D. Dogen

M. Toida

N. Bessho

T. Maeda

Y. Ohsawa

Toida,  M.

Maeda,  T.

Dogen,  D.

Bessho,  N.

Ohsawa,  Y.

NIFS-Repository (National Institute for Fusion Science)

§3S. Simulation Study of Current-Driven Instability in a Multi-lon-Species Plasma Toida, M., Maeda, T., Dogen, D., Bessho, N., Ohsawa, Y. (Department of Physics, Nagoya Univ.) The presence of multiple ion species provides many interesting issues.1- 4) We have studied its effects in magnetosonic waves and current-driven instabilities. We here describe the work on current-driven instabil-ities. The properties of current-driven instabilities in a multi-ion-species plasma can be different from those in a single-ion-species plasma. For example, in a plasma with the same elemental composition as the so-lar corona, for some plasma parameters, ion-cyclotron waves or oblique ion-acoustic waves can have posi-tive growth rates near the cyclotron frequency of 3He, w ~ 03He' 5) At the same time they can have negative growth rates near 4He cyclotron frequency, w ~ 04Hc. These waves could play an essential role in 3He-rich events where the abundance ratio 3He/4He becomes quite high, up to order unity, in the energetic parti-cles produced in solar flares. We have started the simulation study of the current-driven instability in a multi-ion-species plasma using a three-dimensional electrostatic particle code with full ion and electron dynamics. We will investigate effects of the presence of multiple ion species on the growing and saturation of ion cyclotron waves and ion acoustic waves, giving great attention to the energy transport in association with these instabilities. Firstly, we sim-ulate the two-ion-species plasma, where the mC),in com-ponent is hydrogen and the minority component is he-lium; the aboundace ratio is nHe/nH = 0.1 as in space plasmas. The temperature ratios are Tc/TH = 5.0, THc/TH = 1.0. The electron current along the mag-netic field is Vdc/ VTe = -1.0, where Vde is the electron drift velocity parallel to the ambient magnetic field and VTe is the electron thermal velocity. For these parameters, ion acoustic waves are unstable and ion cyclotron waves are stable. Figure 1 shows the time variation of electron cur-rent, light-ion and heavy-ion energies. The dotted lines are energy components parallel to the magnetic field and solid lines are perpendicular components. The heavy ions as well as light ions are heated, un-like the prediction of the linear theory. In both H and He, perpendicular energy EJ.. mainly increases. Inter-estingly, E J.. in He keeps increasing, even though the increasing rate of hydrogen energy quickly goes down. This result indicates that the heavy ions play a signif-icant role in energy transport as well as in the growing of waves. 1.00 0.98 Q;) E-4 0.96 :> -::c 0.94 :> 0.92 0.90 1.15 H o 1.10 El. ~ __ 1.05 ~ ----------------~ ------------------ E ~ ~. H 1.00 0.95 '--'----'---'---'-----'----'----'--..l....--'----'--'---'-----'----'---'--1. 08 c---1---:--r---,----.-----,---.---,----r---r----r-----:----.----.----,--1.06 He 1.04 1.02 1.00 o 2000 6000 8000 Fig. 1. Time variation of electron current, light ion and heavy ion energies. Reference 1) Dogen, D., Toida, M. and Ohsawa, Y.: Phys. Plas-mas 5 (1998) 1298. 2) Maruyama, K., Bessho, N. and Ohsawa, Y.: Phys. Plasmas 5 (1998) 3257 3) Toida, M., Dogen, D. and .Ohsawa, Y.: J. Plasma Fusion Res. JPFR Series 2 (1999) in press. 4) Toida, M., Dogen, D. and Ohsawa, Y.: submitted to J. Phys. Soc. Jpn. 5) Zhang, T. X., Toida, M. and Ohsawa, Y.: J. Phys. Soc. Jpn. 62 (1993) 2545. 309 

Simulation Study of Current-Driven Instability in a Multi-lon-Species Plasma

Simulation Study of Current-Driven Instability in a Multi-lon-Species Plasma

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