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GRH Gas Cerenkov Diagnostics
Workshop on Nuclear Physics in Hot Dense Plasmas
Los Alamos and Lawrence Livermore National Laboratories – National Ignition Campaign
This work performed under the auspices of the U.S. DOE by Los Alamos and Lawrence Livermore National Laboratories under Contracts DE-AC52-06NA25396 and DE-AC52-07NA27344
LLNL-PRES-478331
Wolfgang Stoeffl
Lawrence Livermore National Laboratory
And the GRH Team
Acknowledgments, the fabulous GRH team
Hans Herrmann, Y.H. Kim, N. Hoffman, A. McEvoy, D.C. Wilson, C.S. Young,
J.M. Mack, J.R. Langenbrunner, S. Evans, T. Sedillo, S. Batha,…
Los Alamos Nat’l Lab
W.Stoeffl,L. Bernstein, P. Watts, A. Lee, J. Celeste, T. Thomas, G. Holtmeier, S. Poor, L. Dauffy, S. Azevedo, J. Liebman and the NIF Team
Lawrence Livermore Nat’l Lab
C.J. Horsfield, M. Rubery, W. Garbett
Atomic Weapons Establishment
E.K. Miller, R. Malone, M. Kaufman, B. Cox, Z. Ali, T. Tunnell,…
Nat’l Security Technologies
E. Grafil
CO School of Mines
V. Yu. Glebov, T. Duffy and the OMEGA Team
Laboratory for Laser Energetics
Four identical cells --
-- Variable gas pressure
-- Tunable Gamma Threshold
100 ps response time
10 ps relative accuracy
The GRH
Cherenkov
Detector
at NIF
Fusion gamma rays provide the most
undisturbed diagnostic of the NIF fuel burn
Gamma-Rays provide the opportunity to measure:
• Fusion Reaction History
— Bang-Time & Burn-Width
• Yields of various nuclear reactions from which to infer:
— Total DT neutron yield
— Plastic Ablator Areal Density (R)
— Possibly: Hot Spot Composition?
— Fuel R?, Mix?, …
ICF Gamma-Ray Diagnostics:
• have been well demonstrated on OMEGA
• are now operating on NIF
GRH Summary
155 psia CO2 (N101030,D)
Vacuum (N100923,B)
DT
Snout n- ChernenkovS
ign
al (a
.u.)
Fusion Reaction History can be determined through time-
resolved measurements of escaping fusion products
• Bang Time - used to establish
laser energy coupling to target
(shell velocity)
• Burn Width - used tuning • and many other uses
D + T 5He*
Neutrons or
Gammas
Foot
Time
Reacti
on
Rate
Burn
Width
Dopplerbroadened
no escape(hopefully)
)5.3()1.14(1~
MeVMeVn
nMeVHe )75.16(553e~
ITF I0S3 v
v0
8
0
4
11.2Rhotspot
Kwtd
Rhotspot
4
Mclean
MDT
0.5
Mach
Zehnder
For NIF, GRH diagnostics have been optimized to measure
-rays outside the chamber
Short pulse 40 pscal-laser (PiLas)_
PMT
Adjustable flat mirror
5” diameter Converter
Fiber light insertions
PressureWindow
Port flange
W
Shield
Off-axis Parabolic
Mirror
6 m from TCC
Fidu
Reflected 3laser light
-rays e- →UV/Vis
CO2 or SF6
1 of 4 channels shown
7
NIF 2w Fidu in80 ps 526nm
Scope trigger in
High Voltage Power SupplyPS350
Digital Delay GeneratorDG645 (4 ch.)
DPO71254
35 ps 670nm laser diode
5000V HV
Gate
GRH Control System (4x)
TCC Target 351nm light 50 ns delay
Mach ZehnderSystem (2)
PMT
Converter
1
23
4
Mach Zehnder
HV gate driver Photek
NF 1544B receivers
200V Gate
GRH Cherenkov Cell
TCC
5,12,24V support power
DWDM820MZ driver
Feed fibers
Pulsedoubler
DiagnosticMezzanine
Target Bay
351 filter
1550nm fibers
feedback
DC for gate
Bias
NIF 1-w FIDU, 500 ns ahead of bang
TIA-3000
4x
DG645
PMT HV
PMT Gating
MZ Controls
Timing
Calibrations
Digitizers
GRH Trigger
• Mach Zehnder Modulator– LiNbO3 crystal has E-field dependent index of refraction
– Ramping input produces sinusoidal output
• Mach-Zehnder Fiber links accomplish several tasks:
– Preserve bandwidth over long transmission line distances
– Protect digitizer channels from overdrive
– Extend dynamic range (multi-fringe operation)
Mach Zehnder Optical Transmission Link
Laser Diode
20 mw 1550 nm
GRH
PMT
Mach Zehnder
+
-
+
-
Bias
Controller
Optical
Receiver
Target
Bay
Diagnostic
Mezzanine
DPO
Scope
LiNbO3
Ref
time
Vo
lt
time
Vo
lt
An example how a Mach Zehnder transmits a large pulse
The MZ transfer function is
linear for small signals,
and wraps large signals.
The MZ system time
spread is only about 30 ps.
The limiting factor is
usually the scope, it has to
resolve the wraps for large
pulses.
Just a Mach Zehnder example:
GRH-6m can be configured for -rays or x-rays
8‖ Tungsten
Shielding
PMTshield cube
Mach
Zehnders
-ray mode: Pressure Flange - or -
x-ray mode: Scintillator
GRH-6m began operation in FY10 for THD Tuning Campaign
GRH-15m planned for Ignition and high resolution timing
TCC
ChamberTop
ShieldedStreak
Cameras
PMTsThick
shields
GRH-15m(Streak & PMT)
GRH-6m(PMT)
13º26º
side view
GRH-6m GRH-15m
Optical Detectors PMT Streak Camera (+PMT)
System Temporal Response (FWHM) ~100 ps ~10 ps
Yield Range (DTn) 1014-1017 1016-1020 neutrons
Collimated Field of View
(cm about TCC)
~100 cm 2 cm radius
Allows measurement of background free
delayed gamma rays
X-ray timing pulse is used to absolutely time laser
timing fiducials
1
2
0
5
10
15
20
25
30
-5 0 5 10
0
1
2
3
-150 -145 -140 -135 -130
PM
T Si
gnal
(V)
Time (ns)
Diminishing fiducial
pulse trainScintillator response to
x-ray pulse
Deconvolved
x-ray pulse
Deconvolved x-ray pulse representative of ―88 ps‖ laser pulse defining t0
1
Gamma Reaction History (GRH) diagnostic temporally
resolves fusion & n-induced -Rays (n-)
13
Absolute Time Base based on X-ray Timing Shots
n- from TC wall
DT Cherenkov
DT Expl Pshr (N103030), YDTn~2e14
GRH-D: 5 MeV threshold
155 psia CO2 (N101030,D)
Vacuum (N100923,B)DT
Snout n- Chernenkov
-0.25
0.00
0.25
0.50
0.75
1.00
1.25
1.600 1.650 1.700 1.750 1.800 1.850 1.900
De
con
volv
ed
Sig
nal
(n
orm
aliz
ed
)
Time (ns)
Gaussian Fit
Bang Time = 1.76 ns 50 ps
Burn Width = 130 ps 15 ps
• Cherenkov energy thresholding to
be used to resolve high-energy
fusion -Rays (>10 MeV) from
hohlraum/TMP n- (<10 MeV)
VIEW FROM 64,20 WITH CRYO-TARPOS - PERSPECTIVE
4/4/2011 14
View of Target Center
from GRH port
Note the Cryo Tarpos below
And two DIMs
Lots of material starting at
about 8 cm from TCC
1.E-03
1.E-02
1.E-01
1.E+00
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
0 5 10 15 20
GR
H R
es
po
ns
e(C
hvP
ha
t p
/c
pe
r In
cid
en
t G
am
ma
-ra
y)
Ga
mm
as
pe
r D
T-n
p
er
0.1
Me
V b
inGamma-ray energy (MeV)
1.E-12
1.E-11
1.E-10
1.E-09
1.E-08
0 5 10 15 20
Sp
ec
tru
m f
old
ed
w/
GR
H R
es
po
ns
e(C
kvP
h a
t p
/c p
er
so
urc
e n
pe
r 0
.1 M
eV
)
Gamma-ray energy (MeV)
THD=74/24/6, t0¼ ns
GRH is a 4-channel, Time-resolved, Energy-thresholded,
Gamma-Ray Spectrometer
“Prompt” -rays of interest
from indirectly-driven, THD:
• 19.8 MeV HT fusion -ray
• may infer Hot Spot H/D ratio
• 16.75 MeV DT fusion -ray
• spectrum likely more
complicated
• 4.44 MeV 12C(n,n’) -ray
• may infer Ablator rhoR
• Hohlraum/TMP n- continuum
• Effective n-to- convertor for
low yield BT determination
■ GRH Response curves
validated at Duke HIS
12C
DT
HT
What do we use the codes for ?
Intensity response curves Bang time gas pressure drift / temporal responses
n,n’ signalsDetector conversion statistics
Multiplying excited state by a factor of ~2 produces
a good match to data
Ratio of Intensitities v Threshold Enerery (MeV) as a fraction of the line spectrum case
Normalised to 12 MeV Threshold Intensity case
from Geant4 Simulations
6.00E-01
7.00E-01
8.00E-01
9.00E-01
1.00E+00
1.10E+00
1.20E+00
1.30E+00
1.40E+00
1.50E+00
1.60E+00
6 7 8 9 10 11 12 13 14 15
Threshold Energy (MeV)
Pre
dic
ted
dif
fere
nc
e B
etw
ee
n L
ine
an
d
Mo
dif
ied
Ha
le s
pe
ctr
a
Line Spectrum
Modified Hale Spectrum
Experiment
upper fit
Lower fit
Linear (Modified Hale Spectrum)
Linear (Line Spectrum)
Linear (Experiment)
Linear (upper fit)
Linear (Lower fit)
0.00E+00
2.00E-04
4.00E-04
6.00E-04
8.00E-04
1.00E-03
1.20E-03
1.40E-03
1.60E-03
0 5 10 15 20
Energy (MeV)
Inte
nsit
y (
a.u
.)
Modified Hale Spectrum
Hale Spectrum
The largest uncertainty in the simulated
―Hale spectrum‖ is the ratio of the
intensities of the ground and excited state
spectra.
Evidence from D3He experiments show
large uncertainties in this ratio and also a
variation with CoM energies.
We have modified the relative intensity of
the excited state wrt the ground state to
match the experimental data observed
The ratio of intensities of the ground to
excited state for the modifies hale
spectrum is
(1:1.9 ± 11%)
Which is in agreement with Cecil
although Cecil’s quoted error is very
large
(1:1.7 ±0.8)
Neutron-induced gammas are used to calibrate GCD
GRH
• DT signal measured by GRH
• Neutron-induced gammas
n + 12C 13C 12C + n’ + (4.44-MeV)
DT
DTn
12C
Puck installed
Without puck
Vo
lta
ge
/ Y
n (
V)
sec (s)
0
2
4
6
8
10
Single
DT
Bra
nchin
g R
ation (
1e-5
)
Puck
C Al Si SiO2 Cu Al2O3
Various puck materials are used to improve
systematic uncertainty in cross-section data
(3.3 ± 1.3)×10-5
at 1/0 = 0
at 1/0 = 1, (4.3 ± 1.7)×10-5
at 1/0 = 2, (4.8 ± 1.9)×10-5
1/0 = 0
197Au-n energy spectrum calculated
with a sphere model and MCNP
0 2 4 6 8 10 12 14 16 18 20
10-6
10-5
10-4
10-3
10-2
10-1
100
Gamma Energy (MeV)
Tally
/MeV
/part
icle
197Au sphere model
Is this correct ????
0.0001
0.001
0.01
0.1
1
10
0.1 1 10 100
GRH Pressure scan 10 MeV SF6
ph/gamma
Chere
nkov P
hoto
ns /
Gam
ma [
~arb
]
Pressure [psi]
Example of a solved mystery:
The GRH gas pressure scan allows
us to make extremely accurate
Cherenkov response
measurements.
What is the ―below
threshold‖ emission ???
Transition radiation would be ―flat‖
Solution:
The HIGS gamma beam
contains 0-800 MeV
bremsstrahlung gammas
from electron-rest-gas
interactions in the
synchrotron !
??
An Example of a solved mystery
Gas Cell A: 8 MeV Threshold
23
Examples of recorded scope traces
for one GRH cell.
The 3 different traces have a
gain difference of a factor 15
FIDU
Fusion gammas Neutron on wall
PiLas reference
MZ surface
accoustic
waves
GRH: Gamma-ray spectrum beginning to emerge
Bang Time = 21.49 ns 50 ps
Burn Width = 190 30 ps
Yield = 1.5e14 20%
Preliminary Analysis:
N110212: 4th THD
Fusion’s PMT
ring
Caveats: - D timing issue needs to be resolved (lined up on A’s leading edge)
- C not yet absolutely timed (peak lined up between A & D)
- Response functions are approximate (GEANT updates in process)
Cell: Threshold
The muon catalyzed T-T fusion creates a different
neutron spectrum compared to thermal fusion. Why ?
The muon capture fusion spectrum on T-T
Does not agree with the statistically
shared two-neutron spectrum.
It agrees more with the sequential
emission of one neutron yielding 5-He,
then a second neutron emission to 4-He.
In disagreement with thermal fusion
results.
We have many outstanding nuclear puzzles in fusion
Unsolved problems in muon catalyzed fusion dynamics:
• Measurement of neutron spectra and n–n, n–4He correlations in the p-wave
of the reaction t + t → 4He + 2n for better understanding the level structure
of the lightest neutron-rich nucleus 6He;
• Search for γ -quanta from the d(d, 4He) reaction from J = 1 state of ddμ
muonic molecule at the level about 10−6 per ddμ fusion for looking into the
conspired structure of 4He levels of negative parity;
• Search for e+e− pairs from ptμ fusion and finding out a reason for discrepancy
between E0 transition matrix element from pt (0+) excitation in
e(4He, pt)e reaction and this from non-radiative fusion ptμ → μ + 4He for
understanding the dynamics of electromagnetic transitions in nuclei;
• Microscopic calculations of nuclear reaction rates for radiative and non-radiative
fusion in ptμ muonic molecule for understanding the structure of nonnucleonic
degrees of freedom in A = 4 nuclei.
Unresolved issues in light element fusion
More precise branching ration for DT-fusion: Gammas/neutron
What is the shape of the DT fusion gamma spectrum ?
16.7 MeV vs broad 12 MeV
Better data for high energy gamma emission from the
14 MeV(n,gamma) reaction on materials like 12C, Al, Si, Cu, SiO2,
Al2O3, Au etc. MCNP does not match data well.
Much better cross section data for pT fusion gamma rays (19.8 MeV)
What is the shape of the T-T neutron emission spectrum ?
What is the gamma emission in the T-T fusion ?