I have devoted my research activity to different aspects of turbulent transport, of self-organisation and pattern formation and to various aspects of violent relaxations, both with observational and theoretical approaches, aimed at deeper understanding of nonlinear, out-of-equilibrium systems.
Ü much insight can be gained by inter-disciplinary work connecting gephysics, astrophsics, fluid mechanics with magnetised plasmas to try to unravel basic principles of turbulence self-organisation
Current research builds upon the selected results below:
Proposition of a systematic, operational and fully self-consistent way to characterise and quantify the nonlocal aspects of the turbulent transport in magnetised plasma dynamics (beyond diffusive and local Fick's laws), as a nonlocal Lévy-kernel integral, often reducible to a Lorentzian and establishing avalanches (Lévy flights) as the dominant transport mechanisms in magnetised plasmas.
A new form of self-organisation is proposed: the plasma ExB staircase, of fundamental interest for basic as well as more applied physics across several fields: plasmas, geophysics, astrophysics and fluid dynamics.
Ü Work found in the following paper: G. Dif-Pradalier, P.H. Diamond, V. Grandgirard, Y. Sarazin, et al. On the validity of the local diffusive paradigm in turbulent plasma transport. Phys. Rev. E, 82: 025401(R), 2010
First experimental evidence of the ExB staircase in actual laboratory experiments. Breakthrough possible thanks to recent advances in fast-sweeping fluctuation reflectometry [Clairet 2011, Hornung 2013]
Confirmation of many of its expected theoretical features
Opens new perspectives in the understanding of the onset and dynamics of massive transport barriers in both plasmas and possibly planetary flows
Ü Work found in the following paper: G. Dif-Pradalier, G. Hornung, Ph. Ghendrih, Y. Sarazin, et al. Finding the Elusive E×B Staircase in Magnetized Plasmas. Phys. Rev. Lett., 114:085004, 2015
Proposition of a theoretical framework as to how the ExB staircase may form due to a heat flux jam propagation, based on analogies with "usual" traffic jams
Ü Work found in the following paper: Y. Kosuga, P.H. Diamond, G. Dif-Pradalier, Ö.D. Gürcan. E×B shear pattern formation by radial propagation of heat flux waves. Phys. Plasmas, 21(5):055701, 2014
Collisional dissipation is key to structure formation and flow organisation. A turbulence-borne, large-scale flow can organise and survive in a magnetised plasma and that this flow may significantly deviate from the "traditional" oft-used collisional ansatz, confirming earlier puzzling experimental observations.
Derivation of a nontrivial critical exponent for the resulting transport, function of distance to criticality
Ü Work found in the following paper (PhD prize for this work) G. Dif-Pradalier, V. Grandgirard, Y. Sarazin, X. Garbet and Ph. Ghendrih. Interplay between Gyrokinetic Turbulence, Flows, and Collisions: Perspectives on Transport and Poloidal Rotation. Phys. Rev. Lett., 103(6):065002, 2009.
Collisions (dissipation) in a "full-f" gyrokinetic framework: no scale separations
Ü Work found in the following paper: G. Dif-Pradalier, P.H. Diamond, V. Grandgirard, Y. Sarazin, J. Abiteboul, X., Garbet, Ph. Ghendrih, G. Latu, A. Strugarek, S. Ku and C.S. Chang. Neoclassical physics in full distribution function gyrokinetics. Phys. Plasmas, 18(6):062309, 2011.
First successful evidence of triggered transport barriers in a complete gyrokinetic framework for magnetised plasmas. Along came the surprise of their spontaneous relaxation:
Ü Work found in the following paper: A. Strugarek, Y. Sarazin, D. Zarzoso, J. Abiteboul, A.S. Brun, T. Cartier-Michaud, G. Dif-Pradalier, et al. Unraveling Quasiperiodic Relaxations of Transport Barriers with Gyrokinetic Simulations. Phys. Rev. Lett., 111(14):145001, 2013.
Selected invited presentations (2012—2015)
· 2015: “The ExB Staircase”, Banff International Research Station for Mathematical Innovation and Discovery, Casa Matemática Oaxaca, Oaxaca, Mexico
· 2015: “On the Inevitability of Staircases in drift–Rossby turbulence”, 3rd International Conference on Chaos, Complexity and Transport, Marseille, France
· 2015: “The Plasma Staircase: Turbulence Self-Regulation through Spontaneous Flow Patterning”, 7th IAEA Technical Meeting on “Theory of Plasma Instabilities”, Frascati, Italy
· 2015: “Drift-Rossby layering: plasmas & geophysics”, 7th Festival de Théorie, Aix-en-Provence, France
· 2013: “Spatial Propagation of Turbulence and Formation of Mesoscopic Structures in Plasma Turbulence”, US–EU Joint Transport Task Force Workshop, Santa Rosa, CA, USA
· 2013: “Avalanches & Staircase Formation”, 6th Festival de Théorie, Aix-en-Provence, France
· 2013: “ELM Cycle & Non-linear RMP Modeling in Realistic Plasma Geometries”, 23rd International Conference on Numerical Simulation of Plasmas, Beijing, China
· 2012: “Is ``near edge'' Transport non-local?”, 17th Joint EU–US Transport Task Force Workshop, Padova, Italy