Recent Beam Developments with the LBNL 14 GHz AECR-U Ion Source

Abstract：

A radial sputter probe has been developed for the AECR-U as an additional method of producing metal ion beams. Negative voltage is applied to the probe to incite collisions with target atoms, thereby sputtering material into the plasma. The sputter probe is positioned through one of the 6 radial access slots between the permanent hexapole structure of the AECR-U. The probe position can be varied with respect to the inner edge of the hexapole magnet structure. Charge state distributions and peak beam intensities at bias voltages up to －5kV were obtained for gold samples at varying distances of the probe with respect to the plasma. For high charge states production the radial position with respect to the plasma was more sensitive than for the medium and lower charge states. For high charge state ion production the probe was optimized at a distance of 0.6cm inside the chamber wall (4.1cm from the center of the chamber). Stable beams with peak intensities of up to 28eμA of Au²⁴⁺ and 1.42eμA of Au⁴¹⁺ have been produced using the sputter probe technique.
In addition, a solid state circuit under development by Scientific Solutions, Inc which provides a bandwidth up to 100MHz was used to drive the 14GHz klystron amplifier for the LBNL AECR-U ion source. Various broadband and discrete heating modes were tested and the results for high charge state ion production were compared with single frequency heating.