Upgrade of the Diagnostic Neutral Beam Injector for the RFX-mod2 experiment

Diagnostic Neutral Beam Injectors (DNBI), through the combined use of Charge Exchange Recombination Spectroscopy (CHERS) and Motional Stark effect diagnostics (MSE), are a well-known tool to access important information about magnetically confined plasmas, such as radial profiles of ion temperature, ion flow, impurity content and intensity and direction of the magnetic field. For this purpose, a DNBI was installed and operated in the RFX-mod experiment, which was designed to confine plasma mainly through the Reversed Field Pinch configuration. The DNBI, designed and built by the Budker Institute of Plasma Physics, was based on a source of positive hydrogen ions, accelerated to 50 keV and for a beam current of max. 5 A at the source. The beam could be modulated and the maximum overall duration was 50 ms. With the upgrade RFX-mod to the present RFX-mod2 machine, the DNBI will be renovated in order to solve several plant faults and improve the overall reliability of the system. The 50 kV power supply will be improved, as well as the power supplies in the high voltage deck and its insulation transformer. The control system, originally based on CAMAC technology, will be redesigned and replaced. This contribution will review the technical criticalities emerged in the DNBI check-up and the new solutions adopted to make the DNBI operative and more reliable.