A new Diagnostic for Betatron Phase Space matching at Injection into a circular Accelerator

For proton and ion accelerators, betatron matching at injection is a delicate procedure, vital to preserve phase space density. A new diagnostic is proposed in which a single detector in a circular machine measures the beam size for a dozen successive turns. Applications to SPS and LHC are exemplified. The method is so robust and accurate that it should allow to reduce the emittance blow-up to below 1 % in each plane. Experimentation is ready to start in the SPS.