報告題目： Dispersion-induced beam instability in high-intensity circular accelerators 

　　報告人：苑堯碩

　　時間安排：2018年1月4日9:00 

　　地點：近代物理所6號樓中控室會議廳

　　報告人簡介： 苑堯碩，男，1987年生。2014年畢業(yè)于中科院高能物理研究所。現(xiàn)在德國達姆施塔特工業(yè)大學讀博士學位，從事強流粒子加速器中的束流動力學研究。 

　　報告摘要： 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.