Progress on the scaled beam-combining experiment at LBNL

Transverse beam combining is a cost-saving option employed in many designs for induction linac heavy-ion fusion drivers. The resultant transverse emittance increase, due partly to anharmonic space charge forces, must be kept minimal so that the beam remains focusable at the target. A prototype combining experiment has been built. Four sources each produce 4.5 mA Cs+ beams at 160 keV. Focusing upstream of the merge consists of four quadrupoles and a final combined-function element (quadrupole and dipole). Due to the small distance between beams near the merge (∼3–4 mm), the electrodes of the final element for each beam are a cage of small rods, each at a different voltage. Recent results are presented along with plans for modifications and future measurements.