Design criteria for high intensity H--injector linacs

All proposed pulsed spallation source projects include a high power H^--linac followed by one or more compressor rings or a rapid cycling cyclotron. A key issue for the whole accelerator facility is the loss free ring injection which can be achieved by H^--H ⁺ charge exchange. The design of an H^- injector differs remarkably from the layout of an high intensity H⁺-linac. At the low energy end, a fast chopper operating at the ring revolution frequency has to be installed. No partly filled bunches are allowed. Funneling of two beams is preferred as it relaxes the conditions for the chopping system. The linac itself has to be designed for no emittance growth and small halo production. In order to ensure a loss free injection into the rings, the linac pulse has to be limited in energy and truncated transversely. The energy spread reduction is made by a bunch rotator after the linac. A cost saving option is to use pulsed superconducting cavities for the high β linac