progress toward polar-drive ignition for the nif · 2012-12-24 · i2064 significant progress...
TRANSCRIPT
R. L. McCroryProfessor of Physics and AstronomyProfessor of Mechanical EngineeringDirector, Vice Provost, and Vice PresidentUniversity of RochesterLaboratory for Laser Energetics
Fusion Power Associates Meeting
Washington, DC5–6 December 2012
Progress Toward Polar-Drive Ignition for the NIF
0 50 100 150 200 250 300 350
tR (mg/cm2)
Neu
tro
n y
ield
(×1
013 )
10
1
0.1
1.0
0.5
0.2
0.1
0.05
0.020.01
Si-doped CD ablatorPure CD ablator300-mg series (2009)
EquivalentITFx
I2064
Significant progress toward demonstrating direct-drive ignition on the NIF is being made
• Polardrive(PD) will allow for direct-drive–ignition experiments at the National Ignition Facility (NIF) in the x-ray-drive configuration
• OMEGAdirect-drivecryogenictargetimplosionsaredefiningtheignitiondesign space
• Performancecontinuestoimprove
– the yield and ion temperature increase with implosion velocity up to 3.8 × 107 cm/s (maximum to date)
– the measured areal density agrees with 1-D predictions for adiabats >2.5
– Px increased to ~3.0 atm-s
– a NIF-scaled experimental ignition threshold factor has increased to ~0.15
• Progresstowarddevelopingpolardriveisongoing,includinginitialNIF PD experiments
LLE is making progress toward demonstrating ignition hydro-equivalentperformanceonOMEGA.
Summary
Collaborators
R. Betti1*, T.R. Boehly1, D.T. Casey2, T.J.B. Collins1, R.S. Craxton1, J.A. Delettrez1, D.H. Edgell1, R. Epstein, J.A. Frenje2, D.H. Froula1, M.Gatu-Johnson2,V.Yu.Glebov1,V.N.Goncharov1, D.R. Harding1,
M. Hohenberger1, S.X. Hu1, I.V. Igumenshchev1, T.J. Kessler1, J.P. Knauer1, C.K. Li2, J.A. Marozas1, F.J. Marshall1, P.W. McKenty1, D.D. Meyerhofer 1*,
D.T. Michel1, J.F. Myatt1, P.M. Nilson1, S.J. Padalino3, R.D. Petrasso2, P.B. Radha1, S.P. Regan1, T.C. Sangster1, F.H. Séguin2, W. Seka1, R.W. Short1, A. Shvydky1, S. Skupsky1, J.M. Soures1, C. Stoeckl1,
W. Theobald1, B. Yaakobi1, and J.D. Zuegel1
1Laboratory for Laser Energetics, University of Rochester2Plasma Science and Fusion Center, Massachusetts Institute of Technology
3StateUniversityofNewYorkatGeneseo
*also Depts. of Mechanical Engineering and Physics and Astronomy, University of Rochester
Direct drive is a true alternative to indirect drive
I2004a
• Directdrivecouplesmoreenergytothecapsule
– provides higher margins
• Theconcepthasbeenvalidatedthroughdecadesofresearch,primarilybyLLEonOMEGA,withcontributionsfromNRL
• Shockignitionprovidesanadditionaldirect-driveoptionwiththe possibility of significantly higher gain
– less validated to date
Direct-drive ICF is a viable ignition alternative for the NIF
E18400l
• Directdriveispredicted to couple 7 to 9× more energy to the compressed core than indirect drive
• 2-Dsimulationspredict gains of ~50 on the NIF with symmetric irradiation
• CryogenictargetimplosionsarestudiedonOMEGAat~1/4 of the NIF target scale
– R ~ (EL)1/3
• LLEisdevelopingpolardrive to allow for direct-drive–ignition experiments while the NIF is configured for x-ray drive
0
1
0
2
3
2 4 6 8Time (ns)
Three-picket NIF design
Po
wer
/bea
m (
TW
)
10 12
160 nm DT
37 nm CH
DT gas
1700
nm
Gain1-D= 48
75°
40°
23.5°30°
50°23.5°
Repointing for polar drive*
2-D simulations predict polar-drive ignition on the NIF when appropriate beam smoothing has been added.
The in-flight aspect ratio and adiabat determine the target stability and areal density
TC10126
• In-flight aspect ratio (IFAR): Ratio of the implosion radius to the shell thickness at 2/3 of the in-flight radius
– IFAR determines of the amplitude of the Rayleigh–Taylor (RT) modulations that disrupt the implosion
– the 1-D minimum energy for ignition, Emin ~ 1/(IFAR)3
• Adiabat: Mass-averaged adiabat contributing to the stagnation pressure
– the adiabat determines the target compressibility and the RT growth rate
IFAR2/3 = R2/3/D2/3
. /g cmadiabat
pressure MbarPP
2 2f 5 33t= = ^
^hh
Symmetric direct-drive–ignition designs* can be scaled forhydrodynamicequivalenceonOMEGAscale
TC10256c
Hydrodynamic scaling Direct-driveNIF 1.8 MJ*
3.6 mm
0.86 mm
OMEGA 26 kJ
Scale 1:70in energy
Capsule radius ~ ELShell thickness D ~ ELLaser power ~ ELPulse length ~ ELMass fuel ~ EL
1/3
1/3
1/3
2/3
Hydrodynamic similarity is ensured by keeping the implosion velocity, adiabat, and laser intensity the same at the two scales.**
*V.N.Goncharovet al., Phys. Rev. Lett. 104, 165001 (2010).**R. Betti presented at the 24th IAEA Fusion Energy Conference, SanDiego,CA,8–13October2012.
OMEGAdirect-drivecryogenictargetimplosions are defining the NIF PD design space
TC10127
• Thetargetadiabatischangedwith
– picket-pulse spacing and heights
– step on main pulse rise
• TheIFARisvariedthroughthe
– ablator thickness
– ice thickness
• Theimplosionvelocityisvariedthrough the
– target mass
– laser intensity
0.3
0.2
0.1
0.00 1 2 3 4
Target design
430 nm
Ablator
DT ice
D2/DTgas
Po
wer
(T
W)
Time (ns)
Cryogenic target implosions are validating the physics models used in simulations.
~P YR . .meas
0 6 0 34x t^ h
OMEGAcryogenic-DTimplosionscanaccessthedesignspace for ignition on the NIF
E21735a
• Theprimarydesignparametersintheradiation–hydrodynamic models are
– laser intensity: IL ~ 0.8 to 1 × 1015 W/cm2
– shell velocity at the end of acceleration: Vimp ~ 2.5 to 3.8 × 107 cm/s
– mass-averaged adiabat contributing to the stagnation pressure: a ~ 1.5 to 4.0, where a = P/Pf = P/2.2 t5/3
– in-flight aspect ratio: IFAR ~ 10 to 25, where R/Dr is evaluated at 2/3 the initial radius
30
25
20
101 2 3 4
15
2012 implosion database
370
Polar-drive–ignition designs
Hig
her
sta
bili
tyIF
AR
Adiabathigher stability
Ourdatabaseincludesonlyphysicsquality shots.
The (1-D) predicted implosion velocity is confirmed by the measured burn history
TC9778e
To match the data, the 1-D design code LILAC incorporates nonlocal thermal transport1 and a stimulated Brillouin scattering (SBS) model2 to account for cross-beam energy transfer (CBET).
Without CBETWith CBET
1021
Time (ns)
1020
1019
10183.2 3.4 3.6 3.8
Measurement
Neu
tro
n r
ate
(1/s
)
A 10% changein velocity is atiming shift of 150 ps
The observed shift in the 1-D bang time shows the importance of including the CBET model in the design code.
1V.N.Goncharovet al., Phys. Plasmas 15, 056310 (2008).2I. V. Igumenshchev et al., Phys. Plasmas 19, 056314 (2012).
Cryogenic target performance is parameterized by the ratio of the neutron yield to that predicted by 1-D simulations [yield over clean (YOC)]
TC10123
The 1-D simulations include all of the known physics with no adjustable “knobs.”
IFAR < 22
24
22
20
18
16
14
1.5 2.0 2.5 3.0 3.5
Adiabat
IFA
R
Map of Yexp/Y1-D (YOC)Symmetric point design
25
20
15
10
5
00 1 2 3 4
YO
C (
%)
Adiabat
IFAR $ 22
YOC (%)
>22.520.0 to 22.517.5 to 20.015.0 to 17.512.5 to 15.010.0 to 12.57.5 to 10.0<7.5MeasuredYOC
The neutron yield and ion temperature increase with implosion velocity
E21739a
Ignitionrelevant
2 3 4
1014
1013
1012
Vimp (×107 cm/s)
2012 implosion database
Yie
ld
2
2
3
3 4
Vimp (×107 cm/s)
2012 implosion database
T i (k
eV)
1-D
Measured
1-D
MeasuredIgnitionrelevant
Ignitionrelevant
Ignitionrelevant
The measured tR performance is ~1-D for adiabats > 2.5 and IFAR < 20
E21738
0.01 2 43
0.2
0.4
0.6
0.8
1.0
Adiabat
tR
/tR
1-D
0.010 3020
0.2
0.4
0.6
0.8
1.0
IFAR
tR
/tR
1-D
2012 implosion database 2012 implosion database
Offsets < 20 nmIce < 1.5-nm rms
Note: For most points, the measured tR is an average inferred from two independent measurements.
The ICF Lawson criterion can be used to connect the design parameters to observables
E21737
• Lawsoncriterionisdefinedas| = Px/Pxign > 1
• Ameasurableform*of| is:
| ~ (tR)0.61 × (0.24 Yn/Mfuel)0.34 , where tR is in g/cm2, Yn is in units of 1016, and Mfuel is in mg
• Avalueof| = 0.16 is needed to demonstrate hydro-equivalent ignitionperformanceonOMEGA*
• ThiscorrespondstoatR of ~300 mg/cm2 and a yield of ~4 × 1013
• ThebestimplosionsonOMEGAtodategiveavalueof| = 0.09, where tR ~ 160 mg/cm2 and Y ~ 2.1 × 1013
*R. Betti presented at the 24th IAEA Fusion Energy Conference,SanDiego,CA,8–13October2012.
Hydrodynamic scaling suggests less yield degradation due to nonuniformities on NIF
TC8660a
• TherequiredYOConOMEGAisdifficulttoestimate. Use simple clean volume analysis:
D D=- - –R3 RT1R DR ~R GRT RT0vD G GRTNIF
RT. X
RT spike amplitude Growthfactor Hydro-equivalency
– –YOC 1 1 YOCE
E/
/NIFNIF
NIFL
L
0
01 3
1 33
.v
vX
XXf ^bp h l
R
T
SSSS
V
X
WWWW
Initial seed
YOC’sareexpectedtobehigherontheNIFbecauseof a significantly larger clean volume fraction.
R3-D
Hot spotCold
Shell
R1-DGvoH ≈ 0
• Fusionreactionsoccurin the clean volume (red) YOC
YY
RR
1 D
3 D3
n1 Dn3 D.=
-
--
- f p
Implosion performance can be parameterized by an ignition threshold factor
TC10131a
• LLNLderivedanExperimentalIgnitionThresholdFactor(ITFx)
– ITFx (ID) = (Y/3.2 × 1015) × (DSR/0.07)2.3, where tR (g/cm2) = 21× DSR (%)
– ITFx = 1 corresponds to a 50% likelihood of ignition
– ITFx ~ (Px)3
• ThisformulacanbescaledtoOMEGA(X) energies*
– ITFx (NIF equivalent) = ITFx (IDX) × (ENIF/EX)1.28 × (Mfuel NIF/Mfuel X)
– ENIF = 1.8 MJ, EX = 25 kJ, Mfuel NIF = 0.17 g, Mfuel X = 0.02 g
S. W. Haan et al., Phys. Plasmas 18, 051001 (2011). * C.D. Zhou and R. Betti, Phys. Plasmas 15, 102707 (2008); R. Betti et al., Bull. Am. Phys. Soc. 54, 219 (2009).
†
× YOCNIF/YOCX
TheOMEGAITFxhydro-scaledtotheenergyavailableon the NIF exceeds 0.1
TC10124c
ITFx (NIF Equiv) = 4050 * (Y/3.2 × 1015) × (tR/1.5 g/cm2)2.3
Performance is independent of the ablator indicating that imprint is not (yet) the dominant perturbation source.
0 50 100 150 200 250 300 350
tR (mg/cm2)
Neu
tro
n y
ield
(×1
013 )
10
1
0.1
1.0
0.5
0.2
0.1
0.05
0.020.01
Si-doped CD ablatorPure CD ablator300-mg series (2009)
EquivalentITFx
Core x-ray emission suggests that target performance degradation is caused by ablator carbon mix in the core
E21741a
By raising the adiabat, the shell is stabilized, and mix is reduced even at high implosion velocities.
160
120
80
40
00.0 0.5
1-D calculations Experiment
MixFit: Y0.57
1.0
X-r
ay c
ore
em
issi
on
4 to
7 k
eV (
arb
itra
ry u
nit
s)
Yield (×1014)
3
2
1
01.5 2.0 2.5 3.0 3.5N
orm
aliz
ed e
mis
sio
n/Y
0.57
Adiabat
Simulation
Further improvements in cryogenic target performance are expected over the next year
TC10132a
• Isolatedsurfacedebrisonthetargetappeartobelimitingtheimplosionperformance
– a significant engineering effort is underway to remove the defects
– a2011shotseriesshowedimprovedYOCwhenfewerdefectswerepresent
• Theeffectsofcross-beamenergytransferarebeingunderstood
• DopingtheouterpartoftheablatorwithSiorGewillreduceimprinting and RT growth
Cryo-2093-1664Cryo-2093-1664
DendriteCondensates
Cryo targetimage
0.5
1.0
1.5
2.0
0.020 40 60 80 1000
Yie
ld (
×10
13)
Offset (nm)
Before May ’11May ’11–Apr ’12Aug ’12
LLE is working to demonstrate ignition hydro-equivalent performance in 2013
E21754a
• Eliminatingtheisolatedtargetsurfacedefectswillmean
– lower-adiabat implosions (higher tR) with improved shell stability
– higher-velocity/IFAR implosions at lower adiabats
– imprint and stalk become the dominant perturbation sources
• WhileCBETdoesnotrestrictaccesstothedesignspaceonOMEGA,mitigation would provide more stability across the design space
– thicker shells could be driven to the same Vimp with the same laser energy
– mitigation may be necessary to achieve hydro-equivalent performance (should know within a year)
Improvements to the NIF PD target design have reduced the IFAR and implosion velocity
TC10134
• Anew1.5-MJNIFPDtarget design has enhanced stability
– implosion velocity 4.3 × 107 cm/s " 3.7 × 107 cm/s
– in-flight aspect ratio 36 " 30
• 2-Dgain~70, with PD illumination only
• 2-DsimulationswithfullNIFnonuniformities are underway; expect a gain of ~30
100
50
00 50 100
r (nm)
z (n
m)
0
80
160
240
320
400
480
560
t (g/cm3)
3
4
5
11
2 (keV)2 (keV)
3
4
5
66
77
8899
Improved symmetry has been demonstrated with shimmed shells
TC10362
–10
0
10
20
–203.1 3.2 3.3
DRACO , = 4
DRACO , = 2
3.4 3.53.0
Mo
de
amp
litu
de
(%)
Time (ns)
Experiment , = 4Experiment , = 2
–10
0
10
20
–203.1 3.2 3.3
DRACO , = 4
DRACO , = 2
3.4 3.53.0
Mo
de
amp
litu
de
(%)
Time (ns)
No shim (67343)0 nm, 120 nm, 140 nm
Shimmed (67345)Experiment
500 n
m
500 nm
DRACO/Spect3D Experiment DRACO/Spect3D
Experiment , = 4Experiment , = 2
CR ~ 5 CR ~ 5
R ~ 76 nm R ~ 77 nm
Early NIF experiments will address key issues for PD ignition
TC10147a
• Thegoalisto
– demonstrate drive uniformity
– measure laser coupling
– identify and address laser–plasma interactions- longer coronal density scale lengths in NIF implosions
may result in larger effects of cross-beam energy transfer1
and fast-electron preheat from two-plasmon decay2
• TheseexperimentswillusetheexistingNIFconfiguration (phase plates and beam smoothing)
• Thedesignsuseacombinationofbeamdefocus,repointing,andindependent ring pulse shapes to achieve the required symmetry
• Thefirstshotwillbeperformedthismonth
The primary goal of early NIF experiments is to predictably change implosion symmetry
TC10148
• Implosionsymmetryisvariedbychangingringenergies
Simulated x-ray self-emissionimages* (ho L 2 keV)500
500
0.2
0.6
1.0
Relativeintensity
0
0
0
–5
5Oblate
Prolate
0
2 4 6
–500
–500
y (n
m)
500
0
–500
y (n
m)
500
0
–500
y (n
m)
x (nm)
Time (ns)
P2
mo
de
amp
litu
de
(%)
20
20
40
60
4Time (ns)
Po
wer
(T
W)
6
CH
0.7 atm air1100 nm
80 nm
EL ~ 350 kJ
Spherical
*D. T. Michel et al., Rev. Sci. Instrum. 83, 10E530 (2012).
Substantial IFE technology development will be required after the demonstration of ignition
I2007
• Fusionresearchershavetoooftenmadeclaimsaboutenergyproduction that are not supported by demonstrated technology
• Anyenergydemonstrationmustbecosteffectiveandreliable
• Thepathtoaprototypepowerplantdemonstrationislongerandslowerthan most fusion researchers would like
• Anaggressivetechnologyprogramisrequiredafterthedemonstrationof ignition
The community must not “over-promise.”
I2064
LLE is making progress toward demonstrating ignition hydro-equivalentperformanceonOMEGA.
Summary/Conclusions
Significant progress toward demonstrating direct-drive ignition on the NIF is being made
• Polardrive(PD) will allow for direct-drive–ignition experiments at the National Ignition Facility (NIF) in the x-ray-drive configuration
• OMEGAdirect-drivecryogenictargetimplosionsaredefiningtheignitiondesign space
• Performancecontinuestoimprove
– the yield and ion temperature increase with implosion velocity up to 3.8 × 107 cm/s (maximum to date)
– the measured areal density agrees with 1-D predictions for adiabats >2.5
– Px increased to ~3.0 atm-s
– a NIF-scaled experimental ignition threshold factor has increased to ~0.15
• Progresstowarddevelopingpolardriveisongoing,includinginitialNIF PD experiments