Publications

2014

Comment on "Micronewton electromagnetic thruster
- Lafleur Trevor
Applied Physics Letters, American Institute of Physics, 2014, 105, pp.146101. ... (10.1063/1.4897967)
DOI : 10.1063/1.4897967
Numerical simulations used for a validity check on the laser induced photo-detachment diagnostic method in electronegative plasmas
- Oudini N.
- Taccogna F.
- Bendib A.
- Aanesland Ane
Physics of Plasmas, American Institute of Physics, 2014, 21 (6), pp.063515. Laser photo-detachment is used as a method to measure or determine the negative ion density and temperature in electronegative plasmas. In essence, the method consists of producing an electropositive channel (negative ion free region) via pulsed laser photo-detachment within an electronegative plasma bulk. Electrostatic probes placed in this channel measure the change in the electron density. A second pulse might be used to track the negative ion recovery. From this, the negative ion density and temperature can be determined. We study the formation and relaxation of the electropositive channel via a two-dimensional Particle-In-Cell/Mote Carlo collision model. The simulation is mainly carried out in a Hydrogen plasma with an electronegativity of α = 1, with a parametric study for α up to 20. The temporal and spatial evolution of the plasma potential and the electron densities shows the formation of a double layer (DL) confining the photo-detached electrons within the electropositive channel. This DL evolves into two fronts that move in the opposite directions inside and outside of the laser spot region. As a consequence, within the laser spot region, the background and photo-detached electron energy distribution function relaxes/thermalizes via collisionless effects such as Fermi acceleration and Landau damping. Moreover, the simulations show that collisional effects and the DL electric field strength might play a non-negligible role in the negative ion recovery within the laser spot region, leading to a two-temperature negative ion distribution. The latter result might have important effects in the determination of the negative ion density and temperature from laser photo detachment diagnostic. (10.1063/1.4886144)
DOI : 10.1063/1.4886144
CLUSTER-STAFF search coil magnetometer calibration - comparisons with FGM
- Robert Patrick
- Cornilleau-Wehrlin Nicole
- Piberne Rodrigue
- de Conchy Y.
- Lacombe C.
- Bouzid V.
- Grison B.
- Alison Dominique
- Canu Patrick
Geoscientific Instrumentation, Methods and Data Systems, European Geosciences Union, 2014, 3, pp.153-177. The main part of the Cluster Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment consists of triaxial search coils allowing the measurements of the three magnetic components of the waves from 0.1 Hz up to 4 kHz. Two sets of data are produced, one by a module to filter and transmit the corresponding waveform up to either 10 or 180 Hz (STAFF-SC), and the second by the onboard Spectrum Analyser (STAFF-SA) to compute the elements of the spectral matrix for five components of the waves, 3 × B and 2 × E (from the EFW experiment), in the frequency range 8 Hz to 4 kHz. In order to understand the way the output signals of the search coils are calibrated, the transfer functions of the different parts of the instrument are described as well as the way to transform telemetry data into physical units across various coordinate systems from the spinning sensors to a fixed and known frame. The instrument sensitivity is discussed. Cross-calibration inside STAFF (SC and SA) is presented. Results of cross-calibration between the STAFF search coils and the Cluster Fluxgate Magnetometer (FGM) data are discussed. It is shown that these cross-calibrations lead to an agreement between both data sets at low frequency within a 2% error. By means of statistics done over 10 yr, it is shown that the functionalities and characteristics of both instruments have not changed during this period. (10.5194/gi-3-153-2014)
DOI : 10.5194/gi-3-153-2014
Electron energy distributions in a magnetized inductively coupled plasma
- Song Sang-Heon
- Yang Yang
- Chabert Pascal
- Kushner M.J.
Physics of Plasmas, American Institute of Physics, 2014, 21 (9), pp.093512. Optimizing and controlling electron energy distributions (EEDs) is a continuing goal in plasma materials processing as EEDs determine the rate coefficients for electron impact processes. There are many strategies to customize EEDs in low pressure inductively coupled plasmas (ICPs), for example, pulsing and choice of frequency, to produce the desired plasma properties. Recent experiments have shown that EEDs in low pressure ICPs can be manipulated through the use of static magnetic fields of sufficient magnitudes to magnetize the electrons and confine them to the electromagnetic skin depth. The EED is then a function of the local magnetic field as opposed to having non-local properties in the absence of the magnetic field. In this paper, EEDs in a magnetized inductively coupled plasma (mICP) sustained in Ar are discussed with results from a two-dimensional plasma hydrodynamics model. Results are compared with experimental measurements. We found that the character of the EED transitions from non-local to local with application of the static magnetic field. The reduction in cross-field mobility increases local electron heating in the skin depth and decreases the transport of these hot electrons to larger radii. The tail of the EED is therefore enhanced in the skin depth and depressed at large radii. Plasmas densities are non-monotonic with increasing pressure with the external magnetic field due to transitions between local and non-local kinetics. (10.1063/1.4896711)
DOI : 10.1063/1.4896711
Radiation from mixed multi-planar wire arrays
- Safronova Alla S.
- Kantsyrev Viktor L.
- Esaulov A. A.
- Chuvatin Alexandre S.
- Weller Michael E.
- Shlyaptseva V. V.
- Shrestha Ishor
- Keim S. F.
- Stafford A.
- Coverdale C. A.
- Apruzese J. P.
- Ouart N. D.
- Giuliani J. L.
Physics of Plasmas, American Institute of Physics, 2014, 21 (03), pp.031205. The study of radiation from different wire materials in wire array Z-pinch plasma is a very challenging topic because it is almost impossible to separate different plasmas at the stagnation. A new approach is suggested based on planar wire array (PWA) loads to assess this problem. Multi-planar wire arrays are implemented that consist of few planes, each with the same number of wires and masses but from different wire materials, arranged in parallel rows. In particular, the experimental results obtained with triple PWAs (TPWAs) on the UNR Zebra generator are analyzed with Wire Ablation Dynamics Model, non-local thermodynamic equilibrium kinetic model, and 2D radiation magneto-hydrodynamic to illustrate this new approach. In TPWAs, two wire planes were from mid-atomic-number wire material and another plane was from alloyed Al, placed either in the middle or at the edge of the TPWA. Spatial and temporal properties of K-shell Al and L-shell Cu radiations were analyzed and compared from these two configurations of TPWAs. Advantages of the new approach are demonstrated and future work is discussed. (10.1063/1.4864335)
DOI : 10.1063/1.4864335
Theory and Modeling for the Magnetospheric Multiscale Mission
- Hesse Michael
- Aunai Nicolas
- Birn Joachim
- Cassak P.
- Denton R.~e.
- Drake J. F.
- Gombosi Tamas I.
- Hoshino M.
- Matthaeus W.
- Sibeck David G.
- Zenitani Seiji
Space Science Reviews, Springer Verlag, 2014. The Magnetospheric Multiscale (MMS) mission will provide measurement capabilities, which will exceed those of earlier and even contemporary missions by orders of magnitude. MMS will, for the first time, be able to measure directly and with sufficient resolution key features of the magnetic reconnection process, down to the critical electron scales, which need to be resolved to understand how reconnection works. Owing to the complexity and extremely high spatial resolution required, no prior measurements exist, which could be employed to guide the definition of measurement requirements, and consequently set essential parameters for mission planning and execution. Insight into expected details of the reconnection process could hence only been obtained from theory and modern kinetic modeling. This situation was recognized early on by MMS leadership, which supported the formation of a fully integrated Theory and Modeling Team (TMT). The TMT participated in all aspects of mission planning, from the proposal stage to individual aspects of instrument performance characteristics. It provided and continues to provide to the mission the latest insights regarding the kinetic physics of magnetic reconnection, as well as associated particle acceleration and turbulence, assuring that, to the best of modern knowledge, the mission is prepared to resolve the inner workings of the magnetic reconnection process. The present paper provides a summary of key recent results or reconnection research by TMT members. (10.1007/s11214-014-0078-y)
DOI : 10.1007/s11214-014-0078-y
Quantified energy dissipation rates in the terrestrial bow shock: 1. Analysis techniques and methodology
- Wilson Iii L. B.
- Sibeck David G.
- Breneman A. W.
- Le Contel Olivier
- Cully C. M.
- Turner D. L.
- Angelopoulos V.
- Malaspina D. M.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119 (8), pp.6455-6474. We present a detailed outline and discussion of the analysis techniques used to compare the relevance of different energy dissipation mechanisms at collisionless shock waves. We show that the low-frequency, quasi-static fields contribute less to ohmic energy dissipation, (-j·E), than their high-frequency counterparts. In fact, we found that high-frequency, large-amplitude (>100 mV/m and/or >1 nT) waves are ubiquitous in the transition region of collisionless shocks. We quantitatively show that their fields, through wave-particle interactions, cause enough energy dissipation to regulate the global structure of collisionless shocks. The purpose of this paper, part one of two, is to outline and describe in detail the background, analysis techniques, and theoretical motivation for our new results presented in the companion paper. The companion paper presents the results of our quantitative energy dissipation rate estimates and discusses the implications. Together, the two manuscripts present the first study quantifying the contribution that high-frequency waves provide, through wave-particle interactions, to the total energy dissipation budget of collisionless shock waves. (10.1002/2014JA019929)
DOI : 10.1002/2014JA019929
Observational evidence of electron pitch angle scattering driven by ECH waves
- Kurita S.
- Miyoshi Y.
- Cully C. M.
- Angelopoulos V.
- Le Contel Olivier
- Hikishima M.
- Misawa H.
Geophysical Research Letters, American Geophysical Union, 2014. Using the plasma wave and electron data obtained from Time History of Events and Macroscale Interactions during Substorms, we show a signature of electron pitch angle scattering driven by Electrostatic Cyclotron Harmonic (ECH) waves in the velocity distribution function (VDF). The diffusion curve of whistler mode waves is used as a proxy to identify changes in VDFs due to wave-particle interactions. We confirm that the shape of the VDF well agrees with the diffusion curve of whistler mode waves when whistler mode chorus alone is active. On the other hand, we find that the shape of the VDF deviates from the diffusion curves at low pitch angles when ECH waves are active following the inactivation of chorus waves. The result is observational support for electron pitch angle scattering caused by ECH waves and suggests that ECH waves can contribute to generation of diffuse auroras. (10.1002/2014GL061927)
DOI : 10.1002/2014GL061927
E x B shear pattern formation by radial propagation of heat flux waves
- Kosuga Y.
- Diamond P.H.
- Dif-Pradalier Guilhem
- Gürcan Özgür D.
Physics of Plasmas, American Institute of Physics, 2014, 21 (5). A novel theory to describe the formation of E x B flow patterns by radially propagating heat flux waves is presented. A model for heat avalanche dynamics is extended to include a finite delay time between the instantaneous heat flux and the mean flux, based on an analogy between heat avalanche dynamics and traffic flow dynamics. The response time introduced here is an analogue of the drivers' response time in traffic dynamics. The microscopic foundation for the time delay is the time for mixing of the phase space density. The inclusion of the finite response time changes the model equation for avalanche dynamics from Burgers equation to a nonlinear telegraph equation. Based on the telegraph equation, the formation of heat flux jams is predicted. The growth rate and typical interval of jams are calculated. The connection of the jam interval to the typical step size of the E x B staircase is discussed. (C) 2014 AIP Publishing LLC. (10.1063/1.4872018)
DOI : 10.1063/1.4872018
Acetylene photocatalytic oxidation using continuous flow reactor: Gas phase and adsorbed phase investigation, assessment of the photocatalyst deactivation
- Thevenet F.
- Guillard C.
- Rousseau A.
Chemical Engineering Journal, Elsevier, 2014, 244, pp.50-58. Acetylene, used as a model volatile organic compound (VOC), is submitted to photocatalytic oxidation. This study is based on the simultaneous characterisation of: (i) the gas phase at the reactor outlet; (ii) the adsorbed phase on the photocatalytic media. Experiments are performed in a continuous flow reactor, and analytical procedures have been developed to identify and quantify the gaseous and adsorbed side-products. The photocatalytic media consists in P25 Degussa TiO2 nanoparticles deposited on glass fibres. First, the process efficiency is investigated through C2H2 conversion rate and mineralisation. The treatment performances tend to decrease with time regarding conversion and mineralisation. Then, the oxidation process is investigated through gaseous and adsorbed by-products. Three carboxylic acids have been quantified in the adsorbed phase during oxidative treatment; their temporal evolutions are determined. Their contribution to the carbon balance is discussed. It is evidenced that their adsorption on the photocatalytic media leads to a saturation of the surface. Formaldehyde, glyoxal and formic acid are quantified in the gas phase. Their cumulative temporal profiles and their contribution to the carbon balance confirm the hypothesis of a surface deactivation. The decrease of the process performances with time and the increase of gaseous by-products are correlated with the photocatalyst coverage by adsorbed acids. Carbon balances calculated for various treatment times, give an overview of the process evolution. The regeneration of the photocatalyst surface is possible under synthetic air; 80% of the adsorbed compounds are mineralised. The performances of a cyclic procedure (treatment/regeneration) are evaluated. This approach preserves the photocatalyst performances and ensures a mineralisation of 85% of the converted acetylene. (C) 2014 Elsevier B.V. All rights reserved. (10.1016/j.cej.2014.01.038)
DOI : 10.1016/j.cej.2014.01.038
Radiation from Ag high energy density Z-pinch plasmas and applications to lasing
- Weller Michael E.
- Safronova Alla S.
- Kantsyrev Viktor L.
- Esaulov A. A.
- Shrestha Ishor
- Apruzese J. P.
- Giuliani J. L.
- Chuvatin Alexandre S.
- Stafford A.
- Keim S. F.
- Shlyaptseva V. V.
- Osborne Glenn C.
- Petkov E. E.
Physics of Plasmas, American Institute of Physics, 2014, 21 (03), pp.031206. Silver (Ag) wire arrays were recently introduced as efficient x-ray radiators and have been shown to create L-shell plasmas that have the highest electron temperature (>1.8 keV) observed on the Zebra generator so far and upwards of 30 kJ of energy output. In this paper, results of single planar wire arrays and double planar wire arrays of Ag and mixed Ag and Al that were tested on the UNR Zebra generator are presented and compared. To further understand how L-shell Ag plasma evolves in time, a time-gated x-ray spectrometer was designed and fielded, which has a spectral range of approximately 3.55.0 Å. With this, L-shell Ag as well as cold Lα and Lβ Ag lines was captured and analyzed along with photoconducting diode (PCD) signals (>0.8 keV). Along with PCD signals, other signals, such as filtered XRD (>0.2 keV) and Si-diodes (SiD) (>9 keV), are analyzed covering a broad range of energies from a few eV to greater than 53 keV. The observation and analysis of cold Lα and Lβ lines show possible correlations with electron beams and SiD signals. Recently, an interesting issue regarding these Ag plasmas is whether lasing occurs in the Ne-like soft x-ray range, and if so, at what gains? To help answer this question, a non-local thermodynamic equilibrium (LTE) kinetic model was utilized to calculate theoretical lasing gains. It is shown that the Ag L-shell plasma conditions produced on the Zebra generator at 1.7 maximum current may be adequate to produce gains as high as 6 cm−1 for various 3p → 3s transitions. Other potential lasing transitions, including higher Rydberg states, are also included in detail. The overall importance of Ag wire arrays and plasmas is discussed. (10.1063/1.4865368)
DOI : 10.1063/1.4865368
Regeneration of isopropyl alcohol saturated Mn<SUB>X</SUB>O<SUB>Y</SUB> surface: Comparison of thermal, ozonolysis and non-thermal plasma treatments
- Sivachandiran Loganathan
- Thévenet Frédéric
- Rousseau Antoine
Chemical Engineering Journal, Elsevier, 2014, 246, pp.184-195. IPA saturated MnXOY surface regeneration has been investigated under dry air. MnXOY coated glass beads packed-bed reactor has been designed and used for IPA storage under gas-flowing condition at 296 K. The coated MnXOY material is characterized by BrunauerEmmettTeller (BET), non destructive Optical Pro- filometer and X-ray diffraction (XRD) techniques. Atmospheric pressure gas phase Fourier Transform Infrared Spectroscopy (FTIR) and online Thermal Desorption coupled with Gas Phase Chromatography and Mass Spectrometry (TDGCMS) have been respectively used to quantify and to identify the gas phase species produced during the regeneration processes. This study mainly aims at investigating three different methods to regenerate the IPA saturated MnXOY surface. In this framework, methods have been investigated for IPA saturated MnXOY surface regeneration namely (i) direct thermal treatment (DTT), (ii) ozonolysis and (iii) In-Situ Non Thermal Plasma Treatment (NTP). Among the employed methods, In-Situ NTP treatment has shown better regeneration efficiency, and twice more CO2 selectivity. Notably, dry air In-Situ NTP treatment prior to thermal treatment has significantly improved the mineralization. The order of mineralization efficiency and/or COx selectivity can be written as follows: In-Situ NTP > dry air ozonolysis > dry air DTT. (10.1016/j.cej.2014.02.058)
DOI : 10.1016/j.cej.2014.02.058
Characterization of predator-prey dynamics, using the evolution of free energy in plasma turbulence
- Morel Pierre
- Gürcan Özgür D.
- Berionni Vincent
Plasma Physics and Controlled Fusion, IOP Publishing, 2014, 56 (1), pp.015002. A simple dynamical cascade model for the evolution of free energy is considered in the context of gyrokinetic formalism. It is noted that the dynamics of free energy, that characterize plasma micro-turbulence in magnetic fusion devices, exhibit a predatorprey character. Various key features of predatorprey dynamics such as the time delay between turbulence and large-scale flow structures, or the intermittency of the dynamics are identified in the quasi-steady-state phase of the nonlinear gyrokinetic simulations. A novel prediction on the ratio of turbulence amplitudes in different parts of the wavenumber domain that follows from this simple predatorprey model is compared to a set of nonlinear simulation results and is observed to hold quite well in a large range of physical parameters. Detailed validation of the predatorprey hypothesis using nonlinear gyrokinetics provides a very important input for the effort to apprehend plasma micro-turbulence, since the predatorprey idea can be used as a very effective intuitive tool for understanding and designing efficient transport models. (10.1088/0741-3335/56/1/015002)
DOI : 10.1088/0741-3335/56/1/015002
Radiation in the neighbourhood of a double layer
- Pottelette Raymond
- Berthomier Matthieu
- Pickett J. S.
Annales Geophysicae, European Geosciences Union, 2014, 32, pp.677-687. In the auroral kilometric radiation (AKR) source region, acceleration layers narrow in altitude and associated with parallel field-aligned potential drops of several kV can be identified by using both particles and wave-field high time-resolution measurements from the Fast Auroral SnapshoT explorer spacecraft (FAST). These so-called double layers (DLs) are recorded around density enhancements in the auroral cavity, where the enhancement can be at the edge of the cavity or even within the cavity at a small scale. Once immersed in the plasma, DLs necessarily accelerate particles along the magnetic field lines, thereby generating locally strong turbulent processes leading to the formation of nonlinear phase space holes. The FAST data reveal the asymmetric character of the turbulence: the regions located on the high-potential side of the DLs are characterized by the presence of electron holes, while on the low-potential side, ion holes are recorded. The existence of these nonlinear phase space holes may affect the AKR radiation pattern in the neighbourhood of a DL where the electron distribution function is drastically different from a horseshoe shape. We present some observations which illustrate the systematic generation of elementary radiation events occurring significantly above the local electron gyrofrequency in the presence of electron holes. These fine-scale AKR radiators are associated with a local electron distribution which presents a pronounced beam-like shape. (10.5194/angeo-32-677-2014)
DOI : 10.5194/angeo-32-677-2014
Whistler mode waves at magnetotail dipolarization fronts
- Viberg H.
- Khotyaintsev Y. V.
- Vaivads A.
- André M.
- Fu H.S.
- Cornilleau-Wehrlin Nicole
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119, pp.2605-2611. We report the statistics of whistler mode waves observed in relation to dipolarization fronts (DFs) in Earth's magnetotail using data from the four Cluster spacecraft spanning a period of 9 years, 20012009. We show that whistler mode waves are common in a vicinity of DFs: between 30 and 60% of all DFs are associated with whistlers. Whistlers are about 7 times more likely to be observed near a DF than at any random location in the magnetotail. Therefore, whistlers are a characteristic signature of DFs. We find that whistlers are most often detected in the flux pileup region (FPR) following the DF, close to the center of the current sheet (Bx ∼ 0) and in association with anisotropic electron distributions (Tperp>T∥). This suggests that we typically observe emissions in the source region where they are generated by the anisotropic electrons produced by the betatron process inside the FPR. (10.1002/2014JA019892)
DOI : 10.1002/2014JA019892
Pure airplasma bullets propagating inside microcapillaries and in ambient air
- Lacoste D.A.
- Bourdon Anne
- Kuribara Koichi
- Urabe Keiichiro
- Stauss Sven
- Terashima Kazuo
Plasma Sources Science and Technology, IOP Publishing, 2014, 23, pp.062006. This paper reports on the characterization of airplasma bullets in microcapillary tubes and in ambient air, obtained without the use of inert or noble gases. The bullets were produced by nanosecond repetitively pulsed discharges, applied in a dielectric barrier discharge configuration. The anode was a tungsten wire with a diameter of 50μm, centered in the microcapillary, while the cathode was a silver ring, fixed on the outer surface of the fused silica tube. The effects of the applied voltage and the inner diameter of the microcapillary tube on the plasma behavior were investigated. Inside the tubes, while the topology of the bullets seems to be strongly dependent on the diameter, their velocity is only a function of the amplitude of the applied voltage. In ambient air, the propagation of air bullets with a velocity of about 1.25 × 105 ms−1 is observed. (10.1088/0963-0252/23/6/062006)
DOI : 10.1088/0963-0252/23/6/062006
Helicon plasma thruster discharge model
- Lafleur Trevor
Physics of Plasmas, American Institute of Physics, 2014, 21, pp.043507. By considering particle, momentum, and energy balance equations, we develop a semi-empirical quasi one-dimensional analytical discharge model of radio-frequency and helicon plasma thrusters. The model, which includes both the upstream plasma source region as well as the downstream diverging magnetic nozzle region, is compared with experimental measurements and confirms current performance levels. Analysis of the discharge model identifies plasma power losses on the radial and back wall of the thruster as the major performance reduction factors. These losses serve as sinks for the input power which do not contribute to the thrust, and which reduce the maximum plasma density and hence propellant utilization. With significant radial plasma losses eliminated, the discharge model (with argon) predicts specific impulses in excess of 3000 s, propellant utilizations above 90%, and thruster efficiencies of about 30%. (10.1063/1.4871727)
DOI : 10.1063/1.4871727
Experimental validation of the dual positive and negative ion beam acceleration in the plasma propulsion with electronegative gases thruster
- Rafalskyi D.V.
- Popelier Lara
- Aanesland Ane
Journal of Applied Physics, American Institute of Physics, 2014, 115 (5), pp.053301. The PEGASES (Plasma Propulsion with Electronegative Gases) thruster is a gridded ion thruster, where both positive and negative ions are accelerated to generate thrust. In this way, additional downstream neutralization by electrons is redundant. To achieve this, the thruster accelerates alternately positive and negative ions from an ion-ion plasma where the electron density is three orders of magnitude lower than the ion densities. This paper presents a first experimental study of the alternate acceleration in PEGASES, where SF6 is used as the working gas. Various electrostatic probes are used to investigate the source plasma potential and the energy, composition, and current of the extracted beams. We show here that the plasma potential control in such system is key parameter defining success of ion extraction and is sensitive to both parasitic electron current paths in the source region and deposition of sulphur containing dielectric films on the grids. In addition, large oscillations in the ion-ion plasma potential are found in the negative ion extraction phase. The oscillation occurs when the primary plasma approaches the grounded parts of the main core via sub-millimetres technological inputs. By controlling and suppressing the various undesired effects, we achieve perfect ion-ion plasma potential control with stable oscillation-free operation in the range of the available acceleration voltages (±350 V). The measured positive and negative ion currents in the beam are about 10 mA for each component at RF power of 100 W and non-optimized extraction system. Two different energy analyzers with and without magnetic electron suppression system are used to measure and compare the negative and positive ion and electron fluxes formed by the thruster. It is found that at alternate ion-ion extraction the positive and negative ion energy peaks are similar in areas and symmetrical in position with /− ion energy corresponding to the amplitude of the applied acceleration voltage. (10.1063/1.4863876)
DOI : 10.1063/1.4863876
Investigation of capillary nanosecond discharges in air at moderate pressure: comparison of experiments and 2D numerical modeling
- Klochko A.V.
- Starikovskaia Svetlana
- Xiong Z.
- Kushner M.J.
Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47, pp.365202. Nanosecond electrical discharges in the form of ionization waves are of interest for rapidly ionizing and exciting complex gas mixtures to initiate chemical reactions. Operating with a small discharge tube diameter can significantly increase the specific energy deposition and so enable optimization of the initiation process. Analysis of the uniformity of energy release in small diameter capillary tubes will aid in this optimization. In this paper, results for the experimentally derived characteristics of nanosecond capillary discharges in air at moderate pressure are presented and compared with results from a two-dimensional model. The quartz capillary tube, having inner and outer diameters of 1.5 and 3.4 mm, is about 80 mm long and filled with synthetic dry air at 27 mbar. The capillary tube with two electrodes at the ends is inserted into a break of the central wire of a long coaxial cable. A metal screen around the tube is connected to the cable ground shield. The discharge is driven by a 19 kV 35 ns voltage pulse applied to the powered electrode. The experimental measurements are conducted primarily by using a calibrated capacitive probe and back current shunts. The numerical modelling focuses on the fast ionization wave (FIW) and the plasma properties in the immediate afterglow after the conductive plasma channel has been established between the two electrodes. The FIW produces a highly focused region of electric field on the tube axis that sustains the ionization wave that eventually bridges the electrode gap. Results from the model predict FIW propagation speed and current rise time that agree with the experiment. (10.1088/0022-3727/47/36/365202)
DOI : 10.1088/0022-3727/47/36/365202
Electric field in nanosecond surface dielectric barrier discharge at different polarities of the high voltage pulse: spectroscopy measurements and numerical modeling.
- Stepanyan S.A.
- Victor Soloviev
- Starikovskaia Svetlana
Journal of Physics D: Applied Physics, IOP Publishing, 2014. Has been just accepted
An electric field in nanosecond surface dielectric barrier discharge at different polarities of the high voltage pulse: spectroscopy measurements and numerical modeling
- Stepanyan S.A.
- Soloviev Victor
- Starikovskaia Svetlana
Journal of Physics D: Applied Physics, IOP Publishing, 2014, 47, pp.485201. The ratio of emission intensities of the second positive N2(C3Πu, v' = 0) → N2(B3Πg, v = 0), 337.1 nm and first negative, 391.4 nm systems of nitrogen have been measured in a nanosecond surface dielectric barrier discharge (SDBD). The measurements were carried out in synthetic air for a pressure range 13 bar for different polarities of the high-voltage (HV) pulse. For all the investigated conditions, the ratio of emission intensities at the wavelengthes 391.4 and 337.1 nm, measured experimentally, is systematically higher for the positive polarity of HV electrodes. To analyze the spatial distribution of N2(C3Πu) and emissions, comprehensive two-dimensional numerical modeling for P = 1 bar has been performed. The details of the formation of a narrow gap between the dielectric surface and the streamer channel in the case of positive polarity of HV electrodes are discussed. The ratio of integrated over space calculated emission intensities, , has been analyzed and compared with obtained experimental data. A good agreement was obtained for a negative polarity SDBD. For a positive polarity discharge, for all the considered conditions. Explanation for the observed effect is suggested. (10.1088/0022-3727/47/48/485201)
DOI : 10.1088/0022-3727/47/48/485201
On the relationship between quadrupolar magnetic field and collisionless reconnection
- Smets Roch
- Aunai Nicolas
- Belmont Gérard
- Boniface C.
- Fuchs J. C.
Physics of Plasmas, American Institute of Physics, 2014, 21 (6), pp.062111. Using hybrid simulations, we investigate the onset of fast reconnection between two cylindrical magnetic shells initially close to each other. This initial state mimics the plasma structure in High Energy Density Plasmas induced by a laser-target interaction and the associated self-generated magnetic field. We clearly observe that the classical quadrupolar structure of the out-of-plane magnetic field appears prior to the reconnection onset. Furthermore, a parametric study reveals that, with a non-coplanar initial magnetic topology, the reconnection onset is delayed and possibly suppressed. The relation between the out-of-plane magnetic field and the out-of-plane electric field is discussed. (10.1063/1.4885097)
DOI : 10.1063/1.4885097
Simulation of long term variation of the F2-layer critical frequency f0F2 at the northern tropical crest of ionization at Phu Thuy, Vietnam with the thermosphere-ionosphere-electrodynamics general circulation model (TIE-GCM)
- Pham Thi Thu Hong
- Amory-Mazaudier Christine
- Le Huy Minh
Vietnam Journal of Earth Sciences, Vietnam Academy of Science and Technology (VAST), 2014 (36), pp.470-479. In this work, the long-term variations of the simulated f0F2 by the NCAR thermosphere ionosphere-electrodynamics general circulation model (TIE-GCM) at the northern tropical crest of ionization at Phu Thuy-Vietnam (geographic latitudes 21.030N and longitude: 105.950E) during the period from 1962 to 2002 are examined to evaluate the ability of this model to reproduce the major features of the f0F2 as observed. The TIE-GCM simulates the influences of migrating and non-migrating diurnal and semidiurnal tides at the lower thermosphere, and changes of geomagnetic activity on the long-term variation of the f0F2. It reproduces well the diurnal and seasonal variations. We analyze the diurnal and seasonal variations of the observed f0F2 at Phu Thuy in approximately the same solar activity condition as in 1964, 1996 for the March and September equinoxes and June and December solstices. The local time and seasonal structures of these simulated results correspond well to those that are observed in 1964. On the contrary, the TIE-GCM model does not reproduce the amplitude observed at Thuy Phu in 1996. The TIE-GCM model with the chosen inputs does not yet allow us to explain well the long-term variations observed at Phu Thuy. We also try the different numerical simulations to understand how the long-term variation of the f0F2 is formed, how it relates to the current global system and its relationship with the thermosphere wind. The simulations show that the calculated NmF2 values are lower than the observed values. We find that the modeled contributions of the migrating and non-migrating diurnal and semidiurnal tides may cause them to play a major role in reducing the amplitude of the NmF2. The contributions of the integrated hemispheric power of auroral electrons and the cross polar cap potential seem to play an important role in increasing the amplitude of the NmF2. Keywords: F2 layer; Long-term trends; Ionosphere equatorial ionization anomaly; Ionosphere (ionospheric conductivities, ionospheric currents and electric field), thermospheric tides, Electrodynamics of the ionosphere (ionospheric dynamo).
Waveforms of Langmuir turbulence in inhomogeneous solar wind plasmas
- Krafft C
- Volokitin A.
- Krasnoselskikh V.V.
- Dudok de Wit Thierry
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119, pp.9369–9382. Modulated Langmuir waveforms have been observed by several spacecraft in various regions of the heliosphere, such as the solar wind, the electron foreshock, the magnetotail, or the auroral ionosphere. Many observations revealed the bursty nature of these waves, which appear to be highly modulated, localized, and clumped into spikes with peak amplitudes typically 3 orders of magnitude above the mean. The paper presents Langmuir waveforms calculated using a Hamiltonian model describing self-consistently the resonant interaction of an electron beam with Langmuir wave packets in a plasma with random density fluctuations. These waveforms, obtained for different profiles of density fluctuations and ranges of parameters relevant to solar type III electron beams and plasmas measured at 1 AU, are presented in the form they would appear if recorded by a satellite moving in the solar wind. Comparison with recent measurements by the STEREO and WIND satellites shows that their characteristic features are very similar to the observations. (10.1002/2014JA020329)
DOI : 10.1002/2014JA020329
In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge
- Forsyth C.
- Fazakerley A.
- Rae I. J.
- Watt C. E. J.
- Murphy K.
- Wild James A.
- Karlsson T.
- Mutel R. L.
- Owen C. J.
- Ergun R.
- Masson A.
- Berthomier Matthieu
- Donovan E.
- Frey H.~u.
- Matzka J.
- Stolle C.
- Zhang Y.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2014, 119 (2), pp.927-946. The substorm current wedge (SCW) is a fundamental component of geomagnetic substorms. Models tend to describe the SCW as a simple line current flowing into the ionosphere toward dawn and out of the ionosphere toward dusk, linked by a westward electrojet. We use multispacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 January 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft traveled east-west azimuthally above the auroral region. We show that the SCW has significant azimuthal substructure on scales of 100 km at altitudes of 40007000 km. We identify 26 individual current sheets in the Cluster 4 data and 34 individual current sheets in the Cluster 1 data, with Cluster 1 passing through the SCW 120240 s after Cluster 4 at 13002000 km higher altitude. Both spacecraft observed large-scale regions of net upward and downward field-aligned current, consistent with the large-scale characteristics of the SCW, although sheets of oppositely directed currents were observed within both regions. We show that the majority of these current sheets were closely aligned to a north-south direction, in contrast to the expected east-west orientation of the preonset aurora. Comparing our results with observations of the field-aligned current associated with bursty bulk flows (BBFs), we conclude that significant questions remain for the explanation of SCW structuring by BBF-driven wedgelets. Our results therefore represent constraints on future modeling and theoretical frameworks on the generation of the SCW. (10.1002/2013JA019302)
DOI : 10.1002/2013JA019302

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