High speed laser shadowgraphy for electromagnetically driven cylindrical implosions

A laser shadowgraphy system for high-speed imaging of a convergent cylindri cal shockwave generated by an electromagnetically driven solid density line r implosion in Lucite is described. The laser shadowgraphy system utilizes an advanced high-energy, long-pulse, frequency-doubled Nd:YAG laser for tar get illumination and a fast framing camera for multiple frame imaging of th e shockwave as it radially converges and transits the Lucite. The time wind ow resolution is 10 ns as determined by the fastest exposure time capable w ith the camera. Two on-axis symmetric implosions and two off-axis asymmetri c implosion experiments were fielded at the Air Force Research Laboratory's Shiva Star 4.2 MJ capacitor bank z-pinch facility. For each experimental s hot, the shadowgraphy system captured several frames of shadowgraph images as the shockwave moved through the Lucite. Analysis of the shockwave shadow graph image shapes is done by fitting each shadowgraph image to a generic e lliptical fit function and plotting the resultant two-dimensional image fit s for comparison. For the on-axis symmetric implosion shots, a radial traje ctory plot is extracted and a radial shock velocity is calculated. The Luci te shock speed is seen to increase monotonically from an initial velocity o f 7.9 mm/mus to a near final velocity of 13.4 mm/mus as convergence effects dominate the shock speed calculated at small radii. (C) 2001 American Inst itute of Physics.