Bunch-Resolved 2D Diagnostics - Streaking Combined with Interferometry
332
M. Koopmans, J.-G. Hwang, A. Jankowiak, M. Ries, G. Schiwietz
HZB, Berlin, Germany
Due to the complexity of the filling pattern in the BESSY II electron-storage ring, bunch-resolved diagnostics are required for machine commissioning and to ensure the long-term quality and stability of operation. In addition, low-alpha operation and a possible VSR upgrade demand bunch-length measurements with picosecond resolution. Therefore, a dedicated beamline equipped with a fast streak camera was set up and successfully commissioned. Couplings between time- and space-coordinates also call for bunch-selective and correlated multi-parameter detection methods. Thus, the beamline and the streak camera have been made capable of direct beam-profile imaging and interferometry of the vertical beam size using the X-ray blocker baffle method *,**. The horizontal or vertical dimension can additionally be imaged with the streak camera and bunch-resolved 2D measurements are possible. Imaging the vertical direction, the characteristic dip in the center the interference pattern from pi-polarized synchrotron radiation can be observed and is used to extract bunch resolved information about the vertical beam size. The streak camera measurements are validated with direct imaging measurements from a regular CCD camera at the beamline and compared to model calculations. The results are converted into absolute values by a calibration with the BESSY II pinhole monitors. * J. Breunlin et al., Nucl. Instrum. Methods A803 (2015) 55-64. ** M. Koopmans et al., in: Proc. IPAC’19, Melbourne, Australia, pp. 2491-2494, http://dx.doi.org/10.18429/JACoW-IPAC2019-WEPGW012.
Right click on video for Picture-in-Picture mode or Full screen display.
Absolute Bunch Length Measurements of Low Energy Beams Using Accelerating RF Cavity
337
J.-G. Hwang
HZB, Berlin, Germany
Y. Honda, T. Miyajima
KEK, Ibaraki, Japan
E.-S. Kim
KUS, Sejong, Republic of Korea
The experimental technique has been proposed and demonstrated by authors for measuring the temporal distribution and absolute bunch length of picosecond-level low-energy electron bunch generated by an electron gun using radial electric and azimuthal magnetic fields of an accelerating (TM01 mode) radio frequency cavity. In this scheme, an accelerating RF cavity provides a phase-dependent transverse kick to the electrons, resulting in the linear coupling of the trajectory angle with the longitudinal position inside the bunch like a transverse deflecting cavity. In this paper, we show a detailed estimation of various aspects of the the temporal resolution of this method with feasible parameters and deconvolution of the Gaussian distribution for accurate reconstruction of the temporal distribution. Measurement of bunch length and … Ji-Gwang Hwang (Helmholtz-Zentrum, Berlin), Tsukasa Miyajima, Yosuke Honda (KEK, Tsukuba), Eun-San Kim (Sejong U.) Published in Sci. Rep. 10 (2020) no.1, 18905
Right click on video for Picture-in-Picture mode or Full screen display.
Development of an On-Line Bunch Length Monitoring System at PLS-II Using an Ultrafast Photodiode
384
W.J. Song
POSTECH, Pohang, Republic of Korea
T. Ha, G. Hahn, Y.D. Joo, D. Kim, Y.S. Lee
PAL, Pohang, Republic of Korea
J.-G. Hwang
HZB, Berlin, Germany
Users of time-resolving experiments at 3rd generation synchrotron light sources deem online bunch length and filling pattern monitoring as an important real-time diagnostic. We developed an on-line monitoring system that can measure bunch lengths and filling pattern using a photodiode, a wideband pre-amplifier, and a sampling digitizer. Two different methods were evaluated to reconstruct the bunch lengths: Gaussian deconvolution method as an approximation scheme and Fourier analysis as a method to restore the original signal by using the power transmission characteristics of the electronic devices in the system, including a bias-tee, a wideband amplifier, cables, and the photodiode. A bunch lengthening experiment has been conducted to compare and verify the results of those two methods of the photodiode and the result of the streak camera images by changing the overall gap voltage of the superconducting RF cavities. In this paper, we elaborate upon the said photodiode-based measurement techniques, and present the experimental results.
