Time evolution of fields outside imploding directdrive capsules

1
Time evolution of fields outside imploding
direct-drive capsules
Drive laser
Fredrick Séguin et al., MIT APS
2007
2
Summary
Time-gated radiography shows a rich and complex
evolution of field structures in and around
imploding ICF capsules

• Different field structures appear during
  well-defined time intervals
• The field structures may be connected with
  previous observations
• Shells of charge ? Ablator ion spectrum features
• Radial filaments ? Anisotropies in fluence of
  charged fusion products

Fredrick Séguin et al., MIT APS
2007
3
Collaborators
MIT
U of R LLE
General Atomics
Implosions were supplied by the NLUF program
Fredrick Séguin et al., MIT APS
2007
4
Experiment setup

• Subject capsule
• Spherical
• 20-µm CH shell
• 15-atm H2 fill
• 840-µm OD

• Drive beams
• 40
• 1-ns square
• SSD
• 15 kJ

• Proton backlighter
• 15-MeV p
• 120 ps
• 40 µm FWHM

CR-39 Detector
0.9 cm
30 cm
5
laser
6
Image structures at early times show expanding
charge shells
0.35 ns 0.55 ns
? Fluence
? Energy
Fluence images Darker means more
protons. Energy images Darker means lower
energy, or more matter traversed.
7
Monte Carlo simulations illustrate how the images
have the signature of CH shell charge shells
8
The observed discrete shells of positive
charge may reflect the ablator protons we see in
spectrum peaks
0.35 ns 0.55 ns
9
The observed discrete shells of positive
charge may reflect the ablator protons we see in
spectrum peaks
0.35 ns 0.55 ns

• Our images imply 1011 protons / shell
• Measured spectra typically contain
• 1011 to 1013 protons / peak

D. Hicks, PoP 2001
10
The observed discrete shells of positive
charge may reflect the ablator protons we see in
spectrum peaks
0.35 ns 0.55 ns
D. Hicks, PoP 2001
11
laser
12
Image structures at later times show radial
filaments
0.8 ns 1.2 ns 1.6
ns 1.9 ns
13
Azimuthal lineout
What are the radial filaments?

• Strands of dense matter?
• E fields around filaments of charge?
• B fields around filaments of current?
• Isolated bundles of B?
• More complicated, periodic B fields?

14
Azimuthal lineout
Fluence
What are the radial filaments?

• Strands of dense matter?
• E fields around filaments of charge?
• B fields around filaments of current?
• Isolated bundles of B?
• More complicated, periodic B fields?

15
Azimuthal lineout
Fluence
What are the radial filaments?

• Strands of dense matter?
• E fields around filaments of charge?
• B fields around filaments of current?
• Isolated bundles of B?
• More complicated, periodic B fields?

J
16
Azimuthal lineout
Fluence
What are the radial filaments?

• Strands of dense matter?
• E fields around filaments of charge?
• B fields around filaments of current?
• Isolated bundles of B?
• More complicated, periodic B fields?

B
17
Azimuthal lineout
Fluence
What are the radial filaments?

• Strands of dense matter?
• E fields around filaments of charge?
• B fields around filaments of current?
• Isolated bundles of B?
• More complicated, periodic B fields?

18
Azimuthal lineout
Fluence
Here are the candidates

• Strands of dense matter?
• E fields around filaments of charge 1011
  electrons / µm
• B fields around filaments of current?
• Isolated bundles of B?
• More complicated, periodic B fields B 0.3
  MG

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These fields are probably responsible for
long-wavelength fluence variations seen
previously in charged fusion product self emission
Large-area detectors sometimes see fluence
variations
Fluence
Angle wrt capsule 3.7
Energy
14.7-MeV protons
Séguin et al., PoP (2002)
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Summary
Time-gated radiography shows a rich and complex
evolution of field structures in and around
imploding ICF capsules

• Different field structures appear during
  well-defined time intervals
• The field structures may be connected with
  previous observations
• Shells of charge ? Ablator ion spectrum features
• Radial filaments ? Anisotropies in fluence of
  charged fusion products

Fredrick Séguin et al., MIT APS
2007
21
Time evolution of fields outside imploding
direct-drive capsules
Drive laser
Fredrick Séguin et al., MIT APS
2007