This special issue “Particle Accelerators and their Future” focuses on explanations, progress, and future developments of particle accelerators and related technologies and applications. Accelerators have been applied to various fields and opening up new research areas. We cover six topics from a wide variety of the fields in this issue.

FCC is a project for a next generation circular collider based at CERN, as the next step of LEP/LHC experiments. It will have at least two stages : (i) measurements on electroweak (Z/W), Higgs, tt by e⁺e⁻ collision (FCC-ee) and (ii) energy frontier pp collision (FCC-hh) up to 100 TeV center of mass (CM) energy. Both will be performed by colliders in the same tunnel with 90–100 km circumference built around the Geneva area across the Swiss-French border.

A new 3 GeV light source named “NanoTerasu” is under construction at Aobayama new campus of Tohoku university. NanoTerasu will form a photon science platform together with SPring-8, which covers a wide spectral range from UV to hard X-rays, by delivering brighter and more coherent soft to tender X-rays with superior stability and reliability. Installation of the accelerator system is in progress for the first light in 2023. NanoTerasu employs a four-bend achromat lattice using combined-function bending magnets to achieve a low emittance of about 1 nmrad with a small circumference of 349 m and a beam current of 400 mA. The storage ring consists of 16 cells to provide 28 user beamlines. This paper presents an overview of NanoTerasu and describe details of the storage ring vacuum system.

Particle accelerators and vacuum are inseparable. After a description of the situation surrounding the development of particle accelerators at universities, some related research areas are introduced, i.e., the J-PARC ACS linear accelerator, a liquid lithium target system for BNCT (Boron Neutron Capture therapy) and measurements of secondary electron emission coefficients of dielectrics for RF vacuum windows.

In recent cancer treatment, particle beam therapy, irradiates tumors with high-energy beams of protons or carbon, is spreading due to its capability of reducing radiation exposure to normal tissues. Advances in particle accelerators such as synchrotrons and cyclotrons have played an important role in the spread of particle beam therapy. Development of treatment dedicated accelerators has contributed to the miniaturization of the accelerator systems, and the scanning irradiation method has become a standard irradiation method in particle beam therapy because it can form a precise irradiation area even for tumors with complicated shapes. In the future, superconducting technology will enable further miniaturization of the accelerator system, and improvement of dose rate will contribute to higher throughput and more sophisticated irradiation.

To realize high intensity proton accelerators, it is necessary to design and develop secondary particle production targets and beam windows from the various viewpoints such as secondary particle production and transport, heat generation by the proton beam, degradation of material properties due to irradiation, and maintenance of activation equipment. In order to widely distribute heat generation and material damage due to irradiation, a rotating target system in which the target material is rotated and a liquid metal target system in which liquid metal is circulated as the target material have been implemented. Research and development of materials such as graphite, titanium alloys, and tungsten are underway. In addition, proton beam irradiation tests and subsequent Post-Irradiation-Examination are being conducted under the international cooperation RaDIATE collaboration to investigate the irradiation effects of materials.

A new, developing charged particle acceleration schemes are reviewed. In particular, the laser wakefield acceleration of electrons based on high-peak-power, short-pulse lasers and tenuous gas plasma is focused and a brief principle, historical progress, and current status of the achievement are given as well as future prospect.