Measurements of the electron cloud in the APS storage ring

K. Harkay, R.A. Rosenburg
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引用次数: 5

Abstract

Synchrotron radiation interacting with the vacuum chamber walls in a storage ring produce photoelectrons that can be accelerated by the beam, acquiring sufficient energy to produce secondary electrons in collisions with the walls. If the secondary-electron yield (SEY) coefficient of the wall material is greater than one, as is the case with the aluminum chambers in the 7-GeV Advanced Photon Source (APS) storage ring, a runaway condition can develop. As the electron cloud builds up along a train of stored positron or electron bunches, the possibility exists that a transverse perturbation of the head bunch will be communicated to trailing bunches due to interaction with the cloud. In order to characterize the electron cloud, a special vacuum chamber was built and inserted into the ring. The chamber contains 10 rudimentary electron-energy analyzers, as well as three targets coated with different materials. Measurements show that the intensity and electron energy distribution are highly dependent on the temporal spacing between adjacent bunches and the amount of current contained in each bunch. Furthermore, measurements using the different targets are consistent with what would be expected based on the SEY of the coatings. Data for both positron and electron beams are presented.
APS存储环中电子云的测量
同步辐射与存储环中的真空室壁相互作用产生光电子,光电子可以被束流加速,获得足够的能量在与壁碰撞时产生二次电子。如果壁材的二次电子产率(SEY)系数大于1,就像7-GeV先进光子源(APS)存储环中的铝腔一样,就会出现失控的情况。当电子云沿着一列存储的正电子或电子束形成时,由于与电子云的相互作用,头束的横向扰动可能会传递给尾束。为了表征电子云,一个特殊的真空室被建立并插入到环中。这个实验室内有10个基本的电子能量分析仪,以及三个涂有不同材料的靶。测量表明,强度和电子能量分布高度依赖于相邻束之间的时间间隔和每束中包含的电流量。此外,使用不同目标的测量结果与基于涂层的SEY的预期结果一致。给出了正电子和电子束的数据。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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