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Generation of giga-electron-volt proton beams by micronozzle acceleration
Our proposed ion acceleration scheme, micronozzle acceleration (MNA), generates proton beams with extremely high kinetic energies on the giga-electron-volt (GeV) order. The underlying physics and performance of MNA are studied with two-dimensional particle-in-cell simulations. In MNA targets, a micron-sized hydrogen rod is embedded inside a hollow micronozzle. Subsequent illumination of the target along the symmetric axis by an ultraintense ultrashort laser pulse forms a strong electrostatic field with a long lifetime and an extensive space around the downstream tail of the nozzle. The electric field significantly amplifies the kinetic energies of the accelerated protons, and $$\gtrsim$$ GeV protons are generated at an applied laser intensity of $$10^{22}$$ W/ $$\hbox {cm}^2$$ .
At \(t = 250\) fs, the increase in proton momentum via the afterburner phase is still small, because the measured time is just at the beginning of the free expanding process, corresponding to \(\mathcal {E}_\textrm{max}\sim 600\) MeV (compare Fig. From the good agreement between the simulation results and the analytical model, it is inferred that the protons are continuously accelerated in the afterburner phase by absorbing the thermal energy of the hot electrons under the interplay between the charge-separated two fluids. This cylindrical symmetry is broken at even higher laser intensities (\(I_L\gtrsim 3\times 10^{22}\) W/\(\hbox {cm}^2\)), where a strong shock wave is driven to transmit in the H-rod target to boost the proton acceleration as a result 57, 58, 59.
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