In order to determine the proper position of the dee edge, ion source, puller, and beam-defining clipper with respect to the magnet center, measurements of the structure of the electric field in the surroundings of the ion source were made with a half-scale model in an electrolytic tank. The acceleration process during the first three revolutions was studied for different geometries and starting phases, by a graphical approximation method for orbit plotting. A more detailed study was then made to determine initial conditions—such as orbit-center distribution, energy spread, axial focusing, and energy bunching—as functions of the center geometry and starting phase. By increasing the particle path length during the first half revolution approximately 20 deg—achieved by azimuthal displacement of the source—good results were obtained. The ion-start location was finally determined so as to bring the beam close to an equilibrium orbit at 10 in. radius. This was done with an orbit code, modified to take account of the increased transit time through the acceleration gap of smaller radii. Some experimental results of changes in the cyclotron beam quality, caused by changes in the ion-starting conditions, are presented.