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Title |
Page |
| THPCH092 |
Single-loop Two-dimensional Transverse Feedback for Photon Factory
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3006 |
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- T. Nakamura, K. Kobayashi
JASRI/SPring-8, Hyogo-ken
- W.X. Cheng, T. Honda, M. Izawa, T. Obina, M. Tadano
KEK, Ibaraki
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We installed a 500MS/s single-loop two-dimensional transverse bunch-by-bunch feedback system in the Photon Factory ring at KEK and the system is in operation at its user mode. The system composed of a single feedback loop; one skewed pair of BPM electrodes and one kicker stripline at skewed position to detect position and kick horizontally and vertically with a single signal line, and a SPring-8 feedback processor. Consequently, this system is easy to tune and cost effective. SPring-8 feedback processor employs FPGA that has enough computing power for processing more than 20-tap FIR filter required for newly developed two-dimensional feedback signal processing. We report the principle of the system, the result of test and the experience.
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| THPCH093 |
Bunch-by-bunch Feedback for the Photon Factory Storage Ring
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3009 |
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- W.X. Cheng, T. Honda, M. Izawa, T. Obina, M.T. Tadano, M. Tobiyama
KEK, Ibaraki
- K. Kobayashi, T. Nakamura
JASRI/SPring-8, Hyogo-ken
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After the straight-section upgrade in 2005, the PF (Photon Factory) ring will start the top-up operation or the continuous mode in 2006. Previously the octupole magnets were used to suppress the transverse coupled bunch instability and RF modulation method to enhance the bunch length has been effectively used to suppress the longitudinal instabilities. However, such kind of methods are not suitable for the top-up operation, we are preparing active bunch-by-bunch feedback systems for both transverse and longitudinal plane. The transverse feedback system has been installed along with the straight-section upgrade, this system uses a FPGA based feedback processor board developed at the SPring-8, both horizontal and vertical signals are processed in a single control loop. For the longitudinal feedback, a two-port DAFNE type wide-band cavity has been designed and is now manufacturing, a digital signal processing part is under design, the whole system will start commissioning in autumn 2006.
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| WEPLS028 |
Improvement of Electron Generation from a Laser Plasma Cathode through Modified Preplasma Conditions Using an Artificial Prepulse
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2448 |
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- K. Kinoshita, T. Hosokai, K. Kobayashi, A. Maekawa, T. Ohkubo, T. Tsujii, M. Uesaka
UTNL, Ibaraki
- A. Yamazaki
KURRI, Osaka
- A.G. Zhidkov
NIRS, Chiba-shi
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We have been studying the effects of laser prepulses, plasma cavity formation, wave breaking processes in the laser plasma acceleration. It is important to control the preplasma conditions, so as to stabilize the laser plasma acceleration. The modification of the conditions of the laser plasma interaction through an artificial prepulse, magnetic fields, and/or gas density modulation will affect on the characteristics of accelerated electron beams. As the first step, we carry out experiments with an artificial prepulse. If a shockwave driven by the artificial prepulse matches the main pulse foccal position, localized wave breaking may occur effectively, and consequent electron generation will be enhanced. We use a pulse with 10% energy of the main pulse and 300 ps duration to be focused on the interaction point of the gas jet, to change the plasma distribution there. Using the single-shot diagnosis, we investigate the mechanism and technique to improve the properties of electron beams. We observed a strong correlation between the generation of monoenergetic electrons and optical guiding of the main pulse, during the interaction of 11 TW 37 fs laser pulse and He gas jet.
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| WEPLS029 |
Monoenergetic 200fs (FWHM) Electron Bunch Measurement from the Laser Plasma Cathode
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2451 |
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- A. Maekawa, T. Hosokai, K. Kinoshita, K. Kobayashi, T. Ohkubo, T. Tsujii, M. Uesaka
UTNL, Ibaraki
- Y. Kondo, Y. Shibata
Tohoku University, Sendai
- T. Takahashi, A. Yamazaki
KURRI, Osaka
- A.G. Zhidkov
NIRS, Chiba-shi
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A laser plasma accelerator is the most promising approach to compact accelerators that can generate femtosecond electron bunches. It is expected that the electron bunch duration less than 100fs can be achieved owing to the high frequency of plasma waves. Since the time-resolution of the fastest streak camera is only 200fs, we have to use the coherent transition radiation (CTR) measurement or E/O (electro-optical) method. We plan to perform a single-shot measurement by getting the whole CTR spectrum by a IR polychromator in near future. As the first step forward it, we used a IR bolometer with different filters and obtained the average spectrum. We can generate monoenergetic electron bunches in the condition of laser intensity 3x1019W/cm2 and electron density 6x1019cm-3. The charge is estimated to be about 10pC using ICT (Integrated Current Transformer). The electron bunch accelerated by plasma waves penetrates 300um Ti-foil, and transition radiation is emitted. We measure CTR spectrum using a bolometer. Spectrum distribution of CTR depends on the electron bunch distribution, therefore we can evaluate the bunch duration from it. In the experiment, bunch duration can be estimated.
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| THPCH097 |
Commissioning of the Digital Transverse Bunch-by-bunch Feedback System for the TLS
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3020 |
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- K.H. Hu, J. Chen, P.J. Chou, K.-T. Hsu, S.Y. Hsu, C.H. Kuo, D. Lee, C.-J. Wang
NSRRC, Hsinchu
- A. Chao
SLAC, Menlo Park, California
- K. Kobayashi, T. Nakamura
JASRI/SPring-8, Hyogo-ken
- W.-T. Weng
BNL, Upton, Long Island, New York
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Multi-bunch instabilities degrade the beam quality leading to increased beam emittance, energy spread or even to beam loss. The feedback system is used to suppress multi-bunch instabilities due to resistive wall of the beam ducts, cavity-like structures and trapped ions. A new digital transverse bunch-by-bunch feedback system was commissioned at the Taiwan Light Source recently, and has replaced the previous analog system. The new system has the advantages that it enlarges the tune acceptance compared with the old system, enhances damping for transverse instability at high current, and as a result, top-up operation was achieved. In this new system, a single feedback loop simultaneously suppresses both the horizontal and vertical multi-bunch instabilities. The feedback system employs the latest generation FPGA feedback processor to process bunch signals. Memory installed to capture up to 250 msec bunch oscillation signal has included the considerations for system diagnostic and should be able to support various beam physics study.
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| THPCH098 |
FPGA-based Longitudinal Bunch-by-bunch Feedback System for TLS
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3023 |
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- C.H. Kuo, J. Chen, P.J. Chou, K.-T. Hsu, S.Y. Hsu, K.H. Hu, W.K. Lau, D. Lee, C.-J. Wang, M.-H. Wang, M.-S. Yeh
NSRRC, Hsinchu
- M. Dehler
PSI, Villigen
- K. Kobayashi, T. Nakamura
JASRI/SPring-8, Hyogo-ken
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A FPGA Based Longitudinal Bunch-by-Bunch Feedback System for TLS is commissioning recently to suppress strong longitudinal oscillation. The system consists of pickup, Bunch oscillation detector, FPGA based feedback processor borrow form the design of Spring8. Modulator converts the correction signal to the carrier frequency and longitudinal kicker which was re-designed form SLS' and working at 1374 MHz. The feedback processor is based upon latest generation FPGA feedback processor to process bunch signals. The memory capture is up to 250 msec bunch oscillation signal. The software and hardware design are also included for system diagnostic and support various beam physics study. Preliminary commission result will be summaried in this report.
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