Method for Detection of Separatrix Surface Using Differential Double Probe

A method of detecting the separatrix surface in the edge plasma in a Tokamak is presented. Two sets of double probes whose front surfaces are shifted by a small distance are mounted and the difference of the currents is measured using a differential amplifier. When the separatrix surface reaches the probes, a current increment appears in the differential amplifier, giving a signal of the arrival of the separatrix. Procedures for obtaining plasma parameters including the ion temperature are also described.