Junji Urakawa - Academia.edu (original) (raw)

Papers by Junji Urakawa

Optical Transition Radiation (OTR) appearing when a charged particle crosses a boundary between t... more Optical Transition Radiation (OTR) appearing when a charged particle crosses a boundary between two media with different dielectric properties has widely been used as a tool for transverse profile measurements of charged particle beams in various facilities worldwide. The resolution of the conventional monitors is defined by so-called Point Spread Function (PSF) dimension - the source distribution generated by a single electron and projected by an optical system onto a screen. In our experiment we managed to create a system which can practically measure the PSF distribution. We demonstrated that is it is non-uniform. In this paper we represent the development of a novel sub-micrometer electron beam profile monitor based on the measurements of the PSF structure. The visibility of the structure is sensitive to micrometer electron beam dimensions. In this report we shall represent the recent experimental results. The future plans on the optimization of the monitor will also be presented.

their biological effect on a murine

An X-ray source via laser-Compton scattering has the advantage of small source, energy tunability... more An X-ray source via laser-Compton scattering has the advantage of small source, energy tunability and quasi-monochromaticity and is expected to be applied in a wide range of fields such as the industry and medical care. In laser-Compton scattering, the luminosity, which represents the collision frequency between the electrons and the photons, is very important. Increasing the luminosity is strongly required for increasing the scattered photon flux. One way to increase the luminosity is tilting electron bunches at the collision point, which is called crab crossing. It is the way to create the head-on collision artificially. The purpose of this study is the proof-of-principle of the crab crossing laser-Compton scattering. In this conference, we will report the design optimization and construction of the laser system for the collision and future prospects.

The LUCX facility at KEK is used as the high brightness pre-bunched electron beam source for radi... more The LUCX facility at KEK is used as the high brightness pre-bunched electron beam source for radiation experiments. Emittance measurement and optimization is one of the important research activities for newly developed operation mode of the facility. Characterization of the pre-bunched beam (THz sequence of a hundred femtosecond bunches) properties opens a possibility to establish detailed simulation of the THz FEL radiation yield and continuously improve pre-bunched beam dynamics insight. Emittance has been measured by the Qscan method. The measurement results and possible ways of emittance optimization are discussed. The measurement results are compared with beam dynamics simulation done by self-consistent BEAMDULAC-BL code.

This paper describes a superconducting storage ring dedicated to positron accumulation as part of... more This paper describes a superconducting storage ring dedicated to positron accumulation as part of a polarized positron source based on Compton scattering in a Compton storage ring (CR). The superconducting stacking ring (SR) can provide a synchrotron damping time of order 250 μs. Together with a novel combined injection scheme in the longitudinal and transverse plane, such a ring may solve the problem of accumulating a positron beam of 4 × 10e /bunch and 312 bunches which is the beam charge required for CLIC.

International Journal of Applied Electromagnetics and Mechanics, 2002

Compact inverse Compton scattering hard X-ray source based on the X-band linac is numerically des... more Compact inverse Compton scattering hard X-ray source based on the X-band linac is numerically designed. The theoretical scaling law for emittance vs. charge / RF frequency was confirmed by the numerical analysis. The 3.5 cell RF gun with the field strength at the cathode surface 140 MV/m can produce the 2.1 MeV, 240 pC electron bunch, although the energy spread, 8% (rms), is not good. Because the generated X-ray flux is only 10 5 photons/shot in this system, we have proposed several schemes to achieve 10 11 photons/10ms based on state-of-the-art technologies.

A 1.6cell S-band photo-cathode RF-Gun is one of the good alternatives of the short pulse electron... more A 1.6cell S-band photo-cathode RF-Gun is one of the good alternatives of the short pulse electron source. Therefore, we are operating as a high brightness short pulse electron source for studying a reaction of radiation chemistry (1), an inverse Compton scattering at Waseda University (2) and as an injector at KEK-ATF. To improve an electron beam quality and reduce a dark current, our group decided to improve the RF-Gun cavity. The resonance frequency tuning of the half cell of existing RF-gun was performed by the torque control of Helicoflex seal on the cathode plate and two moving rod type tuners with a tuning hole were installed on the full cell. Newly designed RF-Gun cavity has four compact tuners on each cell, which can be tune the frequency to deform the cavity wall, to remove the Helicoflex seal and tuning holes that were considered to be the major cause of electric discharge and/or dark current source (3). According to these improvements, the Q-value and shunt impedance of t...

A new laser-wire (LW) system has been installed at the ATF extraction line at KEK, Tsukuba. The s... more A new laser-wire (LW) system has been installed at the ATF extraction line at KEK, Tsukuba. The system aims at a micron-scale laser spot size and employs a mode-locked laser system. The purpose-built interaction chamber, light delivery optics, and lens systems are described, and the first results are presented.

Proceedings of the 2005 Particle Accelerator Conference

A bunch by bunch profile monitor system using optical transition radiation (OTR) is developed for... more A bunch by bunch profile monitor system using optical transition radiation (OTR) is developed for an Accelerator Test Facility (ATF) linac. The ATF consists of a 1.5 GeV linac and a damping ring is now under constructing in KEK. The linac accelerates a multi-bunch beam (20 bunches/pulse, 2 × 10 electrons/bunch, 2.8 ns spacing between bunches). The energy spread of the multi-bunch caused by the transient beam loading is a significant problem for the injection of the damping ring. The linac has energy compensation system to compensate the energy spread of the multi-bunch. In order to measure the energy and energy spread of each bunch, we developed the monitor system. The system and the measurement result are reported. I n t r o d u c t i o n The Accelerator Test Facility (ATF) consists of a 1.5 GeV linac and a damping ring(DR) is now under constructing in KEK. The DR is designed to realize a small vertical emittance, eny = ~30 nm, for future Linear Collider. The commissioning of the A...

The International Linear Collider (ILC) is on the table now as a new global energyfrontier accele... more The International Linear Collider (ILC) is on the table now as a new global energyfrontier accelerator laboratory taking data in the 2030's. The ILC addresses key questions for our current understanding of particle physics. It is based on a proven accelerator technology. Its experiments will challenge the Standard Model of particle physics and will provide a new window to look beyond it. This document brings the story of the ILC up to date, emphasizing its strong physics motivation, its readiness for construction, and the opportunity it presents to the US and the global particle physics community.

Aim of Super-conducting Test Facility (STF) at KEK is demonstrating technologies for Internationa... more Aim of Super-conducting Test Facility (STF) at KEK is demonstrating technologies for International Linear Collider. In STF, one full RF unit will be developed and beam acceleration test will be made. In super-conducting accelerator, precise RF control in phase and power is essential because the input RF power should be balanced to beam accelerating power. To demonstrate the system feasibility, the beam accelerating test is an important step in R phase of STF and ILC. To provide ILC format beam for STF, we develop an electron source based on photo-cathode L-band RF gun. To generate ILC format beam, we developed a laser system based on Yb fiber oscillator in 40.6 MHz. The pulse repetition is decreased by picking pulses in 2.7 MHz, which meets ILC bunch spacing, 364 ns. The pulse is then amplified by YLF laser up to 8 uJ per pulse in 1 mm. The light is converted to 266 nm by SHG and FHG. Finally, 1.5 uJ per pulse is obtained and 3.2 nC bunch charge will be made. We report the basic per...

In this paper, we describe a system design and current status of Shintake beam size monitor. Shin... more In this paper, we describe a system design and current status of Shintake beam size monitor. Shintake monitor is a laser-based beam diagnostics tool, which provides a non-invasive measurement of transverse beam sizes. The interaction target probing the electron beam is interference fringes build up by the two coherent lasers that have narrow bandwidth and long coherent length. A scale of the target structure corresponds to approximately one fourth of the laser wave length, and the smallest measurable size reaches down to several tens of nanometers. The monitor we described here is installed at the virtual interaction point of the ATF2 beam line, which is built to confirm the proposed final focus system for Future Linear Colliders. We adopt second harmonics of Nd:YAG laser of 532 nm wavelength, and phase stabilization feedback system to allow to measure the designed beam size of about 37 nm. To widen a measurable range up to about 5 microns (wire scanner's range), we also prepare...

In this paper, we investigate a corrugated mm-scale capillary as a compact accelerating structure... more In this paper, we investigate a corrugated mm-scale capillary as a compact accelerating structure in a drive – witness acceleration scheme, and suggest a methodology to measure acceleration of a witness bunch. Two typical measurements and the energy gain in a witness bunch as a function of the distance between bunches are discussed. A corrugated capillary is considered as an accelerator/decelerator with an adjustable wakefield pattern depending on a transverse beam position.

We have been developing a pulsed-laser storage technique in a super-cavity for a compact x-ray so... more 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 obtaineda pulse-train x-rays throughthe 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 bowtie 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 ...

The motivation for developing a linac-based THz source at KEK LUCX is coming from the growing int... more The motivation for developing a linac-based THz source at KEK LUCX is coming from the growing interest to THz radiation and a possibility to utilize it for soft X-ray production via inverse Compton scattering. We have proposed two approaches to produce the intense radiation beams in the range of 0.1-5 THz based on Coherent Smith-Purcell Radiation and Coherent Undulator Radiation in “super-radiant” regime on a 8 MeV and 30 MeV electron beam at KEK LUCX facility respectively. First radiation type is generated when a charged particle moves in the vicinity of a periodical pattern or grating. When radiation wavelength is comparable to or longer than the bunch length it becomes coherent. Similar radiation enhancement is happening when micro-bunch period coincided with undulator period. To produce such a microbunch train of electrons a new Ti:Sa laser system for LUCX RF gun has been developed and electron micro-train has been confirmed. In this report the status of the experiment, Ti:Sa la...

This paperdescribes a superconductingstorage ring dedicated to positron accumulation as part of a... more This paperdescribes a superconductingstorage ring dedicated to positron accumulation as part of a polarized positron source based on Compton scattering in a Compton storage ring (CR). The superconducting stacking ring (SR) can provide a synchrotron damping time of order 100 μs. Together with a novel combined injection scheme in the longitudinaland transverseplane, such a ring maysolve the problem of accumulating a positron beam with the beam intensity required for CLIC.

Accelerator and laser technologies required for laser Compton scattering (LCS) photon source base... more Accelerator and laser technologies required for laser Compton scattering (LCS) photon source based on an energy-recovery linac (ERL) have been developed at the Compact ERL (cERL) facility. A high-flux, energy tunable, and monochromatic photon source such as the ERL-based LCS photon source is necessary for nondestructive assay of nuclear materials. For the demonstration of the ERL-based LCS photon generation, a laser enhancement cavity was installed at the recirculation loop of the cERL. The electron beam energy, the laser wavelength, and the collision angle are 20 MeV, 1064 nm, and 18 deg., respectively. The calculated maximum energy of the LCS photons is about 7 keV. A silicon drift detector (SDD) with active area of 17 mm placed 16.6 m from the collision point was used for observation of the LCS photons. As a result of the measurement, the flux on the detector, central energy, and energy width of the LCS photons were obtained as 1200 /s, 6.91 keV, and 81 eV, respectively.

Optical Transition Radiation (OTR) appearing when a charged particle crosses a boundary between t... more Optical Transition Radiation (OTR) appearing when a charged particle crosses a boundary between two media with different dielectric properties has widely been used as a tool for transverse profile measurements of charged particle beams in various facilities worldwide. The resolution of the conventional monitors is defined by so-called Point Spread Function (PSF) dimension - the source distribution generated by a single electron and projected by an optical system onto a screen. In our experiment we managed to create a system which can practically measure the PSF distribution. We demonstrated that is it is non-uniform. In this paper we represent the development of a novel sub-micrometer electron beam profile monitor based on the measurements of the PSF structure. The visibility of the structure is sensitive to micrometer electron beam dimensions. In this report we shall represent the recent experimental results. The future plans on the optimization of the monitor will also be presented.

their biological effect on a murine

An X-ray source via laser-Compton scattering has the advantage of small source, energy tunability... more An X-ray source via laser-Compton scattering has the advantage of small source, energy tunability and quasi-monochromaticity and is expected to be applied in a wide range of fields such as the industry and medical care. In laser-Compton scattering, the luminosity, which represents the collision frequency between the electrons and the photons, is very important. Increasing the luminosity is strongly required for increasing the scattered photon flux. One way to increase the luminosity is tilting electron bunches at the collision point, which is called crab crossing. It is the way to create the head-on collision artificially. The purpose of this study is the proof-of-principle of the crab crossing laser-Compton scattering. In this conference, we will report the design optimization and construction of the laser system for the collision and future prospects.

The LUCX facility at KEK is used as the high brightness pre-bunched electron beam source for radi... more The LUCX facility at KEK is used as the high brightness pre-bunched electron beam source for radiation experiments. Emittance measurement and optimization is one of the important research activities for newly developed operation mode of the facility. Characterization of the pre-bunched beam (THz sequence of a hundred femtosecond bunches) properties opens a possibility to establish detailed simulation of the THz FEL radiation yield and continuously improve pre-bunched beam dynamics insight. Emittance has been measured by the Qscan method. The measurement results and possible ways of emittance optimization are discussed. The measurement results are compared with beam dynamics simulation done by self-consistent BEAMDULAC-BL code.

This paper describes a superconducting storage ring dedicated to positron accumulation as part of... more This paper describes a superconducting storage ring dedicated to positron accumulation as part of a polarized positron source based on Compton scattering in a Compton storage ring (CR). The superconducting stacking ring (SR) can provide a synchrotron damping time of order 250 μs. Together with a novel combined injection scheme in the longitudinal and transverse plane, such a ring may solve the problem of accumulating a positron beam of 4 × 10e /bunch and 312 bunches which is the beam charge required for CLIC.

International Journal of Applied Electromagnetics and Mechanics, 2002

Compact inverse Compton scattering hard X-ray source based on the X-band linac is numerically des... more Compact inverse Compton scattering hard X-ray source based on the X-band linac is numerically designed. The theoretical scaling law for emittance vs. charge / RF frequency was confirmed by the numerical analysis. The 3.5 cell RF gun with the field strength at the cathode surface 140 MV/m can produce the 2.1 MeV, 240 pC electron bunch, although the energy spread, 8% (rms), is not good. Because the generated X-ray flux is only 10 5 photons/shot in this system, we have proposed several schemes to achieve 10 11 photons/10ms based on state-of-the-art technologies.

A 1.6cell S-band photo-cathode RF-Gun is one of the good alternatives of the short pulse electron... more A 1.6cell S-band photo-cathode RF-Gun is one of the good alternatives of the short pulse electron source. Therefore, we are operating as a high brightness short pulse electron source for studying a reaction of radiation chemistry (1), an inverse Compton scattering at Waseda University (2) and as an injector at KEK-ATF. To improve an electron beam quality and reduce a dark current, our group decided to improve the RF-Gun cavity. The resonance frequency tuning of the half cell of existing RF-gun was performed by the torque control of Helicoflex seal on the cathode plate and two moving rod type tuners with a tuning hole were installed on the full cell. Newly designed RF-Gun cavity has four compact tuners on each cell, which can be tune the frequency to deform the cavity wall, to remove the Helicoflex seal and tuning holes that were considered to be the major cause of electric discharge and/or dark current source (3). According to these improvements, the Q-value and shunt impedance of t...

A new laser-wire (LW) system has been installed at the ATF extraction line at KEK, Tsukuba. The s... more A new laser-wire (LW) system has been installed at the ATF extraction line at KEK, Tsukuba. The system aims at a micron-scale laser spot size and employs a mode-locked laser system. The purpose-built interaction chamber, light delivery optics, and lens systems are described, and the first results are presented.

Proceedings of the 2005 Particle Accelerator Conference

A bunch by bunch profile monitor system using optical transition radiation (OTR) is developed for... more A bunch by bunch profile monitor system using optical transition radiation (OTR) is developed for an Accelerator Test Facility (ATF) linac. The ATF consists of a 1.5 GeV linac and a damping ring is now under constructing in KEK. The linac accelerates a multi-bunch beam (20 bunches/pulse, 2 × 10 electrons/bunch, 2.8 ns spacing between bunches). The energy spread of the multi-bunch caused by the transient beam loading is a significant problem for the injection of the damping ring. The linac has energy compensation system to compensate the energy spread of the multi-bunch. In order to measure the energy and energy spread of each bunch, we developed the monitor system. The system and the measurement result are reported. I n t r o d u c t i o n The Accelerator Test Facility (ATF) consists of a 1.5 GeV linac and a damping ring(DR) is now under constructing in KEK. The DR is designed to realize a small vertical emittance, eny = ~30 nm, for future Linear Collider. The commissioning of the A...

The International Linear Collider (ILC) is on the table now as a new global energyfrontier accele... more The International Linear Collider (ILC) is on the table now as a new global energyfrontier accelerator laboratory taking data in the 2030's. The ILC addresses key questions for our current understanding of particle physics. It is based on a proven accelerator technology. Its experiments will challenge the Standard Model of particle physics and will provide a new window to look beyond it. This document brings the story of the ILC up to date, emphasizing its strong physics motivation, its readiness for construction, and the opportunity it presents to the US and the global particle physics community.

Aim of Super-conducting Test Facility (STF) at KEK is demonstrating technologies for Internationa... more Aim of Super-conducting Test Facility (STF) at KEK is demonstrating technologies for International Linear Collider. In STF, one full RF unit will be developed and beam acceleration test will be made. In super-conducting accelerator, precise RF control in phase and power is essential because the input RF power should be balanced to beam accelerating power. To demonstrate the system feasibility, the beam accelerating test is an important step in R phase of STF and ILC. To provide ILC format beam for STF, we develop an electron source based on photo-cathode L-band RF gun. To generate ILC format beam, we developed a laser system based on Yb fiber oscillator in 40.6 MHz. The pulse repetition is decreased by picking pulses in 2.7 MHz, which meets ILC bunch spacing, 364 ns. The pulse is then amplified by YLF laser up to 8 uJ per pulse in 1 mm. The light is converted to 266 nm by SHG and FHG. Finally, 1.5 uJ per pulse is obtained and 3.2 nC bunch charge will be made. We report the basic per...

In this paper, we describe a system design and current status of Shintake beam size monitor. Shin... more In this paper, we describe a system design and current status of Shintake beam size monitor. Shintake monitor is a laser-based beam diagnostics tool, which provides a non-invasive measurement of transverse beam sizes. The interaction target probing the electron beam is interference fringes build up by the two coherent lasers that have narrow bandwidth and long coherent length. A scale of the target structure corresponds to approximately one fourth of the laser wave length, and the smallest measurable size reaches down to several tens of nanometers. The monitor we described here is installed at the virtual interaction point of the ATF2 beam line, which is built to confirm the proposed final focus system for Future Linear Colliders. We adopt second harmonics of Nd:YAG laser of 532 nm wavelength, and phase stabilization feedback system to allow to measure the designed beam size of about 37 nm. To widen a measurable range up to about 5 microns (wire scanner's range), we also prepare...

In this paper, we investigate a corrugated mm-scale capillary as a compact accelerating structure... more In this paper, we investigate a corrugated mm-scale capillary as a compact accelerating structure in a drive – witness acceleration scheme, and suggest a methodology to measure acceleration of a witness bunch. Two typical measurements and the energy gain in a witness bunch as a function of the distance between bunches are discussed. A corrugated capillary is considered as an accelerator/decelerator with an adjustable wakefield pattern depending on a transverse beam position.

We have been developing a pulsed-laser storage technique in a super-cavity for a compact x-ray so... more 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 obtaineda pulse-train x-rays throughthe 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 bowtie 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 ...

The motivation for developing a linac-based THz source at KEK LUCX is coming from the growing int... more The motivation for developing a linac-based THz source at KEK LUCX is coming from the growing interest to THz radiation and a possibility to utilize it for soft X-ray production via inverse Compton scattering. We have proposed two approaches to produce the intense radiation beams in the range of 0.1-5 THz based on Coherent Smith-Purcell Radiation and Coherent Undulator Radiation in “super-radiant” regime on a 8 MeV and 30 MeV electron beam at KEK LUCX facility respectively. First radiation type is generated when a charged particle moves in the vicinity of a periodical pattern or grating. When radiation wavelength is comparable to or longer than the bunch length it becomes coherent. Similar radiation enhancement is happening when micro-bunch period coincided with undulator period. To produce such a microbunch train of electrons a new Ti:Sa laser system for LUCX RF gun has been developed and electron micro-train has been confirmed. In this report the status of the experiment, Ti:Sa la...

This paperdescribes a superconductingstorage ring dedicated to positron accumulation as part of a... more This paperdescribes a superconductingstorage ring dedicated to positron accumulation as part of a polarized positron source based on Compton scattering in a Compton storage ring (CR). The superconducting stacking ring (SR) can provide a synchrotron damping time of order 100 μs. Together with a novel combined injection scheme in the longitudinaland transverseplane, such a ring maysolve the problem of accumulating a positron beam with the beam intensity required for CLIC.

Accelerator and laser technologies required for laser Compton scattering (LCS) photon source base... more Accelerator and laser technologies required for laser Compton scattering (LCS) photon source based on an energy-recovery linac (ERL) have been developed at the Compact ERL (cERL) facility. A high-flux, energy tunable, and monochromatic photon source such as the ERL-based LCS photon source is necessary for nondestructive assay of nuclear materials. For the demonstration of the ERL-based LCS photon generation, a laser enhancement cavity was installed at the recirculation loop of the cERL. The electron beam energy, the laser wavelength, and the collision angle are 20 MeV, 1064 nm, and 18 deg., respectively. The calculated maximum energy of the LCS photons is about 7 keV. A silicon drift detector (SDD) with active area of 17 mm placed 16.6 m from the collision point was used for observation of the LCS photons. As a result of the measurement, the flux on the detector, central energy, and energy width of the LCS photons were obtained as 1200 /s, 6.91 keV, and 81 eV, respectively.