Betatron source optimization for single-shot time-resolved x-ray imaging*

Laser wakefield accelerator driven betatron sources are apt for absorption spectroscopy and phase-contrast imaging; however, improvement of x-ray flux is required for many time-resolved applications.Using the 2.5 Hz Advanced Laser Light Source (ALLS) betatron beamline, a betatron source was produced using a He-N₂ gas jet at 2.5 Hz for phase-contrast imaging of dense metal alloys. In this work, the number of photons per shot (~2×10⁹), required integration of multiple shots to resolve micron-scale features in these materials. However, for time-resolved imaging of dynamic processes, a single-shot, high-flux x-ray source is required. To achieve these conditions, ALLS betatron source was optimized using a 7 mm 3D printed gas cell, leading to 6.5× higher photons (13×10⁹ versus 2×10⁹) and ~ 20× reduced pointing fluctuation (0.06×0.05 mrad² versus 1×1 mrad²) compared to He-N₂ gas jet. These optimizations required a series of single parameter scans to locate the global maximum of the source. The high-flux x-ray source was used to perform time-resolved imaging of plasma discharge dynamics in heptane-water interface on the nanosecond timescale, providing novel information on plasma discharge evolution.