# Resistive ballooning mode

**{{#invoke:Portal|portal}}**
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.

## Linear growth rate

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*_{0} is the major radius of the device, *L*_{p} is a characteristic length of the pressure gradient, and *c*_{s} is the plasma sound speed.

## Similarity with the Rayleigh–Taylor instability

The RBM instability is similar to the Rayleigh–Taylor 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.