Nonsingular linear theory for stimulated microwave emission in crossed-field devices

Journal Article · Mon Nov 01 00:00:00 EST 1993 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.860585· OSTI ID:5945026

Riyopoulos, S ^[1]

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1. Science Applications International Corporation, McLean, Virginia 22102 (United States)

The small signal stability of crossed-field devices fed by a thin electron beam is analyzed. The situation differs from diocotron modes in that the interaction cavity supports slow wave eigenmodes in vacuum. The rippling of the beam causes a modification of the vacuum dispersion relation and mode profiles. The growth rate is found by equating the rate of change of the power flux with the fast scale averaged wave--particle energy exchange rate. The radio frequency (rf) power flow including the energy circulating in the anode structure is related to the wave amplitude via the interaction impedance. The singularities at resonance, the trademark of any linear theory, are avoided by following the particle guiding center (GC) orbits in reference frame with the wave synchronous. The small signal gain is found by expansion in powers of the rf amplitude. A finite linear growth results, even for symmetric particle excursions, due to the self-field of the rippled beam. Near resonance the growth rate is independent of the detuning between the phase and drift velocities. Higher-order contributions to the instability are caused by the nonlinear bunching of the GC distribution in space and are [ital symmetric] relative to resonance. Symmetric frequency response is a unique feature of crossed-field devices (CFD's) opposed to the [ital antisymmetric] growth characterizing other unbound electron'' devices [gyrotrons, free-electron lasers (FEL's), traveling-wave tubes (TWT's)]. The growth rate goes over to the diocotron growth when all the impedance comes from the rippled beam (i.e., smooth anode at infinite distance). The perturbed mode profiles are nonsingular; the profile singularities of standard linear theories reflect the singularities of the particle orbits at resonance.

• OSTI ID: 5945026
• Journal Information: Physics of Fluids B; (United States), Vol. 5:11; ISSN 0899-8221
• Country of Publication: United States
• Language: English

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70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ELECTRON TUBES
INSTABILITY GROWTH RATES
MICROWAVE RADIATION
ANODES
CATHODES
CROSSED FIELDS
ELECTRON BEAMS
MAGNETRONS
RADIOWAVE RADIATION
RESONANCE
WAVEGUIDES
BEAMS
ELECTRODES
ELECTROMAGNETIC RADIATION
ELECTRONIC EQUIPMENT
EQUIPMENT
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MICROWAVE TUBES
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