Investigating Secondary Electron Emission (SEE) Properties of Plasma- Facing Components Kevin Pardinas Summer of Learning Symposium October 3, 2014

Princeton Plasma Physics Laboratory (PPPL) 1 Mission: The DOE Princeton Plasma Physics Laboratory works with collaborators across the globe to develop fusion as an energy source for the world, and conducts research along the broad frontier of plasma science and technology. PPPL also nurtures the national research enterprise in these fields, and educates the next generation of plasma and fusion scientists.

Surface Science Laboratory 2 -Worked for Koel Research Group (advisor: Professor Bruce Koel) -Specialize in surface science interactions, surface analysis, catalysis, plasma-facing components -My Research: -I studied secondary electron emission (SEE) of plasma-facing components -Plasma-facing components are materials that are used for the walls of plasma reaction chambers

Project Outline 1.Learn about Secondary Electron Emission from literature and past students’ work 1.Set up operating chamber and learn how to utilize all components to take measurements 1.Take SEE measurements of different materials using two different methods as well as ion sputtering and pulsing and compare them to results obtained by past students and to the values in the literature 2.Repeat experiments to ensure reproducibility 1.Report flaws in experimental setup (problems with the chamber and the positioning unit) 1.Replace positioning system in the operating vacuum chamber to allow for better results 2.Prepare summary of all results obtained 3

Introduction to Secondary Electron Emission Electron bombardment of materials leads to secondary electron emission (SEE), dependent on energy of primary electrons and properties of material SEE is important for: Hall thruster performance and lifetime, diverters and limiters of magnetic fusion devices SEE can lead to wall heating, and cooling of bulk plasma Studied SEE of Graphite, Silver, Tungsten, and Boron Nitride 4 Y. Raitses, I. D. Kaganovich, A. Khrabrov, D. Sydorenko, N. J. Fisch, and A. Smolyakov, IEEE Transactions on Plasma Science 39, 995 (2011) Y. Raitses et al., IEEE TPS 2011

Experimental Setup Turbo molecular Pump Battery Box for Biasing LEED Optics Electron Gun Ion Gun Stage Controls Pulsing Circuitry 5

Schematic of Experimental Chamber 6 Ion Gun LEED Electron Gun SAMPLE Battery Box (Biasing) Picoammeter (Reading Current) 5*10 -8 Torr Vacuum G1 Grid LEED Optics (Electron Gun Controller) Chamber PHI Model Ion Gun Controller

Two Methods of Measuring Secondary Electron Yield 7 Hit sample with electron beam Bias (put positive voltage on) the sample to ensure that no secondary electrons escape Measure current on sample Bias both sample and collector grids Collect secondary electrons on collector grids

Results: Sample Method Gives Lower Yields 8 M E Woods et al 1987 J. Phys. D: Appl. Phys Seiler, H. Secondary Electron Emission in the Scanning Electron Microscope. J. Appl. Phys

Ion Sputtering Improved SEE of Silver 9 Ding, ZJ, Tang XD, Shimizu R: Monte Carlo study of secondary electron emission. J Appl Phys 89, (2001) Bruining H, De Boer JM: Secondary electron emission part I. Secondary electron emission of metals. Physica 5, (1938). Ion Sputtering: Bombarding sample with ions from ion gun in order to clean it

10 Pulsing with the Oscilloscope

Conclusions and Future Plans Throughout the summer I was able to narrow down methods of taking secondary electron emission data for which we can obtain reproducible results, and I was able to assist in improving the operating chamber so that it can be used to obtain more reliable results in the future. My research at PPPL this summer opened my eyes to the many wonders of fusion energy, and helped me realize that this is the type of research I would like to continue doing. I have been looking into continuing my research as independent work in the Mechanical and Aerospace Engineering department. I would welcome the chance to study even more materials, especially those that are crucial to Hall Thrusters used in space. As an aerospace engineer, Hall Thrusters really caught my attention this summer, and it would be great to do research that could provide useful information for their advancement. 11

Acknowledgments Princeton Environmental Institute, Princeton University Bruce Koel (Princeton University) Princeton Plasma Physics Laboratory/PPPL Jelani Hardwick (University of Alabama) Yevgeny Raitses (PPPL) Angela Capece (PPPL) Alex Merzhevskiy (PPPL) Thank You to all! 12