Name	:	Yasutomo ISHII
Title	:	Concurrent Staff, Senior Principal Researcher / BA Project Coordination Group Leader
Address	:	2-116 Omotedate, Obuchi, Rokkasho-mura, Kamikita-gun, Aomori 039-3212, JAPAN

Research Title

• Nonlinear evolution and deformation of the driven magnetic island in the rotating plasma
  
• Formation and Long Term Evolution of an Externally Driven Magnetic Island in Rotating Plasmas

  Nonlinear evolution and deformation of the driven magnetic island in the rotating plasma

Abstract

Novel features of the rapid growth and the nonlinear dynamics of the driven magnetic island in the rotating plasma are studied by nonlinear MHD simulations. The transition phase of the magnetic island evolution is found between the rapid growth phase and the Rutherford-like phase in the low resistivity regime. It is shown that the rapid growth of the magnetic island is associated with its deformation that leads to the secondary magnetic island formation around the original X-points. The suppressed state is characterized by the asymmetric deformation of the magnetic island caused by the non-monotonic torque profile within the island separatrix. In the regime of the high magnetic flux input rate, the critical magnetic island width shows weak dependence on viscosity while noticeably depends on resistivity. It is conjectured that this is a result of the effect of the Alfven type interaction between rotating plasma and fast growing external magnetic perturbation.

	Reference
	[1] Y.Ishii, M.Azumi and A.I.Smolyakov, Nuclear Fusion 47, 1024 (2007).

  Formation and Long Term Evolution of an Externally Driven Magnetic Island in Rotating Plasmas

Abstract

The Alfven resonance effects on the magnetic island evolution driven by the externally applied perturbation are investigated for the rotating plasmas. In a rotating plasma, the radial position of the Alfven Resonance surface is deviates from that of the magnetic neutral surface and the perturbed plasma current is formed at the both sides of the magnetic neutral surface. This deviation screens the penetration of an externally applied perturbation into the resistive layer. This process is important to estimate the critical value of an external perturbation, beyond which the magnetic island grows rapidly. The nonlinear evolution of the externally driven magnetic island is also investigated at the low and high viscosity ν. It is shown that the transition phase accompanying the secondary reconnection at the initial X-point in the driven magnetic island evolution occurs in the low resistivity and viscosity plasma.

	Fig.1: Plasma current profile around a resonant surface in rotating plasma
	Fig.2: Time evolution of the radial position of the Alfven resonance and the maximum and minimum of the perturbed current.

	Reference
	[1] Y.Ishii and A.I.Smolyakov, "Formation and Long Term Evolution of an Externally Driven Magnetic Island in Rotating Plasmas", Plasma and Fusion Research 3, 048 (2008).