Fast-electron transport and induced heating in aluminum foils

Abstract

Beams of fast electrons have been generated from the ultra-intense laser interaction (6×1019W cm−2, 40fs) with aluminum foil targets. The dynamics of fast-electron propagation as well as the level of induced in-depth heating have been investigated using the optical emission from the foil’s rear side. The dependence of the emitted signals spectrum and size on the target thickness allowed the identification of the coherent (coherent transition radiation) and incoherent (thermal radiation) mechanisms of the optical emission. We demonstrate a two-temperature energy distribution for the laser-generated fast-electron population: a divergent bulk component (θbulk=35°±5°) with ≈35% of the laser focal spot energy and a 400–600keV temperature, plus a relativistic tail highly collimated (θtail=7°±3°), with a 10MeV temperature and a periodic modulation in microbunches, representing less than 1% of the laser energy. Important yields of thermal emission, observed for targets thinner than 50μm, are consequence of a hot plasma near the front surface. The important heating at shallow depth (<15μm) results from collective mechanisms associated to the fast-electron transport, in particular from a resistive heating upon the neutralizing return current of background electrons. For deeper layers, because of the bulk component divergence, the fast-electron energy losses are dominated by collisions.

Laser-driven cylindrical compression of targets for fast electron transport study in warm and dense plasmas

“…[18][19][20] These pioneering works lead to the establishment of scaling laws for the laser-to-electron energy conversion efficiency, 7,9,10 the electron beam current average velocity, 6 and divergence. 11,12,15,16 Other experiments were devoted to measure the range, the collimation of these electrons, and the way they lose their energy while propagating through solid samples, either foils, 8,9,13,14,17 wire targets, 21,22 or 1D-compressed foils. 18,19,23 Nonetheless, using solid or even 1D-compressed targets strongly limits the area of investigation to low temperatures (<10 eV) and moderate densities (<5g=cm 3 ), which are far from the plasma parameters of the compressed core of a driven ICF target (100 g=cm 3 , 300 eV).…”

“…To understand both points, numerous experiments were realized using solid targets [6][7][8][9][10][11][12][13][14][15] and a few with 1D laser-compressed targets. [18][19][20] These pioneering works lead to the establishment of scaling laws for the laser-to-electron energy conversion efficiency, 7,9,10 the electron beam current average velocity, 6 and divergence.…”

Fast-electron self-collimation in a plasma density gradient

“…[1][2][3][4][5] The most significant application of fast electrons is in the fast ignition (FI) scheme for inertial confinement fusion (ICF). 6 In this context, collimated fast electron beam transport through the overdense plasma and localized energy deposition into the core are essential requirements.…”

Relativistic High-Current Electron-Beam Stopping-Power Characterization in Solids and Plasmas: Collisional Versus Resistive Effects

“…The tested transport media, ranging from solid to warm dense matter, are much denser than the injected REB, being reasonable to assume an efficient neutralization of the injected current (j h ) by a counterstreaming current (j e ) of background thermal electrons (j h % Àj e ). Under these conditions, the numerical description of the REB transport often uses the so-called hybrid approach, where the incident and weakly collisional electrons are modeled kinetically and the highly collisional return current is described as an inertialess fluid [10,13,14].Most of the REB transport experiments carried out up to now have used solid targets [8,15,16]. Only a few entered in the warm dense matter regime driving the targets by shock compression in planar [17][18][19][20] or cylindrical [21,22] geometries.…”

“…Most of the REB transport experiments carried out up to now have used solid targets [8,15,16]. Only a few entered in the warm dense matter regime driving the targets by shock compression in planar [17][18][19][20] or cylindrical [21,22] geometries.…”