IFE Ion Threat Spectra Effects Upon Chamber Wall Materials

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IFE Ion Threat Spectra Effects Upon Chamber Wall
Materials
G E. Lucas, N. Walker UC Santa Barbara
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Threat Spectra

• Projected number of ions and ion energy levels
• Depends on the type of target drive system
• Lasers
• NRL Direct Drive Target
• High Yield Direct Drive Target
• Heavy Ions
• HI Indirect Drive Target
• Threat spectra consists of both Debris and Burn
  Product Ions

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Threat Spectra
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Analytical Procedure

• SRIM Software
• Stopping and Range of Ions in Matter
• Uses statistical algorithms to simulate ion and
  target material collisions and interactions
• Inputs
• Ion Type
• Ion Energy
• Target Material (C or W)
• of Ions
• Desired output tables
• Outputs
• Displacements per Ion
• Ion range in target material
• Ion Statistics

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Analytical Procedure

• Data Interpolation
• Data for threat spectra is only known at a
  specific set of data points
• Interpolation must be used in order to find data
  points in-between known data points
• Distribution is divided into small finite number
  of bins
• Each data point falling within each bin is
  assumed to have the mid-bin energy
• Reasonable approximation since bin size is small
  compared to range of distribution

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Analytical Procedure

• Initial Damage Profiles
• Utilizing interpolated ion range data, ion
  concentration distribution can be found
• Ion concentration distribution and displacement
  distribution along with physical properties of
  the chamber wall material allow DPA
  (displacements per atom) to be determined
• Initial assessment of damage due to displacement
  can be determined

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Analytical Procedure

• Blistering/Exfoliation
• Ion concentration distribution can be used to
  determine the number of ions per chamber wall
  atom
• The thickness of the blister is determined by the
  location of maximum concentration (region of
  maximum gas concentration)
• Once critical ion/atom concentration is achieved
  blister will exfoliate
• 15 at. for He ions
• 50 at. for H ions
• All material before the blister is exfoliated
  from the chamber wall
• Knowing the critical ion/atom concentration,
  maximum ion concentration as well as the
  operating conditions of the reactor, the time
  needed for a blister to exfoliate can be
  determined

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Analytical Procedure

• Steady-State Exfoliation
• After blister layer exfoliates the penetrating
  ion concentration distribution is the same as
  before
• However, the previous ion concentration
  distribution is still present in the material
• The two concentration distributions add to give
  the final ion concentration distribution
• The final ion concentration distribution dictates
  a new maximum ion concentration and a new
  location of maximum ion concentration

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Analytical Procedure

• Steady-State Exfoliation
• The ion concentration distribution continues to
  change after each exfoliation until it reaches a
  steady-state distribution
• At steady-state
• The exfoliation thickness is constant (controlled
  by location of maximum concentration)
• The time to exfoliate is constant (controlled by
  value of maximum concentration)
• The exfoliation thickness and the time required
  to exfoliate essentially control the decay rate
  of the surface material

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Results

• Initial Damage Profiles
• After the initial fusion reaction the initial ion
  concentration distribution and DPA distribution
  are determined
• As more reactions occur these distributions build
  up on top of one another
• Blisters form and exfoliation eventually occurs
• Representative distributions are shown in the two
  figures for Low Yield Direct Drive Debris Ions
  into C

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Results

• Exfoliation Rates
• After the first exfoliation occurs a new
  concentration distribution evolves
• The new concentration distribution will have a
• Higher maximum concentration value
• Makes time to exfoliate smaller
• Increases exfoliation rate
• Shallower region of maximum concentration
• Makes exfoliation thickness smaller
• Decreases exfoliation rate
• Exfoliation rate and exfoliation thickness vs.
  time plotted in figure, Low Yield Direct Drive
  Debris T into C
• After certain amount of time exfoliation rate and
  exfoliation thickness become constant

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Results

• Steady State Exfoliation Rates

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Diffusion
Check to determine longevity of concentration
profile H diffusivity from literature Run
finite element diffusion simulation
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Diffusion Profiles at Temperature
H profile rapidly decays in W at temperatures
above 150 C H profile does not decay In graphite
below 1750 C
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Conclusions

• Burn Product Ion damage may be survivable
• Debris Ion damage is unacceptably high
• Diffusion may help
• Still need better diffusivities to complete
  analysis