IHEP Beijing, Beijing
CSNS (China Spallation Neutron Source) is a project under construction, which will be a unique facility in China for multi-disciplinary research using neutron scattering techniques. The CSNS accelerator complex is designed to deliver proton beams of 100 kW at Phase One, and progressively upgraded to 200 kW at Phase Two and 500 kW at Phase Three. The upgrading path in beam power is via the increase in linac energy and more accumulated particles in the RCS (Rapid Cycling Synchrotron). Beam losses are key in designing and operating the accelerator complex. Emittance growth, RF trapping loss, and injection/extraction are the major loss sources. The measures to reduce the loss rate and the collimation methods in the accelerators are presented in the talk. Some beam loading effects to the RF systems in the linac and in the RCS, and the uniformization of the beam spot at the spallation target by non-linear magnets are also mentioned.
IHEP Beijing, Beijing
Momentum collimation in a high intensity RCS is a very important issue. Based on the two-stage collimation principle, a combined momentum collimation method is proposed and studied here. The method makes use of the combination of secondary collimators in both the longitudinal and transverse planes. The primary collimator is placed at a high-dispersion location of an arc, and the transverse and longitudinal secondary collimators are in a dispersion-free long straight section and in an arc, respectively. The particles with a positive momentum deviation will be scattered by a carbon scraper and then cleaned by the transverse collimators, whereas the particles with a negative momentum deviation will be scattered by a Tantalum scraper and cleaned by the longitudinal secondary collimators. This is due that a carbon foil produces relatively more scattering than a Tantalum foil if the energy loss is kept the same. The relevant requirements on the lattice design are also discussed, especially for compact rings. The multi-particle simulations using both TURTLE and ORBIT codes are presented to show the physical images of the collimation method, with the input of the CSNS RCS ring.