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

Fusion research at Sandia's z-pinch accelerator has produced an X-ray radia tion source with a confirmed equivalent black body temperature of 1.8 000 0 00 degrees C and an output of about 290 terawatts. This radiation source wa s created by containing the X-rays produced by a z-pinch plasma implosion i n 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 arr ay (a concept called dynamic or internal hohlraum), even higher temperature s can be attained by the rapidly compressing volume. The dynamic hohlraum a s an X-ray source places stringent requirements on the quality of foam targ ets 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 t argets with fine resolution. For example, the uniformity of representative annular and cylindrical foam targets has been nondestructively characterize d in three dimensions by IMT (ion microtomography) with 50-100 mu m spatial resolution. The uniformity of very large diameter annular targets (up to 2 4 mm outer diameter) was measured using STIM (scanning transmission ion mic roscopy) at several angular orientations. The distribution of diagnostic tr acer elements used in some targets to probe the z-pinch plasma was measured by scanned PIXE (particle-induced X-ray emission) and RES (Rutherford back scattering spectroscopy). The results of these analyses show that high qual ity foam targets are being delivered for z-pinch experiments, even when tar get development lead times are as short as 3 weeks. Published by Elsevier S cience S.A..