Beam Feedback Systems

Abstract. Outlines of bunch-by-bunch feedback systems for suppressing multibunch instabilities in electron/positron storage rings are shown. The design principles and functions of the feedback components are reviewed. The application of the feedback system as a tool to analyze instabilities using transient-domain techniques is also shown.

コヒーレント制動放射を用いた原子散乱因子の決定

Contents / p1 1 Introduction / p4 2 Coherent Bremsstrahlung / p7 　2.1 Theoretical foundation / p7 　2.2 Dip-bump structures / p12 　2.3 Effect of the atomic form factor / p14 3 Experimental Set-up / p15 　3.1 General consideration / p15 　3.2 Electron synchrotron / p17 　3.3 Tagging system and electron monitor / p17 　3.4 Target and goniometer / p20 　3.5 Data acquisition methods / p22 4 Experimental Procedure / p22 　4.1 Check runs / p22 　4.2 Silicon runs / p25 　4.3 Aluminum runs / p26 5 Results and discussion / p28 　5.1 Theoretical calculation / p28 　5.2 Atomic form factor of silicon crystal / p30 　5.3 Effect of the imperfection of silicon crystal / p36 　5.4 Atomic form factor of aluminum crystal / p38 　5.5 Possible improvement of experimental methods / p42 6 Conclusion / p43広島大学(Hiroshima University)博士(理学)Physical Sciencedoctora

Coupled-bunch instabilities and related effects due to electron cloud in SuperKEKB LER

Coupled-bunch instabilities due to electron cloud effect have been observed in KEKB LER. The effect was clearly explained by the electron cloud effect (ECE) in the drift space by the numerical simulations. For SuperKEKB collider which is the upgrade of the KEKB collider, several methods to mitigate the ECE have been applied. The effectiveness of those methods has been evaluated using the beam in Phase 1 and Phase 2 operation of SuperKEKB. Preliminary experimental results will be shown

Development of a high-speed digital signal process system for bunch-by-bunch feedback systems

High-speed digital filter systems for bunch-by-bunch feedback systems have been developed at KEK. A two-tap finite impulse response filter with simple hardware realizes the functions of a 90° phase shift, suppression of the static component and digital delay of up to a few hundred turns for the KEKB rings. Difficulties in the circuit board, such as the trimming of the timing skews or the problem of long-term reliability, have been solved using custom GaAs large-scale integrated circuits which demultiplex and multiplex fast parallel-digital data coming from the analog-to-digital converter and going to the digital-to-analog converter. Two major applications of the filter board, the bunch current monitor and the bunch oscillation recorder with 20 MB memories for transient-domain analysis of the instabilities, are also described

Feedback experiments in TRISTAN-AR and the bunch by bunch feedback systems for KEKB

. Beam tests of the KEKB bunch by bunch feedback system prototypes have been performed in the TRISTAN-AR in both longitudinal and transverse planes. A two-tap FIR filter system, consisting of hardware logic's, realized the function of the phase shift by 90 degrees, the suppression of the static component and the delay of up to a few tens of turns in longitudinal plane with 508 MHz of system clock. The transverse systems were purely analog systems without any digital signal processing part. More than 100 bunches with maximum current of 376 mA have been accumulated successfully with the bunch spacing of 2 ns. The growth time and the growing modes of the transverse instabilities has also been measured with the memory function of the two-tap FIR filter. It suggests that the bunch-by-bunch feedback system is a powerful tool to explore the source of the instabilities. Based on the results of the AR experiments, the design and the expected performances of the feedback systems for KE..

DEVELOPMENT OF GATED TURN-BY-TURN POSITION MONITOR SYSTEM FOR THE OPTICS MEASUREMENT DURING COLLISION OF SUPERKEKB

Abstract Gated turn-by-turn monitor system to measure optics functions using non-colliding bunch has been developed for SuperKEKB accelerators. With the fast, glitch canceling beam switch, beam position of the target bunch will be measured without affecting the fine COD measurement using narrow-band detectors. The gate timing and the bunch position detection are controlled by the Spartan-6 FPGA. The performance of the system, such as the gate timing jitter, data transfer speed from the system to EPICS IOC and the noise effect to the downstream narrow-band detector are reported

Observation Of Transverse Coupled Bunch Instability At

Transverse coupled bunch instability was experimentally studied in low energy positron ring (LER) and high energy electron ring (HER) at KEKB. The oscillations of bunches were recorded by a bunch oscillation recorder for the total of 4096 turns. The data were analysed to obtain the mode distribution and the growth rate of oscillation. The result of the analysis is presented in this paper