IPAC2016 - Classification: 03 Alternative Particle Sources and Acceleration Techniques / T02 Electron Sources

Paper	Title	Page
WEOAB02	Record Performance of SRF Gun with CsK2Sb Photocathode	2085
	I. Pinayev, Z. Altinbas, S.A. Belomestnykh, I. Ben-Zvi, K.A. Brown, J.C. Brutus, A.J. Curcio, A. Di Lieto, C. Folz, D.M. Gassner, M. Harvey, T. Hayes, R.L. Hulsart, J.P. Jamilkowski, Y.C. Jing, D. Kayran, R. Kellermann, R.F. Lambiase, V. Litvinenko, G.J. Mahler, M. Mapes, W. Meng, K. Mernick, R.J. Michnoff, T.A. Miller, M.G. Minty, G. Narayan, P. Orfin, D. Phillips, T. Rao, J. Reich, T. Roser, B. Sheehy, J. Skaritka, L. Smart, K.S. Smith, L. Snydstrup, V. Soria, Z. Sorrell, R. Than, C. Theisen, J.E. Tuozzolo, E. Wang, G. Wang, B. P. Xiao, T. Xin, W. Xu, A. Zaltsman, Z. Zhao BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. High-gradient CW photo-injectors operating at high ac-celerating gradients promise to revolutionize many sci-ences and applications. They can establish the basis for super-bright monochromatic X-ray and gamma-ray sources, high luminosity hadron colliders, nuclear- waste transmutation or a new generation of microchip produc-tion. In this paper we report on our operation of a super-conducting RF electron gun with a record-high accelerat-ing gradient at the CsK2Sb photocathode (i.e. ~ 20 MV/m) generating a record-high bunch charge (i.e., 2 nC). We briefly describe the system and then detail our experimental results.
	Slides WEOAB02 [28.500 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEOAB03	Photoemission Properties of LaB6 and CeB6 Under Various Temperature and Incident Photon Energy Conditions	2088
SUPSS038	use link to see paper's listing under its alternate paper code
	K. Morita, T. Katsurayama, T. Kii, K. Masuda, T. Murata, K. Nagasaki, T. Nogi, H. Ohgaki, S. Suphakul, K. Torgasin, H. Yamashita, H. Zen Kyoto University, Kyoto, Japan
	Recently, thermionic cathode materials such as LaB6, Ir5Ce and dispenser cathodes have been also used as photocathode since they have low work function, reasonably high quantum efficiency, and long lifetime,. However, the effect of cathode temperature and laser wavelength on quantum efficiency is known only for limited conditions. Although it is expected to be able to lengthen the required wavelength of photocathode drive laser by heating cathodes, laser with photon energy under the work function has not been tested. Revealing them enables us to design the cost minimum accelerators. In this research, photoemission properties of LaB6 and CeB6 with various excitation photon energies will be investigated under various temperatures of the materials. Those materials have similar work function, but CeB6 have one order of magnitude smaller Richardson constant than LaB6*. By comparing photoemission properties of these materials, impact of Richardson constant on the photoemission properties will be investigated. S. Thorin et al. Proc of FEL2009, 310 D. Satoh et al. Proc of IPAC2014, 679 * J.M. Lafferty, J. Appl. Phys. 22, (1951), 299
	Slides WEOAB03 [0.996 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPMY013	A Spatially Separated Two Frequency RF Gun Design for Beam Brightness Improvement	2572
	Z. Zhang, C.-X. Tang, Z. Zhang TUB, Beijing, People's Republic of China H.J. Qian LBNL, Berkeley, California, USA
	Recent theoretical and experimental studies shows that transverse beam brightness of photoinjector can be improved by cigar beam photoemission, and beam peak current are then increased with a RF buncher following the gun. We apply this concept to a S-band photoinjector by adding a harmonic RF buncher closely to a S-band RF gun, forming a compact spatially separated two frequency RF gun, targeting a 200 pC beam with emittance < 0.2 mm·mrad and 30 A peak current. Both S/X-band and S/C-band combinations are considered, and an optimized solution with 30 A peak current and 0.1 mm·mrad slice emittance are presented.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPMY037	Cold Model Cavity for 20-K Cryocooled C-band Photocathode RF Gun	2635
	T. Tanaka, M. Inagaki, R. Nagashima, K. Nakao, K. Nogami, T. Sakai, K. Takatsuka LEBRA, Funabashi, Japan M.K. Fukuda, T. Takatomi, N. Terunuma, J. Urakawa, M. Yoshida KEK, Ibaraki, Japan D. Satoh TIT, Tokyo, Japan
	Funding: Work supported by the Photon and Quantum Basic Research Coordinated Development Program of the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT). A cryocooled 2.6-cell C-band photocathode RF gun is under development at Nihon University in collaboration with KEK. The RF characteristics of a pillbox-type 2.6-cell C-band RF cavity at 20 K were in agreement with the theoretical predictions. The result of the cold test for a cavity with the input coupler confirmed the same characteristics. Based on these results a refined cold model of the 20-K cryocooled photocathode RF gun has been designed using SUPERFISH and CST-STUDIO. The separation between the TM01 pi and the TM01 half-pi modes has been increased from 20 MHz to 52 MHz by extending the diameter of the cavity iris and reducing the disk thickness. The 2.6-cell structure has been modified from pillbox to ellipsoid-like type. The end-plate of the 0.6-cell cavity has a center hole for bead-pull measurements of the on-axis electric filed through the entire structure. Mounting of a photocathode assembly in the end-plate has not been considered, since the purpose is solely to measure the low-power and low-temperature RF characteristics. A new design for the input coupler has been employed. The cavity will be completed early in 2016.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPMY038	Optimization of C-band RF Input Coupler as a Mode Converter for 20-K Cryocooled Photocathode RF Gun	2638
	T. Tanaka, M. Inagaki, R. Nagashima, K. Nakao, K. Nogami, T. Sakai, K. Takatsuka LEBRA, Funabashi, Japan M.K. Fukuda, T. Takatomi, N. Terunuma, J. Urakawa, M. Yoshida KEK, Ibaraki, Japan D. Satoh TIT, Tokyo, Japan
	Funding: Work supported by the Photon and Quantum Basic Research Coordinated Development Program of the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT). Development of a cryocooled 2.6-cell C-band photocathode RF gun has been conducted at Nihon University in collaboration with KEK. An RF mode converter from square TE10 to circular TM01 mode has been employed as an RF input coupler that has a coupling coefficient of approximately 20 at 20 K to the 2.6-cell accelerating structure. In the previous design, the circular waveguide in the mode converter formed part of the accelerating cavity. After the cold test of the cavity completed in 2014, the coupler design was modified to work as a pure mode converter with a VSWR of 1 at 5712 MHz. From the design simulation using CST-STUDIO, the insertion loss in the converter is 0.2 %. The TM010 and TM011 modes excited in the circular waveguide were separated by several ten MHz from the accelerating frequency. The simulation has suggested that the amplitude of the transverse electric filed on the axis in the circular waveguide is reduced to approximately 2 % of that in the longitudinal direction.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPMY039	Time Response Measurements for Transmission-Type GaAs/GaAsP Superlattice Photocathodes	2641
	N. Yamamoto, X.J. Jin KEK, Ibaraki, Japan M. Hosaka, Y. Takashima, K. Yamaguchi Nagoya University, Nagoya, Japan M. Katoh UVSOR, Okazaki, Japan
	Polarized electron beam is essential for future electron-positron colliders and electron-ion colliders. Recently we have developed the strain compensated superlattice (SL) photocathode. In the strain compensated SLs, the equivalent compressive and tensile strains introduced in the well and barrier SL layers so that strain relaxation is effectively suppressed with increasing the SL layer thickness and high crystal quality can be expected. In this study, we fabricated the GaAs/GaAsP strain compensated SLs with the thickness up to 90-pair SL layers. Up to now, the electron spin polarization of 92 % and the quantum efficiency of 1.6 % were simultaneously achieved from 24-pair sample. In this study, to compare the time response performances with the SL thicknesses, the measurements were carried out for conventional and strain compensated SL PCs. We show the measurement results and discuss the physics.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPMY040	Fabrication of Two Dimensional Nano-Scale Photocathode Arrays in Transparent Conductor for High Coherence Beam Generation	2645
SUPSS039	use link to see paper's listing under its alternate paper code
	T. Shibuya TIT, Tokyo, Japan N. Hayashizaki RLNR, Tokyo, Japan M. Yoshida KEK, Ibaraki, Japan
	Electron beam quality for particle source of diffractometer is mainly characterized by transverse and longitudinal coherent length, beam current density and so on. In order to improve a transverse coherent length, it is practically essential to minimize electrons emission area size as small as possible. However, the size of photoemission area is limited by focused laser beam size on the surface of cathode, and the scale is several microns. Aim to get definite overlap between the focused laser and emitters for effective irradiation, as well as to realize generation of nano-scale size electron beam, nano-scale photocathode arrays in transparent conductor are essential. Therefore, I propose to fabricate the nano-scale emission area in replace of limiting the focused laser size on the photocathode for achieving high coherence beam. The fabrication process of this novel nano-scale emitter configuration and its fundamental properties are presented in this paper.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Record Performance of SRF Gun with CsK2Sb Photocathode

2085

I. Pinayev, Z. Altinbas, S.A. Belomestnykh, I. Ben-Zvi, K.A. Brown, J.C. Brutus, A.J. Curcio, A. Di Lieto, C. Folz, D.M. Gassner, M. Harvey, T. Hayes, R.L. Hulsart, J.P. Jamilkowski, Y.C. Jing, D. Kayran, R. Kellermann, R.F. Lambiase, V. Litvinenko, G.J. Mahler, M. Mapes, W. Meng, K. Mernick, R.J. Michnoff, T.A. Miller, M.G. Minty, G. Narayan, P. Orfin, D. Phillips, T. Rao, J. Reich, T. Roser, B. Sheehy, J. Skaritka, L. Smart, K.S. Smith, L. Snydstrup, V. Soria, Z. Sorrell, R. Than, C. Theisen, J.E. Tuozzolo, E. Wang, G. Wang, B. P. Xiao, T. Xin, W. Xu, A. Zaltsman, Z. Zhao
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
High-gradient CW photo-injectors operating at high ac-celerating gradients promise to revolutionize many sci-ences and applications. They can establish the basis for super-bright monochromatic X-ray and gamma-ray sources, high luminosity hadron colliders, nuclear- waste transmutation or a new generation of microchip produc-tion. In this paper we report on our operation of a super-conducting RF electron gun with a record-high accelerat-ing gradient at the CsK2Sb photocathode (i.e. ~ 20 MV/m) generating a record-high bunch charge (i.e., 2 nC). We briefly describe the system and then detail our experimental results.

Slides WEOAB02 [28.500 MB]

Export •

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

WEOAB03

Photoemission Properties of LaB6 and CeB6 Under Various Temperature and Incident Photon Energy Conditions

2088

SUPSS038

use link to see paper's listing under its alternate paper code

K. Morita, T. Katsurayama, T. Kii, K. Masuda, T. Murata, K. Nagasaki, T. Nogi, H. Ohgaki, S. Suphakul, K. Torgasin, H. Yamashita, H. Zen
Kyoto University, Kyoto, Japan

Recently, thermionic cathode materials such as LaB6, Ir5Ce and dispenser cathodes have been also used as photocathode since they have low work function, reasonably high quantum efficiency, and long lifetime*,**. However, the effect of cathode temperature and laser wavelength on quantum efficiency is known only for limited conditions. Although it is expected to be able to lengthen the required wavelength of photocathode drive laser by heating cathodes, laser with photon energy under the work function has not been tested. Revealing them enables us to design the cost minimum accelerators. In this research, photoemission properties of LaB6 and CeB6 with various excitation photon energies will be investigated under various temperatures of the materials. Those materials have similar work function, but CeB6 have one order of magnitude smaller Richardson constant than LaB6***. By comparing photoemission properties of these materials, impact of Richardson constant on the photoemission properties will be investigated.
* S. Thorin et al. Proc of FEL2009, 310
** D. Satoh et al. Proc of IPAC2014, 679
*** J.M. Lafferty, J. Appl. Phys. 22, (1951), 299

Slides WEOAB03 [0.996 MB]

Export •

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

WEPMY013

A Spatially Separated Two Frequency RF Gun Design for Beam Brightness Improvement

2572

Z. Zhang, C.-X. Tang, Z. Zhang
TUB, Beijing, People's Republic of China
H.J. Qian
LBNL, Berkeley, California, USA

Recent theoretical and experimental studies shows that transverse beam brightness of photoinjector can be improved by cigar beam photoemission, and beam peak current are then increased with a RF buncher following the gun. We apply this concept to a S-band photoinjector by adding a harmonic RF buncher closely to a S-band RF gun, forming a compact spatially separated two frequency RF gun, targeting a 200 pC beam with emittance < 0.2 mm·mrad and 30 A peak current. Both S/X-band and S/C-band combinations are considered, and an optimized solution with 30 A peak current and 0.1 mm·mrad slice emittance are presented.

Export •

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

WEPMY037

Cold Model Cavity for 20-K Cryocooled C-band Photocathode RF Gun

2635

T. Tanaka, M. Inagaki, R. Nagashima, K. Nakao, K. Nogami, T. Sakai, K. Takatsuka
LEBRA, Funabashi, Japan
M.K. Fukuda, T. Takatomi, N. Terunuma, J. Urakawa, M. Yoshida
KEK, Ibaraki, Japan
D. Satoh
TIT, Tokyo, Japan

Funding: Work supported by the Photon and Quantum Basic Research Coordinated Development Program of the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT).
A cryocooled 2.6-cell C-band photocathode RF gun is under development at Nihon University in collaboration with KEK. The RF characteristics of a pillbox-type 2.6-cell C-band RF cavity at 20 K were in agreement with the theoretical predictions. The result of the cold test for a cavity with the input coupler confirmed the same characteristics. Based on these results a refined cold model of the 20-K cryocooled photocathode RF gun has been designed using SUPERFISH and CST-STUDIO. The separation between the TM01 pi and the TM01 half-pi modes has been increased from 20 MHz to 52 MHz by extending the diameter of the cavity iris and reducing the disk thickness. The 2.6-cell structure has been modified from pillbox to ellipsoid-like type. The end-plate of the 0.6-cell cavity has a center hole for bead-pull measurements of the on-axis electric filed through the entire structure. Mounting of a photocathode assembly in the end-plate has not been considered, since the purpose is solely to measure the low-power and low-temperature RF characteristics. A new design for the input coupler has been employed. The cavity will be completed early in 2016.

Export •

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

WEPMY038

Optimization of C-band RF Input Coupler as a Mode Converter for 20-K Cryocooled Photocathode RF Gun

2638

T. Tanaka, M. Inagaki, R. Nagashima, K. Nakao, K. Nogami, T. Sakai, K. Takatsuka
LEBRA, Funabashi, Japan
M.K. Fukuda, T. Takatomi, N. Terunuma, J. Urakawa, M. Yoshida
KEK, Ibaraki, Japan
D. Satoh
TIT, Tokyo, Japan

Funding: Work supported by the Photon and Quantum Basic Research Coordinated Development Program of the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT).
Development of a cryocooled 2.6-cell C-band photocathode RF gun has been conducted at Nihon University in collaboration with KEK. An RF mode converter from square TE10 to circular TM01 mode has been employed as an RF input coupler that has a coupling coefficient of approximately 20 at 20 K to the 2.6-cell accelerating structure. In the previous design, the circular waveguide in the mode converter formed part of the accelerating cavity. After the cold test of the cavity completed in 2014, the coupler design was modified to work as a pure mode converter with a VSWR of 1 at 5712 MHz. From the design simulation using CST-STUDIO, the insertion loss in the converter is 0.2 %. The TM010 and TM011 modes excited in the circular waveguide were separated by several ten MHz from the accelerating frequency. The simulation has suggested that the amplitude of the transverse electric filed on the axis in the circular waveguide is reduced to approximately 2 % of that in the longitudinal direction.

Export •

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

WEPMY039

Time Response Measurements for Transmission-Type GaAs/GaAsP Superlattice Photocathodes

2641

N. Yamamoto, X.J. Jin
KEK, Ibaraki, Japan
M. Hosaka, Y. Takashima, K. Yamaguchi
Nagoya University, Nagoya, Japan
M. Katoh
UVSOR, Okazaki, Japan

Polarized electron beam is essential for future electron-positron colliders and electron-ion colliders. Recently we have developed the strain compensated superlattice (SL) photocathode. In the strain compensated SLs, the equivalent compressive and tensile strains introduced in the well and barrier SL layers so that strain relaxation is effectively suppressed with increasing the SL layer thickness and high crystal quality can be expected. In this study, we fabricated the GaAs/GaAsP strain compensated SLs with the thickness up to 90-pair SL layers. Up to now, the electron spin polarization of 92 % and the quantum efficiency of 1.6 % were simultaneously achieved from 24-pair sample. In this study, to compare the time response performances with the SL thicknesses, the measurements were carried out for conventional and strain compensated SL PCs. We show the measurement results and discuss the physics.

Export •

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

WEPMY040

Fabrication of Two Dimensional Nano-Scale Photocathode Arrays in Transparent Conductor for High Coherence Beam Generation

2645

SUPSS039

use link to see paper's listing under its alternate paper code

T. Shibuya
TIT, Tokyo, Japan
N. Hayashizaki
RLNR, Tokyo, Japan
M. Yoshida
KEK, Ibaraki, Japan

Electron beam quality for particle source of diffractometer is mainly characterized by transverse and longitudinal coherent length, beam current density and so on. In order to improve a transverse coherent length, it is practically essential to minimize electrons emission area size as small as possible. However, the size of photoemission area is limited by focused laser beam size on the surface of cathode, and the scale is several microns. Aim to get definite overlap between the focused laser and emitters for effective irradiation, as well as to realize generation of nano-scale size electron beam, nano-scale photocathode arrays in transparent conductor are essential. Therefore, I propose to fabricate the nano-scale emission area in replace of limiting the focused laser size on the photocathode for achieving high coherence beam. The fabrication process of this novel nano-scale emitter configuration and its fundamental properties are presented in this paper.

Export •

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