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ELECTRO-OPTICS
The Development of A Novel, Cold Electron Source
Paper 328Bruce N Laprade* Francis E Langevin and
Ronald StarcherBURLE Electro-Optics, Inc
Presented at The ASMS Conference June 2002Orlando Florida
ELECTRO-OPTICS
Objective
The Objective of this development project was to determine if the microchannels within a microchannel plate could be modified to function as spontaneous electron emitters.
ELECTRO-OPTICSMicrochannel Plates (MCPs) are arrays of millions of single channel electron multipliers. These devices are routinely used in mass spectrometers to detect and amplify weak ion signals. MCPs are manufactured in sizes ranging from 2 – 150 mm in diameter.
ELECTRO-OPTICS
Experimental MethodMicrochannel Plates operate on the principle of secondary electron emission. When a charged particle impinges on the input side of the channel with sufficient energy, a few secondary electrons are produced. The resultant electrons continue to cascade down the channel until a charge cloud exits the channel.
It was believed that by altering the microstructure within the channel, spontaneously emitted electrons could be produced, which would initiate the cascading of secondary electrons. By controlling the rate of spontaneous emission and the gain of the device, the emission current could be varied over a broad range.
ELECTRO-OPTICS
Theory of Operation
Electrons are spontaneously generated and amplified inside the channel when voltage is applied.
ELECTRO-OPTICS
Theory of Operation
Millions of channels are fused into virtually any shape and size to provide a uniform electron flux.
ELECTRO-OPTICS
1.00E-12
1.00E-11
1.00E-10
1.00E-09
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1 1.5 2 2.5 3 3.5 4
Applied Voltage (Kv)
Am
ps/c
m2
Emission Current 18 mm Format
ELECTRO-OPTICS
50 x 8 mm Emission Current
1.00E-11
1.00E-10
1.00E-09
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
0 0.5 1 1.5 2 2.5 3 3.5
Applied Voltage (kV)
Emis
sion
Cur
rent
(am
ps)
ELECTRO-OPTICS
10 x 12 mm Emission Current
1.00E-11
1.00E-10
1.00E-09
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1 1.5 2 2.5 3 3.5
Applied Voltage (kV)
Emis
sion
Cur
rent
(am
ps) Z stack
Cheveron
ELECTRO-OPTICS8 mm Microtron™ EGA
1.00E-11
1.00E-10
1.00E-09
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1 1.2 1.4 1.6 1.8 2 2.2 2.4
Applied Voltage (kV)
Emis
sion
Cur
rent
(am
ps)
ELECTRO-OPTICS
EGA Electron Source Emission Current vs. Chamber Pressure, Backfill Argon
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-07 1.00E-06 1.00E-05 1.00E-04 5.00E-04 1.00E-03 5.00E-03 1.00E-02
Emission Current(amps)
Chamber Pressure(Torr)
ELECTRO-OPTICS
ELECTROGEN Stability
0
10
20
30
40
50
60
70
80
90
100
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Extracted Charge (Coulombs/cm2)
% of initial Value
ELECTRO-OPTICSZ-Stack 5 um pore, after 144 hours of operation
1.00E-11
1.00E-10
1.00E-09
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2
Applied Voltage (kV)
Emission Current(Amps)
ELECTRO-OPTICSOperational Life Time In PFTBA at 4 x 10-4 torr
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
0 100 200 300 400 500 600 700
Continous Hours Of Operation
Emission Current(amps)
ELECTRO-OPTICS
0
10
20
30
40
50
60
70
80
0 10 20 30 40 50 60 70
Millimeters
Emis
sion
Emission Uniformity and Beam Definition 50 x 8 mm Array, Z-Stack Configuration
ELECTRO-OPTICS
ELECTROGEN Turn-On Time
0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4 5
Minutes After Turn On
% o
f Fin
al V
alue
Filament
Electron Generator Array
ELECTRO-OPTICSEnergy Distribution of Emitted Electrons, Z-Stack Configuration
1.00E-13
3.00E-06
6.00E-06
9.00E-06
1.20E-05
1.50E-05
0 200 400 600 800 1000 1200 1400
eV
Emission Current(Relative Scale Amps)
ELECTRO-OPTICS
Common Ionization Methods• Photo-Ionization
• Chemical Ionization
• Field Ionization
• Electron Impact
ELECTRO-OPTICS
EGA Ionization Source Concept
Ionization SpaceEmissionControl
Electron Accelerating Potentials
ELECTRO-OPTICSResidual Gas Analysis Taken With EGA Prototype Ion Source
Hydrogen
Water
Nitrogen
Oxygen
Carbon Dioxide
ELECTRO-OPTICS
• “Cold” Ionization Source
• Large Emission Area
• Parallel Beam, Not Sensitive to Field Strength Changes
• High Density, Uniform Emission Pattern
• Fine Emission Level Control
• Won’t Burn Out, Durable
• No Photon Noise
ELECTROGEN Advantages I
ELECTRO-OPTICS
• Low Maintenance, Frequent Cleaning not Required Because Of Cold Ionization
• No Heat-Up/Stabilization Time Required
• Bi-Directional Emitter
• Low Power Consumption (e-gun 38 W vs. EGA 0.024 W)
• Simple Single Voltage Supply Design
• No Raster Scanning Electronics Required
ELECTROGEN Advantages II