Abstract:
The cyclotron AIC-144, currently used in proton radiotherapy of eye melanoma, is located in the Institute of Nuclear Physics in Cracow. The efficiency of protons deflection of this cyclotron, after elements of pole tip were precisely installed therein in 2006, amounted to 10%. Several months later micromoves of pole tip elements and decline of effectiveness of proton beams deflection were observed. Attempts to restore previous state led to partial success. The efficiency of deflection was still much lower than the one obtained in 2006 and amounted to 3%. The aim of this paper is to verify the hypothesis about deterioration of magnetic field symmetry in the area of acceleration and to correct the field by introducing micromoves into pole tip elements, under control of magnetic field mapping. The survey has confirmed significant asymmetry in the magnetic field within the acceleration area. After precise correction of the position of pole tip elements essential symmetry improvement was achieved. The correction was successful and after activating the cyclotron the efficiency of deflection reached 12%.
