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: 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: First Laboratory Observations of Residual Energy Generation in Strong Alfvén Wave Interactions
Abstract: In the MHD inertial range (scales larger than ion-kinetic scales) turbulent fluctuations in the solar wind are often Alfvénic in character, meaning that their magnetic and flow velocity fluctuations are proportional to each other and predominantly perpendicular to the background magnetic field. However, observations of the solar wind have shown that there is a significant difference in the energy in velocity fluctuations and normalized magnetic fluctuations. This difference, called the residual energy, should be zero for linear Alfvén waves, but is consistently observed to be negative in the solar wind, with magnetic fluctuations dominating. This work investigates the energy partition in strong three-wave interactions through an experimental campaign on the LArge Plasma Device (LAPD) in an MHD-like regime. Primary (driven) modes are launched from antennas, and secondary modes generated by the strong three-wave interaction are observed. The primary modes are shown to have no residual energy, while the secondary modes have significant residual energy - negative in the “sum” mode and positive in the “difference” mode. These results constitute the first laboratory demonstration that residual energy can indeed be generated by nonlinear mode coupling.
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: Plasma physics in strong laser fields
Abstract: Plasma behavior in extremely strong background electromagnetic fields is substantially modified from that of classical plasma owing to the onset of relativistic quantum electrodynamics (QED) processes. These processes include the stochastic emission of photons by electrons and the decay of a photon into an electron-positron pair. They are important because electron kinetic behavior is affected by momentum loss during the emission of energetic photons (known as “radiation reaction”), and plasma density may continuously vary over time through pair production. Such plasma behavior may be observed in extreme astrophysical environments and in focused laser light at the highest intensities. The coupling of quantum emission processes and relativistic collective particle dynamics results in dramatically new plasma physics phenomena, such as the generation of dense electron-positron pair plasma from near vacuum, complete laser energy absorption through QED processes, modified plasma dispersion properties, and anomalous particle trapping phenomena. This talk will review the fundamental physics of QED in strong fields and address open questions, provide an overview of pioneering experiments conducted in the laboratory, discuss theoretical and computational advances aimed at understanding plasma in strong fields, and explore upcoming and future research involving ultra-high-intensity lasers and high-energy beam facilities worldwide.
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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Website
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.
Date/Time: Thursday 24th October 2024, 4PM BST/11AM EDT
Title: Deployable fusion plasmas?
Abstract: The enormous and urgent challenges to provide the world with sufficient and suitable low carbon energy has given new impetus to fusion research. Some very substantial programmes aimed at pilot or developmental fusion power plants are now underway, usually at a very rapid pace. This pace can challenge the traditional scientific method (decisions based on empirical evidence supported by scientific understanding), so these programmes accept significant or even large uncertainties in the plasma and other systems. However, it seems likely that the uncertainty appetite will be reduced for deployable fusion plants, e.g. those built and operated for energy utilities perhaps part of national energy policies. The pace may still be high with such plants potentially designed in parallel with the pilot plants yet with significant differences. It is worth considering the impact on plasma R&D by asking a few questions about how one might arrive at a plasma which has the desired performance and can be adopted and integrated with sufficient confidence into a deployable plant. Some transitions in thinking and approach may be needed on the way..