The Japan Atomic Energy Research Institute has been proposing the Neutron Science Project (NSP). The joint project of the NSP and the JHF of KEK is under discussion. The new project makes use of the R&D results of the NSP and the JHF. The R&D activities of the proton accelerator at JAERI will be presented in this paper.The development work and characteristics measurements have been made for the low energy components of the linac; performance tests of a negative hydrogen ion source, development of an integrated type RFQ and high duty factor power tests of a DTL model tank. A superconducting linac is a main option for the high energy part of the linac. Vertical tests of a single cell superconducting cavity have been made. The maximum peak surface fields of 44 MV/m and 47 MV/m have been achieved for β=0.5 and 0.89 cavities, respectively. A 600 MHz IOT RF source has been manufactured and dummy load tests at 35 kW CW have been successfully conducted.

The low level RF (LLRF) control systems have been successfully improved for the J-PARC LINAC upgrade. After the installation of 972-MHz high- acceleration section behind the 324-MHz low- section beginning in the summer of 2013, the proton beam was successfully accelerated to 400 MeV in January 2014. Many improvements in the LLRF control systems have been carried out to facilitate the operation of the J-PARC LINAC at 400 MeV. The reference 12-MHz signal delay settings for the feedback control systems have been optimized using 12-MHz delay modules. The stability performances of the 972-MHz RF&CLK (Clock) and Mixer&IQ (Mixer & IQ-modulator) boards have been improved using temperature-compensation techniques. By improving the hardware of the feedback control systems, very good stability of the RF systems has been achieved.

An accelerator driven nuclear transmutation system (ADS) requires high intensity proton beam; the energy is about IGeV and the beam power is several tens MWI A superconducting proton linear accererator is most promising option to provide the high power proton beam R&D ofthe superconducting