Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session UM09: Mini-Conference: Relativistic Plasma Physics in Supercritical Fields IILive Streamed
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Chair: Daniel Seipt, The Helmholtz Institute Jena Room: 206 AB |
Thursday, October 20, 2022 2:00PM - 2:20PM |
UM09.00001: Kinetic model of pair cascades in pulsar polar caps Thomas Grismayer, Fabio Cruz, Luis O Silva Electron-positron pairs have been proposed as a primary ingredient to explain the nature of pulsar radio emission, a longstanding open problem in high-energy astrophysics. During these discharges - positive feedback loops of gamma-ray emission via curvature radiation by TeV electrons and positrons and pair production -, the plasma self-consistently develops waves that couple to EM modes capable of escaping the pulsar dense plasma. A simple kinetic model that can predict the growth rate of the cascade, the screening time, and the subsequent emissions is yet to be known. We show how simplified kinetic equations can be used to provide such predictions in two setups: an uniform electric field and a space-time dependent electric field. All analytical results are illustrated with particle-in-cell simulations performed with OSIRIS. These results are used to interpret new multidimensional simulations including an ab initio description of the Quantum Electrodynamics effects responsible for hard photon emission and pair production in pair discharges. It is shown that the electromagnetic modes generated during pair discharges present direct imprints of QED and plasma kinetic effects in properties (frequency, polarisation and Poynting flux) that are consistent with observations. |
Thursday, October 20, 2022 2:20PM - 2:40PM |
UM09.00002: Free electron laser in guide-field dominated regimes of magnetars Maxim Y Lyutikov We develop a model of the generation of coherent radio emission in the magneosphers of magnetars with nearly critical magnetic field, in application to fast radio bursts (FRBs). Emission is produced by a reconnection-generated beam of particles in a weakly turbulent, guide field-dominated plasma. The model is robust to the underlying plasma parameters (energy spread of the beam and non-harminoc wiggler fields), and succeeds in reproducing a number of subtle observed features (like both broadband emission and the presence of emission stripes, spectral and polariation properties) |
Thursday, October 20, 2022 2:40PM - 3:00PM |
UM09.00003: On low-frequency waves and instabilities in QED-strong field plasmas Mikhail V Medvedev Plasmas with super-strong magnetic field exceeding the Schwinger (or QED) field are of great scientific interest, thanks astrophysical observations of magnetars as well as to the imminent advances in laser-plasma experiments. Importantly, magnetars, which are neutron stars with magnetic fields of ~1e15 Gauss or stronger, do exist in nature. The QED "corrections" on their magnetospheric plasma can produce and order unity effect. We have developed the theoretical 'QED plasma framework', which allows one to explore such strongly magnetized plasmas systematically. We show that the general structure of plasma eigenmodes (shear and compressible Alfven, X and O electromagnetic waves, whistler waves) remains qualitatively the same. We also provide a qualitative discussion of a beam-plasma instability, which may be relevant for understanding of FRBs from a magnetar. |
Thursday, October 20, 2022 3:00PM - 3:20PM |
UM09.00004: Limits on the compression of magnetic islands, a source of synchrotron radiation bursts in PIC simulations of strong-field 3D relativistic magnetic reconnection Kevin Schoeffler, Thomas Grismayer, Dmitri A Uzdensky, Luis O Silva A study employing 2D and 3D particle-in-cell simulations taking advantage of the radiative quantum electrodynamic (QED) module (1) of the OSIRIS framework investigates relativistic magnetic reconnection of a pair plasma with strong fields. These conditions are expected in magnetospheres around compact objects such as neutron stars. Our previous 2D study (2) has shown that reconnection produces concentrated regions at the centers of magnetic islands with higher temperatures and compressed density and magnetic fields, leading to enhanced synchrotron emission. For sufficiently strong fields, this emission can reach the gamma-ray range. In the present work, our simulations show this also to be true in 3D, and we provide a theoretical model for the limits of the compression of the magnetic field and plasma density. These limits can be clearly visualized using a novel 2D histogram diagnostic of the density and magnetic fields measured at each point in space of our simulations. The magnetic field compression is theorized to be limited by dissipation manifested as an effective radiative resistivity, and the density compression to be limited by 3D kinking instabilities. This process of compression and enhancement of radiation may help explain the gamma-ray flares observed near pulsar and magnetar magnetospheres, where strong-field reconnection regimes are expected. (1) T. Grismayer et al., Phys. Plasmas 23, 056706 (2016) ; (2) K. Schoeffler et al., ApJ, 870, 1 (2019) |
Thursday, October 20, 2022 3:20PM - 3:40PM |
UM09.00005: Radiative Magnetic Reconnection in Strong Magnetic Fields in Neutron Star Magnetospheres: an Overview Dmitri A Uzdensky Relativistic collective plasma processes taking place in the presence of very strong magnetic fields play an important role in many high-energy astrophysical systems, most notably, in the magnetospheres of neutron stars (NSs), including radio-pulsars and magnetars. An important example of such processes is magnetic reconnection, which leads to a powerful and rapid release of magnetic energy and its conversion to plasma heating, nonthermal particle acceleration, and, ultimately, radiation, often powering intense X-ray and gamma-ray flares. In contrast to the more familiar examples of reconnection in the Earth’s magnetosphere and the solar corona, the strong magnetic field in NS magnetospheres causes the energized relativistic particles to emit synchrotron radiation and thus suffer radiation-reaction losses. Moreover, at highest field strengths, approaching the critical quantum (Schwinger) field, QED effects, including pair production, come into play. The reconnecting field strength controls the physical regime of magnetic reconnection in such environments, as well as its observational signatures. In this talk I will give a comprehensive overview of the resulting hierarchy of radiative/QED physical regimes of relativistic reconnection across a broad range of astrophysical NS scenarios. I will also discuss the prospects for future experimental exploration of these reconnection regimes using powerful next-generation lasers. |
Thursday, October 20, 2022 3:40PM - 4:00PM |
UM09.00006: Enhanced coherent laser reflection from QED plasma creation Kenan Qu, Nathaniel Fisch QED cascades can generate electron-positron pairs when the field exceeds the Schwinger limit. This condition is expected to become available with the rapid development of ultra-strong laser sources and particle accelerators. Recent studies [1-3] have shown that the formed pairs can exhibit collective plasma effects through, e.g., plasma-induced frequency upshifts in the laser spectrum. We will show that creation of QED plasma also induces strong coherent laser reflection at high reflection coefficient. The enhanced coherent laser reflection, and laser frequency upshift, serve as complementary signatures of QED plasma creation. |
Thursday, October 20, 2022 4:00PM - 4:20PM |
UM09.00007: Progress towards experimental realisation of QED-plasmas Christopher P Ridgers Several large-scale multi-PW laser facilities are being designed or commissioned worldwide, with the expectation of achieving focused intensities exceeding 10^23 W/cm^2 in the near future. At these intensities, the corresponding laser electromagnetic fields are so strong in the laser focus that the plasma rapidly created there is dominated by the feedback between strong field QED and classical plasma processes. These 'QED-plasmas' are relatively poorly understood theoretically and related experiments are still in their infancy. The scale of the challenge is apparent if we consider that in strong field QED, i.e. QED in the presence of strong background electromagnetic fields, even the dynamics of a single electron in an arbitrary field cannot currently be solved from first principles. Yet it is essential that we improve our understanding of QED-plasmas if multi-PW laser-plasma interactions are to be understood. I will disiucss progress we have made towards probing QED-plamas with current PW lasers and disucss the implications of this work for multi-PW laser-plasma experiments. |
Thursday, October 20, 2022 4:20PM - 4:40PM |
UM09.00008: Extreme magnetic field generation in ultra-intense laser solid interactions Brandon K Russell, Marija Vranic, Paul T Campbell, Alexander G Thomas, Kevin M. Schoeffler, Dmitri A Uzdensky, Louise Willingale In the interaction of ultra-intense laser pulses (>1023 W/cm2) with solid targets it is expected that 0.1 MT magnetic fields may be generated, potentially allowing for the experimental study of important collective processes in extreme astrophysical plasmas. At these extreme laser intensities a significant fraction of the pulse energy may be converted to high-energy radiation or electron-positron pairs, potentially limiting magnetic field generation. Using the quantum electrodynamic (QED) module in the OSIRIS particle-in-cell code, we perform a series of 2D simulations to study the generation of target-surface magnetic fields. These simulations are performed from a0 = 50 to 500, allowing us to determine a scaling of the resulting magnetic field strength with laser intensity. The emission of high-energy photons is found to limit field generation, with almost 40% of the total laser energy being converted to radiation at a0 = 500. An analytical model is developed allowing for the estimation of the maximum strength of magnetic fields on the target surface using laser parameters. |
Thursday, October 20, 2022 4:40PM - 5:00PM |
UM09.00009: Radiation Reaction Features in Collective QED Signatures Alec Griffith, Kenan Qu, Nathaniel Fisch Signatures of collective QED driven behavior will be necessary to distinguish the unique aspects of the QED plasma regime. Recent publications [1,2,3] suggest that a laser frequency upshift in a QED cascade, analogous to an upshift in an ionizing plasma, could serve as such a signature. However, this effect is heavily suppressed in the relativistic regime, and great care will need to be taken to ensure detectability. We extend previous work and explore other features of upshifts and other signatures which could arise in similar configurations. |
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