Grating Phase-Contrast Imaging for Diagnostic of High Energy Density Plasmas

D. Stutman, M.P. Valdivia, M. Finkenthal

Department of Physics & AstronomyJohns 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 GratingsGarmisch-Partenkirchen, January 22 2014, Germany

High Energy Density Plasmas are extreme state of matter

ICF ignition108

106

104

1020 1022 1026

Temperature (K)

Electron density (cm-3)

Solar core

Planetarycores

ICF compression

Solids1024

Energy density> 105 J/cm-3 (p>1 Mbar )

102

HEDP in Inertial Confinement Fusion

D-Tfuel

300 TW laser power for 4 ns

6mmBe shell

200µm600 g/cm3

108 K

Ignition Nuclear burn(100x energy gain)

CompressionAblation

Density is fundamental plasma parameter in HEDP

Koch et al JAP 2009

2 1024

1 1024

2 1024

1 1024

Electron density N at mid-compression in ICF (cm-3)

0 0.6 1.2

R (mm)0.53 0.54 0.55 0.56

• 10-1000 µm scales

• 10 µm resolution

Density -> ConfinementGradient-> Stability

Capsule mixing (HYDRA computation)

Density(g/cm-3)

Burnpossible

Burnnot possible

Clark et al LLNL report 2011

Plasma turbulence makes gradients also on the µm scale

50 µm

X-ray radiography for density diagnostic in HEDP

10 µmpinhole

Target plasma

Gated X-raydetector

Backlighterlaser

100 cm

Main laser

2 cm

Pinhole backlighters for <10 keV radiography

Hot V-Geplasma

Micro-foil backlighters for 20-75 keV radiography

High-Z foil

10µm

K-a

100ps/1 kJ(1 petawatt) laser

• Poor attenuation contrast in low-Z plasmas• Density gradient hard to diagnose

Refraction angles in the 100 µrad range expected in HEDP

Koch et al JAP 2009

Refraction angles for 8 keV photons in ICF (µrad)

R (mm)0.53 0.54 0.55 0.56

200

100

0

-100

Talbot-Lau radiography has great potential for HEDP

Attenuation radiograph T-L Moiré deflectometry

3 mm Be rodM=25x25kVp Mo tube

1 mm

• Much more sensitive than attenuation• Direct density gradient diagnostic

How to implement Talbot-Lau interferometry in HEDP

• 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

Removable X-raytube

G0

DetectorP≈2.5 cm

shield

G1G2

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

M.P. Valdivia et al JAP 2013

m=3

100 µm fringe periodat object

SNR fringe periodlimit of ~30 µm

Accurate, high resolution density profiles

• Remarkable accuracy for angles << interferometer angular width

Density gradient in 3 mm Be rodMo anode 25 kVp, M=20x

Areal density profile

Simultaneous density gradient and attenuation maps

RefractionAttenuation

• Simultaneous density and Zeff diagnostic

1.5 mm Al rod, 17 keV, M=20x

1.5 mm

Plastic doped withmicro-particles

Scatter imaging also works

Scatter image

• µ-turbulence diagnostic without µm spatial resolution

• T-L Moiré deflectometry at 8 keV also very encouraging

High magnification interferometry below 10 keV

4 µm

Free-standing phase gratingAu grating on membrane

MICROWORKS INC

40 mm

• Early ICF stages, smaller HEDP experiments

• >30% fringe contrast with free-standing grating

Moiré deflectometry at 8 keV (Cu anode)

Fruit-fly

Wax drop

Be rod

Pinhole aperture (µm)

Will G0 survive long enough to produce useful images?

Pinhole closure experiments

Reighard et al RSI 2008

• 1 GW/cm2 soft X-rays on G0

• Few ns lifetime for G0 on Si substrate + photoresist

Backlighter

Alternate G0 solutions explored

Micro-periodic mirrorMicro-layered backlighter

1 µm

100 ps laser

Pt

Si

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

Grava et al 2008

Moiré deflectometry of 1020 cm-3 plasma jet using soft X-ray laser

Resolution improves with smaller source size

80 micron

40 micron

10 micronMO = 8-25 Weff = 80 µrad

58 µm

30 µm

8 µm

M=20