Tearing-mode stability properties of a diffuse anisotropic field-reversed ion layer at marginal stability

Detailed computational results are presented for the stability of linear tearing modes in low-q cylindrical tokamaks with various radial profiles. The stability properties of a widely used ‘classical’ profile are compared with those of a ‘piecewise’ profile. It is shown that the stability properties of low-q tokamak discharges show a sensitive dependence on small changes in the current density profile near the singular surface. While the ‘classical’ profile is stable for a large range of q0, where q0 is the value of the safety factor on the magnetic axis, a similar ‘piecewise’ profile is unstable for the same set of parameters.

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Tearing-mode stability in a cylindrical plasma with equilibrium flows

Journal of Plasma Physics ◽

10.1017/s0022377800015695 ◽

1991 ◽

Vol 45 (2) ◽

pp. 267-283 ◽

Cited By ~ 19

Author(s):

K. P. Wessen ◽

M. Persson

Keyword(s):

Magnetic Field ◽

Mass Flow ◽

Rational Surface ◽

Flow Speed ◽

Marginal Stability ◽

Tearing Mode ◽

Cylindrical Plasma ◽

Mode Stability

The effect of a sheared equilibrium mass flow on the resistive tearing mode is studied numerically by calculating Δ′. Both stabilizing and destabilizing effects are found, depending on the velocity and magnetic field profiles. Specifically, when q0 ≈ 1, the flow is strongly stabilizing for centrally peaked current profiles, whereas the flow has a strongly destabilizing effect for flatter current profiles. While the extreme effects are more pronounced for larger flows, a smaller flow may have more influence on marginal stability. The case where the flow speed becomes comparable to the Alfvén speed is also examined. It is found that this may lead to the equations being singular at points other than a rational surface, drastically changing the behaviour of the mode.

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Effect of poloidal equilibrium flow and pressure gradient on the m/n = 2/1 tearing mode

Nuclear Fusion ◽

10.1088/1741-4326/ac4947 ◽

2022 ◽

Author(s):

Yue Ming ◽

Deng Zhou ◽

Jinfang Wang

Keyword(s):

Pressure Gradient ◽

Stability Index ◽

Plasma Pressure ◽

Mode Number ◽

Pressure Perturbation ◽

Equilibrium Flow ◽

Tearing Mode ◽

Mode Instability ◽

Mode Stability ◽

Adverse Influence

Abstract The effect of equilibrium poloidal flow and pressure gradient on the m/n = 2/1 (m is the poloidal mode number and n is the toroidal mode number) tearing mode instability for tokamak plasmas is investigated. Based on the condition of ≠0 ( is plasma pressure), the radial part of motion equation is derived and approximately solved for large poloidal mode numbers (m). By solving partial differential equation (Whittaker equation) containing second order singularity, the tearing mode stability index Δ′ is obtained. It is shown that, the effect of equilibrium poloidal flow and pressure gradient has the adverse effect on the tearing mode instability when the pressure gradient is nonzero. The poloidal equilibrium flow with pressure perturbation partially reduces the stability of the classical tearing mode. But the larger pressure gradient in a certain poloidal flow velocity range can abate the adverse influence of equilibrium poloidal flow and pressure gradient. The numerical results do also indicate that the derivative of pressure gradient has a significant influence on the determination of instability region of the poloidal flow with pressure perturbation.

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