T.A. Heltemes and G.A. Moses Fusion Technology Institute High Average Power Laser Program Workshop
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Transcript of T.A. Heltemes and G.A. Moses Fusion Technology Institute High Average Power Laser Program Workshop
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350 MJ Target Thermal Response and Ion Implantation in 1 mm thick silicon carbide armor for 10.5 m HAPL Chamber
T.A. Heltemes and G.A. MosesFusion Technology Institute
High Average Power Laser Program Workshop March 21–22 2006, ORNL
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2Progress is continuing on the BUCKY chamber simulation campaign
Integrated target–chamber simulation
Tungsten Armor
Silicon Carbide Armor
Carbon Armor
Vacuum Chamber (~8 µtorr)
Low pressure buffer gas (~8 mtorr)
Unirradiated SiC
Irradiated SiC
Amorphous
Exotic (Nanotube carpets, etc.)
Graphite
• Simulations will be added as required (porous tungsten, irradiated carbon, etc.)
• Ultimate goal is to produce a streamlined process to perform integrated end-to-end 1-D simulations for chamber thermomechanical performance
Pas
tP
rese
ntFu
ture
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3BUCKY simulations were performed using the HAPL baseline 350 MJ target and 10.5 m chamber
• HAPL baseline chamber geometry was used with a near-vacuum gas condition
• The high-Z (Pd/Au) coated target ion and x-ray spectra were used as inputs to the BUCKY simulation
• Initial armor temperature was set to 727˚C (1000K) for the simulations
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4Perkins’ 350 MJ target ion spectra were used as inputs for the BUCKY simulations.
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5Perkins’ x-ray spectrum was converted to a time-dependent Gaussian pulse
• Perkins’ x-ray spectrum is time-integrated, which must be corrected for in the BUCKY simulation
• A Gaussian function was chosen to generate time-dependence based on results of BUCKY simulations of other direct-drive targets
• The time-integrated x-ray spectrum was multiplied by a Gaussian function with a FWHM of 170 ps
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• Simulation uses a constant thermal conductivity of 15 J/kg-˚C for irradiated SiC
• Simulation uses a SiC sublimation temperature of 2760˚C (from CVD SiC spec sheet produced by Rohm and Haas, http://www.cvdmaterials.com/silicon.htm)
NIST data were used to generate thermal conductivity and specific heat profiles for SiC
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7SiC has different thermal conductivity for the unirradiated and irradiated states
S.J. Zinkle & L.L. Snead (1998)
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8BUCKY simulations were run for both unirradiated and irradiated SiC and the results were compared to the previously conducted tungsten simulation
• Irradiation has a negligible effect on the temperature rise due to the x-ray pulse (~2˚C difference)
• Ion heating in the unirradiated SiC causes a greater peak temperature rise (∆Tmax=1904˚C) at 10.5 m than that of tungsten (∆Tmax=1584˚C)
• Every shot fired in an irradiated SiC armored chamber ablates due to the impinging ions to a depth of 0.5 µm at 125 µs
• Summary of Results:– Irradiated SiC is unsuitable as an armor
material without diversion or buffer gas– Unirradiated SiC does not ablate, but will
exceed engineering limits of 1500–1700˚C
Sublimes
X-rays Only
X-rays and Ions
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9The temperature by depth into the silicon carbide armor was plotted for both unirradiated and irradiated SiC
• Both unirradiated and irradiated SiC show peak ion heating from the kinetic ions between 7–9 µm from the surface
• Largest temperature gradients are caused by the debris ions
Unirradiated
Irradiated
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4He ion implantation data were obtained for comparison with the BUCKY simulation of ion implantation in tungsten
• Debris ions deposit 0–2 µm into the SiC
• Kinetic ions deposit 4–200 µm into the SiC, with peak deposition from 4–20 µm
Range of Debris Ion Deposition
Range of Kinetic Ion Deposition
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11Preliminary conclusions resulting from the simulations
• Irradiated SiC is unsuitable for use as an armor material for the 10.5 m HAPL chamber without diversion of the ions or introduction of a buffer gas into the chamber
• Although unirradiated SiC does not reach its ablation temperature, the temperature rise from a target explosion does exceed the engineering limit of 1500–1700˚C
• If magnetic diversion of ions is used for the HAPL chamber, silicon carbide is preferable to tungsten for mitigating the temperature rise due to the x-rays impinging on the armor
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12Future BUCKY simulation improvements and modifications
• Revise Tsub to 3008˚C, which is the sublimation temperature listed in the NIST ceramics database
• More high-temperature thermal conductivity and specific heat data (T > 1727˚C) for unirradiated SiC are required
• Broader data set for irradiated SiC properties are required
• Need to more accurately model the behavior of silicon carbide near the sublimation temperature
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13Questions?