FEL2012 - List of Authors (Kii, T.)

Paper

Title

Page

Development of Multi-bunch Laser System for Photocathode RF Gun in KU - FEL

173

K. Shimahashi, Y.W. Choi, H. Imon, T. Kii, R. Kinjo, T. Konstantin, K. Masuda, H. Negm, H. Ohgaki, K. Okumura, M. Omer, S. Shibata, K. Yoshida, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan
R. Kuroda
AIST, Tsukuba, Ibaraki, Japan

We have been developing mid-infrared FEL (MIR-FEL) system, KU-FEL (Kyoto University-FEL), which utilizes a 4.5-cell S-band thermionic RF gun, in Institute of Advanced Energy, Kyoto University. We plan to introduce a BNL-type 1.6-cell photocathode RF gun to generate higher peak power MIR-FEL. The purpose of this work is to develop the multi-bunch laser system which excites the photocathode in the RF gun. The target values of the system are bunch number of 300 and pulse energy of 10　uJ perμpulse in 266 nm. The laser system consists of a mode-locked Nd:YVO4 laser as the oscillator, an acousto-optic modulator, a laser beam pointing stabilization system, a flash lamp pumped amplifier and 4th harmonic generation crystals. We will report the current status of multi-bunch laser in this conference.

TUPD41

Practical Design of Resonance Frequency Tuning System for Coaxial RF Cavity for Thermionic Triode RF Gun

333

T. Konstantin, Y.W. Choi, H. Imon, T. Kii, R. Kinjo, K. Masuda, K. Nagasaki, H. Negm, H. Ohgaki, K. Okumura, M. Omer, S. Shibata, K. Shimahashi, M. Takasaki, K. Yoshida, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

The FEL radiation production requires temporal stability of electron beam energy. The latter depends directly on the quality of electron gun. The KUFEL(Kyoto University- FEL) facility uses a thermionic 4.5 cell S-band RF gun for electron beam generation. The main disadvantage of using a thermionic RF gun is the effect of backstreaming electrons, which heats up the cathode material during operation and causes energy drop. An additional cavity, triode cavity, for RF gun was designed and fabricated in order to control the electron injection and to mitigate the amount of backstreaming electrons(*). The quality factor and the coupling coefficient of the triode cavity with the RF feed coaxial cable were designed to ensure the induction of the required cavity voltage and a wide frequency acceptance(***). The corresponded simulations show the power reduction of back streaming electrons for 80% as well as peak current enhancement without emittance degradation(**,***). However the fabricated prototype didn't match the designed parameters as tested at low power(****). In this work we report the strategies for correction of deviation from simulated and tested parameters of triode cavity.
* K.Masuda et al. Prc. FEL 2009, Liverpool
** K.Masuda et al. Prc. FEL 2006, Berlin
*** T. Shiiyama et al. Prc. FEL 2007, Novosibirsk
**** M.Takasaki et al. Prc. FEL 2010, Malmö

WEPD38

Improvement of KU-FEL Performance by Replacing Undulator and Optical Cavity

449

H. Zen, M. A. Bakr, Y.W. Choi, H. Imon, T. Kii, R. Kinjo, T. Konstantin, K. Masuda, H. Negm, H. Ohgaki, K. Okumura, M. Omer, S. Shibata, K. Shimahashi, K. Yoshida
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

A mid-infrared FEL named as KU-FEL (Kyoto University FEL) has been developed for energy related sciences*. The FEL achieved first lasing and saturation in 2008**,***. However, the tunable range was limited from 10 to 13 micro-m because of insufficient macro-pulse duration of e-beam and FEL gain. The undulator of KU-FEL has been replaced with the undulator which was previously used for ERL-FEL in JAEA. The optical cavity has been replaced with optimized one. In addition the diameter of the coupling hole on the upstream cavity mirror has been reduced from 2 to 1 mm for reducing cavity loss. After installation, the tunable range of KU-FEL has been improved to 5-15 micro-m. Estimated FEL gain is greater than 30%, which was 1.5 times larger than original configuration.
*H. Zen, et al., Infrared Physics and Technology, Vol. 51, Issue 5, p.382 (2008)
**H. Ohgaki, et al., Proc. of FEL08, p.4 (2008)
***H. Ohgaki, et al., Proc. of FEL09, p.572 (2009)

WEPD65

Design and Numerical Simulation of THz-FEL Amplifier in Kyoto University

519

M. A. Bakr, Y.W. Choi, T. Kii, R. Kinjo, K. Masuda, H. Negm, H. Ohgaki, M. Omer, K. Shimahashi, K. Yoshida, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan
M. A. Bakr
Assiut University, Assiut, Egypt

Design of a compact and economic THz free-electron laser (FEL) amplifier, which consists of a BNL-type 1.6 cells photocathode radio frequency gun, Solenoid, transport line and short undulator, has been studied at Kyoto University. The electron beam energy to obtain FEL with a wavelength of the range 150~400 μm was calculated to be 4.1~7.0 MeV for a bunch charge of 1.0 nC/bunch. The numerical calculations of the electron beam from the RF gun up to the undulator entrance are carried out using Parmela code and the FEL properties from the undulator will be simulated using GENESIS 1.3. The expected FEL spectral was estimated using 4~5 undulator periods with ~30 cm length and 0.3 T magnetic field. Details of the design concept, numerical calculations and results will be presented in the conference.

THOA03

Use of Fringe-Resolved Autocorrelation for the diagnosis of the wavelength stability of a FEL

Y. Qin, T. Kii, T. Nakajima, H. Ohgaki, X. Wang, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

For the spectroscopic applications of a FEL it is very important to monitor its wavelength stability. The most straightforward way is to take a laser spectrum at once with an array-type photodetector. This, however, is not an easy task at the wavelength regions (<190 nm or >1100 nm) where a Si-based array-type photodetector does not work. An alternative method has to be developed. In this paper we propose to use the autocorrelation setup, which is usually used to measure the pulse duration, to monitor the wavelength stability of a FEL. During the numerical simulation to demonstrate the above idea, we have included various kinds of instabilities such as the central wavelength, intensity, and pulse duration as well as the chirps. Our results show that we can estimate the stability of the wavelength from the width of the upper envelope of fringe-resolved autocorrelation (FRAC) signals: Given the same pulse duration the FEL pulse with larger wavelength instability results narrower envelope width of FRAC signals. Based on this fact, the FRAC can be used as a tool to diagnose the wavelength stability in the wavelength region where a direct spectrum measurement is not possible.

Slides THOA03 [1.580 MB]

THPD05

Observation of High Harmonic Generation from 6H-SiC Irradiated by MIR-FEL

555

K. Yoshida, Y.W. Choi, H. Imon, T. Kii, R. Kinjo, K. Komai, K. Masuda, H. Negm, H. Ohgaki, K. Okumura, M. Omer, S. Shibata, K. Shimahashi, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

Silicon Carbide (SiC) is attractive as the next generation power devices, heat resistance material and so on. In addition, 6H-SiC is investigated as the material for high harmonic generation [1]. For verifying the possibility of high harmonic generation by 6H-SiC irradiated by MIR-FEL, we measured the emission spectrum from 6H-SiC irradiated by MIR-FEL whose center wavelength was 7.8 μm. As the result, we clearly observed the emissions at 963 nm, 861 nm and 775 nm, which correspond to harmonics of 8th, 9th and 10th wavelength respectively. In this meeting, we will present and discuss about the high harmonic generation introduced by MIR-FEL.
[1] Hiroaki Sato, Makoto Abe, Ichiro Shoji, Jun Suda, and Takashi Kondo, J. Opt. Soc. Am. B, Vol. 26, No. 10(2009), 1892-1896

THPD08

Pit Formation on Dental Hard Tissues Using Two Different Free Electron Laser Sources, LEBRA-FEL and KU-FEL

563

T. Sakae
Nihon University School of Dentistry at Matsudo, Matsudo-shi, Japan
K. Hayakawa, Y. Hayakawa, M. Inagaki, T. Kuwada, K. Nakao, K. Nogami, I. Sato, T. Tanaka
LEBRA, Funabashi, Japan
T. Kii, H. Ohgaki, H. Zen
Kyoto University, Institute for Advanced Energy, Kyoto, Japan

Funding: This study was supported by a Grant for Supporting Project for Strategic Research by MEXT, Japan (S0801032) and by the ZE Research Program, IIAE, Kyoto University (A-17).
According to the increased usage and demands of lasers in dentistry, research and development of the more reliable and functional lasers are needed. In the case of caries treatment, the lasers generated by commercial apparatus are not enough to dig the dental enamel and/or dentin tissues. Our previous studies showed that FEL generated at LEBRA has a potential to form pits on these dental hard tissues easily, and that the effective wavelength depends on the tissue types sensitively at about 3000 nm. To progress the FEL study on dental tissues, it is needed to spread the range of wavelengths more than that at LEBRA, between 2000 and 6000 nm. The newly established KU-FEL is able to generate the FEL of wavelength between 5000 and 13000 nm. Combining the two FEL sources, we found a new result that the dental hard tissues were easily dug by 7800 nm KU-FEL, which wavelength has not been presumed before. In the combination of LEBRA-FEL and KU-FEL, the wider knowledge on the FEL action on dental tissues will be achieved.

Paper	Title	Page
MOPD57	Development of Multi-bunch Laser System for Photocathode RF Gun in KU - FEL	173
	K. Shimahashi, Y.W. Choi, H. Imon, T. Kii, R. Kinjo, T. Konstantin, K. Masuda, H. Negm, H. Ohgaki, K. Okumura, M. Omer, S. Shibata, K. Yoshida, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan R. Kuroda AIST, Tsukuba, Ibaraki, Japan
	We have been developing mid-infrared FEL (MIR-FEL) system, KU-FEL (Kyoto University-FEL), which utilizes a 4.5-cell S-band thermionic RF gun, in Institute of Advanced Energy, Kyoto University. We plan to introduce a BNL-type 1.6-cell photocathode RF gun to generate higher peak power MIR-FEL. The purpose of this work is to develop the multi-bunch laser system which excites the photocathode in the RF gun. The target values of the system are bunch number of 300 and pulse energy of 10　uJ perμpulse in 266 nm. The laser system consists of a mode-locked Nd:YVO4 laser as the oscillator, an acousto-optic modulator, a laser beam pointing stabilization system, a flash lamp pumped amplifier and 4th harmonic generation crystals. We will report the current status of multi-bunch laser in this conference.

TUPD41	Practical Design of Resonance Frequency Tuning System for Coaxial RF Cavity for Thermionic Triode RF Gun	333
	T. Konstantin, Y.W. Choi, H. Imon, T. Kii, R. Kinjo, K. Masuda, K. Nagasaki, H. Negm, H. Ohgaki, K. Okumura, M. Omer, S. Shibata, K. Shimahashi, M. Takasaki, K. Yoshida, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	The FEL radiation production requires temporal stability of electron beam energy. The latter depends directly on the quality of electron gun. The KUFEL(Kyoto University- FEL) facility uses a thermionic 4.5 cell S-band RF gun for electron beam generation. The main disadvantage of using a thermionic RF gun is the effect of backstreaming electrons, which heats up the cathode material during operation and causes energy drop. An additional cavity, triode cavity, for RF gun was designed and fabricated in order to control the electron injection and to mitigate the amount of backstreaming electrons(). The quality factor and the coupling coefficient of the triode cavity with the RF feed coaxial cable were designed to ensure the induction of the required cavity voltage and a wide frequency acceptance(). The corresponded simulations show the power reduction of back streaming electrons for 80% as well as peak current enhancement without emittance degradation(,*). However the fabricated prototype didn't match the designed parameters as tested at low power(*). In this work we report the strategies for correction of deviation from simulated and tested parameters of triode cavity. K.Masuda et al. Prc. FEL 2009, Liverpool K.Masuda et al. Prc. FEL 2006, Berlin * T. Shiiyama et al. Prc. FEL 2007, Novosibirsk **** M.Takasaki et al. Prc. FEL 2010, Malmö

WEPD38	Improvement of KU-FEL Performance by Replacing Undulator and Optical Cavity	449
	H. Zen, M. A. Bakr, Y.W. Choi, H. Imon, T. Kii, R. Kinjo, T. Konstantin, K. Masuda, H. Negm, H. Ohgaki, K. Okumura, M. Omer, S. Shibata, K. Shimahashi, K. Yoshida Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	A mid-infrared FEL named as KU-FEL (Kyoto University FEL) has been developed for energy related sciences. The FEL achieved first lasing and saturation in 2008,*. However, the tunable range was limited from 10 to 13 micro-m because of insufficient macro-pulse duration of e-beam and FEL gain. The undulator of KU-FEL has been replaced with the undulator which was previously used for ERL-FEL in JAEA. The optical cavity has been replaced with optimized one. In addition the diameter of the coupling hole on the upstream cavity mirror has been reduced from 2 to 1 mm for reducing cavity loss. After installation, the tunable range of KU-FEL has been improved to 5-15 micro-m. Estimated FEL gain is greater than 30%, which was 1.5 times larger than original configuration. H. Zen, et al., Infrared Physics and Technology, Vol. 51, Issue 5, p.382 (2008) H. Ohgaki, et al., Proc. of FEL08, p.4 (2008) *H. Ohgaki, et al., Proc. of FEL09, p.572 (2009)

WEPD65	Design and Numerical Simulation of THz-FEL Amplifier in Kyoto University	519
	M. A. Bakr, Y.W. Choi, T. Kii, R. Kinjo, K. Masuda, H. Negm, H. Ohgaki, M. Omer, K. Shimahashi, K. Yoshida, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan M. A. Bakr Assiut University, Assiut, Egypt
	Design of a compact and economic THz free-electron laser (FEL) amplifier, which consists of a BNL-type 1.6 cells photocathode radio frequency gun, Solenoid, transport line and short undulator, has been studied at Kyoto University. The electron beam energy to obtain FEL with a wavelength of the range 150~400 μm was calculated to be 4.1~7.0 MeV for a bunch charge of 1.0 nC/bunch. The numerical calculations of the electron beam from the RF gun up to the undulator entrance are carried out using Parmela code and the FEL properties from the undulator will be simulated using GENESIS 1.3. The expected FEL spectral was estimated using 4~5 undulator periods with ~30 cm length and 0.3 T magnetic field. Details of the design concept, numerical calculations and results will be presented in the conference.

THOA03	Use of Fringe-Resolved Autocorrelation for the diagnosis of the wavelength stability of a FEL
	Y. Qin, T. Kii, T. Nakajima, H. Ohgaki, X. Wang, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	For the spectroscopic applications of a FEL it is very important to monitor its wavelength stability. The most straightforward way is to take a laser spectrum at once with an array-type photodetector. This, however, is not an easy task at the wavelength regions (<190 nm or >1100 nm) where a Si-based array-type photodetector does not work. An alternative method has to be developed. In this paper we propose to use the autocorrelation setup, which is usually used to measure the pulse duration, to monitor the wavelength stability of a FEL. During the numerical simulation to demonstrate the above idea, we have included various kinds of instabilities such as the central wavelength, intensity, and pulse duration as well as the chirps. Our results show that we can estimate the stability of the wavelength from the width of the upper envelope of fringe-resolved autocorrelation (FRAC) signals: Given the same pulse duration the FEL pulse with larger wavelength instability results narrower envelope width of FRAC signals. Based on this fact, the FRAC can be used as a tool to diagnose the wavelength stability in the wavelength region where a direct spectrum measurement is not possible.
	Slides THOA03 [1.580 MB]

THPD05	Observation of High Harmonic Generation from 6H-SiC Irradiated by MIR-FEL	555
	K. Yoshida, Y.W. Choi, H. Imon, T. Kii, R. Kinjo, K. Komai, K. Masuda, H. Negm, H. Ohgaki, K. Okumura, M. Omer, S. Shibata, K. Shimahashi, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	Silicon Carbide (SiC) is attractive as the next generation power devices, heat resistance material and so on. In addition, 6H-SiC is investigated as the material for high harmonic generation [1]. For verifying the possibility of high harmonic generation by 6H-SiC irradiated by MIR-FEL, we measured the emission spectrum from 6H-SiC irradiated by MIR-FEL whose center wavelength was 7.8 μm. As the result, we clearly observed the emissions at 963 nm, 861 nm and 775 nm, which correspond to harmonics of 8th, 9th and 10th wavelength respectively. In this meeting, we will present and discuss about the high harmonic generation introduced by MIR-FEL. [1] Hiroaki Sato, Makoto Abe, Ichiro Shoji, Jun Suda, and Takashi Kondo, J. Opt. Soc. Am. B, Vol. 26, No. 10(2009), 1892-1896

THPD08	Pit Formation on Dental Hard Tissues Using Two Different Free Electron Laser Sources, LEBRA-FEL and KU-FEL	563
	T. Sakae Nihon University School of Dentistry at Matsudo, Matsudo-shi, Japan K. Hayakawa, Y. Hayakawa, M. Inagaki, T. Kuwada, K. Nakao, K. Nogami, I. Sato, T. Tanaka LEBRA, Funabashi, Japan T. Kii, H. Ohgaki, H. Zen Kyoto University, Institute for Advanced Energy, Kyoto, Japan
	Funding: This study was supported by a Grant for Supporting Project for Strategic Research by MEXT, Japan (S0801032) and by the ZE Research Program, IIAE, Kyoto University (A-17). According to the increased usage and demands of lasers in dentistry, research and development of the more reliable and functional lasers are needed. In the case of caries treatment, the lasers generated by commercial apparatus are not enough to dig the dental enamel and/or dentin tissues. Our previous studies showed that FEL generated at LEBRA has a potential to form pits on these dental hard tissues easily, and that the effective wavelength depends on the tissue types sensitively at about 3000 nm. To progress the FEL study on dental tissues, it is needed to spread the range of wavelengths more than that at LEBRA, between 2000 and 6000 nm. The newly established KU-FEL is able to generate the FEL of wavelength between 5000 and 13000 nm. Combining the two FEL sources, we found a new result that the dental hard tissues were easily dug by 7800 nm KU-FEL, which wavelength has not been presumed before. In the combination of LEBRA-FEL and KU-FEL, the wider knowledge on the FEL action on dental tissues will be achieved.