The co-excitation of electrostatic ion-cyclotron wave and ion Bernstein-like wave launched from a grid
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Graphical Abstract
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Abstract
Electrostatic ion-cyclotron wave (EICW) and ion-Bernstein wave
(IBW) are two typical normal modes of plasma propagating
vertically to a magnetic field.
These modes satisfy the extreme conditions
\omega \ll k_\parallel v_\rm te and \omega \gg k_\parallel v_\rm te,
where \omega, k_\parallel, and v_\rm te are the wave
angular frequency, wave number parallel to the magnetic field,
and the electron thermal speed. Between these extremities,
there exist IBW-like waves that have not been studied.
In this paper, the co-excitation of the EICW and IBW-like wave in
an experiment is presented. It is shown that, in an argon (Ar)
discharge, the EICW appears in the fundamental and second
harmonic frequency bands of the ion-cyclotron frequency.
In contrast, the IBW-like wave appears in the higher
harmonic frequency bands and in the case of a relatively
strong magnetic field. In a helium (He) discharge, the IBW-like
wave is excited in the fundamental frequency band,
but the wave behaviour becomes complicated in the harmonic
frequency bands. The measured dispersion relations of the
excited EICW are in agreement with the results of the fluid and
kinetic models in some range of frequencies, but those of the
excited IBW-like wave are only in qualitative agreement with
the kinetic model of the IBW.
This study is important for identifying the
IBW-like mode that may have potential application in plasma
heating via Landau damping.
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