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Studies of isochoric heating by electrons and protons. IAEA Chengdu , Oct 2006. Andrew MacKinnon. Plus. Rapport: Papers IF/1 -R2b and 1F/1 - R2c.

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slide1

Studies of isochoric heating by electrons and protons

IAEA

Chengdu , Oct 2006

Andrew MacKinnon

Plus

Rapport: Papers IF/1 -R2b and 1F/1 - R2c

This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

co authors and acknowledgements
Co -authors and acknowledgements

K. Akli, F. Beg, M.H. Chen, H-K Chung, M Foord, K. Fournier, R.R. Freeman,

J. S. Green, P. Gu, J. Gregori, H. Habara, S.P. Hatchett, D. Hey, J.M. Hill

J.A. King, M.H. Key, R. Kodama, J.A. Koch, M Koenig, S. Le Pape, K. Lancaster, B.F.Lasinski, B. Langdon, S.J. Moon, C.D. Murphy,, P.A. Norreys, N. Patel, P.K Patel, H_S.Park, J. Pasley , R.A. Snavely, R.B. Stephens, C Stoeckl, M Tabak, W. Theobold, K. Tanaka, R.P. Town, S.C. Wilks, T. Yabuuchi,B Zhang,

  • This work is from a US Fusion Energy Program Concept Exploration and Advanced concept exploration collaboration between LLNL, General Atomics, UC Davis, Ohio State, UCSD and LLE
  • International collaborations at RAL,LULI and ILE have enabled most of the experiments
  • Synergy within LLNL, through ‘Short Pulse’ S&T Initiative has helped the work
  • US collaboration in FI has recently expanded in a new Fusion Science Centre
  • linking 6 Universities and GA with LLNL and LLE and a new Advanced Concept Exploration project between LLNL,LLE,GA, UC Davis , Ohio State and UCSD
fast ignition entails assembly of compressed fuel followed by fast heating by mev particles

critical surface

Fast Ignition entails assembly of compressed fuel followed by fast heating by MeV particles

Step 1. Compress fuel

Step 2. Ignite fuel

Ignition driver:

short pulse laser

MeV particles

Compression

driver: Laser

Initial concept utilized kJ source of MeV electrons in picosecond pulse to ignite imploded capsule ( M. Tabak et al., Phys Plasmas 1, 1626, 1994)

slide4

Success in fast ignition requires a very large flux of MeV particles to be deposited in 10-20ps

  • FI (1,2) requirements: heat 300 g/cc, (R~2.5 g/cm2) with 18-20 kJ particles at MeV energy in 10 ps over 30-40 m dia.

Cone

  • Electron Fast Ignition1
  • Cone protects ignitor pulse from coronal plasma
  • Laser conversion to fast electrons ~ 30%
  • ~ 60 kJ laser energy required
  • Electron transport most important issue
  • DT fuel at 300g/cc
  • 40 m ignition spot

Laser

Coronal Plasma

MeV electrons

Curved proton rich target

  • Proton Fast Ignition2
  • Currentlylaser conversion into protons ~10%
  • ~180 kJ laser energy required
  • Improving proton conversion efficiency most important issue

MeV protons

Laser

Laser

(1)Atzeni et al.,PoP (1999)

(2) Roth et al.,86,436 PRL 2000, Atzeni et al., 2002; Temporal et al., PoP 9,3102 (2002)

  • DT fuel at 300g/cc
  • 35 m ignition spot

PW laser

slide5

30%

coupling

15%

coupling

There is wide-ranging research in high intensity physics related to Fast Ignition in institutions around the world

Results from Institute for Laser Engineering, Osaka have shown promise of cone focused scheme

Kodama,et.al,Nature 412(2001)798

and 418(2002)933.

“Cone” implosions

Implosion beams

300 TW laser

  • Existing experimental Facilities: United Kingdom,France, LLNL(Titan), SNL, Universities,…
  • Theory: US, UK, France, Germany, Italy, Japan, China, India
  • Upcoming Facilities: Omega EP(Rochester), NIF ARC(LLNL), FIREX I(Japan)
  • Proposed facilities : HIPER(Europe), FIREX II(Japan),China
cone wire targets are being used to study electron transport at fi relevant laser intensities
Cone wire targets are being used to study electron transport at FI relevant laser intensities

Target 10mCu wire /Al cone

  • Cone/Wire represents conductivity channel in FI scheme: test-bed for existing electron transport models
  • K emission images show 100m exponential scalength
  • Bell 1D analytic model* gives similar scale-length to experiment
  • Peak temperature measured by XUV imaging to be 350 eV with 100 m scale length ~ 1.2% of laser energy
  • 1D numerical model injecting 1.2% of laser energy as hot electrons matches observed K
  • 1D transport scaling gives 20% coupling at 40 m diameter - This would be viable for FI

256 XUV

1 mm

Laser 500 J, 0.8 ps

1mm

RAL PW laser Vulcan

500 µm

Cu Ka

1mm 10 mm

* A.R.Bell et al., Cont Plasma 1997

slide7

Proton FI: Proton conversion efficiency optimized by reducing target thickness and increasing hydrogen fraction on surface

Electrons

0.1m CH4 layer

Refluxing hot e

5m Al substrate

H+

Fraction of Injected Energy

Hot e

C+6

Thermal e

Al+4

  • Refluxing hot electrons continuously lose energy to thermal ions and electrons in substrate
  • Contaminant layer containing hydrogen ionized & accelerated by MeV/m electric field
  • Reducing target thickness increase conversion efficiency as hot electron pressure increases
  • Increasing proportion of H+ in layer increases conversion eff -> hydrides or pure H2 should provide highest conversion efficiency
slide8

Varying Z of hydride layer could yield factor 2-3 enhancement in proton conversion efficiency

Efficiency simulations for hydrides

Cryogenic H2

Current experiments with contaminant layers

  • Experiments planned for mid FY07
slide9

Proton focusing: Mesh imaging of the proton beam provides great deal of information on focusing mechanism

Laser view

Fine mesh w/ element separation = 25m

Equatorial Plane

Laser : spot~50µm

Focal Plane

RCF pack for measuring proton dose

x

mesh

Side view

mesh

d = 250m

d

1mm

70mm

Oblique view XUV Imagers at 68 and 256eV to measure size of heated region

Laser

View of xuv

Shot No:060622_s1:

20µm thick, 350µm Diameter Al hemi-shell with 25µmx25µm Cu mesh at 1mm spacing

This technique allows simultaneous determination of location of proton focus, size of proton spot and extent of heated region

slide10

68eV XUV

Mesh image and XUV emission from the proton heated mesh indicates very small proton spot (~30-50m)

Laser

  • 68eV image shows very bright image and large plume - consistent with high Temp
  • 256 eV image also shows ~30-50m heated region
  • RCF shows 3-4 mesh elements in 20MeVproton beam - agrees well with 256eV image
  • Data is being used to test proton focusing models

256eV XUV

Proton dose (20MeV)

30m

30m

slide11

Integrated experiments are being planned for Omega EP: These will test fast ignition concepts at kJ short pulse energy levels

User experiments will begin in 2008

slide12

Fast ignition experiments can also be carried out on

the NIF using the high energy radiography beams

2 x1.2 kJ per beam line

One beam line in FY09

(Option for 13 kJ quad)

slide14

Rapport: Papers IF/1 -R2b and 1F/1 - R2c

  • Paper IF/1 -2b: R. Kodama et al., “ Plasma photonic devices for Fast Ignition Concept in Laser Fusion Research”
  • Paper 1F/1 - 2c: K. Tanaka et al., “Relativistic Electron Generation and its behaviors Relevant to Fast Ignition”
slide15

Paper IF/1 -2b: Describes how cones and other guiding devices modify Electron generation in FI

slide17

Integrated experiments show plasma heating by short pulse, consistent with collimated electron beams

slide19

IF/1-2Rc

Relativistic Electron Generation and Its Behaviors Relevant to Fast Ignition

K. A. Tanaka1,2, H. Habara1,2, R. Kodama1,2, K. Kondo1,2, G.R. Kumar1,2,3, A.L. Lei1,2, K. Mima1, K. Nagai1, T. Norimatsu1, Y. Sentoku4, T. Tanimoto1,2, and T. Yabuuchi1,2

1Institute of Laser Engineering, Osaka University,

2-6 Yamada-Oka, Suita, Osaka 565-0871 Japan

2Graduate School of Engineering, Osaka University,

2-1 Yamada-Oka, Suita, Osaka 565-0871 Japan

3Tata Institute of Fundamental Research,

Homi Bahbha Rd., Mumbai 400 004 India

4 Department of Physics, University of Nevada,

Reno, Nevada 89521-0042 U.S.A.

slide20
Target design improvement: foam cone-in-shell target for increasing the heating efficiency of core plasma
  • To increase the heating efficiency of the core plasma, we propose a foam cone-in-shell target design.

Gold cone with inner tip covering with a foam layer

Relativistic laser

Fuel shell

Multiple implosion beams

slide21

Au foam coating enhances laser absorption and hot electron generation

  • Hot -e yield measurement via the back x-ray emission from the target rear due to the heating from hot –e beams
    • -weak front x-ray emission from the Au foam-coated target. This is due to the low density of the foam.
    • -stronger back x-ray emission from the Au foam coated target. This is attributed to higher laser absorption and more hot electrons generated with the foam coated target. Back x-ray emission is caused by the hot –e beam heating of the target rear.
    • -target is thick so that the front x-ray emission may not be responsible for the enhancement of back x-ray emission with foam coated target. Moreover, if it happens, one would expect weak x-ray emission from the foam coated target rear, contrary to the experimental results.
    • -narrow band-width x-ray image diagnostics needed to give the relative hot –e yield through assuming Plankian emission from the target rear.
    • -quantitative models and simulations needed
slide23

Hot electron distribution differs

for with and without plasmas.

slide25

Summary I

  • We propose a foam cone-in-shell target design aiming at improving the cone-in-shell target design to increase the laser energy deposition in the dense core plasma.
  • Our element experiment results demonstrated increased laser energy coupling efficiency into hot electrons without increasing the electron temperature and beam divergence with foam coated targets in comparison with solid targets. This may enhance the laser energy deposition in the compressed fuel .
  • Phys. Rev. Lett., A.L.Lei, K.A. Tanaka et al., 96, 255006(2006).
summary ii
Summary II
  • Surface direction hot electrons observed at oblique incidence UIL experiment.
  • Relativistic laser self-focusing increases laser intensity causing surface hot electrons.
  • Several tens of MGauss field inferred
  • H. Habara, K.A. Tanaka et al., Phys. Rev. Lett. 97, 095004(2006).
  • Please see poster IF/1- 2Rc for more details
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