Rotational pumping and damping of the {ital m}=1 diocotron mode

Journal Article · Wed Feb 01 04:00:00 EST 1995 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.870962· OSTI ID:171212

Crooks, S M; O`Neil, T M ^[1]

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1. Department of Physics, University of California at San Diego, La Jolla, California 92093 (United States)

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 into 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)

• OSTI ID: 171212
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 2 Vol. 2; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
COLLISIONAL PLASMA
DAMPING
DEBYE LENGTH
ELECTRON GAS
MAGNETIZATION
PLASMA DRIFT
PLASMA EXPANSION
RESONANCE
ROTATING PLASMA
TRANSPORT THEORY