HL-LHC Wakefield Simulations

PyHEADTAIL macro-particle simulations (http://github.com/PyCOMPLETE/PyHEADTAIL) of single bunch stability in the High Luminosity LHC at top energy lead to the present data. Head-tail instabilities driven by the machine impedance can seriously degrade the beam quality and even lead to machine protection issues.<br>Here we simulate with smooth approximation optics and recent versions of the complete HL-LHC impedance model at flat-top conditions at an energy of 7TeV. The influence of the different wake terms (dipolar, dipolar + cross-terms, dipolar + cross-terms + quadrupolar), the longitudinal distribution and the different impedance scenarios (with MoGr coated TCTs) are compared. For each case, we scan the linear chromaticity. The transverse feedback is taken into account with an ideal damper model at 50 turns, moreover longitudinal non-linear synchrotron motion is employed while lattice non-linearities (such as detuning with amplitude from octupoles) are not considered.<br>This particular dataset is based on the following parameters:<br>- beta* of 15cm (STABLE beams conditions)- thermal longitudinal distribution at 8.1cm RMS bunch length, <br>- pre-HL-LHC-optics-v1.2 impedance model with only the dipolar term of the wake function considered<br>