Measurements of the electron temperature fluctuations with a retarding field analyzer on the tokamak ISTTOK

Measurements of the ion temperature fluctuations by retarding field energy analyzed (RFA) based on two point measurements on the exponentially decaying region of the I-V characteristic with two differently DC biased RFA electrodes have been tested and proved in the experiments on the tokamak ISTTOK. In this paper, a DC operation of an RFA has been applied to give direct instantaneous measurements of the electron temperature and electron temperature fluctuations. The results are in good agreement with conventional swept measurements from the RFA. The observed electron temperature fluctuations, 3 mm outside the leading edge of the limiter, have a typical normalized amplitude (standard deviation divided by the average value) of ∼13% (Teav = 6 eV) and are in opposition to the fluctuations of the floating potential simultaneously measured on the RFA slit.