Kαfluorescence measurement of relativistic electron transport in the context of fast ignition

Abstract

Electron transport within solid targets, irradiated by a high-intensity short-pulse laser, has been measured by imaging K(alpha) radiation from high- Z layers (Cu, Ti) buried in low- Z (CH, Al) foils. Although the laser spot is approximately 10 microm [full width at half maximum (FWHM)], the electron beam spreads to > or =70 microm FWHM within <20 microm of penetration into an Al target then, at depths >100 microm, diverges with a 40 degree spreading angle. Monte Carlo and analytic models are compared to our data. We find that a Monte Carlo model with a heuristic model for the electron injection gives a reasonable fit with our data.

Effects of target heating on experiments usingKαandKβdiagnostics

“…It allowed getting high-resolution images of Cu Kα sources and has provided much more insight into the physics of electron transport. For instance, the technique has been applied to study electron beam collimation or spreading in matter compressed by cylindrical implosions [26] and to compare transport of fast electrons in insulators vs metals and assess the effects of collective effects and beam filamentation [27]. Indeed it was the very small spectral acceptance of spherical crystals which drove attention to the Kα shift as matter is heated and ionized.…”

Hot surface ionic line emission and cold K-inner shell emission from petawatt-laser-irradiated Cu foil targets

“…4-7 A precise physical understanding of the MeV electron production and transport in dense plasma is crucial for the success of the fast-ignition concept. This has triggered vigorous research effort in both experimental [8][9][10][11][12] and theoretical studies. [13][14][15][16] Strong laser self-generated magnetic and electric fields influence the transport of relativistic electrons in high-energy-density plasmas.…”

Diagnostics of laser-produced plasmas

“…Such a study is fundamental for high energy density physics (HEDP) research [28,29], from experimental astrophysics to fast ignition (FI) studies. In the FI scheme, for example, the compressed deuterium-tritium (DT) fuel is heated by an ultra-intense laser-generated fast electron beam, which carries the laser energy from the critical surface and deposits it in the DT fuel [30].…”