nuclear diagnostic & physics at nifnsl/lectures/junior_seminar_2010/... · 2010-11-03 ·...
TRANSCRIPT
Nuclear Diagnostic & Physics at NIF
Notre Dame University, Notre Dame, IN10/27/2010
GSI-Helmholtzzentrum Seminar, Darmstad, Germany11/9/2010
D. Schneider / L. BernsteinLLNL
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore
National Laboratory under Contract DE-AC52-07NA27344.
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NIF-National Ignition FacilityDiagnostics (≈$90 M in FY11)
•X-ray diagnostics: ≈20 spectral, imaging and time-resolved diagnostics are planned/operational (developed over 25 years at NOVA, Omega etc.)
Very mature field
•Nuclear Diagnostics: needed for yields >1015-17 neutrons
• nToF, Neutron imaging, Activation, Charged-par ticle spectrometry, Radchem, Gamma Reaction History
First science proposals approved
(“Ride along” exper iments often allowed)
NIF Laser System: 192 laser beams produce 1.8 MJ, IR-UV 3ω=352nm, 2+ ns, 5x1014 Watt in 1mm2 spot)
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3
Cryogenic Layering Prototype Target
UNCLASSIFIED
UNCLASSIFIED
30μmwall
4
NIF Indirect Drive target schematic for NIC((NIC) National Ignition Campaign)
Typical Pulse Shape
Ablator (CH or Be)
DT Ice 0.255g/cc50/50 (0.01 3He)
DT gas fill (~1 3He)
(0.3mg/cm3@18K)Hohlraum Wall: – Au or High-Z
mixture (cocktail) Capsule (Be or Plastic, solid DT fuel)
Laser Beams in 2 Rings (24 Quads illuminate two Rings on HR wall)
Laser Entrance Hole with window
Thermal AlShield
He gas fill (1.3 mg/cc or He/H)
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Ignition REQUIRES that most of the α’s from D(T,n)αreaction are stopped in the nar row shell (≈20 µm) of high
areal density “cold” fuel
DTGas
areal density (“rho-R”)≡ ∫ρ(R)dR
α3.54
DT “Ice”
α0
60 µ
m
20 µ
m
This requires Elaser > 1 MJNIF is the first time that this is a possibility
Ignition means run-away thermonuclear burn
dnT
dt= −nT nD σ v & nT = nD =
n2
⇒ dndt
=−n2
2σ v
f ≈τconf
τburn=
n σ v R2 • 4cs
we find for Ti = 20keV DT a ρR ≥ 3 g/cm2 is required for f ≥ 1/3
τc ≅R
4cs
f ~ 1/3 ⇒ ρ R ≅ 3 g/cm2 ⇒ M =4 π3
ρ R3 =4 π3
ρ R( )ρ2
3
3
final
initial
initial
final3final final
3initial initial
3
43
4
=⇒==
RRRRM
ρρρπρπ
rarefaction propagates into and decompresses the assembled mass at the sound speed cs
ρR
The burn fraction f is determined by the “areal density” ρR
For laboratory exper iments and a reasonable fuel mass a high fuel compression (~ factor of 1000) is required
Lawson Cr iter ion Efusion= n2/4 <vσ> WDTτ =3nkT = Ethermal nτc > 12kT/(<vσ> WDT) > 1014s/cm3
at NIF nτc ITF ≈ dsf2 Y ≈ ρR3 nτc = ρR/4csmi with ρR = 3g/cm2 nτ=2 1015s/cm3
integration from t=0 to t=τc , 1/n-1/n0= ½ <vσ>τc
Density determines total energy in fuel, for ρ = 0.21g/cm3, M =2.6 103 g Yield=2.8 1014 J
ρ = 400g/cm3, M =7 10-4 g Yield=40.7 108 J
Spher ical compression (R3):
7
Ignition and Nuclear Science Experiments BOTH require excellent diagnostics (Laser, Hohlraum and Capsule Implosion)
Full ApertureBackscatter (FABS) HR energetics
(DIM)
Diagnostic Instrument Manipulator (DIM)
X-ray imager Streaked detector (HSXD) synchronization + 20ps
Shock velocity measurements
(VISAR) Static x-rayImager(SXI) pointing
Hard x-ray spectrometer
(FFLEX) Bremstrahlung/Preheat
Near Backscatter Imager (NBI) SBS/SRS
Soft x-ray temperature
(DANTE)
HR temperature
Diagnostic Alignment System
nTOF(3.9m, 4.5m,
20m)
MRS
NAD
RAGS
GRHNI
WRF
I will present a brief description of most of these detectors
Hot Spot
“Cold” Shell
Yn,
‹ρRHS›, ‹ρRTot›,
Ti
tBurn,
mix
8
Radiochemistry: Looking for reaction products on nuclides loaded pre-shot to get information about the capsule at maximum compression
124Xe (ρR) 127I (mix)
Step 1: Isotopes loaded in ablator
• Neutron flux detection Longest range – probes remaining shell.mA + n → m-1A + 2n (124Xe + n → 123Xe + 2n)
Eth = 8.7 MeV 1.4 barn (14.5 MeV)mA + n → m+1A + γ (124Xe + n → 125Xe + γ )
low Eth 0.01 barn (1 MeV) 0.002 barn (5 MeV)
• Deuteron flux detection Intermediate range – probes inner shell.mA + d → mB + 2n (127I + d → 127Xe + 2n), 79Br(d,2n)79Kr
Eth = 4.2 MeV 0.4 barn (10 MeV)
• α-particle flux detection Shortest range – probes hot spot region.mA + α → m+3B + n (18O + α → 21Ne + n)
Eth = 1.8 MeV 0.2 barn (3.5 MeV)
Step 2: Reaction products made in Shot
Step 3: Reaction Products collected and counted
Ablator (Be or CH)
(n,x) reactions tell about areal densityCharged-par ticle reactions tell about energy loss and ablator-fuel mix
9
0.01
0.10
1.00
10.00
0.50 5.50 10.50 15.50 20.50
124Xe Cross Sections
124Xe+n 125Xe + g
124Xe+n 123Xe + 2n
Energy Dependence of (n,x) cross Sections provides neutron downscattered fraction
0.006
0.007
0.008
0.009
0.010
0.011
0.012
0.013
0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.400.00
0.20
0.40
0.60
0.80
1.00
1.20
0 50 100 150 200 250 300
Cro
ss S
ectio
n (b
arns
)
Energy (MeV)
Fuel ρr (gm/cm2)
125/
123
Rat
io
125Xe/123Xe Product RatioCorrelates with Fuel ρr
Hot Spot Mix (ng)
Nor
mal
ized
Abu
ndan
ce
Hot Spot Xe 127 MixSignature-Fill Tube
Production of Xe127 from (d,I127) isdirectly cor related with the amountof mater ial in the capsule hot spot.
Downscattered neutrons “Prim
ary”
neu
trons
D(3He,α)p
H.S.
127I mixed in here give biggest signal
127I(p,n)127Xe
Radiochemical Analysis of Gaseous Samples (RAGS)
Each noble gas would be collected in a separate cryogenic station
T
T
T
NIFchamber(600m3)
Turbos
HeliumGas Puff System
Xenon Cryogenic Fractionation & Detector System
Gas Pre-cleaner System
RGA
CryoCollector
Germanium detectorCryo Trap
MassSpectrometer
He flush
N flush RGA
NIF Target
Chamber
RGA
CryoPre-filter
Getter
Getter
Getter
TPS
Removable Trap
• System cryos are closed before shot
• Gas is removed after shot through system turbos
• Rise of chamber pressure from cryo has been measured (evaluation needed)
• Vibration from cryo closure has been measured (non-issue)
Removes everything but noble gases (nitrogen, oxygen, water, etc.)
Dawn Shaughnessy
4 Cryo-Pumps
RAGS prototype calibration at LBNL
NIF-0610-19423s2.ppt 11Fortner—Presentation to Dr. Steven Koonin, July 7th, 2010
1000000
10000000
1E+08
1E+09
1E+10
1E+11
1E+12
1E+13
1E+14
1E+15
1E+16
1E+17
1E+18
0.00 5.00 10.00 15.00 20.00 25.00 30.00
Neutron Energy (MeV)
C1 (HTD)C2 (HTD)C3 (DT)C4 (HTD)C5 (HT)
115In(n,n’) ⇒ 115mIn (t1/2=4.5 h) 360keV93Nb(n,2n) ⇒ 92mNb (t1/2=10 d) 511keV90Zr(n,2n) ⇒ 91Zr (t1/2=3.3 d) 900keV12C(n,2n) ⇒ 13C (t1/2=20 m) 511keV63Cu(n,2n) ⇒ 62Cu (t1/2=9.8m) 511keV
1-10 MeV (T-T spectrum)
10-13 MeV (Downscattered)
13-15 MeV (Primaries)
15-30 MeV (Tertiaries)
Darren Bleuel
In-115(n,n')In-115mNb-93(n,2n)Nb-93mZr-90(n,2n)Zr-89C-12(n,2n)C-11
Neutron Activation Diagnostic (NAD) – Gives Yield and ρR anisotropy
NToF OMEGA calibrations corroborated against Indium neutron activation for DD Shots
Preliminary Indium activation yields agree with NToF
13NIF-1209-17998.ppt Kilkenny—NIC Review, December 9–11, 2009
Accuracies ofcross sectionsand calibrationsdetermineneutron yield measurement accuracy to better then 10% 20090905 shot
(rescaled 64,209
(0,0 WRF-mount)
Issues:IsotropyDefinition (En)
0 1 1.5 20.5
2
0
1
1.5
0.5
nTOF D2 Yield (n) x 1010
14
Neutron Time of Flight Diagnostic (nToF) Measures Y, Tion and ρR
Requirements
Jac Caggianno
DT
Downscatter TT
1012
1013
1014
1015
81012
14
dn/d
E
E(MeV)
Neutron spectrum
Goal: ITF ≈ dsf2 Y∆ITF ≈ 20%
Issue: nToF Scintillator must be fast enough to see 10-12 MeV neutrons after a HUGE 14 MeV peak
At NIF we need to measure neutron spectra to an accuracy ~ 10 %
1012
1013
1014
550450400350
dn/d
t
t(ns)
Neutron arrival rate
500
Dynamic Range ≈ 100
1015
Measurements of down-scattered fraction with nTOF requiresa detector which recovers quickly from 14 MeV neutrons - Custom new scintillator fabricated for NIF by LLNS -
Fortner—Presentation to Dr. Steven Koonin, July 7th, 2010 15NIF-0610-19423s2.ppt
New scintillators for dsf neutron imaging is in progressSimilar scintillators are tested (calibrated) with neutron beams and
sources (e. g. AmBe)
Fabricated sample
3”
≈ 3 orders of magnitude in 30ns
~3.75"
~2"
The wedged range filter is a small assembly that is to be piggy-backed onto another diagnostic cart in a DIM
Wedge Range Filter (WRF) and Magnetic Recoil Spectrometer (MRS)
ρRMeasurementFrom Proton spectrum (WRF)AndNeutron spectrum (MRS)(down scattered)
Johann Frenje (MIT)
WRF sees protonsFrom target and
in situ foil
MRS sees p or dfrom external foil
Goal: An active readout system
Target
TargetAperture
Imageprocessing
NIFInterface
DAQ
Alignmentsystem
Partial tonon-reflective coating
CCDImager
CCDImager
Opticalgate/intensifiers
Aperture; 3 alignment/mini-penumbra, 18 triangular, 18 um res. pinholes 4 alignment pinholes.
13nsPulser
Pulser
2:1reducer
75 mm MCPII
40 to 75 mm MCPII
Custom lens
Scintillator BCF-99-55160 mm square250 um fibers, 5cm thk.
CCD cameras36.8 mm x 36.8 mm. 9 um pixel size4k by 4k
Coherent fiber bundle36.8 mm x 36.8 mm.10 um fibers
Neutron ImagingDavid Fittinghoff
Neutron imaging on NIF will measure hot spot size and ρRshell from down-scatter imaging
• Two gated neutron images at distance detects primary neutrons from hot spot and down-scatter neutrons from cold shell
• Shape accuracy ~ 2%
nDT
nds
nds
n imaging on NIF is being implemented to work for igniting plasmas
• Use the primary image as a source and match down-scattered image to derive density distribution in the dense fuel shell. (Algorithm under development)
14 MeV Down-scattered Cold shell
T or D
18NIF-1209-17998.ppt Kilkenny—NIC Review, December 9–11, 2009
Mach Zehnder enclosure
The GCD will enable yield measurement complementary to nTOF and NAD
GRH BT, Yield γBang-time (BT) +10%γ energy/intensityYield
1 of 4 “Quad” Channels
γ converted into Cherenkov photons detected in PMT At n-yield of 1013 we detect ≈ 100 γch
[(γCompton 1(MeV)e/γ (1e-3; Al)170γch/(MeV)e 25(PMT)e(gain 10e6)]1e17x50Ω V]
(LANL led collaboration: Hans Hermann, Wolfgang Stoeffl)
AU-Ringn
Gamma Reaction History (GRH) diagnostic based on conversion of fusion γ-ray to Cherenkov photons – Measure “Bang time”, Y, Burn ∆τburn , ρR
GRH will use high band width optical readouts
First NIF GRH data from exploding pusher (low ρR)
20
DT-Fusion γ-ray
∆tGRH≈300 ps due to cable(not Mach-Zehnders)Goal: ∆tGRH<100 ps
Fortner—Presentation to Dr. Steven Koonin, July 7th, 2010 21NIF-0610-19423s2.ppt
TCC
TopShieldedStreak
Cameras
ScopesW
shields
Late 2011: GRH-15m(Streak & PMT)
Now: GRH-6m(PMT)
13°26°
NIF ChamberTwo-stage GRH implementation for improved dynamic range and temporal resolution
Absolute calibrations performed at the High Intensity Gamma Ray Source (HIGS)
12C <ρR> (indicative of ablator mass remaining) can be inferred from 4.44 MeV
γ-ray measurement
Calculated γ-ray Spectrum
γ-ray energy (MeV)
4.4 MeV 12C(n,n’) from capsule
Or 9Be (α, η)
16.7 MeV from D+T(BR≈1e-4)
19.8 MeV from H+T
1e5
1e6
1e7
1e8
1e40 5 10 15 20
γ-ra
y flu
ence
(p
artic
les/
keV
)
TransitionRadiation
GRH Response
(Assumes 0.15 g Au ring)
≈5
Calculated γ-ray yield from neutron capture on the Au in the hohlraum as a function of time. The lower g-yield is due in large part to the lower (total 146J) yield. The t-error bar arises from the convolution of the burn time and the GRH detector temporal response.
GRH might also allow measurement of ρRcold fuel from capture of En< 1 MeV on Au hohlraum
This might also be used to obtain neutron flux for astrophysical
capture cross section measurements
From C. Cerjan
Neutron spectrum from a 251 J rRmac=1.2 g/cm2 HT(+0.5%D) capsule with inelastic scattering on hydrogen isotopes turned off (green) and on (red).
nToF
with D(n,n’)D, T(n,n’)Tw/o D(n,n’)D, T(n,n’)T
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High Neutron Flux≈1031-35 cm-2 s-1
(fluence=1021-24cm-2)
Hot/DensekbT=1-20 keV ρ≈10-1000 g/cm3
(Natom=1023-26cm-3)High γ-Fluxϕγ=1031-35 cm-2s-1
High e- Flux1036 e/cm2•s-1
(fluence=1025 cm-2 )
From a Nuclear Physics perspective the huge photon, electron and neutron fluxes at NIF make it unique
(n,x) onExcited Nuclear
States
(n,x) cross sections
Charged-particleCross sections
( γ fluence=1020-24cm-2)
Flux (n cm-2 s-1): LANSCE/WNR (≈1010); Reactor (1≈018); SNS (≈1015)
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Different fuel creates different neutron spectra, including astrophysical (kT≈10 keV)
(Modeling cour tesy of C. Cer jan)
DD - 146 J
Neutron Energy (keV)
NIF (or stellar)
thermal
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The NIF environment is very similar to that found in star s where (n,γ) forms heavy elements (s-process)
The huge neutron flux in a NIF capsule enables
measurements of (n,γ) cross sections on radioactive nuclei
Zs-process
s-process path near Tm
169Tm 170Tm 172Tm
171Yb 172Yb 173Yb170Yb
171Tm
5.025 keV4.8 ns 3/2+
1/2+
171Tm
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Electron-mediates atomic-nuclear interactions in a NIF capsule cause thermal population of low-lying nuclear states
Photo-absorptionTime Reverse: γ-ray decay
NucleusHEDP
Photons
Electron-mediated interactions are most important at T≈keV
e e
Atomic-nuclear (electron) interactionsNEEC, NEET, IES*
Time Reverse: IC-decay
Atomelectrons electrons
Photons
N N* N N*
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Thermalization time scales for 169Tm R
ate
(s-1
)
109
107
105
103
101
10-1 100 101 102
Temperature (keV)
Compliments of G. Gosselin
5 ns
Photon-absorptiofree-boundbound-boundfree-free
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What γ-ray production rate does GRH see for a D-fuel capsule loaded with a (n,γ) “seed” nucleus
From X-rays: σρR-Tm≈10%
σρR-Au≈5% σAu≈2%
NγTm
NγAu =
εTmγ ρR( )TmσTm En( )φ En( )dEn∫
εAuγ ρR( )Auσ Au En( )φ En( )dEn∫
What we wantFrom hohlraumLate time signal
What we need
169Tm
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The main uncertainty in GRH’s ability to “tag” (n,γ) is the production of statistical γ-rays from the CN
Modeled statistical γ-ray spectrum for 155Gd
We would like to measure Sγ for Eγ≥3 MeV at the 10% level
εstati = εGCD Eγ( )⊗ Si
γ Eγ( )Eth
Q
∫ dEγ
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Thulium in a NIF capsule will exper ience both (n,γ) and (n,2n) on ground and isomer ic states
167Tm 168Tm 169Tm 170Tm1/2+ stable
1- 3 keV
3+ 93 d1/2+ 9.25 d
7/2+ 180 keV
1- stable
7/2- 293 keV
7/2- 316 keV
7/2- 379 keV
171Tm1/2+ 1/9 y
3- 183 keV
7/2- 424 keV
“Normal” Thulium Reaction Network
• Only states with long t1/2 (>10 ns) can be populated by the “low” neutron flux – (n,n’), (n,2n), (n,γ)
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167Tm 168Tm 169Tm 170Tm1/2+ stable
1- 3 keV
3+ 93 d1/2+ 9.25 d
7/2+ 180 keV
1- stable
7/2- 293 keV
7/2- 316 keV
7/2- 379 keV
171Tm1/2+ 1/9 y
3- 183 keV
7/2- 424 keV
“Normal” Thulium Reaction Network
3/2+ 10 keV
? 80 keV4+ 64 keV? 47 keV2- 41 keV
? 17 keV 3/2+ 8.4 keV
11/2 368 keV
9/2- 430 keV
2- 39 keV
2- 220 keV
3/2- 5 keV
HEDP-populated states
• Short-lived states are “targets” in NIF capsule as well due to NEEC, NEET etc.
The case is more complicated when states populated via nuclear -plasma interactions are included
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Collaborators
L.A. Bernstein, C. Cerjan, R. Fortner, D.L. Bleuel, R.D. Hoffman, M.A. Stoyer, K. Moody,
D. Shaughnessy, P. Bedrossia, M. Wiedeking, R. Hatarik, D. H. G. Schneider, Lawrence Livermore National Laboratory, USA
A. Hayes, G. Grim, R. Dunford, Los Alamos National Laboratory
L. W. Phair, Lawrence Berkeley National Laboratory, USA
C. Brune, J. J. Carrol Ohio University, USA
U. Greife, Elliot Grafil, Colorado School of Mines, USA
Chr. Kozhuharov, C. Brandau, Th. Stoehlker, GSI-Helmholtzzentrum Darmstadt, Germany
A. Palffy, H. Keitel, Max Planck Institute of Nuclear Physics, Heidelberg, Germany
D. V. Meot, G. Gosslin, P. Morel, E. Bauge, CEA/DAM, Buyeres-le-Chatel, F rance
P. Walker, University of Sur rey University of Surrey, Guildford, U.K.
Other Institutions: SANDIA; University of Oslo, Norway; iThemba Labs, South Africa
- 33 -
A collaboration is being established to explorenuclear physics @ NIF & statistical γ-ray spectra
Plus any of you that are interested