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

chamber

T.A. Heltemes and G.A. MosesFusion Technology Institute, University of Wisconsin — Madison

18th High Average Power Laser Program Workshop

Santa Fe, NM, April 8–9, 2008

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

Silicon Carbide(Unirradiated)

Pyrolytic Graphite(Unirradiated)

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Chambers simulated with the LLNL 365 MJ target x-ray and ion threat spectra

BUCKY surface temperature plots for 10.5 m bare chamber with 11.6 mtorr helium buffer gas

Silicon Carbide(Unirradiated)

Pyrolytic Graphite(Unirradiated)

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Chambers simulated with the LLNL 365 MJ target x-ray and ion threat spectra

Helium ion ranges in tungsten and graphite were calculated Helium ions primary

penetration ranges tungsten

0–3 µm5–7 µm

carbon8–20 µm40–50 µm100–200 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

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ESLI pyrolytic carbon fiber wall concept

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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 wellAblation of the tips of the fibers

is possible depending on graphite planar orientation

Thermal conduction down the fiber is not accurately modeled

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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

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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 <= 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)

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Comments and Future Work

Questions that need to be addressedThermal conductivity effects of sputtered carbon depositsThermal transport and dust damage issues due to broken fibersEnsuring proper orientation of graphite planes in carbon fibersAblation of fiber tips Ion damage severity as a function of implantation energy to more

accurately assess wall lifetimes for proposed chamber armor configurations

Future WorkRefine carbon fiber wall thermal calculationsExplore heating and damage issues in carbon nanotube composites

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