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Coiled arrays, which are cylindrical arrays in which each wire is formed into a helix, suppress the modulation of ablation at the fundamental wavelength. Outside the vicinity of the wire cores, ablation flow from coiled arrays is modulated at the coil wavelength and has a two-stream structure in the r, [theta] plane. Within the vicinity of the helical wires, ablation is concentrated at positions with the greatest azimuthal displacement, and plasma is axially transported from these positions such that the streams become aligned with the sections of the coil furthest from the array axis. The GORGON MHD code accurately reproduces this observed ablation structure, which can be understood in terms of J x B forces that result from the interaction of the global magnetic field with a helical current path as well as additional current paths suggested by the simulations. With this ability to control where the ablation streamers occur, large wavelength coils were constructed such that the breaks that form in the wires had sufficient axial separation to prevent perturbations in the implosion sheath from merging. This produced a new mode of implosion in which the global instability can be controlled, and perturbations correlated between all wires in an array. For large-wavelength eight-wire coiled arrays, this produced a dramatic increase in X-ray power, equaling that of a 32-wire straight array. These experiments were carried out on the mega ampere generator for plasma implosion experiments (1 MA, 240 ns) at Imperial College London, London, U.K. Index Terms--Ablation, plasma pinch, x-ray production.

We report on the first investigations of the use of carbon fibers in an X-pinch load using a 250-kA linear transformer driver (LTD). Multiframe laser shadowgraphy is used to examine the evolution of the pinch and shows that carbon loads demonstrate wire expansion and cross-point pinch and gap formation as observed in X-pinches constructed from high Z materials. Radiographs taken using the carbon X-pinch as the source demonstrate both that sufficient flux is emitted to provide a good contrast image at source-to-image distances of > 10 cm and that the cross point produces a relatively small hot spot. Radiographs of a series of fine wires (5-30 [micro]m) using X-rays > 500 eV demonstrated that 25-[micro]m wires can be resolved in this energy range. Time-resolved X-ray emission measurements showed that, while emission in the hv > 500 eV range shows long (> 100 ns) timescales, emission in the hv > 1 keV range shows a multiple-peaked structure with durations as short as 20 ns. Index Terms--Carbon fiber, point-projection radiography, X-pinch.

This paper investigates the ablation of wires in two-wire tungsten X-pinches driven by an 80-kA current over 50 ns. High-resolution imaging using a Nomarski interferometer allows measurements close to the X-pinch cross point, where the ablation 'flare' structure is observed to dearly develop during the drive-current rise time. Electron density profiles are recovered as a function of both distance normal to the wire and of time. Results compare favorably to the rocket model of wire ablation. In addition, the density contrast over the ablation 'stream' and 'gap' structure is measured and compared to similar measurements made using quantitative radiography on the 1-MA 250-ns MAGPIE generator at Imperial College London, London, U.K. Index Terms--Precursor plasma, wire ablation, X-pinch.

A new ligand, 8[O.sub.2] 1,4,7,10-tetraazadodecane tetraacetic acid (DOTAM), is synthesized and its lanthanide complexes are examined as potential chemical exchange saturation transfer (CEST) agents. The analysis reveals that the increasing ionic radius of the lanthanide ion leads to an increase in the extent of the distortion, thereby leading to a complete loss of symmetry in the complex.

This paper summarizes observations of precursor-column formation in cylindrical wire arrays on the 1-MA MAGPIE generator at Imperial College London. Direct experimental measurements of the diameter variation during the collapse and formation phase of the precursor column taken from gated soft X-ray images are presented. Three stages in precursor-column formation are identifiable from the data: broad initial density profile, rapid contraction to small diameter, and slow expansion after formation. The variation in the minimum diameter is measured for several materials, and data show good agreement with a pressure-balance model. Stability calculations suggest that the fraction of the drive current flowing the precursor column is Index Terms--Precursor column, precursor plasma, wire-array Z-pinches.

An efficient synthesis of three diastereomers of 9-tert-butoxycarbonyl-2-oxo-3-(N-tert-butoxycarbonylamino)-1-azabicyclo[4.3.0]nonane is described. Acidolytic deprotection after Fmoc-protection provided building blocks suitable for solid-phase synthesis.

Two gadolinium(III) chelates, containing a single nitrophenolic pendant arm plus either three acetate or three amide pendant arms were synthesized and characterized. The extent and mechanism of the changes in water relaxivity with pH of each gadolinium complex was found to differ substantially for the two complexes.