JPP is holding weekly meetings in the Frontiers of Plasma Physics Colloquium series
Organisers: Bill Dorland, Cary Forest and Alex Schekochihin
For information on how to join the Colloquium please sign up here.
Upcoming speakers are listed below. For details of past talks, please see here.
Speaker: Mohamad Shalaby, Leibniz Institute for Astrophysics Potsdam, Germany - Chaired by: Antoine Bret, Associate editor, JPP
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Date/Time: Thursday 18th July 2024, 4PM BST/11AM EDT
Title: Cosmic-Ray Choreography: How Ion-Driven Instabilities Propel Electron Acceleration and Dictate Ion Transport in Astrophysical Plasma
Abstract: Cosmic-ray-driven instabilities are pivotal in accelerating particles at shocks and during the propagation of GeV cosmic rays in galaxies and galaxy clusters. Within the self-confinement picture of cosmic ray (CR) transport, these instabilities amplify magnetic fields, which scatter cosmic rays and self-regulate their movement. This creates a strong coupling between the collisionless cosmic ray population and the thermal background plasma, suggesting potentially significant dynamic feedback. In this talk, I will discuss the inconsistencies between the self-confinement picture in Alfvénic turbulence and certain observations. Attempting to reconcile these inconsistencies by incorporating fast-magnetosonic turbulence cascades requires very fine-tuning to align with the data. I will then introduce a new discovery: a cosmic ray-driven instability termed the intermediate-scale instability. This instability triggers comoving ion-cyclotron electromagnetic waves at sub-ion skin-depth scales and grows notably faster than the resonant ion gyro-scale (streaming) instability, previously considered the dominant instability in the self-confinement model. This breakthrough suggests that the intermediate-scale instability could be crucial in cosmic ray transport in galactic and stellar environments. Next, I will demonstrate how these resonant instabilities saturate in isolation, challenging the fundamental assumptions about saturation in the self-confinement model. This points to a necessary fundamental revision of the theory of CR transport in galaxies and galaxy clusters. Through Particle-in-Cell (PIC) simulations, I will also show that the intermediate-scale instability is the key mechanism for efficient electron injection at parallel electron-ion shocks, addressing the long-standing challenge of electron injection at these shocks. Additionally, the simulations reveal that using reduced ion-to-electron mass ratios in shock simulations, which artificially suppresses the intermediate-scale instability, not only impedes electron acceleration but also leads to incorrect electron and ion heating in downstream and shock transition areas.
Speaker: Fulvio Zonca, ENEA, Frascati, Italy - Chaired by: Alex Schekochihin, Editor, JPP
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Date/Time: Thursday 25th July 2024, 4PM BST/11AM EDT
Title: Structure formation and transport in magnetized fusion plasmas
Abstract: Transport in magnetized fusion plasmas provides an interesting example of how collective behaviors in complex systems lead to structure formation and self-organization. This occurs because transport is dominated by fluctuations that are excited at the system microscales, characterized by the typical width of charged particle orbits in the strong equilibrium magnetic field. These fluctuations can provide nonlinear feedback on the plasma equilibrium profiles, i.e., on the system macroscales. Most importantly, however, fluctuation spectra and transport phenomena also yield to structure formation on the mesoscales, which are intermediate between the micro- and the macro-scales and can be due to both linear wave packet propagation in the slowly evolving and weakly non-uniform plasma medium as well as to nonlinear couplings. Meanwhile, high temperature, weakly collisional, reactor-relevant fusion plasmas can have velocity space distributions, which deviate from local thermodynamic equilibrium. Thus, transport and structure formation in magnetized fusion plasmas must be necessarily described in the phase space, and studying their nonlinear dynamics requires advanced kinetic treatments of thermal as well as supra-thermal components, including realistic geometries and plasma non-uniformities. This work presents the main findings of a comprehensive approach that enables predicting and describing the long time scale behavior of reactor relevant magnetized fusion plasmas as nonlinear equilibria, which evolve self-consistently with fluctuation spectra as well as sources/collisions. Examples of applications to cases of practical interest are also given, focusing on simplified paradigmatic cases for illustrating the workflow of the Advanced Transport model for Energetic Particle (ATEP) code. In particular, the case of neutral beam injected particles in ITER will be shown, which are redistributed under the action of Coulomb collisions and a fixed amplitude toroidal Alfv´en eigenmode.
Speaker: Jena Meinecke, Gettysburg College, USA Chaired by: Dmitri Uzdensky, Associate Editor, JPP
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Date/Time: Thursday 1st August 2024, 4PM BST/11AM EDT
Title: TBC
Abstract: TBC
Speaker: Vincent David, University of New Hampshire, USA - Chaired by: Francesco Califano, Associate Editor, JPP
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Date/Time: Thursday 8th AUGUST 2024, 4PM BST/11AM EDT
Title: Monofractality in the Solar Wind at Electron Scales: Insights from Kinetic Alfvén Waves Turbulence
Abstract: The breakdown of scale invariance in turbulent flows, known as multifractal scaling, is considered a cornerstone of turbulence. In solar wind turbulence, a monofractal behavior can be observed at electron scales, in contrast to larger scales where multifractality always prevails. Why scale invariance appears at electron scales is a challenging theoretical puzzle with important implications for understanding solar wind heating and acceleration. We investigate this long-standing problem using direct numerical simulations of three-dimensional electron reduced magnetohydrodynamics. Both weak and strong kinetic Alfvén waves turbulence regimes are studied in the balanced case. After recovering the expected theoretical predictions for the magnetic spectra, a higher-order multiscale statistical analysis is performed. This study reveals a striking difference between the two regimes, with the emergence of monofractality only in weak turbulence, whereas strong turbulence is multifractal. This result, combined with recent studies, shows the relevance of collisionless weak KAW turbulence to describe the solar wind at electron scales.
Speaker: Robert Ewart, University of Oxford, UK - Chaired by: Luis Silva, Associate Editor, JPP
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Date/Time: Thursday 15th August 2024, 4PM BST/11AM EDT
Title: TBC
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Speaker: Rony Keppens, KU Leuven - Chaired by: Steve Tobias, Associate Editor, JPP
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Date/Time: Thursday 22nd August 2024, 4PM BST/11AM EDT
Title: TBC
Abstract:TBC
Speaker: Charlotte Palmer, Queen’s University Belfast, UK - Chaired by: Louise Willingale, Associate Editor, JPP
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Date/Time: Thursday 29th AUGUST 2024, 4PM BST/11AM EDT
Title: Exploiting novel liquid sheet targets for the generation of bright MeV proton beams
Abstract: Laser-plasma acceleration has enormous potential to provide compact sources of ultra-short ion beams. However, several factors hamper their wider adoption, such as the low shot-to-shot stability, large beam divergence and the difficulty of high-repetition rate operation. In this talk I will outline an approach for overcoming these challenges by using an automated experimental setup incorporating a novel liquid sheet target, developed by collaborators at the SLAC National Accelerator Laboratory. I will report on recent experiments at the GEMINI TA2 laser facility (10 TW, 5 Hz) which demonstrated stable acceleration of few MeV proton beams with high flux and low-divergence proton beams in comparison to typical laser-accelerated ion beams. Supporting PIC simulations have shown that the presence of background vapour around the target plays an important role in the observed collimation of the proton beam. The measured proton beams are already suitable for applications requiring high proton flux and the platform can be extended to kHz repetition rates or higher laser energies extending the utility of the source to a wide range of applications in radiobiology, materials science and fundamental physics.
Speaker: Gabriel Xu, University of Alabama, USA Chaired by: Edward Thomas, Associate Editor, JPP
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Date/Time: Thursday 5th September 2024, 4PM BST/11AM EDT
Title: TBC
Abstract: TBC
Speaker: Dennis Whyte, Massachusetts Institute of Technology, USA - Chaired by: Nuno Loureiro, Associate Editor, JPP
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Date/Time: Thursday 12th Sep 2024, 4PM BST/11AM EDT
Title: TBC
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Speaker: Mel Abler, Space Science Institute, USA - Chaired by: Edward Thomas, Associate Editor, JPP
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Date/Time: Thursday 19th Sep 2024, 4PM BST/11AM EDT
Title: TBC
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Speaker: Alec Thomas, University of Michigan, USA - Chaired by: Luís O.Silva, Associate editor, JPP
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Date/Time: Thursday 26th Sep 2024, 4PM BST/11AM EDT
Title: TBC
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Speaker: Sebastien Le Pape, LULI, Ecole Polytechnique, France - Chaired by: Luís O.Silva, Associate editor, JPP
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Date/Time: Thursday 03rd Oct 2024, 4PM BST/11AM EDT
Title: TBC
Abstract: TBC.
Speaker: Yajie Yuan, Washington University, St Louis, USA - Chaired by: Roger Blandford, Associate Editor, JPP
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Date/Time: Thursday 17th October 2024, 4PM BST/11AM EDT
Title: Nonlinear evolution of Alfven waves and fast waves in magnetar magnetospheres
Abstract: Young and active neutron stars like magnetars may experience star quakes that can launch kHz Alfven waves into the magnetosphere. An Alfven wave packet propagating along the closed field lines undergoes several interesting nonlinear processes: (1) Alfven waves propagating to the outer magnetosphere may break and form an ejecta that accelerates away from the star. This process may be a viable mechanism to produce the simultaneous X-ray bursts and fast radio bursts from the galactic magnetar SGR 1935+2154. (2) The Alfven waves bouncing back and forth in the inner magnetosphere can convert to fast magnetosonic waves that spherically expands out. The fast waves can also become nonlinear before escaping the magnetosphere, producing shocks or regions with E>B that efficiently dissipate the fast wave energy, powering observable emission. In this talk, I’ll present our systematic study of all these processes and discuss their observational consequences.
Speaker: William Morris, UKAEA, UK - Chaired by: Hartmut Zoom, Associate editor, JPP
Date/Time: Thursday 24th October 2024, 4PM BST/11AM EDT
Title: TBC
Abstract: TBC.