Publications

2009

• Cross-scale: multi-scale coupling in space plasmas
  
  • Schwartz S. J.
  • Horbury T.
  • Owen C.
  • Baumjohann W.
  • Nakamura R.
  • Canu Patrick
  • Roux A.
  • Sahraoui Fouad
  • Louarn P.
  • Sauvaud J.-A.
  • Pinçon Jean-Louis
  • Vaivads A.
  • Marcucci M. F.
  • Anastasiadis A.
  • Fujimoto M.
  • Escoubet P.
  • Taylor M.
  • Eckersley S.
  • Allouis E.
  • Perkinson M.-C.
  Experimental Astronomy, Springer Link, 2009, 23, pp.1001-1015. Most of the visible universe is in the highly ionised plasma state, and most of that plasma is collision-free. Three physical phenomena are responsible for nearly all of the processes that accelerate particles, transport material and energy, and mediate flows in systems as diverse as radio galaxy jets and supernovae explosions through to solar flares and planetary magnetospheres. These processes in turn result from the coupling amongst phenomena at macroscopic fluid scales, smaller ion scales, and down to electron scales. Cross-Scale, in concert with its sister mission SCOPE (to be provided by the Japan Aerospace Exploration AgencyJAXA), is dedicated to quantifying that nonlinear, time-varying coupling via the simultaneous in-situ observations of space plasmas performed by a fleet of 12 spacecraft in near-Earth orbit. Cross-Scale has been selected for the Assessment Phase of Cosmic Vision by the European Space Agency. (10.1007/s10686-008-9085-x)
  DOI : 10.1007/s10686-008-9085-x
• Global Scale-Invariant Dissipation in Collisionless Plasma Turbulence
  
  • Dunlop M. W.
  • Sahraoui Fouad
  • Kiyani K. H.
  • Chapman S. C.
  • Khotyaintsev Y. V.
  Physical Review Letters, American Physical Society, 2009, 103, pp.075006. A higher-order multiscale analysis of the dissipation range of collisionless plasma turbulence is presented using in situ high-frequency magnetic field measurements from the Cluster spacecraft in a stationary interval of fast ambient solar wind. The observations, spanning five decades in temporal scales, show a crossover from multifractal intermittent turbulence in the inertial range to non-Gaussian monoscaling in the dissipation range. This presents a strong observational constraint on theories of dissipation mechanisms in turbulent collisionless plasmas. (10.1103/PhysRevLett.103.075006)
  DOI : 10.1103/PhysRevLett.103.075006
• Electron transport coefficients in mixtures of CF<SUB>4</SUB> and CF<SUB>2</SUB> radicals
  
  • Nikitovic Zd
  • Stojanovic Vd
  • Booth Jean-Paul
  • Petrovic Zl
  Plasma Sources Science and Technology, IOP Publishing, 2009, 18, pp.035008. Electron kinetics determines the rate of production of chemically active species in processing plasmas. Precise transport coefficients are needed to describe conditions such as those found in plasma assisted technologies for semiconductor production, but these are affected by the density of free radicals, which in themselves depend on the chemical kinetics. We present transport coefficients for electrons in mixtures of CF4 with CF2 (and we also show similar results for other radicals) for ratios of the electric field to the gas number density E/N from 1 to 1000&#8201;Td (1&#8201;Td = 10&#8722;21&#8201;V&#8201;m2). Our analysis of non-conservative collisions revealed a range of E/N where electron attachment to radicals significantly changes the electron kinetics compared with pure CF4 gas. The results are obtained using simple solutions for Boltzmann's equation and exact Monte Carlo simulations. (10.1088/0963-0252/18/3/035008)
  DOI : 10.1088/0963-0252/18/3/035008
• Cascade models in plasma turbulence: The role of sheared flows
  
  • Gürcan Özgür D.
  • Garbet X.
  • Hennequin Pascale
  • Diamond P.H.
  • Casati A.
  , 2009 (oral).
• Magnetic island formation between large-scale flow vortices at an undulating postnoon magnetopause for northward interplanetary magnetic field
  
  • Cully C. M.
  • Larson D. E.
  • Ergun R. E.
  • Roux A.
  • Carlson C. W.
  • Eriksson S.
  • Hasegawa H.
  • Teh W.-L.
  • Sonnerup B. U. Ö.
  • Mcfadden J. P.
  • Glassmeier K.-H.
  • Le Contel Olivier
  • Angelopoulos V.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2009, 114. Time History of Events and Macroscale Interactions during Substorms multispacecraft observations are presented for a ~2-h-long postnoon magnetopause event on 8 June 2007 that for the first time indicate that the trailing (sunward) edges of Kelvin-Helmholtz (KH) waves are commonly related to small-scale <0.56 R <SUB> E </SUB> magnetic islands or flux transfer events (FTE) during the growth phase of these surface waves. The FTEs typically show a characteristic bipolar B <SUB> N </SUB> structure with enhanced total pressure at their center. Most of the small-scale FTEs are not related to any major plasma acceleration. TH-A observations of one small FTE at a transition from the low-latitude boundary layer (LLBL) into a magnetosheath plasma depletion layer were reconstructed using separate techniques that together confirm the presence of a magnetic island within the LLBL adjacent to the magnetopause. The island was associated with a small plasma vortex and both features appeared between two large-scale (~1 R <SUB> E </SUB> long and 2000 km wide) plasma vortices. We propose that the observed magnetic islands may have been generated from a time-varying reconnection process in a low ion plasma beta (beta <SUB> i </SUB> < 0.2) and low 8.3° field shear environment at the sunward edge of the growing KH waves where the local magnetopause current sheet may be compressed by the converging flow of the large-scale plasma vortices as suggested by numerical simulations of the KH instability. (10.1029/2008JA013505)
  DOI : 10.1029/2008JA013505
• An Observation Linking the Origin of Plasmaspheric Hiss to Discrete Chorus Emissions
  
  • Bortnik J.
  • Li W.
  • Thorne R. M.
  • Angelopoulos V.
  • Cully C. M.
  • Bonnell J. W.
  • Le Contel Olivier
  • Roux A.
  Science, American Association for the Advancement of Science (AAAS), 2009, 324 (5928), pp.775-778. A long-standing problem in the field of space physics has been the origin of plasmaspheric hiss, a naturally occurring electromagnetic wave in the high-density plasmasphere (roughly within 20,000 kilometers of Earth) that is known to remove the high-energy Van Allen Belt electrons that pose a threat to satellites and astronauts. A recent theory tied the origin of plasmaspheric hiss to a seemingly different wave in the outer magnetosphere, but this theory was difficult to test because of a challenging set of observational requirements. Here we report on the experimental verification of the theory, made with a five-satellite NASA mission. This confirmation will allow modeling of plasmaspheric hiss and its effects on the high-energy radiation environment. (10.1126/science.1171273)
  DOI : 10.1126/science.1171273
• Evaluation of whistler-mode chorus intensification on the nightside during an injection event observed on the THEMIS spacecraft
  
  • Li W.
  • Thorne R. M.
  • Angelopoulos V.
  • Bonnell J. W.
  • Mcfadden J. P.
  • Carlson C. W.
  • Le Contel Olivier
  • Roux A.
  • Glassmeier K.-H.
  • Auster H.-U.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2009, 114. The intensification of the nightside whistler-mode chorus emissions is observed in the low-density region outside the plasmapause during the injection of anisotropic plasma sheet electrons into the inner magnetosphere. Time History of Events and Macroscale Interactions During Substorms data of the electron phase space density over the energy range between 0.1 keV and 30 keV are used to develop an analytical model for the distribution of injected suprathermal electrons. The path-integrated gain of chorus waves is then evaluated with the HOTRAY code by tracing whistler-mode chorus waves in a hot magnetized plasma. The simulated wave gain is compared to the observed wave electric field and magnetic field, respectively. The results indicate that lower-energy (<1 keV) plasma sheet electrons can penetrate deeper toward the Earth but cause little chorus intensification, while higher-energy (1 keV to tens of kiloelectron volts) electrons can be injected at relatively higher L-shells and are responsible for the intensification of lower-band and upper-band whistler-mode chorus. Compared to the lower-band chorus, a relatively higher electron anisotropy is required to generate upper-band chorus. In addition, higher plasma density results in stronger wave intensity and a broader frequency band of chorus waves. (10.1029/2008JA013554)
  DOI : 10.1029/2008JA013554
• Quasi-thermal noise in space plasma: ``kappa'' distributions
  
  • Le Chat G.
  • Issautier K.
  • Meyer-Vernet N.
  • Zouganelis I.
  • Maksimovic M.
  • Moncuquet M.
  Physics of Plasmas, American Institute of Physics, 2009, 16, pp.102903. The transport of energy in collisionless plasmas, especially in space plasmas, is far from being understood. Measuring the temperature of the electrons and their nonthermal properties can give important clues to understand the transport properties. Quasi-thermal noise (QTN) spectroscopy is a reliable tool for measuring accurately the electron density and temperature since it is less sensitive to the spacecraft perturbations than particle detectors. This work models the plasma QTN using a generalized Lorentzian (``kappa'') distribution function for the electrons. This noise is produced by the quasi-thermal fluctuations of the electrons and by the Doppler-shifted thermal fluctuations of the ions. A sum of two Maxwellian functions has mainly been used for modeling the QTN of the electrons, but the observations have shown that the electrons are better fitted by a kappa distribution function. Pioneer work on QTN calculation only considered integer values of kappa. This paper extends these calculations to real values of kappa and gives the analytic expressions and numerical calculations of the QTN with a kappa distribution function. This paper shows some generic properties and gives some practical consequences for plasma wave measurements in space. (10.1063/1.3243495)
  DOI : 10.1063/1.3243495
• Auroral evidence for multiple reconnection in the magnetospheric tail plasma sheet
  
  • Treumann R. A.
  • Jaroschek C. H.
  • Pottelette Raymond
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2009, 85, pp.49001. We present auroral evidence for multiple and, most probably, small-scale reconnection in the near-Earth magnetospheric plasma sheet current layer during auroral activity. Hall currents as the source of upward and downward field-aligned currents require the generation of the corresponding electron fluxes. The auroral spatial ordering in a multiple sequence of these fluxes requires the assumption of the existence of several ―-and possibly―- even many tailward reconnection sites. (10.1209/0295-5075/85/49001)
  DOI : 10.1209/0295-5075/85/49001
• Observations of Double Layers in Earth's Plasma Sheet
  
  • Ergun R. E.
  • Andersson L.
  • Tao J. B.
  • Angelopoulos V.
  • Bonnell J. W.
  • Mcfadden J. P.
  • Larson D. E.
  • Eriksson S.
  • Johansson T.
  • Cully C. M.
  • Newman D. N.
  • Goldman M. V.
  • Roux A.
  • Le Contel Olivier
  • Glassmeier K.-H.
  • Baumjohann W.
  Physical Review Letters, American Physical Society, 2009, 102, pp.155002. We report the first direct observations of parallel electric fields (E<SUB>||</SUB>) carried by double layers (DLs) in the plasma sheet of Earth's magnetosphere. The DL observations, made by the THEMIS spacecraft, have E<SUB>||</SUB> signals that are analogous to those reported in the auroral region. DLs are observed during bursty bulk flow events, in the current sheet, and in plasma sheet boundary layer, all during periods of strong magnetic fluctuations. These observations imply that DLs are a universal process and that strongly nonlinear and kinetic behavior is intrinsic to Earth's plasma sheet. (10.1103/PhysRevLett.102.155002)
  DOI : 10.1103/PhysRevLett.102.155002
• NO production on pyrex under, and after plasma exposure
  
  • Marinov Daniil
  • Guaitella Olivier
  • Rousseau Antoine
  , 2009.
• Mechanisms of filamentary plasma/catalyst coupling for air treatment
  
  • Guaitella Olivier
  • Rousseau Antoine
  • Allegraud Katia
  • Celestin S.
  , 2009.
• Kinetics of ignition of saturated hydrocarbons by nonequilibrium plasma : C<SUB>2</SUB>H<SUB>6</SUB>- to C<SUB>5</SUB>H<SUB>12</SUB>-containing mixtures
  
  • Kosarev I.N.
  • Aleksandrov N.L.
  • Kindysheva S.V.
  • Starikovskaia Svetlana
  • Starikovskii A.Yu.
  Combustion and Flame, Elsevier, 2009, 156 (1), pp.221-233. The kinetics of ignition in CnH2n 2:O2:Ar mixtures for n = 2 to 5 has been studied experimentally and numerically after a high-voltage nanosecond discharge. The ignition delay time behind a reflected shock wave was measured with and without the discharge. It was shown that the initiation of the discharge with a specific deposited energy of 1030 mJ/cm3 leads to an order of magnitude decrease in the ignition delay time. Discharge processes and following chain chemical reactions with energy release were simulated. The generation of atoms, radicals and excited and charged particles was numerically simulated using the measured time-resolved discharge current and electric field in the discharge phase. The calculated densities of the active particles were used as input data to simulate plasma-assisted ignition. The sensitivity of the results to variation in electron cross sections, reaction rates and radical composition was investigated. Good agreement was obtained between the calculated ignition delay times and the experimental data. The analysis of the simulation results showed that the effect of nonequilibrium plasma on the ignition delay is associated with faster development of chain reactions, due to atoms and radicals produced by the electron impact dissociation of molecules in the discharge phase. Finally, we studied the role of various hydrocarbon radicals in the plasma-assisted ignition of the mixtures under consideration. (10.1016/j.combustflame.2008.07.013)
  DOI : 10.1016/j.combustflame.2008.07.013
• Edge-to-center plasma density ratio in high density plasma sources
  
  • Raimbault Jean-Luc
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2009, 18, pp.014017. The flux of positive ions leaving a classical low-temperature plasma discharge is proportional to the plasma density at the plasmasheath edge, and the edge-to-center plasma density ratio, the so-called hl factor, normally depends only on the discharge size and the neutral gas pressure. The ion flux leaving the discharge is therefore linearly proportional to the central plasma density. The hl factor has been previously derived by solving the plasma transport equations over a large pressure range, with the assumption of constant neutral gas density within the discharge. Tonks and Langmuir derived the low pressure (collisionless) solution of this problem in 1929. More recent works have shown that the neutral gas density is no longer constant when the plasma pressure becomes comparable to the neutral gas pressure. In this paper, we solve the plasma transport equations in this new situation and we propose a new expression for the hl factor. It is shown that hl becomes a function of the central plasma density which implies that the ion flux leaving the discharge is no longer proportional to this density. This effect has to be included in particle and energy balance equations used in global models of high density plasma sources. (10.1088/0963-0252/18/1/014017)
  DOI : 10.1088/0963-0252/18/1/014017
• Study of hydrogen plasma in the negative-ion extraction region
  
  • Svarnas P.
  • Annaratone B.M.
  • Béchu Stéphane
  • Pelletier J.
  • Bacal M.
  Plasma Sources Science and Technology, IOP Publishing, 2009, 18, pp.045010. (10.1088/0963-0252/18/4/045010)
  DOI : 10.1088/0963-0252/18/4/045010
• Regeneration of adsorbent/catalytic material by a Dielectric Barrier Discharge (DBD)
  
  • Youssef Joseph
  • Bouamra K.
  • Makarov M.
  • Guaitella Olivier
  • Rousseau Antoine
  , 2009.
• Influence of dielectric material on chemistry reactivity in Dielectric Barrier Discharge (DBD)
  
  • Youssef Joseph
  • Bouamra K.
  • Makarov M.
  • Guaitella Olivier
  • Rousseau Antoine
  , 2009.
• Global distribution of whistler-mode chorus waves observed on the THEMIS spacecraft
  
  • Li W.
  • Thorne R. M.
  • Angelopoulos V.
  • Bortnik J.
  • Cully C. M.
  • Ni B.
  • Le Contel Olivier
  • Roux A.
  • Auster U.
  • Magnes W.
  Geophysical Research Letters, American Geophysical Union, 2009, 36, pp.9104. Whistler mode chorus waves are receiving increased scientific attention due to their important roles in both acceleration and loss processes of radiation belt electrons. A new global survey of whistler-mode chorus waves is performed using magnetic field filter bank data from the THEMIS spacecraft with 5 probes in near-equatorial orbits. Our results confirm earlier analyses of the strong dependence of wave amplitudes on geomagnetic activity, confinement of nightside emissions to low magnetic latitudes, and extension of dayside emissions to high latitudes. An important new finding is the strong occurrence rate of chorus on the dayside at L > 7, where moderate dayside chorus is present >10% of the time and can persist even during periods of low geomagnetic activity. (10.1029/2009GL037595)
  DOI : 10.1029/2009GL037595
• Electrostatic solitary waves in current layers: from Cluster observations during a super-substorm to beam experiments at the LAPD
  
  • Pickett J. S.
  • Chen L.-J.
  • Santolík O.
  • Grimald S.
  • Lavraud B.
  • Verkhoglyadova O. P.
  • Tsurutani B. T.
  • Lefebvre B.
  • Fazakerley A.
  • Lakhina G. S.
  • Ghosh S. S.
  • Grison B.
  • Décréau Pierrette
  • Gurnett D. A.
  • Torbert R.
  • Cornilleau-Wehrlin Nicole
  • Dandouras I.
  • Lucek E.
  Nonlinear Processes in Geophysics, European Geosciences Union (EGU), 2009, 16 (3), pp.431-442. Electrostatic Solitary Waves (ESWs) have been observed by several spacecraft in the current layers of Earth's magnetosphere since 1982. ESWs are manifested as isolated pulses (one wave period) in the high time resolution waveform data obtained on these spacecraft. They are thus nonlinear structures generated out of nonlinear instabilities and processes. We report the first observations of ESWs associated with the onset of a super-substorm that occurred on 24 August 2005 while the Cluster spacecraft were located in the magnetotail at around 18-19 R<SUB>E</SUB> and moving northward from the plasma sheet to the lobes. These ESWs were detected in the waveform data of the WBD plasma wave receiver on three of the Cluster spacecraft. The majority of the ESWs were detected about 5 min after the super-substorm onset during which time 1) the PEACE electron instrument detected significant field-aligned electron fluxes from a few 100 eV to 3.5 keV, 2) the EDI instrument detected bursts of field-aligned electron currents, 3) the FGM instrument detected substantial magnetic fluctuations and the presence of Alfvén waves, 4) the STAFF experiment detected broadband electric and magnetic waves, ion cyclotron waves and whistler mode waves, and 5) CIS detected nearly comparable densities of H and O ions and a large tailward H velocity. We compare the characteristics of the ESWs observed during this event to those created in the laboratory at the University of California-Los Angeles Plasma Device (LAPD) with an electron beam. We find that the time durations of both space and LAPD ESWs are only slightly larger than the respective local electron plasma periods, indicating that electron, and not ion, dynamics are responsible for generation of the ESWs. We have discussed possible mechanisms for generating the ESWs in space, including the beam and kinetic Buneman type instabilities and the acoustic instabilities. Future studies will examine these mechanisms in more detail using the space measurements as inputs to models, and better relate the ESW space measurements to the laboratory through PIC code models. (10.5194/npg-16-431-2009)
  DOI : 10.5194/npg-16-431-2009
• Influence of dielectric material in Dielectric Barrier Discharge (DBD) for chemistry reactivity control
  
  • Youssef Joseph
  • Bouamra K.
  • Makarov M.
  • Guaitella Olivier
  • Rousseau Antoine
  , 2009.
• Oblique propagation of whistler mode waves in the chorus source region
  
  • Santolík O.
  • Gurnett D. A.
  • Pickett J. S.
  • Chum J.
  • Cornilleau-Wehrlin Nicole
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2009, 114. Whistler mode chorus has been shown to play a role in the process of local acceleration of electrons in the outer Van Allen radiation belt. Most of the quasi-linear and nonlinear theoretical studies assume that the waves propagate parallel to the terrestrial magnetic field. We show a case where this assumption is invalid. We use data from the Cluster spacecraft to characterize propagation and spectral properties of chorus. The recorded high-resolution waveforms show that chorus in the source region can be formed by a succession of discrete wave packets with decreasing frequency that sometimes change into shapeless hiss. These changes occur at the same time in the entire source region. Multicomponent measurements show that waves in both these regimes can be found at large angles to the terrestrial magnetic field. The hiss intervals contain waves propagating less than one tenth of a degree from the resonance cone. In the regime of discrete wave packets the peak of the wave energy density is found at a few degrees from the resonance cone in a broad interval of azimuth angles. The wave intensity increases with the distance from the magnetic field minimum along a given field line, indicating a gradual amplification of chorus in the source region. (10.1029/2009JA014586)
  DOI : 10.1029/2009JA014586
• Self synchronization of surface discharges in a two electrodes device
  
  • Allegraud Katia
  • Rousseau Antoine
  IEEE Transactions on Dielectrics and Electrical Insulation, Institute of Electrical and Electronics Engineers, 2009, 16 (2), pp.435-439. A twin electrode device coupled to the same high voltage power supply is used to study the propagation of surface streamers. These two identical electrodes are separated from the grounded one by a pyrex plate acting as a dielectric barrier. The gas is dry air, at atmospheric pressure. 1 ns time resolved imaging of the discharge propagation is performed to monitor the discharge ignition and propagation. The discharge consists in filaments which propagate on the dielectric as cathode directed streamers. Each filament transfers 1 nC. The propagation velocities vary from 3.4times107 cm/s at the beginning of the propagation to 7times106 cm/s at the end of the propagation. Ignition at one electrode triggers ignition at the other within 2 ns. (10.1109/TDEI.2009.4815175)
  DOI : 10.1109/TDEI.2009.4815175
• Enhanced confinement with increased extent of the low magnetic shear region in tokamak plasmas
  
  • Nasi L.
  • Firpo Marie-Christine
  Plasma Physics and Controlled Fusion, IOP Publishing, 2009, 51, pp.045006. The Hamiltonian representation of magnetic field lines enables one to study their confinement properties in tokamaks through the use of symplectic maps such as the symmetric tokamap and its bounded version, the latter being introduced here. In this time-independent purely magnetic framework, we observed the drastic improvement in the confinement of magnetic field lines produced by the local vanishing of the shear profile. This amounts to a non-twist condition that notably acts in the same way the safety profile being (non-strictly) monotonic or having a reversed shear. We single out the effect of the amount of flatness of the safety profile in the vicinity of its zero shear point. All other things being equal, the beneficial effect of the vanishing of the shear profile is shown to be increased if the radial extent of the low-shear region is increased. To be specific, the low-shear region induces the formation of a belt of robust KAM tori acting as an internal transport barrier whose width is all the larger as the extent of the low-shear region is broad. (10.1088/0741-3335/51/4/045006)
  DOI : 10.1088/0741-3335/51/4/045006
• Wave-Number Spectrum of Drift-Wave Turbulence
  
  • Gürcan Özgür D.
  • Garbet X.
  • Hennequin Pascale
  • Diamond P.H.
  • Casati A.
  • Falchetto G. L.
  Physical Review Letters, American Physical Society, 2009, 102, pp.255002. A simple model for the evolution of turbulence fluctuation spectra, which includes neighboring interactions leading to the usual dual cascade as well as disparate scale interactions corresponding to refraction by large scale structures, is derived. The model recovers the usual Kraichnan-Kolmogorov picture in the case of exclusively local interactions and midrange drive. On the other hand, when disparate scale interactions are dominant, a simple spectrum for the density fluctuations of the form |nk|2&#8733;k&#8722;3/(1 k2)2 is obtained. This simple prediction is then compared to, and found to be in fair agreement with, Tore Supra CO2 laser scattering data. (10.1103/PhysRevLett.102.255002)
  DOI : 10.1103/PhysRevLett.102.255002
• Time-dependent hydrodynamical simulations of slow solar wind, coronal inflows, and polar plumes
  
  • Pinto Rui
  • Grappin Roland
  • Wang Y-M
  • Léorat Jacques
  Astronomy & Astrophysics - A&A, EDP Sciences, 2009, 497 (2), pp.537--543. Aims. We explore the effects of varying the areal expansion rate and coronal heating function on the solar wind flow. Methods. We use a one-dimensional, time-dependent hydrodynamical code. The computational domain extends from near the photosphere, where nonreflecting boundary conditions are applied, to 30 , and includes a transition region where heat conduction and radiative losses dominate. Results. We confirm that the observed inverse relationship between asymptotic wind speed and expansion factor is obtained if the coronal heating rate is a function of the local magnetic field strength. We show that inflows can be generated by suddenly increasing the rate of flux-tube expansion and suggest that this process may be involved in the closing-down of flux at coronal hole boundaries. We also simulate the formation and decay of a polar plume, by including an additional, time-dependent heating source near the base of the flux tube. (10.1051/0004-6361/200811183)
  DOI : 10.1051/0004-6361/200811183