Download Two laser wavelength Thomson Scattering for high electron

44th EPS Conference on Plasma Physics
P2.106
Two laser wavelength Thomson Scattering for high electron temperature
measurements
E. Pasch, M.N.A. Beurskens, S. Bozhenkov, G. Fuchert and R.C. Wolf
Max-Planck-Institut für Plasmaphysik, Greifswald, Germany
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 wavelength. As an alternative method an additional Nd:YAG laser
with λ=1319 nm, fired directly after the λ=1064 nm Nd:YAG laser, 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.
In this paper 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 two high power laser wavelengths (λ=1064 nm and λ=1319 nm) plus a
coating for a λ=635 nm adjustment laser are shown.