Design of embedded electrostatic sensors for the RFX-mod2 device

RFX-mod experiment is currently under a challenging upgrade of the machine assembly. One of the main purpose of RFX-mod2, the upgraded device, is the achievement of better performances by decreasing the tearing modes amplitude in Reversed-Field Pinch (RFP) configuration thanks to a higher plasma-shell proximity [1, 2]. Moreover, most of the innovations characterizing the device and its diagnostics are conceived with the aim to operate in both RFP and tokamak configurations. This attention on the different configurations is taken into account in the electrostatic sensors design and layout. RFX-mod2 will be equipped with poloidal and toroidal arrays of electrostatic sensors, measuring plasma density and temperature, plasma potential, particle and energy fluxes and floating potential fluctuations. Two toroidal arrays of 72 sensors each (one on the high field side and one on the low field side) are foreseen. Moreover, four poloidal arrays of 28 elements will be housed. A such large amount of sensors is due to the requirement of a better characterization of the numerous instabilities observed in RFP plasma edge, along with the possibility to study the plasma shape in different tokamak configurations (circular, single null, double null). Two different kinds of Langmuir probes configurations will be installed: the so-called single probe and 5-pin balanced triple probe. The conceptual design of the sensors takes inspiration from the model successfully installed on RFX-mod [3], that allows to remove tiles in case of damage, by means of a remote handling manipulator. Each sensor is composed by two parts: the tile side houses pins directly faced to the plasma and connected by springs to the shell side, where specific contacts, conveniently isolated, carry the signals to the cables.