arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2203.04872physics.acc-ph
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FCC-EE对撞机中电子云效应的缓解

Mitigation of Electron Cloud Effects in the FCC-ee Collider

Fatih Yaman, Giovanni Iadarola, Roberto Kersevan, Salim Ogur, Kazuhito Ohmi, Frank Zimmermann, Mikhail Zobov

摘要:

由于光发射和二次发射而在束真空室内形成的电子云可能会限制加速器的性能。具体地说,如果中心电子密度超过某个阈值,则电子云可以通过头-尾型单束团不稳定性来炸毁正电子束的垂直发射度,该阈值可以通过分析来估计。使用代码PyECLOUD和VSim,我们进行了详细的模拟的电子云建立的主弧和阻尼环的FCC-EE对撞机,以确定有效的光电发射率和二次发射产量所需的实现和维持设计发射度。为此,我们提出了模拟的电子密度在束管的中心为各种束团间距,二次发射产率,和光电参数,在阻尼环和对撞机正电子环的弧。为了进一步了解潜在的动力学,云电子的空间和能量分布示出为时间的函数。此外,我们比较了两种不同的二次发射模型(“Furman-Pivi”和“ECLOUD”)获得的结果,从而表明这种类型的研究中固有的不确定性,没有任何原型真空室。我们还指出了一些情况下,两个二次排放模型产生类似的密度值。最后,根据我们对两种不同设计变体的模拟结果,我们得出结论,FCC-ee的新参数基线将有助于电子云的缓解。

英文摘要:

Electron clouds forming inside the beam vacuum chamber due to photoemission and secondary emission may limit the accelerator performance. Specifically, the electron clouds can blow up the vertical emittance of a positron beam, through a head-tail-type single-bunch instability, if the central electron density exceeds a certain threshold value, that can be estimated analytically. Using the codes PyECLOUD and VSim, we carried out detailed simulations of the electron-cloud build up for the main arcs and the damping ring of the FCC-ee collider, in order to identify the effective photoemission rate and secondary emission yield required for achieving and maintaining the design emittance. To this end, we present the simulated electron density at the centre of the beam pipe for various bunch spacings, secondary emission yields, and photoemission parameters, in the damping ring and in the arcs of the collider positron ring. To gain further insight into the underlying dynamics, the obtained spatial and energy distributions of the cloud electrons are illustrated as a function of time. In addition, we compare results obtained for two different secondary emission models ("Furman-Pivi" and "ECLOUD"), thereby indicating the uncertainty inherent in this type of study, without any prototype vacuum chambers yet available. We also point out a few situations where the two secondary-emission models yield similar density values. Finally, based on our simulation results for two different design variants, we conclude that the new parameter baseline of the FCC-ee will facilitate electron-cloud mitigation.

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