Abstract

The effect of an electron cloud on the longitudinal coupling impedance is studied by idealizing it as a cold and uniformly distributed non-neutral plasma of electrons. The beam pipe is assumed to be of circular cross section with a thick resistive wall and the beam charge is idealized as a uniform disk. The electron contribution to the charge and current densities is obtained from the collective electron response to the beam passage through the pipe. In the presence of the electron background, a general closed formula for the longitudinal coupling impedance is obtained. The screening of the coupling impedance with the density of the electron plasma is studied and discussed for typical parameters in an accelerator beam pipe for the under-dense and the over-dense plasma regions.

Highlights

  • Present addressPredicted for the GSI synchrotrons (see [15]), or measured in different ring accelerators, correspond to electron plasma frequencies of the order of fec = ωec/2π = 1 · · · 10 MHz. It turns out that the longitudinal EC effect is governed by the ratio ωec/ω with ω being the excitation frequency

  • Predicted for the GSI synchrotrons, or measured in different ring accelerators, correspond to electron plasma frequencies of the order of fec = ωec/2π = 1 · · · 10 MHz

  • The paper is organized as follows: in section 2, we present the wave equations for the electromagnetic field components in the presence of a beam perturbation and the uniformly distributed non-neutral plasma of electrons

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Summary

Present address

Predicted for the GSI synchrotrons (see [15]), or measured in different ring accelerators, correspond to electron plasma frequencies of the order of fec = ωec/2π = 1 · · · 10 MHz. It turns out that the longitudinal EC effect is governed by the ratio ωec/ω with ω being the excitation frequency. The paper is organized as follows: in section 2, we present the wave equations for the electromagnetic field components in the presence of a beam perturbation and the uniformly distributed non-neutral plasma of electrons.

Model equations with EC
Unique solution of the radial wave equations
Coupling impedance
Numerical examples and discussion
Surface-wave-sustained modes
Summary and outlook

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