Magnetized Plasma Cylinder Research Articles

Low-Frequency Waves in a Strongly Correlated Collisional Magnetized Dusty Plasma Cylinder

Low-Frequency Waves in a Strongly Correlated Collisional Magnetized Dusty Plasma Cylinder

DC electric field generation and distribution in magnetized plasmas

Very large DC and AC electric fields cannot be sustained between conducting electrodes because of volume gas breakdown and/or surface field emission. However, very large potential fields are now routinely generated in plasma structures, such as laser generated wake in unmagnetized plasmas. In magnetized plasmas, large DC fields can also be sustained and controlled perpendicular to the magnetic field, but the metallic end plates limiting the plasma, terminating the magnetic field lines, and usually providing the voltage drop feed between the field lines impose severe restrictions on the maximum field. However, it is shown that very large radial DC voltage drops can be sustained by injecting waves of predetermined frequencies and wave vectors, traveling along the azimuthal direction of an axially magnetized plasma cylinder, or by injecting fast neutral particles beams along this azimuthal direction. The large conductivity along the magnetic field lines and the small conductivity between the field lines then distribute this voltage drop. The global power balance and control parameters of wave and beam generated large DC electric fields in magnetized plasmas are identified, described, and analyzed.

Finite-difference multiple fluid solution for source-driven rotation in highly magnetized linear plasma device

The rotation profile of a magnetized plasma cylinder composed of multiple fluids is investigated analytically, expanding on previous results. The analytic steady-state solution is used as a benchmark for a time-dependent multiple-fluid finite-difference code, MITNS: Multiple-Ion Transport Numerical Solver. Magnetic field evolution is taken into account, both analytically and numerically. Its details are shown to be of importance when particles are allowed out of the domain. MITNS reproduces the asymptotic expansion results for a small parameter δ⋘1. For me/mi∼δ≪1, a slightly different regime, dominated by viscosity-induced transport of ions, is found numerically and analytically. This verification supports the use of this code for more complex time-dependent calculations in the future. Additionally, we derive the angular velocity profile of each species due to radial particle and charge fluxes of various strengths.

ENERGY LOSSES OF A POINT MAGNETIC DIPOLE DUE TO INTERACTION WITH A MAGNETIZED PLASMA CYLINDER

In this work, the excitation problem of bulk-surface helicons by a point magnetic dipole moving in a vacuum parallel to the element of magnetized solid-state plasma cylinder is theoretically studied. The external magnetic field is directed parallel to the cylinder axis. The problem is solved in the magnetostatic approximation. It is shown that hybrid modes of the magnetic type with large values of the azimuthal mode index and one field variation along the radius are most efficiently excited at nonrelativistic velocities of magnetic dipole.

Radial current and rotation profile tailoring in highly ionized linear plasma devices

In a rotating magnetized plasma cylinder with shear, cross field current can arise from inertial mechanisms and from the cross field viscosity. Considering these mechanisms, it is possible to calculate the irreducible radial current draw in a cylindrical geometry as a function of the rotation frequency. The resulting expressions raise novel possibilities for tailoring the electric field profile by controlling the density and temperature profiles of a plasma.

Excitation of a Gould-Trivelpiece (TG) Mode by Relativistic Electron Beam (REB) in Magnetized Dusty Plasma

Gould-Trivelpiece (TG) mode is excited by a relativistic electron beam (REB) via Cerenkov interaction in a magnetized dusty plasma and dusty plasma cylinder. The unstable wave's frequency increases with relative density of negatively charged dust grains \(\delta\) \((=n_{i0}/n_{e0})\), where \(n_{i0}\) is the equilibrium ion density, \(n_{e0}\) is the equilibrium electron density, respectively) in both infinite and finite geometry. The growth rate of the unstable mode increases with beam density and scales as one third power of beam density in both the cases. In addition, the growth rate of the unstable mode decreases with relativistic gamma factor. Moreover, comparison between the infinite and finite geometry indicates that the unstable mode's growth rate is more in case of infinite geometry than that of the finite geometry. Our theoretical results are in line with some of the experimental observations and theoretical findings of previous investigations.

Theoretical Modeling of an Ion-Beam-Driven Kelvin–Helmholtz Instability in a Plasma Cylinder Having Negatively Charged Dust Grains

An ion beam propagating through a magnetized plasma cylinder having negatively charged dust grains drives the Kelvin–Helmholtz instability (KHI) via Cerenkov interaction. The frequency and the growth rate of the KHI increase with the relative density of negatively charged dust grains $\delta $ . However, for large relative density of dust grains $\delta $ , the growth rate of KHI saturates. Moreover, beam density plays an important role in enhancing the growth rate of the KHI. It is also observed that finite boundary effects modify the dispersion properties of the KHI. The growth rate of KHI in a plasma cylinder is destabilized under the effect of dust charge fluctuations for relatively large velocity shears and low density of negatively charged dust grains $\delta $ . A comparative study of results is done for finite and infinite geometries of plasma waveguide.

Simulations of Gyrosynchrotron Microwave Emission from an Oscillating 3D Magnetic Loop

Radio observations of solar flares often reveal various periodic or quasi-periodic oscillations. Most likely, these oscillations are caused by magnetohydrodynamic (MHD) oscillations of flaring loops which modulate the emission. Interpretation of the observations requires comparing them with simulations. We simulate the gyrosynchrotron radio emission from a semi-circular (toroidal-shaped) magnetic loop containing sausage-mode MHD oscillations. The aim is to detect the observable signatures specific to the considered MHD mode and to study their dependence on the various source parameters. The MHD waves are simulated using a linear three-dimensional model of a magnetized plasma cylinder; both standing and propagating waves are considered. The curved loop is formed by replicating the MHD solutions along the plasma cylinder and bending the cylinder; this model allows us to study the effect of varying the viewing angle along the loop. The radio emission is simulated using a three-dimensional model and its spatial and temporal variations are analyzed. We consider several loop orientations and different parameters of the magnetic field, plasma, and energetic electrons in the loop. In the model with low plasma density, the intensity oscillations at all frequencies are synchronous (with the exception of a narrow spectral region below the spectral peak). In the model with high plasma density, the emission at low frequencies (where the Razin effect is important) oscillates in anti-phase with the emissions at higher frequencies. The oscillations at high and low frequencies are more pronounced in different parts of the loop (depending on the loop orientation). The layers where the line-of-sight component of the magnetic field changes sign can produce additional peculiarities in the oscillation patterns.

Electrostatic Ion Cyclotron and Ion Plasma Waves in a Symmetric Pair-Ion Plasma Cylinder

Complicated wave behavior observed in the cylindrical pair-ion (fullerene) experiments by Oohara and co-workers are now identified to be low harmonic ion cyclotron waves combined with ion plasma oscillations inherent to kinetic theory. The electrostatic dispersion equation derived is based on an approximation for the current from the exact solutions of the characteristic cylindrical geometry form of the Vlasov plasma equation in a uniform magnetized plasma cylinder surrounded by a larger metal boundary outside a vacuum gap, which thus differs from that in unbounded plasmas. Positive and negative ions, differing only in the sign of their charge, respond to a potential in the same time scale and cooperate to reflect the enhanced kinetic orbital behaviors to the macroscopic propagation characteristics. In addition, the experimental value of the Larmor radius (comparable to the discharge radius but small enough to make the analytic approximation useful) makes higher harmonic ion cyclotron effects both observable and calculable with the appropriate approximation for the kinetic theory.

Spiraling ion beam driven electrostatic ion cyclotron wave instabilities in collisionless dusty plasma

The numerical calculations of the growth rate in long parallel wavelength are made for a spiraling ion beam propagating through a collision less magnetized dusty plasma cylinder that drives electrostatic ion cyclotron waves to instability via cyclotron interaction. It is found that the growth rate of the instability of the electrostatic ion cyclotron waves increase in the long parallel limit with the density ratio of negatively charged dust grains to electrons. The growth rate of the unstable mode has the maximum value for the modes whose Eigen functions peak at the location of the beam and varies as the one-third power of the beam current in both the limits.

Surface wave excitation by a density modulated electron beam in a magnetized dusty plasma cylinder

AbstractThis paper studies the surface plasma wave excitation via Cerenkov and fast cyclotron interaction by a density modulated electron beam propagating through a magnetized dusty plasma cylinder. The dispersion relation of surface plasma waves has been derived and it has been shown that the phase velocity of waves increases with increase in relative density δ(=nio/ne0,whereni0is the ion plasma density andne0is the electron plasma density) of negatively charged dust grains. The beam radius is taken slightly less than the radius of dusty plasma cylinder. The frequency and the growth rate of the unstable wave instability increases with increase in the value of δ and normalized frequency ω/ωpe. The growth rate of the instability increases with the beam density and scales as one-third power of the beam density in Cerenkov interaction and square root of beam density in fast cyclotron interaction. The dispersion relation of surface plasma waves has been retrieved from the derived dispersion relation by considering that the beam is absent and there are no dust grains in the plasma cylinder.

Excitation of lower hybrid waves by a gyrating ion beam in a negative ion plasma

A gyrating ion beam propagating through a magnetized plasma cylinder containing K+ positive ions, electrons, and SF6− negative ions drives electrostatic lower hybrid waves to instability via Cyclotron interaction. Numerical calculations of the unstable mode frequencies and growth rates of both the unstable positive ion and negative ion modes have been carried out for the existing negative ion plasma parameters. It is found that the unstable mode frequencies of both the modes increase, with the relative density of negative ions. In addition, the growth rates of both the unstable modes also increases with relative density of negative ions. Moreover, the growth rates of both the unstable modes scale as the one-third power of the beam density. The frequencies of both the unstable modes also increase with the magnetic fields. The real part of the unstable wave frequency increases as almost the square root of the beam energy.

Higher harmonics generation by a spiraling ion beam in collisionless magnetized plasma

AbstractA spiraling ion beam propagating through a magnetized plasma cylinder containing K+ light positive ions, electrons, and C7F14− heavy negative ions drives electrostatic ion–cyclotron waves to instability via cyclotron interaction. Higher harmonics of the beam cyclotron frequency can be generated in this way. The unstable mode frequencies and growth rates of both unstable light positive ions and heavy negative ions increase with the relative density of heavy negative ions. Moreover, the growth rate of unstable modes scales as the one-third power of the beam density. The growth rate of unstable modes increases with harmonic number. The frequencies of both unstable modes also increase with magnetic fields. In addition, the real part of both unstable modes (K+ and C7F14−) increases with the beam energy and scales as almost one-half power of the beam energy.

Decay instability of an upper hybrid wave in a magnetized dusty plasmas

The decay instability of an upper hybrid wave into an upper hybrid sideband wave and low frequency ion-cyclotron wave are studied in a magnetized dusty plasma cylinder. The growth rate and ion-cyclotron mode frequencies were evaluated based on existing dusty plasma parameters. It is found that the unstable mode frequency increases linearly with δ (ion-to-electron density ratio). In addition, the growth rate of the unstable ion-cyclotron mode decreases sharply for lower values of δ in the presence of dust charge fluctuations, i.e., the dust grains increases the damping effect in three wave interaction process.

Ion beam driven ion-acoustic waves in a plasma cylinder with negatively charged dust grains

An ion beam propagating through a magnetized potassium plasma cylinder having negatively charged dust grains drives electrostatic ion-acoustic waves to instability via Cerenkov interaction. The phase velocity of sound wave increases with the relative density of negatively charged dust grains. The unstable wave frequencies and the growth rate increase, with the relative density of negatively charged dust grains. The growth rate of the unstable mode scales as one-third power of the beam density. The real part of frequency of the unstable mode increases with the beam energy and scales as almost the one-half power of the beam energy.

Sheared-flow induced confinement transition in a linear magnetized plasma

A magnetized plasma cylinder (12 cm in diameter) is induced by an annular shape obstacle at the Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)]. Sheared azimuthal flow is driven at the edge of the plasma cylinder through edge biasing. Strong fluctuations of density and potential ({delta}n/n{approx}e{delta}{phi}/kT{sub e}{approx}0.5) are observed at the plasma edge, accompanied by a large density gradient (L{sub n}={nabla}lnn{sup -1}{approx}2cm) and shearing rate ({gamma}{approx}300kHz). Edge turbulence and cross-field transport are modified by changing the bias voltage (V{sub bias}) on the obstacle and the axial magnetic field (B{sub z}) strength. In cases with low V{sub bias} and large B{sub z}, improved plasma confinement is observed, along with steeper edge density gradients. The radially sheared flow induced by ExB drift dramatically changes the cross-phase between density and potential fluctuations, which causes the wave-induced particle flux to reverse its direction across the shear layer. In cases with higher bias voltage or smaller B{sub z}, large radial transport and rapid depletion of the central plasma density are observed. Two-dimensional cross-correlation measurement shows that a mode with azimuthal mode number m=1 and large radial correlation length dominates themore » outward transport in these cases. Linear analysis based on a two-fluid Braginskii model suggests that the fluctuations are driven by both density gradient (drift wave like) and flow shear (Kelvin-Helmholtz like) at the plasma edge.« less

Degenerate mixing of plasma waves on cold, magnetized single-species plasmas

In the cold-fluid dispersion relation ω=ωp/[1+(k⊥/kz)2]1/2 for Trivelpiece-Gould waves on an infinitely long magnetized plasma cylinder, the transverse and axial wavenumbers appear only in the combination k⊥/kz. As a result, for any frequency ω<ωp, there are infinitely many degenerate waves, all having the same value of k⊥/kz. On a cold finite-length plasma column, these degenerate waves reflect into one another at the ends; thus, each standing-wave normal mode of the bounded plasma is a mixture of many degenerate waves, not a single standing wave as is often assumed. A striking feature of the many-wave modes is that the short-wavelength waves often add constructively along resonance cones given by dz/dr=±(ωp2/ω2-1)1/2. Also, the presence of short wavelengths in the admixture for a predominantly long-wavelength mode enhances the viscous damping beyond what the single-wave approximation would predict. Here, numerical solutions are obtained for modes of a cylindrical plasma column with rounded ends. Exploiting the fact that the modes of a spheroidal plasma are known analytically (the Dubin modes), a perturbation analysis is used to investigate the mixing of low-order, nearly degenerate Dubin modes caused by small deformations of a plasma spheroid.

The effect of dust charge fluctuations on collisional drift waves in a magnetized plasma cylinder

The nonlinear coupling between collisional drift waves and a lower-hybrid pump wave is studied in a magnetized dusty plasma cylinder. A dispersion relation for the collisional drift wave and growth rate is derived incorporating both pondermotive and Ohmic heating effects. The growth rate and mode frequencies were evaluated based on existing dusty plasma parameters. It is found that the unstable collisional drift mode frequency increases and the growth rate decreases sharply with the relative density of negatively charged dust grains. Moreover, the collisional frequency has no effect on the unstable drift mode frequency. However, the increases in collisional frequency and electron temperature are playing an important role in the damping effect.

Excitation of electrostatic ion-cyclotron waves by an ion beam in a two-ion component plasma

An ion beam propagating through a magnetized plasma cylinder containing electrons, light positive potassium ions (K+), and heavy positive cesium ions (Cs+) drives electrostatic ion cyclotron (EIC) waves to instability via Cerenkov interaction. Two EIC wave modes are present, the K+ and Cs+ modes. The unstable wave frequencies and the growth rate of both the light positive ion and heavy positive ion modes increase with an increase in their relative ion concentrations. The growth rate of both the unstable modes (K+ and Cs+) scales one-third power of the beam density. The real part of the frequency of both the unstable modes (K+ and Cs+) increases with the beam energy and scales as almost one-half power of the beam energy. Numerical calculations of the growth rate and mode frequencies have been carried out for the parameters of the experiment of Suszcynsky et al. [J. Geophys. Res. 94, 8966 (1989)]. It is found that the unstable wave frequencies of both the light positive ion and heavy positive ion modes increase with the magnetic fields in accordance with the experimental observations.

Excitation of surface plasma waves by a density-modulated electron beam in a magnetized plasma cylinder

A density-modulated electron beam propagating through a plasma cylinder excites surface plasma waves (SPWs) via Cerenkov and fast cyclotron interaction. A nonlocal theory of this process has been developed. Numerical calculations of the growth rate and unstable mode frequencies have been carried out for the typical parameters of the SPWs. The growth rate γ (in rad/s) of the unstable wave instability increases with the modulation index Δ and has the largest value for Δ∼1 in addition to when the frequency and wave number of the modulation are comparable to that of the unstable wave. For Δ=0, γ turns out to be ∼6.06×109 rad/s for Cerenkov interaction and ∼5.47×109 rad/s for fast cyclotron interaction. The growth rate of the instability increases with the beam density and scales as one-third power of the beam density in Cerenkov interaction and is proportional to the square root of beam density in fast cyclotron interaction. The real part of the frequency of the unstable wave increases as almost the square root of the beam voltage. The results of the theory are applied to explain some of the experimental observations.