A higher harmonic cavity at 800 MHz for HL-LHC

A superconducting 800 MHz second harmonic system is proposed for HL-LHC. It serves as a cure for beam instabilities with high beam currents by improving Landau damping and will allow for bunch profile manipulation. This can potentially help to reduce intra-beam-scattering, beam induced heating and e-cloud effects, pile-up density in the detectors and beam losses. An overview of the 800 MHz cavity design and RF power requirements is given. In particular the design parameters of the cavity shape and HOM couplers are described. Some other aspects such as RF power requirements and cryomodule layout are also addressed.