X-pinch dynamics close to the time of x-ray burst emission and x-pinch bright spot location using x-ray backlighting

In the final few ns before the moment of the x-ray burst emission near the cross point of the two wires in an X-pinch, an on-axis z-pinch forms, the dynamics of which have been studied using direct (point projection) x-ray backlighting. The rapid collapse of the z-pinch results in a gap in the observable mass distribution, which the authors refer to as a minidiode. Two Mo X-pinches were placed in parallel between the output electrodes of the 450 kA, 100 ns XP pulser at Cornell University. The <0.5 ns radiation burst from each of the two X-pinches was used to generate a magnified x-ray backlighter image on film of the other one. The size of the x-ray source is sufficiently small that the spatial resolution in the images is close to 1 microm. Using different wire sizes in the two X-pinches yields images separated in time by 4--20 ns; using the same wire size yields images separated in time by 0.5--2ns. Therefore, the dynamics of the rapid collapse of the on-axis z-pinch in conjunction with minidiode formation, and the break-up of that z-pinch just as the bright x-ray spots develop can be studied using the successive images from 4 ns before x-ray burst emission, through the moment of burst emission, to a few ns after burst emission. By superimposing images generated by both x-pinches of a grid of fine wires on the same films as the X-pinch images, it has been possible to locate the position of the bright x-ray emission point(s) in the z-pinch/minidiode region to within 10 microm. The emission points are usually within 100 microm of the original cross point of the two wires, near the ends of the collapsing z-pinch. Calibrated density measurements have been made with W X-pinches by including a W step wedge in the film pack. Results from these experiments will also be presented