Edge plasma pressure measurements using a mechanical force sensor on the tokamak ISTTOK

In the present paper we report on a novel mechanical probe, which is able to measure the plasma pressure directly. The probe consists of two pendulums whose heads are exposed to the tokamak edge plasma, while the deflection is measured very sensitively outside the plasma by means of semi-conductor strain gauges. The plasma pressure was successfully measured in the ISTTOK edge plasma, its value being in good agreement with that derived from the electrical probe data ( p p = 1–10 Pa). Furthermore, we discuss the possibility of determining the ion temperature T i = p p / n − T e by combining the pressure measurement with those of n and T e from the electrical probes. Although the derived ion temperatures—besides that in the region close to the limiter—were reasonable, its uncertainty is still very large.