Plasma Physics
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Showing new listings for Tuesday, 26 November 2024
- [1] arXiv:2411.15705 [pdf, html, other]
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Title: Anisotropic anomalous diffusion in microgravity dusty plasma. Part One: Nonequilibrium Statistical AnalysisSubjects: Plasma Physics (physics.plasm-ph)
Anisotropic anomalous dust diffusion in microgravity dusty plasma is investigated using experimental data from the Plasmakristall-4 (PK-4) facility on board the International Space Station. The PK-4 experiment uses video cameras to track individual dust particles, which allows the collection of large amounts of statistical information on the dust particle positions and velocities. These statistics are used to quantify anomalous dust diffusion caused by anisotropies in the plasma-mediated dust-dust interactions in PK-4. Anisotropies are caused by an externally applied polarity-switched electric field, which modifies the ion wakefields surrounding the dust grains. Video data for nine sets of pressure-current conditions are used to recover Mean Squared Displacement (MSD) plots after subtracting particle drift. Position and velocity histograms are fitted to Tsallis nonextensive probability distribution functions (PDFs). Both MSDs and PDFs indicate a crossover from suprathermal to Lévy diffusion in the axial direction at higher pressure conditions. In addition, increasing the pressure enhances dust thermal equilibrium, while increasing the current drives the system away from equilibrium.
- [2] arXiv:2411.16066 [pdf, other]
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Title: Stability of Crossed-Field AmplifiersChristopher Swenson, Ryan Revolinsky, Adam Brusstar, Emma Guerin, Nicholas M. Jordan, Y. Y. Lau, Ronald GilgenbachSubjects: Plasma Physics (physics.plasm-ph)
This research examines the stability of crossed-field amplifiers (CFAs) and characterizes their different modes of operation: amplification, driven oscillation, and self-excited oscillation. The CFA used in this paper is the Recirculating Planar Crossed-Field Amplifier (RPCFA), which is a high power (MW) pulsed (300 ns) amplifier that operates around 3 GHz. Initially, the RPCFA is shown to be a stable amplifier with moderate gain (5.1 dB), but by either reducing the anode-cathode (AK) gap spacing or increasing the driving current, the amplifier operation transitions from amplification to oscillation. Depending on the operating conditions, these oscillations are either driven by the input RF signal or self-excited. These self-excited oscillations can have a lower synchronization phase velocity than the maximum velocity in the electron beam, implying that slower electrons within the Brillouin hub can interact with electromagnetic modes on the RF circuit. A cold tube analysis of the RPCFA shows that the Q-factor of certain modes on the RF circuit varies significantly when the AK gap geometry of the RPCFA is altered which leads to a discrete shift in operating frequency. The operation of the RPCFA close to Hull cutoff is found to share some key features of magnetically insulated transmission line oscillators (MILO) that could also explain the dramatic frequency shift. Instantaneous phase analysis by Hilbert transforms can be used, in conjunction with the frequency and output power analysis, to determine the onset of the transition from amplification to oscillation, and to characterize the oscillation.
- [3] arXiv:2411.16286 [pdf, html, other]
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Title: Dynamics and modulation of cosmic ray modified magnetosonic waves in a galactic gaseous rotating plasmaComments: 14 pages, 10 figures. Submitted to the Physics of FluidsSubjects: Plasma Physics (physics.plasm-ph)
The influence of the presence of cosmic fluid on the magnetosonic waves and modulation instabilities in the interstellar medium of spiral galaxies is investigated. The fluid model is developed by modifying the pressure equation in such dissipative rotating magnetoplasmas incorporating thermal ionized gas and cosmic rays. Applying the normal mode analysis, a modified dispersion relation is derived to study linear magnetosonic wave modes and their instabilities. The cosmic rays influence the wave damping by accelerating the damping rate. The standard reductive perturbation method is employed in the fluid model leading to a Korteweg de Vries Burgers (KdVB) equation in the small-amplitude limit. Several nonlinear wave shapes are assessed by solving the KdVB equation, analytically and numerically. The cosmic ray diffusivity and magnetic resistivity are responsible for the generation of shock waves. The modulational instability (MI) and the rogue wave solutions of the magnetosonic waves are studied by deriving a nonlinear Schrodinger (NLS) equation from the obtained KdVB equation under the assumption that the cosmic ray diffusion and magnetic resistivity are weak and the carrier wave frequency is considerably lower than the wave frequency. The influence of various plasma parameters on the growth rate of MI is examined. The modification of the pressure term due to cosmic fluid reduces the MI growth in the interstellar medium. In addition, a quantitative analysis of the characteristics of rogue wave solutions is presented. Our investigation's applicability to the interstellar medium of spiral galaxies is traced out.
- [4] arXiv:2411.16333 [pdf, html, other]
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Title: Influence of plasma particle flow on dust grain charging and on particle number densityComments: Submitted to Physics of PlasmasSubjects: Plasma Physics (physics.plasm-ph)
This study explores the dynamic evolution of dust electrical potential and plasma particle number densities with a focus on the charging of dust grains through electron and ion absorption, as described by the orbital motion limited (OML) theory. The initial model, which does not account for plasma particle sources and sinks, predicts that dust grains could eventually absorb all plasma particles, leading to a null electrical potential. To address this, we introduced source and sink terms considering a finite region of space in order to simulate real conditions. Our findings indicate that, with the inclusion of plasma particle flow into and out of the region, dust grains reach a stable, non-zero equilibrium potential and the electron and ion densities reach an equilibrium value. This equilibrium is dependent on the size of the region; larger regions result in lower plasma densities and more negative equilibrium potentials. For extensive regions, the dust potential initially mirrors the scenario without sources or sinks but eventually deviates, showing increasing negative values as the region size grows. This behavior is attributed to the electron source term surpassing the combined sink and absorption terms at certain intervals along time evolution.
- [5] arXiv:2411.16411 [pdf, html, other]
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Title: Back to the Figure-8 StellaratorSubjects: Plasma Physics (physics.plasm-ph)
The first stellarator design was a simple tube of plasma twisted and closed on itself in the form of a figure-8. The line of such devices, however, was quickly ended over concerns related to plasma stability. We revisit the figure-8 concept, re-imagined as a modern optimized stellarator, and find the potential for a high degree of stability, as well as exceptionally simple construction. In particular, the design that we find admits planar coils, and is the first quasi-isodynamic stellarator design to have this property. Our work is made possible by recent theoretical progress in the near-axis theory of quasi-isodynamic stellarators, combined with fundamental progress in the numerical solution of three-dimensional magnetohydrodynamic equilibria that cannot be well represented using traditional cylindrical coordinates.
New submissions (showing 5 of 5 entries)
- [6] arXiv:2411.16275 (cross-list from physics.acc-ph) [pdf, html, other]
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Title: Comparative Analysis of Simulation Results of Dielectric Laser Acceleration of Non-relativistic Electrons in Transparent and Reflective Periodic StructuresComments: 8 pages, 11 figuresSubjects: Accelerator Physics (physics.acc-ph); Plasma Physics (physics.plasm-ph)
To support of our experimental studies on dielectric laser acceleration, numerical studies of laser acceleration of nonrelativistic electrons with the initial energy of 33.9 keV in transparent and reflective periodic structures are car-ried out. On the basis of computer simulations, the acceleration rates of electrons and the quality of their beams after acceleration in compact structures of different configurations were determined and compared. Prospective acceleration schemes are proposed, in particular with reflective periodic structures, which can provide higher rates of electron acceleration in periodic structures than in previously obtained studies.
- [7] arXiv:2411.16484 (cross-list from astro-ph.HE) [pdf, html, other]
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Title: Relativistically Magnetized Collisionless Shocks in Pair Plasma: I. Solitons, Chaos, and ThermalizationComments: 11 pages, 8 figuresSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Chaotic Dynamics (nlin.CD); Plasma Physics (physics.plasm-ph)
In this paper, the first in a series, we present a new theoretical model for the global structure and dissipation of relativistically magnetized collisionless shock waves. Quite remarkably, we find that in contrast to unmagnetized shocks, energy dissipation does not involve collective plasma interactions. Rather, it is a consequence of nonlinear particle dynamics. We demonstrate that the kinetic-scale shock transition can be modeled as a stationary system consisting of a large set of cold beams coupled through the magnetic field. The fundamental mechanism governing shock dissipation relies on the onset of chaos in orbital dynamics within quasiperiodic solitonic structures. We discuss the impact of upstream temperature and magnetization on the shock profile, recovering the magnetic field compression, downstream velocities, and heating expected from the Rankine-Hugoniot jump conditions. We deduce a rate of entropy generation from the spectrum of Lyapunov exponents and discuss the thermalization of the beam distribution. Our model provides a general framework to study magnetized collisionless shock structures.
- [8] arXiv:2411.16513 (cross-list from astro-ph.SR) [pdf, html, other]
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Title: Coronal hole picoflare jets are the progenitors of both the fast and the Alfv\'enic slow solar windL. P. Chitta, Z. Huang, R. D'Amicis, D. Calchetti, A. N. Zhukov, E. Kraaikamp, C. Verbeeck, R. Aznar Cuadrado, J. Hirzberger, D. Berghmans, T. S. Horbury, S. K. Solanki, C. J. Owen, L. Harra, H. Peter, U. Schühle, L. Teriaca, P. Louarn, S. Livi, A. S. Giunta, D. M. Hassler, Y.-M. WangComments: Accepted for publication in Astronomy and Astrophysics. Online animations available at this https URLSubjects: Solar and Stellar Astrophysics (astro-ph.SR); Plasma Physics (physics.plasm-ph); Space Physics (physics.space-ph)
The solar wind, classified by its bulk speed and the Alfvénic nature of its fluctuations, generates the heliosphere. The elusive physical processes responsible for the generation of the different types of the wind are a topic of active debate. Recent observations revealed intermittent jets with kinetic energy in the picoflare range, emerging from dark areas of a polar coronal hole threaded by open magnetic field lines. These could substantially contribute to the solar wind. However, their ubiquity and direct links to the solar wind have not been established. Here we report a unique set of remote-sensing and in-situ observations from the Solar Orbiter spacecraft, that establish a unified picture of the fast and Alfvénic slow wind, connected to the similar widespread picoflare jet activity in two coronal holes. Radial expansion of coronal holes ultimately regulates the speed of the emerging wind.
Cross submissions (showing 3 of 3 entries)
- [9] arXiv:2408.12900 (replaced) [pdf, html, other]
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Title: Observation and characterisation of trapped electron modes in Wendelstein 7-XA. Krämer-Flecken, J.H.E. Proll, G. Weir, P. Costello, G. Fuchert, J. Geiger, S. Heuraux, A. Knieps, A. Langenberg, S. Vaz Mendes, N. Pablant, E. Pasch, K. Rahbarnia, R. Sabot, L. Salazar, H.M. Smith, H. Thomsen, T. Windisch, H.M. Xiang, the W7-X-teamComments: Some revisions asked by referees includedSubjects: Plasma Physics (physics.plasm-ph)
In the past, quasi coherent modes were reported for nearly all tokamaks. The general definition describes modes as quasi coherent when the magnitude squared coherence is in the range of \SIrange{0.3}{0.6}{}. Quasi coherent modes are observed in the plasma core as well as in the plasma edge and can have quite different physical origins. The one in the core are observed in plasmas with low collisionality, where the electron temperature exceeds the ion temperature in the plasma core. This is the case for electron cyclotron heating in general. The origin of these modes are electrons trapped within a magnetic mirror, as reported in the past from various fusion devices. The so-called trapped-electron modes (TEMs) belong to drift wave instabilities and can be destabilized by electron-temperature gradients in the plasma core. From the diagnostic point of view, quasi coherent modes appear as fluctuations in electron density and temperature. Therefore, the microwave reflectometer is very well suited to monitor these modes. This paper describes experiments, conducted at the Wendelstein 7-X stellarator (W7-X), which aim at detecting quasi coherent modes at low wave numbers. A Poloidal Correlation Reflectometer (PCR) installed at W7-X, is able to measure low wave numbers ($k_\perp\le 3.5$ cm$^{-1}$). For different magnetic configurations and plasma parameters, broad quasi-coherent structures are observed in the coherence spectra. From the analysis of the rotation and the poloidal structure, these quasi coherent (QC) modes show the properties of electron-temperature-gradient driven TEMs. A linear relation between the mode velocity and the rotation frequency is found. The relation is uniform and confirms the nature of QC-mode observation as TEM in tokamaks, too.
- [10] arXiv:2408.16888 (replaced) [pdf, html, other]
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Title: Stabilization of beam heated plasmas by beam modulationSubjects: Plasma Physics (physics.plasm-ph)
A constant intensity beam that propagates into a stationary plasma results in a bump-on-tail feature in velocity space. This results in an instability that transfers kinetic energy from the plasma to the electric field. We show that there are intensity profiles for the beam (found by numerical optimization) that can largely suppress this instability and drive the system into a state that, after the beam has been switched off, remains stable over long times. The modulated beam intensity requires no feedback, i.e. no knowledge of the physical system during time evolution is required, and the frequency of the modulation scales approximately inversely with system size, which is particularly favorable for large plasma systems. We also show that the results obtained are robust in the sense that perturbations, e.g. deviation from the optimized beam profiles, can be tolerated without losing the ability to suppress the instability.
- [11] arXiv:2411.12607 (replaced) [pdf, html, other]
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Title: Single-fluid simulation of partially-ionized, non-ideal plasma facilitated by a tabulated equation of stateSubjects: Plasma Physics (physics.plasm-ph); Solar and Stellar Astrophysics (astro-ph.SR); Computational Physics (physics.comp-ph); Fluid Dynamics (physics.flu-dyn)
We present a single-fluid approach for the simulation of partially-ionized plasmas (PIPs) which is designed to capture the non-ideal effects introduced by neutrals while remaining close in computational efficiency to single-fluid MHD. This is achieved using a model which treats the entire partially-ionized plasma as a single mixture, which renders internal ionization/recombination source terms unnecessary as both the charged and neutral species are part of the mixture's conservative system. Instead, the effects of ionization and the differing physics of the species are encapsulated as material properties of the mixture. Furthermore, the differing dynamics between the charged and neutral species is captured using a relative-velocity quantity, which impacts the bulk behavior of the mixture in a manner similar to the treatment of the ion-electron relative-velocity as current in MHD. Unlike fully-ionized plasmas, the species composition of a PIP changes rapidly with its thermodynamic state. This is captured through a look-up table referred to as the tabulated equation of state (TabEoS), which is constructed prior to runtime using empirical physicochemical databases and efficiently provides the ionization fraction and other material properties of the PIP specific to the thermodynamic state of each computational cell. Crucially, the use of TabEoS also allows our approach to self-consistently capture the non-linear feedback cycle between the PIP's macroscopic behavior and the microscopic physics of its internal particles, which is neglected in many fluid simulations of plasmas today.
- [12] arXiv:2407.06440 (replaced) [pdf, html, other]
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Title: Deformation of invariant tori under perturbationComments: 7 pages, 4 figuresSubjects: Chaotic Dynamics (nlin.CD); Dynamical Systems (math.DS); Plasma Physics (physics.plasm-ph)
This study extends the functional perturbation theory~(FPT) of dynamical systems, which was initially developed for investigating the shifts of magnetic field line trajectories within the chaotic edge region of plasma when subjected to global perturbations. By contrast, invariant tori reside in the ordered regions of phase space. In magnetic confinement fusion (MCF) devices, these tori manifest as closed flux surfaces, with their nested structure governing radial transport and thus playing a critical role in confinement performance. Using the method of variation as a mathematical foundation, this Letter derives formulae that characterize the deformation of invariant tori under perturbation. These results provide new tools for targeted topology control in tokamak operations and for optimizing stellarator designs by enhancing predictive capability for flux surface behaviour.
- [13] arXiv:2411.14302 (replaced) [pdf, html, other]
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Title: Electrodynamics of Vortices in Quasi-2D Scalar Bose-Einstein CondensatesComments: 15 pages, 1 figureSubjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph); Plasma Physics (physics.plasm-ph); Quantum Physics (quant-ph)
In two spatial dimensions, vortex-vortex interactions approximately vary with the logarithm of the inter-vortex distance, making it possible to describe an ensemble of vortices as a Coulomb gas. We introduce a duality between vortices in a quasi-two-dimensional (quasi-2D) scalar Bose-Einstein condensates (BEC) and effective Maxwell's electrodynamics. Specifically, we address the general scenario of inhomogeneous, time-dependent BEC number density with dissipation or rotation. Starting from the Gross-Pitaevskii equation (GPE), which describes the mean-field dynamics of a quasi-2D scalar BEC without dissipation, we show how to map vortices in a quasi-2D scalar BEC to 2D electrodynamics beyond the point-vortex approximation, even when dissipation is present or in a rotating system. The physical meaning of this duality is discussed.