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.
Highlights
The main ring (MR) of the Japan Proton Accelerator Research Complex (J-PARC)[1] is an intensity-frontier proton accelerator
The increase in the horizontal emittance in the NX21 experiment strongly depended on the horizontal tunes
This is because the number of particles crossing the resonance was changed owing to the tune spread
Summary
The main ring (MR) of the Japan Proton Accelerator Research Complex (J-PARC)[1] is an intensity-frontier proton accelerator. Protons are injected into the MR with a kinetic energy of 3 GeV and an intensity of 3.3 × 1013 protons per bunch (ppb). After injection of 8 bunches, the beam is accelerated to 30 GeV and extracted with an intensity of 2.6 × 1014 protons per pulse (ppp) in operation for neutrino experiment. A maximum beam power of 500 kW has been achieved [2] and we aim to achieve a beam power of 1.3 MW for neutrino operations in the future [3]. It is planned to upgrade the hardware, such as the main magnet power supplies and the rf system and increase the beam intensity to 3.3 × 1014 ppp for the accelerator operation with 1.3-MW beam power [3]. It is crucial to reduce the beam losses to increase the beam intensity. The transverse instability is well suppressed by the feedback system
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