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.

Past

• Ultrarelativistic electron beams accelerated by terawatt scalable kHz laser
  Carlo Maria Lazzarini Phys. Plasmas 31, 030703 (2024), abstract
  [#s1864, 27 Sep 2024]
  We show the laser-driven acceleration of unprecedented, collimated (2 mrad divergence), and quasi-monoenergetic (25% energy spread) electron beams with energy up to at repetition rate. The laser driver is a multi-cycle (⁠ ⁠) optical parametric chirped pulse amplification system, operating at (⁠ ⁠). The scalability of the driver laser technology and the electron beams reported in this work pave the way toward developing high-brilliance x-ray sources for medical imaging and innovative devices for brain cancer treatment and represent a step toward the realization of a kHz GeV electron beamline.
• On the two-dimensional Brillouin flow
  Y. Y. Lau and Ryan Revolinsky Phys. Plasmas 31, 053109 (2024), abstract
  [#s1848, 20 Sep 2024]
  The Brillouin flow is a rectilinear, sheared electron fluid flow in a crossed electric field (E) and magnetic field (B), in the E   B direction with zero flow velocity and zero electric field at the surface with which the flow is in contact. It is broadly considered as the equilibrium electron flow in high power crossed-field devices including the magnetron and magnetically insulated transmission line oscillator. This paper provides an examination of Brillouin flow in two dimensions, in a cylindrical geometry where the anode radius changes abruptly at a single axial location, while the cathode surface has a constant radius. Our simulation confirms the proof that there is no equilibrium Brillouin flow solution for such a geometry. It further reveals that this change in the anode radius introduces novel bunching of the electrons within the Brillouin hub. This bunching occurs at low frequencies and is very pronounced if the Brillouin flow is from the small gap region to the large gap region, but is minimal if the Brillouin flow is from the large gap region to the small gap region. New insights are provided into the physical processes that initiate and sustain the bunching processes that are unique for a crossed-field diode, as compared with a non-magnetized diode. We argue that this enhanced bunching, and its concomitant formation of strong vortices, is not restricted to an abrupt change in the anode–cathode gap spacing.
• ICRF production of plasma with hydrogen minority in Uragan-2M stellarator by two-strap antenna
  Yurii Kovtun Phys. Plasmas 31, 042501 (2024) , abstract
  [#s1814, 28 Jun 2024]
  The experiments on medium-size stellarator Uragan-2M (U-2M) in Kharkiv, Ukraine, are carried on in support of the Wendelstein 7-X (W7-X) experimental program. The scenario ion cyclotron frequency range (ICRF) plasma production at the hydrogen minority regime had been experimentally tested on U-2M and was qualified at the Large Helical Device (LHD). The paper presents the results of further research on the ICRF plasma production. The ICRF discharge studies were carried out in a H2 + He mixture with a controlled hydrogen concentration ranging from few percents to 75%. The two-strap like antenna mimicks the W7-X antenna operated in monopole phasing. The applied RF power was in the range of ∼100 kW. Relatively dense plasma of up to Ne ∼ 1019 m−3 was produced near the first harmonic of the hydrogen cyclotron frequency. The maximum temperature of the electrons and ions was not more than a few tens of electron volt. The characteristic features of RF plasma production and the propagation of electromagnetic waves in the experimental conditions are discussed. The experiments on U-2M and LHD indicate that the minority scenario of ICRF plasma production appears to be scalable and could be used in large stellarator machines. This is, in particular, important for the future experiments ICRF production of target plasma in W-7X in conditions where electron cyclotron resonance heating start-up is not possible.
• Observation of the colliding process of plasma jets in the double-cone ignition scheme using an x-ray streak camera. Video
  Fuyuan Wu and Zhengdong Liu Phys. Plasmas 31,042704 (2024) , abstract
  [#s1810, 17 May 2024]
  The double-cone ignition scheme is a novel approach with the potential to achieve a high gain fusion with a relatively smaller drive laser energy. To optimize the colliding process of the plasma jets formed by the CHCl/CD shells embedded in the gold cones, an x-ray streak camera was used to capture the spontaneous x-ray emission from the CHCl and CD plasma jets. High-density plasma jets with a velocity of 220 ± 25 km/s are observed to collide and stagnate, forming an isochoric plasma with sharp ends. During the head-on colliding process, the self-emission intensity nonlinearly increases because of the rapid increase in the density and temperature of the plasma jets. The CD colliding plasma exhibited stronger self-emission due to its faster implosion process. These experimental findings effectively agree with the two-dimensional fluid simulations.
• Physics and applications of dusty plasmas: The Perspectives 2023. Video,
  Job Beckers and Mikhail Pustylnik Phys. Plasmas 30,120601 (2023) , abstract
  [#s1800, 12 Apr 2024]
  Dusty plasmas are electrically quasi-neutral media that, along with electrons, ions, neutral gas, radiation, and electric and/or magnetic fields, also contain solid or liquid particles with sizes ranging from a few nanometers to a few micrometers. These media can be found in many natural environments as well as in various laboratory setups and industrial applications. As a separate branch of plasma physics, the field of dusty plasma physics was born in the beginning of 1990s at the intersection of the interests of the communities investigating astrophysical and technological plasmas. An additional boost to the development of the field was given by the discovery of plasma crystals leading to a series of microgravity experiments of which the purpose was to investigate generic phenomena in condensed matter physics using strongly coupled complex (dusty) plasmas as model systems. Finally, the field has gained an increasing amount of attention due to its inevitable connection to the development of novel applications ranging from the synthesis of functional nanoparticles to nuclear fusion and from particle sensing and diagnostics to nano-contamination control. The purpose of the present perspectives paper is to identify promising new developments and research directions for the field. As such, dusty plasmas are considered in their entire variety: from classical low-pressure noble-gas dusty discharges to atmospheric pressure plasmas with aerosols and from rarefied astrophysical plasmas to dense plasmas in nuclear fusion devices. Both fundamental and application aspects are covered.
• Electron energization in reconnection: Eulerian vs Lagrangian perspectives Video,
  Stéphane Liberatore Phys. Plasmas 31,122707 (2023) , abstract
  [#s1813, 15 Mar 2024]
  The first indirect drive Inertial Confinement Fusion (ICF) experiments on the Laser Megajoule facility were carried out with approximately 150 kJ of laser energy distributed on 48 beams (12 quads) arranged in two cones. The target consisted of a gold vacuum rugby-shaped hohlraum and a plastic capsule located at its center, filled with deuterium gas fuel. The arrangement of the 12 quads is such that the laser irradiation on the wall generated a three-dimensional (3D) x-ray flux around the capsule creating 3D deformations on the imploding plastic shell. This constraint forced the design of a robust target (relatively thin ablator, around m) driven by a short laser pulse (3 ns) that delivered about 1011 neutrons. Full-integrated 3D radiation hydrodynamics simulations allowed both the target definition and the data interpretation (mainly radiation temperature, x-ray images, and neutron yield). 3D calculations and experiments compare well.
• Electron energization in reconnection: Eulerian vs Lagrangian perspectives Video,
  Jason TenBarge Phys. Plasmas 31,022901 (2024) , abstract
  [#s1812, 23 Feb 2024]
  Particle energization due to magnetic reconnection is an important unsolved problem for myriad space and astrophysical plasmas. Electron energization in magnetic reconnection has traditionally been examined from a particle, or Lagrangian, perspective using particle-in-cell (PIC) simulations. Guiding-center analyses of ensembles of PIC particles have suggested that Fermi (curvature drift) acceleration and direct acceleration via the reconnection electric field are the primary electron energization mechanisms. However, both PIC guiding-center ensemble analyses and spacecraft observations are performed in an Eulerian perspective. For this work, we employ the continuum Vlasov–Maxwell solver within the Gkeyll simulation framework to reexamine electron energization from a kinetic continuum, Eulerian, perspective. We separately examine the contribution of each drift energization component to determine the dominant electron energization mechanisms in a moderate guide-field Gkeyll reconnection simulation. In the Eulerian perspective, we find that the diamagnetic and agyrotropic drifts are the primary electron energization mechanisms away from the reconnection x-point, where direct acceleration dominates. We compare the Eulerian (Vlasov Gkeyll) results with the wisdom gained from Lagrangian (PIC) analyses.
• Algorithms and High-Performance Computing for Kinetic Low-Temperature Plasma Simulations - The Pathway to Whole Device Modeling Video,
  Tasman Powis Phys. Plasmas 30,103509 (2023) , abstract
  [#s1801, 15 Dec 2023]
  Achieving large-scale kinetic modeling is a crucial task for the development and optimization of modern plasma devices. With the trend of decreasing pressure in applications, such as plasma etching, kinetic simulations are necessary to self-consistently capture the particle dynamics. The standard, explicit, electrostatic, momentum-conserving particle-in-cell method suffers from restrictive stability constraints on spatial cell size and temporal time step, requiring resolution of the electron Debye length and electron plasma period, respectively. This results in a very high computational cost, making the technique prohibitive for large volume device modeling. We investigate the direct implicit algorithm and the explicit energy conserving algorithm as alternatives to the standard approach, both of which can reduce computational cost with a minimal (or controllable) impact on results. These algorithms are implemented into the well-tested EDIPIC-2D and LTP-PIC codes, and their performance is evaluated via 2D capacitively coupled plasma discharge simulations. The investigation reveals that both approaches enable the utilization of cell sizes larger than the Debye length, resulting in a reduced runtime, while incurring only minor inaccuracies in plasma parameters. The direct implicit method also allows for time steps larger than the electron plasma period; however, care must be taken to avoid numerical heating or cooling. It is demonstrated that by appropriately adjusting the ratio of cell size to time step, it is possible to mitigate this effect to an acceptable level.
• Radiative cooling effects on reverse shocks formed by magnetized supersonic plasma flows Video,
  Stefano Merlini Phys. Plasmas 30, 092102 (2023) , abstract
  [#s1807, 17 Nov 2023]
  We study the structure of reverse shocks formed by the collision of supersonic, magnetized plasma flows driven by an inverse (or exploding) wire array with a planar conducting obstacle. We observe that the structure of these reverse shocks varies dramatically with wire material, despite the similar upstream flow velocities and mass densities. For aluminum wire arrays, the shock is sharp and well-defined, consistent with magneto-hydrodynamic theory. In contrast, we do not observe a well-defined shock using tungsten wires, and instead we see a broad region dominated by density fluctuations on a wide range of spatial scales. We diagnose these two very different interactions using interferometry, Thomson scattering, shadowgraphy, and a newly developed imaging refractometer that is sensitive to small deflections of the probing laser corresponding to small-scale density perturbations. We conclude that the differences in shock structure are most likely due to radiative cooling instabilities, which create small-scale density perturbations elongated along magnetic field lines in the tungsten plasma. These instabilities grow more slowly and are smoothed by thermal conduction in the aluminum plasma.
• Higher order theory of quasi-isodynamicity near the magnetic axis of stellarators Video,
  Eduardo Rodríguez Phys. Plasmas 30, 062507 (2023) , abstract
  [#s1806, 15 Sep 2023]
  The condition of quasi-isodynamicity is derived to second order in the distance from the magnetic axis. We do so using a formulation of omnigenity that explicitly requires the balance between radial particle drifts at opposite bounce points of a magnetic well. This is a physically intuitive alternative to the integrated condition involving distances between bounce points, used in previous works. We investigate the appearance of topological defects in the magnetic field strength (puddles). A hallmark of quasi-isodynamic fields, the curved contour of minimum field strength, is found to be inextricably linked to these defects. Our results pave the way to construct solutions that satisfy omnigenity to a higher degree of precision and also to simultaneously consider other physical properties, like shaping and stability.
• Theory of the ion–electron temperature relaxation rate in strongly magnetized plasmas Video,
  Louis Jose Phys. Plasmas 30, 052103 (2023) , abstract
  [#s1805, 04 Aug 2023]
  Recent works have shown that strongly magnetized plasmas characterized by having a gyrofrequency greater than the plasma frequency exhibit novel transport properties. One example is that the friction force on a test charge shifts, obtaining components perpendicular to its velocity in addition to the typical stopping power component antiparallel to its velocity. Here, we apply a recent generalization of the Boltzmann equation for strongly magnetized plasmas to calculate the ion–electron temperature relaxation rate. Strong magnetization is generally found to increase the temperature relaxation rate perpendicular to the magnetic field and to cause the temperatures parallel and perpendicular to the magnetic field to not relax at equal rates. This, in turn, causes a temperature anisotropy to develop during the equilibration. Strong magnetization also breaks the symmetry of independence of the sign of the charges of the interacting particles on the collision rate, commonly known as the “Barkas effect.” It is found that the combination of oppositely charged interaction and strong magnetization causes the ion–electron parallel temperature relaxation rate to be significantly suppressed, scaling inversely proportional to the magnetic field strength.
• Development of the neutral model in the nonlinear MHD code JOREK: Application to E × B drifts in ITER PFPO-1 plasmas Video,
  Sven Korving Phys. Plasmas 30, 042509 (2023) , abstract
  [#s1804, 23 Jun 2023]
  The prediction of power fluxes and plasma-wall interactions impacted by MHD processes during ITER operation [disruption, Edge Localized Modes (ELMs), 3D magnetic fields applied for ELM control, etc.] requires models that include an accurate description of the MHD processes themselves, as well as of the edge plasma and plasma-wall interaction processes. In this paper, we report progress on improving the edge plasma physics models in the nonlinear extended MHD code JOREK, which has capabilities to simulate the MHD response of the plasma to the applied external 3D fields, disruptions and ELMs. The extended MHD model includes E × B drifts, diamagnetic drifts, and neoclassical flows. These drifts can have large influences, on e.g., divertor asymmetries. Realistic divertor conditions are important for impurity sputtering, transport, and their effect on the plasma. In this work, we implemented kinetic and fluid neutral physics modules, investigated the influence of poloidal flows under divertor conditions in the ITER PFPO-1 (1.8T/5MA) H-mode plasma scenario, and compared the divertor plasma conditions and heat flux to the wall for both the fluid and kinetic neutral model (in JOREK) to the well-established 2D boundary plasma simulation code suite SOLPS-ITER. As an application of the newly developed model, we investigated time-dependent divertor solutions and the transition from attached to partially detached plasmas. We present the formation of a high-field-side high-density-region and how it is driven by poloidal E × B drifts
• Perspectives on relativistic electron–positron pair plasma experiments of astrophysical relevance using high-power lasers Video,
  Hui Chen and Frederico Fiuza Phys. Plasmas 30,020601 (2023) , abstract
  [#s1803, 19 May 2023]
  The study of relativistic electron–positron pair plasmas is both of fundamental physics interest and important to understand the processes that shape the magnetic field dynamics, particle acceleration, and radiation emission in high-energy astrophysical environments. Although it is highly desirable to study relativistic pair plasmas in the laboratory, their generation and control constitutes a critical challenge. Significant experimental and theoretical progress has been made over recent years to explore the use of intense lasers to produce dense relativistic pair plasma in the laboratory and study the basic collective plasma processes associated with these systems. Important challenges remain in terms of improving the number of pairs, system size, and control over the charge neutrality required to establish laboratory platforms that can expand our understanding of relativistic pair plasma and help validate underlying models in conditions relevant to high-energy astrophysical phenomena. We highlight recent progress in this field, discuss the main challenges, and the exciting prospects for studying relativistic pair plasmas and astrophysics relevant instabilities in the laboratory in the near future.
• The electron diffusion region dominated by electromagnetic turbulence in the reconnection current layer Video,
  Keizo Fujimoto and Richard D. Sydora Phys. Plasmas 30,022106 (2023) , abstract
  [#s1802, 12 Apr 2023]
  Most of the plasma fluid equations have employed the electrical resistivity to generate the magnetic dissipation required for magnetic reconnection to occur in collisionless plasma. However, there has been no clear evidence that such a model is indeed appropriate in the reconnection diffusion region in terms of the kinetic physics. The present study demonstrates that, using a large-scale 3D kinetic simulation and analytical analysis, the spatial distribution of the non-ideal electric field is consistent with the dissipation due to the viscosity rather than the resistivity, when electromagnetic (EM) turbulence is dominant in the electron diffusion region (EDR). The effective viscosity is caused by the EM turbulence that is driven by the flow shear instabilities leading to the electron momentum transport across the EDR. The result suggests a fundamental modification of the fluid equations using the resistivity in the Ohm's law. In contrast, for the 2D current sheet without significant turbulence activity, the non-ideal field profile does not obey the simple form based on the viscosity, so that further investigation is needed for a better description.
• A numerical approach to the calculation of the Alfvén continuum in the presence of magnetic islands. Video,
  Axel Könies Phys. Plasmas 29,092102 (2022) , abstract
  [#s1646, 10 Mar 2023]
  A numerical approach is devised to calculate the shear Alfvén continuum inside and outside magnetic islands in cylindrical and stellarator plasmas. Equations for an appropriate set of coordinates and the arising equations for the continuum are derived and implemented in the CONTI code. An experiment-oriented representation of the results is chosen to allow a radial localization of the modes and a comparison of different magnetic configurations. Comparison is made with results of earlier analytic work for validation. Agreement is good but more details of the spectrum, such as the generation of island induced gaps inside and outside the separatrix, are found. While the code is easily usable and can be applied to any magnetic equilibrium accessible with VMEC, the calculations are plagued with convergence issues close to the separatrix. A calculation for a realistic W7-X equilibrium with islands is done where the island width is estimated with the HINT code.
• The academic research ecosystem required to support the development of fusion energy Video,
  Dennis Whyte Phys. Plasmas 30, 090604 (2023) , abstract
  [#s1808, 19 Jan 2023]
  The advent of a fusion energy industry is being strongly supported by academics and universities, with the majority of fusion companies launching out of universities. Universities also play critical roles in technical innovation, workforce development, and independent arbiters of science and technology. The ability of the US academic landscape to support and grow the fusion energy sector is analyzed via a numerical distribution of full time faculty engaged in fusion and plasma. This data is compared to university support in two existing technology-driven industries: nuclear and aeronautics. This comparison clearly shows that the university system requires not only significant absolute growth but also a wider distribution of faculty at universities and across the required disciplines.
• On the dose of plasma medicine: Plasma-activated medium (PAM) and its effect on cell viability video
  He Cheng Phys. Plasmas 29,063506 (2022)
  [#s1607, 13 Jan 2023]
• Optimization of quasi-symmetric stellarators with self-consistent bootstrap current and energetic particle confinement
  Matt Landreman Phys. Plasmas 29,082501 (2022)
  [#s1592, 02 Dec 2022]
• ​Platform for probing radiation transport properties of hydrogen at conditions found in the deep interiors of red dwarfs. video
  Julian Lütgert Phys. Plasmas 29,083301 (2022)
  [#s1580, 18 Nov 2022]
• ​M​illisecond observations of nonlinear wave–electron interaction in electron phase space holes
  Cecilia Norgren Phys. Plasmas 29,012309 (2022)
  [#s1548, 23 Sep 2022]
• Laser-driven, ion-scale magnetospheres in laboratory plasmas. I. Experimental platform and first results video
  Derek Schaeffer Phys. Plasmas 29,042901 (2022), abstract
  [#s1532, 12 Aug 2022]
  ABSTRACT See also: Physics of Plasmas 29, 032902 (2022) ABSTRACT Magnetospheres are a ubiquitous feature of magnetized bodies embedded in a plasma flow. While large planetary magnetospheres have been studied for decades by spacecraft, ion-scale “mini” magnetospheres can provide a unique environment to study kinetic-scale, collisionless plasma physics in the laboratory to help validate models of larger systems. In this work, we present preliminary experiments of ion-scale magnetospheres performed on a unique high-repetition-rate platform developed for the Large Plasma Device at the University of California, Los Angeles. The experiments utilize a high-repetition-rate laser to drive a fast plasma flow into a pulsed dipole magnetic field embedded in a uniform magnetized background plasma. 2D maps of the magnetic field with high spatial and temporal resolution are measured with magnetic flux probes to examine the evolution of magnetosphere and current density structures for a range of dipole and upstream parameters. The results are further compared to 2D particle-in-cell simulations to identify key observational signatures of the kinetic-scale structures and dynamics of the laser-driven plasma. We find that distinct 2D kinetic-scale magnetopause and diamagnetic current structures are formed at higher dipole moments, and their locations are consistent with predictions based on pressure balances and energy conservation.
• Ionization waves (striations) in a low-current plasma column revisited with kinetic and fluid models ,video
  Jean-Pierre Boeuf Phys. Plasmas 29,022105 (2022), abstract
  [#s1514, 24 Jun 2022]
  ABSTRACT A one-dimensional particle-in-cell Monte Carlo collisions method has been used to model the development and propagation of ionization waves in neon and argon positive columns. Low-current conditions are considered, that is, conditions where stepwise ionization or Coulomb collisions are negligible (linear ionization rate). This self-consistent model describes the development of self-excited moving striations, reproduces many of the well-known experimental characteristics (wavelength, spatial resonances, potential drop over one striation, and electron “bunching” effect) of the ionization waves called p, r, and s waves in the literature, and sheds light on their physical properties and on the mechanisms responsible for their existence. These are the first fully kinetic self-consistent simulations over a large range of conditions reproducing the development of p, r, and s ionization waves. Although the spatial resonances and the detailed properties of the striations in the nonlinear regime are of kinetic nature, the conditions of existence of the instability can be obtained and understood from a linear stability analysis of a three-moment set of quasi-neutral fluid equations where the electron transport coefficients are expressed as a function of electron temperature and are obtained from solutions of a 0D Boltzmann equation. An essential aspect of the instability leading to the development of these striations is the non-Maxwellian nature of the electron energy distribution function in the uniform electric field prior to the instability onset, resulting in an electron diffusion coefficient in space much larger than the energy diffusion coefficient.
• Experimental quantification of the impact of heterogeneous mix on thermonuclear burn video
  Brian Haines Phys. Plasmas 28,022702 (2022), abstract
  [#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
  Emanuele Poli Phys. Plasmas 28,082701 (2021), abstract
  [#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
  Dominik Kraus Phys. Plasmas 28,082701 (2021), abstract
  [#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
  Peter Manz Phys. Plasmas 28,102502 (2021), abstract
  [#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
  Alexandre Lazarian Phys. Plasmas 27,012305(2020), abstract
  [#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
  Alexandre Marcowith Phys. Plasmas 28,080601 (2021), abstract
  [#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
  Andrea Kritcher Phys. Plasmas 28, 072706 (2021), abstract
  [#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
  Yakov Krasik,Phys. Plasmas 28, 063509 (2021) , abstract
  [#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
  Earl Scime and Peiyun,Phys. Plasmas 28, 032101 (2021), abstract
  [#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
  Xavier Garbet, Phys. Plasmas 28, 042302 (2021)
  [#s1293, 11 Jun 2021]
• Efficacy of the radial pair potential approximation for molecular dynamics simulations of dense plasmas, video
  Michael Murillo, Phys. Plasmas 28, 032706 (2021)
  [#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
  Yuan Ping, Phys. Plasmas 27, 100702 (2020)
  [#s1255, 22 Jan 2021]
• For a full list of past colloquia, see the Features in Plasma Physics Webinar. webpage.
  [#s1261, 01 Jan 2020]