Initial Results from the National Ignition Campaign on NIF

Transcription

1 Initial Results from the National Ignition Campaign on NIF Presentation to 23 rd IAEA Fusion Energy Conference October 10-16, 2010 Daejeon, Republic of Korea John Lindl for the National Ignition Campaign Team NIF Programs Chief Scientist

2 The National Ignition Campaign (NIC) on NIF is an International effort

3 Summary Based on our current understanding, following a successful tuning campaign, we will have a high probability of ignition and yields of 5-10 MJ or more with ~1.3 MJ of laser energy using a CH capsule Initial hohlraum energetics experiments put us into the hohlraum temperature range for ignition experiments at ev The laser, diagnostic, target fabrication and other infrastructure capabilities needed for the ignition campaign are now in place. We have carried out the first THD cryo-layered implosion Ignition experiments in lay the ground work for target performance which meets IFE requirements

4 The National Ignition Facility

5 One of two laser bays looking toward the switchyard and target chamber NIF recently delivered 1.3 MJ of 3 light to the target chamber in an ignition pulse meeting ignition power balance requirements

6 Composite view of the NIF target area with the floors at different levels photo-shopped out of the picture

7 Thirty types of diagnostic systems are planned for the National Ignition Campaign One of two Dante soft X-ray Spectrometers One of NIF s 48 quads of beams on the 10 meter diameter target chamber

8 Inside of the NIF chamber: NIF is taking advantage of decades of ICF research to field a sophisticated array of diagnostics systems currently collecting more than 300 channels of Optical, X-ray, and Nuclear data Optics Inspection Camera Streaked X-ray Detector with pinhole snout Target Positioner Static X-ray Imager Near Backscatter Imager Scatter Plate

9 Cryogenic fuel layers will be formed in a new target positioner (cryo-tarpos) recently installed on NIF 1 cm A multi-laboratory effort in fabrication has given NIF the production capability for targets with unprecedented precision

10 On NIF we use a hohlraum driven implosion to generate the R & T needed for ignition (CH or Be) 1000 g/cm g/cm 2

11 Ignition requirements can be specified as a generalized Lawson criterion equivalent to the Ignition Threshold Factor (ITFX) discussed later T avg-thd (kev) Expected performance of NIC CH capsule at 1.3 MJ Gain Omega Cryo Implosions R Total (g/cm 2 ) We have developed an ignition campaign to achieve the compressed fuel R and temperature required to achieve ignition and burn

12 The hohlraum for the initial ignition experiments will be have a Au wall and He gas fill LEH unlined, diameter 3101 μm Window thickness 0.5 ± 0.05 μm Gas fill 100% He 0.96 ±0.02 mg/cc Inner Length ± 20 μm Au Hohlraum wall Inner diameter 5440 μm All dimensions are at cryo temperature.

13 We will begin the ignition campaign with a CH capsule (190) (68) CH at 1.3 MJ and 400 TW 1108 m Tube 10 m OD SiO 2 CH+Ge Hole 5m D 0% g/cc 0.5% g/cc 1.0% g/cc 0.5% g/cc 0% g/cc Amorphous material with no crystal structure issues Large data base from Nova and Omega Reduced Facility impact relative to Be All of the diagnostics and infrastructure needed for optimizing ignition implosions are essentially independent of capsule ablator If the pre-ignition campaign is completed successfully, and all requirements are met, calculations predict this target has an 80% probability of yield >1 MJ on any given shot and an expected mean yield 7.5 MJ

14 Achieving ignition requires constraining or adjusting multiple lower level parameters that roll up to set the ignition conditions Investment in NIF, targets and diagnostics establishes the capabilities to achieve ignition The energetics / capsule tuning campaign sets the key implosion input parameters using surrogate non-layered targets The THD layered implosions optimize the quality of the imploded fuel 1D quantities, e.g: Peak Laser Power Foot Laser Power Shock timing 3D quantities, e.g: Ice Perturbations Capsule Roughness Intrinsic Asymmetry Laser Power Balance >150 actionable parameters Velocity Hot spot Shape Entropy Mix Primary Implosion Inputs T Hot spot R Total R Primary Compressed fuel outputs DT experiments, alpha physics Ignition

15 We expect the 1.3 MJ CH target to have a high probability of ignition following the experimental campaign Performance in ensemble of 2D simulations varying 1D and 2D input parameters Input design metric: ITF Experimentally observable metric: ITFX DT yield [MJ] Expected Performance DT yield [MJ] v ITF = I o v ITF 11.2 R Kwtd hotspot R hotspot 4 Mclean M DT Velocity Entropy Shape Mix 0.5 ITFX ITFX = C cliff Y THD dsf Equivalent to a 3D generalized Lawson Criterion based on yield and neutron down scattered fraction Betti et al.

16 We have more completely mapped out the lower performance part of ITF and ITFX by including a wider range of variability which will typify early experiments Input design metric: ITF Experimentally observable metric: ITFX DT yield [MJ] Expected mean ITF Modified statistics to study failure modes DT yield [MJ] Expected mean ITFX v ITF = I o v ITF 11.2 R Kwtd hotspot R hotspot 4 Mclean M DT Velocity Entropy Shape Mix 0.5 ITFX ITFX = C cliff Y THD dsf Equivalent to a 3D generalized Lawson Criterion based on yield and neutron down scattered fraction Betti et al. 16

17 To compensate for physics uncertainties, the implosion optimization campaign will set 14 laser and 3 target parameters which are sufficient to optimize V, adiabat, mix and shape Adiabat Power & timing R Velocity V Peak power, Beam smoothing (9 laser parameters to set strength and timing of 4 shocks ) Dopant level and ablator thickness R Be +Cu (2 laser + 1 target parameters to set velocity and ablated mass) Relative power at foot & peak Wavelength separation Length M Mix (2 target parameters) (3 laser + 1 target parameters) Shape S

18 Implosion optimization will use an array of measurement techniques demonstrated on Omega employing 6 surrogate targets and ~30 different diagnostics A Adiabat FFLEX (hot electrons) VISAR SOP (shocks) FABS/ NBI (laser coupling) Velocity DANTE (T R ) Shell velocity V RadChem (THD targets) M Mix DANTE (Drive spectrum) GXD (shape of gas filled surrogate implosion) Shape S

19 Initial hohlraum experiments were carried out at 20 ºK using non-layered surrogate capsules with a low density gas fill (symcaps) Temperature: 20 K Hohlraum pressure: 420 torr Capsule pressure: 2634 torr < 20 nm of ice built up << 100 nm (specification)

20 The symmetry of the hohlraum drive up to the peak of the pulse is measured using low yield gas-filled capsules SymCap Target 60 μm HHe 4 or DHHe 3 Gas-filled low yield (< 1e12) capsule Emission pattern of 5-10 kev x-rays are detected NIF data from 2009 Infers time-integrated symmetry, P 2 and P 4 Diagnostic is an x-ray framing camera with multiple imaging pinholes mounted in a diagnostic instrument manipulator (DIM)

21 The NIF Gated X-ray Detectors (GXD), are advanced versions of diagnostics fielded on Nova and Omega The GXD is a key diagnostic for obtaining implosion symmetry and implosion velocity 200ps T o ns ns CCD Power Supply MCP Pulser Electronics 70 ps duration images ns ns Embedded Computer MCP Module CCD Camera P0 = 100 m P2/P0 = /-.008 P4/P0 = /-0.10

22 Symmetry: requires a controlled energy balance between the inner and outer beams We use a plasma-optical-switch, & transfer energy from outer to inner beams by increasing = inners outers The beams transfer energy to one another via Brillouin scattering from ion waves NIC 09 9 kev Capsule emission 10 0 Outer k ion-wave Inner Symmetry: Must be round enough at high convergence to get dense & ignite X(μm) P2/P0 [%] [Å]

23 Coupling: Stimulated scatter within the hohlraum can lead to energy loss: incoming laser reflects back out Coupling: LPI must be low enough, so that enough energy is available for drive SBS of outer cone beams in gold bubble : Laser reflects off of ion wave SRS of inner cone beams in fill-gas & ablator blow-off: Laser reflects off of electron plasma wave Besides reflecting the incident power, that plasma wave also makes hot electrons

24 The Dec MJ shot provided excellent Coupling, Drive, & Symmetry Coupling: ~ 90% of incident laser stayed inside the hohlraum Drive: ~ 285 ev which is already quite close to that needed for ignition Tr (ev) Symmetry: To within ~ 10% of round, and tunable via S. Glenzer et al., Science 327, 1228 (2010) N. Meezan et. al. PoP 17, (2010 P. Michel et. al. PoP 17, (2010)

25 The hohlraum to-do list for the NIC campaign Hot-e s: High energy Bremsstrahlung from hohlraum wall is within spec. But how many hot-e s get to capsule? Drive: Bang times ~200 ps later than predictions. Is it a diagnostic or physics issue? Action: Image with 50 kev GXI Symmetry: Explore schemes that maintain it while: Action: measure velocity and add new bang time measurements (GRH) Increasing coupling & drive Decreasing hotelectrons Actions: Deploy third wavelength ( 3 ) to optimize cross beam energy transfer, Re-optimize hohlraum geometry

26 We will use low Deuterium fraction (THD) low yield cryo implosions to minimize surrogacy and systematic errors before carrying out high yield implosions THD targets address the unique physics issues of cryo-layered targets and are the most challenging step in the implosion optimization campaign Solid THD layer Inner surface ice roughness Interface instability Diagnostics of the imploded fuel will allow us to assess the likelihood of ignition with DT We will explore the tradeoff of velocity and mix

27 THD targets study the hydrodynamic phase of hot spot formation and fuel assembly 15 Hot spot formation and trajectory in R, T DT <T> hot spot (kev) 10 5 Time -heating Ignition and burn THD Hydro assembly R hot spot (g/cm 2 )

28 Cryogenic fuel layers are imaged with x rays from 3 directions through slots in the hohlraum and through the laser entrance hole X-ray image of ice layer CH shell Capsule viewing window structure Ge-doped layer 150 μm 10-m fill line 70 μm ice 70 m ice X-ray images from 3 orthogonal directions Temperature: 18K ±0.001K control Target position stability for X-ray imaging : < 2 m p-p

29 The recently installed CryoTarpos supports formation of cryogenic fuel layers outside the chamber prior to insertion into target chamber center at shot time Cryogenic fuel layers will be formed in a new target positioner (cryo-tarpos) recently installed on NIF

30 Cryogenic fuel layers will be formed in a new target positioner (cryo-tarpos) recently installed on NIF Inserting the target on the tip of the target postitioner Cryo-shroud retracted

31 The first THD cryo-layered shot was successfully carried out on September 29, 2010 Target for the first cryo layered shot mounted on cryo target positioner

32 The main purpose of first cryo-layered experiment was to demonstrate the ability to integrate all the laser, target, and diagnostics capabilities needed for a successful experiment A wide range of new diagnostics was fielded on the first THD shot Several neutron time of flight (NTOF) detectors for yield, ion temperature and fuel R A magnetic recoil detector for yield and fuel R Zirconium and copper activation detectors for yield A Cherenkov gamma reaction history (GRH) diagnostic for bang time A hardened Gated X-ray Detector (hgxi) for implosion shape in the presence of the neutron yields of THD targets On the September 29 shot, essentially all the diagnostics obtained high quality data which is currently being analyzed, the target in the cryo-tarpos had a high-quality layer which was successfully inserted into the chamber, and the laser energy was within 2% of the request

33 This hohlraum and laser for the THD shot behaved as expected based on earlier experiments and calculations The hohlraum x-ray drive for the 1 st THD experiment was consistent with earlier non-layered symcap shots The laser energy delivered was about 2% above the requested 1.06 MJ T RAD (ev) Power (TW/beam) 2 1 Individual outer beam power Individual inner beam power Absorbed Energy (MJ) Time (ns) Based on hohlraum results to date, we expect to achieve Tr ~300 ev with ~1.3 MJ into the ignition scale hohlraum. Routine operations at 1.3 MJ is scheduled for early CY2011

34 The GXD obtained high quality images which indicate we need to further improve capsule surface features from dust and other assembly artifacts A sequence of frames from GXD shows a jet of material passing through and cooling the hot spot as the implosion reaches peak emission 21.1 ns 21.3 ns 21.3 ns 70 m In the coming year, we will adjust symmetry, implosion velocity, shock timing, and mix to optimize the fuel assembly in THD targets in preparation for 50/50 DT experiments

35 Ignition experiments in lay the ground work for target performance which meets IFE requirements Yields versus laser energy for NIF geometry hohlraums Potential NIF performance at 2 based on stored 1 energy Yield (MJ) Expected NIF performance at 2 with optimized conversion crystals and lenses Expected NIF performance at 3 Tr(eV) 300 ev 270 ev 250 ev ev Yield and gain consistent with an optimized DPSSL IFE system Laser energy (MJ)

36 Summary Based on our current understanding, following a successful tuning campaign, we will have a high probability of ignition and yields of 5-10 MJ or more with ~1.3 MJ of laser energy using a CH capsule Initial hohlraum energetics experiments put us into the hohlraum temperature range for ignition experiments at ev The laser, diagnostic, target fabrication and other infrastructure capabilities needed for the ignition campaign are now in place. We have carried out the first THD cryo-layered implosion Ignition experiments in lay the ground work for target performance which meets IFE requirements

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