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

TL;DR

This paper details the upgrade and reliability improvements of the Diagnostic Neutral Beam Injector used in the RFX-mod2 plasma experiment, enhancing its power systems and control architecture.

Contribution

It introduces new solutions for power supply enhancements and a complete redesign of the control system to improve DNBI reliability in the RFX-mod2 experiment.

Findings

Successful upgrade of power supplies and insulation transformer.

Implementation of magnetic field survival tests for electronic components.

Complete control system overhaul from CAMAC to modern technology.

Abstract

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 Nuclear Physics (BINP), was based on a source of positive hydrogen ions, accelerated to 50 keV and for a maximum ion current of 5 A. The beam could be modulated and the maximum overall duration was 50 ms. With the upgrade of RFX-mod to the present RFX-mod2 machine, the DNBI is being renovated to solve several power units faults and improve the overall reliability of the system. The 50 kV power supply is being improved, as well as the power supplies in the high voltage deck and its insulation transformer. Magnetic field survival tests were performed on the toroidal-core-based DC-DC converters that should power the electronic boards in a reliable way. The control system, originally based on CAMAC technology, was redesigned to be fully replaced. This contribution reviews the technical criticalities emerged in the DNBI check-up and the new solutions adopted to make the DNBI operative and more reliable.