Design of embedded electrostatic sensors for the RFX-mod2 device

Abstract

The RFX-mod experiment is currently undergoing a challenging upgrade of the machine assembly. One of the main purposes 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. Moreover, most of the innovations characterizing the device and its diagnostics are conceived with the aim of operating as both RFP and tokamak. These different configurations are taken into account in the electrostatic sensors design and layout. RFX-mod2 will be equipped with poloidal and toroidal arrays of electrostatic probes, measuring plasma density and temperature, plasma potential, particle and energy fluxes and floating potential fluctuations. Two toroidal arrays of 72 probes each (one on the high field side and one on the low field side), along with four poloidal arrays of 28 elements, are foreseen. Such a large amount of sensors is due to the requirement of a better characterization of the numerous instabilities observed in the RFP plasma edge, with the possibility to study the plasma shape in different tokamak configurations (circular, single null, double null). Three different kinds of Langmuir probe configurations will be installed: single probes, 5-pin balanced triple probes and ball-pen probes. The conceptual design of the sensors takes inspiration from the model successfully installed on RFX-mod, that allows the removal of tiles in case of damage, by means of a remote handling manipulator.