  Spallation source dedicated for neutron scattering experiments, as well as
multi-purpose facilities serving several applications call for pulsed mode
operation of a high intensity proton linac. There is general agreement on the
superconducting technology for the high-energy part, which offers some
advantages, like higher gradient capabilities or operational costs reduction,
as compared to room-temperatures accelerating structures. This mode of
operation however could spoil the energy stability of the proton beam and needs
thus to be carefully studied. First, transient beam-loading effects, arising
from the large beam phase slippage along a multi-cell cavity and associated
with the finite RF energy propagation, can induce significant energy modulation
with a too small cell-to-cell coupling or a too large number of cells. Second,
due to beam phase slippage effects along the linac, energy spread exhibits a
larger sensitivity to cavity fields fluctuations than relativistic particles. A
computer code, initially developed for electron beams has been extended to
proton beams. It solves the 6xN coupled differential equations, needed to
describe cavity fields and beam-cavity interactions of a high-energy linac
composed of N cavities. Simulation examples on a typical pulsed accelerator are
given with various error sources, like Lorentz forces or microphonics detuning,
beam injection energy offsets, intensity jitters ...
