High Ion temperatures from buried layers irradiated by VULCAN Petawatt

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High Ion temperatures from buried layers
irradiated by VULCAN Petawatt

• S. Karsch, J. Schreiber, L. Willingale, K.
  Lancaster, M.S. Wei, P. Nilson, S.P.D. Mangles,
  H. Habara, E.L. Clark, R. Clarke, R. Heathcote,
  Z. Najmudin, K. Krushelnick, P.A. Norreys

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• OUTLINE
• Detection method
• Layered target experiments
• (molecular ions, acceleration in the bulk?)

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Thomson Parabola
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CR-39 Analysis
Clear polymer sheets Fast ions lose energy and
break bonds of the polymer matrix ? Damage
depends on local energy deposition
100 µm
After NaOH etching different ion species can be
distinguished by their track size
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Layer targets
to Thomson Parabola
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Molecular ions?
H2
Layer target Mostly molecular ions
Bulk CD target All species
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Bulk acceleration?
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Thermonuclear fusion neutrons
Plane CD 140mm thick
Sandwich target 10mm CH overcoat
Sandwich target 3mm CH overcoat
Counts/MeV
EnergyMeV
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Experimental setup
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Front/rear ion spectra
Small number of deuterons present in each shot (gt
natural deuteron content)
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Correction for origin
Erear,1
Efront,1
Erear,2
Efront,2
Erear,3
Efront,3
Emeasured
Ereal
Use SRIM stopping to correct for the ions energy
loss before exiting the target
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Max. Deuteron Energies
front side
rear side
Strong heating at the rear side!
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Total energy into deuterons
rear side
front side
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Proton content is stable

• Deuteron number
• Deuteron energy
• Conversion efficiency into D

decreases, then increases with layer depth
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• But
• Conclusions hold only, if the ratio of proton
  and deuteron beam divergence is stable
• Constant proton number hints at similar
  conditions for all shots, however, more shots are
  needed.

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Mechanisms ?

• Collisionless shock propagation into the
  deuterated layer injects deuterons into the TNSA
  fields at the target surface
• What about ions coming off front side?

L. O. Silva et al., PRL 92, 015002, (2004)
Return current inhibition close to the target
rear side anomalous stopping of forward
electron current
J.R. Davies et al., PRE 59, 6032 (1999)
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Conclusions

• Deuterons accelerated from the bulk of solid
  plastic targets have been observed
• A strong heating mechanism close to the rear
  target surface seems to exist
• Post-acceleration of low-energy deuterons in the
  TNSA fields cannot explain the enhancement in
  both front and rear direction
• More shots are needed for a reliable
  clarification of the underlying acceleration
  mechanism.