Modeling of an Extraction Lens System

Transcription

1 Modeling of an Extraction Lens System Thesis Defense Bachelor of Applied Science Engineering Physics School of Engineering Science, SFU

2 Overview Dehnel Consulting Ltd. Use of Commercial Cyclotrons Cyclotron Components Extraction Lens System Scope of the Study Computer Simulation Model Results Acknowledgements

3 Current Expertise: Complete Beamline Design Injection System Design Beamline Simulator Software My Project Extraction Lens System Design Future Endeavors Ion Implantation

4 Use of Commercial Cyclotrons 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) Photo Courtesy of Ebco Technologies Inc.

5 Cyclotron Components Extraction Lenses Ion Source Injection Line Inflector Cyclotron Extraction Probe Beamline

6 Cyclotron Components Extraction Lenses Ion Source Injection Line Inflector Cyclotron Extraction Probe Beamline

7 Extraction Lens Assembly Plasma lens vacuum chamber Shoulder lens ion source beamstop Extraction lens z ~ 405mm Assembly drawing courtesy of TRIUMF

8 Scope of the Study Purpose 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

9 Beam Characteristics Normalized Beam Emittance, ε N 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 b I 2 N

10 Phase Space Four 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: longitudinal position

11 Beam Size Beam Size: Area enclosed in beam ellipse Beam Emittance: Proportional to beam size x Beam ellipse x

12 Optimal Beam Characteristics Normalized Beam Emittance, ε N 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

13 Computer Simulation Model SIMION 3D, Version 7.0, INEEL* Model consists of 3 electrostatic lenses *Idaho National Engineering and Environmental Laboratory

14 Assumptions Made ASSUMPTIONS No plasma meniscus No filter magnet JUSTIFICATIONS Beyond the scope of this study e stripped out early Ignored space charge repulsion and image forces Beyond the scope of this study

15 System Parameters E1: Plasma Electrode E2: Extraction Electrode E3: Shoulder Electrode V1: Voltage Potential of E1 V2: of E2 V3: of E3 A1: Aperture of E1 A2: E2 A3: E3 D12: Spacing between E1/E2 D23: E2/E3

16 Table of Parameter Values List of design parameters by name Plasma Electrode Voltage potential Aperture diameter Extraction Electrode ID tags & nominal values E1 V1 = -25 kv A1 = 13 mm E2 Variable parameter test values Voltage potential V2 = -22 kv -23 kv kv kv Aperture diameter A2 = 9.5 mm 10.5mm 11.5mm 12.5mm Shoulder Electrode Voltage potential E3 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

17 beam brightness (mm.mrad) -2 General Trends 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 = kv V2 = -22 kv V2 = kv normalized beam emittance (mm.mrad)

18 General Trends beam brightness (mm.mrad) normalized beam emittance (mm.mrad) 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 = kv V2 = -22 kv V2 = kv

19 Ion Trajectories b in [(mm mrad) -2 ] N in [mm mrad] 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%

20 Limitations/Future Work Test results limited to ranges of parameter values tested Test wider ranges of values Beam 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 repulsion Vary plasma meniscus curvature Implement magnetic filter

21 Acknowledgements Dr. Morgan Dehnel Excellent mentoring and guidance Dr. John F. Cochran and Mr. Steve Whitmore Invaluable feedback My family Support and encouragement The Caskey Family, and friends Support and encouragement

22 Crude Beam Current Adjustment Parameter Suggested value D12 D23 A2 A3 V2 10 mm 16 mm 9.5 mm (same) 10 mm (same) Vary to achieve desired beam current make more positive for higher beam current

23 Beam Optics x X X z

24 Beam Size Beam Emittance: Ellipse Area: Normalized Emittance: x A m aximum x' N i ntercept