High R asymmetry seen in 24 atm D3He shots

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Proton Radiography of Dynamic Electric and
Magnetic Fields in Laser-Produced
High-Energy-Density Plasmas
50th APS DPP Annual Meeting Dallas, TX. 17 Nov.
2008
C. K. Li MIT
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Related talks in this conference
F. H. Séguin CO5.00004 P. A.
Amendt CO5.00005 R. D. Petrasso
GO5.00005 O. V. Gotchev TO5.00001
M. Manuel YP6.00011
MIT
MIT
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Summary
Time-gated, monoenergetic proton radiography
provides unique measurements of EB fields in
laser-produced HED plasmas

• Radiography of laser-foil interactions
• Observations of MG B-field generation, evolution,
  decay dynamics, instabilities and topology change
  due to magnetic reconnection
• Radiography of direct-drive ICF implosions
• Observation of radial, filamentary structures
  with complex striations
• Observation of radial E field and its direction
  reversal
• Radiography of laser-irradiated gold hohlraums
• Observations of the spatial structure and
  temporal evolution of large EB fields

MIT
MIT
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Collaborators
LLNL P. Amendt O. Landen J. Rygg R. Town
MIT F. Séguin J. Frenje R. Petrasso M. Manuel
(G) D. Casey (G) N. Sinenian (G)
GA C. Back J. Kilkenny A. Nikroo
LLE-UR R. Betti J. Delettrez J. Knauer F.
Marshall D. Meyerhofer T. Sangster D. Shvarts V.
Smalyuk J. Soures
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Outline

• Backlighting laser-plasma interactions with
• monoenergetic protons
• Proton radiography of laser-foil interactions
• Proton radiography of direct-drive ICF implosions
  
• Proton radiography of laser-irradiated hohlraums

MIT
MIT
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The proton backlighter is a laser-driven glass
capsule filled with D2 and 3He gas
D 3He ? 4He p (14.7 MeV) D D ? T
p (3.0 MeV)
Source
Emission of protons is pulsed, monoenergetic, and
isotropic
14.7 MeV protons
Spatial resolution 40 mm (FWHM) Energy
resolution 3 Temporal resolution 130 ps
C. K. Li et al., Rev. Sci. Instrum. 77 10E725
(2006)
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Electric and magnetic fields in a plasma are
inferred from proton fluence images
Fluence
14 kJ laser drive
Energy
CR-39 image system uniquely records the position
and energy of every incident proton
J. R. Rygg et al., Science 319 1223 (2008)
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Face-on radiographs of laser-generated plasma
bubbles on opposite sides of a foil prove that
deflecting fields are B rather than E
R. D. Petrasso et al., submitted (2008)
C. K. Li et al., Phys. Rev. Lett. 97 135003
(2006)
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Observations have been made of MG B-field
generation, evolution, decay dynamics, and
instabilities
LASNEXLSP by R. Town
2D code LASNEX produces credible simulations of
the hydrodynamics and field growth as long as the
laser was on, failing only when 3D instabilities
appeared.
C. K. Li et al., Phys. Rev. Lett. 99 015001
(2007)
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A pressure-driven, resistive MHD interchange
instability results in an interchange of field
between the inside and outside of the bubble
surface
In the center region ?mfp lt c/?pe
In the center region ?mfp lt c/?pe,, electron
thermal instability could be triggered and,
driven by the heat flow, leads to random
filamentary structure of ne and Te, as well as B
fields
M. G. Haines, Phys. Rev. Lett. 47 917 (1981)
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The topology is dominated by hydrodynamics and
isnt strongly affected by fields, even though MG
fields are present

• ?Rec. ?exp L / Cs 0.2 ns
• ?SP (?resist ?Alfven )1/2 5 ns (Sweet-Parker)
  
• Where
• ?Alfven L/ vA 1 ns
• ?resist L2 /DB 30 ns

C. K. Li et al., Phys. Rev. Lett. 99 055001
(2007)
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Time-gated, radiography of imploded capsules
displays a dynamic picture of fields associated
with direct-drive, ICF spherical implosions
F. H. Seguin et al., CO5.00004
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Observations of radial filamentation structure
around imploded solid CH spheres indicate that
hydrodynamic instabilities are not the causes of
such striations




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Proton radiographs of at different times provide
the time evolution of a radial E field inside an
imploding capsule
Proton fluence vs position ? field
distributions

C. K. Li et al., Phys. Rev. Lett. 100 225001
(2008)
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Radial profiles of proton fluence provide the
compelling evidence of a radial electric field
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The reversal of radial E field is likely caused
by the direction change of the electron pressure
gradient
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Proton radiography of laser-irradiated gold
hohlraums have resulted in observations of
dynamic E and B fields

• OMEGA-Scale 1.5 Au hohlraum
• 30-mm-thick wall
• 2.4-mm diameter
• 2-mm length
• 100 laser-entrance hole (LEH)

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A dynamic picture of field structure is
complementarily revealed by 15 and 3 MeV protons


15-MeV p images (1) varying beamlet size
(2) chaotic spatial
distributions
3-MeV p images (1) distorted mesh pattern
(2) an asterisk-like
distributions
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A peak B field 106 gauss is inferred in the
proximity of the hohlraum wall
B ? ??p0.5LB-1 Central region dB 0.02 MG ? B
0.2 MG Outer region dB 0.1 MG ? B 1 MG
(assuming 10 asymmetry)
The beamlets are squeezed (? -10 mm) in the
center region but expanded (? 100 mm) in the
out region
At earlier times (before the plasma move to the
center), a hohlraum can be approximately
envisioned as a positively charged hollow
cylinder (cylindrical symmetry), so Gausss law
gives that
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Observed asterisk-like fluence distributions
correlate with the OMEGA cone-3 beam
distributions along P6-P7 axis
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Hohlraum stagnation results in higher plasma
densities in the region of cavity center and the
regions between adjacent plasma bubbles
Including the effects of jets between the bubbles
moving ( 1000 mm/ns), a supersonic fluid (Mach
number 3 - 4) would result in hohlraum center
filling Au plasma ( 0.01 g/cm3) in about 1 ns.
S. H. Glenzer et al., Phys. Plasmas 6 2117 (1999)
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Proton scattering off the stagnating Au plasmas
is responsible for the formation of
asterisk-like fluence pattern
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A dynamic picture of E field, with peak fields
109 V/m, during and after the laser drive are
observed
For a mm-scale hohlraum at the time of peak
fields, this would indicate a 106 volts (MV)
charging potential
E ? 4?pq-1LE-2? Where ? ? A? Lea-1(A-aLE)-1
-- the trajectory displacement ? -- the
characteristic width LE -- the scale length

• Mesh grid is positively charged by
• interactions of laser light glint or soft x
  rays with grid
• material (photoelectric effects)
• laser-plasma interactions (?Pe)

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The measured electric field (potential) is shown
to decay rapidly due to cavity discharge


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Summary
Time-gated, monoenergetic proton radiography
provides unique measurements of EB fields in
laser-produced HED plasmas

• Radiography of laser-foil interactions
• Observations of MG B-field generation, evolution,
  decay dynamics, instabilities and topology change
  due to magnetic reconnection
• Radiography of direct-drive ICF implosions
• Observation of radial, filamentary structures
  with complex striations
• Observation of radial E field and its direction
  reversal
• Radiography of laser-irradiated gold hohlraums
• Observations of the spatial structure and
  temporal evolution of large EB fields

MIT
MIT