Nonlinear tearing mode in inhomogeneous plasma: I. Unmagnetized islands

Abstract

A theory of the nonlinear growth and propagation of magnetic islands in the semi-collisional regime is presented. The theory includes the effects of finite electron temperature gradients and uses a fluid model with cold ions in slab geometry to describe islands that are unmagnetized in the sense that their width is less than ρ s , the ion Larmor radius calculated with the electron temperature. The polarization integral and the natural phase velocity are both calculated. It is found that increasing the electron temperature gradient reduces the natural phase velocity below the electron diamagnetic frequency and thus causes the polarization current to become stabilizing.

Role of singular layers in the plasma response to resonant magnetic perturbations

“…A similar effect was predicted for magnetic islands locked to the wall in Ref. [77], and was later demonstrated through numerical simulations in Ref. [64].…”

Linear and nonlinear stability of drift-tearing mode

“…The mode frequency approaches a higher (lower) value for the smaller (larger) island case. The island drifts in the electron diamagnetic drift direction as expected [15].…”

“…The corresponding deuterium plasma has the following parameters, T e =3.25keV, n e =1. 15 a. The solid curve in figure 1 shows a decay of the mode for…”

“…It is shown in the present paper that, the drift-tearing mode stability depends on the Due to the fast parallel transport in the island region, the local temperature profile is more flattening for a larger island (Figure 7), leading to a weaker effect of the diamagnetic drift (ion polarization current), so that the bootstrap current density perturbation could drive the mode into the NTM regime more easily for a larger value of W 0 , as shown in Figure 5 In existing theories of the ion polarization current perturbation, the effect of the perpendicular electron heat diffusion is not considered, so that the effect of q and the small island regime are not found there [5][6][7][8][9][10][11][12][13][14][15]. Another feature of our numerical results is that the mode frequency due to the diamagnetic drift is self-consistently calculated, and the island is found to rotate in the electron diamagnetic drift direction as expected [15].…”

“…The experimental values of ¡ £ ¢ are usually found to be negative for tearing modes with poloidal mode number m 3. In the nonlinear phase the diamagnetic drift effect leads to the ion polarization current model of the threshold for NTM onset, which has attracted extensive studies [7][8][9][10][11][12][13][14][15]. In addition, the Glasser effect also provides a somewhat smaller stabilizing effect [5,16,17].…”