Effects of target heating on experiments usingKαandKβdiagnostics

Abstract

We describe the impact of heating and ionization on emission from the target of Kα and Kβ radiation induced by the propagation of hot electrons generated by laser-matter interaction. We consider copper as a test case and, starting from basic principles, we calculate the changes in emission wavelength, ionization cross section, and fluorescence yield as Cu is progressively ionized. We have finally considered the more realistic case when hot electrons have a distribution of energies with average energies of 50 and 500 keV (representative respectively of "shock ignition" and of "fast ignition" experiments) and in which the ions are distributed according to ionization equilibrium. In addition, by confronting our theoretical calculations with existing data, we demonstrate that this study offers a generic theoretical background for temperature diagnostics in laser-plasma interactions.

K-α x-ray measurements and their applicability for fast electron generation and transport studies in ultrashort intense laser foil interaction

“…T f is dependent on the dominant laser absorption mechanism, and for J × B heating, T f scales as ∼I L 0.5 for I ≫ 10 18 W cm −2 . Considering the weak dependence of η f for the present intensity variation range, i.e., for constant η f , the scaling becomes ∼I L 0.86 [35]. The experimentally observed scaling (∼I L 0.90 ) is in agreement with the expected scaling, suggesting that the x-ray emission is mainly due to the refluxing electrons generated by J × B heating.…”

“…The conversion efficiency of the laser energy into fast electrons can be estimated by comparing the measured absolute flux of K-α x-ray radiation with that expected from numerical models or spectroscopic code. The fast electron energy distribution is measured by the K-α x-ray radiation from a layered target comprising a transport layer followed by a fluorescence layer [7,22,26,34,35]. In these experiments, K-α x-ray is measured as a function of the transport layer thickness and the fast electron energy distribution is inferred by comparing it with numerical simulations.…”

Experimental characterization of hot-electron emission and shock dynamics in the context of the shock ignition approach to inertial confinement fusion

“…The emission lines, in the case of cold material, are at 8.0478 keV for K α 1 and at 8.0278 keV for K α 2. The heating and the consequent ionization of the material due to the presence of hot-electrons in- duces a wavelength shift of the emission that results in broadening of the peaks [32]. Since the position of the HRS pointed to the front side of the target, the measured temperatures are referred to the first layers of the plate.…”