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.

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Theory of Operation

Electrons are spontaneously generated and amplified inside the channel when voltage is applied.

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Theory of Operation

Millions of channels are fused into virtually any shape and size to provide a uniform electron flux.

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50 x 8 mm 40 mm

18 mm

Various Format Electron Generator Arrays

11 x 12 mm 8 mm

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)

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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)

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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

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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)

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Common Ionization Methods• Photo-Ionization

• Chemical Ionization

• Field Ionization

• Electron Impact

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Conventional Electron Impact Ionization Source Configuration

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EGA Ionization Source Concept

Ionization SpaceEmissionControl

Electron Accelerating Potentials

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Ion Sources

Conventional RGA Ion Source EGA Prototype Ion Source

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

ELECTRO-OPTICS

ELECTROGEN

SpecificationsEmission Area 3 mm -150 mm dia

Electron Flux Density 0 to 50 µA/cm2

(Tunable)

Power Supply Voltage to 3600V Max

Current Required 44 mA Max.

Max Bake Temp 300°C

Max Operating Temp 200°C

Uniformity 10%