Design and Test of Readout Electronics for Thermocouples on Ion Beam Sources

A small radiofrequency ion source named negative ion optimization phase 1 (NIO1) has been recently installed at Consorzio RFX in Padua. The NIO1 source is capable of producing about 130 mA of negative hydrogen ions accelerated at 60 kV and represents a useful test bench for negative ion source optimization. The exploitation of this device is included in the framework of the activities for SPIDER and MITICA and the prototypes of the negative ion source and of the whole neutral beam injector for international thermonuclear experimental reactor (ITER) experiment, respectively. As in SPIDER and MITICA, thermal measurements are performed in NIO1 by several thermocouples (TCs). These measurements are indeed important for the evaluation of the thermal load distribution, plasma generation, and beam extraction uniformities, for the monitoring of different experimental conditions, and for the verification of the reliability of source and beam-line components in the expected range of temperatures. This paper deals with the development of a new electronic frontend for acquisition and transmission (tx) of the thermal signals from the TCs mounted on the ion beam source, preserving signal integrity. It is the updated version of previous circuits initially developed for optical tx of the thermal measurements from the grounded grid in SPIDER. In particular, two of these circuits were installed in the NIFS Neutral Beam Test Stand in Japan and in BATMAN at IPP Garching, Germany. The system presented here is under test in the NIO1 device to check its reliability in monitoring the temperature of some cooling circuits, like in SPIDER and MITICA.