1

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

GRH Graphite Donut

20

Exploding Pusher Target

Anderson et al., Phys. Rev. 111(2), 572

(1958)

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 ?

GammaReactionHistory at NIF