Simultaneous measurements of fluctuations of ion current, electron temperature, and floating potential with a tunnel probe

The tunnel probe is a new kind of Langmuir probe for use in the tokamak scrape-off layer. Two-dimensional kinetic analysis of the ion current distribution on the concave conductors is used to calibrate the probe for making fast dc measurements of ion flux and electron temperature. Qualitative agreement with classical Langmuir-probe measurements is found, but the electron temperature given by the tunnel probe i several times lower. This discrepancy is partly caused by secondary electron emission, and can easily be corrected. Strong reduction of ion flux and electron-temperature fluctuations is observed during electrode biasing. (author)