On the role of self-generated magnetic fields in focused ion beams driven by intense picosecond laser pulses

We investigate the physics of ion beam focusing in the interaction of intense picosecond laser pulses with concave foils, using two-dimensional particle-in-cell simulations. Curved targets have been observed to deliver brighter multi-MeV ion beams than flat targets, and they could be used to ignite pre-compressed ICF fusion capsules in a scheme called ion fast ignition. Focusing is achieved by shaping the target and relying on an ion acceleration mechanism in which the ions are accelerated normal to the target surface; subsequently, the plasma expansion grows magnetic fields that advect with the plasma and deflect ions away from the target symmetry axis, causing the focal spot to shift downstream from its geometric location. The drop in both electric and magnetic field strengths in the expanding plasma makes the ion beam envelope asymmetric with respect to the focusing plane.. Authors: Kemp, A. J. [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)] (ORCID:0000000345186382); Wilks, S. C. [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)] (ORCID:0000000272682683); Tabak, M. [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)] (ORCID:0009000179675750); Higginson, D. P. [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)] (ORCID:0000000276993788). DOE Contract: AC52-07NA27344. Subjects: Focused ion beam; Lasers; Magnetic fields; Particle-in-cell method; Plasma expansion; Plasma properties and parameters