| Paper | Title | Page |
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| WEXAT0101 | Beam-beam Interaction in SuperKEKB: Simulations and Experimental Results | 114 |
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The beam-beam interaction is one of the most critical factors determining the luminosity performance of SuperKEKB. Simulations and experimental results from SuperKEKB have shown that a complete understanding of the beam-beam effects demands reliable models of 1) the nonlinear beam-beam interaction at the interaction point, 2) the one-turn lattice transfer map with machine imperfections, and 3) other intensity-dependent collective effects. The interplay of these factors makes it difficult to predict the luminosity performance of SuperKEKB via simulations. This paper continues the authors’ previous work* to discuss the beam-beam effects on luminosity in SuperKEKB.
* D. Zhou, Y. Funakoshi, K. Ohmi, Y. Ohnishi, and Y. Zhang, Simulations and Measurements of Luminosity at SuperKEKB, in Proc. IPAC’22, Bangkok, Thailand, Jun. 2022, pp. 2011-2014. |
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Slides WEXAT0101 [8.284 MB] | |
| DOI • | reference for this paper ※ doi:10.18429/JACoW-eeFACT2022-WEXAT0101 | |
| About • | Received ※ 26 November 2022 — Revised ※ 06 February 2023 — Accepted ※ 08 February 2023 — Issue date ※ 11 February 2023 | |
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| WEXAT0102 | Study for -1 Mode Instability in SuperKEKB Low Energy Ring | 119 |
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| Emittance increase has been seen in SuperKEKB LER. It is pure single bunch effect: dependent of bunch current but independent of total current. -1 mode signal has been seen in the bunch oscillation recorder at the emittance increase. The emittance increase depends on collimator aperture/impedance and bunch-by-bunch feedback system. We discuss the instability measurement and simulations to explain the phenomenon. | ||
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Slides WEXAT0102 [2.867 MB] | |
| DOI • | reference for this paper ※ doi:10.18429/JACoW-eeFACT2022-WEXAT0102 | |
| About • | Received ※ 31 October 2022 — Revised ※ 04 February 2023 — Accepted ※ 08 February 2023 — Issue date ※ 15 February 2023 | |
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WEXAT0104 |
Beam-beam Simulations including Coupling Impedance | |
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| The design performance of future e+e− ring colliders has been pushed to new extreme based on the crab-waist scheme. The new found coherent head-tail instability (X-Z instability) may induce the horizontal beam size blowup and reduce the machine performance. The longitudinal coupling impedance would distort the phase space: lengthen the bunch and bring incoherent synchrotron tune spread. The simulation study has found the clear influence of longitudinal impedance on the X-Z instability in both CEPC and FCCee. With the evolvement of future machine design process, the transverse impedance has also been included. The results show that a vertical beam-beam TMCI-like instability may be induced when the impedance is considered. It is first found in e+e− colliders. Some similar study at SuperKEKB will also be presented. It could be expected or concluded that different effect would couple and determine the final performance together in present and future high performance crab-waist colliders. Separate effect study seems not enough to evaluate and predict the machine performance/stability. | ||
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Slides WEXAT0104 [3.976 MB] | |
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| WEYAT0102 | Mitigation of Electron Cloud Effect in the SuperKEKB Positron Ring | 146 |
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| One critical issue for the SuperKEKB is the electron cloud effect (ECE) in the positron ring, and various countermeasures had been prepared before starting the commissioning. The ECE, however, was observed during phase-1 commissioning (2016) caused by the electron cloud in the beam pipes at drift spaces of the ring, which had antechambers and a TiN-film coating. Permanent magnets and solenoids to generate magnetic fields in the beam direction were attached to the beam pipes as additional countermeasures before the next phase-2 commissioning (2018). Consequently, the threshold of the current linear density for exciting the ECE increased by a factor of at least 2. During Phase-3 commissioning (2019), it was confirmed that the threshold was over 0.53 mA/bunch/RF bucket, and we have observed no clear evidence of ECE in the usual operation up to now. The effectiveness of the ante-chambers and TiN film coating of the real beam pipe was reevaluated. The present ante-chambers were found to be less effective than expected with regard to reducing the number of photoelectrons in the beam channel. Here we will summarize the mitigation techniques used in the SuperKEKB and the results so far. | ||
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Slides WEYAT0102 [7.521 MB] | |
| DOI • | reference for this paper ※ doi:10.18429/JACoW-eeFACT2022-WEYAT0102 | |
| About • | Received ※ 22 September 2022 — Revised ※ 04 February 2023 — Accepted ※ 08 February 2023 — Issue date ※ 11 February 2023 | |
| Cite • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |