  We present results of energetic laser-ion acceleration from a tailored, near
solid density gas target. Colliding hydrodynamic shocks compress a pure
hydrogen gas jet into a 70 {\mu}m thick target prior to the arrival of the
ultra-intense laser pulse. A density scan reveals the transition from a regime
characterized by a wide angle, low energy beam to one of a more focused beam
with a high energy halo. In the latter case, three dimensional simulations show
the formation of a Z-pinch driven by the axial current resulting from laser
wakefield accelerated electrons. Ions at the rear of the target are then
accelerated by a combination of space charge fields from accelerated electrons
and Coulombic repulsion as the pinch dissipates.
