Studies On New Extraction Methods From Proton Synchrotrons

In recent years, proton synchrotrons have obtained great development. In the aspect of high-intensity proton accelerators, in order to satisfy the needs of high energy phsics, nuclear physics and being as platforms for multidisciplinary research, more and more high power proton synchrotrons have been built or are under construction, e.g. J-PARC, ISIS, CSNS which is under construction and so on. For weak intensity proton accelerators, medical accelerators represented by proton therapy accelerators have also gained rapid development.For proton synchrotrons, beam extraction is very important. Extraction methods have direct impact to the extracted beam quality, thus they are usually the key to meet the needs of different beam applications. During the last decades, a few of mature extraction methods have been developed, e.g. low beam loss single-turn fast extraction for high-intensity synchrotrons, third-order resonant slow extraction for weak intensity synchrotrons, and so on. This paper presentsthree new extraction methods to enrich extraction methods and satisfy the needs of some special applications.In order to carry out detector tests which are important for many research field especially particle physics and studies on space radiation effects, a novel method to extract extremely weak beam in the parasitic mode is designed at high-power proton rapid cycling synchrotrons. This method can obtain extremely weak intensity but stable beam over a long period of time or with a relatively large duty factor, while maintaining the normal fast extraction almost unaffected. Although the studies have been carried out with the CSNS/RCS parameters, the method should be applicable to other high-intensity proton synchrotrons.A new method to extract very short bunches from rapid cycling synchrotrons has been developed. A special bunch compression method by incorporating bunch rotation, desychronization and special low-emittance injection is to generate very short bunches before fast extraction. The method is verified by simulations using the parameters the CSNS/RCS. As one of different schemes, one can obtain about one nineth of the bunch length as compared to the nominal fast extraction method with a sacrifice of two-third beam power. It will benefit much the white neutron applications for nuclear data measurements at CSNS. Certainly, this method should be applicable to other rapid cycling synchrotrons when very short bunch beams are needed.A novel method for resonant slow extraction at the half-integer resonance in synchrotrons by using special anti-symmetric sextupole field has been developed. This method has the potential in applications demanding for very stable slow extraction from synchrotrons and has some advantages compared to the normal sextupole field. One of them is that it can work at a more distant tune from the resonance, so that it can reduce significantly the intensity variation of the extracted beam which is mainly caused by the ripples of magnet power supplies.The studies show that with the same field strength and the same tune distance to the resonance, the area of stable region or the change of the area due to the working point variation in the case of anti-symmetric sextupole is about1/14of the one in the case of standard sextupole. This method could be used in external target experiments in particle physics and nuclear physics, and in proton or heavy ion therapy.In high-intensity proton synchrotrons, the control of beam loss is very important. A new momentum collimation method-combined momentum collimation has been proposed to overcome the inefficiency of the previously used collimation methods for medium-size high-power proton synchrotrons. Through two separate two-stage collimation systems and a single-stage collimation system, this method has greatly improved the momentum collimation efficiency. Besides, the studies also show the important influence of the correlation of the injected beam to the collimation efficiency, with the favor to anti-correlated injection. Detailed studies including multiparticle simulations have been carried out with the CSNS/RCSlattice and parameters. They show the momentum collimation efficiency larger than90%for proton beams up to a few hundreds MeV, thus confirm the effectiveness of the method.