| 1. |
- Chen, Q., et al.
(författare)
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Traveling-wave Thomson scattering for electron-beam spectroscopy
- 2021
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Ingår i: Physical Review Accelerators and Beams. - 2469-9888. ; 24:3
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Tidskriftsartikel (refereegranskat)abstract
- We propose a method to use traveling-wave Thomson scattering for spatiotemporally-resolved electron spectroscopy. This can enable ultrafast time-resolved measurements of the dynamics of relativistic electrons in the presence of extremely intense light fields, either in vacuum or in plasma, such as in laser wakefield accelerators. We demonstrate, with test-particle simulation and analysis, the capability of this technique for measurements of various high field phenomena: radiation reaction of electrons due to scattering, dephasing of a laser wakefield accelerator, and acceleration of electrons in multiple buckets by a laser wakefield. We propose a method to use traveling-wave Thomson scattering for spatiotemporally-resolved electron spectroscopy. This can enable ultrafast time-resolved measurements of the dynamics of relativistic electrons in the presence of extremely intense light fields, either in vacuum or in plasma, such as in laser wakefield accelerators. We demonstrate, with test-particle simulation and analysis, the capability of this technique for measurements of various high field phenomena: radiation reaction of electrons due to scattering, dephasing of a laser wakefield accelerator, and acceleration of electrons in multiple buckets by a laser wakefield.
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| 2. |
- Folsom, B. T., et al.
(författare)
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Stripping mechanisms and remediation for H- beams
- 2021
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Ingår i: Physical Review Accelerators and Beams. - : American Physical Society. - 2469-9888. ; 24:7
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Tidskriftsartikel (refereegranskat)abstract
- Negative hydrogen ions are often used for injecting protons from linacs to storage rings via chargeexchange injection. In this process, the two electrons are stripped by a foil or laser to produce protons which can be merged with an existing beam without significantly affecting its dynamics, allowing high intensities of protons to be accumulated. However, this capability comes with the drawback that the outer electron of an H- ion has a low binding energy and can easily be stripped away prior to injection. This paper addresses the following stripping mechanisms: interactions with residual gas in the beam pipe, blackbody radiation from accelerator components, and electromagnetic fields from accelerator optics (Lorentz-force stripping) and particles within the bunch itself (intrabeam stripping); with a discussion on how to avoid excessive activation from stripped H degrees particles and protons. We also demonstrate that the proportion of stripped H degrees colliding with a nearby beam pipe or machine-element walls presents only roughly 10% of those lost in stripping; the remaining stripped particles traverse to the end of a linac or local straight section, which may relax the limits for allowable stripping-based beam loss in H- accelerators.
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| 3. |
- Longuevergne, D., et al.
(författare)
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Impact of geometry on the magnetic flux trapping of superconducting accelerating cavities
- 2021
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Ingår i: Physical Review Accelerators and Beams. - : American Physical Society. - 2469-9888. ; 24:8
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Tidskriftsartikel (refereegranskat)abstract
- Controlling trapped magnetic flux in superconducting radio frequency (rf) cavities is of crucial importance in modern accelerator projects. In order to study flux trapping efficiency and sensitivity of surface resistance, dedicated experiments have been carried out on different types of low-fl superconducting accelerating cavities. Even under almost full trapping conditions, we found that the measured magnetic sensitivities of these cavity geometries were significantly lower than the theoretical values predicted by commonly used models based on local material properties. This must be resolved by taking account of geometrical effects of flux trapping and flux oscillation under rf surface current in such cavity shape. In this paper, we propose a new approach to convolute the influence of geometries. We point out a puzzling contradiction between sample measurements and recent cavity experiments, which leads to two different hypotheses to simulate oscillating flux trapped in the cavity surface. A critical reconsideration of flux oscillation by the rf Lorentz force, compared with temperature mapping studies in elliptical cavities, favored the results of previous sample measurements, which suggested preferential flux trapping of normal component to the cavity inner surface. Based on this observation, we builded a new model to our experimental results and the discrepancy between old theory and data were resolved.
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| 4. |
- Ziemann, Ingvar, et al.
(författare)
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Noninvasively improving the orbit-response matrix while continuously correcting the orbit
- 2021
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Ingår i: Physical Review Accelerators and Beams. - : American Physical Society (APS). - 2469-9888. ; 24:7
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Tidskriftsartikel (refereegranskat)abstract
- Based on continuously recorded beam positions and corrector excitations from, for example, a closedorbit feedback system we describe an algorithm that continuously updates an estimate of the orbit response matrix. The speed of convergence can be increased by adding very small perturbations, so-called dither, to the corrector excitations. Estimates for the rate of convergence and the asymptotically achievable accuracies are provided.
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