Observation of neoclassical tearing modes in JET

Neoclassical tearing modes have been identified in JET ELMy H mode discharges at medium to high β. The n = 2 modes, as observed in both ECE and SXR data, have a clear island structure and a global character. The critical normalized β at the onset of the modes is found to scale with the normalized Larmor radius. The scaling with collisionality is much weaker and has a negative power. At high β, large amplitude n = 1 modes limit the maximum normalized β.