Modeling of an Extraction Lens System

Modeling of an Extraction Lens SystemThesis DefenseBachelor of Applied Science

Karine Le DuEngineering Physics

School of Engineering Science, SFU

March 2003 Thesis Defence

OverviewDehnel Consulting Ltd.Use of Commercial CyclotronsCyclotron Components Extraction Lens SystemScope of the Study Computer Simulation ModelResultsAcknowledgements

Karine Le Du

March 2003 Thesis Defence Karine Le Du

Current Expertise: Complete Beamline Design Injection System Design Beamline Simulator SoftwareMy Project… Extraction Lens System DesignFuture Endeavors Ion Implantation


Use of Commercial Cyclotrons

Photo Courtesy of Ebco Technologies Inc.

Radioisotopes for medical use Detection of soft tissue damage On-site at hospitals

Short half-lives of radioisotopes Bombard target with protons

Necessitates beam of H¯(hydride ions)

Karine Le Du


Cyclotron Components

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Ion Source

Extraction Lenses

Injection Line

Inflector

Cyclotron

Extraction Probe

Beamline


Cyclotron Components

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Ion Source

Extraction Lenses

Injection Line

Inflector

Cyclotron

Extraction Probe

Beamline


Extraction Lens Assembly

Karine Le Du

Assembly drawing courtesy of TRIUMF

vacuum chamber

beamstopion sourc

e

z ~ 405mm

Plasma lens

Extraction lens

Shoulder lens


Scope of the StudyPurpose Identify how changes to system

parameters (dimensions and voltage potentials) affect H¯ beam characteristics

Provide data to aid an engineer in optimizing the design of an extraction lens system with regards to beam characteristics

Karine Le Du


Beam CharacteristicsNormalized Beam Emittance, εN Describes size of beam in phase space Energy normalized

Beam Current, I Percent of beam transmitted Low and high beam current applications

Beam Brightness, b

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2N

Ib


Phase SpaceFour important coordinates that completely describe an ion’s trajectory are (x, x’, y, y’) (x, y):transverse

position (x’, y’): divergence

from longitudinal axis

z: longitudinalposition

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Beam SizeBeam Size: Area enclosed in beam ellipse

Beam Emittance: Proportional to beam size

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x

x’

Beam ellipse


Optimal Beam Characteristics

Normalized Beam Emittance, εN minimize Small emittance is more efficient

Beam Current, I Depends on application

Beam Brightness, b maximize Achieved by maximizing beam current or

minimizing normalized beam emittance

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Computer Simulation Model

SIMION 3D, Version 7.0, INEEL*Model consists of 3 electrostatic lenses

*Idaho National Engineering and Environmental Laboratory

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Assumptions MadeASSUMPTIONS No plasma

meniscus

JUSTIFICATIONS Beyond the scope

of this study

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No filter magnet

Ignored space charge repulsion and image forces

e¯ stripped out early

Beyond the scope of this study


System ParametersE1: Plasma ElectrodeE2: Extraction ElectrodeE3: Shoulder Electrode

V1: Voltage Potential of E1V2: “ “ of E2V3: “ “ of E3

A1: Aperture of E1A2: “ “ E2A3: “ “ E3

D12: Spacing between E1/E2D23: “ “ E2/E3

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Table of Parameter ValuesList of design parameters by name

ID tags & nominal values

Variable parameter test values

Plasma Electrode E1 Voltage potential V1 = -25 kV Aperture diameter

A1 = 13 mm

Extraction Electrode E2 Voltage potential V2 = -22 kV -23 kV -22.5

kV-21.5 kV

Aperture diameter

A2 = 9.5 mm 10.5mm

11.5mm

12.5mm

Shoulder Electrode E3 Voltage potential V3 = 0 V Aperture diameter

A3 = 10 mm 9 mm 11 mm

Separation between electrodes

E1 & E2 D12 = 4 mm 7 mm 10 mm E2 & E3 D23 = 12 mm 8 mm 16 mm Karine Le

Du

List of design parameters by name




A1 = 13 mm


kV-21.5 kV

Aperture diameter

A2 = 9.5 mm 10.5mm

11.5mm

12.5mm


A3 = 10 mm 9 mm 11 mm


E1 & E2 D12 = 4 mm 7 mm 10 mm E2 & E3 D23 = 12 mm 8 mm 16 mm





A1 = 13 mm


kV-21.5 kV

Aperture diameter

A2 = 9.5 mm 10.5mm

11.5mm

12.5mm


A3 = 10 mm 9 mm 11 mm







A1 = 13 mm


kV-21.5 kV

Aperture diameter

A2 = 9.5 mm 10.5mm

11.5mm

12.5mm


A3 = 10 mm 9 mm 11 mm




General Trends

0

0.5

1

1.5

2

2.5

0.5 0.75 1 1.25 1.5 1.75 2normalized beam emittance (mm.mrad)

beam

brig

htne

ss (m

m.m

rad)

-2

D12 = 4 mm

D12 = 7 mm

D12 = 10 mm

less than 39.9% trans.

40% to 49.9% trans.

50% to 59.9% trans.

60% to 69.9% trans.

70% to 79.9% trans.

80% to 89.9% trans.

90% to 99.9% trans.

100% transmission

V2 = -23 kV

V2 = -22.5 kV

V2 = -22 kV

V2 = -21.5 kV

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General Trends

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1

1.25

1.5

1.75

2

2.25

2.5

0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9

normalized beam emittance (mm.mrad)

beam

brig

htne

ss (m

m.m

rad)

-2

D12 = 10mm 50% to 59.98% trans. 60% to 69.98% trans. 70% to 79.98% trans.

80% to 89.98% trans. 90% to 99.98% trans. 100% transmission V2 = -23 kV

V2 = -22.5 kV V2 = -22 kV V2 = -21.5 kV


Ion Trajectories

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Nominal Configuration,b = 0.341, N =1.136, I = 44%

Highest Beam Brightness,b = 2.351, N =0.508, I = 60.7%

Lowest Beam Brightness,b = 0.127, N =1.916, I = 46.6%

100% Beam Transmission,b = 1.731, N =0.76, I = 100%

b in [(mm·mrad)-2]

N in [mm·mrad]


Limitations/Future WorkTest results limited to ranges of parameter values tested

Test wider ranges of valuesBeam loss occurred at downstream aperture of E2

Downstream aperture had fixed size May be cause of apparent ineffectiveness in changing A2

and A3 parameter values?Implement space charge repulsionVary plasma meniscus curvatureImplement magnetic filter

Karine Le Du


AcknowledgementsDr. Morgan Dehnel Excellent mentoring and guidance

Dr. John F. Cochran andMr. Steve Whitmore Invaluable feedback

My family Support and encouragement

The Caskey Family, and friends Support and encouragement

Karine Le Du


Crude Beam Current Adjustment

Parameter

Suggested value

D12 10 mmD23 16 mmA2 9.5 mm (same)A3 10 mm (same)V2 Vary to achieve desired beam

current make more positive for higher beam current

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Beam Optics

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z

x

X’

X’


Beam Size Beam Emittance: Ellipse Area:

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nterceptiaximumm xx 'A

N Normalized Emittance:

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Modeling of an Extraction Lens System