Progress toward an experiment to study the effect of RF grounding in an internal ion source on axial oscillations of the beam in a cyclotron

Schubert, J.;Bailey, J.D.;Bolomey, L.;Jongen, Yves;Blosser, H.G.;et.al.
(2001) Cyclotrons and their Applications 2001. Sixteenth International Conference — Location: East Lansing, MI, USA (13.May.2001)

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  • Schubert, J.
    Author
  • Bailey, J.D.
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  • Bolomey, L.
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  • Jongen, YvesUCLouvain
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  • Blosser, H.G.
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Abstract
For practical reasons, the chimney of a cyclotron's internal ion source often has RF grounds at only one end, despite the desire for an axially symmetric electric field throughout the cyclotron. It is generally impractical or impossible to measure the shape of the electric fields around the chimney, but one of the authors (H. Blosser of Michigan State University) has observed that in three cyclotrons of similar design built at the National Superconducting Cyclotron Laboratory, the machine with the least axial oscillation of the beam was the only one designed with median plane symmetry in its RF grounding. Based on this he suggests that RF currents in an asymmetrically grounded chimney give the beam an initial vertical kick which starts a coherent oscillation about the median plane. This hypothesis is being tested in the Ion Beam Applications C235 proton therapy cyclotron which uses an internal hot-cathode PIG ion source that is normally grounded only at the bottom. The test uses an insert which can be temporarily installed in the upper yoke hole of the cyclotron in order to make an RF grounding connection to the top of the chimney. A scintillation probe is then used to study the axial beam position on successive turns with and without the symmetric RF grounding.
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Schubert, J., Bailey, J. D., Bolomey, L., Jongen, Y., London, G., Nguyen, Q., Van Meerbeeck, A., & Blosser, H. G. (2001). Progress toward an experiment to study the effect of RF grounding in an internal ion source on axial oscillations of the beam in a cyclotron. AIP Conference Proceedings, p. 274-276.