Optimal power-coupling and beam focusing using a LiF applied-B ion diode on PBFA II

Experiments have been performed on Sandia's PBFA II accelerator using a thin film LiF source studying power and energy coupling to a lithium ion diode, ion divergence, and optimal focusing of the lithium beam to enable target experiments. These experiments have provided insight into the present limitations on focused ion intensity in single-stage applied-B ion diodes using a passive ion source. Power and energy coupling to the ion beam is primarily limited by parallel loads in the diode and in the Magnetically Insulated Transmission Lines (MITLs) that feed the power from the accelerator to the ion diode. Focusing experiments using the ion beams generated in this improved parameter regime have been performed. Anodes have been designed to account for geometric, self- and applied-field focusing to vertically focus lithium ion beams. Gas cells containing neutralizing Argon gas have likewise been shaped to conform to the applied-magnetic field profile and minimize variations in horizontal focus due to variations in canonical angular momentum. Focusing experiments have produced an intensity of ≥ 1 TW/cm2 of lithium ions with an energy of ∼ 9 MeV and with a FWHM on target of up to ∼ 25 ns