Analysis of carbonbearing materials for use as first wall armor in the HAPL chamber

1
Analysis of carbon-bearing materials for use as
first wall armor in the HAPL chamber

• T.A. Heltemes and G.A. Moses
• Fusion Technology Institute, University of
  Wisconsin Madison
• 18th High Average Power Laser Program Workshop
• Santa Fe, NM, April 89, 2008

2
BUCKY surface temperature plots for 10.5 m bare
chamber with 0.5 mtorr helium buffer gas

• Silicon Carbide(Unirradiated)

• Pyrolytic Graphite(Unirradiated)

Chambers simulated with the LLNL 365 MJ target
x-ray and ion threat spectra
3
BUCKY surface temperature plots for 10.5 m bare
chamber with 11.6 mtorr helium buffer gas

• Silicon Carbide(Unirradiated)

• Pyrolytic Graphite(Unirradiated)

Chambers simulated with the LLNL 365 MJ target
x-ray and ion threat spectra
4
Helium ion ranges in tungsten and graphite were
calculated

• Helium ions primary penetration ranges
• tungsten
• 03 µm
• 57 µm
• carbon
• 820 µm
• 4050 µm
• 100200 µm
• Median of helium ion penetration
• tungsten 2 µm
• carbon 8 µm
• Mode of helium ion penetration
• tungsten 1 µm
• carbon 8 µm

• Maximum helium ion penetration depth
• tungsten 56 µm
• carbon 3.2 mm

5
ESLI pyrolytic carbon fiber wall concept
6
Features of an engineered graphite wall

• Effective surface area multiplication of 330
• Equivalent radius of 190.3 m
• R/R0 of 18.125
• Thermal transients appear to be nearly
  suppressed, but we must be careful because a 1-D
  code cannot model this 2-D surface very well
• Ablation of the tips of the fibers is possible
  depending on graphite planar orientation
• Thermal conduction down the fiber is not
  accurately modeled

7
The challenge of transient thermal analysis of
the ESLI pyrolytic carbon fiber wall concept

• Incident x-rays and ions impinge with a variable
  intensity depending on impact location on the
  fiber surface
• The thermal conductivity of pyrolytic graphite is
  highly anisotropic
• The thickness of the fiber changes as well,
  creating a location-specific conduction channel
  size (the central region of the fiber)
• ANSYS calculations will need to be performed to
  determine a more accurate temperature profile

8
How does the equivalent radius scheme affect
armor lifetime?

• Onset of damage is assumed to be 1017 He
  ions/cm2
• Increasing the helium buffer gas pressure from
  0.5 mtorr to 11.6 mtorr will result in the
  absorption of all helium ions with KE0 lt
  271 keV, increasing the chamber time to threshold
  by 24.8
• Standard HAPL target with 10.5 m conventional
  tungsten chamber armor
• 0.5 mtorr He chamber buffer gas
• Shots to reach threshold 8,651
• Time to threshold at 5 Hz 29 minutes
• 11.6 mtorr He chamber buffer gas
• Shots to reach threshold 10,796
• Time to threshold at 5 Hz 36 minutes
• Standard HAPL target with 10.5 m engineered
  carbon fiber chamber armor
• 0.5 mtorr He chamber buffer gas
• Shots to reach threshold 2,841,854
• Time to threshold at 5 Hz 158 hours (6.5 days)
• 11.6 mtorr He chamber buffer gas
• Shots to reach threshold 3,546,634
• Time to threshold at 5 Hz 197 hours (8.2 days)

9
Comments and Future Work

• Questions that need to be addressed
• Thermal conductivity effects of sputtered carbon
  deposits
• Thermal transport and dust damage issues due to
  broken fibers
• Ensuring proper orientation of graphite planes in
  carbon fibers
• Ablation of fiber tips
• Ion damage severity as a function of implantation
  energy to more accurately assess wall lifetimes
  for proposed chamber armor configurations
• Future Work
• Refine carbon fiber wall thermal calculations
• Explore heating and damage issues in carbon
  nanotube composites