H- measurement in the magnetically filtered region of the large negative ion source

H- ion density in the extraction region of a volume-production-type ion source is measured, using the photodetachment method, and directly compared to H- ion beam extracted from the ion source in order to understand the effective production of H- ions. It is observed that there is qualitative similarity between H- density and extracted H- beam current, as expected. Characteristics of H- ion production under two values of magnetic strength are compared to study the effect of the filter field. It was found that the weaker magnetic field of 750 G cm is not sufficient for the filter field since high energy electrons can come into the extraction region across the magnetic field. (C) 1998 American Institute of Physics.