Intensity dependance of the train instability threshold and high pile-up test with 12b trains (MD3294)

As signs of electron cloud driven instabilities at top energy were observed in MDs in 2017 even with short trains(12b), an additional experiment was performed in 2018 to assess the intensity scaling of this instability mechanism using high intensity 12b trains available from the existing injector chain, i.e. without upgrade. An intensity dependence of the instability threshold could be observed at constant brightness, nevertheless the instability detected seem to be of the different type w.r.t. those observed in past experiments. The high intensity 12b trains were used to provide the highest pile-up with 25ns spacing to the experiment in order to probe regimens close to ones expected in the HL-LHC era. The machine and beam aspects are described in this note.