PLAS@PAR PHD DAY
Plas@Par is pleased to announce the organization of its PhD Day, which will take place on June 12, 2026.
This event will highlight PhD students’ research through a series of talks. It will provide an opportunity to showcase ongoing projects within the community, exchange ideas on recent advances, and foster collaborations among doctoral researchers.
The day will also be a friendly occasion to meet fellow PhD students and engage in informal discussions over breakfast and lunch.
We also invite PhD students interested in presenting their work to give a short research talk during the event. Volunteers are encouraged to indicate their interest in the registration form.
Location: Amphithéâtre Charpak, Jussieu Campus (accessible via Tour 22, level SB)
Registration (attendance and talk proposals): Plas@Par PhD Student Day - June 12, 2026
The preliminary program:
Mechanisms at the origin of radio solar bursts by laser-plasma interaction
Type III solar radio bursts are phenomena produced by highly energetic electrons (1 to 100~keV) emitted during solar flares [1]. These electrons then propagate through the solar wind and excite electrostatic waves at the electron plasma frequency ωp. Through wave coupling, these electrostatic waves in turn re-emit electromagnetic waves at the same frequency and at their harmonics n ωp. The analysis of these electromagnetic emissions can provide information on the acceleration and transport of energetic solar electrons, as well as on the coupling mechanisms of these waves, ultimately leading to a better understanding of the physical processes occurring in solar and stellar atmospheres. Since 2020, experiments [2] at LULI2000 (kJ laser facility in France) have shown that laser-plasma interactions can replicate most of these processes by generating Langmuir waves via the stimulated Raman instability. This results in the generation of electromagnetic waves at ωp and 2 ωp, similar to the emissions observed during solar bursts. We also report on a new experimental configuration at LULI2000 designed to approach more realistic solar conditions through the introduction of an external magnetic field representative of the solar wind environment. This configuration allow us to investigate its influence on wave polarization using a dedicated polarimetric diagnostic setup. The Particle-In-Cell code SMILEI [3] is employed to predict the plasma dynamics, guide the experimental design, and identify the wave coupling processes responsible for electromagnetic emission at ωp and its harmonics. These simulations enable systematic parametric studies and provide direct access to electrostatic wave dynamics that are not accessible experimentally. [1] J.P. Wild. Outbursts of radio noise from the sun. Vistas in Astronomy [2] J.-R. Marquès, Laser-Plasma Interaction Experiment for Solar Burst Studies [3] J. Derouillat, SMILEI: A collaborative, open-source multi-purpose particle-in-cell code
CloseMagnetic field from helical plasma waves driven by spatio-temporal Light Spring
Orbital angular momentum (OAM) transfer in laser-plasma interactions is a fundamental process far less understood than energy or linear momentum transfer. However, it has important direct applications, such as the production of strong magnetic fields. Previous studies of angular momentum transfer in laser–plasma interactions have investigated both dissipative processes, as well as single electron motion in laser fields carrying OAM. In this work, we present a novel ray-based approach of laser OAM transfer to plasmas. In this framework, refraction in plasmas with azimuthal density gradients enables non-dissipative transfer of OAM between the laser and plasma. These gradients can be pre-existing in the plasma, or self-generated by a spatiotemporally shaped laser pulse. This process is analogous to the mechanism behind orbital AM transfer in spiral phase plates. Our model provides a simple unified interpretation of OAM transfer in many laser-plasma interactions and can be used to explain previous results. Utilizing recent breakthroughs in spatio-temporal shaping of high power laser systems, we show that light springs, lasers carrying multiple OAM modes in multiple frequency bands, can indeed drive plasma waves with helical density gradients, and self couple into the plasma driving strong axial magnetic fields. Using SMILEI particle-in-cell simulations, we validate this model and show that light springs are efficient at transferring the AM to electrons, leading to the generation of strong longitudinal magnetic fields (a few 100s of Tesla) at moderate laser power (a few 100s of GW to a few TW).
CloseWhole-Sun 3D MHD numerical simulations of the formation of switchbacks induced by solar coronal jets
Switchbacks, which are rapid magnetic field deflections observed by the Parker Solar Probe, remain a puzzling phenomenon in solar wind physics. While their origins are still debated and several mechanisms are under study, recent work by Touresse et al., 2024 showed that a propagating solar jet can produce such magnetic deflections that can help in understanding switchback observations. While none of their simulations produced a full reversal switchback, they noted that the angle of deflection depends on the plasma beta profile, i.e., of the radial magnetic field decay profile. This raises the question of the influence of the magnetic field profile on the formation and properties of switchbacks. We extend this investigation by developing new numerical experiments that intend to study the propagation of a self-induced coronal jet in a more realistic magnetic configuration including the whole 3D magnetic corona. The 3D MHD simulations rely on the Adaptive Refined MHD Solver (ARMS) code. After a relaxation phase, the jet is generated from a small bipolar active region located in an equatorial coronal hole. The system is energized by line-tied boundary motions. We present here the early results from these new simulations.
CloseParametric 3D MHD numerical simulations of the generation of switchbacks induced by solar coronal jets
Building upon the work of Touresse et al. (2024), which demonstrated that torsional magnetic waves driving solar jets can produce SB-like signatures, my PhD project explores the parameter space of these 3D MHD simulations using the Adaptive Refined MHD Solver (ARMS). We investigate the influence of the jet source size on the properties of the induced SB, by varying dipole dimensions, hence assessing how jets and SBs scale with each other. This is coupled with the implementation of diverse driving profiles to test the impact of different magnetic field geometry in the jet source region on the SB structure and properties. I will present early results from this parametric study, focusing on how these variations impact the trigger, onset, and ability of solar jets to induce SB-like signatures into the solar wind.
CloseMartian Atmospheric Ion Energization And Escape During The 2022 Disappearing Solar Wind Event: A Hybrid Simulation Study
Mars has experienced substantial atmospheric loss, largely attributed to the absence of a global intrinsic magnetic field. Without such shielding, the solar wind can interact directly with the upper atmosphere, driving ion escape processes that progressively deplete the atmosphere. This long-term erosion has reduced the planet's capacity to maintain a stable climate and is thought to have contributed to the disappearance of liquid water from its surface. Extreme solar wind events—such as Coronal Mass Ejections (CMEs), Corotating Interaction Regions (CIRs), and radially oriented Interplanetary Magnetic Field (radial IMF)—can significantly modify the plasma environment around Mars and enhance the energization and escape of atmospheric ions. Because these extreme conditions were likely more frequent and intense in the early Solar System, studying such events provides insight into the historical evolution of the Martian atmosphere. In this work, we investigate the response of atmospheric ions during extreme solar wind conditions, focusing on the 2022 "Disappearing Solar Wind" (DSW) event associated with a CIR, during which the solar wind density decreased by more than an order of magnitude. Simulations are performed using the latest Latmos Hybrid Simulation (LatHyS) model, in which ions are treated as macro-particles obeying Newtonian dynamics while electrons are modeled as an inertialess fluid. We analyze how variations in solar wind density—from nominal conditions (n=3.0cm-3) to the DSW regime (n=0.1cm-3)—affect the energization and transport of O+ ions. Particular attention is given to escape rates through the magnetotail and plume structures, as well as to inward precipitation and the associated energy deposition into the ionosphere. The atypical plasma environment created during the DSW event offers a rare opportunity to examine Mars–solar wind coupling under extremely low-density conditions. Combined with the hybrid modeling capabilities of LatHyS, this event provides a useful natural experiment for probing ion energization mechanisms and for constraining scenarios of atmospheric escape that may have been common during the early evolution of Mars.
CloseX-ray spectroscopy diagnostics of metastable ions produced in ECR plasmas for ion-ion and ion-atom collision experiments
Ion–ion and ion–atom collisions play a crucial role in various research fields where highly collisional plasmas are involved (e.g., astrophysics, nuclear fusion, hadron therapy …). A major objective is therefore to improve the understanding and modeling of the electronic processes governing such collisional plasmas. Obtaining accurate measurements of cross sections for electronic processes (capture, ionization, excitation) in ion-ion/atom collisions crucially depends on the initial electronic states of the collision partners. The ion sources used for these collision experiments usually produce ion beams containing not only ground-state ions but also a variety of excited states. Although many of these species decay during the transport between the ion source and the collision chamber, the lifetime of some metastable species is long enough to allow them to reach the collision zone. Different schemes exist to extract the metastable fraction in an ion beam based on Auger spectroscopy techniques [1, 2]. At INSP, our experimental setup includes an ECR ion source delivering keV/u ion beams to a collision chamber located 6 m downstream from the source, corresponding to a flight time of about 3 µs for a 10 kV extraction voltage. We developed a new diagnostic method based on X-ray spectroscopy to determine metastable fractions in the extracted ion beam. The technique consists in measuring the X-ray yield produced during ion-atom collisions as a function of the target gas pressure in the interaction chamber. Under single-collision conditions, a linear dependence is expected, while the presence of metastable ions leads to a non-zero intercept. The method was applied to Ar8+ projectiles colliding with neutral Ar atoms. The recorded X-ray spectra exhibit the n = 3 to n = 2 transition around 250 eV, associated with the 1s2 2s2 2p5 3s 3P metastable state, which has a lifetime of 332 µs. From these measurements, a metastable fraction of 5.3 ± 1.5% was extracted. Measurements performed with O6+ and Ne8+ ion beams, as well as the influence of ECR source parameters on metastable production, will also be presented. [1] Snowdon, K.J. et al. Rev. Sci. Instrum. 1988, 59, 902-905. [2] Benis, E.P. et al. Atoms 2018, 66, 6.
CloseThe Interplay Between the Bell and Firehose Instabilities
In astrophysical shocks, instabilities driven by the streaming of energetic particles into the upstream medium amplify magnetic fields and generate turbulence, enabling efficient cosmic-ray (CR) acceleration (Malkov et al., 2010). However, a complete and self-consistent picture of CR acceleration, spanning the initial generation of magnetic fields through their subsequent amplification and the resulting particle acceleration, remains incomplete. These magnetic fields are expected to arise from the interplay, competition, and nonlinear evolution of several instabilities, notably the Bell (Bell, 2004) and firehose instabilities. These interactions happen across a wide range of scales, making both analytical and numerical investigations challenging. Our work aims at providing a tentative picture of such interplay through a simplified analytical and numerical framework, offering insight into mechanisms responsible for large-scale magnetic-field amplification. We present kinetic simulations performed with the SMILEI particle-in-cell (PIC) code (Derouillat et al., 2018) to study the nonlinear evolution of the Bell and firehose instabilities in counter-streaming monoenergetic proton beams, used here as a minimal model for cosmic-ray–driven turbulence. By varying the beam density ratio, we probe regimes where either the Bell or the firehose instability dominates. Our results constitute, to our knowledge, the first observation in fully kinetic PIC simulations of nonlinear self-coupling of the dominant linear mode, leading to growth of large-scale magnetic fields at twice the linear growth rate, in agreement with earlier magnetohydrodynamic simulations (Bykov et al., 2013). We develop an analytical interpretation of this behavior based on the growth of density perturbations, which drive nonlinear electrostatic modes that subsequently feed back into electromagnetic modes. This mechanism provides a potential pathway for the generation of large-scale magnetic fluctuations required to approach Bohm diffusion regimes for CRs, and thus for efficient particle acceleration in astrophysical shocks.
ClosePlasma Transport and Energization Across Mercury's Magnetopause: Three Distinct Low-Latitude Boundary Layer Populations
Understanding how plasma is transported and energized across the magnetopause is a significant problem in space plasma physics. Mercury, with its weaker magnetic field and compact magnetosphere exposed to more dynamic solar wind conditions, offers a unique environment in which these processes may operate differently from on Earth. Using combined magnetic field and ion measurements from the MESSENGER spacecraft, we analyze 202 Low-Latitude Boundary Layer (LLBL) crossings and identify three distinct types based on proton energy distributions: single-population, double-population, and a newly identified energy-shifted LLBL. While the first two are analogous to those observed on Earth, the energy-shifted LLBL is reported here for the first time in a planetary magnetosphere. These three types of LLBL show clear magnetic local time dependence and a clear dawn-dusk asymmetry, indicating distinct pathways of plasma transport and energization. In particular, energy-shifted LLBLs are primarily observed on the dawnside and exhibit strong perpendicular energization. This likely reflects a scenario in which magnetosheath ions entering the magnetosphere drift dawnward and gain energy through cross-field potential drops, a process that may be enhanced by the stronger magnetic field curvature on Mercury than on Earth. These results offer new insight into plasma transport and energization across Mercury's magnetopause, and highlight Mercury as a natural laboratory for studying space plasma physics under extreme conditions. The BepiColombo mission, scheduled to enter Mercury orbit in November 2026, will deepen our understanding of ion transport and energization mechanisms on Mercury's magnetosphere through multi-point measurements and higher temporal resolution.
CloseWe hope to see many of you there!