Modeling and design of a BES diagnostic for the negative ion source NIO1

TL;DR

This paper presents a model for designing a Beam Emission Spectroscopy diagnostic to monitor ion beam properties in the NIO1 negative ion source, enhancing measurement accuracy for future fusion experiments.

Contribution

The paper introduces a comprehensive model for optimizing BES diagnostic configuration, specifically tailored for the NIO1 ion source, building on previous designs for SPIDER and MITICA.

Findings

Optimized BES configuration reduces measurement errors.

Model successfully applied to NIO1 design process.

Enhanced understanding of factors affecting diagnostic precision.

Abstract

Consorzio RFX and INFN-LNL are building a flexible small ion source (NIO1) capable of producing about 130 mA of H- ions accelerated at 60 KeV. Aim of the experiment is to test and develop the instrumentation for SPIDER and MITICA, the prototypes respectively of the negative ion sources and of the whole neutral beam injectors which will operate in the ITER experiment. As SPIDER and MITICA, NIO1 will be monitored with Beam Emission Spectroscopy (BES), a non-invasive diagnostic based on the analysis of the spectrum of the $H_\alpha$ emission produced by the interaction of the energetic ions with the background gas. Aim of BES is to monitor direction, divergence and uniformity of the ion beam. The precision of these measurements depends on a number of factors related to the physics of production and acceleration of the negative ions, to the geometry of the beam and to the collection optics. These elements were considered in a set of codes developed to identify the configuration of the diagnostic which minimizes the measurement errors. The model was already used to design the BES diagnostic for SPIDER and MITICA. The paper presents the model and describes its application to design the BES diagnostic in NIO1.