Particle transport and electric fields in a laser-generated focused proton beam

Summary form only given. Recent experiments and simulations of proton generation and focusing in cone geometries have led to a better understanding of the important effects of the electric fields in and around the focused beam.¹ The surrounding cone structure is shown to improve the focusing significantly, resulting in beam fluence diameters ≈ 55µm for protons with energies Ep >3 MeV. PIC-hybrid simulations predict that a strong sheath field on the inner surface of the cone wall channels the beam and results in a reduced beam diameter. The electric fields in the plasma due to the hot electron pressure also affect the focusing and particle trajectories, bending the beam near the axis. This combination of fields leads to complicated trajectories, inconsistent with simple linear acceleration near the target surface. Simulations predict that further improvement in focusing is possible by better control of the laser beam uniformity.