Operational experience of the SNS front end and warm linac

The Spallation Neutron Source accelerator complex uses set of pulsed linear accelerators of different types to accelerate beam to 1GeV. The 2.5 MeV beam from the Front End is accelerated to 86 MeV in the Drift Tube Linac, then to 185 MeV in a Coupled-Cavity Linac and finally to 1 GeV in the Superconducting Linac. In the process of the commissioning and beam power ramp up many technical systems, as well as tuning algorithms, have deviated significantly from the original design. Our understanding of beam behavior has been evolving continuously and resulted in a steady reduction of fractional beam losses in the linac. In the same time new unexpected problems have been discovered, which are still in the process of investigation. In this paper we summarize our experience up to date and report on the current directions of experimental study, simulations, and development of tuning methods.