SARDINE

This project addresses issues related to hydrogen negative-ion sources for future fusion reactors. These sources are based on low-pressure low-temperature H2 plasmas in which caesium (Cs) metal is injected in vapor form. Cs is depositing on all surfaces in contact with the plasma and greatly enhances H- negative-ion surface production. Because Cs is polluted very quickly due to its high chemical reactivity, it has to be injected continuously leading to its accumulation inside the source. It implies severe maintenance issues that are manageable in a research reactor but that are unsustainable for a nuclear power plant. Cs alternative materials, besides being efficient for negative-ion production, have also to sustain erosion induced by the plasma, pollution by impurities and harsh mechanical and temperature constraints. As a consequence, no solution has been found to date to replace Cs whose continuous injection guarantees the source efficiency, but at the same time signs its inadequacy with the specifications of a power plant. We propose to extend the advantage of the continuous renewal of Cs to potentially any material efficient for H- surface production. The main idea is to use alternative materials in the form of micro-particles shortly transiting inside the plasma to eliminate pollution or erosion problems. This solution would not only increase the negative-ion production due to the large specific area of the micro-particles, but would also highly enhance H- extraction thanks to their acceleration by the potential difference between micro-particles and plasma. This project aims at addressing the physics required to develop this highly innovative solution, from negative-ion production and extraction to fundamental aspects related to negative-ion emitting micro-particles behavior in plasma.