NEW INSTRUMENT FOR MEASURING MAGNETIC-FIELD TILT PROFILE AND PELLET CLOUDS EMISSION STRUCTURE

Measurements of 2D images of pellet ablatant clouds are very important for development of plasma-pellet interaction models and diagnostic applications. It is known that clouds stretch along the magnetic-field direction with elongation ratios up to 5 for hydrogen pellets, up to 12 for carbon, and up to several tens for lithium. These circumstances open a possibility to measure a magnetic-field pitch angle profile with a precision of ±10 mrad or better. For both goals mentioned, the space-time cloud's evolution measurements, with high enough time and spatial resolutions, are needed. Fast multiframe photography technique, as used in the T-10 experiments, satisfy these requirements. However, photography suffers from shortcomings because of the necessity of chemical developing and processing of the film. A novel technique, constructed for Asdex Upgrade pellet experiments, is reported. This system uses a cooled 2D CCD matrix detector and provides measurements up to 50 frames of the cloud images with a survey rate of about 2-50 μs per frame. For a carbon pellet injected along a major radius in the plasma midplane with typical speed of 500 m/s and observing the pellet along the flight direction from behind, this time resolution corresponds to 0.1-1 cm spatial resolution. In each frame it will be possible to measure up to 20 poloidal distributions of cloud emissivity with 1024 pixels in each of them. These distributions will be spaced on a distance of ∼9 mm for Asdex Upgrade conditions. The camera is planned to be installed during this year. © 1995 American Institute of Physics.