Effect of lateral radiative losses on radiative shock propagation M. Busquet a, * , E. Audit b , M. Gonza ´lez b , C. Stehle ´ a , F. Thais b , O. Acefa , D. Bauduin a , P. Barroso a , B. Rus c , M. Kozlova c , J. Polan c , T. Mocekc a LERMA, Observatoire de Paris, UPMC, CNRS, Place Jules Janssen, 92190 Meudon, France b Service d’Astrophysique, CEA-Saclay, Gif-sur-Yvette, France c Institute of Physics, PALS Center, Prague, Czech Republic Available online 4 February 2007 Abstract Experimental and numerical studies of radiative shocks, of interest as scaled astrophysical objects, have been performed. Experiments were conducted at the PALS facility in Prague with a xenon filled mini-shock tube using a laser accelerated plastic pusher. Numerical simulations ofthe hydrodynamics including radiation effects have been performed with the 3D code HERACLES. Measurements have been made of the elec- tronic density of the shocked gas and of the time history of the position of the radiative precursor. Simulations and experimental results show good agreement when lateral radiative losses are taken into account, including a wall albedo of 40%. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Radiative shocks; Laboratory astrophysics 1. Introduction Radiat ive shock s can be defi ned as shocks of suf fici ent strength that radiation arising from the compressed layer will signifi cantly alter the structure of the shock itself, with radia tive cooling of the downs tre am reg ion and radiat ion heating and ion- izing of a pre cur sor. Radiativesho cks are obs erved aro und ast ro- nomi cal objec ts in a wi de vari ety of en vi ronments, e.g., supern ovae in the ir radiativecooling sta ge, bow sho cks of stel lar jet in galact ic mediu m, collision of interst ellar clouds. Under- standing the underlying physical phenomena is important for the analysis of the time-dependence of these events. However, each astronomical observation is unique and almost fixed in time. Since the late 80s [1] there have been efforts by several groups to scale these astrophysical events to accessible labora- tory conditions for analytical and/or parametric studies. In this study we explore radiative shocks produced by a laser in mini- shock tube. [2e6]. In the experiment we performed on the PALS laser facility in Prague, the aim was to study the time his tory for a muc h longer time tha n in the experi me nt per for med inLULI [5] studyi ng theslo win g down of the rad iati ve pre cursor due to lateral radiative losses. As radiation emissivities and opacities increase with the atomic number, we select xenon for the medium in which the shock will propagate. 2. Target design, experimental setup and results Thetarge ts aredesign ed as min i-s hoc k-t ube s ma de of a 4 mm long glass capillary with a square section of 700 mm filled with xenon at 0. 2 bar. A 1 cm 3 res ervoir pre ven ts reduction of the xe- non pressure during the 20 min between the filling and the laser shot. A 10 mm CH foil is glued at one end of the capillary and is coated by a 0.5 mm layer of gold facin g the xenon gas that pre- vents pre hea ting the gas by rad iation and ele ctr ons cre ate d in the expand ing lase r cre ate d cor ona . This foi l is irradiated by thefre- quencytripled( l¼ 438 mm)iodine700 JPALSlaserwithapulse dur ation of 0.3 5 ns,which is smooth ed wit h a PZP- type ran dom phase plate to have a uniform focal spot ofw650 mm with a re- sulting intensity of up to 1.5 Â 10 14 W/cm 2 on target. Laser ab- lati on of thefront surfac e accele ratethe CH/Au pus her by roc ket effect and launches a strong shock in the gas. The laser pulse is * Corresponding author. E-mail address: [email protected](M. Busquet). 1574-1818/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.hedp.2007.01.002 High Energy Density Physics 3 (2007) 8e11 www.elsevier.com/locate/hedp
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8/3/2019 M. Busquet et al- Effect of lateral radiative losses on radiative shock propagation
Effect of lateral radiative losses on radiative shock propagation
M. Busquet a,*, E. Audit b, M. Gonzalez b, C. Stehle a, F. Thais b, O. Acef a, D. Bauduin a,P. Barroso a, B. Rus c, M. Kozlova c, J. Polan c, T. Mocek c
a LERMA, Observatoire de Paris, UPMC, CNRS, Place Jules Janssen, 92190 Meudon, Franceb Service d’Astrophysique, CEA-Saclay, Gif-sur-Yvette, Francec Institute of Physics, PALS Center, Prague, Czech Republic
Available online 4 February 2007
Abstract
Experimental and numerical studies of radiative shocks, of interest as scaled astrophysical objects, have been performed. Experiments were
conducted at the PALS facility in Prague with a xenon filled mini-shock tube using a laser accelerated plastic pusher. Numerical simulations of
the hydrodynamics including radiation effects have been performed with the 3D code HERACLES. Measurements have been made of the elec-
tronic density of the shocked gas and of the time history of the position of the radiative precursor. Simulations and experimental results show
good agreement when lateral radiative losses are taken into account, including a wall albedo of 40%.
stationary limit, which happens after the region of interest. On
the contrary, the shock is very sensitive to the geometry (pla-
nar or spherical expansion) and to the lateral radiative los-
ses.[13] To address both points we use the hydrocode
HERACLES [14,15] developed in CEA-Service d’Astrophysi-
que. HERACLES is a three dimensional (3D) Eulerian hydro-
code including a gray M1 moment radiative transfer method,
and a state of art opacity for the low temperature xenon.[16]
This method allows a good angular description of the radiative
transfer. In fact it preserve shadows in contrast to usual P1 dif-fusion method [14,15,17]. As the pusher can be approximated
as a constant velocity wall, we use a constant velocity (at
65 km/s) at the bottom boundary of the simulation box. The
glass cell is reproduced with a non-moving solid wall for hy-
drodynamics, and a constant partial reflectivity (or albedo) R
for X-rays. HERACLES can also be used in two dimensional
(2D) configuration to save computing time. We have tested for
one set of conditions that the evolution of the radiative shock
computed in 3D mode in a square cell is well reproduced using
a 2D cylindrical geometry; thus, subsequent parametric studies
have been performed in 2D mode. A typical result of density
and temperature map at a given time is shown in Fig. 4. Fig. 4
displays half section of the cell, the symmetry axis on the left,the wall interface on the right, and the pusher interface at bot-
tom. The shock, shown at 1.7 mm from initial position of
pusher, remains planar, see Fig. 4a; although the density is
higher close to the glass wall, which is on the right in Fig. 4b,
as radiative losses induce decrease of temperature close to the
wall, thus increase compression. The temperature map in
Fig. 4b shows the radiative precursor, heated from radiation
emitted from the shock, which is also colder and denser close
to the wall.
The position of the shock and the precursor front is plotted as
a function of time in Fig. 5 for different value of albedo R. The
parabolic shape is a signature of the damping of the radiative
precursor through energy losses across the walls. At longertime, an asymptotic, stationary limit would finally be found
where the losses will be balanced by feeding from the shock,
with a constant distance between the shock and the precursor.
Here the rate of slowing down is related to the amount of losses.
Note that an albedo of 40% fits the experimental precursor front
position at all times and this is true evenfor slight adjustments of
the distance from the pusher, i.e., the Z -axis. This demonstrates
the effect of lateral radiative losses and provides the amount of
energy lost (here 60% of the X-rays hitting thewall). Finally, the
computed electronic densities in the precursor (1.2e1.3Â
1019 cmÀ3) agree with the measured value (Section 2).
4. Conclusion
We have been able to extract the essential information
about the radiative precursor, electronic density and position
of the front versus time from initial experiments at the
Fig. 3. Mesh positions versus time computed with the 1D Lagrangian codeMULTI for our conditions. Laser shines the pusher from the left.
Fig. 4. Half section of density (a) and temperature (b) maps computed with HERACLES in a cylindrical geometry. Ordinates are distances from pusher and
abscissas are distances from the symmetry axis. Left of plots are then the center of the cell, right of plots are the cell wall. Bottom is the pusher interface.
10 M. Busquet et al. / High Energy Density Physics 3 (2007) 8e11
8/3/2019 M. Busquet et al- Effect of lateral radiative losses on radiative shock propagation