Chaos aided regime of Laser/Electromagnetic Energy Absorption by plasma

The absorption of laser energy by plasma is of paramount importance for various applications. Collisional and resonant processes are often invoked for this purpose. However, in some contexts (e.g. in vacuum and the JxB heating), the energy transfer occurs even when plasma is collisionless, and there is no resonant process involved. The energy absorption in these cases has been attributed to the sheath electrostatic fields that get generated as the electrons are pulled out in the vacuum from the plasma medium. The origin of irreversibility aiding the absorption, in these cases, remains to be understood. Particle-In-Cell (PIC) simulations using the OSIRIS 4.0 platform have been carried out. The nearby trajectories of lighter electron species involved in the interaction with the laser show exponential separation. This is confirmed by the positive Lyapunov index and also by other characterizations. The observations in these cases are contrasted with the electron cyclotron resonant case, which shows negligible chaos in the electron trajectories despite the energy absorption percentage being high.