Comparison of experimental data and three-dimensional simulations of ion beam neutralization from the Neutralized Transport Experiment

The Neutralized Transport Experiment at Lawrence Berkeley National Laboratory has been designed to study the final focus and neutralization of high perveance ion beams [E. Henestroza, S. Eylon, P. Roy, S. Yu, A. Anders, F. Bieniosek, W. Greenway, B. Logan, R. MacGill, D. Shuman, Phys. Rev. ST-Accel. Beams 7, 083501 (2004)]. Preformed plasmas in the last meter before the target of the scaled experiment provide a source of electrons which neutralize the ion current and prevent the space-charge-induced spreading of the beam spot. Neutralized Transport Experiment physics issues are discussed and experimental data are analyzed and compared with three-dimensional (3D) particle-in-cell simulations. Along with detailed target images, 4D phase-space data at the entrance of the neutralization region have been acquired. These data are used to provide a more accurate beam distribution with which to initialize the simulation. Previous treatments have used various idealized beam distributions which lack the detailed features of the experimental ion beam images. Simulation results are compared with experimental measurements for K+ ion beams (~250 keV) with dimensionless perveance of (1-7) × 10-4. In both simulation and experiment, the deduced beam charge neutralization is encouraging for heavy ion fusion and high energy density physics applications.