Research Activities at RISH

Prof. Peter H. Yoon (Institute for Physical Science and Technology, University of Maryland)

I left on the Christmas Day, December 25^th, 2022, to visit Kyoto University, RISH, upon invitation by Professor Yoshiharu Omura, to collaborate with him for three months. I had previously visited Kyoto University back in 2002, so this visit was very special, with 20 years of span in between. During my visit, I collaborated with Professor Omura on a number of research topics, which includes a comparative study between the particle-in-cell computer simulation of the electrostatic upper-hybrid mode instability, and the study of the same instability with the use of analytical quasilinear theory. The so-called upper-hybrid waves and fluctuations are pervasively detected in the magnetized plasma environment of the planetary magnetosphere, which includes the terrestrial magnetosphere, Jupiter and Saturn’s magnetospheres. As such, we believe that our fundamental study can have a wide-ranging applicability in the space and astrophysical plasma physics setting. We have submitted the findings in a peer-reviewed scientific journal. The manuscript information is as follows:

• P. H. Yoon and Y. Omura, Electrostatic upper-hybrid mode instability driven by a ring electron distribution, Physics of Plasmas, submitted for publication.

Figure 1 encapsulates the favorable comparative nature of the two methods. The color-coded background depicts the frequency (vertical axis) and wave number (horizontal axis) spectrogram associated with the upper-hybrid waves and fluctuations generated by the particle-in-cell simulation method. The dark red implies high intensities, while the yellow background designates low intensities. The black curves are theoretically computed upper-hybrid and multiple-harmonic electron cyclotron wave dispersion relation. Notice the good agreement between the theory and simulation.

Figure 1: Comparison between the computer simulation (color-coded background) and theoretical upper-hybrid and multiple-harmonic electron cyclotron wave dispersion relation (black curves).

Professor Omura and I also initiated a research program with Dr. Masafumi Shoji (Nagoya University) on a research problem of potentially great significance. That is,  in the long history of plasma physics the consequence of studying the dynamical processes in an effectively two-dimensional (2D) system, which is often adopted to simplify the analysis, versus a genuine three dimensions, had not been discussed in any significant depths. However, in 2009, Professor Omura and Dr. Shoji had published a paper

• M. Shoji, Y. Omura, B. T. Tsurutani, O. P. Verkhoglyadova, and B. Lembege (2009), Mirror instability and L-mode electromagnetic ion cyclotron instability: Competition in the Earth’s magnetosheath, Journal of Geophysical Research: Space Physics, 114, A10203, doi:10.1029/2008JA014038,

Where they put into question the validity of such a view, even though at the time and since then, such a profound implication seems to have been largely missed by the general plasma physics community. During my visit to Kyoto University, RISH, we have initiated to re-investigate this profoundly interesting problem, and as an initial effort, I have made some progress in explaining the issue, and have presented an oral invited talk at the Joint Workshop of　“Physics and application of whistler waves” and “Future perspective of study on nonlinear wave-particle interaction,” which took place on March 16 and 17, 2023. The title of my talk was

• Three-Dimensional Plasma Dynamics in EMIC and Mirror-Mode Instabilities

I also gave a general seminar at RISH on February 15, 2023, on a topic of interest to space plasma physics specialists. The title of the seminar was

• Kinetic Plasma Processes in the Solar Wind

Finally, during my stay at Uji, I visited a number of places of interests, which includes the historic Byodoin Temple and a beautiful Japanese tea garden (see the enclosed pictures).