Experimental results on ITER‐NBI concept source

A negative ion source, which produces a high current density H− ion beam at a low operating pressure, has been developed. The ion source has the same design concept as the large negative ion source for ITER NBI. The negative ions are produced in a Cs seeded multi‐cusp plasma generator. To produce negative ions efficiently at a low pressure, the plasma generator is designed to have a semi‐cylindrical configuration where the plasma is confined effectively by strong magnetic line cusps with a high volume‐surface ratio. Stable arc was generated at a low operating pressure of under 0.1 Pa. The ion source produced 2.1 A H− ion beams with a current density of 30 mA/cm2 at an operating pressure of as low as 0.2 Pa in a cesium seeded operation. Taking the isotope effect of the H−/D− production into account, the achieved current density is equivalent to the D− current density of 24 mA/cm2, which satisfies the design value for ITER NBI.