Lithium beam generation and focusing on PBFAII

Summary form only given. The time resolved size and position of the Li beam focus from a 15-cm-radius radial focusing applied-B field ion diode on PBFAII are examined to separate the effects of source divergence, virtual cathode instabilities, charge-exchange, and canonical angular momentum. The diode used /spl sim/1000 cm/sup 2/ area LiF anodes to generate 6 TW, 10 MeV Li beams. The focus of a 64" sector of the annular beam, on a gold foil target at the center of the diode, was observed with two ion pinhole cameras (IPCs) and a spatially resolved magnetic spectrometer. The first IPC used an array of 27 PIN diodes to time resolve the focus. The second IPC used an array of six pinholes with different thickness filters to record 6 images of the beam on CR39 track recording film. Subtraction of the images gave beam profiles between the energy cuts of the filters. Each of these diagnostics gave absolute current density measurements at the target which could be converted to horizontal and vertical FWHM, and focus position. These also were used to calculate total Li beam current at the anode. The diode voltage was measured with another spectrometer that observed protons accelerated in the magnetically insulated power feed 33 cm from the midplane. The Li beam energy agreed with the diode voltage early in time but was generally about 1 MeV below the diode voltage late in time. About 40% of this is attributed to range shortening in the gold target. The remainder could be due to charge-exchange of Li beam ions in gas desorbed from the anode surface or virtual cathode instability waves selectively accelerating Li ions at the rear of the waves.