Transverse emittance growth caused by space-charge-induced resonance
Takaaki Yasui, S. Igarashi, Yoichi Sato, Tadashi Koseki, K. Ohmi
Abstract
Transverse emittance growth due to space-charge-induced resonance was studied for high-power beam operation in the J-PARC main ring synchrotron. The turn-by-turn beam sizes were measured near the structure resonance at ${\ensuremath{\nu}}_{x}=21$ and near the nonstructure resonance at ${\ensuremath{\nu}}_{x}=22$. A clear difference in the emittances was observed. The emittance was observed to grow by 5 times at the operating tune ${\ensuremath{\nu}}_{x}=21.10$, and by 1.8 times at ${\ensuremath{\nu}}_{x}=22.05$ in the first 100 turns. The results show the advantage of tuning in the region of ${\ensuremath{\nu}}_{x}=22$ for high intensity beam operation. The turn-by-turn emittance varied depending on the horizontal tune in the region of ${\ensuremath{\nu}}_{x}=21$. This indicates that the mechanism of emittance growth is related to the tune spread distribution. The results were satisfactorily reproduced by the simulations of the beam dynamics, including the space-charge effect incorporated via the particle-in-cell algorithm. To reveal the mechanism of the emittance growth, the space-charge effects on the resonances were evaluated by simulations as well as analytical calculations.