ultra low work function coating for combinedultra low ......ultra low work function coating for...
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Ultra Low Work Function Coating for CombinedUltra Low Work Function Coating for Combined Passive Electron Emission and Collection for
Spacecraft Charging Neutralization and Electrodynamic Tether Applications
Lauren P. Rand, Colorado State UniversitySudhakar Mahalingam, TechX Corporation
Juan Sanmartin Universiad Politécnica de MadridzJuan Sanmartin, Universiad Politécnica de Madridzand
John D. Williams, Colorado State University
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12CaO-7Al2O3 [Ca24Al28O64]4+ 2O2–
.4 n
m0
http://www.nanonet.go.jp/english/mailmag/2006/071a.html
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[Ca24Al28O64]4+ 4e–
Toda, et al. Advanced Materials. 19, 2007.
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Cathode Flange
Cathode Tube
Bottom Crucible with one half insert locatedone half insert located over the C12A7 load
Two Insert
One Half of Insert
Crucibles
Cathode Tube
Two Insert Halves Enclosed
Keeper
Cathode Tube Mounted to Cathode Flange
Enclosed KeeperEnclosed Keeper Mounted to
Cathode Flange
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Plasma Electron Emitters are Nice, but are there Other Applications for Electride Electron Emitters?
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Plasma Contactor
DC-DC Converters& Electronics
Pressure Regulator
Solenoid Valve& Electronics
Hollow Cathode
Xenon Tank
Hollow Cathode with Keeper
Fill & Drain ValvePressure Transducer
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• Why not use electride to coat a tether and passively EMIT and COLLECT electrons?
• One question to answer is where the floating point will end upfloating point will end up.– How long is the negatively biased section
relative to the positively biased section?relative to the positively biased section?
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Electron Collection
Space Plasma
Collection
+V Plasma
0 VSheath
neoTeo
Positively Biased Tether
-
0.10OML
0.08
m2 )
OOPIC Pro
0.06
nsity
(A/
0.04
rent
Den
0.02
Cur
r
0.000 200 400 600 800 10000 200 400 600 800 1000
Tether potential (V)
-
ge (V
)Vo
ltag
-
Electron Emission
-VSpace Plasma
Emission
Plasma
0 VSheath
neoTeo
Negatively Biased Tether
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Thermionic Emission
j AST 2 exp(
ekT
)kT
3V 1 S exp
e3V4d
1kT
4d o kT
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Space Charge Limited CurrentSpace Charge Limited Current
2 e V32
j 2
9e
2mV 2
d29 2m d
j (2 25 106)V
32
j (2.25x10 6)d2
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j j ? V32
jTE > jSCLC ? j (2.25x106)V 2
d2
j AST 2 exp(ekT
)jSCLC > jTE ? kT
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(eV)Some typical
LaB6 2.66Some typical high current density
CeB6 2.43density emitters
Ba-W 2.14C12A7 0.6
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TT (K)Same Geometry?
LaB6 1900Same Applied Voltage?
CeB6 1750Voltage?
Same Emission
Ba-W 1350Same Emission Current!
C12A7 440
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0.10OML
0.08
m2 )
OOPIC Pro
0.06
nsity
(A/
0.04
rent
Den
0.02
Cur
r
0.000 200 400 600 800 10000 200 400 600 800 1000
Tether potential (V)
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1.20 OML ElectronCollectionPreliminary
1.00m
2 )SCL ElectronEmissionTL Electron
Calculation
0 60
0.80
nsity
(A/m TL Electron
Emission
0 40
0.60
rent
Den 270 K, 0.6 eV
0.20
0.40
Cur 5X Higher
0.00
neo = 1011 m-3
0 200 400 600 800 1000
Tether potential (V)
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ConclusionConclusion• A new material may be available soon that has a
l k f ti th t i t bl d hi hvery low work function that is stable under high emission currentP li i l l ti t th t l t• Preliminary calculations suggest that electron emission length of a bare tether might be ~1/5 of the positively biased sectionthe positively biased section
• Ohmic heating might reduce negative bias section length even moresection length even more
• Configuration of electride into gun geometry might be an alternative to coating tether g g
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