THERMAL-INSTABILITY OF A COMPRESSIBLE FINITE-LARMOR-RADIUS HALL PLASMA IN A POROUS-MEDIUM

The thermal instability of a compressible plasma in a porous medium is considered in the presence of a uniform vertical magnetic field to in clude the Hall-current and finite-Larmor-radius effects. The system is found to be stable for (c(p)/g) beta < 1, where c(p), beta and g are the specific heat at constant-pressure, the uniform adverse temperatur e gradient and the acceleration due to gravity respectively. The unifo rm vertical magnetic field, Hall-current and finite-Larmor-radius effe cts introduce oscillatory modes in the system for (c(p)/g) beta > 1, w hich were non-existent in their absence. The Hall current and finite L armor radius (FLR) individually have destabilizing and stabilizing eff ects respectively on the system. In their simultaneous presence there is competition between the destabilizing role of the Hall current and the stabilizing role of the FLR, and each succeeds in stabilizing a ce rtain wavenumber range. In tile absence of a magnetic field (and hence the absence of an FLR and Hall current), the destabilizing effect of medium permeability is seen, but in the presence of a magnetic field ( and hence the presence of an FLR and Hall current), the medium permeab ility may have a stabilizing or a destabilizing effect on the thermal instability of the plasma. The effect of compressibility is found to p ostpone the onset of thermal instability in plasma.