Low-impedance stripline kicker for the transverse instability suppression system of the synchrotron radiation facility "SKIF" light source

TL;DR

This work targets achieving ultra-low emittance of $75\,\mathrm{pm}$ at $3\,\mathrm{GeV}$ and $400\,\mathrm{mA}$ in the SRF SKIF storage ring by addressing collective instabilities with a bunch-by-bunch feedback system. It introduces a low-impedance, two-strip stripline kicker that also functions as a beam position monitor, employing conical end tapers and CST-based optimization to minimize beam impedance, ensure 50 $\Omega$ matching, and enhance transverse pulse uniformity. Key results include a $50\,\Omega$ characteristic impedance, quantified transverse momentum imparted with optimized uniformity (deviation within 2% for $r\le 5\ \mathrm{mm}$), and transfer impedances at the RF reference frequency ($Z_p(f_{RF})=19.0\ \Omega$, $Z'_p(f_{RF})=4.15\ \mathrm{k}\Omega/\mathrm{m}$); the effective strip length is aligned with $\lambda_{RF}/4$ to support BPM functionality, and wakefield analyses indicate overall low beam impedance with minor resonances. The design provides a manufacturable, repairable solution that suppresses transverse instabilities while preserving aperture and enabling simultaneous BPM operation in the SKIF facility.

Abstract

Construction of the new fourth generation synchrotron radiation facility (SRF) "SKIF" near Novosibirsk is nearing completion. "SKIF" uniqueness is ultra-low 75 pm natural emittance at 400 mA beam current and 3 GeV beam energy. Collective effects (beam interaction with the vacuum chamber) are the main obstacles of achieving such emittance and beam current. To suppress these effects the storage ring will be equipped with a bunch-by-bunch feedback system. Important components of the feedback system are a stripline (fast) kicker and a beam position monitor. The paper describes design of the low-impedance stripline kicker for SRF "SKIF" storage ring, optimized for the manufacturing and for the uniformity of the imparted transverse kick. The kicker qualities such as S-parameters, imparted transverse momentum, transfer and beam impedances are presented. The chosen length of the stripline kicker allows its use as a beam position monitor.

Figures (7)

• Figure 1: General view of the stripline kicker. Some parts of the kicker are hidden to demonstrate the design. The main components of the stripline kicker are labeled with numbers.
• Figure 2: Cross-section of the main stripline with principal dimensions.
• Figure 3: Calculation of the $S$ parameter from input to input in antiphase mode. $S_{11}$ is the reflected wave, $S_{21}$ is the transmitted wave.
• Figure 4: Normalized electrostatic potential in odd (a) and even (b) mode.
• Figure 5: Uniformity of the vertical momentum imparted to the beam particles by the vertical stripline kicker in the stationary operating mode (a) and in the operating mode at the maximum frequency (b).