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We have estimated contributions from the lossy and inductive vacuum chamber components 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 loss come from the RF-cavity.Cavity impedance was also estimated with CST Microwave Studio (CST Studio Suite T M 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 σ z = 0.5 cm could be obtained for the designed bunch current of 10 mA and RF-voltage of 250 kV.

The piece of NESTOR vacuum chamber with the ceramic insertion for DC-monitor and RFshields was simulated by using both transient and wake field solvers of CST Studio Suite T M . For a 6 mm gap between two RF-shields the contributions of the assembly considered to the longitudinal broadband (BB) impedance Z /n and the loss factor k loss are 0.71 Ohm and 0.21 V /pC, correspondingly. These estimates are the second largest after those of the RF-cavity that were obtained till now for the NESTOR ring components.Contributions from a beam position monitor (BPM) are also obtained by simulation and compared with analytical estimates obtained earlier.