Diagnosing Implosion Performance at the NIF by Means of - PowerPoint PPT Presentation

Diagnosing Implosion Performance at the NIF by Means of Neutron-Spectrometry and Neutron-Imaging Techniques Presentation to 24 th IAEA Fusion Energy Conference San Diego, CA, USA October 8-13, 2012 Johan Frenje on behalf of the NIF team Massachusetts Institute of Technology

Collaborators MIT LLNL LANL UR GA Imperial College D. Casey R. Ashabranner S. Hatchett J. Chittenden G. Grim J. Knauer J. Kilkenny M. Gatu Johnson R. Bionta R. Hollaway N. Guler V. Glebov A. Nikroo B. Appelbe C. Li E. Bond O. Jones J. Kline T. Sangster L. Reny M. Manuel J. Caggiano R. Kauffmann G. Morgan C. Abbott M. Farrel SNL H. Rinderknecht M. Eckart D. Koen T. Murphy R. Betti D. Jasion M. Rosenberg D. Fittinghoff O. Landen D. Wilson M. Burke F. Séguin E. Hartouni R. Leeper J. Lindl T. Clark N. Sinenian J. McNaney D. Larson N. Fillion A. Zylstra M. Moran S. Le Pape V. Glebov R. Petrasso D. Munro M. Mckernan T. Lewis S. Sepke A. Mackinnon O. Lopez-Raffo P. Springer E. Moses J. Magoon D. Bleuel H. Park P. McKenty A. Carpenter P. Patel D. Meyerhofer C. Cerjan R. Prasad B. Rice J. Edwards B. Remmington P. Radha B. Felker R. Rygg M. Romanovsky S. Glenzer V. Smalyuk J. Szcepanski P. Springer M. Shoup R. Zacharias R. Till M. Yeoman This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Johan Frenje – IAEA 2012 2

Summary The neutron data have been essential to the progress of the experiments on the NIF • The neutron-spectrometry data indicate that the tuning campaigns have improved the implosion performance by ~50 × since the 1 st shot in Sept 2010. • We have achieved a radial convergence of ~35, fuel ρ R values up to ~1.3 g/cm 2 , and inferred hot-spot pressures up to ~150 Gbar. • The maximum pressure is ~2 × lower than point design, and the observed neutron yields are 3-10 × lower than expected. • The pressure and yield deficits are most likely explained by higher than predicted fuel-ablator mix and ρ R asymmetries often observed in the implosions. • A path forward to address these issues has been defined. 3

Neutron spectrum The neutron spectrum is used to diagnose neutron yield ( Y n ), ion temperature ( T i ) and areal density ( ρ R ) 10 19  E Primary neutrons (n): D n Ignition 10 18 • Y n 2   • T E n’ T i i D Yield / MeV 10 17 • Residual kinetic effects S cattered neutrons (n’): 10 16 Y n  r  r R ' • R dsr Y 10 15 n r R (g/cm 2 )  21  dsr 10-12 MeV 1) 10 14 0 5 10 15 20 MeV Measurement of the detailed shape of the low-energy part of neutron spectrum provides 3D information about implosion 1) J.A. Frenje et al., these proceedings; to be submitted to Nucl. Fusion. Johan Frenje – IAEA 2012 4

Neutron images Primary and scattered neutrons are imaged to diagnose neutron- source size (R) and thickness of high-density shell (  R), resp. Images of neutron source and high-density shell 50 Hot DT core High-density Shell (  R) n' n μm 0 n' Neutron Neutron High-density source (R) source shell -50 Primary neutrons (n): • R of neutron source Scattered neutrons (n’):  R of high-density shell • G. Grim et al., APS invited (2012). Johan Frenje – IAEA 2012 5

Neutron spectrometry and neutron imaging Several neutron spectrometers and an imaging system have been fielded at various locations on the NIF nTOF4.5m (64-330) nTOF3.9m (64-275) MRS (77-324) Spec-E (90-174) NITOF/NIS (90-315) This provides good implosion coverage for reliable measurements of Y n , T i , r R , and r R asymmetries M. Gatu Johnson et al., RSI (2012). Spec-A (116-316) F.E Merrill et al., RSI (2012). Johan Frenje – IAEA 2012 6

Data Spectra and images are now measured routinely on the NIF (Example: DT shot N120205) Shot N120205 MRS spectrum 1) Neutron images 2) Y n = (5.6 ± 0.2)×10 14 n R n = 28 ± 3 μ m 4 10 ρ R = 900 ± 40 mg/cm 2 Counts / MeV Primary peak T i = (3.4 ± 0.1) keV (unscattered) 3 10 Single-scattering 2 10 0 5 10 15 Deuteron energy [MeV] Neutron spectrum n ’ R n ’ = 44 ± 5 μ m 15 10 Yield / 100 keV Primary peak 14 10 Single-scattering 13 10 12 10 5 10 15 Neutron energy [MeV] 1) J.A. Frenje et al., PoP (2010). 2) G. Grim APS invited, PoP (2012). Johan Frenje – IAEA 2012 7

Data The spectrometry data indicate that the tuning campaigns have improved the implosion performance by ~50 × since Sept 2010 Untuned 09/10 – 02/11 Symmetry 11/11 – 12/11 Mix/No Coast 03/12 – 07/12 Shock timing 06/11 Velocity 08/11 – 09/11 10 16 Implosion performance 1) : Ignition 2 . 3 conditions r     Y R  Hot-spot energy: 3 kJ  n    ITFx ITFx     3 . 2 e 15 1 . 47 Alpha heating: 0.5 kJ 1.0 Neutron heating: 0.3 kJ 10 15 0.5 Mar 2012 Y n 0.2 0.1 10 14 0.05 Lawson-type parameter 2) : 0.02 Sep 2010 E   ITFx 0.01 E 0.002 0.005 losses 10 13 0 0.50 1.0 1.5 r R [g/cm 2 ] 1) M .J. Edwards et al., PoP (2011); A.J. Mackinnon et al., PRL (2012). 2) R. Betti et al., OV/5-3 Johan Frenje – IAEA 2012 8

Data Spectrometry and imaging data self-consistently indicate that the tuning campaigns have improved the convergence by ~2 × Untuned 09/10 – 02/11 Shock timing 06/11 1.5 Velocity 08/11 – 09/11  R Symmetry 11/11 – 12/11 Mar 2012   0 . 49 0 . 16 Mix/No Coast 03/12 – 07/12 R (fit to all neutron-imaging data) 1.0 r R [g/cm 2 ] High-density fuel shell Sep 2010 0.5 Source m r  fuel R R 2    R Δ R     4 R   2 0 0 500 1000 1500 2000 2500 R 2 [  m 2 ] Sept 2010 R 2 data inferred from x-ray images. Johan Frenje – IAEA 2012 9

Data Inferred hot-spot pressure is ~2 × lower than point design, and yields are ~3-10 × lower than predicted Untuned 09/10 – 02/11 Symmetry 11/11 – 12/11 Mix/No Coast 03/12 – 07/12 Shock timing 06/11 Velocity 08/11 – 09/11 LASNEX 2D sim. 10 17 300 HYDRA 3D sim. DATA Point design: ~300 Gbar 10 16 Hot-spot pressure [Gbar] Mar 2012 200 10 15 Y n 10 14 100 10 13 Sep 2010 10 12 0 N110121 N110212 N110608 N110620 N110826 N110908 N111029 N111112 N120114 N120131 N120213 N120311 N120321 N120405 N120417 N120626 N120720 N120808 0.0 0.50 1.0 1.5 2.0 r R [g/cm 2 ] What’s causing this pressure and yield deficit? 1) P. Springer et al., IFSA (2011). Johan Frenje – IAEA 2012 10

Data The pressure and Y n deficits can be explained partly by larger than predicted CH-ablator mixed into the hot spot Untuned 09/10 – 02/11 Shock timing 06/11 Velocity 08/11 – 09/11 4 . 7 10 15 Y  Symmetry 11/11 – 12/11 T n i Mix/No Coast 03/12 – 07/12 Fuel-ablator mix very significant Y n 10 14 1 2 3 4 5 T i [keV] The higher-convergence implosions display more mix, which reduces T i and Y n . Other data indicate that the “mix - performance cliff” occurs at a remaining shell mass that is ~30-40% larger than the point design Johan Frenje – IAEA 2012 11

Data The Y n and pressure deficits can also be explained partly by the systematic low-mode ρ R asymmetries often observed 2.0 2.0 Spec-E r R [g/cm 2 ] Spec-E r R [g/cm 2 ] 1.5 1.5 1.0 1.0 10-12 MeV 10-12 MeV 0.5 0.5 0 0 0 0.5 1.0 1.5 2.0 0 0.5 1.0 1.5 2.0 Spec-A r R [g/cm 2 ] MRS r R [g/cm 2 ] MRS Neutron measurements of un- Spec-E scattered neutrons also indicate similar low-mode ρ R asymmetries Spec-A Johan Frenje – IAEA 2012 12

Data When using the 6-10 MeV range, Spec-E and Spec-A nTOFs probe similar portion of the implosion, and provide similar ρ R values 2.0 2.0 Spec-E r R [g/cm 2 ] Spec-E r R [g/cm 2 ] 1.5 1.5 6-10 MeV 1.0 1.0 10-12 MeV 10-12 MeV 0.5 0.5 0 0 0 0.5 1.0 1.5 2.0 0 0.5 1.0 1.5 2.0 Spec-A r R [g/cm 2 ] MRS r R [g/cm 2 ] MRS Neutron measurements of un- Spec-E scattered neutrons also indicate similar low-mode ρ R asymmetries Spec-A Johan Frenje – IAEA 2012 13

Path forward Need to address the observed higher-than-predicted levels of mix and low-mode ρR asymmetries • Understand the origin and structure of mix and low-mode ρ R asymmetries. • Lower CR implosions (more 1D) should be examined and understood to improve the modeling capabilities before conducting the high CR implosions necessary for ignition. • Engineering solutions and new diagnostic capabilities need to be implemented: – Implement in-flight 2D x-ray radiography of the ablator. – Implement in-flight Compton radiography of the fuel. Implement a new nTOF-neutron spectrometer for probing r R on the south pole. – – Reduce size and/or patch up diagnostic holes and star burst, and reduce diameter of the fill tube to improve drive symmetry. Johan Frenje – IAEA 2012 14

Summary The neutron data have been essential to the progress of the experiments on the NIF • The neutron-spectrometry data indicate that the tuning campaigns have improved the implosion performance by ~50 × since the 1 st shot in Sept 2010. • We have achieved a radial convergence of ~35, fuel ρ R values up to ~1.3 g/cm 2 , and inferred hot-spot pressures up to ~150 Gbar. • The maximum pressure is ~2 × lower than point design, and the observed neutron yields are 3-10 × lower than expected. • The pressure and yield deficits are most likely explained by higher than predicted fuel-ablator mix and ρ R asymmetries often observed in the implosions. • A path forward to address these issues has been defined. 15