  The normal conducting Annular Coupled Structure (ACS) is applied for 190-400
MeV part of high intensity proton linac for the J-PARC. The ACS operating
frequency is 972 MHz. The J-PARC ACS is strongly based on the results of
previous investigations, especially results of Japan Hadron Project (JHP)
research program in KEK. However, the design was revised and optimized to meet
the requirements of reliability, operation efficiency and cost reduction. The
cells shape of accelerating cells was optimized in total energy range to have
high shunt impedance value together with the careful matching with the
decreased coupling cells. The design of the bridge coupler cells was optimized
to simplify mass production and shape of RF input cell together with matching
window were optimized for higher operational reliability. Collected and
adjusted all together, these modifications result in the significant effect.
The ACS module design doesn't lose to another possible accelerating structures
in RF parameters and dimensions. Previously developed for L-band ACS
fabrication technique is applied to 972 MHz ACS construction. The realized
solutions have the reserve for ACS module use with very high heat loading
during operations with 15% duty factor, the highest heat loading at present
time, as compared to accelerating modules with another normal conducting
accelerating structures, realized in hadron linacs. This report contains the
descriptions and explanations of changes in the ACS module physical design for
the J-PARC linac.
