Surface and sub-surface investigations of the plasma influence on Cs doped Mo as surface converter for negative hydrogen ion sources for fusion^(a)

¹ Laboratoire de Physique des Gaz et Plasmas- LPGP, UMR 8578 CNRS, Université Paris- Sud, Université Paris-Saclay - F-91405 Orsay Cedex, France
² Max- Planck-Institut für Plasmaphysik - Boltzmannstrasse 2, D-85748 Garching, Germany

^(b) loic.schiesko@universite-paris-saclay.fr (corresponding author)

Received: 9 December 2020
Accepted: 6 April 2021

Abstract

The influence of low-pressure and low-temperature hydrogen plasma on a pure molybdenum sample implanted with caesium is investigated by means of sputtering-XPS. A portion of the sample was exposed to the plasma, while the rest of the sample was covered by stainless steel and thus shielded from direct plasma flux. The results show that the part of the sample exposed to the plasma exhibits both on and beneath the surface an increased amount of H₂O and MoO₂ with respect to the covered sample part which can be explained by a chemical reduction of MoO₃ oxides by the hydrogen plasma species. The XPS Cs lines show oxidation peaks. A sputtering depth of roughly 13 nm is necessary to recover an identical spectrum, indicating that the plasma changes the chemical composition of the implanted samples not only on the surface but also inside the material.