Grating Phase-Contrast Imaging for
Diagnostic of High Energy Density Plasmas
D. Stutman, M.P. Valdivia, M. Finkenthal
Department of Physics & Astronomy
Johns Hopkins University, USA
Work supported by US DoE/NNSA Grant DENA0001B35
Presented at the 2014 International Workshop on X-ray and Neutron Phase Imaging with Gratings
Garmisch-Partenkirchen, January 22 2014, Germany
High Energy Density Plasmas are extreme state of matter
Energy density> 105 J/cm-3 (p>1 Mbar )
Temperature (K)
108 ICF compression
ICF ignition
Solar
core
106
104
102
1020
Planetary
cores
Solids
1022
1024
1026
Electron density (cm-3)
HEDP in Inertial Confinement Fusion
300 TW laser power for 4 ns
Ablation
Compression
Ignition
Nuclear burn
(100x energy
gain)
D-T
fuel
6mm
Be shell
200µm
600 g/cm3
108 K
Density is fundamental plasma parameter in HEDP
Electron density N at mid-compression in ICF (cm-3)
2 1024
Density -> Confinement
Gradient-> Stability
1 1024
0
0.6
1.2
2 1024
• 10-1000 µm scales
1 1024
• 10 µm resolution
0.53
0.54
0.55
0.56
R (mm)
Koch et al JAP 2009
Plasma turbulence makes gradients also on the µm scale
Capsule mixing (HYDRA computation)
Burn
possible
Burn
not possible
50 µm
Clark et al LLNL report 2011
Density
(g/cm-3)
X-ray radiography for density diagnostic in HEDP
Pinhole backlighters for <10 keV radiography
10 µm Main laser
Backlighter pinhole
laser
Hot
V-Ge
plasma
Target plasma
2 cm
100 cm
Gated X-ray
detector
Micro-foil backlighters for 20-75 keV radiography
10µm
High-Z
foil
100ps/1 kJ
(1 petawatt)
laser
K-a
• Poor attenuation contrast in low-Z plasmas
• Density gradient hard to diagnose
Refraction angles in the 100 µrad range expected in HEDP
Refraction angles for 8 keV photons in ICF (µrad)
200
100
0
-100
0.53
0.54
0.55
R (mm)
Koch et al JAP 2009
0.56
Talbot-Lau radiography has great potential for HEDP
Attenuation radiograph
T-L Moiré deflectometry
3 mm Be rod
M=25x
25kVp Mo tube
1 mm
• Much more sensitive than attenuation
• Direct density gradient diagnostic
How to implement Talbot-Lau interferometry in HEDP
Removable
X-ray
tube
G0
G1
G2
shield
P≈2.5 cm
Detector
• Small G0 ≤ 2.5 µm (A=G0/P≈100 µrad)
• High Talbot magnification, Talbot order
• Moiré deflectometry with ≥10% contrast
for 10s of µm fringe period at object
• In-situ phase background
Good fringe contrast achieved at high Talbot magnification
G0=2.4 µm, G1=3.8 µm, G2=10 µm (MT=5.2)
E~17 keV (Mo anode 25 kVp), A=80 µrad
100 µm fringe period
at object
M.P. Valdivia et al
JAP 2013
m=3
SNR fringe period
limit of ~30 µm
Accurate, high resolution density profiles
Density gradient in 3 mm Be rod
Mo anode 25 kVp, M=20x
Areal density profile
• Remarkable accuracy for angles << interferometer angular width
Simultaneous density gradient and attenuation maps
1.5 mm Al rod, 17 keV, M=20x
Refraction
Attenuation
• Simultaneous density and Zeff diagnostic
Scatter imaging also works
Plastic doped with
micro-particles
Scatter image
1.5 mm
• µ-turbulence diagnostic without µm spatial resolution
• T-L Moiré deflectometry at 8 keV also very encouraging
High magnification interferometry below 10 keV
Au grating on membrane
Free-standing
phase grating
4 µm
40 mm
MICROWORKS INC
• Early ICF stages, smaller HEDP experiments
Moiré deflectometry at 8 keV (Cu anode)
Be rod
Fruit-fly
Wax drop
• >30% fringe contrast with
free-standing grating
Will G0 survive long enough to produce useful images?
Pinhole closure experiments
Pinhole aperture (µm)
Backlighter
Reighard et al RSI 2008
• 1 GW/cm2 soft X-rays on G0
• Few ns lifetime for G0 on Si substrate + photoresist
Alternate G0 solutions explored
Micro-layered backlighter
Micro-periodic mirror
Pt
100 ps laser
Si
1 µm
SUMMARY
• Talbot-Lau method has great potential for HEDP diagnostic
• G0 survival, 2-D gratings, phase-retrieval without Moiré fringes
• High M interferometry for biomedical, material applications
Moiré deflectometry demonstrated in low density plasmas
Moiré deflectometry of 1020 cm-3
plasma jet using soft X-ray laser
Grava
et al
2008
Resolution improves with smaller source size
M=20
80 micron
58
µm
40 micron
30
µm
10 micron
8 µm
MO = 8-25
Weff = 80 µrad