IPAC2021 - List of Authors (Koshiba, Y.)

Paper	Title	Page
WEPAB405	Supercontinuum Generation for the Improvement of Pulse Radiolysis System	3657
	M. Sato, Y. Kaneko, Y. Koshiba, M. Washio RISE, Tokyo, Japan K. Sakaue The University of Tokyo, Graduate School of Engineering, Bunkyo, Japan
	Pulse radiolysis is one of the absorption measurement methods for investigating the fundamental, ultrafast process of radiation chemical reactions. Analytical light is transmitted simultaneously with the timing of electron beam irradiation, and its absorption by reactive species is detected. Since the target reactions arise in pico second time scale or even shorter, analytical light is required to have such duration. Besides, so as not to be buried in noise of the radiation source, the optical power of the analytical light must be high enough. Furthermore, it is desirable that the analytical light covers visible region because important absorptions caused by irradiation products such as hydrated electron, hydroxyl radical, or so exist in the region. We considered that the supercontinuum light generated from an ultrashort pulse laser is suitable as an analytical light because it has all these characteristics. In this study, we generate the second harmonic (775 nm) of an erbium fiber laser (1550 nm) as a seed laser for supercontinuum generation. In this presentation, we report the current situation of our laser system and prospects.
	Poster WEPAB405 [0.734 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB405
About •	paper received ※ 18 May 2021 paper accepted ※ 01 September 2021 issue date ※ 20 August 2021
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WEPAB048	Design of an Optical Cavity for Generating Intense THz Pulse Based on Coherent Cherenkov Radiation	2711
	P. Wang, Y. Koshiba, T. Murakami, K. Murakoshi, K. Sakaue, Y. Tadenuma, M. Washio Waseda University, Tokyo, Japan R. Kuroda AIST, Tsukuba, Japan K. Sakaue The University of Tokyo, Graduate School of Engineering, Bunkyo, Japan
	We have been studying terahertz (THz) generation via Cherenkov radiation with high-quality electron beams from a photocathode rf (radio frequency) gun. In our early studies, we have succeeded in the generation of coherent Cherenkov radiation by controlling the tilt of the electron beam using an rf-deflector. For further enhancement, we are planning to stack the THz pulses in an optical cavity. Multi-bunch operation of the rf-gun will generate electron beams with a repetition rate of 119 MHz, and THz pulses as well. These pulses will be accumulated in the cavity for up to 150 pulses. In this conference, we report the design study of the enhancement cavity and discuss the performance of the THz source.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB048
About •	paper received ※ 19 May 2021 paper accepted ※ 02 June 2021 issue date ※ 18 August 2021
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WEPAB052	Development of an EO Sampling System for the Analysis of THz Waves Generated by Coherent Cherenkov Radiation	2718
	K. Murakoshi, Y. Koshiba, T. Murakami, K. Sakaue, Y. Tadenuma, P. Wang, M. Washio Waseda University, Tokyo, Japan R. Kuroda AIST, Tsukuba, Japan K. Sakaue The University of Tokyo, Graduate School of Engineering, Bunkyo, Japan
	THz waves, located between microwaves and light waves, have transparency, directionality and fingerprint spectrum of specific materials. Therefore, they are expected to be useful for various applications. We have been studying THz waves generation via Cherenkov radiation with electron beams from a photocathode rf-gun. In our early studies, we have succeeded in the generation of coherent Cherenkov radiation by tilted electron beams using an rf-deflector. Furthermore, we have generated quasi-monochromatic THz waves by spatially modulated electron beams and have succeeded in its measurement by bandpass filters. This study aims to obtain the THz wave form in time domain by electro-optic (EO) sampling, which is an useful detection system for obtaining the information of the electric field and the phase simultaneously with high S/N. In this conference, we report about our probe laser system, results of the time-domain spectroscopy measurement of THz waves by EO sampling, and future prospects.
	Poster WEPAB052 [0.861 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB052
About •	paper received ※ 19 May 2021 paper accepted ※ 07 June 2021 issue date ※ 31 August 2021
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WEPAB055	Development of a Linac for Injection of Ultrashort Electron Bunches Into Laser Plasma Electron Accelerators	2725
	S. Masuda, N. Kumagai, T. Masuda, Y. Otake JASRI, Hyogo, Japan Y. Koshiba, S. Otsuka Waseda University, Tokyo, Japan T. Sakai, T. Tanaka LEBRA, Funabashi, Japan K. Sakaue The University of Tokyo, The School of Engineering, Tokyo, Japan
	Funding: This work is supported by JST-Mirai Program Grant Number JPMJMI17A1, Japan. We are developing a C-band linac that produces ultrashort electron bunches as an injector for laser plasma accelerators. A plasma wave excited by a high intense ultrashort laser pulse has a wavelength of the order of 10 to 100 fs and transverse dimensions of the order of 10 to 100 um. To inject the bunch into a proper phase of the plasma wave, a length and transverse sizes of the bunch must be much smaller than the plasma wave structure. A laser triggered photo cathode electron RF-gun and a 2pi/3 mode traveling wave buncher with 24 cells for ultrashort electron bunch production have been developed based on electron beam tracking simulations that show the bunch length is less than 10 fs with a charge of 100 fC at a focus on the plasma wave. The simulations also show that sufficiently small transverse sizes of the bunch at the focus can be obtained by a Q triplet. A highly accurate timing lower than the plasma wavelength (~10fs) is required for the synchronization between the electron bunch injection and the plasma wave excitation. An RF master oscillator with low SSB phase noise (-150dBc/Hz@10MHz) has been developed for the synchronization. We will report present development status.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB055
About •	paper received ※ 19 May 2021 paper accepted ※ 15 July 2021 issue date ※ 29 August 2021
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WEPAB106	Study on Durability Improvement of Cs-Te Photocathode by Means of Alkali Halide Protective Films	2847
	K. Ezawa, R. Fukuoka, Y. Koshiba, T. Tamba, M. Washio Waseda University, Tokyo, Japan K. Sakaue The University of Tokyo, Graduate School of Engineering, Bunkyo, Japan
	We have been conducting basic and applied research for generating high quality electron beams, using 1.6 cell laser photocathode RF-gun. In our laboratory, Cesium Telluride (Cs-Te), one of the semiconductor photocathodes, is used as an electron source for accelerator experiments. This semiconductor photocathode is known for high quantum efficiency (Q.E.) about 5~10% and 3-month 1/e lifetime. High Q.E. photocathodes can reduce the power requirement of the laser system, and long lifetime photocathodes can decrease the maintenance frequency, contributing to an efficient experimental environment. For these reasons, high Q.E. and long lifetime photocathodes are necessary in accelerator experiments. In order to produce robust photocathodes and extend the lifetime, we have conducted covering Cs-Te photocathodes with CsBr and CsI protective films. In this conference, we report the thickness dependency on the lifetime of Cs-Te photocathodes when we intentionally exposed oxygen gas to coated and non-coated Cs-Te photocathodes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB106
About •	paper received ※ 19 May 2021 paper accepted ※ 02 June 2021 issue date ※ 15 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Supercontinuum Generation for the Improvement of Pulse Radiolysis System

3657

M. Sato, Y. Kaneko, Y. Koshiba, M. Washio
RISE, Tokyo, Japan
K. Sakaue
The University of Tokyo, Graduate School of Engineering, Bunkyo, Japan

Pulse radiolysis is one of the absorption measurement methods for investigating the fundamental, ultrafast process of radiation chemical reactions. Analytical light is transmitted simultaneously with the timing of electron beam irradiation, and its absorption by reactive species is detected. Since the target reactions arise in pico second time scale or even shorter, analytical light is required to have such duration. Besides, so as not to be buried in noise of the radiation source, the optical power of the analytical light must be high enough. Furthermore, it is desirable that the analytical light covers visible region because important absorptions caused by irradiation products such as hydrated electron, hydroxyl radical, or so exist in the region. We considered that the supercontinuum light generated from an ultrashort pulse laser is suitable as an analytical light because it has all these characteristics. In this study, we generate the second harmonic (775 nm) of an erbium fiber laser (1550 nm) as a seed laser for supercontinuum generation. In this presentation, we report the current situation of our laser system and prospects.

Poster WEPAB405 [0.734 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB405

About •

paper received ※ 18 May 2021 paper accepted ※ 01 September 2021 issue date ※ 20 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB048

Design of an Optical Cavity for Generating Intense THz Pulse Based on Coherent Cherenkov Radiation

2711

P. Wang, Y. Koshiba, T. Murakami, K. Murakoshi, K. Sakaue, Y. Tadenuma, M. Washio
Waseda University, Tokyo, Japan
R. Kuroda
AIST, Tsukuba, Japan
K. Sakaue
The University of Tokyo, Graduate School of Engineering, Bunkyo, Japan

We have been studying terahertz (THz) generation via Cherenkov radiation with high-quality electron beams from a photocathode rf (radio frequency) gun. In our early studies, we have succeeded in the generation of coherent Cherenkov radiation by controlling the tilt of the electron beam using an rf-deflector. For further enhancement, we are planning to stack the THz pulses in an optical cavity. Multi-bunch operation of the rf-gun will generate electron beams with a repetition rate of 119 MHz, and THz pulses as well. These pulses will be accumulated in the cavity for up to 150 pulses. In this conference, we report the design study of the enhancement cavity and discuss the performance of the THz source.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB048

About •

paper received ※ 19 May 2021 paper accepted ※ 02 June 2021 issue date ※ 18 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB052

Development of an EO Sampling System for the Analysis of THz Waves Generated by Coherent Cherenkov Radiation

2718

K. Murakoshi, Y. Koshiba, T. Murakami, K. Sakaue, Y. Tadenuma, P. Wang, M. Washio
Waseda University, Tokyo, Japan
R. Kuroda
AIST, Tsukuba, Japan
K. Sakaue
The University of Tokyo, Graduate School of Engineering, Bunkyo, Japan

THz waves, located between microwaves and light waves, have transparency, directionality and fingerprint spectrum of specific materials. Therefore, they are expected to be useful for various applications. We have been studying THz waves generation via Cherenkov radiation with electron beams from a photocathode rf-gun. In our early studies, we have succeeded in the generation of coherent Cherenkov radiation by tilted electron beams using an rf-deflector. Furthermore, we have generated quasi-monochromatic THz waves by spatially modulated electron beams and have succeeded in its measurement by bandpass filters. This study aims to obtain the THz wave form in time domain by electro-optic (EO) sampling, which is an useful detection system for obtaining the information of the electric field and the phase simultaneously with high S/N. In this conference, we report about our probe laser system, results of the time-domain spectroscopy measurement of THz waves by EO sampling, and future prospects.

Poster WEPAB052 [0.861 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB052

About •

paper received ※ 19 May 2021 paper accepted ※ 07 June 2021 issue date ※ 31 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB055

Development of a Linac for Injection of Ultrashort Electron Bunches Into Laser Plasma Electron Accelerators

2725

S. Masuda, N. Kumagai, T. Masuda, Y. Otake
JASRI, Hyogo, Japan
Y. Koshiba, S. Otsuka
Waseda University, Tokyo, Japan
T. Sakai, T. Tanaka
LEBRA, Funabashi, Japan
K. Sakaue
The University of Tokyo, The School of Engineering, Tokyo, Japan

Funding: This work is supported by JST-Mirai Program Grant Number JPMJMI17A1, Japan.
We are developing a C-band linac that produces ultrashort electron bunches as an injector for laser plasma accelerators. A plasma wave excited by a high intense ultrashort laser pulse has a wavelength of the order of 10 to 100 fs and transverse dimensions of the order of 10 to 100 um. To inject the bunch into a proper phase of the plasma wave, a length and transverse sizes of the bunch must be much smaller than the plasma wave structure. A laser triggered photo cathode electron RF-gun and a 2pi/3 mode traveling wave buncher with 24 cells for ultrashort electron bunch production have been developed based on electron beam tracking simulations that show the bunch length is less than 10 fs with a charge of 100 fC at a focus on the plasma wave. The simulations also show that sufficiently small transverse sizes of the bunch at the focus can be obtained by a Q triplet. A highly accurate timing lower than the plasma wavelength (~10fs) is required for the synchronization between the electron bunch injection and the plasma wave excitation. An RF master oscillator with low SSB phase noise (-150dBc/Hz@10MHz) has been developed for the synchronization. We will report present development status.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB055

About •

paper received ※ 19 May 2021 paper accepted ※ 15 July 2021 issue date ※ 29 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB106

Study on Durability Improvement of Cs-Te Photocathode by Means of Alkali Halide Protective Films

2847

K. Ezawa, R. Fukuoka, Y. Koshiba, T. Tamba, M. Washio
Waseda University, Tokyo, Japan
K. Sakaue
The University of Tokyo, Graduate School of Engineering, Bunkyo, Japan

We have been conducting basic and applied research for generating high quality electron beams, using 1.6 cell laser photocathode RF-gun. In our laboratory, Cesium Telluride (Cs-Te), one of the semiconductor photocathodes, is used as an electron source for accelerator experiments. This semiconductor photocathode is known for high quantum efficiency (Q.E.) about 5~10% and 3-month 1/e lifetime. High Q.E. photocathodes can reduce the power requirement of the laser system, and long lifetime photocathodes can decrease the maintenance frequency, contributing to an efficient experimental environment. For these reasons, high Q.E. and long lifetime photocathodes are necessary in accelerator experiments. In order to produce robust photocathodes and extend the lifetime, we have conducted covering Cs-Te photocathodes with CsBr and CsI protective films. In this conference, we report the thickness dependency on the lifetime of Cs-Te photocathodes when we intentionally exposed oxygen gas to coated and non-coated Cs-Te photocathodes.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB106

About •

paper received ※ 19 May 2021 paper accepted ※ 02 June 2021 issue date ※ 15 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)