Catégorie d'emplois: Physics

PhD Thesis (M/F) – Physics -Experimentation – RD/1

PhD project : Ultracold atom experiment for plasma physics

Supervisor : Romain Dubessy – CIML group

Mail : romain.dubessy@univ-amu.fr

Lab : Physique des interactions ioniques et moléculaires UMR7345, Marseille, Campus de Saint-Jérôme1.

Keywords : laser cooling and trapping, ultracold neutral plasma, photo-ionization

 

We are looking for a highly motivated PhD student to start a new experiment at the frontier of quantum and plasma physics [1]. We will create a laser cooled sample of neutral Calcium atom confined in a magneto-optical trap, at milli-Kelvin temperatures. This sample will then be photo-ionized and the dynamics of the resulting plasma of Calcium ions and electrons will be investigated using absorption imaging. We aim at:

  • demonstrating for the first time the control of the initial plasma distribution, thanks to optical shaping of the photo-ionization laser pulse, following a recent proposal [2],
  • studying collisions between ultracold plasmas,
  • applying laser cooling and trapping to a ultracold plasma [3].

The PhD student will contribute to the construction of an original platform implementing a analog simulator of a strongly coupled plasma, aiming at controlling all the microscopic parameters in a bottom-up approach. The project is fully funded for the three years of the PhD and we expect to hire a post-doc in January 2026 to strengthen the team working on this project.

The successful candidate will join a team of about about ten people, including two PhD students and two postdocs, working on three experimental platforms all dedicated to the study of laser cooled atom and ions for basic research and applications. He/She will be offered the opportunity to attend a PhD school on ultracold atom physics in Fall 2025 (in Les Houches, near Chamonix). The CIML group is part of the European ion trapping network.

 Acquired skills: the student will learn state of the art laser control technology, including frequency stabilization on an atomic reference and beam shaping thanks to a spatial light modulator, as well as ultra-high vacuum technology and experiment control.

 Prerequisites: a good knowledge of quantum mechanics is required and prior practical experience in optics or lasers is appreciated.

 

[1] Ultracold neutral plasmas, T.C. Killian, T. Pattard, T. Pohl, J.M. Rost, Phys. Rep. 449, 77-130 (2007).

[2] Sculpted ultracold neutral plasmas, V.S. Dharodi, M.S. Murillo, Phys. Rev. E 101, 023207 (2020).

[3] Laser cooling of ions in a neutral plasma, T.K. Langin, G.M. Gorman, T.C. Killian, Science 363, 61-64 (2019)

 

1 Saint-Jérome campus can be reached by public transportation from the city centre in less than 25 minutes and the University can help PhD students coming from out of Marseilles to find accommodations.

PhD Thesis (M/F) – Physics -Experimentation – NC

Experimental aspects of plasma sheath associated with secondary electron emission

By nature, a plasma is composed of charged particles which, in response to electromagnetic fields they generate or which are applied to them, exhibit collective behaviors from which quasineutrality results on spatial scales larger than the Debye length. This property break-down when the plasma encounters a solid frontiers where non-neutral sheath forms at scales of a few Debye lengths and, potentially, deeply impact on the bulk dynamics, i.e. far from the frontiers.

Ions and electrons dynamics, due to their mass difference, evolve with different temporal scales in the presence of sheaths, which may be the device boundaries in laboratory experiments or solid bodies in astrophysical contexts. Multi-scale physics phenomena emerge especially where the sheath is formed. The physics of plasma sheath is of major interest in the fields of, both, laboratory, astrophysics and fusion by magnetic confinement (tokamaks,…). Many studies have been devoted to the understanding of plasma sheaths in several configurations [1]. The situation is further complicated in the presence of magnetic fields or the emission of electrons from the surface. In the presence of surfaces that emit electrons, either from secondary emission or thermionic emission, the physics of the sheath is deeply modified. Modeling and numerical simulations predict an “inverse sheath” whose experimental observation is still elusive [2–4]. In that context, the long-term goal of the thesis is to improve comparison between magnetic sheath of an electrons emitted surface models and experiments. Models and experiments will be performed and compared at the laboratory PIIM and its partners by two PhD students.

Spatial scales involved in plasma sheaths and the breakdown of quasi-neutrality make it appropriate to use laser-induced fluorescence diagnostics to measure the ion velocity distribution function along the pre-sheath and the sheath. This non intrusive diagnostic already implemented and mastered at PIIM [5] will be used in the vicinity of metallic surface at a floating potential to confirm results from numerical simulations led by our partners. Despite some artefacts [6], its spatial definition is around 0.1mm, which allows to spatially resolve the sheath structure (spanning around 1mm in our experiment). The plasma source, a multipolar device, creates a quiescent Argon plasma with two electron populations: an ionizing energetic one emitted by filaments and a colder electron temperature population, which is the core electron plasma population.

Various experiments will be performed and compared to theories developed within a distinct PhD project, by a fellow PhD student funded by the same research grant:

  • Explore the collisionality of the sheath physics, which are ubiquitous in nature and experiments, by changing the neutral pressure
  • Measurements of the sheath structure of an thermionic, electron emissive surface (LaB6 heated ceramic)
  • Measurements of the sheath structure in the case of surfaces with high secondary electrons emission rates, with a focus on the observation of an “inverse” sheath structure.
  • Explore the effect of magnetic fields on the sheath structure, in regimes where only the electrons will be magnetised. The influence of the the angle between the surface and the magnetic field is known to be a key player [7].
  • Perform experiments in a linear magnetic plasma column[8]

The experimental datas on emissive sheath plasmas will be compared with theoretical/numerical results from PIIM laboratory.

The thesis work will be relevant for, both, space thrusters [9] and laboratory plasmas such as in a non magnetic low temperature plasma [5] and in an linear magnetic plasma column [10] devices of PIIM.

This experimental work could serve as a basis for understanding the magnetic sheath where ions are magnetized as is the case in fusion devices.

The student must have master’s level knowledge in plasma and experimental physics to carry out experiments with laser and compare results with theoretical calculations.

The thesis will be carried out within the framework of A*MIDEX funding and a collaboration between the PIIM, the Laboratoire de Physique at Ecole Normale Supérieure de Lyon (LPENSL) and the Laplace laboratories for the theoretical part. The thesis will take place mainly at PIIM in Marseille although the future student will have to travel regularly to Lyon to the LPENSL.

The thesis will be directed by N. Claire (PIIM) and N. Plihon (LPENSL) and will be supervised by M. Muraglia (PIIM), G. Fubiani (Laplace) and O. Agullo (PIIM) for theoretical comparisons.

@: nicolas.claire@univ-amu.fr and nicolas.plihon@ens-lyon.fr

References

[1] R. N. Franklin, J. Phys. D: Appl. Phys. 36, R309 (2003)

[2] V. Pigeon et al, Phys. Plasmas 27, 043505 (2020)

[3] M. D. Campanell, Phys. Rev E 88, 033103 (2013)

[4] D. Coulette et al, Phys. Plasmas 22, 0043505 (2015)

[5] N. Claire et al, Phys. Plasmas 13, 062103 (2006)

[6] V. Pigeon et al, Phys. Plasmas 26, 023508 (2019)

[7] P. C. Stangeby, Phys. Plasmas 2, 702 (1995)

[8] N. Claire et al, Phys. Plasmas 25, 061203 (2018)

[9] NA.L. Ortega et al, Plasma 3, 550 (2023)

[10] S. Aggarwal et al., Journal of Plasmas Physics, 89, 905890310 (2023)

 

PhD Thesis (M/F) – Physics – Experimentation – CC/1

A laser-cooled trapped ion cloud for heavy particle detection

SUPERVISOR : CAROLINE CHAMPENOIS AND AURIKA JANULYTE

MAIL : CAROLINE.CHAMPENOIS@UNIV-AMU.FR

TEL : +33 413946413

LAB : PHYSIQUE DES INTERACTION IONIQUES ET MOLÉCULAIRES, MARSEILLE, CAMPUS DE SAINT-JÉRÔME. (UMR7345) 1

WEB PAGE OF THE CIML GROUP : HTTPS://PIIM.UNIV-AMU.FR/EN/RESEARCH/ SEVEN-TEAMS-AND-ONE-OPERATION/CIML-TEAM/

keywords : atom trapping and laser cooling, strongly correlated plasma, charged particles guiding

The CIML group has a strong expertise in laser cooling and ion trapping in radio-frequency trap. It is part of the European ion trapping network and one of the few groups trapping ions for fundamental physics purpose, in France. One of the experimental set-up of the group aims at the experimental investigation of the energy exchange between charged particles, sending a projectile onto a target. There, the target is a cold and dense trapped ion cloud which can be considered as a very non-conventional plasma, a one-component plasma (OCP). The projectile is a very heavy molecular ion and the perturbation that it induces in crossing the cloud of trapped ions can be used for its non-destructive detection, to demonstrate a prototype for mass spectrometer detector without mass limitation [1].

In practise, the target is a laser cooled Ca+ ion cloud. As they reach temperature lower than the kelvin, these ions bunch in the trapping potential and arrange in a stationary structure that minimise the trapping+Coulomb repulsion potential energy, to form what is called a Coulomb crystal. An example of these structures, formed by several hundreds of ions, is visible on the figure showing the image of the ion fluorescence on a CCD camera. The exploited signal is the laser induced fluorescence of the cloud. The interplay between the laser cooling efficiency and the non-linear dependence of the RF-heating with the cloud density and temperature turns the phase transition of the cloud as a signal amplifier for an efficient detection [2].

Objectives : We propose as a PhD project to demonstrate and quantify the energy exchange between charged heavy ions and laser cooled Ca+ OCP. It implies to develop a protocol to control the size and temperature of the trapped ions, the trajectory of the projectile and a diagnostic of the energy transferred to the ion cloud. The internship relies on an operational experimental set-up, where the detection will take place. It can also rely on a molecular dynamics simulation code that can be used to test the detection efficiency regarding the projectile characteristics, the trap and the laser-cooling parameters.

The acquired skills concern charged particle trapping and guiding, atom-laser interaction and laser cooling, tight laser control, data acquisition and processing.

REFERENCES :

[1] A. Poindron, et al, J. Chem. Phys. 154, 184203 (2021)

[2] A. Poindron, et al, PRA, 108, 013109 (2023)

1  Saint-Jérôme campus can be reached by public transportation from the city centre in less than 25 minutes. Our group benefits from a completely new technical environment with very good technical conditions.

PhD Thesis (M/F) – Physics – Modeling – YF/1

Multi-Scale Modeling of the Interaction between Hydrogen and Nuclear Materials

 

Directeur de thèse : Y. Ferro (Aix-Marseille Université) yves.ferro@univ-amu.fr

Co-directeur : E. Hodille (CEA – Cadarache) etienne.hodille@cea.fr

Co-encadrant :  J. Tranchida (CEA – IRESNE) julien.tranchida@cea.fr

Three-year PhD funding will be available in September 2025 at the “Physique des Interactions Atomiques et Moléculaires” Laboratory (PIIM).

We are studying the behavior of hydrogen in the first wall materials of the International Thermonuclear Experimental Reactor (ITER). This subject is part of a strongly structured European framework provided by the EUROfusion Horizon Europe consortium, which offers access to a large collaborative network and European EURATOM funding.

To model the behavior of hydrogen in materials, we use electronic structure calculations based on DFT implemented in Plane-Waves. We determine electronic and vibrational properties, solution energies, diffusion barrier for hydrogen in materials. We model defect creation, adsorption phenomenon, surface reconstruction and more. On top of these properties determined at zero temperature, we build thermodynamic models to provide macroscopic properties depending on external parameters like the temperature, pressure or chemical potential. Kinetic models are also developed in collaboration with the “Institut de Recherche sur la Fusion Magnétique” (IRFM) at CEA Cadarache. To complete this multi-scale approach, we have more recently been integrating the dynamics of the system.

The aim of this project is to build a machine-learning ternary interatomic potential for the WCu-H system, based on DFT calculations. This work, which has already begun, is being carried out in collaboration with Julien Tranchida, IRESNE, CEA Cadarache. We will build several models of W/Cu interfaces and determine the defects induced by the connection of two crystal lattices of different geometry and orientation. We will then study the interaction of these defects with hydrogen, and their impact on hydrogen diffusion properties at the copper-tungsten interface.

The candidate will benefit from structured supervision and access to a wide range of scientific skills, with each supervisor covering a specific area of expertise (DFT and Thermodynamics, Kinetics, Molecular Dynamics and ML potentials). The candidate will contribute to a subject developed within an international framework, benefiting from European funding and computational resources.

The interested candidate will ideally have good knowledge of the following methods: electronic structure calculations (plane wave DFT if possible), statistical thermodynamics, molecular dynamics. Skills in Python, bash scripting, Fortran 90 and machine-learning would be appreciated.

 

 

PhD Thesis (M/F) – Physics – Modeling – JR/1

Thesis advisor: Joël Rosato

Email and address: joel.rosato@univ-amu.fr

Tel: +33-413945714

 

Subject’s title: Characterization of white dwarf atmospheres by spectroscopic means

 

Subject description:

The theory of stellar structure knows three final states for a star: black holes, neutron stars and white dwarfs. According to observations and current models, the vast majority (of the order of 90%) of all stars, including our sun, will evolve towards the third final state, that of white dwarf [1,2]. These stars no longer burn nuclear fuel; instead, they are slowly cooling as they radiate away their residual energy. It is known today that white dwarfs support themselves against gravity by the pressure of degenerate electrons. They are referred to as compact objects because of their high density (up to 106 g/cm3). The characteristic cooling time of a white dwarf is closely related to the structure of its atmosphere, in particular its opacity to the radiation coming from the core. Studies have shown that the majority of white dwarfs have an atmosphere of pure hydrogen as a result of gravitational setting, which removes helium and heavier elements from the atmosphere and moves them towards inner layers [3,4]. These atmospheres can be considered as hydrogen plasmas, which are similar to some created in laboratory. Such white dwarfs are classified as of DA type due to the strong hydrogen absorption lines they present. The electron density in a white dwarf atmosphere is high enough (up to 1017 cm-3, and higher) so that the line shapes are dominated by Stark broadening and, hence, can serve as a probe for the electron density Ne. The goal of the PhD thesis is to improve the accuracy of the line shape models involved in white dwarf atmosphere diagnostics. Specific issues, such as the description of ion dynamics effects in Stark broadening [5], must be addressed. The observation of Zeeman pattern on several white dwarf spectra [6,7] has prompted a specific interest in the design of models accounting for the simultaneous action of electric and magnetic fields on the structure of atomic energy levels. Investigations must be done. The problem, which is similar to the modeling of spectra in magnetic fusion experiments, will possibly be tackled using models and codes previously developed in this framework and available at the laboratory. A part of the work will be devoted to the calculation of synthetic spectra and will involve the modeling of the stellar atmosphere structure.

 

Bibliography:

[1] S. L. Shapiro and S. A. Teukolsky, Black Holes, White Dwarfs, and Neutron Stars – The Physics of Compact Objects (Wiley, 2004).

[2] D. Koester and G. Chanmugam, Rep. Prog. Phys. 53, 837 (1990).

[3] G. Fontaine and G. Michaud, Astrophys. J. 231, 826 (1979).

[4] R. D. Rohrmann, Mon. Not. R. Astron. Soc. 323, 699 (2001).

[5] R. Stamm and D. Voslamber, J. Quant. Spectrosc. Radiat. Transfer 22, 599 (1979).

[6] B. Külebi et al., Astron. Astrophys. 506, 1341 (2009).

[7] S. O. Kepler et al., Mon. Not. R. Astron. Soc. 429, 2934 (2013).

PhD Thesis (M/F) – Physics – Modeling – MK/1

Thesis supervisor : Mohammed KOUBITI

Laboratory : PIIM, UMR7345 (http://piim.univ-amu.fr/)

Email & address : mohammed.koubiti@univ-amu.fr, Campus de St-Jérôme, Marseille, France.

Phone : +33 (0)4 13 94 64 47

Funding: Selection process through the Doctoral School ED 352, AMU

 

Exploring Deep Neural Networks for Fusion Plasmas Spectroscopy

Subject description: Artificial intelligence tools are taking an important place in plasma science [1] and particularly in plasma physics [2-4]. However, the integration of machine learning in the field of plasma spectroscopy is not well-developed despite some publications like those concerning 2D beam emission spectroscopy in the DIII-D tokamak for real-time inference of plasma dynamics [5], or neutral helium emission in linear plasma devices to predict plasma parameters using a support vector regression model (SVM) algorithm instead of the standard line ratio technique relying on collisional-radiative modelling [6-7], or a more recent work on the Balmer-b line (Hb /Db) in the WEST tokamak [8].

As non-invasive method, emission spectroscopy is widely used for diagnostics of magnetic fusion plasmas. Several parameters are diagnosed, e.g, the densities and temperatures of the electrons and main plasma ions, the impurity densities, and the temperatures and concentrations of the hydrogen isotope neutrals. Concerning the hydrogen isotopes, the knowledge of the isotopic ratio D/(D+T) is of great importance since tritium inventory is mandatory in magnetic fusion devices operated with DT mixtures for obvious safety reasons. To infer the hydrogen isotopic ratio, we have built a predictive model based on the application of Dense Neural Network (DNN) algorithms to theoretical Balmer Ha/Da line spectra generated for neutral temperatures and magnetic field strengths typical of tokamak edge plasmas [9-10].

More recently, the model was improved by the use of 1D Convolutional Neural Networks (1D-CNN) [11] to HD mixtures. In this thesis, it is proposed to develop predictive models based on different neural networks for more realistic conditions by considering DT as well as HDT plasmas but also to apply the models to experimental spectra from different tokamaks. We consider exploring experimental data measured in WEST (HD), JET (DT) and additionally JT-60SA through the EUROfusion WPTE involvement. Beyond their usefulness for future fusion devices like ITER, the development of predictive models will not be limited to Ha/Da/Ta spectra but extended to H isotopes and impurity spectra.

The selected candidate will have the task to develop, test and validate computer programs coupling NN algorithms to spectra. Such programs should be more general to be extended to various diagnostics.

Python and machine-learning skills as well as fusion plasma knowledges are greatly appreciated.

References

[1] E. Anirudh et al, IEEE Transactions on Plasma Science, 51, 1750 (2023)

[2] C. M. Samuell et al, Rev. Sci. Instrum., 92, 043520 (2021)

[3] B. Dorland, Machine-Learning for Plasma Physics and fusion energy, Journal of Plasma Physics (2022)

[4] Machine-Learning methods in plasma physics, Contrib. Plasma Phys., 63, Issues 5-6 (2023)

[5] L. Malhorta et al, 4th IAEA Technical Meeting on fusion data processing, validation and analysis (2021)

[6] S. Kajita et al, AIP Advances, 10, 025225 (2020)

[7] D. Nishijima et al, Rev. Sci. Instrum., 92, 023505 (2021)

[8] G. Ronchi et al, JQSRT 318, 108925 (2024)

[9] M. Koubiti and M. Kerebel, Appl Sci, 12, 9891 (2022).

Associate professor (M/F) in experimental and/or theoretical physics for Magnetic Confinement Fusion

During the 2025 associate professor recruitment campaign, Aix-Marseille Université will be offering a position for an associate professor in Physics (CNU section 28 ou CNU section 30)to carry out research in the PIIM (Physics of the Interactions of Ions and Molecules) laboratory.

This position will be based in the Faculty of Sciences, which is very committed to gender diversity in its recruitment and encourages a policy of parity in this area.

The profile of this post is shown below. In addition, these duties will require a real ability to communicate and work as part of a team in an international environment.

Applications may be submitted on the Odyssée application from 4 March 2025 10:00 to 4 April 2025 16:00 (Paris time). Applications cannot be submitted directly via this site.

However, applicants who are considering submitting an application may contact the laboratory to prepare their research project (see the research section below).

Candidates whose applications are selected by the selection committee will be interviewed on  May 16th 2025.

Research section

PIIM has a strong activity in the field of Magnetic Confinement Fusion, with 5 teams involved (Hydrogen, Molecules, Materials; Atomic Physics and Transport in Plasmas; Surface Plasma; Plasma, Theory and Modelling; Plasma Turbulence) in the activities of the FR-FCM national federation and the ISFIN institute.

The person recruited will present a project closely linked to the problems of magnetic fusion, as part of the activities of one of the five teams concerned. These teams work on the experimental, theoretical and numerical study of :

  • plasmas and their dynamics
  • plasma-wall interactions
  • surface physics and fusion materials.
    The development, implementation and interpretation of diagnostics is also a key area of activity. This research is carried out with strong international links, particularly at European level as part of the EUROfusion consortium, and in close collaboration with local players (CEA Cadarache, ITER). Experience in the field of fusion by magnetic confinement will be appreciated.

The skills expected for this recruitment are theoretical and/or numerical and/or experimental, depending on the host team and the nature of the project. Candidates should clearly explain their plans for joining the target team.

Teaching section

The teaching part will take place in the Physics Department of the Faculty of Sciences.

The person recruited will teach physics and/or physical chemistry at all levels, in the three entries to L1 (AMNS, ‘L1en2ans’ and portail) and in all the physics courses managed by the department, on four teaching sites (Marseille Saint-Charles, Saint-Jérôme, Luminy and Aix-Montperrin), particularly in the Physics and Physics-Chemistry bachelor’s degrees, the Fundamental Physics and Applications master’s degree, the Instrumentation Measurement Metrology master’s degree, and the ‘Nano2’ master’s degree in Nanosciences and Nanotechnologies. An interest in active and innovative teaching practices adapted to new university audiences, and/or the ability to teach in English in the department’s internationally-oriented courses, would be particularly welcome.

Post-doctoral (M/F) researcher in characterization of innovative carbon-based nanomaterials

A fully-funded post-doctoral position (2 years), as part of the i-DEMO regionalized project (France 2030) M.A.G.I.C. (Matériaux Avancés pour l’Innovation en Graphène et Cristallographie), is available until April 1, 2025 in the “Physique des Interactions Ioniques et Moléculaires” (PIIM) laboratory of Aix-Marseille Université, CNRS (France).

As part of the M.A.G.I.C. project, we are looking for an experimental postdoctoral researcher to work on the development and characterization of innovative carbon-based nanomaterials, such as Ginestium©, multilayer rhombohedral graphene and other relevant systems. Ginestium© could be a revolutionary nanostructured carbon material developed by EffiBLUE (https://effiblue.com). Multilayer rhombohedral graphene and some multilayer twisted graphene are known to be superconductors at temperatures close to 1K. Manipulating the structural properties of carbon-based materials, such as sp2/sp3 ratio and stacking configurations, enables fine-tuning of their physical characteristics, including electronic conductivity, optical response and mechanical strength. These tunable materials have great potential for applications in the electronics, telecommunications and energy sectors.

This complete job offer is available here. Applications should be sent via the candidate space on the CNRS website.

PhD Thesis (M/F) – Physics – 2025/2028 -Experimentation – AE/2

Organism: Aix-Marseille University

Laboratory: PIIM UMR 7345

Location: Campus Saint-Jérôme

Supervisor: Alexandre Escarguel

Funding : AMIDEX Aix-Marseille University project “Table Top Accretion Disks”

e-mail: alexandre.escarguel@univ-amu.fr 

Analysis and control of ExB magnetized plasma column self-organization in the frame of astrophysical accretion mechanisms’ study

This PhD proposes an innovative way to use a laboratory experiment to study Keplerian rotating discs in astrophysics. Indeed, stellar accretion disks are complex systems whose dynamics cover a large number of research fields. They are indeed made of dust, neutral gas and plasmas orbiting around young or rising stars and seed planet formation [1]. In link with the observation capabilities of modern instruments such as James Webb space telescope [2], intense efforts are nowadays undertaken to explain accretion mechanisms and disk formation. How a Keplerian rotation can lead to matter transport toward the center is still a matter of debate, since collisional diffusion is negligible in these systems, and Keplerian discs are stable with respect to classical hydrodynamics instabilities. How instabilities and transport occur, can be elucidated by setting up dedicated experimental devices. Laboratory plasma experiments with controlled plasma rotation is an innovative way to explore such scientific questions.

Mistral is a cold magnetized plasma experiment with a constant magnetic field [3, 4, 5, 6]. It is a canonical experiment to study various kind of instabilities of weakly magnetized ExB plasmas, such as centrifugal instabilities [7]. In the presence of a magnetic field B perpendicular to an electric field E, charged particles drift in the ExB direction. Combined with plasma inhomogeneities, this drift is favorable to the apparition of instabilities that considerably increase the transport across the magnetic field B (« anomalous transport »). These cross-field configurations are exploited in numerous applications.

Rotating plasma are easily obtained in the Mistral experiment, but there is a lack of control of the azimuthal differential rotation. This can be done by a fine control of the radial electric field profile in the plasma. Indeed, the prediction of the rotation properties and the control of the flow profiles is still an open problem regarding rotating plasmas in such devices. Previous works in our SoPlasma network (https://gitlab.com/soplasma/soplasma), including the Mistral device, have shown that rotation of plasmas can be challenging to control. Recent progress however provides a path to achieve this important objective by the use of concentric cold or hot cathodes [8, 9] . Another possible way to control the plasma column rotation specific to Mistral is to control the energetic ionizing electrons in Mistral by independent concentric grids.

Investigation of the plasma self-organization and experimental control of its rotation is the main objective of this PhD proposition. First, PhD student will study the stability/turbulent areas in the parameter space (plasma pressure and boundary conditions) by experimental acquisition of plasma parameters with Langmuir probes, fast camera and optical tomography. Second, new innovative experimental configurations will be studied to better control the plasma azimuthal differential rotation: concentric grids controlling ionizing electrons injection and cold/hot cathodes placed at the end of the plasma column.

Finally, a comparison of experimental results with theory will allow a better understanding of ExB plasma rotation physics to ultimately propose an experimental setup with a Keplerian plasma rotation. The importance of this part will be modulated, according to the student’s motivation for theoretical work.

The project, being within the framework of AMIDEX (“Excellence initiative” of Aix-Marseille University) project “Table Top Accretion Disks”, is 100% funded.

References

[1] G. R. J. Lesur, J. Plasma Phys. 87 205870101 (2021) [2] Burrows et al, Astrophys. J 473, 437 (1996), https://jwst.nasa.gov

[3] N. Claire, A. Escarguel, C. Rebont, F. Doveil, Phys.Plasma 25, 061203 (2018)

[4] A. Escarguel, Eur. Phys. J. D, 56, 209-214 (2010).

[5] Th. Pierre, A. Escarguel, D. Guyomarc’h, R. Barni, C. Riccardi, Phys. Rev. Lett., 92, 065004 (2004).

[6] S. Aggarwal, Y. Camenen, A. Escarguel, and A. Poye, Journal Plasma Phys., 89(3), 905890310 (2023).

[7] R. Gueroult et al, Phys. Plasmas 082102 (2017)

[8] B. Trotabas and R. Gueroult, Plasma Sources Sci. Technol. 31, 025001 (2022)

[9] V.Désangles et al, J. Plasma Phys. 87, 905870308 (2021) and Désangles, Ph.D. thesis, Ecole Normale Supérieure de Lyon, France (2018)

 

M2 internship – 2025 – Physics – Experimentation – TP/AE/3

Organism: Aix-Marseille University

Laboratory: PIIM UMR 7345

Location: Campus Saint-Jérôme

Supervisor: Alexandre Escarguel

Funding : AMIDEX Aix-Marseille University project “Table Top Accretion Disks”

e-mail: alexandre.escarguel@univ-amu.fr

 

Analysis and control of ExB magnetized plasma column self-organization in the frame of astrophysical accretion mechanisms’ study

 

This internship is the first step of a funded PhD subject, in the frame of the “Table Top Accretion Disk” project. It proposes an innovative way to use a laboratory experiment to study Keplerian rotating discs in astrophysics. Indeed, stellar accretion disks are complex systems whose dynamics cover a large number of research fields. They are indeed made of dust, neutral gas and plasmas orbiting around young or rising stars and seed planet formation [1]. In link with the observation capabilities of modern instruments such as James Webb space telescope [2], intense efforts are nowadays undertaken to explain accretion mechanisms and disk formation. How a Keplerian rotation can lead to matter transport toward the center is still a matter of debate, since collisional diffusion is negligible in these systems, and Keplerian discs are stable with respect to classical hydrodynamics instabilities. How instabilities and transport occur, can be elucidated by setting up dedicated experimental devices. Laboratory plasma experiments with controlled plasma rotation is an innovative way to explore such scientific questions.

Mistral is a cold magnetized plasma experiment with a constant magnetic field [3, 4, 5, 6]. It is a canonical experiment to study various kind of instabilities of weakly magnetized ExB plasmas, such as centrifugal instabilities [7]. In the presence of a magnetic field B perpendicular to an electric field E, charged particles drift in the ExB direction. Combined with plasma inhomogeneities, this drift is favorable to the apparition of instabilities that considerably increase the transport across the magnetic field B (« anomalous transport »). These cross-field configurations are exploited in numerous applications.

Rotating plasma are easily obtained in the Mistral experiment, but there is a lack of control of the azimuthal differential rotation. This can be done by a fine control of the radial electric field profile in the plasma. Indeed, the prediction of the rotation properties and the control of the flow profiles is still an open problem regarding rotating plasmas in such devices. Previous works in our SoPlasma network (https://gitlab.com/soplasma/soplasma), including the Mistral device, have shown that rotation of plasmas can be challenging to control. Recent progress however provides a path to achieve this important objective by the use of concentric cold or hot cathodes [8, 9]. Another possible way to control the plasma column rotation specific to Mistral is to control the energetic ionizing electrons in Mistral by independent concentric grids.

Investigation of the plasma self-organization and experimental control of its rotation is the main objective of this work. Student will study the stability/turbulent areas in the parameter space (plasma pressure and boundary conditions) by experimental acquisition of plasma parameters with Langmuir probes and fast camera. This will allow to find the most adapted plasma regime for the control of differential plasma rotation. In parallel, theoretical approach will be started. The importance of this part will be modulated, according to the student’s motivation for theoretical work.

The project, being within the framework of AMIDEX (“Excellence initiative” of Aix-Marseille University) project “Table Top Accretion Disks”, is 100% funded.

 

References

[1] G. R. J. Lesur, J. Plasma Phys. 87 205870101 (2021) [2] Burrows et al, Astrophys. J 473, 437 (1996), https://jwst.nasa.gov

[3] N. Claire, A. Escarguel, C. Rebont, F. Doveil, Phys.Plasma 25, 061203 (2018)

[4] A. Escarguel, Eur. Phys. J. D, 56, 209-214 (2010).

[5] Th. Pierre, A. Escarguel, D. Guyomarc’h, R. Barni, C. Riccardi, Phys. Rev. Lett., 92, 065004 (2004).

[6] S. Aggarwal, Y. Camenen, A. Escarguel, and A. Poye, Journal Plasma Phys., 89(3), 905890310 (2023).

[7] R. Gueroult et al, Phys. Plasmas 082102 (2017)

[8] B. Trotabas and R. Gueroult, Plasma Sources Sci. Technol. 31, 025001 (2022)

[9] V.Désangles et al, J. Plasma Phys. 87, 905870308 (2021) and Désangles, Ph.D. thesis, Ecole Normale Supérieure de Lyon, France (2018)