| Paper | Title | Page |
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| MOPAB039 | Amplitude-Dependent Shift of Betatron Tunes and Its Relation to Long-Term Circumference Variations at NSLS-II | 175 |
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| The comparison of amplitude tune dependence measured for NSLSII lattices with models indicated the large change of amplitude tune dependence over time apparently can not be solely explained by magnets variation or beta function changes, but it seems can be explained by energy changes. On the other hand, the energy change required by fitting with the amplitude tune dependence change is too large to be explained by the RF frequency change and the change of the sum of correctors in the period of the measurements. To explain this apparent contradiction, our analysis shows the long term storage ring circumference change can explain the apparent energy change. Our data indeed shows a seasonal change of the amplitude tune dependence over long term observation. This clearly also indicated a relation to long term closed orbit drift. Hence the current work indicates a new strategy to study how to use amplitude tune dependence as a guideline to analyze long term lattice parameter shifts and closed orbit drift, and improve the orbit and machine performance stability. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB039 | |
| About • | paper received ※ 09 May 2021 paper accepted ※ 26 May 2021 issue date ※ 26 August 2021 | |
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| MOPAB041 | Convergence Map with Action-Angle Variables Based on Square Matrix for Nonlinear Lattice Optimization | 182 |
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| We apply square matrix method to obtain in high speed a "convergence map", which is similar but different from frequency map. The convergence map is obtained from solving nonlinear dynamical equation by iteration of perturbation method and study the convergence. The map provides information about the stability border of dynamical aperture. We compare the map with frequency map from tracking. The result indicates the new method may be applied in nonlinear lattice optimization, taking the advantage of the high speed (about 10~50 times faster) to explore x, y and the off-momentum phase space. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB041 | |
| About • | paper received ※ 09 May 2021 paper accepted ※ 26 May 2021 issue date ※ 18 August 2021 | |
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| TUPAB227 | Simultaneous Compensation of Phase and Amplitude Dependent Geometrical Resonances Using Octupoles | 1960 |
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| As the new generation of light sources are pushing toward diffraction limited storage rings with ultra-low emittance beams, nonlinear beam dynamics become increasingly difficult to control. It is a common practice for modern designs to use a sextupole scheme that allows simultaneous correction of natural chromaticity and energy independent, or geometrical, sextupolar resonances. However, the remaining higher order terms arising from the cross talks of the sextupole families set a strong limitation on the achievable dynamic aperture. This paper presents a simulation-based recipe to use octupoles together with this sextupole scheme to provide simultaneous self-compensation of linear amplitude dependent tune shift together with phase-dependent octupolar and higher order geometrical resonant driving terms. The correction method was built based on observations made on a simple FODO model, then applied to a realistic low emittance lattice, designed in the framework of the upgrade of the National Synchrotron Light Source II (NSLS-II). | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB227 | |
| About • | paper received ※ 19 May 2021 paper accepted ※ 23 June 2021 issue date ※ 14 August 2021 | |
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| THXB04 | Non-Invasive Dispersion Function Measurement during Light Source Operations | 3720 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. We implemented a completely parasitic measurement of lattice dispersion functions in both horizontal and vertical planes, which is fully compatible with light source user operations. The measurement is performed by applying principal component analysis and adaptive filtering to very small residual orbit noise components introduced by the RF system and detected in the beam orbit data, sampled at 10 kHz. No changes in RF frequency are required. The measurement, performed once a minute, was shown to be robust and immune to changes in the beam current, residual orbit noise amplitude and frequency content as well as other factors. At low current it was shown to provide similar accuracy to the traditional method (which shifts the 500 MHz RF frequency by ±500 Hz). In this paper we will explain our measurement technique and present typical dispersion function stability achieved during NSLS-II operations. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THXB04 | |
| About • | paper received ※ 26 June 2021 paper accepted ※ 13 July 2021 issue date ※ 23 August 2021 | |
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| THPAB197 | Enhancing Efficiency of Multi-Objective Neural-Network-Assisted Nonlinear Dynamics Lattice Optimization via 1-D Aperture Objectives & Objective Focusing | 4156 |
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Funding: This work is supported by U.S. DOE under Contract No. DE-SC0012704. Mutli-objective optimizers such as multi-objective genetic algorithm (MOGA) have been quite popular in discovering desirable lattice solutions for accelerators. However, even these successful algorithms can become ineffective as the dimension and range of the search space increase due to exponential growth in the amount of exploration required to find global optima. This difficulty is even more exacerbated by the resource-intensive and time-consuming tendency for the evaluations of nonlinear beam dynamics. Lately the use of surrogate models based on neural network has been drawing attention to alleviate this problem. Following this trend, to further enhance the efficiency of nonlinear lattice optimization for storage rings, we propose to replace typically used objectives with those that are less time-consuming and to focus on a single objective constructed from multiple objectives, which can maximize utilization of the trained models through local optimization and objective gradient extraction. We demonstrate these enhancements using a NSLS-II upgrade lattice candidate as an example. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB197 | |
| About • | paper received ※ 20 May 2021 paper accepted ※ 23 June 2021 issue date ※ 10 August 2021 | |
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| THPAB198 | Commissioning of Current Strips for Elliptically Polarizing Undulators at NSLS-II | 4160 |
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Funding: This work is supported by U.S. DOE under Contract No. DE-SC0012704. Most of the Elliptically Polarizing Undulators (EPUs) at NSLS-II are equipped with current strips (or flat wires), attached to their vacuum chambers. These strips compensate the dynamic field integrals of the EPU to minimize undesirable nonlinear beam dynamics effect that can lead to reduction in injection efficiency and beam lifetime. For each EPU, we measured the field integrals of the insertion device alone, the current strips alone, and both, while creating horizontal bumps of different amplitudes at the straight section to assess the effectiveness of the compensation provided by the design current values for the strips. The commissioning results of these current strips are reported in this article. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB198 | |
| About • | paper received ※ 19 May 2021 paper accepted ※ 23 June 2021 issue date ※ 28 August 2021 | |
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