The LIDAR Thomson scattering diagnostic on JET
By combining the time-of-flight or LIDAR principle with a Thomson backscatter diagnostic, spatial profiles of the electron temperature and density can be measured with a single set of detectors for all spatial points. This approach considerably simplifies the collection optics required for measuring a spatial profile. a ruby laser (3 J pulse energy, 300 ps pulse duration, 0.5 Hz repetition rate) together with a 700 MHz bandwidth detection and registration system yields a spatial resolution of about 12 cm. A large filter spectrometer with 6 spectral channels covering the wavelength range 400-800 nm gives a dynamic range of the temperature measurements of 0.3-20 keV. The stray light problem in the backscatter geometry is overcome by spectral discrimination and effective gating of the MCP photomultipliers. A high rejection ruby notch filter in the spectral channel containing the laser wavelength allows calibration of the vignetting along the line of sight by means of Raman scattering, thus enabling the measurement of density profiles. The low level of plasma background signal due to the short integration time for an individual spatial point yields low statistical errors. Goodness-of-fit tests indicate that the systematic errors are within the same limits. The system is described and examples of measurements are given and compared with the results of other diagnostics.
Bibliographic Reference: Report: JET-R(89)07 EN (1989)
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (UK)
Record Number: 199010096 / Last updated on: 1994-12-01
Original language: en
Available languages: en