Neoclassical Tearing Mode (NTM)

A pressure-driven magnetic island that can cap achievable beta.

NTMs are magnetic islands sustained by the loss of bootstrap current inside them. They are a leading beta-limiting instability and are suppressed by driving replacement current at the island with ECRH.

An NTM is a magnetic island sustained by the loss of bootstrap current inside it, and it can clamp the achievable beta well below the ideal limit. Because it grows from a seed (often a sawtooth), avoiding large sawteeth and driving replacement current with ECRH are the two levers used to keep it in check.