“…There are technological issues regarding the negative ion source toward higher performance H − beam: higher negative hydrogen-ion beam power; higher H − beam current or beam current density; lower electrostatically co-extracted electron current with H − beam; higher wall-plug efficiency; higher operation stability; and lower consumption of cesium (Cs) seeded to increase surface H − production, etc. These are concerns with ion source physics: processes of H − production on and emission from plasma grid electrode (PG), which is an ion source plasma facing electrode as well as the first electrode in accelerator of the ion source; 16) H − transport in the ion source plasma; 17,18) characteristics on the ion-ion plasma where the electron density n e is quite lower than H − in the vicinity of beam extraction aperture of the PG; 19) Cs recycling in the ion source plasma; [20][21][22] beam extraction mechanism; [23][24][25] beam optics; 26,27) beamlets interaction; 28,29) withstanding high voltage; 30) and isotope effect, 4,6,31) etc.…”