The phenomenon of striation observed during pellet ablation in hot magnetized plasma is investigated experimentally injecting aluminum micro-pellets into MT-1M and TEXTOR-94 tokamak and W7-AS stellarator plasmas. Changes in pellet cloud shape and temporal fluctuations of total emitted line radiations are studied. Special attention is paid to the investigation of the dependence of fluctuation frequency on pellet velocity. The results show that the light fluctuation frequency is characterized by a characteristic time rather than by a characteristic length, and that the striation is caused by a phenomenon that occurs during the evolution of the ionized-pellet cloud. The compatibility of these experimental observations with different theories of striation is discussed.
Particle confinement of pellet-fuelled tokamak plasma