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| TUP063 | Physical Design and FEL Performance Study for FEL-III Beamline of SHINE | FEL, undulator, photon, electron | 199 |
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| The first hard X-ray free electron laser (XFEL) facility in China, the Shanghai High-Repetition-Rate XFEL and Extreme Light Facility (SHINE), is under construction, which allows for generating X-ray pulses in the photon energy range from 3 keV to 25 keV. To produce X-ray pulses with photon energy up to 25 keV, FEL-III undulator line of SHINE employs superconducting undulators. However, the smaller gap of the superconducting undulator poses serious wakefield effect reducing the FEL power, compared to the normal planar undulator. For a setup design optimization, the design and performance of the FEL-III undulator line are presented using start-to-end beam simulations at self-amplified spontaneous emission (SASE) and self-seeding mode. The wakefield impact on FEL performance is then investigated. A linear undulator tapering technique is adopted for recovering the FEL power to the non-wakefield level. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP063 | ||
| About • | paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019 | ||
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| WEP042 | Observations of Short-Range Wakefield Effects in TESLA-Type Superconducting RF Cavities | HOM, cavity, FEL, MMI | 412 |
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Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. The accelerators for high power X-ray free-electron laser (FEL) facilities such as the European XFEL and planned LCLS-II X-ray FEL are employing TESLA-type SCRF cavities. Beam propagation off axis in these cavities can result in both short-range and long-range transverse wakefields which can lead to emittance dilution within the micropulses and macropulses, respectively. The Fermilab Accelerator Science and Technology (FAST) facility has a unique configuration of a photocathode RF gun beam injecting two TESLA-type single cavities (CC1 and CC2) in series prior to the cryomodule. To investigate short-range wakefield effects, we used a vertical corrector between these two cavities to steer the beam off axis at an angle into CC2. A Hamamatsu synchroscan streak camera viewing a downstream OTR screen provided an image of y-t effects within the micropulses with resolutions of ~10-micron spatial and 2-ps temporal. At 500 pC/b, 50 b, and 4 mrad off-axis steering, we observed an ~100-micron head-tail centroid shift in the streak camera image. This centroid shift is consistent with a calculated short-range wakefield effect. Additional results for kick-angle compensation will be presented. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP042 | ||
| About • | paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019 | ||
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| THP011 | Experimental Benchmarking of Wakefields at the FERMI FEL Linac and Undulator Line | linac, electron, undulator, FEL | 613 |
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Collective effects such as wakefields affect the dynamics of high brightness electron beams in linear accelerators (linacs), and can degrade the performance of short wavelength free-electron lasers (FELs). If a reliable model of wakefields is made available, the accelerator can be designed and configured with parameters that minimize their disrupting effect. In this work, the simulated effect of geometric (diffractive) wakefields and of coherent synchrotron radiation on the electron beam energy distribution at the FERMI FEL is benchmarked with measurements, so quantifying the accuracy of the model. Wakefields modelling is then extended to the undulator line, where particle tracking confirms the limited impact of the resistive wall wakefield on the lasing process. The study reveals an overall good understanding of collective effects in the facility [1].
[1] S. Di Mitri et al., Phys. Rev. Accel. and Beams, 22, 014401 (2019) |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP011 | ||
| About • | paper received ※ 29 July 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019 | ||
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| THP037 | A Novel One-Dimensional Model for CSR Wakefields | radiation, synchrotron, synchrotron-radiation, electron | 669 |
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| The existing 1D models of the coherent synchrotron radiation (CSR) wakefield in free space assume that the longitudinal bunch distribution remains constant when the beam propagates through a magnetic lattice. In this paper, we derive a formula for a 1D CSR wake that takes into account variation of the bunch length along the orbit. The formula is valid for arbitrary curvilinear beam trajectory. We analyze the validity of the 1D model in a typical implementation of an FEL bunch compressor. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP037 | ||
| About • | paper received ※ 12 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019 | ||
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