Publications

2021

• Chemical kinetics and density measurements of OH in an atmospheric pressure He + O2 + H2O radiofrequency plasma
  
  • Brisset Alexandra
  • Gibson Andrew
  • Schröter Sandra
  • Niemi Kari
  • Booth Jean-Paul
  • Gans Timo
  • O'Connell Deborah
  • Wagenaars Erik
  Journal of Physics D: Applied Physics, IOP Publishing, 2021, 54 (28), pp.285201. This work presents experiments and modelling of OH densities in a radio-frequency driven atmospheric-pressure plasma in a plane-parallel geometry, operated in helium with small admixtures of oxygen and water vapour (He + O2 + H2O). The density of OH is measured under a wide range of conditions by absorption spectroscopy, using an ultra-stable laser-driven broad-band light source. These measurements are compared with 0D plasma chemical kinetics simulations adapted for high levels of O2 (1%). Without O2 admixture, the measured density of OH increases from 1.0 × 1014 to 4.0 × 1014 cm−3 for H2O admixtures from 0.05% to 1%. The density of atomic oxygen is about 1 × 1013 cm−3 and grows with humidity content. With O2 admixture, the OH density stays relatively constant, showing only a small maximum at 0.1% O2. The simulations predict that the atomic oxygen density is strongly increased by O2 addition. It reaches ~1015 cm−3 without humidity, but is limited to ~1014 cm−3 beyond 0.05% water content. The addition of O2 has a weak effect on the OH density because, while atomic oxygen becomes a dominant precursor for the formation of OH, it makes a nearly equal contribution to the loss processes of OH. The small increase in the density of OH with the addition of O2 is instead due to reaction pathways involving increased production of HO2 and O3. The simulations show that the densities of OH, O and O3 can be tailored relatively independently over a wide range of conditions. The densities of O and O3 are strongly affected by the presence of small quantities (0.05%) of water vapour, but further water addition has little effect. Therefore, a greater range and control of the reactive species mix from the plasma can be obtained by the use of well-controlled multiple gas admixtures, instead of relying on ambient air mixing. (10.1088/1361-6463/abefec)
  DOI : 10.1088/1361-6463/abefec
• Study of two interacting interplanetary coronal mass ejections encountered by Solar Orbiter during its first perihelion passage. Observations and modeling
  
  • Telloni D.
  • Scolini C.
  • Möstl C.
  • Zank G.
  • Zhao L.
  • Weiss A.
  • Reiss M.
  • Laker R.
  • Perrone D.
  • Khotyaintsev Y.
  • Steinvall K.
  • Sorriso-Valvo L.
  • Horbury T.
  • Wimmer-Schweingruber R.
  • Bruno R.
  • d'Amicis R.
  • de Marco R.
  • Jagarlamudi V.
  • Marino Raffaele
  • Stangalini M.
  • Nakanotani M.
  • Adhikari L.
  • Liang Haoming
  • Woodham L. D.
  • Davies Emma
  • Hietala H.
  • Perri Silvia
  • Gómez-Herrero R
  • Rodríguez-Pacheco J.
  • Antonucci Ester
  • Romoli Marco
  • Fineschi Silvano
  • Maksimovic M.
  • Souček J.
  • Chust T.
  • Kretzschmar M.
  • Vecchio Antonio
  • Müller Daniela
  • Zouganelis Yannis
  • Winslow R. M.
  • Giorndano S.
  • Mancuso S.
  • Susino R.
  • Ivanovski S. L.
  • Messarotti M.
  • O'Brien H.
  • Evans Vincent
  • Angelini Virginia
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021. Context. Solar Orbiter, the new-generation mission dedicated to solar and heliospheric exploration, was successfully launched on February 10, 2020, 04:03 UTC from Cape Canaveral. During its first perihelion passage in June 2020, two successive interplanetary coronal mass ejections (ICMEs), propagating along the heliospheric current sheet (HCS), impacted the spacecraft. Aims. This paper addresses the investigation of the ICMEs encountered by Solar Orbiter on June 7-8, 2020, from both an observational and a modeling perspective. The aim is to provide a full description of those events, their mutual interaction, and their coupling with the ambient solar wind and the HCS. Methods. Data acquired by the MAG magnetometer, the Energetic Particle Detector (EPD) suite, and the Radio and Plasma Waves (RPW) instrument are used to provide information on the ICMEs’ magnetic topology configuration, their magnetic connectivity to the Sun, and insights into the heliospheric plasma environment where they travel, respectively. On the modeling side, the Heliospheric Upwind eXtrapolation (HUX) model, the 3D COronal Rope Ejection (3DCORE) technique, and the EUropean Heliospheric FORecasting Information Asset (EUHFORIA) tool are used to complement Solar Orbiter observations of the ambient solar wind and ICMEs, and to simulate the evolution and interaction of the ejecta in the inner heliosphere, respectively. Results. Both data analysis and numerical simulations indicate that the passage of two distinct, dynamically and magnetically interacting (via magnetic reconnection processes) ICMEs at Solar Orbiter is a possible scenario, supported by the numerous similarities between EUHFORIA time series at Solar Orbiter and Solar Orbiter data. Conclusions. The combination of in situ measurements and numerical simulations (together with remote sensing observations of the corona and inner heliosphere) will significantly lead to a deeper understanding of the physical processes occurring during the CME-CME interaction (10.1051/0004-6361/202140648)
  DOI : 10.1051/0004-6361/202140648
• The Plasma Universe: A Coherent Science Theme for Voyage 2050
  
  • Verscharen Daniel
  • Wicks Robert T.
  • Branduardi-Raymont Graziella
  • Erdélyi Robertus
  • Frontera Filippo
  • Götz Charlotte
  • Guidorzi Cristiano
  • Lebouteiller Vianney
  • Matthews Sarah A.
  • Nicastro Fabrizio
  • Rae Iain Jonathan
  • Retinò Alessandro
  • Simionescu Aurora
  • Soffitta Paolo
  • Uttley Phil
  • Wimmer-Schweingruber Robert F.
  Frontiers in Astronomy and Space Sciences, Frontiers Media, 2021, 8, pp.651070. In review of the White Papers from the Voyage 2050 process and after the public presentation of a number of these papers in October 2019 in Madrid, we as White Paper lead authors have identified a coherent science theme that transcends the divisions around which the Topical Teams are structured. This note aims to highlight this synergistic science theme and to make the Topical Teams and the Voyage 2050 Senior Committee aware of the wide importance of these topics and the broad support that they have across the worldwide science community. (10.3389/fspas.2021.651070)
  DOI : 10.3389/fspas.2021.651070
• Development of research capacities in space weather: a successful international cooperation
  
  • Amory-Mazaudier Christine
  • Radicella Sandro
  • Doherty Patricia
  • Gadimova Sharafat
  • Fleury Rolland
  • Nava Bruno
  • Anas Emran
  • Petitdidier Monique
  • Migoya-Orué Yenca
  • Alazo-Cuartas Katy
  • Shiokawa Kazuo
  Journal of Space Weather and Space Climate, EDP sciences, 2021, 11, pp.28. This paper presents an international cooperation which has successfully developed research capacities in the scientific disciplines of sun–earth relations and space weather in many countries over the world during the past decades. This success was based on the deployment of scientific instruments in countries that did not have them, on the sharing of knowledge and research tools, on thesis supervision and on the integration of researchers trained in their country. This article will only focus on aspects of training conducted by ICTP, Boston College, ICG, SCOSTEP and GIRGEA. We will highlight what has been enhanced in international cooperation to achieve this success and what remains to be done. (10.1051/swsc/2021006)
  DOI : 10.1051/swsc/2021006
• Solar wind current sheets and deHoffmann-Teller analysis. First results from Solar Orbiter's DC electric field measurements
  
  • Steinvall K.
  • Khotyaintsev Yu. V.
  • Cozzani G.
  • Vaivads A.
  • Yordanova E.
  • Eriksson A. I.
  • Edberg N. J. T.
  • Maksimovic M.
  • Bale S. D.
  • Chust Thomas
  • Krasnoselskikh V.
  • Kretzschmar M.
  • Lorfèvre E.
  • Plettemeier D.
  • Souček J.
  • Steller M.
  • Štverák Š.
  • Vecchio A.
  • Horbury T. S.
  • O'Brien H.
  • Evans V.
  • Fedorov A.
  • Louarn P.
  • Génot V.
  • André N.
  • Lavraud B.
  • Rouillard A. P.
  • Owen C. J.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.7 pp.. Context. Solar Orbiter was launched on 10 February 2020 with the purpose of investigating solar and heliospheric physics using a payload of instruments designed for both remote and in situ studies. Similar to the recently launched Parker Solar Probe, and unlike earlier missions, Solar Orbiter carries instruments designed to measure low-frequency DC electric fields. Aims: In this paper, we assess the quality of the low-frequency DC electric field measured by the Radio and Plasma Waves instrument (RPW) on Solar Orbiter. In particular, we investigate the possibility of using Solar Orbiter's DC electric and magnetic field data to estimate the solar wind speed. Methods: We used a deHoffmann-Teller (HT) analysis, based on measurements of the electric and magnetic fields, to find the velocity of solar wind current sheets, which minimises a single component of the electric field. By comparing the HT velocity to the proton velocity measured by the Proton and Alpha particle Sensor (PAS), we have developed a simple model for the effective antenna length, L<SUB>eff</SUB> of the E-field probes. We then used the HT method to estimate the speed of the solar wind. Results: Using the HT method, we find that the observed variations in E<SUB>y</SUB> are often in excellent agreement with the variations in the magnetic field. The magnitude of E<SUB>y</SUB>, however, is uncertain due to the fact that the L<SUB>eff</SUB> depends on the plasma environment. Here, we derive an empirical model relating L<SUB>eff</SUB> to the Debye length, which we can use to improve the estimate of E<SUB>y</SUB> and, consequently, the estimated solar wind speed. Conclusions: The low-frequency electric field provided by RPW is of high quality. Using the deHoffmann-Teller analysis, Solar Orbiter's magnetic and electric field measurements can be used to estimate the solar wind speed when plasma data are unavailable. (10.1051/0004-6361/202140855)
  DOI : 10.1051/0004-6361/202140855
• Solar Wind—Magnetosphere Coupling During Radial Interplanetary Magnetic Field Conditions: Simultaneous Multi‐Point Observations
  
  • Toledo‐redondo S
  • Hwang K.-J.
  • Escoubet C P
  • Lavraud B
  • Fornieles J
  • Aunai N
  • Fear R C
  • Dargent J
  • Fu H. S
  • Fuselier S. A.
  • Genestreti K. J.
  • Khotyaintsev Yu. V.
  • Li W. Y.
  • Norgren C
  • Phan T. D.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2021, 126 (11), pp.e2021JA029506. In-situ spacecraft missions are powerful assets to study processes that occur in space plasmas. One of their main limitations, however, is extrapolating such local measurements to the global scales of the system. To overcome this problem at least partially, multi-point measurements can be used. There are several multi-spacecraft missions currently operating in the Earth's magnetosphere, and the simultaneous use of the data collected by them provides new insights into the large-scale properties and evolution of magnetospheric plasma processes. In this work, we focus on studying the Earth's magnetopause (MP) using a conjunction between the Magnetospheric Multiscale and Cluster fleets, when both missions skimmed the MP for several hours at distant locations during radial interplanetary magnetic field (IMF) conditions. The observed MP positions as a function of the evolving solar wind conditions are compared to model predictions of the MP. We observe an inflation of the magnetosphere (∼0.7 RE), consistent with magnetosheath pressure decrease during radial IMF conditions, which is less pronounced on the flank (urn:x-wiley:21699380:media:jgra56856:jgra56856-math-00010.2 RE). There is observational evidence of magnetic reconnection in the subsolar region for the whole encounter, and in the dusk flank for the last portion of the encounter, suggesting that reconnection was extending more than 15 RE. However, reconnection jets were not always observed, suggesting that reconnection was patchy, intermittent or both. Shear flows reduce the reconnection rate up to ∼30% in the dusk flank according to predictions, and the plasma β enhancement in the magnetosheath during radial IMF favors reconnection suppression by the diamagnetic drift. (10.1029/2021JA029506)
  DOI : 10.1029/2021JA029506
• Identification of Electron Diffusion Regions with a Machine Learning approach on MMS data at the Earth's magnetopause
  
  • Lenouvel Q.
  • Génot V.
  • Garnier P.
  • Toledo‐redondo S.
  • Lavraud B.
  • Aunai N.
  • Nguyen G.
  • Gershman D.
  • Ergun R.
  • Lindqvist P.‐a.
  • Giles B.
  • Burch J.
  Earth and Space Science, American Geophysical Union/Wiley, 2021. (10.1029/2020EA001530)
  DOI : 10.1029/2020EA001530
• Overview of the isotope effects in the ASDEX Upgrade tokamak
  
  • Schneider P A
  • Hennequin Pascale
  • Bonanomi N
  • Dunne M
  • Conway G D
  • Plank U
  Plasma Physics and Controlled Fusion, IOP Publishing, 2021, 63 (6), pp.064006. In recent years, measurements on the ASDEX Upgrade tokamak and modelling performed for plasmas with hydrogen (H) and deuterium (D) as the main gas have improved our understanding of the ion mass dependencies in fusion plasmas. The observed isotope effects can be explained with established physics processes which highlight the importance of treating heat transport with coupled electron and ion heat channels. In the core of electron heated L-mode plasmas, the mass dependence of the electron–ion equipartition results in a reduction of $q_\textrm{i}/q_\textrm{e}$ with increasing ion mass. Combined with higher profile stiffness in the ions compared to the electrons, this results in improved core confinement for higher ion masses. At the edge of L-mode plasmas where a higher collisionality is observed, parallel electron dynamics is fundamental for turbulence. The parallel electron dynamics term in the gyrokinetic equations directly depends on $m_\textrm{i}/m_\textrm{e}$, resulting in a different kinetic response with different ion mass. Higher turbulent fluxes are expected with lower ion mass. This is consistent with the difference in $L_{n\textrm{e}}$ observed in the experiment. The mass dependence of turbulent transport in the L-mode edge has direct consequences for the L–H transition. More heating power is required to enter the H-mode at lower mass ($P_\textrm{L-H}^\textrm{H}\sim 2 P_\textrm{L-H}^\textrm{D}$). This is expected if the critical E × B shearing rate $\gamma_{E\times B}$ is important for the transition from L to H mode. In the H-mode pedestal, $\gamma_{E\times B}$ remains important to regulate the turbulent transport. The electrons do not contribute to $\gamma_{E\times B}$ and the enhanced equipartition for lower ion masses causes a shift from the ion channel to the electron channel in the absolute heat fluxes. Consequently, the inter edge localised mode (ELM) transport is found to be higher with lower isotope mass. This enhanced transport in H can prevent the pedestal from reaching the peeling–ballooning stability boundary with engineering parameters where D plasmas are peeling–ballooning unstable. Increasing the triangularity reduces the inter ELM transport in H stronger than in comparable D plasmas. For matched pedestal top and matched heat sources, the core heat transport is found to be similar for H and D when the fast-ion content is low. When ion temperature gradient turbulence stabilisation by fast ions becomes relevant, the mass dependent fast-ion slowing down results in higher fast-ion content in D and therefore in a reduction of ion heat transport in the core. Then, even for matched pedestals $\tau_\textrm{E}^\textrm{D}\gt\tau_\textrm{E}^\textrm{H}$. (10.1088/1361-6587/abf540)
  DOI : 10.1088/1361-6587/abf540
• Advances in non-equilibrium CO₂ plasma kinetics: a theoretical and experimental review
  
  • Pietanza Lucia Daniela
  • Guaitella Olivier
  • Aquilanti Vincenzo
  • Armenise Iole
  • Bogaerts Annemie
  • Capitelli Mario
  • Colonna Gianpiero
  • Guerra Vasco
  • Engeln Richard
  • Kustova Elena
  • Lombardi Andrea
  • Palazzetti Federico
  • Silva Tiago
  The European Physical Journal D : Atomic, molecular, optical and plasma physics, EDP Sciences, 2021, 75 (9), pp.237. Numerous applications have required the study of CO₂ plasmas since the 1960s, from CO₂ lasers to spacecraft heat shields. However, in recent years, intense research activities on the subject have restarted because of environmental problems associated with CO₂ emissions. The present review provides a synthesis of the current state of knowledge on the physical chemistry of cold CO₂ plasmas. In particular, the different modeling approaches implemented to address specific aspects of CO₂ plasmas are presented. Throughout the paper, the importance of conducting joint experimental, theoretical and modeling studies to elucidate the complex couplings at play in CO₂ plasmas is emphasized. Therefore the experimental data that are likely to bring relevant constraints to the different modeling approaches are first reviewed. Second, the calculation of some key elementary processes obtained with semi-empirical, classical and quantum methods is presented. In order to describe the electron kinetics, the latest coherent sets of cross section satisfying the constraints of “electron swarm” analyses are introduced, and the need for self-consistent calculations for determining accurate Electron Energy Distribution Function (EEDF) is evidenced. The main findings of the latest zero-dimensional (0D) global models about the complex chemistry of CO₂ and its dissociation products in different plasma discharges are then given, and full State-to-State (STS) models of only the vibrational-dissociation kinetics developed for studies of spacecraft shields are described. Finally, two important points for all applications using CO₂ containing plasma are discussed: the role of surfaces in contact with the plasma, and the need for 2D/3D models to capture the main features of complex reactor geometries including effects induced by fluid dynamics on the plasma properties. In addition to bringing together the latest advances in the description of CO₂ non equilibrium plasmas, the results presented here also highlight the fundamental data that are still missing and the possible routes that still need to be investigated. (10.1140/epjd/s10053-021-00226-0)
  DOI : 10.1140/epjd/s10053-021-00226-0
• Magnetic signatures of ionospheric disturbance dynamo for CME and HSSWs generated storms
  
  • Younas Waqar
  • Amory‐mazaudier C.
  • Khan Majid
  • Le Huy M.
  Space Weather: The International Journal of Research and Applications, American Geophysical Union (AGU), 2021. Ionospheric disturbance dynamo is one of the main processes that causes perturbations in the upper atmosphere during a magnetic storm. We present a new method, based on the least square fitting, for estimation of the magnetic signatures associated with ionospheric disturbance currents. Using a wavelet semblance analysis, the durations of disturbance dynamo electric fields have been investigated at three longitudinal sectors. For that we have analyzed the disturbance dynamo (Ddyn) for 19 magnetic storms. It has been found that during CME generated storms magnetic signature of Ddyn may be observed – depending on strength of the storm as well as on the duration of interplanetary magnetic field (IMF) Bz southward – in one, two or all three longitudes. The Oscillatory behavior of IMF Bz during the high-speed solar wind streams (HSSWs) generates Ddyn globally and the corresponding effects are observed at all low latitude magnetic observatories. In this regard, the Joule heating estimation shows that CME and HSSWs generated storms have very different patterns. The Ddyn duration is found to be maximum for the storms occurring during equinox season. Moreover, the HSSWs events are more likely to cause – because of the oscillatory IMF Bz – long lasting Ddyn as compared to CME generated counterpart. This study presents a detailed analysis of disturbance dynamo as affected by longitudinal and seasonal variations. In this regard the difference in magnetic signatures, of CME and HSSWs originated storms, have been highlighted. (10.1029/2021SW002825)
  DOI : 10.1029/2021SW002825
• Cassini‐Plasma Interaction Simulations Revealing the Cassini Ion Wake Characteristics: Implications for In‐Situ Data Analyses and Ion Temperature Estimates
  
  • Holmberg M.
  • Cipriani F.
  • Nilsson T.
  • Hess S.
  • Huybrighs H.
  • Hadid L. Z.
  • Déprez G.
  • Wilson R.
  • Morooka M.
  • Felici M.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2021, 126 (8), pp.e2020JA029026. We have used Spacecraft Plasma Interaction Software (SPIS) simulations to study the characteristics (i.e., dimensions, ion depletion, and evolution with the changing spacecraft attitude) of the Cassini ion wake. We focus on two regions, the plasma disk at 4.5–4.7 RS, where the most prominent wake structure will be formed, and at 7.6 RS, close to the maximum distance at which a wake structure can be detected in the Cassini Langmuir probe (LP) data. This study also reveals how the ion wake and the spacecraft plasma interaction have impacted the Cassini LP measurements in the studied environments, for example, with a strong decrease in the measured ion density but with minor interference from the photoelectrons and secondary electrons originating from the spacecraft. The simulated ion densities and spacecraft potentials are in very good agreement with the LP measurements. This shows that SPIS is an excellent tool to use for analyses of LP data, when spacecraft material properties and environmental parameters are known and used correctly. The simulation results are also used to put constraints on the ion temperature estimates in the inner magnetosphere of Saturn. The best agreement between the simulated and measured ion density is obtained using an ion temperature of 8 eV at ∼4.6 RS. This study also shows that SPIS simulations can be used in order to better constrain plasma parameters in regions where accurate measurements are not available. (10.1029/2020JA029026)
  DOI : 10.1029/2020JA029026
• Statistical study of electron density turbulence and ion-cyclotron waves in the inner heliosphere: Solar Orbiter observations
  
  • Carbone F.
  • Sorriso-Valvo L.
  • Khotyaintsev Yu. V.
  • Steinvall K.
  • Vecchio A.
  • Telloni D.
  • Yordanova E.
  • Graham D. B.
  • Edberg N. J. T.
  • Eriksson A. I.
  • Johansson E. P. G.
  • Vásconez C. L.
  • Maksimovic M.
  • Bruno R.
  • d'Amicis R.
  • Bale S. D.
  • Chust T.
  • Krasnoselskikh V.
  • Kretzschmar M.
  • Lorfèvre E.
  • Plettemeier D.
  • Souček J.
  • Steller M.
  • Štverák Š.
  • Trávníček P.
  • Vaivads A.
  • Horbury T. S.
  • O'Brien H.
  • Angelini V.
  • Evans V.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.16 pp.. Context. The recently released spacecraft potential measured by the RPW instrument on board Solar Orbiter has been used to estimate the solar wind electron density in the inner heliosphere. Aims: The measurement of the solar wind's electron density, taken in June 2020, has been analysed to obtain a thorough characterization of the turbulence and intermittency properties of the fluctuations. Magnetic field data have been used to describe the presence of ion-scale waves. Methods: To study and quantify the properties of turbulence, we extracted selected intervals. We used empirical mode decomposition to obtain the generalized marginal Hilbert spectrum, equivalent to the structure functions analysis, which additionally reduced issues typical of non-stationary, short time series. The presence of waves was quantitatively determined by introducing a parameter describing the time-dependent, frequency-filtered wave power. Results: A well-defined inertial range with power-law scalng was found almost everywhere in the sample studied. However, the Kolmogorov scaling and the typical intermittency effects are only present in fraction of the samples. Other intervals have shallower spectra and more irregular intermittency, which are not described by models of turbulence. These are observed predominantly during intervals of enhanced ion frequency wave activity. Comparisons with compressible magnetic field intermittency (from the MAG instrument) and with an estimate of the solar wind velocity (using electric and magnetic field) are also provided to give general context and help determine the cause of these anomalous fluctuations. (10.1051/0004-6361/202140931)
  DOI : 10.1051/0004-6361/202140931
• The origin of the breathing mode in Hall thrusters and its stabilization
  
  • Lafleur T.
  • Chabert Pascal
  • Bourdon Anne
  Journal of Applied Physics, American Institute of Physics, 2021, 130 (5), pp.053305. Using both 0D and 1D fluid models, we revisit the formation of the breathing mode in Hall thrusters and show that it is an ionization instability associated with nonlinearity in the electron power absorption. As the plasma density increases, the axial electric field profile changes and the magnitude of the electric field is enhanced in the ionization zone. This causes a nonlinear increase in the power absorbed by electrons, and an increase in the electron temperature and ionization rate factor that is able to partially compensate for the decreasing neutral density to keep the ionization rate high. This sets up a positive feedback mechanism where the electric field continues to be enhanced as the plasma density increases, and consequently the neutral density needs to decrease even further before plasma growth can be halted. At this point the neutral density is so low that the plasma can no longer be "sustained", and time is needed for neutrals to refill the thruster channel before "re-ignition" can occur and the process repeated. By treating the breathing mode as an AC excitation, a carefully designed external circuit can be used to counteract the change in axial electric field by appropriately varying the anode voltage to stabilise the discharge. (10.1063/5.0057095)
  DOI : 10.1063/5.0057095
• Approaching detachment in I-mode—response of core confinement and the edge pedestal in the ASDEX Upgrade tokamak
  
  • Happel T.
  • Reinke M.L.
  • Silvagni D.
  • Bernert M.
  • Grover O.
  • Hennequin Pascale
  • Hubbard A.E.
  • Plank U.
  • Trier E.
  • Brida D.
  • David P.
  • Fischer R.
  • Gil L.
  • Höfler K.
  • Manz P.
  • Mcdermott R.M.
  • Merle A.
  • Stroth U.
  • Viezzer E.
  • Willensdorfer M.
  Nuclear Fusion, IOP Publishing, 2021, 61 (3), pp.036026. Experiments on nitrogen assisted divertor detachment in the improved energy confinement mode (I-mode) are reported from the ASDEX Upgrade tokamak. When nitrogen is introduced into the divertor and radiation losses cool the divertor plasma down, a loss of core confinement is observed, concomitant with an increase in low frequency edge fluctuation levels. The loss in confinement can be compensated and the I-mode can be maintained by additional heating power input. Detachment of the inner divertor leg has been observed for the first time in an I-mode discharge. The outer divertor leg remains attached in these experiments. Good energy confinement properties (H98(y, 2) = 0.9) during the detachment of the inner divertor leg are reported. (10.1088/1741-4326/abd7b7)
  DOI : 10.1088/1741-4326/abd7b7
• Solar Orbiter's encounter with the tail of comet C/2019 Y4 (ATLAS): Magnetic field draping and cometary pick-up ion waves
  
  • Matteini L.
  • Laker R.
  • Horbury T.
  • Woodham L.
  • Bale S. D.
  • Stawarz J. E.
  • Woolley T.
  • Steinvall K.
  • Jones G. H.
  • Grant S. R.
  • Afghan Q.
  • Galand M.
  • O'Brien H.
  • Evans V.
  • Angelini V.
  • Maksimovic M.
  • Chust T.
  • Khotyaintsev Y.
  • Krasnoselskikh V.
  • Kretzschmar Matthieu
  • Lorfèvre E.
  • Plettemeier D.
  • Souček J.
  • Steller M.
  • Štverák Š.
  • Trávníček P.
  • Vaivads A.
  • Vecchio A.
  • Wimmer-Schweingruber R. F.
  • Ho G. C.
  • Gómez-Herrero R.
  • Rodríguez-Pacheco J.
  • Louarn P.
  • Fedorov A.
  • Owen C. J.
  • Bruno R.
  • Livi S.
  • Zouganelis I.
  • Müller D.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.13 pp.. Context. Solar Orbiter is expected to have flown close to the tail of comet C/2019 Y4 (ATLAS) during the spacecraft's first perihelion in June 2020. Models predict a possible crossing of the comet tails by the spacecraft at a distance from the Sun of approximately 0.5 AU. Aims: This study is aimed at identifying possible signatures of the interaction of the solar wind plasma with material released by comet ATLAS, including the detection of draped magnetic field as well as the presence of cometary pick-up ions and of ion-scale waves excited by associated instabilities. This encounter provides us with the first opportunity of addressing such dynamics in the inner Heliosphere and improving our understanding of the plasma interaction between comets and the solar wind. Methods: We analysed data from all in situ instruments on board Solar Orbiter and compared their independent measurements in order to identify and characterize the nature of structures and waves observed in the plasma when the encounter was predicted. Results: We identified a magnetic field structure observed at the start of 4 June, associated with a full magnetic reversal, a local deceleration of the flow and large plasma density, and enhanced dust and energetic ions events. The cross-comparison of all these observations support a possible cometary origin for this structure and suggests the presence of magnetic field draping around some low-field and high-density object. Inside and around this large scale structure, several ion-scale wave-forms are detected that are consistent with small-scale waves and structures generated by cometary pick-up ion instabilities. Conclusions: Solar Orbiter measurements are consistent with the crossing through a magnetic and plasma structure of cometary origin embedded in the ambient solar wind. We suggest that this corresponds to the magnetotail of one of the fragments of comet ATLAS or to a portion of the tail that was previously disconnected and advected past the spacecraft by the solar wind. (10.1051/0004-6361/202141229)
  DOI : 10.1051/0004-6361/202141229
• Direct Multipoint Observations Capturing the Reformation of a Supercritical Fast Magnetosonic Shock
  
  • Turner D.L.
  • Wilson L.B.
  • Goodrich K.A.
  • Madanian H.
  • Schwartz S.J.
  • Liu T.Z.
  • Johlander A.
  • Caprioli D.
  • Cohen I.J.
  • Gershman D.
  • Hietala H.
  • Westlake J.H.
  • Lavraud B.
  • Le Contel O.
  • Burch J.L.
  The Astrophysical Journal Letters, Bristol : IOP Publishing, 2021, 911 (2), pp.L31. Using multipoint Magnetospheric Multiscale (MMS) observations in an unusual string-of-pearls configuration, we examine in detail observations of the reformation of a fast magnetosonic shock observed on the upstream edge of a foreshock transient structure upstream of Earth's bow shock. The four MMS spacecraft were separated by several hundred kilometers, comparable to suprathermal ion gyroradius scales or several ion inertial lengths. At least half of the shock reformation cycle was observed, with a new shock ramp rising up out of the “foot” region of the original shock ramp. Using the multipoint observations, we convert the observed time-series data into distance along the shock normal in the shock's rest frame. That conversion allows for a unique study of the relative spatial scales of the shock's various features, including the shock's growth rate, and how they evolve during the reformation cycle. Analysis indicates that the growth rate increases during reformation, electron-scale physics play an important role in the shock reformation, and energy conversion processes also undergo the same cyclical periodicity as reformation. Strong, thin electron-kinetic-scale current sheets and large-amplitude electrostatic and electromagnetic waves are reported. Results highlight the critical cross-scale coupling between electron-kinetic- and ion-kinetic-scale processes and details of the nature of nonstationarity, shock-front reformation at collisionless, fast magnetosonic shocks. (10.3847/2041-8213/abec78)
  DOI : 10.3847/2041-8213/abec78
• Why switchbacks may be related to solar granulation
  
  • Fargette Naïs
  • Lavraud Benoit
  • Rouillard Alexis
  • Réville Victor
  • Phan Tai
  • Bale Stuart D.
  • Dudok de Wit Thierry
  • Froment Clara
  • Kasper Justin
  • Halekas Jasper S.
  • Louarn Philippe
  • Case Anthony W.
  • Korreck Kelly E.
  • Larson Davin E.
  • Malaspina David
  • Pulupa Marc
  • Stevens Michael L.
  • Whittlesey Phyllis L.
  • Berthomier Matthieu
  , 2021. Parker Solar Probe data below 0.3 AU have revealed a near-Sun magnetic field dominated by Alfvénic structures that display back and forth reversals of the radial magnetic field. They are called magnetic switchbacks, they display no electron strahl variation consistent with magnetic field foldings within the same magnetic sector, and are associated with velocity spikes during an otherwise calmer background. They are thought to originate either at the photosphere through magnetic reconnection processes, or higher up in the corona and solar wind through turbulent processes.In this work, we analyze the spatial and temporal characteristic scales of these magnetic switchbacks. We define switchbacks as a deviation from the parker spiral direction and detect them automatically through perihelia encounters 1 to 6. We analyze the solid angle between the magnetic field and the parker spiral both over time and space. We perform a fast Fourier transformation to the obtained angle and find a periodical spatial variation with scales consistent with solar granulation. This suggests that switchbacks form near the photosphere and may be caused, or at least modulated, by solar convection. (10.5194/egusphere-egu21-15707)
  DOI : 10.5194/egusphere-egu21-15707
• Magnetic Holes in the Solar Wind and Magnetosheath Near Mercury
  
  • Karlsson T.
  • Heyner D.
  • Volwerk M.
  • Morooka M.
  • Plaschke F.
  • Goetz C.
  • Hadid L.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2021, 126 (5), pp.e2020JA028961. We present a comprehensive statistical study of magnetic holes, defined as localized decreases of the magnetic field strength of at least 50%, in the solar wind near Mercury, using MESSENGER orbital data. We investigate the distributions of several properties of the magnetic holes, such as scale size, depth, and associated magnetic field rotation. We show that the distributions are very similar for linear magnetic holes (with a magnetic field rotation across the magnetic holes of less than 25°) and rotational holes (rotations >25°), except for magnetic holes with very large rotations (≳140°). Solar wind magnetic hole scale sizes follow a log-normal distribution, which we discuss in terms of multiplicative growth. We also investigate the background magnetic field strength of the solar wind surrounding the magnetic holes, and conclude that it is lower than the average solar wind magnetic field strength. This is consistent with finding solar wind magnetic holes in high-β regions, as expected if magnetic holes have a connection to magnetic mirror mode structures. We also present, for the first time, comprehensive statistics of isolated magnetic holes in a planetary magnetosheath. The properties of the magnetosheath magnetic holes are very similar to the solar wind counterparts, and we argue that the most likely interpretation is that the magnetosheath magnetic holes have a solar wind origin, rather than being generated locally in the magnetosheath. (10.1029/2020ja028961)
  DOI : 10.1029/2020ja028961
• Solar Orbiter observations of the structure of reconnection outflow layers in the solar wind
  
  • Owen C. J.
  • Foster A. C.
  • Bruno R.
  • Livi S.
  • Louarn P.
  • Berthomier M.
  • Fedorov A.
  • Anekallu C.
  • Kataria D.
  • Kelly C. W.
  • Lewis G. R.
  • Watson G.
  • Berčič L.
  • Stansby D.
  • Suen G.
  • Verscharen D.
  • Fortunato V.
  • Nicolaou G.
  • Wicks R. T.
  • Rae I. J.
  • Lavraud B.
  • Horbury T. S.
  • O'Brien H.
  • Evans V.
  • Angelini V.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656. We briefly review an existing model of the structure of reconnection layers which predicts that several more distinct layers, in the form of contact discontinuities, rotational Alfvèn waves, or slow shocks, should be identifiable in solar wind reconnection events than are typically reported in studies of reconnection outflows associated with bifurcated current sheets. We re-examine this notion and recast the identification of such layers in terms of the changes associated with the boundaries of both the ion and electron outflows from the reconnection current layers. We then present a case study using Solar Orbiter MAG and SWA data, which provides evidence consistent with this picture of extended multiple layers around the bifurcated current sheet. A full confirmation of this picture requires more detailed examination of the particle distributions in this and other events. However, we believe this concept is a valuable framework for considering the nature of reconnection layers in the solar wind. (10.1051/0004-6361/202140944)
  DOI : 10.1051/0004-6361/202140944
• First-year ion-acoustic wave observations in the solar wind by the RPW/TDS instrument on board Solar Orbiter
  
  • Píša D.
  • Souček J.
  • Santolík O.
  • Hanzelka M.
  • Nicolaou G.
  • Maksimovic M.
  • Bale S. D.
  • Chust T.
  • Khotyaintsev Y.
  • Krasnoselskikh V.
  • Kretzschmar M.
  • Lorfèvre E.
  • Plettemeier D.
  • Steller M.
  • Štverák Š.
  • Trávníček P.
  • Vaivads A.
  • Vecchio A.
  • Horbury T.
  • O'Brien H.
  • Evans V.
  • Angelini V.
  • Owen C. J.
  • Louarn P.
  Astronomy & Astrophysics - A&A, EDP Sciences, 2021, 656, pp.9 pp.. Context. Electric field measurements of the Time Domain Sampler (TDS) receiver, part of the Radio and Plasma Waves (RPW) instrument on board Solar Orbiter, often exhibit very intense broadband wave emissions at frequencies below 20 kHz in the spacecraft frame. During the first year of the mission, the RPW/TDS instrument was operating from the first perihelion in mid-June 2020 and through the first flyby of Venus in late December 2020. Aims: In this paper, we present a year-long study of electrostatic fluctuations observed in the solar wind at an interval of heliocentric distances from 0.5 to 1 AU. The RPW/TDS observations provide a nearly continuous data set for a statistical study of intense waves below the local plasma frequency. Methods: The on-board and continuously collected and processed properties of waveform snapshots allow for the mapping plasma waves at frequencies between 200 Hz and 20 kHz. We used the triggered waveform snapshots and a Doppler-shifted solution of the dispersion relation for wave mode identification in order to carry out a detailed spectral and polarization analysis. Results: Electrostatic ion-acoustic waves are the most common wave emissions observed between the local electron and proton plasma frequency by the TDS receiver during the first year of the mission. The occurrence rate of ion-acoustic waves peaks around perihelion at distances of 0.5 AU and decreases with increasing distances, with only a few waves detected per day at 0.9 AU. Waves are more likely to be observed when the local proton moments and magnetic field are highly variable. A more detailed analysis of more than 10 000 triggered waveform snapshots shows the mean wave frequency at about 3 kHz and wave amplitude about 2.5 mV m<SUP>−1</SUP>. The wave amplitude varies as R<SUP>−1.38</SUP> with the heliocentric distance. The relative phase distribution between two components of the E-field projected in the Y − Z Spacecraft Reference Frame (SRF) plane shows a mostly linear wave polarization. Electric field fluctuations are closely aligned with the directions of the ambient field lines. Only a small number (3%) of ion-acoustic waves are observed at larger magnetic discontinuities. (10.1051/0004-6361/202140928)
  DOI : 10.1051/0004-6361/202140928
• SPECTRAL EVOLUTION OF ALFVÉNIC TURBULENCE
  
  • Grappin Roland
  • Verdini A
  • Müller W.-C
  , 2021, pp.222-225. A correct description of solar wind acceleration relies critically on a good understanding of the turbulent cascade in the solar wind. However, no cascade theory is presently able to reproduce the variability of the observed spectral indices in the large scale range of the spectrum (Grappin et al. 1991; Chen et al. 2013). We propose here to test numerically the possibility that expansion is at the origin of some of the still not understood spectral properties, and focus on the scaling of the Elsasser spectra E±, especially with strong Alfvénicity. We use 3D MHD simulations, with moderate ratio B0/brms, with and without expansion. We find that with zero expansion, small-scale pinning of the dominant and subdominant spectra lead to (unobserved) different indices for the two Elsasser spectra, while with expansion, one finds nearly equal spectral exponents, as observed, and a slow spectral steepening with distance, thus leading naturally to the observed variability of spectral indices.
• Joint Europa Mission (JEM): A Multiscale, Multi-Platform Mission to Characterize Europa's Habitability and Search for Extant Life. A White Paper prepared for the NAS 2023-2032 Decadal Survey for Planetary Science and Astrobiology August 15th, 2020
  
  • Blanc Michel
  • Prieto-Ballesteros Olga
  • André Nicolas
  • Gomez-Elvira Javier
  • Jones Geraint
  • Sterken Veerle
  • Desprats William
  • Gurvits Leonid I.
  • Khurana Krishan
  • Balmino Georges
  • Blöcker Aljona
  • Broquet Renaud
  • Bunce Emma
  • Cavel Cyril
  • Choblet Gael
  • Colins Geoffrey
  • Coradini Marcello
  • Cooper John
  • Dirkx Dominic
  • Fontaine D.
  • Garnier Philippe
  • Gaudin David
  • Hartogh Paul
  • Hussmann Hauke
  • Genova Antonio
  • Iess Luciano
  • Jäggi Adrian
  • Kempf Sascha
  • Krupp Norbert
  • Lara Luisa
  • Lasue Jérémie
  • Lainey Valéry
  • Leblanc François
  • Lebreton Jean-Pierre
  • Longobardo Andrea
  • Lorenz Ralph
  • Martins Philippe
  • Martins Zita
  • Marty Jean-Charles
  • Masters Adam
  • Mimoun David
  • Palumba Ernesto
  • Parro Victor
  • Regnier Pascal
  • Saur Joachim
  • Schutte Adriaan
  • Sittler Edward C.
  • Spohn Tilman
  • Srama Ralf
  • Stephan Katrin
  • Szegő Károly
  • Tosi Federico
  • Vance Steve
  • Wagner Roland
  • Hoolst Tim Van
  • Volwerk Martin
  • Wahlund Jan-Erik
  • Westall Frances
  • Wurz Peter
  Bulletin of the American Astronomical Society, American Astronomical Society, 2021, 53 (4), pp.e-id. 380. In this White Paper we propose that NASA works with ESA and other potentially interested international partners to design and fly jointly an ambitious and exciting planetary mission to characterize Europa's habitability and search for bio-signatures in the environment of Europa (surface, subsurface and exosphere). A White Paper prepared for the NAS 2023-2032 Decadal Survey for Planetary Science and Astrobiology August 15th, 2020 (10.3847/25c2cfeb.a4c47358)
  DOI : 10.3847/25c2cfeb.a4c47358
• On the Pre‐Magnetic Storm Signatures in NmF2 in Some Equatorial, Low‐ and Mid‐Latitude Stations
  
  • Joshua B. W
  • Adeniyi J. O
  • Amory‐mazaudier C.
  • Adebiyi S. J
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2021, 126 (8), pp.e2021JA029459. In this paper, the ionospheric quiet-time disturbances otherwise known as Pre-Magnetic Storm Signatures (PMS) have been studied using the F2-layer peak electron density (NmF2) data obtained from 12 Digisonde/ionosonde stations distributed across equatorial, low and mid-latitudes. The datasets used spans the years 2010–2012. Results from this study reveals strong PMS in NmF2 with percentage deviations (ΔNmF2) ranging from −91% to 500% at the equatorial, low and mid-latitudes, with maxima occurring at the equatorial region. Significant effects on the peak height of the F2-layer (hmF2) were also observed, and they are correlated with the variations in NmF2 particularly at the equatorial station during the PMS. The duration of a PMS is found to be 12–48 h. Although, it was difficult to state clearly the connection between the PMS and the geomagnetic storm that usually follows within 24–48 h; but the NmF2 and hmF2 responses during the PMS were quite similar to those observed during geomagnetic storms. A slight increase in the Solar-wind-plasma speed (>20 km/s) was also observed during PMS. The PMS occur under a southward IMF-Bz, moderate aurora activity (AE ranging from 114 to 560 nT) and quiet ring current (Dst >−10 nT). Therefore, it is pertinent to consider a certain threshold of the aurora indices (AE, AL, and AU) in addition to the Dst, ap, and Kp in the definition of a geomagnetically quiet day. This may eliminate the ambiguity in explaining the ionospheric variability that occurs few days before Sudden Storm Commencement (SSC). (10.1029/2021JA029459)
  DOI : 10.1029/2021JA029459
• Climatology of ionosphere over Nepal based on GPS total electron content data from 2008 to 2018
  
  • Pandit Drabindra
  • Ghimire Basudev
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Chapagain Narayan Prasad
  • Adhikari Binod
  Annales Geophysicae, European Geosciences Union, 2021, 39 (4), pp.743-758. In this study, we analyse the climatology of ionosphere over Nepal based on GPS-derived vertical total electron content (VTEC) observed from four stations as defined in Table 1: KKN4 (27.80∘ N, 85.27∘ E), GRHI (27.95∘ N, 82.49∘ E), JMSM (28.80∘ N, 83.74∘ E) and DLPA (28.98∘ N, 82.81∘ E) during the years 2008 to 2018. The study illustrates the diurnal, monthly, annual, seasonal and solar cycle variations in VTEC during all times of solar cycle 24. The results clearly reveal the presence of equinoctial asymmetry in TEC, which is more pronounced in maximum phases of solar cycle in the year 2014 at KKN4 station, followed by descending, ascending and minimum phases. Diurnal variations in VTEC showed the short-lived day minimum which occurs between 05:00 to 06:00 LT (local time) at all the stations considered, with diurnal peaks between 12:00 and 15:00 LT. The maximum value of TEC is observed more often during the spring equinox than the autumn equinox, with a few asymmetries. Seasonal variation in TEC is observed to be a manifestation of variations in solar flux, particularly regarding the level of solar flux in consecutive solstices. (10.5194/angeo-39-743-2021)
  DOI : 10.5194/angeo-39-743-2021
• A spherical cap model of the geomagnetic field over southeast Asia from CHAMP and Swarm satellite observations
  
  • Thanh Le Truong
  • Minh Le Huy
  • Doumbia Vafi
  • Amory-Mazaudier Christine
  • Dung Nguyen Thanh
  • Chau Ha Duyen
  Journal of Earth System Science, Indian Academy of Sciences, 2021, 130 (1), pp.13. In this paper, Spherical Cap Harmonic Analysis (SCHA) method was applied to model the geomagnetic field over Vietnam and adjacent area between 15°S and 25°N latitude and 90°E and 130°E in longitude by using magnetic data recorded on CHAMP and Swarm satellites. The characteristic parameters of the method were set at the maximum index Kint = 8 for internal fields, the spherical cap half-angle θ0 = 20°. The regional geomagnetic field over Vietnam and adjacent areas are modelled for the two epochs (2007.0 and 2015.0). Comparison between the SCHA regional geomagnetic field intensity and its time variation with those from IGRF was carried out. The geomagnetic field intensity (ESCHAF) from SCHA model varies between −90 and 98 nT for epoch 2007.0 and between −139 and 143 nT for epoch 2015.0; however, the trends of their time variations are the same over Vietnam. The RMS between the magnetic components from SCHA model and ground observations are in the same order. The amplitude of time variation of total field intensity from SCHA model is about tens nT greater than from IGRF over Vietnam (10.1007/s12040-020-01507-9)
  DOI : 10.1007/s12040-020-01507-9