Sweeping acceleration of high charge ion beams in the large spot size regime with the high repetition rate BELLA petawatt laser*

We present an experimental study of ion acceleration using the BELLA petawatt laser. Enabled by the high repetition rate  (1 Hz) of the laser, targetry and diagnostic we were able to conduct parameter scans involving >100 shots. In the large laser spot size regime, where the laser pulse length is much shorter than the laser spot size on target and is obliquely incident, the laser pulse duration needs to be optimized to obtain uniform plasma heating across the focal plane. Proton spectra from laser pulse duration scans (35 -600fs) reveal such a geometric optimization of the Target Normal Sheath Acceleration (TNSA). The field dynamics inferred from Particle-in-Cell simulations are used to unravel the interaction dynamics and provide further insights into the ion acceleration process.