Proton Accelerated from a Laser Driven Z-Pinch*

We will present experimental and numerical results of intense laser acceleration of protons from a sharp near critical density plasma-vacuum interface. Protons were accelerated from a hydrodynamically tailored gaseous hydrogen target using the 10TW TFL laser at NRL. At sufficiently high plasma densities (\textgreater 7x10$^{21}$ cm$^{-3}$), the observed proton beam characteristics were consistent with the Target Normal Sheath Acceleration mechanism. At lower densities (\textless 7x10$^{21}$ cm$^{-3}$), the protons were characterized by a \textless 700keV axial beam with a high-energy halo and energies approaching 2MeV. 3D PIC simulations indicate that these energetic protons result from a laser driven Z-pinch that collapses at the plasma-vacuum interface. Further experimental results and laser-plasma scaling will be discussed.