Report on joint experiments in NIFS-RNIS in 2019 - Negative ion source plasma investigation by Compact Retarding Field Energy Analysers

This document reports on the joint experiments carried out at NIFS finalized to further advance the understanding of source plasma physics by measurement of the positive and negative ion energy distributions. NIFS test stand is among the best diagnosed ion sources for negative hydrogen ion beams in the world, and routinely operates low-divergence beamlets at SPIDER-relevant ion energy range. Two newly developed compact diagnostics (gridded retarding field energy analysers) were constructed and installed at the upstream surface of the plasma grid, commissioned, and used to characterize the plasma source with and without caesium. The trends and the ion energy distributions were analysed and a correlation with the source parameters was attempted.