17th International Conference on Ion Sources

Flow Patterns of H− Ions Measured with Directional Photodetachment Langmuir Probe

17 Oct 2017, 09:00

30m

CERN

Oral presentaion Fundamental processes 4th Session

Speaker

Dr Katsuyoshi Tsumori (National Institute for Fusion Science, The Graduate University for Advanced Studies)

Description

Tiny amounts of caesium (Cs) injection into negative ion sources enhances the density of hydrogen/deuterium negative ions (H${}^{-}$/ D${}^{-}$ ions) drastically. Sequential processes through the production to extraction of negative ion is essential to understand the negative-ion dynamics from physics point of view and to improve the performance of negative ion source from engineering point of view. Our primary result obtained by means of a directional photodetachment Langmuir probe (DPLP) shows that the flow of H${}^{-}$ ions comes from metal part of the plasma grid to the bulk plasma region, turned the direction at a certain distance from the grid and moves back to aperture direction where the H${}^{-}$ ions flow due to beam extraction. In order to improve the spatial resolution and expand the region of the flow measurement, a new DPLP whose probe tip aligned along the centre of the probe stem; the probe equips a flow mask plate on the edge of a rotatable tube coaxial to the stem.
In this presentation, changes of the flow patterns of ${\text{H}}^{-}$ ions with respect to the difference between plasma potential and bias potential, filling H${}_2$ gas pressure and work function, which is measured with newly installed work function detector, together with the combined date obtained with cavity ringdown measurement and Cs laser absorption spectroscopy.

Presentation materials

tsumori-ICIS2017.pdf

tsumori-ICIS2017.pptx