Catégorie d'événements: These defence

Adrien Poindron’s thesis defence

Thesis Defence
Adrien Poindron
Aix-Marseille University

Detection of a giant molecule with a trapped ion cloud

Supervisors: Martnina Knoop and Jofre Pedregosa-Gutierrez

Jury composition:

    Rodolphe ANTOINE, Research Professor, Institut Lumière Matière, Examiner
    Laurence CHARLES, Professor, Aix Marseille université, Examiner
    Laurent HILICO, Professor, Laboratoire Kastler Brosse, Reviewer
    Stefan WILLITSCH, Professor, Université de Bâle, Reviewer
    Martina KNOOP, Research Professor, Aix Marseille Université, Thesis Director
    Jofre PEDREGOSA-GUTIERREZ, assistant professor, Aix-Marseille université, Thesis supervisor

 

Keywords: Laser spectroscopy,Mass spectrometry,Trapped ions,Giant Molecules

Abstract : A new application for a laser-cooled trapped ion ensemble is proposed for the non-destructive detection of giant molecules. In this application a molecular ion is projected onto an ensemble of calcium+ ions. The detection signal is expected in the fluorescence of the ion set which may vary after the perturbation induced by the molecule. In parallel with the development of a prototype, we demonstrate the feasibility of the principle through numerical simulations. The thesis is organised in three parts: the first part presents the experimental aspects specific to the ion trapping, the second part deals with the experimental aspects specific to the molecular source and the guidance of a charged particle, the third part presents the numerical simulations conducted in order to numerically reproduce the interaction. With the simulations, we highlight the key roles of the coulombic interaction combined with radio-frequency heating in the cloud destabilisation mechanism leading to detection. The conditions favouring detection are studied, as well as certain aspects of ion trapping alone. The essential elements of the prototype are presented and discussed in the first parts. A description of the trapping of an ion set beyond the adiabatic regime is proposed. The essential characteristics of the large ion sets are presented. In particular, radio-frequency heating is discussed. At the molecular level, all the techniques used to deliver a molecular ion are described, taking into account the recent elements that appeared after the development of the prototype. A particular effort has been made to provide the elements necessary for the understanding and proper implementation of the molecular source elements. A detection of light ions by conventional means is implemented and discussed.

Samuele Mazzi’s thesis defence

Jury composition:

    1. Pascale Hennequin, Ecole Polytechnique (CNRS), France — Commitee president
      Paola Mantica, National Research Council, Italy — Reviewer
      Olivier Sauter, Swiss Plasma Center (EPFL), Switzerland — Reviewer
      Alberto Loarte, ITER Organization — Examiner
      Carlos Hidalgo, CIEMAT, Spain — Examiner
      Gerardo Giruzzi, CEA Cadarache, France — Invited
      Jeronimo Garcia, CEA Cadarache, France — Thesis supervisor
      David Zarzoso, AMU (CNRS), France — Thesis supervisor
      Sadruddin Benkadda, AMU (CNRS), France — Thesis Director

 

Keywords: Fast Ions, Microturbulence, Tokamak

Abstract:
The exploitation of magnetically confined fusion plasmas as a sustainable and clean energy source is limited by the radially outward turbulent transport. Such transport is mainly induced by microinstabilities. Next-generation fusion devices will be mainly heated by the alpha particles born from the nuclear fusion reactions. Alpha particles must be well confined in order to transfer their energy to the bulk ions. However, very little knowledge is available regarding the interaction between alpha particles and microturbulence. Thus, unexpected turbulence and transport regimes may lead to further detrimental effects on the performance of future alpha-heated devices. The study of a tokamak scenario which can mimic the experimental conditions expected in future devices is hence crucial. Numerical investigations on the impact of fast ions on the turbulent transport driven by Ion Temperature Gradient and Trapped Electron Mode instabilities in real experiments have been carried out. It is shown that a suppression of the ion-scale turbulent transport may be achieved. Alfvén Eigenmodes (AEs) destabilized by the highly energetic ions through a wave-particle interaction play an essential role in the multi-scale mechanism leading to the turbulence suppression. Deep analyses further highlight the possibility to recognize hallmarks of the ion-scale transport reduction, regardless the dominant turbulent regime.

Manuela Sisti’s thesis defense

Thesis Defence
Manuela SISTI
Aix-Marseille University

DETECTING AND INVESTIGATING MAGNETIC RECONNECTION IN SPACE PLASMA SIMULATIONS

Supervisors: Olivier Agullo, Matteo Faganello and Francesco Califano

Jury composition:

Clare Parnell, St Andrews University, UK, Rapporteure
Luca Sorriso Valvo, CNR, IT, Rapporteur
Vincent Génot, IRAP, FR, Examinateur
Gaetano Zimbardo, Università della Calabria, IT, Examinateur
Laurence Rezeau, Sorbonne Université, FR, Presidente du jury
Olivier Agullo, AMU, FR, Directeur
Matteo Faganello, AMU, FR, Co-Directeur
Francesco Califano, Università di Pisa, Directeur

Magnetic reconnection is a fundamental process in plasma physics being the only one able to rearrange the large-scale connections of magnetic field lines, allowing for important topological modifications of the field, despite it occurs in very small regions with respect to the system size. This change in the global topology allows the system to reach lower energy states otherwise forbidden and converts large amount of magnetic energy into kinetic energy, thermal energy and particle acceleration. Magnetic reconnection occurs in a large variety of space environments such as the solar corona, the Earth's magnetosphere, the turbulent solar wind.

Due to its importance and uniqueness, during the last decades magnetic reconnection has been extensively studied using theoretical models, numerical simulations and satellites' data. Still, some important questions remain to be elucidated. In particular, for what concerns simulations, detecting magnetic reconnection is a difficult task and finding reconnection signatures ask for a visual, not automatic, investigation. This is particularly true when simulations are not initialized with ``ad-hoc'' configurations, suitable for reconnection, but when current sheets were reconnection possibly develops are randomly generated by the turbulent dynamics, even in a simplified 2D geometry. The 3D case situation is even more complex since 3D reconnection dynamics is still a matter of debate even from a theoretical point of view.

The goal of this PhD thesis is to study magnetic reconnection in the context of space collisionless plasma, in particular in current sheets that are self-consistently generated by the plasma motion either by large-scale magnetohydrodynamic vortices (emerging after the development of the Kelvin-Helmoltz instability at the Earth's magnetospheric flanks) or by small-scale vortices in kinetic turbulence (as those developing in solar wind).

The main work of this Thesis addresses the possibility to use automatic techniques to individuate magnetic reconnection events in 2D Hybrid Kinetic simulations of plasma turbulence. These techniques are based on supervised (CNN) and unsupervised (KMeans and DBscan) machine learning methods. For what concerns the 3D case, the state-of-the-art of our work is presented. In particular, we statistically analyze magnetic reconnection events in a two-fluid 3D simulation of Kelvin-Helmholtz mediated magnetic reconnection at the Earth’s magnetospheric flanks. Finally, concerning 3D Hybrid Kinetic simulations of turbulence, we present a statistical analysis of current structures where potentially reconnection can occur, while the development of a machine learning technique to automatically individuate reconnection in 3D simulations is still ongoing.

Keywords: plasma physics, magnetic reconnection, machine learning