Prompt gamma-ray measurements in ICF experiments

Transcription

1 Prompt gamma-ray measurements in ICF experiments Hans W. Herrmann (LANL) ACS Symposium, San Francisco, CA Aug 10, 2014

2 ICF Gamma Ray Physics a LANL-led collaboration across multiple institutions Acknowledgements: Y.H. Kim, M. Schmitt, N.M. Hoffman, C.S. Young, J.M. Mack, D.C. Wilson, S.E. Caldwell, J. Oertel, F. Lopez, V. Fatherly, J. Jorgenson, A. Hayes-Sterbenz, G. Hale, S.H. Batha W. Stoeffl, J.A. Church, L. Bernstein, D. Sayre, J. Liebman, A.C. Carpenter, D. Casey, C. Cerjan, D. Schneider, D. Fortner, A. Mackinnon & the NIF Team E. Grafil C.J. Horsfield, M. Rubery, S. Gales, A. Leatherland, W. Garbett T. Hilsabeck, J. Kilkenny A. Zylstra, M. Gatu-Johnson, A. J. Frenje, R. Petrasso V. Glebov, W. Shmayda, D. Jacobs-Perkins J. Milnes, J. Howorth E.K. Miller, R. Malone, M. Kauffman 2

3 Outline Intro to Gas Cherenkov Detectors (GCD) Gamma Reaction History Future Gamma Diagnostics 3

4 Gamma-rays provide the most un-perturbed nuclear signature of ICF performance D + T 5 He* Doppler Broadened (T i ) no escape (hopefully) ~1 n (14.1 MeV ) + α (3.5 MeV) ~ 4e 5 5 He + γ (16.75MeV ) n +α Reaction Rate Foot Neutrons or Gammas Burn Width Bang Time - used to establish laser energy coupling to target (shell velocity) v ITF = I 0 S 3 v 0 8 α α ΔR K wtd hotspot R hotspot 4 +ε M clean M DT Burn Width & other RH features - used for failure mode correlation 0.5 Time Slide 4

5 Gas Cherenkov Detectors (GCD) convert MeV gammas to UV/Visible for easy detection γ-e - Converter Cherenkov Radiation DT Implosion Fusion γ s ~20 cm CO 2 PMT Relativistic electron Tungsten Shielding Cassegrainian Optics Bias Voltage PMT Signal GCD-1 Threshold Eγ (MeV) Variable Energy Thresholding SF 6 CO 2 DT-γ v e >c/n 3.0 MeV Threshold 200 psig limit Normalised Counts Pressure (psia) Fast Time Response GCD Impluse Resposne (CO2 at 100 psi = 6.3 MeV threshold) fwhm = 11 ps Time (ns) Slide 5

6 GCD Animation

7 Gamma Ray Diagnostic capability at OMEGA & NIF OMEGA-60 NIF GCD-2 GRH MZ GRH-6m MZ 2ω fidu MZ TCC 3 GCDs (20cm), 1 GRH (187cm) Ø Coax (40ft) & Mach Zehnders Ø Only GRH absolutely timed 4 GRHs (607 cm) Ø Mach Zehnders only (160 ft) Ø All absolutely timed

8 Gamma Reaction History (GRH) is optimized to operate outside target chamber. Reflected 3ω laser light γ-rays 1.9 m or 6m from TCC W Shield 1 gas cell at Omega, 4 at NIF PMT e - UV/Vis CO 2 or SF 6 Mach Zehnder Off-axis Parabolic Mirror Port flange Fidu 5 diameter Converter Adjustable flat mirror Short pulse cal-laser Pressure Window Fiber light insertions

9 Single-channel GRH prototype performance demonstrated at OMEGA (U. of Rochester) in 2009 GRH Data from OMEGA t 0 1ns square Laser Pulse DT-γ 6.3 MeV Threshold (100 psia CO 2 ) Background (no gas) Installed on OMEGA

10 NIF has produced Interesting Direct-Drive Reaction Histories Cherenkov Signal (normalized) CH-coated Glass Capsule N Cell A Y Cell B n = 4.4e13 GRH Cell at C4.5 MeV Cell D Wghtd Ave Shock Fit Compr Fit Total Fit Shock Compression time (ns) snout n-γ Ablatively-driven implosion with shock & compression yields having burnwidths ~600 ps Deconvolved Signal (a.u.) Xe-doped Exploding Pusher N Y n = 1.4e13 8 MeV 6.3 MeV Shock Compression 2.9 MeV 4.5 MeV Time (ns) Comparable shock & compression yield Low-threshold signals (2.9 & 4.5 MeV) more dominant at Compression due to higher shell ρr

11 DT γ-ray Spectrum consists of 2 prominent lines MeV ~3.5 MeV 0 MeV D + T à 5 He* à 4 He (3.5 MeV) + n (14.1 MeV) à 5 He + γ 0 (16.75 MeV) à 5 He* + γ 1 (~13.5 MeV) γ 1 γ 0 5 He Intensity (a. u.) MeV 4 He + n Gamma-Ray Energy (MeV) γ 1 /γ determined experimentally* γ 1 γ 0 * Courtesy C.J. Horsfield (AWE), assuming lines shapes offered Slide by 11 R-Matrix analysis (G. Hale, LANL)

12 GCD & GRH have provided great HED & Burn Physics results at OMEGA Accomplished: DT Branching Ratio = (4.2±2)e-5 γ/n (γ 0 +γ 1 )/n γ 0 /n Characterization of other fusion gammas (D 3 He, HT, T 2, T 3 He, 3 He 3 He, HD, ) (n,n ) gammas from pucks of various materials ablator areal density of CH & SiO2 implosions In Progress: Kinetic Plasma Effects Ø Fuel Ion Segregation Ø Knudsen Reactivity Reduction Ø Transport validation (mass, momentum, energy) Charged-Particle Stopping Power Charged-Particle induced gammas for Mix diagnosis Slide 12

13 The Prompt γ-ray Energy Spectrum from Indirect-Drive, Cryo-Layered Implosions is full of information! Gammas/neutron/bin) 1.E E E E E E E- 08 Calculated γ-ray Spectrum 12 C(n,n γ) Si Au Al DT Fusion Gamma- Ray Energy (MeV) 12 C(n,γ) γ 1 D(n,γ) γ 0 12 C(n,γ) n n TOTAL Y DT ( TDSF) Y DT = B γ/n Y DTγ TDSF=1-(Y n(13-15) /Y DT ) Ablator ρr 12C(n,n γ) 12C(n,γ)? n Cold fuel ρr D(n,γ) Goals n n n Hohl/TMP Mix? 9 Be(α,n) 12 C* 13 C(d,n) 14 N* Other Pucks Dopants Surprises! 13

14 GRH isolates DT fusion and 12 C(n,n ) γ-rays DT D C Total Au Al Si Gammas/neutron/bin Gammas/Source_neutron/(0.1 MeV bin) 1.E E E E E E E MeV 5 MeV 1.E+00 1.E+00 1.E-01 1.E E-02 1.E E-03 1.E Gamma- Ray Energy (MeV) GRH Response GRH (Ch_ph/Inc_g) γ) y Energy (MeV) GRH- 6m Signal Composition 100% 80% 60% 40% 20% GRH Signal Composition DT D C Au Al Si 2.9 MeV 0% 8 MeV 5 MeV Threshold (MeV) 10 MeV 14

15 14 MeV neutron-induced γ-rays from CH Capsule & Hohlraum assembly are simulated in MCNP 544 Holhraum CH Prompt γ-ray Temporal History BT+¼ ns, δ(t=0) 14 MeV n-source 339 um Al cm DT Au CH capsule 30 um Au R=0.2769cm CH Si Si Gammas/n/(5ps bin) 1.E E E E E E+00 Au Al Si C Total DT time after Bang Time (ns) 15

16 Gaussian forward fit decomposition into spectral components provides Total DT & 12 C(n,n γ) yields and absolute timing (BT, BW, t Cγ ) 10 MeV 8 MeV Signal (a.u.) DT Fwd Fit Data Signal (a.u.) bkgnd 4.5 MeV 2.9 MeV Signal (a.u.) Al Si Signal (a.u.) 12 C t Cγ > BT 16 D. Sayre

17 Indirect Drive: DT Symcap produces discernible Re-Shock flash, Cryo-layered implosions do not Symcap uses surrogate CH layer in place of DT ice Ø provides harder boundary for shock reflection Re-Shock flash occurs before Fall Line reaches core Ø Y Compr / Y Re-Shock is a measure of mix Normalized Signal (V) Cryo N N N N Time rel. to BT (ns) T ion (kev) 1130 µm CH: 193 µm Ice: 69 µm 866 µm DT gas 0.3 mg/cc Radius (µm) 810 ps 230 ps DT ice Symcap CH Shock Time (ns) Compr HYDRA courtesy N. Meezan

18 Future gamma diagnostics will add significant capability Gas Cherenkov Detectors (temporal detectors): Super GCD GRH-15m 15m from TCC Shielded Streak Cameras 400 psia C 2 F 6 Scope PMTs Low Threshold, High Sensitivity Ø ~2 MeV threshold Ø 20 cm from TCC (TIM mounted) High Temporal Resolution Ø Streak Camera for ~10ps resolution Ø Camera behind 6 bio shield wall Slide 18

19 Super GCD (GCD-3 at Ω) provides High-Sensitivity, Low- Threshold capability now at OMEGA and eventually at NIF Super GCD Low Threshold, High Sensitivity Ø ~2 MeV threshold Ø 20 cm from TCC (TIM mounted) Physics Driven Requirements: Low Threshold ( 2 MeV) to reveal new portions of gamma-ray spectrum Ø High pressure (400 psia) redesigned pressure boundary Ø Fluorinated gases metal seals to achieve <1e-9 scc/s leak rate to avoid damage to TRS catalyst High Sensitivity Ø TIM-based to capture solid angle Ø Modular optics package to optimize SNR Absolute Timing & Dry Run capability Ø 2ω fidu injection Improved SNR Ø better shielding Ø additional precursor to signal delay

20 Lower Energy Threshold (~ 2 MeV) opens up new portions of gamma-ray study Threshold Eγ (MeV) GCD-1 (CO2) 6.3 MeV GCD-3 (C2F6) New gamma-ray detection (too low E for GCD-1, too dim for GRH): Ø 16 O(n,n γ) at 6.1 MeV (SiO 2 ρr) Ø 13 C(d ko,n) 14 N* at 5.69 MeV (CH Mix) Ø 9 Be(α,n) 12 C* at 4.44 MeV (Be Mix) Ø 9 Be(d ko,n) 10 B* 3.4 MeV (Be Mix) 1.8 MeV Pressure (psia) Ø 10 B(d ko,n) 11 C* at ~7 MeV (B 4 C or BH Mix) Ø HD-γ at 5.5 MeV (MIT Zylstra PhD) Slide 20

21 The p+d reaction relevant to BBN, formation of proto stars, and brown dwarfs, is being investigated at OMEGA in July-August p + D 3 He + γ (5.5 MeV) 5 4 D 3 He- γ (~16 MeV) Brown Dwarf Stars Protostars PMT Signal /Y_DDn (x1e- 11) DH- γ (5.5 MeV) DD- γ (24 MeV) ABZ A. Zylstra (PhD thesis) Keck Telescope 0 HH- γ & Null Time rel. peak (ns) LANL s new GCD- 3 uniquely iden5fied HD fusion gammas at 5.5 MeV for the first 5me (as well as D 3 He- γ & D 2 - γ) 21

22 Integral puck holder allows study of 14 MeV neutron interactions with materials placed near implosion 6 cm puck implosion Y. Kim, et. al, JoP, 2010

23 Gamma Rays may illuminate Dark Mix 12 C vs 13 C pucks at OMEGA will determine feasibility 12 C layer buried in 13 C-based ablator (CH or HDC) Carbon Energy Level Diagrams 12 C gamma signal (γ) inner Low Adiabat Hi Adiabat Ablation front mix? Min detectable (~50 mg/cm 2 ) outer 12 C layer depth (um) from interface To determine where carbon ablator mix is coming from and when Sensi5ve to Dark Mix (unlike x- rays & separated reactants) 4.44 MeV Strong! MeV (how weak?) MCNP predicts ~6x less signal for 13C, but large uncertainty Response 13 C 12 C Concept by W. Stoeffl Slide 23

24 Future gamma diagnostics will add significant capability Spectroscopic detectors: Gamma-to-Electron Magnetic Spectrometer (GEMS) coil γ-to-e - Compton converter 4.4 MeV detector 10 to 20 MeV (3 to 6 MeV) detector plane Slide 24

25 Gamma Spectroscopy will be an enabling technology for NIF GEMS (Gamma-to-Electron Magnetic Spectrometer) Total Yield (no Total Yield measurement currently exists!) D(t,γ 0 ) Total Down Scatter Fraction (TDSF) when combined w/ primary Y n 4π Global Fuel ρr (Fuel ρr currently line-of-sight) D(n,γ) Ablator ρr (reduced uncertainty relative to GRH) 12 C(n,n γ) Mix studies (e.g., 9 Be(α,nγ), 13 C(d ko,nγ), 11 B(d ko,nγ) ) Neutron Interactions on materials (i.e., pucks) Astrophysical studies (e.g., s & r-processes) Analyzing Electro- Magnet e - Graphite Collimator Detector Array (Cherenkov to PMT) Calculated NIF Spectrum X- ray Filter & Collimator (2m from TCC) Reentrant Tube Electron Beam Port Cover Support Structure (modified from MRS) γ- to- e - Converter Sweeper Magnet NIF CDR held in July 2013 Energy Resolution: ΔE/E 5% Energy Range: E 0 ±33% within 2-25 MeV Temporal response < 1.5 ns Viable at Y DTn 5e14

26 Slide 26

27 Mix study A. Hayes-Sterbenz (LANL) Hydro-dynamical Mixing of Ablator into Hotspot 9 Be(α, nγ) 12 C gamma-rays (4.44 MeV) D+T α 9 Be γ/n 10 B(α, p) 13 C gamma-rays (3.68, 3.86 MeV) 10 B α D+T Compare w/ 1.2x10-3 γ/n at 100 mg/cm 2 12 C Slide 27

28 Aerogel Cherenkov Detector (ACD) proposed for lowenergy ( MeV), course spectroscopy Light pipe X-ray Radiator: Aerogel-1 Aerogel-2 Aerogel-3 Aerogel-4 Aerogel-5 water quartz Refractive index, n: Threshold Energy (MeV): Slide 28

29 Options for Future Gamma Diagnostics (cont.) Spectroscopic detectors: Curved Crystal Gamma Spec (W.Stoeffl) useful for <1.5 MeV Furlong (W.Stoeffl) Single-hit, pixelated scintillator detector array ~200m from TCC Gammas/Neutron/(0.1 MeV bin) Calculated DT γ-ray Spectrum 1.E E E E C(n,n γ) 1.E Gamma- Ray Energy (MeV) 12 C(n,γ) DT Fusion D(n,γ) 12 C(n,γ) Furlong 201 meter

30 Gamma Imaging System (GIS) Imaging of 12 C(n,n )γ would reveal ablator mass distribution at bang time NIS GIS γ-ray Imaging of Ablator ( 12 C-γ) (G. Grim, D. Lemieux (U.Ariz)) Slide 30

31 GRH boldly goes courtesy Scott Chambliss, Paramount Pictures and Bad Robot Productions 31

32 Backups

33 GRH continues to inform quest for Ignition at NIF ~500ps late BT indicative of reduced coupling Drive Multipliers (~85%) Scatter of nbt relative to GBT indicative of core velocity Wide GBW indicative of failure modes during NIC Large & late 12 Cγ peak indicative of improper stagnation duration (ps) Δ DGBT GBW Δt Simulation Observed Range Cγ peak delay (ps) Future: 12 C layers in 13 C capsules for Dark Mix studies GBW & 12 Cγ delay (Δt) are strong indicators of ignition failures Slide 33

34 NIF Yield Ranges for Gamma Diagnostics Current Max yield Ignition DTn Color Code: Cherenkov Spectroscopic Imaging Super GCD GRH Furlong GRH-15m GEMS Gamma Imaging