Speaker
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 $\mbox{H}^-$ 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.
