Contact : Olga Alexandrova (olga.alexandrova at obspm.fr)
Co-chairs: Olga Alexandrova, Lina Hadid, Edith Falgarone, Pierre Lesaffre, Frederic Bournaud, Anaelle Maury, Helene Sol
Turbulence is ubiquitous in all the plasmas of the universe. The goal of turbulence studies is to characterize what kind of order emerges from this apparent chaos and quantify the energy trail in the cascade. There are hints that turbulence statistics could be universal in the limit of large Reynolds numbers. This means that turbulence research can hugely benefit from an interplay across a wide range of fields which is what we are aiming for with this session.
Among the different astrophysical plasmas, the solar wind and planetary magnetospheres, represent excellent laboratories for the observation of collisionless astrophysical plasma turbulence. Thanks to the availability of many space missions, we can study in situ the properties of fully developed turbulence over more than 8 decades in scales (from ~100 m to 10^7 km) and 14 decades in power-spectral-densities (PSD). At the magneto- hydrodynamical scales, the PSD of the magnetic fluctuations follows a Kolmogorov scaling, whereas at kinetic plasma scales (less than 10^3 km), the cascade changes its nature and spectrum, it heats charged particles and can be at the origin of non-adiabatic solar wind expansion.
Outside the solar system, all the plasmas in and around galaxies, whether fully or weakly ionized, are highly turbulent. Their supersonic turbulence (10-50 km/s at 100-10^4 K) is known to play a major role in the structuration of the interstellar medium, up to scales of the order of the kpc, compressing interstellar matter from mean densities of a few cm^-3 at the kpc scale to filaments and dense clumps above 10^7 cm^-3 at the parsec scale and below, setting the conditions for stars to ultimately form. Turbulence may trigger phase transitions between the warm and cold neutral media, seeds the formation of molecules in the atomic medium, support molecular clouds against gravitational collapse, and likely plays a key role in the global inefficiency of star formation. Indeed, the fascinating self- regulation of star formation observed in galaxies, up to high-redshift starburst galaxies, appears driven by the conjunction of cosmological gas infall, gravitational instabilities and stellar feedback, and is mediated by turbulence. Hence understanding the origin and cascade of galaxy-scale turbulence and its precise impact on star formation is important to get realistic models and theories of galaxy formation and evolution.
Another major challenge is the role of turbulence in the transport of angular momentum in protoplanetary disks. While recent observations suggest the turbulence is probably weak in the gas of Myrs-old planet-hosting disks surrounding T-Tauri stars, the conditions could be significantly different in disk winds, and in actively accreting, younger, disks which are the cradles of protoplanets.
Last, understanding the nature of turbulence in galactic and extragalactic plasmas is also a key issue to unravel the origin, transport and acceleration of cosmic rays (CR) at all energy ranges, from hundreds keV up to ultra-high-energy cosmic rays (UHECR) in the 10^20 eV domain. Indeed, more than a century after their discovery, the origin of CR is not yet elucidated. The smooth CR energy spectrum close to a power law from 10^9 eV to UHE suggests that transport properties are not strongly energy-dependent and that common acceleration mechanisms are at work, in shocks, turbulence, and possibly magnetic reconnection. The region of the « knee », where the spectral slope changes in the PeV range, is of special importance since it could mark the transition between galactic and extragalactic CR. The search for PeV-atrons is now possible thanks to new generation instruments such as LHAASO or CTA, and should clarify the role of supernova remnants that have for long been proposed as main sources of galactic CR. As for extragalactic CR, the question remains entirely open and requires new observational and theoretical constraints, several cosmic sites hosting very energetic and turbulent plasma flows being likely to accelerate them up to UHE, such as active galactic nuclei, black holes and relativistic jets, gamma-ray bursts, hypernovae, starburst galaxies, large scale shocks.
The two sessions will be devoted to these different facets of turbulence, with an emphasis on what could be unveiled as universal properties pervading all these cosmic plasmas.
|14h10-14h35||Observable signatures of plasmoid-dominated magnetic reconnection in relativistic astrophysical plasmas||Benoît Cerutti||IPAG||Invited||Cerutti||Cerruti|
|14h35-14h50||Local ionization rates by magnetic reconnection events in TTauri disks||V. Brunn, A. Marcowith, C. Sauty, M. Padovani, C. Rab||LUPM||BMSPR||BMSPR|
|14h50-15h15||The hunt for the sources of cosmic rays||Pierre Cristofari||IJCLab||Invited||Cristofari||Cristofari|
|15h15-15h30||A microphysical model for turbulent Fermi acceleration||Martin Lemoine||IAP||Lemoine||Lemoine|
|16h00-16h15||Non-resonant particle Acceleration in strong turbulence: comparison to kinetic and MHD simulations||Virginia Bresci, Martin Lemoine, Laurent Gremillet, Luca Comisso, Lorenzo Sironi, Camilla Demidem||IAP||BLGCSD||BLGCSD|
|16h15-16h40||Turbulent regimes in 3D Alfvén-wave-packet collisions||S. S. Cerri, T. Passot, D. Laveder, P.-L. Sulem, M. W. Kunz||Laboratoire Lagrange||Invited||CPLSK||CPLSK|
|16h40-17h05||The PHANGS view of cloud-scale motions in the cold gas reservoir of nearby galaxies||Annie Hughes, Sharon van der Wel, Raphaël Maris on behalf of the PHANGS collaboration||IRAP||Invited||HWM||HWM|
|17h05-17h20||Angular momentum transport by astrophysical turbulence||C. Gissinger, S. Fauve, F. Marcotte, M. Pereira, L. Petitdemange, M. Vernet||ENS, Paris||GFMPPV||GFMPPV|
|9/06/2022||14h00-14h25||Turbulence in the interstellar medium: from intermediate galactic scales to self-gravitating cores||Patrick Hennebelle||AIM||Invited||Hennebelle||Hennebelle|
|14h25-14h40||Spatial and velocity coherence of dissipation extrema in a turbulent molecular cloud||Hily-Blant, Pierre, Delcamp Simon (IPAG, Grenoble), Falgarone, Edith (LPENS, Paris)||IPAG||HBDF||HBDF|
|14h40-14h55||The interplay of turbulence and magnetic fields in the non–star-forming Pipe nebula||S. Delcamp, P. Hily-Blant, and E. Falgarone||IPAG||DHBF||DHBF|
|14h55-15h20||Turbulence in the diffuse multi-phase interstellar medium||Marc-Antoine Miville-Deschênes (AIM, Paris-Saclay) & Antoine Marchal (CITA, University of Toronto, Canada)||AIM||Invited||MDM||MDM|
|16h00-16h15||New approach to planetesimal formation: clusters of heavy particles in two-dimensional Keplerian turbulence||Fabiola Antonietta Gerosa, Héloïse Méheut, Jérémie Bec||Laboratoire Lagrange||GMB||GMB|
|16h15-16h30||Intermittent structures in solar wind turbulence from MHD to sub-ion scales at 0.17 AU from the Sun||Alexander Vinogradov, Olga Alexandrova, Milan Maksimovic, Anton Artemyev, Andre Mangeney, Alexei Vasiliev, Karine Issautier, Michel Moncuquet and Anatoly Petrukovich||LESIA||VAMAMVIMP||VAMAMVIMP|
|16h30-16h45||Probing the nature of dissipation in compressible MHD turbulence||Thibaud RICHARD, Pierre LESAFFRE, Edith FALGARONE||LPENS||RLF||RLF|
|16h45-17h10||Energy conversion through various channels in turbulent plasmas induced by the Kelvin-Helmholtz instability at the Earth’s magnetopause||R. Kieokaew, Y. Yang, T. Aiamsai, P. Pongkitiwanichakul, T. Pianpanit, D. Ruffolo, W. Matthaeus, S. Dahani, B. Lavraud, V. Génot, D. Gershman, B. Giles, R. Torbert, and J. Burch||IRAP||Invited||KYAPPRMDLGGGTB||KYAPPRMDLGGGTB|
|17h10-17h25||Dissipation range of solar wind turbulence||Olga Alexandrova, Jessica Martin, Vamsee Jagarlamudi, Petr Hellinger, Milan Maksimovic, Catherine Lacombe and Andre Mangeney||LESIA||AMJHMLM||AMJHMLM|