[en] To intensify luminosity of a circulating electron bunch the dynamics of transverse sizes of the beam on the flat-top magnetic field of 600 MeV in the PFI AN synchrocyclotron has been studied experimentally. The investigations were carried out both in the absence of and simultaneously in the presence of other disturbance factors of vertical beam size within the range of magnetic field index values from 0.707 to approximately 0.61. As a result of experiment 2.4 mm vertical size is reduced to 0.68 mm and 4 mm radial size is reduced 1.4 times. Reduction of the transverse bunch sizes beyond the areas of coupling resonances results from pulse modulation of the magnetic field index, by decreasing of vertical oscillation wiggle with quantum fluctuation of radiation under effect of inclination of cross section axis of a circulating beam to the horizontal plane and by the decrease of azimuthal asymmetry of the median plane