Experiments were performed on JET where high-density plasmas with an internal transport barrier (ITB) were
created by means of combined use of lower hybrid current drive (LHCD) and pellet injection before the barrier
formation. Attempts were also made to use pellets to fuel the plasma and to sustain the density during the ITB phase.
It was found that shallow pellets ablating in the region r/a 0.8 and far from the foot of the barrier did not destroy
the ITB, whereas deeper pellets penetrating up to 0.6 ( r/a ) 0.7 affected the barrier and led to its disappearance.
Modelling of these experimental scenarios has been performed with transport and fluid turbulence codes. The codes
used in the analysis were: JETTO, a 1.5 dimensional transport code, TRB, a global electrostatic fluid turbulene
code and CUTIE, a global electromagnetic fluid turbulence code. The results show that for the shallow pellet case all
codes reproduce the general features of the experiment, whereas for the deep pellet case, there are differences in the
degree of agreement between the different codes and the experiment. Runs performed varying the pellet penetration
depth indicate that not only the pellet penetration, but also the barrier strength plays a key role in the dynamics of
the pellet-ITB interaction. |