Physical properties of plasma ion dynamics in various equilibria of field-reversed configuration
T. Takahashi, M. Ubukata, N. Iwasawa, Y. Kondoh
Gunma University, Kiryu, Gunma 376-8515, Japan
The tilt mode stability is the major physical issue of Field-Reversed Configurations (FRCs). Although the ideal MHD predicts the FRC plasmas are unstable against the mode, however, the several experimental measurements show their resilient feature. Since the averaged beta value of FRC is near unity and thus ion Larmor radius is comparable to the scale length, the fluid limit breaks and the velocity distributions become important to expect an FRC's global behavior. In the FRCs, depending on the velocity, there are three types of particle trajectories. A faster ion with large canonical angular momentum exhibits betatron orbit encircling the geometric axis. A fast but with a smaller canonical angular momentum than the betatron particle draws a figure-8 orbit. The direction of gyration is changed due to the field reversal. These two peculiar trajectories may cause a kinetic stability of FRCs, and therefore the properties of ion dynamics should be investigated. On this viewpoint, Hayakawa et al. studied the stochasticity or adiabaticity of ion motion in the deuterium-helium 3 fueled fusion plasma.[1] The existence of adiabatic and trapped particle in the curved magnetic line region was shown in [1], and it may offer a stabilizing flow to the tilt mode activity. However, only Hill's vortex model was employed for the equilibrium of FRC, and how the equilibrium field affects the particle orbit is still unclear.
References
[1]Y. Hayakawa, T. Takahashi, Y. Kondoh, Nucl. Fusion, 42 (2002) 1075
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