M. Toida

S." Ishiguro

Y. "Ohsawa

National Institute for Fusion Science (NIFS-Repository)

We have studied the evolution of magneto-hydrodynamic waves created by a strong disturbance in a collisionless plasma and particle acceleration caused by these waves: specifically, 1) evolution of large-amplitude Alfven waves produced behind a magnetosonic shock front and ultrarelativistic electron acceleration occurring there, 2) effects of the inhomogeneity of the external magnetic field on positron acceleration in a shock wave in an electron-positron-ion plasma, 3) effects of ion composition on nonlinear evolution of oblique magnetosonic waves in two-ion-species plasmas, and 4) multi-dimensional effects on electron trapping and acceleration in an oblique shock wave.1) Evolution of large-amplitude Alfven waves behind a magnetosonic shock front and associated ultrarelativistic electron accelerationA strong disturbance in a magnetized plasma produces a magnetosonic shock wave. Moreover, large-amplitude Alfven waves are generated behind the shock front. We have observed the evolution of these waves with one-dimensional, fully kinetic, relativistic, electromagnetic simulations. Furthermore, we have recognized three types of ultrarelativistic electron acceleration caused by these Alfven waves [1]. These energization processes can take place in both weak and strong external magnetic fields.Fig. 1. Wave trajectories.Figure 1 shows the trajectories of the waves created by a strong disturbance. The two thick lines indicate forward (right going) and backward (left going) shock fronts, while the thin lines represent the trajectories of Alfven waves; the dotted line is the trajectory of a strong-magnetic-field (SMF) pulse, which is thought to be developing into the Alfven wave.Figure 2 displays magnetic-field profiles (the top andFig. 2. Snap shots of magnetic and density profiles and electron phase space (x, ).second panels), electron density (third panel), and electron phase space (x, ) (bottom panel), where  is the Lorentz factor. In this figure, the forward and backward shock fronts are near x/(c/pe)=2370 and 2020, respectively. TheSMF pulse is near x/(c/pe)=2230, and Alfven waves are on its left. In the Alfven wave region including the SMF pulse, we find ultrarelativistic electrons with ~300. 2) Positron acceleration Positron acceleration to ~104 by a shock wave has been demonstrated with particle simulations with real ion-to-electron mass ratio, mi/me=1836. Furthermore, effects of the spatial gradient of the external magnetic field on the acceleration has been investigated in detail [2].3) Oblique magnetosonic waves in two-ion-species plasmasThe study of the effects of ion composition on perpendicular magnetosonic waves [3] has been extended to oblique waves [4].?4) Multi-dimensional simulation of electron trappingMulti-dimensional effects on electrons in an oblique shock wave have been investigated in detail by means of two-dimensional electromagnetic particle simulations and test particle calculations. It has been shown that whistler wave instabilities can cause detrapping of energetic electrons from the shock wave [5].[1] Y. Takeyama, S. Nakayama, and Y. Ohsawa, Phys. Plasmas 18, 092307 (2011).[2] T. Iwata, S. Takahashi, and Y. Ohsawa, Phys. Plasmas19, 022302 (2012). [3] M. Toida, Y. Ohsawa, and T. Jyounouchi, Phys. Plasmas 2, 3329 (1995); M. Toida, H. Higashino, and Y. Ohsawa, J. Phys. Soc. Jpn 76, 104052 (2007).[4] M. Toida and Y. Kondo, Phys. Plasmas 18, 062303 (2011).[5] M. Toida and J. Joho, submitted to J. Phys. Soc. Jpn.374§3. Particle Acceleration in Large-amplitude MHD Waves Created by Strong DisturbancesOhsawa, Y., Toida, M. (Dept. Physics, Nagoya Univ.), Ishiguro, S.

Particle Acceleration in Large-amplitude MHD Waves Created by Strong Disturbances

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