Reduction of the impurity concentration of an intense hydrogen ion beam

An effort was made to measure and reduce the impurity content of an intense hydrogen beam used for neutral injection heating of a stellarator plasma. Originally, the hydrogen ion beam contained 5% water and water-like ions. A simple and very useful method to reduce the contamination turned out to be evaporation of titanium on the inner surfaces of the ion source, which reduced the low-Z impurity content to 0.6%.