Studies for the design of the Wendelstein 7-X Thomson Scattering polychromators

The aim of the Thomson scattering system is the measurement of electron temperature and density profiles with high time and spatial resolution. The whole Thomson scattering optical system is optimized to minimize losses of scattered light with wavelengths from 700 nm up to 1064 nm. A five-channel polychromator serves as spectral analyzer of the scattered light. The light is carried to the polychromator input via fiber bundles of 3 mm diameter. High performance dielectric interference filters will be used for spectral analyzing. Their transmission curves will be chosen according to the range of electron temperature that is supposed during W7-X operation (from 10 eV up to 10 keV). The design of the polychromator must be optimized for a high throughput and size compactness. The article describes three possible polychromator setups. The main difference between these designs is the usage of relay and field lenses. The optical properties of the designs will be derived both by measurements and by simulations. Limitations considering high Numerical Aperture (N.A.) and fiber bundle size are discussed.