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Chung, C. W.

Paper Title Page
TUPMA057 Physics Design of PAL-XFEL Undulator 190
 
  • D. E. Kim, C. W. Chung, J.-S. Oh, K.-H. Park
    PAL, Pohang, Kyungbuk
  • I. S. Ko
    POSTECH, Pohang, Kyungbuk
  
  Pohang Accelerator Laboratory(PAL) is planning a 0.3 nm – 0.45 nm SASE (Self Amplification of Spontaneous Emission) XFEL based on 3.7 GeV linear accelerator. It is targeting utilization of 0.1 nm X-ray radiation using the 3rd harmonic FEL radiation. With 3.7 GeV electron beam energy, achieving 0.3 nm fundamental FEL lazing is very challenging and it requires very low emittance electron beam with minimum energy spread. It also requires small period undulator with very small gap. In this context, application of SPring8 type in vacuum undulator is seriously considered. This reflects the experiences from SPring8 SCSS project. In this report, the physics design efforts of the undulator is described. The periodic parts are optimized to achieve the highest field with other requirements. The end structures were designed to be asymmetric along the beam direction to ensure systematic zero 1st field integral. The thickness of the last magnets were adjusted to minimize the transition distance to the fully developed periodic field. The final design features 4 mm minimum pole gap, 15 mm period, peak effective field of 1.09 Tesla.  
THPMA024 Implementation of High Precision Magnet Power Supply using the DSP 666
 
  • K.-H. Park, J. Choi, C. W. Chung, S.-H. Jeong, D. E. Kim
    PAL, Pohang, Kyungbuk
  • B.-K. Kang
    POSTECH, Pohang, Kyungbuk
  
  This paper presents the precision magnet power supply for the Pohang Light Source using the digitally controlled PWM method. The required current to energize the some magnets was 600 A with the high precision of ~10ppm at least to accomplish a high stable beam operation. This power supply has been implemented using a digital signal processor, TMS320F28 series from Texas Instruments, with high speed external 16-bit ADCs. The designed digital controller includes both a current feedback loop and a DC link voltage feed-forward loop, which was applied by the PI control scheme. To reduce the output current ripple, the damped L-C filter was fabricated at both the DC link and load sides. Various experimental results such as stability, bandwidth and harmonic analysis, as well as simulation are given to verify the characteristics of the DSP based magnet power supply.  
THPMA067 Stability Analysis of a Klystron-Modulator for PAL XFEL 729
 
  • J.-S. Oh, C. W. Chung, S. D. Jang, S. J. Kwon, Y. G. Son, J.-H. Suh
    PAL, Pohang, Kyungbuk
  • I. S. Ko, W. Namkung
    POSTECH, Pohang, Kyungbuk
  
  The PAL (Pohang Accelerator Laboratory) is persuading to construct a SASE-XFEL facility (PAL XFEL). The stable electron beam is essential for the single-pass free electron laser facility. The beam stability is governed by an accelerating RF field, of which fluctuation is mainly caused by the modulation of klystron voltage pulses. Therefore, it is directly determined by the charging stability of a modulator that uses an inverter charging system. The stable charging power supply can be realized by a stable probing and correct manipulating of a charging signal, a fine control of charging current, low noise environment, etc. This paper shows the detail analysis of the stability dependency of a klystron-modulator on the related parameters.  
THPMA076 Development of the Klystron Modulator using a High-voltage Inverter Power Supply 743
 
  • Y. G. Son, C. W. Chung, D. E. Kim, S. J. Kwon, J.-S. Oh
    PAL, Pohang, Kyungbuk
  
  The existing klystron modulator in the Linac use a 60 Hz high voltage power supply and adopt traditional L-C resonant charging scheme with De-Qing circuit. The stability of the output high voltage is not satisfactory especially when the AC line voltage fluctuations. If an inverter power supply is used as a HV generator, it will just meet the demands A high frequency inverter switching makes the overall system size small. The command-charging feature can guarantee the high reliability of switching function. In order to increase the stability, operating reliability and comply with the PLC (programming logic controller) and touch screen control system of PLS, an upgrading works is now in progress. This paper will discuss some inverter power supply design considerations and show the test results.  
THPMA117 Design and Fabrication of Arups U6 Undulator at PLS 806
 
  • H.-G. Lee, C. W. Chung, H. S. Han, Y. G. Jung, D. E. Kim, W. W. Lee, K.-H. Park, H. S. Suh
    PAL, Pohang, Kyungbuk
  
  Pohang Accelerator Laboratory(PAL) had developed and installed an U6 undulator recently to utilize brilliant undulator radiation for ARUPS (Angle Resolved Ultraviolet Photoemission) beamline at Pohang Light Source (PLS). The U6 is a hybrid type device with period of 6 cm, minimum gap of 18 mm, maximum flux density of 0.85 Tesla and total magnetic structure length of 1830 mm. The support locations and structure of an insertion device are optimized to achieve a minimum deflection due to the magnetic loads. A Finite Element Analysis (FEA) is performed to find out the amount of maximum deflection and optimal support positions on the backing beam. The optimized maximu deflection is estimated to be about 11.6 ?, while the deflection before any optimization is 48.8 ?. In this report, all the mechanical design, fabrication and assembly details of the PLS U6 undulator are described.