Laboratory test of an intensity interferometer for measurement of electron temperature fluctuations on Wendelstein 7-AS

Transport relevant electron temperature fluctuations to be measured by electron cyclotron emission (ECE) radiometry might be buried completely in natural fluctuations of the ECE due to the thermal nature of this radiation. The spatial coherence properties of the fluctuations can be utilized in a correlation experiment to make temperature fluctuations accessible to measurement. An intensity interferometer, consisting of two identical 4-channel heterodyne radiometers with a common local oscillator and gaussian beam optics viewing the same emitting volume along crossed lines of sight, allows this type of measurements. With a specially developed quasithermal radiation source the correlation experiment was simulated and the intensity interferometer was tested. Measurements of the spatial coherence properties were in agreement with theoretical predictions. (orig.)