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| TUP018 | Superradiant Emission of Electron Bunches Based on Cherenkov Excitation of Surface Waves in 1D and 2D Periodical Lattices: Theory and Experiments | electron, experiment, radiation, simulation | 80 |
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Funding: The work was supported by RFBR grant no. 17-08-01072 In recent years, significant progress was achieved in generation of high-power ultrashort microwave pulses based on superradiance (SR) of electron bunches extended in the wavelength scale. In this process, coherent emission from the entire volume of the bunch occurs due to the development of microbunching and slippage of the wave with respect to electrons. An obvious method for generation of high-power sub-THz radiation is the implementation of oversized periodical slow-wave structures where evanescent surface waves can be excited. We report of the experiments on Cherenkov generation of 150 ps SR pulses with a central frequency of 0.14 THz, and an extremely high peak power up to 70 MW. In order to generate spatially coherent radiation in shorter wavelength ranges (including THz band) in strongly oversized waveguiding systems, we propose a slow wave structure with double periodic corrugation (2D SWS). Using the quasi-optical theory and PIC simulations, we demonstrate the applicability of such 2D SWS and its advantages against traditional 1D SWS. Proof of principle experiments on observation G-band Cherenkov SR in 2D SWS are currently in progress. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP018 | ||
| About • | paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019 | ||
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| TUP020 | Terahertz Free Electron Maser Based on Excitation of a Talbot-Type Super-Mode in an Oversized Microwave System | electron, cavity, resonance, simulation | 87 |
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Funding: The work is supported by the Russian Science Foundation, Project # 19-12-00212. A natural problem arising in the case of realization of a THz FEM with a high-current relativistic e-beam is an inevitable use of an oversized microwave system, which characteristic transverse size significantly exceeds the wavelength of the operating wave. In this situation, it becomes difficult to provide selective excitation of a chosen transverse mode of the operating cavity. Our basic idea is to give up working on a fixed transverse mode. Instead, we propose to work on a supermode, which is a fixed set of several transverse modes of an oversized wavegude. We propose to use the Talbot effect [1,2,3] as a way to create an oversized microwave system of an electron maser that provides a high Q-factor for this supermode. On the basis of a multi-mode set of self-consistent equations of the electron-wave interaction we demonstrate the possibility of the selective self-excitation of the supermode both in the simplest 2-D model and in the detailed modeling of a THz FEM fed by a 10 MeV / 2 kA / 200 e-beam based on excitation of a Talbot-type supermode at a frequency close to 2 THz. The calculated efficiency at the level of 5-10% corresponds to the GW level of the output power. [1] L. A. Rivlin, Laser Focus, p. 82, 1981 [2] G. G. Denisov, D. A. Lukovnikov, M. Yu. Shmelyov, Digest of 18 Int. Conf. on IR MM Waves, p. 485, 1993 [3] V. L. Bratman et al., Nucl. Instr. Meth. Phys. Res. A, vol. 407, pp. 40-44, 1998 |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP020 | ||
| About • | paper received ※ 14 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019 | ||
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| TUP036 | A Waveguide-Based High Efficiency Super-Radiant FEL Operating in the THz Regime | FEL, radiation, electron, undulator | 127 |
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Funding: DOE grant No. DE-SC0009914 and NSF grant PHY-1734215 In this paper we describe a novel self-consistent 3D simulation approach for a waveguide FEL operating in the zero-slippage regime to generate high power THz radiation. In this interaction regime, the phase and group velocity of the radiation are matched to the relativistic beam traveling in the undulator achieving long interaction lengths. Our numerical approach is based on expanding the existing 3D particle tracking code GPT (General Particle Tracer) to follow the interaction of the particles in the beam with the electromagnetic field modes of the waveguide. We present two separate studies: one for a case which was benchmarked with experimental results and another one for a test case where, using a longer undulator and larger bunch charge, a sizable fraction of the input beam energy can be extracted and converted to THz radiation. The model presented here is an important step in the development of the zero-slippage FEL scheme as a source for high average and peak power THz radiation. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP036 | ||
| About • | paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019 | ||
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| WEP049 | RF Power Waveguide Distribution for the RF Gun of the European XFEL at DESY | gun, FEL, klystron, cryomodule | 434 |
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| The first section of the European XFEL provides the 43 m long injector. The injector consists of a 1.3 GHz RF gun, a 1.3 GHz cryomodule, a 3.9 GHz cryomodule and an extensive diagnostic section. The RF gun operates with a maximum RF peak power up to 6.5 MW, 10 Hz repetition rate and up to 650 µs pulse length. The starting point in the 1.5 cell normal conducting L-Band cavity of the RF gun is a Cs2Te photocathode, which produces electron bunches, which are injected into the superconducting accelerating section of the European XFEL. The RF power is generated by a 10 MW multi beam klystron and distributed to the RF gun through a RF power waveguide distribution system. In order to enhance the reliability of the distribution system, the peak power is minimized in every section of the system by splitting the power in different branches. The RF power reaches its maximum just in front of the RF gun after combination of all branches. An additional air pressure system decreases the break down level in the waveguides of the distribution. We present the layout of the waveguide distribution system for the XFEL RF gun at DESY and report on first operation experience. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP049 | ||
| About • | paper received ※ 19 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019 | ||
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| WEP086 | Capabilities of Terahertz Super-Radiance from Electron Bunches Moving in Micro-Undulators | undulator, electron, radiation, laser | 517 |
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Funding: This work was supported by the Israeli Ministry of Science, Technology and Space and by the Russian Foundation for Basic Research, grant No. 16-02-00794. An available frequency range of coherent radiation from ps bunches with high charge and moderate particle energy significantly enhances if one uses a micro-undulator with a high transverse field. Such an undulator can be implemented by redistributing a strong uniform magnetic field by a helical ferromagnetic or copper insertion. According to simulations and experiments with prototypes, a steel helix with a period of (8-10) mm and an inner diameter of (1.5-2) mm inserted in the 3T-field of solenoid can provide an undulator field with an amplitude of 0.6 T. Using a hybrid system with a permanently magnetized structure can increase this value up to 1.1 T. The necessary steel helices can be manufactured on the machine, assembled from steel wires, formed from powder, or 3D - printed. Simulations based on the WB3D code demonstrate that using such undulators with the length of (30-40) cm enable single-mode super-radiance from bunches with energy of 6 MeV, charge of 1 nC and duration of 2 ps moving in an over-sized waveguide in frequency range of 3-5 THz. The calculated efficiency of such process is (2-4)% that many times exceeds efficiency for short bunches of the same initial density. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP086 | ||
| About • | paper received ※ 14 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019 | ||
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| THP024 | Spontaneous Coherent Radiation of Stabilized Dense Electron Bunches | electron, radiation, undulator, cyclotron | 643 |
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Funding: The work is supported by Russian Foundation for Basic Research Project 18-32-00351, 18-02-00765 Modern sources of dense electron beams allow the formation of compact sources of dense electron bunches with energies of 3-6 MeV, ps pulse durations, and charges of up to 1 nC. Such bunches can be used for the realization of relatively simple and compact powerful terahertz sources based on spontaneous coherent radiation. The power and duration of the process of such type of emission are limited due to an increase in the bunch length under the Coulomb repulsion. This complicates the effective implementation of the regime of spontaneous coherent radiation for dense bunches. Therefore, special methods for stabilization of the length of the operating e-bunch during its motion over a long electron-wave interaction region should be used. We propose several methods of the stabilization based on the axial bunch compression by self-radiated wave fields [1] and by quasi-static Coulomb fields inside a bunch [2]. The latter takes place in the case of the motion of electrons through the undulator in the "negative-mass" regime, when the Coulomb field inside the bunch leads not to repulsion of electrons but to their mutual attraction. [1] I. V. Bandurkin, Yu. S. Oparina and A. V. Savilov, Appl. Phys. Lett. vol 110, p. 263508, 2017 [2] N. Balal, I. V. Bandurkin, V. L. Bratman, E. Magory, and A. V. Savilov, Appl. Phys. Lett. vol. 107, p. 163505, 2015 |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP024 | ||
| About • | paper received ※ 19 August 2019 paper accepted ※ 12 September 2019 issue date ※ 05 November 2019 | ||
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| THP049 | A Versatile THz Source for High-Repetition Rate XFELs | FEL, radiation, undulator, electron | 688 |
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Funding: FL was partially funded by the European Union¿s Horizon 2020 Research and Innovation programme under Grant Agreement No. 730871 The development of high-repetition rate XFELs brings an exciting time for novel fundamental science exploration via pump-probe interactions. Laser-based pump sources can provide a wide range of wavelengths (200-10000~nm) via various gain media. These sources can also be extended with optical parametric amplifiers to cover a largely versatile spectral and bandwidth range. However beyond 10~μm, toward the THz regime, there exists no suitable gain media, and optical-to-THz efficiencies are limited below 1\%. In this paper we discuss the use of Cherenkov-based radiators with conventional electron bunches to generate high-power THz radiation over a wide range of parameters for existing and future XFEL facilities. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP049 | ||
| About • | paper received ※ 25 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019 | ||
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