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The Joint Projects under the Japan-USA Fusion Cooperation Program started in 1981 and has continued for more than 40 years. In the Joint Projects, although a wide range of fusion materials and engineering issues were covered, neutron radiation effects on fusion reactor materials have always been the major research emphases, and the neutron irradiation facilities in the US were jointly used by Japanese and US researchers. Japanese test facilities including neutron and charged particle irradiation facilities were complementarily used.The initial focus of the Joint Projects was on fundamental fusion neutron radiation effects and irradiation correlation. Systematic comparison of fission and fusion radiation effects in comparable damage levels and the effects of transmutation-induced helium were investigated. The collaboration was then focused on the effect of dynamic irradiation effects in variable conditions. In addition to the relatively fundamental studies, the Joint Projects contributed largely to development of candidate materials such as RAFM steels, vanadium alloys, SiC/SiC composites, and tungsten alloys, through a mechanism-oriented approach. The Joint Projects also covered issues specific to materials application to fusion blankets and plasma-facing components, including neutron radiation effects such as tritium retention and permeation of neutron-irradiated plasma-facing materials. Various irradiation technologies were developed and applied to the irradiation experiments, including those for in-situ testing.Considering that high energy neutron sources, such as A-FNS and IFMIF-DONES, now have high viability, the research supporting the neutron source programs is essential. The knowledge obtained through the Joint Projects is valuable and should be advanced for this purpose. To this end, it is of urgent necessity to launch an international scientific program accumulating knowledge of fusion neutron radiation effects, including their fundamental aspects., source:T. Muroga, Y. Hatano, D. Clark, Y. Katoh, Characterization and qualification of neutron radiation effects – Summary of Japan-USA Joint Projects for 40 years –, Journal of Nuclear Materials, Volume 560, 2022, 153494, ISSN 0022-3115, https://doi.org/10.1016/j.jnucmat.2021.153494., source:https://doi.org/10.1016/j.jnucmat.2021.153494

The Magnetospheric Multiscale (MMS) spacecraft observed many enhancements of electromagnetic ion cyclotron (EMIC) waves in an event in the late afternoon outer magnetosphere. These enhancements occurred mainly in the troughs of magnetic field intensity associated with a compressional ultralow frequency (ULF) wave. The ULF wave had a period of similar to 2-5 min (Pc5 frequency range) and was almost static in the plasma rest frame. The magnetic and ion pressures were in antiphase. They are consistent with mirror-mode type structures. We apply the Wave-Particle Interaction Analyzer method, which can quantitatively investigate the energy transfer between hot anisotropic protons and EMIC waves, to burst-mode data obtained by the four MMS spacecraft. The energy transfer near the cyclotron resonance velocity was identified in the vicinity of the center of troughs of magnetic field intensity, which corresponds to the maxima of ion pressure in the compressional ULF wave. This result is consistent with the idea that the EMIC wave generation is modulated by ULF waves, and preferential locations for the cyclotron resonant energy transfer are the troughs of magnetic field intensity. In these troughs, relatively low resonance velocity due to the lower magnetic field intensity and the enhanced hot proton flux likely contribute to the enhanced energy transfer from hot protons to the EMIC waves by cyclotron resonance. Due to the compressional ULF wave, regions of the cyclotron resonant energy transfer can be narrow (only a few times of the gyroradii of hot resonant protons) in magnetic local time., QC 20210622

Recent availability of a considerable amount of satellite and ground-based data has allowed us to analyze rare conjugated events where extremely low and very low frequency waves from the same source region are observed in different locations. Here, we report a quasiperiodic (QP) emission, showing one-to-one correspondence, observed by three satellites in space (Arase and the Van Allen Probes) and a ground station. The main event was on 29 November 2018 from 12:06 to 13:08 UT during geomagnetically quiet times. Using the position of the satellites we estimated the spatial extent of the area where the one-to-one correspondence is observed. We found this to be up to 1.21 Earth's radii by 2.26 hr MLT, in radial and longitudinal directions, respectively. Using simple ray tracing calculations, we discuss the probable source location of these waves. At ∼12:20 UT, changes in the frequency sweep rate of the QP elements are observed at all locations associated with magnetic disturbances. We also discuss temporal changes of the spectral shape of QP observed simultaneously in space and on the ground, suggesting the changes are related to properties of the source mechanisms of the waves. This could be linked to two separate sources or a larger source region with different source intensities (i.e., electron flux). At frequencies below the low hybrid resonance, waves can experience attenuation and/or reflection in the magnetosphere. This could explain the sudden end of the observations at the spacecraft, which are moving away from the area where waves can propagate.

We report the properties of the ionospheric exit point and characteristics of several types of very low frequency waves, including chorus and quasiperiodic emissions, based on a comprehensive dataset of simultaneous observations between ground and space. Whistler‐mode waves were observed at Kannuslehto (L = 5.5, KAN), Finland, and in the inner magnetosphere by the Japanese Arase satellite. During the 2017–2018 winter campaign, we found 13 cases showing one‐to‐one correspondence of wave spectra between KAN and Arase. This is the first time that such a large number of conjugated events have been reported at once. The duration of the events ranged from a few minutes up to 3 h, with 90% of events detected in the afternoon sector. While the occurrence rate is higher during daytime, this can also be related to a majority of the detected waves being quasiperiodic emissions, a known dayside phenomenon. Arase was usually located within 30° of the equator, at L ∼4–5, and detected mostly waves propagating at oblique angles (≥20°). Frequently, the ionospheric magnetic footprint of Arase was located equatorwards (south) from KAN, often in the same geographical area. We investigated the probable location of the ionospheric exit point of the waves from the location of the footprint of Arase and the angle of arrival of waves detected at KAN. Using density measurements at Arase we discuss magnetospheric wave propagation; we find that, in most cases, waves were unducted in their propagation from the satellite to the ground.