Pulsed power accelerators compress electrical energy in space and time to provide versatile experimental platforms for high energy density and inertial confinement fusion science. The 80-TW “Z” pulsed power facility at Sandia National Laboratories is the largest pulsed power device in the world today. Z discharges up to 22 MJ of energy stored in its capacitor banks into a current pulse that rises in 100 ns and peaks at a current as high as 30 MA in low-inductance cylindrical targets. Considerable progress has been made over the past 15 years in the use of pulsed power as a precision scientific tool. This paper reviews developments at Sandia in inertial confinement fusion, dynamic materials science, x-ray radiation science, and pulsed power engineering, with an emphasis on progress since a previous review of research on Z in Physics of Plasmas in 2005.
Implosions of planar wire arrays were performed on the Michigan Accelerator for Inductive Z-pinch Experiments, a linear transformer driver (LTD) at the University of Michigan. These experiments were characterized by lower than expected peak currents and significantly longer risetimes compared to studies performed on higher impedance machines. A circuit analysis showed that the load inductance has a significant impact on the current output due to the comparatively low impedance of the driver; the long risetimes were also attributed to high variability in LTD switch closing times. A circuit model accounting for these effects was employed to measure changes in load inductance as a function of time to determine plasma pinch timing and calculate a minimum effective current-carrying radius. These calculations showed good agreement with available shadowgraphy and x-ray diode measurements.
A 42-yr-old woman presented with hyperthyroidism and a large, firm, irregular goiter. Within a few weeks she became hypothyroid. Five months later she developed increasingly severe neck pain and compressive symptoms. The goiter had become rock hard. A fine needle aspiration biopsy showed features of chronic thyroiditis and fibrosis. She partially responded to a course of glucocorticoids. Tamoxifen was added, with marked improvement in goiter size and pain. Both medications were tapered off. Two months later the patient experienced paresthesias of the fingertips, perioral numbness, and a seizure. She was found to have spontaneous primary hypoparathyroidism. Three months later the patient became hoarse and experienced difficulty in breathing. She was found to have a massively enlarged thyroid with compression of the right internal jugular vein and encasement of the right carotid artery as well as tracheal narrowing. She also had right vocal cord paralysis due to recurrent laryngeal nerve involvement. Because of airway compromise, an emergency isthmusectomy was performed, and the patient was given a postoperative course of glucocorticoids with gradual improvement. Postoperative diagnosis was Riedel's thyroiditis. Two months later she presented with near-syncope and was found to have bradycardia, hypotension, and right Horner's syndrome, presumably due to compression of the right carotid sheath. She was given i.v. glucocorticoids and tamoxifen. Six months later and 18 months after her initial presentation, the patient is doing remarkably well. Her goiter has regressed by more than 50%, and she no longer has any pain or difficulty breathing. She remains a little hoarse and has persistent hypothyroidism and hypoparathyroidism. She is taking prednisone (5 mg, this is being tapered very slowly) and tamoxifen (20 mg) daily. This case illustrates the protean manifestations of Riedel's thyroiditis, a rare but fascinating disease. The epidemiology of this disease, its pathophysiology and complications, and the roles of surgery and medical therapy are reviewed.
In this work, we describe a technique for fabricating ultrathin foils in cylindrical geometry for liner-plasma implosion experiments using sub-MA currents. Liners are formed by wrapping a 400 nm, rectangular strip of aluminum foil around a dumbbell-shaped support structure with a non-conducting center rod, so that the liner dimensions are 1 cm in height, 6.55 mm in diameter, and 400 nm in thickness. The liner-plasmas are imploded by discharging ∼600 kA with ∼200 ns rise time using a 1 MA linear transformer driver, and the resulting implosions are imaged four times per shot using laser-shadowgraphy at 532 nm. This technique enables the study of plasma implosion physics, including the magneto Rayleigh-Taylor, sausage, and kink instabilities on initially solid, imploding metallic liners with university-scale pulsed power machines.
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