STUDY OF THE DISCHARGE OF A MULTICUSP ION-SOURCE OPERATING WITH H2 AND D2

The plasma parameters and relative positive and negative ion concentrations in a small, filtered, multicusp ion source, operating at low plasma density (<1 x 10(11) cm-3) with both hydrogen and deuterium gas have been measured using a Langmuir probe and a small mass spectrometer. Under identical source operating conditions the plasma density in D2 is found always to be higher than in H-2, while the negative ion density is found to be consistently lower in D2 than in H-2. The effect of the different isotopes on transport processes in the discharge can be understood in terms of a simple model. The isotope effect on molecular processes is also discussed.