Description
Laser-driven ion acceleration toward sub-GeV/GeV-class proton energies is fundamentally limited by the trade-off between peak energy and laser-to-proton conversion efficiency, which originates from rapid dephasing between the accelerating field and the ion population. We propose a dual-pulse micronozzle acceleration (DP–MNA) scheme that enforces phase-locked acceleration to alleviate this trade-off. A tightly focused prepulse extracts a compact proton front from a hydrogen rod, while a delay-tuned main pulse drives a quasi-static axial electric field inside a solid-density aluminium micronozzle cavity. By matching the inter-pulse delay to a synchronization window, the proton bunch is injected into and co-propagates with the accelerating field over an extended interaction length, suppressing thermal debunching and prolonging the effective acceleration stage.
Two-dimensional particle-in-cell simulations (EPOCH) show that, at main-pulse intensities of order 10²¹ W/cm², DP–MNA reaches sub-GeV-class proton cutoffs with a total conversion efficiency of ~20%, of which ~13% resides in the application-relevant >100 MeV component. An analytical model predicts the optimal delay and the synchronization-window width directly from the target geometry, in agreement with the simulations. Three-dimensional slit-nozzle simulations confirm that the spectral hardening and confinement advantage persist, yielding cutoff energies ~60% higher than an unconfined hydrogen rod. These results identify phase-locked acceleration as a practical design principle for compact, high-yield proton drivers relevant to secondary-particle and neutron sources.