Publications

2015

Advanced Ion Mass Spectrometer
- Sittler E.C.
- Cooper J.F.
- Paschalidis N.
- Jones S.
- Rodriguez M.
- Ali A.
- Coplan M.A.
- Chornay D.
- Sturners S.J.
- Brown S.
- Bateman F.B.
- Fontaine Dominique
- Verdeil Christophe
- André N.
- Federov A.
- Wurz Peter
, 2015.
E × B probe measurements in molecular and electronegative plasmas
- Renaud D.
- Gerst D.
- Mazouffre S.
- Aanesland Ane
Review of Scientific Instruments, American Institute of Physics, 2015, 86 (12), pp.123507. This paper reports on the design, the building, the calibration, and the use of a compact E × B probe that acts as a velocity filter or a mass filter for ion species. A series of measurements has been performed in the discharge and in the beam of the PEGASES (Plasma Propulsion with Electronegative GASES) ion source. PEGASES is a unique inductively coupled radio-frequency source able to generate a beam of positive and negative ions when operated with an electronegative gas. In this study, experiments have been carried out with SF6. Calibrated E × B probe spectra indicate that the diagnostic tool can be used to determine the ion velocity and the plasma composition even when many molecular fragments are present. In addition, the probe is able to detect both positive and negative ions. Measurements show a large variety of positively charged ions coming from SF6. Conversely, the beam is solely composed of F− and SF−6 negative ions in compliance with computer simulations. (10.1063/1.4937604)
DOI : 10.1063/1.4937604
Charge and energy transferred from a plasma jet to liquid and dielectric surfaces
- Dang van Sung Mussard Marguerite
- Foucher Emeric
- Rousseau Antoine
Journal of Physics D: Applied Physics, IOP Publishing, 2015, 48 (42), pp.424003. A key parameter in using plasma jets for biomedical applications is the transferred energy to the living tissues. The objective of this paper is to understand which parameters control the energy transfer from the plasma jet to a liquid or a dielectric surface. The plasma jet is own with helium and ignited by a 600 Hz ac high voltage (up to 15 kV). Capacitors are connected to two measurement electrodes placed in the plasma source region, and under the sample. Charge and energy transferred are estimated by plotting Lissajous cycles; the number of bullets and the charge probability density function are also calculated. It is shown that the applied voltage and the gap (distance between the end of the tube and the sample) have a dramatic in uence on the energy deposition on the sample as well as on the charge probability density function. Surprisingly, both gap distance and voltage have very little in uence on the number of bullets reaching the sample per cycle. It is also shown that the conductivity of the liquid sample has almost no in uence on the energy deposition and charge probability density function. (10.1088/0022-3727/48/42/424003)
DOI : 10.1088/0022-3727/48/42/424003
Sub-nanosecond delays of light emitted by streamer in atmospheric pressure air: Analysis of N2(C3Piu) and N2+(B2Sigmau+) emissions and fundamental streamer structure
- Hoder Tomas
- Bonaventura Zdenek
- Bourdon Anne
- Simek Milan
Journal of Applied Physics, American Institute of Physics, 2015, 117, pp.073302. Theoretical analysis of ultra-short phenomena occurring during the positive streamer propagation in atmospheric pressure air is presented. Motivated by experimental results obtained with tens-of picoseconds and tens-of-microns precision, it is shown that when the streamer head passes a spatial coordinate, emission maxima from N2 and N2 radiative states follow with different delays. Thesedifferent delays are caused by differences in the dynamics of populating the radiative states, due to different excitation and quenching rates. Associating the position of the streamer head with the maximum value of the self-enhanced electric field, a delay of 160 ps was experimentally found for the peak emission of the first negative system of N2 . A delay dilatation was observed experimentally on early-stage streamers and the general mechanism of this phenomenon is clarified theoretically. In the case of the second positive system of N2, the delay can reach as much as 400 ps. In contrast to the highly nonlinear behavior of streamer events, it is shown theoretically that emission maximum delays linearly depend on the ratio of the streamer radius and its velocity. This is found to be one of the fundamental streamer features and its use in streamer head diagnostics is proposed. Moreover,radially resolved spectra are synthesized for selected subsequent picosecond moments in order to visualize spectrometric fingerprints of radial structures of N2(C3Piu) and N2 (B2Sigma u) populations created by streamer-head electrons (10.1063/1.4913215)
DOI : 10.1063/1.4913215
Fourier spectrum and phases for a signal in a finite interval
- Belmont Gérard
- Dorville Nicolas
- Sahraoui Fouad
- Rezeau Laurence
, 2015, 17, pp.5320. When investigating the physics of turbulent media, as the solar wind or the magnetosheath plasmas, obtaining accurate Fourier spectra and phases is a crucial issue. For the different fields, the spectra allow in particular verifying whether one or several power laws can be determined in different frequency ranges. Accurate phases are necessary as well for all the "higher order statistics" studies in Fourier space, the coherence ones and for the polarization studies. Unfortunately, the Fourier analysis is not unique for a finite time interval of duration T: the frequencies lower than 1/T have a large influence on the result, which can hardly be controlled. This unknown "trend" has in particular the effect of introducing jumps at the edges of the interval, for the function under study itself, as well as for all its derivatives. The Fourier transform obtained directly by FFT (Fast Fourier Transform) is generally much influenced by these effects and cannot be used without care for wide band signals. The interference between the jumps and the signal itself provide in particular characteristic "hairs" on the spectrum, which are clearly visible on it with df≈1/T. These fluctuations are usually eliminated by smoothing the spectrum, or by averaging several successive spectra. Nevertheless, such treatments introduce uncertainties on the spectral laws (the phases being anyway completely lost). Windowing is also a method currently used to suppress or decrease the jumps, but it modifies the signal (the windowed trend has a spectrum, which is convolved with the searched one) and the phases are generally much altered. Here, we present a new data processing technique to circumvent these difficulties. It takes advantage of the fact that the signal is generally not unknown out of the interval under study: the complete signal is tapered to this interval of interest thanks to a new window function, sharp but not square. This window function is chosen such that the spectrum obtained can be deconvolved almost exactly, through a minimization procedure based on the -weak- hypothesis that it is smooth at the scale of a few successive spectral points. Then, a later step allows reconstructing the phases. Tests with synthetic data and first applications to Cluster data are presented, which demonstrate the capability of the method to better estimate the Fourier spectra.
Edge-to-center density ratios in low-temperature plasmas
- Lafleur Trevor
- Chabert Pascal
Plasma Sources Science and Technology, IOP Publishing, 2015, 24 (2), pp.025017. The ion flux leaving a plasma at a boundary can be given by: Γ i = h L n 0 u B , where n 0 is the maximum central plasma density, u B is the Bohm velocity, and h L is the sheath edge-to-center plasma density ratio. Such h L factors have become synonymous with global modeling of plasma discharges, where they play a vital role in the prediction of plasma losses to bounding surfaces. By performing one-dimensional (1D) particle-in-cell simulations of inductively and capacitively coupled plasmas (ICPs and CCPs) over a wide pressure range, we explicitly test the validity of standard heuristic formulae commonly used to estimate h L . The ICP simulation results are found to be in very good agreement, while a large discrepancy is present for the CCP results at high pressures. The onset of this discrepancy is found to be correlated with the bulk-to-sheath edge ionization transition that occurs in CCPs at high pressures. Consequently, global models will strongly underestimate plasma losses in this regime. (10.1088/0963-0252/24/2/025017)
DOI : 10.1088/0963-0252/24/2/025017
The Earth: Plasma Sources, Losses, and Transport Processes
- Welling D. T.
- André M.
- Dandouras Iannis
- Delcourt Dominique C.
- Fazakerley A.
- Fontaine Dominique
- Foster John
- Ilie R.
- Kistler L. M.
- Lee J. H.
- Liemohn M. W.
- Slavin J. A.
- Wang Chih-Ping
- Wiltberger M.
- Yau Andrew
Space Science Reviews, Springer Verlag, 2015, 192 (1-4), pp.145-208. This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed. (10.1007/s11214-015-0187-2)
DOI : 10.1007/s11214-015-0187-2
How to find magnetic nulls and reconstruct field topology with MMS data?
- Fu H.S.
- Vaivads A.
- Khotyaintsev Y. V.
- Olshevsky V.
- André M.
- Cao J.B.
- Huang S. Y.
- Retinò Alessandro
- Lapenta G.
Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2015, 120 (5), pp.3758-3782. In this study, we apply a new method―-the first-order Taylor expansion (FOTE)―-to find magnetic nulls and reconstruct magnetic field topology, in order to use it with the data from the forthcoming MMS mission. We compare this method with the previously used Poincare index (PI), and find that they are generally consistent, except that the PI method can only find a null inside the spacecraft (SC) tetrahedron, while the FOTE method can find a null both inside and outside the tetrahedron and also deduce its drift velocity. In addition, the FOTE method can (1) avoid limitations of the PI method such as data resolution, instrument uncertainty (Bz offset), and SC separation; (2) identify 3-D null types (A, B, As, and Bs) and determine whether these types can degenerate into 2-D (X and O); (3) reconstruct the magnetic field topology. We quantitatively test the accuracy of FOTE in positioning magnetic nulls and reconstructing field topology by using the data from 3-D kinetic simulations. The influences of SC separation (0.05~1 di) and null-SC distance (0~1 di) on the accuracy are both considered. We find that (1) for an isolated null, the method is accurate when the SC separation is smaller than 1 di, and the null-SC distance is smaller than 0.25~0.5 di; (2) for a null pair, the accuracy is same as in the isolated-null situation, except at the separator line, where the field is nonlinear. We define a parameter xi ≡ |( lambda1 lambda2 lambda3 )|/|lambda|max in terms of the eigenvalues (lambdai) of the null to quantify the quality of our method―-the smaller this parameter the better the results. Comparing to the previously used parameter (eta≡|∇ s B|/|∇ × B|), xi is more relevant for null identification. Using the new method, we reconstruct the magnetic field topology around a radial-type null and a spiral-type null, and find that the topologies are well consistent with those predicted in theory. We therefore suggest using this method to find magnetic nulls and reconstruct field topology with four-point measurements, particularly from Cluster and the forthcoming MMS mission. For the MMS mission, this null-finding algorithm can be used to trigger its burst-mode measurements. (10.1002/2015JA021082)
DOI : 10.1002/2015JA021082
Magnetized retarding field energy analyzer measuring the particle flux and ion energy distribution of both positive and negative ions
- Rafalskyi D.V.
- Dudin S.V.
- Aanesland Ane
Review of Scientific Instruments, American Institute of Physics, 2015, 86 (5), pp.053302. This paper presents the development of a magnetized retarding field energy analyzer (MRFEA) used for positive and negative ion analysis. The two-stage analyzer combines a magnetic electron barrier and an electrostatic ion energy barrier allowing both positive and negative ions to be analyzed without the influence of electrons (co-extracted or created downstream). An optimal design of the MRFEA for ion-ion beams has been achieved by a comparative study of three different MRFEA configurations, and from this, scaling laws of an optimal magnetic field strength and topology have been deduced. The optimal design consists of a uniform magnetic field barrier created in a rectangular channel and an electrostatic barrier consisting of a single grid and a collector placed behind the magnetic field. The magnetic barrier alone provides an electron suppression ratio inside the analyzer of up to 6000, while keeping the ion energy resolution below 5 eV. The effective ion transparency combining the magnetic and electrostatic sections of the MRFEA is measured as a function of the ion energy. It is found that the ion transparency of the magnetic barrier increases almost linearly with increasing ion energy in the low-energy range (below 200 eV) and saturates at high ion energies. The ion transparency of the electrostatic section is almost constant and close to the optical transparency of the entrance grid. We show here that the MRFEA can provide both accurate ion flux and ion energy distribution measurements in various experimental setups with ion beams or plasmas run at low pressure and with ion energies above 10 eV. (10.1063/1.4919730)
DOI : 10.1063/1.4919730

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