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... 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.
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their biological effect on a murine
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... 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.
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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... 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.
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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... 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.
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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... 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...
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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... 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...
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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,... 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...
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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... 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...
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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... 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.
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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... 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 ...
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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... 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 polarized positron source based on Compton scattering in a Compton storage ring (CR). The superconducting stacking ring (SR) can provide 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.
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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... 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.
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A nondestructive assay method of isotopes by using quasi-monochromatic gamma-rays based on laser-Compton scattering (LCS) is under development. In order to demon- strate the accelerator and the laser performance required for the gamma-ray... more
A nondestructive assay method of isotopes by using quasi-monochromatic gamma-rays based on laser-Compton scattering (LCS) is under development. In order to demon- strate the accelerator and the laser performance required for the gamma-ray source, a LCS experiment is planned at Compact ERL (cERL) at KEK. An optical cavity which can achieve high finesse and small waist size is under construc- tion for the LCS experiment. The new optical cavity com- prises two sets of planar 4-mirror cavities.
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The Compact Linear Collider (CLIC) is a TeV-scale high-luminosity linear $e^+e^−$ collider under development at CERN. Following the CLIC conceptual design published in 2012, this report provides an overview of the CLIC project, its... more
The Compact Linear Collider (CLIC) is a TeV-scale high-luminosity linear $e^+e^−$ collider under development at CERN. Following the CLIC conceptual design published in 2012, this report provides an overview of the CLIC project, its current status, and future developments. It presents the CLIC physics potential and reports on design, technology, and implementation aspects of the accelerator and the detector. For an optimal exploitation of its physics potential, CLIC is foreseen to be built and operated in stages, at centre-of-mass energies of 380 GeV, 1.5 TeV and 3 TeV, respectively, for a site length ranging from 11 km to 50 km. CLIC uses a two-beam acceleration scheme, in which normal-conducting high-gradient 12 GHz accelerating structures are powered via a high-current drive beam. For the first stage, an alternative with X-band klystron powering is also considered. CLIC accelerator optimisation, technical developments and system tests have resulted in significant progress in recen...
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The laserwire system at the Accelerator Test Facility 2 (ATF2) is a transverse beam profile measurement system capable of measuring a micrometre-size electron beam. We present recent results demonstrating a measured ver-tical size of 1.16... more
The laserwire system at the Accelerator Test Facility 2 (ATF2) is a transverse beam profile measurement system capable of measuring a micrometre-size electron beam. We present recent results demonstrating a measured ver-tical size of 1.16 ± 0.06 µm and a horizontal size of 110.1 ± 3.8 µm. Due to the high aspect ratio of the elec-tron beam, the natural divergence of the tightly focussed laser beam across the electron beam width requires the use of the full overlap integral to deconvolve the scans. For this to be done accurately, the propagation of the 150 mJ, 167 ps long laser pulses was precisely measured at a scaled virtual interaction point.
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Photocathode RF gun can generate high charge and low emittance electron beam, which is the most essential to many research projects. Among the disadvantageous effects to worsen beam emittance in the gun, space charge effect is primary in... more
Photocathode RF gun can generate high charge and low emittance electron beam, which is the most essential to many research projects. Among the disadvantageous effects to worsen beam emittance in the gun, space charge effect is primary in high charge case. Therefore much endeavour has been made to decrease this effect on LUCX facility (Laser Undulator Compact X-ray source at KEK, Japan). Firstly RF gun is tuned into unbalanced, so that the peak field gradient on the cathode surface is relatively higher than that in the full cell. A laser profile shaper and a series of optical beam line designed for it are employed to convert the driving laser from Gaussian profile into uniform profile. With the uniform driving laser and the unbalanced RF gun, the transverse emittance for 1nC electron bunch has been improved effectively from 5.46πmm.mrad to 3.66πmm.mrad.
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Compton scattering hard X-ray source for 10-40 keV are under construction using the X-band (11.424 GHz) elec- tron linear accelerator and Nd:YAG laser at Nuclear Pro- fessional School, University of Tokyo. Main advantage of this system is... more
Compton scattering hard X-ray source for 10-40 keV are under construction using the X-band (11.424 GHz) elec- tron linear accelerator and Nd:YAG laser at Nuclear Pro- fessional School, University of Tokyo. Main advantage of this system is to produce tunable monochromatic hard (10- 40 keV)X-rayswith the intensitiesof 108-109 photons/s(at several stages) and the table-top size. The X-ray yield by the electron beam and Q-switch Nd:YAG laser of 2.5 J/10 ns is 107 photons/RF-pulse (108 photons/sec in 10 pps). X-band beam line for the demonstration is under commis- sioning. At the beam generation experiment by thermionic cathode 3.5 cell X-band RF-gun, 2.0 MeV electron beam with average current 0.2 μA is observed. We also design to adopt a technique of laser pulse circulation to increase the X-ray yield up to 108 photons/pulse (109 photons/s). The laser pulse circulation experiment is performed with low energy (20 mJ/pulse)and enhancement of X-ray yield will be estimated about 10 times.
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The International Linear Collider (ILC) is a 200-500 GeV center-of-mass high-luminosity linear electron-positron collider, based on 1.3 GHz superconducting radio-frequency (SCRF) accelerating cavities. The ILC has a total footprint of... more
The International Linear Collider (ILC) is a 200-500 GeV center-of-mass high-luminosity linear electron-positron collider, based on 1.3 GHz superconducting radio-frequency (SCRF) accelerating cavities. The ILC has a total footprint of about 31 km and is designed for a peak luminosity of 2x10^ 34 cm^-2 s^-1. The complex includes a polarized electron source, an undulator-based positron source, two 6.7 km circumference damping rings, two-stage bunch compressors, two 11 km long main linacs and a 4.5 km long beam ...
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ILC (International Linear Collider) is a future project of high energy physics. In the current baseline design, positron generation by gamma rays from undulator radiation is assumed. However, this approach is totally new and it is very... more
ILC (International Linear Collider) is a future project of high energy physics. In the current baseline design, positron generation by gamma rays from undulator radiation is assumed. However, this approach is totally new and it is very difficult to demonstrate the system prior to the construction because it requires more than 100 GeV beam as the driver. A conventional positron generation (e- driven) has been proposed as a technical backup option. In this method, the technology is well established, but the issue is to obtain an enough amount of positron with a manageable energy deposition on target. We present a result of a systematic study of capture efficiency defined by DR (Damping Ring) acceptance where the beam emittance is reduced by radiation damping. We performed a start-to-end simulation of the positron source of ILC and found that an enough amount of the positron per bunch is obtained with a manageable energy deposition on the production target.
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The current ATF2 Ultra-Low beta proposal was designed to achieve 20nm vertical IP beam size without considering the multipolar components of the FD magnets. In this paper we describe different scenarios that avoid the detrimental effect... more
The current ATF2 Ultra-Low beta proposal was designed to achieve 20nm vertical IP beam size without considering the multipolar components of the FD magnets. In this paper we describe different scenarios that avoid the detrimental effect of these multipolar errors in the FD. The simplest approach consists in modifying the optics but other solutions are studied as the introduction of new higher order magnets or the replacement of the FD with SC technology. The practical aspects of such an upgrade are the tuning performance and the compatibility with existing devices and instrumentation. These are fully addressed in the paper.
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Compton sources are capable to produce intense beams of gamma-rays necessary for numerous applications, e.g. production of polarized positrons for ILC/CLIC projects, nuclear waste monitoring. These sources need high current of electron... more
Compton sources are capable to produce intense beams of gamma-rays necessary for numerous applications, e.g. production of polarized positrons for ILC/CLIC projects, nuclear waste monitoring. These sources need high current of electron beams of GeV energy. Storage rings are able to accumulate a high average current and keep it circulating for a long time. The dynamics of circulating bunches is affected by large recoils due to emission of energetic photons. We report results of both an analytical study and a simulation on the dynamics of electron bunches circulating in storage rings and interacting with the laser pulses. The steady-state transverse emittances and energy spread, and dependence of these parameters on the laser pulse power and dimensions at the collision point were derived analytically and simulated. It is shown that the transverse and longitudinal dimensions of bunches are dependent on the power of laser pulses and on their dimensions as well. Conditions of the laser c...
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A conceptual design work and a basic experimental study of a new beam profile monitor have been performed. The monitor will be used to measure emittance of an electron beam in the ATF damping ring at KEK, in which the transverse beam size... more
A conceptual design work and a basic experimental study of a new beam profile monitor have been performed. The monitor will be used to measure emittance of an electron beam in the ATF damping ring at KEK, in which the transverse beam size of about 10µm is expected. It utilizes a CW laser and an optical cavity, instead of a material wire, to minimize interference with an electron beam. A laser beam with a very thin waist is realized by employing the cavity of nearly concentric mirror configuration while the intensity is amplified by adjusting the cavity length to a Fabry-Perot resonance condition. We built a test cavity to establish a method to measure important parameters such as a laser beam waist and a power enhancement factor. Three independent methods were examined for the measurement of the beam waist. It was found that the cavity realized the beam waist of 20µm with the power enhancement factor of 50.