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Per Helander05/10/2026, 10:00
For several decades, an enormous effort has been devoted to the gyrokinetic theory of instabilities and turbulence in stellarators and tokamaks. Thousands of papers have been published on this subject, and millions of lines of code have been written for the purpose of numerically solving gyrokinetic equations.
As a result of this effort, a great deal of knowledge about various...
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Michele Campisi (Istituto Nanoscienze CNR, Pisa, Italy)05/10/2026, 10:40
Quantifying the ergotropy (also known as available energy), namely the maximal amount of energy that can be extracted from a thermally isolated system, is a central problem in quantum thermodynamics. Notably, the same problem has been long studied for classical systems as well, e.g., in plasma physics and astrophysics, where the basic principles for its solution are known for the case of...
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Ralf Johannes Josephus Mackenbach (EPFL-SPC)05/10/2026, 11:50
Given a collisionless plasma, how much of its energy can turbulence actually extract? A natural answer is to rearrange the distribution function into its lowest-energy configuration, subject to the constraints of the underlying dynamics; an idea that has been used across time and disciplines, from Lorenz's available potential energy in meteorology to Gardner's restacking argument [1] and the...
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Kaixuan Fan (Shanghai Jiao Tong University)05/10/2026, 14:00
We propose a method for predicting the nonlinear saturation level of convective instabilities in neutral and magnetized fluids. The method combines Gardner's restacking algorithm, which computes the available energy and ground states of collisionless plasmas in phase space, and Lagrangian relaxation, where fluid elements find lower-energy equilibria while preserving local invariants. For the...
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Paul Costello (Max Planck Institute for Plasma Physics)05/10/2026, 14:40
The microinstabilities that cause the confinement-limiting turbulence in modern fusion devices are driven by the radial gradients of density and temperature in the plasma. In multi‑scale gyrokinetic theory [1], these gradients act as a source of background free energy that feeds instabilities on the fluctuating micro scales, giving rise to turbulence, and ultimately, energy transport down the...
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DR Hatch05/10/2026, 15:50
Transport barriers in magnetically confined plasmas pose an intriguing thermodynamic problem: large gradients, and hence substantial free energy, can coexist with strongly reduced turbulent transport. We examine this phenomenon from the perspective of constrained nonequilibrium dynamics. A macroscopic thermodynamic model treats the plasma boundary layer as a heat engine in which incoming power...
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Daishi Toriyama (GSES, Kyoto Univ.)05/10/2026, 16:30
Plasma turbulence is a dominant factor limiting energy confinement time in toroidal fusion plasmas, making computationally cheap confinement proxies highly desirable for quickly identifying experimentally attractive scenarios. In this presentation, we investigate whether "Available Energy (AE)” - an upper limit on the thermal energy available to drive Trapped Electron Mode (TEM) turbulence in...
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Dr Robert Ewart (Stanford University)06/10/2026, 10:00
We review the Lynden-Bell formalism of deriving maximum entropy states subject to the short-time conservation of certain (fragile) collisionless invariants. The conservation of these collisionless invariants endows the system with a partial “memory” of its prior conditions but is fragile precisely due to the development of a turbulent cascade to small scales, which breaks the precise...
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Uddipan Banik (Institute for Advanced Study)06/10/2026, 10:40
Non-thermal power-law distribution functions are ubiquitous in astrophysical, space, and laboratory kinetic plasmas, but their origin remains unclear. A related puzzle is the temperature inversion of the solar corona. We show that these phenomena are deeply connected by developing a self-consistent quasilinear theory for electromagnetically driven, unmagnetized kinetic plasmas. The theory...
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Dr W Sengupta06/10/2026, 11:50
The dynamical accessibility of a quasistationary state from the infinitely many formal equilibria of the Vlasov-Poisson system is addressed. We give a first-principles asymptotic selection theory for Bernstein-Greene-Kruskal (BGK) holes produced by two-stream relaxation and cold gravitational clumps produced by collisionless collapse. The analytic construction rests on two central ideas....
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David Hosking (University of Cambridge)06/10/2026, 14:00
Motivated by explosive releases of energy in fusion, space and astrophysical plasmas, we consider the nonlinear stability of stratified magnetohydrodynamic (MHD) equilibria against two-dimensional interchanges of straight magnetic-flux tubes. We demonstrate that, even within this restricted class of dynamics, the linear stability of an equilibrium does not guarantee its nonlinear stability:...
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Michael Nastac (University of Oxford)06/10/2026, 14:40
Nearly collisionless self-gravitating systems far from equilibrium, such as merging galaxies, rapidly relax toward virialized equilibria through violent relaxation. I will present a framework for predicting the equilibria of violent relaxing systems that combines Lynden-Bell statistical mechanics and the time evolution of the system’s Casimir invariants [1]. The Casimirs evolve because...
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Barry Ginat (University of Oxford)06/10/2026, 15:50
Gravitational collapse in large-scale structure formation is a highly non-linear process, governed by the Vlasov-Poisson system. In this talk, I will describe how this process leads to a flow of structure to small phase-space scales, in a manner which gives rise to a universal power-law scaling of the phase-space power-spectrum at small scales. Then, I will describe how this process leads to a...
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Amitava Bhattacharjee (Princeton University)07/10/2026, 10:00
The Gaia Snail—a spiral pattern in stellar phase space caused by a perturbation to the Milky Way disk—is a natural laboratory for one-dimensional collisionless gravitational dynamics, the sign-flipped analog of electrostatic Vlasov–Poisson physics. Linear theory reproduces the spiral but winds it too tightly and fails to reproduce salient observed features. We present nonlinear analytical...
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Sofia Flores07/10/2026, 10:40
Vector Resonant Relaxation (VRR), the collective reorientation of stellar orbits around a black hole, provides an interesting framework for studying turbulence beyond the plasma context. In this talk, I will present numerical simulations of VRR in the strongly turbulent regime and characterize the statistical properties of its fluctuations. I will focus on the emergence of cascade phenomena...
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Jean-Baptiste FOUVRY (Institut d'Astrophysique de Paris)07/10/2026, 11:50
Supermassive black holes dominate the gravitational potential in galactic nuclei. In these dense environments, stars follow nearly Keplerian orbits and see their orbital planes relax through the potential fluctuations generated by the stellar cluster itself. For typical stellar distributions, the most likely long-term outcome of this rearrangement is for the orbital planes of the most massive...
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