The Development of Indirect Drive ICF and the Countdown to Ignition Experiments on the NIF
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The Development of Indirect Drive ICF and the Countdown to Ignition Experiments on the NIF Maxwell Prize Address APS Division of Plasma Physics Meeting November 15, 2007 John Lindl NIF and Photon Science Directorate Chief Scientist Lawrence Livermore National Laboratory Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 The NIF ignition experiments will be the culmination of five decades of development which started with the invention of the laser in 1960 • Ted Maiman demonstrated the first laser in 1960 • John Nuckolls 1972 Nature paper spelled out the essential requirements for high gain laser driven ICF • Indirect drive experiments started at Livermore in the mid-1970’s • Dramatic advances in computations, lasers, diagnostics, and target fabrication over the past 3 decades laid the groundwork for NIF and the National Ignition Campaign (NIC) • We are designing precision experimental campaigns for hohlraum energetics, shock strengths and times, implosion velocity and ablated mass, and symmetry, which will take 100-200 shots leading up to the first ignition attempts • Targets near 1 MJ of laser energy have a credible chance for ignition in early NIF operations • The initial ignition experiments only scratch the surface of NIF’s potential There are two principal approaches to compression in Inertial Confinement Fusion Indirect Drive Low-z Ablator for Efficient Cold, dense absorption main fuel (200-1000 g/cm3) 10 mm DT 2.5 gas mm 0.1 mm Direct Drive Hot spot Cryogenic (10 keV) Fuel for Efficient compression Inertial Confinement Spherical ablation with Spherical collapse of the Fusion uses direct or pulse shaping results in a shell produces a central indirect drive to couple rocket-like implosion of hot spot surrounded by driver energy to the fuel near Fermi-degenerate fuel cold, dense main fuel capsule To illustrate the physics of ICF ignition, we compare a NIF capsule and a possible future high yield capsule High yield capsule NIF capsule 3.25 mm Be CH + 0.25% Br + 5%O 1.11 mm 3.0 DT solid 2.75 (7.2 mg) DT solid (0.2 mg) 0.95 DT gas 0.3 mg/cc 0.87 DT gas 0.3 mg/cm3 Radiation temperature = 300 eV 210 eV Implosion velocity = 4 x 107 cm/sec 3 x 107 cm/sec Capsule absorbed energy = 0.15 MJ 2.0 MJ Capsule yield ~ 15 MJ ~ 1000 MJ Ignition is defined as the point at which α−particle deposition sustains the burn with no additional input of energy Density and temperature Burn propagation after ignition profiles at ignition depends only on fuel ρR 3 3 ) 10 10 ) V V e e 0.2-MJ ) k k 3 ( 12 ( NIF capsule 2 e m e 10 r c r (yield ~20 MJ) 2 / u ρ time 10 u t g t ( a a r 8 r y e t e 1 α- i 2.0 MJ p 10 p s m particle n capsule (yield m e e 1 e t 10 t ~1000 MJ) range at D 4 n 0 10 keV n 10 o T o I i I 10-1 0.2 0.4 0.6 0.8 1.0 0 1 2 3 ρr (g/cm2) ρr (g/cm2) .About 15 kJ of energy is coupled to the fuel for compression and ignition of the 200 kJ NIF sized target .At 1 MJ of yield, 200 kJ of α-particle energy is coupled to the fuel and it is well into the ignition region - definition of ignition adopted by 1996 NRC review of NIF .In ITER with a Q=10, α-deposition is twice the external power needed to sustain the plasma Why do we believe that ignition will work on NIF? • Over 3 decades of experiments on Nova, Omega and other facilities have provided an extensive data base to develop confidence in the numerical codes • Benchmarked numerical simulations with radiation-hydrodynamics codes provide a first principles description of x-ray target performance (Laser-plasma interactions are treated separately with codes which are now becoming predictive for NIF-relevant plasmas) • “The Halite/Centurion experiments using nuclear explosives have demonstrated excellent performance, putting to rest fundamental questions about the basic feasibility to achieve high gain” from 1990 NRC review of ICF Halite/Centurion Power NIF Ignition Nova, Omega Energy The first laser was demonstrated by Theodore Maiman in Malibu, CA, in May 1960 John Nuckolls and John Emmett were central to the development of the LLNL ICF Program Disk Amplifier Prototype from the mid 1970’s John Emmett, who came to LLNL in 1972 was the driving force behind the development of the LLNL laser program John Nuckolls’ vision of small thermonuclear explosions, laid out in his seminal 1972 Nature paper, provided the motivation for an aggressive ICF Program Would you hire these people? John Lindl George Zimmerman Mike Campbell Laser Programs 1978 Manpower Book Ed Moses did not come to Livermore until the 1980’s but he would have fit right in during the 1970’s John Lindl George Zimmerman Mike Campbell Laser Programs Ed Moses 1978 Manpower Book The first steps leading to indirect drive ignition with lasers took place in the mid 1970’s • 1970’s: Radiation driven target designs provided a path forward for high gain ICF with relaxed laser beam quality and hydrodynamic instability compared to direct drive • 1976: first laser driven indirect drive experiment in 1976 on the Cyclops laser —Cyclops was developed as a prototype beamline for Shiva The 20 beam 10 kJ 1.06 µm Shiva laser was a major step forward in the scale and complexity of high energy laser systems Shiva laser bay Shiva target area Experiments on the Argus and Shiva lasers provided key results on achievable hohlraum temperatures . 1979-1981: Shiva and Argus experiments show limits to radiation temperature from LPI and a path to TR>200 eV using frequency converted light (2ω and 3ω) Shorter laser wavelengths can Hot electron fractions approached dramatically reduce hot electrons 50% in 1ω hohlraums on Shiva for a given laser energy into a hohlraum 100 Cairn hohlraum scale size 2 " 6 (scale 1 = 500-µm 10–1 diam " 800 µm long) 3 " 6 ) 12 V 10 Incident energy (kJ) Hot 2 " 3 e 2 " 2 k 3 3 / –2 " Electron 10 2 " 1 V 4 " 6 e Fraction k 10 ( 10 –3 10 e 3 " 1.5 c n –4 e 10 u l 8 2 " 10–4 2 " 10–3 2 " 10–2 2 " 10–1 1 10 F tc fR = 1.0 –! IL dt/Etotal 08-00-0594-2502.pub 30-50% at Tr ~160-170 eV Energy (keV) 1% at Tr = 130 eV From 1984 to 1999, the 10 beam, 30 kJ, 0.35 µm Nova laser was the central facility for indirect drive ICF With Nova, the ICF program brought together advances in laser performance, precision diagnostics, and advanced modeling tools needed to establish the requirements for Ignition. Plasma physics issues constrain the hohlraum temperature and hydrodynamic instabilities establish the minimum required temperature “Bird’s beak” plot from 1990 Hohlraum physics acceptable plasma High P , T , I below about 300 eV r r L instabilities NIF design capabilities ) Ro 400 High vol large symmetry W R T final ( r e large R/DR w o P Hydrodynamic hydroinstability 200 instabilities determine the minimum 0 temperature 0 requirement 1 2 Total energy (MJ) Experiments on the Nova laser demonstrated key target physics results needed for ignition • 1985-1990: Nova experiments demonstrated key target physics requirements for laser driven high gain (pulse shaping, symmetry control, Rayleigh-Taylor stabilization by radiation ablation, TR>200 eV with 3ω light • 1990: 300 eV hohlraum temperature demonstrated on Nova led to a reduced scale ignition facility from the 5-10 MJ LMF to the 1-2 MJ NIF as recommended by the 1990 NRC review of ICF • 1990’s Demonstration of precision control of laser driven hohlraums as required for ignition (Nova Technical Contract from 1990 and 1996 NRC reviews of ICF) Scaling of peak drive temperature 300 ) V e ( r T 250 k a e p x e 200 n s a L 150 150 200 250 300 Hohlraum Length (µm) Experimental peak Tr (eV) Advanced diagnostics have been central to measuring the phenomena critical to understanding NIF Sequence of x-ray backlit Gated MCP x-ray imager images of imploding capsule time 1 m 1.6 ns 1.9 ns 300 µm 2.2 ns 2.5 ns Pinholes MCP + Gating film pack electronics time MCP gated imagers were operated between 100 eV and 10 keV with 5-50 µm, 30 -300 ps resolution The measured growth of ablative hydrodynamic instabilities in ICF agrees with numerical models Growth of Harmonics vs time Face-on: Streaked Time (ns) 3-D 2-D 08-00-0593-1818B Recently, we have been able to produce well characterized NIF-like plasmas on the Omega laser Near Backscatter Imager (NBI) Interaction 3w Transmitted beam Beam Diagnostic Full-Aperture CH gas fill Backscatter Station produces uniform (FABS) L=2 mm and longer ne/ncr=6% Plasma temperatures measured with Thomson A uniform 6%ncr plateau is produced between scattering agree well with simulations 0.5 and 1.0 ns 0.15 ) 4 V e k ( e r 3 Te u t 0.1 a r r e c t=0.5 ns p 2 n / m e e n T 0.05 n o 1 r t T c i t=1.0 ns e l E 0 0 0 500 1000 -1.5 -1 -0.5 0 0.5 1 1.5 Time (ps) Interaction Beam Path (mm) Froula et al., Phys.