Sprecher
Beschreibung
Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
Laser-driven proton acceleration has long been limited by an apparent trade-off between laser-to-ion conversion efficiency and maximum particle energy. While target-normal-sheath acceleration (TNSA) remains robust, it typically suffers from low efficiency and thermal-like spectra at the multi-MeV level. Here we propose and numerically demonstrate a dual-pulse micronozzle acceleration (DP--MNA) scheme that decouples source generation from accelerating-field formation and thereby substantially relaxes this longstanding constraint at intensities around $10^{21}\,\mathrm{W\,cm^{-2}}$.
In DP--MNA, a structured target comprising a hydrogen rod (source) inside an aluminum nozzle (field generator) is driven by a precisely timed dual-pulse sequence. Two-dimensional particle-in-cell simulations (EPOCH) show that a tightly focused prepulse acts as an injector, extracting a compact proton bunch and seeding return currents, while a delayed main pulse drives a long-lived (hundreds of femtoseconds), gigavolt-per-meter axial electric field in the nozzle cavity. By tuning the delay into a robust synchronization window ($\Delta t \approx 0\text{--}40\,\mathrm{fs}$), the proton front becomes spatiotemporally ``phase-locked'' to the advected cavity field, forming a directed acceleration channel that suppresses transverse electron loss compared with unconfined targets.
Within this regime, the DP--MNA scheme sustains laser-to-proton conversion efficiencies exceeding $15\%$ (peaking near $20\%$) while simultaneously maintaining cutoff energies above $0.5\,\mathrm{GeV}$ (up to $\approx 0.8\,\mathrm{GeV}$) for $\sim 100\,\mathrm{fs}$ pulses. These results identify source--field synchronization and geometric confinement as powerful design principles for compact, potentially high-repetition-rate proton sources for high-energy-density applications, including neutron generation, fusion-relevant target driving, and nuclear photonics at next-generation laser facilities.
