PPPL

Plasma Webinars

Motivated by the opportunity to learn first-hand from the authors of outstanding plasma physics research, the Editors of Physics of Plasmas will invite authors of recently published featured articles to present a webinar based on their paper.

Featured articles are selected by the Editors with input from referees and include novel and important research across the whole range of fundamental and applied plasma physics. Features in Plasma Physics webinars will occur monthly.

To view one of the upcoming webinars below, follow the Zoom Link here. Don't forget to use passcode: PLASMA20.

Past

  • Experimental quantification of the impact of heterogeneous mix on thermonuclear burn video
    [#s1479, 13 May 2022]
    In inertial confinement fusion, deuterium–tritium (DT) fuel is brought to densities and temperatures where fusion ignition occurs. However, mixing of the ablator material into the fuel may prevent ignition by diluting and cooling the fuel. MARBLE experiments at the National Ignition Facility provide new insight into how mixing affects thermonuclear burn. These experiments use laser-driven capsules containing deuterated plastic foam and tritium gas. Embedded within the foam are voids of known sizes and locations, which control the degree of heterogeneity of the fuel. Initially, the reactants are separated, with tritium concentrated in the voids and deuterium in the foam. During the implosion, mixing occurs between the foam and gas materials, leading to DT fusion reactions in the mixed region. Here, it is shown that by measuring the ratios of DT and deuterium–deuterium neutron yields for different macropore sizes and gas compositions, the effects of mix heterogeneity on thermonuclear burn may be quantified, supporting an improved understanding of these effects.
  • Critical comparison of collisionless fluid models: Nonlinear simulations of parallel firehose instability video
    Takanobu Amano and Taiki Jikei Phys. Plasmas 29,022102 (2022), abstract
    [#s1478, 22 Apr 2022]
    Two different fluid models for collisionless plasmas are compared. One is based on the classical Chew–Goldberger–Low (CGL) model that includes a finite Larmor radius correction and the Landau closure for the longitudinal mode. Another one takes into account the effect of cyclotron resonance in addition to Landau resonance and is referred to as the cyclotron resonance closure (CRC) model [T. Jikei and T. Amano, Phys. Plasmas 28, 042105 (2021)]. While the linear property of the parallel firehose instability is better described by the CGL model, the electromagnetic ion cyclotron instability driven unstable by the cyclotron resonance is reproduced only by the CRC model. Nonlinear simulation results for the parallel firehose instability performed with the two models are also discussed. Although the linear and quasilinear isotropization phases are consistent with theory in both models, long-term behaviors may be substantially different. The final state obtained by the CRC model may be reasonably understood in terms of the marginal stability condition. In contrast, the lack of cyclotron damping in the CGL model makes it rather difficult to predict the long-term behavior with simple physical arguments. This suggests that incorporating collisionless damping both for longitudinal and transverse modes is crucial for a nonlinear fluid simulation model of collisionless plasmas.
  • Nonlinear dynamics of geodesic-acoustic-mode packets video
    [#s1461, 18 Mar 2022]
    Emanuele Poli is a staff member of the Tokamak Theory Division at the Max Planck Institute for Plasma Physics in Garching bei München, Germany. He was acting director of the division from 2014 to 2016 and is an adjunct professor at the University of Ulm since 2016. He received his PhD in theoretical physics from the University of Pavia (Italy) in 1999, with a thesis on paraxial electron-cyclotron (EC) wave beams. Since then he was actively involved in the modelling of EC waves in several devices, including ITER and DEMO, and contributed to various aspects of the theory of high-frequency waves, in particular concerning methods for the description of beam scattering from density fluctuations in tokamaks. During his postdoc, he started to work also on kinetic simulations of plasma instabilities like the tearing mode, focusing first on neoclassical processes and later on the interaction between disparate scales, like tearing modes and turbulence, and more recently between turbulence and fast-particle-driven modes. His studies of Geodesic Acoustic Modes (GAMs) center on the application of techniques developed in different fields (like beam physics and nonlinear optics) to the description of GAM packets. The talk will review the main results of this work.
  • Demonstration of an x-ray Raman spectroscopy setup to study warm dense carbon at the high energy density instrument of European XFEL video
    [#s1409, 18 Feb 2022]
    Author: Dominik Kraus is a professor for high energy density physics at University of Rostock and group leader at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany. He received his PhD at TU Darmstadt, Germany in 2012 for experimental work at the PHELIX laser of GSI Helmholtzzentrum for heavy ion research. He then moved to UC Berkeley as a postdoc to conduct experiments at the Linac Coherent Light Source of SLAC National Accelerator Laboratory and at the National Ignition Facility of Lawrence Livermore National Laboratory. In 2016, he joined HZDR as a Helmholtz Young Investigator Group Leader to work towards first experiments using the Helmholtz International Beamline for Extreme Fields (HIBEF) at the High Energy Density instrument of European XFEL. Before starting the professorship in Rostock in 2020, he also headed the high energy density division at HZDR from 2018 to 2020. Dominik’s primary research interests are the experimental investigation of chemistry and phase transitions inside giant planets, warm and hot dense matter relevant to the interiors of stars, and the synthesis of new materials via extreme conditions.
  • Gyrofluid simulation of an I-mode pedestal relaxation event video
    [#s1408, 21 Jan 2022]
    Author: Peter Manz is a recently appointed professor at the Institute of Physics at the University of Greifswald. His main field of research is turbulence at the plasma edge of magnetically confined fusion plasmas, from the pedestal to the divertor chamber. Peter Manz studied at the University of Kiel. In the diploma thesis, he dealt with turbulent cascades. During his Ph.D. at Stuttgart University, he studied the interaction of shear flows with turbulence. It was during his time as a postdoc at the University of California at San Diego that he first came into contact with I-mode. The I-mode is a fascinating tokamak confinement regime in which particles and heat transport seem to be decoupled. After returning to Germany to the Max Planck Institute for Plasma Physics in Garching, he first investigated scrape-off layer dynamics. In recent years, together with Dr. Tim Happel, his fellow student from Kiel times, the I-mode in ASDEX Upgrade became one of his favorite topics. The paper 'Gyrofluid simulation of an I-mode pedestal relaxation event' shows simulations of relaxation processes of the outermost edge of the confined plasma. These were previously studied in detail in ASDEX Upgrade by Dr. Davide Silvagni. The paper presented here is a bit of an anniversary, it is Peter Manz's 25th peer-reviewed first author paper.
  • 3D turbulent reconnection: Theory, tests, and astrophysical implications video
    [#s1392, 10 Dec 2021]
    Alexandre Lazarian is a professor of Astronomy at the University of Wisconsin - Madison with a joint appointment at the Department of Physics. He started his research in the theoretical physics group led by Professor Vitaly Ginzburg. Soon after his Diploma work, he got a Soros Fellowship to spend one year at Oxford University. Later, he got an Isaac Newton Studentship to do his PhD at the Department of Applied Mathematics University of Cambridge. Upon getting his PhD from Cambridge, he stayed for a short period in Austin and Harvard and later had his 3 year postdoc in Princeton. After Princeton, he got a 5 year Fellowship at the Canadian Institute for Theoretical Astrophysics (CITA), but spent only one year there, as he got his faculty job at the University of Wisconsin-Madison.
  • The cosmic ray-driven streaming instability in astrophysical and space plasmas video
    [#s1383, 22 Oct 2021]
    Alexandre P. Marcowith (Director of Research at CNRS, Laboratoire Univers et Particules de Montpellier, France) has defended his PhD in Physics in 1996 (university Paris Diderot, Grenoble Observatory, France) on the subject of kinetic theory and gamma-ray emission in relativistic blazar jets. His main research interests are in high-energy Astrophysics of compact objects (active galactic nuclei, X-ray binaries), particle acceleration and transport in turbulent flows and the origin of Cosmic Rays. He is member of the High Energy Stereoscopic System and Cherenkov Telescope Array collaborations. He is member of the International Astronomical Union and the European Astronomical Society.
  • Achieving record hot spot energies with large HDC implosions on NIF in HYBRID-E video
    [#s1359, 17 Sep 2021]
    HYBRID-E is an inertial confinement fusion implosion design that increases energy coupled to the hot spot by increasing the capsule scale in cylindrical hohlraums while operating within the current experimental limits of the National Ignition Facility. HYBRID-E reduces the hohlraum scale at a fixed capsule size compared to previous HYBRID designs, thereby increasing the hohlraum efficiency and energy coupled to the capsule, and uses the cross-beam energy transfer (CBET) to control the implosion symmetry by operating the inner (23 and 30) and outer (44 and 50) laser beams at different wavelengths (Dk > 0). Small case to capsule ratio designs can suffer from insufficient drive at the waist of the hohlraum. We show that only a small amount of wavelength separation between the inner and outer beams (Dk 1–2 A˚) is required to control the symmetry in low-gas-filled hohlraums (0.3 mg/cm3 He) with enough drive at the waist of the hohlraum to symmetrically drive capsules 1180 lm in outer radius. This campaign is the first to use the CBET to control the symmetry in 0.3 mg/cm3 He-filled hohlraums, the lowest gas fill density yet fielded with Dk > 0. We find a stronger sensitivity of hot spot P2 in lm per Angstrom (40–50 lm/A˚ wavelength separation) than observed in high-gas-filled hohlraums and previous longer pulse designs that used a hohlraum gas fill density of 0.6 mg/cm3 . There is currently no indication of transfer roll-off with increasing Dk, indicating that even longer pulses or larger capsules could be driven using the CBET in cylindrical hohlraums. We show that the radiation flux symmetry is well controlled during the foot of the pulse, and that the entire implosion can be tuned symmetrically in the presence of the CBET in this system, with low levels of laser backscatter out of the hohlraum and low levels of hot electron production from intense laser–plasma interactions. Radiation hydrodynamic simulations can accurately represent the early shock symmetry and be used as a design tool, but cannot predict the late-time radiation flux symmetry during the peak of the pulse, and semi-empirical models are used to design the experiments. Deuterium–tritium (DT)-layered tests of 1100 lm inner radius implosions showed performance close to expectations from simulations at velocities up to 360 km/s, and record yields at this velocity, when increasing the DT fuel layer thickness to mitigate hydrodynamic mixing of the ablator into the hot spot as a result of defects in the ablator. However, when the implosion velocity was increased, mixing due to these defects impacted performance. The ratio of measured to simulated yield for these experiments was directly correlated with the level of observed mixing. These simulations suggest that reducing the mixing, e.g., by improving the capsule defects, could result in higher performance. In addition, future experiments are planned to reduce the coast time at this scale, delay between the peak compression and the end of the laser, to increase the hot spot convergence and pressure. To reduce the coast time by several hundred ps compared to the 1100 lm inner radius implosions, HYBRID-E has also fielded 1050 lm inner radius capsules, which resulted in higher hot spot pressure and a fusion energy yield of 170 kJ.
  • Generation of supersonic jets from underwater electrical explosions of wire arrays video
    [#s1334, 27 Aug 2021]
    Underwater electrical explosion experiments of cylindrical or conical wire arrays accompanied by the generation of fast (up to ∼4500 m/s) water jets are presented. In these experiments, a pulse generator with a stored energy of up to ∼5.7 kJ, current amplitude of up to ∼340 kA, and rise time of ∼0.85 μs was used to electrically explode copper and aluminum wire arrays underwater. Streak and fast framing shadow imaging was used to extract the space–time resolved velocity of the ejected jet from the array while it propagates in air. The jet generation occurs due to high pressure and density of water formed in the vicinity of the array axis by the imploding shockwave. It was shown that the velocity of the jet ejected from the array depends on the array geometry and the thickness of the water layer above the array. The results suggest that ≥50% of the energy deposited into the array is transferred to the kinetic energy of this jet and the axial waterflow.
  • Alfvénic modes excited by the kink instability in PHASMA, video
    [#s1322, 16 Jul 2021]
    Earl Scime is the Oleg D. Jefimenko Professor of Physics and Astronomy at West Virginia University (WVU). He currently serves as the Director of the School of Mathematical and Data Sciences at WVU and is a past Chair of the American Physical Society’s Division of Plasma Physics. He moved to WVU in 1994 from Los Alamos National Laboratory, where he was a DoE Distinguished Postdoctoral Fellow. His research interests span fusion plasmas, space plasmas and industrial plasmas – with a cross-cutting focus on particle heating and velocity distribution function measurements. In 1992, he reported the first measurements of dynamo driven ion heating in the Madison Symmetric Torus. He has continued to measure particle velocity distributions in laboratory and space plasmas through a variety of diagnostic techniques including energetic neutral atom imaging, Thomson scattering, single photon laser induced fluorescence, cavity ring-down spectroscopy, and two-photon laser induced fluorescence. He has contributed to over 190 peer-reviewed publications and was named a Fellow of the American Physical Society in 2011. He is also founder and head coach of the award-winning robotics team, Mountaineer Area Robotics, an internationally recognized high school robotics program. Peiyun Shi is currently a postdoctoral research associate in the Center for KINETIC Plasma Physics at West Virginia University. He received his PhD in plasma physics from the University of Science and Technology of China in 2019. Presently, he works on the PHASMA (PHAse Space MApping experiment), a recently commissioned fundamental plasma physics facility designed to simulate and investigate space relevant plasma phenomena in the laboratory. His research focus is on measurements of electron dynamics in flux ropes and during magnetic reconnection at the kinetic scale. Using incoherent Thomson scattering he is able to measure details of the electron velocity distribution function as a function of time during flux rope evolution and mergers of flux ropes.
  • Wave trapping and E × B staircases, video
    [#s1293, 11 Jun 2021]
  • Efficacy of the radial pair potential approximation for molecular dynamics simulations of dense plasmas, video
    [#s1284, 14 May 2021]
  • Dynamics of seeded blobs under the influence of inelastic neutral interactions, video
    Alexander Simon Thrysøe, Phys. Plasmas 27, 052302 (2020)
    [#s1256, 23 Apr 2021]
  • An improved theory of the response of DIII-D H-mode discharges to static resonant magnetic perturbations and its implications for the suppression of edge localized modes, video
    Richard Fitzpatrick, Phys. Plasmas 27, 072501 (2020)
    [#s1257, 19 Mar 2021]
  • Magnetic reconnection and kinetic waves generated in the Earth's quasi-parallel bow shocks, video
    Li-Jen Chen and Naoki Bessho, Phys. Plasmas 27, 092901 (2020)
    [#s1254, 26 Feb 2021]
  • Symmetry tuning and high energy coupling for an Al capsule in a Au rugby hohlraum on NIF, video
    [#s1255, 22 Jan 2021]
  • For a full list of past colloquia, see the Features in Plasma Physics Webinar. webpage.
    [#s1261, 01 Jan 2020]