Plasma Physics Seminar| Katia Falk, Helmholtz-Zentrum Dresden-Rossendorf

Wednesday, December 9, 2020
10:00 a.m.
via ZOOM
Taylor Prendergast
301 405 4951
tprender@umd.edu

Speaker: Katia Falk

Speaker's Institution: Helmholtz-Zentrum Dresden-Rossendorf

Title: "Development of ultra-fast laser-driven x-ray probes with high intensity for Warm Dense Matter probing"

Abstract: 

Warm dense matter (WDM) is an intermediate state of matter at the
transition from a solid to an ideal plasma with characteristic
medium-to-high temperatures (0.1-100 eV), solid densities and pressures
>Mbar. It is common inside the cores of large planets, crusts of ageing
stars, laser-matter interactions or as a transition state during capsule
implosion in inertial confinement fusion (ICF). Under such conditions
quantum degeneracy and ion coupling are significant making the theoretical
description of WDM very challenging. WDM is also extremely difficult to
diagnose experimentally due to its high density and relatively low
temperature, thus active x-ray probes are required. Recently, ultra-fast
probing with x-ray sources for radiography and x-ray Thomson scattering is
now of a great interest, in particular to study transport properties of WDM
in relevance to astrophysical phenomena, has become of a great interest to
the community. Laser-driven K-alpha sources have proven to be excellent for
this purpose, in particular for high energy laser experiments, however due
to relatively low conversion efficiency in comparison to He-alpha and
Ly-alpha sources, their applicability is limited. Recent theoretical
studies have shown that adding micro-scale structures to the laser-driven
solid foils generating the x-rays can significantly enhance the flux of
such sources. So far, experimental studies of the use of these
micro-structured targets have been limited. In this talk, recent
experiments developing bright x-ray sources driven by short-pulse lasers
will be presented and potential applications outlined.

Energetic particle generation is an important component of a variety of
astrophysical systems, from seed particle generation in shocks to the
heating of the solar wind. It has been shown that magnetic pumping is an
efficient mechanism for heating thermal particles, using the largest-scale
magnetic fluctuations. Here we show that when magnetic pumping is extended
to a spatially-varying magnetic flux tube, magnetic trapping of
superthermal particles renders pumping an effective energization method for
particles moving faster than the speed of the waves and naturally generates
power-law distributions. We validated the theory by spacecraft observations
of the strong, compressional magnetic fluctuations near the Earth's bow
shock from the Magnetospheric Multiscale mission. Given the ubiquity of
magnetic fluctuations in different astrophysical systems, this mechanism
has the potential to be transformative to our understanding of how the most
energetic particles in the universe are generated.

Lichko, E., Egedal, J. Magnetic pumping model for energizing superthermal
particles applied to observations of the Earth's bow shock. Nat Commun 11,
2942 (2020). https://doi.org/10.1038/s41467-020-16660-4

Audience: Campus 

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