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Localization of the High Frequency Field in a Beam-Plasma Diode Due to Density Gradients
KTH, Superseded Departments, Alfvén Laboratory.
2001 (English)In: Physica Scripta, ISSN 0281-1847, Vol. 63, 62-69 p.Article in journal (Refereed) Published
Abstract [en]

An experimental study of the high frequency (hf) interaction of a strong, warm electron beam with an inhomogeneous, bounded plasma is presented and compared with particle-in-cell simulations. The density is highest in the center of the diode and decreases towards the boundaries. The electric field in the center is dominated by the unstable slow-space-charge wave, but experimental evidence is found, that reflected waves are present near the beam injection grid, where the oscillation frequency f is higher than the local plasma frequency f(pe)(x). The strong field at the resonance point (f = f(pe)(x)) is proposed to excite the unstable beam mode. Simulations confirm this picture by showing a concentration of the spectral power of the beam waves to the frequencies of the trapped Langmuir waves. Linear growth and Landau damping concentrate the beam wave to a 1.5-2 wavelengths wide region. Trapped Langmuir waves can accordingly determine the frequencies and position of the hf-field even for moderate density gradients and field strengths below the threshold for Langmuir collapse.

Place, publisher, year, edition, pages
2001. Vol. 63, 62-69 p.
National Category
Fusion, Plasma and Space Physics
URN: urn:nbn:se:kth:diva-95035DOI: 10.1238/Physica.Regular.063a00062ISI: 000166471400009OAI: diva2:526468
QC 20120619Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2012-06-19Bibliographically approved

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