Isotope effect of H^-/D^- volume production in low-pressure H_2/D_2 plasmas : Measurement of VUV emissions and negative ion densities

Isotope effect on H^-/D^- volume production is studied by measuring both VUV emission and negative ion density in the source. In a double plasma type source, under some discharge conditions, extracted D^- currents are nearly the same as H^- currents, although VUV emission intensity (corresponding to production of vibrationally excited molecules) in D_2 plasmas is slightly lower than that in H_2 plasmas. Considering the factor √ due to mass difference, D^- ion density in the extraction region of the source is higher than H^- ion density. In another experiment with a rectangular arc chamber, axial distributions of H^-/D^- ion densities in the source are measured directly using a laser photodetachment method. Relationship between H^-/D^- production and plasma parameter control with using a magnetic filter (MF) is discussed. Furthermore, relative intensities of extracted negative ion currents are discussed compared with the negative ion densities in the source. Production and control of D_2 plasmas are well realized with the MF including good combination between the filament position and field intensity of the MF. Extracted H^- and D^- currents depend directly on negative ion densities in the source.