Investigating Secondary Electron
Emission (SEE) Properties of PlasmaFacing Components
Kevin Pardinas
Summer of Learning Symposium
October 3, 2014
Princeton Plasma Physics Laboratory (PPPL)
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.
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Surface Science Laboratory
- 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
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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
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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
Y. Raitses, I. D. Kaganovich, A. Khrabrov, D. Sydorenko, N. J. Fisch, and A. Smolyakov, IEEE Transactions on Plasma Science 39, 995 (2011)
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Y. Raitses et al.,
IEEE TPS 2011
Experimental Setup
Stage Controls
15-120 LEED Optics
Electron Gun
Turbo molecular
Pump
Ion Gun
Battery Box for Biasing
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Pulsing Circuitry
Schematic of Experimental Chamber
Chamber
5*10-8 Torr Vacuum
Battery Box
(Biasing)
SAMPLE
G1 Grid
Picoammeter
(Reading Current)
LEED 15120
Electron
Gun
PHI Model 20-045
Ion Gun Controller
LEED Optics 11-020
(Electron Gun Controller)
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Two Methods of Measuring Secondary Electron Yield
• 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
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Results:
Sample Method Gives Lower Yields
Graphite SEE Yield
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SE E y i e l d , c a r b o n
( Se i l e r , 1 9 8 3 )
0.9
0.8
SEE Yield
0.7
SE E y i e l d , g r a p h i t e
( W o o ds et a l , 1 9 8 7 )
0.6
0.5
0.4
Sa m p l e Y i e l d
0.3
0.2
0.1
Collector Yield
0
0
100
200
300
400
500
Primary Electron Energy [eV]
M E Woods et al 1987 J. Phys. D: Appl. Phys. 20 1136
Seiler, H. Secondary Electron Emission in the Scanning Electron Microscope. J. Appl. Phys. 54 11 1983
8
600
Ion Sputtering Improved SEE of Silver
Ion Sputtering: Bombarding sample with ions from ion gun in order to clean it
Silver SEE Yield
2
Ag (Sublimed) --- Bruining
and de Boer (1938)
1.8
1.6
1.4
Ag --- Ding et. al. (2001)
SEE Yield
1.2
1
0.8
Pre-Sputtering
0.6
0.4
0.2
Post-Sputtering
0
0
100
200
300
400
500
600
700
800
Primary Electron Energy (eV)
Ding, ZJ, Tang XD, Shimizu R: Monte Carlo study of secondary electron emission. J Appl Phys 89, 718-726 (2001)
Bruining H, De Boer JM: Secondary electron emission part I. Secondary electron emission of metals. Physica 5, 17-30 (1938).
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Pulsing with the Oscilloscope
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Conclusions and Future Plans
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•
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.
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!
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