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Fast Ignition Workshop Pravesh Patel. Proton Fast Ignition. Focusability of the proton beam Rear surface thermal measurements (optical, XUV) Quantitative technique based on direct characterision of the proton beam as it goes through focus.

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Fast Ignition Workshop

Pravesh Patel


Proton fast ignition
Proton Fast Ignition

  • Focusability of the proton beam

    • Rear surface thermal measurements (optical, XUV)

    • Quantitative technique based on direct characterision of the proton beam as it goes through focus


Xuv emission measurements with 400j incident laser energy
XUV emission measurements with 400J incident laser energy

Planar foil

1mm diameter foil

360µm diameter foil

500µm

280µm FWHM

94µm FWHM

45µm FWHM

Increasing signal intensity


Rear surface temperature from focused proton heated foils
Rear surface temperature from focused proton-heated foils

Comparison of absolute XUV signal with LASNEX simulations gives peak temperatures of 200eV at rear surface


A quantitative technique for characterizing proton focusing
A quantitative technique for characterizing proton focusing

Beam distribution at focal plane

Counts

80µm

32µm

B. Zhang et al.

100

200

300

400

Distance D (µm)

80% of energy is contained within a 32µm diameter spot

Protons focused from a 120µm diameter region x10-20 enhancement


Lsp simulations indicate focusability can be improved further
LSP simulations indicate focusability can be improved further

10µm

50µm

More uniform laser irradiation produces better focused beam

Requires higher laser energies (to maintain intensity over larger area)


Proton conversion efficiency can be enhanced by tailoring the atomic surface composition
Proton conversion efficiency can be enhanced by tailoring the atomic surface composition

  • Higher Z atomic mixture increases separation between proton and ion fronts and differentially puts more energy into protons

  • Tailored surface can increase hydrogen density, and provide a deeper source of protons compared to thin contaminant layers

Solid Hydrogen

Hydrides

Contaminants

M. Foord et al., J. Appl. Phys. 103, 056106 (2008)

D. Offermann et al., submitted (2008)

Increase of 25% in conversion efficiency with ErH targets has been demonstrated in recent experiments


Characterizing the proton source

6.4MeV the atomic surface composition

8.4MeV

10.1MeV

245µm

190µm

140µm

Characterizing the proton source

8-12Å layer of H20.CH2

Au

Protons originate from a 250µm diameter, very thin 8-12Å layer, at the rear surface


Hybrid particle in cell pic modeling can reproduce most features of proton acceleration
Hybrid Particle-in-Cell (PIC) modeling can reproduce most features of proton acceleration

LSP (Large Scale Plasma) Simulation

8-12Å layer of H20.CH2

r (µm)

Au

M Foord et al.

HEDP 3, 365 (2007)

z (µm)

LSP reproduces energy spectrum, peak energy, and divergence

Simulations confirm rapid acceleration and initial pulse duration (ps)


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