Irradiation of Materials using Short, Intense Ion Beams from an Induction Accelerator*

We present experiments studying material properties created with nanosecond and millimeter-scale ion beam pulses on the Neutralized Drift Compression Experiment-II at Berkeley Lab. 4 The accessible scientific topics include the dynamics of ion induced damage in materials, materials synthesis far from equilibrium and intense beam-plasma physics. We describe the accelerator performance, diagnostics and results of beaminduced irradiation of thin samples of, for example, tin and silicon. Bunches with $>3 \mathrm {x}10 ^{10}$ions/pulse within 1-mm radius and 2–30 ns FWHM duration have been created. To achieve the short pulse durations and mm-scale focal spot radii, the 1.2 MeV He $^{+}$ion beam is accelerated and bunched in the induction accelerator. After the last of twelve acceleration gaps, the beam is neutralized in a drift compression section which removes the space charge defocusing effect during the final compression and focusing. Detailed particle-in-cell simulations include the effects of space charge and image charge fields, finite temperature of the ion beam, plasma neutralization, applied focusing fields and acceleration fields. Quantitative comparison of these simulations with the experiment play an important role in optimizing the accelerator performance and keep pace with the accelerator repetition rate of $< 1 /$minute.