The Japan Atomic Energy Agency (JAEA) has been proposing an accelerator-driven system (ADS) as a future nuclear system to efficiently reduce high-level radioactive waste generated in nuclear power plants. As a first step toward the full-scale design of the CW proton linac for the JAEA-ADS, we are now prototyping a low-beta (around 0.2) single-spoke cavity. The actual cavity fabrication started in 2020. Most of the cavity parts were shaped in fiscal year 2020 by press-forming and machining. In 2021, we started welding the shaped cavity parts together. By preliminarily investigating the optimum welding conditions using mock-up test pieces, each cavity part was joined with a smooth welding bead. So far, we have fabricated the body section and the beam port section of the cavity. By measuring the resonant frequency of the temporarily assembled cavity, we have confirmed that there is no significant problem with the cavity fabrication. In this paper, fabrication progress of the prototype spoke cavity is presented.

The Japan Atomic Energy Agency (JAEA) is designing a 30 MW continuous wave (cw) superconducting proton linear accelerator (linac) for the Accelerator Driven Subcritical System (ADS) proposal. The JAEA-ADS linac's source must provide a proton beam over 20 mA with an energy of 35 keV and a normalized rms emittance of less than 0.1 π mm mrad. As the extraction system determines the beam properties and quality, systematic optimizations in the geometry and input values of the extraction system design were conducted using the AXCEL-INP 2-D simulation program to satisfy the goal requirements. This work describes the extraction system design and reports the beam dynamics results of the first study for the proton source of the JAEA-ADS linac.

Reliability in high power hadron accelerators is a major issue, particularly for Accelerator Driven Systems (ADS). For example, the Japan Atomic Energy Agency (JAEA) ADS maximum frequency of beam trips longer than 5 min was set to 42 per year. A significant number of breakdowns are caused by the failure of accelerating cavities or by their associated systems. Hence, we studied how these can be effectively reduced. To this end, we developed the numerical tool LightWin that aims to determine the compensation settings for any superconducting (SC) linac automatically and systematically [1]. This tool has been successfully used for the MYRRHA SC linac. In this work, we applied LightWin to compensate for several failure scenarios involving the last section of the JAEA linac and compared the associated retuned settings and beam performance to those found in a previous study [2] with TraceWin.