The X pinch, a remarkable X-ray source and high-energy-density plasma

Abstract

Summary form only given, as follows. If someone started to talk about a - I-keV, multiply-ionized high-Z, near-solid-density plasma that lasts for 10 to 30 ps and is about 1 pm in size, it would be natural to assume that an ultra-high intensity, short-wavelength, 5 IO-ps laser was responsible for generating that plasma. In fact, such plasmas are routinely produced using the X-pinch exploding wire configuration on the 45044 peak current, 100-ns (full width at half maximum) XP pulsed power generator at Cornell University. An X-pinch plasma is produced by using two (or more) fine wires arranged so that they cross and touch at a single point, in the form of an X, as the load of a pulsed power generator. Very dense, intensely radiating plasmas, commonly called micropinches,consistently form within about 100 @m of the original cross point of the wires, where the currents in the individual wire plasmas merge. High-resolution diagnostics can, therefore, be concentrated on that portion of the wires, thereby enabling a determination of the dynamics of the plasma and its characteristics as an x-ray source with very high spatial and temporal resolution. For example, using an x-ray streak camera, we have determined that X-pinches made from several different wire materials (e.g., MO and W) produce intense, 3- to IO-keV radiation with pulse durations as short as 10 to 30 ps, and the x-ray spectra recorded by the streak camera indicate that plasma ensities can exceed 1O Z2/cm3a nd electron temperatures can reach well into the keV range. [1,2] From experiments in which slits and thin fibers were imaged, together with detailed wave-optics calculations, we have determined that the (time integrated) size of the 3 to 10-keV x-ray source can be as small as 1 pm for some wire materials (e.g., MO and Nb). [3] Imaging of one X pinch by another enables us to follow the dynamics of micropinch formation and disassembly with - 30-ps time resolution and - I-pm spatial resolution. The methods by which these plasma properties have been determined, along with additional detail on the results, especially the source size measurements, will be discussed. Examples of the capability of an X pinch as an x-ray source for point-projection imaging will also be presented.