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In electron storage ring a temporal perturbation to the beam makes spatial structure in a bunch, which emit short X-ray or coherent THz radiation. For this technique of bunch shape manipulation, it is important to reduce unwanted de-coherence of betatron motion, which would break the intended spatial structure. At NewSUBARU, 1.5 GeV storage ring, we kicked the beam using a vertical fast kicker and investigated the de-coherence of betetron oscillation using mainly a dual-sweep streak camera. The largest is the Landau damping by a well-known chromatic tune spread, although the phase spread comes back to zero at after a synchrotron oscillation period. On the other hand, there exists several non-linear effects, which makes accumulation of the oscillation phase spread. These are, horizontal betatron amplitude dependent vertical tune shift, synchrotron oscillation amplitude dependent synchrotron tune shift, non-linear chromaticity, synchrotron oscillation chromaticity (non-symmetry of rf bucket), longitudinal radiation excitation process, and others. The tuning knobs we had was some sets of non-linear magnets up to octupole and the rf voltage.
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