Abstract
In the present work microwave reflectometry is extended to the outermost part of tokamak plasmas (n{sub e} {approx_equal} 10{sup 11} to 1.5x10{sup 13} cm{sup -3}), which is subject to strong electron density fluctuations. The perturbations of electron density profile measurements by these fluctuations, which lead to strong modulations in intensity and phase of the reflected signal is analysed in detail. By increasing the frequency of the interference fringes to values between 800 kHz and 2.4 MHz it is possible to make reliable profile measurements even in the region of very strong fluctuations. Measurements in the low density region are only possible with reasonable errors in the X-mode (Eperpendicular toB), as only the cut-off frequency of this mode, in contrast to that of the O-mode (EparallelB), takes a finite value (f{sub ce}) for n{sub e}->O. Taking advantage of this property, a method is presented to calibrate the measurements on the first reflection, which occurs directly in front of the microwave antennas (1-4 mm from the opening) thus giving a high precision even in the outermost part of the plasma close to the microwave antennas. For the calculation of the electron density profile a new and numerically stable algorithm has been developed.
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Citation Formats
Schubert, R.
Edge density X-mode reflectometry of RF-heated plasmas on ASDEX; Randschichtreflektometrie hochfrequenzgeheizter Plasmen an ASDEX.
Germany: N. p.,
1991.
Web.
Schubert, R.
Edge density X-mode reflectometry of RF-heated plasmas on ASDEX; Randschichtreflektometrie hochfrequenzgeheizter Plasmen an ASDEX.
Germany.
Schubert, R.
1991.
"Edge density X-mode reflectometry of RF-heated plasmas on ASDEX; Randschichtreflektometrie hochfrequenzgeheizter Plasmen an ASDEX."
Germany.
@misc{etde_10121334,
title = {Edge density X-mode reflectometry of RF-heated plasmas on ASDEX; Randschichtreflektometrie hochfrequenzgeheizter Plasmen an ASDEX}
author = {Schubert, R}
abstractNote = {In the present work microwave reflectometry is extended to the outermost part of tokamak plasmas (n{sub e} {approx_equal} 10{sup 11} to 1.5x10{sup 13} cm{sup -3}), which is subject to strong electron density fluctuations. The perturbations of electron density profile measurements by these fluctuations, which lead to strong modulations in intensity and phase of the reflected signal is analysed in detail. By increasing the frequency of the interference fringes to values between 800 kHz and 2.4 MHz it is possible to make reliable profile measurements even in the region of very strong fluctuations. Measurements in the low density region are only possible with reasonable errors in the X-mode (Eperpendicular toB), as only the cut-off frequency of this mode, in contrast to that of the O-mode (EparallelB), takes a finite value (f{sub ce}) for n{sub e}->O. Taking advantage of this property, a method is presented to calibrate the measurements on the first reflection, which occurs directly in front of the microwave antennas (1-4 mm from the opening) thus giving a high precision even in the outermost part of the plasma close to the microwave antennas. For the calculation of the electron density profile a new and numerically stable algorithm has been developed. Measurements in connection with Lower Hybrid have been made with a set of 2 reflectometer antennas installed in ASDEX. (orig./AH).}
place = {Germany}
year = {1991}
month = {Sep}
}
title = {Edge density X-mode reflectometry of RF-heated plasmas on ASDEX; Randschichtreflektometrie hochfrequenzgeheizter Plasmen an ASDEX}
author = {Schubert, R}
abstractNote = {In the present work microwave reflectometry is extended to the outermost part of tokamak plasmas (n{sub e} {approx_equal} 10{sup 11} to 1.5x10{sup 13} cm{sup -3}), which is subject to strong electron density fluctuations. The perturbations of electron density profile measurements by these fluctuations, which lead to strong modulations in intensity and phase of the reflected signal is analysed in detail. By increasing the frequency of the interference fringes to values between 800 kHz and 2.4 MHz it is possible to make reliable profile measurements even in the region of very strong fluctuations. Measurements in the low density region are only possible with reasonable errors in the X-mode (Eperpendicular toB), as only the cut-off frequency of this mode, in contrast to that of the O-mode (EparallelB), takes a finite value (f{sub ce}) for n{sub e}->O. Taking advantage of this property, a method is presented to calibrate the measurements on the first reflection, which occurs directly in front of the microwave antennas (1-4 mm from the opening) thus giving a high precision even in the outermost part of the plasma close to the microwave antennas. For the calculation of the electron density profile a new and numerically stable algorithm has been developed. Measurements in connection with Lower Hybrid have been made with a set of 2 reflectometer antennas installed in ASDEX. (orig./AH).}
place = {Germany}
year = {1991}
month = {Sep}
}