Development of the Frequency Modulated Cyclotron

Abstract

The experimental development of the phase stability principle as applied to the 37-inch f-m cyclotron is discussed. The ions were required to pass through an over-all radial decrease in magnetic field of 13 percent. Some theoretical estimates of the yield vs. modulation frequency are given and these were found to be in satisfactory agreement with the experimental results. It is found that some of the ions emerge as late as four or five modulation cycles after their initial acceleration. Observations were made of the time of flight of the ions and evidence was found of the actual phase oscillations in the shape of the ion current patterns. The ion current received by a probe at different radii and different pressures using a pulsed source was analyzed, and indicates a considerable loss of beam at dee voltages less the 60 kev. The data confirm the variation of ion beam loss as the reciprocal of the square of the ion energy and extend the validity of this relation to 600 kev for deuterons. The variation of ion current with dee voltage is quite steep. A deflected beam amounting to 10 percent of the circulating current was obtained, taking advantage of the precessional motion of the ion orbits. Circulating ion currents of 3 μa of 7.5-Mev deuterons and 2 μa of 14.6-Mev protons were obtained.