Development and evaluation of an improved positioning scheme for a cyclotron ion source

Cyclotrons are particle accelerators that are used to create radioactive drugs for nuclear medicine. Cyclotron efficiency is affected by the initial positioning of a plasma ion source within a cyclotron. CTI manufactures cyclotrons that use a kinematically inexact positioning scheme which relies on thread clearances to pivot an ion source.

This project analyzes CTI's current scheme, proposes design goals for an improved method, describes analysis and development of the improved mechanism, and presents experimental results and conclusions. The following design goals were defined:Range of Motion:x & y axes: ± 3 mm; zaxis: ± 2 mm.Accuracy of Motion:x, y, & z axes: ± 0.2 mm.Minimum Required Increment of Movement:x, y, & z axes: 0.1 mm.

The design solution is a kinematically exact, non-redundant mechanism which positions the ion source with an accuracy of ± 0.2 mm from a remote actuation point 425 mm away from the ion source. The design uses stepper motors and a differential lead- screw drive system controlled by a personal computer.

A mathematical model describing the three degree-of-freedom system is developed and evaluated. The resultant closed-form solution is incorporated into a C program which operates on an Intel 80286-based personal computer.

The prototype system met the accuracy design goal, minimum increment of motion goal, and the x-axis range of motion goal. Y-axis range of motion was 95% of the design goal while x-axis range of motion was 85% of the design goal. Minor hardware modifications to the prototype hardware are proposed to address x-axis range of motion.

The design is evaluated and experimental data are discussed. Improvements for transition of the first-generation hardware to production use are discussed.