High-Repetition-Rate Proton Acceleration Above 20 MeV from a Liquid Microjet at L3-HAPLS

High-flux, high-repetition-rate laser-driven proton beams are of interest for applications in inertial fusion energy, cancer therapy, and material damage studies. Realizing these beams requires stable, debris-free, self-refreshing targets compatible with modern high-repetition-rate lasers. Liquid microjets have demonstrated this capability in prior campaigns at ALEPH (CSU), Neptun (TAU), and Gemini (RAL), establishing them as an ideal platform for advanced ion acceleration. Building on this foundation, we implemented a converging liquid water jet target at the L3-HAPLS laser using the ELIMAIA beamline (30 fs, 1-5 J, 3.3 Hz) to explore advanced acceleration regimes and target density shaping. Over 19,000 shots, including 2,000 consecutive, were delivered, demonstrating robust and stable operation. We performed systematic scans of target thickness (0.5-1.7 µm), focal spot size, and laser phase. A synchronized few-mJ pre-pulse precisely controlled pre-expansion to access near-critical density conditions. Ion spectra and angular emission were characterized using absolutely calibrated Thomson parabola spectrometers, TOF detectors, and an ion imager. To monitor the interaction, we measured the laser specular reflection and transmission profiles, the reflected laser spectrum, and XUV emission from the plasma. This presentation will introduce the platform and highlight preliminary results demonstrating a stable, high-repetition-rate proton source exceeding 20 MeV.