Characterizing the uniformity of polystyrene and TPX z-pinch fusion targets by nuclear microscopy

摘要

Fusion research at Sandia's z-pinch accelerator has produced an X-ray radiation source with a confirmed equivalent black body temperature of l .8 000 000"C and an output of about 290 terawatts. This radiation source was created by containing the X-rays produced by a z-pinch plasma implosion in a special type of wire array radiation case, about the size of a spool of thread. By placing annular or cylindrical foam targets inside the wire array (a concept called dynamic or internal hohlraum), even higher temperatures can be attained by the rapidly compressing volume. The dynamic hohlraum as an X-ray source places stringent requirements on the quality of foam targets to minimize plasma instabilities during implosion. Nuclear microscopy, which used MeV-energy focused ion beams to characterize materials, provides unique capabilities for quantifying fabrication-induced defects in these targets with fine resolution. For example, the uniformity of representative annular and cylindrical foam targets has been nondestructively characterized in three dimensions by IMT (ion microtomography) with 50--l00 Um spatial resolu- tion. The uniformity of very large diameter annular targets (up to 24 mm outer diameter) was measured using STIM (scanning transmission ion microscopy) at several angular orientations. The distribution of diagnostic tracer elements used in some targets to probe the z-pinch plasma was measured by scanned PIXE (particle-induced X-ray emission) and RBS (Rutherford backscattering spectroscopy). The results of these analyses show that high quality foam targets are being delivered for z-pinch experiments, even when target development lead times are as short as 3 weeks.