Inverse Bremsstrahlung Absorption

Area of Science:

• Plasma physics
• Fusion energy research
• Laser-plasma interactions

Background:

• Inverse bremsstrahlung absorption is a key process in laser-plasma interactions.
• Current models used in radiation-hydrodynamic simulations often lack necessary corrections.
• Accurate modeling is essential for understanding energy coupling in inertial confinement fusion.

Purpose of the Study:

• To experimentally measure inverse bremsstrahlung absorption in a well-characterized plasma.
• To identify and quantify necessary corrections to existing absorption models.
• To inform more accurate simulations of laser-target coupling in fusion implosions.

Main Methods:

• Transmission measurements through a finite-length plasma.
• Spatially resolved Thomson scattering for plasma characterization.
• Comparison of experimental data with theoretical models, varying absorption components.

Main Results:

• Experimental data requires inclusion of the Langdon effect for accurate modeling.
• A laser-frequency dependence in the Coulomb logarithm is necessary, differing from transport theories.
• A correction for ion screening significantly improves model-data agreement.

Conclusions:

• Standard models for inverse bremsstrahlung absorption in fusion simulations are incomplete.
• Updated models incorporating the Langdon effect, laser-frequency dependence, and ion screening are vital.
• Revising these models will enhance our understanding of laser-target coupling in inertial confinement fusion.