Speaker
Description
The production of negative hydrogen ions (H$^-$/D$^-$) in high-current ion sources occurs through two complementary mechanisms; dissociative electron attachment involving ro-vibrationally excited molecules and low energy electrons, and resonant tunneling of electrons from low work function caesiated metal surfaces to the affinity level of hydrogen atoms. We briefly describe the physics principles of the volume and surface production pathways of H$^−$ ions highlighting the importance of discharge power coupling method and plasma-facing material selection for optimising the H$^−$ yield via vibrational excitation or electron transfer at surfaces. We discuss factors affecting the transition rate of electrons from the bulk material and the survival probability of the surface-produced ions. We predict the relative H$^−$ yield of different caesiated metal surfaces and point out an apparent gap in the availability of data on the band structure and conduction electron density of metals covered by fractional monolayer of caesium, which complicates the comparison. Finally, we make recommendations for experimental and theoretical work on this topic.
| Email address | olli.tarvainen@stfc.ac.uk |
|---|---|
| Visitor's Visa | no |
| Classification | Fundamental processes and modelling |