This topical review gathers the last updates concerning caesium-free negative ion sources presented during the 63rd Course of the International school of Quantum Electronics of the Ettore Majorana Foundation and European collaborative works related to these lectures. Hence, beyond the frame of this course this topical review addresses both theoretical and experimental work performed during these last few years and complexities represented by the conception of a negative ion source ranging from the creation of negative ions to their neutralization.

The production of negative ions is of significant interest for applications including mass spectrometry, materials surface processing, and neutral beam injection for magnetic confined fusion. Neutral beam injection sources maximise negative ion production through the use of surface production processes and low work function metals, which introduce complex engineering. Investigating materials and techniques to avoid the use of low work function metals is of interest to broaden the application of negative ion sources and simplify future devices. In this study, we use pulsed sample biasing to investigate the surface production of negative ions from nitrogen doped diamond. The use of a pulsed bias allows for the study of insulating samples in a preserved surface state at temperatures between 150 ∘C and 700 ∘C in a 2 Pa, 130 W, (ne ∼ 109 cm−3, Te ∼ 0.6 eV) inductively coupled deuterium plasma. The negative ion yield during the application of a pulsed negative bias is measured using a mass spectrometer and found to be approximately 20% higher for nitrogen doped diamond compared to non-doped diamond. It is also shown that the pulsed sample bias has a lower peak negative ion yield compared to a continuous sample bias, which suggests that the formation of an optimum ratio of defects on its surface can be favourable for negative ion production.