Update on LLNL FI activities on the Titan

Laser

A.J.Mackinnon

Feb 28, 2007

Fusion Science Center MeetingChicago

Titan laser provides a capability for combined high energy SP and LP beam experiments

Existing Janus Target Existing Janus Target Area (2x 1kJ LP beams)Area (2x 1kJ LP beams)

Short-pulse: Short-pulse: 300J in 400fs300J in 400fsLong-pulse: Long-pulse: 1kJ in 3ns1kJ in 3nsLaser BayLaser Bay

TitanTitanTarget Target AreaArea

Switchyard upgrade will allow simultaneous Titan and Janus 2 beam

• Titan operating reliably - @5-7 shots per day

• Max irradiance = 3x1020 Wcm-2 at 200J, 500fs.

• Prepulse levels low and appear reproducible - working to verify shot to shot diagnostic capability

• Pointing accuracy appears to be very good (5-10m)

• Proton beams with slope Tp ~ 4MeV, Emax ~ 40MeV routinely produced with 10m gold targets

• Fast Ignition relevant experiments to take place in April will study:

• laser to hot e coupling

• proton conversion from hydride targets

• Proton focusing

• Aim for 80 shots in 5 week run

Outline

Titan long-pulse arm has been operational since Aug 06, enabling 2-beam combined SP-LP experiments

Short pulse F/3 focusing optic

Long pulse periscope

The long pulse beam can be moved to any of 6 ports in Horizontal plane

Titan short pulse has very good pointing and target alignment accuracy

150µm square foil target

150µm

Laser and target alignment accuracy and laser pointing stability is 5-10µm

20µm diameter wire target

500µm

Low power images of focal region gives a peak intensity of 1x1020W/cm2 in 200J, 500fs pulse

-400µm -200µm 0µm +400µm+200µm

300µm

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

-25 -20 -15 -10 -5 0 5 10 15 20 25Radius (microns)

Best focus 4.9µm FWHM containing 14% of total energy 3x1020W/cm2

15µm diameter spot encircles 50% of total energy 1x1020W/cm2

Best focus

14%

50%

80µm

On-line fast diode and 2 optical probing are used to monitor the laser contrast and preformed plasma

Diode and preformed plasma measurements can be obtained to examine shot to shot variations

0 25 50 75 100

-250

-200

-150

-100

-50

0

50

100

150

200

250

Distance (um)

Distance (um)

2e+19 4e+19 6e+19 8e+19 1e+20

500µm

Interferogram at -25ps

0

1

2

3

-5 -4 -3 -2 -1 0 1

Time (ns)

Fast diode pre-pulse measurement

0.18ns1.38ns

3.18ns

Density map

Titan data proton beams from gold targets give 2% conversion from laser to protons above 3MeV

• Conversion efficiency, peak proton energy, proton slope all reduce with increasing target thickness and pulse length• Data being used to benchmark PIC and LSP simulations• Good proton beam obtained at 10ps - encouraging for proton FI

Titan Emax vs target thickness

0

5

10

15

20

25

30

35

40

0 100 200 300

y = 89.779x-0.4275R2 = 0.8833

Target thickness (m)

Peak Proton Energy, Ep

(MeV)

Best fit to data

Titan data

Titan lp vs target thickness

Target thickness (m)

Laser to Proton

conversion %

1/L scaling

Titan data

0

2

4

6

8

10

0 10 20 30 40 50 60

2-D LSP PIC Simulations

Foil Thickness ( )m

1/ L scaling

LSP

Au foil60 m laser dia500 , 150 fs J laser50 , 1 J MeV hot electrons= 700 t fs

LSP simulations show very similar behavior to experiments with plausible laser to electron coupling

• LSP shows slightly higher than 1/L scaling - very similar trend to data • Conversion from hot electrons to protons peaks at 8% for 10m Gold• Implies ~ 30% coupling from laser to 1MeV electron source • Future work will couple PIC code results as input to LSP

Gold substrate

1000 A CHO layer

50J, 1MeV electrons

1D simulations predict that High Z hydrides could result in higher conversion efficiency

0

10

20

30

40

Hydrides

BC

H LiH CHn

MgH2

CaH2

CsH ErH3

UH3

CH4

CH2

CH

HZ

ZHn

Thot=880keV5 + 1000 m Au Å ZH

n

Fraction of energy in heavy ion

Fraction of energy in H+

• Heavy ions are left behind at back surface during ion separation

Current experiments with contaminant layersH

ot electron to proton conversion

eff (%)

Erbium Hydride will be tested on Titan in April 07

** M. Allen, P. K. Patel, et al., PRL 93 265004 (2004)

• Surface contaminants and barrier layers will be removed by ion sputtering**

• Films 100nm thick have been manufactured by reactive sputtering*

• Oxide and hydrogen barriers may be necessary to maximize hydrogen content

ErH2 and ErH3

10-15 umgold layer

~1 um Eror U layer

10-30 nm Pd oxidationprotective layer

Laser* Sandia National lab

Main focus of April 07 experiment will be to characterize laser MeV electron coupling

2/26/073/5/07

3/12/073/19/073/26/074/2/074/9/07

4/16/074/23/074/30/075/7/07

5/14/075/21/075/28/076/4/07

6/11/076/18/076/25/077/2/077/9/07

7/16/077/23/077/30/078/6/07

8/13/078/20/078/27/07

Switchyard upgrade

High Energy RadiographyLLNLElectron coupling - planar and cones - LLNL/OFES

X-ray scattering - Falcone

TBD - LLNL - expts + maintenance (?)

ILSA - I - Maryland/Colarado (?)

ILSA - II - FSC - Ohio/UCSD -TBD

2. Prepulse effect inside cones

3. Pointing and effect of defocus (start)

1. Compare coupling for slabs vs cones

Spring expt: Laser to hot E coupling

Long pulse preform beam

The long pulse beam will be used to generate FI scale prepulse inside cones

= 1,

E = 1 to 100J,

= 3ns,

Spot ~ 30m

• Titan operating reliably - @5-7 shots per day (depending on experiment)

• Max irradiance = 3x1020 Wcm-2 at 200J, 500fs.

• Prepulse levels low and appear reproducible - working to verify shot to shot diagnostic capability

• Pointing accuracy appears to be very good (5-10m)

• Proton beams with slope Tp ~ 4MeV, Emax ~ 40MeV routinely produced with 10m gold targets

• Fast Ignition relevant experiments to take place in April will study:

• laser to hot e coupling

• proton conversion from hydride targets

• Proton focusing

• Aim for 80 shots in 5 week run

Summary