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PBFA 2 applied B ion diode beam characteristics at high voltages
An applied B-field ion diode has been operated at 21 TW on PBFA 2 to study beam generation and transport physics. The radial focusing 15-cm-radius diode utilized a pair of magnet coils in disc cathode structures to produce an axial B-field to minimize electron loss in the 16 mm anode-cathode gaps. The diode was different than used in the past with the cathodes 20% closer together and the B-field increased to 3.3 T at the midplane. The 2.5 MA beam originated from a 5-cm-tall ion emitting region and was transported toward the axis in a 12.5-cm-radius gas cell with 2-{mu}m-thick mylar window and a 5-Torr-argon gas fill. A surface flash-over plasma created by electron loss on wax-filled grooves in the anode produced a beam with comparable currents of proton and carbon ions. The experimental results include the spatial uniformity and time dependence of proton and carbon beam emission from the anode and the divergence and focusability of both beams. 10 refs., 13 figs.