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Choi, J.

Paper Title Page
MOPAN060 Compensation of BPM Chamber Motion in PLS Orbit Feedback System 290
  • H.-S. Kang, J. Choi, K. M. Ha, E.-H. Lee, W. W. Lee, I. S. Park
    PAL, Pohang, Kyungbuk
  The false BPM reading resulting from the BPM vacuum chamber motion due to thermal load change by synchrotron radiation is compensated by the real-time monitoring of the chamber position in the PLS orbit feedback system. The BPM chamber moves up to 20 μm during the beam refill and the chamber motion has a time constant of about one and half hour, which is related to thermal equilibrium of the vacuum chamber. To monitor the BPM chamber motion, LVDTs with 0.2 μm reading accuracy were installed on all BPM chambers, and the measured data are used in the orbit feedback every 1 minute. In this paper, we will describe how serious the BPM chamber motion are and how well it is compensated.  
MOPAN061 Compact Output Filter for Switching Frequency Elimination at the PLC Linac New Magnet Power Supply 293
  • S.-C. Kim, J. Choi, K. M. Ha, J. Y. Huang
    PAL, Pohang, Kyungbuk
  Funding: This work is supported by the Ministry of Science and Technology, Korea.

At 2006, PLS Linac magnet power supply (MPS) has been upgraded for the stable beam injection and 4th generation light source research. New MPS are developed new compact MPS of 16-bit resolution and 20ppm stability using four-quadrant switching scheme with 50kHz MOSFET switching device, and consists of main power board, control power board, regulator board and CPU board. Size of each board is only 100mm width and 240mm depth. Output of MPS is 10V, ±10A for the bipolar and 50V, 50A for the unipolar magnet. Main board is consisted four-quadrant FET switch, driver and output filter. Output filter must be perfectly eliminating switch frequency and compact size. In this paper, we report on development and characteristics of compact output filter of the new MPS for PAL linac.

MOPAS037 New Generation Digital Longitudinal Feedback System for Duke FEL and HIGS Facilities 518
  • Y. Kim, M. D. Busch, P. Wang, W. Wu, Y. K. Wu
    FEL/Duke University, Durham, North Carolina
  • J. Choi, I. S. Ko, I. S. Park
    PAL, Pohang, Kyungbuk
  • D. Teytelman
    Dimtel, Redwood City, California
  To increase intensity of the High Intensity Gamma-ray Source (HIGS) which is driven by the Duke storage ring FEL via Compton scattering, stored beam current should be increased. However, high-current multi-bunch operation in the Duke storage ring is limited by strong longitudinal coupled-bunch beam instabilities. To control those instabilities, we have been developing an active longitudinal feedback system which is based on the Integrated Gigasample Processor (iGP) through collaboration with Dimtel, Inc. and Pohang Accelerator Laboratory. In this paper, we report the present status of our longitudinal feedback system.  
WEPMN060 Fabrication of ICHIRO Nine-cell Cavities in PAL for STF of KEK 2173
  • I. S. Park, J. Choi, C. W. Chung, M.-S. Hong, W. H. Hwang, D. T. Kim, Y. C. Kim, I. S. Ko, H. C. Kwon, Y. U. Sohn
    PAL, Pohang, Kyungbuk
  • S. W. Kim, S. H. Kim, S. K. Song
    RIST, Pohang
  Funding: Korea Ministry of Science & Technology

Pohang Accelerator Laboratory has studied SRF cavity and set up SRF test laboratory from January 2006. The first activity for SRF research was to develop SRF 3rd harmonic cavity for Pohang Light Source, which was designed, fabricated and tested in 2006. The cryostat are under design. The fabrication of ICHIRO cavity, which is ILC ACD cavity, is PAL's second activity related to SRF. Deep drawing, trimming and welding by electron beam for a 9-cell ICHIRO cavity were done in PAL. The polishing processes for the RF surface including electropolishing were done in KEK under the collaboration between two institutes. This will be tested with real beam in STF-1 of KEK in second half period of 2007. This paper reports the results of fabrication of ICHIRO single- and nine-cell cavities performed in PAL.

WEPMN062 HOM Analysis and Design of its Removal System for SRF 3rd Harmonic RF Cavity in PLS 2179
  • Y. U. Sohn, J. Choi, M.-H. Chun, J. Y. Huang, I. S. Ko, I. S. Park
    PAL, Pohang, Kyungbuk
  Funding: Korea Ministry of Science & Technology

Pohang Accelerator Laboratory has prepared to SRF 3rd harmonic cavity to increase beam lifetime and to damp orbit instability by lengthening electron bunch in PLS. The SRF cavity was developed and its vertical test was done already with success. Higher order modes were analyzed to optimize its performance in beam orbit. Most of them are not effective to electron beam, while the others have possibility to impact orbit stability. These harmful HOMs can be removed by HOM absorber installed in beam pipe. This paper reports the HOM analysis and design of its removal system.