Small Angle Crab Crossing for the LHC4

A small angle crab compensation ( 0.5 mrad) is foreseen to improve the LHC luminosity independently of the IR upgrade paths to enhance the luminosity of the LHC by 15% for the nominal and factor of 2-3 for various upgrade scenarios. Crab cavities ensure head-on collisions and recover the geometric luminosity loss from the presence of a finite crossing angle at the interaction point (IP). An R&D program is underway to design and fabricate superconducting RF (SRF) prototype cavity at 800 MHz to test several SRF limits in the deflecting mode. If the prototype is installed in the LHC, it can be used for a first demonstration of crab crossing in hadron beams to understand potential emittance growth mechanisms due to crab cavities.