Presented at the IEEE Particle Accelerator Conference (session 9P-116), Vancouver, 1997
Broad-Band Impedance of LHC Shielded Bellows
M. D'Yachkov and F. Ruggiero
May 1997
Abstract:
To compensate for thermal expansion the
LHC ring has to accommodate about 2500 bellows which, together with beam
position monitors, are the main contributors to the LHC broad-band
impedance budget. In order to reduce this impedance to an acceptable value
the bellows have to be shielded. In this paper we compare different
designs proposed for the bellows and calculate their transverse and
longitudinal wake fields and impedances. Owing to the 3D geometry of the
bellows, the code MAFIA was used for the wake field calculations.
The results presented in this paper indicate that the latest bellows design,
in which shielding is provided by sprung fingers which can slide along the
beam screen, has impedances smaller than those previously estimated according
to a rather conservative scaling of SSC calculations and LEP measurements.
Several failure modes,
such as missing fingers and imperfect RF contact, have also been studied.
F. Ruggiero
Mon May 26 17:11:35 1997