We present observations for 20-MA wire-array z pinches of an extended wire ablation period of 57%+/-3% of the stagnation time of the array and non-thin-shell implosion trajectories. These experiments were performed with 20-mm-diam wire arrays used for the double- z -pinch inertial confinement fusion experiments [M. E. Cuneo, Phys. Rev. Lett. 88, 215004 (2002)] on the Z accelerator [R. B. Spielman, Phys. Plasmas 5, 2105 (1998)]. This array has the smallest wire-wire gaps typically used at 20 MA (209 microm ). The extended ablation period for this array indicates that two-dimensional (r-z) thin-shell implosion models that implicitly assume wire ablation and wire-to-wire merger into a shell on a rapid time scale compared to wire acceleration are fundamentally incorrect or incomplete for high-wire-number, massive (>2 mg/cm) , single, tungsten wire arrays. In contrast to earlier work where the wire array accelerated from its initial position at approximately 80% of the stagnation time, our results show that very late acceleration is not a universal aspect of wire array implosions. We also varied the ablation period between 46%+/-2% and 71%+/-3% of the stagnation time, for the first time, by scaling the array diameter between 40 mm (at a wire-wire gap of 524 mum ) and 12 mm (at a wire-wire gap of 209 microm ), at a constant stagnation time of 100+/-6 ns . The deviation of the wire-array trajectory from that of a thin shell scales inversely with the ablation rate per unit mass: f(m) proportional[dm(ablate)/dt]/m(array). The convergence ratio of the effective position of the current at peak x-ray power is approximately 3.6+/-0.6:1 , much less than the > or = 10:1 typically inferred from x-ray pinhole camera measurements of the brightest emitting regions on axis, at peak x-ray power. The trailing mass at the array edge early in the implosion appears to produce wings on the pinch mass profile at stagnation that reduces the rate of compression of the pinch. The observation of precursor pinch formation, trailing mass, and trailing current indicates that all the mass and current do not assemble simultaneously on axis. Precursor and trailing implosions appear to impact the efficiency of the conversion of current (driver energy) to x rays. An instability with the character of an m = 0 sausage grows rapidly on axis at stagnation, during the rise time of pinch power. Just after peak power, a mild m = 1 kink instability of the pinch occurs which is correlated with the higher compression ratio of the pinch after peak power and the decrease of the power pulse. Understanding these three-dimensional, discrete-wire implosion characteristics is critical in order to efficiently scale wire arrays to higher currents and powers for fusion applications.

Spectroscopy is one of the fundamental techniques in as tronomy. However, spectroscopic study of sources emitting in the extreme UV (λ ~ 100-1000 A) and the soft χ ray (λ ~ 10-100 Å) is still in its infancy, in part due to a lack of spectrometer designs suited specifically for grazing incidence optics. We introduce two such designs and variations, which have emerged from a study 1 of spectrometer options for the Extreme Ultraviolet Explorer (EUVE) satellite. 2 Both designs achieve spectral imaging through a smooth

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Analytic calculations are presented which describe aberrations of the in-plane and off-plane varied linespace grating designs we recently proposed [Appl. Opt.22,3921 (1983)]. Ray traces confirming these results to within typical accuracies of 10% are illustrated for several examples. Spectral field aberrations are calculated for convenient focal surfaces, and optimal field curvatures are calculated and ray traced. An improvement of the off-plane fan grating is proposed, where the angular spacings of the grooves are varied to achieve a large decrease in grating aberrations. However it is shown that, in conical diffraction, the net resolution can also be dominated by a diminished dispersive power compared to in-plane grating mounts. Curved groove in-plane grating designs are ray traced, revealing no substantial degradation in imaging performance by restricting such curves to concentric circles. However, it is also shown that the general case of hyperbolic grooves can be fabricated by use of visible or UV holography, with small residual aberrations. We designate this new class of holographic gratings as Type V. Misalignment aberrations of high resolution in-plane gratings, for the in situ cases of off-axis illumination, grating and detector displacements, and grating rotational misalignment, are calculated and found to be generally small.