CAWSES-II Space Weather International Collaborative Research Database in Japan (2009-2013)

We present particle simulations of one of the most fundamental instabilities in plasmas, i.e., two-stream instability induced by two groups of electrons moving with different drift velocities. Electrostatic waves grow from the thermal fluctuation noise with the growth rate predicted by the linear theory, and saturate due to nonlinear trapping of electrons by the coherent electrostatic potentials. After the saturation, the series of the large amplitude potentials coalesce with each other to form isolated potentials. This process was also observed in the past Vlasov code simulations and laboratory experiments and were called as electron holes. The plasma wave observation by the GEOTAIL spacecraft revealed that there also exist electrostatic solitary waves similar to electrons holes in the plasma sheet boundary layer of the Earth’s magnetotail. We performed electrostatic particle simulations for various parameters and found conditions for generation of the ESW. The ESW is generated as a results of nonlinear coalescence of strong electrostatic waves excited by an electrostatic beam instability involving the electron beam drifting relative to the majority of ions and another electrons drifting with the ions. We performed two runs with different initial ion thermal velocities Vi. One is with Vi = 2.0, and the other is with Vi = 0.1. We assumed the same density ratio R = 0.5 for these runs. Namely, two electron beams have the same thermal velocity with drift velocities Vd and 0. The evolution of the instability is shown by the phase diagrams of particle in the (X, Vx) space at different times. As a necessary condition for formation of the ESW, the ion thermal velocity Vi must be large enough so that the electrostatic waves due to the beam instability cannot decay to ion acoustic waves.

All computations were performed on the KDK computer system at Research Institute for Sustainable Humanosphere, Kyoto University.

Detailed description of the simulation runs are found in the following reference.

Y. Omura, H. Kojima and H. Matsumoto, Computer Simulation of Electrostatic Solitary Waves: A Nonlinear Model of Broadband Electrostatic Noise, Geophysical Research Letters, vol. 21, pages 2,923-2,926, 1994.

The simulation code used in producing the present database. is a one-dimensional elelctrostatic coode.

Detailed description of the code is found in the following reference.

Y. Omura and H. Matsumoto, KEMPO1: Technical Guide to One-Dimensional Electromagnetic Particle Code, Computer Space Plasma Physics: Simulation Techniques and Softwares, edited by H. Matsumoto and Y. Omura, pages 21-65, Terra Scientific, Tokyo, 1993.

http://www.terrapub.co.jp/e-library/cspp/index.html

../sramp/cdrom/sm0004/index.html

Also see: Home Page of Geotail Plasma Wave Instrument

http://www.rish.kyoto-u.ac.jp/space/gtlpwi/