In this paper we showed a systematic method of appropriate parameter choice for a circular pp collider by using analytical expression of beam-beam tune shift limit started from given design goal and technical limitations. A parameter space has been explored. Based on parameters scan and considerations from RF systems, a set of appropriate parameter designed for a 50Km and a 100Km circular proton-proton collider was proposed.

Thermal and mechanical characterizations of a substrate-free focal plane array *Cheng Teng(程 腾) a) , Zhang Qing-Chuan(张青川) a) † , Chen Da-Peng(陈大鹏) b) , Shi Hai-Tao(史海涛) a) , Gao Jie(高 杰) a) , Qian Jian(钱 剑) a) , and Wu Xiao-Ping(伍小平) a) a)

An ADS 650 MHz medium beta cavity study and designLIU Zhen-Chao( ) GAO Jie( ) LI Zhong-Quan( ) ZHAI Ji-Yuan( ) ZHAO Tong-Xian( ) LI Da-Zhang( ) LIU Yi-Lin( ) SUN Yi( )

Abstract:In cavities, there exists not only the fundamental mode which is used to accelerate the beam but also higher order modes (HOMs). The higher order modes excited by beam can seriously affect beam quality, especially for the higher R/Q modes. This paper reports on measured results of higher order modes in the IHEP02 1.3GHz low-loss 9-cell superconducting cavity.Using different methods, Q e of the dangerous modes passbands have been got. The results are compared with TESLA cavity results. R/Q of the first three passbands have also been got by simulation and compared with the results of TESLA cavity.Keywords: higher order modes, Q e , experimental measurements PACS: 29.20.Ej IntroductionThe layout of IHEP02 1.3GHz low-loss 9-cell superconducting cavity [1] is shown in Fig.1. In order to damp HOMs, two HOM couplers were mounted respectively at the upstream and downstream beam tube. Distances from the HOM couplers to end cells were 65mm and 50mm, which were different from TESLA cavity [2]. Length of upstream beam tube was also different from downstream. Simulation results of R/QThe ratio R/Q is a very important quantity related to the interaction of the beam and cavity. The higher value of R/Q stands for larger energy change between beam and cavity. For monopole HOMs, beam energy loss will be more. For dipole modes, the transverse displacement of the beam will be larger, which will causes emittance larger and even worse it will leads beam loss. It becomes very important to measure modes with large R/Q.An important parameter describing the transverse beam-cavity interaction is transverse shunt impedance. From the Panofsky-Wenzel theorem [3], the transverse momentum change of the particle passing through a cavity excited in a single mode is proportional to a parameter ( / ) R Q ⊥ . In this paper, for dipole modes,