The Japan Proton Accelerator Research Complex (J-PARC) has achieved stable 1 MW operation test on its neutron target and is advancing toward higher power levels of 1.5 MW to support high-power MR operations and a second target station. This progression presents challenges, including increased intra-beam stripping (IBSt) of H⁻ ions, chop leakage from higher beam currents and emittance, low-energy beam loss due to halo formation, frontend fluctuations affecting beam transmission, and RF phase and amplitude fluctuations. To address these issues, a redesigned lattice mitigates IBSt, a new MEBT1 improves chopping and collimation, and machine learning-based compensation schemes manage frontend and RF fluctuations. Additionally, longitudinal and transverse matching schemes enhance beam quality, validated through benchmarked longitudinal measurements. Results from studies at 50 mA and 60 mA beam currents demonstrate significant progress in overcoming these challenges.

Accelerator-based boron neutron capture therapy (BNCT) has been studied worldwide for a novel cancer therapy using neutrons generated by an accelerator system. The iBNCT (Ibaraki BNCT) project began in collaboration with KEK, the University of Tsukuba, Ibaraki Prefecture, and private companies in Japan. The iBNCT project aims to realize linac-based BNCT with a compact and low-activation accelerator system based on the design and experiences of the J-PARC linac. It consists of an H+ ECR ion source, a 3-MeV RFQ, an 8-MeV Alvarez-DTL, and a beryllium neutron-generation target. Since a high neutron flux is required for the BNCT treatment, an average beam current of more than 1 mA is necessary with the combination of the 8-MeV proton and the beryllium target. By improving the vacuum, cooling water and low-level RF system, stable operation was achieved with an average beam current of 2 mA. After completion of the non-clinical studies in parallel with neutron beam characteristic measurements, the iBNCT project has started a clinical study in January 2024. In this contribution, the present status together with the conducted upgrade and prospects of the iBNCT accelerator will be presented.

The Japan Proton Accelerator Research Complex supplies a high-intensity proton beams for the physics experimental programs in the Material and Life Science Facility (MLF), the Hadron experimental facility and the neutrino target. In such a high-intensity hadron accelerator, losing less than 0.1% of the beam can cause several problems. Such lost protons can cause serious radioactivation and accelerator component malfunctions. Therefore, we have been continuing a beam study to achieve high-power operation with enough smaller loss condition. In addition, we have also improved and maintained the accelerator components, enabling a stable operation. Through these efforts, we established a beam power of 1-MW operation for the MLF users and a beam power of 800-kW operation for the neutrino users. In this paper, Recent achievement is summarized.

The radio-frequency quadrupole test stand (RFQ-TS) was prepared for conditioning the spare RFQ in the J-PARC Linac. Additionally, the RFQ-TS is used for the development of accelerator components and the acquisition of beam parameters. The digital feedback system of the Low-Level RF (LLRF) in the RFQ-TS was previously using the discontinued cPCI system, which had been in use for 20 years since its development. In order to continue improvements of the RFQ-TS and to allow for future development, the system has been upgraded to use $\mu$TCA.4-based system, which can be developed further. In this presentation, we will report the details of the upgrade, as well as the feedback and feedforward adjustments.