INVESTIGATION OF 2 NEGATIVE HYDROGEN AND DEUTERIUM ION SOURCES - EFFECT OF THE VOLUME

We have investigated by probes and by photodetachment the plasma prope rties of two negative ion sources of different volume. We compared the data relevant to these two sources and identify the effects induced b y the change in volume and the isotope effects. The observed scaling l aw for the electron temperature is in each case T-e similar to I-d(0.2 7). Positive ions are predominantly lost to the walls, but due to the increasing influence of their loss by dissociative recombination when the source volume is increased, the scaling laws are n(e) similar to I -d(0.7), for the small source, and n(e) similar to I-d(0.59), for the large source. Atoms limit the production of negative ions and destroy them. Thus we see an isotope effect, with higher negative ion density in hydrogen than in deuterium, and the effect of the source volume, wi th the negative ion density larger in the small source than in the lar ge one. (C) 1996 American Institute of Physics.