Catégorie d'emplois: Physics

Tenure track 4 years (M/F)

The AMUtech institute created in January 2021 aims to lead and coordinate the forces of Aix-Marseille in materials science and nanotechnology by developing collaborations between the 9 joint research units (UMR) it has federated and among which is the PIIM laboratory.

Applications are open between April 13 and May 22, 2023 on the Galaxie website.

The position is expected to start between November 1, 2023 and January 1, 2024

The attached file contains all the information to apply. The English version is included.

If you wish to set up a project in connection with these themes of this tenure track (graphene and modified/functionalized analogues experimentally and/or ab initio ) do not hesitate to contact the laboratory without delay, which will direct you to the researchers concerned.

Thesis subjects (M/F) – physics – 2023/2026

The PIIM laboratory proposes several doctoral theses, over three years, for the period 2023/2026.
These theses are part of the preparation of a doctoral degree at the University of Aix-Marseille.

The thesis topics are available below and on the website of the “Physics and Matter Sciences” doctoral school (ED 352 – choose PIIM laboratory)

 

 

To apply, read the subjects and, from now, contact directly the supervisors whose names and contacts are mentioned on the subjects.At this stage, you will have to provide all or part of a file including a CV, a letter of motivation, a transcript of your master’s grades and honors, letters of recommendation from the person in charge of the program and the person in charge of the master’s internship, and copies of your diplomas.

The selection process will take place in two stages.

First, the applications will be examined internally at the laboratory level. This selection must be completed by the lab on April 3, 2023 ; so apply as soon as possible. Several applications will be selected, each on a different topic, to advance to the second phase of selection.

In the second phase, the selected candidates will be presented by the laboratory to the doctoral school and will have to defend their candidacy in front a jury composed by the doctoral school. The laboratory will help the selected candidates to prepare this audition, which will take place by videoconference via Zoom at the end of May 2023.

The result of this selection will be communicated to the candidates probably at the beginning of June by the doctoral school.

The successful candidates will be offered a 3-year work contract with Aix-Marseille University. This contract will start between October 1 and December 1, 2023, and will of course be conditional first on obtaining the master’s degree and then on renewing the doctoral registration for each of the next three years.

The thesis will take place at the PIIM laboratory, on the Saint-Jérôme site, in Marseille, where the laureates will come to work every day for 3 years.

The selected persons will thus have a double status. They will be both students and staff of the university:

As students, they will have to register at the university and pay tuition fees each year, which in 2023 will amount to €380, to which must be added an annual student and campus life contribution (CVEC) of €95. These amounts are subject to re-evaluation each year by French State. As a student, it may be possible to obtain housing through the CROUS and to access university restaurants at student rates.

As a university employee, a salary of €1975 gross per month (i.e. approximately €1622 net) will be paid and in return the doctoral student will be subject to the rights and obligations of all public employees. This salary will be revised according to the measures taken by the State to reach 2300 € gross monthly in 2025. It could possibly be increased by the exercise of a complementary mission of teaching, diffusion of scientific culture or expertise.

The preparation of the doctorate thus constitutes at the same time a training and a professional experience.

The PIIM laboratory brings a particular attention to the reception and the follow-up of the PhD students who work there. It implements its means in order to make this period as attractive and fruitful as possible.

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

Artificial intelligence (AI) and data science techniques are increasingly used in physics including magnetic fusion plasmas. For instance, the Machine Learning (ML) package Sickitlearn [1] was recently used for plasma parameter predictions in 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, neutral helium line intensities were treated using a support vector machine regression algorithm from sickit-learn to predict electron density and temperature values which were compared to values deduced from independent diagnostic techniques like Langmuir probes or Thomson scattering [2-3].

In this proposal, it is suggested to couple supervised Machine Learning techniques to spectroscopic data for the purpose of plasma diagnostics and predictions for future experiments. As a first step, the work will be focused on spectroscopic data of hydrogen isotopes from tokamaks combined with independent diagnostic systems for isotopic ratio determination. Because tritium inventory is mandatory in magnetic fusion devices operated with D-T mixture for safety reasons, the determination of the hydrogen isotopic ratio D/(D+T) is of great importance. In order to explore experimental data from D-T discharges carried out recently on JET as well a better preparation for future D-T discharges to be operated in fusion devices like ITER, it is necessary to determine the isotopic ratio H/(H+D) and D/(D+T) for H-D and D-T discharges. There are few methods to infer the hydrogen isotopic ratio like the residual gas analysis (RGA) [5] or the use of the Balmer-a line spectra [6-7]. The candidate will have the task to develop a computer program (in Python) allowing to fit experimental spectral measurements of the Hα/Dα line [8]. Hα/Dα/Tα line shapes reflect several recycling mechanisms and are affected principally by Zeeman and Doppler effects.

1. F. Pedregosa et al 2011 the Journal of machine Learning research 12 2825
2. S. Kajita et al 2020 AIP Advances 10 025225
3. D. Nishijima et al 2021 Rev. Sci. Instrum. 92 023505
4. S. Kajita et al 2021 Plasma Phys. Control. Fusion 63 055018
5. A. Drenik et al 2017 Phys. Scr. T170 014021
6. V. S. Neverov et al 2019 Nucl. Fusion 59 046011.
7. M. Koubiti and R. Sheeba 2019 atoms 7 23
8. M. Koubiti and M. Kerebel 2022 Appl Sci 12 9891

This internship can be pursued by a PhD thesis with funding by doctoral school ED352

Thesis – Physics – Modeling – 2212/TP/YE/2

The proposed thesis subject is : advanced shaping of wave-particle interaction in traveling wave tubes

Before addressing the details of this subject further down in the text, it is appropriate to specify for the attention of the candidates (F/M) the practical modalities of this thesis and of the preparation of the doctoral degree in which it is included.

This thesis is in the framework of a French PhD diploma, prepared at the doctoral school “Physics and Material Sciences” (ED252) of Aix-Marseille University. The start is planned for the fall of 2023. Half of the funding is provided by the French Centre National d’Etudes Spatiales (CNES) and the other half by the company Thales. For the successful candidate (F/M), it will take the form of a fixed-term employment contract called “doctoral contract” for a period of 3 years from 01/10/2023 to 30/09/2026. The employer would be the CNES and the thesis would take place at the PIIM laboratory in Marseille with regular travel to Thales in Velizy (Paris area). The selected candidate (F/M) would be consequently employed by CNES for 3 years, the work contract remaining conditioned by the continuation of the preparation of the PhD.

Thus, the applications will have to be, in due time, formalized with the CNES, on its application site, i.e. between 01/02/2023 and 15/03/2023 when the position is posted.

Before applying, it is strongly recommended to read very carefully the subject and then to contact as soon as possible by mail the future co-supervisors, Professor Yves Elskens (yves.elskens (at) univ-amu.fr) at the PIIM laboratory, and Frédéric André (frederic.andre (at) thalesgroup.com), research engineer at Thalesgroup (AVS Microwave and Imaging Systems).

This topic is also closely related to the internship offered at the laboratory from March to July 2023. It goes without saying that a successful internship on this topic finds its natural extension in the preparation of the PhD.

Thesis subject : advanced shaping of wave-particle interaction in traveling wave tubes

Wave-particle interaction is a fundamental process in the physics of hot and natural plasmas, accelerators and beams ; in particular, it is the basis of wave amplifiers such as free electron lasers, gyrotrons, traveling wave tubes… The power in some of these devices and their broad frequency spectrum lead to instabilities, nowadays increasingly critical and hard to simulate. A microscopic description enables a better understanding of the coupling mechanisms between N particles and the amplified radiofrequency waves using hamiltonian dynamics. For N → ∞, the dynamics of this system converges to the one described by vlasovian kinetic equations.

Numerical simulation currently relies on two types of models. Particle-in-Cell (PIC) models rest on a minimal simplification of physics equations but lead to huge computing times, as the number of degrees of freedom is very large. Specialized models, in contrast, allow simulating only particular regimes, but with outstandingly shorter times.

The very popular envelope model is a frequency-domain model in which the amplified wave is represented by the cold wave (the wave propagating in the absence of beams), multiplied with an envelope function varying with the position along the propagation direction. This frequency-domain approach is not fit for investigating nonlinear regimes, like saturation instabilities and intermodulation effects.

We developed a novel time-domain model with few degrees of freedom thanks to an efficient representation of fields, enabling a realistic simulation of amplification in traveling wave tubes. We shall confront these simulations with experiment in space traveling wave tubes and in the 4 metre long device which enabled our laboratory to perform the first direct observation of several fundamental processes of this physics.

The Ph.D. will focus on developing simple nonlinear models and using them numerically toward applications in particular to the traveling wave tubes of Thales Avionics (Vélizy) and in our laboratory (Marseille). Three specific research lines are being considered :

– adapting the current model (designed for uniform structures) to structures with space-dependent characteristics (tapers) ;

– describing more accurately the reflection processes at space-dependent defects ;

– investigating the operation of TWT with pulsed RF input (instead of permanent harmonic input) ; this pulsed regime may enable reachng much higher interaction efficiencies ; this physics is also relevant to other applications, aiming at accelerating particles using short pulses. A master degree internship is open with our team from March 2023.

References :
– Y. Elskens & D. Escande, Microscopic dynamics of plasmas and chaos (IoP Publishing, Bristol, 2003).
– F. André, P. Bernardi, N.M. Ryskin, F. Doveil & Y. Elskens, Hamiltonian description of self-consistent wave-particle dynamics in a periodic structure, Europhys. Lett. 103 (2013) 28004.
– D.F.G. Minenna, Y. Elskens, F. André & F. Doveil, Electromagnetic power and momentum in N-body hamiltonian approach to wave-particle dynamics in a periodic structure, Europhys. Lett. 122 (2018) 44002.
– Kh. Aliane, Y. Elskens, F. André & D.F.G. Minenna, Many-particle models and short pulse amplification in traveling wave tubes, IEEE Trans. El. Dev. 68 (2021) 6476-6481
– D.F.G. Minenna, Kh. Aliane, Y. Elskens, A. Poyé, F. André, J. Puech & F. Doveil, Time simulation of the nonlinear wave-particle interaction in meters long traveling-wave tubes, Phys. Plasmas 28 (2021) 092110
– PhDs in Marseilles : A. Macor (2007), A. Aïssi (2008), P. Bernardi (2011), S. Théveny (2016), D. Minenna (2019), Kh. Aliane (in progress).

M2 Intership – Physics – experimental – TP/NC/1

Plasma experiments on earth all need a container: magnetic confinement fusion devices, electrostatic nuclear fusion devices, experimental bench test, satellite thrusters, magnetrons for industrial thin layer depositions, etching devices, decontamination… For unmagnetized plasmas, the Bohm criterion separates the quasi-neutral presheath from the high potential gradient sheath but it has been theoretically demonstrated by simulations that this sheath criterion disappears in magnetic sheath with a low incidence angle1,2 of magnetic field. Several theoretical analysises3,4 explain our experimental results5 exhibiting a thermalization of the Ion Velocity Distribution Function (IVDF) with two physical contradictory phenomena: collisions and ballistic effects. Langmuir probe6 is the most used diagnostic to measure plasma properties by collecting currents through its own surrounding sheath. The interpretation of this diagnostic is an opened issue since a theoretical sheath model is still needed to analyze measurements. For electron emissive surface sheath, if the rate of electron emission is high enough, inverse sheath is predicted7 but is still not experimentally observed. Because of a very low sheath thickness and a high potential gradient, only the non-intrusive laser-induced fluorescence (LIF) diagnostic can be used. This powerful diagnostic of which the supervisor is an expert, allows the space and time Ionic Velocity distribution Function (IVF)8 measurements even if some artefacts have been identified by authors and must be considered9.

This internship proposes to study electrons emissive sheath by a dedicated plasma experiments measuring IVDF in a non-intrusive way by LIF8 diagnostic in a low pressure DC Argon discharge. This study will start with a classical floating sheath study to validate modelisations (kinetic, fluid and PIC simulations developed in another team of the lab) to an electrons emissive sheath. The emissive cathode will be either a heating conducting metallic surface or a heated insulated ceramic.

1. Chodura, R., Phys. Fluids 25, 1628 (1982).
2. Stangeby, P. C., Nucl. Fusion 52, 083012 (2012).
3. Baalrud, S. D. & Hegna, C. C., Plasma Sources Sci. Technol. 20, 025013 (2011).
4. Coulette, D. & Manfredi, G., Phys. Plasmas 22, 043505 (2015).
5. Claire, N., Bachet, G., Stroth, U. & Doveil, F., Phys. Plasmas 13, 062103 (2006).
6. Chen, F. F. Langmuir Probe Diagnostics. IEEE-ICOPAS Meeting (2003).
7. Campanell, M. D., Phys. Rev. E 88, 033103 (2013).
8. Pigeon, V., Claire, N., Arnas, C., Terasaka, K. & Inagaki, S., Phys. Plasmas 27, 043505 (2020).
9. Pigeon, V., Claire, N., Arnas, C. & Doveil, F., Phys. Plasmas 26, 023508 (2019).

M2 Intership – Physics – modelling – TP/YE/1

Wave-particle interaction is a fundamental process in the physics of hot and natural plasmas, accelerators and beams ; it is the basis of wave amplifiers such as free electron lasers, gyrotrons, traveling wave tubes… where a focused electron beam transfers momentum and power to radiofrequency modes of a waveguide. In particular, traveling wave tubes enable the efficient and robust operation of satellite telecommunications and data transmission from space probes, and they enable analysing beam-plasma interactions without the noise and some nonlinearities inherent to plasma.

The power in some of these devices and their broad frequency spectrum lead to instabilities, nowadays increasingly critical and hard to simulate. A microscopic description enables a better understanding of the coupling mechanisms between N particles (xl, pl) and M waves (with phases φj and intensities Ij) using a so-called self-consistent hamiltonian.

For N → ∞ and fixed M, the dynamics of this system converges to the one described by vlasovian kinetic equations. Numerical simulation currently relies on two types of models. Particle-in-Cell (PIC) models rest on a minimal simplification of physics equations but lead to huge computing times, as the number of degrees of freedom is very large. Specialized models, in contrast, allow simulating only particular regimes, but with outstandingly shorter times. The very popular envelope model is a frequency-domain model in which the amplified wave is represented by the cold wave (the wave propagating in the absence of beams), multiplied with an envelope function varying with position along the propagation direction. This frequency-domain approach is not fit for investigating nonlinear regimes, like saturation instabilities and intermodulation effects.

We developed a novel time-domain model with few degrees of freedom thanks to an efficient representation of fields, enabling a realistic simulation of amplification in traveling wave tubes. We confront these simulations with experiment in space traveling wave tubes and in the 4 metre long device which enabled our laboratory to perform the first direct observation of several fundamental processes of this physics, and at CEA CELIA.

The internship may focus on the interaction of the radiofrequency signal with electron pulses, to use the resulting models in particular for the traveling wave tubes of Thales Avionics (Vélizy), in our laboratory (Marseille), and for the acceleration of protons generated by a laser shot on a metallic target (CEA CELIA).

The project may extend to a Ph.D. if possible.

– Y. Elskens & D. Escande, Microscopic dynamics of plasmas and chaos (IoP Publishing, Bristol, 2003).
– D.F.G. Minenna, Kh. Aliane et al., Time simulation of the nonlinear wave-particle interaction in meterslong traveling-wave tubes, Phys. Plasmas 28 (2021) 092110 (15 pp.).
– J.V. Gomes et al., Low-dimensional chaos in the single wave model for the self-consistent wave-particle hamiltonian, Chaos AIP 31 (2021) 083104 (17 pp.).
– Ph.D.s in Marseilles : A. Macor (2007), A. Aïssi (2008), P. Bernardi (2011), S. Théveny (2016), D.F.G. Minenna (2019), Kh. Aliane (in progress). https://phys.org/news/2019-03-traveling-wave-tubes-unsung-heroes-space.html