On the possibility of multi-MeV proton beam collimation with optically generated magnetic fields

The work considers an optical scheme for collimation of high-energy proton beams using ∼105 T scale magnetic fields induced in a miniature “snail” target by petawatt or multi-petawatt laser irradiation in ps or fs regime. Such magnetic fields are known to be frozen into hot plasma and exist on at least a hundred picoseconds timescale, allowing their use for control of charged particle beams. The high values of the magnetic field along with the compact size perfectly match conditions for an all-in-one optical setup, where first, the laser beam accelerates protons, by, e.g., the target normal sheath acceleration mechanism, and second, the closely positioned “snail” target is driven to guide the proton beam. An important issue is that the laser drivers for both proton acceleration schemes and the magnetic field generation in the considered targets may have the same properties and even be parts of one split beam. Numerical simulations show that the considered setup can be used for efficient collimation of ≃100 MeV protons. The collimation effect weakly depends on the fine magnetic field structure. The obtained results are interesting for the development of intense laser-driven sources of charged particle beams with low divergence and high energy of accelerated particles.