Density Peaking in JET: Driven by Fueling or Transport?

Particle transport has been extensively studied by performing several dimensionally matched collisionality scans in various plasma scenarios in JET. Gas puff modulation technique has been developed in great detail with high quality density measurements to determine particle transport coefficients. Density peaking has been found to increase with decreasing u* in all H-mode scenarios while in L-mode, no dependency was found. The experimentally determined particle transport coefficients suggest that NBI fueling is main contributor to the observed density peaking in H-mode. This is further supported by predictive transport simulations with GLF23 and gyro-kinetic analysis. These results will extrapolate to future tokamaks in such a way that density peaking may be quite moderate even in low collisionality regimes in the absence of core particle sources.