An investigation of the early orbits in the University of Manitoba cyclotron

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Fannon, John Alexander
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The non-uniform electric field in the University of Manitoba Cyclotron gives rise to a radical instability during the first few revolutions of the ion beam. A simple theory has been developed to investigate this instability in terms of the drift of orbit centres of the ions in the beam. It has been found that the addition of a second harmonic magnetic flutter field diminishes the drift of orbit centres. If the flutter field is given a suitable radial variation, the maximum strength required to eliminate the drift is shown to be about 1500 gauss. The effect of the non-uniform electric field on the axial motion of the ion beam has also been examined. It is found that very few modifications need be made in the conclusions of Rose, Cohen and Wilson for a conventional cyclotron. The behavior of the ion beam at grids inserted in the dee openings has been studied in the light of the theory developed earlier. It has been found that there can be a certain amount of radical defocussing at the grid slits and in the region where the grid ends. Methods for reducing this defocussing have been discussed.