Cheng Chang latest fellow to receive PhD degree

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Cheng Chang has recently been awarded aPhD degree as a result of successful defence of the thesis on Precise determination of electron beam energy with Compton backscattered laser photons at ANKA, based on his work developed at KIT, Germany.


ANKA (Angströmquelle Karlsruhe) is a third generation light source, providing users synchrotron radiation from the far-infrared to hard X-rays. Its operation energy is from 0.5 GeV to 2.5 GeV. Since 2004 short bunch operation using ultra-low momentum compaction factor at 1.3 GeV and 1.6 GeV has been provided for THz radiation research. Previously, the method of resonant spin depolarization was used to accurately determine the energy and the momentum compaction factor at 2.5 GeV of the ANKA electron storage ring. However, this method becomes cumbersome or even unrealistic for lower energies, especially for the short bunch operation, since the build-up time of the polarized electron beam becomes extremely long. Therefore an innovative method based on Compton backscattering has been developed to accurately calibrate the entire energy range of ANKA storage ring with typical relative uncertainties of a few 10-4. Especially the nonlinear momentum compaction factors at short bunch operation have also been determined precisely.

The theoretical model, numerical studies, design and implementation of the respective sub-system and component, the measurement procedure as well as the measurement results are presented in Dr. Chang thesis. The possibilities of the setup adaption to other facilities have also been explored and included.