Magnetic damping of ℓ=1 diocotron mode

Roberts, G. A.; Rostoker, N.

doi:10.1063/1.865262

The Physics of Fluids

1985

DOI: 10.1063/1.865262

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Magnetic damping of ℓ=1 diocotron mode

G. A. Roberts

N. Rostoker

Abstract: Previous work has treated the diocotron mode for a low-energy beam and has found that any dissipative effect will cause this mode to grow. However, a treatment that considers the axial velocity of the beam shows that this mode will damp if the beam is relatively thin and the axial velocity of the beam is comparable with c. This damping is attributed to the perturbed magnetic field and is similar to the stabilization of sausage and kink modes in neutral plasmas. The damping rate for this case is compared with t… Show more

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Cited by 4 publications

References 11 publications

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Maser gain determined by the spatial profile of work done by an average electron and the wavelength of density fluctuation driven by the maser field in multi-photon free-electron two-quantum Stark radiation

Kim

2015

J. Plasma Phys.

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We find that the electron in an electron–cyclotron maser (ECM) of Nc = n1/3λ ≫ 1, where n and λ are the electron density and the maser wavelength, respectively, can only lower its energy through masing transition. From this fact and the application of Heisenberg's uncertainty principle on photon emission, we infer that until the electron energy becomes lower to pass through the width of uncertainty in the electron energy, the interval time Tint between two successive radiative transitions is zero. Hence, we find that if the number Nt of radiative transitions during the laser period T under the assumption of Tint = 0 is far larger than the number Nu of radiative transitions required to pass through the half-width ΔE of uncertainty in the electron energy, the radiation power from an electron is equal to ΔE/T. We deduce that the shift in the energy level of an average electron is predominantly produced by the density-deviation mode driven by the laser field so as to be spatially sinusoidal with period λw and amplitude $\mathcal W$. We recognize that the uncertainty in the z position of an electron emitting a laser photon through free-electron two-quantum Stark (FETQS) radiation is the wavelength λe of the electric wiggler. Thus, if λw ≪ λe, then ΔE is equal to $\mathcal W$. Based on the above findings, we identify electron–cyclotron masing in a high-density ECM as a gyration-driven FETQS radiation whose power is given by P = ΔE/T, where ΔE is not caused by gyration but rotation around the waveguide axis. The gain calculated based on this identification agrees with the measured one.

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Maser gain determined by the spatial profile of work done by an average electron and the wavelength of density fluctuation driven by the maser field in multi-photon free-electron two-quantum Stark radiation

Kim

2015

J. Plasma Phys.

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Influence of the return current effects on the diocotron instability of a relativistic hollow electron beam

Choi

Uhm

Song

et al. 1989

Journal of Applied Physics

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Influence of the return current effects on the diocotron instability of a relativistic hollow electron beam propagating through a background plasma is investigated within the framework of a cold fluid model. The return current density induced in the background plasma is taken to be steadily proportional to the axial electron beam current density. By making use of the linearized fluid-Maxwell equations, a dispersion relation for the eigenfrequencies of the system is derived and used to examine instabilities. It is found that as the fraction of current neutralization increases, lower mode instabilities become dominant while higher mode perturbations are stabilized except in the case of very thin beams. It is also observed that for all values of the fraction of current neutralization, increasing the plasma density gradient or decreasing the beam thickness causes a destabilizing influence.

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Equilibrium of non-neutral plasma in toroidal geometry with applied electric field

Bhattacharyya

Khare

1992

Physics of Fluids B: Plasma Physics

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The equilibrium and stability of non-neutral plasma in toroidal geometry with applied electric field is studied. The calculations are done in a large aspect ratio, thin ring approximation, using a circuit model. Toroidal corrections to the I= 1 (I is the poloidal mode number) mode are obtained. These corrections reduce the I= 1 cylindrical diocotron frequency. It is shown that under certain conditions, the external electric field can stabilize dissipative I= 1 diocotron oscillations.

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Magnetic damping of ℓ=1 diocotron mode

Cited by 4 publications

References 11 publications

Maser gain determined by the spatial profile of work done by an average electron and the wavelength of density fluctuation driven by the maser field in multi-photon free-electron two-quantum Stark radiation

Maser gain determined by the spatial profile of work done by an average electron and the wavelength of density fluctuation driven by the maser field in multi-photon free-electron two-quantum Stark radiation

Influence of the return current effects on the diocotron instability of a relativistic hollow electron beam

Equilibrium of non-neutral plasma in toroidal geometry with applied electric field

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