Examination of Scattering Volume Aligment in Thomson Scattering Off of a Shock Front in Argon Page: 3 of 6
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Examination of scattering volume alignment in Thomson scattering off
of a shock front in argon
A.B. Reighardi, D.H. Froulai, R.P. Drake2, J.S. Rossi, L. Divol
Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA, 94550, USA
2 AOSS Department, University of Michigan, 2455 Hayward St, Ann Arbor, MI, 48109, USA
Thomson scattering in argon gas successfully probed the region of plasma just behind the
shock front. The instantaneous shock velocity can be inferred from the duration of the
signal, taking into account the size and shape of the scattering volume. Possible
misalignment of the probe beam and spectrometer slits greatly affects the size and shape ofthe scattering volume, and therefore affects
velocity.the calculation of the instantaneous shock
2. Experimental Design
Thomson scattering is a powerful
technique for plasma diagnosis.
Thomson-scattering measurements use a
coherent light source with an initial
wavelength and wavenumber (Ao and ko) to
scatter light from plasma electrons with a
scattering wavevector k [1],[2]. In the
collective regime, where the scattered light
probes many Debye lengths (AD) in a plasma
(so 1/(kAD) =a >1 ), strong signals are
observed when the probed electrons have a
resonant collective response (e.g. from
ion-acoustic waves, when T,/ZT <a , or
from electron plasma waves) [3]. Many
experiments have used Thomson scattering
(TS) to extract fundamental plasma properties
from the scattered frequency spectrum, and
TS is now widely used as a diagnostic in
fusion research [4-6].
Thomson scattering was successfully
implemented to measure flow velocity and
electron temperature in a driven shock in
argon gas [7]. Careful analysis showed that
the size and shape of the scattering volume
significantly affected conclusions made about
other parameters in the system.
A shock velocity was calculated based
on the duration of the scattered light signal.
However, the following calculations show
that the estimate of the shock velocity
depends heavily on the alignment of the
system. Without better understanding of the
relative alignment of the probe beam with the
collection diagnostic slits, the error bars on
the shock velocity calculation will be very
large.Figure 1 shows the setup of the
experiment, the scattering vector diagram, and
a three-dimensional image of the scattering
volume and shock front. A more detailed
description can be found in Reighard et al.
[8].
(a) Ar gas cell Scattered light
exit hole
Omega _ * /
Drivse-N a
Bems Be . "Gas
isk fill
_ _ _ k tube
kiws. shock directon 4w probe
entry hole
79"
kpro kScattering
(b) volume
Shock Scattering
front volume
Sock
direction
Figure 1: Target geometry and setup. a) 2D drawing of
target features. This gas-tight target was filled with 1.1
ATM argon gas shortly before the shot. b) Scattering
vector diagram. The probed ion-acoustic wave was
parallel to the shock propagation direction. c) 3D
image of scattering volume, showing the relative size
and direction of the shock.1. Introduction
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Reighard, A. B.; Froula, D. H.; Drake, R. P.; Ross, J. S. & Divol, L. Examination of Scattering Volume Aligment in Thomson Scattering Off of a Shock Front in Argon, article, July 26, 2007; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc897016/m1/3/: accessed March 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.