  Space charge is typically one of the performance limitations for the
operation of high intensity and high brightness beams in circular accelerators.
In the Proton Synchrotron (PS) at CERN, losses are observed for vertical tunes
above $Q_y=6.25$, especially for beams with large space charge tune shift. The
work presented here shows that this behaviour is associated to structure
resonances excited by space charge due to the highly symmetric accelerator
lattice of the PS, typical for first generation alternating gradient
synchrotrons. Experimental studies demonstrate the dependency of the losses on
the beam brightness and the harmonic of the resonance, and simulation studies
reveal the incoherent nature of the resonance. Furthermore, the calculation of
the Resonance Driving Terms (RDT) generated by the space charge potential shows
that the operational working point of the PS is surrounded by multiple space
charge driven incoherent resonances. Finally, measurements and simulations on
both lattice driven and space charge driven resonances illustrate the different
behaviour of the beam loss depending on the source of the resonance excitation
and on the beam brightness.
