Upgraded electromagnetic measurement system for RFX-mod

A major refurbishment of the toroidal load assembly is under study to extend the operational space of RFX-mod in both RFP and Tokamak configurations. It includes the removal of the vacuum vessel to increase the plasma-shell proximity and modifications of the support structure to obtain a new vacuum tight chamber. This entails the design of a new electromagnetic measurement system, taking into account the requirements of both the equilibrium and MHD control system and physics analyses requirements in both RFP and shaped Tokamak configurations. The spatial resolution is constrained by the number of graphite tiles, 28 (poloidal) x 72 (toroidal), which cover the inner surface of the toroidal vacuum chamber. Alternative layouts of 4x 72 and 7 x 72 are being considered to assure the calculation of the MHD mode spectrum up to (m=0,1,2 or 3; n= 0,..., +/- 35). A substantial advantage in terms of harmonic spectrum reconstruction is expected also in case of sensor faults with respect to the present 4x48 arrangement. Moreover, 12 poloidal arrays will include 14 sensors to compute the harmonic content needed by the plasma boundary reconstruction algorithm (m = 0,...,6). Due to the reduced room between the copper shell and the graphite tiles, the design of triaxial, vacuum fit pickup probes have started also for their convenience in compensating alignment errors.