Split of the Alfvén wave packet in a dissipative plasma

We have experimentally found that ion-neutral collisions in a magnetized plasma cause a drastic change in the dispersion relation of the Alfvén wave at frequencies below the ion-cyclotron frequency. In a consecutive experiment, we have also found that the measured average velocity of the wave packet does not obey the conventional group velocity that exceeds the velocity of light, but obeys a new defined group velocity that is much lower than the velocity of light. Furthermore, when the initial central frequency of the wave packet is just located on the anomalous dispersion range of frequency, the wave packet splits, when propagating along the magnetic field, into two new wave packets with central frequencies being higher and lower than the initial central frequency. One of the new packets with lower central frequency is confirmed to be the shear Alfvén wave and the other the compressional Alfvén wave; the behaviour of these new wave packets can also be explained by our new theory.