Beam production and propagation in a high power extraction ion diode

An extraction geometry, magnetically insulated ion diode is being used on the 0.8 TW LION accelerator to study ion beam propagation and focusing. The ion diode is annular with pulsed magnetic field coils located on the cathode and a flux excluding anode. The ion beam is extracted through a flux conserving cathode flange into a field free drift and focussing region. In the experiment, time resolved ion aiming measurements have been made with an apertured ion beamlet incident on an array of charge collectors. With this diagnostic one can measure the intrinsic ion beam divergence and the mean motion of the ion beam. Protons in the beam first appear near the peak of the voltage pulse (there is a -20 ns turn-on delay). Initially the protons leave the diode normal to the anode surface. During the -50 ns ion pulse the protons sweep radially inward, and by the end of the pulse they are aimed -10 degrees inward from the normal to the anode. The proton beamlet has a divergence of <3.00 FWHM. The results of this measurement are compared with ion trajectories calculated with a simple single particle code