Characterization of Inertial Confinement Fusion Capsules Using an XPinch Source

1
Characterization of Inertial Confinement Fusion
Capsules Using an X-Pinch Source

• High Energy Density Physics Summer School
  Berkeley California, August 2005
• D. Haas, E. Shipton, Z. Karim, K. Wagschal, and
  B. DeBono, F.N. Beg
• Department of Mechanical and Aerospace
  Engineering, University of California, San Diego,
  California, USA
• R. Stephens,
• General Atomics, San Diego, California, USA

• Review
• National Ignition Facility (NIF) cryo-ignition
  target requires validation of its
  Deuterium-Tritium (DT) fuel ice layer
• 100 µm thick DT ice layer inside a 100 µm thick
  Be Cu capsule
• The ice layer detection requires phase contrast
  x-ray radiography
• Present sources are too large or require long
  exposure times, resulting in blurred images
• X-pinch is a bright and small enough source to
  eliminate blurring as in current techniques
• E 1-10 keV , Source size lt 1 µm ,
  Duration lt 1 ns
• Images produced from a compact system show
  1-10keV x-ray source capability

Pinhole images The x-ray films below show photon
energies in the 1-10 keV range the first film
(left) is closest to the pinhole camera and the
second film sits behind the first.

• Phase Contrast (PC) Radiography
• In this method of analysis the effect of phase
  contrast is used to discern/emphasize boundaries
  of regions with different densities.
• In a normal shadowgraph one would expect there
  to be a smooth gradient in the pixel intensity
  starting from the center of the shell and moving
  outward, corresponding to the density. In a
  phase contrast shot you expect to see an
  emphasized boundary (i.e. a ring of light at the
  interface) this can be seen in the output of the
  algorithm developed by Dr. Richard Stevens (GA)
  as well as the experimental shots below.

• Advantages of a compact X-pinch
• (Conceived by Jiri Ulshmied in 1984)
• Produces a well localized bright x-ray source
• Allowing high magnifications
• Intense pulsed x-ray source
• Sufficient flux for single shot exposure of
  films
• Variable wire arrangement
• Control of X-ray pulse
• Tailor spectral emission (get lines in desired
  range up to 10 keV)

Radiographic setup At the center of the target
chamber (silver) you can see the crossing of the
wires signaling the position of the x-pinch. The
anode (yellow) and cathode (white) hold the
x-pinch in place with a separation of 1cm. The
capsule to be imaged using phase contrast
radiography is placed at the end of the shell
cone (green). An o-ring seals the cone, chamber,
and camera (dark pink) together. At the back of
the camera a film plate (light pink) can be seen,
the x-ray film is placed between these elements
and is later developed. In addition, an
algorithm was developed by Dr. Richard Stevens
from General Atomics to model the transmission of
x-rays through the ICF capsules.

• Experimental PC Radiography
• For the actual experiment the following
  parameters were used
• 5 µm Tungsten wires
• Cu foil filter 10 µm ? X-rays 5-9 keV
• The simulation was done using 7 keV photons and
  a source size of 5µm
• In both cases the source to object distance was
  5cm and the object to film distance was 46.7cm
  yielding a magnification of 10.2.

Marx band and compact X-pinch apparatus in Farhat
Begs laboratory at UCSD

• Facilities at UCSD
• Peak current 80 kA pulsed risetime of 40
  ns
• Using x-ray diodes we can see that the peak of
  the x-ray pulse occurs some time after the onset
  of the current pulse
• 14 ns (two 5 µm W wire)
• 30 ns (four 5 µm W wire)
• X-ray pulse length (FWHM) 2ns
• Using a 20 µm Al filter
• Marx bank made of 4 0.22µF 50kV capacitors
• The line impedance is 1.5 O
• X-pinch occupies about one square meter
• in the laboratory and can be transported
• An array of metal and polypropylene filters
  were used to selectively attenuate the emitted
  x-ray spectrum. In this experiment 9 different
  filter combination were used. They were chosen
  so that only the edges of their transmission
  bands overlap.
• The filters were placed over the hole array
  below. A description of the filters can be seen
  surrounding the shadowgraph at the top of the
  next column

X-ray film
O ring
Capsule
X-pinch

• Contact Radiography
• For this method the ICF capsules were placed
  directly on the imaging film. This method of
  analysis is used to eliminate all phase contrast
  effects and obtain a baseline absorption profile
  for the shells.
• A theoretical curve was not generated due to
  the thin lens approximation in the algorithm.
  This coupled with the close proximity of the
  shell (which acts as a lens) to the image plane
  would render the results futile.
• For the experiment the following parameters
  were used
• 5 µm Tungsten wires
• Al foil filter 30 µm thick

• Applications
• Ice layer characterization in NIF cryo shells
• Time resolved images at sequenced time steps
  can provide an evolution sequence
• Ice layer melting
• Equation of state studies

40µm

• Future work and ongoing research
• Reproducibility in emission brightness
• Develop X-ray scaling with current up to 300 kA
• Select wire material for optimum emission lines
• Control intervals in multiple pinch systems

Notice no bright ring at density interface