Marfes: a magnetohydrodynamic stability study of two-dimensional tokamak equilibria

Abstract

The marfe is studied as a radiative thermal instability in a two-dimensional axisymmetric tokamak model. To obtain a detailed idea of the marfe onset, a linear analysis is performed, using a full set of magnetohydrodynamic equations. Some typical marfe shots from JET are simulated. It is demonstrated how the marfe is a result of a poloidally symmetric temperature decrease and an asymmetric density increase. It is found that the onset of the marfe is accompanied by significant perturbations of pressure and magnetic field. The evolution of the marfe is discussed, based on the linear results. The model proves to give not only qualitative, but also quantitative agreement. The plasma parameters for marfe onset can be predicted accurately. Thermal instabilities belong to a continuum in the MHD spectrum of eigenfrequencies. The thermal stability of an equilibrium can be tested very easily by calculating this continuum.

CASTOR: Normal-Mode Analysis of Resistive MHD Plasmas

“…The numerical method provides a general tool for the evaluation of the spectrum of dissipative MHD systems. Consequently, a generalisation of the method to the analysis of kinetic Alfvén eigenmodes [23] and of thermal instabilities has been successfully performed in the context of a stability analysis of tokamak equilibria concerning MARFE's [24]. Thus a typical matrix element reads…”

On the importance of parallel heat conduction and magnetic geometry for multifaceted radiation from the edge (MARFE)

“…10͒ that this process, which suppresses the instability through smoothing of temperature perturbations, should be significantly engaged in the definition of critical parameters. Later it was recognized, 7,8 however, that for perturbations with a zero parallel component of the wave vector, k ʈ , conductive heat transport along field lines does not work. Such perturbations should start to grow first of all when, e.g., the plasma density is ramped up and, thus, they should provoke MARFE.…”

Ultrahigh Densities and Volume Recombination inside the Separatrix of the Alcator C-Mod Tokamak

“…The poloidal location of the MARFE at the high-field edge and its radial extent reaching to closed flux surfaces has been seen as evidence for poloidally asymmetric transport of power across flux surfaces in the core plasma [1,4]. All of the above characteristics have led to the study of MARFEs both experimentally [1][2][3][5][6][7][8][9] and theoretically [10][11][12][13][14][15][16][17][18]. The modelling of the MARFE as an impurity radiation-condensation instability is fairly well accepted.…”