IPAC2013 - List of Authors (Urakawa, J.)

Paper	Title	Page
MOPFI024	Ultra-short Electron Bunch Generation by an ECC RF Gun	330
	Y. Koshiba, T. Aoki, M. Mizugaki, K. Sakaue, M. Washio Waseda University, Tokyo, Japan T. Takatomi, J. Urakawa KEK, Ibaraki, Japan
	Funding: Work supported by JSPS Grant-in-Aid for Young Scientists (B) 23740203 and Scientific Research (A) 10001690 Energy Chirping Cell attached rf gun (ECC rf gun) is a photocathode rf gun specialized for ultra-short bunch generation. This ECC rf gun has been made with the collaboration of High Energy Accelerator Research Organization (KEK). Although the bunch length could be controlled by the laser pulse width, the bunch length ends up to be more than 1ps due to space charge effect when using a femto-second laser and a normal 1.6 cell cavity. Concerning this phenomenon, ECC is attached right after the 1.6 cell so that the electron bunch would be compressed after the electron bunch is accelerated around 5MeV. The roll of ECC is to chirp the energy with the linear part of the rf electric field. The electron bunch would be compressed by velocity difference as it drifts. Simulation results from PARMELA and GPT show that ECC rf gun can accelerate an 100pC bunch with the bunch length less than 100fs. We already manufactured this ECC rf gun and installed in our system. We demonstrated the ultra-short bunch by measuring the coherent THz light by synchrotron radiation and transition radiation. In this conference, we will report the results of ultra-short bunch generation experiments, and future plans.

MOPME018	BEAM OSCILLATION MONITOR FOR THE MULTI-BUNCH BEAM	506
	T. Naito, S. Araki, H. Hayano, K. Kubo, S. Kuroda, T. Okugi, N. Terunuma, J. Urakawa KEK, Ibaraki, Japan
	In order to observe the motion of bunch-by-bunch beam oscillation of multi-bunch in the storage ring, we developed two measurement tools. One is a signal process electronics circuit using fast analogue switches. The circuit picks up one of the selected bunch signal of the beam position monitor from the multi-bunch. The selected beam position signal can be processed as a single bunch beam. By changing the gate timing, arbitrary bunch signal can be selected. The other is a waveform memory using a high bandwidth oscilloscope. The long waveform memory of the oscilloscope has a capability to acquire the multi-turn waveform of the button electrode signals. The beam test of the circuit has been carried out at KEK-ATF damping ring in the cases of 2.8ns bunch spacing and 5.6ns bunch spacing, respectively. The detail of the hardware and the result of the beam test are reported.

MOPWA052	Short Range Wakefield Measurements of High Resolution RF Cavity Beam Position Monitors at ATF2	792
	J. Snuverink, S.T. Boogert, F.J. Cullinan, Y.I. Kim, A. Lyapin JAI, Egham, Surrey, United Kingdom K. Kubo, T. Okugi, T. Tauchi, N. Terunuma, J. Urakawa KEK, Ibaraki, Japan G.R. White SLAC, Menlo Park, California, USA
	Cavity beam position monitors (CBPM) have been used in several accelerator facilities and are planned to be used in future accelerators and light sources. High position resolution up to tens of nanometres has been achieved, but short range wakefields are a concern, especially for small beam emittances. This paper presents the wakefield calculations as well as the first measurements of the CBPM-generated short range wakefields performed at the Accelerator Test Facility (ATF2).

MOPWA053	Sub-Micrometre Resolution Laserwire Transverse Beam Size Measurement System	795
	L.J. Nevay, G.A. Blair, S.T. Boogert, V. Karataev, K.O. Kruchinin Royal Holloway, University of London, Surrey, United Kingdom A.S. Aryshev, N. Terunuma, J. Urakawa KEK, Ibaraki, Japan L. Corner, R. Walczak Oxford University, Physics Department, Oxford, Oxon, United Kingdom
	Funding: The research leading to these results has received funding from the European Commission under the FP7 Research Infrastructures project Eu-CARD, grant agreement no. 227579 We present the results from the laserwire system at the Accelerator Test Facility 2 (ATF2) during recent operation after relocation to the virtual image point of the ATF2 final focus. The characterisation of the 150 mJ, 77 ps long laser pulses at a scaled virtual interaction point is used to deconvolve the transverse laserwire profile demonstrating a 1.16 ± 0.06 um vertical electron beam profile. Horizontal laserwire scans were used in combination with the vertical scans to measure the electron beam size using a full overlap integral model due to the problems presented by a large aspect ratio electron beam.

MOPWA058	Cavity Beam Position Monitor at Interaction Point Region of Accelerator Test Facility 2	807
	Y.I. Kim, D.R. Bett, N. Blaskovic Kraljevic, P. Burrows, G.B. Christian, M.R. Davis, A. Lyapin JAI, Egham, Surrey, United Kingdom S.T. Boogert Royal Holloway, University of London, Surrey, United Kingdom J.C. Frisch, D.J. McCormick, J. Nelson, G.R. White SLAC, Menlo Park, California, USA Y. Honda, T. Tauchi, N. Terunuma, J. Urakawa KEK, Ibaraki, Japan
	Nanometre resolution cavity beam position monitors (BPMs) have been developed to measure the beam position and linked to a feedback system control the beam position stability within few nanometres in the vertical direction at the focus, or interaction point (IP), of Accelerator Test Facility 2 (ATF2). In addition, for feedback applications a lower-Q and hence faster decay time system is desirable. Two IPBPMs have been installed inside of IP chamber at the ATF2 focus area. To measure the resolution of IPBPMs two additional C-band cavity BPMs have been installed one upstream and one downstream of the IP. One cavity BPM has been installed at an upstream image point of IP. The performance of the BPMs is discussed and the correlation between IP and image point positions is presented along with a discussion of using these BPMs for position stabilisation at the IP.

TUPME045	Turn-by-turn Measurements in the KEK-ATF	1664
	Y. Renier, Y. Papaphilippou, R. Tomás, M. Wendt CERN, Geneva, Switzerland N. Eddy Fermilab, Batavia, USA K. Kubo, S. Kuroda, T. Naito, T. Okugi, N. Terunuma, J. Urakawa KEK, Ibaraki, Japan
	The ATF damping ring has been upgraded with new read-out electronics for the beam position monitors (BPM), capable to acquire the beam orbits on a turn-by-turn basis, as well as in a high resolution averaging mode. The new BPM system allows to improve optic corrections and to achieve an even smaller vertical emittance (<2pm). Experimental results are presented based on turn-by-turn beam orbit measurements in the ring, for estimating the beta functions and dispersion along the lattice. A fast method to measure spectral line amplitude in a few turns is also presented, including the evaluation of chromaticity.

TUPME056	3.5 GeV Superconducting Stacking Ring for Compton Based Polarized Positrons Source of CLIC	1697
	E.V. Bulyak, P. Gladkikh, A.A. Kalamayko NSC/KIPT, Kharkov, Ukraine T. Omori, J. Urakawa, K. Yokoya KEK, Ibaraki, Japan L. Rinolfi, F. Zimmermann CERN, Geneva, Switzerland
	This paper describes 3.5 GeV superconducting storage ring dedicated to positron accumulation as part of a polarized positron source for CLIC, based on Compton scattering in a Compton storage ring. The superconducting stacking ring can provide a synchrotron damping time of order 250 microseconds. Together with combined injection scheme in the longitudinal and transverse plane, such a ring may solve the problem of accumulating a positron beam with efficiency close to 95 % and with the beam intensity required for CLIC.

TUPWA050	Effect of Transverse Coupling on Asymmetric Cooling in Compton Rings	1823
	E.V. Bulyak NSC/KIPT, Kharkov, Ukraine J. Urakawa KEK, Ibaraki, Japan F. Zimmermann CERN, Geneva, Switzerland
	Fast cooling of bunches circulating in a Compton ring is achieved by placing the collision point between electron bunches and laser pulses in a dispersive section and by, in addition, introducing a transverse offset between the laser pulse and the electron-beam closed orbit. Growth of the emittance in the dispersive transversal direction due to the additional excitation of betatron oscillations limits this type of cooling. Here we present the results of further studies on the fast cooling process, looking at the effect of the coupling of the transverse (betatron) oscillations. We first show theoretically that the transverse betatron coupling shortens the cooling time and hence reduces the steady-state energy spread of the electron beam, as well as the quantum losses. The theoretical estimates are then validated by simulations. Finally, a proof-of-principle experiment at the KEK ATF Damping Ring is proposed.

WEPWA017	Development of Laser-Compton X-ray Source using Optical Storage Cavity	2165
	K. Sakaue, M. Washio Waseda University, Tokyo, Japan M.K. Fukuda, Y. Honda, N. Terunuma, J. Urakawa KEK, Ibaraki, Japan
	Funding: Work supported by the Quantum Beam Technology Program of MEXT and JSPS Grant-in-Aid for Young Scientists (B) 23740203 We have been developing a pulsed-laser storage technique in a super-cavity for a compact x-ray sources. The pulsed-laser super-cavity enables to make high peak power and small waist laser at the collision point with the electron beam. We already obtained a pulse-train x-rays through the laser-Compton scattering between a multi-bunch electron beam and an optical super-cavity. And also, we performed a X-ray imaging via laser-Compton X-ray. On these successful results, we decided to upgrade our system for increasing X-ray flux by 3-order of magnitudes for practical use. For an optical cavity, we designed 4-mirrors bow-tie cavity in order to increase the power. On the other hand, electron accelerator was also upgraded to increase the bunch number in the train. We use 3.6cells rf-gun and 12cell standing wave booster linac. As a result, 2-order increase of X-ray flux was achieved. Design of upgraded our laser-Compton X-ray source, the results of X-ray experiments and future prospective will be presented at the conference.

WEPFI023	Study on Two-cell RF-deflector Cavity for Ultra-short Electron Bunch Measurement	2753
	Y. Nishimura, K. Sakaue, T. Takahashi, M. Washio Waseda University, Tokyo, Japan T. Takatomi, J. Urakawa KEK, Ibaraki, Japan
	Funding: Work supported by JSPS Grant-in-Aid for Scientific Research (A) 10001690 and the Quantum Beam Technology Program of MEXT. We have been developing an S-band Cs-Te photocathode rf electron gun system for pulse radiolysis and laser Compton scattering experiment at Waseda University. These researches demand for high quality and well controlled electron beam. In order to measure the ultra-short electron bunch, we decided to use rf-deflector cavity, which can convert the longitudinal distribution to that of transverse. With this technique, the longitudinal bunch profile can be obtained as the transverse profile. We used the 3D electromagnetic simulation codes HFSS for designing rf deflector cavity and GPT for beam tracking. The cavity has 2 cell structures operating on π mode, standing wave, dipole (TM120) mode at 2856MHz. We have confirmed on HFSS that 2 cell rf-deflector cavity can produce 660G magnetic field per cell on beam line with 750kW input rf power. This field strength is enough for our target, which is 100fs bunch length measurement at 4.3MeV. In this conference, we will present the cavity structure design, the present progresses and future plan.

WEPME024	Gaussian Spectrum Fiber Laser Pulses Generated in an All-normal-dispersion Cavity	2983
	Y. You, W.-H. Huang, C.-X. Tang, L.X. Yan TUB, Beijing, People's Republic of China H. Shimizu, J. Urakawa KEK, Ibaraki, Japan
	In this paper, we reported generating a broad bandwidth Gaussian shape spectrum fiber laser pulse directly in an all-normal dispersive cavity. Pulse-shaping is based on spectral filtering. The spectrum has a ~20 nm 20-dB spectrum bandwidth and it is different from the typical spectrum, of steep edge and two spikes. The Gaussian spectrum is preferred since it can be dechirped to transform-limited pulsed duration. The pulse duration corresponds to this kind of spectrum is ~315fs, and pulse energy is up to~9nJ, with a repetition rate of 18.9MHz.

Paper

Title

Page

Ultra-short Electron Bunch Generation by an ECC RF Gun

330

Y. Koshiba, T. Aoki, M. Mizugaki, K. Sakaue, M. Washio
Waseda University, Tokyo, Japan
T. Takatomi, J. Urakawa
KEK, Ibaraki, Japan

Funding: Work supported by JSPS Grant-in-Aid for Young Scientists (B) 23740203 and Scientific Research (A) 10001690
Energy Chirping Cell attached rf gun (ECC rf gun) is a photocathode rf gun specialized for ultra-short bunch generation. This ECC rf gun has been made with the collaboration of High Energy Accelerator Research Organization (KEK). Although the bunch length could be controlled by the laser pulse width, the bunch length ends up to be more than 1ps due to space charge effect when using a femto-second laser and a normal 1.6 cell cavity. Concerning this phenomenon, ECC is attached right after the 1.6 cell so that the electron bunch would be compressed after the electron bunch is accelerated around 5MeV. The roll of ECC is to chirp the energy with the linear part of the rf electric field. The electron bunch would be compressed by velocity difference as it drifts. Simulation results from PARMELA and GPT show that ECC rf gun can accelerate an 100pC bunch with the bunch length less than 100fs. We already manufactured this ECC rf gun and installed in our system. We demonstrated the ultra-short bunch by measuring the coherent THz light by synchrotron radiation and transition radiation. In this conference, we will report the results of ultra-short bunch generation experiments, and future plans.

MOPME018

BEAM OSCILLATION MONITOR FOR THE MULTI-BUNCH BEAM

506

T. Naito, S. Araki, H. Hayano, K. Kubo, S. Kuroda, T. Okugi, N. Terunuma, J. Urakawa
KEK, Ibaraki, Japan

In order to observe the motion of bunch-by-bunch beam oscillation of multi-bunch in the storage ring, we developed two measurement tools. One is a signal process electronics circuit using fast analogue switches. The circuit picks up one of the selected bunch signal of the beam position monitor from the multi-bunch. The selected beam position signal can be processed as a single bunch beam. By changing the gate timing, arbitrary bunch signal can be selected. The other is a waveform memory using a high bandwidth oscilloscope. The long waveform memory of the oscilloscope has a capability to acquire the multi-turn waveform of the button electrode signals. The beam test of the circuit has been carried out at KEK-ATF damping ring in the cases of 2.8ns bunch spacing and 5.6ns bunch spacing, respectively. The detail of the hardware and the result of the beam test are reported.

MOPWA052

Short Range Wakefield Measurements of High Resolution RF Cavity Beam Position Monitors at ATF2

792

J. Snuverink, S.T. Boogert, F.J. Cullinan, Y.I. Kim, A. Lyapin
JAI, Egham, Surrey, United Kingdom
K. Kubo, T. Okugi, T. Tauchi, N. Terunuma, J. Urakawa
KEK, Ibaraki, Japan
G.R. White
SLAC, Menlo Park, California, USA

Cavity beam position monitors (CBPM) have been used in several accelerator facilities and are planned to be used in future accelerators and light sources. High position resolution up to tens of nanometres has been achieved, but short range wakefields are a concern, especially for small beam emittances. This paper presents the wakefield calculations as well as the first measurements of the CBPM-generated short range wakefields performed at the Accelerator Test Facility (ATF2).

MOPWA053

Sub-Micrometre Resolution Laserwire Transverse Beam Size Measurement System

795

L.J. Nevay, G.A. Blair, S.T. Boogert, V. Karataev, K.O. Kruchinin
Royal Holloway, University of London, Surrey, United Kingdom
A.S. Aryshev, N. Terunuma, J. Urakawa
KEK, Ibaraki, Japan
L. Corner, R. Walczak
Oxford University, Physics Department, Oxford, Oxon, United Kingdom

Funding: The research leading to these results has received funding from the European Commission under the FP7 Research Infrastructures project Eu-CARD, grant agreement no. 227579
We present the results from the laserwire system at the Accelerator Test Facility 2 (ATF2) during recent operation after relocation to the virtual image point of the ATF2 final focus. The characterisation of the 150 mJ, 77 ps long laser pulses at a scaled virtual interaction point is used to deconvolve the transverse laserwire profile demonstrating a 1.16 ± 0.06 um vertical electron beam profile. Horizontal laserwire scans were used in combination with the vertical scans to measure the electron beam size using a full overlap integral model due to the problems presented by a large aspect ratio electron beam.

MOPWA058

Cavity Beam Position Monitor at Interaction Point Region of Accelerator Test Facility 2

807

Y.I. Kim, D.R. Bett, N. Blaskovic Kraljevic, P. Burrows, G.B. Christian, M.R. Davis, A. Lyapin
JAI, Egham, Surrey, United Kingdom
S.T. Boogert
Royal Holloway, University of London, Surrey, United Kingdom
J.C. Frisch, D.J. McCormick, J. Nelson, G.R. White
SLAC, Menlo Park, California, USA
Y. Honda, T. Tauchi, N. Terunuma, J. Urakawa
KEK, Ibaraki, Japan

Nanometre resolution cavity beam position monitors (BPMs) have been developed to measure the beam position and linked to a feedback system control the beam position stability within few nanometres in the vertical direction at the focus, or interaction point (IP), of Accelerator Test Facility 2 (ATF2). In addition, for feedback applications a lower-Q and hence faster decay time system is desirable. Two IPBPMs have been installed inside of IP chamber at the ATF2 focus area. To measure the resolution of IPBPMs two additional C-band cavity BPMs have been installed one upstream and one downstream of the IP. One cavity BPM has been installed at an upstream image point of IP. The performance of the BPMs is discussed and the correlation between IP and image point positions is presented along with a discussion of using these BPMs for position stabilisation at the IP.

TUPME045

Turn-by-turn Measurements in the KEK-ATF

1664

Y. Renier, Y. Papaphilippou, R. Tomás, M. Wendt
CERN, Geneva, Switzerland
N. Eddy
Fermilab, Batavia, USA
K. Kubo, S. Kuroda, T. Naito, T. Okugi, N. Terunuma, J. Urakawa
KEK, Ibaraki, Japan

The ATF damping ring has been upgraded with new read-out electronics for the beam position monitors (BPM), capable to acquire the beam orbits on a turn-by-turn basis, as well as in a high resolution averaging mode. The new BPM system allows to improve optic corrections and to achieve an even smaller vertical emittance (<2pm). Experimental results are presented based on turn-by-turn beam orbit measurements in the ring, for estimating the beta functions and dispersion along the lattice. A fast method to measure spectral line amplitude in a few turns is also presented, including the evaluation of chromaticity.

TUPME056

3.5 GeV Superconducting Stacking Ring for Compton Based Polarized Positrons Source of CLIC

1697

E.V. Bulyak, P. Gladkikh, A.A. Kalamayko
NSC/KIPT, Kharkov, Ukraine
T. Omori, J. Urakawa, K. Yokoya
KEK, Ibaraki, Japan
L. Rinolfi, F. Zimmermann
CERN, Geneva, Switzerland

This paper describes 3.5 GeV superconducting storage ring dedicated to positron accumulation as part of a polarized positron source for CLIC, based on Compton scattering in a Compton storage ring. The superconducting stacking ring can provide a synchrotron damping time of order 250 microseconds. Together with combined injection scheme in the longitudinal and transverse plane, such a ring may solve the problem of accumulating a positron beam with efficiency close to 95 % and with the beam intensity required for CLIC.

TUPWA050

Effect of Transverse Coupling on Asymmetric Cooling in Compton Rings

1823

E.V. Bulyak
NSC/KIPT, Kharkov, Ukraine
J. Urakawa
KEK, Ibaraki, Japan
F. Zimmermann
CERN, Geneva, Switzerland

Fast cooling of bunches circulating in a Compton ring is achieved by placing the collision point between electron bunches and laser pulses in a dispersive section and by, in addition, introducing a transverse offset between the laser pulse and the electron-beam closed orbit. Growth of the emittance in the dispersive transversal direction due to the additional excitation of betatron oscillations limits this type of cooling. Here we present the results of further studies on the fast cooling process, looking at the effect of the coupling of the transverse (betatron) oscillations. We first show theoretically that the transverse betatron coupling shortens the cooling time and hence reduces the steady-state energy spread of the electron beam, as well as the quantum losses. The theoretical estimates are then validated by simulations. Finally, a proof-of-principle experiment at the KEK ATF Damping Ring is proposed.

WEPWA017

Development of Laser-Compton X-ray Source using Optical Storage Cavity

2165

K. Sakaue, M. Washio
Waseda University, Tokyo, Japan
M.K. Fukuda, Y. Honda, N. Terunuma, J. Urakawa
KEK, Ibaraki, Japan

Funding: Work supported by the Quantum Beam Technology Program of MEXT and JSPS Grant-in-Aid for Young Scientists (B) 23740203
We have been developing a pulsed-laser storage technique in a super-cavity for a compact x-ray sources. The pulsed-laser super-cavity enables to make high peak power and small waist laser at the collision point with the electron beam. We already obtained a pulse-train x-rays through the laser-Compton scattering between a multi-bunch electron beam and an optical super-cavity. And also, we performed a X-ray imaging via laser-Compton X-ray. On these successful results, we decided to upgrade our system for increasing X-ray flux by 3-order of magnitudes for practical use. For an optical cavity, we designed 4-mirrors bow-tie cavity in order to increase the power. On the other hand, electron accelerator was also upgraded to increase the bunch number in the train. We use 3.6cells rf-gun and 12cell standing wave booster linac. As a result, 2-order increase of X-ray flux was achieved. Design of upgraded our laser-Compton X-ray source, the results of X-ray experiments and future prospective will be presented at the conference.

WEPFI023

Study on Two-cell RF-deflector Cavity for Ultra-short Electron Bunch Measurement

2753

Y. Nishimura, K. Sakaue, T. Takahashi, M. Washio
Waseda University, Tokyo, Japan
T. Takatomi, J. Urakawa
KEK, Ibaraki, Japan

Funding: Work supported by JSPS Grant-in-Aid for Scientific Research (A) 10001690 and the Quantum Beam Technology Program of MEXT.
We have been developing an S-band Cs-Te photocathode rf electron gun system for pulse radiolysis and laser Compton scattering experiment at Waseda University. These researches demand for high quality and well controlled electron beam. In order to measure the ultra-short electron bunch, we decided to use rf-deflector cavity, which can convert the longitudinal distribution to that of transverse. With this technique, the longitudinal bunch profile can be obtained as the transverse profile. We used the 3D electromagnetic simulation codes HFSS for designing rf deflector cavity and GPT for beam tracking. The cavity has 2 cell structures operating on π mode, standing wave, dipole (TM120) mode at 2856MHz. We have confirmed on HFSS that 2 cell rf-deflector cavity can produce 660G magnetic field per cell on beam line with 750kW input rf power. This field strength is enough for our target, which is 100fs bunch length measurement at 4.3MeV. In this conference, we will present the cavity structure design, the present progresses and future plan.

WEPME024

Gaussian Spectrum Fiber Laser Pulses Generated in an All-normal-dispersion Cavity

2983

Y. You, W.-H. Huang, C.-X. Tang, L.X. Yan
TUB, Beijing, People's Republic of China
H. Shimizu, J. Urakawa
KEK, Ibaraki, Japan

In this paper, we reported generating a broad bandwidth Gaussian shape spectrum fiber laser pulse directly in an all-normal dispersive cavity. Pulse-shaping is based on spectral filtering. The spectrum has a ~20 nm 20-dB spectrum bandwidth and it is different from the typical spectrum, of steep edge and two spikes. The Gaussian spectrum is preferred since it can be dechirped to transform-limited pulsed duration. The pulse duration corresponds to this kind of spectrum is ~315fs, and pulse energy is up to~9nJ, with a repetition rate of 18.9MHz.