The acceleration of heavy ions in a fixed-frequency cyclotron

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Abstract
A study has been made of the acceleration of the ions 9Be4+, 12C5+, 13C5+, 13C6+, 14N6+, 15N6+, 16O6+ and 20Ne9+ in a 60 in. fixed-frequency cyclotron. Since the momentum which can be imparted to an ion in a given cyclotron magnet is proportional to the charge carried by the ion, one of the chief problems in accelerating heavy ions to high energies is that of obtaining highly-charged ions. Of particular interest are ions with a final charge which is a multiple of 3, as ions with one-third of the final charge can be extracted from the ion-source and accelerated at closely the same value of magnetic flux-density as the final ion. These ions with one-third of the final charge have a frequency of revolution which is one-third that of the final ions. This preliminary "third harmonic" acceleration of the ions with a low charge gives them such an energy that collisions with gas atoms in the cyclotron tank can strip the ions to the final state of charge desired. This mechanism of acceleration leads to a continuous energy-distribution of the final ions of high charge. The beam current of high energy ions can be increased by increasing the pressure of gas in the cyclotron tank to increase the probability of stripping.