Characteristics of extracted ion beam of cesium-free negative ion source TPDsheet-U

This study reports progress toward realizing a high-performance Cesium (Cs)-free negative ion source, that produces negative ions using volume production in a magnetized-sheet plasma device (TPDsheet-U). Experimental observations show that the ratio of the co-extracted electron current (J
EG
) and hydrogen negativeion current (J
c
), J
EG
/J
c
decreases from 10 to 0.3 with a soft magnetic material plate for a magnetic filter (SMF) with thickness t = 2.0 mm at a discharge current of I
d
=50 A and gas pressure of P = 0.3 Pa. An SMF is a physical filter that prevents electron diffusion from the extraction region and the magnetic field control was effective in reducing the JEG/JC ratio. The J
c
is approximately 6 mA/cm
²
at an extraction voltage (V
ex
) of 10 kV, discharge current (I
d
) of 80 A, gas pressure of 0.3 Pa, and external magnetic field strength of 40 mT. The current density performance of the H
^-
ion beam, J
c
, was found to be approximately one-fifth of that of the negative ion source with Cs seeding in ITER-NBI.