Broadband impedance of the NESTOR storage ring

TL;DR

This paper estimates the broadband impedance of the NESTOR storage ring, identifying the main contributions from the RF-cavity and vacuum chamber components, and evaluates the resulting bunch length under specific operational parameters.

Contribution

It provides analytical and simulation-based estimates of the broadband impedance contributions in the NESTOR ring, including cavity and vacuum chamber effects, with implications for bunch length.

Findings

Main impedance from RF-cavity dominates

Estimated bunch length of 0.5 cm at 10 mA current

Good agreement between analytical and CST simulation results

Abstract

We have estimated contributions from the lossy and inductive vacuum chamber omponents to the broadband impedance of the NESTOR storage ring by using analytical formulas. As was expected considering the small ring circumference (15.44m), the main contributions both to the longitudinal impedance Z/n and the loss factor k come from the RF-cavity. Cavity impedance was also estimated with CST Microwave Studio (CST Studio Suite{TM} 2006) by simulating coaxial wire method commonly used for impedance measurements. Both estimates agree well. The upper limit of impedance of elliptic holes in the vacuum chamber of dipole magnet were also obtained with this approach. We have also evaluated the bunch length in NESTOR taking the conservative estimate of 3 Ohm for the ring broadband impedance and have found that the bunch length sigma_z= 0.5 cm could be obtained for the designed bunch current of 10 mA and RF-voltage of 250 kV.