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Title: Flux-driven algebraic damping of m  = 1 diocotron mode

Authors:
;
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1263690
Grant/Contract Number:
SC0002451
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 7; Related Information: CHORUS Timestamp: 2016-12-27 20:15:49; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics
Country of Publication:
United States
Language:
English

Citation Formats

Chim, Chi Yung, and O'Neil, Thomas M. Flux-driven algebraic damping of m  = 1 diocotron mode. United States: N. p., 2016. Web. doi:10.1063/1.4958317.
Chim, Chi Yung, & O'Neil, Thomas M. Flux-driven algebraic damping of m  = 1 diocotron mode. United States. doi:10.1063/1.4958317.
Chim, Chi Yung, and O'Neil, Thomas M. 2016. "Flux-driven algebraic damping of m  = 1 diocotron mode". United States. doi:10.1063/1.4958317.
@article{osti_1263690,
title = {Flux-driven algebraic damping of m  = 1 diocotron mode},
author = {Chim, Chi Yung and O'Neil, Thomas M.},
abstractNote = {},
doi = {10.1063/1.4958317},
journal = {Physics of Plasmas},
number = 7,
volume = 23,
place = {United States},
year = 2016,
month = 7
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1063/1.4958317

Citation Metrics:
Cited by: 1work
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  • Recent experiments with pure electron plasmas in a Malmberg–Penning trap have observed the algebraic damping of m = 1 diocotron modes. Transport due to small field asymmetries produces a low density halo of electrons moving radially outward from the plasma core, and the mode damping begins when the halo reaches the resonant radius r = R{sub w} at the wall of the trap. The damping rate is proportional to the flux of halo particles through the resonant layer. The damping is related to, but distinct from, spatial Landau damping, in which a linear wave-particle resonance produces exponential damping. This paper explains with analytic theorymore » the new algebraic damping due to particle transport by both mobility and diffusion. As electrons are swept around the “cat's eye” orbits of the resonant wave-particle interaction, they form a dipole (m = 1) density distribution. From this distribution, the electric field component perpendicular to the core displacement produces E × B-drift of the core back to the axis, that is, damps the m = 1 mode. The parallel component produces drift in the azimuthal direction, that is, causes a shift in the mode frequency.« less
  • Recent experiments with pure electron plasmas in a Malmberg-Penning trap have observed the algebraic damping of m = 1 and m = 2 diocotron modes. Transport due to small field asymmetries produces a low density halo of electrons moving radially outward from the plasma core, and the mode damping begins when the halo reaches the resonant radius R{sub m}, where there is a matching of ω{sub m} = mω{sub E} (R{sub m}) for the mode frequency ω{sub m} and E × B-drift rotation frequency ω{sub E}. The damping rate is proportional to the flux of halo particles through the resonantmore » layer. The damping is related to, but distinct from, spatial Landau damping, in which a linear wave-particle resonance produces exponential damping. This new mechanism of damping is due to transfer of canonical angular momentum from the mode to halo particles, as they are swept around the “cat’s eye” orbits of the resonant wave-particle interaction. This paper provides a simple derivation of the time dependence of the mode amplitudes.« less
  • An effect called rotational pumping by the authors causes a slow damping of the {ital m}=1 diocotron mode in non-neutral plasmas. In a frame centered on the plasma and rotating at the diocotron mode frequency, the end confinement potentials are nonaxisymmetric. As a flux tube of plasma undergoes {bold E}{times}{bold B} drift rotation about the center of the column, the length of the tube oscillates about some mean value, and this produces a corresponding oscillation in {ital T}{sub {parallel}}. In turn, the collisional relaxation of {ital T}{sub {parallel}} toward {ital T}{sub {perpendicular}} produces a slow dissipation of electrostatic energy intomore » heat and a consequent radial expansion of the plasma. Since the canonical angular momentum is conserved, the displacement of the column off axis must decrease as the plasma expands. In the limit where the axial bounce frequency of an electron is large compared to its {bold E}{times}{bold B} drift rotation frequency theory predicts the damping rate {gamma}={minus}2{kappa}{sup 2}{nu}{sub {perpendicular},{parallel}} ({ital r}{sup 2}{sub {ital p}}/{ital R}{sup 2}{sub {ital w}})({lambda}{sup 2}{sub D}/{ital L}{sup 2}{sub 0})/(1{minus}{ital r}{sup 2}{sub {ital p}} {ital R}{sup 2}{sub {ital w}}), where {kappa} is a numerical constant, {lambda}{sub D} is the Debye length, {ital R}{sub {ital w}} is the radius of the cylindrical conducting wall, {ital r}{sub {ital p}} is the effective plasma radius, {ital L}{sub 0} is the mean length of the plasma, and {nu}{sub {perpendicular},{parallel}} is the equipartition rate. A novel aspect of this theory is the magnetic field strength enters only through {nu}{sub {perpendicular},{parallel}}. As the field strength is increased, the damping rate is independent of the field strength until the regime of strong magnetization is reached and then the damping rate drops off dramatically. (Abstract Truncated)« less
  • Zonal flow helps reduce and control the level of ion temperature gradient turbulence in a tokamak. The collisional damping of zonal flow has been estimated by Hinton and Rosenbluth (HR) in the large radial wavelength limit. Their calculation shows that the damping of zonal flow is closely related to the frequency response of neoclassical polarization of the plasma. Based on a variational principle, HR calculated the neoclassical polarization in the low and high collisionality limits. A new approach, based on an eigenfunction expansion of the collision operator, is employed to evaluate the neoclassical polarization and the zonal flow residual formore » arbitrary collisionality. An analytical expression for the temporal behavior of the zonal flow is also given showing that the damping rate tends to be somewhat slower than previously thought. These results are expected to be useful extensions of the original HR collisional work that can provide an effective benchmark for numerical codes for all regimes of collisionality.« less
  • Numerical investigations of a warm-fluid model with an isothermal equation of state for the perpendicular dynamics of an axisymmetric, magnetically confined pure electron plasma predict an exponentially unstable, [ital l]=1, diocotron mode for hollow density profiles. The unstable mode can be identified with a stable, nonsmooth mode that exists in cold drift models but which is destabilized by finite temperature effects. The unstable mode has many properties similar to the experimental results reported by Driscoll [Phys. Rev. Lett. [bold 64], 645 (1990)].