In early February, a symposium was held in Japan to promote the importance of the International Linear Collider (ILC) project, a proposed 250 GeV linear accelerator based on superconducting radiofrequency technology. Although the final decision regarding the funding of this project is yet to be made, research and development efforts at facilities such as the High Energy Accelerator Research Organization (KEK) in Japan are proceeding undeterred.
The ILC will collide electrons and positrons, accelerated in two linear accelerators using 8,000 superconducting radiofrequency cavities. This engineering feat requires the design of special niobium cavities (pictured), custom cryogenic systems and the establishment of the mass production of these components. At the KEK testing facility an acceleration of 32 MeV m−1 has already been achieved with eight cavities and by the end of this year researchers hope to achieve 400 MeV m−1 acceleration with 14 cavities.
Technology-wise, researchers are confident that the ILC can be built, but there are other challenges. Currently, the most likely location for the ILC is the Tohoku region, the north-eastern area of Japan. Locals in the Tohoku region are generally positive and supportive of the project, but the general public in Japan is sensitive to the issue of radiation especially after the 2011 Tohoku earthquake that led to the Fukushima Daiichi nuclear accident. There are worries regarding tritium as a by-product of the beam absorption process in the beam dump. “It is important to continue to explain the risks to the local people in Tohoku,” says Shinichiro Michizono, associate director for the ILC.
Regardless of whether the ILC gets a green light, the research and development efforts will bear fruit. The superconducting radiofrequency technology could provide a cheaper, more compact alternative to traditional particle acceleration. “We are looking for new industry and medical applications for superconducting accelerators,” says Michizono. These include accelerator-based production of molybdenum-99, an important medical radioisotope, accelerator-based semiconductor lithography and perhaps even transportable compact accelerators for X-ray and neutron tomography for large infrastructure such as bridges or roads.
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Georgescu, I. Superconducting accelerator technologies. Nat Rev Phys 2, 128 (2020). https://doi.org/10.1038/s42254-020-0155-y