Ion Temperature Measurements In The Tokamak Scrape-Off Layer With High Temporal Resolution

We present a uniquely fast (10 mu s) ion temperature measurements in the tokamak edge plasma. Our approach is based on the sweeping of a ball-pen probe, where the ion temperature is obtained by fitting the electron branch of the corresponding I-V characteristic. We have performed measurements on the COMPASS tokamak during L-mode discharge. The temperature histograms reveal a non-Gaussian shape with a high-temperature tail peaking at low values. The fitted values of fast I-V measurements can be used to reconstruct (emulate) the slow swept I-V characteristic of a retarding field analyzer. The resulting ion temperature profile is nearly flat and provides a ratio of ion to electron temperature close to 1-2 in the vicinity of the last closed flux surface during L-mode discharges, as observed on other tokamaks.