Transient Dynamics of Secondary Radiation From a HF Pumped Magnetised Space Plasma

Details Transient Dynamics of Secondary Radiation From a HF Pumped Magnetised Space Plasma Transient Dynamics of Secondary Radiation From a HF Pumped Magnetised Space Plasma

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsa51a..01n&link_type=abstract

American Geophysical Union, Spring Meeting 2007, abstract #SA51A-01

Physics

2403 Active Experiments, 2471 Plasma Waves And Instabilities (2772)

Scientific paper

In order to systematically analyse the transient wave and radiation processes that are excited by a HF radio wave injected into a magnetised space plasma, we have measured the secondary radiation, or stimulated electromagnetic emission (SEE), from a preconditioned ionosphere. The ionosphere was heated using a pump duty cycle of 200 ms (180 ms on and 20 ms off) and 100~ms (80 ms on and 20 ms off) for various pump frequencies near the fifth harmonic of the electron gyro frequency. The results presented here show that within the first ten milliseconds after pump turn-on, frequency downshifted structures of the SEE exhibit an overshoot with a maximum at tm≍ 8 ms, whereas upshifted spectral components do not exhibit this feature. The relative magnitude of the overshoot is strongly dependent on the frequency offset of the pump from the fifth harmonic of the electron gyro frequency. A new, blue-shifted transient frequency component is identified. This component is upshifted from the pump by 14 kHz < Δ f <50 kHz and exists only for the first ten milliseconds after pump turn-on. On a slower time scale we analyse the amplitude modulation, or "ringings", of the pump, (in the Russian literature also known as "spikes"). The ringings have a frequency fR≍ 17 Hz and we show that this phenomenon is also present in the SEE. Furthermore, the ringings in the SEE are almost perfectly synchronised to the ringings of the pump.

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