New data from the Reversed Field eXperiment (RFX) are presented and analysed,which provide a deeper understanding of pellet experiments in a reversed fieldpinch. In particular, evidence on the ablation cloud density, ablation rateand homogenization process are given by the measurements of twomid-infra-red interferometers located at different toroidal locations, one ofwhich is at the same poloidal plane as the pellet injector. For each pellet,the measurement of the latter interferometer displays a huge peak, which isdue to the crossing of the interferometer chord by the ablation cloud. Itsanalysis yields information on the cloud dimension and radial densitydistribution. The typical cloud density is much lower than that measured intokamaks. Due to such a low density, the stopping power of the ionized part ofthe ablation cloud is weak. As a result the ablation rate is higher than intokamaks. Another characteristic of the density increase measured by both of theinterferometers is the absence of dense plasma structures propagating for longdistances along field lines. This proves that the distance necessary for theablated material to become incorporated into the plasma is less than about 4 min the core of the discharge, due to a rapid mixing of the ablated material.Despite the different features displayed by pellet injection experiments inreversed-field pinches and tokamaks, the ablation and homogenization of thedeposited material can be described within the same general frame for bothmagnetic configurations. The differences arise mainly because of the differentmagnetic field topologies and values of the transport coefficients in the twomachines.
Geometrical, kinetic and atomic physics effects in a two dimensional time dependent fluid simulation of ablating fuel pellets