A fast framing camera system for observation of acceleration and ablation of cryogenic hydrogen pellet in ASDEX Upgrade plasmas

An observation system using fast digital cameras was developed to measure a cryogenic hydrogen pellet’s cloud structure, trajectory, and velocity changes during its ablation in ASDEX Upgrade plasmas. In this article the system, the applied numerical methods, and the results are presented. The three-dimensional pellet trajectory and velocity components were reconstructed from images of observations from two different directions. Pellet acceleration both in the radial and toroidal directions was detected. The pellet cloud distribution was measured with high spatio-temporal resolution. The cloud surrounding the pellet was found to be elongated along the magnetic field lines. Its typical size is 5–7 cm along the field lines and 2 cm in the perpendicular directions. A cloud extension in the poloidal direction was also observed which may be related to the drift of the detached part of the cloud.