Superconducting radio frequency (SRF) accelerating cavities are currently a key technology in many particle accelerator projects for elementary particle physics, nuclear physics, neutron sources and light sources. Present and future SRF accelerator projects and many types of SRF cavity structures being developed worldwide are reported.
Superconducting RF technology has been developed based on electropolishing and ultra-pure water high pressure rinsing. Recently, new technologies, so-called Nitrogen doping and Nitrogen infusion, have been proposed and an improvement in cavity performance was achieved. Nitrogen doping realizes a drastic reduction in surface losses and has become the new standard for CW accelerators. Nitrogen infusion is another attractive technology. It has the possibility of improving the acceleration gradient too. The procedures for current standard surface treatment, Nitrogen doping and Nitrogen infusion are described, and experimental results are shown. New knowledge regarding how to handle magnetic flux to improve surface resistance is also discussed.
We discuss the physics of superconducting resonant cavities for particle accelerators, including the basics of a superconducting cavity, Meissner state stability, and surface resistance together with related scientific and technological challenges. Ongoing research and some proposals for solving the challenges are also discussed.
Use of the Advanced Fusion Neutron Source (A-FNS) for testing materials in a future fusion DEMO reactor aims to provide an accelerator-based D-Li neutron source to produce high-intensity, high-energy neutron flux to test samples as possible candidate materials. As the accelerator system validation activity to demonstrate deuteron acceleration by the low-energy section of an IFMIF deuteron accelerator up to 9 MeV with a beam current of 125 mA in CW, a linear IFMIF prototype accelerator (LIPAc) was commissioned under the Broader Approach (BA) Agreement of the fusion program between Japan and the EU. A SRF linac containing eight half-wave resonators (HWRs) operating at 175 MHz and eight focusing solenoids to accelerate the energy from 5 MeV to 9 MeV and the licensing required by the High-Pressure Gas Safety Law (HPGSL) in Japan are reported.