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| Paper IPM / Physic / 6679 |
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| Abstract: | |||||
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The parametric instability of a predominatly transverse magnetic mode in
a waveguide, partially filled with a magnetized plasma, is considered.
Raman backscattering of the pump wave off the space-charge wave leads to the
scattered radiaiton. Waveguide eigenmodes relevant to the pump wave and the
excited waves are discussed. Formulas are derived for the temporal and
spatial growth rates of the backscattered wave and scatterer wave with
the pump wave frequency near the electron cyclotron frequency.
A numerical study indicates that the phase-matching conditions permit
the approach to cyclotron resonance with substantial enhancement of the
growth rates. Growth rates show considerable dependence on the ratio
of the plasma radius to the waveguide radius a/R and their maximum
values are found to be for a/R ≈ 0.3. The growth rate found from
the electromagnetic treatment was about 20%
less than the one calculated with electrostatic assumption on the
space-charge wave. It is also shown that the electromagnetic effect of the
space-charge wave has considerable influence on the maximum growth
rate near cyclotron resonance by preventing the pump wave from approaching
the resonance. Possible use of the EH waveguide mode as pump for a
free-electron laser is discussed. The results of this theory are found
to be comparable with the results of previous theoretial and experimental
investigations.
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