The HL-LHC beams are injected, accelerated to and stored at their nominal energy of 7 TeV by the existing 400 MHz superconducting RF system of the LHC. A new superconducting RF system consisting of eight cavities per beam for transverse deflection (aka crab cavities) of the bunches will be used to compensate the geometric loss in luminosity due to the non-zero crossing angle and the extreme focusing of the bunches in the HL-LHC.