Study On Extraction System Dynamics Of Heavy Ion Synchrotron

Extraction system is an essential part of accelerator physics design.Different accelerator operation mode and basic optical design have different requirements for extraction system.Meanwhile,in order to verify the reliability and rationality of the extraction system design and avoid beam loss,the dynamics simulation will become more important.In this paper,based on two accelerators with different scientific objectives,the design of the extraction system and the beam dynamics simulation are described in detail,which is of guiding significance to the study of beam extraction in the actual commissioning and operation of the facility in the future.300 Me V proton and heavy ion synchrotron is the first accelerator facility specially designed for irradiation of space devices in China.It can supply 100～300 Me V protons and 7～80 Me V/u heavy ions,and the number of terminal particles can reach1×10⁶～1×10⁹ppp.The linac is used as the injector to improve the quality and intensity of the beam.For the synchrotron,the close orbit correction of injection and extraction platform and the dynamic magnetic field correction during acceleration were first used to further reduce the bam loss.At the same time,extremely high vacuum is obtained by using large pumping speed vacuum pump and high temperature baking scheme.Due to the variety of particles and wide range of energy coverage,the slow extraction used three settings according to different emittance,and the beam extraction efficiency and uniformity were optimized by using the self-developed particle tracking program SESP.Because the AM mode is simplified in the theoretical model and has a certain limitation due to the restriction of beam emittance,it is more sensitive to the RF-KO angle when the emittance is small.Through simulation analysis,the AM curve of polynomial can be selected to further improve the beam extraction uniformity.At the same time,the influence of local orbit bump is analyzed in detail,which provides an important optimization direction for slow extraction design.Meanwhile,for the beam with low energy and large emittance,a new extraction design scheme based on sextupole ramping and dynamic bump is proposed.Through simulation,the beam uniformity and duty factor were improved.Based on the simulation of beam extraction with different emittance in the miniaturized accelerator,the influence of local orbit bump on the extraction system is discussed for the first time,which must be considered in the initial physical design.The experimental test of large emittance and slow extraction further verifies the feasibility of the new extraction scheme and solves practical engineering problems effectively.It also has important reference value for the design of slow extraction system of large scientific facility.BRing is the booster of HIAF,which is characterized by complex operation mode,high magnetic field rising rate during acceleration,and significant space charge effect,impedance and beam instability.In order to save space and cost,fast and slow extraction need share the same extraction channel,so higher requirements are proposed in the design of extraction system.In this paper,the specific physical design scheme is given in detail,and careful and optimized selection is made in the layout of the extraction elements,so that the kick angle and the deflection of electrostatic septum are as small as possible.Aiming at the characteristics of short rising time and stable operation of Kicker,a multi-phased beam dump scheme based on Kicker was proposed,and the dump efficiency of bunch beam could reach 100%during acceleration.Two blocks are placed near the quadrupole and are made of graphite and copper,which has the characteristics of high melting point,irradiation resistance and good thermal conductivity.FLUKA and ANSYS software were used to analyze the change of energy deposition and temperature rise under the interaction between the block and beam.The results show that for ²³⁸U³⁵⁺of 835 Me V/u,the energy loss is mainly concentrated in the position of 3.4 mm at the graphite front,and the temperature rise is only about 60℃,which further verifies the reliability of the design scheme.Finally,the effect of the multipole field in dipole and quadrupole on the slow extraction is studied.The sextupole field has the chromatic effect and resonance drive,and changes the spiral step and angle dispersion.For octupole and higher order field component,the effect on slow extraction beam is weak and can be ignored.The physical design optimization scheme of BRing extraction system effectively solves the problem that the beam center of different energies and species does not coincide in the entrance of MS.At the same time,it also has the function of machine protection,which effectively improves the reliability of device operation.