  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.
