Author: Du, B.
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MOPMY016 Quadrature Directional Coupling Method for Precise RF Power Measurement 549
SUPSS096   use link to see paper's listing under its alternate paper code  
  • B. Du, G. Huang, L. Lin, Y.T. Liu, Z. Zhao
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  The directional coupler is used in the RF transmission and distribution system of accelerator, to measure the forward and backward power. Due to the finite directional isolation of the coupler (20-30dB normally), the crosstalk exists between the bi-directional coupling output signals. For the typical isolation of 26dB, if the bi-directional crosstalk signals are in- or anti- phase, the error of input or reflected power measurement is 10% in case of total reflection, whilst the error of reflected power measurement is 100% in case of VSWR 1.1. A method of quadrature directional coupling measurement is developed to solve the isolation problem. A pair of directional couplers with 90° phase difference are employed to measure the RF power. The influence of the directional crosstalk would be reduced significantly by processing the measurement data. The prototype of quadrature directional couplers is constructed to verify this method. The results showed that the measurement accuracy of quadrature coupler pair after data process is better than 2% for forward measurement, even if the error of single coupler is over 6%. The paper also analyses the error caused by non-ideal quadrature.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMY016  
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TUPMB011 Calculation and Analysis of the Magnetic Field of a Transverse Gradient Undulator 1130
  • J. Li, B. Du, Q.K. Jia, H.T. Li
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  Transverse gradient undulator (TGU) is attracting more and more attentions, especially for the rapid progress of laser plasma accelerator techniques. The transverse gradient of TGU is usually given by an empirical formula simply derived from the empirical formula of a uniform-parameter undulator. In this paper, we numerically investigate the transverse magnetic field of TGUs using the RADIA code. Through many simulations for TGUs with different magnet structures, we have given the dependences of transverse gradient parameter on the cant angle, the undulator period and the average gap. Based on these results, when the cant angle is small and the rate of the gap and period is in the range of 0.4-0.6, the simulation results agree with the empirical formula well. But, with the growing of the cant angle, or with the growing of the deviation of the rate of the gap and period from the range of 0.4-0.6, the difference between the simulation results and the empirical formula becomes larger.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMB011  
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WEPOY001 First Field Integral Measurement Campaign for Air Coil 2991
  • Z. Zhao, B. Du, Q.K. Jia
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • S. Karabekyan, J. Pflüger, M. Yakopov
    XFEL. EU, Hamburg, Germany
  For the operation of the air coils, which are needed for the undulator segments of the European x-ray free-electron laser (E-XFEL), precise conversion constants are needed to properly convert excitation current to steering strength. This paper describes the measurement of all 200 air coils, needed for this purpose using the short moving wire (MW) system. A LabView program was developed to measure the distribution of first field integral of both vertical (By) and horizontal (Bz) magnetic field components in the median plane of an air coil automatically. The program is an adaptation of the existing program, which was used to characterize magnetic properties of the phase shifters (PS). Before doing the measurements the new program automatically finds the centers of By and Bz components, which are found to match with the geometrical centers with sufficient accuracy. After the measuring procedure is complete, the results are presented as graphics output and final tables. It shows that the measurement results can fully meet the design requirements of E-XFEL. For all measurements the excitation current of the coils was set to 1 Ampere.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY001  
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WEPOY002 A Time Domain Analysis Method for RF Noise 2994
  • L. Lin, B. Du, G. Huang, Y.T. Liu
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  A time domain analysis method is developed for the calculation of the longitudinal oscillations caused by the RF noise in the storage ring. This method is based on the impulse response model, and it could calculates the change of transient field caused by beam oscillation and RF noise turn by turn. By means of discrete spectrum analysis, the spectrum of the beam is obtained. According to this analysis method, we developed a simulation pro-gram. The synchronous oscillation of the excited by high RF source with a phase modulation is predicted in this program, and the corresponding experimental measure-ments are carried out on HLS II. The fitting results are in agreed with the experimental measurements.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY002  
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