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Characterization of a Penning discharge for investigation of auroral radio wave generation mechanisms

McConville, Sandra and Koepke, Mark E and Gillespie, Karen and Matheson, Kathleen and Whyte, Colin and Robertson, Craig and Speirs, David (2011) Characterization of a Penning discharge for investigation of auroral radio wave generation mechanisms. Plasma Physics and Controlled Fusion, 53 (12). ISSN 0741-3335

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Abstract

Auroral Kilometric Radiation (AKR), observed by satellites in the Earth’s magnetosphere, is naturally generated in regions of partial plasma depletion (auroral density cavity) in the polar magnetosphere at approximately 3200 km altitude. As an electron descends through these regions of partial plasma depletion along magnetic field lines towards the Earth’s ionosphere, the field lines increases and, through conservation of the magnetic moment, the electron gives up axial velocity in favour of perpendicular velocity. This results in a horseshoe-shaped distribution function in parallel/perpendicular-velocity space which is unstable to X-mode radiation, near the cyclotron frequency. Power levels as high as GW levels have been recorded with frequencies around 300 kHz. The background plasma frequency within the auroral density cavity is approximately 9 kHz corresponding to a plasma density 1cm−3. A laboratory experiment scaled from auroral frequency to microwave frequency has previously been reported. Here, the addition of a Penning trap to simulate the background plasma of the density cavity is reported, with measurements ne∼2×1014–2.17×1015 m−3, fpe ∼128–418MHz and fce ∼5.21GHz giving a ratio of ωce/ωpe comparable to the magnetospheric AKR source region.