Seminar by Dominique ESCANDE – Laboratoire PIIM

A seminar given by

Dr. Dominique Franck Escande,

Emeritus Research Director, Laboratoire PIIM


Plasma-wall self-organization in magnetic fusion, theory and experiments

will take place on
Tuesday, December 19th at 15:00
in the Salle du Conseil, service 322 of the PIIM laboratory (Campus St. Jerome)
Abstract: Increasing the density limit in tokamaks would make easier ITER operation and would enable smaller reactors than presently considered. This sounds possible on the basis of a theory of plasma-wall self-organization published in 2022, and of its first experimental confirmation published in 2023. These results were presented in a poster at the 2023 IAEA Fusion Energy Conference. The basic theoretical idea is the existence of a time delay in the feedback loop relating radiation and impurity production on divertor targets. A way to increase the density limit in tokamaks is suggested by the plasma breakdown in the W7-X stellarator at high density of neutrals and high power electron cyclotron resonance heating: it yields an initial density an order of magnitude higher than in tokamak breakdown. Better performance is expected from plasma-wall self-organization with tungsten walls where physical sputtering dominates, than with carbon ones. Therefore, the first experimental confirmation in the J-TEXT tokamak despite its carbon walls is very encouraging. A proposal is made for the 2024 EUROfusion program of parallel experiments in the TCV, ASDEX Upgrade, and WEST tokamaks, the last two ones with tungsten walls.

Seminar by Jordan DEZALAY – Laboratoire PIIM

A seminar given by

Dr. Jordan Dezalay,

Laboratoire PIIM


Photodissociation spectroscopy: a tool for probing biomolecules excited states properties

will take place on
Thursday, November 30th at 10:30
in the Salle du Conseil, service 322 of the PIIM laboratory (Campus St. Jerome)
Abstract: Understanding the photophysical properties of biomolecules plays an important role in understanding the stability of these molecules or in developing new applications (fluorescence microscopy, photodynamic therapy). Studying photophysical properties in biological medium is quite challenging, the presence of a complex environment (intra/intermolecular bonds, folding, hydration, complexation) can favour the formation of certain isomers, activate charge transfers or modify deactivation processes. To look at these properties several groups have developed electrospray coupled with cryogenic ion storage systems like in ISMO (Orsay) or PIIM. UV/Visible/IR lasers are sent into these traps to perform time- and energy-resolved photodissociation spectroscopy experiments. I will present some of the results obtained with these devices on relaxation processes in DNA bases. Recently, the two groups have developed double-cooled ion traps that produce ion aggregates with precise control over the nature and quantity of the surrounding medium. I will illustrate this progress with results obtained on small hydrated peptide aggregates. Finally, I will present a subject I want to pursue in my research in PIIM, radical ion spectroscopy the production of which is challenging in the gas phase. I will thus present an innovative study on DNA base radical cations.

Seminar by John M. Finn – Tibbar Plasma Technologies (USA)

A seminar given by

Dr. John M. Finn,

Tibbar Plasma Technologies (USA)


Meshfree analysis and stability in particle-based kinetic plasma simulations

will take place on
Monday, November 20th at 10:30
in the Salle du Conseil, service 322 of the PIIM laboratory (Campus St. Jerome)

Abstract: We reconsider a meshfree approach to plasma kinetic theory, specialized to 1D electrostatic plasmas. This method uses kernel density estimation for the charge density and a related Green’s function method, from Gauss’s law, for the electric field. The kernel K(x−y) represents the the charge distribution within each macroparticle, both for computing the electric field E(x) and for using E(x) to compute the force on each macroparticle. This method has good conservation properties, conserving momentum and energy exactly. Similarly, the continuity equation is satisfied exactly, and this Vlasov-Gauss system is exactly equivalent to the Vlasov-Ampere and the Vlasov-Poisson systems. The use of the same kernel above leads to a symmetric / positive definite kernel, the correlation of the original kernel with itself, and allows an analog of the kernel trick in Machine Learning: a single positive definite kernel can be substituted for this correlation. We show how the positive definiteness of the kernel guarantees numerical stability. This analysis uncovers a connection between kernels used for density estimation and positive definite (reproducing) kernels. This analysis is useful for constructing meshfree codes and for analyzing PIC codes, which have a grid. For the latter, I will discuss how the numerical stability in the meshfree formulation can break down or be preserved with a grid, depending on the discretization.

Bio: Dr. Finn is a recognized expert in plasma physics as applied to magnetic fusion devices as well as solar and astrophysical plasmas and nonneutral plasmas. He worked at Los Alamos National Laboratory for 23 years, and at the University of Maryland and the Naval Research Laboratory before that. He has worked in the magnetohydrodynamic (MHD) stability and nonlinear behavior of toroidal devices such as tokamaks, reversed field pinches and spheromaks and in the basic theory of magnetic reconnection in laboratory, solar and astrophysical plasmas.

Seminar by Niels LIGTERINK – University of Bern (Switzerland)

A seminar given by

Dr. Niels F.W. Ligterink

SNSF Ambizione Fellow, Space Research & Planetary Sciences division, Physics Institute, University of Bern


Frozen starships: Studies of comet 67P and the interstellar object ‘Oumuamua

will take place on
Monday, October 23rd at 14:30
in the Salle du Conseil, service 322 of the PIIM laboratory (Campus St. Jerome) or by Zoom

Abstract: Comets are the frozen remnants of planet formation. Their icy composition reflects the physical conditions to which these objects were exposed, such as temperature and radiation. During this talk I present several new studies that help us understand the nature of comet 67P/Churyumov-Gerasimenko and the interstellar object 1I/’Oumuamua.

In the laboratory we simulate the desorption processes of noble gases and nitrogen (N2) from comet-like ice to unravel the ice structure and “warm” formation mechanism of 67P. For ‘Oumuamua I show that accelerating this object by releasing “invisible” H2 molecules requires a highly unusual composition in combination with a much older age than currently thought.
Bio: Niels Ligterink is a physical chemist who studies the behaviour, interactions and reactions of molecules in space, specifically focusing on the building blocks of life and biosignatures. With cutting edge space instruments, laboratory techniques, and telescope observations he tries to understand the chemical processes taking place on planetary objects in our Solar-System and in the depths of space, where new stars are born. Find more information



Seminar by David LUNNEY – Université Paris-Saclay, IJCLab, Orsay (France)

A seminar given by

Dr. David LUNNEY

CNRS researcher at the IJCLab (CNRS/IN2P3), Orsay (France)


The rise or fall of antihydrogen: the GBAR* experiment at CERN

will take place on
Thursday, September 28th at 10:30
in the Salle du Conseil, service 322 of the PIIM laboratory (Campus St. Jerome)

Abstract:  Since its birth a short century ago, General Relativity, with its cornerstone equivalence principle, has resisted withering experimental scrutiny.  Some quantum theories of gravity and models that define physics beyond the standard model include components of the gravitational interaction that are different for matter and antimatter.  While this would allow for a difference in their free fall, no experimental test has yet been made to verify this tantalizing possibility.  GBAR aims to meet this challenge, probing the equivalence principle for the first time with antihydrogen by dropping it to Earth.


Previous experiments attempting such a test with positrons and antiprotons failed due to the overwhelming influence of residual electromagnetic fields many orders of magnitude stronger than terrestrial gravity.  Two other experiments presently running at CERN circumvent this problem by using neutral antihydrogen however the inherent difficulty cooling it limits the eventual precision.  The original approach of GBAR is to use stored antihydrogen ions, created from successive atomic charge-exchange reactions.  The ions will be cooled sympathetically via laser-cooled Be+ crystals.  Once sufficiently cooled, the ion will be neutralized (by photo-detachment) and is subject to Earth’s gravitational field inside a detection chamber. 


In 2012, GBAR was accepted by the CERN Research Board (as experiment AD-7) and after development work in Saclay (on positron accumulation, involving one-component plasmas) and in Orsay (on antiproton deceleration), installation of the different components started in 2017.  GBAR was the first experiment to receive antiproton beams from the new low-energy storage ring ELENA at the end of 2018.


This presentation will address the physics motivation, describe the experimental components (including the AD facility – unique worldwide) and offer some (modest) initial results on the successful synthesis of antihydrogen in flight. 


*Gravitational Behaviour of Antihydrogen at Rest (

Seminar by Marie LANDEIRO DOS REIS – La Rochelle Université, LaSIE (France)

A seminar given by


Enseignante-Chercheuse à La Rochelle Université, LaSIE (France)


Interaction between point-defects and dislocation

will take place on
Thursday, July 6th at 11:00
in the Salle du Conseil, service 322 of the PIIM laboratory (Campus St. Jerome)

Abstract: The plastic properties of crystalline materials are not solely determined by the presence of defects within the crystal structure, but also by the interactions between these defects. In metals, the interactions between point defects and dislocations have been extensively studied and are known to play a crucial role in various mechanical behaviors. For instance, at low or moderate temperatures, point defects significantly influence strain hardening or softening and strain ageing. At higher temperatures, the absorption or emission of point defects along the dislocation lines enables dislocation climb and thus impacts creep. Understanding these interactions is essential for predicting and controlling the mechanical behavior of crystalline materials. The aim of this presentation is to introduce methods for investigating the interaction between dislocations and point defects at different scales. We will explore these methods in the context of several crystalline materials, including aluminum, magnesium oxide, and iron, and examine the interaction for edge and screw dislocations with various point defects such as vacancies and hydrogen.

Dislocations are extended defects with a complex core structure that varies depending on the material. Hence, to fully capture the intricacies of the core and its local interactions with point defects, atomic-scale simulations are necessary. In particular, Density Functional Theory (DFT) simulations are a crucial step in capturing the electronic effects that arise when point defects are located within the dislocation core [1]. Point defects may be trapped by the core, which can hinder dislocation motion influenced by the Peierls barrier which depends on the presence of point defects. They may also experience accelerated diffusion through pipe diffusion mechanism. Alternatively, point defects can be absorbed by the core and participate in dislocation climb, which can affect the material’s creep behavior [2].  In order to accurately simulate the effect of defect concentration on dislocation glide or dislocation climb, larger-scale simulations in time and space are thus necessary. In these cases, an empirical potential approach using molecular dynamic or kinetic monte carlo simulations can be used to describe the interactions between point defects and dislocations, both at short and long ranges.

However, these simulations are extremely computationally expensive and cumbersome. When the distance between a point defect and a dislocation is large enough, their interaction can be modeled within the framework of elasticity theory [3], which is less computationally demanding than atomic-scale simulations. Studies have shown that a good agreement between theory and simulation results can be achieved using an approach based on elasticity theory and the dipole elastic approach [3, 4]. This approach enables us to describe not only the interaction between point defects and the dislocation’s far elastic field but also the diffusion of point defects [3, 5].

[1] Allera, Ribeiro, Perez and Rodney, Phys. Rev. Materials 6 (2022) 013608
[2] Landeiro, Proville, Marinica and Sauzay, Phys. Rev. Materials 4 (2020) 103603
[3] Clouet, Varvenne, Jourdan, Comput. Mater. Sci. 147 (2018) 49-63
[4] Landeiro, Carrez, and Cordier, Phys. Rev. Materials 5 (2021) 063602
[5] Landeiro, Giret, Carrez and Cordier, Comput. Mater. Sci. 211 (2022) 111490

*Corresponding author: (M. Landeiro Dos Reis)

Seminar by Abdou DIAW – Oak Ridge National Laboratory (United States of America)

A seminar given by

Dr. Abdou DIAW

Researcher at the Oak Ridge National Laboratory (United States of America)


Advancing Iterative Synthetic Diagnosis Workflow for Light Impurities on WEST

will take place on
Thursday, June 22th at 10:30
in the meeting room of service 361 (PTM team) of the PIIM laboratory (Campus St. Jerome)

Abstract: Despite limited poloidal diagnostic coverage in fusion devices, understanding impurity distributions across the poloidal extent is crucial for interpreting experimental results. Our developed iterative synthetic diagnosis workflow provides valuable insights into impurity sources and transport in the main Scrape Off Layer (SOL) plasma. The workflow utilizes uses hydrogenic plasma from a multifluid MHD code as fixed background, allowing an impurity transport code to determine poloidal charge state abundances. These abundances are further processed using the collisional radiative code ColRadPy, which converts them into spectral line intensities. To account for 3D effects such as sight lines and reflections off in-vessel components, we employ Raysect.

By comparing experimental measurements with synthetic results generated by the workflow, we iteratively adjust free parameters in the impurity transport code to achieve consistency between the synthetic and experimental outcomes. Our focus lies on oxygen, assumed to be the primary source of tungsten (W) sputtering, and includes experimental and SOLEDGE SOL power scans conducted on the WEST platform. The constructed synthetic workflow demonstrates good agreement with measured O II emission, offering valuable insights for future measurements of higher charge states.

We gratefully acknowledge the support of the U.S. Department of Energy (DOE) under Grant Numbers DE-SC0014664 and DE-AC05-00OR22725.


Seminar by Antonio TEJEDA – Laboratoire de Physique des Solides (Orsay, France)

A seminar given by

Dr. Antonio TEJEDA

Researcher at the Laboratoire de Physique des Solides (Université Paris-Saclay/CNRS)


Many-body effects in phase transitions in Sn/Ge(111) as a function of the temperature

will take place on
Tuesday, June 20th at 15:00
in the salle du Conseil – service 322 of the PIIM laboratory (Campus St. Jerome)

Abstract: We present here an investigation on the phase transitions of 0.33 ML of Sn on Ge(111) at low temperature. We have identified a (3 × 3) phase, characterized by a charge ordering settled by electronic correlation, which appears between the known metallic- (3 × 3) and the root3 insulating phase at very low temperature, The vertical distortion characteristic of the (3 × 3) phase is lost across the phase transition,. We identify the atomistic mechanism behind the stabilization of this charge ordered insulating phase and interpret these findings on the basis of theoretical calculations. Moreover, our experimental and theoretical results show a giant electron-phonon interaction at the (3×3) phase between 150 and 120 K. The electron-phonon interaction in α−Sn/Ge(111)−(3×3) is unusually large, since we find that theoretically λ, the electron mass enhancement for the half-filled band, is λ=1.3. This result is in good agreement with the experimental value obtained from high-resolution angle-resolved photoemission spectroscopy measurements, which yield λ=1.45±0.1. The giant electron-phonon interaction can be considered at least partially responsible for the different phases that this system shows at very low temperature.

Figure (a) Second derivative of the ARPES data along the ΓM3×3 direction. (b) Left: Fermi level region from (a). Right: Momentum distribution curves corresponding to the red lines shown in the left panel. (c) Experimental points and fit to the bare (black line) and the renormalized (dashed purple line) bands. The kink associated to electron phonon coupling is visible.





  1) R. Cortés et al. Phys. Rev. Lett. 96, 126103 (2006).

  2) R. Cortés et al. Phys. Rev. B 88, 125113 (2013).

  3) M.N. Nair et al. Phys. Rev. B 107, 045303 (2023).

Bio: Antonio TEJEDA’s research focuses on the control of electronic properties by structural modifications. His favorite objects are surfaces and other two-dimensional systems where physical properties can be significantly affected by defects, phase transitions or quantum confinement in nanostructures.

Seminar by Ghassan ANTAR – American University of Beirut (Lebanon)

A seminar given by

Dr. Ghassan ANTAR

Professor at the American University of Beirut (Lebanon)


The Suppression of large-scale turbulence in the Tokamak Scrape-off Layer

will take place on
Thursday, May 25th at 11:00
in the salle du Conseil – service 322 of the PIIM laboratory (Campus St. Jerome)

Abstract: Reducing and controlling turbulence at the edge of magnetic fusion devices have been the paradigm of fundamental and applied research for several decades in magnetic fusion. We show that when using radio-frequency waves to heat or drive the current in the plasma, turbulence is reduced and large scales are suppressed. This effect is now confirmed on many tokamaks and is shown to affect the whole scrape-off layer, which indicates that the wave affects the source of the instability. The mechanism by which this interaction takes place is shown to be the excitation by ‘sound waves’ that couple to the turbulent fluctuations.

Bio: Ghassan Antar is professor at the American University of Beirut and leader of the Laboratory for Plasma and Fluid Dynamics. Find more information here

Ghassan Antar.jpg


Seminar by Franciele KRUCZKIEWICZ – LAM (France)

A seminar given by


PhD candidate at Marseille Astrophysics Laboratory (France)


Laboratory constraints on interstellar ices: thermal desorption and far-infrared optical properties

will take place on
Friday, May 5th at 10:30
in the salle du Conseil – service 322 of the PIIM laboratory (Campus St. Jerome)

Abstract: The challenge of revealing the chemical composition, physical structure, and dynamics of the star and planet-forming regions advances when using all available tools, combining information from observations, models, and experiments. In this talk, I will present findings from laboratory experiments on thermal desorption and the optical properties of interstellar ices, which are crucial for refining models and interpreting observations.
We employed the Temperature-Programmed Desorption (TPD) technique to gather a series of ice sublimation data, which serves as a benchmark for current gas-grain astrochemical models. Additionally, we measured broadband optical constants of astrophysical ice analogues in the mid-infrared and terahertz ranges by combining state-of-the-art techniques, such as THz Time-Domain Spectroscopy and Fourier Transform Infrared Spectroscopy. This data is essential for accurately modelling dust continuum emission and radiative transfer in the dense and cold regions of the Interstellar Medium.
In conclusion, I will discuss the role of interstellar ices in the development of molecular complexity during the star formation process. Furthermore, I will highlight the application of novel laboratory techniques as benchmarks for interpreting broadband observations from existing and future ground-based facilities and space telescopes.