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16Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2019
SOLID DENSITY EFFECTS IN TIME-INTEGRATED X-RAY EMISSION SPECTRA OF ULTRA-RELATIVISTIC LASER PLASMA
A.S. Martynenko12, S.A. Pikuz12, I.Yu. Skobelev1,2
1National Research Nuclear University "MEPhl", Moscow, Russia, e-mail: artmarty@mail.ru
Joint Institute for High Temperatures of the Russian Academy of Sciences, Moscow, Russia,
e-mail: spikuz@gmail.com
Study of the interaction of high-power laser radiation with matter remains a very important and interesting topic for over half a century. Almost every experiment on this topic requires measuring the parameters of generated plasma. One of the main diagnostic tools here is an X-ray spectroscopy of multiply charged ions, which has proved to be very informative, for plasma generation by both relatively long (nanosecond) and short laser pulses. But available diagnostic equipment does not provide enough temporal, and often spatial, resolution to distinguish the signal coming from the region and timeframe of outmost interest, where deposited energy density reaches its maximum.
In our study, we describe an approach that makes it possible to estimate the plasma parameters existing at the time of the main laser pulse arrival, as well as on later stages of plasma expansion. It is based on the analysis of X-ray spectral line profiles in multicharged ion spectra registered in a simple time and spatially integrated mode. Therefore, plasma is considered as a stepwise successive stages with different values of ion (and electron) density electrons, the temperatures and the lifetime for each stage. This approach was described in details in [1].
As an example, specific calculations were made for Lyß Heß lines of Si. This data was used to diagnose plasmas generated by the Vulcan facility (UK) [2] laser ablation of 0.5 p,m Si foil.
In this work, we present an adiabatic expansion model based on numerical calculations. An example results of this model usage for plasma parameters measuring and describing of experiment profiles of laser ablated thin Si foil is shown. Other discussed topic is results of the analysis of continuum lowering effect observed experimentally in the same experiment on Vulcan facility. Finally, an impact of the layered (or so-called "sandwich-type") target structure on its laser heating process is demonstrated. The densities and temperatures of the generated plasma were measured based on the analysis of spectral lines profiles and intensities. The spectra were recorded on a Vulcan facility with a laser flux of up to 1021 W/cm2 and a laser contrast of about 1010. It is shown that a plasma with a close to solid-state density and ultrahigh energy density reaching 5 x 107 J/cm3 is created when targets with a layered structure and high-contrast laser are used.
References
[1] C. N. Danson, et al. 2004 Nucl. Fusion 44, S239.
[2] A. S. Martynenko, et al. 2019 Appl. Phys. B 125, 31.
