Speaker
Dr
Ekkehard Pasch
(Max-Planck-Institut für Plasmaphysik)
Description
Thomson scattering (TS) is one of the main diagnostics in nuclear fusion experiments for electron temperature and –density measurements. Most of the TS systems are realized with pulsed, high power Nd:YAG lasers as light source with a wavelength at λ=1064 nm, together with interference filter polychromators for spectral analysis of the scattered light in the near infrared region (typically between 700-1060 nm). Such a system is able to measure electron temperatures up to approximately 15 keV within error bars of 10%. At higher electron temperatures the broadness together with the relativistic blue shift of the spectrum are the causes of inadmissible error bars. Due to background radiation (line emission and Bremsstrahlung) it is not advisable to extend the interference filters of the polychromators to much shorter wavelengths. As an alternative method an additional Nd:YAG laser with λ=1319 nm, fired directly after the λ=1064 nm Nd:YAG laser, which can be used to measure the scattered light from both lasers with the same polychromator, effectively increasing the observed spectral range. Such a TS system is able to measure electron temperatures up to 25-30 keV.
We present the two laser wavelength approach for the Thomson scattering system at the Wendelstein 7-X stellarator. The status of the 1319 nm Nd:YAG laser development and the design of optical components for both high power laser wavelengths (λ=1064 nm and λ=1319 nm) plus a coating for a λ=635 nm adjustment laser are shown.
Primary author
Dr
Ekkehard Pasch
(Max-Planck-Institut für Plasmaphysik)
Co-authors
Dr
Golo Fuchert
(Max-Planck-Institut für Plasmaphysik)
Dr
Marc Beurskens
(Max-Planck-Institut für Plasmaphysik)
Prof.
Robert Wolf
(Max-Planck-Institut für Plasmaphysik)
Dr
Sergey Bozhenkov
(Max-Planck-Institut für Plasmaphysik)
