Hot-Electron Temperature and Laser-Light Absorption in Fast Ignition

Abstract

Experimental data [F. N. Beg, Phys. Plasmas 4, 447 (1997)10.1063/1.872103] indicate that for intense short-pulse laser-solid interactions at intensities up to 5 x 10(18) W cm(-2) the hot-electron temperature proportional, variant(Ilambda(2)) (1/3). A fully relativistic analytic model based on energy and momentum conservation laws for the laser interaction with an overdense plasma is presented here. A general formula for the hot-electron temperature is found that closely agrees with the experimental scaling over the relevant intensity range. This scaling is much lower than ponderomotive scaling. Examination of the electron forward displacement compared to the collisionless skin depth shows that electrons experience only a fraction of a laser-light period before being accelerated forward beyond the laser light's penetration region. Inclusion of backscattered light in a modified model indicates that light absorption approaches 80%-90% for intensity >10(19) W cm(-2).

Effects of filamentation instability on the divergence of relativistic electrons driven by ultraintense laser pulses

“…14MeV, which can be attributed to the fact that the electrons only interact with the laser pulse during a fraction of the laser cycle before being accelerated forward beyond the laser penetration region due to the relatively short preplasma scale-length employed in our simulation 41 .…”

Theory of fast electron transport for fast ignition

“…However, it gives electron energies well over the desired values around 2 MeV for the laser intensities typical of the FI regime (>10 20 Wcm −2 ). Chrisman et al (Chrisman et al 2008), Haines et al (Haines et al 2009) and Kluge et al (Kluge et al 2011) have recently reported scaling laws that provide electron energies lower than those obtained by the ponderomotive scaling and of the same order than those predicted by the Beg's law. In principle, this is very favourable for FI because the optimal electron range is about 1.2 g/cm 2 (Atzeni 1999), which corresponds to an electron energy lower than 2 MeV ) and a laser intensity about 2.4×10 20 Wcm −2 assuming the Beg's scaling.…”

On the origin of super-hot electrons from intense laser interactions with solid targets having moderate scale length preformed plasmas

“…This electron population can often be characterized by a so-called "slope temperature" approximately given by the "ponderomotive energy" kT p kT p = m e c 2 1 + Iλ 2 [ W µm 2 cm 2 ] 1.37 * 10 18 − 1 (1) where m e is the electron mass, c is the speed of light, and λ is the laser wavelength. This scaling has been the subject of experimental 10,17 , computational 9 , and theoretical 18 efforts.…”