Session GP1 - Poster Session IV.
POSTER session, Tuesday afternoon, October 30
Exhibit Hall B,
High field pellet fuelled discharges in FTU have achieved good energy and particle confinement properties in a quasi-steady regime. Peak densities close to 1e21 m-3 have been obtained, showing a post pellet decay time of several energy confinement times. The neutron yield, in excess of 1e13 neutrons/s, is consistent with high plasma purity (Zeff<1.3), good e-i coupling and neoclassical ion transport. This paper analyses the role of impurities in the evolution of these discharges. A very clean target plasma is required in order to avoid a negative central balance between ohmic input and radiation losses.Even if the analysis is difficult on FTU due to the contemporary presence of metallic (Mo, Fe, Ni) and light impurities (0, C), two regimes of pellet fuelled plasma are clearly well identified and discussed. In the first case, impurity accumulation has been observed, when the sawtooth activity is suppressed by pellet injection, in which the impurity density profile follows roughly the peaking of the electron density profile. In the second one, the accumulation is avoided if a slow sawtooth activity persists during the good confinement phase.