Multi-Frame Point-Projection X-Ray Imaging of Tungsten Wire-Array Z-Pinches

Abstract

Summary form only given. X-pinch radiography has been used routinely at Cornell for more than 10 years to produce high quality X-ray images with excellent spatial and temporal resolution. This imaging technique is presently being used on the COBRA accelerator at Cornell University to study the ablation stage of wire-array Z-pinches. Two of four return-current posts in the wire-array load region are replaced by Mo X-pinches. They are approximately 43 mm from the axis of the Z-pinch. The experimental arrangement used here is very similar to the set-up that has been used at the Angara-5-1 facility near Moscow and also on MAGPIE at Imperial College in London. Typically, two X-pinches are used to image one wire in an eight-wire Z-pinch from different angles. Photographic films are typically placed 35-40 cm from the Z-pinch axis yielding a magnification of about 9:1. Titanium filters are used to shield films from visible light and transmit radiation in the spectral range 3-5 keV. Strong collimation is used to prevent radiation from the wire array Z-pinch from exposing the films. The resulting X-ray images have sub-nanosecond temporal resolution because of the extremely short X pinch X-ray pulse duration and about 4mum spatial resolution. Images obtained by this system have been used to accurately measure wire-core expansion rates and to examine the fine details of wire-core structure. Tungsten step wedges (step attenuators), which have steps ranging from 0.015-1.10 mum thick, placed on the Ti filters enable us to make density measurements of the ablation plasmas near the dense wire-cores. These density measurements are the main focus of this presentation. Future work and a general overview of the facility will also be presented.