| Paper | Title | Page |
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| TUP019 | Regime of Multi-Stage Non-Resonant Trapping in Free Electron Lasers | 83 |
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Funding: This work is supported by the RFBR (grants #18-02-40009, #18-02-00765) and by the IAP RAS Project 0035-2019-0001. We describe three works united by the idea of the non-resonant regime [1] providing an effective trapping in a beam with a great energy spread. In this regime, the "bucket" corresponding to the resonant electron-wave interaction passes through the electron layer on the energy-phase plane and traps a fraction of electrons. (I) Operability of this regime was demonstrated in the high-efficient 0.8 MeV Ka-band FEM-amplifier [2]. (II) In short-wavelength FELs the multi-stage trapping in several consecutive sections can be organized [3]. In each section a small e-beam fraction is trapped due to a weak electron-wave interaction. However, repetition of this process from section to section involves in the interaction almost the whole e-beam. We describe efficiency enhancement and improving the frequency wave spectrum in multi-stage SASE FELs. (III) The multi-stage amplification of a single-frequency wave signal can provide cooling of the electron bunch. In this regime, tapering of every section is provided such that the "bucket" goes from maximal initial electron energy down to the minimal one and moves down energies of trapped electrons. [1] A.Savilov et al., Nucl. Instr. Meth. A, vol. 507, p.158, 2003 [2] A.Kaminsky et al., Int. Conf. IRMMW-THz 2018, art. 4057938 [3] S.Kuzikov, A.Savilov, Phys. Plasmas, vol. 25, p.113114, 2018 |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP019 | |
| About • | paper received ※ 14 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 | 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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| THP024 | Spontaneous Coherent Radiation of Stabilized Dense Electron Bunches | 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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