Influence of krypton gas admixture on plasma focus deuterium fusion

摘要

A comparative study of DD fusion in a 1.6 kJ plasma focus (PF) device operated with pure deuterium and a deuterium-krypton (D-Kr) admixture has been performed. Fast-neutron beryllium activation detectors positioned at 0° and 90° to the PF axis measured the time-integrated neutron yield and anisotropy. Typical fusion yields were in the range of 1–3×108 neutrons/shot. A Coded Aperture Imaging (CAI) technique has been employed to image the fusion source using the ∼3 MeV protons emitted from D(d,p)T reactions. The coded mask pattern is based on a Singer cyclic difference set with 341 open pixels in 91×15 array, giving a total open area of almost 31 mm². CR-39 polymer nuclear track detectors (filtered with 75 µm Kapton film) recorded the fusion proton image. The proton coded-image was read from the detectors using an automated scanning system. A deconvolution procedure was applied to recover the fusion image. An x-ray pinhole system (with filtering adapted to the D2 and D-Kr cases) was employed simultaneously to image the hot dense plasma column. By comparison with D2 operation, fusion images for the D-Kr case show a significantly narrower fusion emission region indicating a tighter confinement of the hot plasma interacting with the energetic deuteron beam. Furthermore, no spatial correlation between fusion emission density and micro-pinch formation (as seen particularly in D-Kr x-ray images) is evident.