The diagnostic problem of measuring electron temperature fluctuations
with a relative level below 1% is outlined. It is shown that correlati
on radiometry of electron cyclotron emission provides sufficient sensi
tivity to overcome the limit set by intensity fluctuations of thermal
radiation. The experimental set-up used for the first measurements is
described and the first results obtained at the W7-AS stellarator are
presented. With an extended arrangement a first comparison between the
two different correlation schemes as developed at W7-AS and at TEXT b
ecame possible. (C) 1997 Elsevier Science S.A.