First Direct Measurement of Electron and Positron Bunch Characteristics during Positron Capture Process at the Positron Source of the SuperKEKB B-Factory
146
T. Suwada
KEK, Ibaraki, Japan
Electron (e-) and positron (e+) bunch characteristics were directly measured for the first time using wideband beam monitors (WBMs) and a detection system at the e+ source of the SuperKEKB B-factory. Both secondarily-generated e- and e+ bunches after the e±production target were clearly identified in their dynamical capture process at locations of the WBMs under two-bunch acceleration scheme. Not only the longitudinal but also transverse bunch characteristics, the time intervals between the e- and e+ bunches, the bunch lengths, transverse bunch positions, and bunch charges were simultaneously separately measured for each bunch as functions of the capture phase to investigate their dynamical capture process. The results show that quite symmetric dynamical behaviors for the e- and e+ bunch characteristics were clearly observed. The new WBMs open up a new window for direct measurements of both the e- and e+ bunches during their dynamical capture process and in the optimization procedure of the e+ bunch intensity in multidimensional parameter spaces at any e+ sources. The historical backgrounds for introducing and implementing the new WBMs are also described in this report.
Sub-20 fs Synchronization Between Mode-Locked Laser and Radio Frequency Signal
151
J.G. Wang, B. Liu, W. Wu
SARI-CAS, Pudong, Shanghai, People’s Republic of China
The femtosecond synchronization and distribution system of the Shanghai soft X-ray free-electron laser facility (SXFEL) and Shanghai high repetition rate XFEL and extreme light facility (SHINE) are based on the optical pulse trains generated by passively mode-locked lasers. The passively mode-locked laser has ultralow noise in the high offset frequency (<5 fs, [1 kHz- 1 MHz]). In this paper, we report precise synchronization of the low-noise passively mode-locked laser to the radio frequency (RF) master oscillator. RF-based phase-locked loop scheme, the absolute jitter of the phase-locked passively mode-locked laser is less than 20 fs integrated from 10 Hz up to 1 MHz.
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