A Scaled Beam-combining Experiment for Heavy Ion Inertial Fusion

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 predominantly 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 and preliminary results are presented. Four sources each produce up to 4.8 mA Cs beams at 160 keV. Focusing upstream of the merge consists of four quadrupoles and a final combined-function element (quadrupole & dipole). All lattice elements of the prototype are electrostatic. Due to the small distance between beams near the merge (~ 3-4 mm), the electrodes here are a cage of small rods, each at different voltage.