Progress in the Design of the SPL, an $H ^{-}$ High-Intensity Linac at CERN

The SPL (Superconducting Proton Linac) is a 4 MW 2.2 GeV H- linac, intended to re-use most of the 352 MHz RF equipment from the decommissioned LEP machine. Injecting into the CERN PS, this linac would improve the intensity and quality of the CERN proton beams, while as a stand-alone facility could provide intense beams of radioactive ions or neutrinos (Neutrino Superbeam). Together with accumulator and compressor rings, it would be a suitable driver for a Neutrino Factory. Since the original proposal, many improvements to the design have been introduced, in order to simplify the layout and reduce costs. They include the reduction of the repetition frequency to 50 Hz, the design of a shorter superconducting (SC) linac section that goes up to the full energy with b=0.8 cavities, an improved DTL section including a new CCDTL design, a chopping line based on fast (2 ns rise time) low-voltage choppers and pulser, and a simplified front-end. Moreover, the problem of pulse mode operation of a superconducting linac with more than one cavity per klystron has been analysed in more detail, showing additional limitation but also proposing some possible compensation schemes.