Representative Electrons and Energy Exchange in Strong Laser Fields

Enhanced inverse bremsstrahlung heating rates in a strong laser field

“…This approximation, although well-accepted in the physics community, should be revisited in view of recently discovered nonlinear processes such as harmonic generation and above threshold ionization [11,12,13] that have been explained as being due to strong modifications of electron orbits in the laser field during electronion scattering events. Similar nonlinear modifications of particle trajectories have recently been discussed in numerical studies of inverse bremsstrahlung heating rates [14,15]. Our paper continues this analysis; we examine classical electron trajectories that contribute to enhanced plasma heating [14] and discuss their importance for calculations of effective collision frequencies with certain classes of electron distribution functions.…”

“…Similar nonlinear modifications of particle trajectories have recently been discussed in numerical studies of inverse bremsstrahlung heating rates [14,15]. Our paper continues this analysis; we examine classical electron trajectories that contribute to enhanced plasma heating [14] and discuss their importance for calculations of effective collision frequencies with certain classes of electron distribution functions. We also summarize existing theories of inverse bremsstrahlung heating and compare them with results of our test particle calculations.…”

“…His numerical stud-ies have identified stochastic trajectories for electrons with quiver velocity larger than the initial drift velocity. This effect has been elaborated upon in detail in recent studies by Fraiman et al [14,15]. In addition to irregular trajectories that involve quasi-capture of electrons in complicated orbits encircling ions, a phase space analysis has revealed the existence of initial conditions corresponding to large angle correlated collisions with anomalously large energy transfer from the field to particles.…”

“…A simplified description of electron orbits removes the sensitivity of scattering processes to the initial phase of an electric field. However,it has been demonstrated [14] that groups of electrons entering an ion interaction sphere at specific phase can significantly modify the collisional crosssection and the heating rates.…”

“…By using mechanisms such as the Coulomb focusing [11,12], the parachute effect [14] or quasi-capture [18], we analyze strongly modified electron orbits and classify them in terms of their initial phase, impact parameters, and drift velocities. By means of test particle simulations we examine the statistical importance of these trajectories.…”