  A natural fueling mechanism that helps to maintain the main core deuterium
and tritium (DT) density profiles in a tokamak fusion reactor is discussed. In
H-mode plasmas dominated by ion- temperature gradient (ITG) driven turbulence,
cold DT ions near the edge will naturally pinch radially inward towards the
core. This mechanism is due to the quasi-neutral heat flux dominated nature of
ITG turbulence and still applies when trapped and passing kinetic electron
effects are included. Fueling using shallow pellet injection or supersonic gas
jets is augmented by an inward pinch of could DT fuel. The natural fueling
mechanism is demonstrated using the three-dimensional toroidal electromagnetic
gyrokinetic turbulence code GEM and is analyzed using quasilinear theory.
Profiles similar to those used for conservative ITER transport modeling that
have a completely flat density profile are examined and it is found that
natural fueling actually reduces the linear growth rates and energy transport.
