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| TUPEC008 | Cavity Detuning Method to Compensate Beam Energy Decrement in Thermionic RF Gun due to Back-bombardment Effect | 1725 |
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Thermionic RF guns are compact, economical and high brightness electron sources. However, when the guns are used for a driver linac of oscillator-type Free Electron Lasers (FELs), which requires moderate bunch charge (several tens pico-coulomb) and long macro-pulse duration (several micro-seconds), the guns have been suffered from the back-bombardment effect*. The effect induces beam current increment in a macro-pulse. And consequently the current increment leads to decrement of beam energy during a macro-pulse and significantly limits the beam macro-pulse duration after some bending magnets. Our group found a new energy compensation scheme called as cavity detuning** and the method was introduced to compensate the beam energy decrement in the thermionic RF gun used for KU-FEL***. In this presentation, we will introduce the principle of the method and experimental results. Detailed analysis of the method will be also presented. * C.B. McKee et al., NIM, A296, pp. 716-719, 1990. |
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| WEPEA039 | Status of Top-up Operation in UVSOR-II | 2576 |
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UVSOR-II is a low emittance, 750 MeV synchrotron light source. Low emittance and low energy synchrotron light sources naturally suffered from short electron lifetime due to Touschek effect. Top-up operation is a solution for overcoming the effect. In the UVSOR-II, trials of multi-bunch top-up operation at the full energy were started from 2008. In the trials, we have succeeded in keeping the stored beam current around 300 mA for 12 hours. From this fiscal year, single bunch injection was started for single bunch user operations and for experiments on advanced light source development such as Free Electron Laser (FEL), Coherent Synchrotron Radiation (CSR), Coherent Harmonic Generation (CHG), which require single bunch or 2-bunch filling operation. We have already performed single bunch top-up operation in user time with the stored beam current of 50 mA. And FEL lasing with top-up operation was also achieved at the laser wavelength of 215 nm with the stored beam current of 130 mA / 2-bunch. In the FEL lasing experiment, we succeeded in keeping the average power of FEL around 130 mW for three hours. |
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| TUPD091 | Generation of Ultra-Short Gamma-ray Pulses by Laser Compton Scattering in an Electron Storage Ring | 2117 |
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We are developing an ultra-short gamma ray pulse source based on laser Compton scattering technology at the 750 MeV electron storage ring UVSOR-II. Ultra-short gamma ray pulses can be generated by injecting femtosecond laser pulses into the electron beam circulating in an electron storage ring from the direction perpendicular to the orbital plane. The energy, intensity, and pulse width of the gamma rays have been estimated to be 6.6 MeV, 2.4× 106 photons s-1, and 150 fs, respectively, for the case of UVSOR-II with a commercially available femtosecond laser. These parameters can be tuned by changing the incident angle of the laser to the electron beam, electron energy, and the size of the laser. A preliminary head-on collision experiment was carried out. The measured spectral shape agreed well with simulation including the detector response calculated by the EGS5 code*, which implied the generation of gamma rays by laser Compton scattering and the validity of the estimation of the gamma ray intensity in the case of 90-degree collisions. * H. Hirayama et al., SLAC-R-730, (2005). |
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| TUPE029 | Spectral Measurement of VUV CHG at UVSOR-II | 2206 |
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Light source technologies based on laser seeding are under development at the UVSOR-II electron storage ring. In the past experiments, we have succeeded in generating coherent DUV (Deep Ultra-Violet) harmonics with various polarizations. A spectrum measurement experiment of CHG (Coherent Harmonic Generation) was carried out by using a spectrometer of from visible to DUV range. In order to diagnose spectra of shorter-wavelength CHG, a spectrometer for VUV (Vacuum Ultra-Violet) has been constructed and the VUV CHG was measured. In addition, we try to use a seeding light source based on not only fundamental of Ti: Sapphire laser and the harmonics generated from non-linear crystals but also HHG (High Harmonic Generation) in a gas for the CHG experiment. Now the HHG system is under development. In this presentation, we introduce the VUV spectral measurement system and the HHG system and also report about comparison between the results of the current CHG experiments and design studies of numerical calculation for them. |
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| WEPEA039 | Status of Top-up Operation in UVSOR-II | 2576 |
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UVSOR-II is a low emittance, 750 MeV synchrotron light source. Low emittance and low energy synchrotron light sources naturally suffered from short electron lifetime due to Touschek effect. Top-up operation is a solution for overcoming the effect. In the UVSOR-II, trials of multi-bunch top-up operation at the full energy were started from 2008. In the trials, we have succeeded in keeping the stored beam current around 300 mA for 12 hours. From this fiscal year, single bunch injection was started for single bunch user operations and for experiments on advanced light source development such as Free Electron Laser (FEL), Coherent Synchrotron Radiation (CSR), Coherent Harmonic Generation (CHG), which require single bunch or 2-bunch filling operation. We have already performed single bunch top-up operation in user time with the stored beam current of 50 mA. And FEL lasing with top-up operation was also achieved at the laser wavelength of 215 nm with the stored beam current of 130 mA / 2-bunch. In the FEL lasing experiment, we succeeded in keeping the average power of FEL around 130 mW for three hours. |
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| MOPE016 | Beam Monitor System for Central Japan Synchrotron Radiation Research Facility | 993 |
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Central Japan Synchrotron Radiation Research Facility which provides synchrotron radiation for a large community of users is under construction in the Aichi prefecture, Japan. The light source accelerator complex consists of a linac, a booster synchrotron and a storage ring. We have developed beam monitor systems which play important role especially in the commissioning stage of the accelerators. An RF knockout system to observe betatron tune of the electron beam in the booster synchrotron and the storage ring has been designed. We paid special attention in an RF source fed to a shaker to realize efficient measurement of the tune of electron beam during acceleration. We made a test experiment using electron beam of a booster synchrotron of the UVSOR facility. We have also developed a BPM system which enables a single path beam monitoring. The signal processing is based on a fast digital oscilloscope and a simple preprocessor circuit which was developed to improve position resolution. The performance was evaluated using an injection beam pulse to the storage ring of the UVSOR. |
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| TUPEC029 | Comparison between Hexaboride Materials for Thermionic Cathode RF Gun | 1782 |
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RF gun has been chosen as injector for Kyoto University free electron laser because it can potentially produce an electron beam with high energy, small emittance, moreover inexpensive and compact configuration in comparison with other injectors. As for the RF gun cathode, thermionic cathode is simpler, easier to treat and reliable than photocathode. On the other hand, backbombardment electrons make cathode surface temperature and current density increase within the macropulse, as a result, beam energy and macropulse duration decrease, which means, it is difficult to generate stable FEL. The heating property of cathode not only depends on physical properties of the cathode material such as work function, but also backbombardment electrons energy. We investigated the heating property of six hexaboride materials against the backbombarding electrons by numerical calculation of the range and stopping power. In this investigation, the emission property of the cathode was also taken into account, since high electron emission is required for generation of high brightness electron beam. The results will be discussed. |
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| TUPE091 | Recent Progress in the Energy Recovery Linac Project in Japan | 2338 |
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Future synchrotron light source using a 5-GeV-class energy recovery linac (ERL) is under proposal by our Japanese collaboration team, and we are conducting active R&D efforts for that. We are developing super-brilliant DC photocathode guns, two types of cryomodules for both injector and main superconducting linacs, 1.3 GHz high CW-power rf sources, and other important components. We are also constructing a compact ERL for demonstrating the recirculation of low-emittance, high-current beams using those key components. We present our recent progress in this project. |
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| WEPEA037 | Study of the Coherent Terahertz Radiation by Laser Bunch Slicing at UVSOR-II Electron Storage Ring | 2570 |
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Terahertz (THz) coherent synchrotron radiation (CSR) is emitted not only from shorter electron bunches compared with the radiation wavelength but also from electron bunches withμstructures. Formation ofμstructures at sub picosecond scale in electron bunches by a laser slicing technique is experimentally studied through observation of THz CSR. The properties of the THz CSR such as intensity or spectrum depend strongly on the shape and amplitude of theμstructure created in the electron bunches. To study in detail the formation ofμstructure in electron bunches using the laser slicing technique, we have performed experiments at the UVSOR-II electron storage ring. THz CSR, which contains information on theμstructure, was observed under various laser conditions. The THz CSR spectrum was found to depend strongly on the intensity and the pulse width of the laser. The results agreed qualitatively with a numerical calculation. It was suggested that the evolution of theμstructure during CSR emission is important under some experimental conditions. |
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| WEPEA038 | Present Status and Upgrade Plan on Coherent Light Source Developments at UVSOR-II | 2573 |
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UVSOR, a 750 MeV synchrotron light source of 53m circumference had been operated for more than 20 years. After a major upgrade in 2003, this machine was renamed to UVSOR-II. The ring is now routinely operated with low emittance of 27 nm-rad and with four undulators. By utilizing a part of the existing FEL system and an ultra-short laser system, coherent synchrotron radiation in THz range and coherent harmonic generation in VUV range have been extensively studied under international collaborations. Based on results obtained from previous coherent light source developments, a new five-year research program on the coherent light source developments has been started from FY2008, which includes creation of a new 4-m long straight section by moving the injection point, upgrades of the undulator and the laser system and construction of dedicated beam-lines for these coherent light sources. Present status and upgrade plan on these coherent light sources at UVSOR-II will be presented at the conference. |