4,442
edits
TJ-II:Electron Cyclotron Emission: Difference between revisions
Jump to navigation
Jump to search
Updated reference links
No edit summary |
(Updated reference links) |
||
| (3 intermediate revisions by 2 users not shown) | |||
| Line 2: | Line 2: | ||
Electron temperature profiles are measured at [[TJ-II]] | Electron temperature profiles are measured at [[TJ-II]] | ||
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 [[:Wikipedia:Electron cyclotron resonance|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 (between [[TJ-II:Sectors|sectors]] C4 and C5). | The measurements are performed from the low field side (LFS) in the horizontal midplane (between [[TJ-II:Sectors|sectors]] C4 and C5, φ = 315°), but most of the channels receive radiation from the high field side (HFS). In normal operation conditions, the frequency depends on a known way on the magnitude of the magnetic field B. Tuning properly the receiver system, 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. | ||
| Line 11: | Line 10: | ||
== Calibration == | == 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 name="Luna"> | <ref name="Luna">E. de la Luna, J. Sánchez, V. Tribaldos, and T. Estrada, ''Multichannel electron cyclotron emission radiometry in TJ-II stellarator'', [[doi:10.1063/1.1315636|Rev. Sci. Instrum. '''72''', 379 (2001)]]</ref> | ||
<ref> | <ref>E. de la Luna et al, ''Electron cyclotron emission measurements on TJ-II stellarator plasmas'', [[doi:10.1016/S0920-3796(00)00492-0|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. | 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. | 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. | ||
| Line 20: | Line 19: | ||
The emission can be simulated by the [[TRECE]] ray tracing code. | The emission can be simulated by the [[TRECE]] ray tracing code. | ||
<ref name="Tribal"> | <ref name="Tribal">V. Tribaldos and B. P. van Milligen, ''Electron cyclotron emission calculations for TJ-II stellarator'', [[doi:10.1088/0029-5515/36/3/I02|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 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. | ||