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.

Multifaceted asymmetric radiation from the edge (MARFE) is studied as a radiative thermal instability in a one-dimensional (1-D) cylindrical equilibrium model. In order to get a global idea of the MARFE onset, a linear analysis is performed, using a full set of magnetohydrodynamic (MHD) equations. It is found that the onset of the MARFE is accompanied by perturbations of pressure and magnetic field. These characteristics seem especially important in case the MARFE leads to a disruption and rational surfaces are affected. The experimentally observed relation between critical density and plasma current [Nucl. Fusion 24, 977 (1984)] is studied. The particular role of perpendicular thermal conduction is considered separately. Correspondence with experimentally observed behavior, like toroidal symmetry and poloidal asymmetry, is discussed.

The equations for the continuous subspectra of the linear magnetohydrodynamic (MHD) normal modes spectrum of two-dimensional (2D) plasmas are derived in general curvilinear coordinates, taking nonadiabatic effects in the energy equation into account. Previously published derivations of continuous spectra in the 2D ideal MHD case and in 1D nonadiabatic MHD are thus complemented with calculations for 2D nonadiabatic MHD spectra. The nonadiabatic MHD spectrum contains a thermal continuum in addition to the well-known Alfvén and slow continua. These thermal continuum modes are exponentially decaying or growing in time. The latter unstable modes are widely accepted as an explanation for the onset of marfes in tokamaks and the most favored hypothesis for prominence formation in the solar corona. A numerical code has been developed to calculate the continuum modes. An investigation of a typical ‘pre-MARFE’ (multifaceted asymmetric vadiation from the edge) equilibrium is presented.

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