Ion acceleration by collisionless shocks in high-intensity-laser-underdense-plasma interaction.

Area of Science:

• Plasma Physics
• Laser-Plasma Interactions
• High-Energy-Density Physics

Background:

• Ultraintense short-pulse lasers interacting with underdense plasmas are a key area for studying particle acceleration.
• Understanding ion acceleration mechanisms is crucial for applications in fusion energy and particle accelerators.
• Previous studies have explored laser-driven ion acceleration, but high-intensity regimes reveal complex phenomena.

Purpose of the Study:

• To investigate ion acceleration mechanisms using ultraintense lasers (up to 3 x 10^20 W/cm^2) interacting with underdense plasmas.
• To determine the scaling of maximum ion energy with plasma density.
• To elucidate the role of collisionless shocks in enhanced ion acceleration.

Main Methods:

• Experimental study of ion acceleration using ultraintense laser pulses interacting with helium plasma.
• Measurement of accelerated helium ion energies and angular distribution.
• Two-dimensional particle-in-cell (PIC) simulations to model the laser-plasma interaction and shock formation.

Main Results:

• Helium ions were accelerated to a maximum energy of 13.2 ± 1.0 MeV.
• Maximum ion energy scaled with electron plasma density (n_e) as n_e^(0.70±0.05).
• PIC simulations indicated the formation of multiple collisionless shocks at high plasma densities, consistent with experimental observations.

Conclusions:

• Collisionless shock interactions significantly contribute to enhanced ion acceleration, surpassing the ponderomotive potential of the laser alone.
• The observed plateau structure in the ion energy spectrum is attributed to the interaction of these multiple shocks.
• This study provides insights into novel mechanisms for generating high-energy ions from laser-plasma interactions.