Measurement of Sudden Beam Loss Events Using Bunch-by-Bunch BPMs at SuperKEKB

Abstract

At SuperKEKB, sudden beam loss (SBL) events pose a significant challenge to stable accelerator operation. To investigate and better understand SBL, we have developed a new Bunch Oscillation Recorder (BOR), as reported by R. Nomaru et al. (JINST 19 P12026, 2024). Using this newly developed BOR, we successfully observed SBL events and conducted a detailed analysis of the recorded data. By analyzing the patterns of bunch position oscillations and charge loss, we found a strong correlation between SBL events and pressure burst phenomena occurring inside the vacuum chamber. These pressure bursts are known to accompany almost all SBL events, and our analysis shows that the bunch position oscillation patterns vary depending on the location of the pressure burst. Our observations suggest that bunch positions begin oscillation under some influence at the location of the pressure burst. These observations and analyses have significantly advanced our understanding of the causes and mechanisms behind SBL.

Figures (21)

• Figure 1: Schematic diagram of the SuperKEKB main ring Ishibashi:2020rgt. The red ring represents the LER, and the light blue ring represents the HER. Squares along the ring indicate the locations of vertical collimators, and circles indicate the locations of horizontal collimators. In the LER the blue star marks the beam dumps, and green triangles indicate the locations of the BORs.
• Figure 2: An SBL event recorded by the Fuji-RFSoC (top three panels) and the D5-RFSoC (bottom three panels). The plots show bunch position and charge over the eight turns preceding the beam abort. From top to bottom: horizontal (X) position, vertical (Y) position, and bunch charge recorded by the Fuji-RFSoC, followed by the same measurements from the D5-RFSoC.
• Figure 3: Division of the LER into two sections using the Fuji-RFSoC and the D5-RFSoC. Section 1 spans from the Fuji-RFSoC to the D5-RFSoC (orange arrow), and Section 2 spans from D5-RFSoC back to Fuji-RFSoC (blue arrow).
• Figure 4: Bunch charge evolution during the SBL event at 02:55:30 on October 28, 2024. The upper panel shows data from the Fuji-RFSoC, and the lower panel shows data from the D5-RFSoC.
• Figure 5: Charge loss per Section for the SBL event shown in Fig. \ref{['fig:sbl_10-28-0235530_charge']}. Orange points (labeled “Fuji to D5”) represent charge loss in Section 1, while blue points (“D5 to Fuji”) represent loss in Section 2. Data for Section 1 in the final turn are not available.