A generation mechanism for the frequency up-shifted plasma lines observed in the Tromsq`s HF heating experiments
Conference
·
OSTI ID:330580
- Polytechnic Univ., Farmingdale, NY (United States). Dept. of Electrical Engineering
- Brookhaven National Lab., Upton, NY (United States). Dept. of Applied Science
- Massachusetts Inst. of Tech., Cambridge, MA (United States). Plasma Fusion Center
A new spectral feature in the backscattering spectrum of EIS CAT 933 MHz radar was observed throughout most of the observing period of the heating experiments performed with 0-mode heater transmitting near Tromsq, Norway on August 16--18, 1986. The radar returns were enhanced at frequencies offset from the radar frequency by a frequency a few hundred KHz more than the heater frequency of 4.04 MHz. Moreover, running alternately with the radar in the chirped and in the unchirped mode it was shown that the enhanced plasma lines seemed to emanate from very local regions. It is noted that a similar phenomenon recording frequency upshifted HF-enhanced plasma lines (HFPLs) has also been observed in the Arecibo heating experiments, except the amount of frequency upshift is in the range of a few tens of KHz. A physical mechanism based on a nonlinear scattering process by which the parallelly propagating Langmuir waves generated by the parametric decay instability of the HF pump scatter off the background lower hybrid density fluctuations to produce the observed frequency upshifted plasma lines has successfully explained the Arecibo`s observations and has even been verified recently by a laboratory experiment. However, the amount of frequency shift observed in the Tromsq`s experiments well exceeds the lower hybrid wave frequency. Thus, a different physical mechanism is considered in the present work for explaining the Tromsq`s observations. It is the parametric decay of a right handed circularly polarized pump wave (0-mode) into a Whistler wave (decay mode) and a frequency upshifted Langmuir wave (sideband). Since the frequency of Whistler wave extends to the range of a few hundred kHz, the frequency of the excited Langmuir wave agrees with that of the experimental observation.
- Sponsoring Organization:
- National Science Foundation, Washington, DC (United States); USDOE, Washington, DC (United States)
- OSTI ID:
- 330580
- Report Number(s):
- CONF-970559--
- Country of Publication:
- United States
- Language:
- English
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