**4. Summary**

In Table 4, the MHD stability properties of both prolate and oblate FRCs are summarized (Yamada et al., 2007). In oblate FRC plasma, the global mode (*n* = 1 external tilt and shift mode, co-interchange mode) is unstable. But these modes can be stabilized by employing a close-fitting conducting shell or shaping with a strong external magnetic field. In prolate plasma, the internal tilt mode and co-interchange mode are MHD-unstable. However, these can be stabilized by nonlinear effects, such as FLR, rotation and sheared flow. It is difficult to observe these modes clearly in the experiments. The most destructive rotational mode (*n* = 2), and wobble (*n* = 1) mode, are almost always observable in experiments. Active stabilization methods without degradation of confinement, such as CHI, need to be developed.


Table 4. Stability properties of prolate and oblate FRCs
