Sound and thermal waves propagation in a hydrogen plasma heated by an external radiation field

The thermal equilibrium of a hydrogen plasma heated and ionized by an external radiation field, diluted by a factorW _* and defined by an effective temperatureT _*, is studied. In addition, the problem of propagation of acoustic and thermal waves in the above plasma model is also analysed. It is found that an external radiation field has stabilizing effects against wave amplification. From the dispersion relation obtained, the phase velocity for sound and thermal waves and their respective scale-length of damping (or anti-damping) is calculated as a function of the frequency for representative values of the plasma temperature and the external radiation fieldT _*.