Hollow bunches production

Hollow bunches address the issue of high-brightnessbeams suffering from transverse emittance growth in a strongspace charge regime. During the Proton Synchrotron (PS)injection plateau, the negative space charge tune shift canpush the beam onto theQy=6integer resonance. Modify-ing the longitudinal bunch profile in order to reduce the peakline charge density alleviates the detrimental impact of spacecharge. To this end we first produce longitudinally hollowphase space distributions in the PS Booster by exciting aparametric resonance with the phase loop feedback system.These inherently flat bunches are then transferred to the PS,where the beam becomes less prone to the emittance growthcaused by the integer resonance.During the late 2016 machine development sessions inthe PS Booster we profited from solved issues from 2015and managed to reliably extract hollow bunches of1.3eVsmatched longitudinal area. Furthermore, first results to cre-ate hollow bunches with larger longitudinal emittances to-wards the LHC Injector Upgrade project goals proved suc-cessful. Here, we present the ingredients to the establishedhollow bunch procedure, showing the few involved changesto the PS Booster cycle for nominal LHC beam produc-tion. We also discuss challenges related to the competingphase loop and radial loop feedback systems: their mutualresponsescaneffectivelyinhibittheexcitationoftheparamet-ric resonance which should deplete the core of the initiallyparabolic bunches.