Achromatic telescopic squeezing scheme and application to the LHC and its luminosity upgrade

A novel optics concept, the achromatic telescopic squeezing (ATS) scheme has been invented in the context of the Large Hadron Collider (LHC) upgrade studies, and chosen as the baseline scheme for the optics and layout of the recently approved high luminosity LHC project (HL-LHC). This scheme offers an extremely powerful and flexible machinery in order to strongly reduce ${\ensuremath{\beta}}^{*}$ in a symmetric or asymmetric way (i.e. without necessarily imposing the same ${\ensuremath{\beta}}^{*}$ in both planes), while perfectly controlling the chromatic aberrations induced, namely the linear and nonlinear chromaticities, the off-momentum $\ensuremath{\beta}$ beating, and the spurious dispersion from the large crossing angle which is required at small ${\ensuremath{\beta}}^{*}$ in the particular case of the (HL)-LHC. The initial motivations of the scheme will be reviewed, followed by a detailed description of its fundamental theoretical foundations. An effective construction of ATS optics will be given and its main features illustrated in the case of the LHC and HL-LHC.