PERFORMANCE OF A VOLUME H- ION-SOURCE WITH A TOROIDAL DISCHARGE CHAMBER

A new volume H- ion source with a toroidal discharge chamber has been designed. Its main feature is a full rotational symmetry, including a conically shaped dipole field separating the main toroidal discharge from the central extraction chamber. Measurements of the H- yield and the accompanying electron component have been performed, both for this rotationally symmetric geometry and for a standard line dipole geometry. With the rotationally symmetric geometry, the H- yield was up to 30 mA through an aperture of 1 cm2, while the ratio Ie /I H- depended greatly on the value of I H- and was about 20-30 for the highest currents. The beam emittance was measured for the rotationally symmetric geometry, and was found to be εn (90%)≊0.094 π cm mrad for a 21-mA beam. An estimate of the H- ion temperature from the measured emittance gives a value of approximately 3.6 eV.