A divertor Langmuir probe system for the measurement of plasma parameters in the divertor region such as electron density (ne), electron temperature (Te), floating potential (Vf) and ion saturation current (Isat) will be prepared. The divertor Langmuir probes comprise sensor heads, mineral insulated (MI) cables and a data acquisition system. As shown in Figure 1, the sensor heads are installed on the edge of the JT-60SA divertor cassettes to facilitate replacement of those. The sensor heads will be installed in four toroidal sections. Detected current is transported to the data acquisition system by means of MI cables. Figure 2 shows the spatial resolution of the Langmuir probes on the inner and outer divertor target. The Langmuir probe on Section P-3 and 9 are installed 13.5 mm above those on Section P-4 and 15. Simultaneous measurement, for example, Section P-3 and 4, improves the minimal spatial resolution to 13.5 mm. The Langmuir probes on the other position such as the inner and outer baffles, dome and outer cover are installed at the same poloidal position for the different toroidal section. The specifications of the Langmuir probes are shown in table 1.

Figure 1 The sensor heads installed on (a) the high field side and (b) low field side of the edge of the 10-degree-sector divertor cassette. (c) Detailed structure of the sensor heads installed in part of the vertical targets.
Figure 2 Spatial resolution of the Langmuir probes installed on (a) the inner and (b) outer divertor targets.
Table 1 Specifications of the divertor Langmuir probe system