• A.Y. Molodozhentsev, T. Koseki, M.J. Shirakata, M. Tomizawa
  KEK, Ibaraki
• A. Ando, J. Takano
  J-PARC, KEK & JAEA, Ibaraki-ken

During the early J-PARC Main Ring commissioning and the machine operation with the moderate beam power the 'fast extraction' bare working point has been chosen to provide the machine operation in the safe regime. We discuss main experimental results obtained so far and compare with the results of the computational model of the machine, including the first experimental approach to minimize the effect of the 'sum' linear coupling resonance. The strategy to increase the beam power without changing the operational working point is presented by keeping the moderate space-charge detuning. The advantage of the second harmonic MR RF cavity, including the estimation of the beam losses during the injection and acceleration processes, is discussed.

• A.Y. Molodozhentsev, T. Koseki, M. Tomizawa
  KEK, Ibaraki
• A. Ando
  J-PARC, KEK & JAEA, Ibaraki-ken

During the early J-PARC Main Ring commissioning the emittance growth at the injection energy, caused by the field leakage of the slow extraction septums, has been observed. By using the measured field data in the J-PARC Main Ring computational model we perform the analysis of the resonance excitation for the 'bare' working points around the 3rd order horizontal resonance, used for the slow extraction of the accelerated beam. The space charge effects of the low energy beam with the moderate beam power are taken into this analysis. Some possible ways to reduce the transverse emittance dilution and the particle losses during the machine operation for the 'hadron' experiments are discussed.