Speakers
Description
The Thomson scattering (TS) system is a main diagnostic at the Wendelstein 7-X stellarator for electron temperature (Te) and density (ne) profiles. The TS system includes a pulsed, high power Nd:YAG laser with λ=1064 nm, together with five interference filter polychromators for spectral analysis of the scattered light in the near infrared region between λ=750-1061 nm. The system is able to measure Te up to approximately 10 keV within an error of ~10%, depending on ne and background light. The system will be equipped with an additional Nd:YAG laser with λ=1319 nm, so that the peak of the TS spectrum shifts up by 1319-1064=255nm. This has two advantages: First, the dual laser availability allows an in-situ spectral calibration, based on the two lasers being fired quasi-simultaneously; the two measured TS spectra, covering different wavelength regions, should yield an unchanged Te. Secondly, higher Te >10 keV can be measured as the peak of the TS spectrum shifts to shorter wavelengths. This avoids the polychromators having to cover λ<750 nm, where line emission and Bremsstrahlung increase strongly. The status of the 1319 nm Nd:YAG laser development and the design of optical components of the laser beam path will be shown and simulations will demonstrate the new system capabilities.
