1. Si Nanocrystaline Diamond Foil Hibachi Window Testing and Development Background and Theory Pulsed Power System Electron Beam Electron Transmission Window (Hibachi) Laser Cell Output Optics Laser Output Laser Input Laser Gas Recirculation Key Components of the KrF Laser Amplifier Abstract In support of Inertial Fusion Energy (IFE) a 150 µm thick silicon (Si) wafer coated on one side with a 1.2 µm nanocrystalline diamond foil has been fabricated as an electron beam transmission (hibachi) window for use in a repetitively pulsed e-beam pumped laser. The hibachi window separates the lasing medium from the electron beam source while allowing the electron beam to pass through. The hibachi window must be capable of withstanding the challenging environment presented in the lasing chamber, which can include; fluorine gas, delta pressures > 2 atm @ 5 Hz, and a high heat flux due to the transmission of electrons passing through the foil. Recent tests conducted on single Si window panes under simulated operational conditions have shown that the techniques and materials being developed can withstand the harsh environment for extended periods of operation. The responses to pressure, heat, and chemical attack have all been explored and are discussed. This work is supported by the Naval Research Laboratory (NRL) in collaboration with the Princeton Plasma Physics Laboratory (PPPL). Yield Strength:7000 MPa53000 MPa Young’s Modulus:180 GPa7000 GPa Properties Silicon (SCS) Nanocrystalline Diamond Yield Strength:241 MPa1400 MPa Young’s Modulus:193 GPa120 GPa Properties (comparison) Stainless Steel Titanium Electron Transmission Efficiency of Foil Materials Prototype Testing Results We Can Take the Heat & Pressure Gasket Settling Test Window Configuration 1.5” aperture diameter Si window mounted with RTV silicone sealant inside a modified 4.5” Con-Flat flange pressurized with compressed air. For dynamic testing a solenoid actuated valve alternately pressurized and vented the chamber. Test setup was also placed in ovens to simulate electron heating of the window. Experimental Results TestPress. (psia) Temperature (°C) Rep. Rate (Hz) Cycles Long Duration 44-26 psia (pulsed) 135°C (limited by oven) 5 250,000 Static Pressure 60 psia 21 °C~~ High Temperature 28-18 psia (pulsed) 600 °C 5400 1.5” D 150μm Si Window Deflection Test Flange Undergoing High Temperature Testing As seen through tubing feed thru in oven Diamond Coating Durability Nanocrystalline Diamond Coating Durability Study A Si wafer coated with a 1.2μm thick coat of nanocrystalline diamond applied was subjected to the same deflections that the bare Si window experienced for 50,000 cycles. The window was then removed scribed and prepared into samples for analysis in a SEM. A unstressed wafer was also prepared in a similar manner. Comparison of the two samples showed no discernable degradation of the coating due to mechanical stress (see electrographs above). Scribed and broken edge of wafer showing diamond/silicon interface. Surface of wafer appears to have been damaged as diamond was broken away during the cut. unstressed surfacestressed surface The tests performed on a single pane uncooled flange at PPPL indicate that the Si/Diamond coat windows presents an attractive alternative foil that can survive the challenged to the habachi structure. Chemical, thermal, and mechanical threats have been addressed by this unique combination of materials. A prototype cooled anode insert containing an array of these windows is currently in assembly for near future testing in NRL’s Electra test bed this summer. Further optimization of window geometry and cooling will be conducted with the data collected during Electra testing Summary and Future Work Si material strains are linear/elastic over the range, fatigue should not be a major limitation C. Priniski 1, C. Gentile 1, R. Parsells 1, S. Langish 1, C. Jun 1, L. Ciebiera 1, J.Sethian 2, J. Butler 21 Princeton Plasma Physics Lab, 2 Naval Research Lab