Abstract
In the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex, transverse injection painting is utilized not only to suppress space-charge induced beam loss in the low energy region but also to mitigate foil scattering beam loss during charge-exchange injection. The space-charge induced beam loss is well minimized by the combination of modest transverse painting and full longitudinal painting. But, for sufficiently mitigating the foil scattering part of beam loss, the transverse painting area has to be further expanded. However, such a wide-ranging transverse painting had not been realized until recently due to beta function beating caused by edge focusing of pulsed injection bump magnets during injection. This beta function beating additionally excites random betatron resonances through a distortion of the lattice superperiodicity, and its resultant deterioration of the betatron motion stability causes significant extra beam loss when expanding the transverse painting area. To solve this issue, we newly installed pulse-type quadrupole correctors to compensate the beta function beating. This paper presents recent experimental results on this correction scheme for suppressing the extra beam loss, while discussing the beam loss and its mitigation mechanisms with the corresponding numerical simulations.
Highlights
The 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) is the world’s highest class of high-power pulsed proton driver aiming for a 1-MW output beam power [1]
RCS is in the final beam power ramp-up phase at the moment; the routine output beam power has been increased to 500 kW to date
The transverse painting emittance was set to 100π mm mrad so far. Though this painting area is enough to minimize space-charge induced beam loss in combination with longitudinal painting [10,11], it has to be further expanded to 150π mm mrad or more to sufficiently mitigate the foil scattering beam loss. Such a wide-ranging transverse painting had not been realized until recently due to beta function beating caused by edge focusing of pulsed injection bump magnets during injection
Summary
The 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) is the world’s highest class of high-power pulsed proton driver aiming for a 1-MW output beam power [1]. Injector linac upgrades were completed, by which the injection energy was upgraded from 181 MeV to the design value of 400 MeV in 2013, and the injection peak current was increased from 30 mA to the design value of 50 mA in 2014. By these series of injector linac upgrades, RCS has all the hardware parameters to realize its design performance.
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