  For the first time the pellet cycle of a multiple-isotope plasma is
successfully reproduced with reduced turbulent transport modelling, within an
integrated simulation framework. Future nuclear fusion reactors are likely to
be fuelled by cryogenic pellet injection, due to higher penetration and faster
response times. Accurate pellet cycle modelling is crucial to assess fuelling
efficiency and burn control. In recent JET tokamak experiments, deuterium
pellets with reactor-relevant deposition characteristics were injected into a
pure hydrogen plasma. Measurements of the isotope ratio profile inferred a
Deuterium penetration time comparable to the energy confinement time. The
modelling successfully reproduces the plasma thermodynamic profiles and the
fast deuterium penetration timescale. The predictions of the reduced turbulence
model QuaLiKiz in the presence of a negative density gradient following pellet
deposition are compared with GENE linear and nonlinear higher fidelity
modelling. The results are encouraging with regard to reactor fuelling
capability and burn control.
