Ion Acceleration with a Transverse Flying Focus*

High-intensity laser-plasma interactions can generate extreme electrostatic fields, enabling compact and efficient particle acceleration (~100 GeV/m) compared to conventional radiofrequency accelerators. Despite this promise, accelerating ions to relativistic energies has been challenging due to their substantial mass. Recent advancements in spatiotemporal pulse shaping allow matching the laser group velocity to ion velocities, facilitating GeV-scale ion acceleration in the laser wakefield. Here, we demonstrate that a laser pulse with a focal spot moving transversely to its propagation direction can accelerate ions to GeV energies in underdense plasma within 0.44 cm. We employ a Hamiltonian analysis to reveal detailed particle dynamics and thresholds for efficient acceleration. Our approach circumvents the need for complex targets or currently unavailable laser capabilities, potentially paving the way for widespread adoption of compact, high-repetition-rate ion sources in various applications.