Oscillator-type infrared Free Electron Lasers (FELs) have been used for various applications in material science, chemistry, biology, and so on. Extraction efficiency is the energy conversion efficiency from the kinetic energy of electron beam to the electromagnetic energy of laser light and a key parameter, which determines performances of an FEL oscillator. High extraction efficiency should be achieved to generate intense and ultra-short FEL pulses. In this article, dependence of the extraction efficiency of FEL oscillators on operation parameters and recent activity for increasing the extraction efficiency in Kyoto University FEL are discussed.

Measurement of activated materials and evaluation of activated areas of several types of accelerator facilities were studied for decommissioning planning from FY2017 to FY2020 under the contract of the Nuclear Regulation Authority. The research results were summarized in “Manual of Measurement and Evaluation of Activation for Decommissioning of Accelerator Facilities.” This manual consists of the classification of the activation area of accelerator facilities and the measurement and evaluation of the activation of concrete structures and metallic accelerator components in the decommissioning of accelerator facilities. This manual will be used for the decommissioning of accelerator facilities in Japan.

Coherent edge radiation (CER) is not well known light. However, by understanding the radiation characteristics, it is found that charm of the CER is not only that it is useful as an intense terahertz light source. Because the CER can be observed without damaging free-electron laser (FEL) oscillations, it can reveal the electron bunch shape immediately after FEL interaction. It was confirmed that the electron bunch shape was modulated by FEL oscillations by observing the CER.

Femtosecond atomic-scale imaging is a most challenging subject in materials science and has long been a cherished dream tool for scientists wishing to study ultrafast structural dynamics. In this research, we aim to develop an innovative relativistic femtosecond-pulsed electron microscope by combining a radio-frequency (RF) acceleration-based electron gun technology into high-voltage electron microscope. In this paper, we reported the concept and construction of the relativistic femtosecond-pulsed electron microscope. Some demonstrations of electron microscopy imaging with 3.1-MeV femtosecond electron pulses were presented. The potential of RF gun for electron microscope was discussed.

In the problem of global shortage of Mo-99/Tc-99m and the progress of targeted radionuclide therapy, the production of medical nuclide using accelerators has been attracting attention. An electron linear accelerator based medical radioisotope production system has many advantages in comparison with other accelerator systems: the size of the system is relatively small, increasing of the amount of raw material nuclide is easily achieved, the production amount of impurity nuclides is very little and the cross section of medical radioisotope production reactions are relatively high. These advantages can lead to a cost-effective system. In this paper, we introduce our recent efforts in experimental and simulated studies of the production of Mo-99, Cu-67 and Ac-225 using electron linear accelerator.

The third International School on Beam dynamics and Accelerator technology (ISBA20) was held for seven days from February 25 to March 3, 2021. The school was shifted from December to the end of the Japanese fiscal year in the hope that the COVID-19 epidemic that raged in the spring of 2020 would die down, but our wish was not answered and the school was brought online. Although we were not able to have the hands-on software training for the students that we had originally planned, we were able to finish the school successfully with lectures and presentations by the students. In this paper, we present an overview of the school and discuss the gains and losses of the online approach and the challenges.