Materials Analysis of Transient Plasma-Wall Interactions PI: John Slough Post Doc: Samuel Andreason Graduate Student: Jamie Waldock Plasma Dynamics Laboratory University of Washington Co-PI: Fumio Ohuchi Grad Student: DuWayne Smith Undergraduates: Alex Henderson Department of Materials Science and Engineering University of Washington Co-PI: Richard Milroy Graduate Student: Mike Pfaff Plasma Science and Innovation (PSI) Center University of Washington AFOSR Program Review on Materials and Processes Far from Equilibrium September 10-13, 2012, Arlington, VA

Materials Analysis of Transient Plasma-Wall Interactions Fundamental Science Question: What is the chemical and physical effects on a wide variety of materials from a transient interaction with a non-equilibrium, chemically-reactive, highly magnetized plasma? Critical Material Science Need - I: Pulsed plasma thrusters for space propulsion

Transient loading Pulsed devices have transient wall loading of optical radiation, electric fields, and perhaps some ions. What are the equilibrium temperature and sputtering effects of pulsed wall loading? Sputtering rates are non-linear, how is this affected? Gas deposition and recycling are key to fusion plasmas. Wall chemistry for reactive gases FRC thrusters and fusion devices operate on chemically reactive gases. What effects do high-temperature ion-wall interactions (even if they are very reduced) create if the ions are Oxygen, Nitrogen, or Hydrogen? In fusion plasmas the chemical sputtering rate can be more important than the purely kinetic energy sputtering rates. Effects of magnetized plasma Pulsed thrusters often operate with magnetic fields ( Gauss), large gyroradii (possibly greater than the device), and very large electric fields at the wall (measured up to the kV range). How does pulsed magnetic fields this change the wall interaction and lifetime picture? Optical and Nuclear Radiation A pulsed, high-temperature device will deliver pulsed optical radiation to the wall. This has effects for both contamination as well as the sputtering. What are the effects of pulsed optical radiation on a thruster wall, both in terms of thermal loading and interaction with a neutral gas at the wall boundary. Critical Materials Science Need – II: Transients in Fusion Plasmas and Pulsed Fusion Concepts

Turbo- molecular pump Rotating Magnetic Field Driver Circuits Compression Coils End Guide Coils  20 kV compression bank modules (6) Sample/Probe Chamber Probe Non-equilibrium Materials Testing Facility at the University of Washington Plasma Dynamics Laboratory Facility can produce FRCs with Rotating Magnetic Fields, Reversed Field Theta Pinch. Gases from hydrogen to Xenon. Energy densities from 0.1 – 500 kJ/m 2

The NEMS Transient Piezoelectric Pressure Probe  Directly measures the directed energy density  Small enough to obtain both radial and azimuthal dependence  Microsecond response time

+1/16 +1/24 +1/32 +<1/32 0 (flush) Blank -1/16 Maycor -1/32 Effects of Geometry on Sputtering and Re- deposition During D 2 Plasma Exposure W W W W W W W W W W W W W W -1/16” -1/32” 0 (flush) Maycor support -1/16” -1/32” 0 +<1/32” +1/32” +1/24” +1/16” +<1/32” +1/32” +1/24” +1/16” Tungsten (W) pellets to gauge the sputtering and re-deposition effects Macor as an indicator to average sputtering and re-deposition dynamics for a broad range of the insulating materials. W pellets placed into the Macor holder at different heights relative to the surface

Re-deposition of Macor on W Surface by D 2 plasma +1/16” Maycor + 1/32” < +1/32” Binding Energy (eV) -1/16” W4f Al2p Si2p B1s K2 p C1 s F 1s K2s Si2s Mg2 p MgKL L Na W W W W W W W W Maycor support Thin uniform Thick uniform Thick pin-holed Thick patched Morphology of re-deposition varies with height Thinner and more uniform at higher (+) positions Thicker and less uniform at lower (-) positions Chemical constituents of re-deposited films on W Pronounced deposition of Si and K Migration and deposition of Na Less re-deposition of Mg and Al Vaporization of F(?) * * * *

D 2 Plasma Interactions and Re- deposition 1.Physical sputtering, chemical reactions, heat induced transformations. 2.Momentum exchange caused physical sputtering of Macor. Mass of W >> D, little sputtering of W Reaction of D with O, causing preferential reduction of SiO 2 and Al 2 O 3 Pronounced deposition of SiO 2 and Si on W 3.Temperature spiked evaporation of K and Na, leading to deposition on W. 4.Least deposition of Mg and B spices. 5.Unbinding of F from the lattice, followed by outgassing and re- deposition. Thin uniform deposition Thick deposition with pin-holes Thick deposition with patches

After exposure Before exposure During exposure Chemical and Morphological Effects of Plasma Interactions with Cu, Al, Zr and W C1s Carbide formation with residual C