Internships Archives - Physics of the Interactions of Ions and Molecules

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)

M1 internship – 2025 – Physics – Experimentation – TP/AE/2

Organism: Aix-Marseille University

Laboratory: PIIM UMR 7345

Location: Campus Saint-Jérôme

Supervisor: Alexandre Escarguel

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 M1 internship will take place in the frame of A*MIDEX (“Excellence initiative” of Aix-Marseille University) project “Table Top Accretion Disks”, 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.

Investigation of the energetic ionizing electrons in Mistral is the main objective of this work. The student will study its energy distribution function with Langmuir probes and Retarding field Analysers in the parameter space of Mistral (plasma pressure and boundary conditions). This will allow to find the most adapted plasma regime for the control of differential plasma rotation.

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/1

Laboratory : PIIM/Turbulence Plasma team

Supervisors : Alexandre Escarguel and Laurence Cherigier-Kovacic

Tel: 06 42 54 87 97

Email : alexandre.escarguel@univ-amu.fr ; laurence.kovacic@univ-amu.fr

Subject : Optical electric field diagnostic in a magnetized plasma by Lyman-alpha stimulated emission (EFILE)

Subject description :

Project framework and experiment description:

Plasma, result from the partial or total ionization of neutral gases. Coupling between fields (electric, magnetic) and charged particles leads to collective effects and turbulence, specific to these media. Their behavior and their fields of application depend on the ion temperature: cold plasmas are used in industry for surface treatment (etching of circuits,deposits, production of reactive species, etc.); hot plasmas are produced in tokamaks (Tore-Supra, ITER…) in order to produce energy from controlled fusion. In both cases, it is essential to determine the fundamental parameters associated with the charged species present in the plasmas.

The Turbulence Plasma team has developed an optical diagnostic (EFILE) for direct measurement of an electric field in vacuum or in plasma [1, 2]. This diagnostic is based on the emission of the Lyman-α line by a hydrogen probe beam in the 2s state submitted to an electric field. As a result of the 2s-2p coupling created by the field, atoms in the 2s (metastable) level is transferred to the 2p level, which then rapidly de-excites to the ground level. The intensity of the electric field-induced Lyman-α emission is proportional to the square of the field amplitude. This diagnostic was experimentally validated in a simple cylindrical configuration, in vacuum and in a non-magnetized plasma.

Objective and description of the subject:

The objective of the thesis is to measure the electric field in a magnetized plasma. The EFILE diagnostic is being implemented on the MISTRAL machine of the Turbulence Plasma team of the PIIM laboratory. The MISTRAL machine [3, 4] produces a cold plasma column in a linear magnetic field, over a wide range of parameters. It is a fundamental research machine whose linear configuration simplifies the study of instabilities in a magnetized plasma (compared to tokamaks where the curvature of the magnetic field induces more complex phenomena). Mistral is the ideal device to validate the EFILE diagnostic which is a unique way of measurement of the electric field in a direct and non-intrusive way.

Present work is focused on the study of the influence of the magnetic field on the diagnostic and the measurement of an electric field at different points along the radius of the machine. These two aspects are studied in vacuum or in a plasma, independently of each other, in order to fully understand the capabilities of the diagnostic.

The selected student will proceed to the measurement of the electric field which, together with the magnetic field, is responsible for rotating non linear instabilities of the plasma column [5, 6].

The general objective of this work is to develop a diagnostic for the absolute measurement of a static or oscillating electric field that can be transferred to different systems and applied to various current research problems in plasma physics. Within this framework, the diagnostic will be applied by the student to the study of plasma sheaths, a crossdisciplinary issue involving cold plasmas, hot plasmas, applied mathematics, theories, simulations, and experiments [4].

This project is granted by the FR-FCM (Federation de Recherche sur le Fusion Contrôlée par Confinement Magnétique).

References

[[1] L. Chérigier-Kovacic, P. Ström, A. Lejeune and F. Doveil, Review of Scientific Instruments 86, 063504(2015); doi: 10.1063/1.4922856

[2] L. Chérigier-Kovacic, Static and RF electric field direct measurement based on Lyman-a emission from a hydrogen probe beam ; Invited talk @ XXXIV ICPIG conference, July 14-19 2019, Sapporo, Japan.

[3] A. Escarguel, ExB workshop, nov 2018, Princeton Plasma Physic Lab, USA.

[4] Atelier Gaine Plasma 4-6 novembre 2024, Marseille, https://gaine2024.sciencesconf.org/?lang=fr (consulté le 30 novembre 2024).

M2 Internship – Physics – Modeling – PATP/MK/1

Length: 4-6 months

Laboratory: PIIM, UMR7345, group PATP (Atomic Physics and Transport in Plasmas)

Supervisor: Mohammed KOUBITI (mohammed.koubiti@univ-amu.fr)

Address: Campus St Jérôme, Service 232, Av. Escadrille Normandie Niemen, Marseille

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

Research type: Theory/Numerical Modeling/Comparison with Experimental data

Subject description: Artificial intelligence (AI) is increasingly used in physics including magnetic fusion plasmas. For instance, a Machine Learning (ML) algorithm [1] was used recently to predict the plasma parameters for PISCES-B and NAGDIS linear plasma devices [2-3]. Unlike the standard line ratio technique which relies on collisional-radiative modelling [4], in [2-3] no physical model is combined with the spectroscopic measurements. More precisely, using the intensities of few neutral helium lines the electron density and temperature were predicted by the ML algorithm and compared to their values measured by independent diagnostic techniques like Langmuir probes or Thomson scattering [2-3]. In this internship proposal, we suggest applying deep-learning techniques to line spectra of hydrogen isotopes in tokamak plasmas. We will apply in particular Dense Neural Networks (DNN) and Convolutional Neural Networks (CNN) to generated spectra of hydrogen isotopes for the aim of plasma diagnostics and predictions for future experiments. Our objective of applying DL techniques to the line emission of hydrogen isotopes in tokamaks is the prediction of the hydrogen isotopic ratio (defined as D/(D+T) for a D-T mixture) whose knowledge is of great importance for safety reasons and reaction performance control [5-6]. The algorithms can be also applied to impurity spectra to predict their plasma parameters such as the electron temperature. The candidate will have the task to develop a computer program (in Python) allowing to apply DNN and CNN algorithms to Ha/Da/Ta line spectra generated by an existing code for various conditions in terms of neutral temperatures, neutral population densities, magnetic field strength and hydrogen isotopic ratio. Thanks to the involvement in the tasks of data analysis of the EUROfusion workplan Tokamak Exploitation (TE) for several tokamaks including JET, the candidate may also apply the trained deep-learning models to experimental data from devices like JET and/or WEST.

F. Pedregosa et al 2011 the Journal of machine Learning research 12 2825
S. Kajita et al 2020 AIP Advances 10 025225
D. Nishijima et al 2021 Rev. Sci. Instrum. 92 023505
S. Kajita et al 2021 Plasma Phys. Control. Fusion 63 055018
M. Koubiti and M. Kerebel 2022 Appl Sci 12 9891
N. Saura, M. Koubiti, S. Benkadda, Study of line spectra emitted by hydrogen isotopes in tokamaks through Deep-Learning algorithms, submitted to Journal of Nuclear Material Energy (2024).This internship can be followed by a PhD thesis with funding by doctoral school ED352

M2 INTERNSHIP – Physics – Modeling – PTM/MM/1

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 lengths.

This property break-down when the plasma encounters a solid frontiers where non-neutral sheath forms at Debye length scales 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 particular, when approaching an external object , which can be device boundaries in experiments or bodies in astrophysical contexts, multi-scale physics phenomena emerge especially where the sheath is formed. Surfaces immersed in a plasma could emit secondary electrons which change the physics of the sheath. Even more, some numerical theories predict an “inverse sheath” [1].

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 sheath [2]. However, comparisons of theoretical models to experiment can sometimes show disagreements, in particular in sheath where secondary electrons are emitted [1, 3, 4].

In that context, the first goal of this internship is to improve comparison between models (already existing) and experiments of electrostatic plasma sheath. Models developed during this internship will be compared with experimental results on emissive sheath obtained by the experimental group of the PIIM laboratory. The second goal of the internship is to improve the model adding the impact of an oblique magnetic field on the sheath properties.

Here, it is expected to improve the fundamental knowledge of the physical mechanisms at play in a magnetized plasma sheath that is crucial for fusion plasmas.

The student must have master’s level knowledge in mathematics, numerical calculation and plasma physics to carry out theoretical calculations and participate in numerical code development.

He will have available fluid [5] and kinetic codes developed at the PIIM.

The master’s internship will be supervised at the PIIM laboratory by M. Muraglia.

This subject is associated to a thesis subject funded by AMIDEX which will be directed by M.Muraglia and co-directed by G. Fubiani (Lalpace laboratory at Toulouse) and supervised by N.Claire (PIIM).

References

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

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

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

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

[5] J-H Mun et al [tPhys. Plasmas 31, 073906 (2024)]

[6] M. D. Campanell and M.V. Umansky, Physics of Plasmas 24, 057101 (2017)

M2 INTERNSHIP – Physics – Experimentation – CIML/CC/1

Supervisors: 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-JÉRÔME¹

WEB PAGE OF THE CIML GROUP : https://piim.univ-amu.fr/en/research/seven-teams-and-one-operation/ciml-team/

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

The CIML group has a strong expertise in ion trapping in radio-frequency trap, and laser cooling of these trapped ions. It is part of the European ion trapping group 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, where 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 the non-destructive detection of these heavy ions, to demonstrate a prototype for mass spectrometer detector without mass limitation. The exploited signal is the laser induced fluorescence and the underlying process is the energy transfer between a charged projectile and the plasma target, known as the stopping power of plasmas. 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 well 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 shown on the figure obtained by the image of their induced fluorescence on a CCD camera.

Objectives : We propose to a master student to join this project to observe and study 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, data acquisition and processing. This internship could be continued with a PhD.

¹ Saint-Jérome 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.