Effects of Ar addition are studied by using a beam injection type negative ion source. With adding Ar, IH- increases at low base H-2 pressure. At high base H, pressure, however, IH- decreases. VUV emission intensities also decrease at high base pressure. In other words, Ar addition is adverse effect for production of H-2 (v ''). Therefore, decrease in IH- is caused by decrease in H-2 (V ''). In D-2 plasmas, variation patterns of plasma parameters and VUV intensities by Ar addition are nearly the same as ones in H, plasmas. Even in low base pressure, however, enhancement of ID- is not observed. (c) 2005 Published by Elsevier B.V.