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TJ-II:Electron Cyclotron Emission: Difference between revisions
TJ-II:Electron Cyclotron Emission (view source)
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by means of a 16 channel heterodyne radiometer, | by means of a 16 channel heterodyne radiometer, | ||
covering the frequency range 50–60 GHz, corresponding to the second harmonic of electron cyclotron emission (ECE) in X-mode polarization at a magnetic field of 0.95 T on the plasma axis. | covering the frequency range 50–60 GHz, corresponding to the second harmonic of electron cyclotron emission (ECE) in X-mode polarization at a magnetic field of 0.95 T on the plasma axis. | ||
The measurements are performed from the low field side (LFS) in the horizontal midplane ([[TJ-II:Sectors| | The measurements are performed from the low field side (LFS) in the horizontal midplane (between [[TJ-II:Sectors|sectors]] C4 and C5). | ||
Each frequency corresponds to a different value of the major radius ''R''. | Each frequency corresponds to a different value of the major radius ''R'' (according to ''B(R)''). | ||
The system is operated close to the strong [[TJ-II:Electron Cyclotron Resonant Heating|ECR heating source]] (f<sub>ECRH</sub> = 53.2 GHz). | The system is operated close to the strong [[TJ-II:Electron Cyclotron Resonant Heating|ECR heating source]] (f<sub>ECRH</sub> = 53.2 GHz). | ||
To protect the radiometer against stray radiation from the gyrotron, the radiometer band is split into two parts. | To protect the radiometer against stray radiation from the gyrotron, the radiometer band is split into two parts. | ||
The second harmonic emission above and below 53.2 GHz are measured separately by means of microwave couplers in the signal path. | The second harmonic emission above and below 53.2 GHz are measured separately by means of microwave couplers in the signal path. | ||
== Calibration == | |||
The system is calibrated absolutely by comparing room temperature with liquid nitrogen temperature. | The system is calibrated absolutely by comparing room temperature with liquid nitrogen temperature. | ||
<ref>[http://link.aip.org/link/?RSINAK/72/379/1 E. de la Luna, J. Sánchez, V. Tribaldos, and T. Estrada, ''Multichannel electron cyclotron emission radiometry in TJ-II stellarator'', Rev. Sci. Instrum. '''72''', 379 (2001)]</ref> | <ref name="Luna">[http://link.aip.org/link/?RSINAK/72/379/1 E. de la Luna, J. Sánchez, V. Tribaldos, and T. Estrada, ''Multichannel electron cyclotron emission radiometry in TJ-II stellarator'', Rev. Sci. Instrum. '''72''', 379 (2001)]</ref> | ||
<ref>[http://dx.doi.org/10.1016/S0920-3796(00)00492-0 E. de la Luna et al, ''Electron cyclotron emission measurements on TJ-II stellarator plasmas'', Fusion Engineering and Design '''53''', Issues 1-4 (2001) 147-151]</ref> | <ref>[http://dx.doi.org/10.1016/S0920-3796(00)00492-0 E. de la Luna et al, ''Electron cyclotron emission measurements on TJ-II stellarator plasmas'', Fusion Engineering and Design '''53''', Issues 1-4 (2001) 147-151]</ref> | ||
The optical system and the transmission line of the ECE diagnostic were designed to allow the calibration to be performed outside the vacuum vessel keeping the arrangement of the diagnostic. | |||
To calibrate, the transmission line is opened close to the diagnostic port (C5-bottom). Then the port flange, which holds the optical system and the wave-guide up to that point, is extracted from the torus and assembled with the same alignment outside the vacuum vessel. | |||
A check for the radiometer stability is performed periodically by using a stable noise source at the input of the radiometer. Such a noise source is also used to test the linearity of the system and to calibrate any possible change that may occur in the electronics of the diagnostic. | |||
== Data analysis == | |||
The emission can be simulated by the [[TRECE]] ray tracing code. | The emission can be simulated by the [[TRECE]] ray tracing code. | ||
<ref>[http://dx.doi.org/10.1088/0029-5515/36/3/I02 V. Tribaldos and B. P. van Milligen, ''Electron cyclotron emission calculations for TJ-II stellarator'', Nucl. Fusion '''36''', 283 (1996)]</ref> | <ref name="Tribal">[http://dx.doi.org/10.1088/0029-5515/36/3/I02 V. Tribaldos and B. P. van Milligen, ''Electron cyclotron emission calculations for TJ-II stellarator'', Nucl. Fusion '''36''', 283 (1996)]</ref> | ||
The local radiation temperature is assumed to be a function only of the local electron temperature at the resonant layer; however, if the plasma is not Maxwellian or if the plasma is optically thin, the measured radiation temperature is no longer equal to the electron temperature. | |||
The effect of polarization rotation can be neglected once the correct polarization for the pure X mode on-axis is chosen. Even at high density (worst condition) the radiation coming from the plasma bulk experiences a rotation below 5°.<ref name="Tribal" /> | |||
The spatial resolution is about 1 cm.<ref name="Luna" /> | |||
The typical sampling rate is 100 kHz. | The typical sampling rate is 100 kHz. | ||
The signals | The raw signals in the [[TJ-II:Shot_database|TJ-II database]] are called 'ECE1' ... 'ECE16', and the processed (calibrated) signals 'TECE1_' ... 'TECE16_' (units: keV). | ||
== References == | == References == | ||
<references /> | <references /> | ||