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Emittance is an important characteristic of describing charged particle beams. In hadron accelerators, we often meet irregular beam distributions that are not appropriately described by a single rms emittance or 95% emittance or total emittance. In this paper it is pointed out that in many cases a b...

A conception design of the Advanced Proton Therapy Facility (APTF) has been carried out. The system intentionally employs a slow-cycling synchrotron with a maximum energy of 250 MeV, two rotating gantries and two fixed beam nozzles for the treatment. In this paper, we try to compare the strength and weaknesses between the two treatment methods: the beam spreading and the pencil beam scanning. The application of the pencil beam scanning method and the double-scattering method together with the related nozzle design at APTF is also given. The simulation results of employing the double-scattering method have been given during the preliminary design.

A proton therapy facility based on a linac injector and a slow cycling synchrotron is proposed. To achieve effective treatment of cancer, a scanning gantry is required. The flexible transmission of beam and high beam position accuracy are the most basic requirements for a gantry. The designed gantry optics and scanning system are presented. Great efforts are put into studying the sensitivity of the beam position in the isocenter to the element misalignments. It shows that quadrupole shift makes the largest contribution and special attention should be paid to it.

A proton therapy facility based on a linac injector and a slow-cycling synchrotron is proposed. To obtain good treatments for different cancer types, both the spot scanning method and the double-scattering method are adopted in the facility, whereas the nozzles include both gantry and fixed beam types. The proton accelerator chain includes a synchrotron of 250 MeV in maximum energy, an injector of 7 MeV consisting of an RFQ and a DTL linac, with a repetition rate of 0.5 Hz. The slow extraction using the third-order resonance and together with the RFKO method is considered to be a good method to obtain a stable and more-or-less homogenous beam spill. To benefit the spot scanning method, the extraction energy can be as many as about 200 between 60 MeV and 230 MeV. A new method - the emittance balancing technique of using a solenoid or a quadrupole rotator is proposed to solve the problem of unequal emittance in the two transverse planes with a beam slowly extracted from a synchrotron. The facility has been designed to keep the potential to be upgraded to include the carbon therapy in the future.

The betatron matching of a rotationally asymmetric beam in space charge dominated low-energy beam transports (LEBTs) where solenoids are used for the transverse matching has been studied. For better understanding, the coupling elements of a beam matrix are interpreted in special forms that are products of a term defined by the Larmor rotation angle and another by the difference between the beam matrix elements in the two transverse planes. The coupling form originally derived from the rotationally symmetric field in solenoids still holds when taking into account the rotationally asymmetric space charge forces that are due to the unequal emittance in the two transverse planes. It is shown in this paper that when an LEBT mainly comprising solenoids transports a beam having unequal emittance in the two transverse planes and the linear space charge force is taken into account, the initial Twiss parameters can be modified to obtain the minimum and equal emittance at the LEBT exit. The TRACE3D calculations also prove the principle. However, when quadrupoles that are also rotationally asymmetric are involved in between solenoids, the coupling between the two transverse planes becomes more complicated and the emittance increase is usually unavoidable. A matching example using the CSNS (China Spallation Neutron Source) LEBT conditions is also presented.

China Spallation Neutron Source (CSNS) is a high power proton accelerator-based facility. Uncontrolled beam loss is a major concern in designing the CSNS to control the radioactivation level. For the Rapid Cycling Synchrotron (RCS) of the CSNS, the repetition frequency is too high for the longitudinal motion to be fully adiabatic. Significant beam loss happens during the RF capture and initial acceleration of the injection period. To reduce the longitudinal beam loss, beam chopping and momentum offset painting methods are used in the RCS injection. This paper presents detailed studies on the longitudinal motion in the RCS by using the ORBIT simulations, which include different beam chopping factors, momentum offsets and RF voltage optimization. With a trade-off between the longitudinal beam loss and transverse incoherent tune shift that will also result in beam losses, optimized longitudinal painting schemes are obtained.

In this paper, two injection scenarios with different chopping rate are discussed. The waveforms of the RF voltage are studied and optimized, respectively. Some suggestions are made, concerning chopping and momentum painting of the injected beam. Furthermore, the momentum spread and transverse tune shift are calculated so that the beam aperture and the beam loss can be estimated. Finally, the beam loss with magnet field error is analyzed.

The storage of,long bunches for large time intervals needs flattened stationary buckets with a large bucket height. Collective effects from the space charge and resistive impedance are studied by looking at the incoherent particle motion for the matched and mismatched bunches. Increasing the RF amplitude with particle number provides r.m.s wise matching for modest intensities. The incoherent motion of large amplitude particles depends on the details of the RF system. The resulting debunching process is a combination of the too small full RF acceptance together with the mismatch, enhanced by the collective effects. Irregular single particle motion is not associated with the coherent dipole instability. For the stationary phase space distribution of the Hofmann-Pedersen approach and for the dual harmonic RF system, stability limits are presented, which are too low if using realistic input distributions. For single and dual harmonic RF system with d=0.31, the tracking results are shown for intensities, by a factor of 3 above the threshold values. Small resistive impedances lead to coherent oscillations around the equilibrium phase value, as energy loss by resistive impedance is compensated by the energy gain of the RF system.

The China Spallation Neutron Source (CSNS) is an accelerator-based facility. The accelerator of CSNS consists of a low energy linac, a Rapid Cycling Synchrotron (RCS) and two beam transport lines. The overall physics design of CSNS accelerator is described, including the design principle, the choice of the main parameters and design of each part of accelerators. The key problems of the physics design, such as beam loss and control, are also discussed. The interface between the different parts of accelerator, as well as between accelerator and target, are introduced.