Development and fielding of high speed laser shadowgraphy for electro-magnetically driven cylindrical implosions

Experimental characterization of a converging shockwave in a cylindrical geometry provides fundamental benchmarks used in the modeling of hydrodynamic phenomena from solid density implosions. A high-speed laser shadowgraphy system for detailed imaging of a cylindrical convergent shockwave provides diagnosis where multiple sampling of the shock front position and radial shape are desired. We present the development of an advanced laser shadowgraphy system: a novel laser source, the fiber optic delivery system, double-pass target imaging, and fast frame camera image acquisition, recently fielded on a set of hydrodynamic implosion experiments. Labeled the Near Term Liner Experiments (NTLX), an experimental series of four shots were conducted at the Shiva Star Pulsed Power Facility in Albuquerque, NM for the High Energy Density Hydrodynamics Program at Los Alamos National Laboratory. In these experiments, an electro-magnetically driven cylindrical aluminum liner of 5-cm radius, 4-cm long, 1-mm thick implodes under the force of an axial current of 15 MA. Azimuthal magnetic fields on the liner surfaces exceed 0.5 MG. The liner is accelerated to ∼5km/s and is driven symmetrically onto a concentric Sn/Lucite target, and a convergent shockwave is setup in the 1.5-cm radius Lucite rod. Both, symmetric and asymmetric, shock wave motion in the Lucite are recorded by multiple image sampling with the shadowgraphy system. The main feature of our shadowgraphy system consists of a unique frequency doubled Nd:YAG laser with temporally adjustable (100 ns to 50 μsec) square pulses and high output energy (60 mJ) at 532 nm. Fast framing camera capability allows us to capture multiple images of the shock transit through the Lucite. We describe the details of our shadowgraphy system and present experimental results of our measurements.