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TY - CONF AU - Chae, Y.-C. AU - Dzhingaev, D. AU - Ebert, M. AU - Falkenberg, G. AU - Keil, J. AU - Kube, G. AU - Novokshonov, A.I. AU - Sahoo, G.K. AU - Sprung, M. AU - Wanzenberg, R. AU - Westermeier, F. ED - Koscielniak, Shane ED - Satogata, Todd ED - Schaa, Volker RW ED - Thomson, Jana TI - Microwave Instability and Energy Spread Measurement via Vertical Dispersion Bump in PETRA III J2 - Proc. of IPAC2018, Vancouver, BC, Canada, April 29-May 4, 2018 C1 - Vancouver, BC, Canada T2 - International Particle Accelerator Conference T3 - 9 LA - english AB - The recent measurement of bunch length versus current indicated that the longitudinal impedance (Z/n) is 0.15 Ω in close agreement with the impedance model*. Naive application of Keil-Schnell criteria predicts the threshold of microwave instability at 0.25 mA. Since the single bunch intensity is in the range of 0.2-2.5 mA depending on the fill-pattern of PETRA III, we expect to observe the fill-pattern dependent energy spread according to the theory. However, the 3rd generation light sources comparable to PETRA III often reported the observation which was much greater than the theoretical one. In order to induce the beam size variation we had used skew quadrupoles to generate the dispersion in vertical plane. In particular we made dispersion bump at the undulator sector so that we were able to use the X-ray optics for the precise determination of small vertical beam size. In this paper we report the experimental setup and measurement data with the estimate on the instability threshold. We also report the vertical emittance and energy spread based on the X-ray beam size measurement as well as the RF signal which was excited by the beam at the longitudinal feedback cavity. PB - JACoW Publishing CP - Geneva, Switzerland SP - 1427 EP - 1429 KW - emittance KW - experiment KW - undulator KW - quadrupole KW - wiggler DA - 2018/06 PY - 2018 SN - 978-3-95450-184-7 DO - 10.18429/JACoW-IPAC2018-TUPMF072 UR - http://jacow.org/ipac2018/papers/tupmf072.pdf ER -