Abstract
Short bunch beams of high intensity are required by many applications, and they are usually obtained by using bunch compression before the extraction in relatively slow cycling synchrotrons or accumulator rings. In this article, short bunch extraction by the bunch compression method is proposed to apply to a rapid cycling synchrotron (RCS) where the time duration is very limited to exploit the bunch compression process. The method is practically applied in the RCS of the China Spallation Neutron Source (CSNS) to obtain short-bunch beams for white neutron applications. Different short-bunch extraction scenarios have been studied, from keeping full beam power to reduced beam powers. A special desynchronization method is designed to solve the problem of slow acceleration during the bunch rotation process when the magnetic field is still ramping up. The space charge effect and beam loading effect during the bunch compression have also been taken into account in this high-intensity RCS. Multiparticle simulations have been carried out to show the effectiveness of the method with the input of the CSNS RCS. With a sacrifice of about two-thirds of the beam power, the rms bunch length of the extracted beam can be reduced to about one-ninth of the one in the nominal operation mode.
Highlights
Short-bunch high-intensity hadron beams are required by many applications such as the production of neutrino beams and radioactive ion beams and white neutron sources
The method is practically applied in the rapid cycling synchrotron (RCS) of the China Spallation Neutron Source (CSNS) to obtain short-bunch beams for white neutron applications
In a rapid cycling synchrotron (RCS), the magnetic field ramping is usually driven by a resonant power supply and no evident flat-top field can be provided for applying the nonadiabatic bunch compression method
Summary
Short-bunch high-intensity hadron beams are required by many applications such as the production of neutrino beams and radioactive ion beams and white neutron sources. The bunch compression method just before fast beam extraction has been proposed to obtain very short bunch beams from synchrotrons This is to use the combination of adiabatic bunch lengthening and the nonadiabatic bunch rotation processes. The time structure of the backstreaming neutrons is jointly determined by the pulse length of the impinging proton beam and the thickness of the spallation target. As the target length cannot be changed for this application, it would be interesting to shorten the proton pulse length by designing special dedicated working modes for the CSNS accelerators. This objective drives the studies presented in the article
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