Observation of nonlinear neoclassical {nabla}{sub p}-driven tearing modes in TFTR

Abstract

A quantitative comparison is made between the tearing-type modes observed in TFTR supershot plasmas and the nonlinear, neoclassical p: ssure gradient (Vp) driven tearing mode theory. Good agreement is found on the nonlinear magnetic island evolution of a single helicity mode {mjn = 3/2, 4/3 or 5/4, where m and n are the poloidal and toroidal mode numbers, respectively). Statistical data on the island width and growth rate are also found to be consistent with this theory. The results imply that the supershot plasmas are stable to the classical current-driven tearing modes.

Computational modeling of neoclassical and resistive magnetohydrodynamic tearing modes in tokamaks

“…This simple neoclassical MHD model has shown remarkable dynamical agreement with the experimental observations on the Tokamak Fusion Test Reactor ͑TFTR͒. 1,2,11 To further explore the dynamics of the neoclassical MHD tearing mode in a realistic toroidal geometry, numerical simulations based on neoclassical reduced MHD equations have been conducted. In Section II, the model equations for neoclassical reduced MHD as implemented in the neofar code are presented.…”

“…In an ideal situation, where ʈ / Ќ →ϱ or where the magnetic fluctuations are zero, the pressure contours and field lines would exactly coincide. However, in the vicinity of the island X-point even though the perpendicular transport is slow, the transit time across the X-point for a small distance ␦ x is quite short: 2 . On the other hand, the singular nature of the separatrix requires heat to travel an infinite distance in the parallel direction to cross the X-point:…”

“…1,2 Often, the onset of such oscillations either cause the plasma to disrupt violently 3,4 or the plasma confinement to degrade significantly. 1 Experimental observations indicate that these instabilities are associated with magnetic reconnection-an interpretation based on the observation of the slow growth of these instabilities and mode numbers which are resonant in the plasma.…”

“…Additionally, the electron cyclotron emission diagnostic indicates the presence of flatspots in the electron temperature profile about the resonant surface that are characteristic of magnetic island formation associated with the tearing events. 1,2 One theoretical explanation for such modes is destabilization from the perturbed bootstrap current. Bootstrap currents arise from the viscous damping of the poloidal electron flow.…”

Verification of gyrokinetic particle simulation of current-driven instability in fusion plasmas. I. Internal kink mode

“…These equilibrium currents often excite magnetohydrodynamic (MHD) instabilities including ideal kink modes 1 and resistive tearing modes. 2 The basic physics mechanisms of these current-driven instabilities manifest themselves in tokamak plasmas as various macroscopic MHD modes, such as fishbones, 3 sawteeth, 4 neoclassical tearing modes, 5 and resistive wall modes, 6 which can limit burning plasma performance and threaten fusion device integrity. 7 The studies of the MHD modes typically rely on MHD simulations [8][9][10] or reduced models.…”