CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
© 2002 American Institute of Physics 0-7354-0068-7/02/$ 19.00
HIGH INTENSITY X-RAY COUPLING TO METEORITE TARGETS
J. L. Remo1 and M. D. Furnish2
1
Harvard Smithsonian Center for Astrophysics, Planetary Science Division, Mail Stop 18, 60 Garden
Street, Cambridge Massachusetts 02138.
2
MS 1168, Sandia National Laboratories, P.O. Box 5800, Albuquerque NM87185-1168
Abstract. Experimental results of shock wave effects from high intensity (70 -215 GW) soft X-ray
irradiation on several meteorite targets are presented. From inhomogeneous materials, useful data on
particle velocity and in-situ' velocity were obtained and permitted the computation of the yield stress,
shock wave velocity, compression, as well as the momentum and energy coupling coefficients.
empirical understanding of the high pressure
thermodynamics and material properties, such as
material strength and isentropic compression and
decompression of several different meteorite
materials.
Of particular importance for this research is the
determination of the momentum coupling
coefficient, CM, for the NEO material categories
when subjected to intense (soft) X-ray irradiation.
Knowledge of CM is absolutely necessary to
calculate orbital adjustments of potentially
hazardous NEOs. Another objective is to gain an
understanding of the EOS and constitutive
properties of the different meteorite categories,
which will help in modeling the dynamic response
of asteroids to a high energy density interaction.
These objectives will be somewhat difficult to
achieve due to the inhomogeneous and irregular
nature of these naturally occurring materials.
Nonetheless, the results of the initial experiments
appear to be encouraging. It is noted that this
experimental approach provides significant
advances towards understanding high energy
density X-ray coupling to heterogeneous materials
in general as well as for momentum transfer,
heating, phase changes, and radiative scattering
interactions with materials encountered in space.
Other applications include the interpretation of
momentum coupling and related interactions from
INTRODUCTION
High intensity (> 200 GW/cm2) X-ray pulses
generated from an exploding wire/hohlraum
configuration at the Sandia Z-machine have been
used to generate shock wave driven high pressures
(multi megabar range) on various test samples and
structures in order to determine the equation of
state (EOS) and constitutive properties of materials
at these high pressures1. Following this lead, we
report on the utilization of the Sandia Z-machine to
irradiate several meteorite specimens with soft Xrays (Plankian and line emission) in order to study
the meteorite targets' response to high rates of
dynamic loading provided by the ablation driven
shock waves and the ensuing high pressure
generation throughout the target sample. Previous
work on these same meteorite targets used pulsed
lasers to generate pressures from 0.7 to 11 GPa2,
the results of which provided significant insights
into the response of different meteorite material
categories3 to high strain rate dynamic loading.
The rationale for these Z-pinch experiments is
an outgrowth of a suggestion in 19954 that soft Xray hohlraums be used to provide experimental
approaches
to
understanding
how
the
microstructures of near-earth objects (NEOs)
respond to high pressure and loading conditions,
using meteorites as asteroid analogs. This current
series of experiments is anticipated to lead to an
1410
strong X-radiation with primordial solar nebula
material and the interstellar medium.
EXPERIMENT RESULTS
Velocity Measurements
DESCRIPTION OF THE SANDIA ZrPINCH
EXPERIMENT
Observed velocity profiles are shown in Figure
2, and appear to correspond to attenuating waves.
In most cases dual-delay VISAR (velocity
interferometry) instrumentation was used to
measure velocity histories.
The experimental objective is to demonstrate
the feasibility of obtaining reliable measurements
of shock Hugoniots for meteorite materials
experiencing ablative loading in order to determine
their EOS and momentum coupling coefficients.
The Sandia Z machine is a 4.5 MV accelerator
using Marx generators to store capacitive energies
of about 11MJ which can produce currents of about
20 MA within the thin conductive wires between
the anode and cathode (see Fig. 1) over a time scale
of about 100 ns. Usually, a few hundred wires are
used to generate the Z pinch source within the
primary hohlraum whose typical diameters are 2 5 cm with 1- 2 cm heights and contains the
radiation produced by the imploded pinch. After
implosion of a (tungsten) wire array, a Z pinch
Planckian-like radiation source with a 2 mm
diameter is formed on axis within the primary
hohlraum with temperatures of about 150 eV.
80
Refractory Chondrite
> Octahedrite
r
Meso-Siderite
]ondrite
60
40
20
0.8
0.9
1
Time (j^s; zero arbitrary)
1.1
FIGURE 2. Observed velocity histories.
Shocked States
1 mm sample X*ray drive
Fiber OptkA
I
from laser
Wire Array
Slotted
Hohlraum
Basic experimental results for high intensity soft
X-ray coupling to meteorites targets are
summarized in Table 1, which lists estimated
stress, P, in gigapascals (GPa), the observed
(VISAR) particle velocity, Vp, and the inferred (in
situ) velocity, V.
Anode
Plate
Fiber Optic
to VISAR
TABLE 1. Shocked states achieved in present tests.
FeNi
Refr.
Meso
Sample CVS Allende Chond siderite (Og)
LIF Window
FIGURE 1. Configuration of Z-pinch experiment. Components
on the right side of the figure are cylindrically symmetric about
the heavy line at the center of the array (location of the pinch).
X-ray radiation is delivered to the sample through
slots in the primary hohlraum. For the present
experiments, no radiation filtration was performed.
Instrumentation used to diagnose the sample
response was comprised of a VISAR
interferometer measuring the velocity of a spot at
the back of the sample. For details of Z pinch
instrumentation available, one is referred to many
sources such as Konrad5.
Testtt
Sample
POPa
VP m/s
Vm/s
D km/s
Z675
1/2
0.5
33
30
5.73
(LL6) Vaca- Odessa
Tuxtuac muerta
Z636
Z676
Z676
Z675
2/1
8/1
1/1
3/1
1.20
0.5
1.0
0.53
55
64
33
39
40
30
58
39
4.16
5.71
5.73
3.78
Po
2.91
2.91
3.02
3.60
7.21
1.006
1.006
1.012
1.013
1.013
3
g/cm
p/p0
1411
The shock wave velocity D may be obtained
from the momentum conservation relation:
P=poDV,
Here, D, V, I and P are (respectively) the shock
velocity, the in-situ material velocity, the radiation
intensity, and the resultant pressure.
The energy coupling coefficient, CE, is the
fraction of original input energy coupled to the
target such that,
(1)
where p0 is the pre-shock density. The post shock
density, /?, can be obtained from the mass
conservation equation:
= p0D/(D-V)
(4)
where F is the (time-integrated) X-ray energy
incident on the target (fluence), ESam is the kinetic
energy imparted to the target sample, and d is the
sample thickness.
The Z-pinch is not a point source at these
ranges R from the pinch, but is intermediate
between point and cylindrical, so the intensity
varies approximately as R"3/2.
In the impulse method of calculating coupling
coefficients, the x-ray pulse is taken as providing a
brief impulse which accelerates the plate to a
limiting velocity taken as the in-situ material
velocity just below the monitored surface. Thus,
(2)
All of the particle velocities listed in Table 1
appear to be attenuating (transient) waves, with the
overtaking release wave corresponding to the
decay of the Z -pinch emission. These particle
velocities are corrected for the mechanical effect of
the windows (which reduces the particle velocity at
the interface observed by VISAR by 30 - 50%.
The windows were necessary to preserve the
reflecting
surface,
allowing the velocity
measurements.
The inferred in-situ velocity can be interpreted
as representing a lower bound for the ultimate
velocity a thin slice of sample material would have
reached under an extended X-ray pulse. Although
peak stress is relatively low for natural (meteorite)
materials, as compared to pure materials, they
nonetheless possess high shock velocities because
their particle velocity is very low as compared to
pure materials.
CM.I = Po (d)D V/F.
(5)
TABLE 2. Computation of the momentum, CM,
and energy, CE, coupling coefficients
Sample
Momentum and Energy Coupling
Coefficients
Test#
Sample
d mm*
E kJ
Rcm
Fluence
J/cm2
r(ns)
I
GW/cm2
CM,SS
s/mxlO'5
Momentum and energy coupling coefficients
may be calculated by two methods. The first (SS)
treats the x-ray drive as a steady input stress; the
second (I), as an impulse. The best value for
application to problems is probably intermediate
between the values thereby computed. Inputs and
results from both methods are shown in Table 2.
In the steady input stress method, the input
intensity / is taken as a constant. The momentum
coupling coefficient, representing the momentum
uptake of the target, is the ratio of the pressure P to
the radiation intensity /:
CM,ss= P/I = PoDV/I
(d) V2 /EIn,
CE =
Z675
1/2
1.012
867
14
352
FeNi
Refr.
Meso
Chond siderite (Og)
(LL6) Vaca- Odessa
Tuxtua muerta
c
Z636
Z676
Z676
Z675
1/1
2/1
8/1
3/1
1.014
1.508
1.01
1.013
1187
1116
867
1116
14
10
14
14
945
453
453
352
5.03
70
5.03
90
5.03
90
5.03
70
4.40
215
0.050
0.031
0.078
0.080
0.054
2.51
1.56
3.91
4.0
4.6
Chondrite
(CV3)
Allende
s/mxlO'5
0.38
0.19
1.13
0.79
0.92
xlO'
*Radii of all targets was about 3 mm, yielding an area
of about 0.283 cm2. The volume of each target was
0.029 cm3 except for sample 8 which was 0.038 cm
(3)
1412
Comparison with Laser Results
combination of thermal and line emissions from the
Z-pinch. Both momentum and energy coupling
coefficients were smaller than for 1 micron laser
light (by approximately an order of magnitude). It
will be necessary to establish coupling behavior
with only line emission, or only blackbody
emission, to better understand the physics of this
system.
Future experiments of value would
include those using coupons of pure metal and
homogeneous silicates at comparable fluences
(there exist data for much higher X-ray fluences as
well as for comparable laser fluences).
In analogous experiments conducted with a
laser2, the coupling coefficients may be worked out
in a parallel manner. Samples were subjected to a
22 J/cm2 fluence of 1054 nm Nd-glass laser light
(approx. 20 ns). The configuration is shown in Fig.
3. Note that the presence of the quartz window
substantially increases the coupling coefficients.
0.8- 1mm
Signal to
VlSAR
Laser
Quartz
LiF
Window
ACKNOWLEDGEMENTS
Window
This work was supported in part by Sandia
National Laboratories, a Lockheed Martin
Company, for the United States Department of
Energy under contract DE-AC04-94-AL85000.
FIGURE 3. Configuration of laser experiment.
Experiment parameters and inferred coupling
coefficients are shown in Table 3. The method for
calculating the coupling coefficients follows Eqs. 4
and 5 (i.e. impulse assumption). It is worth noting
that the momentum coupling coefficients are
roughly 50x those obtained for the soft X-rays
(impulse calculation), and the energy coupling
coefficients are 20x those from the soft X-rays.
REFERENCES
1.
TABLE 3. Computation of the momentum, CM,
and energy, CE, coupling coefficients from the laser
experiments
Sample
Testtt
Odessa
(Fe/Ni)
N20
C
D
7.2
7.2
Gibeon
(Fe/Ni)
A1A
Mesosiderite
A1B
LL6
Stony
A2A
7.2
3.6
3.02
Density
g/cm3
d mm*
Vpm/s
Vm/s
CMJs/m
1.0
64
48
157
1.0
72
54
177
0.8
42
31
81
1.0
50
45
74
1.0
42
40
55
CE
38
48
13
17
11
S
2.
3.
4
5.
CONCLUSIONS
Five parasitic experiments were conducted to
begin to assess X-ray coupling for representative
meteorite compositions.
This study used a
1413
(e.g.) M. D. Furnish , R. J. Lawrence, C. A. Hall, J.
R. Asay, D. L. Barker, G. A. Mize, E. A. Marsh and
M. A. Bernard, Radiation-driven shock and debris
propagation down a partitioned pipe, Int. J. Impact
Engrg., 26, 189-200,2001.
Remo, J. L., High-Power-Pulsed 1054 nm Laser
Induced Shock Pressure and Momentum and
Energy Coupling to Iron and Stony Meteorites,
Lasers and Particle Beams, 17 25-44, 1999.
Remo, J. L., Classifying and Modeling NEO
Materials Properties and Interactions in " Hazards
Due to Comets and Asteroids," T. Gehrels, ed.,
551-596, Univ. Arizona Press, Tucson 1994.
Hammerling, P. and Remo, J. L., Laboratory
Planetary Physics, in "Near Earth Objects; The
United Nations International Conference," J. L.
Remo ed. 585 - 602, NY. Acad. Sci, NY 1997.
Konrad, C. R, J. R. Asay, C. A. Hall, W. M. Trott,
B. F. Clark, G. A. Chandler, K. G. Holland, K. J.
Fleming, J. S. Lash, L. C. Chhabildas and T. G.
Trucano, Use of Z-pinch sources for high-pressure
shock wave studies, Sandia National Laboratories
report, SAND98-0047, 1998.