| Paper | Title | Page |
|---|---|---|
| TUXA01 | Advances in Understanding of Ion Effects in Electron Storage Rings | 1267 |
|
||
| Ion instability, in which beam motion couples with trapped ions in an accelerator, is a serious concern for high-brightness electron storage rings. For the APS-Upgrade, we plan to mitigate coherent ion instability using a compensated gap scheme. To study incoherent effects (such as emittance growth), an IONEFFECTS element has been incorporated into the particle tracking code ELEGANT. The simulations include multiple ionization, transverse impedance, and charge variation between bunches. Once these effects are included, the simulations show good agreement with measurements at the present APS. We have also installed a gas injection system, which creates a controlled pressure bump of Nitrogen gas in a short section of the APS ring. The resulting ion instability was studied under a wide variety of beam conditions. For cases with no or insufficient train gaps, large emittance growth was observed. IONEFFECTS simulations of the gas injection experiment and APS-U storage ring show the possibility of runaway emittance blowup, where the blown-up beam traps more ions, driving further instability. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXA01 | |
| About • | paper received ※ 24 June 2021 paper accepted ※ 27 July 2021 issue date ※ 10 August 2021 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
TUXA02 |
Beam Dynamics Optimization in High-Brightness Electron Injectors | |
|
||
|
Funding: The work was supported by the U.S. Department of Energy Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-05CH11231. The next generation of X-ray free electron lasers requires beams with increasingly high peak current and low emittances at ~MHz repetition rates, placing increased demands on the performance of high-brightness electron photoinjector sources. To explore the high- dimensional parameter space associated with photoinjector design, global multiobjective optimization methods based on genetic algorithms or similar tools play a critical role. We review our experience applying these tools both to understand and to optimize simulated injector beam performance for projects such as LCLS-II (at SLAC), the Advanced Photoinjector EXperiment (at LBNL), APEX2, and potential future high-brightness FEL electron sources. |
||
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUXA03 | Progress in Mastering Electron Clouds at the Large Hadron Collider | 1273 |
|
||
| During the second operational run of the Large Hadron Collider (LHC) a bunch spacing of 25 ns was used for the first time for luminosity production. With such a spacing, electron cloud effects are much more severe than with the 50-ns spacing, which had been used in the previous run. Beam-induced conditioning of the beam chambers mitigated the e-cloud formation to an extent that allowed an effective exploitation of 25 ns beams. Nevertheless, even after years of conditioning, e-cloud effects remained very visible, affecting beam stability and beam quality, and generating strong heat loads on the beam screens of the superconducting magnets with puzzling features. In preparation for the High Luminosity LHC upgrade, remarkable progress has been made in the modeling of the e-cloud formation and of its influence on beam stability, slow losses and emittance blow up, as well as in the understanding of the underlying behavior of the beam-chamber surface. In this contribution, we describe the main experimental observations from beam operation, the outcome of laboratory analysis conducted on beam screens extracted after the run, and the main advancements in the modeling of these phenomena. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXA03 | |
| About • | paper received ※ 19 May 2021 paper accepted ※ 12 July 2021 issue date ※ 29 August 2021 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUXA04 | Coherent Excitations and Circular Attractors in Cooled Ion Bunches | 1279 |
|
||
|
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy In electron coolers, under certain conditions, a mismatch in either gamma-factors or trajectory angles between an electron and an ion beam can cause the formation of a circular attractor in the ion beam phase space. This leads to coherent excitations of the ions with a small synchrotron or betatron amplitude and results in unusual beam dynamics, including bifurcations. In this paper, we consider the effect of coherent excitations and discuss its implications both for Low Energy RHIC Electron Cooler (LEReC) and for high energy electron coolers proposed for the Electron-Ion Collider (EIC). |
||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXA04 | |
| About • | paper received ※ 19 May 2021 paper accepted ※ 20 July 2021 issue date ※ 11 August 2021 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUXA05 | Measurements of Beam-Beam Interactions in Gear-Changing Collisions in DESIREE | 1283 |
|
||
|
Funding: Notice: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The U.S. Government retains a license to publish or reproduce this manuscript. In this work, we perform measurements on the interactions of colliding beams in a gear-changing system. Gear-changing was first demonstrated in DESIREE in May of 2020 and showed several promising avenues to measure beam-beam effects. DESIREE has a unique collision scheme where the beams are moving in the same direction, which provides for unique interactions. This experiment used a 4 on 3 gear changing system with one bucket in each ring left empty, this allows us to see the bunch profile while undergoing collisions. We then measured the bunch length over time and used a Fourier transform to extract longitudinal evolution data and compared it to baseline data of uncollided beams. |
||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXA05 | |
| About • | paper received ※ 21 May 2021 paper accepted ※ 14 June 2021 issue date ※ 26 August 2021 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUXA06 | Loss of Transverse Landau Damping by Diffusion in High-Energy Hadron Colliders | 1286 |
|
||
| Circular hadron colliders rely on Landau damping to stabilize the beams. Landau damping depends strongly on the bunch distribution, which is often assumed to be Gaussian in the transverse planes. In this paper, we introduce and explain an instability mechanism observed in the LHC, where Landau damping is eventually lost due to a diffusion that modifies the transverse bunch distribution. The mechanism is caused by a wide-spectrum noise that excites the transverse motion of the beam, which consequently produces wakefields that drive a narrow-spectrum diffusion. It is shown that this diffusion efficiently lowers the stability diagram at the frequency of the least stable coherent mode, leading to a loss of Landau damping after a latency. A semi-analytical model agrees with measurements in dedicated latency experiments performed in the LHC. This instability mechanism explains the need for a stability margin in octupole current in the LHC, relative to the amount needed to stabilize a Gaussian beam. We detail the impact of this mechanism and possible mitigations for the LHC and HL-LHC. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXA06 | |
| About • | paper received ※ 19 May 2021 paper accepted ※ 25 June 2021 issue date ※ 10 August 2021 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUXA07 | Beam Dynamics Study in a Dual Energy Storage Ring for Ion Beam Cooling* | 1290 |
|
||
|
Funding: * Work supported by the U.S. Department of Energy, Office of Science, and Office of Nuclear Physics under Contracts DE-AC05-06OR23177 and DE-AC02-06CH11357. / Jefferson Lab EIC Fellowship2020. A dual energy storage ring designed for beam cooling consists of two closed rings with significantly different energies: the cooling and damping rings. These two rings are connected by an energy recovering superconducting RF structure that provides the necessary energy difference. In our design, the RF acceleration has a main linac and harmonic cavities both running at crest that at first accelerates the beam from low energy EL to high energy EH and then decelerates the beam from EH to EL in the next pass. The purpose of the harmonic cavities is to extend the bunch length in a dual energy storage ring as such a longer bunch length may be very useful in a cooling application. Besides these cavities, a bunching cavity running on zero-crossing phase is used outside of the common beamline to provide the necessary longitudinal focusing for the system. In this paper, we present a preliminary lattice design along with the fundamental beam dynamics study in such a dual energy storage ring. |
||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXA07 | |
| About • | paper received ※ 19 May 2021 paper accepted ※ 07 June 2021 issue date ※ 28 August 2021 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |