Electrostatic Focusing Lens System for Low MeV-Ion Microprobe: A Simulation and Optimization Study
Presentations
WE-B-TRACK 6-1 (Wednesday, 7/28/2021) 11:30 AM - 12:30 PM [Eastern Time (GMT-4)]
Purpose: Low MeV ion microprobe, that focuses an ion beam into submicron size at the cellular matrix plane, plays an important role in advancing fundamental mechanism study in particle-therapy. The dominant state-of-the-art beam focusing systems are electromagnetic quadrupole lens based, which can be hard to duplicate or of high cost. In this work, we investigated the focusing capability of the electrostatic quadrupole (EQ) lens system with a compact, easy-to-adopt, and cost-effective design goal.
Methods: We have performed the investigation with three simulation tools: GICOSY (low accuracy but high efficiency) for raw optimization, SIMION 8.1 (high accuracy but low efficiency) for fine tuning, and WinTRAX for aberration studies. We optimized the lens system with considering the lens numbers, lengths, intervals, applying voltages, and aperture-lens distance (DAL) under a given input beam condition. We compared the performance of the optimized system to that of the state-of-art EQ sextuplet (EQS) system used in the RARAF center of Columbia University and our previously optimized EQ quadruplet (EQQ) system, in the aspects of system length (Ls), working distance (Dw), demagnification factor (Df) and aberrations.
Results: An EQ triplet (EQT) lens system was optimized with superior performance than EQS and EQQ lens for a 3 MeV input proton beam with beam diameter of 30μm and angular divergence of 0.0067mrad. Specifically, comparing to Columbia EQS, Ls for EQT is ~ 2 folds shorter (1.9 vs. 3.887 m), Dw is ~1.4 times longer (170.2 vs. 126 mm) and Df is ~2 times larger (198 vs. 94). Using the ‘Q’ value to comprehensively evaluate the focusing strength and aberration, EQT gains a Q of 30.4, while that for EQS and EQQ are 9.4 and 5.0, respectively.
Conclusion: The results support our goal of compact, stable and high performance EQ design, providing promise to advance relevant radiobiological studies.
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