Lawrence Livermore National Laboratory Andrew G. MacPhee 17 th Topical Conference on High Temperature Plasma Diagnostics Albuquerque, NMWed 14 th May 2008.

Lawrence Livermore National Laboratory

Andrew G. MacPhee17th Topical Conference on High Temperature Plasma Diagnostics

Albuquerque,NM Wed 14th May 2008

UCRL-PRES-403581

Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

Diagnostics for Fast Ignition Science

2Lawrence Livermore National Laboratory

Collaborators

F. Beg, T. Bartal, S. Chawla, T. Ma, J. King, J. Pasley, B. Westover, M.S. Wei

R. Stephens, K. Akli

L. D. Van Woerkom, R.R. Freeman, E. Chowdhury, D.W. Schumacher,D. Offermann, T. Link, V. Ovchinnikov

C. Chen, M. Porkolab, MIT, USA

Y.Y. Tsui, University of Alberta, Canada

J. Bonlie, R. Coombs, H. Chen, M. Foord, S. P. Hatchett, D. Hey, A.J. Kemp, M. H. Key, A. B. Langdon, B. F. Lasinski, A. J. Mackinnon, B. Maddox, N. Izumi, H-S. Park, P. K. Patel, T.H.Phillips, D. Price, M. Tabak, R. Town


Density plot from 2D indirect drive fast ignition hydro design

~100m

For efficient burn with low driver energy 1.5 <R<2 gcm-2

For high gain with low driver energy 300 < < 500 gcm-3

Ignition 18 kJ in 23 ps , =36 m , 1.1x1020 Wcm-2

Laser intensity must reach several 1020 Wcm-2 in ~20ps

1) How efficiently can we couple 1-3 MeV electrons to the imploded plasma?

2) How much pre-formed plasma can we tolerate?

*M. Tabak, J. Hammer, M.E. Glinsky, et al, Phys. Plasmas 1, 1626 (1994); S. Atzeni, et. al, Phys. Plasmas 14, 052702 (2007)

Fast Ignition*: Initiate burn prior to peak compression with an intense beam of energetic electrons

Integrated experiments on Omega-EP, NIF-ARC and FIREX will use neutron yield and fluorescence from tracers to measure efficiency and transport

Short pulse experiments on Titan allow diagnostics development, pre-pulse evaluation and code benchmarking


Scope of talk

On shot laser diagnostics at Titan

Electron energy deposition and transport

Measuring the hot electron spectrum


On shot diagnostics are an essential record for modeling experiments

6m lens

150J 0.6ps, 1 from pulse compressor

Initial set-up microscope

Interferometer

2, 1ps, 10mJ probe beam

0 100 200 300 4000

100

200

300

400

500

600

700

y (

m)

x (m)

Full aperture retro-focus system

Pre-pulse monitor

`

`

Equivalent plane monitor

0 20 40 60 800

20

40

60

80

y (

m)

x (m)


The pre-pulse monitor is vital for modeling laser target interaction

35 36 37 38 39 40 41 42 43 44 45-0.01

0

0.01

0.02

0.03

0.04

0.05Prepulse monitor:080123s2Ch1.txt

Time (NS)

Sign

al (V

)

80 81 82 83 84 85 86 87 88 89 90-0.01

0

0.01

0.02

0.03

0.04


Time (NS)

Sign

al (V

)

80 81 82 83 84 85 86 87 88 89 90-0.01

0

0.01

0.02

0.03

0.04


Time (NS)

Sign

al (V

)

80 81 82 83 84 85 86 87 88 89 90-0.01

0

0.01

0.02

0.03

0.04


Time (NS)

Sign

al (V

)

SF ~ 5 mJ Spike ~ 2.5 mJ

-3 ns

-0.1 ns

Time (ns)0 5-5

*Ying Tsui, University of Alberta

Min Typical Max

~3ns

superfluorescence

0.3mJ 5mJ 70mJ

~1ps pre-pulse 1mJ 2.5mJ 30mJ (at 1.4ns, <Feb)

Combined energy contrast vs main pulse

105 2x104 1.5x103


Electron density from interferograms agree well with 2D hydro using pre-pulse data

0 100 200 300 4000

100

200

300

400

500

600

700

y (m

)

x (m)

150J, 2ps shot on 25m aluminum foil: 70 mJ SF + 30 mJ spike

0 50 100 150 200 250 30010

17

1018

1019

1020

1021

1022

1023

Aluminum: 100mjSuperFl+0mjPrePulse(green), 70mjSF+30mjPP(red); Probe080130s05(+)

Z (um)

XN

E (

cm-3

)

Ne (c

m-3)

(+) ne interferogram data(-------) ne simulation: 100 mJ SF only(-------) ne simulation: 70 mJ SF + 30 mJ spike

Density plateau due to spike

1017

1018

1019

1020

1021

1022

0 50 100 150 200 250Z(um)

Castor2 simulation with U of A EOS for Al:Interferogram:

Together, interferometry and pre-pulse measurements let us benchmark hydro codes

*Ying Tsui, U of A, ** Sebastian Le Pape LLNL


There is good agreement between equivalent plane images for system shots and the low power alignment pulse

0 20 40 60 800

20

40

60

80

y (

m)

x (m)0 20 40 60 80

0

20

40

60

80

y (

m)

x (m)

System shot #02042408Low power (OPCPA) alignment pulse

20 40 60 80 1000.0

0.2

0.4

0.6

0.8

1.0

x(m)

20

40

60

80

100

In

ten

sit

y

y(

m)

Binned lineouts through both spots:

Full shot

1E17 1E18 1E19 1E20 1E210.0

0.2

0.4

0.6

0.8

1.0

Inte

gra

ted

po

wer

fra

ctio

n

Intensity (Wcm-2)

Fraction of power above given intensity:

50% >4x1019

20% >1020

Low power (scaled)

Full shotLow power (scaled)


These experiments rely on k- fluorescence for measuring coupling efficiency and Bremsstrahlung spectra for measuring Thot

Thin front Al layer: No laser excitation of Cu k-

Titan Laser 150J, 0.6ps, ~1020Wcm-2

Thick rear Al layer: Electrons make only one pass through Cu tracer

Cu fluor layer:k- fluorescence measures hot electron yield

e-

e-

e- Bremsstrahlung + k-


Multiple diagnostics on Titan are used to characterize energy deposition, conversion efficiency and the hot electron spectrum

K- crystal imager axis

Hot e- spatial distribution

XUV multilayer imager axis

Temperature map

Specular reflection Single hit CCD Calibrates…

Sig

nal (

Ph/

J/S

r/eV

)

Energy (keV)

…absolute K- yield from HOPG crystal spectrometer

0.1 1 100.01

0.1

1

dN

/dE

(E

lect

ron

s/M

eV

)

Electron energy (MeV)

Thot diagnostic

Long pulse beam introduces controlled pre-pulse

Main pulse ~140J 600fs~1020Wcm-2


The reflection of laser light from oblique targets is important for coupling in cones*

K- image

Ray-trace

Laser bounce

*Tony Link, OSU, HELDA 2008

Grazing angle

Reflectivity (%)

Power on target (TW)

62 1.8 193

15 54 20

15 52 55

15 39 190 Cu foil target

Spectralon™ plate

Laser incident at angle to target surface

Image recorded on 16bit CCD

Laser light reflected from cone wall can provide usefulenergy at the tip

Reflection at 75º to normal ~20x reflection at 28º

S and P have similar reflectivity at 75º

f/3 incident beam scatters ~diffusely into a f/2 cone of rays


XUV images measure the black body temperature at the rear surface of the target*

T e fro

m 2

56eV

cha

nnel

Te from 68eV channel

• Ultra intense laser-target interactions create MeV electrons

• Planckian emission from rear surface peaks in the XUV

• Temperature corresponds to Lasnex 2d rad. hydro run with matching integrated XUV signal within mirror bandwidth

• Used to constrain hybrid PIC codes

Filter

Laser: 1m, 150J0.6ps, ~1020Wcm-2

Back illuminatedCCD

Spherical XUV multilayer mirror

Plane XUVmirror

25m CD target image at 256eV Tight focus peak intensity 1020Wcm-2

*Tammy Ma, These proceedings (B15)


A spherically bent crystal imager is used to measure the k- source size

• Crystal imager for Cu K- radiation: 5eV bandwidth, 10x magnification, 20m resolution => hot electron source size

• Line shift due to ionization of low Z Cu tracer limits crystal imager effectiveness for hot plasmas*

• For higher opacity integrated experiments a 16keV imager (Zr K-) is being developed that if successful will be less sensitive to line shift

Spherically bent quartz (211) 30m Cu foil, 500m x 500m ~5.1018 Wcm-2

500 m Cu foiltargetLaser

2d: 3.082Å, B @ n=2, 8.04keV=1.31°

J.A. Koch et al., Rev. Sci. Instrum. 74, 2130 (2003), *K.U. Akli, Phys. Plasmas 14, 023102 (2007),

Image plate or CCD

~60m FWHM


10 20 30 40 50 600.0

0.2

0.4

0.6

0.8

1.0Zr K-

Tx

Energy (keV)

Mo filter Tx

Pd filter Tx

Ag K-

~12 m Agtarget

Laser

20m Pd

30m Mo

Image plate

6x6 Ta pinhole array

30m , 500m thk

PdFilter

MoFilter

• Contrast K / Brem: ~1.4• Signal to background: ~6:1• Absolute calibration is in progress0 100 200 300

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Sig

nal

(p

sl)

x (m)

Pinhole limited width <30m

A pinhole camera with Ross pair filtering is insensitive to k- line shift in hot plasmas


K- imaging and Lasnex modeling show pre-pulse in cones is a significant issue

15mJ2ns nc

300m1e18

5e21

60m

Density on axis

Lasnex hydro of pre-pulse plasma:

See also Sophie Baton, LULI, submitted to POP

~80% K-yield within 200m of tip

750 m

nc @ 60m

~80% deposited within 200m`

Cu K- image

Titan: 15mJ pre-pulse

4.5J300ps

1e22

1e15

2e19

300m

nc

80m

nc at 80m, ne ~1019 at 300mTitan: ~1J pre-pulse

nc @ 80m

<20% deposited within 200m`

<20% K- yield within 200m of tip

Anticipated NIF-ARC scale pre-pulse

Cu K- image


A HOPG crystal spectrometer measures the absolute K- yield produced by hot electrons in the buried tracer layer

crystal

Image Plate

Direct Block

TCC

9758 eV

HOPG spectrometer

*K. Akli, GA, These proceedings

k- signal from HOPG normalized against single hit CCD averaged over several shots

Cu k- 8keV

Cu k- 8.9keV


Single hit CCD provides absolute calibration for HOPG

~20% error in ccd efficiency CCD

~10% error in single event determination

Filter Tx × solid angle × CCD × Laser energy

k- event countsk yield =

Single events recorded at CCD plane

Histogram of single events

= X-ray spectrum

Zoom

Cu k-

k-


An absolutely calibrated Bremsstrahlung spectrometer is used to measure the hot electron spectrum*

Dosimeters(Image Plates or TLD’s)

CollimatorElectron

Spectrometer

Pb + plastic housing

• Sensitive from 10-400keV X-rays• Vacuum electron spectrometer

removes charges particles from line of sight.

• Sensitive from 0.1-4 MeV electrons**

*R. Nolte et al, Rad. Prot. Dosim., (1999); C. Chen, These proceedings (B3)**H. Chen These proceedings (D37)


Spectrometer Response matrix

(modeled: ITS)

Target Response matrix(modeled: ITS)

he- …

Al Ti Fe Cu

IP 1 IP 4

… Pb

… IP 13…

Recordedsignal

Deconvolvedelectron spectrum

inside target

The hot electron spectrum is deconvolved from the bremsstrahlung spectrum using the Monte Carlo code ITS*

30° full angle

8m diam.

source

Vary I, T minimize SD vs dosimeters TEeIEf /

*C. Chen, These proceedings (B3)


A 1-T Boltzmann distribution provides a good fit to the measured data*

*C. Chen, These proceedings (B3)

100

1000

10000

100000

1 3 5 7 9 11 13

One temperature fit: (1.3±0.15) MeV

using ITS Monte Carlo model

8% conversion (~10J) to 1-3MeV electrons from ITS using Brem.

15% conversion to 1-3MeV electrons from ITS using absolute K- yield

Estimate based on K- yield is more sensitive to lower energy electrons

121J, 1020Wcm-2

Non-refluxing Cu foil target

Next step: 2 Temperature fit, hybrid PIC simulations to include

ohmic potentials, return currents, resistivity

conversion efficiency may drop

MeV

/mm

2

Dosimeter layer


This 1 temperature analysis using ITS shows that Thot scales with intensity at a lower rate than suggested by pondermotive scaling

0

0.5

1

1.5

2

0 50 100 150I (10^18) W/ cm^2

Th

ot

(MeV

)

Ponderomotive scaling

Beg scaling

Bremsstrahlung data

Beg scaling:

Thot(MeV)= 0.1(I 2/(1017W/cm2m2))1/3

Pondermotive scaling:

Thot(MeV)= (I2/(1019W/cm2m2))1/2


Summary

On shot laser diagnostics are crucial for benchmarking simulations:

• Interferometry agrees with 2D hydro for foil targets using the measured pre-pulse

• Equivalent Plane imaging demonstrates consistent intensity distribution between the Titan alignment beam and full system shots

The 1-T hot electron spectrum analysis shows less than pondermotive scaling

We need to include hybrid PIC simulations and a 2-T model to better understand both conversion efficiency and the electron energy spectrum


Backup slides


XUV spectroscopy measurements give a lower bound on black body imaging results*

45°

*Tammy Ma, These proceedings (B15)

Inte

nsi

ty r

atio

Front (plume)

Rear (surface)

Gold coated cylindrical mirror

Harada grating

CD Target

Measured line ratios agree with synthetic spectra at given T,


. . .

92-1

00 M

eV

1-1.

1 ke

V

1389

-100

MeV

0-5

keV

92-100 MeV

1-1.1 keVC1,1C1,2

C1,3 ... C1,150

C2,1

C3,1

C13,1 C13,150 ... ... ...

...

...

...

C2,2

...

... ...

123

Energy per photon deposited in each IP

T1,1T1,2

T1,3 ... T1,80

T2,1

T3,1

T150,1 T150,80 ... ... ...

... ...

...

T2,2

...

... .... . .

Number of photons generated per e-

=××

Target response matrix: ITS150 photon energy bins × 80 electron energy bins

. . .. . .

Cannon response matrix: ITS13 Image Plate Layers

× 150 photon energy bins

Image plate signal:13 dosimeter readings

Electron spectrum:

80 electron energy bins

N1

N2

N3

N80

...

D1

D2

D3

D13

...

Vary I, T minimize SD vs dosimeters TEeIEf /

Bremsstrahlung analysis


20 um Cu

25 um Cu

August conesApril cones

Low mass @ 28 deg

Low mass @ 75 deg

10 Al/30 Cu August

Al/Cu/Al August

1.00E+09

1.00E+10

1.00E+11

1.00E+12

1.00E+17 1.00E+18 1.00E+19 1.00E+20 1.00E+21

20 um Cu 25 um Cu August cones April cones

Low mass @ 28 deg Low mass @ 75 deg 10 Al/30 Cu August Al/Cu/Al August

multiple pass-refluxing

Cones have the highest yield

Single pass

Oblique incidence

*K. Akli, GA, These proceedings

Absolute yield depends on target and laser configuration


Tight focus at tip

FocusDown-stream 800m

FocusDown-stream 400m

FocusUp-stream 400m

68eV XUV channel ~8keV Cu K- channel Ray-trace aberrated Titan beam

0 200 400 600 8000.000

0.002

0.004

0.006

0.008

Sig

na

l (P

SL

/J)

Distance Along Cone Axis (m)

~100m tight and 400m defocus k- peak

Best focus ~1.1MeV

800m defocus~0.25MeV

400m defocus~0.4MeV

nc at ~40m (from hydro)

~155m 800m defocus k- peak

XUV poster GP8.00065: Tammy Ma

Foil Cone:Thot: ~1MeV 1.1MeV

k- yield: 7x109 Ph/J/Sr 2.5x1010 Ph/J/Sr

Efficiency ~50%

~140m to tip

~200m to tip

~180m to tip

~180m to tip

XUV and K- imaging are used to measure coupling and transport in cones S Baton LULI, LVW OSU POP

Lawrence Livermore National Laboratory Andrew G. MacPhee 17 th Topical Conference on High Temperature Plasma Diagnostics Albuquerque, NMWed 14 th May 2008.

Documents

shot low power scaled

titan laser

reflection of laser

ev channel t e

town slide

low driver energy

laser excitation of

low power opcpa alignment