Characterization of suprathermal electrons inside a laser accelerated plasma via highly-resolved K⍺-emission

Abstract

Suprathermal electrons are routinely generated in high-intensity laser produced plasmas via instabilities driven by non-linear laser-plasma interaction. Their accurate characterization is crucial for the performance of inertial confinement fusion as well as for performing experiments in laboratory astrophysics and in general high-energy-density physics. Here, we present studies of non-thermal atomic states excited by suprathermal electrons in kJ-ns-laser produced plasmas. Highly spatially and spectrally resolved X-ray emission from the laser-deflected part of the warm dense Cu foil visualized the hot electrons. A multi-scale two-dimensional hydrodynamic simulation including non-linear laser-plasma interactions and hot electron propagation has provided an input for ab initio non-thermal atomic simulations. The analysis revealed a significant delay between the maximum of laser pulse and presence of suprathermal electrons. Agreement between spectroscopic signatures and simulations demonstrates that combination of advanced high-resolution X-ray spectroscopy and non-thermal atomic physics offers a promising method to characterize suprathermal electrons inside the solid density matter.

Hot electron retention in laser plasma created under terawatt subnanosecond irradiation of Cu targets

“…The number of hot electrons measured by optical diagnostics and the Kα signal is consistent with the internal currents and may be considered in terms of several models of hot electron production [7,[31][32][33]. The main mechanisms discussed in the context of the hot electron generation are resonant absorption and parametric instabilities.…”

Probing ultrafast laser plasma processes inside solids with resonant small-angle X-ray scattering

“…We therefore conclude that the apparent plasma temperature is above 300 eV, which is the necessary temperature to sufficiently ionize copper to open the nitrogen-like Kα resonances at the probe photon energy of 8165 eV [25,27]. However, the plasma evolution is more complex, i.e.…”

“…For resonant scattering, we tuned the energy of the XFEL to an open atomic transition in the plasma, namely to 8165 eV. This is the energy of the Kα transition in nitrogen-like Cu (K1L6 -K2L5) [25]. During the first 300 fs after pump laser irradiation the scattering patterns in those resonant shots exhibited large values of asymmetry compared to the XFEL-only preshots, cf.…”

Enhancement of K-shell spectroscopy for temperature measuring of isochorically heated matter in the sub-keV range

“…based on Ly α and He α analysis [50,54], are not applicable here. Unlike diagnostics by K-shell emission lines, which is normally used for plasma diagnostics in the range of a few tens of electronvolts [16,25,55,56]. So far, however, this method has mainly been used for the diagnosis of WDM with temperatures up to a few tens of electronvolts.…”