Engineered Tungsten Surfaces for IFE Dry Chamber Walls

1. Engineered Tungsten Surfaces for IFE Dry Chamber Walls Scott O’Dell Plasma Processes Inc. 4914 Moores Mill Road Huntsville, AL 35811

2. Introduction • Tungsten is an ideal material for armoring IFE dry chamber walls. • High melting temperature • Low thermal erosion • Techniques for accommodating cyclic energy deposition are needed. • In addition, elimination of helium build-up is desired to prevent premature armor failure. 2

3. Solution • Use a functional gradient material to join the tungsten armor to low activation ferritic steel walls • Minimize stress at the interface due to CTE mismatch • Provide short transport path for removal of helium • Nanometer grain structure to promote grain boundary diffusion (GB diffusion > Bulk diffusion) • Interconnected nanometer size porosity • PPI and UCSD has been awarded a DOE STTR Grant to develop Engineered Tungsten Armor using advanced Vacuum Plasma Spray (VPS) forming techniques 3

4. Vacuum Plasma Spray • Plasma Processes, Inc. is a small business that specializes in the development and fabrication of refractory metals and advanced ceramic materials for High Heat Flux (HHF) applications. • Innovative Vacuum Plasma Spray (VPS) forming techniques are used to produced: • Complex components to near net shape • Advanced high temperature coatings and composite materials • Join materials with dissimilar CTEs Nano-grained, porous W (1-2 microns thick) Dense W Functionally Graded to Ferritic Steel Low Activation Ferritic Steel 4

5. VPS Formed Refractory Metal Components • Plasma facing component heat sinks with in-situ formed helical fins • Thin-walled closed end refractory metal cartridges with ceramic liners for processing samples in microgravity (leak rate of <1x10-8 sccs He) • Nozzle inserts to reduce/eliminate throat erosion solid rocket engines 5

6. Joining of Materials with Dissimilar Coefficients of Thermal Expansion • Gradual transition from one material to the other reduces stress as compared to a typical sharp interface. • Ability to use coatings that enhance bonding between the armor and the substrate. • Recently functional gradients have been used to join thick (3-5mm) VPS W deposits to actively cooled Cu alloy heat sinks for MFE PFCs. 6

7. Medium Scale MFE PFC Armored with VPS Tungsten Medium Scale after Armor Castellation (top view of 0.4m long PFC) Deposition of VPS W Armor Close-up of Castellated Armor 7

8. Influence of Particle Size on VPS W B C A • Average starting particle size: A) 26μm B) 13μm C) 3μm • Micrographs demonstrate by reducing the starting powder size the grain structure of the resulting deposit can be reduced. 8

9. Ultrafine Grained VPS W • Submicron W powder (0.5μm) • Transition metal carbides to pin the grain boundaries (HfC) • VPS formed W components with ultrafine grained structures have been produced. 9

10. Porous VPS Tungsten • By controlling the deposition parameters, porous deposits can be produced. • Porous W deposits between dense W layers have been produced for use as helium cooled heat sinks. • Helium flow tests have demonstrated the porosity is interconnected. • Size of porosity is highly dependent on the size of the starting powder. 10

11. He Cooled W Heat Sink 11

12. Engineered W Surfaces for IFE Dry Chamber Walls • Develop a preliminary model to aid in the design and optimization of engineered W • Develop VPS fabrication techniques based on functional gradient materials for joining engineered W to low activation ferritic steel • Produce engineered W surfaces comprised of nanometer size grains and interconnected nanometer porosity to eliminate He entrapment • Demonstrate migration of helium through the engineered tungsten surface • Produce samples for thermal cycle testing and analysis 12

13. Tungsten Brush Armor for MFE PFCs • PPI, SNLs and Boeing have worked to develop W brush armor for MFE PFCs • PPI was the first to produce medium scale PFCs with W brush armor (PW-8 and PW-14) • 32mm x 100mm armor area comprised of 10mm tall W rods • Medium scale mockups have been thermal response tested to ~23 MW/m2 • Survived 500 thermal cycles at ~20 MW/m2 13

14. Insulator Coating for the University of Washington’s HIT Device • In a recent effort for the University of Washington, PPI applied an alumina dielectric coating on plasma facing surfaces of the Helicity Injected Torous (HIT) device. HIT-SI components before deposition of dielectric coating .. The Helicity Injected Torus with Steady Inductive Helicity Injection (HIT- SI) is a new spheromak under construction at the University of Washington. HIT- SI has several unique features, the most notable being the “bow tie” cross- section of the confinement region and the presence of two semi- toroidal helicity injectors at each end. Inner cone after deposition of dielectric alumina coating 14