Optimization of ECE Diagnostics for the W7-X Stellarator

Accuracy and abilities of the electron cyclotron emission (ECE) diagnostic system planned to be installed in the Wendelstein 7-X stellarator are analysed with help of ray-tracing simulations. For the expected plasma parameters, the spatial resolution of the standard low-field-side (lfs) X2-mode observation scheme is estimated to be sufficiently high, ~5%. Apart from the lfs scheme, the applicability of other complementary schemes is analyzed, in particular, high-field-side (hfs) X2-mode observation. It is shown that in combination with the standard lfs scheme, the hfs scheme can be very informative for the problem of distinguishing thermal and nonthermal contributions in the ECE spectrum.