Instability thresholds and parasitic losses have been estimated using somewhat conservative assumptions. However the LHC impedance budget is not complete and more detailed calculations are still required, although we believe that the most significant contributions have been taken into account. The possibility of a transient bunch-to-bunch detuning during injection and the consequences of closed orbit residuals on the betatron coupling are important topics for future studies: together with a more careful computation of the magnetic Laslett tune shift, they have implications on the injection tolerances and on the strategies for orbit correction and coupling compensation.
Further experimental and theoretical investigations on trapped and high-frequency modes caused by the pumping slots in the beam screen are in order. Their electromagnetic properties, such as detuning due to slot randomization or damping associated with mode conversion at the slots [20], can be measured and their effects on the beam dynamics should be computed.
Power losses through the pumping slots associated, e.g., with a possible microwave structure of the beam spectrum, should also be investigated. This may have an impact on the final design of the beam screen, including the optimal choice of the slot length and the arrangement of microwave absorbers in the outer coaxial region between the screen and the cold bore.