Synchrotron-based high-pressure research in materials science Page: 2 of 5
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SPECTRAL OUTPUT OF Z-MACHINE IMPLOSIONS
G. C. Idzorek, R. E. Chrien, D. L. Peterson, R. G. Watt
Los Alamos National Laboratory'
Los Alamos, New Mexico, USA
G. A. Chandler, D. L. Fehl, T. W. L. Sanford
Sandia National Laboratories*
Albuquerque, New Mexico, USAAbstract
I. THE Z-MACHINE
Sandia National Laboratories Z-machine has developed
into a reproducible, high power (>200 TW), high
temperature (>200 eV) driver for radiation physics
experiments.
Imploding cylindrical wire arrays on the Z-machine
produce a radiation source with a bolometric temperature
of about 200 eV. By surrounding the z-pinch implosion
with a vacuum hohlraum a nearly Planckian source of
about 140 eV temperature is created with peak radiation
powers of about 200 terawatts and integrated energy of 2
megajoules or more. In this energy rich environment we
can field a dozen experiments all being driven by an
identical source.
In addition to 'standard' vacuum hohlraums we also
use dynamic hohlraums consisting of two nested wire
arrays converging onto an axially centered foam cylinder.
Radiation flowing from the ends on the cylinder indicates
a Planckian source temperature well over 200 eV. Only
two experiments can be fielded on a dynamic hohlraum
(one on each end) but the higher source temperature
justifies the added complexity of the set-up.
We routinely use arrays of filtered silicon photodiodes
(SiD) and filtered photocathode x-ray diodes (XRD) to
determine the temperature of the source.
Three different techniques for unfolding spectra from
the XRD and SiD detector data are being used. They are:
1) Treat each detector independently and find the
Planckian temperature for a given source size and solid
angle that would give the measured detector signal, 2)
Use all detector signals and detector spectral responses
simultaneously and find a spectrum that best fits the
observed data, 3) Use all detector signals and averaged
detector spectral responses and find a histogram
spectrum that best fits the observed data. When used as
complementary set of analysis tools these techniques
generate remarkably consistent results showing nearly
Planckian behavior on our vacuum hohlraum
experiments.Sandia National Laboratories Z-machine pulsed power
facility [1] consists of 36 Marx modules driving 36 pulse-
forming lines which converge onto magnetically insulated
transmission lines connected to a cylindrical wire array.
The Marx generators are charged to 90 kV and when fired
dump a 5 MV pulse into the pulse forming lines. The
pulse lines convert the 1.2 microsecond, 15 TW Marx
pulses into 100 nanosecond, 45 TW electrical pulses and
synchronize the pulses to arrive simultaneously at the
wire array target. In our vacuum hohlraum source the
target consists of 300 ten-micron diameter tungsten wires
symmetrically arranged in a 20 mm diameter cylinder 1
cm high. The converging electrical pulses reach a peak
current of 20 MA in the wire array which then implodes
radially due to the J x B forces on the vaporized wires.
When the wire plasma converges on axis the kinetic
energy is converted to heat producing temperatures of
about 200 eV. The 11.4 MJ of stored electrical energy in
the Marx modules is converted to about 2 MJ of radiation
with peak radiation power in the 200 TW range [2].
II. VACUUM HOHLRAUM SOURCE
Surrounding the 20 mm wire array is a 24 mm diameter
gold plated stainless-steel hohlraum can that absorbs the
wire array pinch radiation and then re-emits it in a nearly
Planckian spectrum with a temperature around 140 eV. A
two dimensional radiation magnetohydrodynamic
calculation of a wire implosion implosion inside a gold
hohlraum is shown in figure 1. Diagnostic holes in the can
wall are viewed with arrays of well-characterized x-ray
filtered silicon photodiodes (SiD) [3] and carbon cathode
photoemissive X-Ray Diodes (XRD) [4].' Los Alamos National Laboratory is operated by the University of California for the U. S. Department of Energy under
contract W-7405-ENG-36.
* Sandia National Laboratories is operated by Sandia Corporation, a Lockheed Martin Company, for the U. S.
Department of Energy under contract DE-AC04-94AL85000.
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Synchrotron-based high-pressure research in materials science, article, Date Unknown; [Los Alamos, New Mexico]. (https://digital.library.unt.edu/ark:/67531/metadc934686/m1/2/: accessed May 10, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.