mean flow on zonal flow generation. The main result is that the zonal flow generation is suppressed by the presence of the mean flow. [1]J. Li, Y. Kishimoto, Physics of Plasmas, 9, 1241 (2002)

Dust trajectories and diagnostic applications beyond strongly coupled dusty plasmas

NASA Astrophysics Data System (ADS)

Wang, Zhehui; Ticoş, Cǎtǎlin M.; Wurden, Glen A.

2007-10-01

Plasma interaction with dust is of growing interest for a number of reasons. On the one hand, dusty plasma research has become one of the most vibrant branches of plasma science. On the other hand, substantially less is known about dust dynamics outside the laboratory strongly coupled dusty-plasma regime, which typically corresponds to 1015m-3 electron density with ions at room temperature. Dust dynamics is also important to magnetic fusion because of concerns about safety and potential dust contamination of the fusion core. Dust trajectories are measured under two plasma conditions, both of which have larger densities and hotter ions than in typical dusty plasmas. Plasma-flow drag force, dominating over other forces in flowing plasmas, can explain the dust motion. In addition, quantitative understanding of dust trajectories is the basis for diagnostic applications using dust. Observation of hypervelocity dust in laboratory enables dust as diagnostic tool (hypervelocity dust injection) in magnetic fusion. In colder plasmas (˜10eV or less), dust with known physical and chemical properties can be used as microparticle tracers to measure both the magnitude and directions of flows in plasmas with good spatial resolution as the microparticle tracer velocimetry.

Particle-in-cell simulation of an electronegative plasma under direct current bias studied in a large range of electronegativity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oudini, N.; Laboratoire des plasmas de Decharges, Centre de Developement des Technologies Avancees, Cite du 20 Aout BP 17 Baba Hassen, 16081 Algiers; Raimbault, J.-L.

2013-04-15

A one-dimensional electronegative plasma situated between two symmetrical parallel electrodes under DC bias is studied by Particle-In-Cell simulation with Monte Carlo Collisions. By varying the electronegativity {alpha}{identical_to}n{sub -}/n{sub e} from the limit of electron-ion plasmas (negative ion free) to ion-ion plasmas (electron free), the sheaths formation, the negative ion flux flowing towards the electrodes, and the particle velocities at the sheath edges are investigated. Depending on {alpha}, it is shown that the electronegative plasma behavior can be described by four regimes. In the lowest regime of {alpha}, i.e., {alpha} < 50, negative ions are confined by two positive sheaths withinmore » the plasma, while in the higher regimes of {alpha}, a negative sheath is formed and the negative ion flux can be extracted from the bulk plasma. In the two intermediate regimes of {alpha}, i.e., 50 < {alpha} < 10{sup 5}, both the electron and the negative ion fluxes are involved in the neutralization of the positive ions flux that leaves the plasma. In particular, we show that the velocity of the negative ions entering the negative sheath is affected by the presence of the electrons, and is not given by the modified Bohm velocity generally accepted for electronegative plasmas. For extremely high electronegativity, i.e., {alpha} > 10{sup 5}, the presence of electrons in the plasma is marginal and the electronegative plasma can be considered as an ion-ion plasma (electron free).« less

Analytic model of a magnetically insulated transmission line with collisional flow electrons

NASA Astrophysics Data System (ADS)

Stygar, W. A.; Wagoner, T. C.; Ives, H. C.; Corcoran, P. A.; Cuneo, M. E.; Douglas, J. W.; Gilliland, T. L.; Mazarakis, M. G.; Ramirez, J. J.; Seamen, J. F.; Seidel, D. B.; Spielman, R. B.

2006-09-01

We have developed a relativistic-fluid model of the flow-electron plasma in a steady-state one-dimensional magnetically insulated transmission line (MITL). The model assumes that the electrons are collisional and, as a result, drift toward the anode. The model predicts that in the limit of fully developed collisional flow, the relation between the voltage Va, anode current Ia, cathode current Ik, and geometric impedance Z0 of a 1D planar MITL can be expressed as Va=IaZ0h(χ), where h(χ)≡[(χ+1)/4(χ-1)]1/2-ln⁡⌊χ+(χ2-1)1/2⌋/2χ(χ-1) and χ≡Ia/Ik. The relation is valid when Va≳1MV. In the minimally insulated limit, the anode current Ia,min⁡=1.78Va/Z0, the electron-flow current If,min⁡=1.25Va/Z0, and the flow impedance Zf,min⁡=0.588Z0. {The electron-flow current If≡Ia-Ik. Following Mendel and Rosenthal [Phys. Plasmas 2, 1332 (1995)PHPAEN1070-664X10.1063/1.871345], we define the flow impedance Zf as Va/(Ia2-Ik2)1/2.} In the well-insulated limit (i.e., when Ia≫Ia,min⁡), the electron-flow current If=9Va2/8IaZ02 and the flow impedance Zf=2Z0/3. Similar results are obtained for a 1D collisional MITL with coaxial cylindrical electrodes, when the inner conductor is at a negative potential with respect to the outer, and Z0≲40Ω. We compare the predictions of the collisional model to those of several MITL models that assume the flow electrons are collisionless. We find that at given values of Va and Z0, collisions can significantly increase both Ia,min⁡ and If,min⁡ above the values predicted by the collisionless models, and decrease Zf,min⁡. When Ia≫Ia,min⁡, we find that, at given values of Va, Z0, and Ia, collisions can significantly increase If and decrease Zf. Since the steady-state collisional model is valid only when the drift of electrons toward the anode has had sufficient time to establish fully developed collisional flow, and collisionless models assume there is no net electron drift toward the anode, we expect these two types of models to provide theoretical bounds on Ia, If, and Zf.

Model analysis and electrical characterization of atmospheric pressure cold plasma jet in pin electrode configuration

NASA Astrophysics Data System (ADS)

Deepak, G. Divya; Joshi, N. K.; Prakash, Ram

2018-05-01

In this study, both model analysis and electrical characterization of a dielectric barrier discharge based argon plasma jet have been carried at atmospheric pressure in a pin electrode configuration. The plasma and fluid dynamics modules of COMSOL multi-physics code have been used for the modeling of the plasma jet. The plasma parameters, such as, electron density, electron temperature and electrical potential have been analyzed with respect to the electrical parameters, i.e., supply voltage and supply frequency with and without the flow of gas. In all the experiments, gas flow rate has been kept constant at 1 liter per minute. This electrode configuration is subjected to a range of supply frequencies (10-25 kHz) and supply voltages (3.5-6.5 kV). The power consumed by the device has been estimated at different applied combinations (supply voltage & frequency) for optimum power consumption at maximum jet length. The maximum power consumed by the device in this configuration for maximum jet length of ˜26 mm is just ˜1 W.

Electron distributions in the plasma sheet boundary layer - Time-of-flight effects

NASA Technical Reports Server (NTRS)

Onsager, T. G.; Thomsen, M. F.; Gosling, J. T.; Bame, S. J.

1990-01-01

The electron edge of the plasma sheet boundary layer lies lobeward of the ion edge. Measurements obtained near the electron edge of the boundary layer reveal low-speed cutoffs for earthward and tailward-flowing electrons. These cutoffs progress to lower speeds with deeper penetration into the boundary layer, and are consistently lower for the earthward-directed electrons than for the tailward-direction electrons. The cutoffs and their variation with distance from the edge of the boundary layer can be consistently interpreted in terms of a time-of-flight effect on recently reconnected magnetic field lines. The observed cutoff speeds are used to estimate the downtail location of the reconnection site.

Characteristics of an Electron Cyclotron Resonance Plasma Source for the Production of Active Nitrogen Species in III-V Nitride Epitaxy

NASA Technical Reports Server (NTRS)

Meyyappan, Meyya; Arnold, James O. (Technical Monitor)

1997-01-01

A simple analysis is provided to determine the characteristics of an electron cyclotron resonance (ECR) plasma source for the generation of active nitrogen species in the molecular beam epitaxy of III-V nitrides. The effects of reactor geometry, pressure, power, and flow rate on the dissociation efficiency and ion flux are presented. Pulsing the input power is proposed to reduce the ion flux.

Silicon etching of difluoromethane atmospheric pressure plasma jet combined with its spectroscopic analysis

NASA Astrophysics Data System (ADS)

Sung, Yu-Ching; Wei, Ta-Chin; Liu, You-Chia; Huang, Chun

2018-06-01

A capacitivly coupled radio-frequency double-pipe atmospheric-pressure plasma jet is used for etching. An argon carrier gas is supplied to the plasma discharge jet; and CH2F2 etch gas is inserted into the plasma discharge jet, near the silicon substrate. Silicon etchings rate can be efficiently-controlled by adjusting the feeding etching gas composition and plasma jet operating parameters. The features of silicon etched by the plasma discharge jet are discussed in order to spatially spreading plasma species. Electronic excitation temperature and electron density are detected by increasing plasma power. The etched silicon profile exhibited an anisotropic shape and the etching rate was maximum at the total gas flow rate of 4500 sccm and CH2F2 concentration of 11.1%. An etching rate of 17 µm/min was obtained at a plasma power of 100 W.

Recombination of H(3+) and D(3+) ions with electrons

NASA Technical Reports Server (NTRS)

Johnsen, R.; Gougousi, T.; Golde, M. F.

1994-01-01

Flowing-afterglow measurements in decaying H3(+) or D3(+) plasmas suggest that de-ionization does not occur by simple binary recombination of a single ion species. We find that vibrational excitation of the ions fails to provide an explanation for the effect, contrary to an earlier suggestion. Instead, we suggest that collisional stabilization of H3** Rydberg molecules by ambient electrons introduces an additional dependence on electron density. The proposed mechanism would permit plasma de-ionization to occur without the need for dissociative recombination by the mechanism of potential-surface crossings.

Thomson scattering diagnostic for the measurement of ion species fraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ross, J S; Park, H S; Amendt, A

2012-05-01

Simultaneous Thomson scattering measurements of collective electron-plasma and ion-acoustic fluctuations have been utilized to determine ion species fraction from laser produced CH plasmas. The CH{sub 2} foil is heated with 10 laser beams, 500 J per beam, at the Omega Laser facility. Thomson scattering measurements are made 4 mm from the foil surface using a 30 J 2{omega} probe laser with a 1 ns pulse length. Using a series of target shots the plasma evolution is measured from 2.5 ns to 9 ns after the rise of the heater beams. Measuring the electron density and temperature from the electron-plasma fluctuationsmore » constrains the fit of the two-ion species theoretical form factor for the ion feature such that the ion temperature, plasma flow velocity and ion species fraction are determined. The ion species fraction is determined to an accuracy of {+-}0.06 in species fraction.« less

Ion extraction from a plasma. Ph.D. Thesis. Progress Report, 1 Dec. 1979 - 1 Dec. 1980

NASA Technical Reports Server (NTRS)

Aston, G.

1980-01-01

An experimental investigation of the physical processes governing ion extraction from a plasma is presented. The screen hole plasma sheath of a multiaperture ion accelerator system is defined by equipotential plots for a variety of accelerator system geometries and operating conditions. A sheath thickness of at least fifteen Debye lengths is shown to be typical. The electron density variation within the sheath satisfies a Maxwell Boltzmann density distribution at an effective electron temperature dependent on the discharge plasma primary to Maxwellian electron density ratio. Plasma ion flow up to and through the sheath is predominately one dimensional and the ions enter the sheath with a modified Bohm velocity. Low values of the screen grid thickness to screen hole diameter ratio give good ion focusing and high extracted ion currents because of the effect of screen webbing on ion focusing.

Electrical description of N2 capacitively coupled plasmas with the global model

NASA Astrophysics Data System (ADS)

Cao, Ming-Lu; Lu, Yi-Jia; Cheng, Jia; Ji, Lin-Hong; Engineering Design Team

2016-10-01

N2 discharges in a commercial capacitively coupled plasma reactor are modelled by a combination of an equivalent circuit and the global model, for a range of gas pressure at 1 4 Torr. The ohmic and inductive plasma bulk and the capacitive sheath are represented as LCR elements, with electrical characteristics determined by plasma parameters. The electron density and electron temperature are obtained from the global model in which a Maxwellian electron distribution is assumed. Voltages and currents are recorded by a VI probe installed after the match network. Using the measured voltage as an input, the current flowing through the discharge volume is calculated from the electrical model and shows excellent agreement with the measurements. The experimentally verified electrical model provides a simple and accurate description for the relationship between the external electrical parameters and the plasma properties, which can serve as a guideline for process window planning in industrial applications.

Effects of finite poloidal gyroradius, shaping, and collisions on the zonal flow residuala)

NASA Astrophysics Data System (ADS)

Xiao, Yong; Catto, Peter J.; Dorland, William

2007-05-01

Zonal flow helps reduce and regulate the turbulent transport level in tokamaks. Rosenbluth and Hinton have shown that zonal flow damps to a nonvanishing residual level in collisionless [M. Rosenbluth and F. Hinton, Phys. Rev. Lett. 80, 724 (1998)] and collisional [F. Hinton and M. Rosenbluth, Plasma Phys. Control. Fusion 41, A653 (1999)] banana regime plasmas. Recent zonal flow advances are summarized including the evaluation of the effects on the zonal flow residual by plasma cross-section shaping, shorter wavelengths including those less than an electron gyroradius, and arbitrary ion collisionality relative to the zonal low frequency. In addition to giving a brief summary of these new developments, the analytic results are compared with GS2 numerical simulations [M. Kotschenreuther, G. Rewoldt, and W. Tang, Comput. Phys. Commun. 88, 128 (1991)] to demonstrate their value as benchmarks for turbulence codes.

Bifurcation physics of magnetic islands and stochasticity explored by heat pulse propagation studies in toroidal plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ida, K.; Kobayashi, T.; Yoshinuma, M.

Bifurcation physics of the magnetic island was investigated using the heat pulse propagation technique produced by the modulation of electron cyclotron heating. There are two types of bifurcation phenomena observed in LHD and DIII-D. One is a bifurcation of the magnetic topology between nested and stochastic fields. The nested state is characterized by the bi-directional (inward and outward) propagation of the heat pulse with slow propagation speed. The stochastic state is characterized by the fast propagation of the heat pulse with electron temperature flattening. The other bifurcation is between magnetic island with larger thermal diffusivity and that with smaller thermalmore » diffusivity. The damping of toroidal flow is observed at the O-point of the magnetic island both in helical plasmas and in tokamak plasmas during a mode locking phase with strong flow shears at the boundary of the magnetic island. Associated with the stochastization of the magnetic field, the abrupt damping of toroidal flow is observed in LHD. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. Lastly, this observation suggests that this flow damping is due to the change in the non-diffusive term of momentum transport.« less

Bifurcation physics of magnetic islands and stochasticity explored by heat pulse propagation studies in toroidal plasmas

DOE PAGES

Ida, K.; Kobayashi, T.; Yoshinuma, M.; ...

2016-07-29

Bifurcation physics of the magnetic island was investigated using the heat pulse propagation technique produced by the modulation of electron cyclotron heating. There are two types of bifurcation phenomena observed in LHD and DIII-D. One is a bifurcation of the magnetic topology between nested and stochastic fields. The nested state is characterized by the bi-directional (inward and outward) propagation of the heat pulse with slow propagation speed. The stochastic state is characterized by the fast propagation of the heat pulse with electron temperature flattening. The other bifurcation is between magnetic island with larger thermal diffusivity and that with smaller thermalmore » diffusivity. The damping of toroidal flow is observed at the O-point of the magnetic island both in helical plasmas and in tokamak plasmas during a mode locking phase with strong flow shears at the boundary of the magnetic island. Associated with the stochastization of the magnetic field, the abrupt damping of toroidal flow is observed in LHD. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. Lastly, this observation suggests that this flow damping is due to the change in the non-diffusive term of momentum transport.« less

Ion and electron heating characteristics of magnetic reconnection in tokamak plasma merging experiments

NASA Astrophysics Data System (ADS)

Ono, Y.; Tanabe, H.; Yamada, T.; Inomoto, M.; T, Ii; Inoue, S.; Gi, K.; Watanabe, T.; Gryaznevich, M.; Scannell, R.; Michael, C.; Cheng, C. Z.

2012-12-01

Recently, the TS-3 and TS-4 tokamak merging experiments revealed significant plasma heating during magnetic reconnection. A key question is how and where ions and electrons are heated during magnetic reconnection. Two-dimensional measurements of ion and electron temperatures and plasma flow made clear that electrons are heated inside the current sheet mainly by the Ohmic heating and ions are heated in the downstream areas mainly by the reconnection outflows. The outflow kinetic energy is thermalized by the fast shock formation and viscous damping. The magnetic reconnection converts the reconnecting magnetic field energy mostly to the ion thermal energy in the outflow region whose size is much larger than the current sheet size for electron heating. The ion heating energy is proportional to the square of the reconnection magnetic field component B_p^2 . This scaling of reconnection heating indicates the significant ion heating effect of magnetic reconnection, which leads to a new high-field reconnection heating experiment for fusion plasmas.

Counterstreaming beams and flat-top electron distributions observed with Langmuir, Whistler, and compressional Alfvén waves in earth's magnetic tail.

PubMed

Teste, Alexandra; Parks, George K

2009-02-20

Relevant new clues to wave-particle interactions have been obtained in Earth's plasma sheet (PS). The plasma measurements made on Cluster spacecraft show that broadband (approximately 2-6 kHz) electrostatic emissions, in the PS boundary layer, are associated with cold counterstreaming electrons flowing at 5-12x10(3) km s(-1) through hot Maxwellian plasma. In the current sheet (CS), electromagnetic whistler mode waves (approximately 10-80 Hz) and compressional Alfvén waves (<2 Hz) are detected with flat-topped electron distributions whose cutoff speeds are approximately 15-17x10(3) km s(-1). These waves are damped in the central CS where |B|

Plasma regimes in the deep geomagnetic tail - ISEE 3

NASA Astrophysics Data System (ADS)

Bame, S. J.; Anderson, R. C.; Asbridge, J. R.; Baker, D. N.; Feldman, W. C.; Gosling, J. T.; Hones, E. W., Jr.; McComas, D. J.; Zwickl, R. D.

1983-09-01

The spacecraft remained close to or within a previously unexplored part of the distant (60-220 earth radii) geomagnetic tail nearly continuously from January 1 to March 30, 1983. Analysis of the data reveals that all of the plasma regimes identified previously with near-earth measurements (plasma sheet, low-latitude boundary layer, plasma mantle, lobe, and magnetosheath) remain recognizable in the distant tail. These regimes, however, are found to be intermingled in a more chaotic fashion than near the earth. Within the plasma sheet at approximately 200 earth radii, typical flow velocities are about 500 km/s tailward, considerably higher than in the near-earth plasma sheet. Earthward flow within the plasma sheet is observed occasionally, indicating the temporary presence of a neutral line beyond 220 earth radii. Also found are strong bidirectional electron anisotropies throughout much of the distant plasma sheet, boundary layer, and magnetosheath.

Monitoring Temperature in High Enthalpy Arc-heated Plasma Flows using Tunable Diode Laser Absorption Spectroscopy

NASA Technical Reports Server (NTRS)

Martin, Marcel Nations; Chang, Leyen S.; Jeffries, Jay B.; Hanson, Ronald K.; Nawaz, Anuscheh; Taunk, Jaswinder S.; Driver, David M.; Raiche, George

2013-01-01

A tunable diode laser sensor was designed for in situ monitoring of temperature in the arc heater of the NASA Ames IHF arcjet facility (60 MW). An external cavity diode laser was used to generate light at 777.2 nm and laser absorption used to monitor the population of electronically excited oxygen atoms in an air plasma flow. Under the assumption of thermochemical equilibrium, time-resolved temperature measurements were obtained on four lines-of-sight, which enabled evaluation of the temperature uniformity in the plasma column for different arcjet operating conditions.

Plasma rotation and transport in MAST spherical tokamak

NASA Astrophysics Data System (ADS)

Field, A. R.; Michael, C.; Akers, R. J.; Candy, J.; Colyer, G.; Guttenfelder, W.; Ghim, Y.-c.; Roach, C. M.; Saarelma, S.; MAST Team

2011-06-01

The formation of internal transport barriers (ITBs) is investigated in MAST spherical tokamak plasmas. The relative importance of equilibrium flow shear and magnetic shear in their formation and evolution is investigated using data from high-resolution kinetic- and q-profile diagnostics. In L-mode plasmas, with co-current directed NBI heating, ITBs in the momentum and ion thermal channels form in the negative shear region just inside qmin. In the ITB region the anomalous ion thermal transport is suppressed, with ion thermal transport close to the neo-classical level, although the electron transport remains anomalous. Linear stability analysis with the gyro-kinetic code GS2 shows that all electrostatic micro-instabilities are stable in the negative magnetic shear region in the core, both with and without flow shear. Outside the ITB, in the region of positive magnetic shear and relatively weak flow shear, electrostatic micro-instabilities become unstable over a wide range of wave numbers. Flow shear reduces the linear growth rates of low-k modes but suppression of ITG modes is incomplete, which is consistent with the observed anomalous ion transport in this region; however, flow shear has little impact on growth rates of high-k, electron-scale modes. With counter-NBI ITBs of greater radial extent form outside qmin due to the broader profile of E × B flow shear produced by the greater prompt fast-ion loss torque.

Radio-frequency capacitive discharge with flowing liquid electrodes at reduced gas pressures

NASA Astrophysics Data System (ADS)

Gaisin, Al. F.; Son, E. E.; Petryakov, S. Yu.

2017-07-01

Results are presented from experimental studies of the electrophysical and spectral characteristics of the low-temperature plasma of a radio-frequency capacitive discharge excited between two flowing liquid electrodes at gas pressures of 103-105 Pa. The plasma composition, the electron density, and the vibrational and rotational temperatures of gas molecules are estimated. The types and shapes of discharge are described, and the thermal and gas-hydrodynamic processes in the discharge zone are analyzed.

Experimental Characterization of Plasma Detachment from Magnetic Nozzles

NASA Astrophysics Data System (ADS)

Olsen, Christopher Scott

Magnetic nozzles, like Laval nozzles, are observed in several natural systems and have application in areas such as electric propulsion and plasma processing. Plasma flowing through these nozzles is inherently tied to the field lines and must separate for momentum redirection or particle transport to occur. Plasma detachment and associated mechanisms from a magnetic nozzle are investigated. Experimental results are presented from the plume of the VASIMRRTM VX-200 device flowing along an axisymmetric magnetic nozzle and operated at two ion energies to explore momentum dependent detachment. The argon plume expanded into a 150m3 vacuum chamber where the background pressure was low enough that charge-exchange mean-free-paths were longer than experiment scale lengths. This magnetic nozzle system is demonstrated to hydrodynamically scale up to astrophysical plasmas, particularly the solar chromosphere, implying general relevance to many systems. Plasma parameters were mapped over a large spatial range using measurements from multiple plasma diagnostics. The data show that the plume does not follow the magnetic field lines. A mapped integration of the ion flux shows the plume may be divided into three regions where 1) the plume briefly follows the magnetic flux, 2) diverges quadratically before 3) expanding with linear trajectories. Transitioning from region 1→2, the ion flux departs from the magnetic flux suggesting ion detachment. An instability forms in region 2 driving an oscillating electric field that causes ions to expand before enhancing electron cross-field transport through anomalous resistivity. Transitioning from region 2→3 the electric field dissipates, the trajectories linearize, and the plume effectively detaches. A delineation of sub-to-super Alfvenic flow aligns well with the inflection points of the linearization without a change in magnetic topology. The detachment process is best described as a two part process: First, ions detach by a breakdown of the magnetic moment when the quantity |v/fcLB| becomes of order unity. Second, the turbulent electric field enhances electron transport up to a factor of 4+/-1 above collisional diffusion; electron cross-field velocities approximate that of the ions and depart on more centralized field lines. Electrons are believed to detach by breakdown of magnetic moment further downstream in the weaker magnetic field.

Properties of thermal air plasma with admixing of copper and carbon

NASA Astrophysics Data System (ADS)

Fesenko, S.; Veklich, A.; Boretskij, V.; Cressault, Y.; Gleizes, A.; Teulet, Ph

2014-11-01

This paper deals with investigations of air plasma with admixing of copper and carbon. Model plasma source unit with real breaking arc was used for the simulation of real discharges, which can be occurred during sliding of Cu-C composite electrodes on copper wire at electromotive vehicles. The complex technique of plasma property studies is developed. From one hand, the radial profiles of temperature and electron density in plasma of electric arc discharge in air between Cu-C composite and copper electrodes in air flow were measured by optical spectroscopy techniques. From another hand, the radial profiles of electric conductivity of plasma mixture were calculated by solution of energy balance equation. It was assumed that the thermal conductivity of air plasma is not depending on copper or carbon vapor admixtures. The electron density is obtained from electric conductivity profiles by calculation in assumption of local thermodynamic equilibrium in plasma. Computed in such way radial profiles of electron density in plasma of electric arc discharge in air between copper electrodes were compared with experimentally measured profiles. It is concluded that developed techniques of plasma diagnostics can be reasonably used in investigations of thermal plasma with copper and carbon vapors.

Measurement of xenon plasma properties in an ion thruster using laser Thomson scattering technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamamoto, N.; Tomita, K.; Sugita, K.

2012-07-15

This paper reports on the development of a method for measuring xenon plasma properties using the laser Thomson scattering technique, for application to ion engine system design. The thresholds of photo-ionization of xenon plasma were investigated and the number density of metastable atoms, which are photo-ionized by a probe laser, was measured using laser absorption spectroscopy, for several conditions. The measured threshold energy of the probe laser using a plano-convex lens with a focal length of 200 mm was 150 mJ for a xenon mass flow rate of 20 {mu}g/s and incident microwave power of 6 W; the probe lasermore » energy was therefore set as 80 mJ. Electron number density was found to be (6.2 {+-} 0.4) Multiplication-Sign 10{sup 17} m{sup -3} and electron temperature was found to be 2.2 {+-} 0.4 eV at a xenon mass flow rate of 20 {mu}g/s and incident microwave power of 6 W. The threshold of the probe laser intensity against photo-ionization in a miniature xenon ion thruster is almost constant for various mass flow rates, since the ratio of population of the metastable atoms to the electron number density is little changed.« less

Electron Heating by the Ion Cyclotron Instability in Collisionless Accretion Flows. I. Compression-driven Instabilities and the Electron Heating Mechanism

NASA Astrophysics Data System (ADS)

Sironi, Lorenzo; Narayan, Ramesh

2015-02-01

In systems accreting well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the innermost regions of the disk is believed to be collisionless and have two temperatures, with the ions substantially hotter than the electrons. However, whether a collisionless faster-than-Coulomb energy transfer mechanism exists in two-temperature accretion flows is still an open question. We study the physics of electron heating during the growth of ion velocity-space instabilities by means of multidimensional, fully kinetic, particle-in-cell (PIC) simulations. A background large-scale compression—embedded in a novel form of the PIC equations—continuously amplifies the field. This constantly drives a pressure anisotropy P > P ∥ because of the adiabatic invariance of the particle magnetic moments. We find that, for ion plasma beta values β0i ~ 5-30 appropriate for the midplane of low-luminosity accretion flows (here, β0i is the ratio of ion thermal pressure to magnetic pressure), mirror modes dominate if the electron-to-proton temperature ratio is T 0e /T 0i >~ 0.2, whereas for T 0e /T 0i <~ 0.2 the ion cyclotron instability triggers the growth of strong Alfvén-like waves, which pitch-angle scatter the ions to maintain marginal stability. We develop an analytical model of electron heating during the growth of the ion cyclotron instability, which we validate with PIC simulations. We find that for cold electrons (β0e <~ 2 me /mi , where β0e is the ratio of electron thermal pressure to magnetic pressure), the electron energy gain is controlled by the magnitude of the E-cross-B velocity induced by the ion cyclotron waves. This term is independent of the initial electron temperature, so it provides a solid energy floor even for electrons starting with extremely low temperatures. On the other hand, the electron energy gain for β0e >~ 2 me /mi —governed by the conservation of the particle magnetic moment in the growing fields of the instability—is proportional to the initial electron temperature, and it scales with the magnetic energy of ion cyclotron waves. Our results have implications for two-temperature accretion flows as well as for solar wind and intracluster plasmas.

[The Spectral Analysis of Laser-Induced Plasma in Laser Welding with Various Protecting Conditions].

PubMed

Du, Xiao; Yang, Li-jun; Liu, Tong; Jiao, Jiao; Wang, Hui-chao

2016-01-01

The shielding gas plays an important role in the laser welding process and the variation of the protecting conditions has an obvious effect on the welding quality. This paper studied the influence of the change of protecting conditions on the parameters of laser-induced plasma such as electron temperature and electron density during the laser welding process by designing some experiments of reducing the shielding gas flow rate step by step and simulating the adverse conditions possibly occurring in the actual Nd : YAG laser welding process. The laser-induced plasma was detected by a fiber spectrometer to get the spectral data. So the electron temperature of laser-induced plasma was calculated by using the method of relative spectral intensity and the electron density by the Stark Broadening. The results indicated that the variation of protecting conditions had an important effect on the electron temperature and the electron density in the laser welding. When the protecting conditions were changed, the average electron temperature and the average electron density of the laser-induced plasma would change, so did their fluctuation range. When the weld was in a good protecting condition, the electron temperature, the electron density and their fluctuation were all low. Otherwise, the values would be high. These characteristics would have contribution to monitoring the process of laser welding.

In situ measurements of the plasma bulk velocity near the Io flux tube

NASA Technical Reports Server (NTRS)

Barnett, A.

1985-01-01

The flow around the Io flux tube was studied by analyzing the eleven spectra taken by the Voyager 1 Plasma Science (PLS) experiment in its vicinity. The bulk plasma parameters were determined using a procedure that uses the full response function of the instrument and the data in all four PLS sensors. The mass density of the plasma in the vicinity of Io is found to be 22,500 + or - 2,500 amu/cu cm and its electron density is found to be 1500 + or - 200/cu cm. The Alfven speed was determined using three independent methods; the values obtained are consistent and taken together yield V sub A = 300 + or - 50 km/sec, corresponding to an Alfven Mach number of 0.19 + or - 0.02. For the flow pattern, good agreement was found with the model of Neubauer (1980), and it was concluded that the plasma flows around the flux tube with a pattern similar to the flow of an incompressible fluid around a long cylinder obstacle of radius 1.26 + or - 0.1 R sub Io.

Formation of ECR Plasma in a Dielectric Plasma Guide under Self-Excitation of a Standing Ion-Acoustic Wave

NASA Astrophysics Data System (ADS)

Balmashnov, A. A.; Kalashnikov, A. V.; Kalashnikov, V. V.; Stepina, S. P.; Umnov, A. M.

2018-01-01

The formation of a spatially localized plasma with a high brightness has been experimentally observed in a dielectric plasma guide under the electron cyclotron resonance discharge at the excitation of a standing ion-acoustic wave. The results obtained show the possibility of designing compact high-intensity radiation sources with a spectrum determined by the working gas or gas mixture type, high-intensity chemically active particle flow sources, and plasma thrusters for correcting orbits of light spacecraft.

Computational hydrodynamics and optical performance of inductively-coupled plasma adaptive lenses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mortazavi, M.; Urzay, J., E-mail: jurzay@stanford.edu; Mani, A.

2015-06-15

This study addresses the optical performance of a plasma adaptive lens for aero-optical applications by using both axisymmetric and three-dimensional numerical simulations. Plasma adaptive lenses are based on the effects of free electrons on the phase velocity of incident light, which, in theory, can be used as a phase-conjugation mechanism. A closed cylindrical chamber filled with Argon plasma is used as a model lens into which a beam of light is launched. The plasma is sustained by applying a radio-frequency electric current through a coil that envelops the chamber. Four different operating conditions, ranging from low to high powers andmore » induction frequencies, are employed in the simulations. The numerical simulations reveal complex hydrodynamic phenomena related to buoyant and electromagnetic laminar transport, which generate, respectively, large recirculating cells and wall-normal compression stresses in the form of local stagnation-point flows. In the axisymmetric simulations, the plasma motion is coupled with near-wall axial striations in the electron-density field, some of which propagate in the form of low-frequency traveling disturbances adjacent to vortical quadrupoles that are reminiscent of Taylor-Görtler flow structures in centrifugally unstable flows. Although the refractive-index fields obtained from axisymmetric simulations lead to smooth beam wavefronts, they are found to be unstable to azimuthal disturbances in three of the four three-dimensional cases considered. The azimuthal striations are optically detrimental, since they produce high-order angular aberrations that account for most of the beam wavefront error. A fourth case is computed at high input power and high induction frequency, which displays the best optical properties among all the three-dimensional simulations considered. In particular, the increase in induction frequency prevents local thermalization and leads to an axisymmetric distribution of electrons even after introduction of spatial disturbances. The results highlight the importance of accounting for spatial effects in the numerical computations when optical analyses of plasma lenses are pursued in this range of operating conditions.« less

Asymmetrical flow field-flow fractionation coupled with multiple detections: A complementary approach in the characterization of egg yolk plasma.

PubMed

Dou, Haiyang; Li, Yueqiu; Choi, Jaeyeong; Huo, Shuying; Ding, Liang; Shen, Shigang; Lee, Seungho

2016-09-23

The capability of asymmetrical flow field-flow fractionation (AF4) coupled with UV/VIS, multiangle light scattering (MALS) and quasi-elastic light scattering (QELS) (AF4-UV-MALS-QELS) for separation and characterization of egg yolk plasma was evaluated. The accuracy of hydrodynamic radius (Rh) obtained from QELS and AF4 theory (using both simplified and full expression of AF4 retention equations) was discussed. The conformation of low density lipoprotein (LDL) and its aggregates in egg yolk plasma was discussed based on the ratio of radius of gyration (Rg) to Rh together with the results from bio-transmission electron microscopy (Bio-TEM). The results indicate that the full retention equation is more relevant than simplified version for the Rh determination at high cross flow rate. The Rh from online QELS is reliable only at a specific range of sample concentration. The effect of programmed cross flow rate (linear and exponential decay) on the analysis of egg yolk plasma was also investigated. It was found that the use of an exponentially decaying cross flow rate not only reduces the AF4 analysis time of the egg yolk plasma, but also provides better resolution than the use of either a constant or linearly decaying cross flow rate. A combination of an exponentially decaying cross flow AF4-UV-MALS-QELS and the utilization of full retention equation was proved to be a useful method for the separation and characterization of egg yolk plasma. Copyright © 2016 Elsevier B.V. All rights reserved.

Flow and dynamo measurements during the coaxial helicity injection on HIST

NASA Astrophysics Data System (ADS)

Ando, K.; Higashi, T.; Nakatsuka, M.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

2009-11-01

The current drive by Coaxial Helicity Injection (CHI-CD) was performed on HIST in a wide range of configurations from high-q ST to low-q ST and spheromak generated by the utilization of the toroidal field. It is a key issue to investigate the dynamo mechanism required to maintain each configuration. To identify the detail mechanisms, it is needed to manifest a role of plasma flows in the CHI-CD. For this purpose, we have measured the ion flow and the dynamo electric field using an ion Doppler spectrometer (IDS) system, a Mach probe and a dynamo probe. The new dynamo probe consists of 3-axis Mach probes and magnetic pick-up coils. The flow measurements have shown that the intermittent generation of the flow is correlated to the fluctuation seen on the electron density and current signals during the driven phase. At this time, the toroidal direction of the ion flow in the central open flux column is opposite to that of the toroidal current there, i.e. the same direction as electrons. After the plasma enters to the resistive decay phase, the toroidal flow tends to reverse to the same direction as the toroidal current. The results are consistent with the model of the repetitive plasmoid ejection and coalescence proposed for CHI-CD. The plasma jet emanating from the gun source and magnetic field generations through reconnection during the driven phase is well reflected in the 3D MHD simulation.

Ion Energy Distribution Studies of Ions and Radicals in an Ar/H2 Radio Frequency Magnetron Discharge During a-Si:H Deposition Using Energy-Resolved Mass Spectrometry

NASA Astrophysics Data System (ADS)

Mensah, Samuel; Abu-Safe, Husam; Naseem, Hameed; Gordon, Matt

2012-02-01

Ion energy distributions of sputtered Si particles have been measured by an energy-resolved mass spectrometer, and we correlate the results with measured thin film properties. The plasmas have been generated in a conventional magnetron chamber powered at 150W, 13.56MHz at hydrogen flow rates ranging from 0-25sccm. Various Hn^+, SiHn^+, SiHn fragments (with n = 1, 2, 3) together with Ar^+ and ArH^+ species were detected in the discharge. The most important species for the film deposition is SiHn with n = 0,1,2, and H fragments affect the hydrogen content in the material. The flux of Ar^+ decreases and that of ArH^+ increases when the hydrogen flow rate was increased. However both fluxes saturate at hydrogen flow rates above 15sccm. Plasma parameters, such as plasma potential Vp, electron density ne and electron energy Te, are measured with the Langmuir probe. The ion energy distribution (IED) of all prominent species in the plasma is measured with an energy resolved mass analyzer. The plasma parameters decreased with increasing hydrogen flow rate; Vp, ne and Te decreased from 36.5V, 7.2x10^15 m-3, 5.6eV to 32.8, 2.2x10^15m-3 and 3.8eV respectively. The ion energy of the heavy species, Ar, Ar^+, ArH, ArH^+, SiHn and SiHn^+ radicals have ion energies comparable to the plasma potential. Analysis of the IEDs shows an inter-dependence of the species and their contribution to the thin film growth and properties.

Coating of plasma polymerized film

NASA Technical Reports Server (NTRS)

Morita, S.; Ishibashi, S.

1980-01-01

Plasma polymerized thin film coating and the use of other coatings is suggested for passivation film, thin film used for conducting light, and solid body lubrication film of dielectrics of ultra insulators for electrical conduction, electron accessories, etc. The special features of flow discharge development and the polymerized film growth mechanism are discussed.

Three-dimensional multi-fluid simulations of Titan's interaction with Saturn's magnetosphere: Comparisons with Cassini's T55 flyby

NASA Astrophysics Data System (ADS)

Snowden, D.; Winglee, R.

2013-08-01

We describe a new multi-fluid model of Titan's interaction with Saturn's magnetosphere that includes finer resolution in Titan's ionosphere, photoionization, electron-impact ionization, dissociative recombination, and ion-neutral coupling in the momentum and energy equations. We compare simulation results to data from Cassini's T55 flyby to show that including magnetospheric electron-impact ionization in Titan's nightside ionosphere is necessary to calculate electron densities, electron temperatures, and ion velocities that are consistent with Cassini observations. However, similar to other studies, we find that the electron-impact ionization rate calculated by the model needs to be significantly reduced to produce an electron density that is in agreement with the observations. We also find that an upstream plasma flow with significant components northward and radially outward from Saturn is needed to reproduce the gradual increase in electron density observed during the ingress portion of T55. This suggests that Titan was in a nonideal environment with a plasma flow oriented away from the direction of corotation during T55 and likely during the subsequent flybys T56, T57, T58, and T59 when similar electron density enhancements were seen on the inbound portion of Cassini's trajectory.

Analytical performance of a low-gas-flow torch optimized for inductively coupled plasma atomic emission spectrometry

USGS Publications Warehouse

Montaser, A.; Huse, G.R.; Wax, R.A.; Chan, S.-K.; Golightly, D.W.; Kane, J.S.; Dorrzapf, A.F.

1984-01-01

An inductively coupled Ar plasma (ICP), generated in a lowflow torch, was investigated by the simplex optimization technique for simultaneous, multielement, atomic emission spectrometry (AES). The variables studied included forward power, observation height, gas flow (outer, intermediate, and nebulizer carrier) and sample uptake rate. When the ICP was operated at 720-W forward power with a total gas flow of 5 L/min, the signal-to-background ratios (S/B) of spectral lines from 20 elements were either comparable or inferior, by a factor ranging from 1.5 to 2, to the results obtained from a conventional Ar ICP. Matrix effect studies on the Ca-PO4 system revealed that the plasma generated in the low-flow torch was as free of vaporizatton-atomizatton interferences as the conventional ICP, but easily ionizable elements produced a greater level of suppression or enhancement effects which could be reduced at higher forward powers. Electron number densities, as determined via the series until line merging technique, were tower ht the plasma sustained in the low-flow torch as compared with the conventional ICP. ?? 1984 American Chemical Society.

Distinctive plume formation in atmospheric Ar and He plasmas in microwave frequency band and suitability for biomedical applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, H. Wk.; Kang, S. K.; Won, I. H.

Distinctive discharge formation in atmospheric Ar and He plasmas was observed in the microwave frequency band using coaxial transmission line resonators. Ar plasmas formed a plasma plume whereas He formed only confined plasmas. As the frequency increased from 0.9 GHz to 2.45 GHz, the Ar plasma exhibited contraction and filamentation, and the He plasmas were constricted. Various powers and gas flow rates were applied to identify the effect of the electric field and gas flow rate on plasma plume formation. The He plasmas were more strongly affected by the electric field than the Ar plasmas. The breakdown and sustain powersmore » yielded opposite results from those for low-frequency plasmas (∼kHz). The phenomena could be explained by a change in the dominant ionization process with increasing frequency. Penning ionization and the contribution of secondary electrons in sheath region reduced as the frequency increased, leading to less efficient ionization of He because its ionization and excitation energies are higher than those of Ar. The emission spectra showed an increase in the NO and N{sub 2} second positive band in both the Ar and He plasmas with increasing frequency whereas the hydroxyl radical and atomic O peaks did not increase with increasing frequency but were highest at particular frequencies. Further, the frequency effect of properties such as the plasma impedance, electron density, and device efficiency were presented. The study is expected to be helpful for determining the optimal conditions of plasma systems for biomedical applications.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tierno, S. P., E-mail: sp.tierno@upm.es; Donoso, J. M.; Domenech-Garret, J. L.

The interaction between an electron emissive wall, electrically biased in a plasma, is revisited through a simple fluid model. We search for realistic conditions of the existence of a non-monotonic plasma potential profile with a virtual cathode as it is observed in several experiments. We mainly focus our attention on thermionic emission related to the operation of emissive probes for plasma diagnostics, although most conclusions also apply to other electron emission processes. An extended Bohm criterion is derived involving the ratio between the two different electron densities at the potential minimum and at the background plasma. The model allows amore » phase-diagram analysis, which confirms the existence of the non-monotonic potential profiles with a virtual cathode. This analysis shows that the formation of the potential well critically depends on the emitted electron current and on the velocity at the sheath edge of cold ions flowing from the bulk plasma. As a consequence, a threshold value of the governing parameter is required, in accordance to the physical nature of the electron emission process. The latter is a threshold wall temperature in the case of thermionic electrons. Experimental evidence supports our numerical calculations of this threshold temperature. Besides this, the potential well becomes deeper with increasing electron emission, retaining a fraction of the released current which limits the extent of the bulk plasma perturbation. This noninvasive property would explain the reliable measurements of plasma potential by using the floating potential method of emissive probes operating in the so-called strong emission regime.« less

Generation of waves in the Venus mantle by the ion acoustic beam instability

NASA Technical Reports Server (NTRS)

Huba, J. D.

1993-01-01

The ion acoustic beam instability is suggested as a mechanism to produce wave turbulence observed in the Venus mantle at frequencies 100 Hz and 730 Hz. The plasma is assumed to consist of a stationary cold O(+) ion plasma and a flowing, shocked solar wind plasma. The O(+) ions appear as a beam relative to the flowing ionosheath plasma which provides the free energy to drive the instability. The plasma is driven unstable by inverse electron Landau damping of an ion acoustic wave associated with the cold ionospheric O(+) ions. The instability can directly generate the observed 100 Hz waves in the Venus mantle as well as the observed 730 Hz waves through the Doppler shift of the frequency caused by the satellite motion.

Towards an understanding of flows in avalanche transport phenomena

NASA Astrophysics Data System (ADS)

Jin, Suying; Ramadan, Nikolas; van Compernolle, Bart; Poulos, Matt J.; Morales, George J.

2017-10-01

Recent heat transport experiments conducted in the Large Plasma Device (LAPD) at UCLA, studying avalanche phenomena at steep cross-magnetic field pressure gradients, suggest that flows play a critical role in the evolution of transport phenomena, motivating further characterization. A ring shaped electron beam source injects sub-ionization energy electrons along the strong background magnetic field within a larger quiescent plasma, creating a hollow, high pressure filament. Two distinct regimes are observed as the density decays; the first characterized by multiple small avalanches producing sudden relaxations of the pressure profile which then recovers under continued heating, and the second signaled by a permanent collapse of the density profile after a global avalanche event, then dominated by drift-Alfven waves. The source is modified from previous experiments to gain active control of the flows by controlling the bias between the emitting ring and surrounding carbon masks. The results of flow measurements obtained using a Mach probe and Langmuir/emissive probe are here presented and compared. An analytical model for the behavior of the electron beam source is also in development. Sponsored by NSF Grant 1619505 and by DOE/NSF at BaPSF.

Applying the new HIT results to tokamak and solar plasmas

NASA Astrophysics Data System (ADS)

Jarboe, Thomas; Sutherland, Derek; Hossack, Aaron; Nelson, Brian; Morgan, Kyle; Chris, Hansen; Benedett, Thomas; Everson, Chris; Penna, James

2016-10-01

Understanding sustainment of stable equilibria with helicity injection in HIT-SI has led to a simple picture of several tokamak features. Perturbations cause a viscous-like force on the current that flattens the λ profile, which sustains and stabilizes the equilibrium. An explanation of the mechanism is based on two properties of stable, ideal, two-fluid, magnetized plasma. First, the electron fluid is frozen to magnetic fields and, therefore, current flow is also magnetic field flow. Second, for a stable equilibrium the structure perpendicular to the flux surface resists deformation. Thus toroidal current is from electrons frozen in nested, rotating resilient flux surfaces. Only symmetric flux surfaces allow free differential current flow. Perturbations cause interference of the flux surfaces. Thus, perturbations cause forces that oppose differential electron rotation and forced differential flow produces a symmetrizing force against perturbations and instability. This mechanism can explain the level of field error that spoils tokamak performance and the rate of poloidal flux loss in argon-induced disruptions in DIII-D. This new understanding has led to an explanation of the source of the solar magnetic fields and the power source for the chromosphere, solar wind and corona. Please place in spheromak and FRC section with other HIT posters.

Dielectric barrier structure with hollow electrodes and its recoil effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Shuang; Chen, Qunzhi; Liu, Jiahui

2015-06-15

A dielectric barrier structure with hollow electrodes (HEDBS), in which gas flow oriented parallel to the electric field, was proposed. Results showed that with this structure, air can be effectively ignited, forming atmospheric low temperature plasma, and the proposed HEDBS could achieve much higher electron density (5 × 10{sup 15}/cm{sup 3}). It was also found that the flow condition, including outlet diameter and flow rate, played a key role in the evolution of electron density. Optical emission spectroscopy diagnostic results showed that the concentration of reactive species had the same variation trend as the electron density. The simulated distribution of discharge gasmore » flow indicated that the HEDBS had a strong recoil effect on discharge gas, and could efficiently promote generating electron density as well as reactive species.« less

Simulation of Mach Probes in Non-Uniform Magnetized Plasmas: the Influence of a Background Density Gradient

NASA Astrophysics Data System (ADS)

Haakonsen, Christian Bernt; Hutchinson, Ian H.

2013-10-01

Mach probes can be used to measure transverse flow in magnetized plasmas, but what they actually measure in strongly non-uniform plasmas has not been definitively established. A fluid treatment in previous work has suggested that the diamagnetic drifts associated with background density and temperature gradients affect transverse flow measurements, but detailed computational study is required to validate and elaborate on those results; it is really a kinetic problem, since the probe deforms and introduces voids in the ion and electron distribution functions. A new code, the Plasma-Object Simulator with Iterated Trajectories (POSIT) has been developed to self-consistently compute the steady-state six-dimensional ion and electron distribution functions in the perturbed plasma. Particle trajectories are integrated backwards in time to the domain boundary, where arbitrary background distribution functions can be specified. This allows POSIT to compute the ion and electron density at each node of its unstructured mesh, update the potential based on those densities, and then iterate until convergence. POSIT is used to study the impact of a background density gradient on transverse Mach probe measurements, and the results compared to the previous fluid theory. C.B. Haakonsen was supported in part by NSF/DOE Grant No. DE-FG02-06ER54512, and in part by an SCGF award administered by ORISE under DOE Contract No. DE-AC05-06OR23100.

Anticipated Electrical Environment Within Permanently Shadowed Lunar Craters

NASA Technical Reports Server (NTRS)

Farrell, W. M.; Stubbs, T. J.; Halekas, J. S.; Killen, R. M.; Delory, G. T.; Collier, M. R.; Vondrak, R. R.

2010-01-01

Shadowed locations ncar the lunar poles arc almost certainly electrically complex regions. At these locations near the terminator, the local solar wind flows nearly tangential to the surface and interacts with large-scale topographic features such as mountains and deep large craters, In this work, we study the solar wind orographic effects from topographic obstructions along a rough lunar surface, On the leeward side of large obstructions, plasma voids are formed in the solar wind because of the absorption of plasma on the upstream surface of these obstacles, Solar wind plasma expands into such voids) producing an ambipolar potential that diverts ion flow into the void region. A surface potential is established on these leeward surfaces in order to balance the currents from the expansion-limited electron and ion populations, Wc find that there arc regions ncar the leeward wall of the craters and leeward mountain faces where solar wind ions cannot access the surface, leaving an electron-rich plasma previously identified as an "electron cloud." In this case, some new current is required to complete the closure for current balance at the surface, and we propose herein that lofted negatively charged dust is one possible (nonunique) compensating current source. Given models for both ambipolar and surface plasma processes, we consider the electrical environment around the large topographic features of the south pole (including Shoemaker crater and the highly varied terrain near Nobile crater), as derived from Goldstone radar data, We also apply our model to moving and stationary objects of differing compositions located on the surface and consider the impact of the deflected ion flow on possible hydrogen resources within the craters

A review of studies on ion thruster beam and charge-exchange plasmas

NASA Technical Reports Server (NTRS)

Carruth, M. R., Jr.

1982-01-01

Various experimental and analytical studies of the primary beam and charge-exchange plasmas of ion thrusters are reviewed. The history of plasma beam research is recounted, emphasizing experiments on beam neutralization, expansion of the beam, and determination of beam parameters such as electron temperature, plasma density, and plasma potential. The development of modern electron bombardment ion thrusters is treated, detailing experimental results. Studies on charge-exchange plasma are discussed, showing results such as the relationship between neutralizer emission current and plasma beam potential, ion energies as a function of neutralizer bias, charge-exchange ion current collected by an axially moving Faraday cup-RPA for 8-cm and 30-cm ion thrusters, beam density and potential data from a 15-cm ion thruster, and charge-exchange ion flow around a 30-cm thruster. A 20-cm thruster electrical configuration is depicted and facility effects are discussed. Finally, plasma modeling is covered in detail for plasma beam and charge-exchange plasma.

Floating potential of emitting surfaces in plasmas with respect to the space potential

DOE PAGES

Kraus, B. F.; Raitses, Y.

2018-03-19

The potential difference between a floating emitting surface and the plasma surrounding it has been described by several sheath models, including the space-charge-limited sheath, the electron sheath with high emission current, and the inverse sheath produced by charge-exchange ion trapping. Our measurements reveal that each of these models has its own regime of validity. We determine the potential of an emissive filament relative to the plasma potential, emphasizing variations in emitted current density and neutral particle density. The potential of a filament in a diffuse plasma is first shown to vanish, consistent with the electron sheath model and increasing electronmore » emission. In a denser plasma with ample neutral pressure, the floating filament potential is positive, as predicted by a derived ion trapping condition. In conclusion, the filament floated negatively in a third plasma, where flowing ions and electrons and nonnegligible electric fields may have disrupted ion trapping. Depending on the regime chosen, emitting surfaces can float positively or negatively with respect to the plasma potential.« less

Floating potential of emitting surfaces in plasmas with respect to the space potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kraus, B. F.; Raitses, Y.

The potential difference between a floating emitting surface and the plasma surrounding it has been described by several sheath models, including the space-charge-limited sheath, the electron sheath with high emission current, and the inverse sheath produced by charge-exchange ion trapping. Our measurements reveal that each of these models has its own regime of validity. We determine the potential of an emissive filament relative to the plasma potential, emphasizing variations in emitted current density and neutral particle density. The potential of a filament in a diffuse plasma is first shown to vanish, consistent with the electron sheath model and increasing electronmore » emission. In a denser plasma with ample neutral pressure, the floating filament potential is positive, as predicted by a derived ion trapping condition. In conclusion, the filament floated negatively in a third plasma, where flowing ions and electrons and nonnegligible electric fields may have disrupted ion trapping. Depending on the regime chosen, emitting surfaces can float positively or negatively with respect to the plasma potential.« less

Characterization of high flux magnetized helium plasma in SCU-PSI linear device

NASA Astrophysics Data System (ADS)

Xiaochun, MA; Xiaogang, CAO; Lei, HAN; Zhiyan, ZHANG; Jianjun, WEI; Fujun, GOU

2018-02-01

A high-flux linear plasma device in Sichuan University plasma-surface interaction (SCU-PSI) based on a cascaded arc source has been established to simulate the interactions between helium and hydrogen plasma with the plasma-facing components in fusion reactors. In this paper, the helium plasma has been characterized by a double-pin Langmuir probe. The results show that the stable helium plasma beam with a diameter of 26 mm was constrained very well at a magnetic field strength of 0.3 T. The core density and ion flux of helium plasma have a strong dependence on the applied current, magnetic field strength and gas flow rate. It could reach an electron density of 1.2 × 1019 m-3 and helium ion flux of 3.2 × 1022 m-2 s-1, with a gas flow rate of 4 standard liter per minute, magnetic field strength of 0.2 T and input power of 11 kW. With the addition of -80 V applied to the target to increase the helium ion energy and the exposure time of 2 h, the flat top temperature reached about 530 °C. The different sizes of nanostructured fuzz on irradiated tungsten and molybdenum samples surfaces under the bombardment of helium ions were observed by scanning electron microscopy. These results measured in the SCU-PSI linear device provide a reference for International Thermonuclear Experimental Reactor related PSI research.

Sheath energy transmission in a collisional plasma with collisionless sheath

DOE PAGES

Tang, Xian-Zhu; Guo, Zehua

2015-10-16

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 also 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.

Dielectric response in Bloch’s hydrodynamic model of an electron-ion plasma

NASA Astrophysics Data System (ADS)

Ishikawa, K.; Felderhof, B. U.

The linear response of an electron-ion plasma to an applied oscillating electric field is studied within the framework of Bloch’s classical hydrodynamic model. The ions are assumed to be fixed in space and distributed according to a known probability distribution. The linearized equations of motion for electron density and flow velocity are studied with the aid of a multiple scattering analysis and cluster expansion. This allows systematic reduction of the many-ion problem to a composition of few-ion problems, and shows how the longitudinal dielectric response function can in principle be calculated.

Impact of impurities on zonal flow driven by trapped electron mode turbulence

NASA Astrophysics Data System (ADS)

Guo, Weixin; Wang, Lu; Zhuang, Ge

2017-12-01

The impact of impurities on the generation of zonal flow (ZF) driven by collisonless trapped electron mode turbulence in deuterium (D)-tritium (T) plasmas is investigated. An expression for ZF growth rate with impurities is derived by balancing the ZF potential shielded by polarization effects and the ZF modulated radial turbulent current. Then, it is shown that the maximum normalized ZF growth rate is reduced by the presence of fully ionized non-trace light impurities with relatively flat density profile, and slightly reduced by highly ionized trace tungsten, while the maximum normalized ZF growth rate can be enhanced by fully ionized non-trace light impurities with relatively steep density profile. In particular, the effects of high temperature helium from D-T reaction on ZF depend on the temperature ratio between electrons and high temperature helium. The possible relevance of our findings to recent experimental results and future burning plasmas is also discussed.

Plasma Flowfields Around Low Earth Orbit Objects: Aerodynamics to Underpin Orbit Predictions

NASA Astrophysics Data System (ADS)

Capon, Christopher; Boyce, Russell; Brown, Melrose

2016-07-01

Interactions between orbiting bodies and the charged space environment are complex. The large variation in passive body parameters e.g. size, geometry and materials, makes the plasma-body interaction in Low Earth Orbit (LEO) a region rich in fundamental physical phenomena. The aerodynamic interaction of LEO orbiting bodies with the neutral environment constitutes the largest non-conservative force on the body. However in general, study of the LEO plasma-body interaction has not been concerned with external flow physics, but rather with the effects on surface charging. The impact of ionospheric flow physics on the forces on space debris (and active objects) is not well understood. The work presented here investigates the contribution that plasma-body interactions have on the flow structure and hence on the total atmospheric force vector experienced by a polar orbiting LEO body. This work applies a hybrid Particle-in-Cell (PIC) - Direct Simulation Monte Carlo (DSMC) code, pdFoam, to self-consistently model the electrostatic flowfield about a cylinder with a uniform, fixed surface potential. Flow conditions are representative of the mean conditions experienced by the Earth Observing Satellite (EOS) based on the International Reference Ionosphere model (IRI-86). The electron distribution function is represented by a non-linear Boltzmann electron fluid and ion gas-surface interactions are assumed to be that of a neutralising, conducting, thermally accommodating solid wall with diffuse reflections. The variation in flowfield and aerodynamic properties with surface potential at a fixed flow condition is investigated, and insight into the relative contributions of charged and neutral species to the flow physics experienced by a LEO orbiting body is provided. This in turn is intended to help improve the fidelity of physics-based orbit predictions for space debris and other near-Earth space objects.

Efficiency of plasma actuator ionization in shock wave modification in a rarefied supersonic flow over a flat plate

NASA Astrophysics Data System (ADS)

Joussot, Romain; Lago, Viviana; Parisse, Jean-Denis

2014-12-01

This paper describes experimental and numerical investigations focused on the shock wave modification, induced by a dc glow discharge, of a Mach 2 flow under rarefied regime. The model under investigation is a flat plate equipped with a plasma actuator composed of two electrodes. The glow discharge is generated by applying a negative potential to the upstream electrode, enabling the creation of a weakly ionized plasma. The natural flow (i.e. without the plasma) exhibits a thick laminar boundary layer and a shock wave with a hyperbolic shape. Images of the flow obtained with an ICCD camera revealed that the plasma discharge induces an increase in the shock wave angle. Thermal effects (volumetric, and at the surface) and plasma effects (ionization, and thermal non-equilibrium) are the most relevant processes explaining the observed modifications. The effect induced by the heating of the flat plate surface is studied experimentally by replacing the upstream electrode by a heating element, and numerically by modifying the thermal boundary condition of the model surface. The results show that for a similar temperature distribution over the plate surface, modifications induced by the heating element are lower than those produced by the plasma. This difference shows that other effects than purely thermal effects are involved with the plasma actuator. Measurements of the electron density with a Langmuir probe highlight the fact that the ionization degree plays an important role into the modification of the flow. The gas properties, especially the isentropic exponent, are indeed modified by the plasma above the actuator and upstream the flat plate. This leads to a local modification of the flow conditions, inducing an increase in the shock wave angle.

Probes, Moons, and Kinetic Plasma Wakes

NASA Astrophysics Data System (ADS)

Hutchinson, I. H.; Malaspina, D.; Zhou, C.

2017-10-01

Nonmagnetic objects as varied as probes in tokamaks or moons in space give rise to flowing plasma wakes in which strong distortions of the ion and electron velocity distributions cause electrostatic instabilities. Non-linear phenomena such as electron holes are then produced. Historic probe theory largely ignores the resulting unstable character of the wake, but since we can now simulate computationally the non-linear wake phenomena, a timely challenge is to reassess the influence of these instabilities both on probe measurements and on the wakes themselves. Because the electron instability wavelengths are very short (typically a few Debye-lengths), controlled laboratory experiments face serious challenges in diagnosing them. That is one reason why they have long been neglected as an influence in probe interpretation. Space-craft plasma observations, by contrast, easily obtain sub-Debye-length resolution, but have difficulty with larger-scale reconstruction of the plasma spatial variation. In addition to surveying our developing understanding of wakes in magnetized plasmas, ongoing analysis of Artemis data concerning electron holes observed in the solar-wind lunar wake will be featured. Work partially supported by NASA Grant NNX16AG82G.

Observation of trapped-electron-mode microturbulence in reversed field pinch plasmas

NASA Astrophysics Data System (ADS)

Duff, J. R.; Williams, Z. R.; Brower, D. L.; Chapman, B. E.; Ding, W. X.; Pueschel, M. J.; Sarff, J. S.; Terry, P. W.

2018-01-01

Density fluctuations in the large-density-gradient region of improved confinement Madison Symmetric Torus reversed field pinch (RFP) plasmas exhibit multiple features that are characteristic of the trapped-electron mode (TEM). Core transport in conventional RFP plasmas is governed by magnetic stochasticity stemming from multiple long-wavelength tearing modes. Using inductive current profile control, these tearing modes are reduced, and global confinement is increased to that expected for comparable tokamak plasmas. Under these conditions, new short-wavelength fluctuations distinct from global tearing modes appear in the spectrum at a frequency of f ˜ 50 kHz, which have normalized perpendicular wavenumbers k⊥ρs≲ 0.2 and propagate in the electron diamagnetic drift direction. They exhibit a critical-gradient threshold, and the fluctuation amplitude increases with the local electron density gradient. These characteristics are consistent with predictions from gyrokinetic analysis using the Gene code, including increased TEM turbulence and transport from the interaction of remnant tearing magnetic fluctuations and zonal flow.

Electron cooling and finite potential drop in a magnetized plasma expansion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martinez-Sanchez, M.; Navarro-Cavallé, J.; Ahedo, E.

2015-05-15

The steady, collisionless, slender flow of a magnetized plasma into a surrounding vacuum is considered. The ion component is modeled as mono-energetic, while electrons are assumed Maxwellian upstream. The magnetic field has a convergent-divergent geometry, and attention is restricted to its paraxial region, so that 2D and drift effects are ignored. By using the conservation of energy and magnetic moment of particles and the quasi-neutrality condition, the ambipolar electric field and the distribution functions of both species are calculated self-consistently, paying attention to the existence of effective potential barriers associated to magnetic mirroring. The solution is used to find themore » total potential drop for a set of upstream conditions, plus the axial evolution of various moments of interest (density, temperatures, and heat fluxes). The results illuminate the behavior of magnetic nozzles, plasma jets, and other configurations of interest, showing, in particular, in the divergent plasma the collisionless cooling of electrons, and the generation of collisionless electron heat fluxes.« less

Dynamics of streaming instability with quantum correction

NASA Astrophysics Data System (ADS)

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

2017-05-01

A modified quantum hydrodynamic model (m-QHD) is herein proposed on the basis of the Thomas-Fermi (TF) theory of many fermionic quantum systems to investigate the dynamics of electrostatic streaming instability modes in a complex (dusty) quantum plasma system. The newly formulated m-QHD, as an amelioration over the existing usual QHD, employs a dimensionality-dependent Bohmian quantum correction prefactor, γ = [(D-2)/3D], in the electron quantum dynamics, where D symbolizing the problem dimensionality under consideration. The normal mode analysis of the coupled structure equations reveals the excitation of two distinct streaming modes associated with the flowing ions (against electrons and dust) and the flowing dust particulates (against the electrons and ions). It is mainly shown that the γ-factor introduces a new source of stability and dispersive effects to the ion-streaming instability solely; but not to the dust counterparts. A non-trivial application of our investigation in electrostatic beam-plasma (flow-driven) coupled dynamics leading to the development of self-sustained intense electric current, and hence, of strong magnetic field in compact astrophysical objects (in dwarf-family stars) is summarily indicated.

Presheath and Double Layer Structures in an Argon Helicon Plasma Source

NASA Astrophysics Data System (ADS)

Siddiqui, M. Umair

Ion velocities and temperatures, plasma density, potential, and electron temperatures are measured in a 13.56 MHz helicon produced argon plasma upstream from a grounded plate inside a 10 cm ID cylindrical Pyrex vacuum chamber. The plate is held at psi = 0° → 60° relative to the background axial magnetic field in the system. For the psi = 0° experiment, two distinct helicon discharge equilibria are observed at 500 W rf power, 900 G magnetic field, and a neutral pressure of 3 → 4 mTorr. Both modes exhibit a localized region of hot electrons (Th ≈ 10 eV, Tc ≈ 3.5 eV). For the first mode the hot electrons are confined by a localized potential structure and the density decreases monotonically towards the grounded plate. For the second mode the hot electrons cool off gradually in space due to heat conduction generating a downstream density peak and no major potential structures are observed. It is found that the type of discharge mode is determined by the location of the grounded plate, the length of the presheath, and the rf electron heating mechanism. For the psi = 16° → 60° plate positions, ion flow to the boundary where a 1 kG magnetic field is obliquely incident is measured at 1, 3, and 6.5 mTorr neutral pressure and 450 → 750 W rf power. The results are compared to the magnetic presheath models put forth by Chodura [Phys. Fluids 25, 1628 (1982)], Riemann [Phys. Plasmas 1, 552 (1994)], and Ahedo [Phys. Plasmas 4, 4419 (1997)]. The 1 mTorr dataset is used to benchmark a one-dimensional fluid model for the ion flow in the presheath. Definitions of the "magnetic presheath" are discussed. The fluid model in conjuction with the data show that the ion velocities in the E x B direction can be 10% → 40% percent of the sound speed for the angles investigated. Ion flow to fusion experiment boundaries and Hall thruster walls is discussed.

Rarefaction shock in the near wake

NASA Technical Reports Server (NTRS)

Diebold, D.; Hershkowitz, N.; Eliezer, S.

1987-01-01

Laboratory experiments and fluid theory find a stationary rarefaction shock in the near wake of an electrically grounded obstacle placed in a steady state, supersonic plasma flow. The shock is only found when two electron temperatures, differing by at least an order of magnitude, are present. These shocks are analogous to rarefaction shocks in plasma free expansions.

Strongly-Perturbed Non-Equilibrium Gas Physics Model for the Paraxial Diode Transport Cell

DTIC Science & Technology

2003-06-01

species and energy flow is critical to the plasma chemistry . The new model’s slight underestimate of the electron density may be a consequence of the...beam physics and plasma chemistry allows the modeling of intense charged-particle beam transport environments such as the paraxial diode gas cell

Nonlinear dynamics of electromagnetic turbulence in a nonuniform magnetized plasma

NASA Astrophysics Data System (ADS)

Shukla, P. K.; Mirza, Arshad M.; Faria, R. T.

1998-03-01

By using the hydrodynamic electron response with fixed (kinetic) ions along with Poisson's equation as well as Ampère's law, a system of nonlinear equations for low-frequency (in comparison with the electron gyrofrequency) long-(short-) wavelength electromagnetic waves in a nonuniform resistive magnetoplasma has been derived. The plasma contains equilibrium density gradient and sheared equilibrium plasma flows. In the linear limit, local dispersion relations are obtained and analyzed. It is found that sheared equilibrium flows can cause instability of Alfvén-like electromagnetic waves even in the absence of a density gradient. Furthermore, it is shown that possible stationary solutions of the nonlinear equations without dissipation can be represented in the form of various types of vortices. On the other hand, the temporal behavior of our nonlinear dissipative systems without the equilibrium density inhomogeneity can be described by the generalized Lorenz equations which admit chaotic trajectories. The density inhomogeneity may lead to even qualitative changes in the chaotic dynamics. The results of our investigation should be useful in understanding the linear and nonlinear properties of nonthermal electromagnetic waves in space and laboratory plasmas.

Electromagnetic wave energy flow control with a tunable and reconfigurable coupled plasma split-ring resonator metamaterial: A study of basic conditions and configurations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kourtzanidis, Konstantinos, E-mail: kkourt@utexas.edu; Pederson, Dylan M.; Raja, Laxminarayan L.

2016-05-28

We propose and study numerically a tunable and reconfigurable metamaterial based on coupled split-ring resonators (SRRs) and plasma discharges. The metamaterial couples the magnetic-electric response of the SRR structure with the electric response of a controllable plasma slab discharge that occupies a volume of the metamaterial. Because the electric response of a plasma depends on its constitutive parameters (electron density and collision frequency), the plasma-based metamaterial is tunable and active. Using three-dimensional numerical simulations, we analyze the coupled plasma-SRR metamaterial in terms of transmittance, performing parametric studies on the effects of electron density, collisional frequency, and the position of themore » plasma slab with respect to the SRR array. We find that the resonance frequency can be controlled by the plasma position or the plasma-to-collision frequency ratio, while transmittance is highly dependent on the latter.« less

Non-invasive probe diagnostic method for electron temperature and ion current density in atmospheric pressure plasma jet source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Young-Cheol; Kim, Yu-Sin; Lee, Hyo-Chang

2015-08-15

The electrical probe diagnostics are very hard to be applied to atmospheric plasmas due to severe perturbation by the electrical probes. To overcome this, the probe for measuring electron temperature and ion current density is indirectly contacted with an atmospheric jet source. The plasma parameters are obtained by using floating harmonic analysis. The probe is mounted on the quartz tube that surrounds plasma. When a sinusoidal voltage is applied to a probe contacting on a quartz tube, the electrons near the sheath at dielectric tube are collected and the probe current has harmonic components due to probe sheath nonlinearity. Frommore » the relation of the harmonic currents and amplitude of the sheath voltage, the electron temperature near the wall can be obtained with collisional sheath model. The electron temperatures and ion current densities measured at the discharge region are in the ranges of 2.7–3.4 eV and 1.7–5.2 mA/cm{sup 2} at various flow rates and input powers.« less

Simulation of electrostatic turbulence in the plasma sheet boundary layer with electron currents and bean-shaped ion beams

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Frank, L. A.; Huang, C. Y.

1988-01-01

Plasma data from ISEE-1 show the presence of electron currents as well as energetic ion beams in the plasma sheet boundary layer. Broadband electrostatic noise and low-frequency electromagnetic bursts are detected in the plasma sheet boundary layer, especially in the presence of strong ion flows, currents, and steep spacial gradients in the fluxes of few-keV electrons and ions. Particle simulations have been performed to investigate electrostatic turbulence driven by a cold electron beam and/or ion beams with a bean-shaped velocity distribution. The simulation results show that the counterstreaming ion beams as well as the counterstreaming of the cold electron beam and the ion beam excite ion acoustic waves with a given Doppler-shifted real frequency. However, the effect of the bean-shaped ion velocity distributions reduces the growth rates of ion acoustic instability. The simulation results also show that the slowing down of the ion bean is larger at the larger perpendicular velocity. The wave spectra of the electric fields at some points of the simulations show turbulence generated by growing waves.

Particle flows to shape and voltage surface discontinuities in the electron sheath surrounding a high voltage solar array in LEO

NASA Technical Reports Server (NTRS)

Metz, Roger N.

1991-01-01

This paper discusses the numerical modeling of electron flows from the sheath surrounding high positively biased objects in LEO (Low Earth Orbit) to regions of voltage or shape discontinuity on the biased surfaces. The sheath equations are derived from the Two-fluid, Warm Plasma Model. An equipotential corner and a plane containing strips of alternating voltage bias are treated in two dimensions. A self-consistent field solution of the sheath equations is outlined and is pursued through one cycle. The electron density field is determined by numerical solution of Poisson's equation for the electrostatic potential in the sheath using the NASCAP-LEO relation between electrostatic potential and charge density. Electron flows are calculated numerically from the electron continuity equation. Magnetic field effects are not treated.

Non-thermal equilibrium plasma-liquid interactions with femtolitre droplets

NASA Astrophysics Data System (ADS)

Maguire, Paul; Mahony, Charles; Bingham, Andrew; Patel, Jenish; Rutherford, David; McDowell, David; Mariotti, Davide; Bennet, Euan; Potts, Hugh; Diver, Declan

2014-10-01

Plasma-induced non-equilibrium liquid chemistry is little understood. It depends on a complex interplay of interface and near surface processes, many involving energy-dependent electron-induced reactions and the transport of transient species such as hydrated electrons. Femtolitre liquid droplets, with an ultra-high ratio of surface area to volume, were transported through a low-temperature atmospheric pressure RF microplasma with transit times of 1--10 ms. Under a range of plasma operating conditions, we observe a number of non-equilibrium chemical processes that are dominated by energetic electron bombardment. Gas temperature and plasma parameters (ne ~ 1013 cm-3, Te < 4 eV) were determined while size and droplet velocity profiles were obtained using a microscope coupled to a fast ICCD camera under low light conditions. Laminar mixed-phase droplet flow is achieved and the plasma is seen to significantly deplete only the slower, smaller droplet component due possibly to the interplay between evaporation, Rayleigh instabilities and charge emission. Funding from EPSRC acknowledged (Grants EP/K006088/1 and EP/K006142/1).

Ionospheres of the terrestrial planets

NASA Astrophysics Data System (ADS)

Schunk, R. W.; Nagy, A. F.

1980-11-01

The theory and observations relating to the ionospheres of the terrestrial planets Venus, the earth, and Mars are reviewed. Emphasis is placed on comparing the basic differences and similarities between the planetary ionospheres. The review covers the plasma and electric-magnetic field environments that surround the planets, the theory leading to the creation and transport of ionization in the ionospheres, the relevant observations, and the most recent model calculations. The theory section includes a discussion of ambipolar diffusion in a partially ionized plasma, diffusion in a fully ionized plasma, supersonic plasma flow, photochemistry, and heating and cooling processes. The sections on observations and model calculations cover the neutral atmosphere composition, the ion composition, the electron density, and the electron, ion, and neutral temperatures.

Simulations of a molecular plasma in collisional-radiative nonequilibrium

NASA Technical Reports Server (NTRS)

Cambier, Jean-Luc; Moreau, Stephane

1993-01-01

A code for the simulation of nonequilibrium plasmas is being developed, with the capability to couple the plasma fluid-dynamics for a single fluid with a collisional-radiative model, where electronic states are treated as separate species. The model allows for non-Boltzmann distribution of the electronic states. Deviations from the Boltzmann distributions are expected to occur in the rapidly ionizing regime behind a strong shock or in the recombining regime during a fast expansion. This additional step in modeling complexity is expected to yield more accurate predictions of the nonequilibrium state and the radiation spectrum and intensity. An attempt at extending the code to molecular plasma flows is presented. The numerical techniques used, the thermochemical model, and the results of some numerical tests are described.

Influence of particle velocity on the conductivity of dusty plasma

NASA Astrophysics Data System (ADS)

Xu, C. M.; Chen, Y. Y.; Yu, R. J.; Zhang, Y. Y.

2018-06-01

Conductivity is a popular branch of dusty plasma research. In this paper, on the basis of considering the influence of charged particles' (electrons and ions) flow velocity, the conductivity of dusty plasma is derived and studied. Firstly, the charging currents are deduced on considering the influence of flow velocity, and the theoretical results manifest that it increases with the increase of flow velocity. Secondly, both the real and imaginary parts of the conductivity are derived, based on which, the dependence of conductivity on the flow velocity is discussed. In further, it is found that both the real and imaginary parts have a turning point. Finally, a ratio defined as charged particles' flow velocity to thermal velocity is proposed to analyze the dependence of the conductivity on the velocities. The involved results reveal that both the real and imaginary parts of the conductivity have a turning point in their dependence on the ratio, but the specific ratio value is different.

Dimits shift in realistic gyrokinetic plasma-turbulence simulations.

PubMed

Mikkelsen, D R; Dorland, W

2008-09-26

In simulations of turbulent plasma transport due to long wavelength (k perpendicular rhoi < or = 1) electrostatic drift-type instabilities, we find a persistent nonlinear up-shift of the effective threshold. Next-generation tokamaks will likely benefit from the higher effective threshold for turbulent transport, and transport models should incorporate suitable corrections to linear thresholds. The gyrokinetic simulations reported here are more realistic than previous reports of a Dimits shift because they include nonadiabatic electron dynamics, strong collisional damping of zonal flows, and finite electron and ion collisionality together with realistic shaped magnetic geometry. Reversing previously reported results based on idealized adiabatic electrons, we find that increasing collisionality reduces the heat flux because collisionality reduces the nonadiabatic electron microinstability drive.

Digital holographic interferometry employing Fresnel transform reconstruction for the study of flow shear stabilized Z-pinch plasmas.

PubMed

Ross, M P; Shumlak, U

2016-10-01

The ZaP-HD flow Z-pinch project provides a platform to explore how shear flow stabilized Z-pinches could scale to high-energy-density plasma (plasma with pressures exceeding 1 Mbar) and fusion reactor conditions. The Z-pinch is a linear plasma confinement geometry in which the plasma carries axial electric current and is confined by its self-induced magnetic field. ZaP-HD generates shear stabilized, axisymmetric Z-pinches with stable lifetimes approaching 60 μs. The goal of the project is to increase the plasma density and temperature compared to the previous ZaP project by compressing the plasma to smaller radii (≈1 mm). Radial and axial plasma electron density structure is measured using digital holographic interferometry (DHI), which provides the necessary fine spatial resolution. ZaP-HD's DHI system uses a 2 ns Nd:YAG laser pulse with a second harmonic generator (λ = 532 nm) to produce holograms recorded by a Nikon D3200 digital camera. The holograms are numerically reconstructed with the Fresnel transform reconstruction method to obtain the phase shift caused by the interaction of the laser beam with the plasma. This provides a two-dimensional map of line-integrated electron density, which can be Abel inverted to determine the local number density. The DHI resolves line-integrated densities down to 3 × 10 20 m -2 with spatial resolution near 10 μm. This paper presents the first application of Fresnel transform reconstruction as an analysis technique for a plasma diagnostic, and it analyzes the method's accuracy through study of synthetic data. It then presents an Abel inversion procedure that utilizes data on both sides of a Z-pinch local number density profile to maximize profile symmetry. Error estimation and Abel inversion are applied to the measured data.

Magnetospheric Convection Electric Field Dynamics and Stormtime Particle Energization: Case Study of the Magnetic Storm of May 4,1998

NASA Technical Reports Server (NTRS)

Khazanov, George V.; Liemohn, Michael W.; Newman, Tim S.; Fok, Mei-Ching; Ridley, Aaron

2003-01-01

It is shown that narrow channels of high electric field are an effective mechanism for injecting plasma into the inner magnetosphere. Analytical expressions for the electric field cannot produce these channels of intense plasma flow, and thus result in less entry and energization of the plasma sheet into near-Earth space. For the ions, omission of these channels leads to an underprediction of the strength of the stormtime ring current and therefore an underestimation of the geoeffectiveness of the storm event. For the electrons, omission of these channels leads to the inability to create a seed population of 10-100 keV electrons deep in the inner magnetosphere. These electrons can eventually be accelerated into MeV radiation belt particles.

PIC Modeling of Argon Plasma Flow in MNX

NASA Astrophysics Data System (ADS)

Cohen, Samuel; Sefkow, Adam

2007-11-01

A linear helicon-heated plasma device - the Magnetic Nozzle Experiment (MNX) at the Princeton Plasma Physics Laboratory - is used for studies of the formation of strong electrostatic double layers near mechanical and magnetic apertures and the acceleration of plasma ions into supersonic directed beams. In order to characterize the role of the aperture and its involvement with ion acceleration, detailed particle-in-cell simulations are employed to study the effects of the surrounding boundary geometry on the plasma dynamics near the aperture region, within which the transition from a collisional to collisionless regime occurs. The presence of a small superthermal electron population is examined, and the model includes a background neutral population which can be ionized by energetic electrons. By self-consistently evaluating the temporal evolution of the plasma in the vicinity of the aperture, the formation mechanism of the double layer is investigated.

Ultra-micro analysis of liquids and suspensions based on laser-induced plasma emissions

NASA Astrophysics Data System (ADS)

Cheung, N. H.; Ng, C. W.; Ho, W. F.; Yeung, E. S.

1998-05-01

Spectrochemical analysis of liquids and suspensions using laser-induced plasma emissions was investigated. Nd:YAG pulsed-laser (532-nm) ablation of aqueous samples produced plasmas that were hot (few eV) and extensively ionized, with electron density in the 10 18 cm -3 range. Analyte line signals were initially masked by intense plasma continuum emissions, and would only emerge briefly above the background when the plume temperature dropped below 1 eV during the course of its very rapid cooling. In contrast, 193-nm laser ablation at similar fluence generated plasmas of much lower (<1 eV) temperature but comparable electron density. The plasma continuum emissions were relatively weak and the signal-to-background ratio was a thousand times better. This `cold' plasma was ideal for sampling trace amounts of biologically important elements such as sodium and potassium. By ablating hydrodynamically focused jets in a sheath-flow, and with acoustic normalization for improved precision, the single-shot detection limits of sodium and potassium were 8 and 50 fg, respectively. Using the sheath-flow arrangement, the amounts of sodium and potassium inside single human red blood cells were simultaneously determined for the first time. The intracellular contents for a given blood donor were found to vary significantly, with only very weak correlation between the amounts of sodium and potassium in individual cells.

Supersonic plasma jets in experiments for radiophysical testing of bodies flow

NASA Astrophysics Data System (ADS)

Balakirev, B. A.; Bityurin, V. A.; Bocharov, A. N.; Brovkin, V. G.; Vedenin, P. V.; Lashkov, V. A.; Mashek, I. Ch; Pashchina, A. S.; Petrovskiy, V. P.; Khoronzhuk, R. S.; Dobrovolskaya, A. S.

2018-01-01

The action of differently oriented magnetic fields on the parameters of bow shock created in the vicinity of aerodynamic bodies placed into the supersonic gas-plasma flows is studied. For these experiments two types of the high speed plasma jet sources are used—magneto-plasma compressor (MPC) and powerful pulse capillary type discharge. MPC allows to create the plasma jets with gas flow velocity of 10 ± 2 km/s, lifetime 30-50 μs, temperature Te ≈ 3 ± 0.5 eV, electron density about ne ˜ 1016cm-3 and temperature Te ≈ 3 ± 0.5 eV. The jet source based on powerful capillary discharge creates the flows with lifetime 1-20 ms, Mach numbers 3-8, plasma flow velocity 3-10 km/s, vibration and rotation temperatures 9000-14000 and 3800-6000 K respectively. The results of our first experiments show the possibility of using gas-plasma sources based on MPC and powerful capillary discharge for aerodynamic and radiophysical experiments. Comparatively small magnetic field B = 0.23-0.5 T, applied to the obtained bow shocks, essentially modify them. This can lead to a change in shape and an increase in the distance between the detached shock wave and the streamlined body surface if B is parallel to the jet velocity or to decrease this parameter if B is orthogonal to the oncoming flow. Probably, the first case can be useful for reducing the thermal load and aerodynamic drug of streamlined body and the second case can be used to control the radio-transparency of the plasma layer and solving the blackout problem.

Properties of two-fluid flowing equilibria observed in double-pulsing coaxial helicity injection on HIST

NASA Astrophysics Data System (ADS)

Kanki, T.; Nagata, M.

2013-10-01

Multi-pulsing coaxial helicity injection (M-CHI) method which aims to achieve both quasi-steady sustainment and good confinement has been proposed as a refluxing scenario of the CHI. To explore the usefulness of the M-CHI for spherical torus (ST) configurations, the double-pulsing operations have been carried out in the HIST, verifying the flux amplification and the formation of the closed flux surfaces after the second CHI pulse. The purpose of this study is to investigate the properties of the magnetic field and plasma flow structures during the sustainment by comparing the results of plasma flow, density, and magnetic fields measurements with those of two-fluid equilibrium calculations. The two-fluid flowing equilibrium model which is described by a pair of generalized Grad-Shafranov equations for ion and electron surface variables and Bernoulli equations for density is applied to reconstruct the ST configuration with poloidal flow shear observed in the HIST. Due to the negative steep density gradient in high field side, the toroidal field has a diamagnetic profile (volume average beta, < β > = 68 %) in the central open flux column region. The ion flow velocity with strong flow shear from the separatrix in the inboard side to the core region is the opposite direction to the electron flow velocity due to the diamagentic drift through the density gradient. The electric field is relatively small in the whole region, and thus the Lorentz force nearly balances with the two-fluid effect which is particularly significant in a region with the steep density gradient due to the ion and electron diamagnetic drifts.

Simulation of density fluctuations before the L-H transition for Hydrogen and Deuterium plasmas in the DIII-D tokamak using the BOUT++ code

NASA Astrophysics Data System (ADS)

Wang, Y. M.; Xu, X. Q.; Yan, Z.; Mckee, G. R.; Grierson, B. A.; Xia, T. Y.; Gao, X.

2018-02-01

A six-field two-fluid model has been used to simulate density fluctuations. The equilibrium is generated by experimental measurements for both Deuterium (D) and Hydrogen (H) plasmas at the lowest densities of DIII-D low to high confinement (L-H) transition experiments. In linear simulations, the unstable modes are found to be resistive ballooning modes with the most unstable mode number n  =  30 or k_θρ_i˜0.12 . The ion diamagnetic drift and E× B convection flow are balanced when the radial electric field (E r ) is calculated from the pressure profile without net flow. The curvature drift plays an important role in this stage. Two poloidally counter propagating modes are found in the nonlinear simulation of the D plasma at electron density n_e˜1.5×1019 m-3 near the separatrix while a single ion mode is found in the H plasma at the similar lower density, which are consistent with the experimental results measured by the beam emission spectroscopy (BES) diagnostic on the DIII-D tokamak. The frequency of the electron modes and the ion modes are about 40 kHz and 10 kHz respectively. The poloidal wave number k_θ is about 0.2 cm -1 (k_θρ_i˜0.05 ) for both ion and electron modes. The particle flux, ion and electron heat fluxes are  ˜3.5-6 times larger for the H plasma than the D plasma, which makes it harder to achieve H-mode for the same heating power. The change of the atomic mass number A from 2 to 1 using D plasma equilibrium make little difference on the flux. Increase the electric field will suppress the density fluctuation. The electric field scan and ion mass scan results show that the dual-mode results primarily from differences in the profiles rather than the ion mass.

Evaluating the Uncertainties in the Electron Temperature and Radial Speed Measurements Using White Light Corona Eclipse Observations

NASA Technical Reports Server (NTRS)

Reginald, Nelson L.; Davilla, Joseph M.; St. Cyr, O. C.; Rastaetter, Lutz

2014-01-01

We examine the uncertainties in two plasma parameters from their true values in a simulated asymmetric corona. We use the Corona Heliosphere (CORHEL) and Magnetohydrodynamics Around the Sphere (MAS) models in the Community Coordinated Modeling Center (CCMC) to investigate the differences between an assumed symmetric corona and a more realistic, asymmetric one. We were able to predict the electron temperatures and electron bulk flow speeds to within +/-0.5 MK and +/-100 km s(exp-1), respectively, over coronal heights up to 5.0 R from Sun center.We believe that this technique could be incorporated in next-generation white-light coronagraphs to determine these electron plasma parameters in the low solar corona. We have conducted experiments in the past during total solar eclipses to measure the thermal electron temperature and the electron bulk flow speed in the radial direction in the low solar corona. These measurements were made at different altitudes and latitudes in the low solar corona by measuring the shape of the K-coronal spectra between 350 nm and 450 nm and two brightness ratios through filters centered at 385.0 nm/410.0 nm and 398.7 nm/423.3 nm with a bandwidth of is approximately equal to 4 nm. Based on symmetric coronal models used for these measurements, the two measured plasma parameters were expected to represent those values at the points where the lines of sight intersected the plane of the solar limb.

Characterization of a microwave-excited atmospheric-pressure argon plasma jet using two-parallel-wires transmission line resonator

NASA Astrophysics Data System (ADS)

Choi, J.; Eom, I. S.; Kim, S. J.; Kwon, Y. W.; Joh, H. M.; Jeong, B. S.; Chung, T. H.

2017-09-01

This paper presents a method to produce a microwave-excited atmospheric-pressure plasma jet (ME-APPJ) with argon. The plasma was generated by a microwave-driven micro-plasma source that uses a two-parallel-wire transmission line resonator (TPWR) operating at around 900 MHz. The TPWR has a simple structure and is easier to fabricate than coaxial transmission line resonator (CTLR) devices. In particular, the TPWR can sustain more stable ME-APPJ than the CTLR can because the gap between the electrodes is narrower than that in the CTLR. In experiments performed with an Ar flow rate from 0.5 to 8.0 L.min-1 and an input power from 1 to 6 W, the rotational temperature was determined by comparing the measured and simulated spectra of rotational lines of the OH band and the electron excitation temperature determined by the Boltzmann plot method. The rotational temperature obtained from OH(A-X) spectra was 700 K to 800 K, whereas the apparent gas temperature of the plasma jet remains lower than ˜325 K, which is compatible with biomedical applications. The electron number density was determined using the method based on the Stark broadening of the hydrogen Hβ line, and the measured electron density ranged from 6.5 × 1014 to 7.6 × 1014 cm-3. TPWR ME-APPJ can be operated at low flows of the working gas and at low power and is very stable and effective for interactions of the plasma with cells.

Space plasma research

NASA Technical Reports Server (NTRS)

Comfort, R. H.; Horwitz, J. L.

1986-01-01

Temperature and density analysis in the Automated Analysis Program (for the global empirical model) were modified to use flow velocities produced by the flow velocity analysis. Revisions were started to construct an interactive version of the technique for temperature and density analysis used in the automated analysis program. A sutdy of ion and electron heating at high altitudes in the outer plasmasphere was initiated. Also the analysis of the electron gun experiments on SCATHA were extended to include eclipse operations in order to test a hypothesis that there are interactions between the 50 to 100 eV beam and spacecraft generated photoelectrons. The MASSCOMP software to be used in taking and displaying data in the two-ion plasma experiment was tested and is now working satisfactorily. Papers published during the report period are listed.

Plasma contactor research, 1990

NASA Technical Reports Server (NTRS)

Williams, John D.; Wilbur, Paul J.

1991-01-01

Emissive and Langmuir probes were used to measure plasma potential profiles, plasma densities, electron energy distributions, and plasma noise levels near a hollow cathode-based plasma contactor emitting electrons. The effects of electron emission current (100 to 1500 mA) and contactor flowrate (2 to 10 sccm (Xenon)) on these data are examined. Retarding potential analyzer (RPA) measurements showing that high energy ions generally stream from a contactor along with the electrons being emitted are also presented, and a mechanism by which this occurs is postulated. This mechanism, which involves a high rate of ionization induced between electrons and atoms flowing together from the hollow cathode orifice, results in a region of high positive space charge and high positive potential. Langmuir and RPA probe data suggests that both electrons and ions expand spherically from this potential hill region. In addition to experimental observations, a simple one-dimensional model which describes the electron emission process and predicts the phenomena just mentioned is presented and is shown to agree qualitatively with these observations. Experimental results of the first stage of bilateral cooperation with the Italian Institute of Interplanetary Space Physics (IFSI CNR) are presented. Sharp, well-defined double layers were observed downstream of a contactor collecting electrons from an ambient plasma created in the IFSI Facility. The voltage drop across these double layers was observed to increase with the current drawn from the ambient plasma. This observation, which was not as clear in previous IFSI tests conducted at higher neutral pressures, is in agreement with previous experimental observations made at both Colorado State University and NASA Lewis Research Center. Greater double layer voltage drops, multiple double layers, and higher noise levels in the region near the double layers were also observed when a magnetic field was imposed and oriented perpendicular to the line joining the contactor and simulator.

Density-Gradient-Driven trapped-electron-modes in improved-confinement RFP plasmas

NASA Astrophysics Data System (ADS)

Duff, James

2016-10-01

Short wavelength density fluctuations in improved-confinement MST plasmas exhibit multiple features characteristic of the trapped-electron-mode (TEM), strong evidence that drift wave turbulence emerges in RFP plasmas when transport associated with MHD tearing is reduced. Core transport in the RFP is normally governed by magnetic stochasticity stemming from long wavelength tearing modes that arise from current profile peaking. Using inductive control, the tearing modes are reduced and global confinement is increased to values expected for a comparable tokamak plasma. The improved confinement is associated with a large increase in the pressure gradient that can destabilize drift waves. The measured density fluctuations have frequencies >50 kHz, wavenumbers k_phi*rho_s<0.14, and propagate in the electron drift direction. Their spectral emergence coincides with a sharp decrease in fluctuations associated with global tearing modes. Their amplitude increases with the local density gradient, and they exhibit a density-gradient threshold at R/L_n 15, higher than in tokamak plasmas by R/a. the GENE code, modified for RFP equilibria, predicts the onset of microinstability for these strong-gradient plasma conditions. The density-gradient-driven TEM is the dominant instability in the region where the measured density fluctuations are largest, and the experimental threshold-gradient is close to the predicted critical gradient for linear stability. While nonlinear analysis shows a large Dimits shift associated with predicted strong zonal flows, the inclusion of residual magnetic fluctuations causes a collapse of the zonal flows and an increase in the predicted transport to a level close to the experimentally measured heat flux. Similar circumstances could occur in the edge region of tokamak plasmas when resonant magnetic perturbations are applied for the control of ELMs. Work supported by US DOE.

Using PEACE Data from the four CLUSTER Spacecraft to Measure Compressibility, Vorticity, and the Taylor Microscale in the Magnetosheath and Plasma Sheet

NASA Technical Reports Server (NTRS)

Goldstein, Melvyn L.; Parks, George; Gurgiolo, C.; Fazakerley, Andrew N.

2008-01-01

We present determinations of compressibility and vorticity in the magnetosheath and plasma sheet using moments from the four PEACE thermal electron instruments on CLUSTER. The methodology used assumes a linear variation of the moments throughout the volume defined by the four satellites, which allows spatially independent estimates of the divergence, curl, and gradient. Once the vorticity has been computed, it is possible to estimate directly the Taylor microscale. We have shown previously that the technique works well in the solar wind. Because the background flow speed in the magnetosheath and plasma sheet is usually less than the Alfven speed, the Taylor frozen-in-flow approximation cannot be used. Consequently, this four spacecraft approach is the only viable method for obtaining the wave number properties of the ambient fluctuations. Our results using electron velocity moments will be compared with previous work using magnetometer data from the FGM experiment on Cluster.

Scanning retarding field analyzer for plasma profile measurements in the boundary of the Alcator C-Mod tokamak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brunner, D.; LaBombard, B.; Ochoukov, R.

2013-03-15

A new Retarding Field Analyzer (RFA) head has been created for the outer-midplane scanning probe system on the Alcator C-Mod tokamak. The new probe head contains back-to-back retarding field analyzers aligned with the local magnetic field. One faces 'upstream' into the field-aligned plasma flow and the other faces 'downstream' away from the flow. The RFA was created primarily to benchmark ion temperature measurements of an ion sensitive probe; it may also be used to interrogate electrons. However, its construction is robust enough to be used to measure ion and electron temperatures up to the last-closed flux surface in C-Mod. Amore » RFA probe of identical design has been attached to the side of a limiter to explore direct changes to the boundary plasma due to lower hybrid heating and current drive. Design of the high heat flux (>100 MW/m{sup 2}) handling probe and initial results are presented.« less

A phenomenological model for orificed hollow cathodes. Ph.D. Thesis, 1 Dec. 1981 - 1 Dec. 1982; [electrostatic thruster

NASA Technical Reports Server (NTRS)

Siegfried, D. E.

1982-01-01

A quartz hollow tube cathode was used to determine the operating conditions within a mercury orificed hollow cathode. Insert temperature profiles, cathode current distributions, plasma properties profile, and internal pressure-mass flow rate results are summarized and used in a phenomenological model which qualitatively describes electron emission and plasma production processes taking place within the cathode. By defining an idealized ion production region within which most of the plasma processes are concentrated, this model is expressed analytically as a simple set of equations which relate cathode dimensions and specifiable operating conditions, such as mass flow rate and discharge current, to such important parameters as emission surface temperature and internal plasma properties. Key aspects of the model are examined.

Energy Flow in Dense Off-Equilibrium Plasma

DTIC Science & Technology

2016-07-15

akT e in our system100 i e T T Teller 1966 Smoking Gun Experiment: Laser Breakdown in COLD gas In going from room to liquid Nitrogen temperature...oflaser breakdown have revealed a new phase of off-equilibrium plasma that has a tensile strength similar to a liquid , and reduced ion-electron...approved for public release. Part 1: Energy Balance in Sonoluminescing Dense Plasma Sonoluminescence occurs from rapid implosion of gas bubbles caused to

Investigation of ion and electron heat transport of high- T e ECH heated discharges in the large helical device

DOE PAGES

Pablant, N. A.; Satake, S.; Yokoyama, M.; ...

2016-01-28

An analysis of the radial electric field and heat transport, both for ions and electrons, is presented for a high-more » $${{T}_{\\text{e}}}$$ electron cyclotron heated (ECH) discharge on the large helical device (LHD). Transport analysis is done using the task3d transport suite utilizing experimentally measured profiles for both ions and electrons. Ion temperature and perpendicular flow profiles are measured using the recently installed x-ray imaging crystal spectrometer diagnostic (XICS), while electron temperature and density profiles are measured using Thomson scattering. The analysis also includes calculated ECH power deposition profiles as determined through the travis ray-tracing code. This is the first time on LHD that this type of integrated transport analysis with measured ion temperature profiles has been performed without NBI, allowing the heat transport properties of plasmas with only ECH heating to be more clearly examined. For this study, a plasma discharge is chosen which develops a high central electron temperature ($${{T}_{\\text{eo}}}=9$$ keV) at moderately low densities ($${{n}_{\\text{eo}}}=1.5\\times {{10}^{19}}$$ m-3). The experimentally determined transport properties from task3d are compared to neoclassical predictions as calculated by the gsrake and fortec-3d codes. The predicted electron fluxes are seen to be an order of magnitude less than the measured fluxes, indicating that electron transport is largely anomalous, while the neoclassical and measured ion heat fluxes are of the same magnitude. Neoclassical predictions of a strong positive ambipolar electric field ($${{E}_{\\text{r}}}$$ ) in the plasma core are validated through comparisons to perpendicular flow measurements from the XICS diagnostic. Furthermore, this provides confidence that the predictions are producing physically meaningful results for the particle fluxes and radial electric field, which are a key component in correctly predicting plasma confinement.« less

[The Characteristic Research of ·OH Induced by Water on an Argon Plasma Jet].

PubMed

Liu, Kun; Liao, Hua; Zheng, Pei-chao; Wang, Chen-ying; Liu, Hong-di; Danil, Dobrynin

2015-07-01

·OH plays a crucial role in many fields, having aroused wide public concern in the world. Atmospheric Pressure Plasma Jet, which can be achieved by portable device due to working without the vacuum environment, has the advantages of high concentration of reactive species, high electron temperature and low gas temperature. It has become an important research topic in the field of gas discharge with a strong prospect. Especially, how to induce plasma jet to produce ·OH has become a new hotpot in the field of low-temperature plasma. It has been reported that mass ·OH can be induced successfully when water vapor is added to the working gas, but it will be unstable when the concentrate of water reaches a certain degree. Thus, a device of argon plasma jet with a Ring-to-Ring Electrode Configuration has been designed to interact with water in the surrounding air to generate ·OH under atmospheric pressure. In order to increase the production of ·OH, ultrasonic atomizing device is introduced to promote water concentration around the plasma plume. The generating rule of OH(A2J) induced by water has been extensively studied under different voltages and flow rate. ·OH output induced by the plasma has been tested by emission spectrometry, and at the meanwhile, Ar atomic spectral lines at 810.41 and 811.48 nm are also recorded in order to calculate the electron temperature in argon plasma plume. The results show that the water surrounding the plasma plume can be induced to produce ·OH, and OH(A2 ∑+) output increases with the electrode voltage rising from 20 to 28 kV. When the flow rate increases from 100 to 200 L x h(-1), the OH(A2∑+) output increases, but from 200 to 600 L x h(-1), it decreases. The production rules of OH(A2∑+) is the same as that of electron temperature. Therefore, the presumption is proved that ·OH output mainly affected by electron temperature.

Growth and properties of amorphous silicon films grown using pulsed-flow reactive plasma beam epitaxy

NASA Technical Reports Server (NTRS)

Dalal, Vikram L.; Knox, Ralph; Kandalaft, Nabeeh; Baldwin, Greg

1991-01-01

The growth and properties of a-Si:H films grown using a novel deposition technique, reactive plasma beam epitaxy, are discussed. In this technique, a remote H plasma produced in a microwave-ECR reactor is used to grow a-Si:H films at low pressures. The H ions react with SiH4 introduced near the substrate to produce the film. The flow of SiH4 is pulsed on or off, thereby achieving in-situ annealing of the film during growth by H ions and radicals. The films produced by this technique appear to have good electronic quality, and are more stable than the standard glow discharge films.

Investigation of Magnetic Reconnection Suppression at Saturn's Magnetopause

NASA Astrophysics Data System (ADS)

Sawyer, R.; Fuselier, S. A.; Mukherjee, J.; Steven, P. M.; Masters, A.

2017-12-01

At Earth, one of the fundamental processes that govern the interaction between the solar wind and the magnetosphere is magnetic reconnection. It remains to be seen how significant a role magnetic reconnection plays in the magnetospheric dynamics of the outer planets. In particular, there may be conditions that cause suppression of reconnection. For fast rotators, like Saturn, the strong co-rotation may be dominant throughout the magnetosphere, out to the magnetopause. These strong internal co-rotational flows may create a shear flow across the magnetopause that may act to suppress reconnection, especially on the dawn flank. Cassini has given us an extraordinary insight into the plasma environment around Saturn. The electron spectrometer (ELS) on the Cassini plasma spectrometer (CAPS) instrument provides data on the plasma density and temperatures as well as electron pitch angle distributions and their associated energies. In this study we examine magnetopause crossing events where heated electrons were observed in the magnetosheath. We use a modified empirical model for the location of the reconnection X-line to show where reconnection may be taking place at Saturn's magnetopause. From these results, we determine if any events considered fall in the predicted suppression region along the dawn flanks.

Density-Gradient-Driven trapped-electron-modes in improved-confinement RFP plasmas

NASA Astrophysics Data System (ADS)

Duff, James; Sarff, John; Ding, Weixing; Brower, David; Parke, Eli; Chapman, Brett; Terry, Paul; Pueschel, M. J.; Williams, Zach

2017-10-01

Short wavelength density fluctuations in improved-confinement MST plasmas exhibit multiple features characteristic of the trapped-electron-mode (TEM). Core transport in the RFP is normally governed by magnetic stochasticity stemming from long wavelength tearing modes that arise from current profile peaking, which are suppressed via inductive control for this work. The improved confinement is associated with an increase in the pressure gradient that can destabilize drift waves. The measured density fluctuations have f 50 kHz, kϕρs < 0.14 , and propagate in the electron drift direction. Their spectral emergence coincides with a sharp decrease in global tearing mode associated fluctuations, their amplitude increases with local density gradient, and they exhibit a density-gradient threshold at R /Ln 15 . The GENE code, modified for the RFP, predicts the onset of density-gradient-driven TEM for these strong-gradient plasma conditions. While nonlinear analysis shows a large Dimits shift associated with predicted strong zonal flows, the inclusion of residual magnetic fluctuations, comparable to experimental magnetic fluctuations, causes a collapse of the zonal flows and an increase in the predicted transport to a level close to the experimentally measured heat flux. Work supported by US DOE.

Characterization of argon direct-current glow discharge with a longitudinal electric field applied at ambient air

NASA Astrophysics Data System (ADS)

Jiang, Weiman; Tang, Jie; Wang, Yishan; Zhao, Wei; Duan, Yixiang

2014-09-01

A direct-current-driven plasma jet is developed by applying a longitudinal electric field on the flowing argon at ambient air. This plasma shows a torch shape with its cross-section increased from the anode to the cathode. Comparison with its counterparts indicates that the gas flow plays a key role in variation of the plasma structure and contributes much to enlarging the plasma volume. It is also found that the circular hollow metal base promotes generation of plasma with a high-power volume density in a limited space. The optical emission spectroscopy (OES) diagnosis indicates that the plasma comprises many reactive species, such as OH, O, excited N2, and Ar metastables. Examination of the rotational and vibrational temperature indicates that the plasma is under nonequilibrium condition and the excited species OH(A 2Σ+), O(5P), and N2(C 3Πu) are partly generated by energy transfer from argon metastables. The spatially resolved OES of plasma reveals that the negative glow, Faraday dark space, and positive column are distributed across the gas gap. The absence of the anode glow is attributed to the fact that many electrons in the vicinity of the anode follow ions into the positive column due to the ambipolar diffusion in the flowing gas.

A conservative scheme for electromagnetic simulation of magnetized plasmas with kinetic electrons

NASA Astrophysics Data System (ADS)

Bao, J.; Lin, Z.; Lu, Z. X.

2018-02-01

A conservative scheme has been formulated and verified for gyrokinetic particle simulations of electromagnetic waves and instabilities in magnetized plasmas. An electron continuity equation derived from the drift kinetic equation is used to time advance the electron density perturbation by using the perturbed mechanical flow calculated from the parallel vector potential, and the parallel vector potential is solved by using the perturbed canonical flow from the perturbed distribution function. In gyrokinetic particle simulations using this new scheme, the shear Alfvén wave dispersion relation in the shearless slab and continuum damping in the sheared cylinder have been recovered. The new scheme overcomes the stringent requirement in the conventional perturbative simulation method that perpendicular grid size needs to be as small as electron collisionless skin depth even for the long wavelength Alfvén waves. The new scheme also avoids the problem in the conventional method that an unphysically large parallel electric field arises due to the inconsistency between electrostatic potential calculated from the perturbed density and vector potential calculated from the perturbed canonical flow. Finally, the gyrokinetic particle simulations of the Alfvén waves in sheared cylinder have superior numerical properties compared with the fluid simulations, which suffer from numerical difficulties associated with singular mode structures.

Transverse electron-scale instability in relativistic shear flows.

PubMed

Alves, E P; Grismayer, T; Fonseca, R A; Silva, L O

2015-08-01

Electron-scale surface waves are shown to be unstable in the transverse plane of a sheared flow in an initially unmagnetized collisionless plasma, not captured by (magneto)hydrodynamics. It is found that these unstable modes have a higher growth rate than the closely related electron-scale Kelvin-Helmholtz instability in relativistic shears. Multidimensional particle-in-cell simulations verify the analytic results and further reveal the emergence of mushroomlike electron density structures in the nonlinear phase of the instability, similar to those observed in the Rayleigh Taylor instability despite the great disparity in scales and different underlying physics. This transverse electron-scale instability may play an important role in relativistic and supersonic sheared flow scenarios, which are stable at the (magneto)hydrodynamic level. Macroscopic (≫c/ωpe) fields are shown to be generated by this microscopic shear instability, which are relevant for particle acceleration, radiation emission, and to seed magnetohydrodynamic processes at long time scales.

Measurements of C V flows from thermal charge-exchange excitation in divertor plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaniol, B.; Isler, R. C.; Brooks, N. H.

2001-10-01

Certain transitions of C IV (C{sup 3+}) from n=7 to n=6 ({approx}7226 {angstrom}) and from n=6 to n=5 ({approx}4660 {angstrom}) sometimes appear much brighter in tokamak divertors than expected for electron-impact excitation from the ground state. This situation occurs because of charge exchange between C V (C{sup 4+}) and recycling thermal deuterium atoms in the n=2 level. As a result, it is possible to extend parallel flow measurements of carbon, which have previously been performed on C II--C IV ions using Doppler shift spectroscopy, to include flows of the He-like C V ions. The work described here includes modeling ofmore » the spectral features, correlation of state populations with classical Monte Carlo trajectory (CTMC) predictions, and applications to flow measurements in the DIII-D divertor [Plasma Physics Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque (Institute of Electrical and Electronic Engineers, Piscataway, 1999), p. 515].« less

Measurements of C V flows from thermal charge-exchange excitation in divertor plasmas

NASA Astrophysics Data System (ADS)

Zaniol, B.; Isler, R. C.; Brooks, N. H.; West, W. P.; Olson, R. E.

2001-10-01

Certain transitions of C IV (C3+) from n=7 to n=6 (≈7226 Å) and from n=6 to n=5 (≈4660 Å) sometimes appear much brighter in tokamak divertors than expected for electron-impact excitation from the ground state. This situation occurs because of charge exchange between C V (C4+) and recycling thermal deuterium atoms in the n=2 level. As a result, it is possible to extend parallel flow measurements of carbon, which have previously been performed on C II-C IV ions using Doppler shift spectroscopy, to include flows of the He-like C V ions. The work described here includes modeling of the spectral features, correlation of state populations with classical Monte Carlo trajectory (CTMC) predictions, and applications to flow measurements in the DIII-D divertor [Plasma Physics Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque (Institute of Electrical and Electronic Engineers, Piscataway, 1999), p. 515].

The plasma properties and electron emission characteristics of near-zero differential resistance of hollow cathode-based plasma contactors with a discharge chamber

NASA Astrophysics Data System (ADS)

Xie, Kan; Farnell, Casey C.; Williams, John D.

2014-08-01

The formation of electron emission-bias voltage (I-V) characteristics of near-zero differential resistance in the cathodic plasma contactor for bare electrodynamic tether applications, based on a hollow cathode embedded in a ring-cusp ionization stage, is studied. The existence of such an I-V regime is important to achieve low impedance performance without being affected by the space plasma properties for a cathodic plasma contactor. Experimental data on the plasma structure and properties downstream from the ionization stage are presented as functions of the xenon flow rate and the electron emission current. The electrons were emitted from the cathode to the cylindrical vacuum chamber wall (r = 0.9 m) under ≈10-5 Torr of vacuum pressure. The ring-cusp configuration selected for the plasma contactor created a 125-Gauss axial field near the cathode orifice, along with a large-volume 50-Gauss magnitude pocket in the stage. A baseline ion energy cost of ≈300 eV/ion was measured in the ionization stage when no electrons were emitted to the vacuum chamber wall. In addition, the anode fall growth limited the maximum propellant unitization to below ≈75% in the discharge loss curves for this ion stage. Detailed measurements on the plasma properties were carried out for the no-electron emission and 3 A emission conditions. The experimental data are compared with 1-D models, and the effectiveness of the model is discussed. The four key issues that played important roles in the process of building the near-zero different resistance I-V regime are: a significant amount of ionization by the emission electrons, a decrease in the number of reflected electrons in the plume, the electron-temperature increment, and low initial ion energy at the source outlet.

Gas flow rate dependence of the discharge characteristics of a helium atmospheric pressure plasma jet interacting with a substrate

NASA Astrophysics Data System (ADS)

Yan, Wen; Economou, Demetre J.

2017-10-01

A 2D (axisymmetric) computational study of the discharge characteristics of an atmospheric pressure plasma jet as a function of gas flow rate was performed. The helium jet emerged from a dielectric tube, with an average gas flow velocity in the range 2.5-20 m s-1 (1 atm, 300 K) in a nitrogen ambient, and impinged on a substrate a short distance dowstream. The effect of the substrate conductivity (conductror versus insulator) was also studied. Whenever possible, simulation predictions were compared with published experimental observations. Discharge ignition and propagation in the dielectric tube were hardly affected by the He gas flow velocity. Most properties of the plasma jet, however, depended sensitively on the He gas flow velocity, which determined the concentration distributions of helium and nitrogen in the mixing layer forming in the gap between the tube exit and the substrate. At low gas flow velocity, the plasma jet evolved from a hollow (donut-shaped) feature to one where the maximum of electron density was on axis. When the gas flow velocity was high, the plasma jet maintained its hollow structure until it struck the substrate. For a conductive substrate, the radial ion fluxes to the surface were relatively uniform over a radius of ~0.4-0.8 mm, and the dominant ion flux was that of He+. For a dielectric substrate, the radial ion fluxes to the surface peaked on the symmetry axis at low He gas flow velocity, but a hollow ion flux distribution was observed at high gas flow velocity. At the same time, the main ion flux switched from N2+ to He2+ as the He gas flow velocity increased from a low to a high value. The diameter of the plasma ‘footprint’ on the substrate first increased with increasing He gas flow velocity, and eventually saturated with further increases in velocity.

Laboratory plasma with cold electron temperature of the lower ionosphere

NASA Astrophysics Data System (ADS)

Dickson, Shannon; Robertson, Scott

2009-10-01

For the first time, plasma with cold electron temperatures less than 300K has been created continuously in the laboratory. The plasma is created in a cylindrical double-walled vacuum chamber in which the inner chamber (18cm in diameter and 30cm long) is wrapped in copper tubing through which vapor from liquid nitrogen flows, providing a cooling mechanism for the neutral gas. The inner chamber has two negatively-biased filaments for plasma generation and a platinum wire Langmuir probe for diagnostic measurements. Neutral gas pressures of 1.6mTorr and a total filament emission current of 2mA are used to obtain plasma densities near 4 x 10^8 cm-3. When carbon monoxide is used as the working gas, decreasing the neutral gas temperature also decreases the cold electron temperatures, yielding cold electrons with 21meV (240K) when the neutral CO is at 150K. The same experiment conducted with H2, He, or Ar results in a doubling of the cold electron temperatures, yielding 80meV (930K) when the neutral gas is at 150K. The lower electron temperature with CO is attributed to the asymmetric CO molecule having a nonzero electric dipole moment which increases the cross section for electron energy exchange. Nitric oxide, a dominant constituent of the ionosphere, has a similar dipole moment and collision cross section as carbon monoxide and is likely to be equally effective at cooling electrons.

Shear flow driven tripolar vortices in a nonuniform electron-ion magnetoplasma with non-Maxwellian electrons

NASA Astrophysics Data System (ADS)

Masood, W.; Mirza, Arshad M.

2014-04-01

A set of nonlinear equations governing the dynamics of finite amplitude drift-ion acoustic-waves is derived for sheared ion flows parallel and perpendicular to the ambient magnetic field in the presence of Cairns and Kappa distributed electrons. It is shown that stationary solution of the nonlinear equations can be represented in the form of a tripolar vortex for specific profiles of the equilibrium sheared flows. The tripolar vortices are, however, observed to form on a scale of the order of ion Larmor radius ρ i which is calculated to be around a Kilometer for the plasma parameters found in the Saturn's E-ring. The relevance of the present investigation in planetary environments is also pointed out.

The Jupiter hot plasma torus - Observed electron temperature and energy flows

NASA Technical Reports Server (NTRS)

Brown, R. A.

1981-01-01

The detection of the optical emission /O I/ 6300 A (8 + or - 4 R) and /S III/ 6312 A (48 + or - 5 R) is reported. It is noted that these emissions are indicators of the ion source morphology and the plasma physical state and that the S III emitters have a kinetic temperature of approximately 10 to the 6th K. When combined with observations of UV lines from the same species, the optical measurements separately imply effective electron temperatures for radiative processes that are mutually consistent (approximately 50,000 K).

Fundamental experiment of ion thruster using ECR discharge

NASA Astrophysics Data System (ADS)

Yasui, Toshiaki; Kitayama, Jiro; Tahara, Hirokazu; Onoe, Ken-Ichi; Yoshikawa, Takao

A microwave ion thruster has the potential to overcome a lifetime problem of electric propulsion by eliminating electrodes. Two types of microwave ion thruster have been investigated to examine the operational characteristics. The one is the thruster using cavity-resonance microwave discharge, and the other is the thruster using Electron Cyclotron Resonance (ECR) discharge. Cavity-resonance microwave discharge produced plasmas by strong electric field in the resonant cavity and sustained plasmas at argon mass flow rates above 10 sccm. However, ECR discharge was capable of sustaining plasmas at lower mass flow rate, because ECR discharge efficiently produced plasmas by resonance absorption. From these generated microwave plasmas, ions were electrostatically extracted by two multiaperture grids. In ECR discharge, the maximum ion beam current of 75 mA and the highest mass utilization efficiency of 18.7% were achieved at a total extraction voltage of 950 V.

Modelling of plasma generation and thin film deposition by a non-thermal plasma jet at atmospheric pressure

NASA Astrophysics Data System (ADS)

Sigeneger, F.; Becker, M. M.; Foest, R.; Loffhagen, D.

2016-09-01

The gas flow and plasma in a miniaturized non-thermal atmospheric pressure plasma jet for plasma enhanced chemical vapour deposition has been investigated by means of hydrodynamic modelling. The investigation focuses on the interplay between the plasma generation in the active zone where the power is supplied by an rf voltage to the filaments, the transport of active plasma particles due to the gas flow into the effluent, their reactions with the thin film precursor molecules and the transport of precursor fragments towards the substrate. The main features of the spatially two-dimensional model used are given. The results of the numerical modelling show that most active particles of the argon plasma are mainly confined within the active volume in the outer capillary of the plasma jet, with the exception of molecular argon ions which are transported remarkably into the effluent together with slow electrons. A simplified model of the precursor kinetics yields radial profiles of precursor fragment fluxes onto the substrate, which agree qualitatively with the measured profiles of thin films obtained by static film deposition experiments.

Titan's ion exosphere observed from Voyager 1

NASA Technical Reports Server (NTRS)

Hartle, R. E.; Sittler, E. C., Jr.; Ogilvie, K. W.; Scudder, J. D.; Lazarus, A. J.; Atreya, S. K.

1982-01-01

The plasma wake surrounding Titan in Saturn's rotating magnetosphere is characterized by a plasma which is denser and cooler than the surrounding subsonic magnetospheric plasma, and which is produced by the deflection of magnetospheric plasma around Titan and the addition of exospheric ions picked up by the rotating magnetosphere. A resemblance to the interaction between the solar wind and Venus is shown for the case of ion pickup in the ion exosphere outside Titan's magnetic tail and ion flow within the boundaries of the tail as Saturn's rotating magnetosphere interacts with Titan. The boundary of the tail is indicated by a sharp reduction in the flux of high-energy electrons, which are removed by inelastic scattering with the atmosphere and centrifugal drift produced when the electrons traverse the magnetic field draped around Saturn.

The cathode material for a plasma-arc heater

NASA Astrophysics Data System (ADS)

Yelyutin, A. V.; Berlin, I. K.; Averyanov, V. V.; Kadyshevskii, V. S.; Savchenko, A. A.; Putintseva, R. G.

1983-11-01

The cathode of a plasma arc heater experiences a large thermal load. The temperature of its working surface, which is in contact with the plasma, reaches high values, as a result of which the electrode material is subject to erosion. Refractory metals are usually employed for the cathode material, but because of the severe erosion do not usually have a long working life. The most important electrophysical characteristic of the electrode is the electron work function. The use of materials with a low electron work function allows a decrease in the heat flow to the cathode, and this leads to an increase in its erosion resistance and working life. The electroerosion of certain materials employed for the cathode in an electric arc plasma generator in the process of reduction smelting of refractory metals was studied.

Plasma flow reactor for steady state monitoring of physical and chemical processes at high temperatures.

PubMed

Koroglu, Batikan; Mehl, Marco; Armstrong, Michael R; Crowhurst, Jonathan C; Weisz, David G; Zaug, Joseph M; Dai, Zurong; Radousky, Harry B; Chernov, Alex; Ramon, Erick; Stavrou, Elissaios; Knight, Kim; Fabris, Andrea L; Cappelli, Mark A; Rose, Timothy P

2017-09-01

We present the development of a steady state plasma flow reactor to investigate gas phase physical and chemical processes that occur at high temperature (1000 < T < 5000 K) and atmospheric pressure. The reactor consists of a glass tube that is attached to an inductively coupled argon plasma generator via an adaptor (ring flow injector). We have modeled the system using computational fluid dynamics simulations that are bounded by measured temperatures. In situ line-of-sight optical emission and absorption spectroscopy have been used to determine the structures and concentrations of molecules formed during rapid cooling of reactants after they pass through the plasma. Emission spectroscopy also enables us to determine the temperatures at which these dynamic processes occur. A sample collection probe inserted from the open end of the reactor is used to collect condensed materials and analyze them ex situ using electron microscopy. The preliminary results of two separate investigations involving the condensation of metal oxides and chemical kinetics of high-temperature gas reactions are discussed.

Capacitively Coupled RF Plasmas for the Synthesis of Silicon Nanocrystals: Scaling and Mechanisms

NASA Astrophysics Data System (ADS)

Markosyan, Aram H.; Le Picard, Romain; Porter, David H.; Girshick, Steven L.; Kushner, Mark J.

2015-09-01

Silicon nanocrystals (SNCs) are of interest for light emitting electronics, photovoltaics, and biotechnology. SNCs are produced in low pressure capacitively coupled plasmas (CCPs) sustained in SiH4 containing mixtures. To optimize these applications, it is necessary to control the size distribution of the SNCs. Particles 3-5 nm diameter are typically tailored by flow rates and power, however the fundamental processes responsible for this size control are not well understood. We developed a 2-d computer model for RF powered CCPs to predict the synthesis of SNCs. An aerosol sectional model was incorporated into the Hybrid Plasma Equipment Model. The reactor is a quartz tube a few mm in diameter through which 100 sccm Ar and 15 sccm He/SiH4 = 95/5 at 2 Torr are flowed. The SNC residence time is 1-2 ms in the dense plasma region near the electrodes. We found that the distribution of plasma potential is important in determining the growth and size distribution of the SNCs. The SNCs having long residence times in the plasma, thereby enabling growth, are usually negatively charged. To ultimately allow these SNCs to flow out of the plasma, the distribution of the plasma potential must enable the particles to be entrained in the neutral gas flow without a significant potential barrier. We also found that agglomeration of particles of <1 nm is important in the rate of growth of SNCs. Work supported by DOE (DE-SC0001939) and NSF (CHE-124752).

Investigations of the role of nonlinear couplings in structure formation and transport regulation in plasma turbulence

NASA Astrophysics Data System (ADS)

Holland, Christopher George

Studies of nonlinear couplings and dynamics in plasma turbulence are presented. Particular areas of focus are analytic studies of coherent structure formation in electron temperature gradient turbulence, measurement of nonlinear energy transfer in simulations of plasma turbulence, and bispectral analysis of experimental and computational data. The motivation for these works has been to develop and expand the existing theories of plasma transport, and verify the nonlinear predictions of those theories in simulation and experiment. In Chapter II, we study electromagnetic secondary instabilities of electron temperature gradient turbulence. The growth rate for zonal flow generation via modulational instability of electromagnetic ETG turbulence is calculated, as well as that for zonal (magnetic) field generation. In Chapter III, the stability and saturation of streamers in ETG turbulence is considered, and shown to depend sensitively upon geometry and the damping rates of the Kelvin-Helmholtz mode. Requirements for a credible theory of streamer transport are presented. In addition, a self-consistent model for interactions between ETG and ITG (ion temperature gradient) turbulence is presented. In Chapter IV, the nonlinear transfer of kinetic and internal energy is measured in simulations of plasma turbulence. The regulation of turbulence by radial decorrelation due to zonal flows and generation of zonal flows via the Reynolds stress are explicitly demonstrated, and shown to be symmetric facets of a single nonlinear process. Novel nonlinear saturation mechanisms for zonal flows are discussed. In Chapter V, measurements of fluctuation bicoherence in the edge of the DIII-D tokamak are presented. It is shown that the bicoherence increases transiently before a L-H transition, and decays to its initial value after the barrier has formed. The increase in bicoherence is localized to the region where the transport barrier forms, and shows strong coupling between well-separated frequencies. These results are qualitatively reproduced in a simple numerical "thought experiment," described in Chapter VI, which suggests that zonal flows may trigger the L-H transition.

3-Dimensional Modeling of Capacitively and Inductively Coupled Plasma Etching Systems

NASA Astrophysics Data System (ADS)

Rauf, Shahid

2008-10-01

Low temperature plasmas are widely used for thin film etching during micro and nano-electronic device fabrication. Fluid and hybrid plasma models were developed 15-20 years ago to understand the fundamentals of these plasmas and plasma etching. These models have significantly evolved since then, and are now a major tool used for new plasma hardware design and problem resolution. Plasma etching is a complex physical phenomenon, where inter-coupled plasma, electromagnetic, fluid dynamics, and thermal effects all have a major influence. The next frontier in the evolution of fluid-based plasma models is where these models are able to self-consistently treat the inter-coupling of plasma physics with fluid dynamics, electromagnetics, heat transfer and magnetostatics. We describe one such model in this paper and illustrate its use in solving engineering problems of interest for next generation plasma etcher design. Our 3-dimensional plasma model includes the full set of Maxwell equations, transport equations for all charged and neutral species in the plasma, the Navier-Stokes equation for fluid flow, and Kirchhoff's equations for the lumped external circuit. This model also includes Monte Carlo based kinetic models for secondary electrons and stochastic heating, and can take account of plasma chemistry. This modeling formalism allows us to self-consistently treat the dynamics in commercial inductively and capacitively coupled plasma etching reactors with realistic plasma chemistries, magnetic fields, and reactor geometries. We are also able to investigate the influence of the distributed electromagnetic circuit at very high frequencies (VHF) on the plasma dynamics. The model is used to assess the impact of azimuthal asymmetries in plasma reactor design (e.g., off-center pump, 3D magnetic field, slit valve, flow restrictor) on plasma characteristics at frequencies from 2 -- 180 MHz. With Jason Kenney, Ankur Agarwal, Ajit Balakrishna, Kallol Bera, and Ken Collins.

Research progress on ionic plasmas generated in an intense hydrogen negative ion source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takeiri, Y., E-mail: takeiri@nifs.ac.jp; Tsumori, K.; Nagaoka, K.

2015-04-08

Characteristics of ionic plasmas, observed in a high-density hydrogen negative ion source, are investigated with a multi-diagnostics system. The ionic plasma, which consists of hydrogen positive- and negative-ions with a significantly low-density of electrons, is generated in the ion extraction region, from which the negative ions are extracted through the plasma grid. The negative ion density, i.e., the ionic plasma density, as high as the order of 1×10{sup 17}m{sup −3}, is measured with cavity ring-down spectroscopy, while the electron density is lower than 1×10{sup 16}m{sup −3}, which is confirmed with millimeter-wave interferometer. Reduction of the negative ion density is observedmore » at the negative ion extraction, and at that time the electron flow into the ionic plasma region is observed to conserve the charge neutrality. Distribution of the plasma potential is measured in the extraction region in the direction normal to the plasma grid surface with a Langmuir probe, and the results suggest that the sheath is formed at the plasma boundary to the plasma grid to which the bias voltage is applied. The beam extraction should drive the negative ion transport in the ionic plasma across the sheath formed on the extraction surface. Larger reduction of the negative ions at the beam extraction is observed in a region above the extraction aperture on the plasma grid, which is confirmed with 2D image measurement of the Hα emission and cavity ring-down spectroscopy. The electron distribution is also measured near the plasma grid surface. These various properties observed in the ionic plasma are discussed.« less

Decontamination of Chemical/Biological Warfare (CBW) Agents Using an Atmospheric Pressure Plasma Jet (APPJ)

NASA Astrophysics Data System (ADS)

Herrmann, Hans W.

1998-11-01

The atmospheric pressure plasma jet (APPJ) is a non-thermal, high pressure, uniform glow discharge that produces a high velocity effluent stream of highly reactive chemical species. The discharge operates on a feedstock gas (e.g. He/O_2/H_2O) which flows between an outer, grounded, cylindrical electrode and an inner, coaxial electrode powered at 13.56 MHz RF. While passing through the plasma, the feedgas becomes excited, dissociated or ionized by electron impact. Once the gas exits the discharge volume, ions and electrons are rapidly lost by recombination, but the fast-flowing effluent still contains metastables (e.g. O2*, He*) and radicals (e.g. O, OH). These reactive species have been shown to be effective neutralizers of surrogates for anthrax spores, mustard blister agent and VX nerve gas. Unlike conventional, wet decontamination methods, the plasma effluent does not cause corrosion of most surfaces and does not damage wiring, electronics, nor most plastics. This makes it highly suitable for decontamination of high value sensitive equipment such as is found in vehicle interiors (i.e. tanks, planes...) for which there is currently no good decontamination technique. Furthermore, the reactive species rapidly degrade into harmless products leaving no lingering residue or harmful byproducts. Physics of the APPJ will be discussed and results of surface decontamination experiments using simulant and actual CBW agents will be presented.

A droplet in the inter-electrode gap during gas metal arc welding

NASA Astrophysics Data System (ADS)

Nemchinsky, Valerian

2011-11-01

Electrical current flowing through a metallic droplet after its detachment from the wire anode during gas metal arc welding (GMAW) is considered. Although the droplet has much higher electrical conductivity compared with the conductivity of the surrounding plasma, current cannot enter the droplet freely since doing so demands igniting of the cathode spot responsible for electron emission. A new mechanism of current flow through a metallic droplet is suggested: one part of the droplet has a potential, which is slightly below the floating potential; this part of the droplet collects ions from the plasma. The remaining portion of the droplet has a potential difference, which is slightly above the floating one. The latter section collects electrons which recombine with the ions collected by the rest of the droplet's surface. The maximum electric current that can flow through the droplet is estimated. It is shown that this current is on the order of a few tens of amperes.

Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam.

PubMed

Warwick, J; Dzelzainis, T; Dieckmann, M E; Schumaker, W; Doria, D; Romagnani, L; Poder, K; Cole, J M; Alejo, A; Yeung, M; Krushelnick, K; Mangles, S P D; Najmudin, Z; Reville, B; Samarin, G M; Symes, D D; Thomas, A G R; Borghesi, M; Sarri, G

2017-11-03

We report on the first experimental observation of a current-driven instability developing in a quasineutral matter-antimatter beam. Strong magnetic fields (≥1  T) are measured, via means of a proton radiography technique, after the propagation of a neutral electron-positron beam through a background electron-ion plasma. The experimentally determined equipartition parameter of ε_{B}≈10^{-3} is typical of values inferred from models of astrophysical gamma-ray bursts, in which the relativistic flows are also expected to be pair dominated. The data, supported by particle-in-cell simulations and simple analytical estimates, indicate that these magnetic fields persist in the background plasma for thousands of inverse plasma frequencies. The existence of such long-lived magnetic fields can be related to analog astrophysical systems, such as those prevalent in lepton-dominated jets.

Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam

NASA Astrophysics Data System (ADS)

Warwick, J.; Dzelzainis, T.; Dieckmann, M. E.; Schumaker, W.; Doria, D.; Romagnani, L.; Poder, K.; Cole, J. M.; Alejo, A.; Yeung, M.; Krushelnick, K.; Mangles, S. P. D.; Najmudin, Z.; Reville, B.; Samarin, G. M.; Symes, D. D.; Thomas, A. G. R.; Borghesi, M.; Sarri, G.

2017-11-01

We report on the first experimental observation of a current-driven instability developing in a quasineutral matter-antimatter beam. Strong magnetic fields (≥1 T ) are measured, via means of a proton radiography technique, after the propagation of a neutral electron-positron beam through a background electron-ion plasma. The experimentally determined equipartition parameter of ɛB≈10-3 is typical of values inferred from models of astrophysical gamma-ray bursts, in which the relativistic flows are also expected to be pair dominated. The data, supported by particle-in-cell simulations and simple analytical estimates, indicate that these magnetic fields persist in the background plasma for thousands of inverse plasma frequencies. The existence of such long-lived magnetic fields can be related to analog astrophysical systems, such as those prevalent in lepton-dominated jets.

The response of the ionosphere to the injection of chemically reactive vapors

NASA Technical Reports Server (NTRS)

Bernhardt, P. A.

1976-01-01

As a gas released in the ionosphere expands, it is rapidly cooled. When the vapor becomes sufficiently tenuous, it is reheated by collisions with the ambient atmosphere and its flow is then governed by diffusive expansion. As the injected gas becomes well mixed with the plasma, a hole is created by chemical processes. In the case of diatomic hydrogen release, depression of the electron concentrations is governed by the charge exchange reaction between oxygen ions and hydrogen, producing positive hydroxyl ions. Hydroxyl ions rapidly react with the electron gas to produce excited oxygen and hydrogen atoms. Enhanced airglow emissions result from the transition of the excited atoms to lower energy states. The electron temperature in the depleted region rises sharply causing a thermal expansion of the plasma and a further reduction in the local plasma concentration.

Measurement of hydroxyl radical density generated from the atmospheric pressure bioplasma jet

NASA Astrophysics Data System (ADS)

Hong, Y. J.; Nam, C. J.; Song, K. B.; Cho, G. S.; Uhm, H. S.; Choi, D. I.; Choi, E. H.

2012-03-01

Atmospheric pressure bioplasmas are being used in a variety of bio-medical and material processing applications, surface modifications of polymers. This plasma can generate the various kinds of radicals when it contacs with the water. Especially, hydroxyl radical species have very important role in the biological and chemical decontamination of media in this situation. It is very important to investigate the hydroxyl radical density in needle-typed plasma jet since it plays a crucial role in interaction between the living body and plasma. We have generated the needle-typed plasma jet bombarding the water surface by using an Ar gas flow and investigated the emission lines by OES (optical emission spectroscopy). It is noted that the electron temperature and plasma density are measured to be about 1.7 eV and 3.4 × 1012 cm-3, respectively, under Ar gas flow ranged from 80 to 300 sccm (standard cubic centimeter per minute) in this experiment. The hydroxyl radical density has also been investigated and measured to be maximum value of 2.6 × 1015 cm-3 for the gas flow rate of 150 sccm in the needle-typed plasma jet by the ultraviolet optical absorption spectroscopy.

Particle and field characteristics of the high-latitude plasma sheet boundary layer

NASA Technical Reports Server (NTRS)

Parks, G. K.; Mccarthy, M.; Fitzenreiter, R. J.; Ogilvie, K. W.; Etcheto, J.; Anderson, K. A.; Lin, R. P.; Anderson, R. R.; Eastman, T. E.; Frank, L. A.

1984-01-01

Particle and field data obtained by eight ISEE spacecraft experiments are used to define more precisely the characteristics of the high-latitude boundary region of the plasma sheet. A region immediately adjacent to the high-latitude plasma sheet boundary has particle and field characteristics distinctly different from those observed in the lobe and deeper in the central plasma sheet. Electrons over a broad energy interval are 'field-aligned' and bidirectional, whereas in the plasma sheet the distributions are more isotropic. The region supports intense ion flows, large-amplitude electric fields, and enhanced broad-band electrostatic noise.

Condensed Plasmas under Microgravity

NASA Technical Reports Server (NTRS)

Morfill, G. E.; Thomas, H. M.; Konopka, U.; Rothermel, H.; Zuzic, M.; Ivlev, A.; Goree, J.; Rogers, Rick (Technical Monitor)

1999-01-01

Experiments under microgravity conditions were carried out to study 'condensed' (liquid and crystalline) states of a colloidal plasma (ions, electrons, and charged microspheres). Systems with approximately 10(exp 6) microspheres were produced. The observed systems represent new forms of matter--quasineutral, self-organized plasmas--the properties of which are largely unexplored. In contrast to laboratory measurements, the systems under microgravity are clearly three dimensional (as expected); they exhibit stable vortex flows, sometimes adjacent to crystalline regions, and a central 'void,' free of microspheres.

Diagnosing the Fine Structure of Electron Energy Within the ECRIT Ion Source

NASA Astrophysics Data System (ADS)

Jin, Yizhou; Yang, Juan; Tang, Mingjie; Luo, Litao; Feng, Bingbing

2016-07-01

The ion source of the electron cyclotron resonance ion thruster (ECRIT) extracts ions from its ECR plasma to generate thrust, and has the property of low gas consumption (2 sccm, standard-state cubic centimeter per minute) and high durability. Due to the indispensable effects of the primary electron in gas discharge, it is important to experimentally clarify the electron energy structure within the ion source of the ECRIT through analyzing the electron energy distribution function (EEDF) of the plasma inside the thruster. In this article the Langmuir probe diagnosing method was used to diagnose the EEDF, from which the effective electron temperature, plasma density and the electron energy probability function (EEPF) were deduced. The experimental results show that the magnetic field influences the curves of EEDF and EEPF and make the effective plasma parameter nonuniform. The diagnosed electron temperature and density from sample points increased from 4 eV/2×1016 m-3 to 10 eV/4×1016 m-3 with increasing distances from both the axis and the screen grid of the ion source. Electron temperature and density peaking near the wall coincided with the discharge process. However, a double Maxwellian electron distribution was unexpectedly observed at the position near the axis of the ion source and about 30 mm from the screen grid. Besides, the double Maxwellian electron distribution was more likely to emerge at high power and a low gas flow rate. These phenomena were believed to relate to the arrangements of the gas inlets and the magnetic field where the double Maxwellian electron distribution exits. The results of this research may enhance the understanding of the plasma generation process in the ion source of this type and help to improve its performance. supported by National Natural Science Foundation of China (No. 11475137)

The Madison plasma dynamo experiment: A facility for studying laboratory plasma astrophysics

NASA Astrophysics Data System (ADS)

Cooper, C. M.; Wallace, J.; Brookhart, M.; Clark, M.; Collins, C.; Ding, W. X.; Flanagan, K.; Khalzov, I.; Li, Y.; Milhone, J.; Nornberg, M.; Nonn, P.; Weisberg, D.; Whyte, D. G.; Zweibel, E.; Forest, C. B.

2014-01-01

The Madison plasma dynamo experiment (MPDX) is a novel, versatile, basic plasma research device designed to investigate flow driven magnetohydrodynamic instabilities and other high-β phenomena with astrophysically relevant parameters. A 3 m diameter vacuum vessel is lined with 36 rings of alternately oriented 4000 G samarium cobalt magnets, which create an axisymmetric multicusp that contains ˜14 m3 of nearly magnetic field free plasma that is well confined and highly ionized (>50%). At present, 8 lanthanum hexaboride (LaB6) cathodes and 10 molybdenum anodes are inserted into the vessel and biased up to 500 V, drawing 40 A each cathode, ionizing a low pressure Ar or He fill gas and heating it. Up to 100 kW of electron cyclotron heating power is planned for additional electron heating. The LaB6 cathodes are positioned in the magnetized edge to drive toroidal rotation through J × B torques that propagate into the unmagnetized core plasma. Dynamo studies on MPDX require a high magnetic Reynolds number Rm > 1000, and an adjustable fluid Reynolds number 10 < Re < 1000, in the regime where the kinetic energy of the flow exceeds the magnetic energy (MA2=(v/vA)2>1). Initial results from MPDX are presented along with a 0-dimensional power and particle balance model to predict the viscosity and resistivity to achieve dynamo action.

Efficient production of high-energy nonthermal particles during magnetic reconnection in a magnetically dominated ion-electron plasma

DOE PAGES

Guo, Fan; Li, Xiaocan; Li, Hui; ...

2016-02-03

Magnetic reconnection is a leading mechanism for dissipating magnetic energy and accelerating nonthermal particles in Poynting-flux-dominated flows. We investigate nonthermal particle acceleration during magnetic reconnection in a magnetically dominated ion–electron plasma using fully kinetic simulations. For an ion–electron plasma with a total magnetization ofmore » $${\\sigma }_{0}={B}^{2}/(4\\pi n({m}_{i}+{m}_{e}){c}^{2})$$, the magnetization for each species is $${\\sigma }_{i}\\sim {\\sigma }_{0}$$ and $${\\sigma }_{e}\\sim ({m}_{i}/{m}_{e}){\\sigma }_{0}$$, respectively. We have studied the magnetically dominated regime by varying σe = 103–105 with initial ion and electron temperatures $${T}_{i}={T}_{e}=5-20{m}_{e}{c}^{2}$$ and mass ratio $${m}_{i}/{m}_{e}=1-1836$$. Our results demonstrate that reconnection quickly establishes power-law energy distributions for both electrons and ions within several (2–3) light-crossing times. For the cases with periodic boundary conditions, the power-law index is $$1\\lt s\\lt 2$$ for both electrons and ions. The hard spectra limit the power-law energies for electrons and ions to be $${\\gamma }_{{be}}\\sim {\\sigma }_{e}$$ and $${\\gamma }_{{bi}}\\sim {\\sigma }_{i}$$, respectively. The main acceleration mechanism is a Fermi-like acceleration through the drift motions of charged particles. When comparing the spectra for electrons and ions in momentum space, the spectral indices sp are identical as predicted in Fermi acceleration. We also find that the bulk flow can carry a significant amount of energy during the simulations. Finally, we discuss the implication of this study in the context of Poynting-flux dominated jets and pulsar winds, especially the applications for explaining nonthermal high-energy emissions.« less

The Pioneer 10 plasma analyzer results at Jupiter

NASA Technical Reports Server (NTRS)

Wolfe, J. H.

1975-01-01

Results are reported for the Pioneer 10 plasma-analyzer experiment at Jupiter. The analyzer system consisted of dual 90-deg quadrispherical electrostatic analyzers, multiple charged-particle detectors, and attendant electronics; it was capable of determining the incident plasma-distribution parameters over the energy range from 100 to 18,000 eV for protons and from approximately 1 to 500 eV for electrons. Data are presented on the interaction between the solar wind and the Jovian magnetosphere, the interplanetary ion flux, observations of the magnetosheath plasma, and traversals of the bow shock and magnetopause. Values are estimated for the proton isotropic temperature, number density, and bulk velocity within the magnetosheath flow field as well as for the beta parameter, ion number density, and magnetic-energy density of the magnetospheric plasma. It is argued that Jupiter has a reasonably thick magnetosphere somewhat similar to earth's except for the vastly different scale sizes involved.

Impurities, temperature, and density in a miniature electrostatic plasma and current source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Den Hartog, D.J.; Craig, D.J.; Fiksel, G.

1996-10-01

We have spectroscopically investigated the Sterling Scientific miniature electrostatic plasma source-a plasma gun. This gun is a clean source of high density (10{sup 19} - 10{sup 20} m{sup -3}), low temperature (5 - 15 eV) plasma. A key result of our investigation is that molybdenum from the gun electrodes is largely trapped in the internal gun discharge; only a small amount escapes in the plasma flowing out of the gun. In addition, the gun plasma parameters actually improve (even lower impurity contamination and higher ion temperature) when up to 1 kA of electron current is extracted from the gun viamore » the application of an external bias. This improvement occurs because the internal gun anode no longer acts as the current return for the internal gun discharge. The gun plasma is a virtual plasma electrode capable of sourcing an electron emission current density of 1 kA/cm{sup 2}. The high emission current, small size (3 - 4 cm diameter), and low impurity generation make this gun attractive for a variety of fusion and plasma technology applications.« less

The value of swarm data for practical modeling of plasma devices

NASA Astrophysics Data System (ADS)

Napartovich, A. P.; Kochetov, I. V.

2011-04-01

The non-thermal plasma is a key component in gas lasers, waste gas cleaners, ozone generators, plasma igniters, flame holders, flow control in high-speed aerodynamics and other applications. The specific feature of the non-thermal plasma is its high sensitivity to variations in governing parameters (gas composition, pressure, pulse duration, E/N parameter). The reactivity of the plasma is due to the appearance of atoms and chemical radicals. For the efficient production of chemically active species high average electron energy is required, which is controlled by the balance of gain from the electric field and loss in inelastic collisions. In low-ionized plasma the electron energy distribution function is far from Maxwellian and must be found numerically for specified conditions. Numerical modeling of processes in plasma technologies requires vast databases on electron scattering cross sections to be available. The only reliable criterion for evaluations of validity of a set of cross sections for a particular species is a correct prediction of electron transport and kinetic coefficients measured in swarm experiments. This criterion is used traditionally to improve experimentally measured cross sections, as was suggested earlier by Phelps. The set of cross sections subjected to this procedure is called a self-consistent set. Nowadays, such reliable self-consistent sets are known for many species. Problems encountered in implementation of the fitting procedure and examples of its successful applications are described in the paper. .

PREFACE: International Congress on Energy Fluxes and Radiation Effects (EFRE-2014)

NASA Astrophysics Data System (ADS)

2014-11-01

The International Congress on Energy Fluxes and Radiation Effects 2014 (EFRE 2014) was held in Tomsk, Russia, on September 21-26, 2014. The organizers of the Congress were the Institute of High Current Electronics SB RAS and Tomsk Polytechnic University. EFRE 2014 combines three international conferences which are regularly held in Tomsk, Russia: the 18th International Symposium on High-Current Electronics (18th SHCE), the 12th International Conference on Modification of Materials with Particle Beams and Plasma Flows (12th CMM) and the 16th International Conference on Radiation Physics and Chemistry of Condensed Matter (16th RPC). The International Conference on Radiation Physics and Chemistry of Condensed Matter is a traditional representative forum devoted to the discussion of the fundamental problems of physical and chemical non-linear processes in condensed matter (mainly inorganic dielectrics) under the action of particle and photon beams of all types including pulsed power laser radiation. The International Symposium on High-Current Electronics is held biannually in Tomsk, Russia. The program of the conferences covers a wide range of scientific and technical areas including pulsed power technology, ion and electron beams, high-power microwaves, plasma and particle beam sources, modification of materials, and pulsed power applications in chemistry, biology and medicine. The 12th International Conference on Modification of Materials with Particle Beams and Plasma Flows is devoted to the discussion of the fundamental and applied issues in the field of modification of materials properties with particle beams and plasma flows. The six-day Congress brought together more than 250 specialists and scientists from different countries and organizations and provided an excellent opportunity to exchange knowledge, make oral contributions and poster presentations, and initiate discussion on the topics of interest. The proceedings were edited by Victor Lisitsyn, Vladimir Lopatin, and Anna Bogdan. We appreciate the contribution of the invited speakers and all participants, as well as sponsors "Intech Analytics" and "MICROSPLAV" for making the Congress successful.

Poker flat radar observations of the magnetosphere-ionosphere coupling electrodynamics of the earthward penetrating plasma sheet following convection enhancements

NASA Astrophysics Data System (ADS)

Lyons, L. R.; Zou, S.; Heinselman, C. J.; Nicolls, M. J.; Anderson, P. C.

2009-05-01

The plasma sheet moves earthward (equatorward in the ionosphere) after enhancements in convection, and the electrodynamics of this response is strongly influenced by Region 2 magnetosphere-ionosphere coupling. We have used Poker Flat Advanced Modular Incoherent Scatter Radar (PFISR) observations associated with two relatively abrupt southward turnings of the IMF to provide an initial evaluation of aspects of this response. The observations show that strong westward sub-auroral polarization streams (SAPS) flow regions moved equatorward as the plasma sheet electron precipitation (the diffuse aurora) penetrated equatorward following the IMF southward turnings. Consistent with our identification of these flows as SAPS, concurrent DMSP particle precipitation measurements show the equatorial boundary of ion precipitation equatorward of the electron precipitation boundary and that westward flows lie within the low-conductivity region between the two boundaries where the plasma sheet ion pressure gradient is expected to drive downward R2 currents. Evidence for these downward currents is seen in the DMSP magnetometer observations. Preliminary examination indicates that the SAPS response seen in the examples presented here may be common. However, detailed analysis will be required for many more events to reliably determine if this is the case. If so, it would imply that SAPS are frequently an important aspect of the inner magnetospheric electric field distribution, and that they are critical for understanding the response of the magnetosphere-ionosphere system to enhancements in convection, including understanding the earthward penetration of the plasma sheet. This earthward penetration is critical to geomagnetic disturbance phenomena such as the substorm growth phase and the formation of the stormtime ring current. Additionally, for one example, a prompt electric field response to the IMF southward turnings is seen within the inner plasma sheet.

Kadomtsev−Petviashvili equation for a flow of highly nonisothermal collisionless plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Movsesyants, Yu. B., E-mail: yumovsesyants@gmail.com; Rukhadze, A. A., E-mail: rukh@fpl.gpi.ru; Tyuryukanov, P. M.

2016-01-15

It is shown that the equations of two-fluid electrodynamics for a cold ions flow and Boltzmann electrons in the vicinity of the ion-sound point can be reduced to the Kadomtsev−Petviashvili equation. Examples of two-dimensional equilibria with pole singularities obtained by exactly solving the equations are presented. An exact self-similar solution describing a two-dimensional transonic flow and having no pole singularities is found.

Kadomtsev-Petviashvili equation for a flow of highly nonisothermal collisionless plasma

NASA Astrophysics Data System (ADS)

Movsesyants, Yu. B.; Rukhadze, A. A.; Tyuryukanov, P. M.

2016-01-01

It is shown that the equations of two-fluid electrodynamics for a cold ions flow and Boltzmann electrons in the vicinity of the ion-sound point can be reduced to the Kadomtsev-Petviashvili equation. Examples of two-dimensional equilibria with pole singularities obtained by exactly solving the equations are presented. An exact self-similar solution describing a two-dimensional transonic flow and having no pole singularities is found.

Investigations of Particle Transport in the Texas Helimak

NASA Astrophysics Data System (ADS)

Taylor, E. I.; Rowan, W. L.; Gentle, K. W.; Huang, H.; Williams, C. B.

2016-10-01

The correlation between electrostatic turbulence and particle flux is investigated in a simple magnetic torus, the Helimak. The Helimak is an experimental realization of a sheared cylindrical slab that generates and heats a plasma with microwaves at 2.45 GHz and confines it in a helical magnetic field. Although it is MHD stable, the plasma is always in a nonlinearly saturated state of microturbulence. The causes of this turbulence are diverse and it is thought that it is either due to drift wave instabilities or interchange instabilites. The local particle flux is estimated over most of the plasma cross section by measuring the particle source using filtered cameras. Plasma flow along the field lines is physically similar to SOL flows in tokamaks. It is significant and can be measured directly as well as inferred from asymmetries in the electron density. The cross field transport due to electrostatic turbulence is measured as the cross correlation of radial electric field fluctuations with electron density fluctuations with the data acquired using Langmuir probes. This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Fusion Energy Sciences under Award Number DE-FG02-04ER54766.

ICPP: Beltrami fields in plasmas -- H-mode boundary layers and high beta equilibria

NASA Astrophysics Data System (ADS)

Yoshida, Zensho

2000-10-01

The Beltrami fields, eigenfunctions of the curl operator, represent essential characteristics of twisted, spiral, chiral or helical structures in various vector fields. Amongst diverse applications of the theory of Beltrami fields, the present paper focuses on the self-organized states of plasmas. The Taylor relaxed state is the principal example of self-organized Beltrami fields. Suppose that a plasma is produced in an external magnetic field (harmonic field). If we do not apply any drive, the plasma will disappear and the system will relax into the harmonic magnetic field. When we drive a current and sustain the total helicity, the plasma relaxes into the Taylor state and achieves the Beltrami magnetic field. When a strong flow is implemented to a plasma, self-organized states becomes qualitatively different from the conventional relaxed stats. The two-fluid effect induces a coupling among the flow, magnetic field, electric field and the pressure, resulting in a "singular perturbation" to the MHD system. To invoke this effect, one must supply a driving force to sustain a strong flow. It is equivalent to giving an internal electric field or applying a steep gradient in pressure, because these fields are tightly coupled. In the two-fluid model, the Beltrami condition demands that the vorticity parallels the flow in both electron and ion fluids. We find that a superposition of two Beltrami magnetic fields (and also two Beltrami flows) solves the simultaneous two-fluid Beltrami conditions [1]. Despite this simple mathematical structure, the set of solutions contains field configurations that are far richer than the conventional theory. The hydrodynamic pressure of a shear flow yields a diamagnetic state that is suitable for confining a high-beta plasma. The H-mode boundary layer is an example, which is spontaneously generated by the core plasma pressure [2]. Active control of shear flow will significantly extend the scope of such self-organized states [3]. [1] S. M. Mahajan and Z. Yoshida, Phys. Rev. Lett. 81, 4863 (1998). [2] S. M. Mahajan and Z. Yoshida, Phys. Plasmas 7, 635 (2000). [3] Z. Yoshida et al., in Non-Neutral Plasma Physics III (ed. J.J. Bollinger, AIP, 1999), 397.

Plasma Instabilities in Hall Thrusters

NASA Astrophysics Data System (ADS)

Litvak, Andrei A.; Fisch, Nathaniel J.

2000-10-01

We describe theoretically waves in the channel of a Hall thruster, propagating transversely to the accelerated ion flow. In slab geometry, a two-fluid hydrodynamic theory with collisional terms shows that azimuthal lower-hybrid and Alfven waves will be unstable due to electron collisions in the presence of ExB drift. In addition, plasma inhomogeneities can drive other instabilities that can be analyzed through a dispersion relation in the well-known form of the Rayleigh equation. An instability condition is derived for azimuthal electrostatic waves, synchronized with the electron drift flow. Propagation with nonzero wavenumber along the magnetic field is also studied. Thus, several different aspects of wave propagation during thruster operation are explored. These waves may be important to understand and possibly to control in view of the possible influence of thruster electromagnetic effects on communication signal propagation.

Current leakage for low altitude satellites - Modeling applications. [simulation of high voltage solar cell array in ionospheric plasma environment

NASA Technical Reports Server (NTRS)

Konradi, A.; Mccoy, J. E.; Garriott, O. K.

1979-01-01

To simulate the behavior of a high voltage solar cell array in the ionospheric plasma environment, the large (90 ft x 55 ft diameter) vacuum chamber was used to measure the high-voltage plasma interactions of a 3 ft x 30 ft conductive panel. The chamber was filled with Nitrogen and Argon plasma at electron densities of up to 1,000,000 per cu cm. Measurements of current flow to the plasma were made in three configurations: (a) with one end of the panel grounded, (b) with the whole panel floating while a high bias was applied between the ends of the panel, and (c) with the whole panel at high negative voltage with respect to the chamber walls. The results indicate that a simple model with a constant panel conductivity and plasma resistance can adequately describe the voltage distribution along the panel and the plasma current flow. As expected, when a high potential difference is applied to the panel ends more than 95% of the panel floats negative with respect to the plasma.

Slowing of magnetic reconnection concurrent with weakening plasma inflows and increasing collisionality in strongly-driven laser-plasma experiments

DOE PAGES

Rosenberg, M.  J.; Li, C.  K.; Fox, W.; ...

2015-05-20

An evolution of magnetic reconnection behavior, from fast jets to the slowing of reconnection and the establishment of a stable current sheet, has been observed in strongly-driven, β ≲ 20 laser-produced plasma experiments. This process has been inferred to occur alongside a slowing of plasma inflows carrying the oppositely-directed magnetic fields as well as the evolution of plasma conditions from collisionless to collisional. High-resolution proton radiography has revealed unprecedented detail of the forced interaction of magnetic fields and super-Alfvénic electron jets (V jet~ 20V A) ejected from the reconnection region, indicating that two-fluid or collisionless magnetic reconnection occurs early inmore » time. The absence of jets and the persistence of strong, stable magnetic fields at late times indicates that the reconnection process slows down, while plasma flows stagnate and plasma conditions evolve to a cooler, denser, more collisional state. These results demonstrate that powerful initial plasma flows are not sufficient to force a complete reconnection of magnetic fields, even in the strongly-driven regime.« less

Study of plasma natural convection induced by electron beam in atmosphere [

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, Yongfeng, E-mail: yfdeng@mail.dlut.edu.cn; Han, Xianwei; Tan, Yonghua

2014-06-15

Using high-energy electron beams to ionize air is an effective way to produce a large-size plasma in the atmosphere. In particular, with a steady-state high power generator, some unique phenomena can be achieved, including natural convection of the plasma. The characteristics of this convection are studied both experimentally and numerically. The results show that an asymmetrical temperature field develops with magnitudes that vary from 295 K to 389 K at a pressure of 100 Torr. Natural convection is greatly enhanced under 760 Torr. Nevertheless, plasma transport is negligible in this convection flow field and only the plasma core tends to move upward. Parameter analysismore » is performed to discern influencing factors on this phenomenon. The beam current, reflecting the Rayleigh number Ra effect, correlates with convection intensity, which indicates that energy deposition is the underlying key factor in determining such convections. Finally, natural convection is concluded to be an intrinsic property of the electron beam when focused into dense air, and can be achieved by carefully adjusting equipment operations parameters.« less

Spatial structure of ion beams in an expanding plasma

NASA Astrophysics Data System (ADS)

Aguirre, E. M.; Scime, E. E.; Thompson, D. S.; Good, T. N.

2017-12-01

We report spatially resolved perpendicular and parallel, to the magnetic field, ion velocity distribution function (IVDF) measurements in an expanding argon helicon plasma. The parallel IVDFs, obtained through laser induced fluorescence (LIF), show an ion beam with v ≈ 8000 m/s flowing downstream and confined to the center of the discharge. The ion beam is measurable for tens of centimeters along the expansion axis before the LIF signal fades, likely a result of metastable quenching of the beam ions. The parallel ion beam velocity slows in agreement with expectations for the measured parallel electric field. The perpendicular IVDFs show an ion population with a radially outward flow that increases with distance from the plasma axis. Structures aligned to the expanding magnetic field appear in the DC electric field, the electron temperature, and the plasma density in the plasma plume. These measurements demonstrate that at least two-dimensional and perhaps fully three-dimensional models are needed to accurately describe the spontaneous acceleration of ion beams in expanding plasmas.

Experimental results from magnetized-jet experiments executed at the Jupiter Laser Facility

NASA Astrophysics Data System (ADS)

Manuel, M. J.-E.; Kuranz, C. C.; Rasmus, A. M.; Klein, S. R.; MacDonald, M. J.; Trantham, M. R.; Fein, J. R.; Belancourt, P. X.; Young, R. P.; Keiter, P. A.; Drake, R. P.; Pollock, B. B.; Park, J.; Hazi, A. U.; Williams, G. J.; Chen, H.

2015-12-01

Recent experiments at the Jupiter Laser Facility investigated magnetization effects on collimated plasma jets. Laser-irradiated plastic-cone-targets produced collimated, millimeter-scale plasma flows as indicated by optical interferometry. Proton radiography of these jets showed no indication of strong, self-generated magnetic fields, suggesting a dominantly hydrodynamic collimating mechanism. Targets were placed in a custom-designed solenoid capable of generating field strengths up to 5 T. Proton radiographs of the well-characterized B-field, without a plasma jet, suggested an external source of trapped electrons that affects proton trajectories. The background magnetic field was aligned with the jet propagation direction, as is the case in many astrophysical systems. Optical interferometry showed that magnetization of the plasma results in disruption of the collimated flow and instead produces a hollow cavity. This result is a topic of ongoing investigation.

Collisionless damping of flows in the TJ-II stellarator

NASA Astrophysics Data System (ADS)

Sánchez, E.; Kleiber, R.; Hatzky, R.; Borchardt, M.; Monreal, P.; Castejón, F.; López-Fraguas, A.; Sáez, X.; Velasco, J. L.; Calvo, I.; Alonso, A.; López-Bruna, D.

2013-01-01

The results of global linear gyrokinetic simulations of residual flows carried out with the code EUTERPE in the TJ-II three-dimensional geometry are reported. The linear response of the plasma to potential perturbations homogeneous in a magnetic surface shows several oscillation frequencies: a Geodesic-acoustic-mode-like frequency, in qualitative agreement with the formula given by Sugama and Watanabe (2006 Plasma Phys. 72 825), and a much lower frequency oscillation in agreement with the predictions of Mishchenko et al (2008 Phys. Plasmas 15 072309) and Helander et al (2011 Plasma Phys. Control. Fusion 53 054006) for stellarators. The dependence of both oscillations on ion and electron temperatures and the magnetic configuration is studied. The low-frequency oscillations are in the frequency range supporting the long-range correlations between potential signals experimentally observed in TJ-II.

Magnetic reconnection in plasma under inertial confinement fusion conditions driven by heat flux effects in Ohm's law.

PubMed

Joglekar, A S; Thomas, A G R; Fox, W; Bhattacharjee, A

2014-03-14

In the interaction of high-power laser beams with solid density plasma there are a number of mechanisms that generate strong magnetic fields. Such fields subsequently inhibit or redirect electron flows, but can themselves be advected by heat fluxes, resulting in complex interplay between thermal transport and magnetic fields. We show that for heating by multiple laser spots reconnection of magnetic field lines can occur, mediated by these heat fluxes, using a fully implicit 2D Vlasov-Fokker-Planck code. Under such conditions, the reconnection rate is dictated by heat flows rather than Alfvènic flows. We find that this mechanism is only relevant in a high β plasma. However, the Hall parameter ωcτei can be large so that thermal transport is strongly modified by these magnetic fields, which can impact longer time scale temperature homogeneity and ion dynamics in the system.

Quantitative characterization of arc discharge as vacuum interface

DOE PAGES

Huang, S.; Zhu, K.; Lu, Y. R.; ...

2014-12-19

An arc discharge with channel diameters of 3 mm and 6 mm and lengths between 30mm and 60mm was experimentally investigated for its potential to function as plasma window, i.e., interface vacuum regions of different pressures. In this study, electron temperature of the plasma channel measured spectroscopically varied in the range of 7000K to 15000K, increasing with discharge current while decreasing with gas flow rate. The plasma window had a slightly positive I-V characteristics over the whole range of investigated current 30A–70 A. Measurements of pressure separation capability, which were determined by input current, gas flow rate, discharge channel diameter,more » and length, were well explained by viscosity effect and “thermal-block” effect. The experimental results of global parameters including temperature, gas flow rate, and voltage had a good agreement with the simulation results calculated by an axis-symmetry Fluent-based magneto-hydrodynamic model.« less

Investigating the role of hydrogen in silicon deposition using an energy-resolved mass spectrometer and a Langmuir probe in an Ar/H2 radio frequency magnetron discharge

NASA Astrophysics Data System (ADS)

Mensah, S. L.; Naseem, Hameed H.; Abu-Safe, Husam; Gordon, M. H.

2012-07-01

The plasma parameters and ion energy distributions (IED) of the dominant species in an Ar-H2 discharge are investigated with an energy resolved mass spectrometer and a Langmuir probe. The plasmas are generated in a conventional magnetron chamber powered at 150 W, 13.56 MHz at hydrogen flow rates ranging from 0 to 25 sccm with a fixed argon gas flow rate of 15 sccm. Various Hn+, SiHn+, SiHn fragments (with n = 1, 2, 3) together with Ar+ and ArH+ species are detected in the discharge. The most important species for the film deposition is SiHn (with n = 0, 1, 2). H fragments affect the hydrogen content in the material. The flux of Ar+ decreases and the flux of ArH+ increases when the hydrogen flow rate is increased; however, both fluxes saturate at hydrogen flow rates above 15 sccm. Electron density, ne, electron energy, Te, and ion density, ni, are estimated from the Langmuir probe data. Te is below 1.2 eV at hydrogen flow rates below 8 sccm, and about 2 eV at flow rates above 8 sccm. ne and ni decrease with increased hydrogen flow but the ratio of ni to ne increases. The formation of H+ ions with energies above 36 eV and electrons with energies greater than 2 eV contributes to the decrease in hydrogen content at hydrogen flow rates above 8 sccm. Analysis of the IEDs indicates an inter-dependence of the species and their contribution to the thin film growth and properties.

Properties of Minor Ions in the Solar Wind and Implications for the Background Solar Wind Plasma

NASA Technical Reports Server (NTRS)

Esser, Ruth; Wagner, William (Technical Monitor)

2003-01-01

Ion charge states measured in situ in interplanetary space are formed in the inner coronal regions below 5 solar radii, hence they carry information on the properties of the solar wind plasma in that region. The plasma parameters that are important in the ion forming processes are the electron density, the electron temperature and the flow speeds of the individual ion species. In addition, if the electron distribution function deviates from a Maxwellian already in the inner corona, then the enhanced tail of that distribution function, also called halo, greatly effects the ion composition. The goal of the proposal is to make use of ion fractions observed in situ in the solar wind to learn about both, the plasma conditions in the inner corona and the expansion and ion formation itself. This study is carried out using solar wind models, coronal observations, and ion fraction calculations in conjunction with the in situ observations.

Axisymmetric plasma equilibria in a Kerr metric

NASA Astrophysics Data System (ADS)

Elsässer, Klaus

2001-10-01

Plasma equilibria near a rotating black hole are considered within the multifluid description. An isothermal two-component plasma with electrons and positrons or ions is determined by four structure functions and the boundary conditions. These structure functions are the Bernoulli function and the toroidal canonical momentum per mass for each species. The quasi-neutrality assumption (no charge density, no toroidal current) allows to solve Maxwell's equations analytically for any axisymmetric stationary metric, and to reduce the fluid equations to one single scalar equation for the stream function \\chi of the positrons or ions, respectively. The basic smallness parameter is the ratio of the skin depth of electrons to the scale length of the metric and fluid quantities, and, in the case of an electron-ion plasma, the mass ratio m_e/m_i. The \\chi-equation can be solved by standard methods, and simple solutions for a Kerr geometry are available; they show characteristic flow patterns, depending on the structure functions and the boundary conditions.

Design of novel dual-port tapered waveguide plasma apparatus by numerical analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, D.; Zhou, R.; Yang, X. Q., E-mail: yyxxqq-mail@163.com

Microwave plasma apparatus is often of particular interest due to their superiority of low cost, electrode contamination free, and suitability for industrial production. However, there exist problems of unstable plasma and low electron density in conventional waveguide apparatus based on single port, due to low strength and non-uniformity of microwave field. This study proposes a novel dual-port tapered waveguide plasma apparatus based on power-combining technique, to improve the strength and uniformity of microwave field for the applications of plasma. A 3D model of microwave-induced plasma (field frequency 2.45 GHz) in argon at atmospheric pressure is presented. On the condition thatmore » the total input power is 500 W, simulations indicate that coherent power-combining will maximize the electric-field strength to 3.32 × 10{sup 5 }V/m and improve the uniformity of distributed microwave field, which raised 36.7% and 47.2%, respectively, compared to conventional waveguide apparatus of single port. To study the optimum conditions for industrial application, a 2D argon fluid model based on above structure is presented. It demonstrates that relatively uniform and high-density plasma is obtained at an argon flow rate of 200 ml/min. The contrastive result of electric-field distribution, electron density, and gas temperature is also valid and clearly proves the superiority of coherent power-combining to conventional technique in flow field.« less

Parallel and perpendicular velocity sheared flows driven tripolar vortices in an inhomogeneous electron-ion quantum magnetoplasma

NASA Astrophysics Data System (ADS)

Mirza, Arshad M.; Masood, W.

2011-12-01

Nonlinear equations governing the dynamics of finite amplitude drift-ion acoustic-waves are derived by taking into account sheared ion flows parallel and perpendicular to the ambient magnetic field in a quantum magnetoplasma comprised of electrons and ions. It is shown that stationary solution of the nonlinear equations can be represented in the form of a tripolar vortex for specific profiles of the equilibrium sheared flows. The tripolar vortices are, however, observed to form on very short scales in dense quantum plasmas. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.

Simulations of Solar Wind Plasma Flow Around a Simple Solar Sail

NASA Technical Reports Server (NTRS)

Garrett, Henry B.; Wang, Joseph

2004-01-01

In recent years, a number of solar sail missions of various designs and sizes have been proposed (e.g., Geostorm). Of importance to these missions is the interaction between the ambient solar wind plasma environment and the sail. Assuming a typical 1 AU solar wind environment of 400 km/s velocity, 3.5 cu cm density, ion temperature of approx.10 eV, electron temperature of 40 eV, and an ambient magnetic field strength of 10(exp -4) G, a first order estimate of the plasma interaction with square solar sails on the order of the sizes being considered for a Geostorm mission (50 m x 50 m and 75 m x 75 m corresponding to approx.2 and approx.3 times the Debye length in the plasma) is carried out. First, a crude current balance for the sail surface immersed in the plasma environment and in sunlight was used to estimate the surface potential of the model sails. This gave surface potentials of approx.10 V positive relative to the solar wind plasma. A 3-D, Electrostatic Particle-in-Cell (PIC) code was then used to simulate the solar wind flowing around the solar sail. It is assumed in the code that the solar wind protons can be treated as particles while the electrons follow a Boltzmann distribution. Next, the electric field and particle trajectories are solved self-consistently to give the proton flow field, the electrostatic field around the sail, and the plasma density in 3-D. The model sail was found to be surrounded by a plasma sheath within which the potential is positive compared to the ambient plasma and followed by a separate plasma wake which is negative relative to the plasma. This structure departs dramatically from a negatively charged plate such as might be found in the Earth s ionosphere on the night side where both the plate and its negative wake are contiguous. The implications of these findings are discussed as they apply to the proposed Geostorm solar sail mission.

The formation of relativistic plasma structures and their potential role in the generation of cosmic ray electrons

NASA Astrophysics Data System (ADS)

Dieckmann, M. E.

2008-11-01

Recent particle-in-cell (PIC) simulation studies have addressed particle acceleration and magnetic field generation in relativistic astrophysical flows by plasma phase space structures. We discuss the astrophysical environments such as the jets of compact objects, and we give an overview of the global PIC simulations of shocks. These reveal several types of phase space structures, which are relevant for the energy dissipation. These structures are typically coupled in shocks, but we choose to consider them here in an isolated form. Three structures are reviewed. (1) Simulations of interpenetrating or colliding plasma clouds can trigger filamentation instabilities, while simulations of thermally anisotropic plasmas observe the Weibel instability. Both transform a spatially uniform plasma into current filaments. These filament structures cause the growth of the magnetic fields. (2) The development of a modified two-stream instability is discussed. It saturates first by the formation of electron phase space holes. The relativistic electron clouds modulate the ion beam and a secondary, spatially localized electrostatic instability grows, which saturates by forming a relativistic ion phase space hole. It accelerates electrons to ultra-relativistic speeds. (3) A simulation is also revised, in which two clouds of an electron-ion plasma collide at the speed 0.9c. The inequal densities of both clouds and a magnetic field that is oblique to the collision velocity vector result in waves with a mixed electrostatic and electromagnetic polarity. The waves give rise to growing corkscrew distributions in the electrons and ions that establish an equipartition between the electron, the ion and the magnetic energy. The filament-, phase space hole- and corkscrew structures are discussed with respect to electron acceleration and magnetic field generation.

Influence of the magnetic field configuration on the plasma flow in Hall thrusters

NASA Astrophysics Data System (ADS)

Andreussi, T.; Giannetti, V.; Leporini, A.; Saravia, M. M.; Andrenucci, M.

2018-01-01

In Hall propulsion, the thrust is provided by the acceleration of ions in a plasma generated in a cross-field configuration. Standard thruster configurations have annular channels with an almost radial magnetic field at the channel exit. A potential difference is imposed in the axial direction and the intensity of the magnetic field is calibrated in order to hinder the electron motion, while leaving the ions non-magnetised. Magnetic field lines can be assumed, as a first approximation, as lines of constant electron temperature and of thermalized potential. In typical thruster configurations, the discharge occurs inside a ceramic channel and, due to plasma-wall interactions, the electron temperature is typically low, less than few tens of eV. Hence, the magnetic field lines can be effectively used to tailor the distribution of the electrostatic potential. However, the erosion of the ceramic walls caused by the ion bombardment represents the main limiting factor of the thruster lifetime and new thruster configurations are currently under development. For these configurations, classical first order models of the plasma dynamics fail to grasp the influence of the magnetic topology on the plasma flow. In the present paper, a novel approach to investigate the correlation between magnetic field topology and thruster performance is presented. Due to the anisotropy induced by the magnetic field, the gradients of the plasma properties are assumed to be mainly in the direction orthogonal to the local magnetic field, thus enabling a quasi-one-dimensional description in magnetic coordinates. Theoretical and experimental investigations performed on a 5 kW class Hall thruster with different magnetic field configurations are then presented and discussed.

Plasma separation from magnetic field lines in a magnetic nozzle

NASA Technical Reports Server (NTRS)

Kaufman, D. A.; Goodwin, D. G.; Sercel, J. C.

1993-01-01

This paper discusses conditions for separation of a plasma from the magnetic field of a magnetic nozzle. The analysis assumes a collisionless, quasineutral plasma, and therefore the results represent a lower bound on the amount of detachment possible for a given set of plasma conditions. We show that collisionless separation can occur because finite electron mass inhibits the flow of azimuthal currents in the nozzle. Separation conditions are governed by a parameter G which depends on plasma and nozzle conditions. Several methods of improving plasma detachment are presented, including moving the plasma generation zone downstream from the region of strongest magnetic field and using dual magnets to focus the plasma beam. Plasma detachment can be enhanced by manipulation of the nozzle configuration.

Spatial electron density and electric field strength measurements in microwave cavity experiments

NASA Technical Reports Server (NTRS)

Peters, M.; Rogers, J.; Whitehair, S.; Asmussen, J.; Kerber, R.

1984-01-01

Measurements of electron density and electric field strength have been made in an argon plasma contained in a resonant microwave cavity at 2.45 GHz. Spatial measurements of electron density, n sub e, are correlated with fluorescence observations of the discharge. Measurements of n sub e were made with Stark broadening and compared with n sub 3 calculated from measured plasma conductivity. Additional measurements of n sub 3 as a function of pressure and in mixtures of argon and oxygen are presented for pressures from 10 Torr to 1 atm. Measurements in flowing gases and in static systems are presented. In addition, limitations of these measurements are identified.

Validation of DSMC results for chemically nonequilibrium air flows against measurements of the electron number density in RAM-C II flight experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shevyrin, Alexander A.; Vashchenkov, Pavel V.; Bondar, Yevgeniy A.

An ionized flow around the RAM C-II vehicle in the range of altitudes from 73 to 81 km is studied by the Direct Simulation Monte Carlo (DSMC) method with three models of chemical reactions. It is demonstrated that vibration favoring in reactions of dissociation of neutral molecules affects significantly the predicted values of plasma density in the shock layer, and good agreement between the results of experiments and DSMC computations can be achieved in terms of the plasma density as a function of the flight altitude.

Effects of Sheared Flow on Microinstabilities and Transport in Plasmas

NASA Astrophysics Data System (ADS)

H, Sanuki; K, Itoh; A, Fujisawa; J, Q. Dong

2005-02-01

Theoretical and experimental studies associated with electric field effects on the stability and transport are briefly surveyed. The effects of radial electric field on the suppression and/or enhancement of various microinstabilities such as drift waves, flute mode and temperature gradient modes are discussed. The suppression of flow shear on the electron temperature gradient mode in plasmas with slightly hollow density profiles is investigated by solving the gyrokinetic integral eigenvalue equation. Comparison between theoretical predictions and experimental observations based on the HIBP measurements with high temporal and spatial resolutions is made in bumpy tori and heliotron (CHS) devices.

The effect of radio-frequency self bias on ion acceleration in expanding argon plasmas in helicon sources

NASA Astrophysics Data System (ADS)

Wiebold, Matthew D.

Time-averaged plasma potential differences up to ˜ 165 V over several hundred Debye lengths are observed in low pressure (pn < 1 mTorr) expanding argon plasmas in the Madison Helicon Experiment. The potential gradient leads to ion acceleration exceeding Ei ≈ 7 kTe in some cases. Up to 1 kW of 13.56 MHz RF power is supplied to a half-turn, double-helix antenna in the presence of a nozzle magnetic field up to 1 kG. An RPA measures the IEDF and an emissive probe measures the plasma potential. Single and double probes measure the electron density and temperature. Two distinct mode hops, the capacitive-inductive (E-H) and inductive-helicon (H-W) transitions, are identified by jumps in electron density as RF power is increased. In the capacitive mode, large fluctuations of the plasma potential (Vp--p ≳ 140 V, Vp--p/Vp ≈ 150%) exist at the RF frequency, leading to formation of a self-bias voltage. The mobile electrons can flow from the upstream region during an RF cycle whereas ions cannot, leading to an initial imbalance of flux, and the self-bias voltage builds as a result. The plasma potential in the expansion chamber is held near the floating potential for argon (Vp ≈ 5kTe/e). In the capacitive mode, the ion acceleration is not well described by an ambipolar relation. The accelerated population decay is consistent with that predicted by charge-exchange collisions. Grounding the upstream endplate increases the self-bias voltage compared to a floating endplate. In the inductive and helicon modes, the ion acceleration more closely follows an ambipolar relation, a result of decreased capacitive coupling due to the decreased RF skin depth. The scaling of the potential gradient with the argon flow rate, magnetic field and RF power are investigated, with the highest potential gradients observed for the lowest flow rates in the capacitive mode. The magnitude of the self-bias voltage agrees well with that predicted for RF sheaths. Use of the self-bias effect in a plasma thruster is explored, possibly for a low thrust, high specific impulse mode in a multi-mode helicon thruster. This work could also explain similar potential gradients in expanding helicon plasmas that are ascribed to double layer formation in the literature.

VLF and HF Plasma Waves Associated with Spread-F Plasma Depletions Observed on the C/NOFS Satellite

NASA Technical Reports Server (NTRS)

Pfaff, Robert; Freudenreich, H.; Schuck, P.; Klenzing, J.

2011-01-01

The C/NOFS spacecraft frequently encounters structured plasma depletions associated with equatorial spread-F along its trajectory that varies between 401 km perigee and 867 km apogee in the low latitude ionosphere. We report two classes of plasma waves detected with the Vector Electric Field Investigation (VEFI) that appear when the plasma frequency is less than the electron gyro frequency, as is common in spread-F depletions where the plasma number density typically decreases below 10(exp 4)/cu cm. In these conditions, both broadband VLF waves with a clear cutoff at the lower hybrid frequency and broadband HF waves with a clear cutoff at the plasma frequency are observed. We interpret these waves as "hiss-type" emissions possibly associated with the flow of suprathermal electrons within the inter-hemispherical magnetic flux tubes. We also report evidence of enhanced wave "transients" sometimes embedded in the broader band emissions that are associated with lightning sferics detected within the depleted plasma regions that appear in both the VLF and HF data. Theoretical implications of these observations are discussed.

Two stream instability in n-type gallium arsenide semiconductor quantum plasma

NASA Astrophysics Data System (ADS)

Ghosh, S.; Muley, Apurva

2018-01-01

By using quantum hydrodynamic model, we derive a generalized dielectric response function for two stream instability (convective only) in n-type gallium arsenide semiconductor plasma. We investigate the phase and amplification profiles of two stream instability with externally applied electric field ranging from 2600 to 4000 kV m-1 in presence of non-dimensional quantum parameter- H. In this range, a significant number of electrons in satellite valley become comparable to the number of electrons in central valley. The presence of quantum corrections in plasma medium induces two novel modes; one of it has amplifying nature and propagates in forward direction. It also modifies the spectral profile of four pre-existing modes in classical plasma. The existence of two stream instability is also established analytically by deriving the real part of longitudinal electrokinetic power flow density.

Patterning of graphene for flexible electronics with remote atmospheric-pressure plasma using dielectric barrier

NASA Astrophysics Data System (ADS)

Kim, Duk Jae; Park, Jeongwon; Geon Han, Jeon

2016-08-01

We show results of the patterning of graphene layers on poly(ethylene terephthalate) (PET) films through remote atmospheric-pressure dielectric barrier discharge plasma. The size of plasma discharge electrodes was adjusted for large-area and role-to-role-type substrates. Optical emission spectroscopy (OES) was used to analyze the characteristics of charge species in atmospheric-pressure plasma. The OES emission intensity of the O2* peaks (248.8 and 259.3 nm) shows the highest value at the ratio of \\text{N}2:\\text{clean dry air (CDA)} = 100:1 due to the highest plasma discharge. The PET surface roughness and hydrophilic behavior were controlled with CDA flow rate during the process. Although the atmospheric-pressure plasma treatment of the PET film led to an increase in the FT-IR intensity of C-O bonding at 1240 cm-1, the peak intensity at 1710 cm-1 (C=O bonding) decreased. The patterning of graphene layers was confirmed by scanning electron microscopy and Raman spectroscopy.

A Transport Model for Non-Local Heating of Electrons in ICP Reactors

NASA Technical Reports Server (NTRS)

Chang, C. H.; Bose, Deepak; Arnold, James O. (Technical Monitor)

1998-01-01

A new model has been developed for non-local heating of electrons in ICP reactors, based on a hydrodynamic approach. The model has been derived using the electron momentum conservation in azimuthal direction with electromagnetic and frictional forces respectively as driving force and damper of harmonic oscillatory motion of electrons. The resulting transport equations include the convection of azimuthal electron momentum in radial and axial directions, thereby accounting for the non-local effects. The azimuthal velocity of electrons and the resulting electrical current are coupled to the Maxwell's relations, thus forming a self-consistent model for non-local heating. This model is being implemented along with a set of Navier-Stokes equations for plasma dynamics and gas flow to simulate low-pressure (few mTorr's) ICP discharges. Characteristics of nitrogen plasma in a TCP 300mm etch reactor is being studied. The results will be compared against the available Langmuir probe measurements.

Flowing Plasma Interaction with an Electric Sail Tether Element

NASA Technical Reports Server (NTRS)

Schneider, Todd; Vaughn, Jason; Wright, Kenneth; Anderson, Allen; Stone, Nobie

2017-01-01

Harnessing the power of the solar wind, an Electric Sail, or E-sail, is a relatively new concept that promises to deliver high speed propellant-less propulsion. The electric sail is an invention made in 2006 at the Kumpula Space Centre in Finland by Pekka Janhunen [Janhunen and Sandroos, 2007]. At its core, an electric sail utilizes multiple positively biased tethers which exchange momentum with solar wind protons via the repelling electric field established around each tether, in other words, by reflecting the solar wind protons. Recognizing the solar wind is a plasma, the effective repelling area of each tether is increased significantly by the formation a plasma sheath around each tether. Fig. 1 shows schematically a spacecraft employing an electric sail. The positive voltage bias (greater than10kV) applied to each tether naturally results in electron collection. Therefore, the electric sail concept necessarily includes an electron source (electron gun) to return collected electrons to space and maintain the positive bias of the tether system.

Development of a Computationally Efficient, High Fidelity, Finite Element Based Hall Thruster Model

NASA Technical Reports Server (NTRS)

Jacobson, David (Technical Monitor); Roy, Subrata

2004-01-01

This report documents the development of a two dimensional finite element based numerical model for efficient characterization of the Hall thruster plasma dynamics in the framework of multi-fluid model. Effect of the ionization and the recombination has been included in the present model. Based on the experimental data, a third order polynomial in electron temperature is used to calculate the ionization rate. The neutral dynamics is included only through the neutral continuity equation in the presence of a uniform neutral flow. The electrons are modeled as magnetized and hot, whereas ions are assumed magnetized and cold. The dynamics of Hall thruster is also investigated in the presence of plasma-wall interaction. The plasma-wall interaction is a function of wall potential, which in turn is determined by the secondary electron emission and sputtering yield. The effect of secondary electron emission and sputter yield has been considered simultaneously, Simulation results are interpreted in the light of experimental observations and available numerical solutions in the literature.

Formation of electrostatic structures by wakefield acceleration in ultrarelativistic plasma flows: Electron acceleration to cosmic ray energies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dieckmann, M.E.; Shukla, P.K.; Eliasson, B.

2006-06-15

The ever increasing performance of supercomputers is now enabling kinetic simulations of extreme astrophysical and laser produced plasmas. Three-dimensional particle-in-cell (PIC) simulations of relativistic shocks have revealed highly filamented spatial structures and their ability to accelerate particles to ultrarelativistic speeds. However, these PIC simulations have not yet revealed mechanisms that could produce particles with tera-electron volt energies and beyond. In this work, PIC simulations in one dimension (1D) of the foreshock region of an internal shock in a gamma ray burst are performed to address this issue. The large spatiotemporal range accessible to a 1D simulation enables the self-consistent evolutionmore » of proton phase space structures that can accelerate particles to giga-electron volt energies in the jet frame of reference, and to tens of tera-electron volt in the Earth's frame of reference. One potential source of ultrahigh energy cosmic rays may thus be the thermalization of relativistically moving plasma.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferrario, Lorenzo, E-mail: lorenzo.ferrario@polimi.it; Little, Justin M., E-mail: jml@princeton.edu; Choueiri, Edgar Y., E-mail: choueiri@princeton.edu

The plasma flow in a finite-electron-temperature magnetic nozzle, under the influence of an applied azimuthal current at the throat, is modeled analytically to assess its propulsive performance. A correction to the nozzle throat boundary conditions is derived by modifying the radial equilibrium of a magnetized infinite two-population cylindrical plasma column with the insertion of an external azimuthal body force for the electrons. Inclusion of finite-temperature effects, which leads to a modification of the radial density profile, is necessary for calculating the propulsive performance, which is represented by nozzle divergence efficiency and thrust coefficient. The solutions show that the application ofmore » the azimuthal current enhances all the calculated performance parameters through the narrowing of the radial density profile at the throat, and that investing power in this beam focusing effect is more effective than using the same power to pre-heat the electrons. The results open the possibility for the design of a focusing stage between the plasma source and the nozzle that can significantly enhance the propulsive performance of electron-driven magnetic nozzles.« less

Supersonic plasma beams with controlled speed generated by the alternative low power hybrid ion engine (ALPHIE) for space propulsion

NASA Astrophysics Data System (ADS)

Conde, L.; Domenech-Garret, J. L.; Donoso, J. M.; Damba, J.; Tierno, S. P.; Alamillo-Gamboa, E.; Castillo, M. A.

2017-12-01

The characteristics of supersonic ion beams from the alternative low power hybrid ion engine (ALPHIE) are discussed. This simple concept of a DC powered plasma accelerator that only needs one electron source for both neutral gas ionization and ion beam neutralization is also examined. The plasma production and space charge neutralization processes are thus coupled in this plasma thruster that has a total DC power consumption of below 450 W, and uses xenon or argon gas as a propellant. The operation parameters of the plasma engine are studied in the laboratory in connection with the ion energy distribution function obtained with a retarding-field energy analyzer. The ALPHIE plasma beam expansion produces a mesothermal plasma flow with two-peaked ion energy distribution functions composed of low and high speed ion groups. The characteristic drift velocities of the fast ion groups, in the range 36.6-43.5 Km/s, are controlled by the acceleration voltage. These supersonic speeds are higher than the typical ion sound velocities of the low energy ion group produced by the expansion of the plasma jet. The temperatures of the slow ion population lead to ion Debye lengths longer than the electron Debye lengths. Furthermore, the electron impact ionization can coexist with collisional ionization by fast ions downstream the grids. Finally, the performance characteristics and comparisons with other plasma accelerator schemes are also discussed.

Acceleration and focusing of plasma flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Griswold, Martin Elias

The acceleration of flowing plasmas is a fundamental problem that is useful in a wide variety of technological applications. We consider the problem from the perspective of plasma propulsion. Gridded ion thrusters and Hall thrusters are the most commonly used devices to create flowing plasma for space propulsion, but both suffer from fundamental limitations. Gridded ion sources create good quality beams in terms of energy spread and spatial divergence, but the Child-Langmuir law in the non-neutral acceleration region limits the maximum achievable current density. Hall thrusters avoid this limitation by accelerating ions in quasi-neutral plasma but, as a result, producemore » plumes with high spatial divergence and large energy spread. In addition the more complicated magnetized plasma in the Hall Thruster produces oscillations that can reduce the efficiency of the thruster by increasing electron transport to the anode. We present investigations of three techniques to address the fundamental limitations on the performance of each thruster. First, we propose a method to increase the time-averaged current density (and thus thrust density) produced by a gridded ion source above the Child-Langmuir limit by introducing time-varying boundary conditions. Next, we use an electrostatic plasma lens to focus the Hall thruster plume, and finally we develop a technique to suppress a prominent oscillation that degrades the performance of Hall thrusters. The technique to loosen the constraints on current density from gridded ion thrusters actually applies much more broadly to any space charge limited flow. We investigate the technique with a numerical simulation and by proving a theoretical upper bound. While we ultimately conclude that the approach is not suitable for space propulsion, our results proved useful in another area, providing a benchmark for research into the spontaneously time-dependent current that arises in microdiodes. Next, we experimentally demonstrate a novel approach to reducing plume divergence by using a PL located in the plume of the thruster to focus ions after they were ionized and accelerated. Finally we further improve thruster operation by suppressing a prominent low frequency oscillation in the thruster known as the rotating spoke. The suppression leads to decreased electron transport and more control over the operating conditions in the thruster.« less

Current-voltage characteristics of a cathodic plasma contactor with discharge chamber for application in electrodynamic tether propulsion

NASA Astrophysics Data System (ADS)

Xie, Kan; Martinez, Rafael A.; Williams, John D.

2014-04-01

This paper focuses on the net electron-emission current as a function of bias voltage of a plasma source that is being used as the cathodic element in a bare electrodynamic tether system. An analysis is made that enables an understanding of the basic issues determining the current-voltage (C-V) behaviour. This is important for the efficiency of the electrodynamic tether and for low impedance performance without relying on the properties of space plasma for varying orbital altitudes, inclinations, day-night cycles or the position of the plasma contactor relative to the wake of the spacecraft. The cathodic plasma contactor considered has a cylindrical discharge chamber (10 cm in diameter and ˜11 cm in length) and is driven by a hollow cathode. Experiments and a 1D spherical model are both used to study the contactor's C-V curves. The experiments demonstrate how the cathodic contactor would emit electrons into space for anode voltages in the range of 25-40 V, discharge currents in the range of 1-2.5 A, and low xenon gas flows of 2-4 sccm. Plasma properties are measured and compared with (3 A) and without net electron emission. A study of the dependence of relevant parameters found that the C-V behaviour strongly depends on electron temperature, initial ion energy and ion emission current at the contactor exit. However, it depended only weakly on ambient plasma density. The error in the developed model compared with the experimental C-V curves is within 5% at low electron-emission currents (0-2 A). The external ionization processes and high ion production rate caused by the discharge chamber, which dominate the C-V behaviour at electron-emission currents over 2 A, are further highlighted and discussed.

The hybrid reactor project based on the straight field line mirror concept

NASA Astrophysics Data System (ADS)

Ågren, O.; Noack, K.; Moiseenko, V. E.; Hagnestâl, A.; Källne, J.; Anglart, H.

2012-06-01

The straight field line mirror (SFLM) concept is aiming towards a steady-state compact fusion neutron source. Besides the possibility for steady state operation for a year or more, the geometry is chosen to avoid high loads on materials and plasma facing components. A comparatively small fusion hybrid device with "semi-poor" plasma confinement (with a low fusion Q factor) may be developed for industrial transmutation and energy production from spent nuclear fuel. This opportunity arises from a large fission to fusion energy multiplication ratio, Qr = Pfis/Pfus>>1. The upper bound on Qr is primarily determined by geometry and reactor safety. For the SFLM, the upper bound is Qr≈150, corresponding to a neutron multiplicity of keff=0.97. Power production in a mirror hybrid is predicted for a substantially lower electron temperature than the requirement Te≈10 keV for a fusion reactor. Power production in the SFLM seems possible with Q≈0.15, which is 10 times lower than typically anticipated for hybrids (and 100 times smaller than required for a fusion reactor). This relaxes plasma confinement demands, and broadens the range for use of plasmas with supra-thermal ions in hybrid reactors. The SFLM concept is based on a mirror machine stabilized by qudrupolar magnetic fields and large expander tanks beyond the confinement region. The purpose of the expander tanks is to distribute axial plasma loss flow over a sufficiently large area so that the receiving plates can withstand the heat. Plasma stability is not relying on a plasma flow into the expander regions. With a suppressed plasma flow into the expander tanks, a possibility arise for higher electron temperature. A brief presentation will be given on basic theory for the SFLM with plasma stability and electron temperature issues, RF heating computations with sloshing ion formation, neutron transport computations with reactor safety margins and material load estimates, magnetic coil designs as well as a discussion on the implications of the geometry for possible diagnostics. Reactor safety issues are addressed and a vertical orientation of the device could assist passive coolant circulation. Specific attention is put to a device with a 25 m long confinement region and 40 cm plasma radius in the mid-plane. In an optimal case (keff = 0.97) with a fusion power of only 10 MW, such a device may be capable of producing a power of 1.5 GWth.

Properties of Minor Ions in the Solar Wind and Implications for the Background Solar Wind Plasma

NASA Technical Reports Server (NTRS)

Wagner, William (Technical Monitor); Esser, Ruth

2004-01-01

The scope of the investigation is to extract information on the properties of the bulk solar wind from the minor ion observations that are provided by instruments on board NASA space craft and theoretical model studies. Ion charge states measured in situ in interplanetary space are formed in the inner coronal regions below 5 solar radii, hence they carry information on the properties of the solar wind plasma in that region. The plasma parameters that are important in the ion forming processes are the electron density, the electron temperature and the flow speeds of the individual ion species. In addition, if the electron distribution function deviates from a Maxwellian already in the inner corona, then the enhanced tail of that distribution function, also called halo, greatly effects the ion composition. This study is carried out using solar wind models, coronal observations, and ion calculations in conjunction with the in situ observations.

Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warwick, J.; Dzelzainis, T.; Dieckmann, M. E.

Here, we report on the first experimental observation of a current-driven instability developing in a quasineutral matter-antimatter beam. Strong magnetic fields (≥ 1T) are measured, via means of a proton radiography technique, after the propagation of a neutral electron-positron beam through a background electron-ion plasma. The experimentally determined equipartition parameter of ε B ≈ 10 -3 is typical of values inferred from models of astrophysical gamma-ray bursts, in which the relativistic flows are also expected to be pair dominated. The data, supported by particle-in-cell simulations and simple analytical estimates, indicate that these magnetic fields persist in the background plasma formore » thousands of inverse plasma frequencies. The existence of such long-lived magnetic fields can be related to analog astrophysical systems, such as those prevalent in lepton-dominated jets.« less

Relativistic shock waves in an electron-positron plasma

NASA Astrophysics Data System (ADS)

Tsintsadze, Levan N.

1995-12-01

The equations describing the detailed structure of radiation electromagnetic hydrodynamics for a relativistically hot electron-positron plasma are derived. Various discontinuities are studied by these equations. It is shown that the dependence of the electron (positron) mass on the temperature changes the structure of discontinuities, including shock waves, both qualitatively and quantitatively. Steady radiative shocks are considered, which can arise in steady flows, and which also can be used to describe the propagation of shocks when the shock thickness is very small as compared to the characteristic length over which the ambient medium changes significantly. First, the magnetohydrodynamic shock wave is treated as a discontinuity and jump relations, which relate the equilibrium states of the upstream and downstream plasma far from the front, are derived. Then the structure of the front itself is considered and tangential, contact (or entropy) and rotational discontinuities are investigated.

Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam

DOE PAGES

Warwick, J.; Dzelzainis, T.; Dieckmann, M. E.; ...

2017-11-03

Here, we report on the first experimental observation of a current-driven instability developing in a quasineutral matter-antimatter beam. Strong magnetic fields (≥ 1T) are measured, via means of a proton radiography technique, after the propagation of a neutral electron-positron beam through a background electron-ion plasma. The experimentally determined equipartition parameter of ε B ≈ 10 -3 is typical of values inferred from models of astrophysical gamma-ray bursts, in which the relativistic flows are also expected to be pair dominated. The data, supported by particle-in-cell simulations and simple analytical estimates, indicate that these magnetic fields persist in the background plasma formore » thousands of inverse plasma frequencies. The existence of such long-lived magnetic fields can be related to analog astrophysical systems, such as those prevalent in lepton-dominated jets.« less

On the use of the double floating probe method to infer the difference between the electron and the heavy particles temperatures in an atmospheric pressure, vortex-stabilized nitrogen plasma jet

NASA Astrophysics Data System (ADS)

Prevosto, L.; Kelly, H.; Mancinelli, B. R.

2014-05-01

Sweeping double probe measurements in an atmospheric pressure direct current vortex-stabilized plasma jet are reported (plasma conditions: 100 A discharge current, N2 gas flow rate of 25 Nl/min, thoriated tungsten rod-type cathode, copper anode with 5 mm inner diameter). The interpretation of the double probe characteristic was based on a generalization of the standard double floating probe formulae for non-uniform plasmas coupled to a non-equilibrium plasma composition model. Perturbations caused by the current to the probe together with collisional and thermal processes inside the probe perturbed region were taken into account. Radial values of the average electron and heavy particle temperatures as well as the electron density were obtained. The calculation of the temperature values did not require any specific assumption about a temperature relationship between different particle species. An electron temperature of 10 900 ± 900 K, a heavy particle temperature of 9300 ± 900 K, and an electron density of about 3.5 × 1022 m-3 were found at the jet centre at 3.5 mm downstream from the torch exit. Large deviations from kinetic equilibrium were found toward the outer border of the plasma jet. These results showed good agreement with those previously reported by the authors by using a single probe technique. The calculations have shown that this method is particularly useful for studying spraying-type plasma torches operated at power levels of about 15 kW.

On the use of the double floating probe method to infer the difference between the electron and the heavy particles temperatures in an atmospheric pressure, vortex-stabilized nitrogen plasma jet.

PubMed

Prevosto, L; Kelly, H; Mancinelli, B R

2014-05-01

Sweeping double probe measurements in an atmospheric pressure direct current vortex-stabilized plasma jet are reported (plasma conditions: 100 A discharge current, N2 gas flow rate of 25 Nl/min, thoriated tungsten rod-type cathode, copper anode with 5 mm inner diameter). The interpretation of the double probe characteristic was based on a generalization of the standard double floating probe formulae for non-uniform plasmas coupled to a non-equilibrium plasma composition model. Perturbations caused by the current to the probe together with collisional and thermal processes inside the probe perturbed region were taken into account. Radial values of the average electron and heavy particle temperatures as well as the electron density were obtained. The calculation of the temperature values did not require any specific assumption about a temperature relationship between different particle species. An electron temperature of 10,900 ± 900 K, a heavy particle temperature of 9300 ± 900 K, and an electron density of about 3.5 × 10(22) m(-3) were found at the jet centre at 3.5 mm downstream from the torch exit. Large deviations from kinetic equilibrium were found toward the outer border of the plasma jet. These results showed good agreement with those previously reported by the authors by using a single probe technique. The calculations have shown that this method is particularly useful for studying spraying-type plasma torches operated at power levels of about 15 kW.

Spatial nonlinear absorption of Alfven waves by dissipative plasma taking account bremsstrahlung

NASA Astrophysics Data System (ADS)

Taiurskii, A. A.; Gavrikov, M. B.

2016-10-01

We study numerically the nonlinear absorption of a plane Alfven wave falling on the stationary boundary of dissipative plasma. This absorption is caused by such factors as the magnetic viscosity, hydrodynamic viscosity, and thermal conductivity of electrons and ions, bremsstrahlung and energy exchange between plasma components. The relevance of this investigation is due to some works, published in 2011, with regard to the heating mechanism of the solar corona and solar wind generation as a result of the absorption of plasma Alfven waves generated in the lower significantly colder layers of the Sun. Numerical analysis shows that the absorption of Alfven waves occurs at wavelengths of the order of skin depth, in which case the classical MHD equations are inapplicable. Therefore, our research is based on equations of two-fluid magnetohydrodynamics that take into account the inertia of the electrons. The implicit difference scheme proposed here for calculating plane-parallel flows of two-fluid plasma reveals a number of important patterns of absorption and thus allows us to study the dependence of the absorption on the Alfven wave frequency and the electron thermal conductivity and viscosity, as well as to evaluate the depth and the velocity of plasma heating during the penetration of Alfven waves interacting with dissipative plasma.

Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch

DOE PAGES

Vogman, G. V.; Shumlak, U.

2011-10-13

Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian functionmore » associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. As a result, these measurements are used to gain a better understanding of Z-pinch equilibria.« less

Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vogman, G. V.; Shumlak, U.

2011-10-15

Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian functionmore » associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. These measurements are used to gain a better understanding of Z-pinch equilibria.« less

Experimental Simulation of Solar Wind Interactions with Magnetic Dipole Fields above Insulating Surfaces

NASA Astrophysics Data System (ADS)

Munsat, Tobin; Deca, Jan; Han, Jia; Horanyi, Mihaly; Wang, Xu; Werner, Greg; Yeo, Li Hsia; Fuentes, Dominic

2017-10-01

Magnetic anomalies on the surfaces of airless bodies such as the Moon interact with the solar wind, resulting in both magnetic and electrostatic deflection of the charged particles and thus localized surface charging. This interaction is studied in the Colorado Solar Wind Experiment with large-cross-section ( 300 cm2) high-energy flowing plasmas (100-800 eV beam ions) that are incident upon a magnetic dipole embedded under various insulating surfaces. Measured 2D plasma potential profiles indicate that in the dipole lobe regions, the surfaces are charged to high positive potentials due to the collection of unmagnetized ions, while the electrons are magnetically shielded. At low ion beam energies, the surface potential follows the beam energy in eV. However, at high energies, the surface potentials in the electron-shielded regions are significantly lower than the beam energies. A series of studies indicate that secondary electrons are likely to play a dominant role in determining the surface potential. Early results will also be presented from a second experiment, in which a strong permanent magnet with large dipole moment (0.55 T, 275 A*m2) is inserted into the flowing plasma beam to replicate aspects of the solar wind interaction with the earth's magnetic field. This work is supported by the NASA SSERVI program.

Improved analysis techniques for cylindrical and spherical double probes.

PubMed

Beal, Brian; Johnson, Lee; Brown, Daniel; Blakely, Joseph; Bromaghim, Daron

2012-07-01

A versatile double Langmuir probe technique has been developed by incorporating analytical fits to Laframboise's numerical results for ion current collection by biased electrodes of various sizes relative to the local electron Debye length. Application of these fits to the double probe circuit has produced a set of coupled equations that express the potential of each electrode relative to the plasma potential as well as the resulting probe current as a function of applied probe voltage. These equations can be readily solved via standard numerical techniques in order to determine electron temperature and plasma density from probe current and voltage measurements. Because this method self-consistently accounts for the effects of sheath expansion, it can be readily applied to plasmas with a wide range of densities and low ion temperature (T(i)/T(e) ≪ 1) without requiring probe dimensions to be asymptotically large or small with respect to the electron Debye length. The presented approach has been successfully applied to experimental measurements obtained in the plume of a low-power Hall thruster, which produced a quasineutral, flowing xenon plasma during operation at 200 W on xenon. The measured plasma densities and electron temperatures were in the range of 1 × 10(12)-1 × 10(17) m(-3) and 0.5-5.0 eV, respectively. The estimated measurement uncertainty is +6%∕-34% in density and +∕-30% in electron temperature.

Electron-Ion Recombination Rate Coefficient Measurements in a Flowing Afterglow Plasma

NASA Technical Reports Server (NTRS)

Gougousi, Theodosia; Golde, Michael F.; Johnsen, Rainer

1996-01-01

The flowing-afterglow technique in conjunction with computer modeling of the flowing plasma has been used to determine accurate dissociative-recombination rate coefficients alpha for the ions O2(+), HCO(+), CH5(+), C2H5(+), H3O(+), CO2(+), HCO2(+), HN2O(+), and N2O(+) at 295 K. We find that the simple form of data analysis that was employed in earlier experiments was adequate and we largely confirm earlier results. In the case of HCO(+) ions, published coefficients range from 1.1 X 10(exp -7) to 2.8 x 10(exp -7) cu cm/S, while our measurements give a value of 1.9 x 10(exp -7) cu cm/S.

Measurement of the dynamo effect in a plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ji, H.; Prager, S.C.; Almagri, A.F.

1995-11-01

A series of the detailed experiments has been conducted in three laboratory plasma devices to measure the dynamo electric field along the equilibrium field line (the {alpha} effect) arising from the correlation between the fluctuating flow velocity and magnetic field. The fluctuating flow velocity is obtained from probe measurement of the fluctuating E x B drift and electron diamagnetic drift. The three major findings are (1) the {alpha} effect accounts for the dynamo current generation, even in the time dependence through a ``sawtooth`` cycle; (2) at low collisionality the dynamo is explained primarily by the widely studied pressureless Magnetohydrodynamic (MHD)more » model, i.e., the fluctuating velocity is dominated by the E x B drift; (3) at high collisionality, a new ``electron diamagnetic dynamo`` is observed, in which the fluctuating velocity is dominated by the diamagnetic drift. In addition, direct measurements of the helicity flux indicate that the dynamo activity transports magnetic helicity from one part of the plasma to another, but the total helicity is roughly conserved, verifying J.B. Taylor`s conjecture.« less

Nonequilibrium in a low power arcjet nozzle

NASA Technical Reports Server (NTRS)

Zube, Dieter M.; Myers, Roger M.

1991-01-01

Emission spectroscopy measurements were made of the plasma flow inside the nozzle of a 1 kW class arcjet thruster. The thruster propellant was a hydrogen-nitrogen mixture used to simulate fully decomposed hydrazine. The 0.25 mm diameter holes were drilled into the diverging section of the tungsten thruster nozzle to provide optical access to the internal flow. Atomic electron excitation, vibrational, and rotational temperatures were determined for the expanding plasma using relative line intensity techniques. The atomic excitation temperatures decreased from 18,000K at a location 3 mm downstream of the constrictor to 9,000K at a location 9 mm from the constrictor, while the molecular vibrational and rotational temperatures decreased from 6,500K to 2,500K and from 8,000K to 3,000K, respectively, between the same locations. The electron density measured using hydrogen H line Stark broadening decreased from about 10(exp 15) cm(-3) to about 2 times 10(exp 14) cm(-3) during the expansion. The results show that the plasma is highly nonequilibrium throughout the nozzle, with most relaxation times equal or exceeding the particle residence time.

Transport processes in magnetically confined plasmas in the nonlinear regime.

PubMed

Sonnino, Giorgio

2006-06-01

A field theory approach to transport phenomena in magnetically confined plasmas is presented. The thermodynamic field theory (TFT), previously developed for treating the generic thermodynamic system out of equilibrium, is applied to plasmas physics. Transport phenomena are treated here as the effect of the field linking the thermodynamic forces with their conjugate flows combined with statistical mechanics. In particular, the Classical and the Pfirsch-Schluter regimes are analyzed by solving the thermodynamic field equations of the TFT in the weak-field approximation. We found that, the TFT does not correct the expressions of the ionic heat fluxes evaluated by the neoclassical theory in these two regimes. On the other hand, the fluxes of matter and electronic energy (heat flow) is further enhanced in the nonlinear Classical and Pfirsch-Schluter regimes. These results seem to be in line with the experimental observations. The complete set of the electronic and ionic transport equations in the nonlinear Banana regime, is also reported. A paper showing the comparison between our theoretic results and the experimental observations in the JET machine is currently in preparation.

Dependence of Lunar Surface Charging on Solar Wind Plasma Conditions and Solar Irradiation

NASA Technical Reports Server (NTRS)

Stubbs, T. J.; Farrell, W. M.; Halekas, J. S.; Burchill, J. K.; Collier, M. R.; Zimmerman, M. I.; Vondrak, R. R.; Delory, G. T.; Pfaff, R. F.

2014-01-01

The surface of the Moon is electrically charged by exposure to solar radiation on its dayside, as well as by the continuous flux of charged particles from the various plasma environments that surround it. An electric potential develops between the lunar surface and ambient plasma, which manifests itself in a near-surface plasma sheath with a scale height of order the Debye length. This study investigates surface charging on the lunar dayside and near-terminator regions in the solar wind, for which the dominant current sources are usually from the pohotoemission of electrons, J(sub p), and the collection of plasma electrons J(sub e) and ions J(sub i). These currents are dependent on the following six parameters: plasma concentration n(sub 0), electron temperature T(sub e), ion temperature T(sub i), bulk flow velocity V, photoemission current at normal incidence J(sub P0), and photo electron temperature T(sub p). Using a numerical model, derived from a set of eleven basic assumptions, the influence of these six parameters on surface charging - characterized by the equilibrium surface potential, Debye length, and surface electric field - is investigated as a function of solar zenith angle. Overall, T(sub e) is the most important parameter, especially near the terminator, while J(sub P0) and T(sub p) dominate over most of the dayside.

Simulation of density fluctuations before the L-H transition for Hydrogen and Deuterium plasmas in the DIII-D tokamak using the BOUT++ code

DOE PAGES

Wang, Y. M.; Xu, X. Q.; Yan, Z.; ...

2018-01-05

A six-field two-fluid model has been used to simulate density fluctuations. The equilibrium is generated by experimental measurements for both Deuterium (D) and Hydrogen (H) plasmas at the lowest densities of DIII-D low to high confinement (L-H) transition experiments. In linear simulations, the unstable modes are found to be resistive ballooning modes with the most unstable mode number n=30 ormore » $$k_\\theta\\rho_i\\sim0.12$$ . The ion diamagnetic drift and $$E\\times B$$ convection flow are balanced when the radial electric field (E r) is calculated from the pressure profile without net flow. The curvature drift plays an important role in this stage. Two poloidally counter propagating modes are found in the nonlinear simulation of the D plasma at electron density $$n_e\\sim1.5\\times10^{19}$$ m -3 near the separatrix while a single ion mode is found in the H plasma at the similar lower density, which are consistent with the experimental results measured by the beam emission spectroscopy (BES) diagnostic on the DIII-D tokamak. The frequency of the electron modes and the ion modes are about 40kHz and 10 kHz respectively. The poloidal wave number $$k_\\theta$$ is about 0.2 cm -1 ($$k_\\theta\\rho_i\\sim0.05$$ ) for both ion and electron modes. The particle flux, ion and electron heat fluxes are~3.5–6 times larger for the H plasma than the D plasma, which makes it harder to achieve H-mode for the same heating power. The change of the atomic mass number A from 2 to 1 using D plasma equilibrium make little difference on the flux. Increase the electric field will suppress the density fluctuation. In conclusion, the electric field scan and ion mass scan results show that the dual-mode results primarily from differences in the profiles rather than the ion mass.« less

Simulation of density fluctuations before the L-H transition for Hydrogen and Deuterium plasmas in the DIII-D tokamak using the BOUT++ code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Y. M.; Xu, X. Q.; Yan, Z.

A six-field two-fluid model has been used to simulate density fluctuations. The equilibrium is generated by experimental measurements for both Deuterium (D) and Hydrogen (H) plasmas at the lowest densities of DIII-D low to high confinement (L-H) transition experiments. In linear simulations, the unstable modes are found to be resistive ballooning modes with the most unstable mode number n=30 ormore » $$k_\\theta\\rho_i\\sim0.12$$ . The ion diamagnetic drift and $$E\\times B$$ convection flow are balanced when the radial electric field (E r) is calculated from the pressure profile without net flow. The curvature drift plays an important role in this stage. Two poloidally counter propagating modes are found in the nonlinear simulation of the D plasma at electron density $$n_e\\sim1.5\\times10^{19}$$ m -3 near the separatrix while a single ion mode is found in the H plasma at the similar lower density, which are consistent with the experimental results measured by the beam emission spectroscopy (BES) diagnostic on the DIII-D tokamak. The frequency of the electron modes and the ion modes are about 40kHz and 10 kHz respectively. The poloidal wave number $$k_\\theta$$ is about 0.2 cm -1 ($$k_\\theta\\rho_i\\sim0.05$$ ) for both ion and electron modes. The particle flux, ion and electron heat fluxes are~3.5–6 times larger for the H plasma than the D plasma, which makes it harder to achieve H-mode for the same heating power. The change of the atomic mass number A from 2 to 1 using D plasma equilibrium make little difference on the flux. Increase the electric field will suppress the density fluctuation. In conclusion, the electric field scan and ion mass scan results show that the dual-mode results primarily from differences in the profiles rather than the ion mass.« less

Nonlinear saturation of the slab ITG instability and zonal flow generation with fully kinetic ions

NASA Astrophysics Data System (ADS)

Miecnikowski, Matthew T.; Sturdevant, Benjamin J.; Chen, Yang; Parker, Scott E.

2018-05-01

Fully kinetic turbulence models are of interest for their potential to validate or replace gyrokinetic models in plasma regimes where the gyrokinetic expansion parameters are marginal. Here, we demonstrate fully kinetic ion capability by simulating the growth and nonlinear saturation of the ion-temperature-gradient instability in shearless slab geometry assuming adiabatic electrons and including zonal flow dynamics. The ion trajectories are integrated using the Lorentz force, and the cyclotron motion is fully resolved. Linear growth and nonlinear saturation characteristics show excellent agreement with analogous gyrokinetic simulations across a wide range of parameters. The fully kinetic simulation accurately reproduces the nonlinearly generated zonal flow. This work demonstrates nonlinear capability, resolution of weak gradient drive, and zonal flow physics, which are critical aspects of modeling plasma turbulence with full ion dynamics.

Plasma transport in a simulated magnetic-divertor configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strawitch, C. M.

1981-03-01

The transport properties of plasma on magnetic field lines that intersect a conducting plate are studied experimentally in the Wisconsin internal ring D.C. machine. The magnetic geometry is intended to simulate certain aspects of plasma phenomena that may take place in a tokamak divertor. It is found by a variety of measurements that the cross field transport is non-ambipolar; this may have important implications in heat loading considerations in tokamak divertors. The undesirable effects of nonambipolar flow make it preferable to be able to eliminate it. However, we find that though the non-ambipolarity may be reduced, it is difficult tomore » eliminate entirely. The plasma flow velocity parallel to the magnetic field is found to be near the ion acoustic velocity in all cases. The experimental density and electron temperature profiles are compared to the solutions to a one dimensional transport model that is commonly used in divertor theory.« less

Experimental results from magnetized-jet experiments executed at the Jupiter Laser Facility

DOE PAGES

Manuel, M. J. -E.; Kuranz, C. C.; Rasmus, A. M.; ...

2014-08-20

Recent experiments at the Jupiter Laser Facility investigated magnetization effects on collimated plasma jets. Laser-irradiated plastic-cone-targets produced collimated, millimeter-scale plasma flows as indicated by optical interferometry. Proton radiography of these jets showed no indication of strong, self-generated magnetic fields, suggesting a dominantly hydrodynamic collimating mechanism. Targets were placed in a custom-designed solenoid capable of generating field strengths up to 5 T. Proton radiographs of the well-characterized B-field, without a plasma jet, suggested an external source of trapped electrons that affects proton trajectories. The background magnetic field was aligned with the jet propagation direction, as is the case in many astrophysicalmore » systems. Optical interferometry showed that magnetization of the plasma results in disruption of the collimated flow and instead produces a hollow cavity. Furthermore, this result is a topic of ongoing investigation.« less

Experimental results from magnetized-jet experiments executed at the Jupiter Laser Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manuel, M. J. -E.; Kuranz, C. C.; Rasmus, A. M.

Recent experiments at the Jupiter Laser Facility investigated magnetization effects on collimated plasma jets. Laser-irradiated plastic-cone-targets produced collimated, millimeter-scale plasma flows as indicated by optical interferometry. Proton radiography of these jets showed no indication of strong, self-generated magnetic fields, suggesting a dominantly hydrodynamic collimating mechanism. Targets were placed in a custom-designed solenoid capable of generating field strengths up to 5 T. Proton radiographs of the well-characterized B-field, without a plasma jet, suggested an external source of trapped electrons that affects proton trajectories. The background magnetic field was aligned with the jet propagation direction, as is the case in many astrophysicalmore » systems. Optical interferometry showed that magnetization of the plasma results in disruption of the collimated flow and instead produces a hollow cavity. Furthermore, this result is a topic of ongoing investigation.« less

Neutralization of an ion beam from the end-Hall ion source by a plasma electron source based on a discharge in crossed E × H fields

NASA Astrophysics Data System (ADS)

Dostanko, A. P.; Golosov, D. A.

2009-10-01

The possibility of using a plasma electron source (PES) with a discharge in crossed E × H field for compensating the ion beam from an end-Hall ion source (EHIS) is analyzed. The PES used as a neutralizer is mounted in the immediate vicinity of the EHIS ion generation and acceleration region at 90° to the source axis. The behavior of the discharge and emission parameters of the EHIS is determined for operation with a filament neutralizer and a plasma electron source. It is found that the maximal discharge current from the ion source attains a value of 3.8 A for operation with a PES and 4 A for operation with a filament compensator. It is established that the maximal discharge current for the ion source strongly depends on the working gas flow rate for low flow rates (up to 10 ml/min) in the EHIS; for higher flow rates, the maximum discharge current in the EHIS depends only on the emissivity of the PES. Analysis of the emission parameters of EHISs with filament and plasma neutralizers shows that the ion beam current and the ion current density distribution profile are independent of the type of the electron source and the ion current density can be as high as 0.2 mA/cm2 at a distance of 25 cm from the EHIS anode. The balance of currents in the ion source-electron source system is considered on the basis of analysis of operation of EHISs with various sources of electrons. It is concluded that the neutralization current required for operation of an ion source in the discharge compensation mode must be equal to or larger than the discharge current of the ion source. The use of PES for compensating the ion beam from an end-Hall ion source proved to be effective in processes of ion-assisted deposition of thin films using reactive gases like O2 or N2. The application of the PES technique makes it possible to increase the lifetime of the ion-assisted deposition system by an order of magnitude (the lifetime with a Ti cathode is at least 60 h and is limited by the replacement life of the deposited cathode insertion).

Plasma flow reactor for steady state monitoring of physical and chemical processes at high temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koroglu, Batikan; Mehl, Marco; Armstrong, Michael R.

Here, we present the development of a steady state plasma flow reactor to investigate gas phase physical and chemical processes that occur at high temperature (1000 < T < 5000 K) and atmospheric pressure. The reactor consists of a glass tube that is attached to an inductively coupled argon plasma generator via an adaptor (ring flow injector). We have modeled the system using computational fluid dynamics simulations that are bounded by measured temperatures. In situ line-of-sight optical emission and absorption spectroscopy have been used to determine the structures and concentrations of molecules formed during rapid cooling of reactants after theymore » pass through the plasma. Emission spectroscopy also enables us to determine the temperatures at which these dynamic processes occur. A sample collection probe inserted from the open end of the reactor is used to collect condensed materials and analyze them ex situ using electron microscopy. The preliminary results of two separate investigations involving the condensation of metal oxides and chemical kinetics of high-temperature gas reactions are discussed.« less

Plasma flow reactor for steady state monitoring of physical and chemical processes at high temperatures

DOE PAGES

Koroglu, Batikan; Mehl, Marco; Armstrong, Michael R.; ...

2017-09-11

Here, we present the development of a steady state plasma flow reactor to investigate gas phase physical and chemical processes that occur at high temperature (1000 < T < 5000 K) and atmospheric pressure. The reactor consists of a glass tube that is attached to an inductively coupled argon plasma generator via an adaptor (ring flow injector). We have modeled the system using computational fluid dynamics simulations that are bounded by measured temperatures. In situ line-of-sight optical emission and absorption spectroscopy have been used to determine the structures and concentrations of molecules formed during rapid cooling of reactants after theymore » pass through the plasma. Emission spectroscopy also enables us to determine the temperatures at which these dynamic processes occur. A sample collection probe inserted from the open end of the reactor is used to collect condensed materials and analyze them ex situ using electron microscopy. The preliminary results of two separate investigations involving the condensation of metal oxides and chemical kinetics of high-temperature gas reactions are discussed.« less

The Madison plasma dynamo experiment: A facility for studying laboratory plasma astrophysics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cooper, C. M.; Brookhart, M.; Collins, C.

2014-01-15

The Madison plasma dynamo experiment (MPDX) is a novel, versatile, basic plasma research device designed to investigate flow driven magnetohydrodynamic instabilities and other high-β phenomena with astrophysically relevant parameters. A 3 m diameter vacuum vessel is lined with 36 rings of alternately oriented 4000 G samarium cobalt magnets, which create an axisymmetric multicusp that contains ∼14 m{sup 3} of nearly magnetic field free plasma that is well confined and highly ionized (>50%). At present, 8 lanthanum hexaboride (LaB{sub 6}) cathodes and 10 molybdenum anodes are inserted into the vessel and biased up to 500 V, drawing 40 A each cathode, ionizing a low pressuremore » Ar or He fill gas and heating it. Up to 100 kW of electron cyclotron heating power is planned for additional electron heating. The LaB{sub 6} cathodes are positioned in the magnetized edge to drive toroidal rotation through J × B torques that propagate into the unmagnetized core plasma. Dynamo studies on MPDX require a high magnetic Reynolds number Rm > 1000, and an adjustable fluid Reynolds number 10 < Re < 1000, in the regime where the kinetic energy of the flow exceeds the magnetic energy (M{sub A}{sup 2}=(v/v{sub A}){sup 2}>1). Initial results from MPDX are presented along with a 0-dimensional power and particle balance model to predict the viscosity and resistivity to achieve dynamo action.« less

Microwave plasma enabled synthesis of free standing carbon nanostructures at atmospheric pressure conditions.

PubMed

Bundaleska, N; Tsyganov, D; Dias, A; Felizardo, E; Henriques, J; Dias, F M; Abrashev, M; Kissovski, J; Tatarova, E

2018-05-23

An experimental and theoretical study on microwave (2.45 GHz) plasma enabled assembly of carbon nanostructures, such as multilayer graphene sheets and nanoparticles, was performed. The carbon nanostructures were fabricated at different Ar-CH4 gas mixture composition and flows at atmospheric pressure conditions. The synthesis method is based on decomposition of the carbon-containing precursor (CH4) in the "hot" microwave plasma environment into carbon atoms and molecules, which are further converted into solid carbon nuclei in the "colder" plasma zones. By tailoring of the plasma environment, a controlled synthesis of graphene sheets and diamond-like nanoparticles was achieved. Selective synthesis of graphene flakes was achieved at a microwave power of 1 kW, Ar and methane flow rates of 600 sccm and 2 sccm respectively, while the predominant synthesis of diamond-like nanoparticles was obtained at the same power, but with higher flow rates, i.e. 1000 and 7.5 sccm, respectively. Optical emission spectroscopy was applied to detect the plasma emission related to carbon species from the 'hot' plasma zone and to determine the main plasma parameters. Raman spectroscopy and scanning electron microscopy have been applied to characterize the synthesized nanostructures. A previously developed theoretical model was further updated and employed to understand the mechanism of CH4 decomposition and formation of the main building units, i.e. C and C2, of the carbon nanostructures. An insight into the physical chemistry of carbon nanostructure formation in a high energy density microwave plasma environment is presented.

Experimental results from plasma transport on Prototype-Material Plasma Exposure eXperiment and comparison with B2-Eirene modeling

NASA Astrophysics Data System (ADS)

Kafle, N.; Caneses, J. F.; Biewer, T. M.; Owen, L.; Showers, M.; Donovan, D.; Caughman, J. B.; Goulding, R. H.; Rapp, Juergen

2017-10-01

Proto-MPEX at ORNL is a linear plasma device that combines a helicon plasma source with additional microwave and RF heating to deliver high plasma heat and particle fluxes to a target. Double Langmuir probes and Thomson scattering are being used to measure local Te and ne at various radial and axial locations. A recently constructed Mach- double probe provides the added capability of simultaneously measuring Te, ne, and Mach number. With this diagnostic, it is possible to infer the plasma flow, particle flux, and convective heat flux at different locations along the plasma column in Proto-MPEX. Preliminary results show Mach numbers of 0.6 and 0.8 in either direction away from the helicon source, and no flow near the source for the case where the peak magnetic field was 1.0 T. In addition, the Thomson Scattering system has been upgraded to measure ne and Te profiles at two axial locations, upstream at the electron heating location and downstream close to the target. Measurements of particle flow and flux profiles, heat flux, and profiles of ne and Te will be discussed. The extensive coverage provided by these diagnostics permits data-constrained B2-Eirene modeling of the entire plasma column, and comparison with results of modeling of high density mode plasmas will be presented. Supported by the US. D.O.E. contract DE-AC05-00OR22725.

Langmuir probe diagnostics of an atmospheric pressure, vortex-stabilized nitrogen plasma jet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prevosto, L.; Mancinelli, B. R.; Kelly, H.

Langmuir probe measurements in an atmospheric pressure direct current (dc) plasma jet are reported. Sweeping probes were used. The experiment was carried out using a dc non-transferred arc torch with a rod-type cathode and an anode of 5 mm diameter. The torch was operated at a nominal power level of 15 kW with a nitrogen flow rate of 25 Nl min{sup -1}. A flat ion saturation region was found in the current-voltage curve of the probe. The ion saturation current to a cylindrical probe in a high-pressure non local thermal equilibrium (LTE) plasma was modeled. Thermal effects and ionization/recombination processesmore » inside the probe perturbed region were taken into account. Averaged radial profiles of the electron and heavy particle temperatures as well as the electron density were obtained. An electron temperature around 11 000 K, a heavy particle temperature around 9500 K and an electron density of about 4 Multiplication-Sign 10{sup 22} m{sup -3}, were found at the jet centre at 3.5 mm downstream from the torch exit. Large deviations from kinetic equilibrium were found throughout the plasma jet. The electron and heavy particle temperature profiles showed good agreement with those reported in the literature by using spectroscopic techniques. It was also found that the temperature radial profile based on LTE was very close to that of the electrons. The calculations have shown that this method is particularly useful for studying spraying-type plasma jets characterized by electron temperatures in the range 9000-14 000 K.« less

Bohm criterion and plasma particle/power exhaust to and recycling at the wall

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Xianzhu; Guo, Zehua

The plasma particle and power exhaust to the divertor surface drives both particle and power recycling at the surface, which in return constrains the plasma density and temperature at the target and their profile further upstream. Both particle and power exhaust fluxes are mediated by the plasma sheath next to the divertor surface. In particular, the Bohm criterion constrains the ion exit flow speed, which enters directly into the particle flux and the kinetic flow energy component of the ion power flux, and indirectly into the electron power flux through the sheath potential drop. Here we give an overview onmore » how the Bohm speed is set in a general plasma and how it enters power exhaust and power recycling at the divertor surface, and the implication on the correct implementation of sheath boundary conditions in numerical codes. The cases of ideal and non-ideal Bohm speed are distinguished as a result of the physics discussion.« less

Bohm criterion and plasma particle/power exhaust to and recycling at the wall

DOE PAGES

Tang, Xianzhu; Guo, Zehua

2017-06-07

The plasma particle and power exhaust to the divertor surface drives both particle and power recycling at the surface, which in return constrains the plasma density and temperature at the target and their profile further upstream. Both particle and power exhaust fluxes are mediated by the plasma sheath next to the divertor surface. In particular, the Bohm criterion constrains the ion exit flow speed, which enters directly into the particle flux and the kinetic flow energy component of the ion power flux, and indirectly into the electron power flux through the sheath potential drop. Here we give an overview onmore » how the Bohm speed is set in a general plasma and how it enters power exhaust and power recycling at the divertor surface, and the implication on the correct implementation of sheath boundary conditions in numerical codes. The cases of ideal and non-ideal Bohm speed are distinguished as a result of the physics discussion.« less

Gyrokinetic and kinetic particle-in-cell simulations of guide-field reconnection. I. Macroscopic effects of the electron flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muñoz, P. A., E-mail: munozp@mps.mpg.de; Kilian, P.; Büchner, J.

In this work, we compare gyrokinetic (GK) with fully kinetic Particle-in-Cell (PIC) simulations of magnetic reconnection in the limit of strong guide field. In particular, we analyze the limits of applicability of the GK plasma model compared to a fully kinetic description of force free current sheets for finite guide fields (b{sub g}). Here, we report the first part of an extended comparison, focusing on the macroscopic effects of the electron flows. For a low beta plasma (β{sub i} = 0.01), it is shown that both plasma models develop magnetic reconnection with similar features in the secondary magnetic islands if a sufficientlymore » high guide field (b{sub g} ≳ 30) is imposed in the kinetic PIC simulations. Outside of these regions, in the separatrices close to the X points, the convergence between both plasma descriptions is less restrictive (b{sub g} ≳ 5). Kinetic PIC simulations using guide fields b{sub g} ≲ 30 reveal secondary magnetic islands with a core magnetic field and less energetic flows inside of them in comparison to the GK or kinetic PIC runs with stronger guide fields. We find that these processes are mostly due to an initial shear flow absent in the GK initialization and negligible in the kinetic PIC high guide field regime, in addition to fast outflows on the order of the ion thermal speed that violate the GK ordering. Since secondary magnetic islands appear after the reconnection peak time, a kinetic PIC/GK comparison is more accurate in the linear phase of magnetic reconnection. For a high beta plasma (β{sub i} = 1.0) where reconnection rates and fluctuations levels are reduced, similar processes happen in the secondary magnetic islands in the fully kinetic description, but requiring much lower guide fields (b{sub g} ≲ 3)« less

Ion thruster performance model

NASA Technical Reports Server (NTRS)

Brophy, J. R.

1984-01-01

A model of ion thruster performance is developed for high flux density, cusped magnetic field thruster designs. This model is formulated in terms of the average energy required to produce an ion in the discharge chamber plasma and the fraction of these ions that are extracted to form the beam. The direct loss of high energy (primary) electrons from the plasma to the anode is shown to have a major effect on thruster performance. The model provides simple algebraic equations enabling one to calculate the beam ion energy cost, the average discharge chamber plasma ion energy cost, the primary electron density, the primary-to-Maxwellian electron density ratio and the Maxwellian electron temperature. Experiments indicate that the model correctly predicts the variation in plasma ion energy cost for changes in propellant gas (Ar, Kr and Xe), grid transparency to neutral atoms, beam extraction area, discharge voltage, and discharge chamber wall temperature. The model and experiments indicate that thruster performance may be described in terms of only four thruster configuration dependent parameters and two operating parameters. The model also suggests that improved performance should be exhibited by thruster designs which extract a large fraction of the ions produced in the discharge chamber, which have good primary electron and neutral atom containment and which operate at high propellant flow rates.

Proton Radiography of Spontaneous Fields, Plasma Flows and Dynamics in X-Ray Driven Inertial-Confinement Fusion Implosions

NASA Astrophysics Data System (ADS)

Li, C. K.; Seguin, F. H.; Frenje, J. A.; Rosenberg, M.; Zylstra, A. B.; Rinderknecht, H. G.; Petrasso, R. D.; Amendt, P. A.; Landen, O. L.; Town, R. P. J.; Betti, R.; Knauer, J. P.; Meyerhofer, D. D.; Back, C. A.; Kilkenny, J. D.; Nikroo, A.

2010-11-01

Backlighting of x-ray-driven implosions in empty hohlraums with mono-energetic protons on the OMEGA laser facility has allowed a number of important phenomena to be observed. Several critical parameters were determined, including plasma flow, three types of spontaneous electric fields and megaGauss magnetic fields. These results provide insight into important issues in indirect-drive ICF. Even though the cavity is effectively a Faraday cage, the strong, local fields inside the hohlraum can affect laser-plasma instabilities, electron distributions and implosion symmetry. They are of fundamental scientific importance for a range of new experiments at the frontiers of high-energy-density physics. Future experiments designed to characterize the field formation and evolution in low-Z gas fill hohlraums will be discussed.

Parallel 3-D numerical simulation of dielectric barrier discharge plasma actuators

NASA Astrophysics Data System (ADS)

Houba, Tomas

Dielectric barrier discharge plasma actuators have shown promise in a range of applications including flow control, sterilization and ozone generation. Developing numerical models of plasma actuators is of great importance, because a high-fidelity parallel numerical model allows new design configurations to be tested rapidly. Additionally, it provides a better understanding of the plasma actuator physics which is useful for further innovation. The physics of plasma actuators is studied numerically. A loosely coupled approach is utilized for the coupling of the plasma to the neutral fluid. The state of the art in numerical plasma modeling is advanced by the development of a parallel, three-dimensional, first-principles model with detailed air chemistry. The model incorporates 7 charged species and 18 reactions, along with a solution of the electron energy equation. To the author's knowledge, a parallel three-dimensional model of a gas discharge with a detailed air chemistry model and the solution of electron energy is unique. Three representative geometries are studied using the gas discharge model. The discharge of gas between two parallel electrodes is used to validate the air chemistry model developed for the gas discharge code. The gas discharge model is then applied to the discharge produced by placing a dc powered wire and grounded plate electrodes in a channel. Finally, a three-dimensional simulation of gas discharge produced by electrodes placed inside a riblet is carried out. The body force calculated with the gas discharge model is loosely coupled with a fluid model to predict the induced flow inside the riblet.

Hybrid simulation of the shock wave formation behind the Moon

NASA Astrophysics Data System (ADS)

Israelevich, P.; Ofman, L.

2012-09-01

A standing shock wave behind the Moon was predicted by Michel (1967) but never observed nor simulated. We use 1D hybrid code in order to simulate the collapse of the plasma-free cavity behind the Moon and for the first time to model the formation of this shock. Starting immediately downstream of the obstacle we consider the evolution of plasma expansion into the cavity in the frame of reference moving along with the solar wind. Wellknown effects as electric charging of the cavity affecting the plasma flow and counter streaming ion beams in the wake are reproduced. Near the apex of the inner Mach cone where the plasma flows from the opposite sides of the obstacle meet, a shock wave arises. The shock is produced by the interaction of oppositely directed proton beams in the plane containing solar wind velocity and interplanetary magnetic field vectors. In the direction across the magnetic field and the solar wind velocity, the shock results from the interaction of the plasma flow with the region of the enhanced magnetic field inside the cavity that plays the role of the magnetic barrier. Simulations with lower electron temperatures (Te~20eV) show weakened shock formation behind the moon at much greater distances. The shock disappears for typical solar wind conditions (Ti ~ Te) Therefore, in order to observe the trailing shock, a satellite should have a trajectory passing very close to the wake axis during the period of hot solar wind streams. We expect the shock to be produced at periods of high electron temperature solar wind streams (Ti<

Development and studies on a compact electron cyclotron resonance plasma source

NASA Astrophysics Data System (ADS)

Ganguli, A.; Tarey, R. D.; Arora, N.; Narayanan, R.

2016-04-01

It is well known that electron cyclotron resonance (ECR) produced plasmas are efficient, high-density plasma sources and have many industrial applications. The concept of a portable compact ECR plasma source (CEPS) would thus become important from an application point of view. This paper gives details of such a CEPS that is both portable and easily mountable on a chamber of any size. It uses a fully integrated microwave line operating at 2.45 GHz, up to 800 W, cw. The required magnetic field is produced by a set of suitably designed NdFeB ring magnets; the device has an overall length of  ≈60 cm and weighs  ≈14 kg including the permanent magnets. The CEPS was attached to a small experimental chamber to judge its efficacy for plasma production. In the pressure range of 0.5-10 mTorr and microwave power of  ≈400-500 W the experiments indicate that the CEPS is capable of producing high-density plasma (≈9  ×  1011-1012 cm-3) with bulk electron temperature in the range  ≈2-3 eV. In addition, a warm electron population with density and temperature in the range ≈7  ×  108-109 cm-3 and  ≈45-80 eV, respectively has been detected. This warm population plays an important role at high pressures in maintaining the high-density plasma, when plasma flow from the CEPS into the test chamber is strongly affected.

Measurements of shock-front structure in multi-species plasmas on OMEGA

NASA Astrophysics Data System (ADS)

Rinderknecht, Hans G.; Park, H.-S.; Ross, J. S.; Wilks, S. C.; Amendt, P. A.; Heeter, R. F.; Katz, J.; Hoffman, N. M.; Vold, E.; Taitano, W.; Simakov, A.; Chacon, L.

2016-10-01

The structure of a shock front in a plasma with multiple ion species is measured for the first time in experiments on the OMEGA laser. Thomson scattering of a 263.25 nm probe beam is used to diagnose electron density, electron and ion temperature, ion species concentration, and flow velocity in strong shocks (M 5) propagating through low-density (ρ 0.1 mg/cc) plasmas composed of H(98%)+Ne(2%) and H(98%)+C(2%). Separation of the ion species within the shock front is inferred. Although shocks play an important role in ICF and astrophysical plasmas, the intrinsically kinetic nature of the shock front indicates the need for experiments to benchmark hydrodynamic models. Comparison with PIC, Vlasov-Fokker-Planck, and multi-component hydrodynamic simulations will be presented. This work performed under auspices of U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Numerical simulation of electromagnetic wave attenuation in a nonequilibrium chemically reacting hypervelocity flow

NASA Astrophysics Data System (ADS)

Nusca, Michael Joseph, Jr.

The effects of various gasdynamic phenomena on the attenuation of an electromagnetic wave propagating through the nonequilibrium chemically reacting air flow field generated by an aerodynamic body travelling at high velocity is investigated. The nonequilibrium flow field is assumed to consist of seven species including nitric oxide ions and free electrons. The ionization of oxygen and nitrogen atoms is ignored. The aerodynamic body considered is a blunt wedge. The nonequilibrium chemically reacting flow field around this body is numerically simulated using a computer code based on computational fluid dynamics. The computer code solves the Navier-Stokes equations including mass diffusion and heat transfer, using a time-marching, explicit Runge-Kutta scheme. A nonequilibrium air kinetics model consisting of seven species and twenty-eight reactions as well as an equilibrium air model consisting of the same seven species are used. The body surface boundaries are considered as adiabatic or isothermal walls, as well as fully-catalytic and non-catalytic surfaces. Both laminar and turbulent flows are considered; wall generated flow turbulence is simulated using an algebraic mixing length model. An electromagnetic wave is considered as originating from an antenna within the body and is effected by the free electrons in the chemically reacting flow. Analysis of the electromagnetics is performed separately from the fluid dynamic analysis using a series solution of Maxwell's equations valid for the propagation of a long-wavelength plane electromagnetic wave through a thin (i.e., in comparison to wavelength) inhomogeneous plasma layer. The plasma layer is the chemically reacting shock layer around the body. The Navier-Stokes equations are uncoupled from Maxwell's equations. The results of this computational study demonstrate for the first time and in a systematic fashion, the importance of several parameters including equilibrium chemistry, nonequilibrium chemical kinetics, the reaction mechanism, flow viscosity, mass diffusion, and wall boundary conditions on modeling wave attenuation resulting from the interaction of an electromagnetic wave with an aerodynamic plasma. Comparison is made with experimental data.

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.

Simplified Numerical Description of SPT Operations

NASA Technical Reports Server (NTRS)

Manzella, David H.

1995-01-01

A simplified numerical model of the plasma discharge within the SPT-100 stationary plasma thruster was developed to aid in understanding thruster operation. A one dimensional description was used. Non-axial velocities were neglected except for the azimuthal electron velocity. A nominal operating condition of 4.5 mg/s of xenon anode flow was considered with 4.5 Amperes of discharge current, and a peak radial magnetic field strength of 130 Gauss. For these conditions, the calculated results indicated ionization fractions of 0.99 near the thruster exit with a potential drop across the discharge of approximately 250 Volts. Peak calculated electron temperatures were found to be sensitive to the choice of total ionization cross section for ionization of atomic xenon by electron bombardment and ranged from 51 eV to 60 eV. The calculated ionization fraction, potential drop, and electron number density agree favorably with previous experiments. Calculated electron temperatures are higher than previously measured.

Electromagnetic plasma particle simulations on Solar Probe Plus spacecraft interaction with near-Sun plasma environment

NASA Astrophysics Data System (ADS)

Miyake, Yohei; Usui, Hideyuki

It is necessary to predict the nature of spacecraft-plasma interactions in extreme plasma conditions such as in the near-Sun environment. The spacecraft environment immersed in the solar corona is characterized by the small Debye length due to dense (7000 mathrm{/cc}) plasmas and a large photo-/secondary electron emission current emitted from the spacecraft surfaces, which lead to distinctive nature of spacecraft-plasma interactions [1,2,3]. In the present study, electromagnetic field perturbation around the Solar Probe Plus (SPP) spacecraft is examined by using our original EM-PIC (electromagnetic particle-in-cell) plasma simulation code called EMSES. In the simulations, we consider the SPP spacecraft at perihelion (0.04 mathrm{AU} from the Sun) and important physical effects such as spacecraft charging, photoelectron and secondary electron emission, solar wind plasma flow including the effect of spacecraft orbital velocity, and the presence of a background magnetic field. Our preliminary results show that both photoelectrons and secondary electrons from the spacecraft are magnetized in a spatial scale of several meters, and make drift motion due the presence of the background convection electric field. This effect leads to non-axisymmetric distributions of the electron density and the resultant electric potential near the spacecraft. Our simulations predict that a strong (˜ 100 mathrm{mV/m}) spurious electric field can be observed by the probe measurement on the spacecraft due to such a non-axisymmetric effect. We also confirm that the large photo-/secondary electron current alters magnetic field intensity around the spacecraft, but the field variation is much smaller than the background magnetic field magnitude (a few mathrm{nT} compared to a few mathrm{mu T}). [1] Ergun et al., textit{Phys. Plasmas}, textbf{17}, 072903, 2010. [2] Guillemant et al., textit{Ann. Geophys.}, textbf{30}, 1075-1092, 2012. [3] Guillemant et al., textit{IEEE Trans. Plasma Sci.}, textbf{41}, 3338-3348, 2013.

Numerical simulation of heat fluxes in a two-temperature plasma at shock tube walls

NASA Astrophysics Data System (ADS)

Kuznetsov, E. A.; Poniaev, S. A.

2015-12-01

Numerical simulation of a two-temperature three-component Xenon plasma flow is presented. A solver based on the OpenFOAM CFD software package is developed. The heat flux at the shock tube end wall is calculated and compared with experimental data. It is shown that the heat flux due to electrons can be as high as 14% of the total heat flux.

High Current Hollow Cathode Plasma Plume Measurements

NASA Technical Reports Server (NTRS)

Thomas, Robert E.; Kamhawi, Hani; Williams, George J., Jr.

2014-01-01

Plasma plume measurements are reported for a hollow cathode assembly (HCA) operated at discharge currents of 50, 70, and 100 A at xenon flow rates between 19 - 46 standard cubic centimeter per minute. The HCA was centrally mounted in the NASA-300MS Hall Thruster and was operated in the "spot" and "plume" modes with additional data taken with an applied magnetic field. Langmuir probes, retarding potential analyzers, and optical emission spectroscopy were employed to measure plasma properties near the orifice of the HCA and to assess the charge state of the near-field plasma. Electron temperatures (2-6 electron volt) and plasma potentials are consistent with probe-measured values in previous investigations. Operation with an applied-field yields higher discharge voltages, increased Xe III production, and increased signals from the 833.5 nm C I line. While operating in plume mode and with an applied field, ion energy distribution measurements yield ions with energies significantly exceeding the applied discharge voltage. These findings are correlated with high-frequency oscillations associated with each mode.

Diagnostics of Plasma Propulsion Devices

NASA Astrophysics Data System (ADS)

Cappelli, Mark A.

1998-11-01

Plasma rockets are rapidly emerging as critical technologies in future space flight. These devices take on various forms, ranging from electro-thermal to electromagnetic accelerators, generally categorized by the method in which electrical energy is converted to thrust. As is the case in many plasma devices, non-intrusive optical (emission, or laser-based) diagnostics is an essential element in the characterization of these plasma sources, as access to the discharges in these plasma engines is often limited. Furthermore, laser-based diagnostics offer additional benefits, including improved spatial resolution, and can provide state-specific measurements of species densities, velocities and energy distributions. In recent years, we have developed and applied a variety of emission and laser-based diagnostics strategies to the characterization of arcjet plasma and closed-drift xenon Hall plasma accelerators. Both of these types of plasma propulsion devices are of immediate interest to the space propulsion community, and are under varying stages of development. Arcjet thrusters have unique properties, with strong plasma density, temperature and velocity gradients, which enhance the coupling between the gasdynamic and plasma physics. Closed-drift Hall plasma thrusters are low density electrostatic devices that are inherently turbulent, and exhibit varying degrees of anomalous cross-field electron transport. Our most extensive, collective effort has been to apply laser-induced fluorescence, Doppler-free laser absorption, and Raman scattering to the characterization of hydrogen and helium arcjet flows. Detailed measurements of velocity, temperatures, and electron densities are compared to the results of magneto-hydrodynamic flowfield simulations. The results show that while the simulations capture many aspects of the flow, there are still some unresolved discrepancies. The database established for Hall thrusters is less extensive, as the laser absorption spectroscopy of xenon is somewhat more complicated due to the hyperfine and isotopic structure of electronic transitions. With an understanding of the spectroscopic absorption lineshape for two select transitions in neutral and ionized xenon, we have successfully mapped out the neutral and singly ionized xenon velocities in the acceleration zone of Hall thrusters. These results indicate that the acceleration zone in a short-channel thruster is outside of the device, consistent with the measurements of plasma potential using more conventional Langmuir electrostatic probes. The spectroscopic data has also been used to identify limitations in ground-test facilities.

Validation of theoretical models of intrinsic torque in DIII-D

NASA Astrophysics Data System (ADS)

Grierson, B. A.; Wang, W. X.; Battaglia, D. J.; Chrystal, C.; Solomon, W. M.; Degrassie, J. S.; Staebler, G. M.; Boedo, J. A.

2016-10-01

Plasma rotation experiments in DIII-D are validating models of main-ion intrinsic rotation by testing Reynolds stress induced toroidal flow in the plasma core and intrinsic rotation induced by ion orbit losses in the plasma edge. In the core of dominantly electron heated plasmas with Te=Ti, the main-ion intrinsic toroidal rotation undergoes a reversal that correlates with the critical gradient for ITG turbulence. Residual stress arising from zonal-flow ExB shear and turbulence intensity gradient produce residual stress and counter-current intrinsic torque, which is balanced by momentum diffusion, creating the hollow profile. Quantitative agreement is obtained for the first time between the measured main-ion toroidal rotation and the rotation profile predicted by nonlinear GTS gyrokinetic simulations. At the plasma boundary, new main-ion CER measurements show a co-current rotation layer and this is tested against ion orbit loss models as the source of bulk plasma rotation. Work supported by the US Department of Energy under DE-AC02-09CH11466 and DE-FC02-04ER54698.

Explosive plasma flows in a solar flare

NASA Technical Reports Server (NTRS)

Zarro, Dominic M.; Canfield, Richard C.; Metcalf, Thomas R.; Strong, Keith T.

1988-01-01

Solar Maximum Mission soft X-ray data and Sacramento Peak Observatory H-alpha observations are combined in a study of the impulsive phase of a solar flare. A blue asymmetry, indicative of upflows, was observed in the coronal Ca XIX line during the soft X-ray rise phase. A red asymmetry, indicative of downflows, was observed simultaneously in chromospheric H-alpha emitted from bright flare kernels during the period of hard X-ray emission. Combining the velocity data with a measurement of coronal electron density, it is shown that the impulsive phase momentum of upflowing soft X-ray-emitting plasma equalled that of the downflowing H-alpha-emitting plasma to within one order of magnitude. In particular, the momentum of the upflowing plasma was 2 x 10 to the 21st g cm/s while that of the downflowing plasma was 7 x 10 to the 21st g cm/s, with a factor of 2 uncertainty on each value. This equality supports the explosive chromospheric evaporation model of solar flares, in which a sudden pressure increase at the footprint of a coronal loop produces oppositely directed flows in the heated plasma.

Spectroscopic investigations of beam-plasma interactions in an ion plume

NASA Technical Reports Server (NTRS)

Ruyten, W. M.; Friedly, V. J.; Peng, X.; Celenza, J. A.; Keefer, D.

1993-01-01

We report the results of spectroscopic investigations of beam-plasma interactions in the plume from a 3 cm ion source operated on argon. Ion-electron, ion-neutral, and electron-neutral scattering are identified by studying the dependence of neutral and ion emission intensities on chamber pressure and mass flow rate, and by analyzing the emission lineshapes at a non-orthogonal angle to the plume axis. Through the Doppler shift, we are able to separate contributions from fast beam ions and fast charge-exchange neutrals on the one hand, and of slow neutrals and slow ions on the other. We discuss the application of this new technique to the characterization of beam plasma interactions in the downstream region of ion thruster engines, and its potential for identifying the processes which lead to grid erosion.

Plasma Wake Simulations and Object Charging in a Shadowed Lunar Crater During a Solar Storm

NASA Technical Reports Server (NTRS)

Zimmerman, Michael I.; Jackson, T. L.; Farrell, W. W.; Stubbs, T. J.

2012-01-01

Within a permanently shadowed lunar crater the horizontal flow of solar wind is obstructed by upstream topography, forming a plasma wake that electrostatically diverts ions toward the crater floor and generates a surface potential that can reach kilovolts. In the present work kinetic plasma simulations are employed to investigate the morphology of a lunar crater wake during passage of a solar storm. Results are cast in terms of leading dimensionless ratios including the ion Mach number, ratio of crater depth to plasma Debye length, peak secondary electron yield, and electron temperature vs. electron impact energy at peak secondary yield. This small set of ratios allows generalization to a much wider range of scenarios. The kinetic simulation results are fed forward into an equivalent-circuit model of a roving astronaut. In very low-plasma-current environments triboelectric charging of the astronaut suit becomes effectively perpetual, representing a critical engineering concern for roving within shadowed lunar regions. Finally, simulated ion fluxes are used to explore sputtering and implantation processes within an idealized crater. It is suggested that the physics of plasma mini-wakes formed in the vicinity of permanently shadowed topography may play a critical role in modulating the enigmatic spatial distribution of volatiles at the lunar poles.

Plasma wake simulations and object charging in a shadowed lunar crater during a solar storm

NASA Astrophysics Data System (ADS)

Zimmerman, M. I.; Jackson, T. L.; Farrell, W. M.; Stubbs, T. J.

2012-08-01

Within a permanently shadowed lunar crater the horizontal flow of solar wind is obstructed by upstream topography, forming a plasma wake that electrostatically diverts ions toward the crater floor and generates a surface potential that can reach kilovolts. In the present work kinetic plasma simulations are employed to investigate the morphology of a lunar crater wake during passage of a solar storm. Results are cast in terms of leading dimensionless ratios including the ion Mach number, ratio of crater depth to plasma Debye length, peak secondary electron yield, and electron temperature versus electron impact energy at peak secondary yield. This small set of ratios allows generalization to a much wider range of scenarios. The kinetic simulation results are fed forward into an equivalent-circuit model of a roving astronaut. In very low-plasma-current environments triboelectric charging of the astronaut suit becomes effectively perpetual, representing a critical engineering concern for roving within shadowed lunar regions. Finally, simulated ion fluxes are used to explore sputtering and implantation processes within an idealized crater. It is suggested that the physics of plasma miniwakes formed in the vicinity of permanently shadowed topography may play a critical role in modulating the enigmatic spatial distribution of volatiles at the lunar poles.

Plasma flow disturbances in the magnetospheric plasma sheet during substorm activations

NASA Astrophysics Data System (ADS)

Kozelova, T. V.; Kozelov, B. V.; Turyanskii, V. A.

2017-11-01

We have considered variations in fields and particle fluxes in the near-Earth plasma sheet on the THEMIS-D satellite together with the auroral dynamics in the satellite-conjugate ionospheric part during two substorm activations on December 19, 2014 with K p = 2. The satellite was at 8.5 R E and MLT = 21.8 in the outer region of captured energetic particles with isotropic ion fluxes near the convection boundary of electrons with an energy of 10 keV. During substorm activations, the satellite recorded energetic particle injections and magnetic field oscillations with a period of 90 s. In the satellite-conjugate ionospheric part, the activations were preceded by wavelike disturbances of auroral brightness along the southern azimuthal arc. In the expansion phase of activations, large-scale vortex structures appeared in the structure of auroras. The sudden enhancements of auroral activity (brightening of arcs, auroral breakup, and appearance of NS forms) coincided with moments of local magnetic field dipolarization and an increase in the amplitude Pi2 of pulsations of the B z component of the magnetic field on the satellite. Approximately 30-50 s before these moments, the magnetosphere was characterized by an increased rate of plasma flow in the radial direction, which initiated the formation of plasma vortices. The auroral activation delays relative to the times when plasma vortices appear in the magnetosphere decreased with decreasing latitude of the satellite projection. The plasma vortices in the magnetosphere are assumed to be responsible for the observed auroral vortex structures and the manifestation of the hybrid vortex instability (or shear flow ballooning instability) that develops in the equatorial magnetospheric plane in the presence of a shear plasma flow in the region of strong pressure gradients in the Earthward direction.

Simulation of Noise in a Traveling Wave Tube

NASA Astrophysics Data System (ADS)

Verboncoeur, J. P.; Christenson, P. J.; Smith, H. B.

1999-11-01

Low frequency noise, manifested as close-in sidebands, has long been a significant limit to the performance of many traveling wave tubes. In this study, we investigate oscillations in the gun region due to the presence of plasma formed by electron-impact ionization of a background gas. The gun region of a coupled-cavity traveling wave tube is modeled using the two-dimensional XOOPIC particle-in-cell Monte Carlo collision code (J. P. Verboncoeur et al. Comput. Phys. Comm.) 87, 199-211 (1995). (available via the web: http://ptsg.eecs.berkeley.edu). The beam is 20.5 kV, 2.8 A, in near-confined flow in a solenoidal magnetic field with peak axial value of 0.263 T. Beam scalloping leads to trapping of plasma generated via electron-impact ionization of a background gas. The trapped plasma periodically leaves the system rapidly, and the density begins regenerating at a slow rate, leading to characteristic sawtooth oscillations. Plasma electrons are observed to exit the system axially about 20 ns before the ions exit primarily radially.

Anode power in quasisteady magnetoplasmadynamic accelerators

NASA Technical Reports Server (NTRS)

Saber, A. J.; Jahn, R. G.

1978-01-01

Anode heat flux in a quasi-steady MPD accelerator has been measured directly and locally by thermocouples attached to the inside surface of a shell anode. These measurements show that over a range of arc current from 5.5 to 44 kA, and argon mass flow from 1 to 48 g/s, the fraction of the total arc power deposited in the anode decreases from 50% at 200 kW to 10% at 20 MW. A theoretical model of the anode heat transfer asserts that energy exchange between electrons and heavy particles in the plasma near the anode occurs over distances greater than the anode sheath thickness, and hence the usual anode fall voltage, electron temperature, and work function contributions to the anode heat flux are supplemented by a contribution from the interelectrode potential. Calculations of anode heat flux using the measured current density, plasma potential, and electron temperature in the plasma adjacent to the anode agree with the direct measurements and indicate that the decrease in anode power fraction at higher arc powers can be attributed to the smaller mean free paths in the interelectrode plasma.

Early time evolution of a chemically produced electron depletion

NASA Technical Reports Server (NTRS)

Scales, W. A.; Bernhardt, P. A.; Ganguli, G.

1995-01-01

The early time evolution of an ionospheric electron depletion produced by a radially expanding electron attachment chemical release is studied with a two-dimensional simulation model. The model includes electron attachment chemistry, incorporates fluid electrons, particle ions and neutrals, and considers the evolution in a plane perpendicular to the geomagnetic field for a low beta plasma. Timescales considered are of the order of or less than the cyclotron period of the negative ions that result as a by-product of the electron attacment reaction. This corresponds to time periods of tenths of seconds during recent experiemts. Simulation results show that a highly sheared azimuthal electron flow velocity develops in the radially expanding depletion boundary. This sheared electron flow velocity and the steep density gradients in the boundary give rise to small-scale irregulatities in the form of electron density cavities and spikes. The nonlinear evolution of these irregularities results in trapping and ultimately turbulent heating of the negative ions.

A titanium hydride gun for plasma injection into the T2-reversed field pinch device

NASA Astrophysics Data System (ADS)

Voronin, A. V.; Hellblom, K. G.

1999-02-01

A study of a plasma gun (modified Bostic type) with titanium hydride electrodes has been carried out. The total number of released hydrogen atoms was in the range 1016-1018 and the maximum plasma flow velocity was 2.5×105 m s-1. The ion density near the gun edge reached 1.8×1020 m-3 and the electron temperature was around 40 eV as estimated from probe measurements. No species other than hydrogen or titanium were seen in the plasma line radiation. The plasma injector was successfully used for gas pre-ionization in the Extrap T2 reversed-field pinch device (ohmic heating toroidal experiment (OHTE)).

Impact of Gas Heating in Inductively Coupled Plasmas

NASA Technical Reports Server (NTRS)

Hash, D. B.; Bose, D.; Rao, M. V. V. S.; Cruden, B. A.; Meyyappan, M.; Sharma, S. P.; Biegel, Bryan (Technical Monitor)

2001-01-01

Recently it has been recognized that the neutral gas in inductively coupled plasma reactors heats up significantly during processing. The resulting gas density variations across the reactor affect reaction rates, radical densities, plasma characteristics, and uniformity within the reactor. A self-consistent model that couples the plasma generation and transport to the gas flow and heating has been developed and used to study CF4 discharges. A Langmuir probe has been used to measure radial profiles of electron density and temperature. The model predictions agree well with the experimental results. As a result of these comparisons along with the poorer performance of the model without the gas-plasma coupling, the importance of gas heating in plasma processing has been verified.

Physics and chemistry of plasma-assisted combustion.

PubMed

Starikovskiy, Andrey

2015-08-13

There are several mechanisms that affect a gas when using discharge plasma to initiate combustion or to stabilize a flame. There are two thermal mechanisms-the homogeneous and inhomogeneous heating of the gas due to 'hot' atom thermalization and vibrational and electronic energy relaxation. The homogeneous heating causes the acceleration of the chemical reactions. The inhomogeneous heating generates flow perturbations, which promote increased turbulence and mixing. Non-thermal mechanisms include the ionic wind effect (the momentum transfer from an electric field to the gas due to the space charge), ion and electron drift (which can lead to additional fluxes of active radicals in the gradient flows in the electric field) and the excitation, dissociation and ionization of the gas by e-impact, which leads to non-equilibrium radical production and changes the kinetic mechanisms of ignition and combustion. These mechanisms, either together or separately, can provide additional combustion control which is necessary for ultra-lean flames, high-speed flows, cold low-pressure conditions of high-altitude gas turbine engine relight, detonation initiation in pulsed detonation engines and distributed ignition control in homogeneous charge-compression ignition engines, among others. Despite the lack of knowledge in mechanism details, non-equilibrium plasma demonstrates great potential for controlling ultra-lean, ultra-fast, low-temperature flames and is extremely promising technology for a very wide range of applications. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Basic analytical investigation of plasma-chemically modified carbon fibers1

NASA Astrophysics Data System (ADS)

Bubert, H.; Ai, X.; Haiber, S.; Heintze, M.; Brüser, V.; Pasch, E.; Brandl, W.; Marginean, G.

2002-10-01

The background of the present investigation is to enhance the overall adherence of vapor grown carbon fibers (VGCF) to the surrounding polymer matrix in different applications by forming polar groups at their surfaces and by modifying the surface morphology. This has been done by plasma treatments using a low-pressure plasma with different gases, flow rates, pressures and powers. Two different types of carbon fibers were investigated: carbon microfibers and carbon nanofibers. The characterization of fiber surfaces was achieved by photoelectron spectroscopy (XPS), contact angle measurements and titration. These investigations were accompanied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The oxygen plasma treatment of the fibers changes the surfaces by forming a layer with a thickness of the order of one nanometer mainly consisting of functional groups like hydroxyl, carbonyl and carboxyl. After functionalization of the complete surface, a further plasma treatment does not enhance the superficial oxygen content but changes slightly the portions of the functional groups. A comparison of the methods applied provides a largely consistent image of the effect of plasma treatment.

SuperGaussian distribution functions in inhomogenous plasmas

NASA Astrophysics Data System (ADS)

Matte, Jean-Pierre

2008-11-01

In plasmas heated by a narrow laser beam, the shape of the distribution function is influenced by both the absorption, which tends to give a superGaussian (DLM) distribution function [1], and the effects of heat flow, which tends to make the distribution more Maxwellian, when the hot region is considerably wider than the laser beam [2]. Thus, it is only at early times that the deformation is as strong as predicted by our uniform intensity formula [1]. A large number of electron kinetic simulations of a finite width laser beam heating a uniform density plasma were performed with the electron kinetic code FPI [1] to study the competition between these two mechanisms. In some cases, the deformation is approximately given by this formula if we average the laser intensity over the entire plasma. This may explain why distributions were more Maxwellian than expected in some experiments [3]. [0pt] [1] J.-P. Matte et al., Plasma Phys. Contr. Fusion 30, 1665 (1988) [2] S. Brunner and E. Valeo, Phys. Plasmas 9, 923 (2002) [3] S.H. Glenzer et al., Phys. Rev. Lett. 82, 97 (1999).

TGLF Recalibration for ITER Standard Case Parameters FY2015: Theory and Simulation Performance Target Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Candy, J.

2015-12-01

This work was motivated by the observation, as early as 2008, that GYRO simulations of some ITER operating scenarios exhibited nonlinear zonal-flow generation large enough to effectively quench turbulence inside r /a ~ 0.5. This observation of flow-dominated, low-transport states persisted even as more accurate and comprehensive predictions of ITER profiles were made using the state-of-the-art TGLF transport model. This core stabilization is in stark contrast to GYRO-TGLF comparisons for modern-day tokamaks, for which GYRO and TGLF are typically in very close agreement. So, we began to suspect that TGLF needed to be generalized to include the effect of zonal-flowmore » stabilization in order to be more accurate for the conditions of reactor simulations. While the precise cause of the GYRO-TGLF discrepancy for ITER parameters was not known, it was speculated that closeness to threshold in the absence of driven rotation, as well as electromagnetic stabilization, created conditions more sensitive the self-generated zonal-flow stabilization than in modern tokamaks. Need for nonlinear zonal-flow stabilization: To explore the inclusion of a zonal-flow stabilization mechanism in TGLF, we started with a nominal ITER profile predicted by TGLF, and then performed linear and nonlinear GYRO simulations to characterize the behavior at and slightly above the nominal temperature gradients for finite levels of energy transport. Then, we ran TGLF on these cases to see where the discrepancies were largest. The predicted ITER profiles were indeed near to the TGLF threshold over most of the plasma core in the hybrid discharge studied (weak magnetic shear, q > 1). Scanning temperature gradients above the TGLF power balance values also showed that TGLF overpredicted the electron energy transport in the low-collisionality ITER plasma. At first (in Q3), a model of only the zonal-flow stabilization (Dimits shift) was attempted. Although we were able to construct an ad hoc model of the zonal flows that fit the GYRO simulations, the parameters of the model had to be tuned to each case. A physics basis for the zonal flow model was lacking. Electron energy transport at short wavelength: A secondary issue – the high-k electron energy flux – was initially assumed to be independent of the zonal flow effect. However, detailed studies of the fluctuation spectra from recent multiscale (electron and ion scale) GYRO simulations provided a critical new insight into the role of zonal flows. The multiscale simulations suggested that advection by the zonal flows strongly suppressed electron-scale turbulence. Radial shear of the zonal E×B fluctuation could not compete with the large electron-scale linear growth rate, but the k x-mixing rate of the E×B advection could. This insight led to a preliminary new model for the way zonal flows saturate both electron- and ion-scale turbulence. It was also discovered that the strength of the zonal E×B velocity could be computed from the linear growth rate spectrum. The new saturation model (SAT1), which replaces the original model (SAT0), was fit to the multiscale GYRO simulations as well as the ion-scale GYRO simulations used to calibrate the original SAT0 model. Thus, SAT1 captures the physics of both multiscale electron transport and zonal-flow stabilization. In future work, the SAT1 model will require significant further testing and (expensive) calibration with nonlinear multiscale gyrokinetic simulations over a wider variety of plasma conditions – certainly more than the small set of scans about a single C-Mod L-mode discharge. We believe the SAT1 model holds great promise as a physics-based model of the multiscale turbulent transport in fusion devices. Correction to ITER performance predictions: Finally, the impact of the SAT1model on the ITER hybrid case is mixed. Without the electron-scale contribution to the fluxes, the Dimits shift makes a significant improvement in the predicted fusion power as originally posited. Alas, including the high-k electron transport reduces the improvement, yielding a modest net increase in predicted fusion power compared to the TGLF prediction with the original SAT0 model.« less

Hydrodynamics of the Dirac fluid in graphene

NASA Astrophysics Data System (ADS)

Lucas, Andrew

Recent advances in materials physics have allowed us to observe hydrodynamic electron flow in multiple materials. A uniquely interesting possibility is the emergence of a quasi-relativistic plasma of electrons and holes appearing in Dirac semimetals such as graphene. I will briefly review the unique features of the hydrodynamics of the Dirac fluid, and then discuss the theroetical signatures for the Dirac fluid, and its observation in experiment.

Coupled interactions between tungsten surfaces and transient high-heat-flux deuterium plasmas

NASA Astrophysics Data System (ADS)

Takamura, S.; Uesugi, Y.

2015-03-01

Fundamental studies on the interactions between transient deuterium-plasma heat pulses and tungsten surfaces were carried out in terms of electrical, mechanical and thermal response in a compact plasma device AIT-PID (Aichi Institute of Technology-Plasma Irradiation Device). Firstly, electron-emission-induced surface-temperature increase is discussed in the surface-temperature range near tungsten's melting point, which is accomplished by controlling the sheath voltage and power transmission factor. Secondly, anomalous penetration of tungsten atomic efflux into the surrounding plasma was observed in addition to a normal layered population; it is discussed in terms of the effect of substantial tungsten influx into the deuterium plasma, which causes dissipation of plasma electron energy. Thirdly, a momentum input from pulsed plasma onto a tungsten target was observed visually. The force is estimated numerically by the accelerated ion flow to the target as well as the reaction of tungsten-vapour efflux. Finally, a discussion follows on the effects of the plasma heat pulses on the morphology of tungsten surface (originally a helium-induced ‘fuzzy’ nanostructure). A kind of bifurcated effect is obtained: melting and annealing. Open questions remain for all the phenomena observed, although sheath-voltage-dependent plasma-heat input may be a key parameter. Discussions on all these phenomena are provided by considering their implications to tokamak fusion devices.

Formation of an optical pulsed discharge in a supersonic air flow by radiation of a repetitively pulsed CO{sub 2} laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malov, Aleksei N; Orishich, Anatolii M

Results of optimisation of repetitively pulsed CO{sub 2}-laser generation are presented for finding physical conditions of forming stable burning of an optical pulsed discharge (OPD) in a supersonic air flow and for studying the influence of pulse parameters on the energy absorption efficiency of laser radiation in plasma. The optical discharge in a supersonic air flow was formed by radiation of a repetitively pulsed CO{sub 2} laser with mechanical Q-switching excited by a discharge with a convective cooling of the working gas. For the first time the influence of radiation pulse parameters on the ignition conditions and stable burning ofmore » the OPD in a supersonic air flow was investigated and the efficiency of laser radiation absorption in plasma was studied. The influence of the air flow velocity on stability of plasma production was investigated. It was shown that stable burning of the OPD in a supersonic flow is realised at a high pulse repetition rate where the interval between radiation pulses is shorter than the time of plasma blowing-off. Study of the instantaneous value of the absorption coefficient shows that after a breakdown in a time lapse of 100 - 150 ns, a quasi-stationary 'absorption phase' is formed with the duration of {approx}1.5 ms, which exists independently of air flow and radiation pulse repetition rate. This phase of strong absorption is, seemingly, related to evolution of the ionisation wave. (laser applications and other topics in quantum electronics)« less

Multi-fluid MHD simulations of Europa's interaction with Jupiter's magnetosphere

NASA Astrophysics Data System (ADS)

Harris, C. D. K.; Jia, X.; Slavin, J. A.; Rubin, M.; Toth, G.

2017-12-01

Several distinct physical processes generate the interaction between Europa, the smallest of Jupiter's Galilean moons, and Jupiter's magnetosphere. The 10˚ tilt of Jupiter's dipole causes time varying magnetic fields at Europa's orbit which interact with Europa's subsurface conducting ocean to induce magnetic perturbations around the moon. Jovian plasma interacts with Europa's icy surface to sputter off neutral particles, forming a tenuous exosphere which is then ionized by impact and photo-ionization to form an ionosphere. As jovian plasma flows towards the moon, mass-loading and interaction with the ionosphere slow the flow, producing magnetic perturbations that propagate along the field lines to form an Alfvén wing current system, which connects Europa to its bright footprint in Jupiter's ionosphere. The Galileo mission has shown that the plasma interaction generates significant magnetic perturbations that obscure signatures of the induced field from the subsurface ocean. Modeling the plasma-related perturbations is critical to interpreting the magnetic signatures of Europa's induction field, and therefore to magnetic sounding of its interior, a central goal of the upcoming Europa Clipper mission. Here we model the Europa-Jupiter interaction with multi-fluid magnetohydrodynamic simulations to understand quantitatively how these physical processes affect the plasma and magnetic environment around the moon. Our model separately tracks the bulk motion of three different ion fluids (exospheric O2+, O+, and magnetospheric O+), and includes sources and losses of mass, momentum and energy to each of the ion fluids due to ionization, charge-exchange and recombination. We include calculations of the electron temperature allowing for field-aligned electron heat conduction, and Hall effects due to differential ion-electron motion. Compared to previous simulations, this multi-fluid model allows us to more accurately determine the precipitation flux of jovian plasma to Europa's surface, which has significant implications for space weathering at the moon. Including the Hall effect in our simulations enables us to determine the effects of separate ion-electron bulk motion throughout the interaction, and our simulations reveal noticeable asymmetries and small-scale features in the Alfvén wings.

Isolation of Highly Purified Fractions of Plasma Membrane and Tonoplast from the Same Homogenate of Soybean Hypocotyls by Free-Flow Electrophoresis 1

PubMed Central

Sandelius, Anna Stina; Penel, Claude; Auderset, Guy; Brightman, Andrew; Millard, Merle; Morré, D. James

1986-01-01

A procedure is described whereby highly purified fractions of plasma membrane and tonoplast were isolated from hypocotyls of dark-grown soybean (Glycine max L. var Wayne) by the technique of preparative free-flow electrophoresis. Fractions migrating the slowest toward the anode were enriched in thick (10 nanometers) membranes identified as plasma membranes based on ability to bind N-1-naphthylphthalamic acid (NPA), glucan synthetase-II, and K+-stimulated, vanadate-inhibited Mg2+ ATPase, reaction with phosphotungstic acid at low pH on electron microscope sections, and morphological evaluations. Fractions migrating farthest toward the anode (farthest from the point of sample injection) were enriched in membrane vesicles with thick (7-9 nanometers) membranes that did not stain with phosphotungstic acid at low pH, contained a nitrate-inhibited, Cl-stimulated ATPase and had the in situ morphological characteristics of tonoplast including the presence of flocculent contents. These vesicles neither bound NPA nor contained levels of glucan synthetase II above background. Other membranous cell components such as dictyosomes (fucosyltransferase, latent nucleosidediphosphate phosphatase), endoplasmic reticulum vesicles (NADH- and NADPH- cytochrome c reductase), mitochondria (succinate-2(p-indophenyl)-3-p-nitrophenyl)-5-phenyl tetrazolium-reductase and cytochrome oxidase) and plastids (carotenoids and monogalactosyl diglyceride synthetase) were identified on the basis of appropriate marker constituents and, except for plastid thylakoids, had thin (<7 nanometers) membranes. They were located in the fractions intermediate between plasma membrane and tonoplast after free-flow electrophoretic separation and did not contaminate either the plasma membrane or the tonoplast fraction as determined from marker activities. From electron microscope morphometry (using both membrane measurements and staining with phosphotungstic acid at low pH) and analysis of marker enzymes, both plasma membrane and tonoplast fractions were estimated to be about 90% pure. Neither fraction appeared to be contaminated by the other by more than 3%. Images Fig. 1 Fig. 3 Fig. 4 Fig. 5 Fig. 9 PMID:16664771

Numerical modeling of a glow discharge through a supersonic bow shock in air

NASA Astrophysics Data System (ADS)

Rassou, S.; Packan, D.; Elias, P.-Q.; Tholin, F.; Chemartin, L.; Labaune, J.

2017-03-01

The interaction between a glow discharge and the bow shock of a Mach 3 air flow around a truncated conical model with a central spike is modeled, and comparison is made with prior experimental results. The KRONOS workflow for plasma modeling in flow fields, which has recently been developed at ONERA, was used for the modeling. Based on the quasi-neutral approximation, it couples hypersonic and reactive flow fields with electron chemistry, including the effect of non-Maxwellian electron energy distribution function. The model used for the discharge involves 12 species and 82 reactions, including ionization, electronic and vibrational excitation, and attachment. The simulations reproduce the main features of the discharge observed experimentally well, in particular, the very recognizable topology of the discharge. It was found from the simulations that behind the bow shock, in the afterglow, the negative ion flow ensures the electrical conduction and the establishment of the glow discharge. The influence of kinetic rates on the voltage-current characteristics is discussed.

A Signature of Self-Organized Criticality in the HT-6M Edge Plasma Turbulence

NASA Astrophysics Data System (ADS)

Wang, Wen-Hao; Yu, Chang-Xuan; Wen, Yi-Zhi; Xu, Yu-Hong; Ling, Bi-Li; Gong, Xian-Zu; Liu, Bao-Hua; Wan, Bao-Nian

2001-03-01

Power spectra of electron density and floating potential fluctuations in the velocity shear layer of the HT-6M edge region have been measured and analysed. All the spectra have three distinct frequency regions with the spectral decay indices typical of self-organized criticality systems (0, -1 and -4) when Doppler shift effects induced by the plasma E×B flow velocity have been taken into account. These results are consistent with the predictions of the self-organized criticality models, which may be an indication of edge plasma turbulence in the HT-6M tokamak evolving into a critical state independent of local plasma parameters.

Tantalum Etching with an Atmospheric Pressure Plasma Jet

NASA Astrophysics Data System (ADS)

Teslow, Hilary; Herrmann, Hans; Rosocha, Louis

2002-10-01

The APPJ is a non-thermal, atmospheric-pressure, glow discharge. A feedgas, composed of an inert carrier gas (e.g., He) and small concentrations of additives (e.g., O2, or CF4), flows between closely spaced electrodes powered at 13.56 MHz rf in a coaxial or parallel plate arrangement. The plasma has Te ˜ 2 eV and ne ˜ 10^11 cm-3. Electrons are not in thermal equilibrium with ions and neutrals: the electrons are ``hot", while the overall gas temperature is quite ``cold", typically 50-300 C. In the plasma, the gas is excited, dissociated or ionized by energetic electron impact. As the gas exits the discharge volume, ions and electrons are rapidly lost by recombination, leaving metastables (e.g. O2*, He*) and radicals (e.g. O, F, OF, O2F, CFO). These reactive species are then directed onto a surface to be processed. The APPJ has been developed for decontaminating nuclear, chemical, and biological agents. Atomic fluorine, and possibly other reactive species, can be used to convert actinides (e.g., U and Pu), into volatile fluorides (e.g., UF6, PuF6) that can be trapped, resulting in significant volume reduction of radioactive waste. In this talk, we will present results on using Ta as a surrogate for Pu in He/O2/CF4 etching plasmas. Results of experimental measurements of Ta etch rates for various gas mixtures and plasma jet standoff distance will be compared with plasma chemistry modeling of the concentrations of several active species produced in the plasma.

Surface current balance and thermoelectric whistler wings at airless astrophysical bodies: Cassini at Rhea

NASA Astrophysics Data System (ADS)

Teolis, B. D.; Sillanpää, I.; Waite, J. H.; Khurana, K. K.

2014-11-01

Sharp magnetic perturbations found by the Cassini spacecraft at the edge of the Rhea flux tube are consistent with field-aligned flux tube currents. The current system results from the difference of ion and electron gyroradii and the requirement to balance currents on the sharp Rhea surface. Differential-type hybrid codes that solve for ion velocity and magnetic field have an intrinsic difficulty modeling the plasma absorber's sharp surface. We overcome this problem by instead using integral equations to solve for ion and electron currents and obtain agreement with the magnetic perturbations at Rhea's flux tube edge. An analysis of the plasma dispersion relations and Cassini data reveals that field-guided whistler waves initiated by (1) the electron velocity anisotropy in the flux tube and (2) interaction with surface sheath electrostatic waves on topographic scales may facilitate propagation of the current system to large distances from Rhea. Current systems like those at Rhea should occur generally, for plasma absorbers of any size such as spacecraft or planetary bodies, in a wide range of space plasma environments. Motion through the plasma is not essential since the current system is thermodynamic in origin, excited by heat flow into the object. The requirements are a difference of ion and electron gyroradii and a sharp surface, i.e., without a significant thick atmosphere.

A transport model for non-local heating of electrons in ICP reactors

NASA Astrophysics Data System (ADS)

Chang, C. H.; Bose, Deepak

1998-10-01

A new model has been developed for non-local heating of electrons in ICP reactors, based on a hydrodynamic approach. The model has been derived using the electron momentum conservation in azimuthal direction with electromagnetic and frictional forces respectively as driving force and damper of harmonic oscillatory motion of electrons. The resulting transport equations include the convection of azimuthal electron momentum in radial and axial directions, thereby accounting for the non-local effects. The azimuthal velocity of electrons and the resulting electrical current are coupled to the Maxwell's relations, thus forming a self-consistent model for non-local heating. This model is being implemented along with a set of Navier-Stokes equations for plasma dynamics and gas flow to simulate low-pressure (few mTorr's) ICP discharges. Characteristics of nitrogen plasma in a TCP 300mm etch reactor is being studied. The results will be compared against the available Langmuir probe measurements [Collison et al. JVST-A 16(1),1998].

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

NASA Astrophysics Data System (ADS)

Wu, Hongchen; Anders, André

2008-08-01

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 in. (25.4 mm) diameter. The amplitude and width of the negative high voltage pulses (HVPs) were 2 kV, 5 kV, 10 kV, and 2 µs, 4 µs, 10 µs, 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.

Parallel momentum input by tangential neutral beam injections in stellarator and heliotron plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishimura, S., E-mail: nishimura.shin@lhd.nifs.ac.jp; Nakamura, Y.; Nishioka, K.

The configuration dependence of parallel momentum inputs to target plasma particle species by tangentially injected neutral beams is investigated in non-axisymmetric stellarator/heliotron model magnetic fields by assuming the existence of magnetic flux-surfaces. In parallel friction integrals of the full Rosenbluth-MacDonald-Judd collision operator in thermal particles' kinetic equations, numerically obtained eigenfunctions are used for excluding trapped fast ions that cannot contribute to the friction integrals. It is found that the momentum inputs to thermal ions strongly depend on magnetic field strength modulations on the flux-surfaces, while the input to electrons is insensitive to the modulation. In future plasma flow studies requiringmore » flow calculations of all particle species in more general non-symmetric toroidal configurations, the eigenfunction method investigated here will be useful.« less

Investigating the role of hydrogen in silicon deposition using an energy-resolved mass spectrometer and a Langmuir probe in an Ar/H{sub 2} radio frequency magnetron discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mensah, S. L.; Naseem, Hameed H.; Abu-Safe, Husam

2012-07-15

The plasma parameters and ion energy distributions (IED) of the dominant species in an Ar-H{sub 2} discharge are investigated with an energy resolved mass spectrometer and a Langmuir probe. The plasmas are generated in a conventional magnetron chamber powered at 150 W, 13.56 MHz at hydrogen flow rates ranging from 0 to 25 sccm with a fixed argon gas flow rate of 15 sccm. Various H{sub n}{sup +}, SiH{sub n}{sup +}, SiH{sub n} fragments (with n = 1, 2, 3) together with Ar{sup +} and ArH{sup +} species are detected in the discharge. The most important species for the filmmore » deposition is SiH{sub n} (with n = 0, 1, 2). H fragments affect the hydrogen content in the material. The flux of Ar{sup +} decreases and the flux of ArH{sup +} increases when the hydrogen flow rate is increased; however, both fluxes saturate at hydrogen flow rates above 15 sccm. Electron density, n{sub e}, electron energy, T{sub e}, and ion density, n{sub i}, are estimated from the Langmuir probe data. T{sub e} is below 1.2 eV at hydrogen flow rates below 8 sccm, and about 2 eV at flow rates above 8 sccm. n{sub e} and n{sub i} decrease with increased hydrogen flow but the ratio of n{sub i} to n{sub e} increases. The formation of H{sup +} ions with energies above 36 eV and electrons with energies greater than 2 eV contributes to the decrease in hydrogen content at hydrogen flow rates above 8 sccm. Analysis of the IEDs indicates an inter-dependence of the species and their contribution to the thin film growth and properties.« less

Field emission microplasma actuation for microchannel flows

NASA Astrophysics Data System (ADS)

Sashank Tholeti, Siva; Shivkumar, Gayathri; Alexeenko, Alina A.

2016-06-01

Microplasmas offer attractive flow control methodology for gas transport in microsystems where large viscous losses make conventional pumping methods highly inefficient. We study microscale flow actuation by dielectric-barrier discharge (DBD) with field emission (FE) of electrons, which allows lowering the operational voltage from kV to a few hundred volts and below. A feasibility study of FE-DBD for flow actuation is performed using 2D particle-in-cell method with Monte Carlo collisions (PIC/MCC) at 10 MHz in nitrogen at atmospheric pressure. The free diffusion dominated, high velocity field emission electrons create a large positive space charge and a body force on the order of 106 N m-3. The body force and Joule heat decrease with increase in dielectric thickness and electrode thickness. The body force also decreases at lower pressures. The plasma body force distribution along with the Joule heating is then used in the Navier-Stokes simulations to quantify the flow actuation in a microchannel. Theoretical analysis and simulations for plasma actuated planar Poiseuille flow show that the gain in flow rate is inversely proportional to Reynolds number. This theoretical analysis is in good agreement with the simulations for a microchannel with closely placed actuators under incompressible conditions. Flow rate of FE-DBD driven 2D microchannel is around 100 ml min-1 mm-1 for an input power of 64 μW mm-1. The gas temperature rises by 1500 K due to the Joule heating, indicating FE-DBD’s potential for microcombustion, micropropulsion and chemical sensing in addition to microscale pumping and mixing applications.

Observations at Mercury encounter by the plasma science experiment on Mariner 10

NASA Technical Reports Server (NTRS)

Ogilvie, K. W.; Scudder, J. D.; Hartle, R. E.; Siscoe, G. L.; Bridge, H. S.; Lazarus, A. J.; Asbridge, J. R.; Bame, S. J.; Yeates, C. M.

1974-01-01

A fully developed bow shock and magnetosheath were observed near Mercury, providing unambiguous evidence for a strong interaction between Mercury and the solar wind. Inside the sheath there is a distinct region analogous to the magnetosphere or magnetotail of earth, populated by electrons with lower density and higher temperature than the electrons observed in the solar wind or magnetosheath. At the time of encounter, conditions were such that a perpendicular shock was observed on the inbound leg and a parallel shock was observed on the outbound leg of the trajectory, and energetic plasma electron events were detected upstream from the outbound shock crossing. The interaction is most likely not atmospheric, but the data clearly indicate that the obstacle to solar wind flow is magnetic, either intrinsic or induced.

E and F region study of the evening sector auroral oval - A Chatanika/Dynamics Explorer 2/NOAA 6 comparison

NASA Technical Reports Server (NTRS)

Senior, C.; Sharber, J. R.; Winningham, J. D.; De La Beaujardiere, O.; Heelis, R. A.; Evans, D. S.; Sugiura, M.; Hoegy, W. R.

1987-01-01

Simultaneous data from the Chatanika radar and the DE 2 and NOAA 6 satellites are used to study the typical behavior of the winter evening-sector auroral plasma during moderate and steady magnetic activity. The equatorward edge of the auroral E layer, of the region 2 field-aligned currents, and of the region of intense convection are colocated. The auroral E layer extends several degrees south of the equatorward edge of the keV electron precipitation from the CPS. Although the main trough and ionization channel are embedded in a region of intense electric field where the plasma flows sunward at high speed, the flux tubes associated with these two features have different time histories. The midlatitude trough is located south of the region of electron precipitation, above a proton aurora. The ionization channel marks the poleward edge of the main trough and is colocated with the equatorward boundary of the electron precipitation from the central plasma sheet.

Return current instability driven by a temperature gradient in ICF plasmas

DOE PAGES

Rozmus, W.; Brantov, A. V.; Sherlock, M.; ...

2017-10-12

Here, hot plasmas with strong temperature gradients in inertial confinement fusion (ICF) experiments are examined for ion acoustic instabilities produced by electron heat flow. The return current instability (RCI) due to a neutralizing current of cold electrons arising in response to a large electron heat flux has been considered. First, the linear threshold and growth rates are derived in the nonlocal regime of thermal transport. They are compared with the results of Vlasov-Fokker-Planck (VFP) simulations in one spatial dimension. Very good agreement has been found between kinetic VFP simulations and the linear theory of the RCI. A quasi-stationary state ofmore » ion acoustic turbulence produced by the RCI is achieved in the VFP simulations. Saturation of the RCI involves heating of ions in the tail of the ion distribution function and convection of the enhanced ion acoustic fluctuations from the unstable region of the plasma. Further evolution of the ion acoustic turbulence and its effects on absorption and transport are also discussed.« less

Numerical analysis of azimuthal rotating spokes in a crossed-field discharge plasma

NASA Astrophysics Data System (ADS)

Kawashima, R.; Hara, K.; Komurasaki, K.

2018-03-01

Low-frequency rotating spokes are obtained in a cross-field discharge plasma using two-dimensional numerical simulations. A particle-fluid hybrid model is used to model the plasma flow in a configuration similar to a Hall thruster. It has been reported that the drift-diffusion approximation for an electron fluid results in an ill-conditioned matrix when solving for the potential because of the differences in the electron mobilities across the magnetic field and in the direction of the E × B drift. In this paper, we employ a hyperbolic approach that enables stable calculation, namely, better iterative convergence of the electron fluid model. Our simulation results show a coherent rotating structure propagating in the E × B direction with a phase velocity of 2500 m s‑1, which agrees with experimental data. The phase velocity obtained from the numerical simulations shows good agreement with that predicted by the dispersion relation of the gradient drift instability.

Return current instability driven by a temperature gradient in ICF plasmas

NASA Astrophysics Data System (ADS)

Rozmus, W.; Brantov, A. V.; Sherlock, M.; Bychenkov, V. Yu

2018-01-01

Hot plasmas with strong temperature gradients in inertial confinement fusion experiments are examined for ion acoustic instabilities produced by electron heat flow. The return current instability (RCI) due to a neutralizing current of cold electrons arising in response to a large electron heat flux has been considered. First, the linear threshold and growth rates are derived in the non-local regime of thermal transport. They are compared with the results of Vlasov-Fokker-Planck (VFP) simulations in one spatial dimension. Very good agreement has been found between kinetic VFP simulations and the linear theory of the RCI. A quasi-stationary state of ion acoustic turbulence (IAT) produced by the RCI is achieved in the VFP simulations. Saturation of the RCI involves heating of ions in the tail of the ion distribution function and convection of the enhanced ion acoustic fluctuations from the unstable region of the plasma. Further evolution of the IAT and its effects on absorption and transport are also discussed.

Ion beam enhancement in magnetically insulated ion diodes for high-intensity pulsed ion beam generation in non-relativistic mode

NASA Astrophysics Data System (ADS)

Zhu, X. P.; Zhang, Z. C.; Pushkarev, A. I.; Lei, M. K.

2016-01-01

High-intensity pulsed ion beam (HIPIB) with ion current density above Child-Langmuir limit is achieved by extracting ion beam from anode plasma of ion diodes with suppressing electron flow under magnetic field insulation. It was theoretically estimated that with increasing the magnetic field, a maximal value of ion current density may reach nearly 3 times that of Child-Langmuir limit in a non-relativistic mode and close to 6 times in a highly relativistic mode. In this study, the behavior of ion beam enhancement by magnetic insulation is systematically investigated in three types of magnetically insulated ion diodes (MIDs) with passive anode, taking into account the anode plasma generation process on the anode surface. A maximal enhancement factor higher than 6 over the Child-Langmuir limit can be obtained in the non-relativistic mode with accelerating voltage of 200-300 kV. The MIDs differ in two anode plasma formation mechanisms, i.e., surface flashover of a dielectric coating on the anode and explosive emission of electrons from the anode, as well as in two insulation modes of external-magnetic field and self-magnetic field with either non-closed or closed drift of electrons in the anode-cathode (A-K) gap, respectively. Combined with ion current density measurement, energy density characterization is employed to resolve the spatial distribution of energy density before focusing for exploring the ion beam generation process. Consistent results are obtained on three types of MIDs concerning control of neutralizing electron flows for the space charge of ions where the high ion beam enhancement is determined by effective electron neutralization in the A-K gap, while the HIPIB composition of different ion species downstream from the diode may be considerably affected by the ion beam neutralization during propagation.

Sterilization/disinfection using reduced-pressure plasmas: some differences between direct exposure of bacterial spores to a discharge and their exposure to a flowing afterglow

NASA Astrophysics Data System (ADS)

Moisan, M.; Levif, P.; Séguin, J.; Barbeau, J.

2014-07-01

The use of plasma for sterilization or disinfection offers a promising alternative to conventional steam or chemical approaches. Plasma can operate at temperatures less damaging to some heat-sensitive medical devices and, in contrast to chemicals, can be non-toxic and non-polluting for the operator and the environment, respectively. Direct exposure to the gaseous discharge (comprising an electric field and ions/electrons) or exposure to its afterglow (no E-field) can both be envisaged a priori, since these two methods can achieve sterility. However, important issues must be considered besides the sterility goal. Direct exposure to the discharge, although yielding a faster inactivation of microorganisms, is shown to be potentially more aggressive to materials and sometimes subjected to the shadowing effect that precludes the sterilization of complex-form items. These two drawbacks can be successfully minimized with an adequate flowing-afterglow exposure. Most importantly, the current paper shows that direct exposure to the discharge can lead to the dislodgment and release of viable microorganisms from their substratum. Such a phenomenon could be responsible for the recontamination of sterilized devices as well as possible contamination of the ambient surroundings, additionally yielding an erroneous over-appreciation of the inactivation efficiency. The operation of the N2-O2 flowing afterglow system being developed in our group is such that there are no ions and electrons left in the process chamber (late-afterglow regime) in full contrast with their presence in the discharge. The dislodgment and release of spores could be attributed, based on the literature, to their electrostatic charging by electrons, leading to an (outward) electrostatic stress that exceeds the adhesion of the spores on their substrate.

Particle-in-cell Simulation of Dipolarization Front Associated Whistlers

NASA Astrophysics Data System (ADS)

Lin, D.; Scales, W.; Ganguli, G.; Crabtree, C. E.

2017-12-01

Dipolarization fronts (DFs) are dipolarized magnetic field embedded in the Earthward propagating bursty bulk flows (BBFs), which separates the hot, tenuous high-speed flow from the cold, dense, and slowly convecting surrounding plasma [Runov et al. 2011]. Broadband fluctuations have been observed at DFs including the electromagnetic whistler waves and electrostatic lower hybrid waves in the Very Low Frequency (VLF) range [e.g., Zhou et al. 2009, Deng et al. 2010]. There waves are suggested to be able heat electrons and play a critical role in the plasma sheet dynamics [Chaston et al., 2012, Angelopoulos et al., 2013]. However, their generation mechanism and role in the energy conversion are still under debate. The gradient scale of magnetic field, plasma density at DFs in the near-Earth magnetotail is comparable to or lower than the ion gyro radius [Runov et al., 2011, Fu et al., 2012, Breuillard et al., 2016]. Such strongly inhomogeneous configuration could be unstable to the electron-ion hybrid (EIH) instability, which arises from strongly sheared transverse flow and is in the VLF range [Ganguli et al. 1988, Ganguli et al. 2014]. The equilibrium of the EIH theory implies an anisotropy of electron temperature, which are likely to drive the whistler waves observed in DFs [Deng et al., 2010, Gary et al., 2011]. In order to better understand how the whistler waves are generated in DFs and whether the EIH theory is applicable, a fully electromagnetic particle-in-cell (EMPIC) model is used to simulate the EIH instability with similar equilibrium configurations in DF observations. The EMPIC model deals with three dimensions in the velocity space and two dimensions in the configuration space, which is quite ready to include the third configuration dimension. Simulation results will be shown in this presentation.

Plasmasphere Modeling with Ring Current Heating

NASA Technical Reports Server (NTRS)

Guiter, S. M.; Fok, M.-C.; Moore, T. E.

1995-01-01

Coulomb collisions between ring current ions and the thermal plasma in the plasmasphere will heat the plasmaspheric electrons and ions. During a storm such heating would lead to significant changes in the temperature and density of the thermal plasma. This was modeled using a time- dependent, one-stream hydrodynamic model for plasmaspheric flows, in which the model flux tube is connected to the ionosphere. The model simultaneously solves the coupled continuity, momentum, and energy equations of a two-ion (H(+) and O(+) quasineutral, currentless plasma. Heating rates due to collisions with ring current ions were calculated along the field line using a kinetic ring current model. First, diurnally reproducible results were found assuming only photoelectron heating of the thermal electrons. Then results were found with heating of the H(+) ions by the ring current during the recovery phase of a magnetic storm.

Guided flows in coronal magnetic flux tubes

NASA Astrophysics Data System (ADS)

Petralia, A.; Reale, F.; Testa, P.

2018-01-01

Context. There is evidence that coronal plasma flows break down into fragments and become laminar. Aims: We investigate this effect by modelling flows confined along magnetic channels. Methods: We consider a full magnetohydrodynamic (MHD) model of a solar atmosphere box with a dipole magnetic field. We compare the propagation of a cylindrical flow perfectly aligned with the field to that of another flow with a slight misalignment. We assume a flow speed of 200 km s-1 and an ambient magnetic field of 30 G. Results: We find that although the aligned flow maintains its cylindrical symmetry while it travels along the magnetic tube, the misaligned one is rapidly squashed on one side, becoming laminar and eventually fragmented because of the interaction and back-reaction of the magnetic field. This model could explain an observation made by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory of erupted fragments that fall back onto the solar surface as thin and elongated strands and end up in a hedge-like configuration. Conclusions: The initial alignment of plasma flow plays an important role in determining the possible laminar structure and fragmentation of flows while they travel along magnetic channels. Movies are available in electronic form at http://www.aanda.org

CO2 Dissociation by Low Current Gliding Discharge in the Reverse Vortex Flow

NASA Astrophysics Data System (ADS)

Gutsol, Alexander

2012-10-01

If performed with high energy efficiency, plasma-chemical dissociation of carbon dioxide can be a way of converting and storing energy when there is an excess of electric energy, for example generated by solar elements of wind turbines. CO2 dissociation with efficiency of up to 90% was reported earlier for low pressure microwave discharge in supersonic flow. A new plasma-chemical system uses a low current gliding discharge in the reverse vortex flow of plasma gas. The system is a development of the Gliding Arc in Tornado reactor. The system was used to study dissociation of CO2 in wide ranges of the following experimental parameters: reactor pressure (15-150 kPa), discharge current (50-500 mA), gas flow rate (3-30 liters per minute), and electrode gap length (1-10 cm). Additionally, the effect of thermal energy recuperation on CO2 dissociation efficiency was tested. Plasma chemical efficiency of CO2 dissociation is very low (about 3%) in a short discharge at low pressures (about 15 kPa) when it is defined by electronic excitation. The highest efficiency (above 40%) was reached at pressures 50-70 kPa in a long discharge with thermal energy recuperation. It means that the process is controlled by thermal dissociation with subsequent effective quenching. Plasma chemical efficiency was determined from the data of chromatographic analysis and oscilloscope electric power integration, and also was checked calorimetrically by the thermal balance of the system.

Experimental plasma studies

NASA Technical Reports Server (NTRS)

Dunn, M. G.

1972-01-01

The rate coefficients for the reactions C(+) + e(-) + e(-) yields C + e(-) and CO(+) + e(-) yields C + O were measured over the electron temperature range of approximately 1500 deg K to 7000 deg K. The measurements were performed in CO that had expanded from equilibrium reservoir conditions of 7060 deg K at 17.3 atm pressure and from 6260 deg K at 10.0 atm pressure. Two RAM flight probes were used to measure electron density and electron temperature in the expanding flow of a shock tunnel. Experiments were performed in the inviscid flow with both probes and in the nozzle-wall boundary layer with the constant bias-voltage probe. The distributions of electron density and electron temperature were independently measured using voltage-swept thin-wire probes. Thin-wire Langmuir probes were also used to measure the electron-density and electron-temperature distributions in the boundary layer of a sharp flat plate located on the nozzle centerline. Admittance measurements were performed with the RAM C and RAM C-C S-band antennas in the presence of an ionized boundary layer.

The Earth's Plasmasphere

NASA Technical Reports Server (NTRS)

Gallagher, D. L.

2015-01-01

The Earth's plasmasphere is an inner part of the magneteosphere. It is located just outside the upper ionosphere located in Earth's atmosphere. It is a region of dense, cold plasma that surrounds the Earth. Although plasma is found throughout the magnetosphere, the plasmasphere usually contains the coldest plasma. Here's how it works: The upper reaches of our planet's atmosphere are exposed to ultraviolet light from the Sun, and they are ionized with electrons that are freed from neutral atmospheric particles. The results are electrically charged negative and positive particles. The negative particles are electrons, and the positive particles are now called ions (formerly atoms and molecules). If the density of these particles is low enough, this electrically charged gas behaves differently than it would if it were neutral. Now this gas is called plasma. The atmospheric gas density becomes low enough to support the conditions for a plasma around earth at about 90 kilometers above Earth's surface. The electrons in plasma gain more energy, and they are very low in mass. They move along Earth's magnetic field lines and their increased energy is enough to escape Earth's gravity. Because electrons are very light, they don't have to gain too much kinetic energy from the Sun's ultraviolet light before gravity loses its grip on them. Gravity is not all that holds them back, however. As more and more electrons begin to escape outward, they leave behind a growing net positive electric charge in the ionosphere and create a growing net negative electric charge above the ionosphere; an electric field begins to develop (the Pannekoek-Rosseland E-field). Thus, these different interacting charges result in a positively charged ionosphere and negatively charged region of space above it. Very quickly this resulting electric field opposed upward movement of the electrons out of the ionosphere. The electrons still have this increased energy, however, so the electric field doesn't just go away. Instead the ions react to the electric field and are attracted to it. They begin to move upward out of the ionosphere too. Since all this happens on a small scale, it simply looks like the electrons and ions move out of the ionosphere together. Ultimately the effect is that the lighter ions of hydrogen, helium and oxygen are able to escape from the ionosphere. For a planet like Earth with a strong planetary magnetic field, these outward moving particles remain trapped near the planet unless other processes further draw them away and into interplanetary space. As is always the case with nature, there is much more story to tell about this "upwardly mobile" plasma and these other processes. Over only a short time period of hours and days this escaping plasma can, in some places, build up in concentration until an equilibrium is reached where as much plasma flows inward into the ionosphere as flows outward. This "donut shaped" region of cold (about 1 electron volt in energy) plasma encircling the planet is called the plasmasphere. Because of space weather storms (kind of a generic phrase for those other processes) this cold and dense plasmaspheric plasma can actually end up all over the place. Generally, that region of space where plasma from the ionosphere has the time to build up to become identified as the plasmasphere rotates or nearly rotates with the Earth. That region shrinks in size with increased space weather activity and expands or refills during times of inactivity. As it shrinks with increasing activity, some of the plasmasphere is drawn away from its main body (plasmaspheric erosion) in the sunward direction toward the boundary in space between that region dominated by Earth's magnetic field and the much larger region dominated by the Sun's magnetic field. The region dominated by Earth's magnetic field is called the magnetosphere. The larger Sun dominated region is called the heliosphere.

Magnetosheath jets: MMS observations of internal structures and jet interactions with ambient plasma

NASA Astrophysics Data System (ADS)

Plaschke, F.; Karlsson, T.; Hietala, H.; Archer, M. O.; Voros, Z.; Nakamura, R.; Magnes, W.; Baumjohann, W.; Torbert, R. B.; Russell, C. T.; Giles, B. L.

2017-12-01

The dayside magnetosheath downstream of the quasi-parallel bow shock is commonly permeated by high-speed jets. Under low IMF cone angle conditions, large scale jets alone (with cross-sectional diameters of over 2 Earth radii) have been found to impact the subsolar magnetopause once every 6 minutes - smaller scale jets occurring much more frequently. The consequences of jet impacts on the magnetopause can be significant: they may trigger local reconnection and waves, alter radiation belt electron drift paths, disturb the geomagnetic field, and potentially generate diffuse throat aurora at the dayside ionosphere. Although some basic statistical properties of jets are well-established, their internal structure and interactions with the surrounding magnetosheath plasma are rather unknown. We present Magnetospheric Multiscale (MMS) observations which reveal a rich jet-internal structure of high-amplitude plasma moment and magnetic field variations and associated currents. These variations/structures are generally found to be in thermal and magnetic pressure balance; they mostly (but not always) convect with the plasma flow. Small velocity differences between plasma and structures are revealed via four-spacecraft timing analysis. Inside a jet core region, where the plasma velocity maximizes, structures are found to propagate forward (i.e., with the jet), whereas backward propagation is found outside that core region. Although super-magnetosonic flows are detected by MMS in the spacecraft frame of reference, no fast shock is seen as the jet plasma is sub-magnetosonic with respect to the ambient magnetosheath plasma. Instead, the fast jet plasma pushes ambient magnetosheath plasma ahead of the jet out of the way, possibly generating anomalous sunward flows in the vicinity, and modifies the magnetic field aligning it with the direction of jet propagation.

Three dimensional instabilities of an electron scale current sheet in collisionless magnetic reconnection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jain, Neeraj; Büchner, Jörg; Max Planck Institute for Solar System Research, Justus-Von-Liebig-Weg-3, Göttingen

In collisionless magnetic reconnection, electron current sheets (ECS) with thickness of the order of an electron inertial length form embedded inside ion current sheets with thickness of the order of an ion inertial length. These ECS's are susceptible to a variety of instabilities which have the potential to affect the reconnection rate and/or the structure of reconnection. We carry out a three dimensional linear eigen mode stability analysis of electron shear flow driven instabilities of an electron scale current sheet using an electron-magnetohydrodynamic plasma model. The linear growth rate of the fastest unstable mode was found to drop with themore » thickness of the ECS. We show how the nature of the instability depends on the thickness of the ECS. As long as the half-thickness of the ECS is close to the electron inertial length, the fastest instability is that of a translational symmetric two-dimensional (no variations along flow direction) tearing mode. For an ECS half thickness sufficiently larger or smaller than the electron inertial length, the fastest mode is not a tearing mode any more and may have finite variations along the flow direction. Therefore, the generation of plasmoids in a nonlinear evolution of ECS is likely only when the half-thickness is close to an electron inertial length.« less

The characterization of exosome from blood plasma of patients with colorectal cancer

NASA Astrophysics Data System (ADS)

Yunusova, N. V.; Tamkovich, S. N.; Stakheeva, M. N.; Afanas'ev, S. G.; Frolova, A. Y.; Kondakova, I. V.

2016-08-01

Exosomes are extracellular membrane structures involved in many physiological and pathological processes including cancerogenesis and metastasis. The clarification of the criteria for exosome isolating and identifying is the purpose of this study. Exosome samples from the plasma of patients with colorectal cancer and healthy donors were examined using transmission electron microscopy and flow cytometry in accordance with the minimum requirements of "International Society for Extracellular Vesicles". The choice of the method for isolation of exosomes from the blood plasma by ultrafiltration and ultracentrifugation allowed obtaining highly purified samples of exosomes, in which all the structural components were clearly seen. The results obtained with flow cytometry suggest that exosomes of blood plasma from patients with colorectal cancer can be produced by epithelial cells. Moreover, cells produce different types of exosomes, which correspond to different mechanisms in sorting macromolecules in the membrane of multivesicular bodies. Determination of significant differences in the expression of specific exosomal proteins from colorectal cancer patients compared to healthy donors suggests a high diagnostic potential significance of circulating exosomes.

Gas and plasma dynamics of RF discharge jet of low pressure in a vacuum chamber with flat electrodes and inside tube, influence of RF discharge on the steel surface parameters

NASA Astrophysics Data System (ADS)

Khristoliubova, V. I.; Kashapov, N. F.; Shaekhov, M. F.

2016-06-01

Researches results of the characteristics of the RF discharge jet of low pressure and the discharge influence on the surface modification of high speed and structural steels are introduced in the article. Gas dynamics, power and energy parameters of the RF low pressure discharge flow in the discharge chamber and the electrode gap are studied in the presence of the materials. Plasma flow rate, discharge power, the concentration of electrons, the density of RF power, the ion current density, and the energy of the ions bombarding the surface materials are considered for the definition of basic properties crucial for the process of surface modification of materials as they were put in the plasma jet. The influence of the workpiece and effect of products complex configuration on the RF discharge jet of low pressure is defined. The correlation of the input parameters of the plasma unit on the characteristics of the discharge is established.

Suppressed ion-scale turbulence in a hot high-β plasma

NASA Astrophysics Data System (ADS)

Schmitz, L.; Fulton, D. P.; Ruskov, E.; Lau, C.; Deng, B. H.; Tajima, T.; Binderbauer, M. W.; Holod, I.; Lin, Z.; Gota, H.; Tuszewski, M.; Dettrick, S. A.; Steinhauer, L. C.

2016-12-01

An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. Field-reversed configuration (FRC) plasmas are potentially attractive as a reactor concept, achieving high plasma pressure in a simple axisymmetric geometry. Here, we show that FRC plasmas have unique, beneficial microstability properties that differ from typical regimes in toroidal confinement devices. Ion-scale fluctuations are found to be absent or strongly suppressed in the plasma core, mainly due to the large FRC ion orbits, resulting in near-classical thermal ion confinement. In the surrounding boundary layer plasma, ion- and electron-scale turbulence is observed once a critical pressure gradient is exceeded. The critical gradient increases in the presence of sheared plasma flow induced via electrostatic biasing, opening the prospect of active boundary and transport control in view of reactor requirements.

Suppressed ion-scale turbulence in a hot high-β plasma

PubMed Central

Schmitz, L.; Fulton, D. P.; Ruskov, E.; Lau, C.; Deng, B. H.; Tajima, T.; Binderbauer, M. W.; Holod, I.; Lin, Z.; Gota, H.; Tuszewski, M.; Dettrick, S. A.; Steinhauer, L. C.

2016-01-01

An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. Field-reversed configuration (FRC) plasmas are potentially attractive as a reactor concept, achieving high plasma pressure in a simple axisymmetric geometry. Here, we show that FRC plasmas have unique, beneficial microstability properties that differ from typical regimes in toroidal confinement devices. Ion-scale fluctuations are found to be absent or strongly suppressed in the plasma core, mainly due to the large FRC ion orbits, resulting in near-classical thermal ion confinement. In the surrounding boundary layer plasma, ion- and electron-scale turbulence is observed once a critical pressure gradient is exceeded. The critical gradient increases in the presence of sheared plasma flow induced via electrostatic biasing, opening the prospect of active boundary and transport control in view of reactor requirements. PMID:28000675

Spheroidization of molybdenum powder by radio frequency thermal plasma

NASA Astrophysics Data System (ADS)

Liu, Xiao-ping; Wang, Kuai-she; Hu, Ping; Chen, Qiang; Volinsky, Alex A.

2015-11-01

To control the morphology and particle size of dense spherical molybdenum powder prepared by radio frequency (RF) plasma from irregular molybdenum powder as a precursor, plasma process parameters were optimized in this paper. The effects of the carrier gas flow rate and molybdenum powder feeding rate on the shape and size of the final products were studied. The molybdenum powder morphology was examined using high-resolution scanning electron microscopy. The powder phases were analyzed by X-ray diffraction. The tap density and apparent density of the molybdenum powder were investigated using a Hall flow meter and a Scott volumeter. The optimal process parameters for the spherical molybdenum powder preparation are 50 g/min powder feeding rate and 0.6 m3/h carrier gas rate. In addition, pure spherical molybdenum powder can be obtained from irregular powder, and the tap density is enhanced after plasma processing. The average size is reduced from 72 to 62 µm, and the tap density is increased from 2.7 to 6.2 g/cm3. Therefore, RF plasma is a promising method for the preparation of high-density and high-purity spherical powders.

High enthalpy arc-heated plasma flow diagnostics by tunable diode laser absorption spectroscopy

NASA Astrophysics Data System (ADS)

Lin, Xin; Chen, Lianzhong; Zeng, Hui; Ou, Dongbin; Dong, Yonghui

2017-05-01

This paper reports the laser absorption measurements of atomic oxygen in the FD04 arc-heater at China Academy of Aerospace Aerodynamics (CAAA). An atomic oxygen absorption line at 777.19 nm is utilizied for detecting the population of electronically excited oxygen atom in an air plasma flow. A scanned-wavelength direct absorption mode is used in this study. The laser is scanned in wavelength across the absorption feature at a rate of 200 Hz. Under the assumption of thermal equilibrium, time-resolved temperature measurements are obtained on one line-of-sight in the arc-heater. The good agreement of the temperature inferred from the sonic throat method suggests the equilibrium assumption is valid. These results illustrate the feasibility of the diode laser sensors for flow parameters in high enthalpy arc-heated facilities.

Physics of the diffusion region in the Magnetospheric Multiscale era

NASA Astrophysics Data System (ADS)

Chen, L. J.; Hesse, M.; Wang, S.; Ergun, R.; Bessho, N.; Burch, J. L.; Giles, B. L.; Torbert, R. B.; Gershman, D. J.; Wilson, L. B., III; Dorelli, J.; Pollock, C. J.; Moore, T. E.; Lavraud, B.; Strangeway, R. J.; Russell, C. T.; Khotyaintsev, Y. V.; Le Contel, O.; Avanov, L. A.

2016-12-01

Encounters of reconnection diffusion regions by the Magnetospheric Multiscale (MMS) mission during its first magnetopause scan are studied in combination with theories and simulations. The goal is to understand by first-principles how stored magnetic energy is converted into plasma thermal and bulk flow energies via particle energization, mixing and interaction with waves. The magnetosheath population having much higher density than the magnetospheric plasma is an outstanding narrator for and participant in the magnetospheric part of the diffusion region. For reconnection with negligible guide fields, the accelerated magnetosheath population (for both electrons and ions) is cyclotron turned by the reconnected magnetic field to form outflow jets, and then gyrotropized downstream. Wave fluctuations are reduced in the central electron diffusion region (EDR) and do not dominate the energy conversion there. For an event with a significant guide field to magnetize the electrons, wave fluctuations at the lower hybrid frequency dominate the energy conversion in the EDR, and the fastest electron outflow is established dominantly by a strong perpendicular electric field via the ExB flow in one exhaust and by time-of-flight effects along with parallel electric field acceleration in the other. Whether the above features are common threads to magnetopause reconnection diffusion regions is a question to be further examined.

Volumetric Studies of Earth's Electron Foreshock Using PEACE Data

NASA Technical Reports Server (NTRS)

Goldstein, Melvyn L.; Gurgiolo, Chris; Fazakersley, Andrew

2010-01-01

We describe the methodology used to set up and compute spatial derivatives of the electron moments using data acquired by the Plasma Electron And Current Experiment (PEACE) electron data from the four Cluster spacecraft. The results are used to investigate electron vorticity in the foreshock. What is found is that much of the measured vorticity, under nominal conditions, appears to be caused by changes in the flow direction of the return (either reflected or leakage from the magnetosheath) and strahl electron populations as they couple to changes in the magnetic field orientation. This in turn results in deflections in the total bulk velocity.

Axisymmetric Plasma Equilibria in General Relativity

NASA Astrophysics Data System (ADS)

Elsässer, Klaus

Axisymmetric plasma equilibria near a rotating black hole are considered within the multifluid description. An isothermal two-component plasma with electrons and positrons or ions is determined by four structure functions and the boundary conditions. These structure functions are the Bernoulli function and the toroidal canonical momentum per mass for each species; they remain arbitrary if no gain and loss processes are considered, in close analogy to the free flux functions in ideal magnetohydrodynamics. Several simplifying assumptions allow the reduction of the basic equations to one single scalar equation for the stream function χ of positrons or ions, respectively, playing the rôle of the Grad/Shafranov equation in magnetohydrodynamics; in particular, Maxwell's equations can be solved analytically for a quasineutral plasma when both the charge density and the toroidal electric current density are negligible (in contrast to the Tokamak situation). The basic smallness parameter is the ratio of the skin depth of electrons to the scale length of the metric and fluid quantities, and, in the case of an electron-ion plasma, the mass ratio me/mi. The χ-equation can be solved by standard methods, and simple solutions for a Kerr geometry are available; they show characteristic flow patterns, depending on the structure functions and the boundary conditions.

Control of Internal Transport Barriers in Magnetically Confined Fusion Plasmas

NASA Astrophysics Data System (ADS)

Panta, Soma; Newman, David; Sanchez, Raul; Terry, Paul

2016-10-01

In magnetic confinement fusion devices the best performance often involves some sort of transport barriers to reduce the energy and particle flow from core to edge. Those barriers create gradients in the temperature and density profiles. If gradients in the profiles are too steep that can lead to instabilities and the system collapses. Control of these barriers is therefore an important challenge for fusion devices (burning plasmas). In this work we focus on the dynamics of internal transport barriers. Using a simple 7 field transport model, extensively used for barrier dynamics and control studies, we explore the use of RF heating to control the local gradients and therefore the growth rates and shearing rates for barrier initiation and control in self-heated fusion plasmas. Ion channel barriers can be formed in self-heated plasmas with some NBI heating but electron channel barriers are very sensitive. They can be formed in self-heated plasmas with additional auxiliary heating i.e. NBI and radio-frequency(RF). Using RF heating on both electrons and ions at proper locations, electron channel barriers along with ion channel barriers can be formed and removed demonstrating a control technique. Investigating the role of pellet injection in controlling the barriers is our next goal. Work supported by DOE Grant DE-FG02-04ER54741.

Highly tunable electronic properties in plasma-synthesized B-doped microcrystalline-to-amorphous silicon nanostructure for solar cell applications

NASA Astrophysics Data System (ADS)

Lim, J. W. M.; Ong, J. G. D.; Guo, Y.; Bazaka, K.; Levchenko, I.; Xu, S.

2017-10-01

Highly controllable electronic properties (carrier mobility and conductivity) were obtained in the sophisticatedly devised, structure-controlled, boron-doped microcrystalline silicon structure. Variation of plasma parameters enabled fabrication of films with the structure ranging from a highly crystalline (89.8%) to semi-amorphous (45.4%) phase. Application of the innovative process based on custom-designed, optimized, remote inductively coupled plasma implied all advantages of the plasma-driven technique and simultaneously avoided plasma-intrinsic disadvantages associated with ion bombardment and overheating. The high degree of SiH4, H2 and B2H6 precursor dissociation ensured very high boron incorporation into the structure, thus causing intense carrier scattering. Moreover, the microcrystalline-to-amorphous phase transition triggered by the heavy incorporation of the boron dopant with increasing B2H6 flow was revealed, thus demonstrating a very high level of the structural control intrinsic to the process. Control over the electronic properties through variation of impurity incorporation enabled tailoring the carrier concentrations over two orders of magnitude (1018-1020 cm-3). These results could contribute to boosting the properties of solar cells by paving the way to a cheap and efficient industry-oriented technique, guaranteeing a new application niche for this new generation of nanomaterials.

Tempest Neoclassical Simulation of Fusion Edge Plasmas

NASA Astrophysics Data System (ADS)

Xu, X. Q.; Xiong, Z.; Cohen, B. I.; Cohen, R. H.; Dorr, M.; Hittinger, J.; Kerbel, G. D.; Nevins, W. M.; Rognlien, T. D.

2006-04-01

We are developing a continuum gyrokinetic full-F code, TEMPEST, to simulate edge plasmas. The geometry is that of a fully diverted tokamak and so includes boundary conditions for both closed magnetic flux surfaces and open field lines. The code, presently 4-dimensional (2D2V), includes kinetic ions and electrons, a gyrokinetic Poisson solver for electric field, and the nonlinear Fokker-Planck collision operator. Here we present the simulation results of neoclassical transport with Boltzmann electrons. In a large aspect ratio circular geometry, excellent agreement is found for neoclassical equilibrium with parallel flows in the banana regime without a temperature gradient. In divertor geometry, it is found that the endloss of particles and energy induces pedestal-like density and temperature profiles inside the magnetic separatrix and parallel flow stronger than the neoclassical predictions in the SOL. The impact of the X-point divertor geometry on the self-consistent electric field and geo-acoustic oscillations will be reported. We will also discuss the status of extending TEMPEST into a 5-D code.

The variable magnetic baffle as a control device for Kaufman thrusters.

NASA Technical Reports Server (NTRS)

Poeschel, R. L.

1972-01-01

The variable magnetic baffle described in this paper aids in control of electron flow from the hollow cathode plasma into the main discharge region by augmenting the fringe magnetic field which impedes this electron flow in conventionally baffled Kaufman thrusters. A passive, low loss, and automatic control device is obtained by using the discharge current to excite the control winding. Used in conjunction with typical thruster control loops, stable operation has been obtained over a 10:1 throttling range with a 30 cm thruster. Discharge ignition and overcurrent recycling is also facilitated through use of this device in a permanent magnet thruster.

Strong-Field Control of Laser Filamentation Mechanisms

NASA Astrophysics Data System (ADS)

Levis, Robert; Romanov, Dmitri; Filin, Aleskey; Compton, Ryan

2008-05-01

The propagation of short strong-file laser pulses in gas and solution phases often result in formation of filaments. This phenomenon involves many nonlinear processes including Kerr lensing, group velocity dispersion, multi-photon ionization, plasma defocusing, intensity clamping, and self-steepening. Of these, formation and dynamics of pencil-shape plasma areas plays a crucial role. The fundamental understanding of these laser-induced plasmas requires additional effort, because the process is highly nonlinear and complex. We studied the ultrafast laser-generated plasma dynamics both experimentally and theoretically. Ultrafast plasma dynamics was probed using Coherent Anti-Stokes Raman Scattering. The measurements were made in a room temperature gas maintained at 1 atm in a flowing cell. The time dependent scattering was measured by delaying the CARS probe with respect to the intense laser excitation pulse. A general trend is observed between the spacing of the ground state and the first allowed excited state with the rise time for the noble gas series and the molecular gases. This trend is consistent with our theoretical model, which considers the ultrafast dynamics of the strong field generated plasma as a three-step process; (i) strong-field ionization followed by the electron gaining considerable kinetic energy during the pulse; (ii) immediate post-pulse dynamics: fast thermalization, impact-ionization-driven electron multiplication and cooling; (iii) ensuing relaxation: evolution to electron-ion equilibrium and eventual recombination.

Rayleigh-Taylor Instability as the Reason for the Particle Acceleration and Plasma Heating in Solar Chromosphere

NASA Astrophysics Data System (ADS)

Stepanov, Alexander; Zaitsev, Valerii

New mechanism of electron acceleration in the solar chromosphere and chromospheric plasma heating is proposed. The main role in acceleration and heating belongs to the Rayleigh-Tailor instability. Ballooning mode of the instability develops at the chromospheric footpoints of a flare loop and deforms here the magnetic field. Thus the electric current flowing in the loop changes and an inductive electric field appears. This electric field is the reason for the acceleration of 300-500 keV electrons which do not escape from the chromosphere, providing the excitation of plasma waves and the heating of chromospheric plasma in situ. Observations with New Solar Telescope at Big Bear Solar Observatory (Ji et al. ApJ 750, L25, 2012) give us good evidences on the heating of chromospheric footpoints of coronal loops to the coronal temperatures as well as upward injection of hot plasma that excite the fine loops from the photosphere to the base of the corona. We discuss also other consequences of the Rayleigh-Taylor instability: non-thermal plasma emission at 212 and 405 GHz from the ionized chromosphere with the electron density as high as 10 (15) cm (-3) (Zaitsev et al. Astron.Lett. 39, 650, 2013), and the model of sub-second pulsations at THz observed by Kaufmann et al. (ApJ 697, 420, 2009).

Contact discontinuities in a cold collision-free two-beam plasma

NASA Technical Reports Server (NTRS)

Kirkland, K. B.; Sonnerup, B. U. O.

1982-01-01

The structure of contact discontinuities in a collision-free plasma is examined using a model of a plasma which consists of two oppositely directed cold ion beams and a background of cold massless electrons such that exact charge neutrality is maintained and that the electric field is zero. The basic equations describing self-consistent equilibria are obtained for the more general situation where a net flow across the layer takes place and where the magnetic field has two nonzero tangential components but where the electric field remains zero. These equations are then specialized to the case of no net plasma flow where one of the tangential components is zero, and four different classes of sheets are obtained, all having thickness the order of the ion inertial length. The first class is for layers separating two identical plasma and magnetic field regions, the second is for an infinite array of parallel layers producing an undulated magnetic field, the third is for layers containing trapped ions in closed orbits which separate two vacuum regions with uniform identical magnetic fields, and the fourth is for layers which reflect a single plasma beam, leaving a vacuum with a reversed and compressed tangential field on the other side.

Reactive ion etching of indium-tin oxide films by CCl4-based Inductivity Coupled Plasma

NASA Astrophysics Data System (ADS)

Juneja, Sucheta; Poletayev, Sergey D.; Fomchenkov, Sergey; Khonina, Svetlana N.; Skidanov, Roman V.; Kazanskiy, Nikolay L.

2016-08-01

Indium tin oxide (ITO) films have been a subject of extensive studies in fabrication of micro-electronic devices for opto-electronic applications ranging from anti-reflection coatings to transparent contacts in photovoltaic devices. In this paper, a new and effective way of reactive ion etching of a conducting indium-tin oxide (ITO) film with Carbon tetrachloride (CCl4) has been investigated. CCl4 plasma containing an addition of gases mixture of dissociated argon and oxygen were used. Oxygen is added to increase the etchant percentage whereas argon was used for stabilization of plasma. The etching characteristics obtained with these gaseous mixtures were explained based on plasma etch chemistry and etching regime of ITO films. An etch rate as high as ∼20 nm/min can be achieved with a controlled process parameter such as power density, total flow rate, composition of reactive gases gas and pressure. Our Investigation represents some of the extensive work in this area.

Plasma plume diagnostics of low power stationary plasma thruster (SPT-20M8) with collisional radiative model

NASA Astrophysics Data System (ADS)

Uttamsing Rajput, Rajendrasing; Alona, Khaustova; Loyan, Andriy V.

2017-03-01

Electric propulsion offers higher specific impulse compared to the chemical propulsion systems. It reduces the overall propellant mass and enables high operational lifetimes. Scientific Technological Center of Space Power and Energy (STC SPE), KhAI is involved in designing, manufacturing and testing of stationary plasma thrusters (SPT). Efforts are made to perform plasma diagnostics with corona and collisional radiative models (C-R model), as expected corona model falls short below 4 eV because of the heavy particle collisions elimination, whereas the C-R model's applicability is confirmed. Several tests are performed to analyze the electron temperature at various operational parameters of thruster like discharge voltage and mass flow rate. SPT-20M8 far and near-field plumes diagnostics are performed. Feasibility of C-R model by comparing its result to optical emission spectroscopy (OES) to investigate the electron temperature is validated with the probe measurements within the 10% of discrepancy.

Pedestal bifurcation and resonant field penetration at the threshold of edge-localized mode suppression in the DIII-D Tokamak.

PubMed

Nazikian, R; Paz-Soldan, C; Callen, J D; deGrassie, J S; Eldon, D; Evans, T E; Ferraro, N M; Grierson, B A; Groebner, R J; Haskey, S R; Hegna, C C; King, J D; Logan, N C; McKee, G R; Moyer, R A; Okabayashi, M; Orlov, D M; Osborne, T H; Park, J-K; Rhodes, T L; Shafer, M W; Snyder, P B; Solomon, W M; Strait, E J; Wade, M R

2015-03-13

Rapid bifurcations in the plasma response to slowly varying n=2 magnetic fields are observed as the plasma transitions into and out of edge-localized mode (ELM) suppression. The rapid transition to ELM suppression is characterized by an increase in the toroidal rotation and a reduction in the electron pressure gradient at the top of the pedestal that reduces the perpendicular electron flow there to near zero. These events occur simultaneously with an increase in the inner-wall magnetic response. These observations are consistent with strong resonant field penetration of n=2 fields at the onset of ELM suppression, based on extended MHD simulations using measured plasma profiles. Spontaneous transitions into (and out of) ELM suppression with a static applied n=2 field indicate competing mechanisms of screening and penetration of resonant fields near threshold conditions. Magnetic measurements reveal evidence for the unlocking and rotation of tearinglike structures as the plasma transitions out of ELM suppression.

Numerical simulations of a sounding rocket in ionospheric plasma: Effects of magnetic field on the wake formation and rocket potential

NASA Astrophysics Data System (ADS)

Darian, D.; Marholm, S.; Paulsson, J. J. P.; Miyake, Y.; Usui, H.; Mortensen, M.; Miloch, W. J.

2017-09-01

The charging of a sounding rocket in subsonic and supersonic plasma flows with external magnetic field is studied with numerical particle-in-cell (PIC) simulations. A weakly magnetized plasma regime is considered that corresponds to the ionospheric F2 layer, with electrons being strongly magnetized, while the magnetization of ions is weak. It is demonstrated that the magnetic field orientation influences the floating potential of the rocket and that with increasing angle between the rocket axis and the magnetic field direction the rocket potential becomes less negative. External magnetic field gives rise to asymmetric wake downstream of the rocket. The simulated wake in the potential and density may extend as far as 30 electron Debye lengths; thus, it is important to account for these plasma perturbations when analyzing in situ measurements. A qualitative agreement between simulation results and the actual measurements with a sounding rocket is also shown.

Comparing the Richtmyer-Meshkov instability of thermal and ion-species interfaces in two-fluid plasmas

NASA Astrophysics Data System (ADS)

Wheatley, Vincent; Bond, Daryl; Li, Yuan; Samtaney, Ravi; Pullin, Dale

2017-11-01

The Richtmyer-Meshkov instability (RMI) of a shock accelerated perturbed density interface is important in both inertial confinement fusion and astrophysics, where the materials involved are typically in the plasma state. Initial density interfaces can be due to either temperature or ion-species discontinuities. If the Atwood number of the interfaces and specific heat ratios of the fluids are matched, these two cases behave similarly when modeled using the equations of either hydrodynamics or magnetohydrodynamics. In the two-fluid ion-electron plasma model, however, there is a significant difference between them: In the thermal interface case, there is a discontinuity in electron density that is also subject to the RMI, while for the ion-species interface case there is not. It will be shown via ideal two-fluid plasma simulations that this causes substantial differences in the dynamics of the flow between the two cases. This work was partially supported by the KAUST Office of Sponsored Research under Award URF/1/2162-01.

Pedestal Bifurcation and Resonant Field Penetration at the Threshold of Edge-Localized Mode Suppression in the DIII-D Tokamak

DOE PAGES

Nazikian, Raffi; Paz-Soldan, Carlos; Callen, James D.; ...

2015-03-12

Rapid bifurcations in the plasma response to slowly varying n=2 magnetic fields are observed as the plasma transitions into and out of edge localized mode (ELM) suppression. The rapid transition to ELM suppression is characterized by an increase in the toroidal rotation and a reduction in the electron pressure gradient at the top of the pedestal which reduces the perpendicular electron flow to near zero. These events occur simultaneously with an increase in the inner wall magnetic response. These observations are consistent strong resonant field penetration of n=2 fields at the onset of ELM suppression, based on extended MHD simulationsmore » using measured plasma profiles. Spontaneous transitions into (and out of) ELM suppression with a static applied n=2 field indicate competing mechanisms of screening and penetration of resonant fields near threshold conditions. Magnetic measurements reveal evidence for the unlocking and rotation of tearing-like structures as the plasma transitions out of ELM suppression.« less

Energy balance in the core of the Saturn plasma sheet: H2O chemistry

NASA Astrophysics Data System (ADS)

Shemansky, D. E.; Yoshii, J.; Liu, X.

2011-10-01

A model of the weakly ionized plasma at Saturn has been developed to investigate the properties of the system. Energy balance is a critical consideration. The present model is based on two sources of mass, H2O, and HI. H2O is a variable. HI is a significant volume of gas flowing through the plasma imposed by the source at Saturn [1,2,3]. The energy sources are solar radiation and heterogeneous magnetosphere electrons. The model calculations produce energy rates, species partitioning, and relaxation lifetimes. For the first time the state of the ambient plasma sheet electrons is directly connected to the energy forcing functions. Within limits of knowledge, the predicted state of the core region of the plasma sheet in neutral and ionized gas corresponds satisfactorily to observation. The dominant ions in these calculations are H2O+ and H3O+ with lifetimes of several days. The lifetime of H2O is roughly 60 days. In calculations carried out so far the predicted source rate for H2O is lower than the rates quoted from the Enceladus encounters.

Frictional Heating of Ions In The F2-region of The Ionosphere

NASA Astrophysics Data System (ADS)

Zhizhko, G. O.; Vlasov, V. G.

Auroral electron beams unstable on the Cherenkov resonance are stabilized by large- scale inhomogeneity of the plasma density during all their way from the acceleration region to the E-region of the ionosphere. The generation of plasma waves by beam is possible only in the region of small plasma density gradients, that always is the area of the F2-region maximum. Thus, collective dissipation of the electron beam energy occurs in the local region with the length about several tens of kilometers. This leads to the intensive heating of the electrons(up to temperatures about 10000 K) and will give origin to the ion upflows with velocity about 1 km/s and density about 109 cm-2 s-1. These flows can result in the ion frictional heating. At the same time ion temperatures reach the values about 5000 K. A numerical simulation of the ion frictional heating in the presence of collective elec- tron heating in the high-latitude F2-region of the ionosphere was performed. The sim- ulation has shown that the most critical parameter for the occurence of the ion fric- tional heating was the the steepness of the plasma density profile above the F2-region maximum.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verigin, M.I.; Gringauz, K.I.; Gombosi, T.

Preliminary results of ion and electron plasma measurements near Venus are presented and discussed. The data were obtained with wide-angle plasma analyzers carried on the Venera 9 and 10 spacecraft. On the basis of 33 bow shock crossings the position of the shock is quite stable and agrees well with theoretical predictions of Spreiter et al. with H/r/sub 0/=0.01 and a stagnation point altitude of approx.500 km. This observation lends strong support to the assumption that the solar wind interacts with the upper ionosphere of Venus and not with a planetary magnetic field. These spacecraft are the first to exploremore » the optical umbra of Venus. Close to the planet a stable population of electrons and an ill-defined population of positive ions were found; this region is called the corpuscular umbra. The corpuscular umbra and the transition region are separated by a zone which contains both positive ions and electrons and is characterized by a flow velocity reduced in comparison with that of the transition region. This zone is called the corpuscular penumbra. The distribution of plasma density behind the bow shock (including the optical umbra of the planet) is given, and the existence of a Venusian plasma magnetic til is revealed.« less

Measurement of the aerothermodynamic state in a high enthalpy plasma wind-tunnel flow

NASA Astrophysics Data System (ADS)

Hermann, Tobias; Löhle, Stefan; Zander, Fabian; Fasoulas, Stefanos

2017-11-01

This paper presents spatially resolved measurements of absolute particle densities of N2, N2+, N, O, N+ , O+ , e- and excitation temperatures of electronic, rotational and vibrational modes of an air plasma free stream. All results are based on optical emission spectroscopy data. The measured parameters are combined to determine the local mass-specific enthalpy of the free stream. The analysis of the radiative transport, relative and absolute intensities, and spectral shape is used to determine various thermochemical parameters. The model uncertainty of each analysis method is assessed. The plasma flow is shown to be close to equilibrium. The strongest deviations from equilibrium occur for N, N+ and N2+ number densities in the free stream. Additional measurements of the local mass-specific enthalpy are conducted using a mass injection probe as well as a heat flux and total pressure probe. The agreement between all methods of enthalpy determination is good.

Dynamic contraction of the positive column of a self-sustained glow discharge in air flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shneider, M. N.; Mokrov, M. S.; Milikh, G. M.

We study the dynamic contraction of a self-sustained glow discharge in air in a rectangular duct with convective cooling. A two dimensional numerical model of the plasma contraction was developed in a cylindrical frame. The process is described by a set of time-dependent continuity equations for the electrons, positive and negative ions; gas and vibrational temperature; and equations which account for the convective heat and plasma losses by the transverse flux. Transition from the uniform to contracted state was analyzed. It was shown that such transition experiences a hysteresis, and that the critical current of the transition increases when themore » gas density drops. Possible coexistence of the contracted and uniform state of the plasma in the discharge, where the current flows along the density gradient of the background gas, is discussed.« less

Development of a Double Hemispherical Probe for Improved Space Plasma Measurements

NASA Astrophysics Data System (ADS)

Wang, X.; Samaniego, J. I.; Hsu, H.-W.; Horányi, M.; Wahlund, J.-E.; Ergun, R. E.; Bering, E. A.

2018-04-01

Langmuir probes have been widely used for space plasma measurements for decades. However, there are still challenges in the interpretation of their measurements. Due to the interaction of the ambient plasma with a spacecraft and an onboard probe itself, the local plasma conditions around the probe could be very different from the true ambient plasma of interest. These local plasma conditions are often anisotropic and/or inhomogeneous. Most of the Langmuir probes that are made of a single electrode have difficulties to remove these local plasma effects, introducing errors in the derived plasma characteristics. Directional probes are able to characterize anisotropic and inhomogeneous plasmas. The split Langmuir probe and the Segmented Langmuir Probe have been developed to characterize the plasma flow in the Earth's ionosphere. Here we introduce a new type of a directional Langmuir probe, the Double Hemispherical Probe (DHP), to improve the space plasma measurements in a broad range of scenarios: (a) low-density plasmas, (b) high surface-emission (photo and/or secondary electron emission) environments, (c) flowing plasmas, and (d) dust-rich plasma environments. The DHP consists of two identical hemispheres that are electrically insulated and swept with the same voltages simultaneously. The difference currents between the two hemispheres are used to characterize the anisotropic/inhomogeneous plasma conditions created around the probe, which will be then removed or minimized on the interpretation of their current-voltage curves. This paper describes the basic concept and design of the DHP sensor, as well as its initial results tested in the laboratory plasma environments.

Surface current balance and thermoelectric whistler wings at airless astrophysical bodies: Cassini at Rhea.

PubMed

Teolis, B D; Sillanpää, I; Waite, J H; Khurana, K K

2014-11-01

Sharp magnetic perturbations found by the Cassini spacecraft at the edge of the Rhea flux tube are consistent with field-aligned flux tube currents. The current system results from the difference of ion and electron gyroradii and the requirement to balance currents on the sharp Rhea surface. Differential-type hybrid codes that solve for ion velocity and magnetic field have an intrinsic difficulty modeling the plasma absorber's sharp surface. We overcome this problem by instead using integral equations to solve for ion and electron currents and obtain agreement with the magnetic perturbations at Rhea's flux tube edge. An analysis of the plasma dispersion relations and Cassini data reveals that field-guided whistler waves initiated by (1) the electron velocity anisotropy in the flux tube and (2) interaction with surface sheath electrostatic waves on topographic scales may facilitate propagation of the current system to large distances from Rhea. Current systems like those at Rhea should occur generally, for plasma absorbers of any size such as spacecraft or planetary bodies, in a wide range of space plasma environments. Motion through the plasma is not essential since the current system is thermodynamic in origin, excited by heat flow into the object. The requirements are a difference of ion and electron gyroradii and a sharp surface, i.e., without a significant thick atmosphere. Surface current balance condition yields a current system at astronomical bodiesCurrent system possible for sharp (airless) objects of any sizeCurrent system is thermoelectric and motion through the plasma nonessential.

Surface current balance and thermoelectric whistler wings at airless astrophysical bodies: Cassini at Rhea

PubMed Central

Teolis, B D; Sillanpää, I; Waite, J H; Khurana, K K

2014-01-01

Sharp magnetic perturbations found by the Cassini spacecraft at the edge of the Rhea flux tube are consistent with field-aligned flux tube currents. The current system results from the difference of ion and electron gyroradii and the requirement to balance currents on the sharp Rhea surface. Differential-type hybrid codes that solve for ion velocity and magnetic field have an intrinsic difficulty modeling the plasma absorber's sharp surface. We overcome this problem by instead using integral equations to solve for ion and electron currents and obtain agreement with the magnetic perturbations at Rhea's flux tube edge. An analysis of the plasma dispersion relations and Cassini data reveals that field-guided whistler waves initiated by (1) the electron velocity anisotropy in the flux tube and (2) interaction with surface sheath electrostatic waves on topographic scales may facilitate propagation of the current system to large distances from Rhea. Current systems like those at Rhea should occur generally, for plasma absorbers of any size such as spacecraft or planetary bodies, in a wide range of space plasma environments. Motion through the plasma is not essential since the current system is thermodynamic in origin, excited by heat flow into the object. The requirements are a difference of ion and electron gyroradii and a sharp surface, i.e., without a significant thick atmosphere. Key Points Surface current balance condition yields a current system at astronomical bodies Current system possible for sharp (airless) objects of any size Current system is thermoelectric and motion through the plasma nonessential PMID:26167436

Theoretical and experimental studies of reentry plasmas

NASA Technical Reports Server (NTRS)

Dunn, M. G.; Kang, S.

1973-01-01

A viscous shock-layer analysis was developed and used to calculate nonequilibrium-flow species distributions in the plasma layer of the RAM vehicle. The theoretical electron-density results obtained are in good agreement with those measured in flight. A circular-aperture flush-mounted antenna was used to obtain a comparison between theoretical and experimental antenna admittance in the presence of ionized boundary layers of low collision frequency. The electron-temperature and electron-density distributions in the boundary layer were independently measured. The antenna admittance was measured using a four-probe microwave reflectometer and these measured values were found to be in good agreement with those predicted. Measurements were also performed with another type of circular-aperture antenna and good agreement was obtained between the calculations and the experimental results. A theoretical analysis has been completed which permits calculation of the nonequilibrium, viscous shock-layer flow field for a sphere-cone body. Results are presented for two different bodies at several different altitudes illustrating the influences of bluntness and chemical nonequilibrium on several gas dynamic parameters of interest. Plane-wave transmission coefficients were calculated for an approximate space-shuttle body using a typical trajectory.

Drift dust acoustic soliton in the presence of field-aligned sheared flow and nonextensivity effects

NASA Astrophysics Data System (ADS)

Shah, AttaUllah; Mushtaq, A.; Farooq, M.; Khan, Aurangzeb; Aman-ur-Rehman

2018-05-01

Low frequency electrostatic dust drift acoustic (DDA) waves are studied in an inhomogeneous dust magnetoplasma comprised of dust components of opposite polarity, Boltzmannian ions, and nonextensive distributed electrons. The magnetic-field-aligned dust sheared flow drives the electrostatic drift waves in the presence of ions and electrons. The sheared flow decreases or increases the frequency of the DDA wave, mostly depending on its polarity. The conditions of instability for this mode, with nonextensivity and dust streaming effects, are discussed. The nonlinear dynamics is then investigated for the DDA wave by deriving the Koeteweg-deVries (KdV) nonlinear equation. The KdV equation yields an electrostatic structure in the form of a DDA soliton. The relevancy of the work to laboratory four component dusty plasmas is illustrated.

Statistical Physics Experiments Using Dusty Plasmas

NASA Astrophysics Data System (ADS)

Goree, John

2016-10-01

Compared to other areas of physics research, Statistical Physics is heavily dominated by theory, with comparatively little experiment. One reason for the lack of experiments is the impracticality of tracking of individual atoms and molecules within a substance. Thus, there is a need for a different kind of experimental system, one where individual particles not only move stochastically as they collide with one another, but also are large enough to allow tracking. A dusty plasma can meet this need. A dusty plasma is a partially ionized gas containing small particles of solid matter. These micron-size particles gain thousands of electronic charges by collecting more electrons than ions. Their motions are dominated by Coulomb collisions with neighboring particles. In this so-called strongly coupled plasma, the dust particles self-organize in much the same way as atoms in a liquid or solid. Unlike atoms, however, these particles are large and slow, so that they can be tracked easily by video microscopy. Advantages of dusty plasma for experimental statistical physics research include particle tracking, lack of frictional contact with solid surfaces, and avoidance of overdamped motion. Moreover, the motion of a collection of dust particles can mimic an equilibrium system with a Maxwellian velocity distribution, even though the dust particles themselves are not truly in thermal equilibrium. Nonequilibrium statistical physics can be studied by applying gradients, for example by imposing a shear flow. In this talk I will review some of our recent experiments with shear flow. First, we performed the first experimental test to verify the Fluctuation Theorem for a shear flow, showing that brief violations of the Second Law of Thermodynamics occur with the predicted probabilities, for a small system. Second, we discovered a skewness of a shear-stress distribution in a shear flow. This skewness is a phenomenon that likely has wide applicability in nonequilibrium steady states. Third, we performed the first experimental test of a statistical physics theory (the Green-Kubo model) that is widely used by physical chemists to compute viscosity coefficients, and we found that it fails. Work supported by the U.S. Department of Energy, NSF, and NASA.

Summary of initial results from the Magnetized Dusty Plasma Experiment (MDPX) device

NASA Astrophysics Data System (ADS)

Thomas, Edward

2015-11-01

Dusty (or complex) plasmas are four-component plasma systems consisting of electrons, ions, neutral atoms and charged, solid particulates. These particulates, i.e., the ``dust,'' become charged through interactions with the surrounding plasma particles and are therefore fully coupled to the background. The study of dusty plasmas began with astrophysical studies and has developed into a distinct area of plasma science with contributions to industrial, space, and fundamental plasma science. However, the vast majority of the laboratory studies are performed without the presence of a magnetic field. This is because, compared to the masses of the electrons and ions, the dust particles are significantly more massive and therefore the charge-to-mass ratio of the dust is very small. As a result, large (B > 1 T) magnetic fields are required to achieve conditions in which the dynamics of electrons, ions, and dust particles are dominated by the magnetic field. This presentation will provide a brief description of the design of the large bore (50 cm diameter x 158 cm long), multi-configuration, 4-Tesla class, superconducting magnet and integrated plasma chamber optimized for the study of dusty plasmas at high magnetic field - the MDPX device. The presentation will then focus on initial results of measurements made using MDPX - including observations of a new type of imposed ordered structures formed by the dust particles in a magnetized plasma, E x B driven flows of the particles, and observations of instabilities. This work is a collaboration of the author with Uwe Konopka (Auburn), Robert L. Merlino (Univ. of Iowa), Marlene Rosenberg (UCSD), and the MDPX team at Auburn University. Construction of the MDPX device was supported by the NSF-MRI program. Operations are supported by the NSF and DOE.

Suppression of Electron Thermal Conduction by Whistler Turbulence in a Sustained Thermal Gradient

NASA Astrophysics Data System (ADS)

Roberg-Clark, G. T.; Drake, J. F.; Reynolds, C. S.; Swisdak, M.

2018-01-01

The dynamics of weakly magnetized collisionless plasmas in the presence of an imposed temperature gradient along an ambient magnetic field is explored with particle-in-cell simulations and modeling. Two thermal reservoirs at different temperatures drive an electron heat flux that destabilizes off-angle whistler-type modes. The whistlers grow to large amplitude, δ B /B0≃1 , and resonantly scatter the electrons, significantly reducing the heat flux. Surprisingly, the resulting steady-state heat flux is largely independent of the thermal gradient. The rate of thermal conduction is instead controlled by the finite propagation speed of the whistlers, which act as mobile scattering centers that convect the thermal energy of the hot reservoir. The results are relevant to thermal transport in high-β astrophysical plasmas such as hot accretion flows and the intracluster medium of galaxy clusters.

Parallel closure theory for toroidally confined plasmas

NASA Astrophysics Data System (ADS)

Ji, Jeong-Young; Held, Eric D.

2017-10-01

We solve a system of general moment equations to obtain parallel closures for electrons and ions in an axisymmetric toroidal magnetic field. Magnetic field gradient terms are kept and treated using the Fourier series method. Assuming lowest order density (pressure) and temperature to be flux labels, the parallel heat flow, friction, and viscosity are expressed in terms of radial gradients of the lowest-order temperature and pressure, parallel gradients of temperature and parallel flow, and the relative electron-ion parallel flow velocity. Convergence of closure quantities is demonstrated as the number of moments and Fourier modes are increased. Properties of the moment equations in the collisionless limit are also discussed. Combining closures with fluid equations parallel mass flow and electric current are also obtained. Work in collaboration with the PSI Center and supported by the U.S. DOE under Grant Nos. DE-SC0014033, DE-SC0016256, and DE-FG02-04ER54746.

Thermal Electron Contributions to Current-Driven Instabilities: SCIFER Observations in the 1400-km Cleft Ion Fountain and Their Implications to Thermal Ion Energization

NASA Technical Reports Server (NTRS)

Adrian, Mark L.; Pollock, C. J.; Moore, T. E.; Kintner, P. M.; Arnoldy, R. L.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

SCIFER TECHS observations of the variations in the thermal electron distribution in the 1400-km altitude cleft are associated with periods of intense ion heating and field-aligned currents. Energization of the thermal ion plasma in the mid-altitude cleft occurs within density cavities accompanied by enhanced thermal electron temperatures, large field-aligned thermal electron plasma flows and broadband low-frequency electric fields. Variations in the thermal electron contribution to field-aligned current densities indicate small scale (approximately 100's m) filamentary structure embedded within the ion energization periods. TECHS observations of the field-aligned drift velocities and temperatures of the thermal electron distribution are presented to evaluate the critical velocity thresholds necessary for the generation of electrostatic ion cyclotron and ion acoustic instabilities. This analysis suggests that, during periods of thermal ion energization, sufficient drift exists in the thermal electron distribution to excite the electrostatic ion cyclotron instability. In addition, brief periods exist within the same interval where the drift of the thermal electron distribution is sufficient to marginally excite the ion acoustic instability. In addition, the presence an enhancement in Langmuir emission at the plasma frequency at the center of the ion energization region, accompanied by the emission's second-harmonic, and collocated with observations of high-frequency electric field solitary structures suggest the presence of electron beam driven decay of Langmuir waves to ion acoustic modes as an additional free energy source for ion energization.

Observations of kinetic scale magnetic holes in terrestrial space

NASA Astrophysics Data System (ADS)

Shutao, Y.; Shi, Q.; Wang, X.; Zong, Q.; Tian, A.; Yao, Z.; Hamrin, M.; Pitkänen, T.; Pu, Z.; Xiao, C.; Fu, S.; Zhang, H.; Giles, B. L.; Russell, C. T.; Guo, R.; Sun, W. J.; Li, W.; Zhou, X.; De Spiegeleer, A.

2017-12-01

Plasma is a macroscopically neutral system. It contains a mass of interacting ionized particles. Because of the much higher mass ratio between ions and electrons, plasma is a complicated multiple characteristic scales system with complicated properties. Thus it is necessary to carefully choose different models corresponding to the relevant scale when analyzing magnetic holes (MHs). Although there are many studies for the magnetohydrodynamics (MHD) scale MHs, few of them are for kinetic scale MHs (KSMHs). In this study, several multi-point spacecraft techniques are used to determine the propagating velocity of plasma sheet KSMHs. Based on the electronmagnetohydrodynamics (EMHD) theory, the width, depth and propagating velocity of electron solitary wave are calculated and compared to the observations. Furthermore, we report a series of the KSMHs in the magnetosheath whereby we use measurements from the Magnetospheric Multiscale (MMS) mission. The KSMHs have been observed with a scale of 10-20 ρe (electron gyroradii) and lasted 0.1-0.3 s. Distinctive electron dynamics features are observed. We find that at the 90° pitch angle, the flux of electrons with energy 34-66 eV decreased, while for electrons of energy 109-1024 eV increased inside the KSMHs. We also find the electron flow vortex perpendicular to the magnetic field, a feature self-consistent with the magnetic depression. The calculated current density is mainly contributed by the electron diamagnetic drift. Test particle is used to simulate the electron acceleration of the KSMHs.

Electrical characterization of the flowing afterglow of N{sub 2} and N{sub 2}/O{sub 2} microwave plasmas at reduced pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Afonso Ferreira, J.; Stafford, L., E-mail: luc.stafford@umontreal.ca; Leonelli, R.

2014-04-28

A cylindrical Langmuir probe was used to analyze the spatial distribution of the number density of positive ions and electrons as well as the electron energy distribution function (EEDF) in the flowing afterglow of a 6 Torr N{sub 2} and N{sub 2}/O{sub 2} plasma sustained by a propagating electromagnetic surface wave in the microwave regime. In pure N{sub 2} discharges, ion densities were in the mid 10{sup 14} m{sup −3} in the pink afterglow and in the mid 10{sup 12} m{sup −3} early in the late afterglow. In both pink and late afterglows, the ion population was much higher than the electron population,more » indicating non-macroscopically neutral media. The EEDF was close to a Maxwellian with an electron temperature of 0.5 ± 0.1 eV, except in the pink afterglow where the temperature rose to 1.1 ± 0.2 eV. This latter behavior is ascribed to N{sub 2} vibration-vibration pumping in the pink afterglow that increases the concentration of high N{sub 2} vibrational states and thus rises the electron temperature by vibration-electron collisions. After addition of small amounts of O{sub 2} in the nominally pure N{sub 2} discharge, the charged particles densities and average electron energy first strongly increased and then decreased with increasing O{sub 2} concentration. Based on these data and the evolution of the N{sub 2}{sup +}(B) band emission intensities, it is concluded that a significant change in the positive ion composition of the flowing afterglow occurs, going from N{sub 2}{sup +} in nominally pure N{sub 2} discharges to NO{sup +} after addition of trace amounts of O{sub 2} in N{sub 2}.« less

TOPICAL REVIEW: Plasma assisted ignition and combustion

NASA Astrophysics Data System (ADS)

Starikovskaia, S. M.

2006-08-01

In recent decades particular interest in applications of nonequilibrium plasma for the problems of plasma-assisted ignition and plasma-assisted combustion has been observed. A great amount of experimental data has been accumulated during this period which provided the grounds for using low temperature plasma of nonequilibrium gas discharges for a number of applications at conditions of high speed flows and also at conditions similar to automotive engines. The paper is aimed at reviewing the data obtained and discusses their treatment. Basic possibilities of low temperature plasma to ignite gas mixtures are evaluated and historical references highlighting pioneering works in the area are presented. The first part of the review discusses plasmas applied to plasma-assisted ignition and combustion. The paper pays special attention to experimental and theoretical analysis of some plasma parameters, such as reduced electric field, electron density and energy branching for different gas discharges. Streamers, pulsed nanosecond discharges, dielectric barrier discharges, radio frequency discharges and atmospheric pressure glow discharges are considered. The second part depicts applications of discharges to reduce the ignition delay time of combustible mixtures, to ignite transonic and supersonic flows, to intensify ignition and to sustain combustion of lean mixtures. The results obtained by different authors are cited, and ways of numerical modelling are discussed. Finally, the paper draws some conclusions on the main achievements and prospects of future investigations in the field.

Ion heating and magnetic flux pile-up in a magnetic reconnection experiment with super-Alfvénic plasma inflows

NASA Astrophysics Data System (ADS)

Suttle, L. G.; Hare, J. D.; Lebedev, S. V.; Ciardi, A.; Loureiro, N. F.; Burdiak, G. C.; Chittenden, J. P.; Clayson, T.; Halliday, J. W. D.; Niasse, N.; Russell, D.; Suzuki-Vidal, F.; Tubman, E.; Lane, T.; Ma, J.; Robinson, T.; Smith, R. A.; Stuart, N.

2018-04-01

This work presents a magnetic reconnection experiment in which the kinetic, magnetic, and thermal properties of the plasma each play an important role in the overall energy balance and structure of the generated reconnection layer. Magnetic reconnection occurs during the interaction of continuous and steady flows of super-Alfvénic, magnetized, aluminum plasma, which collide in a geometry with two-dimensional symmetry, producing a stable and long-lasting reconnection layer. Optical Thomson scattering measurements show that when the layer forms, ions inside the layer are more strongly heated than electrons, reaching temperatures of Ti˜Z ¯ Te≳300 eV—much greater than can be expected from strong shock and viscous heating alone. Later in time, as the plasma density in the layer increases, the electron and ion temperatures are found to equilibrate, and a constant plasma temperature is achieved through a balance of the heating mechanisms and radiative losses of the plasma. Measurements from Faraday rotation polarimetry also indicate the presence of significant magnetic field pile-up occurring at the boundary of the reconnection region, which is consistent with the super-Alfvénic velocity of the inflows.

Modeling Plasma Turbulence and Flows in LAPD using BOUT++

NASA Astrophysics Data System (ADS)

Friedman, B.; Carter, T. A.; Schaffner, D.; Popovich, P.; Umansky, M. V.; Dudson, B.

2010-11-01

A Braginskii fluid model of plasma turbulence in the BOUT code has recently been applied to LAPD at UCLA [1]. While these initial simulations with a reduced model and periodic axial boundary conditions have shown good agreement with measurements (e.g. power spectrum, correlation lengths), these simulations have lacked physics essential for modeling self-consistent, quantitatively correct flows. In particular, the model did not contain parallel plasma flow induced by sheath boundary conditions, and the axisymmetric radial electric field was not consistent with experiment. This work addresses these issues by extending the simulation model in the BOUT++ code [2], a more advanced version of BOUT. Specifically, end-plate sheath boundary conditions are added, as well as equations to evolve electron temperature and parallel ion velocity. Finally, various techniques are used to attempt to match the experimental electric potential profile, including fixing an equilibrium profile, fixing the radial boundaries, and adding an angular momentum source. [4pt] [1] Popovich et al., http://arxiv.org/abs/1005.2418 (2010).[0pt] [2] Dudson et al., Computer Physics Communications 180 (2009).

In situ measurements of plasma properties during gas-condensation of Cu nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koten, M. A., E-mail: mark.koten@gmail.com; Shield, J. E.; Voeller, S. A.

2016-03-21

Since the mean, standard deviation, and modality of nanoparticle size distributions can vary greatly between similar input conditions (e.g., power and gas flow rate), plasma diagnostics were carried out in situ using a double-sided, planar Langmuir probe to determine the effect the plasma has on the heating of clusters and their final size distributions. The formation of Cu nanoparticles was analyzed using cluster-plasma physics, which relates the processes of condensation and evaporation to internal plasma properties (e.g., electron temperature and density). Monitoring these plasma properties while depositing Cu nanoparticles with different size distributions revealed a negative correlation between average particlemore » size and electron temperature. Furthermore, the modality of the size distributions also correlated with the modality of the electron energy distributions. It was found that the maximum cluster temperature reached during plasma heating and the material's evaporation point regulates the growth process inside the plasma. In the case of Cu, size distributions with average sizes of 8.2, 17.3, and 24.9 nm in diameter were monitored with the Langmuir probe, and from the measurements made, the cluster temperatures for each deposition were calculated to be 1028, 1009, and 863 K. These values are then compared with the onset evaporation temperature of particles of this size, which was estimated to be 1059, 1068, and 1071 K. Thus, when the cluster temperature is too close to the evaporation temperature, less particle growth occurs, resulting in the formation of smaller particles.« less

Annual Gaseous Electronics Conference (39th) Held in Madison, Wisconsin on 7-10 October 1986. Program and Abstracts.

DTIC Science & Technology

1986-01-01

However, since the electron flux is nonuniform , current flows through the particle. Expressions for the distorted plasma potential distribution, the...Segregation of additive species can lead to significant axial and radial nonuniformities in enclosed, vertical high-pressure arcs. A diagnostic...Wisconsin, and EDWARD T. P. LEE, Air Force Geophysics Lab.-- Direct measurement of the cross sections for long-wave infrared ( LWIR ) emission of the N

Development Status of the Helicon Hall Thruster

DTIC Science & Technology

2009-09-15

Hall thruster , the Helicon Hall Thruster , is presented. The Helicon Hall Thruster combines the efficient ionization mechanism of a helicon source with the favorable plasma acceleration properties of a Hall thruster . Conventional Hall thrusters rely on direct current electron bombardment to ionize the flow in order to generate thrust. Electron bombardment typically results in an ionization cost that can be on the order of ten times the ionization potential, leading to reduced efficiency, particularly at low

Anode Sheath Contributions in Plasma Thrusters

DTIC Science & Technology

1994-03-01

and considerable throat erosion, is shown to be related to the electron temperature’s (T) rise above the gas temperature (To). An elementary one...surface damage and considerable throat erosion, is shown to be related to the electron temperature’s (T.) rise above the gas temperature (T.). An...Exhaust velocity is also limited hy material heating limitations of the combustion chamber and nozzle throat , and "frozen flow Losses" (unrecoverable energy

Maintenance of Surface Current Balance by Field-Aligned Thermoelectric Currents at Astronomical Bodies: Cassini at Rhea

NASA Astrophysics Data System (ADS)

Teolis, B. D.

2014-12-01

Cassini spacecraft magnetic field data at Saturn's moon Rhea reveal a field-aligned electric current system in the flux tube, which forms to satisfy the requirement to balance ion and electron currents on the moon's sharp surface. Unlike induction currents at bodies surrounded by significant atmospheres, Rhea's flux tube current system is not driven by motion through the plasma, but rather thermoelectrically, by heat flow into the object. In addition to Rhea, the requirements for the current system are easily satisfied at many plasma absorbing bodies: (1) a difference of average ion and electron gyroradii radii, and (2) a "sharp" body of any size, i.e., without a significant thick atmosphere. This type of current system is therefore expected to occur generally, e.g. at other airless planetary satellites, asteroids, and even spacecraft; and accordingly, represents a fundamental aspect of the physics of the interaction of astrophysical objects with space plasmas.

Energetic electron bursts in the plasma sheet and their relation with BBFs

NASA Astrophysics Data System (ADS)

Duan, A. Y.; Cao, J. B.; Dunlop, M.; Wang, Z. Q.

2014-11-01

We studied energetic electron bursts (EEBs) (40-250 keV) in the plasma sheet (PS) and their relation to bursty bulk flows (BBFs) using the data recorded by Cluster from 2001 to 2009. The EEBs in the PS can be classified into four types. Three types of EEBs are dispersionless, including EEBs accompanied with BBFs (V > 250 km/s) but without dipolarization front (DF); EEBs accompanied with both dipolarization front (DF) and BBF; and EEBs accompanied with DF and fast flow with V < 250 km/s. One type of EEB, i.e., EEBs not accompanied with BBFs and DFs, is dispersed. The energetic electrons (40-130 keV) can be easily transported earthward by BBFs due to the strong dawn-dusk electric field embedded in BBFs. The DFs in BBFs can produce energetic electrons (40 to 250 keV). For the EEBs with DF and BBFs, the superposed epoch analyses show that the increase of energetic electron flux has two phases: gradual increase phase before DF and rapid increase phase concurrent with DF. In the PS around x = -18 RE, 60%-70% of EEBs are accompanied with BBFs, indicating that although hitherto there have been various acceleration mechanisms of energetic electrons, most of the energetic electrons in the PS are related with magnetic reconnection, and they are produced either directly by magnetic reconnection or indirectly by the DFs within BBFs. In the BBF's braking region of -12 RE < x < -10 RE, 20% of EEBs are accompanied with BBFs. The corresponding ratio between EEBs and BBFs shows a dawn-dusk asymmetry.

Larger sized wire arrays on 1.5 MA Z-pinch generator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Safronova, A. S., E-mail: alla@unr.edu; Kantsyrev, V. L., E-mail: alla@unr.edu; Weller, M. E., E-mail: alla@unr.edu

Experiments on the UNR Zebra generator with Load Current Multiplier (LCM) allow for implosions of larger sized wire array loads than at standard current of 1 MA. Advantages of larger sized planar wire array implosions include enhanced energy coupling to plasmas, better diagnostic access to observable plasma regions, and more complex geometries of the wire loads. The experiments with larger sized wire arrays were performed on 1.5 MA Zebra with LCM (the anode-cathode gap was 1 cm, which is half the gap used in the standard mode). In particular, larger sized multi-planar wire arrays had two outer wire planes frommore » mid-atomic-number wires to create a global magnetic field (gmf) and plasma flow between them. A modified central plane with a few Al wires at the edges was put in the middle between outer planes to influence gmf and to create Al plasma flow in the perpendicular direction (to the outer arrays plasma flow). Such modified plane has different number of empty slots: it was increased from 6 up to 10, hence increasing the gap inside the middle plane from 4.9 to 7.7 mm, respectively. Such load configuration allows for more independent study of the flows of L-shell mid-atomic-number plasma (between the outer planes) and K-shell Al plasma (which first fills the gap between the edge wires along the middle plane) and their radiation in space and time. We demonstrate that such configuration produces higher linear radiation yield and electron temperatures as well as advantages of better diagnostics access to observable plasma regions and how the load geometry (size of the gap in the middle plane) influences K-shell Al radiation. In particular, K-shell Al radiation was delayed compared to L-shell mid-atomic-number radiation when the gap in the middle plane was large enough (when the number of empty slots was increased up to ten)« less

Magnetosheath-ionspheric plasma interactions in the cusp/cleft. 2: Mesoscale particle simulations

NASA Technical Reports Server (NTRS)

Winglee, R. M.; Menietti, J. D.; Lin, C. S.

1993-01-01

Ionospheric plasma flowing out from the cusp can be an important source of plasma to the magnetosphere. One source of free energy that can drive this outflow is the injection of magnetosheath plasma into the cusp. Two-dimensional (three velocity) mesoscale particle simulations are used to investigate the particle dynamics in the cusp during southward interplanetary magnetic field. This mesoscale model self-consistently incorporates (1) global influences such as the convection of plasma across the cusp, the action of the mirror force, and the injection of the magnetosheath plasma, and (2) wave-particle interactions which produce the actual coupling between the magnetosheath and ionospheric plasmas. It is shown that, because the thermal speed of the electrons is higher than the bulk motion of the magnetosheath plasma, an upward current is formed on the equatorward edge of the injection region with return currents on either side. However, the poleward return currents are the stronger due to the convection and mirroring of many of the magnetosheath electrons. The electron distribution in this latter region evolves from upward directed streams to single-sided loss cones or possibly electron conics. The ion distribution also shows a variety of distinct features that are produced by spatial and/or temporal effects associated with varying convection patterns and wave-particle interactions. On the equatorward edge the distribution has a downflowing magnetosheath component and an upflowing cold ionospheric component due to continuous convection of ionospheric plasma into the region. In the center of the magnetosheath region, heating from the development of an ion-ion streaming instability causes the suppression of the cold ionospheric component and the formation of downward ionospheric streams. Further poleward there is velocity filtering of ions with low pitch angles, so that the magnetosheath ions develop a ring-beam distribution and the ensuing wave instabilities generate downward ionospheric conics. These downward ionospheric components are eventually turned by the mirror force, leading to the production of upward conics at elevated energies throughout the region.

Hybrid Simulation of the Shock Wave Trailing the Moon

NASA Technical Reports Server (NTRS)

Israelevich, P.; Ofman, Leon

2012-01-01

A standing shock wave behind the Moon was predicted by Michel (1967) but never observed nor simulated. We use 1D hybrid code in order to simulate the collapse of the plasma-free cavity behind the Moon and for the first time to model the formation of this shock. Starting immediately downstream of the obstacle we consider the evolution of plasma expansion into the cavity in the frame of reference moving along with the solar wind. Well-known effects as electric charging of the cavity affecting the plasma flow and counterstreaming ion beams in the wake are reproduced. Near the apex of the inner Mach cone where the plasma flows from the opposite sides of the obstacle meet, a shock wave arises. We expect the shock to be produced at periods of high electron temperature solar wind streams (T(sub i) much less than T(sub e) approximately 100 eV). The shock is produced by the interaction of oppositely directed proton beams in the plane containing solar wind velocity and interplanetary magnetic field vectors. In the direction across the magnetic field and the solar wind velocity, the shock results from the interaction of the plasma flow with the region of the enhanced magnetic field inside the cavity that plays the role of the magnetic barrier. The appearance of the standing shock wave is expected at the distance of approximately 7R(sub M) downstream of the Moon.

Hybrid simulation of the shock wave trailing the Moon

NASA Astrophysics Data System (ADS)

Israelevich, P.; Ofman, L.

2012-08-01

A standing shock wave behind the Moon was predicted by Michel (1967) but never observed nor simulated. We use 1D hybrid code in order to simulate the collapse of the plasma-free cavity behind the Moon and for the first time to model the formation of this shock. Starting immediately downstream of the obstacle we consider the evolution of plasma expansion into the cavity in the frame of reference moving along with the solar wind. Well-known effects as electric charging of the cavity affecting the plasma flow and counterstreaming ion beams in the wake are reproduced. Near the apex of the inner Mach cone where the plasma flows from the opposite sides of the obstacle meet, a shock wave arises. We expect the shock to be produced at periods of high electron temperature solar wind streams (Ti ≪ Te ˜ 100 eV). The shock is produced by the interaction of oppositely directed proton beams in the plane containing solar wind velocity and interplanetary magnetic field vectors. In the direction across the magnetic field and the solar wind velocity, the shock results from the interaction of the plasma flow with the region of the enhanced magnetic field inside the cavity that plays the role of the magnetic barrier. The appearance of the standing shock wave is expected at the distance of ˜7RM downstream of the Moon.

Comparative study on extinction process of gas-blasted air and CO2 arc discharge using two-dimensional electron density imaging sensor

NASA Astrophysics Data System (ADS)

Inada, Yuki; Kumada, Akiko; Ikeda, Hisatoshi; Hidaka, Kunihiko; Nakano, Tomoyuki; Murai, Kosuke; Tanaka, Yasunori; Shinkai, Takeshi

2017-05-01

Shack-Hartmann type laser wavefront sensors were applied to gas-blasted arc discharges under current-zero phases, generated in a 50 mm-long interelectrode gap confined by a gas flow nozzle, in order to conduct a systematic comparison of electron density decaying processes for two kinds of arc-quenching gas media: air and \\text{C}{{\\text{O}}2} . The experimental results for the air and \\text{C}{{\\text{O}}2} arc plasmas showed that the electron densities and arc diameters became thinner toward the nozzle-throat inlet due to a stronger convection loss in the arc radial direction. In addition, \\text{C}{{\\text{O}}2} had a shorter electron density decaying time constant than air, which could be caused by convection loss and turbulent flow of \\text{C}{{\\text{O}}2} stronger than air.

Fine structure of microwave spike bursts and associated cross-field energy transport

NASA Technical Reports Server (NTRS)

Winglee, R. M.; Dulk, G. A.; Pritchett, P. L.

1988-01-01

The characteristics of the maser emission from a driven system where energetic electrons continue to flow through the source region is investigated using electronic particle simulations. It is shown that, under appropriate conditions, the maser can efficiently radiate a significant portion of the energy of the fast electrons in a very short time. The radiation is emitted in pulses even though the flow of electrons through the system is at a constant rate. The mission of these pulses is proposed as the source of the fine structure. Under other conditions the dominant maser emission changes from fundamental x-mode to either fundamental z-mode or to electrostatic upper hybrid or Bernstein modes. The bulk of the emission from the maser instability cannot propagate across field lines in this regime, and hence strong local plasma heating is expected, with little energy transport across the magnetic field lines.

Electron holes observed in the Moon Plasma Wake

NASA Astrophysics Data System (ADS)

Hutchinson, I. H.; Malaspina, D.; Zhou, C.

2017-10-01

Electrostatic instabilities are predicted in the magnetized wake of plasma flowing past a non-magnetic absorbing object such as a probe or the moon. Analysis of the data from the Artemis satellites, now orbiting the moon at distances ten moon radii and less, shows very clear evidence of fast-moving isolated solitary potential structures causing bipolar electric field excursions as they pass the satellite's probes. These structures have all the hallmarks of electron holes: BGK solitons typically a few Debye-lengths in size, self-sustaining by a deficit of phase-space density on trapped orbits. Electron holes are now observed to be widespread in space plasmas. They have been observed in PIC simulations of the moon wake to be the non-linear consequence of the predicted electron instabilities. Simulations document hole prevalence, speed, length, and depth; and theory can explain many of these features from kinetic analysis. The solar wind wake is certainly the cause of the overwhelming majority of the holes observed by Artemis, because we observe almost all holes to be in or very near to the wake. We compare theory and simulation of the hole generation, lifetime, and transport mechanisms with observations. Work partially supported by NASA Grant NNX16AG82G.

Influence of the configuration of the magnetic filter field on the discharge structure in the RF driven negative ion source prototype for fusion

NASA Astrophysics Data System (ADS)

Lishev, S.; Schiesko, L.; Wünderlich, D.; Fantz, U.

2017-08-01

The study provides results for the influence of the filter field topology on the plasma parameters in the RF prototype negative ion source for ITER NBI. A previously developed 2D fluid plasma model of the prototype source was extended towards accounting for the particles and energy losses along the magnetic field lines and the presence of a magnetic field in the driver which is the case at the BATMAN and ELISE test-beds. The effect of the magnetic field in the driver is shown for the magnetic field configuration of the prototype source (i.e. a magnetic field produced by an external magnet frame) by comparison of plasma parameters without and with the magnetic field in the driver and for different axial positions of the filter. Since the ELISE-like magnetic field (i.e. a magnetic field produced by a current flowing through the plasma grid) is a new feature planned to be installed at the BATMAN test-bed, its effect on the discharge structure was studied for different strengths of the magnetic field. The obtained results show for both configurations of the magnetic filter the same main features in the patterns of the plasma parameters in the expansion chamber: a strong axial drop of the electron temperature and the formation of a groove accompanied with accumulation of electrons in front of the plasma grid. The presence of a magnetic field in the driver has a local impact on the plasma parameters: the formation of a second groove of the electron temperature in the case of BATMAN (due to the reversed direction of the filter field in the driver) and a strong asymmetry of the electron density. Accounting for the additional losses in the third dimension suppresses the drifts across the magnetic field and, thus, the variations of the electron density in the expansion chamber are less pronounced.

Gyrokinetic simulation study of magnetic island effects on neoclassical physics and micro-instabilities in a realistic KSTAR plasma

NASA Astrophysics Data System (ADS)

Kwon, Jae-Min; Ku, S.; Choi, M. J.; Chang, C. S.; Hager, R.; Yoon, E. S.; Lee, H. H.; Kim, H. S.

2018-05-01

We perform gyrokinetic simulations to study the effects of a stationary magnetic island on neoclassical flow and micro-instability in a realistic KSTAR plasma condition. Through the simulations, we aim to analyze a recent KSTAR experiment, which was to measure the details of poloidal flow and fluctuation around a stationary (2, 1) magnetic island [M. J. Choi et al., Nucl. Fusion 57, 126058 (2017)]. From the simulations, it is found that the magnetic island can significantly enhance the equilibrium E × B flow. The corresponding flow shearing is strong enough to suppress a substantial portion of ambient micro-instabilities, particularly ∇Te -driven trapped electron modes. This implies that the enhanced E × B flow can sustain a quasi-internal transport barrier for Te in an inner region neighboring the magnetic island. The enhanced E × B flow has a (2, 1) mode structure with a finite phase shift from the mode structure of the magnetic island. It is shown that the flow shear and the fluctuation suppression patterns implied from the simulations are consistent with the observations on the KSTAR experiment.

Gyrokinetic simulation study of magnetic island effects on neoclassical physics and micro-instabilities in a realistic KSTAR plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwon, Jae-Min; Ku, S.; Choi, M. J.

Here, we perform gyrokinetic simulations to study the effects of a stationary magnetic island on neoclassical flow and micro-instability in a realistic KSTAR plasma condition. Through the simulations, we aim to analyze a recent KSTAR experiment, which was to measure the details of poloidal flow and fluctuation around a stationary (2, 1) magnetic island [M. J. Choi et al., Nucl. Fusion 57, 126058 (2017)]. From the simulations, it is found that the magnetic island can significantly enhance the equilibrium E x B flow. The corresponding flow shearing is strong enough to suppress a substantial portion of ambient micro-instabilities, particularly ∇Tmore » e-driven trapped electron modes. This implies that the enhanced E x B flow can sustain a quasi-internal transport barrier for T e in an inner region neighboring the magnetic island. The enhanced E x B flow has a (2, 1) mode structure with a finite phase shift from the mode structure of the magnetic island. It is shown that the flow shear and the fluctuation suppression patterns implied from the simulations are consistent with the observations on the KSTAR experiment.« less

Gyrokinetic simulation study of magnetic island effects on neoclassical physics and micro-instabilities in a realistic KSTAR plasma

DOE PAGES

Kwon, Jae-Min; Ku, S.; Choi, M. J.; ...

2018-05-01

Here, we perform gyrokinetic simulations to study the effects of a stationary magnetic island on neoclassical flow and micro-instability in a realistic KSTAR plasma condition. Through the simulations, we aim to analyze a recent KSTAR experiment, which was to measure the details of poloidal flow and fluctuation around a stationary (2, 1) magnetic island [M. J. Choi et al., Nucl. Fusion 57, 126058 (2017)]. From the simulations, it is found that the magnetic island can significantly enhance the equilibrium E x B flow. The corresponding flow shearing is strong enough to suppress a substantial portion of ambient micro-instabilities, particularly ∇Tmore » e-driven trapped electron modes. This implies that the enhanced E x B flow can sustain a quasi-internal transport barrier for T e in an inner region neighboring the magnetic island. The enhanced E x B flow has a (2, 1) mode structure with a finite phase shift from the mode structure of the magnetic island. It is shown that the flow shear and the fluctuation suppression patterns implied from the simulations are consistent with the observations on the KSTAR experiment.« less

Internal transport barrier in tokamak and helical plasmas

NASA Astrophysics Data System (ADS)

Ida, K.; Fujita, T.

2018-03-01

The differences and similarities between the internal transport barriers (ITBs) of tokamak and helical plasmas are reviewed. By comparing the characteristics of the ITBs in tokamak and helical plasmas, the mechanisms of the physics for the formation and dynamics of the ITB are clarified. The ITB is defined as the appearance of discontinuity of temperature, flow velocity, or density gradient in the radius. From the radial profiles of temperature, flow velocity, and density the ITB is characterized by the three parameters of normalized temperature gradient, R/{L}T, the location, {ρ }{ITB}, and the width, W/a, and can be expressed by ‘weak’ ITB (small R/{L}T) or ‘strong’ (large R/{L}T), ‘small’ ITB (small {ρ }{ITB}) or ‘large’ ITB (large {ρ }{ITB}), and ‘narrow’ (small W/a) or ‘wide’ (large W/a). Three key physics elements for the ITB formation, radial electric field shear, magnetic shear, and rational surface (and/or magnetic island) are described. The characteristics of electron and ion heat transport and electron and impurity transport are reviewed. There are significant differences in ion heat transport and electron heat transport. The dynamics of ITB formation and termination is also discussed. The emergence of the location of the ITB is sometimes far inside the ITB foot in the steady-state phase and the ITB region shows radial propagation during the formation of the ITB. The non-diffusive terms in momentum transport and impurity transport become more dominant in the plasma with the ITB. The reversal of the sign of non-diffusive terms in momentum transport and impurity transport associated with the formation of the ITB reported in helical plasma is described. Non-local transport plays an important role in determining the radial profile of temperature and density. The spontaneous change in temperature curvature (second radial derivative of temperature) in the ITB region is described. In addition, the key parameters of the control of the ITB and future prospects are discussed.

Development of GEM gas detectors for X-ray crystal spectrometry

NASA Astrophysics Data System (ADS)

Chernyshova, M.; Czarski, T.; Dominik, W.; Jakubowska, K.; Rzadkiewicz, J.; Scholz, M.; Pozniak, K.; Kasprowicz, G.; Zabolotny, W.

2014-03-01

Two Triple Gas Electron Multiplier (Triple-GEM) detectors were developed for high-resolution X-ray spectroscopy measurements for tokamak plasma to serve as plasma evolution monitoring in soft X-ray region (SXR). They provide energy resolved fast dynamic plasma radiation imaging in the SXR with 0.1 kHz frequency. Detectors were designed and constructed for continuous data-flow precise energy and position measurement of plasma radiation emitted by metal impurities, W46+ and Ni26+ ions, at 2.4 keV and 7.8 keV photon energies, respectively. High counting rate capability of the detecting units has been achieved with good position resolution. This article presents results of the laboratory and tokamak experiments together with the system performance under irradiation by photon flux from the plasma core.

CALL FOR PAPERS: Special cluster issue on `Experimental studies of zonal flow and turbulence'

NASA Astrophysics Data System (ADS)

Itoh, S.-I.

2005-07-01

Plasma Physics and Controlled Fusion (PPCF) invites submissions on the topic of `Experimental studies of zonal flow and turbulence', for consideration for a special topical cluster of articles to be published early in 2006. The topical cluster will be published in an issue of PPCF, combined with regular articles. The Guest Editor for the special cluster will be S-I Itoh, Kyushu University, Japan. There has been remarkable progress in the area of structure formation by turbulence. One of the highlights has been the physics of zonal flow and drift wave turbulence in toroidal plasmas. Extensive theoretical as well as computational studies have revealed the various mechanisms in turbulence and zonal flows. At the same time, experimental research on the zonal flow, geodesic acoustic modes and generation of global electric field by turbulence has evolved rapidly. Fast growth in reports of experimental results has stimulated further efforts to develop increased knowledge and systematic understanding. Each paper considered for the special cluster should describe the present research status and new scientific knowledge/results from the authors on experimental studies of zonal flow, geodesic acoustic modes and generation of electric field by turbulence (including studies of Reynolds-Maxwell stresses, etc). Manuscripts submitted to this special cluster in Plasma Physics and Controlled Fusion will be refereed according to the normal criteria and procedures of the journal. The Guest Editor guides the progress of the cluster from the initial open call, through the standard refereeing process, to publication. To be considered for inclusion in the special cluster, articles must be submitted by 2 September 2005 and must clearly state `for inclusion in the Turbulent Plasma Cluster'. Articles submitted after this deadline may not be included in the cluster issue but may be published in a later issue of the journal. Please submit your manuscript electronically via our web site at www.iop.org/journals/ppcf or by e-mail to mailto:ppcf@iop.org. Electronic submissions are encouraged but if you wish to submit a hard copy of your article then please send your typescript, a set of original figures and a covering letter to: The Publishing Administrator Plasma Physics and Controlled Fusion Institute of Physics Publishing Dirac House Temple Back Bristol BS1 6BE UK Further information on how to submit may be obtained on request by e-mailing the journal at the above address. Alternatively, visit the homepage of the journal (www.iop.org/journals/ppcf).

Investigation of the Arcjet near Field Plume Using Electrostatic Probes

NASA Technical Reports Server (NTRS)

Sankovic, John M.

1990-01-01

The near field plume of a 1 kW class arcjet thruster was investigated using electrostatic probes of various geometries. The electron number densities and temperatures were determined in a simulated hydrazine plume at axial distances between 3 cm (1.2 in.) and 15 cm (5.9 in.) and radial distances extending to 10 cm (3.9 in.) off centerline. Values of electron number densities obtained using cylindrical and spherical probes of different geometries agreed very well. The electron density on centerline followed a source flow approximation for axial distances as near as 3 cm (1.2 in.) from the nozzle exit plane. The model agreed well with previously obtained data in the far field. The effects of propellant mass flow rate and input power level were also studied. Cylindrical probes were used to obtain ion streamlines by changing the probe orientation with respect to the flow. The effects of electrical configuration on the plasma characteristics of the plume were also investigated by using a segmented anode/nozzle thruster. The results showed that the electrical configuration in the nozzle affected the distribution of electrons in the plume.

Investigation of the arcjet plume near field using electrostatic probes

NASA Technical Reports Server (NTRS)

Sankovic, John M.

1990-01-01

The near field plum of a 1 kW class arcjet thruster was investigated using electrostatic probes of various geometries. The electron number densities and temperatures were determined in a simulated hydrazine plume at axial distances between 3 cm (1.2 in) and 15 cm (5.9 in) and radial distances extending to 10 cm (3.9 in) off centerline. Values of electron number densities obtained using cylindrical and spherical probes of different geometries agreed very well. The electron density on centerline followed a source flow approximation for axial distances as near as 3 cm (1.2 in) from the nozzle exit plane. The model agreed well with previously obtained data in the far field. The effects of propellant mass flow rate and input power level were also studied. Cylindrical probes were used to obtain ion streamlines by changing the probe orientation with respect to the flow. The effects of electrical configuration on the plasma characteristics of the plume were also investigated by using a segmented anode/nozzle thruster. The results showed that the electrical configuration in the nozzle affected the distribution of electrons in the plume.

Advancement of In-Flight Alumina Powder Spheroidization Process with Water Droplet Injection Using a Small Power DC-RF Hybrid Plasma Flow System

NASA Astrophysics Data System (ADS)

Jang, Juyong; Takana, Hidemasa; Park, Sangkyu; Nishiyama, Hideya

2012-09-01

The correlation between plasma thermofluid characteristics and alumina powder spheroidization processes with water droplet injection using a small power DC-RF hybrid plasma flow system was experimentally clarified. Micro-sized water droplets with a low water flow rate were injected into the tail of thermal plasma flow so as not to disturb the plasma flow directly. Injected water droplets were vaporized in the thermal plasma flow and were transported upstream in the plasma flow to the torch by the backflow. After dissociation of water, the production of hydrogen was detected by the optical emission spectroscopy in the downstream RF plasma flow. The emission area of the DC plasma jet expanded and elongated in the vicinity of the RF coils. Additionally, the emission area of RF plasma flow enlarged and was visible as red emission in the downstream RF plasma flow in the vicinity below the RF coils due to hydrogen production. Therefore, the plasma flow mixed with produced hydrogen increased the plasma enthalpy and the highest spheroidization rate of 97% was obtained at a water flow rate of 15 Sm l/min and an atomizing gas flow rate of 8 S l/min using a small power DC-RF hybrid plasma flow system.

Titan's Variable Plasma Interaction

NASA Astrophysics Data System (ADS)

Ledvina, S. A.; Brecht, S. H.

2015-12-01

Cassini observations have found that the plasma and magnetic field conditions upstream of Titan are far more complex than they were thought to be after the Voyager encounter. Rymer et al., (2009) used the Cassini Plasma Spectrometer (CAPS) electron observations to classify the plasma conditions along Titan's orbit into 5 types (Plasma Sheet, Lobe, Mixed, Magnetosheath and Misc.). Nemeth et al., (2011) found that the CAPS ion observations could also be separated into the same plasma regions as defined by Rymer et al. Additionally the T-96 encounter found Titan in the solar wind adding a sixth classification. Understanding the effects of the variable upstream plasma conditions on Titan's plasma interaction and the evolution of Titan's ionosphere/atmosphere is one of the main objectives of the Cassini mission. To compliment the mission we perform hybrid simulations of Titan's plasma interaction to examine the effects of the incident plasma distribution function and the flow velocity. We closely examine the results on Titan's induced magnetosphere and the resulting pickup ion properties.

High Power Light Gas Helicon Plasma Source For VASMIR

NASA Technical Reports Server (NTRS)

Squire, J. P.; Chang-Diaz, F. R.; Glover, T. W.; Jacobson, V. T.; McCaskill, G. E.; Winter, D. S.; Baity, F. W.; Carter, M. D.; Goulding, R. H.

2004-01-01

The VASIMR space propulsion development effort relies on a high power (greater than 10kW) helicon source to produce a dense flowing plasma (H, D and He) target for ion cyclotron resonance (ICR) acceleration of the ions. Subsequent expansion in an expanding magnetic field (magnetic nozzle) converts ion lunetic energy to directed momentum. This plasma source must have critical features to enable an effective propulsion device. First, it must ionize most of the input neutral flux of gas, thus producing a plasma stream with a high degree of ionization for application of ICR power. This avoids propellant waste and potential power losses due to charge exchange. Next, the plasma stream must flow into a region of high magnetic field (approximately 0.5 T) for efficient ICR acceleration. Third, the ratio of input power to plasma flux must be low, providing an energy per ion-electron pair approaching 100 eV. Lastly, the source must be robust and capable of very long life-times (years). In our helicon experiment (VX-10) we have measured a ratio of input gas to plasma flux near 100%. The plasma flows from the helicon region (B approximately 0.1 T) into a region with a peak magnetic field of 0.8 T. The energy input per ion-electron pair has been measured at 300 plus or minus 100 eV. Recent results at Oak Ridge National Laboratory (ORNL) show an enhanced efficiency mode of operation with a high power density, over 5 kW in a 5 cm diameter tube. Our helicon is presently 9 cm in diameter and operates up to 3.5 kW of input power. An upgrade to a power level of 10 kW is underway. Much of our recent work has been with a Boswell double-saddle antenna design. We are also converting the antenna design to a helical type. With these modifications, we anticipate an improvement in the ionization efficiency. This paper presents the results from scaling the helicon in the VX-10 device from 3.5 to 10 kW. We also compare the operation with a double-saddle to a helical antenna design. Finally, we discuss modeling of these configurations using ORNL's EMIR code.

Measurements of the canonical helicity evolution of a gyrating kinked plasma column

NASA Astrophysics Data System (ADS)

von der Linden, Jens; Sears, Jason; Intrator, Thomas; You, Setthivoine

2017-10-01

Conversions between kinetic and magnetic energy occur over a wide range of plasma scales as exhibited in astrophysical and solar dynamos, and reconnection in the solar corona and laboratory experiments. Canonical flux tubes present the distinct advantage of reconciling all plasma regimes - e.g. kinetic, two-fluid, and MHD - with the topological concept of helicity: twists, writhes, and linkages. This poster presents the first visualization and analysis of the 3D dynamics of canonical flux tubes and their relative helicity evolution from experimental measurements. Ion and electron canonical flux tubes are visualized from Mach, triple, and Ḃ probe measurements at over 10,000 spatial locations of a gyrating kinked plasma column. The flux tubes co-gyrate with the peak density and electron temperature in and out of a measurement volume. The electron and ion canonical flux tubes twist with opposite handedness and the ion flux tube writhes around the electron flux tube. The relative cross helicity between the magnetic and ion flow vorticity flux tubes dominates the relative ion canonical helicity and is anticorrelated with the relative magnetic helicity. The 3D nature of the kink and a reverse eddy current affect the helicity evolution. This work is supported by DOE Grant DE-SC0010340 and the DOE Office of Science Graduate Student Research Program and prepared in part by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-734669.

Simulation of electrostatic turbulence in the plasma sheet boundary layer with electron currents and bean-shaped ion beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishikawa, K.; Frank, L.A.; Huang, C.Y.

Plasma data from ISEE 1 show the presence of electron currents as well as energetic ion beams in the plasma sheet boundary layer. Broadband electrostatic noise and low-frequency electromagnetic bursts are detected in the plasma sheet boundary layer, especially in the presence of strong ion flows, currents, and steep spacial gradients in the fluxes of few-keV electrons and ions. Particle simulations have been performed to investigate electrostatic turbulence driven by a cold electron beam and/or ion beams with a bean-shaped velocity distribution. The simulation results show that the counterstreaming ion beams as well as the counterstreaming of the cold electronmore » beam and the ion beam excite ion acoustic waves with the Doppler-shifted real frequency ..omega..approx. = +- k/sub parallel/(c/sub s/-V/sub i//sub //sub parallel/). However, the effect of the bean-shaped ion velocity distributions reduces the growth rates of ion acoustic instability. The simulation results also show that the slowing down of the ion beam is larger at the larger perpendicular velocity. The wave spectra of the electric fields at some points for simulations show turbulence generated by growing waves. The frequency of these spectra ranges from ..cap omega../sub i/ to ..omega../sub p//sub e/, which is in qualitative agreement with the satellite data. copyright American Geophysical Union 1988« less

A preliminary study of extended magnetic field structures in the ionosphere

NASA Technical Reports Server (NTRS)

Sullivan, James D.; Lane, Barton G.; Post, Richard S.

1987-01-01

Several plasma phenomena which are to be expected around a magnet in LEO were identified and analyzed qualitatively. The ASTROMAG cusp magnet will create an extended field whose strength drops to the ambient level over a scale length of approx. 15 m; the combined field has a complex topology with ring nulls and open and closed field lines. The entire configuration is moving through the partially ionized F-layer of the ionosphere at a speed slow compared to the local Alfven speed but fast compared to the ion sound speed. The ambient plasma crosses the extended field structure in a time short compared to the ion Larmor period yet long relative to the electron Larmor period. Thus, electrons behave as a magnetized fluid while ions move ballistically until reflected from higher fields near the cusp. Since the Debye length is short compared to the field scale length, an electrostatic shock-like structure forms to equilibrate the flows and achieve quasi-neutrality. The ambient plasma will be excluded from a cavity near the magnet. The size and nature of the strong interaction region in which the magnet significantly perturbs the ambient flow were determined by studying ion orbits numerically. Lecture viewgraphs summarizing these results are presented.

Growth of ultrananocrystalline diamond film by DC Arcjet plasma enhanced chemical vapor deposition

NASA Astrophysics Data System (ADS)

Chen, G. C.; Li, B.; Yan, Z. Q.; Liu, J.; Lu, F. X.; Ye, H.

2012-06-01

Self-standing diamond films were grown by DC Arcjet plasma enhanced chemical vapor deposition (CVD). The feed gasses were Ar/H2/CH4, in which the flow ratio of CH4 to H2 (F/F) was varied from 5% to 20%. Two distinct morphologies were observed by scanning electron microscope (SEM), i.e. the "pineapple-like" morphology and the "cauliflower-like" morphology. It was found that the morphologies of the as-grown films are strongly dependent on the flow ratio of CH4 to H2 in the feed gasses. High resolution transmission electron microscope (HRTEM) survey results revealed that there were nanocrystalline grains within the "pineapple-like" films whilst there were ultrananocrystalline grains within "cauliflower-like" films. X-ray diffraction (XRD) results suggested that (110) crystalline plane was the dominant surface in the "cauliflower-like" films whilst (100) crystalline plane was the dominant surface in the "pineapple-like" films. Raman spectroscopy revealed that nanostructured carbon features could be observed in both types of films. Plasma diagnosis was carried out in order to understand the morphology dependent growth mechanism. It could be concluded that the film morphology was strongly influenced by the density of gas phases. The gradient of C2 radical was found to be different along the growth direction under the different growth conditions.

[INVITED] Coupling of polarisation of high frequency electric field and electronic heat conduction in laser created plasma

NASA Astrophysics Data System (ADS)

Gamaly, Eugene G.; Rode, Andrei V.

2016-08-01

Powerful short laser pulse focused on a surface swiftly transforms the solid into the thermally and electrically inhomogeneous conductive plasma with the large temperature and dielectric permeability gradients across the focal spot. The laser-affected spot becomes thermally inhomogeneous with where temperature has maximum in the centre and gradually decreasing to the boundaries of the spot in accord to the spatial intensity distribution of the Gaussian pulse. Here we study the influence of laser polarisation on ionization and absorption of laser radiation in the focal spot. In this paper we would like to discuss new effect in thermally inhomogeneous plasma under the action of imposed high frequency electric field. We demonstrate that high-frequency (HF) electric field is coupled with the temperature gradient generating the additional contribution to the conventional electronic heat flow. The additional heat flow strongly depends on the polarisation of the external field. It appears that effect has maximum when the imposed electric field is collinear to the thermal gradient directed along the radius of a circular focal spot. Therefore, the linear polarised field converts the circular laser affected spot into an oval with the larger oval's axis parallel to the field direction. We compare the developed theory to the available experiments, discuss the results and future directions.

Evolution of ionosphere-thermosphere (IT) parameters in the cusp region related to ion upflow events

NASA Astrophysics Data System (ADS)

Kervalishvili, Guram; Lühr, Hermann

2017-04-01

In this study we investigate the relationships of various IT parameters with the intensity of vertical ion flow. Our study area is the ionospheric cusp region in the northern hemisphere. The approach uses superposed epoch analysis (SEA) method, centered alternately on peaks of the three different variables: neutral density enhancement, vertical plasma flow, and electron temperature. Further parameters included are large-scale field-aligned currents (LSFACs) and thermospheric zonal wind velocity profiles over magnetic latitude (MLat), which are centered at the event time and location. The dependence on the interplanetary magnetic field (IMF) By component orientation and the local (Lloyd) season is of particular interest. Our investigations are based on CHAMP and DMSP (F13 and F15) satellite observations and the OMNI online database collected during the years 2002-2007. The three Lloyd seasons of 130 days each are defined as follows: local winter (1 January ± 65 days), combined equinoxes (1 April and 1 October ± 32 days), and local summer (1 July ± 65 days). A period of 130 days corresponds to the time needed by CHAMP to sample all local times. The SEA MLat profiles with respect to neutral density enhancement and vertical plasma flow peaks show no significant but only slight (decreasing towards local summer) seasonal variations for both IMF By orientations. The latitude profiles of median LSFACs show a clear dependence on the IMF By orientation. As expected, the maximum and minimum values of LSFAC amplitudes are increasing towards local summer for both IMF By signs. With respect to zero epoch latitude, FAC peaks appear equatorward (negative MLat) related to Region 1 (R1) and poleward (positive MLat) to Region 0 (R0) FACs. However, there is an imbalance between the amplitudes of LSFACs, depending on the current latitude. R1 currents are systematically stronger than R0 FACs. A somewhat different distribution of density enhancements and large-scale FACs emerges when the SEA is centered on electron temperature peaks. As expected, the background electron temperature increases towards summer and shows no dependence on the IMF By orientation. In contrast to the previous sorting the mass density enhancement shows a dependence on the IMF By sign and increases towards local summer in case of IMF By<0. As before LSFAC peak values are increasing towards local summer, but there is no clear latitudinal profile of upward and downward FACs. We think that intense precipitation of soft electrons (<100 eV) cause the electron temperature enhancement in the cusp region. But there is no direct dependence on the FAC intensity. But for neutral density enhancement and vertical plasma flow the combination of Joule heating and soft electron precipitation, causing electron temperature and conductivity enhancements, are required.

By-controlled convection and field-aligned currents near midnight auroral oval for northward interplanetary magnetic field

NASA Technical Reports Server (NTRS)

Taguchi, S.; Sugiura, M.; Iyemori, T.; Winningham, J. D.; Slavin, J. A.

1994-01-01

Using the Dynamics Explorer (DE) 2 magnetic and electric field and plasma data, B(sub y)- controlled convection and field-aligned currents in the midnight sector for northward interplanetary magnetic field (IMF) are examined. The results of an analysis of the electric field data show that when IMF is stable and when its magnitude is large, a coherent B(sub y)-controlled convection exists near the midnight auroral oval in the ionosphere having adequate conductivities. When B(sub y) is negative, the convection consists of a westward (eastward) plasma flow at the lower latitudes and an eastward (westward) plasma flow at the higher latitudes in the midnight sector in the northern (southern) ionosphere. When B(sub y) is positive, the flow directions are reversed. The distribution of the field-aligned currents associated with the B(sub y)-controlled convection, in most cases, shows a three-sheet structure. In accordance with the convection the directions of the three sheets are dependent on the sign of B(sub y). The location of disappearance of the precipitating intense electrons having energies of a few keV is close to the convection reversal surface. However, the more detailed relationship between the electron precipitation boundary and the convection reversal surface depends on the case. In some cases the precipitating electrons extend beyond the convection reversal surface, and in others the poleward boundary terminates at a latitude lower than the reversal surface. Previous studies suggest that the poleward boundary of the electrons having energies of a few keV is not necessarily coincident with an open/closed bounary. Thus the open/closed boundary may be at a latitude higher than the poleward boundary of the electron precipitation, or it may be at a latitude lower than the poleward boundary of the electron precipitation. We discuss relationships between the open/closed boundary and the convection reversal surface. When as a possible choice we adopt a view that the open/closed boundary agrees with the convection reversal surface, we can explain qualitatively the configuration of the B(sub y)-controlled convection on the open and close field line regions by proposing a mapping modified in accordance with IMF B(sub y).

Mechanisms of Ionospheric Mass Escape

NASA Technical Reports Server (NTRS)

Moore, T. E.; Khazanov, G. V.

2010-01-01

The dependence of ionospheric O+ escape flux on electromagnetic energy flux and electron precipitation into the ionosphere is derived for a hypothetical ambipolar pick-up process, powered the relative motion of plasmas and neutral upper atmosphere, and by electron precipitation, at heights where the ions are magnetized but influenced by photo-ionization, collisions with gas atoms, ambipolar and centrifugal acceleration. Ion pick-up by the convection electric field produces "ring-beam" or toroidal velocity distributions, as inferred from direct plasma measurements, from observations of the associated waves, and from the spectra of incoherent radar echoes. Ring-beams are unstable to plasma wave growth, resulting in rapid relaxation via transverse velocity diffusion, into transversely accelerated ion populations. Ion escape is substantially facilitated by the ambipolar potential, but is only weakly affected by centrifugal acceleration. If, as cited simulations suggest, ion ring beams relax into non-thermal velocity distributions with characteristic speed equal to the local ion-neutral flow speed, a generalized "Jeans escape" calculation shows that the escape flux of ionospheric O+ increases with Poynting flux and with precipitating electron density in rough agreement with observations.

Electron molecular ion recombination: product excitation and fragmentation.

PubMed

Adams, Nigel G; Poterya, Viktoriya; Babcock, Lucia M

2006-01-01

Electron-ion dissociative recombination is an important ionization loss process in any ionized gas containing molecular ions. This includes the interstellar medium, circumstellar shells, cometary comae, planetary ionospheres, fusion plasma boundaries, combustion flames, laser plasmas and chemical deposition and etching plasmas. In addition to controlling the ionization density, the process generates many radical species, which can contribute to a parallel neutral chemistry. Techniques used to obtain rate data and product information (flowing afterglows and storage rings) are discussed and recent data are reviewed including diatomic to polyatomic ions and cluster ions. The data are divided into rate coefficients and cross sections, including their temperature/energy dependencies, and quantitative identification of neutral reaction products. The latter involve both ground and electronically excited states and including vibrational excitation. The data from the different techniques are compared and trends in the data are examined. The reactions are considered in terms of the basic mechanisms (direct and indirect processes including tunneling) and recent theoretical developments are discussed. Finally, new techniques are mentioned (for product identification; electrostatic storage rings, including single and double rings; Coulomb explosion) and new ways forward are suggested.

Dropper for micron and submicron size powders for a plasma mass filter

NASA Astrophysics Data System (ADS)

Evans, Eugene S.; Zweben, Stewart J.; Gueroult, Renaud; Fisch, Nathaniel J.; Levinton, Fred

2014-10-01

The goal of the Plasma Mass Filter (PMF) experiment at PPPL, in collaboration with Nova Photonics, Inc., is to achieve separation between high-Z and low-Z atoms, for possible application to processing of nuclear waste to remove the highly radioactive high-Z components. The PMF features a rotating plasma column in which centrifugal forces push high-mass ions out of the plasma radially, while low-mass ions exit the plasma axially. In order to control the injection location, high-Z materials are introduced in powder form into the PMF plasma. The current experiment is limted to ~1 kW RF, giving a calculated maximum flow rate of ~0.1 mg/s. An electron temperature of a few eV and assumptions about the residence time of the dust particles in the PMF plasma limits the calculated maximum particle size to ~1 μm. While previous dusty plasma experiments have dealt with particles on the order of 2-3 μm, submicron particles are comparatively more difficult to manipulate under vacuum due to increased Van Der Waals and electrostatic forces. A powder dropper capable of reliably dropping micron and submicron-size particles at this flow rate is being developed, consisting of a mesh-bottomed container that is coupled to vibration motors. This work supported by DOE contract DE-AC02-09CH11466.

GTC Turbulence Simulations near H-mode Pedestal with Resonant Magnetic Perturbations

NASA Astrophysics Data System (ADS)

Shi, Lei; Ferraro, Nathaniel; Taimourzadeh, Sam; Fu, Jingyuan; Lin, Zhihong; Nazikian, Raffi

2017-10-01

Full plasma responses to Resonant Magnetic Perturbations (RMPs) as provided by the resistive MHD code M3D-C1 are implemented into Gyrokinetic Toroidal Code (GTC) to study the effect of magnetic islands and stochastic field regions on microturbulence in realistic DIII-D geometry. Electrostatic turbulence simulations with adiabatic electrons show no significant increase of the saturated ion heat conductivity in the presence of RMP-induced islands. However, electron response to zonal flow in the presence of magnetic islands and stochastic fields can drastically increase zonal flow dielectric constant for long wavelength fluctuations. Zonal flow generation can then be reduced and the microturbulence can be enhanced greatly. Furthermore, because the RMP magnetic island size is comparable to the ion banana width, electron and ion responses to these islands may be fundamentally different, which could drive non-ambipolar particles fluxes leading to changes of the radial electric field shear. This work is supported by General Atomics subcontract.

Nonuniform discharge currents in active plasma lenses

DOE PAGES

van Tilborg, J.; Barber, S. K.; Tsai, H. -E.; ...

2017-03-24

Active plasma lenses have attracted interest in novel accelerator applications due to their ability to provide large-field-gradient (short focal length), tunable, and radially symmetric focusing for charged particle beams. However, if the discharge current is not flowing uniformly as a function of radius, one can expect a radially varying field gradient as well as potential emittance degradation. We have investigated this experimentally for a 1-mm-diameter active plasma lens. The measured near-axis field gradient is approximately 35% larger than expected for a uniform current distribution, and at overfocusing currents ring-shaped electron beams are observed. These observations are explained by simulations.

Nonuniform discharge currents in active plasma lenses

NASA Astrophysics Data System (ADS)

van Tilborg, J.; Barber, S. K.; Tsai, H.-E.; Swanson, K. K.; Steinke, S.; Geddes, C. G. R.; Gonsalves, A. J.; Schroeder, C. B.; Esarey, E.; Bulanov, S. S.; Bobrova, N. A.; Sasorov, P. V.; Leemans, W. P.

2017-03-01

Active plasma lenses have attracted interest in novel accelerator applications due to their ability to provide large-field-gradient (short focal length), tunable, and radially symmetric focusing for charged particle beams. However, if the discharge current is not flowing uniformly as a function of radius, one can expect a radially varying field gradient as well as potential emittance degradation. We have investigated this experimentally for a 1-mm-diameter active plasma lens. The measured near-axis field gradient is approximately 35% larger than expected for a uniform current distribution, and at overfocusing currents ring-shaped electron beams are observed. These observations are explained by simulations.

Parallel plate radiofrequency ion thruster

NASA Technical Reports Server (NTRS)

Nakanishi, S.

1982-01-01

An 8-cm-diam. argon ion thruster is described. It is operated by applying 100 to 160 Mhz rf power across a thin plasma volume in a strongly divergent static magnetic field. No cathode or electron emitter is required to sustain a continuous wave plasma discharge over a broad range of propellant gas flow. Preliminary results indicate that a large fraction of the incident power is being reflected by impedance mismatching in the coupling structure. Resonance effects due to plasma thickness, magnetic field strength, and distribution are presented. Typical discharge losses obtained to date are 500 to 600 W per beam ampere at extracted beam currents up to 60 mA.

TEMPEST Simulations of Collisionless Damping of Geodesic-Acoustic Mode in Edge Plasma Pedestal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, X Q; Xiong, Z; Nevins, W M

The fully nonlinear (full-f) 4D TEMPEST gyrokinetic continuum code produces frequency, collisionless damping of GAM and zonal flow with fully nonlinear Boltzmann electrons for the inverse aspect ratio {epsilon}-scan and the tokamak safety factor q-scan in homogeneous plasmas. The TEMPEST simulation shows that GAM exists in edge plasma pedestal for steep density and temperature gradients, and an initial GAM relaxes to the standard neoclassical residual, rather than Rosenbluth-Hinton residual due to the presence of ion-ion collisions. The enhanced GAM damping explains experimental BES measurements on the edge q scaling of the GAM amplitude.

TEMPEST Simulations of Collisionless Damping of Geodesic-Acoustic Mode in Edge Plasma Pedestal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, X; Xiong, Z; Nevins, W

The fully nonlinear 4D TEMPEST gyrokinetic continuum code produces frequency, collisionless damping of geodesic-acoustic mode (GAM) and zonal flow with fully nonlinear Boltzmann electrons for the inverse aspect ratio {epsilon}-scan and the tokamak safety factor q-scan in homogeneous plasmas. The TEMPEST simulation shows that GAM exists in edge plasma pedestal for steep density and temperature gradients, and an initial GAM relaxes to the standard neoclassical residual, rather than Rosenbluth-Hinton residual due to the presence of ion-ion collisions. The enhanced GAM damping explains experimental BES measurements on the edge q scaling of the GAM amplitude.

Multiscale Currents Observed by MMS in the Flow Braking Region

NASA Astrophysics Data System (ADS)

Nakamura, Rumi; Varsani, Ali; Genestreti, Kevin J.; Le Contel, Olivier; Nakamura, Takuma; Baumjohann, Wolfgang; Nagai, Tsugunobu; Artemyev, Anton; Birn, Joachim; Sergeev, Victor A.; Apatenkov, Sergey; Ergun, Robert E.; Fuselier, Stephen A.; Gershman, Daniel J.; Giles, Barbara J.; Khotyaintsev, Yuri V.; Lindqvist, Per-Arne; Magnes, Werner; Mauk, Barry; Petrukovich, Anatoli; Russell, Christopher T.; Stawarz, Julia; Strangeway, Robert J.; Anderson, Brian; Burch, James L.; Bromund, Ken R.; Cohen, Ian; Fischer, David; Jaynes, Allison; Kepko, Laurence; Le, Guan; Plaschke, Ferdinand; Reeves, Geoff; Singer, Howard J.; Slavin, James A.; Torbert, Roy B.; Turner, Drew L.

2018-02-01

We present characteristics of current layers in the off-equatorial near-Earth plasma sheet boundary observed with high time-resolution measurements from the Magnetospheric Multiscale mission during an intense substorm associated with multiple dipolarizations. The four Magnetospheric Multiscale spacecraft, separated by distances of about 50 km, were located in the southern hemisphere in the dusk portion of a substorm current wedge. They observed fast flow disturbances (up to about 500 km/s), most intense in the dawn-dusk direction. Field-aligned currents were observed initially within the expanding plasma sheet, where the flow and field disturbances showed the distinct pattern expected in the braking region of localized flows. Subsequently, intense thin field-aligned current layers were detected at the inner boundary of equatorward moving flux tubes together with Earthward streaming hot ions. Intense Hall current layers were found adjacent to the field-aligned currents. In particular, we found a Hall current structure in the vicinity of the Earthward streaming ion jet that consisted of mixed ion components, that is, hot unmagnetized ions, cold E × B drifting ions, and magnetized electrons. Our observations show that both the near-Earth plasma jet diversion and the thin Hall current layers formed around the reconnection jet boundary are the sites where diversion of the perpendicular currents take place that contribute to the observed field-aligned current pattern as predicted by simulations of reconnection jets. Hence, multiscale structure of flow braking is preserved in the field-aligned currents in the off-equatorial plasma sheet and is also translated to ionosphere to become a part of the substorm field-aligned current system.

Thermodynamic properties and transport coefficients of a two-temperature polytetrafluoroethylene vapor plasma for ablation-controlled discharge applications

NASA Astrophysics Data System (ADS)

Wang, Haiyan; Wang, Weizong; Yan, Joseph D.; Qi, Haiyang; Geng, Jinyue; Wu, Yaowu

2017-10-01

Ablation-controlled plasmas have been used in a range of technical applications where local thermodynamic equilibrium (LTE) is often violated near the wall due to the strong cooling effect caused by the ablation of wall materials. The thermodynamic and transport properties of ablated polytetrafluoroethylene (PTFE) vapor, which determine the flowing plasma behavior in such applications, are calculated based on a two-temperature model at atmospheric pressure. To our knowledge, no data for PTFE have been reported in the literature. The species composition and thermodynamic properties are numerically determined using the two-temperature Saha equation and the Guldberg-Waage equation according to van de Sanden et al’s derivation. The transport coefficients, including viscosity, thermal conductivity and electrical conductivity, are calculated with the most recent collision interaction potentials using Devoto’s electron and heavy-particle decoupling approach but expanded to the third-order approximation (second-order for viscosity) in the frame of the Chapman-Enskog method. Results are computed for different degrees of thermal non-equilibrium, i.e. the ratio of electron to heavy-particle temperatures, from 1 to 10, with electron temperature ranging from 300 to 40 000 K. Plasma transport properties in the LTE state obtained from the present work are compared with existing published results and the causes for the discrepancy analyzed. The two-temperature plasma properties calculated in the present work enable the modeling of wall ablation-controlled plasma processes.

Inner Plasma Structure of the Low-Latitude Reconnection Layer

NASA Technical Reports Server (NTRS)

Zhang, Q.-H.; Dunlop, M. W.; Lockwood, M.; Lavraud, B.; Bogdanova, Y. V.; Hasegawa, H.; Yang, H. -G.; Liu, R. -Y.; Hu, H. -Q.; Zhang, B. -C.;

A Preliminary Investigation of Hall Thruster Technology

NASA Technical Reports Server (NTRS)

Gallimore, Alec D.

1997-01-01

A three-year, NASA/BMDO-sponsored experimental program to conduct performance and plume plasma property measurements on two Russian Stationary Plasma Thrusters (SPTs) has been completed. The program utilized experimental facilitates at the University of Michigan's Plasmadynamics and Electric Propulsion Laboratory (PEPL). The main features of the proposed effort were as follows: We Characterized Hall thruster [and arcjet] performance by measuring ion exhaust velocity with probes at various thruster conditions. Used a variety of probe diagnostics in the thruster plume to measure plasma properties and flow properties including T(sub e) and n(sub e), ion current density and ion energy distribution, and electric fields by mapping plasma potential. Used emission spectroscopy to identify species within the plume and to measure electron temperatures.

Working group report on beam plasmas, electronic propulsion, and active experiments using beams

NASA Technical Reports Server (NTRS)

Dawson, J. M.; Eastman, T.; Gabriel, S.; Hawkins, J.; Matossian, J.; Raitt, J.; Reeves, G.; Sasaki, S.; Szuszczewicz, E.; Winkler, J. R.

1986-01-01

The JPL Workshop addressed a number of plasma issues that bear on advanced spaceborne technology for the years 2000 and beyond. Primary interest was on the permanently manned space station with a focus on identifying environmentally related issues requiring early clarification by spaceborne plasma experimentation. The Beams Working Group focused on environmentally related threats that platform operations could have on the conduct and integrity of spaceborne beam experiments and vice versa. Considerations were to include particle beams and plumes. For purposes of definition it was agreed that the term particle beams described a directed flow of charged or neutral particles allowing single-particle trajectories to represent the characteristics of the beam and its propagation. On the other hand, the word plume was adopted to describe a multidimensional flow (or expansion) of a plasma or neutral gas cloud. Within the framework of these definitions, experiment categories included: (1) Neutral- and charged-particle beam propagation, with considerations extending to high powers and currents. (2) Evolution and dynamics of naturally occurring and man-made plasma and neutral gas clouds. In both categories, scientific interest focused on interactions with the ambient geoplasma and the evolution of particle densities, energy distribution functions, waves, and fields.

Characteristics of Muti-pulsing CHI driven ST plasmas on HIST

NASA Astrophysics Data System (ADS)

Ishihara, M.; Hanao, T.; Ito, K.; Matsumoto, K.; Higashi, T.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

2011-10-01

The flux amplification and sustainment of the ST configurations by operating in Multi-pulsing Coaxial Helicity Injection (M-CHI) method have been demonstrated on HIST. The multi-pulsing experiment was demonstrated in the SSPX spheromak device at LLNL. In the double pulsing discharges, we have observed that the plasma current has been sustained much longer against the resistive decay as compared to the single CHI. We have measured the radial profiles of the flow velocities by using Ion Doppler Spectrometer and Mach probes. The result shows that poloidal shear flow exists between the open flux column and the most outer closed flux surface. The poloidal velocity shear at the interface may be caused by the ion diamagnetic drift, because of a steep density gradient there. The radial electric field is determined by the flow velocities and the ion pressure gradient through the radial momentum balance equation. We have investigated the contribution of ExB or the ion pressure gradient on the poloidal velocity shear by comparing the impurity ion flow obtained from the IDS with the bulk ion flow from the Mach probe. It should be noted that the diamagnetic drift velocity of the impurity is much smaller than ExB drift velocity. We will discuss characteristics of M-CHI-driven ST plasmas by varying TF coil current and the line averaged electron density.

Observations at mercury encounter by the plasma science experiment on mariner 10.

PubMed

Ogilvie, K W; Scudder, J D; Hartle, R E; Siscoe, G L; Bridge, H S; Lazarus, A J; Asbridge, J R; Bame, S J; Yeates, C M

1974-07-12

A fully developed bow shock and magnetosheath were observed near Mercury, providing unambiguous evidence for a strong interaction between Mercury and the solar wind. Inside the sheath there is a distinct region analogous to the magnetosphere or magnetotail of Earth, populated by electrons with lower density and higher temperature than the electrons observed in the solar wind or magnetosheath. At the time of encounter, conditions were such that a perpendicular shock was observed on the inbound leg and a parallel shock was observed on the outbound leg of the trajectory, and energetic plasma electron events were detected upstream from the outbound shock crossing. The interaction is most likely not atmospheric, but the data clearly indicate that the obstacle to solar wind flow is magnetic, either intrinsic or induced. The particle fluxes and energy spectra showed large variations while the spacecraft was inside the magnetosphere, and these variations could be either spatial or temporal.

Field electron emission from diamond and related films synthesized by plasma enhanced chemical vapor deposition

NASA Astrophysics Data System (ADS)

Lu, Xianfeng

The focus of this thesis is the study of the field electron emission (FEE) of diamond and related films synthesized by plasma enhanced chemical vapor deposition. The diamond and related films with different morphologies and compositions were prepared in a microwave plasma-enhanced chemical vapor deposition (CVD) reactor and a hot filament CVD reactor. Various analytical techniques including scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy were employed to characterize the surface morphology and chemical composition. The influence of surface morphology on the field electron emission property of diamond films was studied. The emission current of well-oriented microcrystalline diamond films is relatively small compared to that of randomly oriented microcrystalline diamond films. Meanwhile, the nanocrystalline diamond film has demonstrated a larger emission current than microcrystalline diamond films. The nanocone structure significantly improves the electron emission current of diamond films due to its strong field enhancement effect. The sp2 phase concentration also has significant influence on the field electron emission property of diamond films. For the diamond films synthesized by gas mixture of hydrogen and methane, their field electron emission properties were enhanced with the increase of methane concentration. The field electron emission enhancement was attributed to the increase of sp2 phase concentration, which increases the electrical conductivity of diamond films. For the diamond films synthesized through graphite etching, the growth rate and nucleation density of diamond films increase significantly with decreasing hydrogen flow rate. The field electron emission properties of the diamond films were also enhanced with the decrease of hydrogen flow rate. The field electron emission enhancement can be also attributed to the increase of the sp 2 phase concentration. In addition, the deviation of the experimental Fowler-Nordheim (F-N) plot from a straight line was observed for graphitic nanocone films. The deviation can be mainly attributed to the nonuniform field enhancement factor of the graphitic nanocones. In low macroscopic electric field regions, electrons are emitted mainly from nanocone or nanocones with the largest field enhancement factor, which corresponds to the smallest slope magnitude. With the increase of electric field, nanocones with small field enhancement factors also contribute to the emission current, which results in a reduced average field enhancement factor and therefore a large slope magnitude.

Prompt Ion Outflows and Artificial Ducts during High-Power HF Heating at HAARP: Effect of Suprathermal Electrons?

NASA Astrophysics Data System (ADS)

Mishin, E. V.; Milikh, G. M.

2014-12-01

In situ observations from the DMSP and Demeter satellites established that high-power HF heating of the ionosphere F-region results in significant ion outflows associated with 10-30% density enhancements in the topside ionosphere magnetically-conjugate to the heated region. As follows from the SAMI2 two-fluid model calculations, their formation time should exceed 5-7 minutes. However, specially designed DMSP-HAARP experiments have shown that artificial ducts and ion outflows appear on the topside within 2 minutes. We describe the results of these observations and present a semi-quantitative explanation of the fast timescale due to suprathermal electrons accelerated by HF-induced plasma turbulence. There are two possible effects of suprathermal electrons: (1) the increase of the ambipolar electric field over the usual thermal ambipolar diffusion and (2) excitation of heat flux-driven plasma instability resulting in an anomalous electron-ion momentum exchange. Both effects result in faster upward ion flows.

Electron acceleration in pulsed-power driven magnetic-reconnection experiments

NASA Astrophysics Data System (ADS)

Halliday, Jonathan; Hare, Jack; Lebedev, Sergey; Suttle, Lee; Bland, Simon; Clayson, Thomas; Tubman, Eleanor; Pikuz, Sergei; Shelkovenko, Tanya

2017-10-01

We present recent results from pulsed-power driven magnetic reconnection experiments, fielded on the MAGPIE generator (1.2 MA, 250 ns). The setup used in these experiments produces plasma inflows which are intrinsically magnetised; persist for many hydrodynamic time-scales; and are supersonic. Previous work has focussed on characterising the dynamics of bulk plasma flows, using a suite of diagnostics including laser interferometry, (imaging) Faraday rotation, and Thompson scattering. Measurements show the formation of a well defined, long lasting reconnection layer and demonstrate a power balance between the power into and out of the reconnection region. The work presented here focuses on diagnosing non-thermal electron acceleration by the reconnecting electric field. To achieve this, metal foils were placed in the path of accelerated electrons. Atomic transitions in the foil were collisionally exited by the electron beam, producing a characteristic X-Ray spectrum. This X-Ray emission was diagnosed using spherically bent crystal X-Ray spectrometry, filtered X-Ray pinhole imaging, and X-Ray sensitive PIN diodes.