Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session ZO06: Fundamental: Dynamics and Stability of Complex SystemsOn Demand
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Chair: James Danielson, UCSD Room: Rooms 310-311 |
Friday, November 12, 2021 9:30AM - 9:42AM |
ZO06.00001: Modelling phase locking of large-scale modes Johan Anderson, Sara Moradi Turbulence is often characterized by energetic couplings between different scales of a flow. However, in the context of turbulence driven transport, such as the case of magnetically confined fusion plasmas or the diffusion of cosmic rays, typical flow structures are identified by dominant modes and the global turbulent state is approximated by a superposition of linear contributions (waves in general). These theoretical studies consider the amplitudes of the fluctuating quantities but disregard the dynamics of the phases by using the so-called random-phase approximation (RPA) for which the existence of a Chirikov-like criterion for the onset of wave stochasticity is assumed. In this approximation one assumes that the dynamical amplitudes have a slow variation compared to the rapid change of the phases. It has been observed that the phase dynamic shows significant departure from the well-known RPA assumptions, with phases locking occasionally (but not in the dissipative high-k range). In non-linear turbulent flow however, three-body interactions between the phases of the various modes is of importance. We will consider examples of synchronization in different fluid system such as Burgers and Navier-Stokes turbulence and in more advanced models such as those for Edge Localized Modes (ELMs) in tokamaks which remain a critical issue for plasma stability and the lifetime of fusion reactors such as ITER. |
Friday, November 12, 2021 9:42AM - 9:54AM |
ZO06.00002: Magnetized Collisionless Shock Formation Mediated by the Modified Two-Stream Instability Yu Zhang, Jonathan R Davies, Peter V Heuer, Chuang Ren Two-dimensional particle-in-cell simulations are used to study the feasibility of using terawatt laser systems to form perpendicular magnetized collisionless shocks in hydrogen and neon plasmas. With experimentally accessible parameters, shocks can form within a few tenths of a nanosecond. Ions are reflected from the shock front, indicating that these shocks reach supercriticality. A modified two-stream instability (MTSI) from the incoming and reflected ions is shown to be the operating microinstability mediating shock formation, and the shock formation time and shock width are determined by MTSI. With the realistic ion/electron mass ratios used, the MTSI growth rates are much larger than the ion gyrofrequencies. These perpendicular collisionless shocks form within approximately a tenth of an ion gyroperiod. Mode analysis in the shock transition further confirms MTSI is the operating instability. |
Friday, November 12, 2021 9:54AM - 10:06AM |
ZO06.00003: On the instability mechanism of a slab microtearing mode Mitsuyoshi Yagyu, Ryusuke Numata The electron temperature gradient destabilizes short-wavelength magnetic field perturbations and enhances transport to degrade performance of fusion devices[1]. The theoretical works predicted that the energy dependent electron-ion collisions leading to the thermal force are indispensable for such an electromagnetic micro-instability, called the microtearing mode [1][2]. More recent work have reported there exists a collisionless electromagnetic ETG mode causing magnetic reconnection in a slab [3], while in more realistic magnetic geometry for fusion devices, the collisionless MTM has been demonstrated [4]. |
Friday, November 12, 2021 10:06AM - 10:18AM |
ZO06.00004: Generation of Mega-Gauss Magnetic Vortices in Plasmas Yipeng Wu, Chaojie Zhang, Zan Nie, Mitchell Sinclair, Kenneth A Marsh, Chandrashekhar Joshi Magnetic fields play an essential role in numerous fields, such as material physics, condensed matter physics, accelerator physics and astrophysics. As these fields rapidly expand, the ability to generate small-scale intense magnetic structures with different topologies becomes increasingly important. Plasma is an attractive medium to generate such structures due to its extraordinary ability to sustain strong currents with microscopic spatial scales. Here, using theory and three-dimensional particle-in-cell simulations, we show that a mega-gauss magnetic vortex with a helical rotating structure can be generated when a relativistic ionization front passes through a Laguerre Gaussian (LG) long-wavelength IR laser pulse with orbital angular momentum (OAM). By changing the OAM mode, the plasma current and thus the topology of the magnetic structure can be controlled. We also show that, by employing an ionization front generated by a superposition of co-propagating, beating short-wavelength LG ionization laser pulses, the topological charge of the magnetic vortex can be further manipulated. This is interesting from a fundamental perspective and important for applications, such as quantum topological system manipulation. This magnetic structure also has the potential to be used as an ultrashort-wavelength and high-amplitude vortical undulator, which would provide ultrashort-wavelength X-ray with OAM in compact systems, with no need for helically bunched electron beams. |
Friday, November 12, 2021 10:18AM - 10:30AM |
ZO06.00005: Effects of distribution structure on predictions of plasma behavior in marginally unstable plasma Emily R Lichko, Kristopher G Klein Due to low collisionality in space and astrophysical plasmas, distributions of ions and electrons observed by spacecraft exist in a state far from thermodynamic equilibrium.The non-Maxwellian features in these distribution functions can trigger microinstabilities, which likely play a role in some of the largest open questions in solar physics, including coronal heating, heating of the bulk solar wind, and accounting for high-frequency waves observed alongside the Alfvenic turbulent cascade. While there is a tremendous amount of information in the structure of these distribution functions, they are typically only represented by a fit of one or two Maxwellian or bi-Maxwellian distributions. In this work, we examine how the fidelity of the model to the observed distribution function affects our predictions for the stability of the plasma, and how much of the information in the distribution function is needed to accurately predict the behavior of the plasma. To do this, we use marginally stable one-dimensional, electrostatic simulations of the electron two-stream instability. For these simulations, there is significantly better agreement between the behavior of the plasma and the predictions of linear theory when a higher-fidelity representation of the distribution function is used. These electrostatic results will also be extended to the electromagnetic regime and used to compare predictions of linear wave activity with the behavior of the plasma using data from Parker Solar Probe. |
Friday, November 12, 2021 10:30AM - 10:42AM |
ZO06.00006: Suppression of Non-linear Saturation in Collisionless, High-Beta Slow Modes Stephen P Majeski, Matthew W Kunz, Jonathan Squire With the support of hybrid-kinetic simulations and analytical theory, we demonstrate that large-amplitude (δB‖/B0 ~ 1/2), long-wavelength slow modes in a high-beta collisionless plasma can suppress non-linear saturation of their transit-time damping. Due to their polarization, collisionless slow modes (non-propagating modes) of sufficient amplitude induce significant positive pressure anisotropy (p⊥> p‖) in regions where the plasma beta is enhanced, facilitating rapid growth of the mirror instability. Conversely, regions of negative anisotropy are accompanied by a decreased plasma beta, impeding activation of the firehose instability. Once the mirrors are of sufficient amplitude, they pitch-angle scatter the plasma ions, eroding the non-linear plateau and allowing the slow mode to resume its decay at the linear damping rate. The mirror-induced effective collisionality is investigated with respect to the slow-mode amplitude and the scale separation between the slow and mirror modes. These results provide yet another simple example, alongside self-interrupting Alfvén waves (Squire et al. 2016, 2017) and self-sustaining sound (Kunz et al. 2020), of how energetically weak magnetic fields fundamentally change the transport properties of a low-collisionality, magnetized plasma. |
Friday, November 12, 2021 10:42AM - 10:54AM |
ZO06.00007: Resonant absorption of laser energy in X-mode configuration of magnetised plasma Ayushi Vashistha, Devshree Mandal, Amita Das, Srimanta Maity There are several well-known mechanisms for the absorption of EM energy into plasma. For the case of magnetised plasma, electron-cyclotron resonance heating, ion-cyclotron resonance heating have been widely studied in the context of plasma heating. We propose a mechanism which relies on the excitation of lower hybrid mode in the system. It has been recently reported that with the application of an external magnetic field, it is possible to couple laser energy directly into ions via excitation of lower hybrid mode in plasma [1,2]. Our work further extends this and propose a new heating mechanism in X-mode configuration of laser plasma system. We will discuss lower hybrid resonance heating mechanism to couple laser energy directly into ions. Our proposed mechanism is a three-fold process, laser first excites compressional Alfven mode in plasma which converts into electrostatic mode at the lower hybrid resonance point. This electrostatic mode then couples its energy into ions via wave-particle interaction. We will also discuss the role of appropriate gradient for the proposed mechanism. This work can find application where high energy needs to be dumped at a specified location in plasma. |
Friday, November 12, 2021 10:54AM - 11:06AM |
ZO06.00008: Examining the Electric Potential Near Self-Organized Dust Structures Katrina Vermillion, Abbie Terrell, Dustin L Sanford, Lorin S Matthews, Marlene Rosenberg, Peter Hartmann, Truell W Hyde It has been previously shown that a negatively charged dust grain immersed in a flowing plasma leads to the formation of a positively charged ion wake downstream from the dust. The presence of these ion wakes mediates the non-reciprocal interaction between dust grains and can result in many interesting collective behaviors. Dust grains have been observed in certain experimental conditions to form long single chains of particles. By manipulating the experimental conditions, the dust chain can be forced to undergo a reversible transition into other stable configurations such as the zig-zag and helical structures. An accurate description of the electric potential near the location of the dust structures is necessary to be able to model the motions of charged dust and ions realistically. Here we present an analysis of the electric potential near stable configurations of charged dust obtained from the results from a molecular dynamics simulation of the ion and dust motion and dust charging. |
Friday, November 12, 2021 11:06AM - 11:18AM |
ZO06.00009: Berry Curvature and Topological Phase: From Cold to Hot Plasmas Jeffrey Parker Nontrivial topology in bulk matter has been linked with the existence of topologically protected interfacial states in a diverse set of physical systems, including condensed matter, photonic systems, and recently, fluids and plasmas. The geometrical Berry curvature is also associated with corrections to the ray-tracing equations. Standard methods allow calculation of the Berry curvature and topological phase of a cold plasma. This has led, for example, to the prediction of a gaseous plasmon polariton of topological origin [1]. But so far there is no theoretical framework for determining the Berry curvature and topological phase of hot plasmas. Here, we propose a formalism for computing these quantities based on the hot-plasma dielectric tensor. Moreover, we explicitly calculate the Berry curvature and topological phase of generalized (electromagnetic) Bernstein modes in a Maxwellian plasma. |
Friday, November 12, 2021 11:18AM - 11:30AM |
ZO06.00010: Continuum damping of topologically-protected edge modes at the boundary of magnetized plasma Gennady Shvets, Roopendra Singh Rajawat, Vladimir Khudik The topological properties of the magnetized cold gaseous plasma have recently been explored and the existence of topologically protected edge states have been established [1,2]. These studies are limited to undamped edge states [1,2]. Taking a step further, we include collisionless damping of topological edge states at the interface of an inhomogeneous magnetized plasma and vacuum. We find that at the plasma-vacuum interface a continuous spectrum of modes exists. In this continuum, the frequency of the edge state matches with a local upper-hybrid electrostatic mode, and a resonant coupling between the modes results in collisionless damping of the former. Nevertheless, we show using 3D particle-in-cell simulations that edge states remain unidirectional and topologically protected with respect to backscattering. A theoretical model predicting the spatial damping rate will also be presented. These findings broaden the possible applications of these exotic excitations in space and laboratory plasmas. |
Friday, November 12, 2021 11:30AM - 11:42AM |
ZO06.00011: Tearing, Reconnection, and Anomalous Resistivity in a Mirror-infested Plasma Himawan W Winarto, Matthew W Kunz Various Larmor-scale kinetic instabilities can change the fundamental behavior of plasmas. To show this we study the time-dependent formation and evolution of a current sheet (CS) in a magnetized, collisionless, high-beta plasma using hybrid-kinetic particle-in-cell simulations. As the CS is thinned using a persistently driven incompressible shear flow, it becomes increasingly unstable to tearing while the strength of inflowing reconnecting field increases. Conservation of adiabatic invariance will then produces a field-based pressure anisotropy triggering mirror instability, which deforms the reconnecting field on ion-Larmor scales. These deformations are shown to accelerate the onset of reconnection via the tearing instability. In addition, using full particle-in-cell simulations, we assess the impact of various other Larmor-scale kinetic instabilities on the effective resistivity of a collisionless, high-beta plasma. These results find context in the structure of magnetic folds produced by the turbulent plasma dynamo, whose reversal scale is thought to be controlled by the plasma resistivity. |
Friday, November 12, 2021 11:42AM - 11:54AM |
ZO06.00012: Inhomogenous Mixing and the Fundamentals of Layering and Staircases Patrick H Diamond, Mikhail A Malkov Layered structures — often referred to as staircases — are ubiquitous. The many hypotheses for the mechanism of layering lead one to attempt to realize the simplest possible path to the formation of layered structure. More specifically, one also aims to understand how layered structures escape the predicted fate of homogenization. To this end, we examine the physics of passive scalar mixing in a bistable Cahn–Hilliard–Navier–Stokes cell. We show how the system first undergoes piecewise homogenization, in which deviation from uniformity is first reduced to a finite number of asymptotically small domain walls. These subsequently mix to a homogenous state on long time scales. This analysis shows that layering does not depend on elaborate feedback processes. |
Friday, November 12, 2021 11:54AM - 12:06PM |
ZO06.00013: Coherent emission in pulsars, magnetars and Fast Radio Bursts: Free Electron Laser in guide field-dominated regime Maxim Y Lyutikov We develop a model of the generation of coherent radio emission in the Crab pulsar, magnetars and Fast Radio Bursts (FRBs). We first consider nonlinear Thomson scattering in a guide-field dominated regime, and apply to model to explain emission bands observed in Crab pulsar and in Fast Radio Bursts. We consider particle motion in a combined fields of the electromagnetic wave and the electromagnetic (Alfvenic) wiggler. Charge bunches, created via a ponderomotive force, Compton/Raman scatter the wiggler field coherently. The model is both robust to the underlying plasma parameters and succeeds in reproducing a number of subtle observed features |
Friday, November 12, 2021 12:06PM - 12:18PM |
ZO06.00014: Attractive Non-thermal Fusion Burning Plasma Regimes Alessandro Cardinali, Bruno Coppi, Bruno Coppi Self-organization processes that are present in current experiments of non-burning plasmas can be expected to manifest themselves also through new effects in plasmas where the density and temperature profiles are interconnected with energy deposition (heating) by fusion reaction products. In this context, radially “captive” ballooning modes [1], capable of sustaining the transfer of energy from fusion reaction products to the reacting nuclei, have been identified. These modes, which involve high power transfers with acceptable particle density fluctuation levels, can lead to so-called “cool fusion” scenarios with considerably lower temperatures of the fusing nuclei than those associated with simple Maxwellian distributions. The needed electron temperatures have to be adequate (e.g., around the ideal ignition temperature for DT plasmas) to avoid significant electron damping by the relevant ballooning mode-particle resonances [1]. These findings, which are consistent with recent experimental observations [2], suggest that a serious experimental effort should be devoted to exploit the non-thermal physics of fusion burning regimes. |
Friday, November 12, 2021 12:18PM - 12:30PM |
ZO06.00015: Investigation of Shear Driven Wave Generation at Dipolarization Fronts Landry Horimbere, Erik M Tejero, William E Amatucci, Lon Enloe The highly stressed, Earth-ward propagating plasma resulting from a reconnection event is known as a dipolarization front because of its strong dipole (Bz) field. At its Earth-facing edge, there are sharp discontinuities in plasma flow, density, temperature, and electromagnetic fields. This region of space contains large releases of energy driven by sheared flows and fields. Our work is based on a non-local theory for the generation of shear-driven electrostatic Electron-Ion Hybrid waves (EIH) with frequencies near the lower hybrid frequency. We compare analytical and numerical dispersion relations to find their range of agreement. We find that the spatial length scale of the waves diverges at low-velocity shears. We then compare numerical simulations and experimental data to establish a threshold for wave growth. We expect that the likely length scale of the threshold for wave growth is at the electron Larmore radius. |
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