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12 pages, 4801 KiB

Open AccessArticle

Investigation of Bunch Compressor and Compressed Electron Beam Characteristics by Coherent Transition Radiation

by Sikharin Suphakul, Heishun Zen, Toshiteru Kii and Hideaki Ohgaki

Particles 2019, 2(1), 32-43; https://0-doi-org.brum.beds.ac.uk/10.3390/particles2010003 - 31 Dec 2018

Viewed by 3737

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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10 pages, 2731 KiB

Open AccessArticle

Bunch Length Measurement Employing Cherenkov Radiation from a Thin Silica Aerogel

by Ken-ichi Nanbu, Yuki Saito, Hirotoshi Saito, Shigeru Kashiwagi, Fujio Hinode, Toshiya Muto and Hiroyuki Hama

Particles 2018, 1(1), 305-314; https://0-doi-org.brum.beds.ac.uk/10.3390/particles1010025 - 11 Dec 2018

Cited by 6 | Viewed by 3285

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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6 pages, 928 KiB

Open AccessArticle

High-Gradient Cherenkov Radiation Based on a New Dielectric-Loaded Waveguide

by Shimin Jiang, Weiwei Li, Zhigang He and Qika Jia

Particles 2018, 1(1), 279-284; https://0-doi-org.brum.beds.ac.uk/10.3390/particles1010022 - 25 Nov 2018

Cited by 1 | Viewed by 2588

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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12 pages, 1907 KiB

Open AccessArticle

Design of a Pre-Bunched THz Free Electron Laser

by Ruixuan Huang, Weiwei Li, Zhouyu Zhao, Heting Li, Jigang Wang, Tian Ma, Qiuping Huang, Zhigang He, Qika Jia, Lin Wang and Yalin Lu

Particles 2018, 1(1), 267-278; https://0-doi-org.brum.beds.ac.uk/10.3390/particles1010021 - 19 Nov 2018

Cited by 5 | Viewed by 3699

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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7 pages, 2629 KiB

Open AccessArticle

Primary Design of Extended Interaction Klystron with Multi-Gap Cavity at 225 GHz

by Kaichun Zhang, Ke Chen, Qian Xu, Wangju Xu, Neng Xiong, Xiaoxing Chen and Diwei Liu

Particles 2018, 1(1), 260-266; https://0-doi-org.brum.beds.ac.uk/10.3390/particles1010020 - 11 Nov 2018

Viewed by 2296

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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7 pages, 13415 KiB

Open AccessArticle

Generation of THz Modulated Electron Bunches Using Transversally Polarized Waves to Drive a Dielectric Dual-Grating

by Linbo Liang, Weihao Liu, Qika Jia and Yalin Lu

Particles 2018, 1(1), 253-259; https://0-doi-org.brum.beds.ac.uk/10.3390/particles1010019 - 09 Nov 2018

Viewed by 2066

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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15 pages, 7501 KiB

Open AccessArticle

Manipulation of Laser Distribution to Mitigate the Space-Charge Effect for Improving the Performance of a THz Coherent Undulator Radiation Source

by Siriwan Krainara, Shuya Chatani, Heishun Zen, Toshiteru Kii and Hideaki Ohgaki

Particles 2018, 1(1), 238-252; https://0-doi-org.brum.beds.ac.uk/10.3390/particles1010018 - 07 Nov 2018

Cited by 5 | Viewed by 2836

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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9 pages, 4899 KiB

Open AccessArticle

Development of a Multialkali Photocathode Dc Gun for a Smith-Purcell Terahertz Free-Electron Laser

by Nobuyuki Nishimori, Ryoji Nagai, Masaru Sawamura and Ryoichi Hajima

Particles 2018, 1(1), 166-174; https://0-doi-org.brum.beds.ac.uk/10.3390/particles1010012 - 13 Jul 2018

Cited by 2 | Viewed by 5880

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

Jump to: Research

20 pages, 3714 KiB

Open AccessReview

Polarization-Sensitive Electro-Optic Sampling of Elliptically-Polarized Terahertz Pulses: Theoretical Description and Experimental Demonstration

by Kenichi Oguchi, Makoto Okano and Shinichi Watanabe

Particles 2019, 2(1), 70-89; https://0-doi-org.brum.beds.ac.uk/10.3390/particles2010006 - 17 Jan 2019

Cited by 1 | Viewed by 4626

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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