High-power ion beam characteristics of a magnetic multi-pole line-cusp ion source for the HL-2A tokamak

A circular magnetic multi-pole line-cusp ion source with a nominal 45 keV 25 A hydrogen ion beam is developed for the neutral beam injector of the HL-2A tokamak. At present, this bucket ion source can produce a 40 keV 20 A hydrogen ion beam for less than 100 ms on a test bed, and a 35 keV 13A ion beam for 300 ms on the injector of the HL-2A tokamak. The 1/e half-width of the ion beam power profile is about 6.0 ± 0.2 cm at the position of 3.26 m downstream from ion source, and the corresponding divergence degree is nearly 1.1. The optimum perveance matched conditions were obtained experimentally, and were in good agreement with the values from experiential equation of Uhlemann et al. The maximum of optimum perveance reached 2.2 x 10-6 A/V1.5 for 38 keV beam energy. An ion beam with above 60% H+ species fraction can be achieved, which was measured by Hα light Doppler shift spectroscopy. According to research results, a neutral beam with a total power of more than 0.6 MW was successfully injected into the plasma of the HL-2A Tokamak in 2008. (authors)