On density and temperature fluctuations observed by ECE diagnostics in Wendelstein VII-AS stellarator

A multichannel heterodyne radiometer system with two times 12 channels is used on WVII-AS to measure the electron cyclotron emission (ECE) both time and space resolved. In this paper we report about sporadic observations of density and temperature fluctuations using this system. The observations are made under different operation conditions concerning field, rotational transform, and heating scenario. In the case of density fluctuations no direct measurement it possible using ECE diagnostics. The conclusions are drawn from observations near the cut off conditions and are of qualitative character. The fluctuation level necessary to explain the observed phenomena seems to be model dependent. (orig.)