Abstract
The resonance cavity diagnostics is applied on the magnetized plasma of a reflex discharge as well as an inductive rf discharge. Special attention is focussed on the evaluation of the collisional frequency from the cavity Q and the underlying physical mechanism. When the conventional transmission method is used, a strong broadening of the frequency response curve is observed: the time-averaged transmission profile turns out to be a Voigt profile that arises from the Lorentzian profile of the instantaneous transmission curve and the Gaussian probability distribution of the density fluctuations. Obviously, the resonance broadening is not caused by collisional damping, but mainly by large scale density fluctuations. To measure the real absorption of the microwave power, the temporal decay of the electromagnetic wave energy in the cavity is detected. Two charateristic features are observed: (i) At magnetic field strengths well below the electron cyclotron resonance field the measured (effective) collisional frequency {nu}{sub eff} shows a threshold behaviour as a function of the electron density. Below 7 x 10{sup 15}m{sup -3} the measured collisional frequency fits to the electron-neutral collisional frequency, whereas above 9 x 10{sup 15}m{sup -3}, {nu}{sub eff} tends to a twice higher value. (ii) Near the cyclotron resonance a
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Citation Formats
Kraemer, M, and Bruesehaber, B.
Cavity diagnostics on fluctuating discharges.
Germany: N. p.,
1991.
Web.
Kraemer, M, & Bruesehaber, B.
Cavity diagnostics on fluctuating discharges.
Germany.
Kraemer, M, and Bruesehaber, B.
1991.
"Cavity diagnostics on fluctuating discharges."
Germany.
@misc{etde_10129181,
title = {Cavity diagnostics on fluctuating discharges}
author = {Kraemer, M, and Bruesehaber, B}
abstractNote = {The resonance cavity diagnostics is applied on the magnetized plasma of a reflex discharge as well as an inductive rf discharge. Special attention is focussed on the evaluation of the collisional frequency from the cavity Q and the underlying physical mechanism. When the conventional transmission method is used, a strong broadening of the frequency response curve is observed: the time-averaged transmission profile turns out to be a Voigt profile that arises from the Lorentzian profile of the instantaneous transmission curve and the Gaussian probability distribution of the density fluctuations. Obviously, the resonance broadening is not caused by collisional damping, but mainly by large scale density fluctuations. To measure the real absorption of the microwave power, the temporal decay of the electromagnetic wave energy in the cavity is detected. Two charateristic features are observed: (i) At magnetic field strengths well below the electron cyclotron resonance field the measured (effective) collisional frequency {nu}{sub eff} shows a threshold behaviour as a function of the electron density. Below 7 x 10{sup 15}m{sup -3} the measured collisional frequency fits to the electron-neutral collisional frequency, whereas above 9 x 10{sup 15}m{sup -3}, {nu}{sub eff} tends to a twice higher value. (ii) Near the cyclotron resonance a strongly enhanced absorption is observed at low densities, though the TM{sub 010} cavity mode used has no electric field components perpendicular to the constant magnetic field. Both effects cannot be attributed to the observed density fluctuations in the discharges. Various absorption processes are discussed to explain our findings. (orig.).}
place = {Germany}
year = {1991}
month = {Jul}
}
title = {Cavity diagnostics on fluctuating discharges}
author = {Kraemer, M, and Bruesehaber, B}
abstractNote = {The resonance cavity diagnostics is applied on the magnetized plasma of a reflex discharge as well as an inductive rf discharge. Special attention is focussed on the evaluation of the collisional frequency from the cavity Q and the underlying physical mechanism. When the conventional transmission method is used, a strong broadening of the frequency response curve is observed: the time-averaged transmission profile turns out to be a Voigt profile that arises from the Lorentzian profile of the instantaneous transmission curve and the Gaussian probability distribution of the density fluctuations. Obviously, the resonance broadening is not caused by collisional damping, but mainly by large scale density fluctuations. To measure the real absorption of the microwave power, the temporal decay of the electromagnetic wave energy in the cavity is detected. Two charateristic features are observed: (i) At magnetic field strengths well below the electron cyclotron resonance field the measured (effective) collisional frequency {nu}{sub eff} shows a threshold behaviour as a function of the electron density. Below 7 x 10{sup 15}m{sup -3} the measured collisional frequency fits to the electron-neutral collisional frequency, whereas above 9 x 10{sup 15}m{sup -3}, {nu}{sub eff} tends to a twice higher value. (ii) Near the cyclotron resonance a strongly enhanced absorption is observed at low densities, though the TM{sub 010} cavity mode used has no electric field components perpendicular to the constant magnetic field. Both effects cannot be attributed to the observed density fluctuations in the discharges. Various absorption processes are discussed to explain our findings. (orig.).}
place = {Germany}
year = {1991}
month = {Jul}
}