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/cm2 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.