Multiple beam two-plasmon decay: linear threshold to nonlinear saturation in three dimensions.

Area of Science:

• Plasma physics
• Laser-plasma interactions
• Nonlinear phenomena

Background:

• Two-plasmon-decay instability is a key process in laser-plasma interactions.
• Understanding instability thresholds is crucial for inertial confinement fusion.
• The behavior of multiple laser beams is complex and requires detailed analysis.

Purpose of the Study:

• To determine the linear stability of multiple coherent laser beams in inhomogeneous plasma.
• To investigate the role of beam cooperation in two-plasmon-decay instability.
• To analyze the nonlinear evolution of instabilities and their impact on shorter-wavelength modes.

Main Methods:

• Linear stability analysis in three dimensions.
• Investigation of cooperative effects between multiple laser beams.
• Nonlinear calculations using a three-dimensional extended Zakharov model.

Main Results:

• Cooperation between beams leads to absolute instability for long-wavelength decays.
• Shorter-wavelength shared waves saturate convectively.
• The multibeam configuration exhibits the lowest threshold for absolute instability in most cases.
• Langmuir turbulence modifies convective saturation, leading to dominance of shorter-wavelength modes at late times.

Conclusions:

• Multiple laser beams can exhibit complex instability dynamics.
• Absolute instability, driven by beam cooperation, is a significant factor.
• Turbulence plays a crucial role in the saturation and late-time evolution of instabilities.