  Laser ion acceleration is a promising concept for generation of fast ions
using a compact laser-solid interaction setup. In this study, we theoretically
investigate the feasibility of ion acceleration from the interaction of
petawatt-scale laser pulses with a structured target that embodies a
micron-scale channel filled with relativistically transparent plasma. Using 2D
and 3D Particle-In-Cell (PIC) simulations and theoretical estimates, we show
that it is possible to generate GeV protons with high volumetric charge and
quasi-monoenergetic feature in the energy spectrum. We interpret the
acceleration mechanism as a combination of Target Normal Sheath Acceleration
and Radiation Pressure Acceleration. Optimal parameters of the target are
formulated theoretically and verified using 2D PIC simulations. 3D PIC
simulations and realistic preplasma profile runs with 2D PIC show the
feasibility of the presented laser ion acceleration scheme for the experimental
implementation at the currently available petawatt laser facilities.
