The construction of the low-enegy front (60 MeV) of the proton linac started in 1998. The linac comprises a volume-production type of negative hydrogen ion source, a 3-MeV radiofrequecy quadrupole (RFQ) linac, a 50-MeV drift-tube linac (DTL), and a 60-MeV separated DTL (SDTL). The SDTL will be extended up to 200 MeV in the Joint Project linac, followed by the annular-ring coupled structure (ACS) up to 400 MeV. The RFQ linac is well field-stabilized by π-mode stabilizing loops (PISLs) devised in KEK. The prototype of the 3-MeV RFQ linac with PISLs had been beam-tested several years ago, accelerating an H− beam of 13 mA in peak. The design beam current of the present one is 30 mA. The SDTL devised in KEK has excellent power efficiency over the conventional DTL. The ACS is axially symmetric in contrast to the commonly used side-coupled structure, which is axially asymmetric. Because the axial symmetry is one of important factors in order to reduce the beam loss, the ACS has been studied and realized in KEK first. The several prototypes of the ACS have already been power-tested.

The conventional accelerator technology is not sufficient for realizing the proposed beam power. For this reason, the results of many innovations have already been incorporated for the Joint Project accelerators in order to push forward the beam power front of the accelerator technology. Yet, further development will be necessary to realize the challenging features of the Joint Project.

Young, ambitious scientists and engineers are thus invited to join the project.

	RFQ installed in a tunnel in KEK

	The author of this article, Professor Yoshishige YAMAZAKI, has been the group leader of the accelerator group in the Joint Project.