Workshop: Kinetic physics of astrophysical plasmas

18 mai 2026, 09:00 → 20 mai 2026, 17:00 Europe/Paris

Bâtiment 20 Amphithéâtre (Montpellier)

The mechanisms of energy dissipation (magnetic or kinetic) that lead to plasma heating or the generation of suprathermal particles occupy a central place in both the heliospheric plasma community and the high energy astrophysics community.  This workshop aims to bring these two communities together to discuss issues of common interest and to share the knowledge gained, both in terms of the physics studied and the numerical methods used. This workshop will leave plenty of room for discussion and exchange between participants. It will focus on three main topics: reconnection, turbulence and shock waves.

This workshop will take place on the campus of Université de Montpellier from May 18 to May 20. The scientific program will be divided into long, didactic review presentations (45 minutes) and shorter presentations on more specialized topics (30 minutes). 

For practical reasons, we will not be able to accommodate more than 60 participants. There will be no registration fee. 

This page will be updated on a regular basis.

Local organizing committee: C. Guépin (LUPM), A. Marcowith (LUPM), C. Sauty (LUPM), M. Lemoine (APC).

Organizing Committee: M. Lemoine (APC - Chair), O. Alexandrova (Obs. Paris), S. Cerri (OCA), B. Cerutti (IPAG), A. Ciardi (LUX), A. Grassi (LULI), A. Marcowith (LUPM), T. Passot (OCA), J. Pétri (Obs. Strasbourg), I. Plotnikov (IRAP), F. Sahraoui (LPP), A. Vanthieghem (LUX).

lun. 18 mai

09:15 → 09:45 Welcome & coffee

09:45 → 12:30 Turbulence & Transport

Invited speakers : Y.Dubois (IAP), G. Giacinti (APC), P.Lesaffre (ENS)

09:45 Magnetized turbulence and dynamos in compact objects

Turbulence plays a fundamental role in the transfer, amplification, and dissipation of magnetic and kinetic energy in astrophysical plasmas, from the solar corona to the vicinity of compact objects. In compact objects, including neutron stars, neutron star merger remnants and black-hole accretion flows, turbulent motions are crucial as they drive angular momentum transport, magnetic reconnection, particle acceleration, plasma heating and the generation of large-scale magnetic fields through dynamo action.
This talk will describe our current understanding of turbulence and dynamos in compact-object systems, with a particular emphasis on neutron stars in core-collapse supernova and neutron-star mergers and their remnants, but also on accretion disks around black holes. I will discuss how small-scale instabilities, such as convective instabilities, shear-driven turbulence the magneto-rotational instability, amplify magnetic fields and drive nonlinear turbulent cascades. I will show how these may lead to the generation of large-scale magnetic fields through mean-field dynamo processes and notably form the most magnetized neutron stars, magnetars. These large-scale magnetic fields can also launch relativistic jets in both core-collapse supernova and binary neutron star mergers. The goal of this talk is to provide a broad overview of how turbulence and dynamo action shape compact-object environments and to stimulate discussion on the common plasma processes that connect high-energy astrophysics and heliospheric science.

Orateur: Dr Alexis Reboul-Salze (Max-Planck Institute for Gravitational Physics)

10:45 Coffee break

11:30 TBA

Orateur: Dr Yohan Dubois (IAP)

12:30 → 14:00 Lunch break

14:00 → 17:30 Turbulence & Transport

Invited speakers : Y.Dubois (IAP), G. Giacinti (APC), P.Lesaffre (ENS)

14:00 Cosmic-ray propagation in our Galaxy: Insights from the diffuse emission, TeV halos and the CR anisotropy

Gamma-ray observations provide important information on cosmic-ray (CR) propagation in our Galaxy.
First, we present a new model of CR propagation in the Milky Way, where CRs are injected at discrete transient sources in the disc. We then calculate the corresponding diffuse Galactic gamma-ray emission. We find that the diffuse gamma-ray emission at >~ 100 TeV is very clumpy, and does not correlate with the gas density along the line of sight. It is substantially different from the relatively smoother emission detected by Fermi at ~ GeV energies. We also discuss how many hadronic and leptonic PeVatrons would be detectable in our simulations, and compare with LHAASO data. We show that this allows to place new constraints on PeV CR sources.
Second, we discuss TeV gamma-ray halos around old pulsars. We show that current gamma-ray measurements place interesting constraints on the turbulent magnetic fields around these pulsars, and we examine the implications for CR transport. In particular, we study the case of LHAASO’s “peanut-shaped” source.
Finally, we discuss the implications of the observed TeV-PeV cosmic-ray anisotropies on CR propagation in the ISM.

Orateur: Dr Gwenael Giacinti (APC Paris)

15:00 TBA

Orateur: M. Matthieu Bouchet (LAPTH)

15:20 Coffee break

16:05 Interstellar medium turbulence from numerical experiments

I will very briefly review the basics of the legacy of Kolmogorov
turbulence statistics. Interstellar turbulence is very far from the
simplicity of incompressible flows where Kolmogorov ideas
apply. Indeed, the interstellar medium is very dilute, extremely
compressible, multiphase, partially ionised, magnetised, and both dust
and cosmic rays travel are coupled with it. Nevertheless, we still use
the tools Kolmogorov devised to probe a variety of flows in
astrophysics. I will show how statistical laws (such as the extended
self-similarity) unexpectedly apply in isothermal
magnetohydrodynamical (MHD) simulations, and how this might be used to
detect the coherent discontinuities which quickly form in supersonic
turbulence. One of the suprising result lies in the lack of
sensitivity of the macroscopic parameters of these discontinuities to
the dissipation coefficients. This is also supported by recent work
with JB Durrive on analytical solutions of Burgers equations. I will
finally present our attempts to generate realistic (in the sense that
coherent structures are reproduced) turbulent fields at a much lower
cost than full fledge numerical simulations.

Orateur: Dr Pierre Lesaffre (CNRS/LEPNS)

17:05 contribution 2

mar. 19 mai

09:25 → 12:30 Shocks

Invited speakers: A.R. Bell (Univ Oxford, UK), G Fichet de ClaireFontaine (Univ Valencia, Spain), P. Cristofari (LUX)

09:25 Cosmic ray PeVatrons

Recent observations have opened a new window on the long-standing question of the origin of Galactic cosmic rays up to PeV energies. In particular, the LHAASO experiment has revealed a population of ultra-high-energy gamma-ray sources extending beyond 100 TeV, providing compelling evidence for Galactic pevatrons (accelerating CRs up to 10$^{15}$ eV). These results challenge the traditional paradigm in which supernova remnants (SNRs) are the dominant sources of PeV cosmic rays, as most of the sources detected sources seem to not be associated with any SNR.

Additional candidates such as microquasars and X-ray binaries—where powerful jets and strong shocks can potentially accelerate particles to extreme energies—are gaining increasing attention alongside young massive stellar clusters, pulsar wind nebulae, and superbubbles. The latest observational breakthroughs will be reviewed, along with their implications and open questions on particle acceleration and escape.

Orateur: Dr Pierre Cristofari (Observatoire de Paris)

10:25 coffee break

11:10 Does the Bohm limit determine the maximum of energy of shock-accelerated cosmic rays?

Ever since the classic papers of Lagage & Cesarsky (1983) and Hillas (1984), the Bohm limit uBR has been taken as the measure of the maximum energy to which cosmic rays can be accelerated by shocks. The obvious problem in the 1980s was that the Bohm limit for supernova remnants fell well short of the knee in the spectrum at a few PeV. This problem appeared to be solved when fields of a few hundred microGauss fields were observed in young supernova remnants and the theory of non-resonant magnetic field amplification said this should be so. But the problem was not solved. Gamma-ray observations imply a turnover in the cosmic ray spectrum at a few hundred TeV. Furthermore, the time-dependent theory of non-resonant amplification said again that this should be so since there is insufficient time to amplify the field on the Larmor scale of PeV cosmic rays.
The Bohm limit is based on the assumption that cosmic ray transport is diffusive and that the minimum mean free path is the Larmor radius. As early as 1966 Jokipii pointed out the possibility that cosmic rays could be confined by mirrors ahead of the shock, but he did not integrate this into a broader model in which cosmic rays cross the shock many times. Mirroring has recently been receiving attention in cosmic ray transport in general. Here I examine the possibility that non-diffusive transport with mirroring may explain cosmic ray acceleration beyond the Bohm limit (Bell et al 2025).

Orateur: Prof. Tony Bell (University of Oxford)

12:10 Contribution 3

12:30 → 14:00 Lunch break

14:00 → 14:30 Presentation of the COST action

Orateurs: Dr Anna Grassi (LULI), Arno Vanthieghem (Observatoire de Paris)

14:30 → 16:35 Shocks

Invited speakers: A.R. Bell (Univ Oxford, UK), G Fichet de ClaireFontaine (Univ Valencia, Spain), P. Cristofari (LUX)

14:30 Multimessenger emissions from active galactic nuclei

Jets of active galactic nuclei (AGN) rank among the most promising candidates for the sources of extragalactic high-energy neutrinos. In this presentation, I will begin by briefly building a broad picture of these jets first from recent observations, then by covering our current theoretical interpretations of their dynamics and multi-wavelength emissions, which will define a set of open questions. I will then turn to recent theoretical advances, ranging from analytical models to relativistic magnetohydrodynamic simulations of jets, which together shed light on some of these open questions. In particular, I will present a scenario in which the interaction of an AGN jet with red giant stars provides a site for particle acceleration and, potentially, high-energy neutrino production. I will close by discussing what these results imply for the future of multi-messenger astronomy.

Orateur: Dr Gaëtan Fichet de Clairfontaine (University of Würzburg)

15:30 coffee break

16:15 Contribution 4

16:35 → 17:15 TBA

Orateur: Dr Anabella Araudo (Institute of Physics, Czech Academy of Sciences)

19:30 → 22:30 Dinner

mer. 20 mai

09:00 → 12:30 Magnetic Reconnection

Invited Speakers: N. Aunai (LULI), V. Brunn (Obs Arcetri, Italy), S. Masson (LPP)

09:25 TBA

Orateur: Dr Pierre Henri ((1) Laboratoire Lagrange, Observatoire Côte d'Azur, Université Côte d'Azur, CNRS, Nice, France & (2) LPC2E, CNRS, Univ. Orléans, CNES, Orléans, France)

10:25 Contribution 5

10:45 coffee break

11:30 Solar energetic particles : observations and modelling

Solar eruptions are initiated and develop in the solar corona and are one of the most extreme manifestation of the sun impulsive release of energy. Solar particles are accelerated during solar eruption. We observe their radiative signatures in the solar atmosphere over a large range of wavelengths from EUV to gamma rays and measure them in-situ in the heliosphere. Solar energetic particles provide a unique opportunity to study particle acceleration and transport processes in astrophysical plasmas. I will present a comprehensive overview of the current understanding of Solar Energetic Particles, focusing on their observational diagnostics and theoretical modeling.
I will first describe how complementary multi-wavelength and multi-messenger diagnostics offer powerful constraints on the physical processes governing particle acceleration, injection, and propagation. Then I will focus on the main physical mechanisms proposed to explain solar particle acceleration such as acceleration at CME-driven shocks, magnetic reconnection in solar flares, and stochastic acceleration in turbulent environments. I will highlight the strengths and limitations of existing models, as well as the challenges in reconciling them with the observations. Finally, while a wide range of observational diagnostics and theoretical modelling have provided valuable insights, they are often interpreted within simplified and/or localized frameworks. In many cases, the global dynamics of the eruptive event are not taken into account. This can lead to ambiguities or even misconceptions regarding the timing, location, and efficiency of particle acceleration and injection. I will discuss how developing multi-scale models to simulate the global context of solar eruptions is essential to interpret SEP observations and to go beyond our current understanding of their acceleration, injection and propagation.

Orateur: Dr Sophie Masson (LPP - Observatoire de Paris)

12:30 → 14:00 Lunch break

14:00 → 16:50 Magnetic Reconnection

Invited Speakers: N. Aunai (LULI), V. Brunn (Obs Arcetri, Italy), S. Masson (LPP)

14:00 A new view on magnetic reconnection in the Earth’s magnetosphere

Magnetic reconnection at Earth’s magnetopause is the key process controlling the coupling between the solar wind and the magnetosphere, enabling plasma and magnetic flux from the interplanetary medium to enter an otherwise largely closed cavity. A central question is where reconnection develops along the magnetopause, since its location strongly influences the efficiency of this coupling. Despite decades of work, predicting the reconnection line remains difficult because the process is inherently multiscale, while spacecraft observations provide only local, in situ measurements and kinetic numerical modeling at large scale is extremely costly.

Recent progress has become possible by combining decades of observations from multiple missions with innovative machine-learning-based analysis. These approaches have yielded new insight into the environmental and physical constraints that govern both the location of the dayside reconnection line and the reconnection efficiency. This presentation will review these advances, from large-scale statistical results based on in situ measurements to new models of the X-line and recent developments in multiscale modeling to offer a complementary perspective on magnetopause reconnection.

Orateur: Dr Nicolas Aunai

15:00 Contribution 6

15:20 short break

15:50 In-situ particle acceleration by magnetic reconnection in young stellar objects

Young stellar objects host strongly magnetised and highly variable plasma environments in which several acceleration processes may generate suprathermal and non-thermal particles. In this talk, I will discuss two complementary regimes of particle acceleration in the star-disc system. The first is associated with large-scale magnetic reconnection during flares in the innermost regions, where impulsive energy release can produce intense bursts of energetic particles. The second is related to turbulence-driven reconnection operating from the inner to intermediate disc regions, where particle acceleration may occur in a more distributed and persistent way.

I will present the physical conditions under which these two mechanisms can operate and the expected properties of the accelerated particle populations. This comparison provides a framework to distinguish between impulsive and continuous sources of non-thermal ionisation in young stellar environments.

I will then show how these particles can affect the chemistry of the inner disc by enhancing ionisation in layers that are important for molecular processing and line formation in the JWST band. In particular, I will discuss how flare-accelerated and turbulence-accelerated particles may modify the abundances of key molecules in the warm inner disc, and how these changes could translate into observable signatures in infrared molecular tracers. More broadly, the aim is to connect kinetic plasma processes in young stellar objects with their chemical and observational consequences, and to assess whether energetic particles accelerated by flares and turbulent reconnection should be considered as an important ingredient of inner-disc physics.

Orateur: Dr Valentin Brunn (Arcetri Observatory)

16:50 → 16:55 End of the workshop