Development of the "Hybrid" Scenario in JET

In the last campaigns, JET has extended the hybrid scenario with q profile close to unity in the plasma core to different q95 (from 5 to 2.7), larger normalised pressure (bN) up to 3.6, density up to the Greenwald density and also long duration up to 20s. In contrast to other machine the confinement improvement has not exceeded 1.2 with respect to the H98y2 scaling law. Differences in critical temperature gradient length in terms of rotational shear and magnetic shear might explain this difference. Recent experiments have transiently reached an improvement factor of H=1.4 by raising the magnetic shear in the outer half of the plasma. In addition, the stability at high bN has been address experimentally using MHD spectroscopy using error field correction coils and indicates that hybridlike q profile are ideally stable at JET.
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