Update on electron - cloud power deposition for the Large Hadron Collider

We revisit the estimation of the power deposited by the electron cloud (EC) in the arc dipoles of the LHC by means of simulations. We adopt, as simulation input, a set of electron-related parameters closely resembling those used in recent simulations at CERN [1]. We explore values for the bunch population Nb in the range 0.4× 10 ≤ Nb ≤ 1.6× 10, peak secondary electron yield (SEY) δmax in the range 1.0 ≤ δmax ≤ 2.0, and bunch spacing tb either 25 or 75 ns. For tb = 25 ns we find that the EC average power deposition per unit length of beam pipe, dP̄ /dz, will exceed the available cooling capacity, which we take to be 1.7 W/m at nominal Nb [2], if δmax exceeds ∼1.3, but dP̄ /dz will be comfortably within the cooling capacity if δmax ≤ 1.2. For tb = 75 ns dP̄ /dz exceeds the cooling capacity only when δmax > 2 and Nb > 1.5× 10 taken in combination. The rediffused component of the secondary electron emission spectrum plays a significant role: if we artificially suppress this component while keeping δmax fixed, dP̄ /dz is roughly cut in half for most values of Nb explored here, and in this case we find good agreement with the results in Ref. 1, as expected. We provide a fairly detailed explanation of the mechanism responsible for such a relatively large effect. We assess the sensitivity of our results to numerical simulation parameters, and to physical parameters such as the photoelectric yield, bunch train length, etc. Owing to the lack of detailed knowledge of the electron emission spectrum, the sensitivity of dP̄ /dz to the rediffused component appears to be the most significant source of uncertainty in our results. Nevertheless, taking our results as a whole, the condition δmax ≤ 1.2 seems to be a conservative requirement for the cooling capacity not to be exceeded.