The resistive ballooning mode (RBM) is an instability occurring in magnetized plasmas, particularly in magnetic confinement devices such as tokamaks, when the pressure gradient is opposite to the effective gravity created by a magnetic field.
The linear growth rate of the RBM instability is given as
where is the pressure gradient is the effective gravity produced by a non-homogeneous magnetic field, R<sub>0</sub> is the major radius of the device, L<sub>p</sub> is a characteristic length of the pressure gradient, and c<sub>s</sub> is the plasma sound speed.
The RBM instability is similar to the RayleighâÂÂTaylor instability (RT), with Earth gravity replaced by the effective gravity , except that for the RT instability, acts on the mass density of the fluid, whereas for the RBM instability, acts on the pressure of the plasma.