Isolated proton bunch acceleration by a petawatt laser pulse.

Area of Science:

• Plasma Physics
• Laser-driven particle acceleration

Background:

• Interpreting laser-accelerated ion signals is challenging due to competing dynamic processes.
• Developing clean ion beams is crucial for advanced applications.

Purpose of the Study:

• To experimentally demonstrate the acceleration of a clean proton bunch.
• To investigate the underlying acceleration mechanisms and their limitations.

Main Methods:

• Utilizing a microscopic, 3D confined near-critical density plasma target (1 µm plastic sphere).
• Employing a levitated and precisely positioned target in a Petawatt laser focus.
• Conducting 3D particle-in-cell simulations to model the acceleration process.

Main Results:

• Reproducibly observed proton bunches with central energies of 20–40 MeV.
• Achieved narrow energy spread (down to 25%) with minimal low-energy background.
• Simulations revealed the transition from organized acceleration to Coulomb repulsion.

Conclusions:

• A microscopic plasma target enables clean proton bunch acceleration.
• Identified limitations in current high-power laser systems for ion acceleration.
• Proposed viable strategies for optimizing laser-driven ion sources.