ELMs are instabilities driven by pressure gradients and currents at the edge of high performance tokamak plasmas. They result in repetitive bursts which could result in large heat heat loads on the walls of large tokamaks, and so are a concern for ITER.

The elm-pb model included in the BOUT++ repository solves a 4-field model for pressure, vorticity, the parallel component of the plasma velocity and electromagnetic potential. It has been used for studies of ELM eruptions, mainly in circular geometry plasmas.