Speaker
Description
SPIDER (Source for the Production of Ions
of Deuterium Extracted from a Radio frequency plasma)
is currently in a major shutdown period dedicated to
the upgrade of several components in order to enhance
its performances and guarantee their agreement with
the ITER requirements. During this phase, an indepth inspection of beam source components has been
fundamental to understand SPIDER’s behaviour during
the previous experimental campaigns, and in particular
caesium evaporation inside the source by means of Cs
ovens. Caesium evaporation and its deposition on the
plasma grid (PG) is fundamental to minimize the work
function of PG surface and to optimize the generation
and extraction of negative ions. This work presents the
analysis of the caesium ovens’ performances and their
status after removal. The experimental data obtained
via chemical analysis using environmental sampling with
Inductively Coupled Plasma Mass Spectrometry (ICPMS) are compared to previously developed numerical
models for the caesium evaporation and deposition, to
the results of a chemical surface analysis performed in
strategical locations of the source walls and extraction
grid, and to the Laser Absorption Spectroscopy (LAS)
measurements. This study helps understanding the nonuniformity of the negative ion beam extraction observed
during SPIDER experimental campaigns. In addition,
the future implementation of permanent magnets in the
back plate of the source is analysed in terms of caesium
deposition efficiency on the source walls.
