Design and Simulation of Strong-focusing Pole Tips for the Houghton University Cyclotron

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Hotchkiss, Andrew
Yuly, Mark
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Houghton University
The Houghton University cyclotron accelerates ions inside of a 17 cm inner diameter evacuated aluminum chamber placed between the poles of a 1.2 T electromagnet. Two hollow “dee” electrodes, one grounded and one oscillating between a positive and negative potential, apply an electric force that with the magnetic field, accelerates the ions. Previously, weak magnetic focusing, which requires the magnetic field to decrease with larger radius, was used to force the ions back toward the central plane between dees. For large numbers of orbits, however, this made the ions get out of phase with the oscillating electric field. Strong focusing can fix this problem by creating a restoring force while keeping the cyclotron frequency the same. Mathematica and Radia, a 3D magnetic field modeling software package, were used to model the magnetic field of a strong-focusing sector pole tip, then calculate resulting ion orbits. In simulations, the original weak focusing pole tips allowed an ion orbit radius of 3.7 cm to be reached. Using newly designed strong focusing pole tips a radius of 4.9 cm corresponding to 165 keV for protons was achieved. The maximum radius theoretically achievable is 7.2 cm resulting in 360 keV of proton energy.
XLII Annual Rochester Symposium for Physics Students, University of Rochester, April 20, 2024
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