Experiments performed in a volume production negative ion source show that the use of a tent or supercusp magnetic filter leads to a more uniform plasma at the normal extraction plane than that obtained with a dipole filter. For the tent filter geometry the extracted negative ion current density, increased as the accelerator was moved into the source to a maximu~ value of about 30% greater than that measured at the normal extraction plane. There is evidence that the primary electrons were well confined by the magnets on the walls of the source, but that significant numbers of positive ions were able to escape from the source by cross-field diffusion, at pressures in excess of 7 mTorr.
