Animation of a Tokamak TAE Instability

The above animation shows the evolution of a large-scale toroidal Alfven instability in a tokamak. The multiple magenta/light blue lobes correspond to positive/negative variations in the electrostatic potential. The twisting, rotating movement is driven by the pressure gradient of the energetic plasma component (which is also driving the instability). This pressure gradient results in what are known as diamagnetic flows which cause the observed motion.

Diamagnetic flows are a very general feature of confined plasmas and result from the fact that plasma ions and electrons in a strong magnetic field execute small scale helical orbits known as gyro- or cyclotron orbits about the confining magnetic field lines. In the presence of a density or temperature gradient, the local circular gyro-velocities do not perfectly cancel as one moves in the direction of the gradient, resulting in a macroscopic flow. This lack of cancellation also results in diamagnetic currents in the plasma which are in such a direction as to reduce the magnetic field within the plasma from its external value.