Shaping ion beams into hollow profiles using sextupole magnets

It is essential to properly shape the intensity distribution or irradiation field of high-energy charged-particle beams to improve their utilization, e.g., high energy density physics and heavy-ion fusion. Recently, unique beam profile shaping that cannot be realized through conventional linear focusing (i.e., the formation of hollow transverse profiles) was achieved through nonlinear focusing using octupole magnets. In this paper, we experimentally demonstrate hollow profile shaping using sextupole magnets, and numerically and analytically verify the beam dynamics of second-order sextupole focusing. We found that both triangular and ellipticalshaped hollow beams can be formed despite the three-fold symmetry of transverse beam cross-sections and asymmetric phase-space evolution. The characteristics of the sextupole-focused beams are compared with those of octupole-focused beams