Long timescale density peaking in JET

Long timescale density peaking has been observed in JET plasmas leading to densities exceeding the Greenwald value. These neutral beam heated discharges are characterized by type-I ELMs and good energy confinement. Central density is limited by neoclassical tearing modes or by termination of H-mode preceded by loss of sawteeth. When these limiting factors are avoided (i.e. at intermediate power level and with optimization of gas puffing) quasi-stationary high density plasmas with peaked density profile are obtained.