Laser plasma-based ion acceleration has drawn significant interest due to its unique properties. However, achieving protons with higher kinetic energy remains a challenge. We propose a novel ion acceleration scheme, Expanding Nozzle Acceleration (ENA), to generate proton beams with substantially higher kinetic energies than with conventional schemes. The performance of ENA is studied with 2D-PIC (Particles-in-cell) simulations. In ENA, the target consists of a micron-sized hydrogen bullet place inside a micro-nozzle at the narrowing position. Under the illumination of ultra-intense laser with intensities at 10²⁰ - 10²² W/cm², the entrance of the nozzle focuses the laser, thereby increasing the intensity on the bullet, the protons are accelerated by the two-fold electrostatic forces: (1) the electric field generated on the bullet itself due to the charge separation and (2) the electric filed generated at exit arms of the nozzle. Illuminating the system with a laser intensity of 3 x 10² W/cm², remarkable results were observed, including a 6.25- fold enhancement in laser intensity onto the hydrogen sphere and protons attaining an energy of 400 Mev. This signifies a three-fold increase in proton energy compared to a planer target and a two-fold increase compared to spherical target. Notably, the maximum proton energy scales with E_max α I₀^0.88, where I₀ is the laser intensity.

Ion acceleration,micro nozzle,target normal sheath acceleration