Power Losses in Enlarged Experimental Chambers of the LHC

Expressions for resonant frequencies and shunt impedances are derived for enlarged interaction region vacuum pipes of the type proposed in CMS. They are used to compute the power that the multi-bunch LHC beams can dissipate in such a structure if one of its resonant frequencies is equal to a harmonic of the beam intensity. This power can be several kilowatts for a specific rigid geometry. It is demonstrated that the actual power dissipation in a resonance is reduced to only a few watts for beam pipes that are not thermally constrained. The maximum local temperature increase is at most 45°K, which can be considered to be acceptable.