报告题目： Dispersion-induced beam instability in high-intensity circular accelerators 

　　报告人：苑尧硕

　　时间安排：2018年1月4日9:00 

　　地点：近代物理所6号楼中控室会议厅

　　报告人简介： 苑尧硕，男，1987年生。2014年毕业于中科院高能物理研究所。现在德国达姆施塔特工业大学读博士学位，从事强流粒子加速器中的束流动力学研究。 

　　报告摘要： Space charge effect in high-intensity accelerators can trigger collective beam instability, lead to beam loss and limit the maximum beam intensity. In this context, study of beam intensity limitation by space charge effect and method to increase the space charge limit are of essential importance for high-intensity design, operation and optimization. For example, the phase advance for one periodical cell in high-intensity linear accelerators are usually designed to be less than 90 degree to avoid the occurrence of the well-known envelope instability. Based on the perturbation theory on the generalized envelope equation including dispersion, as well as particle-in-cell simulations, in this report we show that in circular accelerators, a newly discovered instability—dispersion-induced beam instability exists because of the combined effect of space charge and dispersion, which is characterized by a resonance between envelope mode and the newly-identified dispersion mode [Phys. Rev. Lett. 118, 154801 (2017)]. Several potential applications of the dispersion mode on the characterization of intense beams in circular accelerators and method to measure the mode are also briefly introduced.