Areal-Density-Growth Measurements with Proton Spectroscopy on OMEGA

Transcription

1 Areal-Density-Growth Measurements with Proton Spectroscopy on OMEGA Areal density (mg/cm ) atm D 3 He Neutron rate (s 1 ) V. A. Smalyuk Laboratory for Laser Energetics University of Rochester 3nd Anomalous Absorption Conference Oahu, Hawaii 1 6 July

2 Contributors P. B. Radha, J. A. Delettrez, V. Yu. Glebov, V. N. Goncharov, J. P. Knauer, F. J. Marshall, D. D. Meyerhofer, S. P. Regan, S. Roberts, T. C. Sangster, S. Skupsky, J. M. Soures, and C. Stoeckl Laboratory for Laser Energetics University of Rochester J. A. Frenje, C. K. Li, R. D. Petrasso, and F. H. Séguin Plasma Science and Fusion Center Massachusetts Institute of Technology

3 Summary Areal density grows by ~ times over time of neutron production (~4 ps) in implosions with -mm-thick shells and 4 atm D 3 He fuel Neutron production history and 14.7-MeV proton spectra are used to infer target areal-density growth. ~7% of the proton spectral width is due to areal-density evolution. ~% is due to geometrical effects. ~1% is due to shell modulations, ion temperatures, and instrumental broadening. Areal-density grows by a factor of for 4 ps, reaching 13±16 mg/cm at peak compression. For 1 atm fill targets, areal density reaches 19±14 mg/cm at peak compression, close to 1-D predictions. For 4 atm fill targets, areal density reaches 13±16 mg/cm at peak compression a factor of lower 1-D predictions. E11746

4 Outline Principle of areal-density-growth measurements using neutron production history and 14.7-MeV proton spectrum Geometrical broadening effects on proton spectra Short-scale shell modulation effects on proton spectra Results E11747

5 Two types of targets were used in these experiments -mm, Ti-doped layer 1 mm CH 4 & 1 atm D 3 He mm Pure CH shells are used for areal-density-growth measurements. Titanium-doped shells are used for shell-modulation measurements. E11745

6 Shape of 14.7-Mev D 3 He proton spectrum depends on proton-production rate and areal-density evolution E11593 Proton rate (1/s) ( 1 1 ) Energy downshift (MeV) Areal density (mg/cm ) Areal density (mg/cm ) Proton yield per MeV Shell areal density Fuel areal density

7 The shape of the D 3 He proton spectrum is primarily due to target areal density evolution in implosions with -mm-thick shells ~7% target-areal-density evolution; ~% geometric broadening; ~1% shell-areal-density modulations with l > 6; ion temperature and diagnostic broadening Assumptions: Bethe-Bloch stopping power in plasma -[ de dx]= ew p v p [ ] ln 1.4 mu ( p hwp ) Proton production history is the same as neutron production history. The effective ion temperature is the same throughout implosions. Geometrical broadening depends primarily on areal density and less on proton source size and shell thickness. E1174

8 Areal-density evolution is inferred by fitting to measured proton spectrum Proton rate (1/s) ( 1 1 ) Areal density (mg/cm ) Yield per Mev ( 1 ) Areal density (mg/cm ) E11595

9 Geometrical broadening of D 3 He proton spectrum depends primarily on a target areal density Fuel R R 1 z R 3 Shell y Protons to distant detector Proton source Normalized yield per MeV mg/cm Parameters R 1 and R are calculated using experimentally measured neutron yield on burn time, fuel areal density, and ion temperature. E11594

10 Areal-density evolution is measured in seven directions for approximately uniform coverage of the shell Shot 5, 1 atm D 3 He Yield per MeV ( 1 ) 6 4 K K TIM TIM Data Fitting Yield per MeV ( 1 ) 6 4 TIM4 TIM5 TIM Areal density (mg/cm ) rr evolution Neutron rate ( 1 19 ) E11591

11 In 4 atm D 3 He shot areal density grows by a factor of over time of neutron production (4 ps) Shot 519, 4 atm D 3 He Yield per MeV ( 1 ) 1 K1 K3 TIM1 TIM Data Fitting Yield per MeV ( 1 ) 1 TIM4 TIM5 TIM Areal density (mg/cm ) rr evolution Neutron rate ( 1 19 ) E1159

12 The ratio of images above and below the K edge is related to areal-density modulations in the shell I <K, below K edge I >K, above K edge Shot 1, 4 atm D 3 He, -mm shell ns 5 mm Ï Ê d ln I ˆ Ì Á <K ý Ó Ë I drr ( ) = >K þ m >K -m <K m >K, m <K : titanium absorption rates above and below the K edge E mm d(rr)

13 At peak neutron production, areal-density modulations are ~15% at inner layer and ~7% for whole shell 1. Wavelength (mm) 5 5 Shot 1 Power per mode of d(rr) rr.1.1 Peak compression ~5% Peak neutron production ~15% ns. ns 1.9 ns E1137a Spatial frequency (mm 1 )

14 Areal-density with more-stable 1-atm-D 3 He fill is closer to 1-D prediction than with 4 atm D 3 He Areal density (mg/cm ) atm D 3 He 4 atm D 3 He Neutron rate (s 1 ) E1159

15 At peak compression, core images are slightly larger for 1-atm than for 4-atm-filled targets Intensity (arbitrary units) Measured 4 6 Radius (mm) E mm