HB2025 - the 71st ICFA Advanced Beam Dynamics workshop on High-Intensity and High-Brightness Hadron Beams

Third-order resonances and the correction in J-PARC MR

THPT66

Oct 23, 2025, 3:30 PM

2h

third floor (conference center)

Poster Presentation WGA:Beam Dynamics in Rings THPT poster session

Speaker

Susumu Igarashi (High Energy Accelerator Research Organization)

Description

Beam loss reduction is essential to achieve higher beam intensity in the main ring synchrotron (MR) of the Japan Proton Accelerator Research Complex (J-PARC). We have observed the effect of the third order non-structure resonances of 3νx=64 and νx+2νy=64. The resonance driving terms were measured with the current settings of the trim coils of the sextupole magnets. Both resonances have been corrected with four sets of the trim coil systems. Consequently, the beam loss was significantly reduced. Further correction of the resonances is planned to include the effect of off-momentum particles for the beam intensity upgrade. For that purpose, we have searched for sextupole error fields as causes of the resonances. An effective procedure for the search was devised using measurements of the nonlinear dispersion function. Because the sextupole field contributes to the first order nonlinear dispersion function, the distribution of the sextupole fields can be derived from the distribution of the nonlinear dispersion function measured using the beam position monitors.