Free energy relaxation in a drift-tube linac

A beam that is injected in a state that is not in equilibrium has free energy that can be thermalized as the density profile relaxes. Relaxation will also occur as the beam evolves through a channel with changes in energy, size and shape, and this relaxation will affect the subsequent beam behavior in the channel. PARMILA is used to simulate various input distributions for beams in a drift-tube linear accelerator. Properties of the final beam state, including size, shape, emittance and the presence of halo particles, are found for each of the initial phase space distributions.