Special Issue "Superradiances from Ultra Short Electron Bunch Beam"

A special issue of Particles (ISSN 2571-712X).

Deadline for manuscript submissions: closed (31 October 2018)

Special Issue Editors

Guest Editor
Prof. Dr. Hideaki Ohgaki

Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
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Interests: accelerator physics; quantum radiation
Co-Guest Editor
Prof. Dr. Qika Jia

National Synchrotron Radiation Laboratory, University of Science and Technology of China, 443 Huangshan Rd, Hefei, Anhui, China
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Interests: free electron laser; synchronous radiation physics
Co-Guest Editor
Prof. Dr. Hiroyuki Hama

Research Center for Electron Photon Science, Tohoku University, Japan
Website | E-Mail
Interests: free electron laser; non-linear dynamics; particle accelerators

Special Issue Information

Dear Colleagues,

Terahertz (THz) radiation, which lies in the frequency gap between infrared and microwaves, and typically refers to frequencies from 100 GHz to 10 THz, is finding use in an increasingly wide variety of applications: Information and communications technology; non-destructive evaluation; biology and medical sciences; and energy chemistry and material science. In the field of material science, THz radiation can be used for linear and nonlinear control of the physical properties, and measurement of the ultra-fast dynamic process of materials. There is great demand for THz sources that feature high power, ultra-short pulse, high-precision synchronization performance, and a broadly-tunable range of frequencies. An accelerator-based THz radiation source is one option to fulfil the feature listed above, especially in terms of high peak power, and easy and broad tunability. Particularly, free-electron laser and coherent synchrotron/transition radiations from ultra-short bunch electron beams are promising THz sources. However, further efforts are needed to bring such THz sources into the laboratory. Research and development has been carried out around the world, in particular in the East-Asia region. This Special Issue is a collaboration between Particles and the "2nd International Workshop on CSR and Free Electron Lasers from Ultra-Short Bunch Electron Beams". It is also an attempt to summarize the developments in relevant research areas, and is open to researchers (not only workshop attendees). Original contributions of experimental work, computational work, or combinations of the two, or review papers, are highly welcome.

Prof. Dr. Hideaki Ohgaki
Prof. Dr. Qika Jia
Prof. Dr. Hiroyuki Hama
Guest Editors

Manuscript Submission Information

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Keywords

  • THz source
  • Accelerator
  • Ultra-short bunch electron beam
  • Free-electron laser
  • Coherent radiation

Published Papers (9 papers)

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Research

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Open AccessArticle
Investigation of Bunch Compressor and Compressed Electron Beam Characteristics by Coherent Transition Radiation
Particles 2019, 2(1), 32-43; https://doi.org/10.3390/particles2010003
Received: 31 October 2018 / Revised: 23 December 2018 / Accepted: 25 December 2018 / Published: 31 December 2018
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Abstract
A magnetic chicane bunch compressor for a new compact accelerator-based terahertz (THz) radiation source at the Institute of Advanced Energy, Kyoto University, was completely installed in March 2016. The chicane is employed to compress an electron bunch with an energy of 4.6 MeV [...] Read more.
A magnetic chicane bunch compressor for a new compact accelerator-based terahertz (THz) radiation source at the Institute of Advanced Energy, Kyoto University, was completely installed in March 2016. The chicane is employed to compress an electron bunch with an energy of 4.6 MeV generated by a 1.6-cell photocathode radio frequency (RF)-gun. The compressed bunch is injected into a short planar undulator for THz generation by coherent undulator radiation (CUR). The characteristics of the bunch compressor and the compressed bunch were investigated by observing the coherent transition radiation (CTR). The CTR spectra, which were analyzed by using a Michelson interferometer, and the compressed bunch length were also estimated. The results were that the chicane could compress the electron bunch at a laser injection phase less than 45 degrees, and the maximum CTR intensity was observed at a laser injection phase around 24 degrees. The optimum value of the first momentum compaction factor was around −45 mm, which provided an estimated rms bunch length less than 1 ps. Full article
(This article belongs to the Special Issue Superradiances from Ultra Short Electron Bunch Beam)
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Open AccessArticle
Bunch Length Measurement Employing Cherenkov Radiation from a Thin Silica Aerogel
Particles 2018, 1(1), 305-314; https://doi.org/10.3390/particles1010025
Received: 24 October 2018 / Revised: 4 December 2018 / Accepted: 7 December 2018 / Published: 11 December 2018
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Abstract
The temporal profile measurement for ultra-short electron bunches is one of the key issues for accelerator-based coherent light sources. A bunch length measurement system using Cherenkov radiation (CR) is under development at the Research Center for Electron Photon Science, Tohoku University. This system [...] Read more.
The temporal profile measurement for ultra-short electron bunches is one of the key issues for accelerator-based coherent light sources. A bunch length measurement system using Cherenkov radiation (CR) is under development at the Research Center for Electron Photon Science, Tohoku University. This system allows for the real-time diagnostics of electron bunches. The system comprises a thin silica aerogel as the Cherenkov radiator, a specially designed optical transport line, and a high-speed streak camera. The electron bunch length can be obtained by measuring the time spread of the CR from the electrons passing through the radiator medium using the streak camera. In this paper, we describe the novel bunch length measurement system using CR, discuss the expected time resolution of the system, and finally present the measurement results. Full article
(This article belongs to the Special Issue Superradiances from Ultra Short Electron Bunch Beam)
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Open AccessArticle
High-Gradient Cherenkov Radiation Based on a New Dielectric-Loaded Waveguide
Particles 2018, 1(1), 279-284; https://doi.org/10.3390/particles1010022
Received: 30 October 2018 / Revised: 21 November 2018 / Accepted: 22 November 2018 / Published: 25 November 2018
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Abstract
A new type of dielectric-loaded waveguide, the high-gradient dielectric-loaded waveguide (HG-DLW), where the Cherenkov radiation with a high gradient can be excited by relativistic electron, is proposed in this paper. Based on the simulation results, the process of the high-gradient Cherenkov radiation excited [...] Read more.
A new type of dielectric-loaded waveguide, the high-gradient dielectric-loaded waveguide (HG-DLW), where the Cherenkov radiation with a high gradient can be excited by relativistic electron, is proposed in this paper. Based on the simulation results, the process of the high-gradient Cherenkov radiation excited in the proposed structure is studied in details, and the amplitude of wakefields excited in proposed structure can be enhanced by over six times compared with that from ordinary dielectric-loaded waveguides. Full article
(This article belongs to the Special Issue Superradiances from Ultra Short Electron Bunch Beam)
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Open AccessArticle
Design of a Pre-Bunched THz Free Electron Laser
Particles 2018, 1(1), 267-278; https://doi.org/10.3390/particles1010021
Received: 30 October 2018 / Revised: 12 November 2018 / Accepted: 14 November 2018 / Published: 19 November 2018
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Abstract
Terahertz (THz) radiation has attracted much attention in new scientific and industrial applications. There has been significant recent progress in generating THz with accelerators. To investigate the collective behavior of electron dynamics, we have proposed a new high throughput material characterization system, which [...] Read more.
Terahertz (THz) radiation has attracted much attention in new scientific and industrial applications. There has been significant recent progress in generating THz with accelerators. To investigate the collective behavior of electron dynamics, we have proposed a new high throughput material characterization system, which supplies a multiple light source. The system includes a pre-bunched THz free electron laser (FEL), which is a high-power narrow-band THz source with a wide tuning range of frequency. The physical design with the main components of the facility is introduced, and the simulation results are illustrated. Radiation of 0.5–3.0 THz is obtained by the fundamental wave of the pre-bunched beam, and radiation covering 3.0–5.0 THz is realized by second harmonic generation. As the simulation shows, intense THz radiation could be achieved in a frequency from 0.5–5.0 THz, with a peak power of several megawatts (MWs) and a bandwidth of a few percent. Full article
(This article belongs to the Special Issue Superradiances from Ultra Short Electron Bunch Beam)
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Open AccessArticle
Primary Design of Extended Interaction Klystron with Multi-Gap Cavity at 225 GHz
Particles 2018, 1(1), 260-266; https://doi.org/10.3390/particles1010020
Received: 16 October 2018 / Revised: 7 November 2018 / Accepted: 8 November 2018 / Published: 11 November 2018
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Abstract
The analytical expressions of the beam–wave coupling coefficients and the beam loading conductance for a 2π mode in a multi-gap cavity is proposed as a circuit of the extended interaction klystron (EIK), are derived by space-charge wave theory. The mechanism of the [...] Read more.
The analytical expressions of the beam–wave coupling coefficients and the beam loading conductance for a 2π mode in a multi-gap cavity is proposed as a circuit of the extended interaction klystron (EIK), are derived by space-charge wave theory. The mechanism of the beam–wave synchronization and the coupling in the multi-gap cavity at 225 GHz are studied in detail by calculating the coupling coefficient and the normalized beam loading conductance as a function of gap number, gap dimension, and beam voltage as well as the perveance. The stability of the circuit is analyzed by considering the quality factor of the electron beam. It is found that the stability of the operating 2π mode is more sensitive to the beam voltage and gap number. Based on the theory and analysis, a 5-gap coupled cavity is proposed as a section of EIK’s circuit. A low voltage EIK with a 4-cavity circuit at 225 GHz is designed and is simulated by a particle-in-cell (PIC) code. The EIK can achieve a maximum output power of ~36 W with more than 30 dB gain at 225 GHz. Full article
(This article belongs to the Special Issue Superradiances from Ultra Short Electron Bunch Beam)
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Open AccessArticle
Generation of THz Modulated Electron Bunches Using Transversally Polarized Waves to Drive a Dielectric Dual-Grating
Particles 2018, 1(1), 253-259; https://doi.org/10.3390/particles1010019
Received: 12 October 2018 / Revised: 8 November 2018 / Accepted: 8 November 2018 / Published: 9 November 2018
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Abstract
We propose and design a dual dielectric grating structure for generating electron bunches with THz repetition frequency. Here we apply transversally polarized sub-terahertz waves to transversally illuminate a dielectric dual-grating, within which the sinusoidally varied deflection fields are induced and exerted on the [...] Read more.
We propose and design a dual dielectric grating structure for generating electron bunches with THz repetition frequency. Here we apply transversally polarized sub-terahertz waves to transversally illuminate a dielectric dual-grating, within which the sinusoidally varied deflection fields are induced and exerted on the electron bunches passing through the structure. The velocities of electrons within the bunches are modulated in the transversal direction, which then leads to the generation of a train of micro-bunches. The spectra of these micro-bunches have a series of profound high harmonics in the terahertz region. The simulation result of the electron beam’s bunching behavior is discussed in this paper. Full article
(This article belongs to the Special Issue Superradiances from Ultra Short Electron Bunch Beam)
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Open AccessArticle
Manipulation of Laser Distribution to Mitigate the Space-Charge Effect for Improving the Performance of a THz Coherent Undulator Radiation Source
Particles 2018, 1(1), 238-252; https://doi.org/10.3390/particles1010018
Received: 9 October 2018 / Revised: 2 November 2018 / Accepted: 5 November 2018 / Published: 7 November 2018
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Abstract
A THz coherent undulator radiation (THz-CUR) source has been developed at the Institute of Advanced Energy, Kyoto University. A photocathode Radio-Frequency (RF) gun and a bunch compressor chicane are used for generating short-bunch electron beams. When the electron beam energy is low, the [...] Read more.
A THz coherent undulator radiation (THz-CUR) source has been developed at the Institute of Advanced Energy, Kyoto University. A photocathode Radio-Frequency (RF) gun and a bunch compressor chicane are used for generating short-bunch electron beams. When the electron beam energy is low, the space-charge effect strongly degrades the beam quality, such as the bunch length and the energy spread at the high bunch charge condition at around 160 pC, and results in the reduction of the highest frequency and the maximum radiated power of the THz-CUR. To mitigate the space charge effect, we have investigated the dependence of the electron beam quality on the laser distribution in transverse and longitudinal directions by using a numerical simulation code, General Particle Tracer GPT. The manipulation of the laser distribution has potential for improving the performance of the THz-CUR source. The electron bunch was effectively compressed with the chicane magnet when the laser transverse distribution was the truncated Gaussian profile, illuminating a cathode. Moreover, the compressed electron bunch was shortened by enlarging the laser pulse width. Consequently, an enhancement of the radiated power of the THz-CUR has been indicated. Full article
(This article belongs to the Special Issue Superradiances from Ultra Short Electron Bunch Beam)
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Open AccessArticle
Development of a Multialkali Photocathode Dc Gun for a Smith-Purcell Terahertz Free-Electron Laser
Particles 2018, 1(1), 166-174; https://doi.org/10.3390/particles1010012
Received: 25 June 2018 / Revised: 9 July 2018 / Accepted: 11 July 2018 / Published: 13 July 2018
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Abstract
We have developed a photocathode dc gun for a compact Smith-Purcell free-electron laser in the terahertz wavelength region. The gun system consists of an alkali antimonide photocathode preparation chamber, a dc gun with a 250 kV-50 mA Cockcroft-Walton high-voltage power supply, and a [...] Read more.
We have developed a photocathode dc gun for a compact Smith-Purcell free-electron laser in the terahertz wavelength region. The gun system consists of an alkali antimonide photocathode preparation chamber, a dc gun with a 250 kV-50 mA Cockcroft-Walton high-voltage power supply, and a downstream beamline with a water-cooled beam dump to accommodate a beam power of 5 kW. We fabricated a Cs3Sb photocathode with quantum efficiency of 5.8% at a wavelength of 532 nm and generated a 150 keV beam with current of up to 4.3 mA with a 500 mW laser. A vacuum chamber for the Smith-Purcell free-electron laser has been installed in the downstream beamline. We describe the present status of our work. Full article
(This article belongs to the Special Issue Superradiances from Ultra Short Electron Bunch Beam)
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Review

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Open AccessReview
Polarization-Sensitive Electro-Optic Sampling of Elliptically-Polarized Terahertz Pulses: Theoretical Description and Experimental Demonstration
Particles 2019, 2(1), 70-89; https://doi.org/10.3390/particles2010006
Received: 4 December 2018 / Revised: 31 December 2018 / Accepted: 4 January 2019 / Published: 17 January 2019
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Abstract
We review our recent works on polarization-sensitive electro-optic (PS-EO) sampling, which is a method that allows us to measure elliptically-polarized terahertz time-domain waveforms without using wire-grid polarizers. Because of the phase mismatch between the employed probe pulse and the elliptically-polarized terahertz pulse that [...] Read more.
We review our recent works on polarization-sensitive electro-optic (PS-EO) sampling, which is a method that allows us to measure elliptically-polarized terahertz time-domain waveforms without using wire-grid polarizers. Because of the phase mismatch between the employed probe pulse and the elliptically-polarized terahertz pulse that is to be analyzed, the probe pulse senses different terahertz electric-field (E-field) vectors during the propagation inside the EO crystal. To interpret the complex condition inside the EO crystal, we expressed the expected EO signal by “frequency-domain description” instead of relying on the conventional Pockels effect description. Using this approach, we derived two important conclusions: (i) the polarization state of each frequency component can be accurately measured, irrespective of the choice of the EO crystal because the relative amplitude and phase of the E-field of two mutually orthogonal directions are not affected by the phase mismatch; and, (ii) the time-domain waveform of the elliptically-polarized E-field vector can be retrieved by considering the phase mismatch, absorption, and the effect of the probe pulse width. We experimentally confirm the above two conclusions by using different EO crystals that are used for detection. This clarifies the validity of our theoretical analysis based on the frequency-domain description and the usefulness of PS-EO sampling. Full article
(This article belongs to the Special Issue Superradiances from Ultra Short Electron Bunch Beam)
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