  The JAERI/KEK Joint Project for the high-intensity proton accelerator
facility has been proposed with a superconducting (SC) linac option from 400
MeV to 600MeV. System design of the SC linac has been carried out based on the
equipartitioning concept. The SC linac is planned to use as an injector to a
3GeV rapid cycling synchrotron (RCS) for spallation neutron source after it
meets requirement to momentum spread less than +-0.1%. In the R&D work for SC
cavities, vertical tests of single-cell and 5 cell cavities were performed.
Experiments on multi-cell (5 cell) cavities of b=0.50 and b=0.89 at 2K were
carried out with values of maximum electric surface peak fields of 23MV/m and
31MV/m, respectively. A model describing dynamic Lorentz detuning for SC
cavities has been developed for pulse mode operation. Validity of the model was
confirmed experimentally to simulate the performance.
